Tumor suppressor Ras-association domain family 1 isoform A is a novel regulator of cardiac hypertrophy.

BACKGROUND: Ras signaling regulates a number of important processes in the heart, including cell growth and hypertrophy. Although it is known that defective Ras signaling is associated with Noonan, Costello, and other syndromes that are characterized by tumor formation and cardiac hypertrophy, little is known about factors that may control it. Here we investigate the role of Ras effector Ras-association domain family 1 isoform A (RASSF1A) in regulating myocardial hypertrophy. METHODS AND RESULTS: A significant downregulation of RASSF1A expression was observed in hypertrophic mouse hearts, as well as in failing human hearts. To further investigate the role of RASSF1A in cardiac (patho)physiology, we used RASSF1A knock-out (RASSF1A(-)(/)(-)) mice and neonatal rat cardiomyocytes with adenoviral overexpression of RASSF1A. Ablation of RASSF1A in mice significantly enhanced the hypertrophic response to transverse aortic constriction (64.2% increase in heart weight/body weight ratio in RASSF1A(-)(/)(-) mice compared with 32.4% in wild type). Consistent with the in vivo data, overexpression of RASSF1A in cardiomyocytes markedly reduced the cellular hypertrophic response to phenylephrine stimulation. Analysis of molecular signaling events in isolated cardiomyocytes indicated that RASSF1A inhibited extracellular regulated kinase 1/2 activation, likely by blocking the binding of Raf1 to active Ras. CONCLUSIONS: Our data establish RASSF1A as a novel inhibitor of cardiac hypertrophy by modulating the extracellular regulated kinase 1/2 pathway.

The maternal environment programs postnatal weight gain and glucose tolerance of male offspring, but placental and fetal growth are determined by fetal genotype in the Leprdb/+ model of gestational diabetes.

Mice heterozygous for a signaling-deficient leptin receptor (Leprdb/+ [db/+]) are widely used as a model of gestational diabetes that results in poor fetal outcomes. This study investigated the importance of fetal genotype (db/+) relative to abnormal maternal metabolism for placental function and therefore fetal growth and offspring health. Wild-type (WT) and db/+ females were mated to db/+ and WT males, respectively, generating litters of mixed genotype. Placentas and fetuses were weighed at embryonic day 18.5; offspring weight, hormone levels, glucose tolerance, and blood pressure were assessed at 3 and 6 months. Pregnant db/+, but not WT, dams had impaired glucose tolerance. The db/+ placentas and fetuses were heavier than WT, but the maternal environment had no effect; WT placentas/fetuses from db/+ mothers were no bigger than WT placentas/fetuses carried by WT mothers. Postnatal weight gain, glucose metabolism, and leptin levels were all influenced by offspring genotype. However, maternal environment affected aspects of offspring health because WT male offspring born to db/+ dams were heavier and had worse glucose tolerance than the sex-matched WT offspring of WT mothers. Blood pressure was not affected by maternal or offspring genotype. These data reveal that studies using the db/+ mouse to model outcomes of pregnancy complicated by gestational diabetes should be mindful of the genetically predisposed fetal/postnatal overgrowth. Although inappropriate for dissecting the effect of maternal hyperglycemia on the contribution of placental function to macrosomia, the db/+ mouse may prove useful for investigating mechanisms underlying programming of suboptimal postnatal weight gain and glucose metabolism by an adverse maternal metabolic environment.

Specific role of neuronal nitric-oxide synthase when tethered to the plasma membrane calcium pump in regulating the beta-adrenergic signal in the myocardium.

The cardiac neuronal nitric-oxide synthase (nNOS) has been described as a modulator of cardiac contractility. We have demonstrated previously that isoform 4b of the sarcolemmal calcium pump (PMCA4b) binds to nNOS in the heart and that this complex regulates beta-adrenergic signal transmission in vivo. Here, we investigated whether the nNOS-PMCA4b complex serves as a specific signaling modulator in the heart. PMCA4b transgenic mice (PMCA4b-TG) showed a significant reduction in nNOS and total NOS activities as well as in cGMP levels in the heart compared with their wild type (WT) littermates. In contrast, PMCA4b-TG hearts showed an elevation in cAMP levels compared with the WT. Adult cardiomyocytes isolated from PMCA4b-TG mice demonstrated a 3-fold increase in Ser(16) phospholamban (PLB) phosphorylation as well as Ser(22) and Ser(23) cardiac troponin I (cTnI) phosphorylation at base line compared with the WT. In addition, the relative induction of PLB phosphorylation and cTnI phosphorylation following isoproterenol treatment was severely reduced in PMCA4b-TG myocytes, explaining the blunted physiological response to the beta-adrenergic stimulation. In keeping with the data from the transgenic animals, neonatal rat cardiomyocytes overexpressing PMCA4b showed a significant reduction in nitric oxide and cGMP levels. This was accompanied by an increase in cAMP levels, which led to an increase in both PLB and cTnI phosphorylation at base line. Elevated cAMP levels were likely due to the modulation of cardiac phosphodiesterase, which determined the balance between cGMP and cAMP following PMCA4b overexpression. In conclusion, these results showed that the nNOS-PMCA4b complex regulates contractility via cAMP and phosphorylation of both PLB and cTnI.