EXTENDED REPORT

Fibroblasts from the inner granulation tissue of the pseudocapsule in hips at revision arthroplasty induce osteoclast differentiation, as do stromal cells

H Sakai¹, S Jingushi¹, T Shuto¹, K Urabe¹, T Ikenoue¹, K Okazaki¹, T Kukita², A Kukita³, Y Iwamoto¹

¹ Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
² Second Department of Anatomy, Faculty of Dentistry, Kyushu University, Fukuoka, Japan
³ Department of Microbiology, Saga Medical School, Saga, Japan

Correspondence to:
Correspondence to:
Dr S Jingushi, Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3–1–1 Maidashi, Higashi-ku, Fukuoka 812–8582, Japan;
jingushi{at}ortho.med.kyushu-u.ac.jp

Background: It has previously been shown that many osteoclast precursors are included in the granulation tissue within the pseudocapsule obtained at revision arthroplasty from hips with osteolysis. In vitro culture of only cells isolated from the granulation tissue has been previously shown to generate many mature osteoclasts.

Objective: To investigate the presence or otherwise of supporting cells, similar to stromal cells, which differentiate osteoclasts within the granulation tissue.

Methods: Cells isolated from the granulation tissue were cultured alone, and after four weeks fibroblast-like cells (granulation fibroblasts) remained. Rat non-adherent bone marrow cells (NA-BMCs) were co-cultured with the granulation fibroblasts with or without 1,25(OH)₂D₃ (10^-8 M) or heat treated ROS 17/2.8 cell conditioned medium (ht ROSCM), or both. Multinucleated cells (MNCs), which formed, were assessed by biochemical and functional characterisation of osteoclasts. Receptor activator of NFB ligand (RANKL) was investigated by immunohistochemistry.

Results: Co-culture of NA-BMCs and granulation fibroblasts caused the formation of tartrate resistant acid phosphatase (TRAP) positive MNCs, which had the calcitonin receptor (CTR), the Kat-1 antigen, which is specific to the surface of rat osteoclasts, and the ability to form pits in the presence of both 1,25(OH)₂D₃ and ht ROSCM or in the presence of just ht ROSCM. RANKL was detected in fibroblast-like cells in the granulation tissue.

Conclusion: These data suggest that granulation fibroblasts support osteoclast differentiation, as do osteoblasts/stromal cells, and may play a part in aseptic loosening.

Keywords: aseptic loosening; osteolysis; osteoclasts; fibroblasts

Abbreviations: CTR, calcitonin receptor; FBS, fetal buffered saline; ht ROSCM, heat treated ROS 17/2.8 cell conditioned medium; mAb, monoclonal antibody; -MEM, -minimum essential medium; MNCs, multinucleated cells; NA-BMCs, non-adherent bone marrow cells; ODF, osteoclast differentiation factor, OPGL, osteoprotegerin ligand; PBS, phosphate buffered saline; PCR, polymerase chain reaction; RANKL, receptor activator of NFB ligand; RT, reverse transcriptase; [¹²⁵I]sCT; [¹²⁵I]salmon calcitonin; SEM, scanning electron microscopy; TRAP, tartrate resistant acid phosphatase

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