Trpv4-Mediated Mitophagy Regulates Endochondral Ossification In The Condylar Cartilage

This study aims to elucidate the mechanism by which mouth breathing-induced condylar stress change (MB-CSC) disrupts endochondral ossification in the posterior zone of condyle. Fibrocartilage stem cells (FCSCs), cultured in media with/without exogenous Ca2+, were treated with/without MB-CSC with/without TRPV4-enhancer/inhibitor, with/without PINK1-enhancer/inhibitor. TRPV4, Ca2+ influx, PINK1/Parkin, mitophage, and FCSCs differentiation were assessed using Western blotting or immunofluorescence. MB-CSC rat model was induced by intermittent nasal obstruction with 25% oxygen and real-time blood oxygen monitoring in 4-weeek-old male rats. Endochondral ossifications were evaluateed by hematoxylin-eosin and immunohistochemistry staining of the condylar cartilage of rats with/without MB-CSC with/without TRPV4-enhancer/inhibitor with/without PINK1-enhancer/inhibitor. MB-CSC and/or TRPV4-enhancer increasd TRPV4, Ca2+ influx, PINK1/Parkin, mitophagy, decreased differentiation of FCSCs in media containing Ca2+, but not without Ca2+. Downregulating TRPV4 blunted the effects induced by MB-CSC. Upregulating PINK1 increased mitophagy and decreased differentiations with/without MB-CSC and/or TRPV4-enhancer/inhibitor, whereas silencing PINK1 reversed the effects induced by MB-CSC and/or TRPV4-enhancer except TRPV4 and Ca2+ influx. Endochondral ossifications of the condylar cartilage were decreased in MB-CSC with/without TRPV4-enhancer rats. Downregulating TRPV4 and/or silencing PINK1 maintained the endochondral ossification in MB-CSC and/or TRPV4-enhancer rats. MB-CSC upregulates TRPV4 and activates Ca2+-dependent PINK1/Parkin/mitophagy, resulting in impaired endochondral ossification in the posterior zone of condyle.