Single-cell transcriptomic and proteomic analyses identify cellular programs associated with post-traumatic osteoarthritis resistance in MRL/MpJ mice

Osteoarthritis affects over 30 million U.S. adults and is a leading cause of pain and disability. Post-traumatic osteoarthritis (PTOA) develops after joint injury and can progress to chronic disease; however, no approved therapies halt structural joint degeneration. We previously showed that “super-healer” MRL/MpJ (MRL) mice are protected from injury-induced cartilage damage. Here, we used single-cell RNA sequencing and mass spectrometry-based proteomics to compare injury-induced molecular changes in joint connective-tissue cell populations from PTOA-resistant MRL and PTOA-susceptible C57BL/6J (B6) mice at 4 weeks after noninvasive anterior cruciate ligament rupture. Anabolic cartilage genes, including Col2a1, Acan, and Col9a2 , were downregulated in chondrocytes from both strains after injury relative to uninjured controls, with similar transcript levels in injured MRL and B6 joints but higher expression in MRL at baseline. However, extracellular matrix-enriched proteomic analysis revealed a higher abundance of the corresponding cartilage-matrix proteins in MRL than in B6 in both uninjured and injured joints. Joint connective tissue cells from MRL also exhibited increased expression of antioxidant and detoxification-associated genes, including Gpx1 , Glo1 , Gstm1 , Gstm2 , and Gstp1 , consistent with an enhanced stress-adaptive program. In contrast, chondrocytes, fibroblasts, and synovial fibroblasts from B6 showed increased expression of fibrosis- and remodeling-associated genes, including Col1a1 , Col1a2 and Spp1 , following injury compared with MRL. We also identified strain-specific gene expression differences that were evident independent of injury, including higher expression of Vwa5a, Glo1, and Lysmd2 in MRL and of Ubc, Capg, and Pttg1 in B6. Consistent with these transcriptomic patterns, proteomic analysis identified differential abundance of proteins involved in cellular stress responses, metabolism, and cytoskeletal dynamics, including Vwa5a , Glo1 , Gstp1 , and Capg. Together, these findings point to differential engagement of antioxidant and fibrotic pathways associated with PTOA resistance and susceptibility and identify candidate pathways for disease-modifying therapy development.