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.

Renin Cell Baroreceptor, a Nuclear Mechanotransducer Central for Homeostasis

[Figure: see text].

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.

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.

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.

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 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.

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.

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.

Human rhabdomyosarcoma cell lines for rhabdomyosarcoma research: utility and pitfalls

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Despite intergroup clinical trials conducted in Europe and North America, outcomes for high risk patients with this disease have not significantly improved in the last several decades, and survival of metastatic or relapsed disease remains extremely poor. Accrual into new clinical trials is slow and difficult, so in vitro cell-line research and in vivo xenograft models present an attractive alternative for preclinical research for this cancer type. Currently, 30 commonly used human RMS cell lines exist, with differing origins, karyotypes, histologies, and methods of validation. Selecting an appropriate cell line for RMS research has important implications for outcomes. There are also potential pitfalls in using certain cell lines including contamination with murine stromal cells, cross-contamination between cell lines, discordance between the cell line and its associated original tumor, imposter cell lines, and nomenclature errors that result in the circulation of two or more presumed unique cell lines that are actually from the same origin. These pitfalls can be avoided by testing for species-specific isoenzymes, microarray analysis, assays for subtype-specific fusion products, and short tandem repeat analysis.

Inhibition of the Notch-Hey1 axis blocks embryonal rhabdomyosarcoma tumorigenesis

PURPOSE

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and remains refractory to combined-modality therapy in patients with high risk disease. In skeletal myogenesis, Notch signaling prevents muscle differentiation and promotes proliferation of satellite cell progeny. Given its physiologic role in myogenesis and oncogenic role in other human cancers, we hypothesized that aberrant Notch signaling may contribute to RMS tumorigenesis and present novel therapeutic opportunities.

EXPERIMENTAL DESIGN

Human RMS cell lines and tumors were evaluated by immunoblot, IHC, and RT-PCR to measure Notch ligand, receptor, and target gene expression. Manipulation of Notch signaling was accomplished using genetic and pharmacologic approaches. In vitro cell growth, proliferation, and differentiation were assessed using colorimetric MTT and BrdU assays, and biochemical/morphologic changes after incubation in differentiation-promoting media, respectively. In vivo tumorigenesis was assessed using xenograft formation in SCID/beige mice.

RESULTS

Notch signaling is upregulated in human RMS cell lines and tumors compared with primary skeletal muscle, especially in the embryonal (eRMS) subtype. Inhibition of Notch signaling using Notch1 RNAi or γ-secretase inhibitors reduced eRMS cell proliferation in vitro. Hey1 RNAi phenocopied Notch1 loss and permitted modest myogenic differentiation, while overexpression of an activated Notch moiety, ICN1, promoted eRMS cell proliferation and rescued pharmacologic inhibition. Finally, Notch inhibition using RNAi or γ-secretase inhibitors blocked tumorigenesis in vivo.

CONCLUSIONS

Aberrant Notch-Hey1 signaling contributes to eRMS by impeding differentiation and promoting proliferation. The efficacy of Notch pathway inhibition in vivo supports the development of Notch-Hey1 axis inhibitors in the treatment of eRMS.

Epidermal growth factor potentiates renal cell death in hydronephrotic neonatal mice, but cell survival in rats

BACKGROUND

Epidermal growth factor (EGF) markedly attenuates tubular apoptosis induced by unilateral ureteral obstruction (UUO) in the neonatal rat, and reduces apoptosis induced by mechanical stretch of cultured rat tubular cells.

METHODS

To investigate the role of EGF in modulating apoptosis resulting from UUO, neonatal wild type and mutant mice lacking EGF (knockout), or with diminished EGF receptor activity (waved-2 mutant) were compared to control mice for tubular apoptosis and atrophy. Rat and mouse kidneys were compared for localization of the EGF receptor. Apoptosis was also measured in cultured mouse tubular cells subjected to stretch and exposed to EGF.

RESULTS

UUO reduced endogenous renal EGF expression in wild-type mice. Unlike the rat, exogenous EGF did not decrease tubular apoptosis or atrophy in the obstructed kidney, and significantly increased stretch-induced apoptosis of cultured mouse tubular cells. Tubular apoptosis was 50% lower in the obstructed kidney of EGF knockout and waved-2 mice relative to wild type and heterozygous animals. Exogenous EGF increased tubular apoptosis and doubled atrophy in the obstructed kidney of waved-2 mice. Species differences in EGF receptor localization were detected in 3-day-old kidneys.

CONCLUSION

EGF acts as a survival factor in the neonatal rat, but potentiates tubular cell death in the neonatal mouse. Species differences are maintained in cultured cells, suggesting that differences in EGF receptor signaling underlie these opposing effects.