Key points: Abnormal mitochondrial morphology and function in cardiomyocytes are frequently observed under persistent G q protein-coupled receptor (G q PCR) stimulation. Cardiac signalling mechanisms for regulating mitochondrial morphology and function under pathophysiological conditions in the heart are still poorly understood. We demonstrate that a downstream kinase of G q PCR, protein kinase D (PKD) induces mitochondrial fragmentation via phosphorylation of dynamin-like protein 1 (DLP1), a mitochondrial fission protein. The fragmented mitochondria enhance reactive oxygen species generation and permeability transition pore opening in mitochondria, which initiate apoptotic signalling activation. This study identifies a novel PKD-specific substrate in cardiac mitochondria and uncovers the role of PKD on cardiac mitochondria, with special emphasis on the molecular mechanism(s) underlying mitochondrial injury with abnormal mitochondrial morphology under persistent G q PCR stimulation. These findings provide new insights into the molecular basis of cardiac mitochondrial physiology and pathophysiology, linking G q PCR signalling with the regulation of mitochondrial morphology and function. Abstract: Regulation of mitochondrial morphology is crucial for the maintenance of physiological functions in many cell types including cardiomyocytes. Small and fragmented mitochondria are frequently observed in pathological conditions, but it is still unclear which cardiac signalling pathway is responsible for regulating the abnormal mitochondrial morphology in cardiomyocytes. Here we demonstrate that a downstream kinase of G q protein-coupled receptor (G q PCR) signalling, protein kinase D (PKD), mediates pathophysiological modifications in mitochondrial morphology and function, which consequently contribute to the activation of apoptotic signalling. We show that G q PCR stimulation induced by α 1 -adrenergic stimulation mediates mitochondrial fragmentation in a fission- and PKD-dependent manner in H9c2 cardiac myoblasts and rat neonatal cardiomyocytes. Upon G q PCR stimulation, PKD translocates from the cytoplasm to the outer mitochondrial membrane (OMM) and phosphorylates a mitochondrial fission protein, dynamin-like protein 1 (DLP1), at S637. PKD-dependent phosphorylation of DLP1 initiates DLP1 association with the OMM, which then enhances mitochondrial fragmentation, mitochondrial superoxide generation, mitochondrial permeability transition pore opening and apoptotic signalling. Finally, we demonstrate that DLP1 phosphorylation at S637 by PKD occurs in vivo using ventricular tissues from transgenic mice with cardiac-specific overexpression of constitutively active Gα q protein. In conclusion, G q PCR-PKD signalling induces mitochondrial fragmentation and dysfunction via PKD-dependent DLP1 phosphorylation in cardiomyocytes. This study is the first to identify a novel PKD-specific substrate, DLP1 in mitochondria, as well as the functional role of PKD in cardiac mitochondria. Elucidation of these molecular mechanisms by which PKD-dependent enhanced fission mediates cardiac mitochondrial injury will provide novel insight into the relationship among mitochondrial form, function and G q PCR signalling.
Bibliographical noteFunding Information:
B.S.J was supported by NIH/NIGMS U54GM115677 and P30GM1114750. J.O.-U. was supported by NIH/NHLBI R01HL136757, NIH/NIGMS P30GM1114750, American Heart Association (AHA) 4BGIA18830032, AHA 16SDG27260248, W.W. Smith Charitable Trust No. H1403 Medical Research Award, Rhode Island Foundation No. 20164376 Medical Research Grant, American Physiological Society (APS) 2017 Shih-Chun Wang Young Investigator Award, and Physiological Society of Japan (PSJ) 2011 Irisawa Memorial Promotion Award. R.T.C. was supported by AHA GRNT20460376 and NIH/NIGMS U54GM115677. G.C. was supported by VA Merit 5IO1BX000711 and NIH/NHLBI 1R01HL128661. U.M. was supported by NIH/NHLBI R01HL114784. S.-S.S was supported by NIH/NHLBI R01HL093671 and R01HL122124. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of National Institutes of Health.