Renin-angiotensin system-growth factor cross-talk: a novel mechanism for ureteric bud morphogenesis

Identification of the regulatory mechanism of ACE2 in COVID-19-induced kidney damage with systems genetics approach

Studies showed that SARS-CoV-2 can directly target the kidney and induce renal damage. As the cell surface receptor for SARS-CoV-2 infection, the angiotensin-converting enzyme 2 (ACE2) plays a pivotal role for renal physiology and function. Thus, it is important to understand ACE2 through which pathway influences the pathogenesis of renal damage induced by COVID-19. In this study, we first performed an eQTL mapping for Ace2 in kidney tissues in 53 BXD mice strains. Results demonstrated that Ace2 is highly expressed and strongly controlled by a genetic locus on chromosome 16 in the kidney, with six genes (Dnase1, Vasn, Usp7, Abat, Mgrn1, and Rbfox1) dominated as the upstream modulator, as they are highly correlated with Ace2 expression. Gene co-expression analysis showed that Ace2 co-variates are significantly involved in the renin-angiotensin system (RAS) pathway which acts as a reno-protector. Importantly, we also found that Ace2 is positively correlated with Pdgf family members, particularly Pdgfc, which showed the most association among the 76 investigated growth factors. Mammalian Phenotype Ontology enrichment indicated that the cognate transcripts for both Ace2 and Pdgfc were mainly involved in regulating renal physiology and morphology. Among which, Cd44, Egfr, Met, Smad3, and Stat3 were identified as hub genes through protein-protein interaction analysis. Finally, in aligning with our systems genetics findings, we found ACE2, pdgf family members, and RAS genes decreased significantly in the CAKI-1 kidney cancer cells treated with S protein and receptor binding domain structural protein. Collectively, our data suggested that ACE2 work with RAS, PDGFC, as well as their cognate hub genes to regulate renal function, which could guide for future clinical prevention and targeted treatment for COVID-19-induced renal damage outcomes. KEY MESSAGES: • Ace2 is highly expressed and strongly controlled by a genetic locus on chromosome 16 in the kidney. • Ace2 co-variates are enriched in the RAS pathway. • Ace2 is strongly correlated with the growth factor Pdgfc. • Ace2 and Pdgfc co-expressed genes involved in the regulation of renal physiology and morphology. • SARS-CoV-2 spike glycoprotein induces down-regulation of Ace2, RAS, and Pdgfc.

Prenatal caffeine exposure induced renal developmental toxicity and transgenerational effect in rat offspring

Epidemiological studies revealed that prenatal caffeine exposure (PCE) is associated with adverse gestational outcomes and susceptibility to chronic diseases in offspring, yet the effects of PCE on glomerulosclerosis susceptibility in adult female offspring and its intergenerational transmission remain to be further investigated. Here, we found that PCE caused fetal kidney dysplasia and glomerulosclerosis of the female offspring. Besides, the kidney of F1 offspring in PCE group exhibited the "low expressional programming of AT2R" and "GC-IGF1 programming" alteration. Intergenerational genetic studies revealed that the renal defect and GC-IGF1 programming alteration was inherited to F2 adult female offspring derived from the female germ line, but Low expression of AT2R did not extend to the F2 female offspring. Taken together, PCE caused renal dysplasia and adult glomerulosclerosis in the F1 female offspring, which might be mediated by renal AT2R low expressional programming and GC-IGF1 axis alteration. Furthermore, PCE induced transgenerational toxicity on kidney, and GC-IGF1 programming alteration might be the potential molecular mechanism. This study provided experimental evidence for the mechanism study of the intergenerational inheritance of kidney developmental toxicity caused by PCE.

Decreased H3K9ac level of AT2R mediates the developmental origin of glomerulosclerosis induced by prenatal dexamethasone exposure in male offspring rats

This study aimed to demonstrate that prenatal dexamethasone exposure (PDE) can induce kidney dysplasia in utero and adult glomerulosclerosis in male offspring, and to explore the underlying intrauterine programming mechanisms. Pregnant rats were subcutaneously administered dexamethasone 0.2 mg/kg.d from gestational day (GD) 9 to GD20. The male fetus on GD20 and the adult offspring at age of postnatal week 28 were analyzed. The adult offspring kidneys in the PDE group displayed glomerulosclerosis, elevated levels of serum creatinine and urine protein, ultrastructural damage of podocytes, the reduced expression levels of podocyte marker genes, nephrin and podocin. The histone 3 lysine 9 acetylation (H3K9ac) level in the promoter of renal angiotensin II receptor type 2 (AT2R) and its expression were reduced, whereas the angiotensin II receptor type 1a (AT1aR)/AT2R expression ratio was increased. The fetal kidneys in the PDE group displayed an enlarged Bowman's space and a shrunken glomerular tuft, a reduced cortex width and an increase in the nephrogenic zone/cortical zone ratio, reduced the expression level of glial-cell-line derived neurotrophic factor/c-Ret tyrosine kinase receptor (GDNF/c-Ret) signal pathway and podocyte marker genes. Moreover, the H3K9ac and H3K27ac levels of AT2R as well as the gene and protein expression levels of AT2R in fetal kidneys were inhibited by PDE. In vitro, primary metanephric mesenchyme stem cells (MMSCs) were treated with dexamethasone. Overexpression of AT2R reversed the inhibited expression of GDNF/c-Ret and podocin/nephrin induced by dexamethasone, and glucocorticoids receptor antagonist abolished the decreased H3K9ac level and gene expression of AT2R. In conclusion, PDE induced the offspring's kidney dysplasia as well as adult glomerulosclerosis, which was mediated by a sustained decrease in renal AT2R expression via decreasing the H3 K9ac level.

The expressional disorder of the renal RAS mediates nephrotic syndrome of male rat offspring induced by prenatal ethanol exposure

This study aimed to prove that prenatal ethanol exposure (PEE) can induce nephrotic syndrome in male rat offspring and to explore the underlying intrauterine programming mechanisms. Pregnant Wistar rats were intragastrically administered ethanol (4 g/kg d) from gestational day (GD) 9 to GD 20, and the male fetuses were delivered by cesarean section at GD20 and the male adult offspring were euthanized at postnatal week (PW) 24. In vitro, the primary metanephric mesenchyme cells were treated with ethanol at concentrations of 15-60 mM. The results indicated that the kidneys of adult offspring in the PEE group exhibited glomerulosclerosis as well as interstitial fibrosis. The levels of serum creatinine and urine protein were elevated; the serum total cholesterol level was increased and the serum albumin concentration was reduced. In the fetal kidney, developmental retardation was presented in the PEE group via pathological examinations, accompanied by the expressional inhibition of the glial-cell-line-derived neurotrophic factor/c-ret tyrosine kinase receptor (GDNF/c-ret) signaling pathway. Although serum angiotensin II (Ang II) level and the gene expression of renal angiotensin-converting enzyme (ACE) were increased in the PEE group, the expression of renal angiotensin II type 2 receptor (AT₂R) was significantly inhibited, accompanied by a reduction in the H3K27ac level on the AT₂R gene promoter. In the non-classical renin-angiotensin system (RAS), the expression of renal angiotensin converting enzyme 2 (ACE2) and Mas receptor (MasR) were inhibited in the PEE group. The above changes of the classical and non-classical RAS all sustained from utero to adulthood. In vitro, ethanol elevated the gene expression of ACE and angiotensin II type 1a receptor (AT_1aR) whereas it reduced the expression of AT₂R, ACE2, and MasR, accompanied by a reduction in the H3K27ac level on AT₂R gene promoter. Taken together, these results suggested that PEE can induce fetal kidney developmental retardation and adult nephrotic syndrome, and direct regulation of ethanol to the renal RAS was involved in the mechanism of nephrotic syndrome induced by PEE.

Prenatal nicotine exposure induced GDNF/c-Ret pathway repression-related fetal renal dysplasia and adult glomerulosclerosis in male offspring

Prenatal nicotine exposure could induce fetal renal dysplasia associated with the suppression of the GDNF/c-Ret pathway and adult glomerulosclerosis in male offspring, which might be mediated by alterations in angiotensin II receptors.

Angiotensin II regulates collagen metabolism through modulating tissue inhibitor of metalloproteinase-1 in diabetic skin tissues

We investigated the effect of angiotensin II (Ang II) on matrix metalloproteinase-1 (MMP-1)/tissue inhibitor of metalloproteinase-1 (TIMP-1) balance in regulating collagen metabolism of diabetic skin. Skin tissues from diabetic model were collected, and the primary cultured fibroblasts were treated with Ang II receptor inhibitors before Ang II treatment. The collagen type I (Coll I) and collagen type III (Coll III) were measured by histochemistry. The expressions of transforming growth factor-β (TGF-β), MMP-1, TIMP-1 and propeptides of types I and III procollagens in skin tissues and fibroblasts were quantified using polymerase chain reaction (PCR), Western blot or enzyme-linked immunosorbent assay (ELISA). Collagen dysfunction was documented by changed collagen I/III ratio in streptozotocin (STZ)-injected mice compared with controls. This was accompanied by increased expression of TGF-β, TIMP-1 and propeptides of types I and III procollagens in diabetic skin tissues. In primary cultured fibroblasts, Ang II prompted collagen synthesis accompanied by increases in the expressions of TGF-β, TIMP-1 and types I and III procollagens, and these increases were inhibited by losartan, an Ang II type 1 (AT1) receptor blocker, but not affected by PD123319, an Ang II type 2 (AT2) receptor antagonist. These findings present evidence that Ang-II-mediated changes in the productions of MMP-1 and TIMP-1 occur via AT1 receptors and a TGF-β-dependent mechanism.

[The cortical collecting duct plays a pivotal role in the kidney's local renin-angiotensin system]

The renin-angiotensin system is one of the most important hormone systems in the body, and the regulations as well as the role in the juxtaglomerular apparatus are well known. The present review focuses on renin secretion in a recently described localization, the cortical collecting duct. The authors display it in parallel of the copying strategy of an adult and a developing kidney. Furthermore, based on different animal studies it highlights the local role of renin released from the collecting duct. In chronic angiotensin II-infused, 2-kidney, 1-clip hypertensive model as well as in diabetic rats the major source of (pro)renin is indeed the collecting duct. In this localization this hormone can reach both the systemic circulation and the interstitial renin-angiotensin system components including the newly described (pro)renin receptor, by which (pro)renin is able to locally activate pro-fibrotic intracellular signal pathways. Consequently, one can postulate that in the future renin may serve either as a new therapeutic target in nephropathy associated with both hypertension and diabetes or as an early diagnostic marker in chronic diseases leading to nephropathy.

An insertion/deletion ACE polymorphism and kidney size in Polish full-term newborns

The number of nephrons is a multifactorial trait controlled by the interaction of environmental factors and genetic variants that influence the extent of branching nephrogenesis during foetal life. A correlation between renal mass and nephron number in newborns allows the use of the total kidney volume at birth as a surrogate for congenital nephron number. Since the renin-angiotensin system plays an important role in renal development we hypothesized that the common, functional insertion/deletion (I/D) polymorphism in the ACE gene might be responsible for the variation in kidney size amongst healthy individuals. We recruited 210 healthy Polish full-term newborns born to healthy women with uncomplicated pregnancies. The kidney volume was measured sonographically. Total kidney volume (TKV) was calculated as the sum of left kidney volume and right kidney volume. TKV was normalized to body surface area (TKV/BSA). The I and D alleles were identified using polymerase chain reaction. TKV/BSA in newborns carrying at least one insertion ACE allele was significantly reduced by approximately 8% as compared with homozygous newborns for the D allele (DD genotype) (105.1±23.6 vs. 114.2±28.2 cm(3)/m(2), p<0.05). The results of this study suggest that I/D ACE polymorphism may account for subtle variation in kidney size at birth, which reflects congenital nephron endowment.

Ontogeny of angiotensin-converting enzyme 2

INTRODUCTION

This study examined the temporal expression of angiotensin (Ang)-converting enzyme 2 (ACE2) during renal, heart, lung, and brain organogenesis in the mouse.

RESULTS

We demonstrate that kidney ACE2 mRNA levels are low on embryonic day (E) 12.5, increase fourfold during development, and decline in adulthood. In extrarenal tissues, ACE2 mRNA levels are also low during early gestation, increase in perinatal period, and peak in adulthood. The lung shows the highest age-related increase in ACE2 mRNA levels followed by the brain, kidney, and heart. ACE2 protein levels and enzymatic activity are high in all organs studied during gestation and decline postnatally. Ang II decreases ACE2 mRNA levels and enzymatic activity in kidneys grown ex vivo. These effects of Ang II are blocked by the specific Ang II AT(1) receptor (AT(1)R) antagonist candesartan, but not by the AT(2) receptor (AT(2)R) antagonist PD123319.

DISCUSSION

We conclude that ACE2 gene and protein expression and enzymatic activity are developmentally regulated in a tissue-specific manner. Ang II, acting through AT(1)R, exerts a negative feedback on ACE2 during kidney development. We postulate that relatively high ACE2 protein levels and enzymatic activity observed during gestation may play a role in kidney, lung, brain, and heart organogenesis.

Wnt signaling and renal medulla formation

The renal medulla, the inner compartment of the metanephric kidney, plays vital roles in the regulation of body water, electrolyte homeostasis, and systemic blood pressure. It is composed of the loops-of-Henle, the medullary collecting ducts, the vasa recta, and the medullary interstitium. Its epithelial and endothelial components display ordered spatial organization. This organization serves as the structural basis for its function in urine concentration. The urine concentration ability of a renal medulla is also related to its length among species. In this review, the current understanding of the molecular and cellular mechanisms underlying renal medulla formation (elongation) is summarized, with a focus on the role of Wnt signaling in this developmental process. Renal medulla blunting and effacement is a common symptom of many renal and urological destructions. The knowledge in renal medulla formation should assist efforts in repair and regeneration of a damaged renal medulla, so to improve renal physiology in diseased situations.

Activation of skin renin-angiotensin system in diabetic rats

The renin-angiotensin system (RAS) is reportedly involved in chronic diabetic complications such as diabetic nephropathy, but changes of the RAS in diabetic skin remain unknown. The aim of this study was to investigate the expression of angiotensin (Ang) II and its type 1 (AT1) and type 2 (AT2) receptors in diabetic skin tissues, and explore the relationship between the local RAS and pathological changes of diabetic skin. Our results showed that thinning of epidermis, degeneration of collagen, fracture of dermal layer, and atrophy/disappearance of subcutaneous fat were observed in diabetic skin. The expression level of AngII was increased in diabetic skin tissues compared to that in controls. mRNA and protein expression of AT1 receptor were also increased while the level of AT2 receptor decreased; the relative expression of AT1 to AT2 receptors was approximately threefold higher in diabetes than in controls. Furthermore, in the culture medium of primary cultured fibroblasts from diabetic skin, the concentration of AngII was significantly higher than that of normal control. The mRNA and protein expression of AT1 receptor was also increased in fibroblasts of diabetic skin compared to controls, while the protein expression of AT2 receptor was decreased. Taken together, our results suggest that the local RAS system is activated in diabetic skin and AngII receptor is likely to mediate the pathological changes of diabetic skin.

Receptor tyrosine kinases in kidney development

The kidney plays a fundamental role in the regulation of arterial blood pressure and fluid/electrolyte homeostasis. As congenital anomalies of the kidney and urinary tract (CAKUT) constitute one of the most common human birth defects, improved understanding of the cellular and molecular mechanisms that lead to CAKUT is critical. Accumulating evidence indicates that aberrant signaling via receptor tyrosine kinases (RTKs) is causally linked to CAKUT. Upon activation by their ligands, RTKs dimerize, undergo autophosphorylation on specific tyrosine residues, and interact with adaptor proteins to activate intracellular signal transduction pathways that regulate diverse cell behaviours such as cell proliferation, survival, and movement. Here, we review the current understanding of role of RTKs and their downstream signaling pathways in the pathogenesis of CAKUT.

Genetics of congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) occur in 1 in 500 births and are a major cause of morbidity in children. Notably, CAKUT account for the most cases of pediatric end-stage renal disease and predispose the individual to hypertension and cardiovascular disease throughout life. Although some forms of CAKUT are a part of a syndrome or are associated with a positive family history, most cases of renal system anomalies are sporadic and isolated to the urinary tract. Broad phenotypic spectrum of CAKUT and variability in genotype-phenotype correlation indicate that pathogenesis of CAKUT is a complex process that depends on interplay of many factors. This review focuses on the genetic mechanisms (single-gene mutations, modifier genes) leading to renal system anomalies in humans and discusses emerging insights into the role of epigenetics, in utero environmental factors, and micro-RNAs (miRNAs) in the pathogenesis of CAKUT. Common gene networks that function in defined temporospatial fashion to orchestrate renal system morphogenesis are highlighted. Derangements in cellular, molecular, and morphogenetic mechanisms that direct normal renal system development are emphasized as a major cause of CAKUT. Integrated understanding of how morphogenetic process disruptions are linked to CAKUT will enable improved diagnosis, treatment, and prevention of congenital renal system anomalies and their consequences.

Renal programming: cause for concern?

Development of the kidney can be altered in utero in response to a suboptimal environment. The intrarenal factors that have been most well characterized as being sensitive to programming events are kidney mass/nephron endowment, the renin-angiotensin system, tubular sodium handling, and the renal sympathetic nerves. Newborns that have been subjected to an adverse intrauterine environment may thus begin life at a distinct disadvantage, in terms of renal function, at a time when the kidney must take over the primary role for extracellular fluid homeostasis from the placenta. A poor beginning, causing renal programming, has been linked to increased risk of hypertension and renal disease in adulthood. However, although a cause for concern, increasingly, evidence demonstrates that renal programming is not a fait accompli in terms of future cardiovascular and renal disease. A greater understanding of postnatal renal maturation and the impact of secondary factors (genes, sex, diet, stress, and disease) on this process is required to predict which babies are at risk of increased cardiovascular and renal disease as adults and to be able to devise preventative measures.

Cyst formation in the PKD2 (1-703) transgenic rat precedes deregulation of proliferation-related pathways

Background

Polycystic Kidney Disease is characterized by the formation of large fluid-filled cysts that eventually destroy the renal parenchyma leading to end-stage renal failure. Although remarkable progress has been made in understanding the pathologic mechanism of the disease, the precise orchestration of the early events leading to cyst formation is still unclear. Abnormal cellular proliferation was traditionally considered to be one of the primary irregularities leading to cyst initiation and growth. Consequently, many therapeutic interventions have focused on targeting this abnormal proliferation, and some have even progressed to clinical trials. However, the role of proliferation in cyst development was primarily examined at stages where cysts are already visible in the kidneys and therefore at later stages of disease development.

Methods

In this study we focused on the cystic phenotype since birth in an attempt to clarify the temporal contribution of cellular proliferation in cyst development. Using a PKD2 transgenic rat model (PKD2 (1-703)) of different ages (0-60 days after birth) we performed gene expression profiling and phenotype analysis by measuring various kidney parameters.

Results

Phenotype analysis demonstrated that renal cysts appear immediately after birth in the PKD2 transgenic rat model (PKD2 (1-703)). On the other hand, abnormal proliferation occurs at later stages of the disease as identified by gene expression profiling. Interestingly, other pathways appear to be deregulated at early stages of the disease in this PKD model. Specifically, gene expression analysis demonstrated that at day 0 the RAS system is involved. This is altered at day 6, when Wnt signaling and focal adhesion pathways are affected. However, at and after 24 days, proliferation, apoptosis, altered ECM signaling and many other factors become involved.

Conclusions

Our data suggest that cystogenesis precedes deregulation of proliferation-related pathways, suggesting that proliferation abnormalities may contribute in cyst growth rather than cyst formation.

Characterization of mesonephric development and regeneration using transgenic zebrafish

The zebrafish is a valuable vertebrate model for kidney research. The majority of previous studies focused on the zebrafish pronephros, which comprises only two nephrons and is structurally simpler than the mesonephros of adult fish and the metanephros of mammals. To evaluate the zebrafish system for more complex studies of kidney development and regeneration, we investigated the development and postinjury regeneration of the mesonephros in adult zebrafish. Utilizing two transgenic zebrafish lines (wt1b::GFP and pod::NTR-mCherry), we characterized the developmental stages of individual mesonephric nephrons and the temporal-spatial pattern of mesonephrogenesis. We found that mesonephrogenesis continues throughout the life of zebrafish, with a rapid growth phase during the juvenile period and a slower phase in adulthood such that the total nephron number of juvenile and adult fish linearly correlates with body mass. Following gentamicin-induced renal injury, the zebrafish mesonephros can undergo de novo regeneration of mesonephric nephrons, a process known as neonephrogenesis. We found that wt1b expression was induced in individually dispersed cells in the mesonephric interstitium as early as 48 h following injury. These wt1b-expressing cells formed aggregates by 72-96 h following injury which proceeded to form nephrons. This suggests that wt1b may serve as an early marker of fated renal progenitor cells. The synchronous nature of regenerative neonephrogenesis suggests that this process may be useful for studies of nephron development.

Type 2a sodium-phosphate co-transporter serves as a histological predictor of renal dysfunction and tubular apical damage in the kidneys of septic mice

Acute renal failure (ARF) occurs in septic patients and is histologically characterized by tubular apical damages, including brush border breakdown. Nevertheless, little information is available to identify the apical injury at a molecular level. Type 2a Na-phosphate (Pi) co-transporter (NaPiT2a) is constitutively expressed by brush borders of proximal tubules under a healthy condition. Therefore, we investigated if NaPiT2a could be used as a negative marker to predict the renal dysfunction, using an animal model of septic ARF. After the treatment of lipopolysaccharide (LPS), mice manifested the tubular apical injury and renal dysfunction, as evidenced by the increase in blood urea nitrogen (BUN) levels. Immunohistochemical examination revealed that the expression of NaPiT2a by renal proximal tubules became faint, being reciprocal to the development of tubular hypoxia during sepsis. Inversely, the loss in apical NaPiT2a was restored in a regenerating stage, associated with the recovery from renal hypoxia. Overall, there was a negative correlation between the NaPiT2a expression and BUN levels or tubular injury scores in septic mice. Our data indicate that the loss of NaPiT2a is a reliable marker for predicting the progression of septic ARF, while local hypoxia might be involved in the decrease of NaPiT2a expression.