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The decrease of renin-producing cells is not associated with a phenotype switch into vascular smooth muscle cells. (A) Abundance of renin, EPO, AQP2, a-SMA, SM22, and myocardin mRNAs in isolated glomeruli with attached afferent arterioles and their original whole kidneys from Vhl fl/fl and Vhl 2/2REN mice. mRNA abundance is given as ratio over GAPDH mRNA, which was considered as a standard. Ratio values are depicted on a logarithmic scale to allow the estimation of both accumulation and depletion of mRNAs in the isolated afferent arterioles relative to their original kidneys. G and K indicate glomeruli with afferent arterioles and kidney, respectively . (B) Distribution of renin and EPO mRNA in kidneys and extrarenal tissues of Vhl fl/fl and Vhl 2/2REN mice. Data are means 6 SEM of five mice in each group. *P,0.05 by t test.
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States of low perfusion pressure of the kidney associate with hyperplasia or expansion of renin-producing cells, but it is unknown whether hypoxia-triggered genes contribute to these changes. Here, we stabilized hypoxia-inducible transcription factors (HIFs) in mice by conditionally deleting their negative regulator, Vhl, using the Cre/loxP system...
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Context 1
... We, therefore, performed gene expression studies to investigate if the decrease of renin-producing cells in afferent arterioles of Vhl 2/2REN kidneys was associated with an increase of gene expression characteristic for vascular smooth muscle cells. Compar- isons of gene expression between isolated glomeruli containing attached afferent arterioles and whole kidneys confirmed strong enrichment of renin mRNA as ex- pected and a markedly reduced expression of aquaporin-2 (AQP2) mRNA, indicating the absence of significant contamination of the preparation with collecting duct cells in both Vhl fl/fl and Vhl 2/2REN kidneys (Fig- ure 7A). EPO mRNA showed a strong en- richment in isolated glomeruli/arterioles of Vhl 2/2REN kidneys and a clear depletion in glomeruli/arterioles of Vhl fl/fl kidneys ( Figure 7A), con- firming the expression of EPO in preglomerular vessels of Vhl 2/2REN kidneys as opposed to expression outside the glo- meruli/arterioles in Vhl fl/fl kidneys. ...
Context 2
... isons of gene expression between isolated glomeruli containing attached afferent arterioles and whole kidneys confirmed strong enrichment of renin mRNA as ex- pected and a markedly reduced expression of aquaporin-2 (AQP2) mRNA, indicating the absence of significant contamination of the preparation with collecting duct cells in both Vhl fl/fl and Vhl 2/2REN kidneys (Fig- ure 7A). EPO mRNA showed a strong en- richment in isolated glomeruli/arterioles of Vhl 2/2REN kidneys and a clear depletion in glomeruli/arterioles of Vhl fl/fl kidneys ( Figure 7A), con- firming the expression of EPO in preglomerular vessels of Vhl 2/2REN kidneys as opposed to expression outside the glo- meruli/arterioles in Vhl fl/fl kidneys. The smooth muscle cell markers SM22, a-smooth muscle actin (a-SMA), myocardin, and smooth muscle myosin heavy chain (not shown) dis- played lower rather than higher enrichments in glomeruli/ afferent arterioles of Vhl 2/2REN kidneys compared with Vhl fl/fl kidneys ( Figure 7A), thus not supporting the idea of a phe- notype shift to smooth muscle cells in afferent arterioles of Vhl 2/2REN kidneys. ...
Context 3
... mRNA showed a strong en- richment in isolated glomeruli/arterioles of Vhl 2/2REN kidneys and a clear depletion in glomeruli/arterioles of Vhl fl/fl kidneys ( Figure 7A), con- firming the expression of EPO in preglomerular vessels of Vhl 2/2REN kidneys as opposed to expression outside the glo- meruli/arterioles in Vhl fl/fl kidneys. The smooth muscle cell markers SM22, a-smooth muscle actin (a-SMA), myocardin, and smooth muscle myosin heavy chain (not shown) dis- played lower rather than higher enrichments in glomeruli/ afferent arterioles of Vhl 2/2REN kidneys compared with Vhl fl/fl kidneys ( Figure 7A), thus not supporting the idea of a phe- notype shift to smooth muscle cells in afferent arterioles of Vhl 2/2REN kidneys. ...
Citations
... Our findings illustrate the cellular plasticity observed in renal stromal cells. When exposed to hypoxia, renin-producing JG cells are converted to EPO-producing cells Kurt et al., 2013). Conversely, in rodent and human cases of pronounced interstitial fibrosis, myofibroblasts, which have lost their ability to synthetize EPO (Asada et al., 2011;Kaneko et al., 2022), start to produce renin (Miyauchi et al., 2021). ...
Renin is the key enzyme of the systemic renin–angiotensin–aldosterone system, which plays an essential role in regulating blood pressure and maintaining electrolyte and extracellular volume homeostasis. Renin is mainly produced and secreted by specialized juxtaglomerular (JG) cells in the kidney. In the present study, we report for the first time that the conserved transmembrane receptor neuropilin‐1 (NRP1) participates in the development of JG cells and plays a key role in renin production. We used the myelin protein zero‐Cre (P0‐Cre) to abrogate Nrp1 constitutively in P0‐Cre lineage‐labelled cells of the kidney. We found that the P0‐Cre precursor cells differentiate into renin‐producing JG cells. We employed a lineage‐tracing strategy combined with RNAscope quantification and metabolic studies to reveal a cell‐autonomous role for NRP1 in JG cell function. Nrp1‐deficient animals displayed abnormal levels of tissue renin expression and failed to adapt properly to a homeostatic challenge to sodium balance. These findings provide new insights into cell fate decisions and cellular plasticity operating in P0‐Cre–expressing precursors and identify NRP1 as a novel key regulator of JG cell maturation. image
Key points
Renin is a centrepiece of the renin–angiotensin–aldosterone system and is produced by specialized juxtaglomerular cells (JG) of the kidney.
Neuropilin‐1 (NRP1) is a conserved membrane‐bound receptor that regulates vascular and neuronal development, cancer aggressiveness and fibrosis progression.
We used conditional mutagenesis and lineage tracing to show that NRP1 is expressed in JG cells where it regulates their function.
Cell‐specific Nrp1 knockout mice present with renin paucity in JG cells and struggle to adapt to a homeostatic challenge to sodium balance.
The results support the versatility of renin‐producing cells in the kidney and may open new avenues for therapeutic approaches.
... Also, the mice-specific deletion of VHL also has an attenuated expansion in renin-expressing cells, even under the stimulation of the RAS (a low-salt diet combined with an ACE inhibitor). The deletion of VHL in renin-expressing cells activates EPO expression [64]. ...
The renin–angiotensin system (RAS) and hypoxia have a complex interaction: RAS is activated under hypoxia and activated RAS aggravates hypoxia in reverse. Renin is an aspartyl protease that catalyzes the first step of RAS and tightly regulates RAS activation. Here, we outline kidney renin expression and release under hypoxia and discuss the putative mechanisms involved. It is important that renin generally increases in response to acute hypoxemic hypoxia and intermittent hypoxemic hypoxia, but not under chronic hypoxemic hypoxia. The increase in renin activity can also be observed in anemic hypoxia and carbon monoxide-induced histotoxic hypoxia. The increased renin is contributed to by juxtaglomerular cells and the recruitment of renin lineage cells. Potential mechanisms regulating hypoxic renin expression involve hypoxia-inducible factor signaling, natriuretic peptides, nitric oxide, and Notch signaling-induced renin transcription.
... Conditionally targeted mouse models are of limited help because REP cells are rare and specific marker genes, other than Epo itself, which would be suitable to drive REP-specific Cre expression, are currently unknown. Moreover, Cre drivers with REP cell overlapping expression patterns used for conditional knockouts of VHL and PHDs cause unphysiologically high, constitutive, and isoform-independent HIFα stabilization, often leading to ectopic Epo production [13,32,37,38,55,61,62]. ...
... Because (i) REP cells are rare, (ii) normoxic Epo protein is basically undetectable, and (iii) hypoxic Epo mRNA expression occurs only transiently; independent markers to target and analyze these cells are urgently required. A number of Cre drivers have been used to target REP cells, including promoter elements derived from the genes encoding CD68, renin, connexin 40, PDGFRβ, and FOXD1 [13,32,37,38,54,55,61,62]. Because these genes are also expressed in non-REP cells, the corresponding models are probably of limited use to study physiological Epo regulation. ...
Renal erythropoietin (Epo)-producing (REP) cells represent a rare and incompletely understood cell type. REP cells are fibroblast-like cells located in close proximity to blood vessels and tubules of the corticomedullary border region. Epo mRNA in REP cells is produced in a pronounced “on–off” mode, showing transient transcriptional bursts upon exposure to hypoxia. In contrast to “ordinary” fibroblasts, REP cells do not proliferate ex vivo, cease to produce Epo, and lose their identity following immortalization and prolonged in vitro culture, consistent with the loss of Epo production following REP cell proliferation during tissue remodelling in chronic kidney disease. Because Epo protein is usually not detectable in kidney tissue, and Epo mRNA is only transiently induced under hypoxic conditions, transgenic mouse models have been developed to permanently label REP cell precursors, active Epo producers, and inactive descendants. Future single-cell analyses of the renal stromal compartment will identify novel characteristic markers of tagged REP cells, which will provide novel insights into the regulation of Epo expression in this unique cell type.
... Renin-lineage cells can also fulfill a kind of stem cell function as progenitor cells for the regeneration of mesangial cells and podocytes after kidney injury This article is part of the special issue on Kidney Control of Homeostasis in Pflügers Archiv-European Journal of Physiology [43,86,105]. Moreover, it was found that juxtaglomerular renin cells can transform into erythropoietin (EPO)-producing cells due to genetic activation of the hypoxia signaling pathway [6,48]. ...
... In contrast to interstitial renin + cells, EPO expression is not induced in juxtaglomerular renin-producing cells after treatment with a single-dose of a PHD inhibitor or after renin cell-specific deletion of PHD2 [6]. At first glance, these findings appear contradictory to the original observation that renin cell-specific deletion of Vhl induces EPO expression in juxtaglomerular cells [19,48]. It turned out, that it requires a codeletion of PHD2 with PHD3 to induce EPO expression in juxtaglomerular renin cells [6]. ...
... However, the pathways interacting with the hypoxia signaling pathway to mediate this transformation are still elusive [19,46]. It is conceivable that activation of the hypoxia signaling pathway via HIF-2 leads to a change in the microRNA expression pattern [48,63]. miRNAs can directly affect chromatin structure by targeting factors like DNA methyltransferases or histone deacetylases [4]. ...
The protease renin, the key enzyme of the renin–angiotensin–aldosterone system, is mainly produced and secreted by juxtaglomerular cells in the kidney, which are located in the walls of the afferent arterioles at their entrance into the glomeruli. When the body’s demand for renin rises, the renin production capacity of the kidneys commonly increases by induction of renin expression in vascular smooth muscle cells and in extraglomerular mesangial cells. These cells undergo a reversible metaplastic cellular transformation in order to produce renin. Juxtaglomerular cells of the renin lineage have also been described to migrate into the glomerulus and differentiate into podocytes, epithelial cells or mesangial cells to restore damaged cells in states of glomerular disease. More recently, it could be shown that renin cells can also undergo an endocrine and metaplastic switch to erythropoietin-producing cells. This review aims to describe the high degree of plasticity of renin-producing cells of the kidneys and to analyze the underlying mechanisms.
... This finding is in line with the generally accepted view that Hif-2α is expressed in fibroblasts and some peritubular endothelial cells but not in tubular cells of the nephron, whereas Hif-1α expression can be detected predominantly in tubular epithelial cells [36,37]. It is noteworthy that the targeted deletion of VHL in renin-producing cells leads to an accumulation of Hif-1α, but not Hif-2α, in collecting duct cells in adult mouse kidneys [38], further supporting a possible Hif-1α function in this part of the nephron. ...
The kidney is strongly dependent on a continuous oxygen supply, and is conversely highly sensitive to hypoxia. Controlled oxygen gradients are essential for renal control of solutes and urine-concentrating mechanisms, which also depend on various hormones including aldosterone. The cortical collecting duct (CCD) is part of the aldosterone-sensitive distal nephron and possesses a key function in fine-tuned distal salt handling. It is well known that aldosterone is consistently decreased upon hypoxia. Furthermore, a recent study reported a hypoxia-dependent down-regulation of sodium currents within CCD cells. We thus investigated the possibility that cells from the cortical collecting duct are responsive to hypoxia, using the mouse cortical collecting duct cell line mCCDcl1 as a model. By analyzing the hypoxia-dependent transcriptome of mCCDcl1 cells, we found a large number of differentially-expressed genes (3086 in total logFC< −1 or >1) following 24 h of hypoxic conditions (0.2% O2). A gene ontology analysis of the differentially-regulated pathways revealed a strong decrease in oxygen-linked processes such as ATP metabolic functions, oxidative phosphorylation, and cellular and aerobic respiration, while pathways associated with hypoxic responses were robustly increased. The most pronounced regulated genes were confirmed by RT-qPCR. The low expression levels of Epas1 under both normoxic and hypoxic conditions suggest that Hif-1α, rather than Hif-2α, mediates the hypoxic response in mCCDcl1 cells. Accordingly, we generated shRNA-mediated Hif-1α knockdown cells and found Hif-1α to be responsible for the hypoxic induction of established hypoxically-induced genes. Interestingly, we could show that following shRNA-mediated knockdown of Esrra, Hif-1α protein levels were unaffected, but the gene expression levels of Egln3 and Serpine1 were significantly reduced, indicating that Esrra might contribute to the hypoxia-mediated expression of these and possibly other genes. Collectively, mCCDcl1 cells display a broad response to hypoxia and represent an adequate cellular model to study additional factors regulating the response to hypoxia.
... Another example of a remarkable change in the phenotype of renin cells was evidenced by the conditional deletion of the Vhl gene in cells of the renin lineage. 65 Juxtaglomerular cells stopped expressing renin and other renin cell-specific markers such as Akr1b7 and produced instead erythropoietin-an effect that was stimulated by the accumulation of HIF-2α leading to increased levels of circulating erythropoietin and policytemia. 66 Whereas, in this case, the preglomerular arterial tree did not seem to be affected, 65 deletion of Vhl in the Foxd1+ progenitors resulted in vascular abnormalities due to impaired differentiation of vascular SMCs, mesangial cells, and renin cells. ...
... 65 Juxtaglomerular cells stopped expressing renin and other renin cell-specific markers such as Akr1b7 and produced instead erythropoietin-an effect that was stimulated by the accumulation of HIF-2α leading to increased levels of circulating erythropoietin and policytemia. 66 Whereas, in this case, the preglomerular arterial tree did not seem to be affected, 65 deletion of Vhl in the Foxd1+ progenitors resulted in vascular abnormalities due to impaired differentiation of vascular SMCs, mesangial cells, and renin cells. 67 A recent study in rodents showed that in response to either acute or chronic anemia, some erythropoietin-producing renal interstitial fibroblasts also make renin, likely due to a decrease in blood volume and pressure but not in response solely to hypoxia. ...
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.
... In addition to the endocrine control of fluid-electrolyte balance, renin cells are involved in kidney morphogenesis, regeneration of injured glomeruli, and erythropoietin production [4][5][6][7][8][9]. In extrarenal locations such as in hematopoietic organs, specialized renin-producing cells may play a role in innate immunity to fight infections. ...
Hypotension and changes in fluid–electrolyte balance pose immediate threats to survival. Juxtaglomerular cells respond to such threats by increasing the synthesis and secretion of renin. In addition, smooth muscle cells (SMCs) along the renal arterioles transform into renin cells until homeostasis has been regained. However, chronic unrelenting stimulation of renin cells leads to severe kidney damage. Here, we discuss the origin, distribution, function, and plasticity of renin cells within the kidney and immune compartments and the consequences of distorting the renin program. Understanding how chronic stimulation of these cells in the context of hypertension may lead to vascular pathology will serve as a foundation for targeted molecular therapies.
... This article is protected by copyright. All rights reserved recruitment of renin cells while switching cells to EPO-producing cells 10 These recent observations decipher the molecular machinery necessary for renin cell phenotype and reveal a striking plasticity that does not require cell division but rather a phenotypic switch. It shall be interesting to follow the future development in the understanding of signaling cues that control renin cell number important for blood pressure homeostasis. ...
In the current issue of Acta Physiologica, Guessoum et al. address a question that has intrigued investigators for decades within kidney and blood pressure research fields1 . In conditions where the renin-angiotensin aldosterone system (RAAS) is chronically challenged, the renin-producing cells increase significantly in number and their localization expands from a juxtaglomerular position to a widespread distribution upstream the afferent glomerular arterioles and to extraglomerular mesangial cells.
... 51,68,69 Lack of connexin 40 in renin cells leads to malignant hypertension, 70 and deletion of the Von Hippel-Lindau gene in renin cells leads to a remarkable phenotypic switch: the former renin-producing cells stop making renin and transcribe erythropoietin. 71 As a result, the animals display secondary erythrocytosis. Because the RAS is at the crux of our armamentarium to treat hypertension and other disorders, understanding the mechanisms involved in normal and abnormal renin cell fate may help design new strategies to prevent and better treat our patients with hypertension, cardiovascular, and renal diseases. ...
A lthough renin cells are crucial for blood pressure homeo-stasis, little is known about their nature. We now know that renin cells are precursors that appear early and in multiple tissues during embryonic development. They participate in morphogenetic events, vascular development and injury, tissue repair, and regeneration. When confronted to a homeostatic threat, renin cell descendants have the capability to switch the renin gene on or off. This poorly understood switch or molecular memory enables the organism to maintain constancy of the internal milieu and tissue perfusion. Here, we discuss briefly the major events that govern the acquisition and maintenance of renin cell identity and how manipulations that alter the fate of renin cells can lead to serious disease. We also advance the concept that renin cells are at the center of an ancestral system of defense linking the endocrine, the immune, and the repair responses of the organism. Renin-Angiotensin System The renin-angiotensin system (RAS) is crucial in the regulation of blood pressure and fluid-electrolyte homeostasis. 1,2 In the traditional view of the RAS, renin is released by the kidney juxtaglomerular cells, and on reaching the circulation, it acts on its only known substrate, angiotensinogen, produced mainly in the liver to yield angiotensin I (Ang I), a decapep-tide and Des-Ang I-angiotensinogen, a large molecule of unclear function. Thereafter, Ang I is hydrolyzed by angio-tensin-converting enzyme to yield the octapeptide Ang II, a fast acting and powerful vasoconstrictor that regulates peripheral vascular resistance, renal hemodynamics, and sodium reabsorption via several mechanisms, including the stimulation of aldosterone secretion by the adrenal glands. Most of the known cardiovascular and renal actions of the RAS are achieved by the actions of Ang II on its receptors, mainly AT1 receptors. It should be noted that for the system to operate properly, it needs to respond accurately and rapidly to changes in the composition and volume of the extracel-lular fluid and to variations in systemic blood pressure. The key regulated event in this enzymatic cascade is the tightly controlled, minute-to-minute regulation of renin release by the juxtaglomerular cells. This is possible because juxtaglo-merular cells are sensors strategically located in the juxtaglo-merular apparatus (JGA), where they receive and interpret signals that convey the composition and volume of the extra-cellular fluid and the level of perfusion pressure. The JGA is composed of the afferent and efferent arterioles, the macula densa, and the extraglomerular mesangium or polkissen. 1,3,4 In the adult unstressed mammalian kidney, juxtaglomerular cells are located in the afferent arteriole at the entrance to the glomerulus, where they make contact with macula densa cells, extraglomerular mesangial cells, and other renin and smooth muscle cells along the arteriole. 3,4 Juxtaglomerular cells have a myoepithelioid appearance; they are densely innervated by sympathetic terminals arising from the renal nerve; and they contain granules from where renin is stored and released in response to a diverse number of stimuli emanating from nearby cells, sympathetic terminal, and from the circulation. 5 Three major mechanisms control renin release by juxtaglomerular cells: (1) the renal baroreceptor mechanism, whereby renin release is elicited by a decrease in renal perfu-sion pressure as it occurs during hypotension, shock, hemorrhage , or cardiac failure. The nature of the renal baroreceptor has not been determined since its original 1959 description by Tobian et al, 6 (2) the macula densa mechanism, whereby renin release is stimulated by a decrease in sodium chloride in the distal tubule as it occurs during sodium depletion, and (3) the β-receptor-mediated mechanism, whereby stimulation of β-receptors elicited by sympathetic terminals or via circulating catecholamines such as during hypoxia results in increased renin release. Interestingly, the renal baroreceptor mechanism continues to function in the absence of the other 2 mechanisms: in the denervated, nonfiltering kidney, the barorecep-tor mechanism continues to operate suggesting that the renal baroreceptor mechanism is independent from the influence of the macula densa or the β-receptor. 2 Under normal circumstances , however, these mechanisms operate together to finely regulate renin output. For instance, the β-receptor mechanism, the baroreceptor mechanism, and the macula densa mechanism are all activated during hemorrhage, a situation where there is decreased perfusion pressure, decreased delivery of sodium chloride to the macula densa, and stimulation of the sympathetic system. It should be noted that Ang II exerts a negative feedback on renin release, a typical case where the byproduct of an enzymatic reaction controls its own production , in this case governed by the underlying physiological status of the animal. When angiotensin production and its actions are limited, such as when animals are exposed to angiotensin-converting enzyme inhibitors or AT1 receptor blockers, renin synthesis and release is increased. This is accomplished in great part by an increase in the number of cells that synthesize and release renin as described below. 7-9
... Other stud ies of pVHL inactivation in specific renal cell popu lations have revealed marked effects on differentiation. For instance, inactivation of the Vhl gene in the mouse using renin1d driven Cre recombinase resulted in aber rant expression of the Epo gene in cells that ordinarily produce renin 233 . In mouse podocytes, activation of HIF by Cre mediated inactivation of Vhl leads to a rapidly progressive glomerulonephritis, an effect that was attri buted, at least in part, to the increased expression of the HIF target gene Cxcr4 (reF. ...
Studies of the regulation of erythropoietin (EPO) production by the liver and kidneys, one of the classical physiological responses to hypoxia, led to the discovery of human oxygen-sensing mechanisms, which are now being targeted therapeutically. The oxygen-sensitive signal is generated by 2-oxoglutarate-dependent dioxygenases that deploy molecular oxygen as a co-substrate to catalyse the post-translational hydroxylation of specific prolyl and asparaginyl residues in hypoxia-inducible factor (HIF), a key transcription factor that regulates transcriptional responses to hypoxia. Hydroxylation of HIF at different sites promotes both its degradation and inactivation. Under hypoxic conditions, these processes are suppressed, enabling HIF to escape destruction and form active transcriptional complexes at thousands of loci across the human genome. Accordingly, HIF prolyl hydroxylase inhibitors stabilize HIF and stimulate expression of HIF target genes, including the EPO gene. These molecules activate endogenous EPO gene expression in diseased kidneys and are being developed, or are already in clinical use, for the treatment of renal anaemia. In this Review, we summarize information on the molecular circuitry of hypoxia signalling pathways underlying these new treatments and highlight some of the outstanding questions relevant to their clinical use.
