The role of COQ8A and COQ8B proteins in mitochondrial function

Coenzyme Q (CoQ) is a key redox and antioxidant molecule widely present in biological membranes, yet its synthesis and regulation are still unclear. Coq8p in yeast is required for CoQ biosynthesis supporting the stability of Coq synthesis proteins through an unknown mechanism. COQ8A and COQ8B are two mammalian orthologs of yeast Coq8 that share over 50% sequence identity. Intriguingly, mutations to human COQ8A cause cerebellar ataxia while mutations to human COQ8B cause steroid-resistant nephrotic syndrome. In this work, we aim to study the mitochondrial role of COQ8A and COQ8B in human cells. We analyzed HEK cell lines WT and knockout for COQ8A (COQ8A-/-), COQ8B (COQ8B-/-) or both (COQ8A/B-/-) previously developed in our lab. We measured the biochemical activity of the respiratory complexes by spectrophotometric assays and the organization of the respiratory chain by Blue Native PAGE. In addition, since preliminary experiments showed differences in proline levels in single KO cells, we start investigating the link between proline and OXPHOS. Our results showed an impairment in respiratory chain complexes activity and assembly in COQ8A/B-/- cells and an increase in PRODH activity in COQ8A-/-, COQB8-/- cells. Overall, these findings indicate some overlapping and specific roles of COQ8A and COQ8B in human mitochondria.