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Review
Microenvironment in subchondral bone: predominant regulator for the treatment of osteoarthritis
  1. Wenhui Hu1,
  2. Yueqi Chen1,2,
  3. Ce Dou1,2,
  4. Shiwu Dong1,2,3
  1. 1 Department of Biomedical Materials Science, Third Military Medical University, Chongqing, China
  2. 2 Department of Orthopedics, Southwest Hospital, Third Military Medical University, Chongqing, China
  3. 3 State Key Laboratory of Trauma, Burns and Combined Injury, Third Military Medical University, Chongqing, China
  1. Correspondence to Professor Shiwu Dong, Department of Biomedical Materials Science, Third Military Medical University, Chongqing 400038, China; dongshiwu{at}tmmu.edu.cn; Dr Ce Dou; lance.douce{at}gmail.com

Abstract

Osteoarthritis (OA) is a degenerative joint disease in the elderly. Although OA has been considered as primarily a disease of the articular cartilage, the participation of subchondral bone in the pathogenesis of OA has attracted increasing attention. This review summarises the microstructural and histopathological changes in subchondral bone during OA progression that are due, at the cellular level, to changes in the interactions among osteocytes, osteoblasts, osteoclasts (OCs), endothelial cells and sensory neurons. Therefore, we focus on how pathological cellular interactions in the subchondral bone microenvironment promote subchondral bone destruction at different stages of OA progression. In addition, the limited amount of research on the communication between OCs in subchondral bone and chondrocytes (CCs) in articular cartilage during OA progression is reviewed. We propose the concept of ‘OC–CC crosstalk’ and describe the various pathways by which the two cell types might interact. Based on the ‘OC–CC crosstalk’, we elaborate potential therapeutic strategies for the treatment of OA, including restoring abnormal subchondral bone remodelling and blocking the bridge—subchondral type H vessels. Finally, the review summarises the current understanding of how the subchondral bone microenvironment is related to OA pain and describes potential interventions to reduce OA pain by targeting the subchondral bone microenvironment.

  • osteoarthritis
  • chondrocytes
  • cytokines
  • osteoarthritis
  • knee
https://creativecommons.org/licenses/by/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.

https://doi.org/10.1136/annrheumdis-2020-218089

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    Introduction

    Osteoarthritis (OA) is the most frequent form of arthritis with a high incidence and a prolonged course.1 OA affects articular and periarticular tissues, such as articular cartilage, subchondral bone and synovium.2 Over recent years, the role of subchondral bone during OA progression has gradually attracted researchers’ attention.3 4 Imaging techniques have revealed microstructural alterations in subchondral bone in OA joints, including early-stage bone loss, late-stage bone sclerosis and histopathological alterations, caused by subchondral bone cysts, bone marrow oedema-like lesions (BMOLs) and osteophyte formation.5 These alterations are caused by biological processes involving uncoupling and coupling interactions among osteocytes, osteoblasts (OBs), osteoclasts (OCs), endothelial cells (ECs) and sensory neurons in the subchondral bone microenvironment,6 and therefore they will help in understanding OA pathogenesis from the perspective of subchondral bone. Notably, bone remodelling rates are altered during the development of OA due to the spontaneous activation or inactivation of osteoclastic bone resorption activity. As a result, activation of bone resorption may be evident in the subchondral bone microenvironment in early-stage OA, while late-stage OA is characterised by inactivation of bone resorption activity and a bias towards activation of bone formation activity.7 Subchondral bone and cartilage form a functional complex called the bone–cartilage unit, which is involved in the pathophysiology of OA at the biochemical and mechanical levels.8 9 In this review, we summarise the various pathways by which OCs interact with CCs, thus providing a novel research direction for the investigation of the crosstalk between these two types of cells in OA. Furthermore, we have noted the reported and potential communication pathways between OCs and CCs, and we propose promising therapeutic strategies to restrain the progression of OA by targeting the subchondral bone microenvironment. Moreover, arthritic pain is a major complaint of patients with OA during the progression of the disease. Recent studies indicate that neuronal factors may contribute to the innervation of pain-related sensory nerves in OA subchondral bone.10 11 Intriguingly, the evidence suggests a close relationship between OCs/OBs and sensory nerves in the microenvironment of subchondral bone.10 11 Based on this, it may be useful to develop specific drugs for the treatment of OA-related pain by targeting the subchondral bone microenvironment.

    Osteoarthritic subchondral bone microenvironment

    Normal subchondral bone architecture

    Subchondral bone is divided into two anatomical entities: the subchondral bone plate and subchondral trabeculae. Subchondral bone plate is a thin cortical plate subjacent to calcified cartilage. It is a penetrable structure with interconnected porosity. Numerous vessels and nerves pass through the porosity, sending branches into calcified cartilage.12 The subchondral trabeculae, which are subjacent to the subchondral bone plate, are porous structures with abundant vessels and nerves that play an important role in load absorption and structural support as well as nutritional supply to cartilage.13 Subchondral bone adapts to mechanical forces exerted on the joint dynamically via coordinated bone remodelling.14 Bone remodelling involves the coupling of osteoclastic bone resorption and osteoblastic bone formation to replace damaged bone with new bone.15 However, subchondral bone and cartilage exhibit distinct capacities of mechanical adaptation. Although cartilage modulates the functional state in response to mechanical damage, its capacity to repair and modify the surrounding extracellular matrix is more limited than that of subchondral bone.16 Subchondral bone responds rapidly to mechanical loading by bone remodelling and then re-establishes normal physiological conditions.17

    Microstructural and histopathological alterations in OA subchondral bone

    The occurrence of cartilage degeneration and subchondral bone destruction has always been a controversial issue.18 Not all patients with OA exhibit the progression from abnormal bone formation in subchondral bone. Moreover, a fraction of patients with OA exhibit the earliest changes at the sites of subchondral bone. OA is commonly thought to be a degenerative disease related to ageing and trauma. In ageing-induced OA, it could be confirmed that aberrant chondrocyte metabolism plays a crucial role in the occurrence of cartilage damage prior to abnormal subchondral bone formation.19 Conversely, early microdamage at the sites of subchondral bone is detected in trauma-induced OA.20 Notably, the alterations of subchondral bone are not exactly the same in different articulating joints in OA. There is good evidence that pathological alterations in different joints (such as the knee, spine and temporomandibular joint) exhibit several kinds of features.21–25

    At different stages of OA, there are distinct microstructural alterations in subchondral bone. In early OA, enhanced subchondral bone turnover is observed. In addition, the subchondral bone sclerosis is observed during the advanced and late stages.26–28 In early OA, subchondral bone plate becomes thinner and more porous during the initial cartilage degeneration. Subchondral trabeculae deteriorate, with increased trabecular separation and decreased trabecular thickness.29 Conversely, the subchondral bone plate and trabeculae become thicker, which is accompanied by subchondral bone sclerosis and decreased bone marrow spacing in late OA. At the same time, non-calcified cartilage shows progressive damage, and becomes thicker with tidemark replication.29 Despite the increased bone volume, high local bone turnover and a decreased calcium:collagen ratio lead to insufficient bone mineralisation and a decreased bone tissue elastic modulus. Consequently, the mechanical property is compromised, and it becomes easier to deform bone under mechanical loads (figure 1).30 31

    Figure 1
    Figure 1

    Microstructural and histopathological alterations in osteoarthritis (OA) subchondral bone. In early-stage OA, subchondral bone plate becomes thinner and more porous, together with deteriorated subchondral trabeculae and initial cartilage degradation. In late-stage OA, calcified cartilage and subchondral bone plate become thicker, along with sclerotic subchondral trabeculae and progressive cartilage destruction. During OA progression, growing vessels and nerves send branches from subchondral bone into cartilage. OA subchondral bone exhibits subchondral bone cysts, bone marrow oedema-like lesions and osteophyte formation.

    Abnormal cellular interactions in the OA subchondral bone microenvironment

    Subchondral bone in OA undergoes an uncoupling of remodelling process, in which enhanced osteoclast-mediated bone resorption and osteoblast-mediated bone formation could be displayed at different stages during OA progression.32 Normally, biomechanical coupling of articular cartilage and subchondral bone has been well established. In early-stage OA, the self-repair of articular cartilage reduces excessive mechanical loads on subjacent subchondral bone. As a result, loading of subchondral bone falls below a predetermined level. In turn, this underloading increases the ratio of the expression of receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin (OPG) in osteocytes, which leads to excessive osteoclastogenesis and enhanced bone resorption activity.33 34 Overactivated bone remodelling is commonly found at microdamage sites in subchondral bone in patients with OA and OA animal models.35 36 Osteocytes directly adjacent to microdamage sites undergo apoptosis, whereas osteocytes adjacent to apoptotic populations upregulate the expression of pro-osteoclastic molecules at the early stage of OA.37 38 Conversely, osteocytes also regulate osteoblast mineralisation by activating the Wnt signalling pathway via increased production of Wnt proteins and decreased secretion of sclerostin (SOST) in response to increased mechanical loading, which is caused by progressive cartilage destruction in OA during progression to the advanced and late stages.39 40 In addition, it was confirmed in vitro that transforming growth factor-β1 (TGF-β1) from osteocytes could enhance osteoblast-mediated bone anabolic metabolism by activating Smad2/3 in the subchondral bone in advanced-stage OA.41 As a result, the concomitant increase in osteoblast activity leads to spatial remineralisation and osteosclerosis in the end stage of OA.

    In parallel, osteoclastic bone resorption leads to a sharp increase in active TGF-β1 in OA subchondral bone, recruiting osteoprogenitors to bone remodelling sites via activation of the Smad2/3 pathway to promote the formation of osteoid islets.42 Abnormal mechanical strain triggers dysregulated metabolism in osteoblasts, which is characterised by increased expression of interleukin (IL)−6, prostaglandin E2 (PGE2), the degradative metalloproteinases matrix metalloproteinase (MMP)–3, –9, −13 and RANKL and decreased production of OPG.43 IL-6 and PGE2 stimulate osteoclast formation by inhibiting the secretion of OPG and stimulating the production of RANKL in osteoblasts or by upregulating the expression of RANK in osteoclasts.44 Moreover, PGE2 promotes the secretion of IL-6, and in turn, IL-6 promotes the secretion of PGE2 by osteoblasts.45 Hence, the positive feedback loop between PGE2 and IL-6 signalling promotes osteoclast differentiation via affecting the OPG/RANKL/RANK system. In addition, RANKL and vascular endothelial growth factor (VEGF) secreted by osteoblasts in subchondral bone in OA could trigger osteoclast chemotaxis by inducing extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation.46–48

    Evidence has shown that the crosstalk between osteoblast or osteoclast lineage cells and type H ECs promotes subchondral angiogenesis and aggravates subchondral bone remodelling.49–51 Type H ECs surrounded by osterix-expressing osteoprogenitors produce high levels of angiocrine factors (such as platelet-derived growth factor (PDGF)–A, TGF-β1 and fibroblast growth factor (FGF)−1), stimulating survival, proliferation and differentiation of these osteoprogenitors to promote local bone formation.52 53 Type H ECs intercommunicate via the intercellular Notch/delta-like protein 4 (DLL4) signalling pathway to induce the production of Noggin,54 which stimulates the differentiation of osteoprogenitors surrounding vessels.55 Type H vessels also stimulate osteoclast migration and differentiation by producing RANKL and MMP-9, which regulate bone remodelling to promote longitudinal bone growth.56 In addition, slit guidance ligand 3 (SLIT3) and TGF-β1 derived from osteoblasts acts as pro-angiogenic factors to increase the number of type H ECs.57–59 Notably, TGF-β1 derived from osteoclastic resorption is primarily responsible for subchondral angiogenesis in early-stage OA,60 while the increase in preosteoclast-derived PDGF-BB plays a relatively predominant role in angiogenic and osteogenic differentiation in late-stage OA (figure 2).61

    Figure 2
    Figure 2

    Pathological cellular interactions in the osteoarthritis (OA) subchondral microenvironment. (A) In early-stage OA, osteocytes upregulate the expression of RANKL:OPG ratio to enhance osteoclast differentiation. According to relative production of PGE2, IL-6 and OPG to RANKL, osteoblasts are separated into two subgroups: ‘low-synthesiser cells’ and ‘high-synthesisers’. PGE2, IL-6, MMP-9 and VEGF from the two subgroups mediate the pro-osteoclastic effect, while the former acts as primary effectors of subchondral bone loss by high levels of RANKL. In parallel, osteoclastic bone resorption is primarily responsible for angiogenesis and osteogenesis by released TGF-β1. Moreover, sensory innervation is induced by H+ and Netrin-1 secreted from mature osteoclasts. RANKL and MMP-9 produced by type H ECs may facilitate osteoclast chemotaxis and formation. (B) In late-stage OA, osteocytes regulate osteoblast mineralisation by increased Wnt proteins and TGF-β1 in response to increased mechanical loading. Multiple cells produce factors to support type H vessel formation, including VEGF and TGF-β1 from osteocyte, PDGF-BB from pre-osteoclasts, and VEGF, TGF-β1 and SLIT3 from osteoblasts. Sustained nerve sprouting is supported by NGF from preosteoclasts and PGE2 from osteoblasts. The latter subgroup promotes subchondral bone sclerosis, primarily regulated by angiocrine factors (PDGF-A, TGF-β1 and FGF-1). ASIC, acid-sensing ion channel; DCC, deleted in colon cancer; DLL4, delta-like protein 4; DP1R, DP1 receptor; IL-6, interleukin-6; MMP-9, matrix metalloproteinase-9; PDGF, platelet-derived growth factor; PG, prostaglandin; RANKL, receptor activator of NF-κB ligand; SLIT3, slit guidance ligand 3; SOST, sclerostin; TGF-β1, transforming growth factor-β1; TRPV1, transient receptor potential vanilloid 1; VEGF, vascular endothelial growth factor.

    Regulation feedback loop of ‘osteoclast–chondrocyte crosstalk’

    Various pathways for the ‘osteoclast–chondrocyte crosstalk’

    A large number of vessels from subchondral bone penetrate calcified cartilage and invade non-calcified cartilage through vertical microcracks observed in OA joints.62 Consequently, mediators originating from osteoclasts and chondrocytes may diffuse and transport across microcracks or via invasive vessels. Intriguingly, osteoclast precursors invade the hypertrophic area of cartilage during the growth of periosteal vessels and then function together with hypertrophic chondrocytes to remodel cartilage matrix and form a primary ossification centre.63 64 Similarly, an in vivo cell tracking technique revealed that bone marrow–derived CX3CR1-positive osteoclast precursors enter the inflammatory cartilage layer via the blood circulation and differentiate into mature osteoclasts, promoting cartilage destruction in rheumatoid arthritis.65 Collectively, these data suggest that osteoclast precursors migrate into the cartilage layer and then make direct contact with hypertrophic chondrocytes and even interact with chondrocytes with normal phenotype. In addition, recent data have identified the capability of osteoclasts to degrade the osteochondral junction and articular cartilage in an MMP-dependent and cysteine protease–dependent manner,66 indicating the potential of mature osteoclasts to function as direct regulators of neighbour chondrocytes. During ‘mechanical OC-CC crosstalk’, on the one hand, the cartilage layer exhibits abnormal alterations in OA progression, which reduce its ability to absorb mechanical pressure and result in excessive loads on subchondral bone.67 On the other hand, high turnover of subchondral bone leads to alterations in the biomechanical properties of bone tissue in early OA, transferring shear forces to the cartilage layer and causing continued cartilage damage (figure 3).68

    Figure 3
    Figure 3

    Various pathways for the ‘osteoclast–chondrocyte crosstalk’. (A) Osteoclasts (OC) and chondrocytes (CC) interplay through secreted mediators crossing microcracks and vessels. (B) Bone marrow mononuclear cells are brought to the cartilage layer through invasive vessels. Osteoclast lineage cells directly contact with chondrocytes at different stages of differentiation. (C) Mature osteoclasts tunnel their way into subchondral bone and overlying cartilage and interact with chondrocytes in the cartilage layer. (D) Subchondral bone destruction mediated by osteoclasts transfers shear forces to the cartilage layer and consequently leads to abnormal chondrocyte metabolism. In turn, osteocytes and osteoblasts sense overloads from the damaged cartilage layer and send pro-osteoclastic signals, resulting in accelerated subchondral bone remodelling.

    Regulation of chondrocytes by osteoclasts promotes cartilage deterioration

    Growth factors released from the bone matrix through osteoclastic bone resorption regulate chondrocyte metabolism and participate in cartilage deterioration. Mature osteoclasts attach to the bone surface through sealing zones and dissolve bone during bone remodelling. Consequently, various factors are released from the bone matrix, including TGF-β1, insulin-like growth factor (IGF)−1 and calcium-phosphate complexes.69 Zhang et al 70 found that the expression of TGF-β1 in osteoclasts was significantly upregulated in a time-dependent and dose-dependent manner under mechanical stimulation. Meanwhile, chondrocytes showed increased apoptosis when cultured with osteoclasts. Furthermore, intraperitoneal injection of TGF-β1R inhibitors reversed chondrocyte apoptosis and reduced cartilage degradation in a rat OA model.70 TGF-β1 is not derived from osteoclastic bone resorption in the study, no matter what, it implied that TGF-β1 in subchondral bone could be transferred to the cartilage layer by diffusion or blood transport to adversely affect chondrocytes. Intriguingly, IGF-1, another bone-released growth factor, was shown to play a protective role in chondrocyte anabolism. IGF-1 promotes the expression of Col2a1 and inhibits the expression and enzyme activity of MMP-13 by activating the phosphatidylinositol 3 kinase (PI3K)/Akt and ERK1/2 pathways in rat endplate chondrocytes.71 In addition, IGF-1 signalling protects chondrocytes from apoptosis by reducing caspase-3 activity and DNA fragmentation.72 73 Cartilage also obtains calcium–phosphate complexes from subchondral bone, which increases the production of MMP-13 in chondrocytes via activation of nuclear factor-kappa B (NF-κB), p38 and ERK1/2, and signal transducer and activator of transcription 3 (STAT3) signalling.74 Lu et al 50 reported a nutrient-sensing mechanism in which vascular-derived nutrients (such as amino acids) induced hypertrophic differentiation by activating mechanistic target of rapamycin complex 1 (mTORC1). Osteoclasts at distinct stages of differentiation derived from bone marrow mononuclear cells (BMMCs) may affect the normal phenotype of chondrocytes. Our group reported that exosomal let-7a-5p from preosteoclasts and mature osteoclasts targets Smad2 to promote the hypertrophic differentiation of chondrocytes,75 providing insights into ‘OC–CC coupling’ during OA progression.

    Regulation of osteoclasts by chondrocytes promotes subchondral bone loss

    Subchondral bone cells may be exposed to various pro-inflammatory cytokines produced by OA chondrocytes. Changes in joint biomechanical properties induce the upregulation of IL-1β in primary chondrocytes.76 IL-1β upregulates the expression of RANKL by osteoblasts to indirectly induce osteoclast formation and directly induces osteoclast precursors to form multinucleated osteoclasts.77 The excessive production of tumour necrosis factor (TNF)-α and IL-6 in chondrocytes in OA was detected in a surgical OA model of destabilisation of the medial meniscus.78 TNF-α directly induces osteoclast differentiation by activating NF-κB and c-Jun NH2-terminal protein kinase (JNK) in a RANKL-independent manner79 and indirectly induces osteoclastogenesis by stimulating osteoblasts to express RANKL.80 IL-6 induces CD14-positive peripheral blood mononuclear cells to form tartrate-resistant acid phosphatase (TRAP) and calcitonin receptor–positive osteoclasts in a RANKL-independent manner by activating the signal transduction factor gp130.81 In addition, VEGF-positive and RANKL-positive chondrocytes are increased in the hypertrophic layer by applying mechanical stress to the temporomandibular joint. In parallel, TRAP-positive osteoclasts increase in the mineralised layer subjacent to the hypertrophic layer.82 Furthermore, RANKL and VEGF induced osteoclast chemotaxis through the phosphorylation of ERK1/2 in a modified model of osteoclasts cultured in a Boyden chamber.83 High-mobility group box 1 (HMGB1) is expressed in and around OA chondrocytes in vivo.84 Taniguchi et al 85 analysed the bone development of Hmgb1 −/− in hypertrophic chondrocytes in the growth plate of mice and found that the endochondral bone formation was disrupted due to the delayed invasion of osteoclast precursors into the primary ossification centre. In addition, senescent chondrocytes occur alongside hypertrophic chondrocytes, which produce catabolic enzymes, pro-inflammatory mediators and chemokines (collectively known as the senescence-associated secretory phenotype (SASP)),86 87 potentially modulating the behaviours of subchondral osteoclast lineage cells.

    The presence of chondrocytes with morphological features consistent with apoptosis in OA cartilage is positively correlated with OA severity.88–90 Tang et al 91 found that the conditioned medium of apoptotic chondrocytes following dexamethasone treatment enhanced the recruitment of RAW264.7 osteoclast precursor cells and increased their differentiation potential. Further explorations confirmed that CXC motif chemokine 12 (CXCL12) released from apoptotic chondrocytes had the strongest pro-osteoclastic effect by activating the ERK1/2 and p38 pathways in BMMCs.91 AMD3100 (an inhibitor of CXCR4) effectively prevented subchondral trabecular destruction and cartilage loss in the tibia of mice after anterior cruciate ligament transection (ACLT).92 93 The cartilage matrix is the main obstacle for phagocytic cells, resulting in late apoptotic chondrocytes undergoing the transition to necrosis, which is called secondary necrosis.94 Necrosis causes plasma membrane rupture and the release of damage-associated molecular patterns (DAMPs), such as nucleotides, HMGB1 and pro-inflammatory cytokines.95 DAMPs act on nearby cartilage and synovium to trigger inflammation, and may regulate the behaviours of subchondral osteoclast lineage cells (figure 4, table 1).

    Figure 4
    Figure 4

    Role of the ‘osteoclast–chondrocyte crosstalk’ in the pathogenesis of OA. Multiple subchondral factors arrive at the cartilage layer through blood transport to regulate chondrocyte metabolism. For example, various factors are released from bone matrix, including TGF-β1, IGF-1 and Ca–Pi complexes. Moreover, BMMCs migrate into the cartilage layer. Mediators produced by chondrocytes are transported to the subchondral bone layer through blood transport. Hypertrophic, senescent and necrotic chondrocytes produce high levels of pro-osteoclastic molecules, which act on BMMCs in the subchondral bone or cartilage layer to promote osteoclast recruitment and formation. Preosteoclasts and mature osteoclasts in the cartilage layer induce chondrocyte hypertrophy through exosomal let-7a-5p. In addition, osteoclasts and chondrocytes influence each other by ‘OC–CC coupling via channels’ or ‘mechanical OC–CC crosstalk’. BMMC, bone marrow mononuclear cell; CXCL12, CXC motif chemokine 12; DAMP, damage-associated molecular pattern; FGF, fibroblast growth factor; HMGB1, high mobility group box 1; IGF, insulin-like growth factor; IL, interleukin; MMP-9, matrix metalloproteinase-9; PDGF, platelet-derived growth factor; PG, prostaglandin; RANKL, receptor activator of NF-κB ligand; SASP, senescence-associated secretory phenotype; SLIT3, slit guidance ligand 3; TGF-β1, transforming growth factor-β1; TNF-α, tumour necrosis factor-α; VEGF, vascular endothelial growth factor.

    View this table:
    Table 1

    Role of the ‘osteoclast–chondrocyte crosstalk’ in the pathogenesis of OA

    Targeting the subchondrol bone microenvironment for the treatment of OA

    Restoring abnormal subchondral bone remodelling

    In fact, the efficacy of antiresorptive agents in OA treatment has been evaluated in clinical trials by restoring abnormal subchondral bone remodelling. Regrettably, there are currently few or no data on the beneficial effect of strategies targeting abnormal bone remodelling in patients with OA. Bisphosphonates approved for osteoporosis management belong to classical antiresorptive agents. Risedronate reduced biochemical markers of cartilage degradation but did not improve signs or symptoms or slow radiographic progression in a prospective 2-year trial involving 2483 patients with medial compartment knee OA at dosages of 5 mg/day, 15 mg/day, 35 mg/week or 50 mg/week.96Alendronate treatment improved the Western Ontario and McMaster University Osteoarthritis Index pain score, decreased biochemical markers and increased the BMD in a prospective 2-year trial involving 50 patients with symptomatic hip OA.97 Moreover, compared with those receiving placebo, patients with symptomatic knee OA who received intravenous zoledronic acid yearly did not show a significant reduction in cartilage volume loss, the size of BMOLs or the pain score over 24 months.98 There are other antiresorptive agents (such as OPG, cathepsin K (CTSK) inhibitors and strontium ranelate) that may exert protective effects on subchondral bone and cartilage in animal models and serve as disease-modifying OA drugs for clinical treatment of OA.99–101 Intriguingly, calcitonin, which is known for targeting subchondral bone remodelling, also leads to intracellular cAMP accumulation and then promotes chondrocyte anabolism by binding to its receptors on human OA chondrocytes.102 Two phase III trials have reported a beneficial effect of bioactive oral calcitonin on joint pain and biochemical indicators of bone and cartilage degradation in patients with OA.103 Enhanced osteoclast activity leads to the overactivation of TGF-β1 signalling in subchondral bone, and therefore subchondral TGF-β1 is a pharmacological target for OA. Implantation of alginic acid microbeads with TGF-β1 antibody into subchondral bone or deletion of Tgfbr2 prevented the phosphorylation of Smad2/3 in osteoblastic precursor cells, thus reducing their subchondral localisation and improving bone parameters and cartilage structure in a mouse ACLT model.60 Accumulating evidence suggests that restoring subchondral bone remodelling could improve OA symptoms and the structure of bone and cartilage, but these agents require large clinical trials with plenty of subjects to verify their effects.

    Blocking the bridge—subchondral type H vessels

    Invasive subchondral type H vessels serve as a bridge between subchondral bone and articular cartilage. Current treatments for OA focus on the inhibition of inflammation and subchondral bone remodelling, while therapeutic strategies targeting subchondral angiogenesis are limited. In fact, blocking type H vessel formation in animal models of OA has been shown to reduce cartilage destruction and subchondral bone loss.104 For example, bevacizumab (a VEGF blocking antibody) attenuated the formation of subchondral type H vessels in an OA model, thereby inhibiting chondrocyte hypertrophy and delaying OA progression.50 In addition to pharmacological VEGF inhibition, secretory factors derived from osteoclast or osteoblast lineage cells in the OA subchondral bone microenvironment, such as TGF-β1, PDGF-BB and SLIT3, promote subchondral angiogenesis. Therefore, antagonists of those molecules might be developed as potential agents for OA. For example, the small molecule compound halofuginone inhibits Smad2/3-dependent TGF-β1 signalling to restore the coupling of subchondral bone remodelling, alleviate type H vessel formation and attenuate cartilage degradation in the rodent ACLT joint.105

    Ameliorating OA-related pain by modulating subchondral bone microenvironment

    The detailed mechanisms of OA contributing to pain remained unclear for decades until recent studies found that particular neuronal factors related to aberrant bone remodelling cause the innervation of sensory nerves in the subchondral bone of patients with OA.106 107 Bone-resorbing osteoclasts create an acidic microenvironment by secreting H+ to cause bone pain in animal models of bone metastasis. Mechanistically, acidosis induces the expression and activation of acid-sensing receptor transient receptor potential vanilloid 1 (TRPV1) in dorsal root ganglions (DRGs). TRPV1 activation promotes extracellular Ca2+ influx and then activates calmodulin-dependent protein kinase II (CaMKII) and transcription factor cAMP-responsive element-binding protein (CREB), leading to the transcriptional activation of the pain-related molecule calcitonin gene-related peptide (CGRP).108 109 Similarly, acid-sensing ion channel 3 (ASIC3) is upregulated in mono-iodoacetate-induced OA model and is associated with hyperalgesia caused by increased Ca2+ influx.110 Netrin-1 secreted by osteoclasts induces sensory innervation and pain in OA through its receptor deleted in colon cancer (DCC).10 Preosteoclasts produce nerve growth factor (NGF), serving as key drivers of subchondral nerve innervation during OA development.61 In addition, PGE2 is synthesised by osteoblasts in response to low bone density and contributes to skeletal allodynia in OA mice by upregulating the voltage-gated sodium channel Nav1.8 and increasing Na+ influx in subchondral nociceptive neurons.11

    Pain medications recommended in the current guidelines for OA include non-steroidal anti-inflammatory drugs, paracetamol, opioids and corticosteroids administered via the oral, topical or intra­articular route. Several new pain treatments are currently moving forward in preclinical and clinical evaluation processes, potentially marking the beginning of a new era in the management of OA-related pain. Tanezumab (a human monoclonal antibody against NGF) is significantly superior to placebo in reducing pain and improving joint function with fewer adverse events based on a meta-analysis of 10 studies.111 112 Evidence suggests that a small molecule conjugate linking the TGF-βR inhibitor TLY-2109761 and alendronate substantially reduces excessive PGE2 production by osteoblasts and alleviates OA-induced pain in OA mice by restoring aberrant bone remodelling.11 In addition, nociceptive signals were blunted in subchondral sensory neurons in OA mice by the administration of a cyclooxygenase 2 (COX2) inhibitor, the Nav1.8 inhibitor A-803467 and an EP4 receptor antagonist.11 113 114 Furthermore, Ca2+ influx into the cytoplasm in sensory neuron was inhibited by the TRPV1 antagonist SB366791 and the ASIC3 antagonist APETx2 to reduce acid-induced pain in a murine model of bone cancer pain and a rat model of OA, respectively.110 115 Collectively, further exploration of how the subchondral bone microenvironment is related to OA pain may be an excellent approach to develop specific drugs useful for the treatment of OA (table 2).

    View this table:
    Table 2

    Targeting the subchondral bone microenvironment for the treatment of osteoarthritis (OA)

    Conclusion and perspective

    The bone–cartilage unit composed of subchondral bone and cartilage plays a significant role in joint homeostasis and OA development. During OA progression, the two joint compartments of the functional unit experience abnormal alterations in tissue structure and cellular activity. Therefore, therapeutic strategies targeting one of the abnormal joint compartments could restrain the progression of the pathology of the whole joint. Furthermore, this strategy may be an effective disease-modifying method to block pathological interactions between the two joint compartments through pharmacological interventions. More extensive cellular and molecular studies of bone–cartilage interface crosstalk will help us to better understand the pathophysiology of OA and modify existing OA therapies. In particular, the microenvironment in subchondral bone serves as the predominant regulator of the development of OA. Therefore, future studies should focus on how pathological cellular interactions in the subchondral bone microenvironment promote subchondral bone destruction and OA pain and the development of novel drugs to treat OA by targeting the subchondral bone microenvironment.

    References

    1. ↵
      2. Glyn-Jones S ,
      3. Palmer AJR ,
      4. Agricola R , et al
      . Osteoarthritis. Lancet 2015;386:376–87.doi:10.1016/S0140-6736(14)60802-3 pmid:http://www.ncbi.nlm.nih.gov/pubmed/25748615
      OpenUrlCrossRefPubMed
    2. ↵
      2. Perrot S
      . Osteoarthritis pain. Best Pract Res Clin Rheumatol 2015;29:90–7.doi:10.1016/j.berh.2015.04.017 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26267003
      OpenUrlCrossRefPubMed
    3. ↵
      2. Hoshi H ,
      3. Akagi R ,
      4. Yamaguchi S , et al
      . Effect of inhibiting MMP13 and ADAMTS5 by intra-articular injection of small interfering RNA in a surgically induced osteoarthritis model of mice. Cell Tissue Res 2017;368:379–87.doi:10.1007/s00441-016-2563-y pmid:http://www.ncbi.nlm.nih.gov/pubmed/28120109
      OpenUrlPubMed
    4. ↵
      2. Castañeda S ,
      3. Roman-Blas JA ,
      4. Largo R , et al
      . Subchondral bone as a key target for osteoarthritis treatment. Biochem Pharmacol 2012;83:315–23.doi:10.1016/j.bcp.2011.09.018 pmid:http://www.ncbi.nlm.nih.gov/pubmed/21964345
      OpenUrlCrossRefPubMed
    5. ↵
      2. Li G ,
      3. Yin J ,
      4. Gao J , et al
      . Subchondral bone in osteoarthritis: insight into risk factors and microstructural changes. Arthritis Res Ther 2013;15:223.doi:10.1186/ar4405 pmid:http://www.ncbi.nlm.nih.gov/pubmed/24321104
      OpenUrlCrossRefPubMed
    6. ↵
      2. Henrotin Y ,
      3. Pesesse L ,
      4. Sanchez C
      . Subchondral bone and osteoarthritis: biological and cellular aspects. Osteoporos Int 2012;23:847–51.doi:10.1007/s00198-012-2162-z pmid:http://www.ncbi.nlm.nih.gov/pubmed/23179567
      OpenUrlCrossRefPubMed
    7. ↵
      2. Funck-Brentano T ,
      3. Cohen-Solal M
      . Crosstalk between cartilage and bone: when bone cytokines matter. Cytokine Growth Factor Rev 2011;22:91–7.doi:10.1016/j.cytogfr.2011.04.003 pmid:http://www.ncbi.nlm.nih.gov/pubmed/21596615
      OpenUrlCrossRefPubMed
    8. ↵
      2. Suri S ,
      3. Walsh DA
      . Osteochondral alterations in osteoarthritis. Bone 2012;51:204–11.doi:10.1016/j.bone.2011.10.010 pmid:http://www.ncbi.nlm.nih.gov/pubmed/22023932
      OpenUrlCrossRefPubMedWeb of Science
    9. ↵
      2. Goldring SR
      . Role of bone in osteoarthritis pathogenesis. Med Clin North Am 2009;93:25–35.doi:10.1016/j.mcna.2008.09.006 pmid:http://www.ncbi.nlm.nih.gov/pubmed/19059019
      OpenUrlCrossRefPubMedWeb of Science
    10. ↵
      2. Zhu S ,
      3. Zhu J ,
      4. Zhen G , et al
      . Subchondral bone osteoclasts induce sensory innervation and osteoarthritis pain. J Clin Invest 2019;129:1076–93.doi:10.1172/JCI121561 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30530994
      OpenUrlPubMed
    11. ↵
      2. Zhu J ,
      3. Zhen G ,
      4. An S , et al
      . Aberrant subchondral osteoblastic metabolism modifies NaV1.8 for osteoarthritis. Elife 2020;9:e57656. doi:10.7554/eLife.57656 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32441256
      OpenUrlPubMed
    12. ↵
      2. Goldring MB ,
      3. Goldring SR
      . Articular cartilage and subchondral bone in the pathogenesis of osteoarthritis. Ann N Y Acad Sci 2010;1192:230–7.doi:10.1111/j.1749-6632.2009.05240.x pmid:http://www.ncbi.nlm.nih.gov/pubmed/20392241
      OpenUrlCrossRefPubMedWeb of Science
    13. ↵
      2. Holopainen JT ,
      3. Brama PAJ ,
      4. Halmesmäki E , et al
      . Changes in subchondral bone mineral density and collagen matrix organization in growing horses. Bone 2008;43:1108–14.doi:10.1016/j.bone.2008.07.254 pmid:http://www.ncbi.nlm.nih.gov/pubmed/18757048
      OpenUrlPubMed
    14. ↵
      2. Goldring SR
      . Alterations in periarticular bone and cross talk between subchondral bone and articular cartilage in osteoarthritis. Ther Adv Musculoskelet Dis 2012;4:249–58.doi:10.1177/1759720X12437353 pmid:http://www.ncbi.nlm.nih.gov/pubmed/22859924
      OpenUrlCrossRefPubMed
    15. ↵
      2. Hu W ,
      3. Zhang L ,
      4. Dong Y , et al
      . Tumour dormancy in inflammatory microenvironment: a promising therapeutic strategy for cancer-related bone metastasis. Cell Mol Life Sci 2020. doi:doi:10.1007/s00018-020-03572-1. [Epub ahead of print: 16 Jun 2020].pmid:http://www.ncbi.nlm.nih.gov/pubmed/32556373
    16. ↵
      2. Day JS ,
      3. Van Der Linden JC ,
      4. Bank RA , et al
      . Adaptation of subchondral bone in osteoarthritis. Biorheology 2004;41:359–68.pmid:http://www.ncbi.nlm.nih.gov/pubmed/15299268
      OpenUrlPubMed
    17. ↵
      2. Goldring SR ,
      3. Goldring MB
      . Changes in the osteochondral unit during osteoarthritis: structure, function and cartilage-bone crosstalk. Nat Rev Rheumatol 2016;12:632–44.doi:10.1038/nrrheum.2016.148 pmid:http://www.ncbi.nlm.nih.gov/pubmed/27652499
      OpenUrlPubMed
    18. ↵
      2. Thielen N ,
      3. van der Kraan P ,
      4. van Caam A
      . TGFβ/BMP signaling pathway in cartilage homeostasis. Cells 2019;8:969.doi:10.3390/cells8090969
      OpenUrl
    19. ↵
      2. Peffers MJ ,
      3. Chabronova A ,
      4. Balaskas P , et al
      . SnoRNA signatures in cartilage ageing and osteoarthritis. Sci Rep 2020;10:10641. doi:10.1038/s41598-020-67446-z pmid:http://www.ncbi.nlm.nih.gov/pubmed/32606371
      OpenUrlPubMed
    20. ↵
      2. Barton KI ,
      3. Shekarforoush M ,
      4. Heard BJ , et al
      . Use of pre-clinical surgically induced models to understand biomechanical and biological consequences of PTOA development. J Orthop Res 2017;35:454–65.doi:10.1002/jor.23322 pmid:http://www.ncbi.nlm.nih.gov/pubmed/27256202
      OpenUrlPubMed
    21. ↵
      2. Goode AP ,
      3. Carey TS ,
      4. Jordan JM
      . Low back pain and lumbar spine osteoarthritis: how are they related? Curr Rheumatol Rep 2013;15:305. doi:10.1007/s11926-012-0305-z pmid:http://www.ncbi.nlm.nih.gov/pubmed/23307577
      OpenUrlCrossRefPubMed
    22. ↵
      2. Courties A
      . [Is there one or more osteoarthritis?]. Rev Prat 2019;69:502–4.pmid:31626451
      OpenUrlPubMed
    23. ↵
      2. Gellhorn AC ,
      3. Katz JN ,
      4. Suri P
      . Osteoarthritis of the spine: the facet joints. Nat Rev Rheumatol 2013;9:216–24.doi:10.1038/nrrheum.2012.199 pmid:http://www.ncbi.nlm.nih.gov/pubmed/23147891
      OpenUrlPubMed
    24. ↵
      2. Larheim TA ,
      3. Hol C ,
      4. Ottersen MK , et al
      . The role of imaging in the diagnosis of temporomandibular joint pathology. Oral Maxillofac Surg Clin North Am 2018;30:239–49.doi:10.1016/j.coms.2018.04.001 pmid:http://www.ncbi.nlm.nih.gov/pubmed/29866450
      OpenUrlPubMed
    25. ↵
      2. Morales H ,
      3. Cornelius R
      . Imaging approach to temporomandibular joint disorders. Clin Neuroradiol 2016;26:5–22.doi:10.1007/s00062-015-0465-0 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26374243
      OpenUrlPubMed
    26. ↵
      2. Bettica P ,
      3. Cline G ,
      4. Hart DJ , et al
      . Evidence for increased bone resorption in patients with progressive knee osteoarthritis: longitudinal results from the Chingford study. Arthritis Rheum 2002;46:3178–84.doi:10.1002/art.10630 pmid:http://www.ncbi.nlm.nih.gov/pubmed/12483721
      OpenUrlCrossRefPubMedWeb of Science
    27. ↵
      2. Klose-Jensen R ,
      3. Hartlev LB ,
      4. Boel LWT , et al
      . Subchondral bone turnover, but not bone volume, is increased in early stage osteoarthritic lesions in the human hip joint. Osteoarthritis Cartilage 2015;23:2167–73.doi:10.1016/j.joca.2015.06.001 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26074361
      OpenUrlPubMed
    28. ↵
      2. Botter SM ,
      3. van Osch GJVM ,
      4. Clockaerts S , et al
      . Osteoarthritis induction leads to early and temporal subchondral plate porosity in the tibial plateau of mice: an in vivo microfocal computed tomography study. Arthritis Rheum 2011;63:2690–9.doi:10.1002/art.30307 pmid:http://www.ncbi.nlm.nih.gov/pubmed/21360519
      OpenUrlCrossRefPubMedWeb of Science
    29. ↵
      2. Hügle T ,
      3. Geurts J
      . What drives osteoarthritis?—synovial versus subchondral bone pathology. Rheumatology 2017;56:1461–71.doi:10.1093/rheumatology/kew389 pmid:28003493
      OpenUrlPubMed
    30. ↵
      2. Day JS ,
      3. Ding M ,
      4. van der Linden JC , et al
      . A decreased subchondral trabecular bone tissue elastic modulus is associated with pre-arthritic cartilage damage. J Orthop Res 2001;19:914–8.doi:10.1016/S0736-0266(01)00012-2 pmid:http://www.ncbi.nlm.nih.gov/pubmed/11562141
      OpenUrlCrossRefPubMedWeb of Science
    31. ↵
      2. Burr DB
      . Anatomy and physiology of the mineralized tissues: role in the pathogenesis of osteoarthrosis. Osteoarthritis Cartilage 2004;12:20–30.doi:10.1016/j.joca.2003.09.016 pmid:http://www.ncbi.nlm.nih.gov/pubmed/14698637
      OpenUrlCrossRefPubMed
    32. ↵
      2. Pu P ,
      3. Qingyuan M ,
      4. Weishan W , et al
      . Protein-degrading enzymes in osteoarthritis. Z Orthop Unfall 2019. doi:doi:10.1055/a-1019-8117. [Epub ahead of print: 19 Nov 2019].pmid:http://www.ncbi.nlm.nih.gov/pubmed/31746442
    33. ↵
      2. Cabahug-Zuckerman P ,
      3. Frikha-Benayed D ,
      4. Majeska RJ , et al
      . Osteocyte apoptosis caused by hindlimb unloading is required to trigger osteocyte RANKL production and subsequent resorption of cortical and trabecular bone in mice femurs. J Bone Miner Res 2016;31:1356–65.doi:10.1002/jbmr.2807 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26852281
      OpenUrlCrossRefPubMed
    34. ↵
      2. Plotkin LI ,
      3. Gortazar AR ,
      4. Davis HM , et al
      . Inhibition of osteocyte apoptosis prevents the increase in osteocytic receptor activator of nuclear factor κB ligand (RANKL) but does not stop bone resorption or the loss of bone induced by unloading. J Biol Chem 2015;290:18934–42.doi:10.1074/jbc.M115.642090 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26085098
      OpenUrlAbstract/FREE Full Text
    35. ↵
      2. Lacourt M ,
      3. Gao C ,
      4. Li A , et al
      . Relationship between cartilage and subchondral bone lesions in repetitive impact trauma-induced equine osteoarthritis. Osteoarthritis Cartilage 2012;20:572–83.doi:10.1016/j.joca.2012.02.004 pmid:http://www.ncbi.nlm.nih.gov/pubmed/22343573
      OpenUrlCrossRefPubMed
    36. ↵
      2. Boyde A ,
      3. Firth EC
      . High resolution microscopic survey of third metacarpal articular calcified cartilage and subchondral bone in the juvenile horse: possible implications in chondro-osseous disease. Microsc Res Tech 2008;71:477–88.doi:10.1002/jemt.20575 pmid:http://www.ncbi.nlm.nih.gov/pubmed/18320577
      OpenUrlCrossRefPubMedWeb of Science
    37. ↵
      2. Kennedy OD ,
      3. Herman BC ,
      4. Laudier DM , et al
      . Activation of resorption in fatigue-loaded bone involves both apoptosis and active pro-osteoclastogenic signaling by distinct osteocyte populations. Bone 2012;50:1115–22.doi:10.1016/j.bone.2012.01.025 pmid:http://www.ncbi.nlm.nih.gov/pubmed/22342796
      OpenUrlCrossRefPubMedWeb of Science
    38. ↵
      2. Kennedy OD ,
      3. Laudier DM ,
      4. Majeska RJ , et al
      . Osteocyte apoptosis is required for production of osteoclastogenic signals following bone fatigue in vivo. Bone 2014;64:132–7.doi:10.1016/j.bone.2014.03.049 pmid:http://www.ncbi.nlm.nih.gov/pubmed/24709687
      OpenUrlCrossRefPubMedWeb of Science
    39. ↵
      2. Li J ,
      3. Xue J ,
      4. Jing Y , et al
      . SOST deficiency aggravates osteoarthritis in mice by promoting sclerosis of subchondral bone. Biomed Res Int 2019;2019:1–8.doi:10.1155/2019/7623562 pmid:http://www.ncbi.nlm.nih.gov/pubmed/31828128
      OpenUrlPubMed
    40. ↵
      2. Ganesh T ,
      3. Laughrey LE ,
      4. Niroobakhsh M , et al
      . Multiscale finite element modeling of mechanical strains and fluid flow in osteocyte lacunocanalicular system. Bone 2020;137:115328. doi:10.1016/j.bone.2020.115328 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32201360
      OpenUrlPubMed
    41. ↵
      2. Dai G ,
      3. Xiao H ,
      4. Liao J , et al
      . Osteocyte TGFβ1–Smad2/3 is positively associated with bone turnover parameters in subchondral bone of advanced osteoarthritis. Int J Mol Med 2020;46:167–78.doi:10.3892/ijmm.2020.4576 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32319543
      OpenUrlPubMed
    42. ↵
      2. Zhen G ,
      3. Cao X
      . Targeting TGFβ signaling in subchondral bone and articular cartilage homeostasis. Trends Pharmacol Sci 2014;35:227–36.doi:10.1016/j.tips.2014.03.005 pmid:http://www.ncbi.nlm.nih.gov/pubmed/24745631
      OpenUrlCrossRefPubMed
    43. ↵
      2. Ni G-X ,
      3. Zhan L-Q ,
      4. Gao M-Q , et al
      . Matrix metalloproteinase-3 inhibitor retards treadmill running-induced cartilage degradation in rats. Arthritis Res Ther 2011;13:R192.doi:10.1186/ar3521 pmid:http://www.ncbi.nlm.nih.gov/pubmed/22114772
      OpenUrlPubMed
    44. ↵
      2. Liu X-H ,
      3. Kirschenbaum A ,
      4. Yao S , et al
      . Interactive effect of interleukin-6 and prostaglandin E2 on osteoclastogenesis via the OPG/RANKL/RANK system. Ann N Y Acad Sci 2006;1068:225–33.doi:10.1196/annals.1346.047 pmid:http://www.ncbi.nlm.nih.gov/pubmed/16831922
      OpenUrlCrossRefPubMed
    45. ↵
      2. Liu X-H ,
      3. Kirschenbaum A ,
      4. Yao S , et al
      . Cross-talk between the interleukin-6 and prostaglandin E(2) signaling systems results in enhancement of osteoclastogenesis through effects on the osteoprotegerin/receptor activator of nuclear factor-{kappa}B (RANK) ligand/RANK system. Endocrinology 2005;146:1991–8.doi:10.1210/en.2004-1167 pmid:http://www.ncbi.nlm.nih.gov/pubmed/15618359
      OpenUrlCrossRefPubMedWeb of Science
    46. ↵
      2. Sanchez C ,
      3. Deberg MA ,
      4. Bellahcène A , et al
      . Phenotypic characterization of osteoblasts from the sclerotic zones of osteoarthritic subchondral bone. Arthritis Rheum 2008;58:442–55.doi:10.1002/art.23159 pmid:http://www.ncbi.nlm.nih.gov/pubmed/18240211
      OpenUrlCrossRefPubMedWeb of Science
    47. ↵
      2. Lee SE ,
      3. Woo KM ,
      4. Kim SY , et al
      . The phosphatidylinositol 3-kinase, p38, and extracellular signal-regulated kinase pathways are involved in osteoclast differentiation. Bone 2002;30:71–7.doi:10.1016/S8756-3282(01)00657-3 pmid:http://www.ncbi.nlm.nih.gov/pubmed/11792567
      OpenUrlCrossRefPubMedWeb of Science
    48. ↵
      2. Paiva KBS ,
      3. Granjeiro JM
      . Matrix metalloproteinases in bone resorption, remodeling, and repair. Prog Mol Biol Transl Sci 2017;148:203–303.doi:10.1016/bs.pmbts.2017.05.001 pmid:http://www.ncbi.nlm.nih.gov/pubmed/28662823
      OpenUrlPubMed
    49. ↵
      2. Zhu S ,
      3. Bennett S ,
      4. Kuek V , et al
      . Endothelial cells produce angiocrine factors to regulate bone and cartilage via versatile mechanisms. Theranostics 2020;10:5957–65.doi:10.7150/thno.45422 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32483430
      OpenUrlPubMed
    50. ↵
      2. Lu J ,
      3. Zhang H ,
      4. Cai D , et al
      . Positive-feedback regulation of subchondral H-type vessel formation by chondrocyte promotes osteoarthritis development in mice. J Bone Miner Res 2018;33:909–20.doi:10.1002/jbmr.3388 pmid:http://www.ncbi.nlm.nih.gov/pubmed/29329496
      OpenUrlPubMed
    51. ↵
      2. Zhao Y ,
      3. Xie L
      . Unique bone marrow blood vessels couple angiogenesis and osteogenesis in bone homeostasis and diseases. Ann N Y Acad Sci 2020.
    52. ↵
      2. Hasegawa T ,
      3. Tsuchiya E ,
      4. Abe M , et al
      . [Cellular interplay of bone cells and vascular endothelial cells in bone]. Clin Calcium 2016;26:677–82.doi:CliCa1605677682 pmid:http://www.ncbi.nlm.nih.gov/pubmed/27117612
      OpenUrlPubMed
    53. ↵
      2. Peng Y ,
      3. Wu S ,
      4. Li Y , et al
      . Type H blood vessels in bone modeling and remodeling. Theranostics 2020;10:426–36.doi:10.7150/thno.34126 pmid:http://www.ncbi.nlm.nih.gov/pubmed/31903130
      OpenUrlPubMed
    54. ↵
      2. Ramasamy SK ,
      3. Kusumbe AP ,
      4. Wang L , et al
      . Endothelial Notch activity promotes angiogenesis and osteogenesis in bone. Nature 2014;507:376–80.doi:10.1038/nature13146 pmid:http://www.ncbi.nlm.nih.gov/pubmed/24647000
      OpenUrlCrossRefPubMedWeb of Science
    55. ↵
      2. Kusumbe AP ,
      3. Ramasamy SK ,
      4. Adams RH
      . Coupling of angiogenesis and osteogenesis by a specific vessel subtype in bone. Nature 2014;507:323–8.doi:10.1038/nature13145 pmid:http://www.ncbi.nlm.nih.gov/pubmed/24646994
      OpenUrlCrossRefPubMedWeb of Science
    56. ↵
      2. Romeo SG ,
      3. Alawi KM ,
      4. Rodrigues J , et al
      . Endothelial proteolytic activity and interaction with non-resorbing osteoclasts mediate bone elongation. Nat Cell Biol 2019;21:430–41.doi:10.1038/s41556-019-0304-7 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30936475
      OpenUrlPubMed
    57. ↵
      2. Sanchez C ,
      3. Mazzucchelli G ,
      4. Lambert C , et al
      . Comparison of secretome from osteoblasts derived from sclerotic versus non-sclerotic subchondral bone in oa: a pilot study. PLoS One 2018;13:e0194591. doi:10.1371/journal.pone.0194591 pmid:http://www.ncbi.nlm.nih.gov/pubmed/29547667
      OpenUrlPubMed
    58. ↵
      2. Gerber HP ,
      3. Vu TH ,
      4. Ryan AM , et al
      . VEGF couples hypertrophic cartilage remodeling, ossification and angiogenesis during endochondral bone formation. Nat Med 1999;5:623–8.doi:10.1038/9467 pmid:http://www.ncbi.nlm.nih.gov/pubmed/10371499
      OpenUrlCrossRefPubMedWeb of Science
    59. ↵
      2. Xu R ,
      3. Yallowitz A ,
      4. Qin A , et al
      . Targeting skeletal endothelium to ameliorate bone loss. Nat Med 2018;24:823–33.doi:10.1038/s41591-018-0020-z pmid:http://www.ncbi.nlm.nih.gov/pubmed/29785024
      OpenUrlCrossRefPubMed
    60. ↵
      2. Zhen G ,
      3. Wen C ,
      4. Jia X , et al
      . Inhibition of TGF-β signaling in mesenchymal stem cells of subchondral bone attenuates osteoarthritis. Nat Med 2013;19:704–12.doi:10.1038/nm.3143 pmid:http://www.ncbi.nlm.nih.gov/pubmed/23685840
      OpenUrlCrossRefPubMed
    61. ↵
      2. Xie H ,
      3. Cui Z ,
      4. Wang L , et al
      . PDGF-BB secreted by preosteoclasts induces angiogenesis during coupling with osteogenesis. Nat Med 2014;20:1270–8.doi:10.1038/nm.3668 pmid:http://www.ncbi.nlm.nih.gov/pubmed/25282358
      OpenUrlCrossRefPubMed
    62. ↵
      2. Chen Y ,
      3. Wang T ,
      4. Guan M , et al
      . Bone turnover and articular cartilage differences localized to subchondral cysts in knees with advanced osteoarthritis. Osteoarthritis Cartilage 2015;23:2174–83.doi:10.1016/j.joca.2015.07.012 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26241776
      OpenUrlPubMed
    63. ↵
      2. Tonna S ,
      3. Poulton IJ ,
      4. Taykar F , et al
      . Chondrocytic ephrin B2 promotes cartilage destruction by osteoclasts in endochondral ossification. Development 2016;143:648–57.doi:10.1242/dev.125625 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26755702
      OpenUrlAbstract/FREE Full Text
    64. ↵
      2. Wang B ,
      3. Jin H ,
      4. Shu B , et al
      . Chondrocytes-specific expression of osteoprotegerin modulates osteoclast formation in metaphyseal bone. Sci Rep 2015;5:13667. doi:10.1038/srep13667 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26329493
      OpenUrlPubMed
    65. ↵
      2. Hasegawa T ,
      3. Kikuta J ,
      4. Sudo T , et al
      . Identification of a novel arthritis-associated osteoclast precursor macrophage regulated by FOXM1. Nat Immunol 2019;20:1631–43.doi:10.1038/s41590-019-0526-7 pmid:http://www.ncbi.nlm.nih.gov/pubmed/31740799
      OpenUrlPubMed
    66. ↵
      2. Löfvall H ,
      3. Newbould H ,
      4. Karsdal MA , et al
      . Osteoclasts degrade bone and cartilage knee joint compartments through different resorption processes. Arthritis Res Ther 2018;20:67.doi:10.1186/s13075-018-1564-5 pmid:http://www.ncbi.nlm.nih.gov/pubmed/29636095
      OpenUrlCrossRefPubMed
    67. ↵
      2. Chen L ,
      3. Yao F ,
      4. Wang T , et al
      . Horizontal fissuring at the osteochondral interface: a novel and unique pathological feature in patients with obesity-related osteoarthritis. Ann Rheum Dis 2020;79:811–8.doi:10.1136/annrheumdis-2020-216942 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32269059
      OpenUrlAbstract/FREE Full Text
    68. ↵
      2. Yuan XL ,
      3. Meng HY ,
      4. Wang YC , et al
      . Bone–cartilage interface crosstalk in osteoarthritis: potential pathways and future therapeutic strategies. Osteoarthritis Cartilage 2014;22:1077–89.doi:10.1016/j.joca.2014.05.023 pmid:24928319
      OpenUrlPubMed
    69. ↵
      2. Croucher PI ,
      3. McDonald MM ,
      4. Martin TJ
      . Bone metastasis: the importance of the neighbourhood. Nat Rev Cancer 2016;16:373–86.doi:10.1038/nrc.2016.44 pmid:http://www.ncbi.nlm.nih.gov/pubmed/27220481
      OpenUrlCrossRefPubMed
    70. ↵
      2. Zhang R-K ,
      3. Li G-W ,
      4. Zeng C , et al
      . Mechanical stress contributes to osteoarthritis development through the activation of transforming growth factor beta 1 (TGF-β1). Bone Joint Res 2018;7:587–94.doi:10.1302/2046-3758.711.BJR-2018-0057.R1 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30581556
      OpenUrlPubMed
    71. ↵
      2. Zhang M ,
      3. Zhou Q ,
      4. Liang Q-Q , et al
      . IGF-1 regulation of type II collagen and MMP-13 expression in rat endplate chondrocytes via distinct signaling pathways. Osteoarthritis Cartilage 2009;17:100–6.doi:10.1016/j.joca.2008.05.007 pmid:http://www.ncbi.nlm.nih.gov/pubmed/18595745
      OpenUrlCrossRefPubMedWeb of Science
    72. ↵
      2. Párrizas M ,
      3. Saltiel AR ,
      4. LeRoith D
      . Insulin-like growth factor 1 inhibits apoptosis using the phosphatidylinositol 3'-kinase and mitogen-activated protein kinase pathways. J Biol Chem 1997;272:154–61.doi:10.1074/jbc.272.1.154 pmid:http://www.ncbi.nlm.nih.gov/pubmed/8995241
      OpenUrlAbstract/FREE Full Text
    73. ↵
      2. Loeser RF ,
      3. Shanker G
      . Autocrine stimulation by insulin-like growth factor 1 and insulin-like growth factor 2 mediates chondrocyte survival in vitro. Arthritis Rheum 2000;43:1552–9.doi:10.1002/1529-0131(200007)43:7<1552::AID-ANR20>3.0.CO;2-W pmid:http://www.ncbi.nlm.nih.gov/pubmed/10902760
      OpenUrlCrossRefPubMedWeb of Science
    74. ↵
      2. Jung Y-K ,
      3. Han M-S ,
      4. Park H-R , et al
      . Calcium-phosphate complex increased during subchondral bone remodeling affects earlystage osteoarthritis. Sci Rep 2018;8:487. doi:10.1038/s41598-017-18946-y pmid:http://www.ncbi.nlm.nih.gov/pubmed/29323204
      OpenUrlPubMed
    75. ↵
      2. Dai J ,
      3. Dong R ,
      4. Han X , et al
      . Osteoclast-derived exosomal let-7a-5p targets Smad2 to promote the hypertrophic differentiation of chondrocytes. Am J Physiol Cell Physiol 2020. doi:doi:10.1152/ajpcell.00039.2020. [Epub ahead of print: 06 May 2020].pmid:http://www.ncbi.nlm.nih.gov/pubmed/32374679
    76. ↵
      2. Fujisawa T ,
      3. Hattori T ,
      4. Takahashi K , et al
      . Cyclic mechanical stress induces extracellular matrix degradation in cultured chondrocytes via gene expression of matrix metalloproteinases and interleukin-1. J Biochem 1999;125:966–75.doi:10.1093/oxfordjournals.jbchem.a022376 pmid:http://www.ncbi.nlm.nih.gov/pubmed/10220591
      OpenUrlCrossRefPubMedWeb of Science
    77. ↵
      2. Cao Y ,
      3. Jansen IDC ,
      4. Sprangers S , et al
      . IL-1β differently stimulates proliferation and multinucleation of distinct mouse bone marrow osteoclast precursor subsets. J Leukoc Biol 2016;100:513–23.doi:10.1189/jlb.1A1215-543R pmid:http://www.ncbi.nlm.nih.gov/pubmed/26957213
      OpenUrlCrossRefPubMed
    78. ↵
      2. Pearson MJ ,
      3. Herndler-Brandstetter D ,
      4. Tariq MA , et al
      . Il-6 secretion in osteoarthritis patients is mediated by chondrocyte-synovial fibroblast cross-talk and is enhanced by obesity. Sci Rep 2017;7:3451. doi:10.1038/s41598-017-03759-w pmid:http://www.ncbi.nlm.nih.gov/pubmed/28615667
      OpenUrlPubMed
    79. ↵
      2. Kobayashi K ,
      3. Takahashi N ,
      4. Jimi E , et al
      . Tumor necrosis factor alpha stimulates osteoclast differentiation by a mechanism independent of the ODF/RANKL-RANK interaction. J Exp Med 2000;191:275–86.doi:10.1084/jem.191.2.275 pmid:http://www.ncbi.nlm.nih.gov/pubmed/10637272
      OpenUrlAbstract/FREE Full Text
    80. ↵
      2. Lam J ,
      3. Takeshita S ,
      4. Barker JE , et al
      . TNF-alpha induces osteoclastogenesis by direct stimulation of macrophages exposed to permissive levels of RANK ligand. J Clin Invest 2000;106:1481–8.doi:10.1172/JCI11176 pmid:http://www.ncbi.nlm.nih.gov/pubmed/11120755
      OpenUrlCrossRefPubMedWeb of Science
    81. ↵
      2. Kudo O ,
      3. Sabokbar A ,
      4. Pocock A , et al
      . Interleukin-6 and interleukin-11 support human osteoclast formation by a RANKL-independent mechanism. Bone 2003;32:1–7.doi:10.1016/S8756-3282(02)00915-8 pmid:http://www.ncbi.nlm.nih.gov/pubmed/12584029
      OpenUrlCrossRefPubMedWeb of Science
    82. ↵
      2. Tanaka E ,
      3. Aoyama J ,
      4. Miyauchi M , et al
      . Vascular endothelial growth factor plays an important autocrine/paracrine role in the progression of osteoarthritis. Histochem Cell Biol 2005;123:275–81.doi:10.1007/s00418-005-0773-6 pmid:http://www.ncbi.nlm.nih.gov/pubmed/15856277
      OpenUrlCrossRefPubMedWeb of Science
    83. ↵
      2. Henriksen K ,
      3. Karsdal M ,
      4. Delaisse J-M , et al
      . Rankl and vascular endothelial growth factor (VEGF) induce osteoclast chemotaxis through an ERK1/2-dependent mechanism. J Biol Chem 2003;278:48745–53.doi:10.1074/jbc.M309193200 pmid:http://www.ncbi.nlm.nih.gov/pubmed/14506249
      OpenUrlAbstract/FREE Full Text
    84. ↵
      2. Aulin C ,
      3. Lassacher T ,
      4. Palmblad K , et al
      . Early stage blockade of the alarmin HMGB1 reduces cartilage destruction in experimental OA. Osteoarthritis Cartilage 2020;28:698–707.doi:10.1016/j.joca.2020.01.003 pmid:http://www.ncbi.nlm.nih.gov/pubmed/31982563
      OpenUrlPubMed
    85. ↵
      2. Taniguchi N ,
      3. Yoshida K ,
      4. Ito T , et al
      . Stage-specific secretion of HMGB1 in cartilage regulates endochondral ossification. Mol Cell Biol 2007;27:5650–63.doi:10.1128/MCB.00130-07 pmid:http://www.ncbi.nlm.nih.gov/pubmed/17548469
      OpenUrlAbstract/FREE Full Text
    86. ↵
      2. Engsig MT ,
      3. Chen QJ ,
      4. Vu TH , et al
      . Matrix metalloproteinase 9 and vascular endothelial growth factor are essential for osteoclast recruitment into developing long bones. J Cell Biol 2000;151:879–90.doi:10.1083/jcb.151.4.879 pmid:http://www.ncbi.nlm.nih.gov/pubmed/11076971
      OpenUrlAbstract/FREE Full Text
    87. ↵
      2. Rim YA ,
      3. Nam Y ,
      4. Ju JH
      . The role of chondrocyte hypertrophy and senescence in osteoarthritis initiation and progression. Int J Mol Sci 2020;21:2358. doi:10.3390/ijms21072358 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32235300
      OpenUrlPubMed
    88. ↵
      2. Riegger J ,
      3. Brenner RE
      . Pathomechanisms of posttraumatic osteoarthritis: chondrocyte behavior and fate in a precarious environment. Int J Mol Sci 2020;21:1560. doi:10.3390/ijms21051560
    89. ↵
      2. Musumeci G ,
      3. Loreto C ,
      4. Carnazza ML , et al
      . Characterization of apoptosis in articular cartilage derived from the knee joints of patients with osteoarthritis. Knee Surg Sports Traumatol Arthrosc 2011;19:307–13.doi:10.1007/s00167-010-1215-0 pmid:http://www.ncbi.nlm.nih.gov/pubmed/20644910
      OpenUrlCrossRefPubMed
    90. ↵
      2. Thomas CM ,
      3. Fuller CJ ,
      4. Whittles CE , et al
      . Chondrocyte death by apoptosis is associated with cartilage matrix degradation. Osteoarthritis Cartilage 2007;15:27–34.doi:10.1016/j.joca.2006.06.012 pmid:http://www.ncbi.nlm.nih.gov/pubmed/16859932
      OpenUrlCrossRefPubMedWeb of Science
    91. ↵
      2. Tang Q ,
      3. Su Y-W ,
      4. Fan C-M , et al
      . Release of CXCL12 from apoptotic skeletal cells contributes to bone growth defects following dexamethasone therapy in rats. J Bone Miner Res 2019;34:310–26.doi:10.1002/jbmr.3597 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30395366
      OpenUrlPubMed
    92. ↵
      2. Dong Y ,
      3. Liu H ,
      4. Zhang X , et al
      . Inhibition of SDF-1α/CXCR4 signalling in subchondral bone attenuates post-traumatic osteoarthritis. Int J Mol Sci 2016;17. doi:doi:10.3390/ijms17060943. [Epub ahead of print: 16 Jun 2016].pmid:27322244
      OpenUrlPubMed
    93. ↵
      2. Chen Y ,
      3. Lin S ,
      4. Sun Y , et al
      . Attenuation of subchondral bone abnormal changes in osteoarthritis by inhibition of SDF-1 signaling. Osteoarthritis Cartilage 2017;25:986–94.doi:10.1016/j.joca.2017.01.008 pmid:http://www.ncbi.nlm.nih.gov/pubmed/28131784
      OpenUrlPubMed
    94. ↵
      2. Jiao K ,
      3. Zhang J ,
      4. Zhang M , et al
      . The identification of CD163 expressing phagocytic chondrocytes in joint cartilage and its novel scavenger role in cartilage degradation. PLoS One 2013;8:e53312. doi:10.1371/journal.pone.0053312 pmid:http://www.ncbi.nlm.nih.gov/pubmed/23326413
      OpenUrlCrossRefPubMed
    95. ↵
      2. Linkermann A ,
      3. Stockwell BR ,
      4. Krautwald S , et al
      . Regulated cell death and inflammation: an auto-amplification loop causes organ failure. Nat Rev Immunol 2014;14:759–67.doi:10.1038/nri3743 pmid:http://www.ncbi.nlm.nih.gov/pubmed/25324125
      OpenUrlCrossRefPubMed
    96. ↵
      2. Bingham CO ,
      3. Buckland-Wright JC ,
      4. Garnero P , et al
      . Risedronate decreases biochemical markers of cartilage degradation but does not decrease symptoms or slow radiographic progression in patients with medial compartment osteoarthritis of the knee: results of the two-year multinational knee osteoarthritis structural arthritis study. Arthritis Rheum 2006;54:3494–507.doi:10.1002/art.22160 pmid:http://www.ncbi.nlm.nih.gov/pubmed/17075851
      OpenUrlCrossRefPubMedWeb of Science
    97. ↵
      2. Nishii T ,
      3. Tamura S ,
      4. Shiomi T , et al
      . Alendronate treatment for hip osteoarthritis: prospective randomized 2-year trial. Clin Rheumatol 2013;32:1759–66.doi:10.1007/s10067-013-2338-8 pmid:http://www.ncbi.nlm.nih.gov/pubmed/23881439
      OpenUrlCrossRefPubMed
    98. ↵
      2. Aitken D ,
      3. Laslett LL ,
      4. Cai G , et al
      . A protocol for a multicentre, randomised, double-blind, placebo-controlled trial to compare the effect of annual infusions of zoledronic acid to placebo on knee structural change and knee pain over 24 months in knee osteoarthritis patients - ZAP2. BMC Musculoskelet Disord 2018;19:217. doi:10.1186/s12891-018-2143-2 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30021646
      OpenUrlPubMed
    99. ↵
      2. Kadri A ,
      3. Ea HK ,
      4. Bazille C , et al
      . Osteoprotegerin inhibits cartilage degradation through an effect on trabecular bone in murine experimental osteoarthritis. Arthritis Rheum 2008;58:2379–86.doi:10.1002/art.23638 pmid:http://www.ncbi.nlm.nih.gov/pubmed/18668550
      OpenUrlCrossRefPubMedWeb of Science
    100. ↵
      2. Connor JR ,
      3. LePage C ,
      4. Swift BA , et al
      . Protective effects of a cathepsin K inhibitor, SB-553484, in the canine partial medial meniscectomy model of osteoarthritis. Osteoarthritis Cartilage 2009;17:1236–43.doi:10.1016/j.joca.2009.03.015 pmid:http://www.ncbi.nlm.nih.gov/pubmed/19361586
      OpenUrlCrossRefPubMedWeb of Science
    101. ↵
      2. Rodrigues TA ,
      3. de Oliveira Freire A ,
      4. Carvalho HCO , et al
      . Prophylactic and therapeutic use of strontium ranelate reduces the progression of experimental osteoarthritis. Front Pharmacol 2018;9:975. doi:10.3389/fphar.2018.00975 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30283333
      OpenUrlPubMed
    102. ↵
      2. Segovia-Silvestre T ,
      3. Bonnefond C ,
      4. Sondergaard BC , et al
      . Identification of the calcitonin receptor in osteoarthritic chondrocytes. BMC Res Notes 2011;4:407. doi:10.1186/1756-0500-4-407 pmid:http://www.ncbi.nlm.nih.gov/pubmed/21996094
      OpenUrlCrossRefPubMed
    103. ↵
      2. Karsdal MA ,
      3. Byrjalsen I ,
      4. Alexandersen P , et al
      . Treatment of symptomatic knee osteoarthritis with oral salmon calcitonin: results from two phase 3 trials. Osteoarthritis Cartilage 2015;23:532–43.doi:10.1016/j.joca.2014.12.019 pmid:http://www.ncbi.nlm.nih.gov/pubmed/25582279
      OpenUrlPubMed
    104. ↵
      2. Nagai T ,
      3. Sato M ,
      4. Kutsuna T , et al
      . Intravenous administration of anti-vascular endothelial growth factor humanized monoclonal antibody bevacizumab improves articular cartilage repair. Arthritis Res Ther 2010;12:R178.doi:10.1186/ar3142 pmid:http://www.ncbi.nlm.nih.gov/pubmed/20868495
      OpenUrlPubMed
    105. ↵
      2. Cui Z ,
      3. Crane J ,
      4. Xie H , et al
      . Halofuginone attenuates osteoarthritis by inhibition of TGF-β activity and H-type vessel formation in subchondral bone. Ann Rheum Dis 2016;75:1714–21.doi:10.1136/annrheumdis-2015-207923 pmid:http://www.ncbi.nlm.nih.gov/pubmed/26470720
      OpenUrlAbstract/FREE Full Text
    106. ↵
      2. Martel-Pelletier J ,
      3. Barr AJ ,
      4. Cicuttini FM , et al
      . Osteoarthritis. Nat Rev Dis Primers 2016;2:16072.doi:10.1038/nrdp.2016.72 pmid:http://www.ncbi.nlm.nih.gov/pubmed/27734845
      OpenUrlPubMed
    107. ↵
      2. Walsh DA ,
      3. McWilliams DF ,
      4. Turley MJ , et al
      . Angiogenesis and nerve growth factor at the osteochondral junction in rheumatoid arthritis and osteoarthritis. Rheumatology 2010;49:1852–61.doi:10.1093/rheumatology/keq188 pmid:http://www.ncbi.nlm.nih.gov/pubmed/20581375
      OpenUrlCrossRefPubMedWeb of Science
    108. ↵
      2. Nagae M ,
      3. Hiraga T ,
      4. Yoneda T
      . Acidic microenvironment created by osteoclasts causes bone pain associated with tumor colonization. J Bone Miner Metab 2007;25:99–104.doi:10.1007/s00774-006-0734-8 pmid:http://www.ncbi.nlm.nih.gov/pubmed/17323179
      OpenUrlCrossRefPubMedWeb of Science
    109. ↵
      2. Yoneda T ,
      3. Hiasa M ,
      4. Nagata Y , et al
      . Contribution of acidic extracellular microenvironment of cancer-colonized bone to bone pain. Biochim Biophys Acta 2015;1848:2677–84.doi:10.1016/j.bbamem.2015.02.004 pmid:http://www.ncbi.nlm.nih.gov/pubmed/25687976
      OpenUrlCrossRefPubMed
    110. ↵
      2. Izumi M ,
      3. Ikeuchi M ,
      4. Ji Q , et al
      . Local ASIC3 modulates pain and disease progression in a rat model of osteoarthritis. J Biomed Sci 2012;19:77. doi:10.1186/1423-0127-19-77 pmid:http://www.ncbi.nlm.nih.gov/pubmed/22909215
      OpenUrlCrossRefPubMed
    111. ↵
      2. Chen J ,
      3. Li J ,
      4. Li R , et al
      . Efficacy and safety of tanezumab on osteoarthritis knee and hip pains: a meta-analysis of randomized controlled trials. Pain Med 2017;18:374–85.doi:10.1093/pm/pnw262 pmid:http://www.ncbi.nlm.nih.gov/pubmed/28034979
      OpenUrlPubMed
    112. ↵
      2. Tive L ,
      3. Bello AE ,
      4. Radin D , et al
      . Pooled analysis of tanezumab efficacy and safety with subgroup analyses of phase III clinical trials in patients with osteoarthritis pain of the knee or hip. J Pain Res 2019;12:975–95.doi:10.2147/JPR.S191297 pmid:http://www.ncbi.nlm.nih.gov/pubmed/30936738
      OpenUrlPubMed
    113. ↵
      2. Liu B ,
      3. Ji C ,
      4. Shao Y , et al
      . Etoricoxib decreases subchondral bone mass and attenuates biomechanical properties at the early stage of osteoarthritis in a mouse model. Biomed Pharmacother 2020;127:110144.doi:10.1016/j.biopha.2020.110144 pmid:http://www.ncbi.nlm.nih.gov/pubmed/32330796
      OpenUrlPubMed
    114. ↵
      2. Abdel-Magid AF
      . Selective EP4 antagonist may be useful in treating arthritis and arthritic pain. ACS Med Chem Lett 2014;5:104–5.doi:10.1021/ml5000367 pmid:http://www.ncbi.nlm.nih.gov/pubmed/24900798
      OpenUrlPubMed
    115. ↵
      2. Niiyama Y ,
      3. Kawamata T ,
      4. Yamamoto J , et al
      . SB366791, a TRPV1 antagonist, potentiates analgesic effects of systemic morphine in a murine model of bone cancer pain. Br J Anaesth 2009;102:251–8.doi:10.1093/bja/aen347 pmid:http://www.ncbi.nlm.nih.gov/pubmed/19038965
      OpenUrlCrossRefPubMedWeb of Science

    Footnotes

    • Handling editor Josef S Smolen

    • WH and YC contributed equally.

    • Contributors All authors provided a substantial contribution to the conception, design and interpretation of the work, drafted the work or revised it critically for important intellectual content, and provided final approval of the submitted version of the manuscript.

    • Funding This work was supported by the Key Programme of Natural Science Foundation of China (81930067), the Project of Nature Science Foundation of China (31870962), the Medical Science and Technology Youth Cultivation Project of PLA (20QNPY022), the Innovation Funding of TMMU (2018XYY05), the Medical Innovation Capability Upgrading Plan of Southwest Hospital (SWH2018LJ-03) and the Medical Innovation of Graduate Students in Chongqing (CYS19360).

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

    • Patient consent for publication Not required.

    • Provenance and peer review Not commissioned; externally peer reviewed.