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Regulation of cardiomyocyte survival by 14-3-3tau
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ABSTRACTS / Journal of Molecular and Cellular Cardiology 42 (2007) S80–S87
mitochondrial permeability transition pore (PT-pore) and can be inhibited by Akt activation. Mitochondrial depolarization induced by H2O2 is prevented by activation of Akt with leukemia inhibitory factor (LIF). This protective effect of LIF is still observed when cells treated with LIF are permeabilized to remove soluble second messengers and mitochondrial depolarization elicited by elevating Ca 2+ . Fractionation studies demonstrate that LIF treatment increases both total and phosphorylated Akt in the mitochondrial fraction. Immunoprecipitation studies demonstrate that LIF treatment increases the association of Akt with outer mitochondrial components of the PT-pore, VDAC and HK-II. HK-II contains consensus sequences for phosphorylation by Akt and LIF induces PI3K and Akt dependent HK-II phosphorylation. Addition of recombinant active Akt to isolated mouse heart mitochondria also elicits a robust increase in HKII phosphorylation and concomitantly inhibits Ca2+-induced cytochrome c release. Finally functional studies demonstrate that forced dissociation of HK-II from mitochondria attenuates the protective effect of LIF on H2O2 induced mitochondrial depolarization. We conclude that Akt has a direct effect at the level of the mitochondrion which is mediated via phosphorylation of HK-II, and that this results in protection of mitochondria against PT-pore opening and of cardiomyocytes against subsequent apoptosis. Keywords: Akt; Cardioprotection; Mitochondria doi:10.1016/j.yjmcc.2007.03.756
Akt2 regulates cardiomyocyte survival and glucose metabolism Anthony J. Muslin, Brian DeBosch. Center for Cardiovascular Research, Washington University School of Medicine, St. Louis, MO, USA Akt proteins regulate cell survival, metabolism and protein synthesis. All three Akt family members, including Akt1, Akt2 and Akt3, are expressed in the myocardium, but Akt1 and Akt2 are most abundant. Akt1 and Akt3 overexpression results in enhanced myocardial size and function, but little is known about the role of Akt2 in cardiac physiology. Mice with targeted disruption of the akt2 gene appear normal at birth but gradually develop insulin resistance and hyperglycemia. Adult murine cardiomyocytes (AMCMs) isolated from akt2−/− mice were resistant to insulin-stimulated glucose uptake. In contrast, AMCMs isolated from akt1−/− mice exhibited normal glucose uptake. Cardiac metabolism was evaluated by use of ex vivo working heart preparations. By this method, akt2−/− hearts exhibited significantly reduced glucose utilization and increased fatty acid utilization when compared to wild type mice. Akt2 null mice displayed normal cardiac growth responses to provocative stimulation, including ligand stimulation of cultured cardiomyocytes and pressure overload by transverse aortic constriction. However, akt2−/− mice were found to be sensitized to cardiomyocyte apoptosis, both in cultured cells and in intact animals. In response to experimental myocardial
infarction, akt2 −/− mice exhibited significantly increased apoptosis in the peri-infarct zone 7 days after occlusion of the left coronary artery. These results implicate Akt2 in the regulation of cardiomyocyte metabolism and survival. Keywords: Akt; Cardiomyocyte; Apoptosis doi:10.1016/j.yjmcc.2007.03.757
Regulation of cardiomyocyte survival by 14-3-3tau Anthony J. Muslin, Jeffrey M.C. Lau. Center for Cardiovascular Research, Washington University School of Medicine, St. Louis, MO, USA The 14-3-3 family of proteins are intracellular dimeric phosphoserine-binding molecules that regulate apoptotic, signal transduction, cell cycle, and metabolic cascades. Experiments with global 14-3-3 protein inhibitors suggested that these proteins play a critical role in antagonizing apoptotic cell death in response to provocative stimuli. To determine the specific role of one family member in apoptosis, mice were generated with targeted disruption of the 14-3-3τ gene. 14-3-3τ−/− mice did not survive embryonic development and embryos exhibited generalized developmental arrest at 8–11 days post-coitum. In contrast, haploinsufficient mice appeared normal at birth and were fertile. Cultured adult cardiomyocytes derived from 14-3-3τ+/− mice were sensitized to apoptosis in response to hydrogen peroxide or UV irradiation. 14-3-3τ+/− mice were intolerant of experimental myocardial infarction and 59% of animals died in the 7 days following infarct surgery (n = 17), compared to 27% of wild type animals (n = 15). 14-3-3τ+/− mice that survived for 7 days after experimental infarction developed enhanced pathological ventricular remodeling with increased cardiomyocyte apoptosis. ASK1, JNK and p38 MAPK activation was increased, but ERK MAPK activation was reduced, in 14-3-3τ+/− cardiac tissue when compared to wild type tissue. Inhibition of p38 MAPK by systemic administration of SB202190 increased survival in 143-3τ+/− mice subjected to myocardial infarction. These results demonstrate that 14-3-3τ plays a vital anti-apoptotic function in cardiomyocytes and therapeutic agents that increase 14-3-3τ activity may benefit patients with myocardial infarction. Keywords: Heart failure; Apoptosis; Infarction doi:10.1016/j.yjmcc.2007.03.758
FGF-16 interferes with FGF-2 induced growth in neonatal cardiac myocytes P.A. Cattini, S.Y. Lu. Department of Physiology, University of Manitoba, Winnipeg, MB, Canada Fibroblast growth factor-16 (FGF-16) expression increases in the mouse myocardium at birth, and is released from cardiac myocytes, correlating with their transition to hypertrophic growth. FGF-2 stimulates the proliferative potential of neonatal
ABSTRACTS / Journal of Molecular and Cellular Cardiology 42 (2007) S80–S87
mitochondrial permeability transition pore (PT-pore) and can be inhibited by Akt activation. Mitochondrial depolarization induced by H2O2 is prevented by activation of Akt with leukemia inhibitory factor (LIF). This protective effect of LIF is still observed when cells treated with LIF are permeabilized to remove soluble second messengers and mitochondrial depolarization elicited by elevating Ca 2+ . Fractionation studies demonstrate that LIF treatment increases both total and phosphorylated Akt in the mitochondrial fraction. Immunoprecipitation studies demonstrate that LIF treatment increases the association of Akt with outer mitochondrial components of the PT-pore, VDAC and HK-II. HK-II contains consensus sequences for phosphorylation by Akt and LIF induces PI3K and Akt dependent HK-II phosphorylation. Addition of recombinant active Akt to isolated mouse heart mitochondria also elicits a robust increase in HKII phosphorylation and concomitantly inhibits Ca2+-induced cytochrome c release. Finally functional studies demonstrate that forced dissociation of HK-II from mitochondria attenuates the protective effect of LIF on H2O2 induced mitochondrial depolarization. We conclude that Akt has a direct effect at the level of the mitochondrion which is mediated via phosphorylation of HK-II, and that this results in protection of mitochondria against PT-pore opening and of cardiomyocytes against subsequent apoptosis. Keywords: Akt; Cardioprotection; Mitochondria doi:10.1016/j.yjmcc.2007.03.756
Akt2 regulates cardiomyocyte survival and glucose metabolism Anthony J. Muslin, Brian DeBosch. Center for Cardiovascular Research, Washington University School of Medicine, St. Louis, MO, USA Akt proteins regulate cell survival, metabolism and protein synthesis. All three Akt family members, including Akt1, Akt2 and Akt3, are expressed in the myocardium, but Akt1 and Akt2 are most abundant. Akt1 and Akt3 overexpression results in enhanced myocardial size and function, but little is known about the role of Akt2 in cardiac physiology. Mice with targeted disruption of the akt2 gene appear normal at birth but gradually develop insulin resistance and hyperglycemia. Adult murine cardiomyocytes (AMCMs) isolated from akt2−/− mice were resistant to insulin-stimulated glucose uptake. In contrast, AMCMs isolated from akt1−/− mice exhibited normal glucose uptake. Cardiac metabolism was evaluated by use of ex vivo working heart preparations. By this method, akt2−/− hearts exhibited significantly reduced glucose utilization and increased fatty acid utilization when compared to wild type mice. Akt2 null mice displayed normal cardiac growth responses to provocative stimulation, including ligand stimulation of cultured cardiomyocytes and pressure overload by transverse aortic constriction. However, akt2−/− mice were found to be sensitized to cardiomyocyte apoptosis, both in cultured cells and in intact animals. In response to experimental myocardial
infarction, akt2 −/− mice exhibited significantly increased apoptosis in the peri-infarct zone 7 days after occlusion of the left coronary artery. These results implicate Akt2 in the regulation of cardiomyocyte metabolism and survival. Keywords: Akt; Cardiomyocyte; Apoptosis doi:10.1016/j.yjmcc.2007.03.757
Regulation of cardiomyocyte survival by 14-3-3tau Anthony J. Muslin, Jeffrey M.C. Lau. Center for Cardiovascular Research, Washington University School of Medicine, St. Louis, MO, USA The 14-3-3 family of proteins are intracellular dimeric phosphoserine-binding molecules that regulate apoptotic, signal transduction, cell cycle, and metabolic cascades. Experiments with global 14-3-3 protein inhibitors suggested that these proteins play a critical role in antagonizing apoptotic cell death in response to provocative stimuli. To determine the specific role of one family member in apoptosis, mice were generated with targeted disruption of the 14-3-3τ gene. 14-3-3τ−/− mice did not survive embryonic development and embryos exhibited generalized developmental arrest at 8–11 days post-coitum. In contrast, haploinsufficient mice appeared normal at birth and were fertile. Cultured adult cardiomyocytes derived from 14-3-3τ+/− mice were sensitized to apoptosis in response to hydrogen peroxide or UV irradiation. 14-3-3τ+/− mice were intolerant of experimental myocardial infarction and 59% of animals died in the 7 days following infarct surgery (n = 17), compared to 27% of wild type animals (n = 15). 14-3-3τ+/− mice that survived for 7 days after experimental infarction developed enhanced pathological ventricular remodeling with increased cardiomyocyte apoptosis. ASK1, JNK and p38 MAPK activation was increased, but ERK MAPK activation was reduced, in 14-3-3τ+/− cardiac tissue when compared to wild type tissue. Inhibition of p38 MAPK by systemic administration of SB202190 increased survival in 143-3τ+/− mice subjected to myocardial infarction. These results demonstrate that 14-3-3τ plays a vital anti-apoptotic function in cardiomyocytes and therapeutic agents that increase 14-3-3τ activity may benefit patients with myocardial infarction. Keywords: Heart failure; Apoptosis; Infarction doi:10.1016/j.yjmcc.2007.03.758
FGF-16 interferes with FGF-2 induced growth in neonatal cardiac myocytes P.A. Cattini, S.Y. Lu. Department of Physiology, University of Manitoba, Winnipeg, MB, Canada Fibroblast growth factor-16 (FGF-16) expression increases in the mouse myocardium at birth, and is released from cardiac myocytes, correlating with their transition to hypertrophic growth. FGF-2 stimulates the proliferative potential of neonatal