The Role And Molecular Mechanism Of Mic10 In Regulating Cristae Morphology

Mitochondria are bilayer membrane organelles in eukaryotes.Outer mitochondrial membrane(OMM)lies parallel to inner boundary membrane(IBM).Inner mitochondrial membrane folds with complex molecular mechanism to form cristae.Highly curved tubular openings called cristae junctions(CJ)separate cristae membrane from inner boundary membrane.Respiration complexes mainly locate at cristae membrane.Therefore cristae is essential for ATP production in mitochondria.Mitochondrial dysfunctions associate with lethal diseases.Cristae plays crucial role in many cellular processes such as aerobic respiration and apoptosis,but the detailed mechanism of cristae formation and remodeling remain elusive.In recent years,a new complex MICOS(mitochondrial contact site and cristae organization system)has been identified.MICOS is essential for maintaining cristae junctions(CJ),regulating inter-membrane architecture and formation of orthodox cristae.MICOS is composed of Mic60,Mic19,Mic10,Mic13,Mic25,Mi26 and Mic27.Studies with deletion mutants identified Mic60 and Mic10 as core subunits of MICOS complex.Though progress has been made,the function and mechanism of MICOS in regulating mitochondrial morphology and organizing inner membrane system remain elusive.In this study,we investigate the role of Mic10 in cristae morphology regulation.Our results show that deletion of Mic10 leads to the disappearance of CJ,elongation of cristae membrane,and most obvious the orientation of cristae changed.STED and Immuno-electron microscopy reveal that Mic10 locates at both cristae junctions and cristae lumen.Mic10 interacts with PHB2 and OPA1.Either knockdown PHB2 or knockout Mic19 leads to down regulation of Mic10 and OPA1 simultaneously.Over-expression of Mic10 can not rescue the cristae junctions perturbed by Mic19 deletion.Thus,integrity of MICOS complex is vital for CJ maintenance.However,L-OPA1(long isoform of OPA1)can rescue Mic10 in Mic19 KO cells.Thus,Mic10 plays a central role in the formation and maintenance of CJ,while PHB2 and OPA1 are epistatic to Mic10 in regulating cristae morphology.We further explored the role of Mic10 in cristae remodeling under certain physiological conditions such as hypoxia.We found hypoxia induces the fragmentation of cristae,and the fragmentation of cristae is especially obvious in Mic10 deletion cells.Fragmented cristae can be clustered locally in mitochondria and form a network structure.It has been reported that L-OPA1 plays an vital role in the regulation of mitochondrial cristae morphology.Meanwhile,hypoxia induces the down-regulation of L-OPA1.Our results indicate that over-expressed Mic10 could delay the down-regulation of L-OPA1 by interacting with L-OPA1.In contrast,Mic10 deletion accelerates the down-regulation of L-OPA1 induced by hypoxia.Therefore,Mic10 interacts with L-OPA1 and they regulate cristae synergistically.In summary,our studies reveals the important role of Mic10 in the regulation of crisatae morphology,and further demonstrate that OPA1,PHB2 and Mic10 regulate cristae morphology synergistically.Our findings provide new evidence for the link between MICOS complex and certain mitochondrial inner membrane proteins,and help to understand the formation and regulation of mitochondral cristae.