Small-Molecule PKD Inhibitor Prevents Mitochondrial Fragmentation and Dysfunction during Gq-Protein Coupled Receptor Stimulation in Cardiac Cells

Regulation of mitochondrial morphology and dynamics is crucial for the maintenance of various cellular functions in cardiomyocytes. Abnormal mitochondrial morphologies concomitant with mitochondrial dysfunction are frequently observed both in human heart failure (HF) and in animal HF models. However, it is still unclear which cardiac signaling pathways regulate mitochondrial morphology and function under pathophysiological conditions. Recent reports suggest that Gq-protein coupled receptor (GqPCR) signaling pathways are critical for the development and progression of HF. Therefore, we hypothesize that GqPCR stimulation induces mitochondrial fragmentation and dysfunction, which initiates cardiomyocyte death. We found that protein kinase D (PKD) activated by GqPCR signaling was translocated to outer mitochondrial membrane (OMM) observed by Western blot analysis of cytosolic and mitochondria-enriched fractionated proteins and by live cell imaging of fluorescence resonance energy transfer (FRET). We also found that GqPCR-mediated PKD activation induced mitochondrial fragmentation, leading to increased reactive oxygen species (ROS) generation as well as increased mitochondrial permeability transition pore (mPTP) opening, which initiates apoptotic signaling activation and cardiomyocyte death. These morphological and functional changes in cardiac mitochondria were mediated via PKD-dependent phosphorylation of mitochondrial fission protein, Dynamin-Like Protein 1 (DLP1) at S637. Moreover, pretreatment with a novel potent PKD inhibitor CRT0066101 effectively inhibited GqPCR-mediated PKD translocation to OMM, DLP1 phosphorylation at S637, mitochondrial fragmentation, ROS generation and mPTP activation. In conclusion, we demonstrate that GqPCR stimulation induces mitochondrial fragmentation and dysfunction through PKD-dependent phosphorylation of DLP1 at S637, which likely contributes to cardiomyocyte injury. Thus, small-molecule PKD inhibitor may become a novel and potent therapeutic for preventing cardiac cell injury and death during HF.