Critical role for stromal interaction molecule 1 in cardiac hypertrophy.

BACKGROUND: Cardiomyocytes use Ca2+ not only in excitation-contraction coupling but also as a signaling molecule promoting, for example, cardiac hypertrophy. It is largely unclear how Ca2+ triggers signaling in cardiomyocytes in the presence of the rapid and large Ca2+ fluctuations that occur during excitation-contraction coupling. A potential route is store-operated Ca2+ entry, a drug-inducible mechanism for Ca2+ signaling that requires stromal interaction molecule 1 (STIM1). Store-operated Ca2+ entry can also be induced in cardiomyocytes, which prompted us to study STIM1-dependent Ca2+ entry with respect to cardiac hypertrophy in vitro and in vivo. METHODS AND RESULTS: Consistent with earlier reports, we found drug-inducible store-operated Ca2+ entry in neonatal rat cardiomyocytes, which was dependent on STIM1. Although this STIM1-dependent, drug-inducible store-operated Ca2+ entry was only marginal in adult cardiomyocytes isolated from control hearts, it increased significantly in cardiomyocytes isolated from adult rats that had developed compensated cardiac hypertrophy after abdominal aortic banding. Moreover, we detected an inwardly rectifying current in hypertrophic cardiomyocytes that occurs under native conditions (i.e., in the absence of drug-induced store depletion) and is dependent on STIM1. By manipulating its expression, we found STIM1 to be both sufficient and necessary for cardiomyocyte hypertrophy in vitro and in the adult heart in vivo. Stim1 silencing by adeno-associated viruses of serotype 9-mediated gene transfer protected rats from pressure overload-induced cardiac hypertrophy. CONCLUSION: By controlling a previously unrecognized sarcolemmal current, STIM1 promotes cardiac hypertrophy.

Profiling of aortic smooth muscle cell gene expression in response to chronic inhibition of nitric oxide synthase in rats.

BACKGROUND: Chronic inhibition of nitric oxide (NO) synthesis by N(omega)-nitro-L-arginine methyl ester (L-NAME) induces hypertension associated with remodeling of the arterial wall. In this study, we aimed at identifying genes and pathways involved in this process in aortic smooth muscle cells from Fischer 344 rats, which exhibit an accelerated hypertension after administration of L-NAME. METHODS AND RESULTS: We studied the transcriptional profile of aortic media after 15 days (moderate hypertension) and 30 days (accelerated hypertension) of L-NAME administration (50 mg x kg(-1) x d(-1)) by using rat Affymetrix Genechips, and we present a large-scale validation of the DNA chip results by real-time reverse transcription-polymerase chain reaction (RT-PCR). We observed, in aortic media, a progressive increase in the number of modulated genes during L-NAME administration, with 53 genes significantly modulated after 15 days and 147 genes after 30 days. These expression changes were confirmed at 87% by RT-PCR. We found 28 known genes regulated at both 15 and 30 days (96% confirmation by RT-PCR). The functional classification of the regulated genes highlights 3 major biological pathways modulated in aortic media during L-NAME administration: genes regulating cell proliferation, genes involved in the extracellular matrix remodeling, and genes of the NO/cGMP signaling pathway. CONCLUSIONS: As a consequence of the genomic approach, we observed a large increase in modulation of gene expression along the evolution of the model and the progressive implication of compensatory mechanisms, making expression profile analysis more complex.

Counter-regulation by atorvastatin of gene modulations induced by L-NAME hypertension is associated with vascular protection.

Statins, 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, protect against deleterious effects of chronic nitric oxide inhibition. We aimed at determining the genes and pathways involved in the protective effect of statin treatment during hypertension. Chronic inhibition of nitric oxide synthesis by Nomega-nitro-L-arginine methyl ester (L-NAME) induced accelerated hypertension which was slightly reduced by cotreatment with atorvastatin (100 mg/kg/day). Gene expression profile of aortic media was strongly modified by atorvastatin cotreatment which prevented modulation of many genes regulated by L-NAME administration (described in Dupuis, M., Soubrier, F., Brocheriou, I., Raoux, S., Haloui, M., Louedec, L., Michel, J.B., Nadaud, S., 2004. Profiling of aortic smooth muscle cell gene expression in response to chronic inhibition of nitric oxide synthase in rats. Circulation 110, 867-873). The functional classification of these genes highlighted several major biological pathways modulated in aortic media by atorvastatin: effectors involved in smooth muscle tone; extracellular matrix; intracellular mediators of cell proliferation. Moreover, atorvastatin partially prevented arterial wall thickening, TGF-beta pathway activation, MCP-1 induction and smooth muscle cell proliferation induced by L-NAME treatment although blood pressure was only slightly reduced, suggesting mechanisms independent of blood pressure levels. The induction of PPARalpha mRNA expression by atorvastatin in L-NAME treated rats also suggests that this pathway could participate in the protective effect. In conclusion, our data show that atorvastatin specifically antagonizes a set of genes modulated by L-NAME-induced accelerated hypertension.

Proteomic analysis permits the identification of new biomarkers of arterial wall remodeling in hypertension.

Hypertension represents one of the main risk factors for vascular diseases. Genetic susceptibility may influence the rate of its development and the associated vascular remodeling. To explore markers of hypertension-related morbidity, we have used surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry to study changes in proteins released by the aorta of two rat strains with different susceptibilities to hypertension. Fischer and Brown Norway (BN) rats were divided into a control group and a group receiving low-dose N(Omega)-nitro-L-arginine methyl ester (L-NAME), a hypertensive drug, interfering with endothelial function. In spite of a significant elevation of blood pressure in both strains in response to L-NAME, BN rats exhibited a lower vascular remodeling in response to hypertension. Proteomic analysis of secreted aortic proteins by SELDI-TOF MS allowed detection of four mass-to-charge ratio (m/z) peaks whose corresponding proteins were identified as ubiquitin, smooth muscle (SM) 22alpha, thymosin beta4, and C-terminal fragment of filamin A, differentially secreted in Fischer rats in response to L-NAME. We have confirmed a strain-dependent difference in susceptibility to L-NAME-induced hypertension between BN and Fischer rats. The greater susceptibility of Fischer rats is associated with aortic wall hypertrophic remodeling, reflected by increased aortic secretion of four identified biomarkers. Similar variations in one of them, SM22alpha, also were observed in plasma, suggesting that this marker could be used to assess vascular damage induced by hypertension.

Functional coupling of rat myometrial alpha 1-adrenergic receptors to Gh alpha/tissue transglutaminase 2 during pregnancy.

Gh alpha protein, which exhibits both transglutaminase and GTPase activities, represents a new class of GTP-binding proteins. In the present study, we characterized Gh alpha in rat uterine smooth muscle (myometrium) and followed its expression during pregnancy by reverse transcription-PCR and Western blot. We also measured transglutaminase and GTP binding functions and used a smooth muscle cell line to evaluate the role of Gh alpha in cell proliferation. The results show that pregnancy is associated with an up-regulation of Gh alpha expression at both the mRNA and protein level. Gh alpha induced during pregnancy is preferentially localized to the plasma membrane. This was found associated with an increased ability of plasma membrane preparations to catalyze Ca(2+)-dependent incorporation of [(3)H]putrescine into casein in vitro. In the cytosol, significant changes in the level of immunodetected Gh alpha and transglutaminase activity were seen only at term. Activation of alpha1-adrenergic receptors (alpha1-AR) enhanced photoaffinity labeling of plasma membrane Gh alpha. Moreover, the level of alpha1-AR-coupled Gh alpha increased progressively with pregnancy, which parallels the active period of myometrial cell proliferation. Overexpression of wild type Gh alpha in smooth muscle cell line DDT1-MF2 increased alpha1-AR-induced [(3)H]thymidine incorporation. A similar response was obtained in cells expressing the transglutaminase inactive mutant (C277S) of Gh alpha. Together, these findings underscore the role of Gh alpha as signal transducer of alpha1-AR-induced smooth muscle cell proliferation. In this context, pregnant rat myometrium provides an interesting physiological model to study the mechanisms underlying the regulation of the GTPase function of Gh alpha