Cartes-Saavedra, B. | bioRxiv Science

bioRxiv2025

Disease-causing MFN2 mutants impair mitochondrial fission dynamics by distinct DRP1 dysregulation

Mitochondria undergo fusion and fission. While DRP1 regulates fission, fusion is controlled by OPA1, MFN1, and MFN2. The balance between these processes and the crosstalk between machineries remains poorly understood. MFN2 mutations cause Charcot-Marie-Tooth disease type 2A (CMT2A), affecting mitochondrial fusion and morphology. However, their role in fission is unclear. Using skin fibroblasts from CMT2A patients (L248H and M376V MFN2 mutations) and wild-type mouse embryonic fibroblasts expressing these variants we studied how MFN2 mutations impact mitochondrial dynamics beyond fusion. We analysed mitochondrial morphology and dynamics, by live-cell confocal microscopy, and tested fusion/fission protein levels, oxygen consumption rate (OCR), extracellular acidification rate (ECAR), and oxidative phosphorylation complex subunits. MFN2 mutations impaired mitochondrial fusion and displayed distinct effects on fission and cellular metabolism. L248H-expressing cells showed hyper-elongated mitochondria, impaired fission, and increased OCR, while, M376V cells exhibited fragmentation, enhanced fission, and elevated ECAR. These effects correlated with differential Drp1 phosphorylation. Our findings demonstrate that MFN2 mutants differentially influences fission and metabolism, highlighting the need to consider these effects in therapies aimed at modulating mitochondrial dynamics.

cell biology↗

bioRxiv2024

OPA1 and disease-causing mutants perturb mitochondrial nucleoid distribution

Optic atrophy protein 1 (OPA1) mediates inner mitochondrial membrane (IMM) fusion and cristae organization. Mutations in OPA1 cause autosomal dominant optic atrophy (ADOA), a leading cause of blindness. Cells from ADOA patients show impaired mitochondrial fusion, cristae structure, bioenergetic function, and mitochondrial DNA (mtDNA) integrity. The mtDNA encodes electron transport chain subunits and is packaged into nucleoids spread within the mitochondrial population. Nucleoids interact with the IMM, and their distribution is tightly linked to mitochondrial fusion and cristae shaping. Yet, little is known about the physio-pathological relevance of nucleoid distribution. We studied the effect of OPA1 and ADOA-associated mutants on nucleoid distribution using high-resolution confocal microscopy. We applied a novel model incorporating the mitochondrial context, separating nucleoid distribution into the array in the mitochondrial population and intramitochondrial longitudinal distribution. Opa1-null cells showed decreased mtDNA levels and nucleoid abundance. Also, loss of Opa1 lead to an altered distribution of nucleoids in the mitochondrial population, loss of cristae periodicity, and altered nucleoids to cristae proximity partly rescued by OPA1 isoform 1. Overexpression of WT OPA1 or ADOA-causing mutants c.870+5G>A or c.2713C>T in WT cells, showed perturbed nucleoid array in the mitochondria population associated with cristae disorganization. Opa1-null and cells overexpressing ADOA mutants accumulated mitochondria without nucleoids. Interestingly, intramitochondrial nucleoid distribution was only altered in Opa1-null cells. Altogether, our results highlight the relevance of OPA1 in nucleoid distribution in the mitochondrial landscape and at a single-organelle level and shed light on new components of ADOA etiology.

cell biology↗