Mitochondrial dynamics and antiviral responses in Atlantic salmon cardiomyocytes during piscine myocarditis virus infection

Viral infections in higher vertebrates are known to remodel mitochondrial dynamics, which play a critical role in regulating immune responses, energy production and cellular homeostasis. Currently, understanding of mitochondrial dynamics during viral infection in teleost is limited. This study provides the first detailed investigation of mitochondrial responses to piscine myocarditis virus (PMCV) infection, the causative agent of cardiomyopathy syndrome (CMS) and a severe cardiac disease in Atlantic salmon causing economic losses in aquaculture. This study investigates the temporal effects of PMCV infection in cardiomyocytes on mitochondrial dynamics, associated molecular responses using fluorescence microscopy, transmission electron microscopy, histopathology and RT-qPCR. Distinct mitochondrial subpopulations with specific morphologies and spatial distributions were identified. PMCV infection induced marked mitochondrial remodeling, characterized by early fission, followed by swelling and elongation at peak viral RNA levels. These findings link viral kinetics and immune response to mitochondrial remodeling, providing mechanistic insight into CMS pathogenesis and cardiac health.