Assembly defects induce oxidative stress in inherited mitochondrial complex I deficiency

Area of Science:

• Mitochondrial biology
• Biochemistry
• Genetics

Background:

• Complex I (CI) deficiency is the most prevalent mitochondrial disease, accounting for over 30% of cases.
• CI is a crucial enzyme in the respiratory chain, essential for cellular energy production.
• CI assembly involves distinct modules: P (pumping), Q (Quinone), and N (NADH dehydrogenase).

Purpose of the Study:

• To investigate the consequences of inherited CI deficiency on enzyme assembly and cellular function.
• To analyze patient-derived fibroblast cell lines with mutations affecting different CI modules.
• To explore the link between CI assembly defects and oxidative stress.

Main Methods:

• Analysis of 11 fibroblast cell lines from patients with inherited CI deficiency.
• Blue native-polyacrylamide gel electrophoresis (BN-PAGE) to assess CI assembly and intermediates.
• Measurement of NADH dehydrogenase activity and reactive oxygen species (ROS) production.

Main Results:

• Mutations in the matrix arm of CI led to reduced fully assembled enzyme and accumulation of N module intermediates.
• Despite incomplete assembly, the N module retained partial NADH dehydrogenase activity.
• This functional N module contributed to ROS production via reduced flavin mononucleotide (FMN), causing oxidative stress.

Conclusions:

• CI assembly defects are directly linked to increased oxidative stress.
• BN-PAGE is a valuable tool for evaluating CI dysfunction and its consequences.
• Antioxidant therapies may be beneficial for patients with CI assembly defects.