Abstract
Chronic hemodynamic overload on the heart results in pathological myocardial hypertrophy, eventually followed by heart failure. Phosphatase calcineurin is a crucial mediator of this response. Little is known, however, about the role of calcineurin in response to acute alterations in loading conditions of the heart, where it could be mediating beneficial adaptational processes. We therefore analyzed proteome changes following a short-term increase in preload in rabbit myocardium in the absence or presence of the calcineurin inhibitor cyclosporine A. Rabbit right ventricular isolated papillary muscles were cultivated in a muscle chamber system under physiological conditions and remained either completely unloaded or were stretched to a preload of 3 mN/mm(2), while performing isotonic contractions (zero afterload). After 6 h, proteome changes were detected by two-dimensional gel electrophoresis and ESI-MS/MS. We identified 28 proteins that were upregulated by preload compared to the unloaded group (at least 1.75-fold regulation, all P < 0.05). Specifically, mechanical load upregulated a variety of enzymes involved in energy metabolism (i.e., aconitase, pyruvate kinase, fructose bisphosphate aldolase, ATP synthase alpha chain, acetyl-CoA acetyltransferase, NADH ubiquinone oxidoreductase, ubiquinol cytochrome c reductase, hydroxyacyl-CoA dehydrogenase). Cyclosporine A treatment (1 micromol/l) abolished the preload-induced upregulation of these proteins. We demonstrate for the first time that an acute increase in the myocardial preload causes upregulation of metabolic enzymes, thereby increasing the capacity of the myocardium to generate ATP production. This short-term adaptation to enhanced mechanical load appears to critically depend on calcineurin phosphatase activity.