The role of OPA1 and mitochondrial dynamics in the biology of cardiac fibroblasts

Cardiac fibroblasts (CFs) are central drivers of fibrosis and pathological remodeling in heart failure. While mitochondrial function is critical for cardiac health, its specific role in CF activation remains poorly understood. This thesis investigates the role of the mitochondrial fusion protein Optic Atrophy 1 (OPA1) and mitochondrial dynamics in regulating CF biology and their response to profibrotic stimuli. Using primary mouse CFs, we demonstrate that the pro-fibrotic stimulus TGFβ1 induces a biphasic mitochondrial remodeling response, characterized by transient fusion and increased metabolic activity followed by fission. Silencing OPA1 disrupted this dynamic, causing mitochondrial fragmentation and bioenergetic failure. Transcriptomic analysis (RNA-seq) revealed that OPA1 depletion significantly blunted the TGFβ1-induced gene expression profile related to extracellular matrix organization and cytoskeletal dynamics. Phenotypically, this resulted in impaired myofibroblast differentiation, evidenced by reduced α-smooth muscle actin (αSMA) expression, decreased procollagen secretion, and defective 3D spheroid formation. These findings establish OPA1-mediated mitochondrial integrity as a fundamental prerequisite for CF activation. We propose that OPA1 acts as a metabolic checkpoint, enabling the necessary metabolic reprogramming required for the initial reparative response following cardiac injury.