A high-impactCOL6A3mutation alters the response of chondrocytes in neo-cartilage organoids to hyper-physiologic mechanical loading

ObjectivesThe etiology of osteoarthritis revolves around the interplay between genetic predisposition and perturbing environmental cues, such as mechanical stress. The pericellular matrix, with its hallmark proteins collagen type VI and fibronectin, surrounds chondrocytes and is critical in transducing the biomechanical cues. The objective is to study the functional effects of an OA disease-risk mutation inCOL6A3in interaction with hyper-physiological mechanical cues in a tailored human induced pluripotent stem cells (hiPSCs) derived cartilage organoid model.MethodTo identify pathogenic OA mutations exome sequencing in symptomatic OA patients was performed. To study functional effects, CRISPR-Cas9 genome engineering was used to introduce the mutation in our established human induced pluripotent stem cell-derived in-vitro neo-cartilage organoid model in interaction with hyper-physiological mechanical loading conditions.ResultsA high-impact mutation inCOL6A3was identified that resulted in significantly lower binding between the PCM proteins COLVI and fibronectin (FN) and provoked an osteoarthritic chondrocyte state. Moreover, aberrant function of the PCM, secondary to theCOL6A3mutation, abolished the initial stress responses marked particularly by upregulation ofPTGS2encoding cyclooxygenase-2 (COX-2), after hyper-physiological mechanical loading conditions.ConclusionThese findings demonstrate that ablating the characteristic transient COX-2 response after injurious mechanical cues may have a direct negative impact on chondrocyte health.What is already knownThe etiology of osteoarthritis revolves around the interplay between genetic predisposition and perturbing environmental cues, such as mechanical stress.The pericellular matrix, with its hallmark proteins collagen type VI and fibronectin, surrounds the chondrocytes and is critical in transducing biomechanical cues from the extracellular matrix to chondrocytes henceforth it determines the chondrocyte mechanical environment.The mechanical environment of the chondrocytes is a critical factor that influences chondrocyte health as it determines the balance between synthesis and degradation of the articular cartilage extracellular matrix.What this study addsA sustainable human induced pluripotent stem cell-derived in-vitro neo-cartilage organoid model that is tailored to study detailed biologic effects of mechanical cues to chondrocytes.An OA disease-risk mutation inCOL6A3reduces the binding between collagen type VI to fibronectin and provoked an osteoarthritic chondrocyte state.Upon hyper-physiological mechanical loading, aberrant function of the pericellular matrix, secondary to theCOL6A3mutation, ablates the initial transient inflammatory response, characterized particularly byPTGS2encoding cyclooxygenase-2 (COX-2).How this study might affect research practice or policyInhibiting COX-2, as an important transient inflammatory response after hyper-physiological mechanical cues, could worsen the loss of structural integrity of the cartilage in osteoarthritis patients. Henceforth, prescription of COX-2 inhibitors as pain treatment for OA patients should be reconsidered.