Mitochondrial complex I deficiency: from organelle dysfunction to clinical disease

Area of Science:

• Cellular Biology
• Neurogenetics
• Mitochondrial Medicine

Background:

• Mitochondria generate cellular energy via oxidative phosphorylation using five protein complexes.
• Complex I (NADH:ubiquinone oxidoreductase) is the largest and most complex of these.
• Mutations in nuclear genes encoding Complex I subunits cause severe early-onset neurodegenerative disorders.

Purpose of the Study:

• To provide a comprehensive overview of clinical, biochemical, and cell physiological data from 15 children with isolated, nuclear-encoded Complex I deficiency.
• To elucidate the cell physiological underpinnings of Complex I deficiency-related neurodegeneration.
• To explore potential therapeutic strategies.

Main Methods:

• Clinical assessment and biochemical analysis of 15 affected children.
• Live cell studies using patient-derived skin fibroblasts.
• Analysis of reactive oxygen species production and mitochondrial membrane potential.

Main Results:

• A homogeneous clinical presentation was observed across the studied children, underscoring disease severity.
• Cellular studies revealed a critical role for reactive oxygen species production and altered mitochondrial membrane potential in pathogenesis.
• Therapeutic responses varied based on the catalytic defect's severity, with Ca(2+) homeostasis modulators emerging as potential treatments.

Conclusions:

• Nuclear-encoded Complex I deficiency presents a severe, clinically homogeneous neurodegenerative condition.
• Cellular pathology involves dysregulated reactive oxygen species and mitochondrial membrane potential.
• Targeting Ca(2+) homeostasis may offer new therapeutic avenues for Complex I deficiency.