BPS2026 – VDAC isoform-specific modulation of mitochondria structure and function

The voltage-dependent anion channel (VDAC) is the major metabolite channel of the mitochondrial outer membrane and the primary regulator of the exchange of ions and metabolites between the cytosol and mitochondria. The three mammalian VDAC isoforms share a 70% sequence similarity, and mouse knockout (KO) studies have revealed isoform-specific differences in their phenotypes, with the VDAC2KO being particularly lethal. To better elucidate the physiological role of each isoform, we studied structural changes in mitochondria of HeLa cells with CRISPR-Cas9 KOs of each VDAC isoform using electron microscopy and fluorescent confocal microscopy. Mitochondria are exceptionally dynamic organelles that can regulate oxidative phosphorylation and reductive biosynthesis in response to nutrient availability and cellular needs. They alter their shape and size through the processes of fusion and fission, and dysregulation of these mitochondrial dynamics is linked to a variety of pathologies, most notably cancer. Our mitochondrial image analysis revealed a variety of mitochondrial morphologies for wild-type (WT) HeLa cells, which may be important for cancer cell survival and adaptivity. The mitochondrial network complexity of the VDAC2KO cells was comparable to that of the WT cells; however, the cristae density was considerably increased. Paired with Seahorse analyzer respiration studies, this indicates increased dependence of HeLa cells on oxidative phosphorylation upon VDAC2KO. VDAC1KO and VDAC3KO decreased mitochondrial size and network complexities, where VDAC1KO decreased cristae density while VDAC3KO resulted in enlarged mitochondria. Despite the drastic effect of VDAC1KO on mitochondrial structure, no effect on mitochondrial respiration and cell growth was observed. Surprisingly, the KO of VDAC3, the minor isoform, displayed the most impact on mitochondrial structure and respiration. Our results suggest that VDAC plays an isoform-specific role in the dynamic regulation of mitochondrial structure and function in cancer cells.