Defective mitochondrial dynamics through aberrant interactions between mitochondria and actin cytoskeleton is increasingly recognized as a key determinant of cardiac fragility after myocardial infarction (MI). Dynamin-related protein 1 (Drp1), a mitochondrial fission-accelerating factor, is activated locally at the fission site through interactions with actin. Here, we report that the actin-binding protein filamin A acted as a guanine nucleotide exchange factor for Drp1 and mediated mitochondrial fission-associated myocardial senescence in mice after MI. In peri-infarct regions characterized by mitochondrial hyperfission and associated with myocardial senescence, filamin A colocalized with Drp1 around mitochondria. Hypoxic stress induced the interaction of filamin A with the GTPase domain of Drp1 and increased Drp1 activity in an actin-binding-dependent manner in rat cardiomyocytes. Expression of the A1545T filamin mutant, which potentiates actin aggregation, promoted mitochondrial hyperfission under normoxia. Furthermore, pharmacological perturbation of the Drp1-filamin A interaction by cilnidipine suppressed mitochondrial hyperfission-associated myocardial senescence and heart failure after MI. Together, these data demonstrate that Drp1 association with filamin and the actin cytoskeleton contributes to cardiac fragility after MI and suggests a potential repurposing of cilnidipine, as well as provides a starting point for innovative Drp1 inhibitor development. , Hypoxia-induced interaction of filamin with Drp1 causes mitochondrial hyperfission-associated myocardial senescence.

Cardiac hypertrophy, induced by neurohumoral factors, including angiotensin II and endothelin-1, is a major predisposing factor for heart failure. These ligands can induce hypertrophic growth of neonatal rat cardiomyocytes (NRCMs) mainly through Ca2+-dependent calcineurin/nuclear factor of activated T cell (NFAT) signaling pathways activated by diacylglycerol-activated transient receptor potential canonical 3 and 6 (TRPC3/6) heteromultimer channels. Although extracellular nucleotide, adenosine 5′-triphosphate (ATP), is also known as most potent Ca2+-mobilizing ligand that acts on purinergic receptors, ATP never induces cardiomyocyte hypertrophy. Here we show that ATP-induced production of nitric oxide (NO) negatively regulates hypertrophic signaling mediated by TRPC3/6 channels in NRCMs. Pharmacological inhibition of NO synthase (NOS) potentiated ATP-induced increases in NFAT activity, protein synthesis, and transcriptional activity of brain natriuretic peptide. ATP significantly increased NO production and protein kinase G (PKG) activity compared to angiotensin II and endothelin-1. We found that ATP-induced Ca2+ signaling requires inositol 1,4,5-trisphosphate (IP3) receptor activation. Interestingly, inhibition of TRPC5, but not TRPC6 attenuated ATP-induced activation of Ca2+/NFAT-dependent signaling. As inhibition of TRPC5 attenuates ATP-stimulated NOS activation, these results suggest that NO-cGMP-PKG axis activated by IP3-mediated TRPC5 channels underlies negative regulation of TRPC3/6-dependent hypertrophic signaling induced by ATP stimulation.

Chronic exposure to methylmercury (MeHg), an environmental electrophilic pollutant, reportedly increases the risk of human cardiac events. We report that exposure to a low, non-neurotoxic dose of MeHg precipitated heart failure induced by pressure overload in mice. Exposure to MeHg at 10 ppm did not induce weight loss typical of higher doses but caused mitochondrial hyperfission in myocardium through the activation of Drp1 by its guanine nucleotide exchange factor filamin-A. Treatment of neonatal rat cardiomyocytes with cilnidipine, an inhibitor of the interaction between Drp1 and filamin-A, suppressed mitochondrial hyperfission caused by low-dose MeHg exposure. Modification of cysteine residues in proteins with polysulfides is important for redox signaling and mitochondrial homeostasis in mammalian cells. We found that MeHg targeted rat Drp1 at Cys624, a redox-sensitive residue whose SH side chain forms a bulky and nucleophilic polysulfide (Cys624-S(n)H). MeHg exposure induced the depolysulfidation of Cys624-S(n)H in Drp1, which led to filamin-dependent activation of Drp1 and mitochondrial hyperfission. Treatment with NaHS, which acts as a donor for reactive polysulfides, reversed MeHg-evoked Drp1 depolysulfidation and vulnerability to mechanical load in rodent and human cardiomyocytes and mouse hearts. These results suggest that depolysulfidation of Drp1 at Cys624-S(n)H by low-dose MeHg increases cardiac fragility to mechanical load through filamin-dependent mitochondrial hyperfission.

Cysteine modification of the purinergic receptor P2Y 6 R promotes internalization and degradation and limits colitis progression.

No abstract

Cardiac tissue remodeling caused by hemodynamic overload is a major clinical outcome of heart failure. Uridine-responsive purinergic P2Y 6 receptor (P2Y 6 R) contributes to the progression of cardiovascular remodeling in rodents, but it is not known whether inhibition of P2Y 6 R prevents or promotes heart failure. We demonstrate that inhibition of P2Y 6 R promotes pressure overload-induced sudden death and heart failure in mice. In neonatal cardiomyocytes, knockdown of P2Y 6 R significantly attenuated hypertrophic growth and cell death caused by hypotonic stimulation, indicating the involvement of P2Y 6 R in mechanical stress-induced myocardial dysfunction. Unexpectedly, compared with wild-type mice, deletion of P2Y 6 R promoted pressure overload-induced sudden death, as well as cardiac remodeling and dysfunction. Mice with cardiomyocyte-specific overexpression of P2Y 6 R also exhibited cardiac dysfunction and severe fibrosis. In contrast, P2Y 6 R deletion had little impact on oxidative stress-mediated cardiac dysfunction induced by doxorubicin treatment. These findings provide overwhelming evidence that systemic inhibition of P2Y 6 R exacerbates pressure overloadinduced heart failure in mice, although P2Y 6 R in cardiomyocytes contributes to the progression of cardiac fibrosis. Cardiac remodeling is characterized by structural and morphological changes of the heart, including hypertrophy and fibrosis, and is a major clinical outcome of heart failure after cardiac injury 1,2. Structural remodeling is thought to be a plasticity process of the heart to overcome hemodynamic overload, but cardiac resistance (i.e., robustness) to mechanical stress may be reduced by additional environmental factors, such as physical and chemical stresses 3. Purinergic receptors are activated by extracellular nucleotides and play important roles in cardiovascular physiology and pathophysiology 4. Purinergic receptors are divided into two main groups, P1 and P2. P1 receptors are activated by adenosine, and mediate cardiodepressant and cardioprotective effects 4. P2 receptors are subdivided into P2X and P2Y subfamilies, which consist of ligand-gated ion channels and G protein coupled receptors (GPCRs), respectively 4. The P2Y family has eight subtypes (P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 , P2Y 11 , P2Y 12 , P2Y 13 and P2Y 14) that differ in their coupling G protein and ligand selectivity 5. Purinergic signaling must be important for cardiovascular homeostasis because many purinergic receptors are expressed in human and mouse hearts 6,7. The nucleotide, uridine triphosphate (UTP), induces a profibrotic response via P2Y 2 R 8 , while adenosine triphosphate (ATP) induces contraction 9 and negatively regulates hypertrophic growth of cardiomyocytes 10,11 .

No abstract

No abstract