Enhanced Cardiac S100A1 Expression Improves Recovery from Global Ischemia-Reperfusion Injury.

Gene-targeted therapy with the inotropic Ca2 + -sensor protein S100A1 rescues contractile function in post-ischemic heart failure and is being developed towards clinical trials. Its proven beneficial effect on cardiac metabolism and mitochondrial function suggests a cardioprotective effect of S100A1 in myocardial ischemia-reperfusion injury (IRI). Fivefold cardiomyocyte-specific S100A1 overexpressing, isolated rat hearts perfused in working mode were subjected to 28 min ischemia (37 °C) followed by 60 min reperfusion. S100A1 overexpressing hearts showed superior hemodynamic recover: Left ventricular pressure recovered to 57 ± 7.3% of baseline compared to 51 ± 4.6% in control (p = 0.025), this effect mirrored in LV work and dP/dt(max). Troponin T and lactate dehydrogenase was decreased in the S100A1 group, as well as FoxO pro-apoptotic transcription factor, indicating less tissue necrosis, whereas phosphocreatine content was higher after reperfusion. This is the first report of a cardioprotective effect of S100A1 overexpression in a global IRI model.

Insulin signalling downstream of protein kinase B is potentiated by 5'AMP-activated protein kinase in rat hearts in vivo.

AIMS/HYPOTHESIS: 5'AMP-activated protein kinase (AMPK) and insulin stimulate glucose transport in heart and muscle. AMPK acts in an additive manner with insulin to increase glucose uptake, thereby suggesting that AMPK activation may be a useful strategy for ameliorating glucose uptake, especially in cases of insulin resistance. In order to characterise interactions between the insulin- and AMPK-signalling pathways, we investigated the effects of AMPK activation on insulin signalling in the rat heart in vivo. METHODS: Male rats (350-400 g) were injected with 1 g/kg 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) or 250 mg/kg metformin in order to activate AMPK. Rats were administered insulin 30 min later and after another 30 min their hearts were removed. The activities and phosphorylation levels of components of the insulin-signalling pathway were subsequently analysed in individual rat hearts. RESULTS: AICAR and metformin administration activated AMPK and enhanced insulin signalling downstream of protein kinase B in rat hearts in vivo. Insulin-induced phosphorylation of glycogen synthase kinase 3 (GSK3) beta, p70 S6 kinase (p70S6K)(Thr389) and IRS1(Ser636/639) were significantly increased following AMPK activation. To the best of our knowledge, this is the first report of heightened insulin responses of GSK3beta and p70S6K following AMPK activation. In addition, we found that AMPK inhibits insulin stimulation of IRS1-associated phosphatidylinositol 3-kinase activity, and that AMPK activates atypical protein kinase C and extracellular signal-regulated kinase in the heart. CONCLUSIONS/INTERPRETATIONS: Our data are indicative of differential effects of AMPK on the activation of components in the cardiac insulin-signalling pathway. These intriguing observations are critical for characterisation of the crosstalk between AMPK and insulin signalling.

Hypertrophied rat hearts are less responsive to the metabolic and functional effects of insulin.

We determined the effect of insulin on the fate of glucose and contractile function in isolated working hypertrophied hearts from rats with an aortic constriction (n = 27) and control hearts from sham-operated rats (n = 27). Insulin increased glycolysis and glycogen in control and hypertrophied hearts. The change in glycogen was brought about by increased glycogen synthesis and decreased glycogenolysis in both groups. However, the magnitude of change in glycolysis, glycogen synthesis, and glycogenolysis caused by insulin was lower in hypertrophied hearts than in control hearts. Insulin also increased glucose oxidation and contractile function in control hearts but not in hypertrophied hearts. Protein content of glucose transporters, protein kinase B, and phosphatidylinositol 3-kinase was not different between the two groups. Thus hypertrophied hearts are less responsive to the metabolic and functional effects of insulin. The reduced responsiveness involves multiple aspects of glucose metabolism, including glycolysis, glucose oxidation, and glycogen metabolism. The absence of changes in content of key regulatory molecules indicates that other sites, pathways, or factors regulating glucose utilization are responsible for these findings.