Pentz ES, Sequeira Lopez ML, Cordaillat M, Gomez RA. Identity of the renin cell is mediated by cAMP and chromatin remodeling: an in vitro model for studying cell recruitment and plasticity. Am J Physiol Heart Circ Physiol 294: H699-H707, 2008. First published November 30, 2007 doi:10.1152/ajpheart.01152.2007.-The renin-angiotensin system (RAS) regulates blood pressure and fluid-electrolyte homeostasis. A key step in the RAS cascade is the regulation of renin synthesis and release by the kidney. We and others have shown that a major mechanism to control renin availability is the regulation of the number of cells capable of making renin. The kidney possesses a pool of cells, mainly in its vasculature but also in the glomeruli, capable of switching from smooth muscle to endocrine renin-producing cells when homeostasis is threatened. The molecular mechanisms governing the ability of these cells to turn the renin phenotype on and off have been very difficult to study in vivo. We, therefore, developed an in vitro model in which cells of the renin lineage are labeled with cyan fluorescent protein and cells actively making renin mRNA are labeled with yellow fluorescent protein. The model allowed us to determine that it is possible to culture cells of the renin lineage for numerous passages and that the memory to express the renin gene is maintained in culture and can be reenacted by cAMP and chromatin remodeling (histone H4 acetylation) at the cAMPresponsive element in the renin gene.

The mechanisms that govern the identity of renin cells are not well understood. We and others have identified cAMP as an important pathway in the regulation of renin synthesis and release. Recently, experiments in cells from the renin lineage led us to propose that acquisition and maintenance of renin cell identity are mediated by cAMP and histone acetylation at the cAMP responsive element (CRE) of the renin gene. Ultimately, the transcriptional effects of cAMP depend on binding of the appropriate transcription factors to CRE. It has been suggested that access of transcription factors to this region of the promoter is facilitated by the coactivators CREB-binding protein (CBP) and p300, which possess histone acetyltransferase activity and may be, in turn, responsible for the remodeling of chromatin underlying expression of the renin gene. We hypothesized that CBP and p300 are therefore required for expression of the renin gene and maintenance of the renin cell. Because mice homozygous for the deletion of CBP or p300 die before kidney organogenesis begins, no data on kidney or juxtaglomerular cell development in these mice are available. Therefore, to define the role of these histone acetyltransferases in renin cell identity in vivo, we used a conditional deletion approach, in which floxed CBP and p300 mice were crossed with mice expressing cre recombinase in renin cells. Results show that the histone acetyltransferases CBP and p300 are necessary for maintenance of renin cell identity and structural integrity of the kidney.

BackgroundDespite increasing evidence for the presence of voltage-gated Na+ channels (Nav) isoforms and measurements of Nav channel currents with the patch-clamp technique in arterial myocytes, no information is available to date as to whether or not Nav channels play a functional role in arteries. The aim of the present work was to look for a physiological role of Nav channels in the control of rat aortic contraction.Methodology/Principal FindingsNav channels were detected in the aortic media by Western blot analysis and double immunofluorescence labeling for Nav channels and smooth muscle α-actin using specific antibodies. In parallel, using real time RT-PCR, we identified three Nav transcripts: Nav1.2, Nav1.3, and Nav1.5. Only the Nav1.2 isoform was found in the intact media and in freshly isolated myocytes excluding contamination by other cell types. Using the specific Nav channel agonist veratridine and antagonist tetrodotoxin (TTX), we unmasked a contribution of these channels in the response to the depolarizing agent KCl on rat aortic isometric tension recorded from endothelium-denuded aortic rings. Experimental conditions excluded a contribution of Nav channels from the perivascular sympathetic nerve terminals. Addition of low concentrations of KCl (2–10 mM), which induced moderate membrane depolarization (e.g., from −55.9±1.4 mV to −45.9±1.2 mV at 10 mmol/L as measured with microelectrodes), triggered a contraction potentiated by veratridine (100 µM) and blocked by TTX (1 µM). KB-R7943, an inhibitor of the reverse mode of the Na+/Ca2+ exchanger, mimicked the effect of TTX and had no additive effect in presence of TTX.Conclusions/SignificanceThese results define a new role for Nav channels in arterial physiology, and suggest that the TTX-sensitive Nav1.2 isoform, together with the Na+/Ca2+ exchanger, contributes to the contractile response of aortic myocytes at physiological range of membrane depolarization.

Cordaillat, Magali, Caroline Rugale, Daniel Casellas, Albert Mimran, and Bernard Jover. Cardiorenal abnormalities associated with high sodium intake: correction by spironolactone in rats. Am J Physiol Regul Integr Comp Physiol 289: R1137-R1143, 2005. First published May 26, 2005; doi:10.1152/ajpregu.00154.2005.-Reversal by the mineralocorticoid receptor antagonist spironolactone on cardiac and renal abnormalities, associated with long-term (since weaning) administration of a high (2 and 8% NaCl chow, HS2 and HS8) sodium diet, was assessed in Sprague-Dawley rats. At the age of 5 mo, spironolactone (20 or 100 mg/kg, gavage) or placebo were given for 14 days to HS2 and HS8 rats. A group fed a regular diet (0.8% NaCl, NS) remained untreated. High sodium intake had no detectable effect on blood pressure; however, cardiac mass index and cross-sectional area of the carotid artery, as well as albuminuria, were increased only in the HS8 group compared with the control group on NS diet. In addition, a marked reduction in glomerular filtration rate (by 40%), associated with a nonproportional fall in renal plasma flow (thus resulting in a decrease in filtration fraction), was observed only in the HS8 group. No change in cardiac and renal fibrosis was detected. Production of the reactive oxygen species (ROS) by aortic tissue was increased in HS8 rats, whereas ROS production by the heart was unaffected. Only the high dose of spironolactone was effective, as it markedly reversed the cardiac hypertrophy and renal hypofiltration associated with the HS8 feeding. The changes were observed in the absence of any effect on systemic blood pressure and production of ROS. These observations favor aldosterone's role in the deleterious effects of marked and prolonged increases in sodium intake. spironolactone; renal function; reactive oxygen species; cardiac hypertrophy IN ADDITION TO ITS WIDELY debated effect on blood pressure, chronic variation of sodium intake has been reported to modulate the cardiovascular morphology in human and experimental models. In animal studies, dietary sodium restriction has been shown to prevent the development of cardiac hypertrophy in renovascular (13) and ANG II-induced hypertension (14), independently of blood pressure. Reversal of cardiac hypertrophy was achieved by 6 wk on a low-sodium diet in 2-kidney, one-clip hypertensive rats (17). Administration of a diet containing 8% sodium chloride for more than 4 wk was associated with the development of left ventricular hypertrophy, cardiac fibrosis, and an increase in collagen content (10,23).Because an increase in systemic pressure associated with high sodium was not consistently observed, it was suggested that a direct effect of sodium may underlie the increased sensitivity of target organs to blood pressure. Interestingly, in a cohort of normotensive subjects and never-treated patients with essential hypertension, it was recently demonstrated that increasing dietary sodium (as estimated by 24-h natriuresis), enhanced the slope of the relationship between...