Insulin induces myocardial protection and Hsp70 localization to plasma membranes in rat hearts

Abstract

Li, Gefeng, Imtiaz S. Ali, and R. William Currie. Insulin induces myocardial protection and Hsp70 localization to plasma membranes in rat hearts. Am J Physiol Heart Circ Physiol 291: H1709 -H1721, 2006. First published May 26, 2006 doi:10.1152/ajpheart.00201.2006.-Insulin induces the expression of the 70-kDa heat shock protein (Hsp70) in rat hearts. In this study, we examined insulin-and heat shock-treated hearts for improved contractile recovery after 30 min of ischemia, activation of the heat shock transcription factor, and localization of the Hsp70 in relation to dystrophin and ␣-tubulin. Adult male SpragueDawley rats were assigned to groups: 1) control, 2) sham control, 3) insulin injected (200 U/g body wt), 4) heat shock treated (core body temperature 42°C for 15 min), and 5) heat shock and insulin treated. Six hours later, hearts were isolated for Langendorff perfusion to determine cardiac function, or myocardial tissues were collected and prepared for either electrophoretic mobility shift assay, Western blot analysis, or immunofluorescence microscopy. Insulin treatment with 6 h of recovery enhances postischemic myocardial recovery of contractile function and increases Hsp70 expression through activation of the heat shock transcription factor. Insulin-treated hearts had elevated levels of Hsp70, particularly in the membrane fraction. In contrast, heat-shocked hearts had elevated levels of Hsp70 in the cytosol, membrane, and pellet fractions. After insulin treatment, Hsp70 was mostly colocalized to the plasma membrane with dystrophin. In contrast, after heat shock, Hsp70 was localized mostly between cardiomyocytes in apparent vascular or perivascular elements. The localization of Hsp70 is dependent on the inducing stimuli of either heat shock or insulin treatment. The cell membrane versus vascular localization of Hsp70 suggests the interesting possibility of functionally distinct roles for Hsp70 in the heart, whether induced by insulin or heat shock treatment. heat shock; heat shock protein 70; heat shock transcription factor; ischemia/reperfusion INSULIN IS A CRUCIAL REGULATOR of metabolism, and in cardiac muscle, insulin induces glycogen and protein synthesis, and in fat, lipid storage is favored. Insulin also mediates other diverse effects in a wide variety of cells and tissues (57). Sodi-Pallares et al. (67) initially introduced the concept of infusing a metabolic cocktail of glucose, insulin, and potassium to improve recovery from myocardial infarction. Clinical studies (20,22,63) suggest that this cocktail might have an important role in reducing in-hospital mortality after acute cardiac infarction. Initially, two possible mechanisms for the effectiveness of the glucose, insulin, and potassium cocktail were suggested: 1) the promotion of cardiac glycolysis and 2) the uptake of free fatty acids into adipocytes (58). More recently, insulin alone has been shown to be as effective as the glucose, insulin, and potassium cocktail at reducing myocardial ischemia-reperfusion injury (32). The cardioprotective...

Insulin-induced myocardial protection in isolated ischemic rat hearts requires p38 MAPK phosphorylation of Hsp27

“…Isolated hearts were perfused in the nonejecting-modified Langendorff mode as previously described in detail (42). Modified Krebs-Henseleit bicarbonate buffer gassed with 95% O 2-5% CO2 at 37°C was perfused into hearts at a constant rate of 10 ml/min with a static roller pump.…”

“…1-9) during preischemic perfusion and at 5, 30, 60, 90, and 120 min of reperfusion. An analysis of left ventricular function and a calculation of the pressure-volume relationship were done according to Burkhoff and Sagawa (8) and as recently described by Li et al (42).…”

“…In our previous study at 6 h after insulin treatment, hearts had increased expression of Hsp70 and were resistant to ischemia-reperfusion injury (42). We hypothesized that at 1 h after insulin treatment, insufficient time would have limited any increase in the abundance of newly synthesized Hsps, and if myocardial protection where evident, other mechanisms such as MAPK activation and Hsp27 phosphorylation would be involved.…”

“…Activation and phosphorylation of intermediates within these pathways regulate transcription, translation, and various aspects of glucose metabolism. In addition, insulin is effective at reducing myocardial ischemia-reperfusion injury (32,42). The cardioprotective effect of insulin may be mediated via PI3K, PKB/Akt, and p70S6 kinase cell signaling (64) or by increasing nitric oxide bioavailability (23,33).…”

“…We recently reported that Hsp70 is induced by insulin at a relatively low level in rat heart at 6 h after insulin treatment. Insulin increased the expression of Hsp70 in rat heart via the activation of heat shock factor-1 (HSF-1) and appeared to modulate the localization of Hsp70 to cardiomyocyte membranes in rat heart (42,43).…”