SPG7 Variant Escapes Phosphorylation-Regulated Processing by AFG3L2, Elevates Mitochondrial ROS, and Is Associated with Multiple Clinical Phenotypes

Mitochondrial production of reactive oxygen species (ROS) affects many processes in health and disease. SPG7 assembles with AFG3L2 into the mAAA protease at the inner membrane of mitochondria, degrades damaged proteins, and regulates the synthesis of mitochondrial ribosomes. SPG7 is cleaved and activated by AFG3L2 upon assembly. A variant in SPG7 that replaces arginine 688 with glutamine (Q688) is associated with several phenotypes, including toxicity of chemotherapeutic agents, type 2 diabetes mellitus, and (as reported here) coronary artery disease. We demonstrate that SPG7 processing is regulated by tyrosine phosphorylation of AFG3L2. Carriers of Q688 bypass this regulation and constitutively process and activate SPG7 mAAA protease. Cells expressing Q688 produce higher ATP levels and ROS, promoting cell proliferation. Our results thus reveal an unexpected link between the phosphorylation-dependent regulation of the mitochondria mAAA protease affecting ROS production and several clinical phenotypes.