Background-Cardiac hypertrophy is a common response to pressure overload and is associated with increased mortality.Mechanical stress in the heart results in the activation of the small GTPase ras and the Raf-1/MEK/ERK signaling cascade in addition to other signaling pathways. Methods and Results-In an attempt to determine the requirement for the serine/threonine kinase Raf-1 in the pathogenesis of cardiac hypertrophy, we generated transgenic mice with cardiac-specific expression of a dominant negative form of Raf-1 (DN-Raf). DN-Raf mice appeared normal at birth, were fertile, and had normal cardiac structure and function in the absence of provocative stimulation. In response to pressure overload, cardiac extracellular signal-regulated kinase (ERK) activation was inhibited, but c-Jun N-terminal kinase (JNK) activation and p38 mitogen-activated protein kinase (MAPK) activation were normal. DN-Raf mice were sensitized to pressure overload and the development of cardiomyocyte apoptosis, and Ͼ35% of animals died within 7 days of aortic banding. Surviving DN-Raf animals were markedly resistant to the development of cardiac hypertrophy and hypertrophic gene induction in response to transverse aortic constriction. Conclusions-These results establish that Raf-1 kinase activity is essential for cardiac hypertrophy and cardiomyocyte survival in response to pressure overload.

14-3-3 family members are intracellular dimeric phosphoserine-binding proteins that regulate signal transduction, cell cycle, apoptotic, and metabolic cascades. Previous work with global 14-3-3 protein inhibitors suggested that these proteins play a critical role in antagonizing apoptotic cell death in response to provocative stimuli. To determine the specific role of one family member in apoptosis, mice were generated with targeted disruption of the 14-3-3τ gene. 14-3-3τ−/− mice did not survive embryonic development, but haploinsufficient mice appeared normal at birth and were fertile. Cultured adult cardiomyocytes derived from 14-3-3τ+/− mice were sensitized to apoptosis in response to hydrogen peroxide or UV irradiation. 14-3-3τ+/− mice were intolerant of experimental myocardial infarction and developed pathological ventricular remodeling with increased cardiomyocyte apoptosis. ASK1, c-jun NH2-terminal kinase, and p38 mitogen-activated protein kinase (MAPK) activation was increased, but extracellular signal-regulated kinase MAPK activation was reduced, in 14-3-3τ+/− cardiac tissue. Inhibition of p38 MAPK increased survival in 14-3-3τ+/− mice subjected to myocardial infarction. These results demonstrate that 14-3-3τ plays a critical antiapoptotic function in cardiomyocytes and that therapeutic agents that increase 14-3-3τ activity may be beneficial to patients with myocardial infarction.

14-3-3 family members are dimeric phosphoserinebinding proteins that regulate signal transduction, apoptotic, and checkpoint control pathways. Targeted expression of dominant-negative 14-3-3 (DN-14-3-3) to murine postnatal cardiac tissue potentiates Ask1, c-jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) activation. DN-14-3-3 mice are unable to compensate for pressure overload, which results in increased mortality, dilated cardiomyopathy, and cardiac myocyte apoptosis. To evaluate the relative role of p38 MAPK activity in the DN-14-3-3 phenotype, we inhibited cardiac p38 MAPK activity by pharmacological and genetic methods. Intraperitoneal injection of SB202190, an inhibitor of p38␣ and p38␤ MAPK activity, markedly increased the ability of DN-14-3-3 mice to compensate for pressure overload, with decreased mortality. DN-14-3-3 mice were bred with transgenic mice in which dominant-negative p38␣ (DN-p38␣) or dominantnegative p38␤ (DN-p38␤) MAPK expression was targeted to the heart. Compound transgenic DN-14-3-3/DNp38␤ mice, and to a lesser extent compound transgenic DN-14-3-3/DN-p38␣ mice, exhibited reduced mortality and cardiac myocyte apoptosis in response to pressure overload, demonstrating that DN-14-3-3 promotes cardiac apoptosis due to stimulation of p38 MAPK activity.

Diabetic patients develop a cardiomyopathy that consists of ventricular hypertrophy and diastolic dysfunction. Although the pathogenesis of this condition is poorly understood, previous studies implicated abnormal G-protein activation. In this work, mice with cardiac overexpression of the transcription factor peroxisome proliferator-activated receptor-␣ (PPAR-␣) were examined as a model of diabetic cardiomyopathy. PPAR-␣ transgenic mice develop spontaneous cardiac hypertrophy, contractile dysfunction, and "fetal" gene induction. We examined the role of abnormal G-protein activation in the pathogenesis of cardiac dysfunction by crossing PPAR-␣ mice with transgenic mice with cardiac-specific overexpression of regulator of G-protein signaling subtype 4 (RGS4), a GTPase activating protein for G q and G i . Generation of compound transgenic mice demonstrated that cardiac RGS4 overexpression ameliorated the cardiomyopathic phenotype that occurred as a result of PPAR-␣ overexpression without affecting the metabolic abnormalities seen in these hearts. Next, transgenic mice with increased or decreased cardiac G q signaling were made diabetic by injection with streptozotocin (STZ). RGS4 transgenic mice were resistant to STZ-induced cardiac fetal gene induction. Transgenic mice with cardiac-specific expression of mutant G ␣q , G ␣q -G188S, that is resistant to RGS protein action were sensitized to the development of STZ-induced cardiac fetal gene induction and bradycardia. These results establish that G q -mediated signaling plays a critical role in the pathogenesis of diabetic cardiomyopathy. Diabetes 53:3082-3090, 2004 B oth insulin-dependent (type 1) and non-insulindependent (type 2) forms of diabetes in humans are accompanied by a greatly increased risk of cardiovascular death (1-3). Both types of diabetes are associated with cardiomyopathy that share many similar characteristics, including ventricular hypertrophy, decreased ventricular diastolic relaxation, and a reduced peak filling rate (4 -7). Diabetic cardiomyopathy is distinct from ischemic cardiomyopathy because it is present in diabetic patients and animal models of diabetes in the absence of coronary artery disease.Recently, rodent models of diabetes were used to uncover the pathogenesis of diabetic cardiomyopathy. One animal model of diabetic cardiomyopathy was developed that consists of cardiac-specific overexpression of the transcription factor myosin heavy chain (MHC)-peroxisome proliferator-activated receptor-␣ (PPAR-␣) (8). PPAR-␣ is a ligand-activated transcription factor that regulates genes involved in cardiac fatty acid uptake and oxidation. PPAR-␣ is activated in the diabetic heart (8). MHC-PPAR transgenic mice develop a metabolic phenotype that is similar to the diabetic state in the heart but not in other tissues, with increased lipid uptake and oxidation and reduced glucose uptake and oxidation (8). Furthermore, MHC-PPAR mice develop a cardiomyopathy with ventricular hypertrophy, activation of gene markers of pathological hypertrophic growth, and...