The transcription factor Tcf21 is required for specifying Foxd1 cells to the juxtaglomerular cell lineage

Renin is a crucial enzyme involved in the regulation of blood pressure and electrolyte balance. It has been shown that renin expressing cells arise from the Foxd1+ stromal progenitors, however the factors involved in guiding Foxd1+ cells towards the renin-secreting cell fate remain poorly understood. Tcf21, also known as Pod1 or Capsulin, is a bHLH transcription factor that is expressed in the metanephric mesenchyme and plays a crucial role in kidney development. We have previously shown that deletion of Tcf21 in Foxd1+ cells ( Foxd1 Cre/+ ;Tcf21 f/f ) results in paucity of vascular mural cells and in disorganized renal arterial tree with fewer, shorter, and thinner arterioles. Here, we sought to examine the relationship between Tcf21 and renin cells during kidney development and test whether Tcf21 is implicated in the regulation of juxtaglomerular cell differentiation. Immunostaining for renin demonstrated that kidneys of Foxd1 Cre/+ ;Tcf21 f/f have fewer renin-positive spots at E16.5 and E18.5 compared with controls. In-situ hybridization for renin mRNA showed reduced expression in Foxd1 Cre/+ ;Tcf21 f/f kidneys at E14.5, E16.5, and E18.5. Together, these data suggest that stromal expression of Tcf21 is required for the emergence of renin cells. To dissect the role of Tcf21 in juxtaglomerular (JG) cells, we deleted Tcf21 upon renin promoter activation ( Ren1 dCre/+ ;Tcf21 f/f ). Interestingly, the Ren1 dCre/+ ;Tcf21 f/f kidney showed normal arterial tree at E16.5 identical to controls. Furthermore, inactivation of Tcf21 upon renin expression did not alter kidney morphology in two- and four-month-old mice. Finally, expression renin mRNA was similar between Ren1 dCre/+ ;Tcf21 f/f and controls at 2 months. Taken together, these findings suggest that Tcf21 expression in Foxd1+ cells is essential for specifying the fate of these cells into juxtaglomerular cells. However, once renin cell identity is assumed, Tcf21 is dispensable. Uncovering the regulation of Foxd1+ cells and their derivatives, including the JG cell lineage, is crucial for understanding the mechanisms underlying renal vasculature formation.

Renin Cells, From Vascular Development to Blood Pressure Sensing

During embryonic and neonatal life, renin cells contribute to the assembly and branching of the intrarenal arterial tree. During kidney arteriolar development renin cells are widely distributed throughout the renal vasculature. As the arterioles mature, renin cells differentiate into smooth muscle cells, pericytes, and mesangial cells. In adult life, renin cells are confined to the tips of the renal arterioles, thus their name juxtaglomerular cells. Juxtaglomerular cells are sensors that release renin to control blood pressure and fluid-electrolyte homeostasis. Three major mechanisms control renin release: (1) β-adrenergic stimulation, (2) macula densa signaling, and (3) the renin baroreceptor, whereby a decrease in arterial pressure leads to increased renin release whereas an increase in pressure results in decrease renin release. Cells from the renin lineage exhibit plasticity in response to hypotension or hypovolemia, whereas relentless, chronic stimulation induces concentric arterial and arteriolar hypertrophy, leading to focal renal ischemia. The renin cell baroreceptor is a nuclear mechanotransducer within the renin cell that transmits external forces to the chromatin to regulate Ren1 gene expression. In addition to mechanotransduction, the pressure sensor of the renin cell may enlist additional molecules and structures including soluble signals and membrane proteins such as gap junctions and ion channels. How these various components integrate their actions to deliver the exact amounts of renin to meet the organism needs is unknown. This review describes the nature and origins of renin cells, their role in kidney vascular development and arteriolar diseases, and the current understanding of the blood pressure sensing mechanism.

Cells of the renin lineage promote kidney regeneration post-release of ureteral obstruction in neonatal mice

AIM

Ureteral obstruction leads to significant changes in kidney renin expression. It is unclear whether those changes are responsible for the progression of kidney damage, repair, or regeneration. In the current study, we aimed to elucidate the contribution of renin-producing cells (RPCs) and the cells of the renin lineage (CoRL) towards kidney damage and regeneration using a model of partial and reversible unilateral ureteral obstruction (pUUO) in neonatal mice.

METHODS

Renin cells are progenitors for other renal cell types collectively called CoRL. We labeled the CoRL with green fluorescent protein (GFP) using genetic approaches. We performed lineage tracing to analyze the changes in the distribution of CoRL during and after the release of obstruction. We also ablated the RPCs and CoRL by cell-specific expression of Diphtheria Toxin Sub-unit A (DTA). Finally, we evaluated the kidney damage and regeneration during and after the release of obstruction in the absence of CoRL.

RESULTS

In the obstructed kidneys, there was a 163% increase in the renin-positive area and a remarkable increase in the distribution of GFP+ CoRL. Relief of obstruction abrogated these changes. In addition, DTA-expressing animals did not respond to pUUO with increased RPCs and CoRL. Moreover, reduction in CoRL significantly compromised the kidney's ability to recover from the damage after the release of obstruction.

CONCLUSIONS

CoRL play a role in the regeneration of the kidneys post-relief of obstruction.

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.

Determinants of renin cell differentiation: a single cell epi-transcriptomics approach

Rationale

Renin cells are essential for survival. They control the morphogenesis of the kidney arterioles, and the composition and volume of our extracellular fluid, arterial blood pressure, tissue perfusion, and oxygen delivery. It is known that renin cells and associated arteriolar cells descend from FoxD1 + progenitor cells, yet renin cells remain challenging to study due in no small part to their rarity within the kidney. As such, the molecular mechanisms underlying the differentiation and maintenance of these cells remain insufficiently understood.

Objective

We sought to comprehensively evaluate the chromatin states and transcription factors (TFs) that drive the differentiation of FoxD1 + progenitor cells into those that compose the kidney vasculature with a focus on renin cells.

Methods and Results

We isolated single nuclei of FoxD1 + progenitor cells and their descendants from FoxD1 ^cre/+ ; R26R-mTmG mice at embryonic day 12 (E12) (n _cells =1234), embryonic day 18 (E18) (n _cells =3696), postnatal day 5 (P5) (n _cells =1986), and postnatal day 30 (P30) (n _cells =1196). Using integrated scRNA-seq and scATAC-seq we established the developmental trajectory that leads to the mosaic of cells that compose the kidney arterioles, and specifically identified the factors that determine the elusive, myo-endocrine adult renin-secreting juxtaglomerular (JG) cell. We confirm the role of Nfix in JG cell development and renin expression, and identified the myocyte enhancer factor-2 (MEF2) family of TFs as putative drivers of JG cell differentiation.

Conclusions

We provide the first developmental trajectory of renin cell differentiation as they become JG cells in a single-cell atlas of kidney vascular open chromatin and highlighted novel factors important for their stage-specific differentiation. This improved understanding of the regulatory landscape of renin expressing JG cells is necessary to better learn the control and function of this rare cell population as overactivation or aberrant activity of the RAS is a key factor in cardiovascular and kidney pathologies.

Comparative Studies of Renin-Null Zebrafish and Mice Provide New Functional Insights

BACKGROUND

The renin-angiotensin system is highly conserved across vertebrates, including zebrafish, which possess orthologous genes coding for renin-angiotensin system proteins, and specialized mural cells of the kidney arterioles, capable of synthesising and secreting renin.

METHODS

We generated zebrafish with CRISPR-Cas9-targeted knockout of renin (ren^-/-) to investigate renin function in a low blood pressure environment. We used single-cell (10×) RNA sequencing analysis to compare the transcriptome profiles of renin lineage cells from mesonephric kidneys of ren^-/- with ren^+/+ zebrafish and with the metanephric kidneys of Ren1^c-/- and Ren1^c+/+ mice.

RESULTS

The ren^-/- larvae exhibited delays in larval growth, glomerular fusion and appearance of a swim bladder, but were viable and withstood low salinity during early larval stages. Optogenetic ablation of renin-expressing cells, located at the anterior mesenteric artery of 3-day-old larvae, caused a loss of tone, due to diminished contractility. The ren^-/- mesonephric kidney exhibited vacuolated cells in the proximal tubule, which were also observed in Ren1^c-/- mouse kidney. Fluorescent reporters for renin and smooth muscle actin (tg(ren:LifeAct-RFP; acta2:EGFP)), revealed a dramatic recruitment of renin lineage cells along the renal vasculature of adult ren^-/- fish, suggesting a continued requirement for renin, in the absence of detectable angiotensin metabolites, as seen in the Ren1YFP Ren1^c-/- mouse. Both phenotypes were rescued by alleles lacking the potential for glycosylation at exon 2, suggesting that glycosylation is not essential for normal physiological function.

CONCLUSIONS

Phenotypic similarities and transcriptional variations between mouse and zebrafish renin knockouts suggests evolution of renin cell function with terrestrial survival.

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.

Patterns of differentiation of renin lineage cells during nephrogenesis

Developmentally heterogeneous renin expressing cells serve as progenitors for mural, glomerular and tubular cells during nephrogenesis and are collectively termed renin lineage cells (RLCs). In this study, we quantified different renal vascular and tubular cell types based on specific markers, assessed proliferation, and de-novo differentiation in the RLC population. We used kidney sections of mRenCre-mT/mG mice throughout nephrogenesis. Marker positivity was evaluated in whole digitalized sections. At embryonic day 16, RLCs appeared in the developing kidney, and expression of all stained markers in RLCs was observed. The proliferation rate of RLCs did not differ from the proliferation rate of non-RLCs. The RLCs expanded mainly by de-novo differentiation (neogenesis). The fractions of RLCs originating from the stromal progenitors of the metanephric mesenchyme (renin producing cells, vascular smooth muscle cells, mesangial cells) decreased during nephrogenesis. In contrast, aquaporin 2 positive RLCs in the collecting duct system that embryonically emerges almost exclusively from the ureteric bud, expanded postpartum. The cubilin positive RLC fraction in the proximal tubule, deriving from the cap mesenchyme, remained constant. During nephrogenesis, RLCs were continuously detectable in the vascular and tubular compartments of the kidney. Therein, various patterns of RLC differentiation that depend on the embryonic origin of the cells were identified.

Renin Cell Baroreceptor, a Nuclear Mechanotransducer Central for Homeostasis

[Figure: see text].

Vitamin D Deficiency Induces Macrophage Pro-Inflammatory Phenotype via ER Stress-Mediated Activation of Renin-Angiotensin System

Chronic inflammation and local activation of the renin-angiotensin-aldosterone system (RAAS) play a pivotal role in the pathogenesis and progression of diabetic complications. In patients with type 2 diabetes (T2DM), the prevalence of vitamin D deficiency is almost twice that of non-diabetics, and vitamin d deficiency nearly doubles the risk of developing hypertension and cardiovascular complications compared to diabetics with normal vitamin D levels. Interestingly, mice lacking the vitamin D receptor (VDR) in macrophages (KODMAC) develop renin-dependent hypertension, insulin resistance, and inflammation via up-regulation of macrophage ER stress. Macrophages also express all major components of the RAAS system. However, little is known about the regulation of macrophage-generated renin and its role in modulating the sequelae of VDR signaling in macrophage function and cytokine production. This study found that KODMAC macrophages and vitamin D-deficient macrophages have increased expression and secretion of renin, angiotensin II, ACE, and AT1 receptor and that adhesion, migration, and cytokine release were also increased. Inhibition of ER stress in KODMAC macrophages and vitamin D-deficient macrophages with 4-Phenylbutyric acid (PBA) reduced RAS gene expression and macrophage pro-inflammatory phenotype. Renin 1c gene deletion decreased macrophage adhesion, migration, and cytokine release compared to macrophages with disrupted VDR signaling. Notably, disruption of VDR signaling induced peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) expression in macrophages, and upregulation of renin expression in response to vitamin D deficiency was blunted in PCG1α-deficient macrophages. In conclusion, our findings delineate a mechanism by which impaired VDR signaling induces ER stress to drive PGC1α-dependent expression of renin and RAAS hyperactivation, thereby altering macrophage function and cytokine production. These data implicate RAAS as an essential mediator of VDR-mediated macrophage function and support ongoing investigations of VDR and RAAS modulation as therapeutic approaches in the management of T2DM and its complications.

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.

A primitive type of renin-expressing lymphocyte protects the organism against infections

The hormone renin plays a crucial role in the regulation of blood pressure and fluid-electrolyte homeostasis. Normally, renin is synthesized by juxtaglomerular (JG) cells, a specialized group of myoepithelial cells located near the entrance to the kidney glomeruli. In response to low blood pressure and/or a decrease in extracellular fluid volume (as it occurs during dehydration, hypotension, or septic shock) JG cells respond by releasing renin to the circulation to reestablish homeostasis. Interestingly, renin-expressing cells also exist outside of the kidney, where their function has remained a mystery. We discovered a unique type of renin-expressing B-1 lymphocyte that may have unrecognized roles in defending the organism against infections. These cells synthesize renin, entrap and phagocyte bacteria and control bacterial growth. The ability of renin-bearing lymphocytes to control infections-which is enhanced by the presence of renin-adds a novel, previously unsuspected dimension to the defense role of renin-expressing cells, linking the endocrine control of circulatory homeostasis with the immune control of infections to ensure survival.

Deciphering the Identity of Renin Cells in Health and Disease

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.

Ontogeny of renin gene expression in the chicken, Gallus gallus

Renin or a renin-like enzyme evolved in ancestral vertebrates and is conserved along the vertebrate phylogeny. The ontogenic development of renin, however, is not well understood in nonmammalian vertebrates. We aimed to determine the expression patterns and relative abundance of renin mRNA in pre- and postnatal chickens (Gallus gallus, White Leghorn breed). Embryonic day 13 (E13) embryos show renal tubules, undifferentiated mesenchymal structures, and a small number of developing glomeruli. Maturing glomeruli are seen in post-hatch day 4 (D4) and day 30 (D30) kidneys, indicating that nephrogenic activity still exists in kidneys of 4-week-old chickens. In E13 embryos, renin mRNA measured by quantitative polymerase chain reaction in the adrenal glands is equivalent to the expression in the kidneys, whereas in post-hatch D4 and D30 maturing chicks, renal renin expressions increased 2-fold and 11-fold, respectively. In contrast, relative renin expression in the adrenals became lower than in the kidneys. Furthermore, renin expression is clearly visible by in situ hybridization in the juxtaglomerular (JG) area in D4 and D30 chicks, but not in E13 embryos. The results suggest that in chickens, renin evolved in both renal and extrarenal organs at an early stage of ontogeny and, with maturation, became localized to the JG area. Clear JG structures are not morphologically detectable in E13 embryos, but are visible in 30-day-old chicks, supporting this concept.

Expression of Acsm2, a kidney-specific gene, parallels the function and maturation of proximal tubular cells

The acyl-CoA synthetase medium-chain family member 2 (Acsm2) gene was first identified and cloned by our group as a kidney-specific "KS" gene. However, its expression pattern and function remain to be clarified. In the present study, we found that the Acsm2 gene was expressed specifically and at a high level in normal adult kidneys. Expression of Acsm2 in kidneys followed a maturational pattern: it was low in newborn mice and increased with kidney development and maturation. In situ hybridization and immunohistochemistry revealed that Acsm2 was expressed specifically in proximal tubular cells of adult kidneys. Data from the Encyclopedia of DNA Elements database revealed that the Acsm2 gene locus in the mouse has specific histone modifications related to the active transcription of the gene exclusively in kidney cells. Following acute kidney injury, partial unilateral ureteral obstruction, and chronic kidney diseases, expression of Acsm2 in the proximal tubules was significantly decreased. In human samples, the expression pattern of ACSM2A, a homolog of mouse Acsm2, was similar to that in mice, and its expression decreased with several types of renal injuries. These results indicate that the expression of Acsm2 parallels the structural and functional maturation of proximal tubular cells. Downregulation of its expression in several models of kidney disease suggests that Acms2 may serve as a novel marker of proximal tubular injury and/or dysfunction.

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.

Ctcf is required for renin expression and maintenance of the structural integrity of the kidney

Renin cells are crucial for the regulation of blood pressure and fluid electrolyte homeostasis. We have recently shown that renin cells possess unique chromatin features at regulatory regions throughout the genome that may determine the identity and memory of the renin phenotype. The 3-D structure of chromatin may be equally important in the determination of cell identity and fate. CCCTC-binding factor (Ctcf) is a highly conserved chromatin organizer that may regulate the renin phenotype by controlling chromatin structure. We found that Ctcf binds at several conserved DNA sites surrounding and within the renin locus, suggesting that Ctcf may regulate the transcriptional activity of renin cells. In fact, deletion of Ctcf in cells of the renin lineage led to decreased endowment of renin-expressing cells accompanied by decreased circulating renin, hypotension, and severe morphological abnormalities of the kidney, including defects in arteriolar branching, and ultimately renal failure. We conclude that control of chromatin architecture by Ctcf is necessary for the appropriate expression of renin, control of renin cell number and structural integrity of the kidney.

Renin-Expressing Cells Require β1-Integrin for Survival and for Development and Maintenance of the Renal Vasculature

Juxtaglomerular cells are crucial for blood pressure and fluid-electrolyte homeostasis. The factors that maintain the life of renin cells are unknown. In vivo, renin cells receive constant cell-to-cell, mechanical, and neurohumoral stimulation that maintain their identity and function. Whether the presence of this niche is crucial for the vitality of the juxtaglomerular cells is unknown. Integrins are the largest family of cell adhesion molecules that mediate cell-to-cell and cell-to-matrix interactions. Of those, β1-integrin is the most abundant in juxtaglomerular cells. However, its role in renin cell identity and function has not been ascertained. To test the hypothesis that cell-matrix interactions are fundamental not only to maintain the identity and function of juxtaglomerular cells but also to keep them alive, we deleted β1-integrin in vivo in cells of the renin lineage. In mutant mice, renin cells died by apoptosis, resulting in decreased circulating renin, hypotension, severe renal-vascular abnormalities, and renal failure. Results indicate that cell-to-cell and cell-to-matrix interactions via β1-integrin is essential for juxtaglomerular cells survival, suggesting that the juxtaglomerular niche is crucial not only for the tight regulation of renin release but also for juxtaglomerular cell survival-a sine qua non condition to maintain homeostasis.

Pannexin 1 channels in renin-expressing cells influence renin secretion and blood pressure homeostasis

Kidney function and blood pressure homeostasis are regulated by purinergic signaling mechanisms. These autocrine/paracrine signaling pathways are initiated by the release of cellular ATP, which influences kidney hemodynamics and steady-state renin secretion from juxtaglomerular cells. However, the mechanism responsible for ATP release that supports tonic inputs to juxtaglomerular cells and regulates renin secretion remains unclear. Pannexin 1 (Panx1) channels localize to both afferent arterioles and juxtaglomerular cells and provide a transmembrane conduit for ATP release and ion permeability in the kidney and the vasculature. We hypothesized that Panx1 channels in renin-expressing cells regulate renin secretion in vivo. Using a renin cell-specific Panx1 knockout model, we found that male Panx1 deficient mice exhibiting a heightened activation of the renin-angiotensin-aldosterone system have markedly increased plasma renin and aldosterone concentrations, and elevated mean arterial pressure with altered peripheral hemodynamics. Following ovariectomy, female mice mirrored the male phenotype. Furthermore, constitutive Panx1 channel activity was observed in As4.1 renin-secreting cells, whereby Panx1 knockdown reduced extracellular ATP accumulation, lowered basal intracellular calcium concentrations and recapitulated a hyper-secretory renin phenotype. Moreover, in response to stress stimuli that lower blood pressure, Panx1-deficient mice exhibited aberrant "renin recruitment" as evidenced by reactivation of renin expression in pre-glomerular arteriolar smooth muscle cells. Thus, renin-cell Panx1 channels suppress renin secretion and influence adaptive renin responses when blood pressure homeostasis is threatened.

Super-enhancers maintain renin-expressing cell identity and memory to preserve multi-system homeostasis

Renin cells are crucial for survival - they control fluid-electrolyte and blood pressure homeostasis, vascular development, regeneration, and oxygen delivery to tissues. During embryonic development, renin cells are progenitors for multiple cell types that retain the memory of the renin phenotype. When there is a threat to survival, those descendants are transformed and reenact the renin phenotype to restore homeostasis. We tested the hypothesis that the molecular memory of the renin phenotype resides in unique regions and states of these cells' chromatin. Using renin cells at various stages of stimulation, we identified regions in the genome where the chromatin is open for transcription, mapped histone modifications characteristic of active enhancers such as H3K27ac, and tracked deposition of transcriptional activators such as Med1, whose deletion results in ablation of renin expression and low blood pressure. Using the rank ordering of super-enhancers, epigenetic rewriting, and enhancer deletion analysis, we found that renin cells harbor a unique set of super-enhancers that determine their identity. The most prominent renin super-enhancer may act as a chromatin sensor of signals that convey the physiologic status of the organism, and is responsible for the transformation of renin cell descendants to the renin phenotype, a fundamental process to ensure homeostasis.

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.

Abstract 015: Ctcf is Required for Renin Expression and Maintenance of the Structural Integrity of the Kidney

Renin is crucial for the regulation of blood pressure and fluid electrolyte homeostasis. The transcriptional machinery that regulates renin expression and thus determines the identity of renin cells is not completely understood. CCCTC-binding factor ( Ctcf ), is an important chromatin organizer of genes that confer cell identity and tissue-specificity. Because Ctcf binds to several sites in the neighborhood of the renin locus, we hypothesized that Ctcf may regulate renin expression. To test this hypothesis, we generated mice with conditional deletion of Ctcf in cells of the renin lineage ( Ctcf cKO). Ctcf cKO mice showed fewer renin-positive cells as shown by immunostaining, and a 70% reduction of renin mRNA levels when compared to control mice (0.292 ± 0.246 vs 1.003 ± 0.097, p<0.001 ). In addition, plasma renin levels were significantly decreased in Ctcf cKO versus control mice (15276.544 ± 6778.735 pg/ml vs 62321.62 ± 21881.99 pg/ml, p<0.001 ). Consistent with reduced renin levels, Ctcf cKO mice had lower mean arterial pressures (60.09 ± 3.12 mmHg vs 75.07 ± 3.06 mmHg, p<0.001 ). The kidney/body weight ratio in Ctcf cKO mice was markedly reduced (1.05 ± 0.228 % vs 1.29 ± 0.074 %, p<0.05 ), indicating a more pronounced effect in kidney than in somatic growth (20.09 ± 1.47 g vs 22.95 ± 2.95 g, p<0.05 ). Masson’s trichrome staining revealed interstitial fibrosis coinciding with cortical depressions in Ctcf cKO kidneys. Moreover, PAS staining of Ctcf cKO kidneys showed dilated tubules with intraluminal casts, and areas with crowded sclerotic and crescent glomeruli surrounded by disorganized packed cells. Finally, Ctcf cKO mice exhibited renal failure evidenced by increased BUN (44.29 ± 17.62 mg/dL vs 26 ± 3.39 mg/dL, p<0.05) , and inability to concentrate their urine (448 ± 85.57 mOsm/kg vs 1519.33 ± 382.39 mOsm/kg, p<0.001 ). In summary, deletion of Ctcf in cells from the renin lineage leads to decreased endowment of renin-expressing cells accompanied by decreased circulating renin, hypotension, severe morphological abnormalities of the kidney and ultimately renal failure. We conclude that Ctcf is necessary for the appropriate expression of renin, control of renin cell number and structural integrity of the kidney.

Abstract 013: The Molecular Program of Renin Null Cells

Mice homozygous for the Ren1c gene disruption ( Ren1c -/- ) display structural and functional defects characterized by a poorly developed renal medulla, urine concentration failure, polydipsia, polyuria, hydronephrosis, renal failure and anemia. Underlying this complex phenotype, mice exhibit unique renal vascular abnormalities, including concentric arteriolar hypertrophy. Using lineage and promoter activity tracking, we showed that renin null cells contribute directly to blood vessel thickening and distribute throughout renal arterial trees. We hypothesize that renin null cells synthesize factors that lead to arterial thickening and maintain an active molecular memory of the renin phenotype.

To test this hypothesis, we performed RNA-seq of YFP sorted single cells from kidneys of Ren1c -/- ; Ren1c -YFP (KO) and Ren1c +/+ ; Ren1c -YFP (wildtype, WT) adult mice. We captured individual cells using a microfluidic C1 system and sequenced cDNA from cellular mRNA. We also performed ATAC-seq of KO cells to identify open chromatin regions available for transcription factor binding.

KO and WT cell populations were distinct, with the average Euclidean distance between genotypes 1.9x greater than within genotypes. Differential expression analysis revealed that KO cells upregulated 1395 genes and downregulated 364 compared to WT (log fold change > 1, p < 0.05). Among the upregulated genes were 107 potentially secreted proteins and 64 putative transcription factors. Secreted protein genes were enriched for GO terms such as angiogenesis and cell proliferation (p < 0.01), suggesting a possible cause of arteriolar abnormalities in KO kidneys. We identified several upregulated transcription factors, including Foxp1, Stat1, and KLF family genes, that had predicted binding motifs in open chromatin regions, such as upstream the Ren1 gene (p < 1.0E-10). These factors are key candidates for regulating the molecular memory of the renin cell.

This study shows that over activation of the renin program due to lack of renin causes expression of a distinct suite of genes that may be responsible for vascular pathologies observed in KO mice. These data also provide insight into how the cell regulates the renin cell program in response to chronic stimuli that jeopardize homeostasis.

Plasticity of Renin Cells in the Kidney Vasculature

During development, renin cells are precursors for arteriolar smooth muscle, mesangial cells, and interstitial pericytes. Those seemingly differentiated descendants retain the memory to re-express renin when there is a threat to homeostasis. Understanding how such molecular memory is constructed and regulated would be crucial to comprehend cell identity which is, in turn, intimately linked to homeostasis.

Persistent and inducible neogenesis repopulates progenitor renin lineage cells in the kidney

Renin lineage cells (RLCs) serve as a progenitor cell reservoir during nephrogenesis and after renal injury. The maintenance mechanisms of the RLC pool are still poorly understood. Since RLCs were also identified as a progenitor cell population in bone marrow we first considered that these may be their source in the kidney. However, transplantation experiments in adult mice demonstrated that bone marrow-derived cells do not give rise to RLCs in the kidney indicating their non-hematopoietic origin. Therefore we tested whether RLCs develop in the kidney through neogenesis (de novo differentiation) from cells that have never expressed renin before. We used a murine model to track neogenesis of RLCs by flow cytometry, histochemistry, and intravital kidney imaging. During nephrogenesis RLCs first appear at e14, form a distinct population at e16, and expand to reach a steady state level of 8-10% of all kidney cells in adulthood. De novo differentiated RLCs persist as a clearly detectable population through embryogenesis until at least eight months after birth. Pharmacologic stimulation of renin production with enalapril or glomerular injury induced the rate of RLC neogenesis in the adult mouse kidney by 14% or more than three-fold, respectively. Thus, the renal RLC niche is constantly filled by local de novo differentiation. This process could be stimulated consequently representing a new potential target to beneficially influence repair and regeneration after kidney injury.

Tracking the stochastic fate of cells of the renin lineage after podocyte depletion using multicolor reporters and intravital imaging

Podocyte depletion plays a major role in focal segmental glomerular sclerosis (FSGS). Because cells of the renin lineage (CoRL) serve as adult podocyte and parietal epithelial cell (PEC) progenitor candidates, we generated Ren1cCre/R26R-ConfettiTG/WT and Ren1dCre/R26R-ConfettiTG/WT mice to determine CoRL clonality during podocyte replacement. Four CoRL reporters (GFP, YFP, RFP, CFP) were restricted to cells in the juxtaglomerular compartment (JGC) at baseline. Following abrupt podocyte depletion in experimental FSGS, all four CoRL reporters were detected in a subset of glomeruli at day 28, where they co-expressed de novo four podocyte proteins (podocin, nephrin, WT-1 and p57) and two glomerular parietal epithelial cell (PEC) proteins (claudin-1, PAX8). To monitor the precise migration of a subset of CoRL over a 2w period following podocyte depletion, intravital multiphoton microscopy was used. Our findings demonstrate direct visual support for the migration of single CoRL from the JGC to the parietal Bowman's capsule, early proximal tubule, mesangium and glomerular tuft. In summary, these results suggest that following podocyte depletion, multi-clonal CoRL migrate to the glomerulus and replace podocyte and PECs in experimental FSGS.

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.

Abstract P191: The Origin and Fate of Renin Progenitors During Hematopoiesis

Our lab previously discovered the presence of novel renin-expressing progenitors within the hematopoietic system. These progenitors have cell surface markers, gene expression, and growth characteristics of B lymphocytes. Further, these cells represent a subset of total B lymphocytes, are numerous at birth, and diminish with age, suggesting renin expression may be prominent during embryonic hematopoiesis. However, it is unknown when renin progenitors first appear and what function they serve during hematopoietic development. In this study, we sought to further define the temporal appearance, identity, and evolution of renin progenitors throughout hematopoietic ontogeny. We used in vivo lineage-tracing techniques, flow cytometry, immunofluorescence, and polymerase chain reaction (PCR) analysis to investigate the origin and fate of renin hematopoietic progenitors. We found that renin expressing hematopoietic progenitors first appear within the yolk sac during mid gestation (E11.5 by PCR and E12.5 by flow cytometry) and peak in number at E13.5 (14.9 ± 4.8% of nucleated single cells by flow cytometry). Subsequently, renin lineage cells leave the yolk sac and colonize the fetal liver and spleen at E15.5. In the fetal liver and fetal spleen, renin lineage cells express B cell surface markers including CD19 and CD43, however they have dim B220 expression, consistent with a B-1 progenitor immunophenotype. Renin lineage cells within the bone marrow, spleen, and peripheral blood peak in number shortly after birth and then decrease with post-natal age and have a phenotype consistent with B-2 B lymphocytes (B220 + CD19 + CD23 + CD11b - ). Conversely, renin progenitors in the peritoneal cavity persist throughout adult life as B-1 B cells (B220 dim CD19 + CD23 - CD11b + ). These studies suggest that renin progenitors originate within the yolk sac during the initial wave of primitive B lymphopoiesis and then expand to the fetal liver and spleen prior to the development of definitive hematopoiesis. Renin-lineage cells persist during adult life as B-1 B cells in the peritoneal cavity and, to a lesser extent, as B-2 B cells in the bone marrow, spleen, and peripheral blood. The function of these renin progenitors is currently being investigated.

Abstract 066: Enhancer Repertoires That Define Renin Cell Identity

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

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

Renin is a key enzyme/hormone that controls blood pressure and fluid-electrolyte homeostasis. Renin transcription is subject to complex developmental, physiological, and pathological regulation. We have identified the cAMP pathway and associated epigenetic marks as crucial regulators of renin expression. However, those studies involved the use of cAMP activators or analogues or histone deacetylase inhibitors that alter the transcriptome and epigenome of the whole cell without exclusively targeting the renin locus.

The CRISPR/Cas9 Type II bacterial immune system has been modified for genome editing in eukaryotes. This system consists of a CRISPR-associated endonuclease (Cas9) and single guide RNA (sgRNA) to target specific genomic areas. Modifications to the Cas9 enzyme have allowed the use of CRISPR to regulate gene expression by targeted modification of epigenetic marks.

In this study we tested whether renin expression can be induced by a nuclease-null dCas9 protein fused to the catalytic core of the acetyltransferase p300 (dCas9p300) and sgRNAs directed to the renin promoter and enhancer.

We used cultured arteriolar smooth muscle cells of the renin lineage that constitutively express CFP (a renin lineage marker) and YFP only when the renin gene is turned on. Cells were transfected with a dCas9p300 and sgRNA expression vectors and analyzed for YFP expression 48h after transfection.

We tested four sgRNAs targeting the renin enhancer and five sgRNAs targeting the renin promoter either individually or in combination. We found few YFP+ cells when all 4 enhancer sgRNAs or 5 promoter sgRNAs were simultaneously used. The highest YFP expression (32±9 cells/well) was observed when two enhancer sgRNAs (at positions -2,757 and -2,631) and three promoter sgRNAs (at positions -719, -50 and -25) were simultaneously added to the cells. We did not find any YFP+ cells when the dCas9p300 plasmid was transfected without sgRNAs or when cells were transfected with a control plasmid.

Our data support targeted acetylation as a causal mechanism of renin transactivation. CRISPR/Cas9 provides a tool to study the regulation of renin expression by targeting epigenetic marks in the promoter and enhancer of renin.

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

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

Abstract 010: CD44 and CD44+ Cells are Dispensable for the Recruitment of Renin Expressing Cells

In response to a homeostatic stress the number of cells that make renin increases dramatically along the renal arteriolar tree resembling the embryonic pattern. We have shown that this “recruitment” occurs by re-expression of renin in smooth muscle cells that differentiated from embryonic renin cells. A recent study proposed that during recruitment, renal CD44+ mesenchymal stem-like cells can differentiate into juxtaglomerular (JG)-like renin-producing cells. To test such hypothesis, we assessed the distribution and role of CD44+ cells in renin cell recruitment. Mice with homozygous (KO) and heterozygous (het) deletion of CD44 (knockin for LacZ) were treated with low-sodium diet (0.05%) plus captopril (0.5 g/l) for 10 days (n: 9 treated, 7 controls). Body and kidney weights and BP were not different between KO and het mice. BUN and creatinine were significantly increased in both KO and Het treated mice. The number of renin expressing cells in the kidney and circulating renin increased similarly in treated mice (ELISA, untreated: het 131,503 ± 19,319 pg/mL vs KO 84,714 ± 29,065 pg/mL p=0.2517; treated: het 367,850 ± 38,189 pg/mL vs KO 495,120 ± 80,311 pg/mL p=0.2311). Interestingly, immunostaining for CD44 was negative in kidneys of untreated and treated wild type mice. We occasionally observed in CD44-LacZ het or KO mice isolated LacZ positive cells inside the glomeruli (1 or less per sagittal kidney section) and none in the JG area. On the other hand, immunostaining for CD44 on kidney sections of Ren1cKO mice revealed positive cells within perivascular infiltrates. To confirm these results we performed qRT-PCR for CD44 on kidney samples from CD44 het and KO treated, untreated, control, and Ren1cKO mice. CD44 mRNA expression confirmed the histological findings. In summary: 1) CD44 is dispensable for renin expression and recruitment, and 2) CD44+ cells do not contribute to the pool of renin expressing cells in the kidney during basal conditions or in response to a homeostatic stress as previously suggested. However, they do participate in the inflammatory process observed surrounding the vessels in mice with deletion of the renin gene, suggesting that they derived from the circulation and not from the kidney.

Estrogen Receptor α Is Required for Maintaining Baseline Renin Expression

Enzymatic cleavage of angiotensinogen by renin represents the critical rate-limiting step in the production of angiotensin II, but the mechanisms regulating the initial expression of the renin gene remain incomplete. The purpose of this study is to unravel the molecular mechanism controlling renin expression. We identified a subset of nuclear receptors that exhibited an expression pattern similar to renin by reanalyzing a publicly available microarray data set. Expression of some of these nuclear receptors was similarly regulated as renin in response to physiological cues, which are known to regulate renin. Among these, only estrogen receptor α (ERα) and hepatic nuclear factor α have no known function in regulating renin expression. We determined that ERα is essential for the maintenance of renin expression by transfection of small interfering RNAs targeting Esr1, the gene encoding ERα, in renin-expressing As4.1 cells. We also observed that previously characterized negative regulators of renin expression, Nr2f2 and vitamin D receptor, exhibited elevated expression in response to ERα inhibition. Therefore, we tested whether ERα regulates renin expression through an interaction with Nr2f2 and vitamin D receptor. Renin expression did not return to baseline when we concurrently suppressed both Esr1 and Nr2f2 or Esr1 and vitamin D receptor mRNAs, strongly suggesting that Esr1 regulates renin expression independent of Nr2f2 and vitamin D receptor. ERα directly binds to the hormone response element within the renin enhancer region. We conclude that ERα is a previously unknown regulator of renin that directly binds to the renin enhancer hormone response element sequence and is critical in maintaining renin expression in renin-expressing As4.1 cells.

Identification of renin progenitors in the mouse bone marrow that give rise to B-cell leukaemia

The cell of origin and triggering events for leukaemia are mostly unknown. Here we show that the bone marrow contains a progenitor that expresses renin throughout development and possesses a B-lymphocyte pedigree. This cell requires RBP-J to differentiate. Deletion of RBP-J in these renin-expressing progenitors enriches the precursor B-cell gene programme and constrains lymphocyte differentiation, facilitated by H3K4me3 activating marks in genes that control the pre-B stage. Mutant cells undergo neoplastic transformation, and mice develop a highly penetrant B-cell leukaemia with multi-organ infiltration and early death. These renin-expressing cells appear uniquely vulnerable as other conditional models of RBP-J deletion do not result in leukaemia. The discovery of these unique renin progenitors in the bone marrow and the model of leukaemia described herein may enhance our understanding of normal and neoplastic haematopoiesis.

Loss of Jagged1 in renin progenitors leads to focal kidney fibrosis

The Notch signaling pathway is required to maintain renin expression within juxtaglomerular (JG) cells. However, the specific ligand which activates Notch signaling in renin-expressing cells remains undefined. In this study, we found that among all Notch ligands, Jagged1 is differentially expressed in renin cells with higher expression during neonatal life. We therefore hypothesized that Jagged1 was involved in renin expression and/or vascular integrity. We used a conditional knockout approach to delete Jagged1 in cells of the renin lineage. Deletion of Jagged1 specifically within renin cells did not result in decreased renin production within the kidney. However, animals with conditional deletion of Jagged1 did develop focal kidney fibrosis and elevated blood urea nitrogen. Our data demonstrate that Jagged1-mediated Notch signaling is dispensable in renin cells of the kidney in regard to renin expression. However, deletion of Jagged1 in renin cells descendants affects perivascular–interstitial integrity leading to focal fibrosis and diminished renal function.

Hemovascular Progenitors in the Kidney Require Sphingosine-1-Phosphate Receptor 1 for Vascular Development

The close relationship between endothelial and hematopoietic precursors during early development of the vascular system suggested the possibility of a common yet elusive precursor for both cell types. Whether similar or related progenitors for endothelial and hematopoietic cells are present during organogenesis is unclear. Using inducible transgenic mice that specifically label endothelial and hematopoietic precursors, we performed fate-tracing studies combined with colony-forming assays and crosstransplantation studies. We identified a progenitor, marked by the expression of helix-loop-helix transcription factor stem cell leukemia (SCL/Tal1). During organogenesis of the kidney, SCL/Tal1(+) progenitors gave rise to endothelium and blood precursors with multipotential colony-forming capacity. Furthermore, appropriate morphogenesis of the kidney vasculature, including glomerular capillary development, arterial mural cell coating, and lymphatic vessel development, required sphingosine 1-phosphate (S1P) signaling via the G protein-coupled S1P receptor 1 in these progenitors. Overall, these results show that SCL/Tal1(+) progenitors with hemogenic capacity originate and differentiate within the early embryonic kidney by hemovasculogenesis (the concomitant formation of blood and vessels) and underscore the importance of the S1P pathway in vascular development.

Abstract MP01: Vascular versus Tubular Renin: Role in Kidney Development

Renin, the key regulated enzyme of the renin angiotensin system regulates blood pressure and fluid electrolyte homeostasis as well as morphogenesis of the kidney. Classically, renin is synthesized and released from juxtaglomerular cells located in the afferent arterioles at the entrance to the glomeruli. It has also been suggested that renin may also be synthesized by tubular cells. Interestingly, whole body deletion of the renin gene results in striking vascular and tubular abnormalities, hydronephrosis and a urine-concentrating defect. Given the complexity of such phenotype, it has not been possible to discriminate the relative contributions of vascular versus tubular renin. To investigate the relative contribution of renin in the vascular versus tubular compartments during kidney development we deleted renin independently in either compartment by crossing Ren1cfl/fl mice to Foxd1-cre or to Hoxb7-cre mice. We performed blood chemistries, histological analysis, immunostaining for specific cell markers, total kidney renin mRNA quantification and ELISA for renin in plasma. Vascular deletion of renin (Foxd1 lineage) resulted in neonatal mortality that could be rescued with daily injections of saline suggesting that this phenotype is due to an inability to concentrate the urine and improper medullary development. These mice showed absence of renal renin and negligible levels of plasma renin. Histologically, the kidneys had abnormal development of its arterioles, which became progressively thickened by disorganized, concentric hypertrophy of smooth muscle cells and marked hydronephrosis. On the other hand, lack of renin in the collecting ducts (Hoxb7 descendants) did not affect kidney morphology, intra-renal renin distribution, kidney renin mRNA expression or circulating renin during basal conditions or in response to a homeostatic stress such as low sodium diet. We conclude that renin generated in the renal vascular compartment is fundamental for the development and integrity of the kidney whereas the presence of renin in the collecting duct system is dispensable for normal kidney development and cannot compensate for the lack of renin in the vascular compartment. Further, the main source of circulating renin is the kidney vasculature.

Vascular versus tubular renin: role in kidney development

Renin, the key regulated enzyme of the renin-angiotensin system regulates blood pressure, fluid-electrolyte homeostasis, and renal morphogenesis. Whole body deletion of the renin gene results in severe morphological and functional derangements, including thickening of renal arterioles, hydronephrosis, and inability to concentrate the urine. Because renin is found in vascular and tubular cells, it has been impossible to discern the relative contribution of tubular versus vascular renin to such a complex phenotype. Therefore, we deleted renin independently in the vascular and tubular compartments by crossing Ren1(c fl/fl) mice to Foxd1-cre and Hoxb7-cre mice, respectively. Deletion of renin in the vasculature resulted in neonatal mortality that could be rescued with daily injections of saline. The kidneys of surviving mice showed the absence of renin, hypertrophic arteries, hydronephrosis, and negligible levels of plasma renin. In contrast, lack of renin in the collecting ducts did not affect kidney morphology, intra-renal renin, or circulating renin in basal conditions or in response to a homeostatic stress, such as sodium depletion. We conclude that renin generated in the renal vasculature is fundamental for the development and integrity of the kidney, whereas renin in the collecting ducts is dispensable for normal kidney development and cannot compensate for the lack of renin in the vascular compartment. Further, the main source of circulating renin is the kidney vasculature.

Aldo-keto reductase 1b7, a novel marker for renin cells, is regulated by cyclic AMP signaling

We previously identified aldo-keto reductase 1b7 (AKR1B7) as a marker for juxtaglomerular renin cells in the adult mouse kidney. However, the distribution of renin cells varies dynamically, and it was unknown whether AKR1B7 maintains coexpression with renin in response to different developmental, physiological, and pathological situations, and furthermore, whether similar factor(s) simultaneously regulate both proteins. We show here that throughout kidney development, AKR1B7 expression-together with renin-is progressively restricted in the kidney arteries toward the glomerulus. Subsequently, when formerly renin-expressing cells reacquire renin expression, AKR1B7 is reexpressed as well. This pattern of coexpression persists in extreme pathological situations, such as deletion of the genes for aldosterone synthase or Dicer. However, the two proteins do not colocalize within the same organelles: renin is found in the secretory granules, whereas AKR1B7 localizes to the endoplasmic reticulum. Interestingly, upon deletion of the renin gene, AKR1B7 expression is maintained in a pattern mimicking the embryonic expression of renin, while ablation of renin cells resulted in complete abolition of AKR1B7 expression. Finally, we demonstrate that AKR1B7 transcription is controlled by cAMP. Cultured cells of the renin lineage reacquire the ability to express both renin and AKR1B7 upon elevation of intracellular cAMP. In vivo, deleting elements of the cAMP-response pathway (CBP/P300) results in a stark decrease in AKR1B7- and renin-positive cells. In summary, AKR1B7 is expressed within the renin cell throughout development and perturbations to homeostasis, and AKR1B7 is regulated by cAMP levels within the renin cell.

Deletion of the miR-143/145 cluster leads to hydronephrosis in mice

Obstructive nephropathy, the leading cause of kidney failure in children, can be anatomic or functional. The underlying causes of functional hydronephrosis are not well understood. miRNAs, which are small noncoding RNAs, regulate gene expression at the post-transcriptional level. We found that miR-145-5p, a member of the miR-143/145 cluster that is highly expressed in smooth muscle cells of the renal vasculature, was present in the pelvicalyceal system and the ureter. To evaluate whether the miR-143/145 cluster is involved in urinary tract function we performed morphologic, functional, and gene expression studies in mice carrying a whole-body deletion of miR-143/145. miR-143/145-deficient mice developed hydronephrosis, characterized by severe papillary atrophy and dilatation of the pelvicalyceal system without obvious physical obstruction. Moreover, mutant mice showed abnormal ureteral peristalsis. The number of ureter contractions was significantly higher in miR-143/145-deficient mice. Peristalsis was replaced by incomplete, short, and more frequent contractions that failed to completely propagate in a proximal-distal direction. Microarray analysis showed 108 differentially expressed genes in ureters of miR-143/145-deficient mice. Ninety genes were up-regulated and 18 genes were down-regulated, including genes with potential regulatory roles in smooth muscle contraction and extracellular matrix-receptor interaction. We show that miR-143/145 are important for the normal peristalsis of the ureter and report an association between the expression of these miRNAs and hydronephrosis.

The earliest metanephric arteriolar progenitors and their role in kidney vascular development

The development of the kidney arterioles is poorly understood. Mature arterioles contain several functionally and morphologically distinct cell types, including smooth muscle, endothelial, and juxtaglomerular cells, and they are surrounded by interconnected pericytes, fibroblasts, and other interstitial cells. We have shown that the embryonic kidney possesses all of the necessary precursors for the development of the renal arterial tree, and those precursors assemble in situ to form the kidney arterioles. However, the identity of those precursors was unclear. Within the embryonic kidney, several putative progenitors marked by the expression of either the winged-forkhead transcription factor 1 (Foxd1+ progenitor), the aspartyl-protease renin (Ren+ progenitor), and/or hemangioblasts (Scl+ progenitor) are likely to differentiate and endow most of the cells of the renal arterial tree. However, the lineage relationships and the role of these distinct progenitors in renal vascular morphogenesis have not been delineated. We, therefore, designed a series of experiments to ascertain the hierarchical lineage relationships between Foxd1+ and Ren+ progenitors and the role of these two precursors in the morphogenesis and patterning of the renal arterial tree. Results show that 1) Foxd1+ cells are the precursors for all the mural cells (renin cells, smooth muscle cells, perivascular fibroblasts, and pericytes) of the renal arterial tree and glomerular mesangium, and 2) Foxd1 per se directs the origin, number, orientation, and cellular composition of the renal vessels.

Abstract 040: Cells of the Renin Lineage in the Peritoneal Cavity

Renin cells have been traditionally associated with the control of blood pressure and fluid/electrolyte homeostasis. We recently described the presence of renin-expressing cells in the bone marrow, spleen and blood of mice. These cells are B-lymphocyte progenitors and show remarkable developmental, biochemical/transcriptional and functional similarities with the seemingly more distant kidney renin cell. While the function of these B renin cells within hematopoietic tissues remains unknown, we found that these progenitors are a vulnerable population for leukemic transformation: deletion of the Notch effector RBP-J within renin-expressing cells in mice leads to development of B-cell leukemia. Given their medical relevance, we sought to fully characterize the identity of renin cell descendants within the hematopoietic system. We generated Ren1 dcre/ + ; mT/mG mice which after Cre -mediated recombination express GFP in renin precursors and their descendants and then performed lineage tracing and transplantation studies. We found that cells from the renin lineage are enriched in the peritoneal fluid (12.3 +/- 1.7% at 4 months) when compared to bone marrow (1.2 +/- 0.02%), blood (2.6 +/- 0.72%) and spleen (5.3 +/- 0.4%). Further, while renin-expressing cells in the bone marrow are pro-B cells, cells from the renin lineage within the peritoneal fluid exhibit increased expression of CD11b and CD5, and overall have an immunophenotype consistent with B-1 lymphocytes. Whereas the proportion of cells from the renin lineage in bone marrow, blood, and spleen decreases with age, renin lineage B-1 cells within the peritoneal fluid persist into adulthood. Finally, we found that renin lineage cells from the bone marrow of donor mice can repopulate the B-1 cell peritoneal compartment in irradiated host mice. This preliminary work suggests an association between renin, the key regulatory enzyme of the renin angiotensin cascade and the innate immune system, two major systems in the control of homeostasis.

Abstract 312: Jagged1 and Morphological Integrity of the Kidney

Renal vascular development is dependent on the participation of renin precursor cells, which localize to areas of new vessel formation and differentiate into smooth muscle cells (SMCs), mesangial and juxtaglomerular (JG) cells. However, the mechanisms that enforce this particular fate of renin precursor cells remain unclear. During embryogenesis, renin cells express a significant number of angiogenic factors including the Notch signaling ligand Jagged1. We therefore hypothesized that Jagged1 is necessary for renin precursors to differentiate into the various mural cells of the renal arterioles and that Jagged1 plays a critical role in renal vascular development. To generate conditional Jagged1 deletion in cells of the renin lineage, we crossed Jagged1 fl/fl mice with Ren1d cre/+ mice. We investigated kidney weight, morphology, and vascular architecture as well as the identity of cells composing the kidney arterioles including renin cells and SMCs. We performed quantitative RT-PCR on kidney cortex mRNA for Jagged1 and Renin expression levels and immunohistochemistry for renin. The expression of Jagged1 mRNA in conditional knockout (cKO) animals was reduced at 2 weeks (68.3% reduction) and 4 weeks (66.5% reduction) compared to control mice. We found no significant differences between control and cKO animals in their kidney weights, renin mRNA expression, and renin staining. The number of renin-positive juxtaglomerular apparatuses (JGA) was 49.25 +/- 3.301 (n=4) and 38.00 +/- 4.830 (n=4) for control and cKO mice respectively under physiologic conditions. Staining for α-smooth muscle actin (α-SMA) demonstrated an overall normal vascular anatomy in cKO kidneys, however there were focal areas containing activated pericytes and injured mesangial cells expressing α-SMA indicating an active fibrotic process. Mason’s trichrome staining confirmed areas of glomerular and interstitial fibrosis in cKO kidneys. This work suggests that while Jagged1 is dispensable for renin expression, its loss in renin cell descendants affects perivascular-interstitial integrity and glomerular structure. The findings indicate an important role of Jagged1 in the maintenance of the morphologic integrity of the kidney.

Local renal circadian clocks control fluid-electrolyte homeostasis and BP

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