alpha 1AMP-Activated Protein Kinase Mediates Vascular Protective Effects of Exercise
ABSTRACT We investigated whether AMP-activated protein kinase (AMPK) may be involved in the signaling processes leading to exercise-mediated vascular protection.
The effects of voluntary exercise on AMPK activity, endothelial NO synthase expression and phosphorylation, vascular reactive oxygen species formation, and cell senescence were tested in α1AMPK knockout and corresponding wild-type mice. Exercise significantly improved endothelial function, and increased plasma nitrite production in wild-type mice, associated with an activation of aortic AMPK assessed by its phosphorylation at threonine 172. In addition, regular physical activity resulted in an upregulation of endothelial NO synthase protein, serine 1177 endothelial NO synthase phosphorylation, and an increase of circulating Tie-2(+)Sca-1(+)Flk-1(+) myeloid progenitor cells. All these changes were absent after α1AMPK deletion. In addition, exercise increased the expression of important regulators of the antioxidative defense including heme oxygenase-1 and peroxisome proliferator-activated receptor γ coactivator 1α, decreased aortic reactive oxygen species levels, and prevented endothelial cell senescence in an α1AMPK-dependent manner.
Intact α1AMPK signaling is required for the signaling events leading to the manifestation of vascular protective effects during exercise. Pharmacological AMPK activation might be a novel approach in the near future to simulate the beneficial vascular effects of physical activity.
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ABSTRACT: It is well established that chronic exposure to excess nutrients leads to insulin resistance (IR) in skeletal muscle. Since skeletal muscle is responsible for 70-80% of insulin-stimulated glucose uptake, skeletal muscle IR is a key pathological component of type 2 diabetes (T2D). Recent evidence suggests that inhibition of the nutrient-sensing enzyme AMP-activated protein kinase (AMPK) is an early event in the development of IR in response to high glucose, branched chain amino acids (BCAA), or fatty acids (FA). Whether the decrease in AMPK activity is causal to the events leading to insulin resistance (increased mTOR/p70S6K signaling) remains to be determined. Interestingly, pharmacological activation of AMPK can prevent activation of mTOR/p70S6K and insulin resistance, while inhibition of mTOR with rapamycin prevents insulin resistance, but not AMPK downregulation. AMPK can be inhibited by increased energy state (reduced AMP/ATP ratio), decreased phosphorylation of its activation site (αThr172) (by decreased upstream kinase activity or increased phosphatase activity), increased inhibitory phosphorylation at αSer485/491, changes in redox state or hormone levels, or other yet to be identified mechanisms. Excess nutrients also lead to an accumulation of the toxic lipid intermediates diacylglycerol (DAG) and ceramides, both of which can activate various protein kinase C (PKC) isoforms, and contribute to IR. The mechanism responsible for the initial downregulation of AMPK in response to excess nutrients, and whether glucose, BCAA, and FA act through similar or different pathways requires further study. Identification of this mechanism and the relative importance of other events would be beneficial for designing novel pharmacological interventions to prevent and/or reverse IR. This review will focus on the some of the mechanisms responsible for AMPK downregulation and the relative sequence and importance of these events.07/2013; 1(1):1008.
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ABSTRACT: Purpose. We tested the hypothesis that nonalcoholic fatty liver disease (NAFLD) is associated with reduced hepatic endothelial nitric oxide synthase (eNOS) activation status via S1177 phosphorylation (p-eNOS) and is prevented by daily voluntary wheel running (VWR). Methods. Hyperphagic Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an established model of obesity, type 2 diabetes (T2D) and NAFLD, and normophagic controls (Long-Evans Tokushima Otsuka, LETO) were studied at 8-, 20-, and 40-wks of age. Results. Basal hepatic eNOS phosphorylation (p-eNOS/eNOS) was similar between LETO and OLETFs with early hepatic steatosis (8-wks of age) and advanced steatosis, hyperinsulinemia, and hyperglycemia (20-wks of age). In contrast, hepatic p-eNOS/eNOS was significantly lower (p<0.05) in OLETF rats with T2D advancement and the transition to more advanced NAFLD with inflammation and fibrosis (increased TNFα, CD68, and CD163 mRNA expression; 40-wks of age). Reduced hepatic eNOS activation status in 40-wk OLETF rats was significantly correlated with reduced p-Akt/Akt (r = 0.73, p < 0.05), reduced serum insulin (r = 0.59, p < 0.05) and elevated serum glucose (r = -0.78, p < 0.05), suggesting a link between impaired glycemic control and altered hepatic nitric oxide metabolism. VWR by OLETF rats, in conjunction with NAFLD and T2D prevention, normalized p-eNOS/eNOS and p-Akt/Akt to LETO levels. Conclusion. Basal activation of hepatic eNOS and Akt are maintained until advanced NAFLD and T2D development in obese OLETF rats. The prevention of this reduction by VWR may result from maintained insulin sensitivity and glycemic control.Journal of Applied Physiology 02/2014; 116(9). DOI:10.1152/japplphysiol.01275.2013 · 3.43 Impact Factor
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ABSTRACT: OBJECTIVE - Vascular endothelium plays an important role to maintain cardiovascular homeostasis through several mechanisms, including endothelium-dependent hyperpolarization (EDH). We have recently demonstrated that EDH is involved in endothelial metabolic regulation in mice. However, it remains to be examined whether AMP-activated protein kinase (AMPK), an important metabolic regulator, is involved in EDH and if so, whether endothelial AMPK (eAMPK) plays a role for circulatory regulation. APPROACH AND RESULTS - We examined the role of eAMPK in EDH, using mice with endothelium-specific deficiency of α-catalytic subunit of AMPK, either α1 (eAMPKα1-/-α2+/+) or α2 (eAMPKα1+/+α 2-/-) alone or both of them (eAMPKα1-/-α2-/-). We performed telemetry, organ chamber, electrophysiological, and Langendorff experiments to examine blood pressure, vascular responses, hyperpolarization of membrane potential, and coronary flow responses, respectively. Hypertension was noted throughout the day in eAMPKα1-/-α2-/- and eAMPKα1α2 but not in eAMPKα 1+/+α2-/- mice when compared with respective control. Importantly, endothelium-dependent relaxations, EDH, and coronary flow increase were all significantly reduced in eAMPKα1α2 and eAMPKα1-/-α2-/- but not in eAMPKα 1-/-α2+/+ mice. In contrast, endothelium-independent relaxations to sodium nitroprusside (a NO donor), NS-1619 (a Ca2+-activated K+ channel opener), and exogenous H2O2 were almost comparable among the groups. In eAMPKα1-/-α2-/- mice, antihypertensive treatment with hydralazine or long-term treatment with metformin (a stimulator of AMPK) failed to restore EDH-mediated responses. CONCLUSIONS - These results provide the first direct evidence that α1 subunit of eAMPK substantially mediates EDH responses of microvessels and regulates blood pressure and coronary flow responses in mice in vivo, demonstrating the novel role of eAMPK in cardiovascular homeostasis.Arteriosclerosis Thrombosis and Vascular Biology 05/2014; 34(7). DOI:10.1161/ATVBAHA.114.303735 · 5.53 Impact Factor