Renin Promoter Research Articles

Levistolide A ameliorates fibrosis in chronic kidney disease via modulating multitarget actions in vitro and in vivo.

The increasing incidence of chronic kidney disease (CKD) urgently calls for effective nephroprotective agents. Traditional Chinese Medicine Angelica sinensis and its formula are well known for CKD therapy, but the underlying mechanisms and effective substances of reno-protective effects remain unclear. To this end, we isolated eleven ligustilide dimers (1-11) from A. sinensis and examined the molecular mechanism of their nephroprotective effects. Because of internal RAS playing an important role in CKD, we used renin expression as a target and screened preliminarily for antifibrotic effects of ligustilide dimers (1-11) by constructing a dual luciferase reporter gene in vitro. Furthermore, the reno-protective effects of the ligustilides and their underlying mechanism were investigated in TGF-β1-stimulated HK-2 cells and 5/6 nephrectomy (Nx) mice. The ligustilide dimers exhibited anti-fibrotic effects by inhibiting human renin (hREN) promoter activity to decrease renin expression and down-regulate the expression of fibrosis-related factors, including α-SMA, collagen I, and fibronectin in vitro. Levistolide A (LA) and angeolide keto ester (AK) were screened out to identify their ability and underlying mechanism for treating CKD. Experimental validation further indicated that LA or AK treatment inhibited the expression of key molecules in RAS, TGF-β1/Smad, and MAPK pathways to downregulate ECM deposition. Furthermore, LA obviously meliorated renal injury in 5/6 Nx mice through ameliorating oxidant stress, inflammation, apoptosis and renal fibrosis. The experimental results demonstrated that ligustilide dimers were potential nephroprotective agents. LA might be an attractive drug candidate for renin-targeted CKD therapy.

Decipher the complexity of cis-regulatory regions by a modified Cas9.

Understanding complex mechanisms of human transcriptional regulation remains a major challenge. Classical reporter studies already enabled the discovery of cis-regulatory elements within the non-coding DNA; however, the influence of genomic context and potential interactions are still largely unknown. Using a modified Cas9 activation complex we explore the complexity of renin transcription in its native genomic context. With the help of genomic editing, we stably tagged the native renin on chromosome 1 with the firefly luciferase and stably integrated a programmable modified Cas9 based trans-activation complex (SAM-complex) by lentiviral transduction into human cells. By delivering five specific guide-RNA homologous to specific promoter regions of renin we were able to guide this SAM-complex to these regions of interest. We measured gene expression and generated and compared computational models. SAM complexes induced activation of renin in our cells after renin specific guide-RNA had been provided. All possible combinations of the five guides were subjected to model analysis in linear models. Quantifying the prediction error and the calculation of an estimator of the relative quality of the statistical models for our given set of data revealed that a model incorporating interactions in the proximal promoter is the superior model for explanation of the data. By applying our combined experimental and modelling approach we can show that interactions occur within the selected sequences of the proximal renin promoter region. This combined approach might potentially be useful to investigate other genomic regions. Our findings may help to better understand the transcriptional regulation of human renin.

Prorenin Induces Intracellular Signaling And Reactive Oxygen Species In The Brainstem

The importance of the brain renin angiotensin system (RAS) in blood pressure (BP) regulation and water homeostasis is well accepted. However, it remains unclear whether renin and/or its precursor, prorenin, are expressed in the brain and whether they trigger signaling pathways in specific brain regions. We previously used double transgenic mice expressing enhanced green fluorescent protein controlled by renin promoter and beta‐galactosidase controlled by the human angiotensinogen (AGT) promoter to localize their expression in the brain. We reported that neurons expressing renin are localized in close proximity to AGT‐expressing cells in the rostral ventrolateral medulla (RVLM), a brainstem nucleus involved in sympathetic activity and BP control. Here, we hypothesized that prorenin induces phosphorylation of intracellular cascades such as extracellular signal‐regulated kinases (ERK1/2) and activation of nicotinamide adenine dinucleotide phosphate oxidase (NADPHox) in the brainstem. Neonatal brainstem cells were cultured from C57BL/6J mice at postnatal day 1–3 and maintained for 7–10 days in B27‐supplemented neurobasal medium. Immunofluorescence experiments demonstrated the cultures contain both MAP2+ neurons and GFAP+ astrocytes. Expression of type 1 angiotensin receptor (AT1R), renin, and prorenin receptor (PRR) was confirmed by qPCR. To quantify ERK1/2 phosphorylation, cells were stimulated with recombinant prorenin (rProrenin) at 100 nM for 0, 30, and 60 min. Total and phosphorylated ERK1/2 were detected by Western Blot. The effect of rProrenin on NADPHox activity was measured by lucigenin chemiluminescence assay. Specific activity of NADPHox was expressed as chemiluminescence units per min per microgram of protein. Vehicle and phorbol myristate acetate were used as negative and positive controls, respectively. Incubation with rProrenin increased the ratio of phosphorylated‐to‐total ERK1/2 from 0.65±0.07 A.U. at baseline to 1.01±0.13 A.U. at 30 min (54% increase; p=0.0035; n=7) and 1.29±0.09 A.U. at 60 min (102% increase; p<0.0001; n=7). We generated preliminary data showing that both PRO20, a PRR blocker, and Ro‐31, a protein kinase C inhibitor, abrogated prorenin‐induced ERK1/2 phosphorylation. In an additional experiment, we observed that Angiotensin II (Ang II) at 100 nM induced ERK1/2 phosphorylation from 0.98 A.U. to 1.52 A.U. at 15 min (55 % increase), 1.61 A.U. at 30 min (65% increase), and 1.35 A.U. at 60 min (38% increase). Incubation of cells with 100 nM rProrenin for 6 hours resulted in 47.2±9.5 % induction of NADPHox activity compared to vehicle control (p<0.05, n=5). Finally, fluorescent in situ hybridization (RNAscope) data suggests that PRR is expressed in the RVLM neurons and RVLM‐targeted stereotactic microinjection of glutamate, rProrenin, or Ang II, but not vehicle, induced an acute BP elevation in isoflurane‐anesthetized mice. We conclude that prorenin in the brainstem induces downstream signaling involving ERK/2 phosphorylation and generation of ROS, which might contribute to BP elevation and sympathoexcitation. Future studies will determine whether prorenin‐elicited signaling in the brainstem requires binding to PRR, generation of Ang II, and/or AT1R.Support or Funding InformationP01 HL084207 to Sigmund and 5T32HL134643 to Nakagawa

Systemic ß adrenergic stimulation/ sympathetic nerve system stimulation influences intraocular RAS through cAMP in the RPE

Several lines of evidence support the existence of a renin-angiotensin system (RAS) in the retina that is separated from the blood stream by the retinal pigment epithelium (RPE). Under physiological conditions, increased activity of intraretinal RAS regulates neuronal activity of the retina but patho-physiologically participates in retinal degeneration such as hypertensive or diabetic retinopathy. Interestingly, the RPE appears to be a modulator of intraretinal RAS in response to changes in systemic RAS. As increased systemic RAS activity is associated with increased sympathetic tonus, we investigated whether systemic β-adrenergic stimulation of the RPE also modulates renin expression in the RPE. In vivo, the mouse RPE expresses the β-adrenergic receptor subtypes 1 and 2. Staining of retina sagittal sections showed tyrosine hydroxylase positive nerve endings in the choroid indicating adrenaline/noradrenaline production sites in close proximity to the RPE. Systemic infusion of isoproterenol increased renin expression in the RPE but not in the retina. This increase was sensitive to concomitant systemic application of the angiotensin-2 receptor-type-1 blocker losartan. In vitro analysis of renin gene expression using polarized porcine RPE showed that the activity of the renin promoter can be increased by cAMP stimulation (IBMX/forskolin) but was not influenced by angiotensin-2. Thus, with the identification of the β-adrenergic system we added a new regulator of the retinal RAS with relevance for retinal function and pathology. Furthermore, it appears that the RPE is not only a close interaction partner of the photoreceptors but also a regulator or retinal activity in general.

Abstract P160: A Genome-spanning Map of Chromatin Structure Near the Renin Proximal Promoter

Chromatin conformation capture technologies (3C, 4C-seq) allow mapping of the three dimensional spatial structure of the genome. Physical proximity mapping, which captures these 3 dimensional interactions, fills an important gap in our understanding of enhancer-gene relationship by linking possible regulatory regions to specific genes that may be distant from the enhancer by thousands or millions of base pairs or even located on different chromosomes. The goal of the current study was to expand our understanding of renin regulation by identifying regions containing potential regulatory elements of renin more than a few kilobases from the renin proximal promoter, using 4C-seq technology, in isolated SS/JrHrdMcwi cardiac microvascular endothelial cells. Three replicates of ten million cells were fixed, digested with EcoRI, ligated, and then decrosslinked. Secondary digestion with NlaIII followed by a second ligation captured an unknown sequence surrounded by the sequence of the renin promoter. A sequencing library was prepared using primers specific to the renin promoter to identify the captured sequences. Sequence reads were mapped to rat genome (Rn 5) divided into fragments cut by EcoRI. Reads were verified to contain the renin proximal promoter sequence and a uniquely mapped captured sequence. The read counts were binarized and Z-scores were calculated based on a windowed average reads relative to background, and Z-scores corresponding to FDR < 0.01 were considered significant. We found 62 loci spanning the genome in contact with the renin proximal promoter. Clusters of interactions were found on Chr13 at 39.6-40.5Mpb and at 53.9-56.3Mbp where the Renin gene is located. Additional contacting loci were found on all chromosomes except X. Quantitative PCR in newly isolated endothelial cells processed as 3C samples (fixed, digested, ligated, decrosslinked) were used to test 9 of the interactions, of which 8 were validated. These loci are enriched with genes whose expression is correlated with renin (53 of 268 genes, p = 7x10 -10 ) in humans, rats and mice. The present study generated a genome-wide map of segments physically interacting with the renin proximal promoter producing the first such map for a gene that is essential for cardiovascular physiology.

Chronic Stimulation of Renin Cells Leads to Vascular Pathology.

Experimental or spontaneous genomic mutations of the renin-angiotensin system or its pharmacological inhibition in early life leads to renal abnormalities, including poorly developed renal medulla, papillary atrophy, hydronephrosis, inability to concentrate the urine, polyuria, polydipsia, renal failure, and anemia. At the core of such complex phenotype is the presence of unique vascular abnormalities: the renal arterioles do not branch or elongate properly and they have disorganized, concentric hypertrophy. This lesion has been puzzling because it is often found in hypertensive individuals whereas mutant or pharmacologically inhibited animals are hypotensive. Remarkably, when renin cells are ablated with diphtheria toxin, the vascular hypertrophy does not occur, suggesting that renin cells per se may contribute to the vascular disease. To test this hypothesis, on a Ren1c-/- background, we generated mutant mice with reporter expression (Ren1c-/-;Ren1c-Cre;R26R.mTmG and Ren1c-/-;Ren1c-Cre;R26R.LacZ) to trace the fate of reninnull cells. To assess whether reninnull cells maintain their renin promoter active, we used Ren1c-/-;Ren1c-YFP mice that transcribe YFP (yellow fluorescent protein) directed by the renin promoter. We also followed the expression of Akr1b7 and miR-330-5p, markers of cells programmed for the renin phenotype. Contrary to what we expected, reninnull cells did not die or disappear. Instead, they survived, increased in number along the renal arterial tree, and maintained an active molecular memory of the myoepitheliod renin phenotype. Furthermore, null cells of the renin lineage occupied the walls of the arteries and arterioles in a chaotic, directionless pattern directly contributing to the concentric arterial hypertrophy.

Abstract P282: Use of a CRISPR/Cas9 System for Specification of the Renin Cell Phenotype

Renin is a key enzyme/hormone that controls blood pressure and fluid-electrolyte homeostasis. Renin transcription is subject to complex developmental, physiological, and pathological regulation. We have identified the cAMP pathway and associated epigenetic marks as crucial regulators of renin expression. However, those studies involved the use of cAMP activators or analogues or histone deacetylase inhibitors that alter the transcriptome and epigenome of the whole cell without exclusively targeting the renin locus. The CRISPR/Cas9 Type II bacterial immune system has been modified for genome editing in eukaryotes. This system consists of a CRISPR-associated endonuclease (Cas9) and single guide RNA (sgRNA) to target specific genomic areas. Modifications to the Cas9 enzyme have allowed the use of CRISPR to regulate gene expression by targeted modification of epigenetic marks. In this study we tested whether renin expression can be induced by a nuclease-null dCas9 protein fused to the catalytic core of the acetyltransferase p300 (dCas9p300) and sgRNAs directed to the renin promoter and enhancer. We used cultured arteriolar smooth muscle cells of the renin lineage that constitutively express CFP (a renin lineage marker) and YFP only when the renin gene is turned on. Cells were transfected with a dCas9p300 and sgRNA expression vectors and analyzed for YFP expression 48h after transfection. We tested four sgRNAs targeting the renin enhancer and five sgRNAs targeting the renin promoter either individually or in combination. We found few YFP+ cells when all 4 enhancer sgRNAs or 5 promoter sgRNAs were simultaneously used. The highest YFP expression (32±9 cells/well) was observed when two enhancer sgRNAs (at positions -2,757 and -2,631) and three promoter sgRNAs (at positions -719, -50 and -25) were simultaneously added to the cells. We did not find any YFP+ cells when the dCas9p300 plasmid was transfected without sgRNAs or when cells were transfected with a control plasmid. Our data support targeted acetylation as a causal mechanism of renin transactivation. CRISPR/Cas9 provides a tool to study the regulation of renin expression by targeting epigenetic marks in the promoter and enhancer of renin.

Abstract 066: Enhancer Repertoires That Define Renin Cell Identity

Control of the renin cell phenotype is crucial for the regulation of blood pressure and fluid- electrolyte homeostasis. Enhancers are cis -acting DNA sequences that harbor distinct chromatin features and regulate gene expression in an orientation-independent manner. Recently, clusters of enhancers or super-enhancers (SE) highly enriched with master transcription factors, possessing open chromatin configuration and in close proximity to cell-identity genes have been proposed. We tested the hypothesis that renin cells have unique repertoires of enhancers and super-enhancers, distinct from other cell types. Those regulatory clusters may in turn confer the identity of renin cells. To define the genome-wide enhancer landscape characteristic of renin cells, we studied As4.1 cells, kidney tumor cells that express renin constitutively, and native renin cells sorted from the kidneys of Ren1cKO-YFP + mice. In these mice, the renin promoter drives YFP expression thus marking the renin cells. We used genome-wide ChIP-Seq for Med1 (subunit 1 of the Mediator complex), H3K27Ac (active enhancers) and Pol II (to visualize putative genomic areas undergoing transcription). The ROSE algorithm we used to ascertain super-enhancers. Chromatin accessibility genome-wide was assessed using ATAC-Seq. The results were compared to twenty-one other cell types that do not express renin. In As4.1 cells, we identified 14,871 enhancers based on H3K27Ac. Of those, 888 were classified as super-enhancers. The Med1 signal in As4.1 cells showed a SE localized 5kb upstream the Ren1 gene, which was ranked at position 25 among other SEs. The H3K27Ac signal showed highest occupancy in the same region. ChIP-Seq for H3K27Ac in YFP + cells showed 211 SEs of 2,987 peaks. The SE for the renin gene possessed the highest signal and ranked number 1, indicating its importance in renin cells. One hundred and thirteen SEs were unique to renin cells, including the SE associated with the renin gene. ATAC-Seq signals overlapped with the renin SE and the classical enhancer indicating that the chromatin was accessible for transcription. In summary, renin-expressing cells possess distinct repertoires of unique enhancers and super-enhancers that acting in concert are likely to determine the renin phenotype.

Abstract 016: Cells Programmed for the Renin Phenotype Contribute to Vascular Pathology in Renin Deficient Mice

Deletions of the renin-angiotensin system genes or pharmacological inhibition in early life result in a distinctive renal pathology: concentric and disorganized intra-renal arteriolar thickening. The origin and distribution of the cells contributing to the arterial disease are not known. Because the arteriolar thickening disappears with ablation of renin cells, we hypothesized that renin cell precursors contribute to the arterial pathology. To reveal the origin and distribution of the cells responsible for the arterial thickening we generated several mouse lines for fate tracing and also stained for cell identity specific proteins. Kidneys from Ren1c-/- (n=6) and Ren1c+/- (n=6) mice were immunostained for renin, αSMA and PECAM1. Arterial wall thickness was measured using a light microscope and the Leica MM AF ® version1.5 software. Renin cells (unable to produce renin because of the knock out) were identified using Ren1c-/-; Ren1c-YFP mice, where the yellow fluorescent protein is expressed by the Ren1c-YFP transgene designed to label all cells with an active renin promoter. In addition, we tracked the expression and distribution of aldo-keto reductase 1b7, AKR1b7, which mark cells programmed for the renin phenotype even when renin is absent. As expected, Ren1c-/- kidneys showed no renin and thicker intra-renal arteries (Arterioles: Ren1c+/- , 8.26 ± 2.5 μm vs. Ren1c-/- , 14.3 ± 3.8 μm, P<0.0001 , larger arteries: Ren1c+/- , 29.2 ± 11.1 μm vs. Ren1c-/- , 42.1 ± 11.1 μm, P<0.0001 ) AKR1b7+ and YFP+ cells were retained and observed throughout the renal arterioles. To investigate the fate and distribution of cells from the renin lineage, we used Ren1c-Cre and R26R.LacZ or mT/mG reporter mice (6 knock out and 6 control mice per strain). Cells from the renin lineage surrounded arterioles and persisted within larger arterial walls whereas PECAM1+ endothelial cells did not contribute to the arterial wall thickening. In control mice, renin cells were confined to the juxtaglomerular area. We conclude that precursor cells programmed for the renin phenotype maintain their molecular program and together with vascular smooth muscle cells contribute to nephro-vascular disease.

Abstract 043: A Gwas Prioritized Candidate Gene,Nr2f2, Attenuates Salt-sensitive Hypertension and Associated Renal Function

A haplotype-based re-analysis of the GWAS study by the Wellcome Trust Case Control consortium prioritized the transcription factor, Nuclear receptor2, family2 (NR2F2) also known as Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) as a gene associated with essential hypertension in humans. This gene is also prioritized as a differentially expressed positional BP QTL candidate gene on rat chromosome 1. To further examine Nr2f2 as a determinant of blood pressure, a mutant Dahl salt-sensitive (S) rat model was generated using the zinc-finger nuclease (ZFN) technology. As a result of this ZFN mediated disruption, a 15-bp deletion occurred within exon 2 of the Nr2f2 locus, resulting in the loss of 5 amino acids from the hinge region of the Nr2f2 protein. Systolic BP of the homozygous Nr2f2mutant rats was lower than that of the S rats (179±3 vs. 197±5 mmHg; p<0.001) as measured by the tail-cuff method and (165±2 vs. 201±3 mmHg; p<0.001) as monitored by the radio-telemetry method. Nr2f2mutant rats demonstrated lower proteinuria compared to S rats (87.97±7.07 vs. 122.63±7.07mg/day; p<0.05). Since Nr2f2 is reported to negatively regulate renin promoter activity, we tested renin activity in the Nr2f2mutant rats. However, there was no significant difference in either the plasma renin activity or renal renin protein expression when compared with S rats. Renal histological analysis showed that Nr2f2mutant rats have decreased collagen compared with the S rats. Furthermore, Nr2f2mutant rats showed significantly decreased TGF-β protein levels, when compared with S rat kidney (p<0.05). These data, taken together with our recently published data on the improved cardiac and vascular function in the Nr2f2mutant rats (Nat Commun. 2015 Feb 17;6:6252), lend support to Nr2f2 as a determinant of blood pressure and associated renal function. While the observed improvement in renal function could be a secondary consequence of lower hypertension, our data, combined with the important mechanistic finding that the enhanced transcription factor-transcription factor interaction of Nr2f2 with Fog2 (Friend of GATA4), suggest that the hinge region of Nr2f2 is important for regulating blood pressure and associated cardiac and renal functions.

Similarities and differences of X and Y chromosome homologous genes, SRY and SOX3, in regulating the renin-angiotensin system promoters.

The renin-angiotensin system (RAS) is subject to sex-specific modulation by hormones and gene products. However, sex differences in the balance between the vasoconstrictor/proliferative ACE/ANG II/AT1 axis, and the vasodilator/antiproliferative ACE2/ANG-(1-7)/MAS axis are poorly known. Data in the rat have suggested the male-specific Y-chromosome gene Sry to contribute to balance between these two axes, but why the testis-determining gene has these functions remains unknown. A combination of in silico genetic/protein comparisons, functional luciferase assays for promoters of the human RAS, and RNA-Seq profiling in rat were used to address if regulation of Sry on the RAS is conserved in the homologous X-chromosome gene, Sox3. Both SRY and SOX3 upregulated the promoter of Angiotensinogen (AGT) and downregulated the promoters of ACE2, AT2, and MAS, likely through overlapping mechanisms. The regulation by both SRY and SOX3 on the MAS promoter indicates a cis regulation through multiple SOX binding sites. The Renin (REN) promoter is upregulated by SRY and downregulated by SOX3, likely through trans and cis mechanisms, respectively. Sry transcripts are found in all analyzed male rat tissues including the kidney, while Sox3 transcripts are found only in the brain and testis, suggesting that the primary tissue for renin production (kidney) can only be regulated by SRY and not SOX3. These results suggest that SRY regulation of the RAS is partially shared with its X-chromosome homolog SOX3, but SRY gained a sex-specific control in the kidney for the rate-limiting step of the RAS, potentially resulting in male-specific blood pressure regulation.

Recombination signal binding protein for Ig-κJ region regulates juxtaglomerular cell phenotype by activating the myo-endocrine program and suppressing ectopic gene expression.

Recombination signal binding protein for Ig-κJ region (RBP-J), the major downstream effector of Notch signaling, is necessary to maintain the number of renin-positive juxtaglomerular cells and the plasticity of arteriolar smooth muscle cells to re-express renin when homeostasis is threatened. We hypothesized that RBP-J controls a repertoire of genes that defines the phenotype of the renin cell. Mice bearing a bacterial artificial chromosome reporter with a mutated RBP-J binding site in the renin promoter had markedly reduced reporter expression at the basal state and in response to a homeostatic challenge. Mice with conditional deletion of RBP-J in renin cells had decreased expression of endocrine (renin and Akr1b7) and smooth muscle (Acta2, Myh11, Cnn1, and Smtn) genes and regulators of smooth muscle expression (miR-145, SRF, Nfatc4, and Crip1). To determine whether RBP-J deletion decreased the endowment of renin cells, we traced the fate of these cells in RBP-J conditional deletion mice. Notably, the lineage staining patterns in mutant and control kidneys were identical, although mutant kidneys had fewer or no renin-expressing cells in the juxtaglomerular apparatus. Microarray analysis of mutant arterioles revealed upregulation of genes usually expressed in hematopoietic cells. Thus, these results suggest that RBP-J maintains the identity of the renin cell by not only activating genes characteristic of the myo-endocrine phenotype but also, preventing ectopic gene expression and adoption of an aberrant phenotype, which could have severe consequences for the control of homeostasis.

A mouse renin distal enhancer is essential for blood pressure homeostasis in BAC-rescued renin-null mutant mice

Renin is predominantly expressed in juxtaglomerular cells in the kidney and regulates blood pressure homeostasis. To examine possible in vivo functions of a mouse distal enhancer (mdE), we generated transgenic mice (TgM) carrying either wild-type or mdE-deficient renin BACs (bacterial artificial chromosome), integrated at the identical chromosomal site. In the kidneys of the TgM, the mdE contributed 80% to basal renin promoter activity. To test for possible physiological roles for the mdE, renin BAC transgenes were used to rescue the hypotensive renin-null mice. Interestingly, renal renin expression in the TgBAC:renin-null compound mice was indistinguishable between the wild-type and mutant BAC carriers. Surprisingly, however, the plasma renin activity and angiotensin I concentration in the mdE compound mutant mice were significantly lower than the same parameters in the control mice, and the mutants were consistently hypotensive, demonstrating that blood pressure homeostasis is regulated through transcriptional cis elements controlling renin activity.

Local Renal Circadian Clocks Control Fluid–Electrolyte Homeostasis and BP

The circadian timing system is critically involved in the maintenance of fluid and electrolyte balance and BP control. However, the role of peripheral circadian clocks in these homeostatic mechanisms remains unknown. We addressed this question in a mouse model carrying a conditional allele of the circadian clock gene Bmal1 and expressing Cre recombinase under the endogenous Renin promoter (Bmal1(lox/lox)/Ren1(d)Cre mice). Analysis of Bmal1(lox/lox)/Ren1(d)Cre mice showed that the floxed Bmal1 allele was excised in the kidney. In the kidney, BMAL1 protein expression was absent in the renin-secreting granular cells of the juxtaglomerular apparatus and the collecting duct. A partial reduction of BMAL1 expression was observed in the medullary thick ascending limb. Functional analyses showed that Bmal1(lox/lox)/Ren1(d)Cre mice exhibited multiple abnormalities, including increased urine volume, changes in the circadian rhythm of urinary sodium excretion, increased GFR, and significantly reduced plasma aldosterone levels. These changes were accompanied by a reduction in BP. These results show that local renal circadian clocks control body fluid and BP homeostasis.

Conditional deletion of p53 and Rb in the renin-expressing compartment of the pancreas leads to a highly penetrant metastatic pancreatic neuroendocrine carcinoma

Efforts to model human pancreatic neuroendocrine tumors (PanNETs) in animals have been moderately successful, with minimal evidence for glucagonomas or metastatic spread. The renin gene, although classically associated with expression in the kidney, is also expressed in many other extrarenal tissues including the pancreas. To induce tumorigenesis within rennin-specific tissues, floxed alleles of p53 and Rb were selectively abrogated using Cre-recombinase driven by the renin promoter. The primary neoplasm generated is a highly metastatic islet cell carcinoma of the pancreas. Lineage tracing identifies descendants of renin-expressing cells as pancreatic alpha cells despite a lack of active renin expression in the mature pancreas. Both primary and metastatic tumors express high levels of glucagon; furthermore, an increased level of glucagon is found in the serum, identifying the pancreatic cancer as a functional glucagonoma. This new model is highly penetrant and exhibits robust frequency of metastases to the lymph nodes and the liver, mimicking human disease, and provides a useful platform for better understanding pancreatic endocrine differentiation and development, as well as islet cell carcinogenesis. The use of fluorescent reporters for lineage tracing of the cells contributing to disease initiation and progression provides an unique opportunity to dissect the timeline of disease, examining mechanisms of the metastatic process, as well as recovering primary and metastatic cells for identifying cooperating mutations that are necessary for progression of disease.

Renin gene expression is regulated by Chicken Ovalbumin Upstream Promoter Transcription Factor II (COUP‐TF II)

We aimed to investigate the involvement of the nuclear receptor COUP‐TFII in the regulation of renin gene expression.Protein‐DNA binding studies demonstrated that COUP‐TFII binds to the proxDR sequence in the proximal renin promoter. Knockdown of COUP‐TFII in the renin‐producing cell lines As4.1 and Calu‐6 reduced the stimulation of renin mRNA expression by cAMP agonists. The mutation of the proxDR element in renin promoter reporter gene constructs abrogated the inducibility by cAMP. The proxDR sequence was essential for the function of a renin promoter cAMP‐response element. Knockdown of COUP‐TFII or cAMP‐binding protein (CREB) decreased the basal renin gene expression. When CREB was knocked down, the deficiency of COUP‐TFII did not further diminish the renin expression. Mice deficient in COUP‐TFII have lower renin expression than their control strain. Surprisingly, there was no significant difference in both plasma renin concentration and blood pressure between wildtype and COUP‐TFII‐deficient mice. Altogether our data show that COUP‐TFII is involved in the control of renin gene expression. To better characterize the role of COUP‐TFII for the renin production in vivo we are generating mice with selective COUP‐TFII deletion in the renin‐producing cells of the kidney.

Chicken Ovalbumin Upstream Promoter Transcription Factor II Regulates Renin Gene Expression

This study aimed to investigate the possible involvement of the orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) in the regulation of renin gene expression. COUP-TFII colocalized with renin in the juxtaglomerular cells of the kidney, which are the main source of renin in vivo. Protein-DNA binding studies demonstrated that COUP-TFII binds to an imperfect direct repeat COUP-TFII recognition sequence (termed hereafter proxDR) in the proximal renin promoter. Because cAMP signaling plays a central role in the control of the renin gene expression, we suggested that COUP-TFII may modulate this cAMP effect. Accordingly, knockdown of COUP-TFII in the clonal renin-producing cell lines As4.1 and Calu-6 diminished the stimulation of the renin mRNA expression by cAMP agonists. In addition, the mutation of the proxDR element in renin promoter reporter gene constructs abrogated the inducibility by cAMP. The proxDR sequence was found to be necessary for the function of a proximal renin promoter cAMP-response element (CRE). Knockdown of COUP-TFII or cAMP-binding protein (CREB), which is the archetypal transcription factor binding to CRE, decreased the basal renin gene expression. However, the deficiency of COUP-TFII did not further diminish the renin expression when CREB was knocked down. In agreement with the cell culture studies, mutant mice deficient in COUP-TFII have lower renin expression than their control strain. Altogether our data show that COUP-TFII is involved in the control of renin gene expression.

Histone acetyl transferases CBP and p300 are necessary for maintenance of renin cell identity and transformation of smooth muscle cells to the renin phenotype.

In response to a homeostatic threat circulating renin increases by increasing the number of cells expressing renin by dedifferentiation and re-expression of renin in arteriolar smooth muscle cells (aSMCs) that descended from cells that expressed renin in early life. However, the mechanisms that govern the maintenance and reacquisition of the renin phenotype are not well understood. The cAMP pathway is important for renin synthesis and release: the transcriptional effects are mediated by binding of cAMP responsive element binding protein with its co-activators, CBP and p300, to the cAMP response element in the renin promoter. We have shown previously that mice with conditional deletion of CBP and p300 (cKO) in renin cells had severely reduced renin expression in adult life. In this study we investigated when the loss of renin-expressing cells in the cKO occurred and found that the loss of renin expression becomes evident after differentiation of the kidney is completed during postnatal life. To determine whether CBP/p300 is necessary for re-expression of renin we subjected cKO mice to low sodium diet + captopril to induce retransformation of aSMCs to the renin phenotype. The cKO mice did not increase circulating renin, their renin mRNA and protein expression were greatly diminished compared with controls, and only a few aSMCs re-expressed renin. These studies underline the crucial importance of the CREB/CBP/p300 complex for the ability of renin cells to retain their cellular memory and regain renin expression, a fundamental survival mechanism, in response to a threat to homeostasis.

Regulation of renin expression by the orphan nuclear receptors Nr2f2 and Nr2f6

Understanding the transcriptional mechanisms of renin expression is key to understanding the regulation of the renin-angiotensin system. We previously identified the nuclear receptors RAR/RXR and Nr2f6 (EAR2) as positive and negative transcriptional regulators of renin expression, respectively (Liu X, Huang X, Sigmund CD. Circ Res 92: 1033-1040, 2003). Both mediate their effects through a hormone response element (HRE) within the renin enhancer. Here, we determined whether another nuclear receptor, Nr2f2 (Coup-TFII, Arp-1), identified in a screen of proteins that bind the HRE, also regulates renin expression. Luciferase assays indicate that Nr2f2 negatively regulates the renin promoter more potently than Nr2f6. Gel-shift and chromatin immunoprecipitation (ChIP) indicate that Nr2f2 and Nr2f6 can bind directly to the renin enhancer through the HRE. Surprisingly, baseline expression of endogenous renin was not effected when Nr2f2 was knocked down in As4.1 cells, whereas knockdown of Nr2f6 increased renin expression twofold. Interestingly, however, knockdown of Nr2f2 augmented the induction of renin expression caused by retinoic acid. These data indicate that both Nr2f6 and Nr2f2 can negatively regulate the renin promoter, under baseline conditions and in response to physiological queues, respectively. Therefore, Nr2f2 may require an initiating signal that results in a change at the chromatin level or activation of another transcription factor to exert its effects. We conclude that both Nr2f2 and Nr2f6 negatively regulate renin promoter activity, but may do so by divergent mechanisms.

Regulation of Renin Gene Expression by Oxidative Stress

Increased arterial pressure, angiotensin II(AII), and cytokines each result in feedback inhibition of renin gene expression. Because AII and cytokines can stimulate reactive oxygen species (ROS) production, we tested the hypothesis that oxidative stress may be a mediator of this inhibition. Treatment of renin‐expressing As4.1 cells with the potent cytokine tumor necrosis factor‐á (TNFá) caused an increase in the steady‐state levels of cellular ROS, which was reversed by the antioxidant NAC. Exogenous H2O2 (HP) caused a dose‐ and time‐dependent decrease in the level of endogenous renin mRNA and decreased the transcriptional activity of a 4.1‐kb renin promoter fused to luciferase, which was maximal when the renin enhancer was present. The TNFá–induced decrease in renin mRNA was partially reversed by either NAC or panepoxydone, a nuclear factor êB (NFêB) inhibitor. Interestingly, HP did not induce NFêB in As4.1 cells, and panepoxydone had no effect on the downregulation of renin mRNA by HP. The transcriptional activity of a cAMP response element‐luciferase construct was decreased by both TNFá and HP. These data suggest that cellular ROS can negatively regulate renin gene expression via an NFêB‐independent mechanism involving the renin enhancer and inhibiting cAMP response element–mediated transcription. TNFá decreases renin expression through both NFêB‐dependent and NFêB‐independent mechanisms.