[Show abstract][Hide abstract]ABSTRACT: Background Glycogen synthase kinase-3 (GSK-3) is a highly conserved serine/threonine kinase implicated in developmental myocardial growth and in the adult heart response to hypertrophic stress and adverse ventricular remodelling. Two isoforms exist and are expressed in equal measure within the heart, GSK-3α and GSK-3β. Phosphorylation and inactivation of GSK-3β occurs in both pharmacological and afterload modulation (aortic banding) models of cardiac hypertrophy. Strategies that maintain GSK-3β active appear protective. Conversely, GSK-3α activation is associated with a pro-fibrotic response to stress and inactivation in this setting may therefore be protective.
Objective We set out to characterise the chronic myocardial remodelling response to LAD ligation in mice expressing inactivation-resistant GSK-3α/β isoforms.
Methods Experiments were performed in knockin mice (KI), with targeted ser-21/9-ala mutations encoding ubiquitous expression of inactivation-resistant GSK-3α/β kinases, and their wild type (WT) counterparts. Age and weight-matched male adult mice were subjected to permanent LAD ligation or sham procedure. At 4 weeks echocardiography and invasive pressure-volume measurements were performed for a comprehensive interrogation of cardiac structure and function. Hearts were then excised, fixed in formaldehyde at set end-diastolic pressure and sectioned (700 μm) for morphometry.
Conclusion Inactivation-resistant GSK-3α/β expression in hearts of KI mice does not prevent chronic adverse ventricular remodelling in response to LAD ligation. At 4 weeks there were comparable increases in ventricular dilatation, volume loading and contractile dysfunction as that demonstrated in infarcted WT hearts. Accordingly, GSK-3 inactivation is not a necessary signalling mediator in post-infarct ventricular remodelling.
[Show abstract][Hide abstract]ABSTRACT: Numerous studies show that pharmacological inhibition of p38 mitogen-activated protein kinases (p38s) before lethal ischemia prevents conditioning. However, these inhibitors have off-target effects and do not discriminate between the alpha and beta isoforms; the activation of which is thought to have diverse and perhaps opposing actions with p38 alpha aggravating, and p38 beta reducing, myocardial injury. We adopted a chemical genetic approach using mice in which either the p38 alpha (DR alpha) or p38 beta (DR beta) alleles were targeted to substitute the "gatekeeper" threonine residue for methionine, thereby preventing the binding of a pharmacological inhibitor, SB203580. Isolated, perfused wild-type (WT), DR alpha and DR beta mouse hearts underwent ischemic preconditioning with 4 cycles of 4 min ischemia/6 min reperfusion, with or without SB203580 (10 microM), followed by 30 min of global ischemia and 120 min of reperfusion. In WT and DR beta hearts, SB203580 completely abolished the reduction in myocardial infarction seen with preconditioning and also the phosphorylation of downstream substrates of p38. These effects of SB203580 were not seen in DR alpha hearts. Furthermore ischemic preconditioning occurred unaltered in p38 beta null hearts. Contrary to expectation the activation of p38 alpha, and not p38 beta, is necessary for ischemic preconditioning. Since p38 alpha is also the isoform that leads to lethal myocardial injury, it is unlikely that targeted therapeutic strategies to achieve isoform-selective inhibition will only prevent the harmful consequences of activation.
Full-text · Article · Feb 2010 · Journal of Molecular and Cellular Cardiology