A damaging mutation in COL6A3 alters the mechanobiologic response of chondrocytes derived from human induced pluripotent stem cells

Osteoarthritis (OA) is a complex disease associated with genetic, biological, and mechanical risk factors that act, in part, to alter chondrocyte homeostasis. Our recent exome sequencing studies identified a damaging genetic variant in COL6A3, a monomeric unit of collagen type VI and a distinguishing component of the pericellular matrix (PCM) of articular cartilage, a transducer of mechanical and biochemical signals for the chondrocyte. To study the effect of this genetic variant, human induced pluripotent stem cell (hiPSC)-derived chondrocytes, genetically edited to harbor the COL6A3 mutation, were used as an in vitro model to investigate chondrocyte mechanobiology and pathobiology. The COL6A3 variant resulted in lower PCM elastic modulus and reduced expression of key matrix proteins, suggesting altered PCM structural composition and mechanical properties. Functional analyses revealed altered mechanotransduction, characterized by heightened osmotically-induced calcium signaling, consistent with reduced PCM modulus, and reduced anabolic response to TRPV4 activation, both at the transcriptional level and in matrix biosynthesis. RNA-sequencing identified dysregulated pathways and aberrant TRPV4 signaling in mutant chondrocytes following mechanical loading. The presence of the COL6A3 variant also resulted in disrupted circadian rhythms, with increased BMAL1 expression and a significant phase shift, suggesting that PCM properties influence the circadian clock. Finally, COL6A3 mutant chondrocytes exhibited an exacerbated catabolic response to interleukin-1, an inflammatory cytokine implicated in OA. Our study demonstrates the utility of human iPSCs for studying the pathophysiology of specific OA risk alleles. These findings highlight the impact of the COL6A3 variant on chondrocyte physiology and support targeting mechanotransduction signaling pathways as a potential strategy for OA intervention.