Synovium secretome as a disease-modifying treatment for equine osteoarthritis

To identify chondroprotective factors as potential disease-modifying osteoarthritis treatments using an unbiased, bottom-up proteomics approach.

Paired equine cartilage explants and synovial membrane were collected postmortem from 4 horses with no history of lameness and grossly normal joints at necropsy.

Six groups were established: cartilage, synoviocytes, and cartilage + synoviocytes (coculture), all with or without interleukin (IL)-1β. The catabolic effect of IL-1β was verified by glycosaminoglycan (GAG) released from cartilage into media by 1,9-dimethyl-methylene blue assay and cartilage toluidine blue histochemistry. Conditioned media from cocultures with or with IL-1β were submitted for bottom-up proteomic analysis. Synoviocyte gene expression was evaluated using reverse transcription-quantitative PCR (RT-qPCR) for proteins of interest identified in the proteomics scan.

GAG content was retained in cartilage when in cocultures treated with IL-1β. Fourteen proteins of interest were selected from the proteomic analysis. From these 14 proteins, metalloproteinase inhibitor 3 precursor (TIMP3), tumor necrosis factor receptor superfamily member 11B (TNFRSF11B), insulin-like growth factor-binding protein 2 (IGFBP2), and alpha-2 macroglobulin (A2M) were selected for synoviocyte gene expression analysis by RT-qPCR. Gene expression of TIMP3 (P = .02) and TNFRSF11B (P = .04) were significantly increased in synoviocytes from cocultures treated with IL-1β compared to controls. Contrary to expectations based on protein expression, IGFBP2 gene expression (P = .04) was significantly decreased in IL-1β-stimulated coculture synoviocytes compared to control coculture synoviocytes. A2M gene expression in synoviocytes was not different between coculture groups.

The secretome from synoviocytes could provide a milieu of bioactive factors to restore joint homeostasis in osteoarthritis.