The absence of SNF8 in the yeast Saccharomyces cerevisiae leads to mitochondrial dysfunction

Introduction: SNF8 encodes for the ESCRT-II subunit, one of the three endosomal sorting complexes required for transport (ESCRT) machinery and essential for membrane remodeling and autophagy. Mutations in the SNF8 gene lead to a phenotypic spectrum, ranging from patients characterized by severe developmental and epileptic encephalopathy to patients with milder phenotypes (Brugger et al, 2024). To gain insights into the possible impact of SNF8 pathogenic variants on mitochondrial function, we used the yeast S. cerevisiae as a model system comparing the respiratory phenotype of the BY4741 wild-type strain and its isogenic BY4741 snf8Δ. Material and methods: Spot assay analysis was performed on plates supplemented with oxidative carbon sources. Oxygen consumption rate (OCR), complex activities, steady-state protein levels, petite frequency, and mtDNA levels were measured as previously reported (Nolli et al, 2015; Gilea et al, 2021). Results and discussion: Oxidative growth of the snf8Δ strain was decreased, suggesting that Snf8 is involved in OXPHOS activity too. This result was confirmed by an 80% reduction of the OCR activity and a 50% to 60% reduction of the respiratory complexes II, III, and IV activities. The steady-state levels of a subunit from each complex, as well as porins, were strongly reduced when normalized to Pgk1, suggesting both a defect of the OXPHOS machinery and of the mitochondrial mass. Extended mtDNA instability and decreased mtDNA levels were also observed, indicating that Snf8 is involved in mtDNA maintenance. Conclusions: Besides the phenotypes linked to the lack of functional ESCRT complex, the absence of the SNF8 gene in yeast seriously compromises the OXPHOS activity. To gain insight into the association between Snf8 function and mitochondrial function, the search for multicopy suppressors is ongoing, and transcriptomic analysis will be performed.