OPA1 processing controls mitochondrial fusion and is regulated by mRNA splicing, membrane potential, and Yme1L

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The OPA1 protein, a dynamin-related GTPase, is essential for mitochondrial fusion and is implicated in dominant optic atrophy.
• OPA1 undergoes proteolytic cleavage, producing long isoforms from mRNA splice variants and short forms via S1/S2 protease sites.

Purpose of the Study:

• To investigate the functional roles of individual OPA1 splice forms in mitochondrial fusion using a cellular system.
• To elucidate the interplay between OPA1 long and short isoforms and their regulation.

Main Methods:

• Development of OPA1-null cells to create a controlled system for studying OPA1 splice forms.
• Analysis of mitochondrial fusion activity in relation to specific OPA1 isoforms and their co-expression.
• Investigation of OPA1 isoform stability and cleavage under conditions of altered mitochondrial membrane potential.

Main Results:

• Only OPA1 mRNA splice forms yielding both long and short isoforms supported significant mitochondrial fusion.
• Long and short OPA1 isoforms exhibited complementary functions, with limited activity when expressed alone.
• Loss of mitochondrial membrane potential destabilized long OPA1 isoforms and promoted S1 cleavage, while S2 cleavage was regulated by Yme1L.

Conclusions:

• Mammalian cells possess multiple regulatory pathways for mitochondrial fusion, controlled by the balance of OPA1 isoforms.
• The functional complementation between OPA1 long and short isoforms is critical for efficient mitochondrial fusion.
• Regulation of OPA1 cleavage and isoform spectrum provides a mechanism for controlling mitochondrial dynamics.