39 research outputs found
AMP-activated protein kinase inhibits K<sub>v</sub>1.5 channel currents of pulmonary arterial myocytes in response to hypoxia and inhibition of mitochondrial oxidative phosphorylation
KEY POINTS: Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltageâgated potassium channels (K(v)) in pulmonary arterial smooth muscle by hypoxia, although the precise molecular mechanisms have been unclear. AMPâactivated protein kinase (AMPK) has been proposed to couple inhibition of mitochondrial metabolism by hypoxia to acute hypoxic pulmonary vasoconstriction and progression of pulmonary hypertension. Inhibition of complex I of the mitochondrial electron transport chain activated AMPK and inhibited K(v)1.5 channels in pulmonary arterial myocytes. AMPK activation by 5âaminoimidazoleâ4âcarboxamide riboside, A769662 or C13 attenuated K(v)1.5 currents in pulmonary arterial myocytes, and this effect was nonâadditive with respect to K(v)1.5 inhibition by hypoxia and mitochondrial poisons. Recombinant AMPK phosphorylated recombinant human K(v)1.5 channels in cellâfree assays, and inhibited K(+) currents when introduced into HEK 293 cells stably expressing K(v)1.5. These results suggest that AMPK is the primary mediator of reductions in K(v)1.5 channels following inhibition of mitochondrial oxidative phosphorylation during hypoxia and by mitochondrial poisons. ABSTRACT: Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltageâgated potassium channels (K(v)) in pulmonary arterial smooth muscle cells that is mediated by the inhibition of mitochondrial oxidative phosphorylation. We sought to determine the role in this process of the AMPâactivated protein kinase (AMPK), which is intimately coupled to mitochondrial function due to its activation by LKB1âdependent phosphorylation in response to increases in the cellular AMP:ATP and/or ADP:ATP ratios. Inhibition of complex I of the mitochondrial electron transport chain using phenformin activated AMPK and inhibited K(v) currents in pulmonary arterial myocytes, consistent with previously reported effects of mitochondrial inhibitors. Myocyte K(v) currents were also markedly inhibited upon AMPK activation by A769662, 5âaminoimidazoleâ4âcarboxamide riboside and C13 and by intracellular dialysis from a patchâpipette of activated (thiophosphorylated) recombinant AMPK heterotrimers (Îą2β2Îł1 or Îą1β1Îł1). Hypoxia and inhibitors of mitochondrial oxidative phosphorylation reduced AMPKâsensitive K(+) currents, which were also blocked by the selective K(v)1.5 channel inhibitor diphenyl phosphine oxideâ1 but unaffected by the presence of the BK(Ca) channel blocker paxilline. Moreover, recombinant human K(v)1.5 channels were phosphorylated by AMPK in cellâfree assays, and K(+) currents carried by K(v)1.5 stably expressed in HEK 293 cells were inhibited by intracellular dialysis of AMPK heterotrimers and by A769662, the effects of which were blocked by compound C. We conclude that AMPK mediates K(v) channel inhibition by hypoxia in pulmonary arterial myocytes, at least in part, through phosphorylation of K(v)1.5 and/or an associated protein
Intracellular Function of Interleukin-1 Receptor Antagonist in Ischemic Cardiomyocytes
Background: Loss of cardiac myocytes due to apoptosis is a relevant feature of ischemic heart disease. It has been described in infarct and peri-infarct regions of the myocardium in coronary syndromes and in ischemia-linked heart remodeling. Previous studies have provided protection against ischemia-induced cardiomyocyte apoptosis by the anti-inflammatory cytokine interleukin-1 receptor-antagonist (IL-1Ra). Mitochondria triggering of caspases plays a central role in ischemia-induced apoptosis. We examined the production of IL-1Ra in the ischemic heart and, based on dual intra/extracellular function of some other interleukins, we hypothesized that IL-1Ra may also directly inhibit mitochondria-activated caspases and cardiomyocyte apoptosis.
Methodology/Principal Findings: Synthesis of IL-1Ra was evidenced in the hearts explanted from patients with ischemic heart disease. In the mouse ischemic heart and in a mouse cardiomyocyte cell line exposed to long-lasting hypoxia, IL-1Ra bound and inhibited mitochondria-activated caspases, whereas inhibition of caspase activation was not observed in the heart of mice lacking IL-1Ra (Il-1raâ/â) or in siRNA to IL-1Ra-interfered cells. An impressive 6-fold increase of hypoxia-induced apoptosis was observed in cells lacking IL-1Ra. IL-1Ra down-regulated cells were not protected against caspase activation and apoptosis by knocking down of the IL-1 receptor, confirming the intracellular, receptor-independent, anti-apoptotic function of IL-1Ra. Notably, the inhibitory effect of IL-1Ra was not influenced by enduring ischemic conditions in which previously described physiologic inhibitors of apoptosis are neutralized.
Conclusions/Significance: These observations point to intracellular IL-1Ra as a critical mechanism of the cell self-protection against ischemia-induced apoptosis and suggest that this cytokine plays an important role in the remodeling of heart by promoting survival of cardiomyocytes in the ischemic regions