Chronic treatment with red wine polyphenol compounds mediates neuroprotection in a rat model of ischemic cerebral stroke

In this study, we investigated the in vivo effects of red wine polyphenol compounds (RWPC) in rats that were submitted to middle cerebral occlusion as an experimental model of stroke. Male Wistar rats were given RWPC [30 mg/(kg x d) dissolved in drinking water] or water for 1 wk before being subjected to transient middle cerebral artery occlusion followed by reperfusion. Sham-operated rats were subjected to transient occlusion in which the filament was not completely introduced. The release of amino acids and energy metabolites were monitored by intracerebral microdialysis. The volume of the ischemic lesion was assessed 24 h after reperfusion. Proteomic analysis of brain tissue was performed to study the effects of ischemia and RWPC on specific protein expression. Treatment with RWPC completely prevented the burst of excitatory amino acids that occurred in response to ischemia in untreated rats and significantly reduced brain infarct volumes. Rats chronically treated with RWPC, however, had lower basal concentrations of energy metabolites, including glucose and lactate in the brain parenchyma, compared with untreated rats. Chronic RWPC treatment significantly enhanced the residual cerebral blood flow during occlusion and reperfusion in rats subjected to transient occlusion compared with untreated rats. This effect resulted from arterial vasodilatation, as the internal diameters of several arteries were significantly enlarged after RWPC treatment. Proteomic studies revealed the modulation by RWPC of the expression of proteins involved in the maintenance of neuronal caliber and axon formation, in the protection against oxidative stress, and in energy metabolism. These findings provide an experimental basis for the beneficial effects of RWPC on the neurovascular unit during stroke.

The proteome and secretome of human arterial smooth muscle cell

Smooth muscle cells (SMCs) play a crucial role in cardiovascular diseases. Proteomic analysis using two-dimensional gel electrophoresis (2DE) associated with mass spectrometry allows characterization of the proteome and secretome of human smooth muscle. The presence of a distinct SMC population in the arterial wall implies that under normal conditions, SMCs are phenotypically heterogeneous. Intracellular and secreted proteins from a primary culture of SMCs obtained from patients undergoing coronary bypass surgery were analyzed using 2DE in order to determine their specific features. The 2D reference maps show that SMCs are involved in a wide range of biological functions. They could constitute a useful tool for a wide range of investigators involved in vascular biology, allowing them to investigate SMC protein changes associated with cardiovascular disorders or environmental stimuli.

[Proteomics in cardiology]

Cardiovascular diseases are among the major causes of morbidity and mortality in the developed world. The molecular mechanisms responsible for dysfunction of the heart in most cardiac pathologies are still largely unknown, except that the expression of certain genes/proteins is altered. Proteomic analysis is a technology which can provide an overall understanding of changes in the level of protein expression. Especially with differential analysis, it now represents a powerful tool for interpreting all biochemical responses and their regulation. The principal technique employed is two dimensional electrophoresis (2-D gel) to separate the proteins followed by mass spectometry in order to identify them. Recently SELDI-TOF analysis, which is a complementary 2-D electrophoresis technique based on the combination of two principles, chromatography by retention on protein chips and mass spectometry, has allowed the comparison of protein profiles obtained from diverse biological samples. The publication of genome sequences for humans as well as for other species has provided evidence for the biochemical complexity, and in particular the fact that a gene does not just code for a single protein but for several, due to various alternative splicing processes, post-translational modifications etc... The combination of these various approaches has proved to be particularly interesting in the study of cardiovascular diseases with the aim of understanding the molecular mechanisms involved, providing evidence for protein interactions and identifying new biochemical factors / markers involved in the different cardiovascular pathologies.

[The best of fundamental research in 2006]

The Cardiovascular Research Study Group attempts to organise round tables during its annual meetings based around themes that will allow clinical and fundamental researchers, especially the younger ones, to present their work. For example, certain round table subjects at the Spring cardiology meeting, such as 'Genetics: monogenic and polygenic diseases', 'Cellular therapy', and 'Ionic homoeostasis and cardiac arrhythmias', allowed several French laboratories to publish in some of the best journals such as Nature Genetics, Nature Methods, Circulation, and Circulation Research. During the Toulouse congress, eight poster prizes were awarded to young nonstatutory researchers under the age of 32 years. For the American Heart Association congress, eight travel grants were allocated to students whose abstracts had been accepted, paving the way for future publications from young French researchers in the best journals.

Profiling of membrane proteins from human macrophages: Comparison of two approaches

Macrophages are involved in various important biological processes and their functions are tightly regulated. Hydrophobic proteins are difficult to analyse by 2-DE because of their intrinsic tendency to self-aggregate during the first dimension (IEF). We have compared two protocols for extracting, separating and identifying membrane proteins from human macrophages by MALDI-TOF MS. The first protocol used protein extraction by solvent, followed by 2-DE and allowed us to identify 10% membrane proteins among the proteins identified a being like the peroxisome-activated receptor delta. The second method is based on solubilizing the membranes with Triton X-100, separating the proteins by anion-exchange chromatography followed by SDS-PAGE. This method allowed us to identify 49 membrane proteins, including four integral membrane proteins, ten type I, two type II and one type III membrane proteins. Several receptors were identified, including integrin alpha-3 and ephrin type A receptor 7. Interestingly, several proteins involved in macrophage functions were identified, such as integrin alpha-X and macrophage mannose receptor. These findings show that techniques are available to identify membrane proteins, but that they require large quantities of cells which means that they are not suitable for the limiting amounts of precious samples available from clinical studies.

[The best of fundamental research in 2005]

The cardiovascular research and reflection group aims to hold round tables between the annual congresses on themes allowing clinicians, fundamental research workers, especially the younger generation, to present their work. For example, a number of subjects of these round tables, "Genomic Modification and Integrated Physiology", "Adhesion and Extracellular Matrix", or "Electrophysiological Features of Ventricular Arrhythmias" of the 2005 Congress led to many laboratories publishing their results in the most reputable journals, such as Nature Medicine, Circulation. During the Strasbourg Congress, six poster prizes were attributed to young, nonstatutory research workers, under 32 years of age. Six voyage grants for the American Heart Association Meeting were given to students who had their summaries accepted, in the expectation of upcoming publications by young French workers in the best journals.

The endothelin system and renin in human fetal membranes

Term human fetal membranes express prorenin, a key enzyme within the renin-angiotensin system. High levels of another vasoactive peptide, endothelin-1 (ET-1), are found in human amniotic fluid. To address the question of the relationship between these two vasoactive systems, we analyzed the expression of the components of the ET-1 system in fetal membranes in which cell types had been identified using different markers. Immunohistochemistry was performed with antibodies raised against the human proteins of the ET system. Term fetal membranes displayed ubiquitous labeling of endothelin-converting enzyme-1 (ECE-1) and ET-1. ETA receptors were detected in the chorionic connective tissue and the attached decidua; ETB receptors were localized to chorionic trophoblast cells and decidua. The localization of the ET-1 receptor subtype was confirmed by in-situ receptor binding. Renin immunoreactivity was detected in the chorionic connective tissue and the decidua. These findings suggest that ET-1 is produced ubiquitously in human fetal membranes, and its targets may be, trophoblast cells following ETB receptor activation, vascular structures and fibroblasts in the connective tissue and decidua via ETA and ETB receptors. It appears possible that renin and ET may contribute to the pathophysiological changes associated with premature labor and preeclampsia.

[Contribution of proteomic analysis to study cardiovascular physiopathology]

Proteomic is an innovative approach for determining without any priori the coordinated changes in protein levels contained in a biological sample. This technique now constitutes a powerful tool for revealing, in particular by differential analysis, biological responses and regulation of proteins. This field is becoming essential in each domain for fundamental and clinical biology, mainly in human medicine. It leads to improve the understanding of complex physiopathological processes like those involved in human pathologies, but also for identifying new biomarkers in order to consider new diagnostic and prognostic approaches and original therapeutic targets. The different proteomic techniques, essentially bi-dimensional electrophoresis and mass spectrometry, which benefit from recent technological developments, are presented in this article. A literature review summarize data obtained from proteomic works performed to have better understanding of mechanisms involved in cardiovascular diseases, first cause of morbidity and mortality in the world. Proteomic analysis performed in this area of research are promising, because of the lack of knowledge in the molecular interactions and the complexity of mechanisms involved, and of the impact of environmental risk factors. This impact is being generally only detectable at protein level. These works are only at the beginning and these approaches applied in cardiovascular field will meet a large success in the immediate future and should be promising.

The proteome and secretome of human arterial smooth muscle cells

Smooth muscle cells (SMCs) play a crucial role in cardiovascular disorders. A differential proteomic approach should help to elucidate SMC dysfunctions involved in these diseases. With this goal in mind, we plotted the first 2-dimensional (2-D) maps of the proteome and secretome of human arterial smooth muscle cell (ASMC). Intracellular and secreted proteins were extracted from a primary culture of SMCs obtained from patients undergoing coronary artery bypass surgery (n = 11) and separated by 2-dimensional gel electrophoresis. Silver-stained gels were analyzed using Progenesis software. A high level of between-gel reproducibility was obtained, allowing us to generate two protein patterns specific to the ASMC proteome and secretome, respectively. A total of 121 and 40 distinct intracellular and secreted polypeptide spots, corresponding to 83 and 18 different proteins, respectively, were identified by matrix-assisted laser desorption/ionization mass spectrometry. The 2-D reference maps and database resulting from this study confirm that SMCs are involved in a wide range of biological functions. They could constitute a useful tool for a wide range of investigators involved in vascular biology, allowing them to investigate SMC protein changes associated with cardiovascular disorders or environmental stimuli.

Two-dimensional maps and databases of the human macrophage proteome and secretome

Macrophages exert a crucial, but still incompletely known, role in complex disorders such inflammatory, immunological, and infectious diseases. A differential proteomic approach should help to elucidate the macrophage dysfunctions involved in these diseases. With this goal in mind, we established the first two-dimensional maps of the human macrophage proteome and secretome. Intracellular and secreted proteins were extracted from monocyte-derived macrophages obtained from healthy donors (n = 16), and separated by two-dimensional gel electrophoresis. Silver-stained gels were analyzed using Progenesis software. A high level of between-gel reproducibility was obtained, allowing us to generate two patterns specific of the macrophage proteome and secretome, respectively. A total of 127 and 66 distinct intracellular and secreted polypeptide spots, corresponding to 100 and 38 different proteins, respectively, were identified by matrix assisted laser desorption/ionisation-mass spectrometry. The two-dimensional reference maps and databases resulting from this study confirm that macrophages are involved in a wide range of biological functions, and that they provide a useful tool for a wide array of investigators involved in macrophage biology, allowing to investigate the macrophage protein changes associated with various disorders or environmental stimuli.

Cardiac Specific Increase in Aldosterone Production Induces Coronary Dysfunction in Aldosterone Synthase–Transgenic Mice

BACKGROUND

Elevated circulating aldosterone level is associated with impaired cardiovascular function. Although the mechanisms are not fully understood, aldosterone antagonists decrease total and cardiovascular mortality in heart failure and myocardial infarction. Aldosterone induces cardiac fibrosis in experimental models, and it is synthesized locally in rat heart. These observations suggest pathological effects of aldosterone in heart that remain unclear.

METHODS AND RESULTS

Transgenic mice (TG) that overexpress the terminal enzyme of aldosterone biosynthesis, aldosterone synthase (AS), in heart have been raised by gene targeting with the alpha-myosin heavy chain promoter. AS mRNA increased 100-fold and aldosterone concentration 1.7-fold in hearts of male TG mice relative to wild-type. No structural or myocardial alterations were evidenced, because ventricle/body weight, AT1 and AT2 receptor binding, and collagen content were unchanged in TG. No alteration in cardiac function was evidenced by echocardiography, isolated perfused heart, or whole-cell patch clamp experiments. In contrast, coronary function was impaired, because basal coronary flow was decreased in isolated perfused heart (-55% of baseline values), and vasodilatation to acetylcholine, bradykinin, and sodium nitroprusside was decreased by 75%, 60%, and 75%, respectively, in TG mice compared with wild-type, showing that the defect was not related to NO production.

CONCLUSIONS

Increased cardiac aldosterone production in male mice induces a major coronary endothelium-independent dysfunction with no detectable alterations in cardiac structure and function. However, coronary dysfunction may be harmful for coronary adaptation to increased flow demand.

[Proteomic analysis of proteins involved in the renal phenotype in renovascular hypertension]

Renovascular hypertension is characterised by stenosis of the renal artery and high plasma renin levels due to the recruitment of renin-producing cells along the afferent arterioles. This increase in myoepithelioid cells is mainly a result of the differentiation of existing smooth muscle cells with acquisition of a secretory phenotype. To understand the molecular mechanisms involved in this recruitment, we used the model of renovascular hypertension known as the two-kidney, one-clip model in the Lewis rat. Renal arterioles were isolated using magnetised iron suspension. Differential proteomic analysis was performed using two-dimensional electrophoresis gel followed by mass spectrometry for identification. The most striking protein revealed by proteomics is troponin T, which is down-regulated in the afferent arterioles of the clipped kidney. Confocal microscopy showed that troponin T is specific to the smooth muscle phenotype and absent in the myoepithelioid phenotype.

À quoi sert le système endothéline ?

Endothelins are a family of three peptides of 21 amino acids with strong vasoconstrictor effects. The three peptides are encoded by three different genes and derived from precursors (" big endothelins") which are cleaved by metalloproteases, named endothelin-converting enzyme. Two receptors have been cloned, ET-A and ET-B which bind the three endothelins with various affinities. The diverse expression pattern of the endothelin system (ET) components is associated with a complex pharmacology and its counteracting physiological actions. New modulators of the ET system have been described : retinoic acid, leptin, prostaglandins, hypoxia. Endothelins can be considered as regulators working in paracrine and autocrine fashion in a variety of organs in different cellular types. The ET system has beneficial and detrimental roles in mammals. The different components have been shown to be essential for a normal embryonic and neonatal development, for renal homeostasis and maintenance of basal vascular tone. They are involved in physiological and tumoral angiogenesis. They affect the physiology and pathophysiology of the liver, muscle, skin, adipose tissue and reproductive tract. The endothelin system participates in the development of atherosclerosis as well as pulmonary hypertension, and mediates cardiac remodeling in heart failure. Elaboration of new animal models (knock-out, pathophysiological models em leader ) will allow the clear genetic dissection of physiological and pathophysiological roles of the endothelin system.

Troponin T as a marker of differentiation revealed by proteomic analysis in renal arterioles

Renovascular hypertension is characterized by stenosis of the renal artery and high plasma renin levels. The renal phenotype is characterized by high levels of renin in the hypoperfused kidney due to the recruitment of renin-producing cells along the afferent arterioles. This increase in myoepithelioïd cells is due mainly to the differentiation of existing smooth muscle cells with acquisition of a secretory phenotype. To understand the molecular mechanisms involved in this recruitment, we used the established rat model of renovascular hypertension known as the two-kidney, one-clip model in the Lewis rat. Renal arterioles were isolated using magnetized iron suspension. Differential proteomic analysis was performed using 2-D polyacrylamide gel electrophoresis followed by mass spectrometry. Comparative analysis of soluble proteins extracted from afferent arterioles of clipped and contralateral kidneys showed 14 proteins significantly differentially expressed by at least a factor of 2. These proteins were identified by mass spectrometry. The most striking protein revealed by proteomics is troponin T, which is down-regulated in the afferent arterioles of the clipped kidney. Confocal microscopy showed that troponin T is specific of the smooth muscle phenotype and absent in the myoepithelioïd phenotype. Our data suggest that troponin T is only present in renal smooth muscle cells.

Morphology, homogeneity and functionality of human monocytes-derived macrophages

Primary cultures of human monocyte-derived macrophages (n = 50) were characterized in order to use this cellular model to establish a proteomic map of macrophages. Peripheral blood mononuclear cells were isolated from healthy donors' blood using density gradient centrifugation. The cell culture quality was checked in respect of several morphological and molecular aspects. The homogeneity and purity of cells was assessed after 12 days' primary culture with phase microscopy, immunocytochemistry and flow cytometry. Monocytes were completely differentiated into macrophages within 12 days as shown by phase microscopy. On day 12, all cells expressed CD68 antigen and were negative for CD3. Flow cytometry experiments showed a purity of the primary culture on day 12, in a range between 76% and 98% of CD14+ cells. The functionality of cells was characterized for the presence of ECE-1 as an intracellular marker and for the presence of MMP-9 as a marker secreted into the culture medium. This study allowed to determine criteria of quality and functionality for the primary culture of monocyte-derived macrophages. Cultures meeting these criteria will be used for the proteomic analysis and the establishment of the reference map.

Implication of Ref-1 in the repression of renin gene transcription by intracellular calcium

OBJECTIVE

The production of renin, which catalyzes the rate-limiting step of the renin-angiotensin system, is tightly regulated by intracellular second messengers. Among them, an increase of intracellular calcium represses renin gene expression. This inhibition of gene expression by intracellular calcium is exceptional, and the molecular mechanism supporting this phenomenon has not yet been identified. As the renin gene is negatively regulated by calcium in the same way as the parathormone (PTH) gene, we hypothesized that a similar molecular transcriptional mechanism could be involved.

RESULTS

Analysis of the human renin proximal promoter led to the identification of a negative calcium response element (nCaRE), which is identical to the region of the PTH promoter and is involved in its repression by calcium. Transfection experiments in renin-expressing chorio-decidual cells demonstrated the transcriptional functionality of the human renin promoter nCaRE. In addition, mutation of nCaRE suppressed the sensitivity of the renin promoter to the increase in intracellular calcium. Gel shift assays demonstrated that Redox factor 1, a multifunctional protein involved in the repair of damaged DNA and the redox activation of AP-1 transcriptional factors, binds specifically to nCaRE. Immunostaining showed that this factor is translocated from the cytoplasm to the nucleus in response to an increase in the intracellular calcium concentration.

CONCLUSION

Thus, the repression of renin expression by intracellular calcium may be mediated by the calcium-induced translocation of Ref-1 to the nucleus, where it binds to the renin promoter nCaRE, to repress the transcription of the renin gene.

Functionality of two new polymorphisms in the human renin gene enhancer region

BACKGROUND

The production of renin, which catalyses the rate-limiting step of the renin-angiotensin system, is strongly stimulated by a 225 bp enhancer element in the distal region of the promoter of the human gene (-5777 to -5552).

OBJECTIVE

To demonstrate the major role played by this enhancer in decoy experiments, to identify variants in this region, and to determine their effects on renin gene transcription.

METHODS AND RESULTS

We used this element as a decoy for transcription factors in human choriodecidual cells. The activity of the renin gene promoter was inhibited by 95% in the presence of this 225 bp enhancer element. This confirmation of the key role of this element suggested that changes in this region would be likely to affect renin gene expression. We therefore sequenced 70 genomic DNAs to identify variations in this region. We identified two new single nucleotide polymorphisms (SNPs) downstream from the 225 bp enhancer element at positions -5434 and -5312. We transfected choriodecidual cells with the four variants and found that a 592 bp region (-5870 to -5312) including the 225 bp element and the two SNPs had stronger enhancer activity than the 225 bp element alone, and that levels of transcription were 45% greater with the -5312T variant than with the -5312C variant, whereas none of the -5434 variants had an effect on renin transcription. Cis-regulatory elements close to the -5312 variant were identified in gel mobility shift assays on the basis of specific interactions between human choriodecidual cell nuclear extracts and an oligonucleotide including this polymorphism.

CONCLUSION

This study demonstrates that the human renin enhancer not only comprises the 225 bp element, but also extends to the region containing the -5312 SNP.

Expression of renin in large arteries outside the kidney revealed by human renin promoter/LacZ transgenic mouse

Renin plays a central role in controlling blood pressure as it catalyzes the first step in the production of angiotensin II. The aim of this study was to isolate fragments of the human renin (hREN) promoter able to direct tissue-specific and regulated expression of a LacZ reporter gene mimicking endogenous renin. We screened several hREN promoter/LacZ constructs for transgene expression in transient embryos at E15 when renin expression begins. We found that a 12-kb hREN promoter conferred high expression in the kidney at both embryonic and adult stages and that the transgene was expressed in the same cells as endogenous renin. We explored two pathophysiological models in which renin is stimulated and showed concomitant increases in beta-galactosidase and renin activities. In situ beta-galactosidase staining showed renin/transgene-expressing cells are recruited in the juxtaglomerular apparatus and in the afferent arterioles as well as in larger arteries outside the kidney. Using our model, renin expression in interlobular arteries was confirmed as being striped and, for the first time, expression of renin in larger arteries outside the kidney was shown. Therefore, this strain is a suitable model to investigate renin gene pathophysiological regulations in vivo.

New elements in human renin promoter involved in cell-specific expression

1. The renin-angiotensin system plays a major role in blood pressure regulation and electrolyte homeostasis through the action of angiotensin (Ang) II. The first and rate-limiting step in the production of AngII is the conversion of angiotensinogen into AngI, which is catalysed by the aspartyl protease renin (EC 3.4.23.15). Circulating active renin is mainly synthesized, processed and secreted by the juxtaglomerular cells within the kidney. 2. To determine the renin 5'-flanking sequences involved in cell and tissue specificity, ex vivo and in vivo studies were performed. Several constructs of various lengths of renin promoter linked to the luciferase gene were first tested ex vivo by transfection in primary cultures of human chorionic cells. The constructs giving a high and specific expression in renin-producing cells were then tested in vivo in a transgenic mice model. 3. The reporter gene chosen to generate transgenic mice was LacZ and the screening was performed in embryos at the embryonic day (E) 15 stage, at which mouse renin is expressed in the developing vessels of the kidney. 4. Only constructs containing more than 5.7 kb of the human renin promoter lead to specific expression of beta-galactosidase in the kidney. 5. Our results demonstrate that the human renin distal promoter region allows a more restricted expression of LacZ in the renin-expressing cells in transgenic mice.

Localization of the endothelin system in aldosterone-producing adenomas

Endothelin-1 (ET-1) could play a role in the regulation of aldosterone secretion of the human adrenal gland. The presence of the endothelin-converting enzyme 1 (ECE-1) and ET-1 suggests that there is a local ET system in the adrenal cortex, but the in situ synthesis of ET-1 remains to be confirmed. The cellular distribution of the whole ET system was evaluated in 20 cases of aldosterone-producing adenomas. Polymerase chain reaction studies gave strong signals for ECE-1 mRNA and the mRNAs for endothelin type A (ET(A)) and B (ET(B)) receptors and faint signals for prepro-ET-1 mRNA. In situ hybridization showed ET(A) receptors scattered throughout the adenoma, in both secretory cells and vascular structures (score, +). There were more ET(B) receptors (score, ++), but they were restricted mainly to the endothelium. ECE-1 mRNA and protein were ubiquitous and abundant in secretory cells (score, +++) and vascular structures (score, ++); the enzyme was active on big ET-1. There was no prepro-ET-1 mRNA in the cortex, except in the thickened precapillary arterioles present in only 30% of the aldosterone-producing adenomas studied. ET-1 immunoreactivity was detected in vascular structures (score, +), probably bound to receptors, suggesting that ET-1 has an endocrine action. The low concentrations of ET-1 could also indicate that it acts in a paracrine-autocrine fashion to control adrenal blood flow. The discrepancy between the concentrations of ECE-1 and its substrate suggests that ECE-1 has another role in the adrenal secretory cells. Our data indicate that ET probably is not a primary cause of the development or maintenance of the adenoma.

Functional characterization of three mutations of the endothelin B receptor gene in patients with Hirschsprung's disease: evidence for selective loss of Gi coupling

BACKGROUND

Hirschsprung's disease (HSCR) is one the most common congenital intestinal disease. It leads to aganglionic megacolon in the early childhood. Several susceptibility genes have been identified : RET protooncogene and its ligand, glial cell derived neutrophic factor (GDNF), Sox 10, Endothelin-3 (EDN3) and its receptor B (EDNRB). EDNRB mutations are found in 5% of familial or sporadic HSCR. Only few EDNRB mutations found in HSCR have been explored and some of them seem to be non fonctional variants.

MATERIALS AND METHODS

The properties of three mutant human endothelin B receptor (hETB) (G57S, R319W and P383L) in isolated HSCR were analyzed. Stable recombinant cells expressing the three mutants and the wild-type (WT) were established. The hETB receptors were characterized for 125I ET-1 binding, ET-1 induced signaling: calcium transient, AP-1 transcriptional factor activation and cAMP accumulation.

RESULTS

Immunofluorescence experiments showed normal cellular distributions of the mutant G57S, R319W and WT hETB receptors. In contrast, the P383L hETB mutant receptor was concentrated near the nucleus and essentially no ET-1 binding was detected. The two other mutants (G57S and R319W) bound ET-1 normally, induced calcium transients and activated the AP-1 pathway in the same way as wild type, but did not inhibit adenylate cyclase. The G57S hETB mutant even stimulated cAMP accumulation which was blocked by pertussis toxin.

CONCLUSION

The absence of the P383L mutant receptor from the membrane clearly indicates that this mutation could be involved in HSCR. The G57S and R319W mutant receptors, despite their normal coupling to Gaq, have a defect in the Galphai signaling pathway and the G57S mutation couples to Galphas. These observations allow us to hypothesize that cAMP signaling might be involved in the differenciation of neural cells in the bowel.

Modulation of human colon tumor-stromal interactions by the endothelin system

Tumor neovascularization is considered to be a critical step in the development of a malignant tumor. Endothelin (ET)-1 is a powerful vasoconstrictor and mitogenic peptide that is produced by many cancer cell lines. The cellular distribution of the ET components was evaluated in human colon tumors and compared to normal colon. There was more of the ET components (preproET-1, endothelin-converting enzyme-1, and ETA and ETB receptors) in adenomas and adenocarcinomas than in the normal colon. There was overproduction of preproET-1 and endothelin-converting enzyme-1 in carcinoma cells and stromal vessels, suggesting that they are a local source of ET-1. ETA receptors were present in stromal myofibroblasts of neoplastic tissue, and there were large amounts of ETB receptors in the endothelium and myofibroblasts. There was also a redistribution of alpha-smooth muscle actin-positive cells in the vascular structures of tumors. An experimental rat model of induced colon cancer treated for 30 days with bosentan, a mixed antagonist of both ET receptors, confirmed the morphological changes observed during the tumor vascularization. Our data suggest that ET-1 and its receptor play a role in colon cancer progression, with ET-1 functioning as a negative modulator of the stromal response.

Endothelin receptor blockade potentiates FasL-induced apoptosis in colon carcinoma cells via the protein kinase C-pathway

An imbalance between proliferation and apoptosis is important in tumor progression. Endothelin-1 (ET-1) has vasoconstricting and mitogenic activities and may be involved in apoptosis regulation. We found that ET-1 and FasL systems were colocalized in human colon tumors and that ET-1 was secreted by human (HT-29, SW480) and rat (PROb, REGb) colon carcinoma cell lines. Bosentan, a mixed endothelin-A- and -B- (ET(A)/ET(B)) receptor antagonist, potentiated FasL- (APO-1, CD95) induced apoptosis in these cells. The specific inhibition of enzymes involved in ceramide production did not restore survival of cells exposed to FasL and bosentan. Inhibition of PKC with bisindolylmaleimide IX enhanced FasL-induced apoptosis in HT-29, PROb and REGb cells in the absence of bosentan. These results suggest that ET-1 is an autocrine survival factor able to protect colon carcinoma cells against FasL-induced apoptosis, involving the protein kinase C (PKC) but not the sphingomyelin-ceramide signaling transduction pathways.

The endothelin system in human glioblastoma

Endothelin-1 (ET-1) is a powerful mitogenic and/or anti-apoptotic peptide produced by many cancer cells. To evaluate the potential role of the endothelin system in glioblastoma we first determined the cellular distribution of the mRNA and proteins of the components of the endothelin system, preproendothelin-1 (PPET-1), endothelin-converting enzyme-1 (ECE-1), and ET(A) and ET(B) receptors in human glioblastoma tissue and glioblastoma cell lines. PPET-1, ECE-1, and ET(A) receptor were highly expressed in glioblastoma vessels and in some scattered glioblastoma areas whereas ET(B) receptor was mainly found in cancer cells. This suggests that glioblastoma vessels constitute an important source of ET-1 that acts on cancer cells via the ET(B) receptor. Four human glioblastoma cell lines expressed mRNA for all of the components of the ET-1 pathway. Bosentan, a mixed ET(A) and ET(B) receptor antagonist, induced apoptosis in these cell lines in a dose-dependent manner. Apoptosis was potentiated by Fas Ligand (APO-1L, CD95L), a pro-apoptotic peptide, only in LNZ308 cells, corresponding to the known functional Fas expression in these cell lines. LNZ308 cells also expressed the long and short forms of the cellular FLICE/caspase-8 inhibitory protein (FLIP). Bosentan and a protein kinase C inhibitor down-regulated short FLIP in these cells. ET-1 induced transient phosphorylation of extracellular signal-regulated kinase but did not induce long-term thymidine incorporation in LNZ308 glioblastoma cells. These results suggest that, in glioblastoma cells, ET-1, mainly acting via the ET(B) receptor, is a survival/antiapoptotic factor produced by tumor vasculature, but not a proliferation factor, involving protein kinase C and extracellular signal-regulated kinase pathways, and stabilization of the short form of FLIP.

Expression of the endothelin-converting enzyme-1 isoforms in endothelial cells

The transformed human endothelial cell line EA.hy926 is commonly used for studying in vitro different aspects of endothelial cell biology such as signal transduction, expression or angiogenesis. These cells have the ability to process big endothelin (big-ET) into endothelin (ET), and express the endothelin-converting enzyme ECE-1. Several isoforms of ECE-1 which differ only in their N-terminal part (i.e. the end of the cytosolic domain) have now been identified. We could detect the co-expression of all four isoforms. Recent works have shown that the variable cytosolic domain is responsible for the differential intracellular localization of ECE-1 isoforms. Using antibodies directed against ECE-1a and ECE-1b/c/d, we have characterized the intracellular distribution of these isoforms in EA.hy926 cells by immunofluorescence. Electron microscopy allowed us to identify further the intracellular compartment that contains ECE-1 as multivesicular bodies, a compartment involved in the endocytic pathway. In addition, using an antibody directed against the catalytic domain, we could demonstrate that no monomeric ECE-1 is present at the plasma membrane. Indeed, detection of ECE-1 immunoreactivity at the cell surface of living cells required a dithiothreitol (DTT) treatment. Altogether, these results demonstrate that the EA.hy926 cell line is a helpful model for studying the regulation of the production of endothelin by ECE.

The genetic basis of cardiac function: dissection by zebrafish (Danio rerio) screens

The vertebrate heart differs from chordate ancestors both structurally and functionally. Genetic units of form, termed 'modules', are identifiable by mutation, both in zebrafish and mouse, and correspond to features recently acquired in evolution, such as the ventricular chamber or endothelial lining of the vessels and heart. Zebrafish (Danio rerio) genetic screens have provided a reasonably inclusive set of such genes. Normal cardiac function may also be disrupted by single-gene mutations in zebrafish. Individual mutations may perturb contractility or rhythm generation. The zebrafish mutations which principally disturb cardiac contractility fall into two broad phenotypic categories, 'dilated' and 'hypertrophic'. Interestingly, these correspond to the two primary types of heart failure in humans. These disorders of early cardiac function provide candidate genes to be examined in complex human heart diseases, including arrhythmias and heart failure.

The endothelin system in normal human colon

Endothelin (ET)-1 is a potent vasoconstrictor and mitogenic peptide that has a variety of biological effects in noncardiovascular tissues. The precise cellular distribution of the ET-1 system in the wall of the normal human colon was studied to identify the physiological role of ET in the gut. In situ hybridization revealed ET-converting enzyme-1 (ECE-1) mRNA in all vessels, the colon epithelium, and macrophages. Prepro-ET-1 (PPET-1) mRNA had a similar distribution except for a scattered signal in mucosal microvessels. ET(A) and ET(B) receptor mRNAs were mainly in the lamina propria, pericryptal myofibroblasts, microvessels, and mononuclear cells, with ET(A) mRNA more abundant than ET(B) mRNA. (125)I-ET-1 binding showed ET(B) along the crypts and in nerve fibers descending from the ganglionic plexus that contained PPET-1, ECE-1, and ET(B) transcripts, whereas glia contained ET(A) receptors. The finding of the entire ET system in the normal mucosa suggests its implication in some characteristic functions of the colon and its secretion as both a neuroactive and a vasoactive peptide.

Regulation of aminopeptidase A in human brain tumor vasculature: evidence for a role of transforming growth factor-beta

Angiotensin peptides are potent vasoconstrictors, cell growth factors, and neuromodulators in normal and pathological situations. To assess the potential role of the angiotensins in brain tumor-associated vessels, the expression of the enzymes of the angiotensin cascade were evaluated in these tumors. The production of these bioactive peptides is dependent on the activities of exopeptidases, including several aminopeptidases and carboxypeptidases, producing angiotensin (Ang) I, II, III, IV and Ang 1-7. Human cerebral parenchymal and glioblastoma cells expressed renin, and tumor vasculature, but not glioblastoma cells, expressed angiotensin-converting enzyme. High aminopeptidase A (APA) activity, but no aminopeptidase N/B activity, was observed in human brain tumor vasculature, suggesting a predominant production of Ang III. Grafting of rat glioma cells in rat brains yielded tumors with high APA and low aminopeptidase N/B activities in tumor vessels, confirming human results. Tumor growth and APA activity in tumor vessels were not affected by chronic angiotensin-converting enzyme inhibition. The brain-derived EC219 endothelial cells expressed high APA activity, which was not involved in endothelial cell proliferation, but was down-regulated by exposure of cells to transforming growth factor-beta (TGF beta) or to TGF beta-secreting tumor cells, suggesting a role for this peptide in the control of APA activity in cerebral vasculature. Thus, APA is a potential marker of chronic dysfunction, involving loss of TGF beta function, of the metabolic blood-brain barrier, but not of neovascularization.

Two di-leucine-based motifs account for the different subcellular localizations of the human endothelin-converting enzyme (ECE-1) isoforms

Endothelin-converting enzyme (ECE-1) is a type II integral membrane protein which plays a key role in the biosynthetic pathway of the vasoconstricting endothelins. Three ECE-1 isoforms, differing by their N-terminal cytoplasmic tails, are generated from a single gene. When expressed in CHO cells, they display comparable enzymatic activity but whereas ECE-1a is strongly expressed at the cell surface, ECE-1b is exclusively intracellular and ECE-1c presents an intermediate distribution. In the present study these different localizations were further described at the ultrastructural level, by electron microscope immunocytochemistry. To characterize the motifs responsible for the intracellular localization of ECE-1b we constructed chimeric proteins and point mutants. Two di-leucine-based motifs, contained in the N-terminal part of ECE-1b, were thus identified. One of these motifs (LV), displayed by both ECE-1b and ECE-1c, accounts for the reduced surface expression of ECE-1c as compared to ECE-1a. Mutation of both motifs (LL and LV) induces a very strong appearance of ECE-1b at the cell surface indicating that their presence in the N-terminal extremity of ECE-1b is critical for its exclusively intracellular localization.

Dissection of silencer elements in first intron controlling the human renin gene

OBJECTIVE

A silencer within the renin first intron (intron A) was identified using Calu-6 cells, a pulmonary carcinoma cell line which produced renin. In the present study, a dissection of the first intron was performed to determine precisely the cis-regulatory elements involved in the silencer transcriptional effects.

MATERIALS AND METHODS

Intron A was completely sequenced to characterize potential binding sites for known transcription factors. Partial portions of intron A were subcloned upstream the 892 bp of the renin promoter and transfected in different models of renin-producing cells: primary culture of human chorionic cells, human Calu-6 cells and mouse As4.1 cells.

RESULTS

There is significant DNA homology (67%) between the 3' and 5' ends of the human and rat renin first intron. Several transcription factor binding sites identified in human first intron, but not in rat intron, do not contribute to the reported silencer activity. Transfections of renin/ luciferase constructs containing partial portions of first intron inserted upstream of the 892 bp in both renin-producing cells do not allow the precise characterization of cis-elements involved in the silencer effect.

CONCLUSIONS

The silencer located renin intron A is cell specific. The integrity of the human first intron seems necessary for its repressor activity on renin proximal promoter in renin-producing cells.

Cellular distribution of endothelin-converting enzyme-1 in human tissues

Endothelin-converting enzyme-1 (ECE-1) is the key enzyme of endothelin biosynthesis, catalyzing the final processing step. As shown by the targeted disruption of the ECE-1 gene, mature endothelins must be produced at specific sites for normal embryonic development. Therefore, it is important to know the exact pattern of ECE-1 gene expression. In this study we investigated the cellular distribution of ECE-1 in a variety of human tissues by in situ hybridization and immunohistochemistry. Widespread expression of the ECE-1 gene was noted, with a similar distribution pattern for mRNA and protein in normal human tissues, suggesting a major biological role for ECE-1. ECE-1 levels were particularly high in the cardiovascular, reproductive, and endocrine systems. There was strong and consistent labeling for ECE-1 in the vascular endothelial cells of all organs examined and in various nonvascular cells, especially some glandular cells. A large amount of ECE-1 protein and mRNA was detected in the Leydig cells of the testis and in the granulosa and theca cells of the ovary. In the adrenal gland, ECE-1 was detected in the cortex and medulla, with the strongest labeling in the zona glomerulosa. Therefore, ECE-1 may be involved in other systems, such as the regulation of hormone secretion, rather than exclusively generating ET-1 from its precursor. These results point out the potential side effects of ECE-1 inhibitors that are currently under development for treatment of cardiovascular diseases. (J Histochem Cytochem 47:447-461, 1999)

A novel distal enhancer confers chorionic expression on the human renin gene

Renin catalyzes the rate-limiting step of the renin-angiotensin system, which regulates blood pressure and electrolyte homeostasis. To determine cell-specific human renin gene control elements, the transcriptional activity of promoter regions up to position -8876 was studied in renin-expressing cells. A positive regulatory region conferring approximately 57-fold higher transcriptional activity to the human renin gene promoter in chorionic cells was identified between nucleotides -5777 and -5552. It had the orientation-independent activity typical of classical enhancers. It also conferred approximately 59-fold higher transcriptional levels from the heterologous simian virus 40 (SV40) promoter in chorionic cells and approximately 6-fold higher transcriptional levels in Calu-6 and As4.1 cells, whereas no effect was measured in non-renin-expressing cells. DNase I footprinting showed that this enhancer contains three binding sites for chorionic cell nuclear extracts. Functional analysis suggested that the activity of the enhancer is regulated by differential mechanisms in the three renin-expressing cells involving a complex arrangement of AP-1 motifs binding cell-specific members of the basic leucine zipper family of transcription factors. Thus, our results demonstrate that this enhancer plays a key role in the expression of the human renin gene in the chorion and may also be involved in its regulated expression in other tissues.

Characterization of the enzyme involved in the processing of big endothelin-1 in human lung epithelial cells

Biosynthesis of active endothelin-1 (ET-1) implies an enzymatic processing of the inactive precursor Big ET-1 (1-39) into the mature, 21 amino acid peptide. The aim of this study was to characterize in airway and alveolar epithelial cells the enzymes responsible for this activation. BEAS-2B and A549 cells, which both produce ET-1, were studied in vitro as models for bronchiolar and alveolar cells, respectively. Both cell lines were able to convert exogenously added Big ET-1 (0.1 microM) into ET-1, suggesting a cell surface or an extracellular processing. The conversion was inhibited by phosphoramidon in both cell lines with an IC50 approximately 1 microM, but not by thiorphan, a specific inhibitor of neutral endopeptidase 24.11 (NEP). The endogenous production of serum-stimulated BEAS-2B and A549 cells was not inhibited by thiorphan, and phosphoramidon showed inhibition only at high concentration (>100 microM). Western blotting following electrophoresis in reducing conditions demonstrated a protein of MR 110 corresponding to the ECE-1 monomer in both BEAS-2B and A549 cells, as well as in whole lung extracts. By RT-PCR we revealed the mRNA encoding for the ECE-1b and/or -1c subtype, but not ECE-1a, in both cell lines. We conclude that BEAS-2B and A549 cells are able to process either endogenous or exogenous Big ET-1 by ECE-1 and that isoforms 1b and 1c could be involved in this processing with no significant role of NEP.

Construction, expression and characterization of a soluble form of human endothelin-converting-enzyme-1

Endothelin-converting-enzyme-1 (ECE-1) belongs to the family of zinc metallopeptidases and is responsible for generating endothelin (ET) peptides from their inactive precursors the big endothelins (bigET). The enzyme is a type II integral membrane protein consisting of a short amino-terminal cytosolic domain of 56 amino acids, a single transmembrane domain and a large putative extracellular domain containing the catalytic site. Recombinant and native ECE-1 are expressed as a dimer. We have constructed a soluble form of ECE, named sECE*, by fusing the cleavable signal peptide of pro-opiomelanocortin in frame to the complete extracellular domain of human ECE-1. Stable expression of this construct in CHO cells resulted in the secretion of a fully active enzyme. In contrast to membrane-bound ECE, sECE* was expressed as a monomer, highly glycosylated, as assessed by gel filtration and Western blot. However, recombinant sECE* converted bigET-1 with similar specific activity as ECE-1a. This activity was completely inhibited by phosphoramidon, but not by thiorphan and captopril. sECE* was active in a broad range of pH, showing an optimum of 6.6-6.8 for bigET-1. Thus, the extracellular domain alone is sufficient for conferring full ECE-1 activity, inhibitors recognition and substrate specificity.

A live-cell assay for studying extracellular and intracellular endothelin-converting enzyme activity

Endothelin-1 (ET-1) is formed from its precursor preproET-1 via the cleavage of the intermediate bigET-1 by endothelin-converting enzyme (ECE-1). However, the subcellular site at which this step occurs is not clear: It could occur intravesicularly along the secretory pathway or bigET-1 might be released and processed extracellularly. To address this point, we have developed an integrated autocrine system that uses a recombinant Chinese hamster ovary (CHO) luciferase reporter cell line that permanently expresses the human ET(A) receptor. Into these cells we transiently transfected human ECE-1a cDNA, either together with the human preproET-1 cDNA (as an endogenous source of bigET-1), or alone (in which case exogenous bigET-1 was added). Phosphoramidon inhibited the conversion of exogenous bigET-1 (IC50 = 5 to 30 micromol/L) much better than that of endogenous bigET-1 (IC50 > 1 mmol/L). Both conversions showed similar high yields (20% to 100%) that depended on the amount of ECE-1a expressed. Thus, ECE-1a has two equally relevant activities in this recombinant system for CHO cells: (1) an intracellular, probably intravesicular activity, corresponding to the ECE-1a-mediated step of ET-1 biosynthesis and (2) an extracellular activity at the plasma membrane. If this is also the case for endothelial cells, ECE-1a inhibitors would have to cross the plasma and vesicle membranes to be effective. The present system could be useful for screening such inhibitors.

Regulation of human renin gene transcription by cAMP

To delineate the cis-acting elements of the proximal promoter responsible for cAMP-induced human renin gene transcription, 5'-flanking regions of the human renin gene were fused to a luciferase reporter gene and transfected in chorionic cells. Forskolin treatment induced the expression of luciferase by 2.4 fold when the reporter plasmid contained the promoter region (-582 to +16). Mutation or deletion of the CRE diminished (1.7 fold) but did not abolish cAMP-induced transcription, demonstrating that region containing the CRE and region containing a Pit-1 site were both necessary for cAMP maximal induction. Taken together, these results show that the cAMP response of the human renin gene may involve CREB binding the CRE and tissue-specific factors (from chorionic and kidney cell origin), different from Pit-1, that interact with the Pit-1 response DNA elements.

Regulation of human renin secretion and gene transcription in Calu-6 cells

Calu-6 cells were characterized for studying the transcriptional regulation of the human renin gene. Analysis of cis-acting elements of the renin promoter showed the highest activity within the first 582 bp in serum-free conditions and of the 892 bp in the presence of serum. cAMP activates renin mRNA synthesis parallel to renin production (20-fold increase) as well renin promoter activity (2-fold). cAMP response element and the (-77 to -67) element are both necessary for activation of the renin promoter but do not act independently. Functional analysis of Intron A revealed the presence of a silencer specific to renin-producing cells.

A sensitive reverse transcriptase polymerase chain reaction assay for measuring the effects of dehydration and gestation on rat amounts of vasopressin and ocytocin mRNAs

This study describes a competitive reverse transcriptase polymerase chain reaction (RT-PCR) method for assaying the amounts of vasopressin (AVP) and ocytocin (OT) mRNAs in the rat hypothalamus and uterus. Despite the low concentrations of these mRNAs, the RT-PCR method readily measured both AVP and OT mRNAs in the same sample. A common internal standard for both reactions was designed to quantify the reaction. Both AVP and OT mRNAs were readily quantified in a 75 ng sample of total RNA from the hypothalamus. Water deprivation stimulated AVP mRNA production 3-fold and OT mRNA production 1.7-fold in the hypothalamus. Gestation only influenced the amount of OT mRNA in the hypothalamus (3-fold increase) and uterus (38-fold increase). The amount of AVP mRNA in the hypothalamus remained unchanged and no AVP mRNA was detected in the uteri of either non-pregnant or pregnant rats. This competitive RT-PCR is a powerful tool that provides rapid and precise assays of AVP and OT mRNAs.

Evidence that renal and chorionic tissues contain similar nuclear binding proteins that recognize the human renin promoter

This study examines whether the human renal cortex, the major renin producing site, contains nuclear factors that bind to the human renin proximal promoter. Footprint analysis of the human renin promoter region showed that human renal cortex cell nuclear extracts interacted with 6 putative cis-elements (the Ets domain-protein, a Pit-1 like binding site, a CRE sequence, an ARP-1 like binding site, an AGE3 like region, and a unknown consensus region, designated element C). Transient DNA transfection studies on chorionic cells implicated the CRE and Pit-1 consensus sites in the regulation of renin gene transcription by cAMP. Electromobility shift assays showed that renal proteins bind specifically to these sequences, and that one of them is CREB; two others seem to be Ets-1 and ARP-1. These results raise the possibility that the human renal cortex and human chorionic cells have the same trans-acting factors that bind to the proximal human renin promoter.

Transcriptional induction of the human renin gene by cyclic AMP requires cyclic AMP response element-binding protein (CREB) and a factor binding a pituitary-specific trans-acting factor (Pit-1) motif

To delineate the cis-acting elements of the proximal promoter responsible for cyclic AMP (cAMP)-induced human renin gene transcription, 5'-flanking regions of the human renin gene were fused to a luciferase reporter gene and transfected in chorionic cells. Forskolin treatment induced the expression of luciferase by 2.4-fold when the reporter plasmid contained the promoter region (-582 to + 16). Mutation or deletion of the cAMP response element (CRE) diminished (1.7-fold) but did not abolish cAMP-induced transcription, demonstrating that the (-582 to -145) region containing the CRE and the region (-145 to -38) containing a Pit-1 (pituitary-specific trans-acting factor) site were both necessary for cAMP maximal induction. To study the molecular events mediating the cAMP induction, DNase I footprinting and electromobility shift assays (EMSAs) were performed with renin-producing chorionic cell and kidney cortex cell nuclear extracts, showing that the CRE-binding protein (CREB) interacts with the CRE and that tissue-specific factors, distinct from Pit-1, specifically bind the renin Pit-1 motif. Taken together, these results demonstrate that the cAMP response of the human renin gene may involve CREB binding the CRE and tissue-specific factors, different from Pit-1, that interact with the Pit-1 response DNA elements.

Regulation of renin release is impaired after nitric oxide inhibition

The aim of the present study was dual: first to establish that a preparation of afferent arterioles freshly isolated from the rat kidney is a suitable model to study renin release and synthesis, and second to investigate the effect(s) of nitric oxide (NO) inhibition on renin release in this model. Purification of renal microvessels was based on iron oxide infusion into the kidneys and separation of the afferent arterioles from glomeruli and connective tissue with a magnet. These microvessels express preprorenin mRNA, contain renin granules and release renin as evidenced by RT-PCR, immunocytochemistry and measurement of renin activity, respectively. Renin secretion was increased in isolated afferent arterioles after in vivo treatment with the diuretic furosemide (+300%) or in vitro treatment with the adenylyl cyclase activator forskolin (+50%), indicating that this vascular preparation responds appropriately to regulators of the renin-angiotensin system. Furthermore, in afferent arterioles isolated from control rats, renin release was positively correlated with total renin content (r = 0.85). In afferent arterioles isolated from rats chronically treated with the NO-synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), forskolin was ineffective in modifying renin release despite stimulation of cAMP levels. In addition, the correlation between renin release and tissue renin content was disrupted. Similar results were obtained when cortical slices were used instead of afferent arterioles, suggesting that this defect in the regulation of renin release is independent of the presence of macula densa cells. To verify that the lack of regulation of renin release after L-NAME treatment was due to NO inhibition, the NO donor 3-morpholino-syndonimin-hydrochloride (SIN-1) was administered in afferent arterioles or cortical slices from kidneys of L-NAME-treated rats. In both preparations, SIN-1 reversed the L-NAME effect and re-established the responsiveness of renin release to forskolin and the relationship between renin release and renin content. These data indicate that the adenylyl cyclase-mediated mechanism regulating renin release is impaired when NO synthesis is inhibited.

Renin gene expression in the aging kidney: effect of sodium restriction

The activity of the renin-angiotensin system as well as the ability of the kidney to retain sodium following salt restriction are reduced with age. The relationship between these age-related changes in renal function and the renin gene expression was presently investigated. The concentrations of renin and its mRNA were measured in kidney of 10- and 30-month-old control female WAG/Rij rats and of animals which were salt restricted for 4 days. In the senescent rats, the kidney renin concentration, like the plasma concentration of angiotensin II, was half that in adult rats. The intrarenal content of renin mRNA did not differ between 10- and 30-month-old animals, suggesting that the transcriptional rate of the renin gene is unchanged with age. During the early phase of adaptation to sodium depletion, the systemic angiotensin II concentration was not modified in either age groups. Four-days salt restriction did not significantly change the renal storage of renin. In contrast, this short term salt restriction induced a 2.3-fold increase in the renin mRNA in adult kidney, and a 1.9-fold increase in the senescent kidney. These data suggest that the age-related decrease in renal concentration of renin is linked to a modification in the rate of translation of renin mRNA, or to an alteration in the protein maturation. The difference in adaptation to the early phase of salt restriction with age should not be linked to changes in renin gene transcription, but more likely to a change in the tissue response to the local renin-angiotensin system.

Opposite regulation of renin gene expression by cyclic AMP and calcium in isolated mouse juxtaglomerular cells

A quantitative reverse transcriptase-polymerase chain reaction for mouse renin mRNA was utilized to study the influence of classic second messenger molecules on renin mRNA levels in primary cultures of juxtaglomerular (JG) cells isolated from the kidneys of C57/B16 mice. We found that forskolin (3 microM), an activator of adenylate cyclase led to proportional increases of renin secretion and renin mRNA levels. The nitric oxide (NO) donor, sodium nitroprusside (100 microM), stimulated both renin secretion and renin gene expression, the effect on secretion being stronger than that on renin mRNA levels. An increase of the extracellular concentration of calcium from 0.5 to 3 mM led to a transient inhibition of renin secretion, followed by a marked stimulation of secretion and to a continuous suppression of renin mRNA levels. These were also decreased by the calcium ionophore A 23187 (1 microM). The membrane permeable 8-bromo-cyclic GMP (100 microM) inhibited basal renin secretion without an effect on renin mRNA levels. The phorbol ester phorbol-12-myristate-13-acetate (1 to 100 nM), which was used to stimulate protein kinase C activity, had no significant effects on renin secretion and renin mRNA levels, neither alone nor in combination with forskolin. These findings suggest that cAMP, NO and calcium are effective regulators of renin gene expression in renal JG cells, in a way that cAMP and NO are stimulators and calcium acts as an inhibitor. Moreover, in these acute experiments there appears to be no obligatory link between the secretion and the expression of renin, suggesting that both parameters are separately regulated.

A mutant renin gene in familial elevation of prorenin

A case of familial elevation of plasma prorenin levels was discovered during an epidemiological survey of a Dutch population. Trypsin-activated prorenin was elevated in the 58-year-old father, his son, and one of his sisters. All family members were normotensive and had normal plasma renin activities. Exon sequencing of the renin gene of the proband and of his son after polymerase chain reaction amplification identified a point mutation in the last exon of the gene (exon 10). A cytosine to thymine transition creates a premature stop codon at position 387 resulting in a truncated form of renin with 20 amino acids deleted from the carboxyl terminus. All family members presenting high levels of plasma prorenin were heterozygous for the mutation. Expression vectors carrying normal or mutated renin cDNA were transiently transfected into AtT-20 cells to test in vitro the functional consequences of this mutation. Measurements of renin activity and pulse-chase experiments indicated that the truncated renin is inactive and not secreted from transfected cells. We hypothesize that the abnormal gene product of the mutated allele alters renin sorting and propose that plasma prorenin elevation may result from a compensatory mechanism.

Renin-secreting tumors

An analysis of the renin-secreting tumors published in the literature suggests the diagnosis of JGC tumor should be evoked systematically in a young patient with severe hypertension and hypokalemia in whom a renovascular lesion has been eliminated by arteriography. A very high PRA usually is observed and blood pressure drops during converting enzyme treatment. Under acute administration of captopril, plasma renin may or may not increase, showing the inconsistency of the secretory autonomy of the tumor. The most useful examination for the localization of the tumor is the CT scan. Excessive renin production may provoke vascular lesions, left ventricular hypertrophy, and impairment of renin function that all disappear after surgical treatment, at the time when blood pressure returns to normal. Primary reninism has great physiologic importance for the hypothesis that favors the essential role of the kidney in determining the level of blood pressure. It can be considered as a unique, purely renin-dependent form of hypertension. This syndrome has no experimental equivalent and is the most caricatural form of other renin-dependent hypertension, such as renovascular disease, and probably some other forms of essential hypertension. The discovery of a renin-secreting tumor therefore constitutes a life-saving diagnosis for the patient, a subject of reflection for the specialist, and a useful tool for studies of the general mechanisms involved in enzyme biosynthesis and tumoral endocrine cell function.