OPA1 and disease-causing mutants perturb mitochondrial nucleoid distribution.

Area of Science:

• Mitochondrial biology
• Cellular and molecular medicine
• Genetics and genomics

Background:

• Optic atrophy protein 1 (OPA1) is essential for inner mitochondrial membrane fusion and mitochondrial cristae organization.
• Mutations in OPA1 cause autosomal dominant optic atrophy (ADOA), a leading hereditary optic neuropathy.
• ADOA is characterized by impaired mitochondrial function, including fusion, cristae structure, and mitochondrial DNA (mtDNA) integrity.

Purpose of the Study:

• To investigate the physio-pathological relevance of mitochondrial nucleoid distribution in relation to OPA1 function.
• To analyze the impact of OPA1 loss-of-function and ADOA-associated mutations on nucleoid distribution within the mitochondrial network.
• To elucidate the role of OPA1 in organizing mtDNA nucleoids and their proximity to mitochondrial cristae.

Main Methods:

• Utilized high-resolution confocal microscopy to visualize mitochondrial nucleoid distribution in cells with altered OPA1 expression.
• Developed a novel analytical model to quantify nucleoid distribution within the mitochondrial population and longitudinally within single mitochondria.
• Studied Opa1-null cells, cells overexpressing wild-type OPA1 or ADOA mutants, and fibroblasts from ADOA patients.

Main Results:

• Opa1-null cells exhibited reduced mtDNA levels, decreased nucleoid abundance, and altered nucleoid distribution within the mitochondrial population.
• Loss of OPA1 function led to cristae disorganization and altered nucleoid-cristae proximity, partially rescued by OPA1 isoform 1.
• Overexpression of ADOA-associated OPA1 mutants in wild-type cells perturbed nucleoid distribution and caused cristae disorganization, mirroring findings in patient-derived fibroblasts.
• Mitochondria lacking nucleoids accumulated in both Opa1-null cells and cells expressing ADOA mutants.

Conclusions:

• OPA1 plays a critical role in regulating mitochondrial nucleoid distribution within the mitochondrial landscape and at the single-organelle level.
• Disrupted nucleoid distribution and cristae organization due to OPA1 dysfunction are significant contributors to ADOA etiology.
• These findings reveal novel insights into the pathogenesis of ADOA, emphasizing the importance of OPA1-mediated mitochondrial organization.