Cardiac overexpression of Mammalian enabled (Mena) exacerbates heart failure in mice.

Mammalian enabled (Mena) is a key regulator of cytoskeletal actin dynamics, which has been implicated in heart failure (HF). We have previously demonstrated that cardiac Mena deletion produced cardiac dysfunction with conduction abnormalities and hypertrophy. Moreover, elevated Mena expression correlates with HF in human and animal models, yet the precise role of Mena in cardiac pathophysiology is unclear. In these studies, we evaluated mice with cardiac myocyte-specific Mena overexpression (TTA/TgTetMena) comparable to that observed in cardiac pathology. We found that the hearts of TTA/TgTetMena mice were functionally and morphologically comparable to wild-type littermates, except for mildly increased heart mass in the transgenic mice. Interestingly, TTA/TgTetMena mice were particularly susceptible to cardiac injury, as these animals experienced pronounced decreases in ejection fraction and fractional shortening as well as heart dilatation and hypertrophy after transverse aortic constriction (TAC). By "turning off" Mena overexpression in TTA/TgTetMena mice either immediately prior to or immediately after TAC surgery, we discovered that normalizing Mena levels eliminated cardiac hypertrophy in TTA/TgTetMena animals but did not preclude post-TAC cardiac functional deterioration. These findings indicate that hearts with increased levels of Mena fare worse when subjected to cardiac injury and suggest that Mena contributes to HF pathophysiology.

Conducting the G-protein Coupled Receptor (GPCR) Signaling Symphony in Cardiovascular Diseases: New Therapeutic Approaches.

G protein-coupled receptors (GPCRs) are a virtually ubiquitous class of membrane-bound receptors, which functionally couple hormone or neurotransmitter signals to physiological responses. Dysregulation of GPCR signaling contributes to the pathophysiology of a host of cardiovascular disorders. Pharmacological agents targeting GPCRs have been established as therapeutic options for decades. Nevertheless, the persistent burden of cardiovascular diseases necessitates improved treatments. To that end, exciting drug development efforts have begun to focus on novel compounds that discriminately activate particular GPCR signaling pathways.

G protein coupled receptor kinase 2 interacting protein 1 (GIT1) is a novel regulator of mitochondrial biogenesis in heart.

G-protein-coupled receptor (GPCR)-kinase interacting protein-1 (GIT1) is a multi-function scaffold protein. However, little is known about its physiological role in the heart. Here we sought to identify the cardiac function of GIT1. Global GIT1 knockout (KO) mice were generated and exhibited significant cardiac hypertrophy that progressed to heart failure. Electron microscopy revealed that the hearts of GIT1 KO mice demonstrated significant morphological abnormities in mitochondria, including decreased mitochondrial volume density, cristae density and increased vacuoles. Moreover, mitochondrial biogenesis-related gene peroxisome proliferator-activated receptor γ (PPARγ) co-activator-1α (PGC-1α), PGC-1ß, mitochondrial transcription factor A (Tfam) expression, and total mitochondrial DNA were remarkably decreased in hearts of GIT1 KO mice. These animals also had impaired mitochondrial function, as evidenced by reduced ATP production and dissipated mitochondrial membrane potential (Ψ(m)) in adult cardiomyocytes. Concordant with these mitochondrial observations, GIT1 KO mice showed enhanced cardiomyocyte apoptosis and cardiac dysfunction. In conclusion, our findings identify GIT1 as a new regulator of mitochondrial biogenesis and function, which is necessary for postnatal cardiac maturation.

G protein coupled receptor kinases as therapeutic targets in cardiovascular disease.

G protein-coupled receptors (GPCRs) represent the largest family of membrane receptors and are responsible for regulating a wide variety of physiological processes. This is accomplished via ligand binding to GPCRs, activating associated heterotrimeric G proteins and intracellular signaling pathways. G protein-coupled receptor kinases (GRKs), in concert with ß-arrestins, classically desensitize receptor signal transduction, thus preventing hyperactivation of GPCR second-messenger cascades. As changes in GRK expression have featured prominently in many cardiovascular pathologies, including heart failure, myocardial infarction, hypertension, and cardiac hypertrophy, GRKs have been intensively studied as potential diagnostic or therapeutic targets. Herein, we review our evolving understanding of the role of GRKs in cardiovascular pathophysiology.

Mammalian enabled (Mena) is a critical regulator of cardiac function.

Mammalian enabled (Mena) of the Drosophila enabled/vasodilator-stimulated phosphoprotein gene family is a cytoskeletal protein implicated in actin regulation and cell motility. Cardiac Mena expression is enriched in intercalated discs (ICD), the critical intercellular communication nexus between adjacent muscle cells. We previously identified Mena gene expression to be a key predictor of human and murine heart failure (HF). To determine the in vivo function of Mena in the heart, we assessed Mena protein expression in multiple HF models and characterized the effects of genetic Mena deletion on cardiac structure and function. Immunoblot analysis revealed significant upregulation of Mena protein expression in left ventricle tissue from patients with end-stage HF, calsequestrin-overexpressing mice, and isoproterenol-infused mice. Characterization of the baseline cardiac function of adult Mena knockout mice (Mena(-/-)) via echocardiography demonstrated persistent cardiac dysfunction, including a significant reduction in percent fractional shortening compared with wild-type littermates. Electrocardiogram PR and QRS intervals were significantly prolonged in Mena(-/-) mice, manifested by slowed conduction on optical mapping studies. Ultrastructural analysis of Mena(-/-) hearts revealed disrupted organization and widening of ICD structures, mislocalization of the gap junction protein connexin 43 (Cx43) to the lateral borders of cardiomyoycytes, and increased Cx43 expression. Furthermore, the expression of vinculin (an adherens junction protein) was significantly reduced in Mena(-/-) mice. We report for the first time that genetic ablation of Mena results in cardiac dysfunction, highlighted by diminished contractile performance, disrupted ICD structure, and slowed electrical conduction.

Small molecule disruption of G beta gamma signaling inhibits the progression of heart failure.

RATIONALE: Excess signaling through cardiac Gbetagamma subunits is an important component of heart failure (HF) pathophysiology. They recruit elevated levels of cytosolic G protein-coupled receptor kinase (GRK)2 to agonist-stimulated beta-adrenergic receptors (beta-ARs) in HF, leading to chronic beta-AR desensitization and downregulation; these events are all hallmarks of HF. Previous data suggested that inhibiting Gbetagamma signaling and its interaction with GRK2 could be of therapeutic value in HF. OBJECTIVE: We sought to investigate small molecule Gbetagamma inhibition in HF. METHODS AND RESULTS: We recently described novel small molecule Gbetagamma inhibitors that selectively block Gbetagamma-binding interactions, including M119 and its highly related analog, gallein. These compounds blocked interaction of Gbetagamma and GRK2 in vitro and in HL60 cells. Here, we show they reduced beta-AR-mediated membrane recruitment of GRK2 in isolated adult mouse cardiomyocytes. Furthermore, M119 enhanced both adenylyl cyclase activity and cardiomyocyte contractility in response to beta-AR agonist. To evaluate their cardiac-specific effects in vivo, we initially used an acute pharmacological HF model (30 mg/kg per day isoproterenol, 7 days). Concurrent daily injections prevented HF and partially normalized cardiac morphology and GRK2 expression in this acute HF model. To investigate possible efficacy in halting progression of preexisting HF, calsequestrin cardiac transgenic mice (CSQ) with extant HF received daily injections for 28 days. The compound alone halted HF progression and partially normalized heart size, morphology, and cardiac expression of HF marker genes (GRK2, atrial natriuretic factor, and beta-myosin heavy chain). CONCLUSIONS: These data suggest a promising therapeutic role for small molecule inhibition of pathological Gbetagamma signaling in the treatment of HF.