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Abstract
Objectives Osteoarthritis (OA) is the most common joint disease; however, the indeterminate nature of mechanisms by which OA develops has restrained advancement of therapeutic targets. TNF signalling has been implicated in the pathogenesis of OA. TNFR1 primarily mediates inflammation, whereas emerging evidences demonstrate that TNFR2 plays an anti-inflammatory and protective role in several diseases and conditions. This study aims to decipher TNFR2 signalling in chondrocytes and OA.
Methods Biochemical copurification and proteomics screen were performed to isolate the intracellular cofactors of TNFR2 complex. Bulk and single cell RNA-seq were employed to determine 14-3-3 epsilon (14-3-3ε) expression in human normal and OA cartilage. Transcription factor activity screen was used to isolate the transcription factors downstream of TNFR2/14-3-3ε. Various cell-based assays and genetically modified mice with naturally occurring and surgically induced OA were performed to examine the importance of this pathway in chondrocytes and OA.
Results Signalling molecule 14-3-3ε was identified as an intracellular component of TNFR2 complexes in chondrocytes in response to progranulin (PGRN), a growth factor known to protect against OA primarily through activating TNFR2. 14-3-3ε was downregulated in OA and its deficiency deteriorated OA. 14-3-3ε was required for PGRN regulation of chondrocyte metabolism. In addition, both global and chondrocyte-specific deletion of 14-3-3ε largely abolished PGRN’s therapeutic effects against OA. Furthermore, PGRN/TNFR2/14-3-3ε signalled through activating extracellular signal-regulated kinase (ERK)-dependent Elk-1 while suppressing nuclear factor kappa B (NF-κB) in chondrocytes.
Conclusions This study identifies 14-3-3ε as an inducible component of TNFR2 receptor complex in response to PGRN in chondrocytes and presents a previously unrecognised TNFR2 pathway in the pathogenesis of OA.
- Osteoarthritis
- Chondrocytes
- Inflammation
Data availability statement
Data are available in a public, open access repository. Data are available on reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information. Bulk and single-cell RNA-seq data that support the findings of this study have been deposited in Gene Expression Omnibus (GEO) with the accession codes GSE168505 and GSE169454. All the data relevant to the study are included in the article or uploaded as supplementary information.
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Data availability statement
Data are available in a public, open access repository. Data are available on reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information. Bulk and single-cell RNA-seq data that support the findings of this study have been deposited in Gene Expression Omnibus (GEO) with the accession codes GSE168505 and GSE169454. All the data relevant to the study are included in the article or uploaded as supplementary information.
Footnotes
Handling editor Josef S Smolen
Contributors WF and CL designed the experimental plan and wrote the manuscript. WF executed most experiments. AH assisted with human OA sample collection and µCT data analysis. YC collected OA sample for single cell RNA-Seq and data analysis. WH performed RNA-seq data analysis. XD assisted with µCT data analysis. MC assisted with macrophage immunohistochemical staining. JM and YY assisted with protein immunoprecipitation. YD, WS and RL assisted with mouse studies. MA and JS provided cDNAs extracted from human normal and arthritic cartilage for qRT-PCR. ES, PL and RS provided human cartilage samples for bulk RNA-sea, scRNA-seq and for Immunoblotting. All authors were involved in editing the manuscript.
Funding This work is supported partly by NIH research grants R01AR062207, R01AR061484, R01AR076900, R01NS103931, R01AR054817 and a DOD research grant W81XWH-16-1-0482.
Competing interests None declared.
Patient and public involvement statement Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.
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