OPTN-TRIP6-mediated F-actin mechanical support regulates phagophore closure to govern craniofacial skeletal development

Optn loss causes severe bone defects. • OPTN is vital for craniofacial bone development and OMSC osteogenesis. • OPTN cooperates with TRIP6 to recruit F-actin for mitophagy closure. • Actin-driven mitophagy dictates ACP packaging and EV-mediated release. The development of craniofacial bones is highly dependent on the intramembranous ossification process driven by orofacial mesenchymal stem cells (OMSCs). Optineurin (OPTN), a traditional mitophagy receptor, promotes OMSC matrix mineralization by mediating the extracellular release of amorphous calcium phosphate (ACP) through the initiation of mitophagy via liquid-liquid phase separation. However, the dynamic mechanisms by which OPTN regulates mitochondrial engulfment remain elusive. In this work, we show that in both zebrafish and mouse models, Optn absence causes systemic bone loss and craniofacial abnormalities. Mechanistically, OPTN recruits thyroid receptor-interacting protein 6 (TRIP6) to the surface of damaged mitochondria, inducing local F-actin polymerization and remodeling, which relies on cytoskeletal mechanical forces to support the bending and closure of the phagophore. The depletion of OPTN or TRIP6 significantly impairs mitophagy flux, triggering a massive accumulation of dysfunctional mitochondria. Overall, this study elucidates that the OPTN-TRIP6-F-actin axis ensures autophagosome closure through cytoskeletal remodeling, revealing a novel paradigm in which cytoskeletal mechanical regulation maintains mitochondrial homeostasis to orchestrate craniofacial osteogenesis. Download: Download high-res image (615KB) Download: Download full-size image