Hypertrophic cardiomyopathy (HCM) is an inherited form of heart disease that affects 1 in 500 individuals. Here it is shown that calcineurin, a calcium-regulated phosphatase, plays a critical role in the pathogenesis of HCM. Administration of the calcineurin inhibitors cyclosporin and FK506 prevented disease in mice that were genetically predisposed to develop HCM as a result of aberrant expression of tropomodulin, myosin light chain-2, or fetal beta-tropomyosin in the heart. Cyclosporin had a similar effect in a rat model of pressure-overload hypertrophy. These results suggest that calcineurin inhibitors merit investigation as potential therapeutics for certain forms of human heart disease.

Cardiac hypertrophy is a major predictor of future morbidity and mortality. Recent investigation has centered around identifying the molecular signaling pathways that regulate cardiac myocyte reactivity with the goal of modulating pathologic hypertrophic programs. One potential regulator of cardiomyocyte hypertrophy is the calciumsensitive phosphatase calcineurin. We show here that calcineurin enzymatic activity, mRNA, and protein levels are increased in cultured neonatal rat cardiomyocytes by hypertrophic agonists such as angiotensin II, phenylephrine, and 1% fetal bovine serum.

Abstract-We have previously shown that the calcium-calmodulin-regulated phosphatase calcineurin (PP2B) is sufficient to induce cardiac hypertrophy that transitions to heart failure in transgenic mice. Given the rapid onset of heart failure in these mice, we hypothesized that calcineurin signaling would stimulate myocardial cell apoptosis. However, utilizing multiple approaches, we determined that calcineurin-mediated hypertrophy protected cardiac myocytes from apoptosis, suggesting a model of heart failure that is independent of apoptosis. Adenovirally mediated gene transfer of a constitutively active calcineurin cDNA (AdCnA) was performed in cultured neonatal rat cardiomyocytes to elucidate the mechanism whereby calcineurin affected myocardial cell viability. AdCnA infection, which induced myocyte hypertrophy and atrial natriuretic factor expression, protected against apoptosis induced by 2-deoxyglucose or staurosporine, as assessed by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) labeling, caspase-3 activation, DNA laddering, and cellular morphology. The level of protection conferred by AdCnA was similar to that of adenoviral Bcl-x L gene transfer or hypertrophy induced by phenylephrine. In vivo, failing hearts from calcineurin-transgenic mice did not demonstrate increased TUNEL labeling and, in fact, demonstrated a resistance to ischemia/reperfusion-induced apoptosis. We determined that the mechanism whereby calcineurin afforded protection from apoptosis was partially mediated by nuclear factor of activated T cells (NFAT3) signaling and partially by Akt/protein kinase B (PKB) signaling. Although calcineurin activation protected myocytes from apoptosis, inhibition of calcineurin with cyclosporine was not sufficient to induce TUNEL labeling in Gq␣-transgenic mice or in cultured cardiomyocytes. Collectively, these data identify a calcineurin-dependent mouse model of dilated heart failure that is independent of apoptosis. (Circ Res. 2000;86:255-263.)