A human mitofusin 2 mutation can cause mitophagic cardiomyopathy

Area of Science:

• Molecular Biology
• Genetics
• Cardiology

Background:

• Cardiac muscle has high mitochondrial density, yet mitochondrial dysfunction is not a recognized cause of isolated cardiomyopathy.
• Mitofusin 2 (MFN2) mutations are known to cause Charcot-Marie-Tooth disease type 2A (CMT2A), a peripheral neuropathy.
• The MFN2 R400Q mutation is disproportionately found in patients with clinical cardiomyopathy.

Purpose of the Study:

• To investigate the enzymatic, biophysical, and functional characteristics of the MFN2 R400Q mutation.
• To determine the specific mechanism by which MFN2 R400Q causes cardiomyopathy.
• To compare the effects of MFN2 R400Q with wild-type and CMT2A-associated MFN2 mutants.

Main Methods:

• Biochemical assays to assess GTPase activity and conformational changes in MFN2 mutants.
• Mitochondrial function assays including fusion, motility, and respiration.
• CRISPR gene editing in mice to introduce MFN2 mutations and subsequent RNA sequencing and metabolomics of affected tissues.
• Cellular studies using cardiomyoblasts and cardiomyocytes to assess mitophagy and drug sensitivity.

Main Results:

• All MFN2 mutants showed impaired mitochondrial fusion; MFN2 R400Q exhibited normal GTPase activity but defective conformational shifting.
• MFN2 R400Q specifically impaired Parkin recruitment to mitochondria, a key step in mitophagy, unlike other mutants.
• CRISPR-edited mice with the MFN2 R400Q mutation developed perinatal cardiomyopathy without other organ involvement, while other mutants did not affect the heart.
• RNA sequencing and metabolomics revealed abnormalities in MFN2 R400Q hearts consistent with mitophagic cardiomyopathy.
• Cells expressing MFN2 R400Q showed mitophagy defects and increased sensitivity to doxorubicin.

Conclusions:

• MFN2 R400Q is the first identified natural MFN2 mutant with a specific defect in mitophagy.
• The unique dysfunction of MFN2 R400Q leads to mitophagic cardiomyopathy, explaining its over-representation in clinical cardiomyopathy cases.
• This study establishes a novel link between MFN2, mitophagy, and heart disease.