Mitochondrial Nm23-H4/Ndpk-D Supports Cardiolipin Signaling To Eliminate Depolarized Mitochondria By Mitophagy

The well-established function of the hexameric intermembrane space protein, NDPK-D/NM23-H4, is phosphotransfer activity as a nucleoside diphosphate kinase. However, recent data revealed a second function in lipid signaling that is involved in mitophagy, a critical process for cell homeostasis. Externalization of the inner mitochondrial membrane phospholipid, cardiolipin (CL), to the mitochondrial surface was identified as a mitophageal signal, recognized by the microtubule-associated protein 1 light chain 3. Here we demonstrate that NDPK-D binds CL and facilitates its re-distribution to the outer mitochondrial membrane. We found that mitophagy induced by a protonophoric uncoupler, CCCP, caused externalization of CL to the surface of mitochondria in murine lung epithelial MLE-12 cells and human cervical adenocarcinoma HeLa cells. RNAi knockdown of endogenous NDPK-D decreased CCCP-induced CL externalization and mitochondrial degradation. A R90D NDPK-D mutant which does not bind CL was inactive in promoting mitophagy. In situ proximity ligation assay showed that mitophagy-inducing CL transfer activity of NDPK-D is closely associated with the dynamin-like GTPase OPA1, and OPA1 silencing favored NDPK-D supported CL transfer, implicating fission-fusion dynamics in mitophagy regulation. Support: FRM DPM20121125557, ANR France, NIH PO1HL114453, U19AIO68021, NS076511, ES020693, NS065789, AG026389, NIOSH OH008282, HFSP, and Barth Syndrome Foundation of Canada.