MTP18 maintains mitochondrial morphology and cellular homeostasis 1Donnarumma E,1Patitucci C, 3Caicci F, 2,3Giacomello M, 1Wai T. 1Institute Necker Enfantes Malades, Paris, France 2Venetian Institute of Molecular Medicine, Padua, Italy 3Department of Biology, University of Padua, Italy Background: Mitochondria regulate their network via balanced membrane fusion and fission events. Imbalanced mitochondrial dynamics has been associated with defects in energy metabolism and cell viability. The machinery responsible for outer membrane fusion and fission is well-characterized yet much less is known about the proteins required for these processes at the inner membrane. Mitochondrial protein 18 kDa (MTP18) is an inner membrane protein unique to metazoans that exhibits characteristics of a fission factor. MTP18 overexpression drives fragmentation via the dynamin-like GTPase DRP1. How MTP18 regulates mitochondrial morphology, function and metabolism is unclear. Aim:To characterize the role of MTP18 in mitochondria and its importance in maintaining cellular homeostasis.
Results:We generated MTP18 KO mouse embryonic fibroblasts by CRISPR/Cas9 genome editing approaches. Consistent with its pro-fission role, MTP18 ablation promotes mitochondrial elongation associated with decreased DRP1 recruitment on the mitochondrial surface. MTP18 KO cells retain normal mitochondrial membrane potential and cristae yet are resistant to mitochondrial fragmentation induced by the membrane uncoupler CCCP despite an activation of OMA1 and stress-induced processing of OPA1. MTP18 ablation does not inhibit cell proliferation although MTP18 KO cells do exhibit increased sensitivity to apoptotic stimuli. MTP18 KO cells exhibit reduced rates of oxygen consumption and glycolysis. To address the importance of MTP18 in vivo, we generated KO miceby crossing conditional MTP18Flox/Flox with CMV-CRE recombinase mice. These KO mice are viable at birth and display no macroscopic cardiac abnormalities: the heart appears normal in mass and structure. However, oxygen consumption rates measured in isolated cardiac mitochondria of adult KO mice was significantly reduced suggesting a defect in mitochondrial function that could be pathological under stress conditions and/or during ageing.
Conclusions:Our results indicate that MTP18 plays an important role in the form and function of mitochondria and may be an important factor in maintaining cardiac health.