Aberrant ER-mitochondria communication is a common pathomechanism in mitochondrial disease

Area of Science:

• Cellular Biology
• Genetics
• Biochemistry

Background:

• Primary mitochondrial diseases stem from genetic mutations impacting oxidative phosphorylation (OxPhos), leading to reduced cellular energy production.
• These diseases exhibit significant clinical variability, with the underlying causes remaining largely unknown.
• The role of communication between the endoplasmic reticulum (ER) and mitochondria, specifically at mitochondria-associated ER membranes (MAMs), in disease pathogenesis is under investigation.

Purpose of the Study:

• To investigate the hypothesis that impaired ER-mitochondrial communication at MAMs contributes to the clinical variability observed in primary mitochondrial diseases.
• To analyze MAM function and ER-mitochondrial connectivity in cells with OxPhos deficiencies caused by pathogenic mitochondrial DNA (mtDNA) mutations.

Main Methods:

• Assayed MAM function and ER-mitochondrial communication in OxPhos-deficient cells.
• Utilized cybrids derived from patients with specific pathogenic mtDNA mutations.
• Measured mitochondrial membrane potential and its influence on ER-mitochondrial connectivity.

Main Results:

• Each pathogenic mtDNA mutation studied altered MAM functions, creating a distinct MAM 'signature' for each disorder.
• Mitochondrial membrane potential was identified as a critical factor regulating ER-mitochondrial connectivity.
• Disruption of ER-mitochondrial communication led to cell survivability issues exceeding those caused solely by reduced ATP output.

Conclusions:

• A novel 'MAM-OxPhos' axis was identified, linking mitochondrial function to ER-mitochondrial communication.
• Mitochondrial membrane potential plays a key role in controlling this axis.
• MAM dysfunction contributes significantly to cell death in primary mitochondrial diseases, offering new diagnostic and therapeutic insights.