Genetic mapping of soluble guanylyl cyclase genes: implications for linkage to blood pressure in the Dahl rat

Molecular adaptations in vasoactive systems during acute stroke in salt-induced hypertension

Investigations regarding hypertension and dietary sodium, both factors that influence stroke risk, have previously been limited to using genetically disparate treatment and control groups, namely the stroke-prone, spontaneously hypertensive rat and Wistar-Kyoto rat. In this investigation, we have characterized and compared cerebral vasoactive system adaptations following stroke in genetically identical, salt-induced hypertensive, and normotensive control mice. Briefly, ANP(+/-) (C57BJ/6 × SV129 background) mice were fed chow containing either 0.8% NaCl (NS) or 8.0% NaCl (HS) for 7 weeks. Transient cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). Infarct volumes were measured 24-h post-reperfusion and the mRNA expression of five major vasoactive systems was characterized using qPCR. Along with previous publications, our data validate a salt-induced hypertensive state in ANP(+/-) mice fed HS chow as they displayed left ventricular hypertrophy, increased systolic blood pressure, and increased urinary sodium excretion. Following MCAO, mice fed HS exhibited larger infarct volumes than their dietary counterparts. In addition, significant up-regulation in Et-1 and Nos3 mRNA expression in response to salt and stroke suggests implications with increased cerebral damage in this group. In conclusion, our data demonstrate increased cerebral susceptibility to stroke in salt-induced hypertensive mice. More importantly, however, we have characterized a novel method of investigating hypertension and stroke with the use of genetically identical treatment and control groups. This is the first investigation in which genetic confounding variables have been eliminated.

Genetic modifiers of hypertension in soluble guanylate cyclase α1-deficient mice

Nitric oxide (NO) plays an essential role in regulating hypertension and blood flow by inducing relaxation of vascular smooth muscle. Male mice deficient in a NO receptor component, the α1 subunit of soluble guanylate cyclase (sGCα1), are prone to hypertension in some, but not all, mouse strains, suggesting that additional genetic factors contribute to the onset of hypertension. Using linkage analyses, we discovered a quantitative trait locus (QTL) on chromosome 1 that was linked to mean arterial pressure (MAP) in the context of sGCα1 deficiency. This region is syntenic with previously identified blood pressure-related QTLs in the human and rat genome and contains the genes coding for renin. Hypertension was associated with increased activity of the renin-angiotensin-aldosterone system (RAAS). Further, we found that RAAS inhibition normalized MAP and improved endothelium-dependent vasorelaxation in sGCα1-deficient mice. These data identify the RAAS as a blood pressure-modifying mechanism in a setting of impaired NO/cGMP signaling.

Renal functional, not morphological, abnormalities account for salt sensitivity in Dahl rats

BACKGROUND

The kidney's role in the pathogenesis of salt-induced hypertension remains unclear. However, it has been suggested that inherited morphological renal abnormalities may cause hypertension. We hypothesized that functional, not morphological, derangements in Dahl salt-sensitive rats' kidneys cause NaCl retention that leads to hypertension accompanied by renal pathologic changes and proteinuria.

METHOD

We studied hemodynamic, renal morphologic, and biochemical differences in Dahl salt-resistant and Dahl salt-sensitive rats fed low (0.05-0.23% NaCl) or elevated (1% NaCl) salt diets.

RESULTS

We found similar hemodynamics, equal numbers of glomeruli, normal renal medullary interstitial cells and their osmiophilic granules, and cortical morphology in normotensive Dahl salt-resistant and Dahl salt-sensitive rats fed low dietary salt. Furthermore, aldosterone secretion, caused by angiotensin II infusion in normotensive rats fed 0.23% NaCl, was significantly less in Dahl salt-sensitive than Dahl salt-resistant rats. Increasing NaCl to 1% caused renal vasoconstriction without changing cyclic GMP excretion in Dahl salt-sensitive rats; in Dahl salt-resistant rats, cyclic GMP increased markedly and renal vascular resistance remained unchanged. On 1% NaCl for 9 months, Dahl salt-sensitive rats developed marked hypertension, severe renal vasoconstriction, glomerulosclerosis, tubulointerstitial abnormalities, and marked proteinuria; hypertension resulted from increased total peripheral resistance, as occurs in essential hypertensive humans. No hemodynamic or renal pathologic changes occurred in Dahl salt-resistant rats, and proteinuria was minimal.

CONCLUSION

We conclude that renal functional, not morphological, abnormalities cause salt sensitivity in Dahl rats.

Characterization of the human alpha1 beta1 soluble guanylyl cyclase promoter: key role for NF-kappaB(p50) and CCAAT-binding factors in regulating expression of the nitric oxide receptor

Soluble guanylyl cyclase (sGC) is the principal receptor for NO and plays a ubiquitous role in regulating cellular function. This is exemplified in the cardiovascular system where sGC governs smooth muscle tone and growth, vascular permeability, leukocyte flux, and platelet aggregation. As a consequence, aberrant NO-sGC signaling has been linked to diseases including hypertension, atherosclerosis, and stroke. Despite these key (patho)physiological roles, little is known about the expressional regulation of sGC. To address this deficit, we have characterized the promoter activity of human α₁ and β₁ sGC genes in a cell type relevant to cardiovascular (patho)physiology, primary human aortic smooth muscle cells. Luciferase reporter constructs revealed that the 0.3- and 0.5-kb regions upstream of the transcription start sites were optimal for α₁ and β₁ sGC promoter activity, respectively. Deletion of consensus sites for c-Myb, GAGA, NFAT, NF-κB(p50), and CCAAT-binding factor(s) (CCAAT-BF) revealed that these are the principal transcription factors regulating basal sGC expression. In addition, under pro-inflammatory conditions, the effects of the strongest α₁ and β₁ sGC repressors were enhanced, and enzyme expression and activity were reduced; in particular, NF-κB(p50) is pivotal in regulating enzyme expression under such conditions. NO itself also elicited a cGMP-independent negative feedback effect on sGC promoter activity that is mediated, in part, via CCAAT-BF activity. In sum, these data provide a systematic characterization of the promoter activity of human sGC α₁ and β₁ subunits and identify key transcription factors that govern subunit expression under basal and pro-inflammatory (i.e. atherogenic) conditions and in the presence of ligand NO.

Molecular cloning of a novel variant of the rat soluble guanylate cyclase beta2 subunit

Soluble guanylate cyclases (sGCs) are heterodimeric enzymes consisting of alpha and beta subunits and catalyze the formation of cGMP from GTP. The beta1 subunit has been characterized in detail, whereas the function and physiological role of the beta2 subunit are poorly understood. In this study, I isolated two distinct cDNA fragments for the beta2 subunit of sGC (beta2a and beta2b) from a rat brain cDNA library by 3' rapid amplification of cDNA ends using degenerate sense primers based on amino acid sequences conserved among membrane-bound guanylate cyclases. The deduced amino acid sequence of beta2a is identical with the corresponding sequence of the previously described beta2 subunit, whereas that of beta2b is C-terminally shorter by 46 amino acids and thus does not contain a consensus sequence for isoprenylation/carboxymethylation. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that both variants are expressed in various tissues, including kidney, liver, and brain. Although the functional significance of the C-terminal region containing the consensus sequence for isoprenylation/carboxymethylation of beta2a remains unclear yet, it is likely that these beta2 subunits play some physiological or pathophysiological role in various tissues.

Regulation of nitric oxide and soluble guanylyl cyclase

Since the discoveries that have verified nitric oxide (NO) as an endogenously produced cell signaling molecule, research surrounding its production and mechanisms of action have been studied at an exponentially increasing rate. NO is produced by a family of enzymes termed the NO synthases (NOS), which are regulated independently by various stimuli. Once produced, NO can solicit numerous biological events by reacting with various metals, thiols, and oxygen species to modify proteins, DNA and lipids. One of the most biologically relevant actions of NO is its binding to the heme moiety in the heterodimeric enzyme, soluble guanylyl cyclase (sGC). Activation of sGC by NO results in the production of the second messenger molecule, 3',5'-cyclic guanosine monophosphate (cGMP), which can regulate numerous physiological events such as vasodilatation and neurotransmission. Here we will review the synthesis and fate of NO, and discuss the activation and regulation of the NO receptor, sGC.

Molecular dissection of mouse soluble guanylyl cyclase alpha1 promoter

Soluble guanylyl cyclase (sGC) is the only known receptor for nitric oxide (NO) and is downregulated in aging and hypertension. Little is known about sGC gene transcriptional regulation. In order to characterize the sGC transcriptional system, we cloned and sequenced the 5(') flanking region of mouse sGC alpha(1) gene (AY116663). Structurally, it is a non-canonical TATA-less promoter that we mapped to chromosome 3 with many putative regulation sites for Sp-1, NF-kappaB, and AP-1 transcription factors amongst others, and two (TG:CA)(n) dinucleotide microsatellites near the transcriptional start point. The cloned upstream sequence produced a 5-fold increase in luciferase activity in Cos7, HeLa, NIH3T3, and 293 cells as well as in mouse VSMC-like kidney mesangial cells. In the latter cell type, we showed that sGC alpha(1) promoter activity was dependent on the presence of its 5(') unstranslated region (5(')UTR).

Participation of renal and circulating endothelin in salt-sensitive essential hypertension

Salt sensitivity of blood pressure is a cardiovascular risk factor, independent of and in addition to hypertension. In essential hypertension, a conglomerate of clinical and biochemical characteristics defines a salt-sensitive phenotype. Despite extensive research on multiple natriuretic and antinatriuretic systems, there is no definitive answer yet about the major causes of salt-sensitivity, probably reflecting the complexity of salt-balance regulation. The endothelins, ubiquitous peptides first described as potent vasoconstrictors, also have vasodilator, natriuretic and antinatriuretic actions, depending on their site of generation and binding to different receptors. We review the available data on endothelin in salt-sensitive essential hypertension and conclude that abnormalities of renal endothelin may play a primary role. More importantly, the salt-sensitive patient may have blood pressure-dependency on endothelin in all states of salt balance, thus predicting that endothelin receptor blockers will have a major therapeutic role in salt-sensitive essential hypertension.

Promoter activity of the 5'-flanking regions of medaka fish soluble guanylate cyclase alpha1 and beta1 subunit genes

We examined the spatial expression pattern of medaka fish (Oryzias latipes) soluble guanylate cyclase alpha(1) and beta(1) subunit genes, OlGCS-alpha(1) and OlGCS-beta(1), and characterized the 5'-flanking region required for expression of both genes by introducing various promoter-luciferase fusion-gene constructs into COS-1 cells and medaka fish embryos. The OlGCS-alpha(1) and OlGCS-beta(1) gene transcripts were detected in whole brain and kidney in 7-day and 9-day embryos. Primer-extension analysis demonstrated that there were no differences among various adult organs (brain, eye, kidney, ovary and testis) in the transcription start site of the OlGCS-alpha(1) and OlGCS-beta(1) genes. Neither gene contained the functional TATA box within its 5'-flanking region, and the basal promoter activity was found between nucleotides +33 and +42 in the OlGCS-alpha(1) gene and between nucleotides +146 and +155 in the OlGCS-beta(1) gene. In the assay of medaka fish embryos, the 5'-flanking region of the OlGCS-beta(1) gene exhibited lower promoter activity than that of the OlGCS-alpha(1) gene. In the experiments on dual-luciferase fusion-gene constructs, the 5'-flanking region of the OlGCS-alpha(1) gene connected to the 5'-flanking region of the OlGCS-beta(1) gene was introduced into medaka fish embryos, and the 5'-flanking regions of both subunit genes were shown to mutually influence each other's promoter activity.

Downregulation of vascular soluble guanylate cyclase induced by high salt intake in spontaneously hypertensive rats

1. Cyclic guanosine monophosphate (cyclic GMP)-mediated mechanism plays an important role in vasodilatation and blood pressure regulation. We investigated the effects of high salt intake on the nitric oxide (NO) - cyclic GMP signal transduction pathway regulating relaxation in aortas of spontaneously hypertensive rats (SHR). 2. Four-week-old SHR and normotensive Wistar-Kyoto rats (WKY) received a normal salt diet (0.3% NaCl) or a high salt diet (8% NaCl) for 4 weeks. 3. In aortic rings from SHR, endothelium-dependent relaxations in response to acetylcholine (ACh), adenosine diphosphate (ADP) and calcium ionophore A23187 were significantly impaired by the high salt intake. The endothelium-independent relaxations in response to sodium nitroprusside (SNP) and nitroglycerin were also impaired, but that to 8-bromo-cyclic GMP remained unchanged. On the other hand, high salt diet had no significant effects on the relaxations of aortic rings from WKY. 4. In aortas from SHR, the release of NO stimulated by ACh was significantly enhanced, whereas the production of cyclic GMP induced by either ACh or SNP was decreased by the high salt intake. 5. Western blot analysis showed that the protein level of endothelial NO synthase (eNOS) was slightly increased, whereas that of soluble guanylate cyclase (sGC) was dramatically reduced by the high salt intake. 6. These results indicate that in SHR, excessive dietary salt can result in downregulation of sGC followed by decreased cyclic GMP production, which leads to impairment of vascular relaxation in responses to NO. It is notable that chronic high salt intake impairs the sGC/cyclic GMP pathway but not the eNOS/NO pathway.

Genomic organization of alpha1 and beta1 subunits of the mammalian soluble guanylyl cyclase genes

The structures of the genes encoding the alpha(1) and beta(1) subunits of murine soluble guanylyl cyclase (sGC) were determined. Full-length cDNAs isolated from mouse lungs encoding the alpha(1) (2.5 kb) and beta(1) (3.3 kb) subunits are presented in this report. The alpha(1) sGC gene is approximately 26.4 kb and contains nine exons, whereas the beta(1) sGC gene spans 22 kb and consists of 14 exons. The positions of exon/intron boundaries and the sizes of introns for both genes are described. Comparison of mouse genomic organization with the Human Genome Database predicted the exon/intron boundaries of the human genes and revealed that human and mouse alpha1 and beta1 sGC genes have similar structures. Both mouse genes are localized on the third chromosome, band 3E3-F1, and are separated by a fragment that is 2% of the chromosomal length. The 5' untranscribed regions of alpha(1) and beta(1) subunit genes were subcloned into luciferase reporter constructs, and the functional analysis of promoter activity was performed in murine neuroblastoma N1E-115 cells. Our results indicate that the 5' untranscribed regions for both genes possess independent promoter activities and, together with the data on chromosomal localization, suggest independent regulation of both genes.

The molecular basis of hypertension

More than 50 million Americans display blood pressures outside the safe physiological range. Unfortunately for most individuals, the molecular basis of hypertension is unknown, in part because pathological elevations of blood pressure are the result of abnormal expression of multiple genes. This review identifies a number of important blood pressure regulatory genes including their loci in the human, mouse, and rat genome. Phenotypes of gene deletions and overexpression in mice are summarized. More detailed discussion of selected gene products follows, beginning with proteins involved in ion transport, specifically the epithelial sodium channel and sodium proton exchangers. Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide. The renin angiotensin aldosterone system has an important role antagonizing the vasodilatory cyclic GMP system.

The beta(2) subunit of soluble guanylyl cyclase contains a human-specific frameshift and is expressed in gastric carcinoma

Soluble or nitric oxide (NO) stimulated guanylyl cyclases are obligate heme-containing heterodimers (alpha/beta). We report the full-length cDNA of the human ortholog of the rat beta(2)-subunit from human kidney. A database search yielded matches of the 3' non-coding sequence with previously unassigned expressed sequence tags from kidney and stomach signet ring cell carcinoma. PCR comparison of cDNA from stomach signet ring cell carcinoma and normal stomach tissue demonstrated beta(2) subunit expression in cancer but not in normal tissue. On the cDNA level a frameshift deletion of one nucleotide was present in the novel human sequence which was confirmed on the genomic DNA level. In four closely related nonhuman primate species the frameshift deletion was absent while analysis of genomic DNA from different ethnic backgrounds revealed the uniform presence of the frameshift deletion in the human population.

Evaluation of heterodimeric guanylyl cyclase genes as candidates for human hypertension

OBJECTIVE

Both physiologic and pharmacological data have implicated the nitric oxide (NO) signaling cascade in the regulation of blood pressure in humans and its impairment in the pathogenesis of hypertension. In biological systems, the principal receptor for NO is NO-stimulated guanylyl cyclase. NO-stimulated guanylyl cyclases are obligate heterodimers (alpha/beta). The genes for guanylyl cyclase subunits alpha1, beta, and beta2 are likely candidates for causing hypertension in the Dahl rat as their expression is altered and their gene loci are closely linked to known quantitative trait loci for blood pressure in Dahl rat crosses. The objective of the current study was to test whether markers near guanylyl cyclase subunit genes were linked to hypertension in Caucasians.

DESIGN

To test for linkage of genetic markers in or near the guanylyl cyclase genes to hypertension in Caucasians, a sample of 124 Utah hypertensive sib pairs was genotyped.

RESULTS

Four highly polymorphic markers in or near the human guanylyl cyclase subunits homologous to the rat alpha1 (human chromosome 8), rat beta1 (human chromosome 4), and rat beta2 (human chromosome 13) genes showed no evidence of excess allele sharing in the set of hypertensive sibships.

CONCLUSION

We conclude that the heterodimeric guanylyl cyclase subunit loci do not appear to be linked to hypertension in Caucasians.

Molecular aspects of soluble guanylyl cyclase regulation

Soluble guanylyl cyclase (sGC) is a heterodimeric enzyme (comprised of alpha and beta subunits) that generates the intracellular second messenger cyclic guanosine monophosphate (cGMP) from guanosine triphosphate (GTP). cGMP is subsequently important for the regulation of protein kinases, ion channels, and phosphodiesterases. Since recent evidence has demonstrated that heterodimerization of the alpha/beta subunits is essential for basal and stimulated enzymatic activity, the existence of several types of isoforms for each of the two subunits, along with their varying degrees of expression in different tissues, implies that multiple regulatory mechanisms exist for sGC. Yet, progress in studying and clarifying the regulatory processes that can alter sGC expression and activity has only slowly started being elucidated. In the following paper, we elaborate on sGC structure, function, and distribution along with recently described signaling pathways that modulate sGC gene expression.

Tandem organization of medaka fish soluble guanylyl cyclase alpha1 and beta1 subunit genes. Implications for coordinated transcription of two subunit genes

We determined the complete nucleotide sequences of the alpha1 subunit gene (OlGCS-alpha1) and the beta1 subunit gene (OlGCS-beta1) of medaka fish soluble guanylyl cyclase. In the genome, OlGCS-alpha1 and OlGCS-beta1 are organized in tandem. The two genes are only 986 base pairs apart and span approximately 34 kilobase pairs in the order of OlGCS-alpha1 and OlGCS-beta1. The nucleotide sequence of a large part of the 5'-upstream region of OlGCS-alpha1 is complimentarily conserved in that of OlGCS-beta1. To analyze the promoter activity of each gene, a fusion gene construct in which the 5'-upstream region was fused with the green fluorescent protein gene was injected into medaka fish 2-cell embryos. When the fusion gene containing the OlGCS-alpha1 upstream region was injected, green fluorescent protein fluorescence was detected in the embryonic brain. The 5'-upstream region of OlGCS-beta1 alone was insufficient for the reporter gene expression in the embryos. When the OlGCS-alpha1 upstream region was located upstream of the OlGCS-beta1-green fluorescence protein fusion gene, the reporter gene was expressed in the brain and trunk region of the embryos. These results suggest that the 5'-upstream region of OlGCS-alpha1 can affect the expression of OlGCS-beta1. It is therefore possible that the expression of OlGCS-alpha1 and OlGCS-beta1 is coordinated.