Impaired complex IV activity in response to loss of LRPPRC function can be compensated by mitochondrial hyperfusion

Area of Science:

• Cell Biology
• Genetics
• Biochemistry

Background:

• Mitochondrial morphology is dynamic and changes with stimuli, but its functional significance remains largely unknown.
• Leucine-rich pentatricopeptide repeat containing (LRPPRC) is implicated in French Canadian Leigh Syndrome, a neurodegenerative disorder.

Purpose of the Study:

• To investigate the role of mitochondrial morphology changes in response to cellular stress.
• To identify genes involved in regulating mitochondrial morphology and function.

Main Methods:

• Conducted a screen for Caenorhabditis elegans mutants with abnormal mitochondrial morphology.
• Utilized RNA interference (RNAi) to reduce the function of mma-1 and LRPPRC.
• Assessed mitochondrial morphology, electron transport chain complex IV activity, and ATP levels in wild-type and mutant organisms/cells.
• Observed developmental outcomes (larval arrest, embryonic lethality) in mma-1 mutants.

Main Results:

• Identified MMA-1, the C. elegans homolog of LRPPRC, as a key regulator of mitochondrial morphology.
• Reduced mma-1/LRPPRC function leads to mitochondrial hyperfusion and decreased complex IV activity, without altering ATP levels.
• Preventing hyperfusion in mma-1 mutants results in developmental arrest and lethality.
• LRPPRC knockdown in mammalian cells causes mitochondrial fragmentation and reduced ATP levels.

Conclusions:

• Mitochondrial hyperfusion is an evolutionarily conserved mechanism to compensate for reduced electron transport chain activity.
• MMA-1/LRPPRC plays a critical role in maintaining mitochondrial function and organismal viability under conditions of impaired respiration.
• This study reveals a novel adaptive response of mitochondria to functional deficits, highlighting the importance of mitochondrial dynamics in cellular homeostasis.