Hossain, M. G. | bioRxiv Science

bioRxiv2021

Joint degeneration in a mouse model of pseudoachondroplasia: ER stress, inflammation and autophagy blockage

Pseudoachondroplasia (PSACH), a short limb skeletal dysplasia, associated with premature joint degeneration is caused by misfolding mutations in cartilage oligomeric matrix protein (COMP). Here, we define mutant-COMP-induced stress mechanisms that occur in articular chondrocytes of MT-COMP mice, a murine model of PSACH. The accumulation of mutant-COMP in the ER occurred early in MT-COMP articular chondrocytes and stimulated inflammation (TNF) at 4 wks. Articular chondrocyte death increased at 8 wks and ER stress through CHOP was elevated by 12 wks. Importantly, blockage of autophagy (pS6), the major mechanism which clears the ER, sustained cellular stress in MT-COMP articular chondrocytes. Degeneration of MT-COMP articular cartilage was similar to that observed in PSACH and was associated with increased MMPs, degradative enzymes. Moreover, chronic cellular stresses stimulated senescence. Senescence-associated secretory phenotype (SASP) may play a role in generating and propagating a pro-degradative environment in the MT-COMP murine joint. The loss of CHOP or resveratrol treatment from birth preserved joint health in MT-COMP mice. Taken together, these results indicate that ER stress/CHOP signaling and autophagy blockage are central to mutant-COMP joint degeneration and MT-COMP mice joint health can be preserved by decreasing articular chondrocyte stress. Future joint sparing therapeutics for PSACH may include resveratrol.

pathology↗

bioRxiv2020

Resveratrol reduces COMPopathy in mice through activation of autophagy

Misfolding mutations in cartilage oligomeric matrix protein (COMP) cause it to be retained within in ER of chondrocytes, stimulating a multitude of damaging cellular responses including ER stress, inflammation and oxidative stress which ultimately culminates in the death of growth plate chondrocytes and pseudoachondroplasia (PSACH). Previously, we demonstrated that an antioxidant, resveratrol, substantially reduces the intracellular accumulation of mutant COMP, dampens cellular stress and lowers the level of growth plate chondrocyte death. In addition, we showed that resveratrol reduces mTORC1 (mammalian target of rapamycin complex 1) signaling, suggesting a potential mechanism. In this work, we investigate the role of autophagy in treatment of COMPopathies. In cultured chondrocytes expressing wild type or mutant COMP (MT-COMP), resveratrol significantly increased the number of large LC3 vesicles, directly demonstrating that resveratrol stimulated autophagy is an important component of the resveratrol-driven mechanism responsible for the degradation of mutant COMP. Moreover, pharmacological inhibitors of autophagy suppressed degradation of MT-COMP in our established mouse model of PSACH. In contrast, blockage of the proteasome did not substantially alter resveratrol clearance of mutant COMP from growth plate chondrocytes. Mechanistically, resveratrol increased SIRT1 and PP2A expression and reduced MID1 expression and activation of pAKT and mTORC1 signaling in growth plate chondrocytes, allowing clearance of mutant COMP by autophagy. Importantly, we show that optimal reduction in growth plate pathology, including decreased mutant COMP retention, decreased mTORC1 signaling and restoration of chondrocyte proliferation was attained when treatment was initiated between birth to one week of age in MT-COMP mice, translating to birth to approximately 2 years of age in PSACH children. These results clearly demonstrate that resveratrol stimulates clearance of mutant COMP by an autophagy-centric mechanism.

pathology↗