In response to numerous pathologic stimuli, the myocardium undergoes a hypertrophic response characterized by increased myocardial cell size and activation of fetal cardiac genes. We show that cardiac hypertrophy is induced by the calcium-dependent phosphatase calcineurin, which dephosphorylates the transcription factor NF-AT3, enabling it to translocate to the nucleus. NF-AT3 interacts with the cardiac zinc finger transcription factor GATA4, resulting in synergistic activation of cardiac transcription. Transgenic mice that express activated forms of calcineurin or NF-AT3 in the heart develop cardiac hypertrophy and heart failure that mimic human heart disease. Pharmacologic inhibition of calcineurin activity blocks hypertrophy in vivo and in vitro. These results define a novel hypertrophic signaling pathway and suggest pharmacologic approaches to prevent cardiac hypertrophy and heart failure.

The heart responds to stress signals by hypertrophic growth, which is accompanied by activation of the MEF2 transcription factor and reprogramming of cardiac gene expression. We show here that class II histone deacetylases (HDACs), which repress MEF2 activity, are substrates for a stress-responsive kinase specific for conserved serines that regulate MEF2-HDAC interactions. Signal-resistant HDAC mutants lacking these phosphorylation sites are refractory to hypertrophic signaling and inhibit cardiomyocyte hypertrophy. Conversely, mutant mice lacking the class II HDAC, HDAC9, are sensitized to hypertrophic signals and exhibit stress-dependent cardiomegaly. Thus, class II HDACs act as signal-responsive suppressors of the transcriptional program governing cardiac hypertrophy and heart failure.

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3β (GSK-3β). Alternatively, receptor tyrosine kinase or certain G protein-coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3β, via protein kinase B/Akt and mTOR/p70 s6k pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3β on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.

The adult myocardium responds to a variety of pathologic stimuli by hypertrophic growth that frequently progresses to heart failure. The calcium͞calmodulin-dependent protein phosphatase calcineurin is a potent transducer of hypertrophic stimuli. Calcineurin dephosphorylates members of the nuclear factor of activated T cell (NFAT) family of transcription factors, which results in their translocation to the nucleus and activation of calcium-dependent genes. Glycogen synthase kinase-3 (GSK-3) phosphorylates NFAT proteins and antagonizes the actions of calcineurin by stimulating NFAT nuclear export. To determine whether activated GSK-3 can act as an antagonist of hypertrophic signaling in the adult heart in vivo, we generated transgenic mice that express a constitutively active form of GSK-3␤ under control of a cardiac-specific promoter. These mice were physiologically normal under nonstressed conditions, but their ability to mount a hypertrophic response to calcineurin activation was severely impaired. Similarly, cardiac-specific expression of activated GSK-3␤ diminished hypertrophy in response to chronic ␤-adrenergic stimulation and pressure overload. These findings reveal a role for GSK-3␤ as an inhibitor of hypertrophic signaling in the intact myocardium and suggest that elevation of cardiac GSK-3␤ activity may provide clinical benefit in the treatment of pathologic hypertrophy and heart failure.

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3β (GSK-3β). Alternatively, receptor tyrosine kinase or certain G protein-coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3β, via protein kinase B/Akt and mTOR/p70 s6k pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3β on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.