AMP-activated protein kinase inhibits K_v1.5 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 voltage‐gated potassium channels (K(v)) in pulmonary arterial smooth muscle by hypoxia, although the precise molecular mechanisms have been unclear. AMP‐activated 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 5‐aminoimidazole‐4‐carboxamide riboside, A769662 or C13 attenuated K(v)1.5 currents in pulmonary arterial myocytes, and this effect was non‐additive with respect to K(v)1.5 inhibition by hypoxia and mitochondrial poisons. Recombinant AMPK phosphorylated recombinant human K(v)1.5 channels in cell‐free 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 voltage‐gated 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 AMP‐activated protein kinase (AMPK), which is intimately coupled to mitochondrial function due to its activation by LKB1‐dependent 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, 5‐aminoimidazole‐4‐carboxamide riboside and C13 and by intracellular dialysis from a patch‐pipette of activated (thiophosphorylated) recombinant AMPK heterotrimers (α2β2γ1 or α1β1γ1). Hypoxia and inhibitors of mitochondrial oxidative phosphorylation reduced AMPK‐sensitive K(+) currents, which were also blocked by the selective K(v)1.5 channel inhibitor diphenyl phosphine oxide‐1 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 cell‐free 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-1ra−/−) 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

Retroviral vector-mediated transfer of the bacterial neomycin resistance gene into fetal and adult sheep and human hematopoietic progenitors in vitro

Abstract We compared the efficiency of retroviral vector (N2)-mediated transfer of the bacterial neomycin resistance gene (NeoR) into adult and fetal hematopoietic progenitors of sheep and humans by assessing their ability to form colonies in the presence of lethal doses of the neomycin analogue G418 in vitro. Fetal cells from both sheep and humans exhibited a higher degree of NeoR transfer than adult cells. The overall level of NeoR expression was significantly higher for sheep than human cells. The transfer/expression of NeoR into adult human bone marrow hematopoietic progenitors was not affected by the presence or absence of T cells and monocyte/macrophages. The efficiency of NeoR transfer into both adult and fetal human cells, however, was improved when transduction was carried out in the presence of recombinant human interleukin-3 and granulocyte-macrophage colony-stimulating factor. These results demonstrate the greater efficiency of NeoR gene transfer into fetal hematopoietic progenitors, which may provide a basis for the relatively higher efficiency of the in utero approach to gene therapy.</jats:p

Retroviral vector-mediated transfer of the bacterial neomycin resistance gene into fetal and adult sheep and human hematopoietic progenitors in vitro

We compared the efficiency of retroviral vector (N2)-mediated transfer of the bacterial neomycin resistance gene (NeoR) into adult and fetal hematopoietic progenitors of sheep and humans by assessing their ability to form colonies in the presence of lethal doses of the neomycin analogue G418 in vitro. Fetal cells from both sheep and humans exhibited a higher degree of NeoR transfer than adult cells. The overall level of NeoR expression was significantly higher for sheep than human cells. The transfer/expression of NeoR into adult human bone marrow hematopoietic progenitors was not affected by the presence or absence of T cells and monocyte/macrophages. The efficiency of NeoR transfer into both adult and fetal human cells, however, was improved when transduction was carried out in the presence of recombinant human interleukin-3 and granulocyte-macrophage colony-stimulating factor. These results demonstrate the greater efficiency of NeoR gene transfer into fetal hematopoietic progenitors, which may provide a basis for the relatively higher efficiency of the in utero approach to gene therapy.</jats:p

Genomic organization, promoter region analysis, and chromosome localization of the mouse bcl-x gene.

Abstract The bcl-x gene, a bcl-2 family member, is highly regulated during lymphoid development, and its expression modulates apoptosis in lymphoid and other cell populations. Several forms of bcl-x mRNAs with different biologic functions have been described in rodents and humans. In this study, we have determined the organization and promoter region of the mouse bcl-x gene in an effort to understand the molecular basis for the different bcl-x mRNA species identified in tissues. We show that mouse bcl-x maps to the distal mouse chromosome 2 at approximately 89 cM, and exhibits a three-exon structure with an untranslated first exon and a facultative first intron. The coding region of bcl-xL is generated by the juncture of exons II and III through a splicing reaction, whereas bcl-xS is generated by an alternatively utilized donor splice site located within exon II. Analysis of multiple cDNAs and primer extension experiments revealed major transcription initiation sites in brain and thymus within a GC-rich region, with multiple Sp1-binding motifs located upstream of exon I. Another promoter was mapped to a 57-bp region localized upstream of the translation initiation codon by transfection of reporter constructs into FL5.12 and K562 cell lines. The remarkable similarity between the genomic regions of bcl-2 and bcl-x suggests that these genes have evolved from a common ancestral gene or through gene duplication.</jats:p