Cardiolipin Regulates Mitophagy through the Protein Kinase C Pathway

Cardiolipin (CL), the signature phospholipid of mitochondrial membranes, is important for cardiovascular health, and perturbation of CL metabolism is implicated in cardiovascular disease. Although the role of CL in mitochondrial function, biogenesis, and genome stability has been studied, recent findings indicate that it is essential for functions apart from mitochondrial bioenergetics. In this study, we report that mitophagy is perturbed in CL-deficient yeast cells. Mutants of autophagy/ mitophagy genes ATG8, ATG18, and ATG32 synthetically interact with CL synthase mutant crd1 Delta. CL-deficient cells exhibited decreased GFP-tagged mitochondrial proteins inside the vacuole and decreased free GFP, consistent with decreased mitophagy. Both PKC and high osmolarity glycerol (HOG) MAPK pathways were shown previously to be required for mitophagy. Activation of both MAPKs was defective in CL-deficient cells. Deletion of HOG pathway genes SHO1, SSK1, STE50, and HOG1 exacerbated crd1 Delta growth. 1 M sorbitol and 0.2 M NaCl, which induce the HOG pathway, rescued growth of the mutant. Activation of the MAPK Slt2p was defective in crd1 Delta cells, and up-regulation of the PKC pathway by expression of the PKC1(R398P) gene, which encodes constitutively activated Pkc1p, rescued crd1 Delta growth and mitophagy defects. These findings indicate that loss of CL impairs MAPK pathway activation, and decreased activation of thePKCpathway leads to defective mitophagy.