Rationale: Apoptosis signal-regulating kinase (ASK)1 is a central upstream kinase in the greater mitogen-activated protein kinase cascade that mediates growth and death decisions in cardiac myocytes in response to diverse pathological stimuli.

Objective: However, the role that ASK1 plays in regulating the cardiac hypertrophic response in vivo remains controversial.

Methods and Results: Here, we generated mice with cardiac-specific and inducible overexpression of ASK1 in the heart to assess its gain-of-function effect. ASK1 transgenic mice exhibited no induction of cardiac hypertrophy or pathology at 3 and 12 months of age, and these mice showed an identical hypertrophic response to controls following 2 weeks of pressure-overload stimulation or isoproterenol infusion. Although ASK1 overexpression did not alter the cardiac hypertrophic response, it promoted cardiomyopathy and greater TUNEL following pressure-overload stimulation and myocardial infarction. Indeed, ASK1 transgenic mice showed a greater than 2-fold increase in ischemia reperfusion-induced injury to the heart compared with controls. Examination of downstream signaling showed a prominent activation of mitogen-activated protein kinase kinase 4/6 and c-Jun NH₂-terminal kinase (JNK)1/2 (but not p38 or extracellular signal-regulated kinases [ERKs]), inhibition of calcineurin-NFAT (nuclear factor of activated T cells), and induction of Bax in the hearts of ASK1 transgenic mice following 1 and 8 weeks of pressure-overload stimulation. Mechanistically, cardiomyopathy associated with ASK1 overexpression after 8 weeks of pressure overload was significantly reduced in the calcineurin A–null (CnA^-/-) background.

Conclusions: These results indicate that ASK1 does not directly regulate the cardiac hypertrophic response in vivo, but it does alter cell death and propensity to cardiomyopathy, in part, through a calcineurin-dependent mechanism.