Homeostasis in mice with genetically decreased angiotensinogen is primarily by an increased number of renin-producing cells

The role of Gata3 in renin cell identity

Renin cells are precursors for other cell types in the kidney and show high plasticity in postnatal life in response to challenges to homeostasis. Our previous single-cell RNA-sequencing studies revealed that the dual zinc-finger transcription factor Gata3, which is important for cell lineage commitment and differentiation, is expressed in mouse renin cells under normal conditions and homeostatic threats. We identified a potential Gata3-binding site upstream of the renin gene leading us to hypothesize that Gata3 is essential for renin cell identity. We studied adult mice with conditional deletion of Gata3 in renin cells: Gata3fl/fl;Ren1dCre/+ (Gata3-cKO) and control Gata3fl/fl;Ren1d+/+ counterparts. Gata3 immunostaining revealed that Gata3-cKO mice had significantly reduced Gata3 expression in juxtaglomerular, mesangial, and smooth muscle cells, indicating a high degree of deletion of Gata3 in renin lineage cells. Gata3-cKO mice exhibited a significant increase in blood urea nitrogen, suggesting hypovolemia and/or compromised renal function. By immunostaining, renin-expressing cells appeared very thin compared with their normal plump shape in control mice. Renin cells were ectopically localized to Bowman's capsule in some glomeruli, and there was aberrant expression of actin-α2 signals in the mesangium, interstitium, and Bowman's capsule in Gata3-cKO mice. Distal tubules showed dilated morphology with visible intraluminal casts. Under physiological threat, Gata3-cKO mice exhibited a lower increase in mRNA levels than controls. Hematoxylin-eosin, periodic acid-Schiff, and Masson's trichrome staining showed increased glomerular fusion, absent cubical epithelial cells in Bowman's capsule, intraglomerular aneurysms, and tubular dilation. In conclusion, our results indicate that Gata3 is crucial to the identity of cells of the renin lineage.NEW & NOTEWORTHY Gata3, a dual zinc-finger transcription factor, is responsible for the identity and localization of renin cells in the kidney. Mice with a conditional deletion of Gata3 in renin lineage cells have abnormal kidneys with juxtaglomerular cells that lose their characteristic location and are misplaced outside and around arterioles and glomeruli. The fundamental role of Gata3 in renin cell development offers a new model to understand how transcription factors control cell location, function, and pathology.

Inhibition of the renin-angiotensin system causes concentric hypertrophy of renal arterioles in mice and humans

Inhibitors of the renin-angiotensin system (RAS) are widely used to treat hypertension. Using mice harboring fluorescent cell lineage tracers, single-cell RNA-Seq, and long-term inhibition of RAS in both mice and humans, we found that deletion of renin or inhibition of the RAS leads to concentric thickening of the intrarenal arteries and arterioles. This severe disease was caused by the multiclonal expansion and transformation of renin cells from a classical endocrine phenotype to a matrix-secretory phenotype: the cells surrounded the vessel walls and induced the accumulation of adjacent smooth muscle cells and extracellular matrix, resulting in blood flow obstruction, focal ischemia, and fibrosis. Ablation of the renin cells via conditional deletion of β1 integrin prevented arteriolar hypertrophy, indicating that renin cells are responsible for vascular disease. Given these findings, prospective morphological studies in humans are necessary to determine the extent of renal vascular damage caused by the widespread use of inhibitors of the RAS.

Renin Cells, the Kidney, and Hypertension

Renin cells are essential for survival perfected throughout evolution to ensure normal development and defend the organism against a variety of homeostatic threats. During embryonic and early postnatal life, they are progenitors that participate in the morphogenesis of the renal arterial tree. In adult life, they are capable of regenerating injured glomeruli, control blood pressure, fluid-electrolyte balance, tissue perfusion, and in turn, the delivery of oxygen and nutrients to cells. Throughout life, renin cell descendants retain the plasticity or memory to regain the renin phenotype when homeostasis is threatened. To perform all of these functions and maintain well-being, renin cells must regulate their identity and fate. Here, we review the major mechanisms that control the differentiation and fate of renin cells, the chromatin events that control the memory of the renin phenotype, and the major pathways that determine their plasticity. We also examine how chronic stimulation of renin cells alters their fate leading to the development of a severe and concentric hypertrophy of the intrarenal arteries and arterioles. Lastly, we provide examples of additional changes in renin cell fate that contribute to equally severe kidney disorders.

Proliferation does not contribute to murine models of renin cell recruitment

Aim

Renin cells are essential for regulation of blood pressure and fluid‐electrolyte homeostasis. During homeostatic threat, the number of renin cells in the kidney increases, a process termed as recruitment. It has been proposed that recruitment occurs by proliferation, yet no systematic studies have been performed. We sought to determine the extent to which proliferation contributes to the recruitment process.

Methods

Mice were subjected to recruitment before analysing the renin cells’ cell cycle. For acute threats, we subjected SV129 and C57Bl6 mice to a low sodium diet plus captopril. Tissue sections from treated mice were co‐stained for proliferation markers (Ki67, PCNA, pH3 and BrdU) and renin. Chronic recruitment was studied in deletion models of aldosterone synthase and angiotensinogen through co‐immunostaining and counting mitotic figures in periodic acid‐Schiff‐stained sections. Finally, RNA‐seq of renin cells isolated from recruited mice was performed to study mitotic signature.

Results

Mice subjected to low salt and captopril displayed increases in renin cell number (312 ± 40 in controls to 692 ± 85 in recruited animals, P<.0001), 10‐fold increases in renin mRNA and fourfold increases in circulating renin. Co‐staining these kidney sections for proliferation markers revealed negligible proliferation of renin cells (<2%), indistinguishable from control animals. Similarly, chronic models of recruitment—aldosterone synthase KO and angiotensinogen KO—had negligible proliferation. Additionally, the transcriptome of recruited renin cells revealed overall downregulation of mitotic pathways when compared to proliferative cell lines.

Conclusion

Acute and chronic physiological threats to homeostasis produced a distinct increase in renin‐synthesizing cells, but we found no evidence to suggest the involvement of proliferation.

Urinary Renin in Patients and Mice With Diabetic Kidney Disease

In patients with diabetic kidney disease (DKD), plasma renin activity is usually decreased, but there is limited information on urinary renin and its origin. Urinary renin was evaluated in samples from patients with longstanding type I diabetes mellitus and mice with streptozotocin-induced diabetes mellitus. Renin-reporter mouse model (Ren1d-Cre;mT/mG) was made diabetic with streptozotocin to examine whether the distribution of cells of the renin lineage was altered in a chronic diabetic environment. Active renin was increased in urine samples from patients with DKD (n=36), compared with those without DKD (n=38; 3.2 versus 1.3 pg/mg creatinine; P<0.001). In mice with streptozotocin-induced diabetes mellitus, urine renin was also increased compared with nondiabetic controls. By immunohistochemistry, in mice with streptozotocin-induced diabetes mellitus, juxtaglomerular apparatus and proximal tubular renin staining were reduced, whereas collecting tubule staining, by contrast, was increased. To examine the role of filtration and tubular reabsorption on urinary renin, mice were either infused with either mouse or human recombinant renin and lysine (a blocker of proximal tubular protein reabsorption). Infusion of either form of renin together with lysine markedly increased urinary renin such that it was no longer different between nondiabetic and diabetic mice. Megalin mRNA was reduced in the kidney cortex of streptozotocin-treated mice (0.70±0.09 versus 1.01±0.04 in controls, P=0.01) consistent with impaired tubular reabsorption. In Ren1d-Cre;mT/mG with streptozotocin-induced diabetes mellitus, the distribution of renin lineage cells within the kidney was similar to nondiabetic renin-reporter mice. No evidence for migration of cells of renin linage to the collecting duct in diabetic mice could be found. Renin mRNA in microdissected collecting ducts from streptozotocin-treated mice, moreover, was not significantly different than in controls, whereas in kidney cortex, largely reflecting juxtaglomerular apparatus renin, it was significantly reduced. In conclusion, in urine from patients with type 1 diabetes mellitus and DKD and from mice with streptozotocin-induced diabetes mellitus, renin is elevated. This cannot be attributed to production from cells of the renin lineage migrating to the collecting duct in a chronic hyperglycemic environment. Rather, the elevated levels of urinary renin found in DKD are best attributed to altered glomerular filteration and impaired proximal tubular reabsorption.

Angiotensin II Short-Loop Feedback: Is There a Role of Ang II for the Regulation of the Renin System In Vivo?

The activity of the renin-angiotensin-aldosterone system is triggered by the release of the protease renin from the kidneys, which in turn is controlled in the sense of negative feedback loops. It is widely assumed that Ang II (angiotensin II) directly inhibits renin expression and secretion via a short-loop feedback by an effect on renin-producing cells (RPCs) mediated by AT₁ (Ang II type 1) receptors. Because the concept of such a direct short-loop negative feedback control, which originates mostly from in vitro experiments, has not yet been systematically proven in vivo, we aimed to test the validity of this concept by studying the regulation of renin synthesis and secretion in mice lacking Ang II-AT₁ receptors on RPCs. We found that RPCs of the kidney express Ang II-AT₁ receptors. Mice with conditional deletion of Ang II-AT₁ receptors in RPCs were normal with regard to the number of renin cells, renal renin mRNA, and plasma renin concentrations. Renin expression and secretion of these mice responded to Ang I (angiotensin I)-converting enzyme inhibition and to Ang II infusion like in wild-type (WT) controls. In summary, we did not obtain evidence that Ang II-AT₁ receptors on RPCs are of major relevance for the normal regulation of renin expression and secretion in mice. Therefore, we doubt the existence of a direct negative feedback function of Ang II on RPCs.

COX-2-derived PGE2 triggers hyperplastic renin expression and hyperreninemia in aldosterone synthase-deficient mice

Pharmacological inhibition or genetic loss of function defects of the renin angiotensin aldosterone system (RAAS) causes compensatory renin cell hyperplasia and hyperreninemia. The triggers for the compensatory stimulation of renin synthesis and secretion in this situation may be multimodal. Since cyclooxygenase-2 (COX-2) expression in the macula densa is frequently increased in states of a defective RAAS, we have investigated a potential role of COX-2 and its derived prostaglandins for renin expression and secretion in aldosterone synthase-deficient mice (AS^−/−) as a model for a genetic defect of the RAAS. In comparison with wild-type mice (WT), AS^−/− mice had 9-fold and 30-fold increases of renin mRNA and of plasma renin concentrations (PRC), respectively. Renin immunoreactivity in the kidney cortex of AS^−/− mice was 10-fold higher than in WT. Macula densa COX-2 expression was 5-fold increased in AS^−/− kidneys relative to WT kidneys. Treatment of AS^−/− mice with the COX-2 inhibitor SC-236 for 1 week lowered both renal renin mRNA and PRC by 70%. Hyperplastic renin cells in AS^−/− kidneys were found to express the prostaglandin E₂ receptors EP2 and EP4. Global deletion of EP2 receptors did not alter renin mRNA nor PRC values in AS^−/− mice. Renin cell-specific inducible deletion of the EP4 receptor lowered renin mRNA and PRC by 25% in AS^−/− mice. Renin cell-specific inducible deletion of the EP4 receptor in combination with global deletion of the EP2 receptor lowered renin mRNA and PRC by 70–75% in AS^−/− mice. Lineage tracing of renin-expressing cells revealed that deletion of EP2 and EP4 leads to a preferential downregulation of perivascular renin expression. Our findings suggest that increased macula densa COX-2 activity in AS^−/− mice triggers perivascular renin expression and secretion via prostaglandin E₂.

Renin cells in homeostasis, regeneration and immune defence mechanisms

An accumulating body of evidence suggests that renin-expressing cells have developed throughout evolution as a mechanism to preserve blood pressure and fluid volume homeostasis as well as to counteract a number of homeostatic and immunological threats. In the developing embryo, renin precursor cells emerge in multiple tissues, where they differentiate into a variety of cell types. The function of those precursors and their progeny is beginning to be unravelled. In the developing kidney, renin-expressing cells control the morphogenesis and branching of the renal arterial tree. The cells do not seem to fully differentiate but instead retain a degree of developmental plasticity or molecular memory, which enables them to regenerate injured glomeruli or to alter their phenotype to control blood pressure and fluid-electrolyte homeostasis. In haematopoietic tissues, renin-expressing cells might regulate bone marrow differentiation and participate in a circulating leukocyte renin-angiotensin system, which acts as a defence mechanism against infections or tissue injury. Furthermore, renin-expressing cells have an intricate lineage and functional relationship with erythropoietin-producing cells and are therefore central to two endocrine systems - the renin-angiotensin and erythropoietin systems - that sustain life by controlling fluid volume and composition, perfusion pressure and oxygen delivery to tissues. However, loss of the homeostatic control of these systems following dysregulation of renin-expressing cells can be detrimental, with serious pathological events.

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 Ren1^c-/- background, we generated mutant mice with reporter expression (Ren1^c-/-;Ren1^c-Cre;R26R.mTmG and Ren1^c-/-;Ren1^c-Cre;R26R.LacZ) to trace the fate of renin^null cells. To assess whether renin^null cells maintain their renin promoter active, we used Ren1^c-/-;Ren1^c-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, renin^null 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.

Novel Functions of Renin Precursors in Homeostasis and Disease

Renin progenitors appear early and are found in multiple tissues throughout the embryo. Besides their well known role in blood pressure and fluid homeostasis, renin progenitors participate in tissue morphogenesis, repair, and regeneration, and may integrate immune and endocrine responses. In the bone marrow, renin cells offer clues to understand normal and neoplastic hematopoiesis.

Renin-Angiotensin-Aldosterone System Inhibition Increases Podocyte Derivation from Cells of Renin Lineage

Because adult podocytes cannot proliferate and are therefore unable to self-renew, replacement of these cells depends on stem/progenitor cells. Although podocyte number is higher after renin-angiotensin-aldosterone system (RAAS) inhibition in glomerular diseases, the events explaining this increase are unclear. Cells of renin lineage (CoRL) have marked plasticity, including the ability to acquire a podocyte phenotype. To test the hypothesis that RAAS inhibition partially replenishes adult podocytes by increasing CoRL number, migration, and/or transdifferentiation, we administered tamoxifen to Ren1cCreERxRs-tdTomato-R CoRL reporter mice to induce permanent labeling of CoRL with red fluorescent protein variant tdTomato. We then induced experimental FSGS, typified by abrupt podocyte depletion, with a cytopathic antipodocyte antibody. RAAS inhibition by enalapril (angiotensin-converting enzyme inhibitor) or losartan (angiotensin-receptor blocker) in FSGS mice stimulated the proliferation of CoRL, increasing the reservoir of these cells in the juxtaglomerular compartment (JGC). Compared with water or hydralazine, RAAS inhibition significantly increased the migration of CoRL from the JGC to the intraglomerular compartment (IGC), with more glomeruli containing RFP⁺CoRL and, within these glomeruli, more RFP⁺CoRL. Moreover, RAAS inhibition in FSGS mice increased RFP⁺CoRL transdifferentiation in the IGC to phenotypes, consistent with those of podocytes (coexpression of synaptopodin and Wilms tumor protein), parietal epithelial cells (PAX 8), and mesangial cells (α8 integrin). These results show that in the context of podocyte depletion in FSGS, RAAS inhibition augments CoRL proliferation and plasticity toward three different glomerular cell lineages.

Physiology of the Renal Interstitium

Long overlooked as the virtual compartment and then strictly characterized through descriptive morphologic analysis, the renal interstitium has finally been associated with function. With identification of interstitial renin- and erythropoietin-producing cells, the most prominent endocrine functions of the kidney have now been attributed to the renal interstitium. This article reviews the functional role of renal interstitium.

Fate and plasticity of renin precursors in development and disease

Renin-expressing cells appear early in the embryo and are distributed broadly throughout the body as organogenesis ensues. Their appearance in the metanephric kidney is a relatively late event in comparison with other organs such as the fetal adrenal gland. The functions of renin cells in extra renal tissues remain to be investigated. In the kidney, they participate locally in the assembly and branching of the renal arterial tree and later in the endocrine control of blood pressure and fluid-electrolyte homeostasis. Interestingly, this endocrine function is accomplished by the remarkable plasticity of renin cell descendants along the kidney arterioles and glomeruli which are capable of reacquiring the renin phenotype in response to physiological demands, increasing circulating renin and maintaining homeostasis. Given that renin cells are sensors of the status of the extracellular fluid and perfusion pressure, several signaling mechanisms (β-adrenergic receptors, Notch pathway, gap junctions and the renal baroreceptor) must be coordinated to ensure the maintenance of renin phenotype--and ultimately the availability of renin--during basal conditions and in response to homeostatic threats. Notably, key transcriptional (Creb/CBP/p300, RBP-J) and posttranscriptional (miR-330, miR125b-5p) effectors of those signaling pathways are prominent in the regulation of renin cell identity. The next challenge, it seems, would be to understand how those factors coordinate their efforts to control the endocrine and contractile phenotypes of the myoepithelioid granulated renin-expressing cell.

Cells of renin lineage are progenitors of podocytes and parietal epithelial cells in experimental glomerular disease

Glomerular injury leads to podocyte loss, a process directly underlying progressive glomerular scarring and decline of kidney function. The inherent repair process is limited by the inability of podocytes to regenerate. Cells of renin lineage residing alongside glomerular capillaries are reported to have progenitor capacity. We investigated whether cells of renin lineage can repopulate the glomerulus after podocyte injury and serve as glomerular epithelial cell progenitors. Kidney cells expressing renin were genetically fate-mapped in adult Ren1cCreER×Rs-tdTomato-R, Ren1cCre×Rs-ZsGreen-R, and Ren1dCre×Z/EG reporter mice. Podocyte depletion was induced in all three cell-specific reporter mice by cytotoxic anti-podocyte antibodies. After a decrease in podocyte number, a significant increase in the number of labeled cells of renin lineage was observed in glomeruli in a focal distribution along Bowman's capsule, within the glomerular tuft, or in both locations. A subset of cells lining Bowman's capsule activated expression of the glomerular parietal epithelial cell markers paired box protein PAX2 and claudin-1. A subset of labeled cells within the glomerular tuft expressed the podocyte markers Wilms tumor protein 1, nephrin, podocin, and synaptopodin. Neither renin mRNA nor renin protein was detected de novo in diseased glomeruli. These findings provide initial evidence that cells of renin lineage may enhance glomerular regeneration by serving as progenitors for glomerular epithelial cells in glomerular disease characterized by podocyte depletion.

Pericytes synthesize renin

AIM: To investigate renin expression in pericytes during normal kidney development and after deletion of angiotensinogen, the precursor for all angiotensins.

METHODS: We examined the distribution of renin expressing cells by immunoshistochemistry in the interstitial compartment of wild type (WT) and angiotensinogen deficient (AGT -/-) mice at different developmental stages from embryonic day 18 (E18: WT, n = 4; AGT -/-, n = 5) and at day 1 (P1: WT, n = 5; AGT -/-, n = 5), 5 (P5: WT, n = 7; AGT -/-, n = 8), 10 (P10: WT, n = 3; AGT -/-, n = 5), 21 (P21: WT, n = 7; AGT -/-, n = 5), 45 (P45: WT, n = 3; AGT -/-, n = 3), and 70 (P70: WT, n = 2; AGT -/-, n = 2) of postnatal life. We quantified the number of pericytes positive for renin at all the developmental stages mentioned above and compared the results of AGT -/- mice to their WT counterparts.

RESULTS: In WT mice, renal interstitial pericytes synthesize renin in early life supporting a lineage relationship with renin cells in the vasculature. The number of pericytes positive for renin per area of 0.32 mm² (density) in WT mice was maintained from fetal life till weaning age (E18 = 4.25 ± 0.63, P1 = 3.75 ± 0.48, P5 = 3.75 ± 0.48, P10 = 4 ± 0.71, P21 = 3.8 ± 0.58) and markedly decreased in adult life (P45 = 1.2 ± 0.37, P70 = 0.8 ± 0.20). On the other hand, in AGT -/- mice the density of pericytes expressing renin was not significantly different from WT mice at E18 and P1: E18 = 5.75 ± 0.50 vs 4.25 ± 0.63 (P = 0.106), P1 = 9.25 ± 3.50 vs 3.75 ± 0.48 (P = 0.175) but significantly increased from P5 till P70: P5 = 38.25 ± 5 vs 3.75 ± 0.48 (P = 0.0004), P10 = 173 ± 7.50 vs 4 ± 0.70 (P = 5.24567 × 10^-7), P21 = 83 ± 6.70 vs 3.8 ± 0.58 (P = 2.97358 × 10^-6), P45 = 49 ± 3.50 vs 1.2 ± 0.37 (P = 8.18274 x 10^-7) and P70 = 17.8 ± 2.30 vs 0.8 ± 0.20 (P = 3.51151 × 10^-5). The AGT -/- mice showed a marked increase in the number of pericytes per field studied starting from P5, reaching its peak at P10, and then a gradually decreasing until P70.

CONCLUSION: Interstitial pericytes synthesize renin during development and the number of renin-expressing pericytes increases in response to a homeostatic threat imposed early in life such as lack of angiotensinogen.

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.

Genetic architecture of complex traits predisposing to nephropathy: hypertension

Blood pressure and hypertension have significant genetic underpinnings that may be age-dependent. The age-dependency, significant contributions from environmental factors such as diet and exercise, and inherent moment-to-moment variability complicate the identification of the genes contributing to the development of hypertension. Although genetic abnormalities may have moderate effects, the physiologic pathways involving these genes have redundant compensating mechanisms to bring the system back into equilibrium. This has the effect of reducing or completely masking the initial genetic defects, one of the hypothesized reasons for the small genetic effects found by the recent genome-wide association studies. This review article discusses the concept of initiators versus compensators in the context of finding genes related to hypertension development. A brief review is provided of some key genes found to be associated with hypertension, including the genes identified from the nine genome-wide association studies published to date.

The microRNA-processing enzyme dicer maintains juxtaglomerular cells

Juxtaglomerular cells are highly specialized myoepithelioid granulated cells located in the glomerular afferent arterioles. These cells synthesize and release renin, which distinguishes them from other cells. How these cells maintain their identity, restricted localization, and fate is unknown and is fundamental to the control of BP and homeostasis of fluid and electrolytes. Because microRNAs may control cell fate via temporal and spatial gene regulation, we generated mice with a conditional deletion of Dicer, the RNase III endonuclease that produces mature microRNAs in cells of the renin lineage. Deletion of Dicer severely reduced the number of juxtaglomerular cells, decreased expression of the renin genes (Ren1 and Ren2), lowered plasma renin concentration, and decreased BP. As a consequence of the disappearance of renin-producing cells, the kidneys developed striking vascular abnormalities and prominent striped fibrosis. We conclude that microRNAs maintain the renin-producing juxtaglomerular cells and the morphologic integrity and function of the kidney.

Methods for imaging Renin-synthesizing, -storing, and -secreting cells

Renin-producing cells have been the object of intense research efforts for the past fifty years within the field of hypertension. Two decades ago, research focused on the concept and characterization of the intrarenal renin-angiotensin system. Early morphological studies led to the concept of the juxtaglomerular apparatus, a minute organ that links tubulovascular structures and function at the single nephron level. The kidney, thus, appears as a highly "topological organ" in which anatomy and function are intimately linked. This point is reflected by a concurrent and constant development of functional and structural approaches. After summarizing our current knowledge about renin cells and their distribution along the renal vascular tree, particularly along glomerular afferent arterioles, we reviewed a variety of imaging techniques that permit a fine characterization of renin synthesis, storage, and release at the single-arteriolar, -cell, or -granule level. Powerful tools such as multiphoton microscopy and transgenesis bear the promises of future developments of the field.

Preservation of intracellular renin expression is insufficient to compensate for genetic loss of secreted renin

The primary product of the renin gene is preprorenin. A signal peptide sorts renin to the secretory pathway in juxtaglomerular cells where it is released into the circulation to initiate the renin-angiotensin system cascade. In the brain, transcription of renin occurs from an alternative promoter encoding an mRNA starting with a new first exon (exon 1b). Exon 1b initiating transcripts skip over the classical first exon (exon 1a) containing the initiation codon for preprorenin. Exon 1b transcripts are predicted to use a highly conserved initiation codon within exon 2, producing renin, which should remain intracellular, because it lacks the signal peptide. To evaluate the roles of secreted and intracellular renin, we took advantage of the organization of the renin locus to generate a secreted renin (sRen)-specific knockout, which preserves intracellular renin expression. Expression of sRen mRNA was ablated in the brain and kidney, whereas intracellular renin mRNA expression was preserved in fetal and adult brains. We noted a developmental shift from the expression of sRen mRNA in the fetal brain to intracellular renin mRNA in the adult brain. Homozygous sRen knockout mice exhibited very poor survival at weaning. The survivors exhibited renal lesions, low hematocrit, an inability to generate a concentrated urine, decreased arterial pressure, and impaired aortic contraction. These results suggest that preservation of intracellular renin expression in the brain is not sufficient to compensate for a loss of sRen, and sRen plays a pivotal role in renal development and function, survival, and the regulation of arterial pressure.

CBP and p300 are essential for renin cell identity and morphological integrity of the kidney

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

Identity of the renin cell is mediated by cAMP and chromatin remodeling: an in vitro model for studying cell recruitment and plasticity

The renin-angiotensin system (RAS) regulates blood pressure and fluid-electrolyte homeostasis. A key step in the RAS cascade is the regulation of renin synthesis and release by the kidney. We and others have shown that a major mechanism to control renin availability is the regulation of the number of cells capable of making renin. The kidney possesses a pool of cells, mainly in its vasculature but also in the glomeruli, capable of switching from smooth muscle to endocrine renin-producing cells when homeostasis is threatened. The molecular mechanisms governing the ability of these cells to turn the renin phenotype on and off have been very difficult to study in vivo. We, therefore, developed an in vitro model in which cells of the renin lineage are labeled with cyan fluorescent protein and cells actively making renin mRNA are labeled with yellow fluorescent protein. The model allowed us to determine that it is possible to culture cells of the renin lineage for numerous passages and that the memory to express the renin gene is maintained in culture and can be reenacted by cAMP and chromatin remodeling (histone H4 acetylation) at the cAMP-responsive element in the renin gene.

Pharmacogenomics of Renin Angiotensin System Inhibitors in Coronary Artery Disease

Renin Angiotensin System (RAS) inhibitors comprise some of the most commonly used medications in coronary artery disease (CAD) and its related syndromes. Unfortunately, significant inter-patient variability seems likely in response to these agents; of which, the influence of genetic determinants is of interest. This review summarizes the available RAS inhibitor pharmacogenomic studies which have evaluated RAS polymorphisms that either elucidate mechanism via surrogate endpoint measurements, or predict efficacy via clinical outcomes in CAD related syndromes.Regardless of the endpoint, none of the RAS genotypes conclusively predicts efficacy of RAS inhibitors. In fact, the results of the pharmacogenomic studies were often in direct conflict with one another. Varied results appear due to methodological limitations (e.g., inadequate study power, genotyping error, methods of endpoint measurement), study conceptualization (e.g., overestimating the contribution of polymorphism to disease, lack of haplotype approach), and differences between studies (e.g., genotype frequency, study subject characteristics, the specific medication and dose used). Thus investigators should consider the various methodological limitations to improve upon the current approach to RAS inhibitor pharmacogenomic research in the vast CAD population.

Effect of the angiotensinogen genotype on experimental hypertension in mice

Polymorphisms of the angiotensinogen (Agt) gene may affect blood pressure. We used a mouse model to test for the role of the Agt genotype in low-renin or high-renin forms of hypertension. Mice bearing one, two, three, or four copies of the Agt gene underwent renal artery clipping to induce high-renin two-kidney, one-clip renovascular hypertension (2K1C), or uninephrectomy, salt loading, and application of deoxycorticosterone-acetate (DOCA) pellets to induce low-renin mineralocorticoid hypertension. Appropriate control animals were also studied. Blood pressure was measured by tail cuff as well as by direct intra-arterial recordings. There was a small effect of the Agt genotype on baseline blood pressure before induction of hypertension. The extent of 2K1C hypertension was not affected by the genotype. In contrast, there was a marked gene-dose effect on DOCA-hypertension (21.2 mmHg over all genotypes). Treatment of DOCA mice with the angiotensin II type 1 receptor antagonist abolished the genotype effect on blood pressure and left ventricular hypertrophy. There was a trend towards less suppression of endogenous aldosterone by DOCA treatment with increasing number of Agt gene copies. We conclude that the Agt genotype exerts a marked effect on blood pressure in a low-renin form of hypertension but no effect in the face of stimulated renin, at least in mice.

ACE gene dosage modulates pressure-induced cardiac hypertrophy in mice and men

The influence of genetic factors on complex phenotypes is context dependent, posing a challenge to quantify the role of single gene variants on this process. Moreover, redundancy and reserve capacity among control systems prevent most physiological stimuli to destabilize these processes. To test whether small gene perturbation can disrupt this equilibrium under pathological conditions, mice harboring one, two, or three copies of the angiotensin converting enzyme ( Ace) gene were submitted to 3 and 6 wk of pressure overload (PO). Direct systolic blood pressure (SBP), as an index of cardiac afterload, and left ventricle mass index (LVMI) were measured. LVMI under normotension was the same regardless of the Ace genotype, but the slopes of the LVMI/SBP curves increased in the three- vs. one-copy group by ∼50% upon 3- or 6-wk PO. Angiotensin II AT1 receptor blocker treatment produced a significant pressure independent decrease in the LVMI/SBP ratio. Unlike the one-copy group, PO resulted in a significant reduction in angiotensinogen and an increase in Ace mRNA expression accompanied by an increase in cardiac angiotensin II levels in the three-copy group. Similarly, the human ACE D gene variant influenced cardiac mass, estimated by Sokolov-Lyon index, in a sample of 1,507 individuals from an urban population only in individuals in the 4th quartile of the blood pressure distribution. Collectively, these data provide direct evidence that ACE gene dosage per se does not influence cardiac mass but upon a pathological stimulus, such as elevation in blood pressure, it modulates cardiac mass in both mice and humans.

Renin enhancer is critical for control of renin gene expression and cardiovascular function

The important cardiovascular regulator renin contains a strong in vitro enhancer 2.7 kb upstream of its gene. Here we tested the in vivo role of the mouse Ren-1c enhancer. In renin-expressing As4.1 cells stably transfected with Ren-1c promoter with or without enhancer, expression of linked beta-geo reporter, stable expression, and colony formation were dependent on the presence of the enhancer. We then generated mice carrying a targeted deletion of the enhancer (REKO mice) and found marked depletion of renin in renal juxtaglomerular and submandibular ductal cells, as well as hyperplasia of macula densa cells. Plasma creatinine was increased, but electrolytes were normal. Male REKO mice implanted with telemetry devices had 9 +/- 1 mm Hg lower mean arterial pressure (p < 0.001), which was partly normalized by a high NaCl diet. Locomotor activity was lower, and baroreflex sensitivity was normal. Markedly reduced mean arterial pressure variability in the midfrequency band indicated a contribution of reduced sympathetic vasomotor tone to the hypotension. In conclusion, the renin enhancer is critical for renin gene expression and physiological sequelae, including response to alteration in salt intake. The REKO mouse may be useful as a low renin expression model.

Kidney function in mice lacking aldosterone

To explore the effects of decreased amounts or absence of aldosterone, we have disrupted the gene coding for aldosterone synthase (AS) in mice and investigated blood pressure and kidney function in AS+/+, AS+/-, and AS-/- mice. AS+/- mice have normal blood pressures and show no abnormalities in electrolytes or kidney gene expression, but they have significantly higher than normal urine volume and lower urine osmolality. In contrast, the AS-/- mice have low blood pressure, abnormal electrolyte homeostasis (increased plasma concentrations of K+, Ca2+, and Mg2+ and decreased concentrations of HCO3(-) and Cl- but no difference in the plasma Na+ level), and disturbances in water metabolism (higher urine output, decreased urine osmolality, and impaired urine concentrating and diluting ability). Absence of aldosterone in the AS-/- mice induced several compensatory changes: an increased food intake-to-body weight ratio, an elevated plasma concentration of glucocorticoids, and strong activation of the renin-angiotensin system. Parallel with the markedly increased synthesis and release of renin, the AS-/- mice showed increased expression of cyclooxygenase-2 (COX-2) in macula densa. On salt supplementation, plasma electrolyte concentrations and kidney renin and COX-2 levels became similar to those of wild-type mice, but the lower blood pressure of the AS-/- mice was not corrected. Thus absence of aldosterone in AS-/- mice results in impairment of Na+ reabsorption in the distal nephron, decreased blood pressure, and strong renin-angiotensin system activation. Our data show the substantial correction of these abnormalities, except the low blood pressure, by high dietary salt does not depend on aldosterone.

Biology of natriuretic peptides and their receptors

Increasing evidence suggests that natriuretic peptides (NPs) play diverse roles in mammals, including renal hemodynamics, neuroendocrine, and cardiovascular functions. Collectively, NPs are classified as hypotensive hormones; the main actions of NPs are implicated in eliciting natriuretic, diuretic, steroidogenic, antiproliferative, and vasorelaxant effects, important factors in the control of body fluid volume and blood pressure homeostasis. One of the principal loci involved in the regulatory actions of NPs is their cognate plasma membrane receptor molecules, which are activated by binding with specific NPs. Interaction of NPs with their receptors plays a central role in physiology and pathophysiology of hypertension and cardiovascular disorders. Gaining insight into the intricacies of NPs-specific receptor signaling pathways is of pivotal importance for understanding both hormone-receptor biology and the disease states arising from abnormal hormone receptor interplay. During the last decade there has been a surge in interest in NP receptors; consequently, a wealth of information has emerged concerning molecular structure and function, signaling mechanisms, and use of transgenics and gene-targeted mouse models. The objective of this present review is to summarize and document the previous findings and recent discoveries in the field of the natriuretic peptide hormone family and receptor systems with emphasis on the structure-function relationship, signaling mechanisms, and the physiological and pathophysiological significance in health and disease.

Homeostatic responses in the adrenal cortex to the absence of aldosterone in mice

To study the effects of decreased amounts or absence of aldosterone on development and endocrine function, we have disrupted the mouse gene, Cyp11b2, coding for aldosterone synthase (AS) by replacing its first two exons with sequences coding for enhanced green fluorescent protein. The null pups fail to thrive postnatally, and about 30% die between d 7 and 28. Aldosterone in plasma and AS mRNA in adrenal glands are undetectable in the null mice. Adult AS-null mice are small, weigh 75% of wild type, are hypotensive, have increased concentrations of plasma K(+) and corticosterone, and a decreased concentration of plasma Cl(-). Their plasma renin and angiotensin II concentrations are 45x and 4x wild type. The adrenal cortex is disorganized and has cells that contain marked accumulations of lipid. The zona glomerulosa is widened and includes easily detectable renin-containing cells, not seen in the wild-type adrenal gland. In the AS-/- adrenals, the level of mRNA for Cyp11b1, coding for 11beta-hydroxylase, is 150% wild type. The adrenal glands of the null mice consequently show evidence of a greatly activated renin-angiotensin system and up-regulation of glucocorticoid production. In the AS-null mice enhanced green fluorescent protein fluorescence is mainly at the boundary between the cortex and medulla, where apoptotic cells are numerous. These data are consistent with the absence of aldosterone in the AS-null mice inducing an increased cell-turnover of cells in the adrenals that normally become AS expressing and their migration to the medullary boundary where they apoptose.

Angiotensinogen and angiotensin-converting enzyme gene copy number and angiotensin and bradykinin peptide levels in mice

OBJECTIVE

To test the hypothesis that changes in gene expression that may accompany angiotensinogen (AGT) and angiotensin-converting enzyme (ACE) gene polymorphism cause alteration in angiotensin and bradykinin peptide levels.

DESIGN

Mice with one or two genes for AGT and ACE allow assessment of the effects of modest alteration in AGT and ACE gene expression on angiotensin and bradykinin peptide levels.

METHODS

Angiotensin and bradykinin peptides were measured in the blood, kidney, heart, lung, adrenal, brain, and aorta of mice that were either wild-type (+/+), heterozygous (+/-) or null (-/-) for either the AGT or ACE gene.

RESULTS

Angiotensin I and angiotensin II were not detectable in blood or tissues of AGT -/- mice, which had increased bradykinin levels in kidney and lung. ACE -/- mice had markedly reduced angiotensin II levels and increased bradykinin levels in blood and tissues. However, despite reduced AGT and ACE gene expression, angiotensin and bradykinin peptide levels in AGT and ACE +/- mice were no different from the levels in wild-type mice.

CONCLUSION

Although the AGT and ACE genes are fundamental determinants of angiotensin and bradykinin peptide levels, compensatory mechanisms attenuate the effect of modest change in AGT and ACE gene expression on the levels of these peptides. Identification of these compensatory mechanisms may provide new candidate genes for investigation in humans.

Ren1cHomozygous Null Mice Are Hypotensive and Polyuric, but Heterozygotes Are Indistinguishable from Wild-Type

Mice lacking Ren1c were generated using C57BL/6-derived embryonic stem cells. Mice homozygous for Ren1c disruption (Ren1c-/-) are born at the expected ratio, but approximately 80% die of dehydration within a few days. The surviving Ren1c-/- mice have no renin mRNA expression in the kidney, hydronephrosis, thickening of renal arterial walls, and fibrosis in the kidney. Plasma renin and angiotensins I and II are undetectable. Urinary aldosterone is 6% wild-type. They have low tail-cuff BP (84 +/- 4 versus 116 +/- 5 mmHg in +/+) and excrete large amounts of urine (5.2 +/- 0.8 ml/d, 725 +/- 34 mOsm versus 1.1 +/- 0.1 ml/d, 2460 +/- 170 mOsm in +/+). After 5 d of drinking 5% dextrose, desmopressin does not increase the osmolality of the urine in -/- mice (624 +/- 19 to 656 +/- 25 mOsm), whereas in +/+, it increases severalfold (583 +/- 44 to 2630 +/- 174 mOsm). Minipump infusion of angiotensin II to Ren1c-/- mice restores BP to wild-type level, but preexisting damage to the medulla prevents complete restoration of the ability of the kidney to concentrate urine. Heterozygous Ren1c+/- mice, in contrast, are indistinguishable from +/+ in BP, urine volume, and osmolality. Kidney renin mRNA, the number of kidney cells producing renin, and plasma renin concentration in the Ren1c+/- mice are also indistinguishable from +/+. These results demonstrate that renin is the only enzyme capable of maintaining plasma angiotensins and that renin expression in the kidney is very tightly regulated at the mRNA level.

Plasma renin in mice with one or two renin genes

AIM

In the present study we have investigated whether the presence of a second renin gene exerts an overriding influence on plasma renin such that mice with two renin genes have consistently higher renin levels than mice with only one renin gene.

METHODS

Plasma renin was determined as the rate of angiotensin I generation using a radioimmunoassay (RIA) kit with (plasma renin concentration, PRC) or without (plasma renin activity, PRA) the addition of purified rat angiotensinogen as substrate.

RESULTS

In male 129SvJ, DBA/2 and Swiss Webster mice, strains possessing both Ren-1 and Ren-2, PRC (ng Ang I mL(-1) h(-1)) averaged 178 +/- 36, 563 +/- 57 and 550 +/- 43 while PRA was 2.9 +/- 0.5, 3.6 +/- 0.8 and 7.8 +/- 1.2. In male C57BL/6, C3H and BALB/c mice that express only Ren-1, PRC averaged 426 +/- 133, 917 +/- 105 and 315 +/- 72, and PRA was 3.4 +/- 1.0, 6.9 +/- 1.7 and 4.5 +/- 1.2. In the two renin gene A1AR-/- mice compared with the one renin gene A1AR+/+, PRC averaged 538 +/- 321 and 415 +/- 159 while PRA averaged 3.2 +/- 1.1 and 4.4 +/- 1.4 ng Ang I mL(-1) h(-1). Aldosterone levels showed no significant differences between one renin (C57BL/6, C3H and BALB/c) and two renin (129SvJ, DBA/2 and Swiss Webster) gene mice. Furthermore, by quantitative real-time polymerase chain reaction (RT-PCR) we found no correlation between the number of renin genes and whole kidney renin mRNA levels from one and two renin gene mice.

CONCLUSION

Our data show that baseline plasma renin is not systematically higher in mice with two renin genes than in one renin gene mice. Thus, the presence of a second renin gene does not seem to be a major determinant of differences in PRC between different mouse strains.

Renin cells are precursors for multiple cell types that switch to the renin phenotype when homeostasis is threatened

Renin-synthesizing cells are crucial in the regulation of blood pressure and fluid-electrolyte homeostasis. Adult mammals subjected to manipulations that threaten homeostasis increase circulating renin by increasing the number of renin-expressing/-releasing cells. We hypothesize that the ability of adult cells to synthesize renin does not occur randomly in any cell type, depending instead on the cell's lineage. To determine the fate of renin-expressing cells, we generated knockin mice expressing cre recombinase in renin-expressing cells and crossed them with reporter mice. Results show that renin-expressing cells are precursors for a variety of cells that differentiate into non-renin-expressing cells such as smooth-muscle, epithelial, mesangial, and extrarenal cells. In the kidney, these cells retain the capability to synthesize renin when additional hormone is required to reestablish homeostasis: specific subpopulations of apparently differentiated cells are "held in reserve" to respond (repeatedly) by de-differentiating and expressing renin in response to stress, and re-differentiating when the crisis passes.

Salt handling and hypertension

The kidney plays a central role in our ability to maintain appropriate sodium balance, which is critical to determination of blood pressure. In this review we outline current knowledge of renal salt handling at the molecular level, and, given that Westernized societies consume more salt than is required for normal physiology, we examine evidence that the lowering of salt intake can combat hypertension.

Renin activity and angiotensin I concentration in genetically selective inbred line of hypertensive mice

Blood pressure lowering kallikrein-kinin and blood pressure raising renin-angiotensin systems play a major role in the maintenance of normal blood pressure. In a previous study, we have shown that a kallikrein-like prorenin converting enzyme (PRCE C) is elevated in the submandibular gland tissue of a mouse line (BPH) that was genetically selected and inbred for high blood pressure in comparison to normotensive line (BPN) that was derived from the ancestors of BPH line. In the present investigation we wanted to find out if elevated levels of PRCE C were involved in the modulation of tissue (local) renin-angiotensin system in the submandibular gland tissue. Results indicate significantly high renin activity but low angiotensin I level in the tissue of BPH mouse model. These results tend to suggest PRCE C's involvement in tissue (local) renin-angiotensin system.

Ablation of renin-expressing juxtaglomerular cells results in a distinct kidney phenotype

Renin-expressing cells are peculiar in that they act as differentiated cells, producing the hormone renin, while they also seem to act as progenitors for other renal cell types. As such, they may have functions independent of their ability to generate renin/angiotensin. To test this hypothesis, we ablated renin-expressing cells during development by placing diphtheria toxin A chain (DTA) under control of the Ren1d mouse renin promoter by homologous recombination in a two-renin gene strain (Ren2 and Ren1d). Renin-expressing cells are essentially absent from kidneys in homozygotes (DTA/DTA) which, unlike wild-type mice, are unable to recruit renin-expressing cells when homeostasis is threatened. In contrast, renin staining in the submandibular gland (SMG), which expresses mainly Ren2, is normal. Homozygous mice survive normally, but the kidneys are small and have morphological abnormalities: 25% of the glomeruli are hyperplastic or atrophic, tubules are dilated and atrophic, and areas of undifferentiated cells exist near the atrophic glomeruli and tubules. However, in contrast to the very abnormal renal vessels found when renin-angiotensin system genes are deleted, the kidney vessels in homozygotes have normal wall thickness and no decrease in lumen size. Homozygotes have severely reduced kidney and plasma renin concentrations and females have reduced blood pressure. Homozygotes have elevated blood urea nitrogen and potassium levels, which are suggestive of altered renal function. We conclude that renin cells per se are necessary for the morphological integrity of the kidney and may have a role in maintenance of normal kidney function.

Altered renin synthesis and secretion in the kidneys of heterozygous mice with a null mutation in the TGF-beta(2) gene

Transforming growth factors beta (TGF-betas) are peptides involved in autocrine and paracrine control of cell growth and differentiation. In the kidneys, TGF-beta(2) has been shown to localize specifically in renin-producing cells in various conditions stimulating the renin response. To test in vivo the functional role of TGF-beta(2), the renin response was investigated in mice heterozygous for a null mutation of the TGF-beta(2) gene, which had a twofold reduction in the amount of TGF-beta(2) mRNA. Although the increase in plasma renin concentration triggered by dehydration was not different from wild-type mice, renal renin mRNA and protein levels were higher in mutant mice under hydrated or dehydrated conditions. These data suggest that TGF-beta(2) exerts an inhibitory effect on renin synthesis and release from the juxtaglomerular apparatuses.

Molecular phenotyping for analyzing subtle genetic effects in mice: application to an angiotensinogen gene titration

The angiotensinogen M235T polymorphism in humans is linked to differential expression of the human angiotensinogen gene (AGT) gene and hypertension, but the homeostatic responses resulting from this polymorphism are not known. We therefore investigated how mice respond to five genetically determined levels of mouse angiotensinogen gene (Agt) expression covering the range associated with the M235T variants. By using high-throughput molecular phenotyping, tissue RNAs were assayed for expression of 10 genes important in hypertension. Significant positive and negative responses occurred in both sexes as Agt expression increased twofold, including a three-fold increase in aldosterone synthase expression in adrenal gland, and a two-fold decrease in renin expression in kidney. In males, cardiac expression of the precursor of atrial natriuretic peptide B and of adrenomedullin also increased approximately twofold. The relative expression of all genes studied except Agt differed significantly in the two sexes, and several unexpected relationships were encountered. A highly significant correlation between renal expression of the angiotensin type 1a receptor and kallikrein, independent of Agt genotype, is present in females (P < 0.0001) but not males (P = 0.4). The correlation between blood pressure (BP) and liver Agt expression within the five Agt genotypes is significant in females (P = 0.0005) but not in males (P = 0.2), whereas correlation of BP with differences between the genotypes is less in females (P = 0.06) than in males (P = 0.001). The marked gender differences in gene expression in wild-type mice and the changes induced by moderate alterations in Agt expression and BP emphasize the need to look for similar differences in humans.

Blood pressure and NaCl-sensitive hypertension are influenced by angiotensin-converting enzyme gene expression in transgenic mice

ACE plays an important role in the regulation of arterial pressure; however, a linear relationship between ACE expression and arterial pressure has not been demonstrated. The present study employed telemetric monitoring in female transgenic mice to determine the influence of partial and complete deletion of the ACE gene on basal arterial pressure and arterial pressure responses to a high-NaCl diet. On the basal NaCl diet, 24-hour mean arterial pressure was significantly correlated with the number of functional copies of the ACE gene; ie, arterial pressure was lowest in 0-copy (80 +/- 1 mm Hg), intermediate in 1-copy (100 +/- 1 mm Hg), and highest in 2-copy (113 +/- 1 mm Hg) ACE mice. The high-NaCl diet significantly increased mean arterial pressure in 0-copy (99 +/- 1 mm Hg) and 1-copy (108 +/- 1 mm Hg) mice but not in 2-copy mice (114 +/- 1 mm Hg). These results demonstrate a copy-dependent relationship between ACE gene expression and both basal arterial pressure and arterial pressure responses to a high-NaCl diet, suggesting that either partial or complete reduction in the ACE gene can alter arterial pressure.

Effects of long-term inhibition of neuronal nitric oxide synthase on blood pressure and renin release

Nitric oxide (NO) produced by neuronal NO-synthase (nNOS) in macula densa cells may be involved in the control of renin release. 7-Nitro indazole (7-NI) inhibits nNOS, and we investigated the effect of short- (4 days) and long-term (4 weeks) 7-NI treatment on blood pressure (BP), plasma renin concentration (PRC) and glomerular filtration rate (GFR) in rats on different salt diets. Rats were divided into three groups and given low-salt (LS), normal (C) and high-salt (HS) diets. Each diet group was subdivided into two groups treated either with 7-NI or vehicle. Long-term 7-NI-treated rats (LS and C) showed increased BP compared with controls (LS: 149 +/- 4 vs. 133 +/- 3; C: 146 +/- 4 vs. 127 +/- 4 mmHg). Blood pressure in HS rats did not differ from that in controls. Plasma renin concentration was stimulated in LS-rats (251 +/- 64 mGU mL(-1)) compared with C and HS rats (42 +/- 8 and 39 +/- 5 mGU mL(-1), respectively) but was not significantly affected by chronic 7-NI treatment (350 +/- 103, 49 +/- 10 and 50 +/- 15 mGU mL(-1) in LS, C and HS, respectively). In rats treated with 7-NI for 4 days, no effect on BP was seen, but PRC was increased in 7-NI treated LS rats compared with vehicle treated LS rats (107 +/- 15 vs. 56 +/- 1 mGU mL(-1)). Stimulation of PRC in LS rats was further enhanced by 7-NI after 4 days of treatment, but not affected in rats treated for 4 weeks. This suggests that inhibition of nNOS stimulates renin release but that this stimulatory effect in the long run might be depressed by the increase in blood pressure.

Adipose angiotensinogen is involved in adipose tissue growth and blood pressure regulation

White adipose tissue and liver are important angiotensinogen (AGT) production sites. Until now, plasma AGT was considered to be a reflection of hepatic production. Because plasma AGT concentration has been reported to correlate with blood pressure, and to be associated with body mass index, we investigated whether adipose AGT is released locally and into the blood stream. For this purpose, we have generated transgenic mice either in which adipose AGT is overexpressed or in which AGT expression is restricted to adipose tissue. This was achieved by the use of the aP2 adipocyte-specific promoter driving the expression of rat agt cDNA in both wild-type and hypotensive AGT-deficient mice. Our results show that in both genotypes, targeted expression of AGT in adipose tissue increases fat mass. Mice whose AGT expression is restricted to adipose tissue have AGT circulating in the blood stream, are normotensive, and exhibit restored renal function compared with AGT-deficient mice. Moreover, mice that overexpress adipose AGT have increased levels of circulating AGT, compared with wild-type mice, and are hypertensive. These animal models demonstrate that AGT produced by adipose tissue plays a role in both local adipose tissue development and in the endocrine system, which supports a role of adipose AGT in hypertensive obese patients.

Genetic disruption of atrial natriuretic peptide receptor-A alters renin and angiotensin II levels

We have studied cardiovascular and renal phenotypes in Npr1 (genetic determinant of natriuretic peptide receptor-A; NPRA) gene-disrupted mutant mouse model. The baseline systolic arterial pressure (SAP) in 0-copy mutant (-/-) mice (143 +/- 2 mmHg) was significantly higher than in 2-copy wild-type (+/+) animals (104 +/- 2 mmHg); however, the SAP in 1-copy heterozygotes (+/-) was at an intermediate value (120 +/- 4 mmHg). To determine whether Npr1 gene function affects the renin-angiotensin-aldosterone system (RAAS), we measured the components of RAAS in plasma, kidney, and adrenal gland of 0-copy, 1-copy, and 2-copy male mice. Newborn (2 days after the birth) 0-copy pups showed 2.5-fold higher intrarenal renin contents compared with 2-copy wild-type counterparts (0-copy 72 +/- 12 vs. 2-copy 30 +/- 7 microg ANG I. mg protein(-1). h(-1), respectively). The intrarenal ANG II level in 0-copy pups was also higher than in 2-copy controls (0-copy 33 +/- 5 vs. 2-copy 20 +/- 2 pg/mg protein, respectively). However, both young (3 wk) and adult (16 wk) 0-copy mutant mice showed a dramatic 50-80% reduction in plasma renin concentrations (PRCs) and in expression of renal renin message compared with 2-copy control animals. In contrast, the adrenal renin content and mRNA expression levels were 1.5- to 2-fold higher in 0-copy adult mice than in 2-copy animals. The results suggest that inhibition of renal and systemic RAAS is a compensatory response that prevents greater increases in elevated arterial pressures in adult NPRA null mutant mice. However, the greater renin and ANG II levels seen in 0-copy newborn pups provide evidence that the direct effect of NPRA activation on renin is an inhibitory response.

NaCl consumption is attenuated in female KCNE1 null mutant mice

The role of potassium channels in the regulation of NaCl intake has not been investigated previously. One potassium channel, KCNQ1, and its regulator, KCNE1, are expressed in salivary glands and kidneys, and KCNE1 null mutant mice are deficient in KCNQ1 potassium currents. To understand the role of the KCNQ1/KCNE1 channel complex in NaCl taste and intake, we compared the NaCl consumption of KCNE1 +/+ (129/Sv), KCNE1 +/-, and KCNE1 -/- mice using two-bottle intake tests and lick rate tests. Although KCNE1 +/+ and KCNE1 +/- mice exhibited consumption patterns for 75-150 mM NaCl solutions considered typical for 129/Sv mice, the KCNE1 -/- null mutant 129/Sv mice were indifferent to or rejected them. This effect was observed in female mice only, required prior exposure to NaCl solutions, and the extent of rejection was greater after prior exposure to 150 mM NaCl solution than 75 mM NaCl solution. No differences were observed in the avidity for KCl solutions or in lick rates of naive mice for 150 or 300 mM NaCl solutions. These results demonstrate that a single potassium channel gene can influence voluntary NaCl intake. We speculate that disruption of the KCNE1 gene impairs sodium metabolism in female mice drinking high levels of 150 mM NaCl, which causes malaise that becomes associated with NaCl taste, and as a consequence, reduced preference for NaCl.

Important role of endogenous norepinephrine and epinephrine in the development of in vivo pressure-overload cardiac hypertrophy

OBJECTIVES

We sought to define the role of norepinephrine and epinephrine in the development of cardiac hypertrophy and to determine whether the absence of circulating catecholamines alters the activation of downstream myocardial signaling pathways.

BACKGROUND

Cardiac hypertrophy is associated with elevated plasma catecholamine levels and an increase in cardiac morbidity and mortality. Although considerable evidence suggests that G-protein-coupled receptors are involved in the hypertrophic response, it remains controversial whether catecholamines are required for the development of in vivo cardiac hypertrophy.

METHODS

We performed transverse aortic constriction (TAC) in dopamine beta-hydroxylase knockout mice (Dbh(-/-), genetically altered mice that are completely devoid of endogenous norepinephrine and epinephrine) and littermate control mice. After induction of cardiac hypertrophy, the mitogen-activated protein kinase (MAPK) signaling pathways were measured in pressure-overloaded/wild-type and Dbh(-/-) hearts.

RESULTS

Compared with the control animals, cardiac hypertrophy was significantly blunted in Dbh(-/-) mice, which was not associated with altered cardiac function, as assessed by transthoracic echocardiography in conscious mice. The extracellularly regulated kinase (ERK 1/2), c-jun-NH(2)-terminal kinase (JNK) and p38 MAPK pathways were all activated by two- to threefold after TAC in the control animals. In contrast, induction of the three pathways (ERK 1/2, JNK and p38) was completely abolished in Dbh(-/-) mice.

CONCLUSIONS

These data demonstrate a nearly complete requirement of endogenous norepinephrine and epinephrine for the induction of in vivo pressure-overload cardiac hypertrophy and for the activation of hypertrophic signaling pathways.

Ren1d and Ren2 cooperate to preserve homeostasis: evidence from mice expressing GFP in place of Ren1d

To distinguish the contributions of Ren1(d) and Ren2 to kidney development and blood pressure homeostasis, we placed green fluorescent protein (GFP) under control of the Ren1(d) renin locus by homologous recombination in mice. Homozygous Ren1(d)-GFP animals make GFP mRNA in place of Ren1(d) mRNA in the kidney and maintain Ren2 synthesis in the juxtaglomerular (JG) cells. GFP expression provides an accurate marker of Ren1(d) expression during development. Kidneys from homozygous animals are histologically normal, although with fewer secretory granules in the JG cells. Blood pressure and circulating renin are reduced in Ren1(d)-GFP homozygotes. Acute administration of losartan decreases blood pressure further, suggesting a role for Ren2 protein in blood pressure homeostasis. These studies demonstrate that, in the absence of Ren1(d), Ren2 preserves normal kidney development and prevents severe hypotension. Chronic losartan treatment results in compensation via recruitment of both Ren1(d)- and Ren2-expressing cells along the preglomerular vessels. This response is achieved by metaplastic transformation of arteriolar smooth muscle cells, a major mechanism to control renin bioavailability and blood pressure homeostasis.

Importance of quantitative genetic variations in the etiology of hypertension

Recent progress has been remarkable in identifying mutations which cause diseases (mostly uncommon) that are inherited simply. Unfortunately, the common diseases of humankind with a strong genetic component, such as those affecting cardiovascular function, have proved less tractable. Their etiology is complex with substantial environmental components and strong indications that multiple genes are implicated. In this article, we consider the genetic etiology of essential hypertension. After presenting the distribution of blood pressures in the population, we propose the hypothesis that essential hypertension is the consequence of different combinations of genetic variations that are individually of little consequence. The candidate gene approach to finding relevant genes is exemplified by studies that identified potentially causative variations associated with quantitative differences in the expression of the angiotensinogen gene (AGT). Experiments to test causation directly are possible in mice, and we describe their use to establish that blood pressures are indeed altered by genetic changes in AGT expression. Tests of differences in expression of the genes coding for the angiotensin-converting enzyme (ACE) and for the natriuretic peptide receptor A are also considered, and we provide a tabulation of all comparable experiments in mice. Computer simulations are presented that resolve the paradoxical finding that while ACE inhibitors are effective, genetic variations in the expression of the ACE gene do not affect blood pressure. We emphasize the usefulness of studying animals heterozygous for an inactivating mutation and a wild-type allele, and briefly discuss a way of establishing causative links between complex phenotypes and single nucleotide polymorphisms.