DNM1L-mediated fission governs mitophagy & mitochondrial biogenesis during myogenic differentiation.

Background: Remodeling of the mitochondrial network is implicated in myogenesis. Remodeling processes including mitochondrial fission, mitophagy, and biogenesis are important as they finetune the mitochondrial network to meet the increased energetic demand of myotubes. Evidence suggests that mitochondrial fission governs other mitochondrial remodeling processes; however, this relationship is unclear in the context of myogenesis.

Methods: We used C2C12 myoblasts to study changes in mitochondrial remodeling processes and their role in regulating myogenesis. To investigate this, we employed genetic manipulation with adenoviruses to modify the levels of key molecules involved in mitochondrial remodeling, including DNM1L, BNIP3, and PPARGC1A.

Results: We demonstrate that overexpression of fission protein DNM1L accelerated mitophagic flux, but reduced myotube size without affecting mitochondrial biogenesis. Conversely, DNM1L knockdown reduced mitophagic flux, impaired myoblast differentiation, and suppressed mitochondrial biogenesis signaling. Additionally, DNM1L knockdown increased mitochondrial apoptotic signaling through CASP9 and CASP3 activation. Attempts to rescue myogenesis through overexpression of the mitophagy receptor BNIP3 or the biogenesis regulator PPARGC1A were unsuccessful in the absence of proper mitochondrial fission. Furthermore, DNM1L overexpression in BNIP3-deficient cells enhanced mitophagic flux, but did not promote myogenesis.

Conclusion: These results underscore the complex interdependencies among mitochondrial remodeling processes and highlight the necessity for sequential activation of mitochondrial fission, mitophagy, and biogenesis.