Gq-coupled receptor signaling in pathological ventricular remodeling

Signaling to cardiac hypertrophy: insights from human and mouse RASopathies

Cardiac hypertrophy is the heart's response to a variety of extrinsic and intrinsic stimuli, some of which might finally lead up to a maladaptive state. An integral part of the pathogenesis of the hypertrophic cardiomyopathy disease (HCM) is the activation of the rat sarcoma (RAS)/RAF/MEK (mitogen-activated protein kinase kinase)/MAPK (mitogen-activated protein kinase) cascade. Therefore, the molecular signaling involving RAS has been the subject of intense research efforts, particularly after the identification of the RASopathies. These constitute a class of developmental disorders caused by germline mutations affecting proteins contributing to the RAS pathway. Among other phenotypic features, a subset of these syndromes is characterized by HCM, prompting researchers and clinicians to delve into the chief signaling constituents of cardiac hypertrophy. In this review, we summarize current advances in the knowledge of the molecular signaling events involved in the pathogenesis of cardiac hypertrophy through work completed on patients and on genetically manipulated animals with HCM and RASopathies. Important insights are drawn from the recognition of parallels between cardiac hypertrophy and cancer. Future research promises to further elucidate the complex molecular interactions responsible for cardiac hypertrophy, possibly pointing the way for the identification of new specific targets for the treatment of HCM.

Cardiac-specific overexpression of catalase identifies hydrogen peroxide-dependent and -independent phases of myocardial remodeling and prevents the progression to overt heart failure in G(alpha)q-overexpressing transgenic mice

BACKGROUND

Although it seems that reactive oxygen species contribute to chronic myocardial remodeling, questions remain about (1) the specific types of reactive oxygen species involved, (2) the role of reactive oxygen species in mediating specific cellular events, and (3) the cause-and-effect relationship between myocardial reactive oxygen species and the progression to heart failure. Transgenic mice with myocyte-specific overexpression of G(alpha)q develop a dilated cardiomyopathy that progresses to heart failure. We used this model to examine the role of H(2)O(2) in mediating myocardial remodeling and the progression to failure.

METHODS AND RESULTS

In G(alpha)q myocardium, markers of oxidative stress were increased at 4 weeks and increased further at 20 weeks. G(alpha)q mice were crossbred with transgenic mice having myocyte-specific overexpression of catalase. At 4 weeks of age, left ventricular end-diastolic dimension was increased and left ventricular fractional shortening decreased in G(alpha)q mice and deteriorated further through 20 weeks. In G(alpha)q mice, myocardial catalase overexpression had no effect on left ventricular end-diastolic dimension or fractional shortening at 4 weeks but prevented the subsequent deterioration in both. In G(alpha)q mice, myocyte hypertrophy; myocyte apoptosis; interstitial fibrosis; and the progression to overt heart failure, as reflected by lung congestion and exercise intolerance, were prevented by catalase overexpression.

CONCLUSIONS

In G(alpha)q mice, myocyte-specific overexpression of catalase had no effect on the initial phenotype of left ventricular dilation and contractile dysfunction but prevented the subsequent progressive remodeling phase leading to heart failure. Catalase prevented the cellular hallmarks of adverse remodeling (myocyte hypertrophy, myocyte apoptosis, and interstitial fibrosis) and the progression to overt heart failure. Thus, H(2)O(2), associated oxidant pathways, or both play a critical role in adverse myocardial remodeling and the progression to failure.

Dance band on the Titanic: biomechanical signaling in cardiac hypertrophy

Biomechanical signaling is a complex interaction of both intracellular and extracellular components. Both passive and active components are involved in the extracellular environment to signal through specific receptors to multiple signaling pathways. This review provides an overview of extracellular matrix, specific receptors, and signaling pathways for biomechanical stimulation in cardiac hypertrophy.

Interplay between the cardiac renin angiotensin system and JAK-STAT signaling: role in cardiac hypertrophy, ischemia/reperfusion dysfunction, and heart failure

Recent studies have shown that the JAK-STAT signaling pathway plays a central role in cardiac pathophysiology. JAK-STAT signaling has been implicated in pressure overload-induced cardiac hypertrophy and remodeling, ischemic preconditioning, and ischemia/reperfusion-induced cardiac dysfunction. The different STAT family members expressed in cardiac myocytes appear to be linked to different, and at times, opposite responses, such as cell growth/survival and apoptosis. Thus, differential activation and/or selective inhibition of the STAT proteins by agonists for G-protein coupled receptors, such as angiotensin II, may contribute to cardiac dysfunction during ischemia and heart failure. In addition, JAK-STAT signaling may represent one limb of an autocrine loop for angiotensin II generation, that serves to amplify the actions of angiotensin II on cardiac muscle. The purpose of this article is to provide an overview of recent findings that have been made for JAK-STAT signaling in cardiac myocytes and to highlight some unresolved issues for future investigation. The central focus of this review is on recent studies suggesting that modulation or activation of JAK-STAT signaling by ANG II has pathological consequences for heart function.

Role of USF1 phosphorylation on cardiac alpha-myosin heavy chain promoter activity

Contractile activity of the cardiac myocyte is required for maintaining cell mass and phenotype, including expression of the cardiac-specific alpha-myosin heavy chain (alpha-MHC) gene. An E-box hemodynamic response element (HME) located at position -47 within the alpha-MHC promoter is both necessary and sufficient to confer contractile responsiveness to the gene and has been shown to bind upstream stimulatory factor-1 (USF1). When studied in spontaneously contracting cardiac myocytes, there is enhanced binding of USF1 to the HME compared with quiescent cells, which correlates with a threefold increase in alpha-MHC promoter activity. A molecular mechanism by which contractile function modulates alpha-MHC transcriptional activity may involve signaling via phosphorylation of USF1. The present studies showed that purified rat USF1 was phosphorylated in vitro by protein kinase C (PKC) and cAMP-dependent protein kinase (PKA) but not casein kinase II. Phosphorylated USF1 by either PKC or PKA had increased DNA binding activity to the HME. PKC-mediated phosphorylation also leads to the formation of USF1 multimers as assessed by gel shift assay. Analysis of in vivo phosphorylated nuclear proteins from cultured ventricular myocytes showed that USF1 was phosphorylated, and resolution by two-dimensional gel electrophoresis identified at least two distinct phosphorylated USF1 molecules. These results suggest that endogenous kinases can covalently modify USF1 and provide a potential molecular mechanism by which the contractile stimulus mediates changes in myocyte gene transcription.