Cell and molecular biology of kidney development

Kidney volume-to-birth weight ratio as an estimate of nephron endowment in extremely low birth weight preterm infants

In humans, nephrogenesis is completed by 32-36 weeks gestation, with a highly variable total number of nephrons, ranging from 200,000 to over 2 million. Premature birth disrupts the development and maturation of the kidneys, leading to a reduction in the final number of nephrons. Due to significant genetic variability in the number of nephrons among individuals, it is crucial to identify premature infants with fewer nephrons at birth as early as possible. These infants are more susceptible to developing renal failure with advancing age compared to those with a higher nephron endowment. Bedside ultrasound, an effective and non-invasive tool, is practical for identifying newborns with a lower nephron count. However, renal volume alone cannot reliably indicate the number of nephrons due to substantial variability at birth, influenced by gestational age when nephron maturation is incomplete. This variability in kidney volumes persists as newborns grow. In this observational study we hypothesize that the relationship between renal volume and birth weight may serve as an indicator of nephron endowment in premature infants with birth weight less than 1000 g. This finding could represent the basis for defining appropriate surveillance protocols and developing targeted therapeutic approaches.

Plasma D-asparagine and the D/L-serine ratio reflect chronic kidney diseases in children regardless of physique

Biomarkers that accurately reflect renal function are essential in management of chronic kidney diseases (CKD). However, in children, age/physique and medication often alter established renal biomarkers. We studied whether amino acid enantiomers in body fluids correlate with renal function and whether they are influenced by physique or steroid medication during development. We conducted a prospective study of children 2 to 18 years old with and without CKD. We analyzed associations of serine/asparagine enantiomers in body fluids with major biochemical parameters as well as physique. To study consequences of kidney dysfunction and steroids on serine/asparagine enantiomers, we generated juvenile mice with uninephrectomy, ischemic reperfusion injury, or dexamethasone treatment. We obtained samples from 27 children, of which 12 had CKD due to congenital (n = 7) and perinatal (n = 5) causes. Plasma D-asparagine and the D/L-serine ratio had robust, positive linear associations with serum creatinine and cystatin C, and detected CKD with high sensitivity and specificity, uninfluenced by body size or biochemical parameters. In the animal study, kidney dysfunction increased plasma D-asparagine and the D/L-serine ratio, but dexamethasone treatment did not. Thus, plasma D-asparagine and the D/L-serine ratio can be useful markers for renal function in children.

Detection, Monitoring, and Mitigation of Drug-Induced Nephrotoxicity: A Pragmatic Approach

The kidneys play a pivotal role in elimination of most drugs; therefore, a comprehensive understanding of renal physiology and pathology is important for those involved in drug development. High filtration capacity and metabolic activity make the kidneys vulnerable to drug-induced nephrotoxicity (DIN). Acute DIN may manifest on a background of renal impairment that has resulted from underlying disease, previously administered nephrotoxic medications, congenital renal abnormalities, or the natural aging process. The ability of the kidneys to compensate for DIN depends on the degree of pre-insult renal function. Therefore, it can be difficult to identify. The discovery and development of novel biomarkers that can diagnose kidney damage earlier and more accurately than current clinical measures and may be effective in detecting DIN. The goal of this manuscript is to provide a pragmatic and evidence-based supportive guidance for the early identification and management of DIN during the drug development process for clinical trial participants of all ages. The overall objective is to minimize the impact of DIN on kidney function and to collect renal safety data enabling risk analysis and mitigation.

Serum levels of sonic hedgehog in patients with IgA nephropathy are closely associated with intrarenal arteriolar lesions

BACKGROUND

Intrarenal arteriolar disease is a major risk factor for poor prognosis in immunoglobulin A nephropathy (IgAN). The morphologic factor sonic hedgehog (SHH) plays an important role in a variety of vascular diseases, so it may be directly or indirectly involved in the process of renal arteriolar disease. The purpose of this study was to investigate the correlation between serum SHH levels and renal arteriole disease in patients with IgAN.

METHODS

Subjects with primary IgAN diagnosed by renal biopsy performed between October 2018 and August 2019 at the First Medical Center of the Chinese PLA General Hospital were recruited. Blood specimens were collected from the patients within 1 week before renal biopsy after they signed an informed consent form, and healthy controls were recruited for blood specimen collection during the same period. The concentration of serum SHH was measured by enzyme-linked immunosorbent assay in this population.

RESULTS

Serum SHH levels were significantly lower in the IgAN group than in the control group. 41 of the 94 subjects diagnosed with IgAN had severe renal arteriolosclerosis and, compared to their less severely affected counterparts, were older, more hypertensive, and characterized by lower levels of SHH, higher levels of tubular atrophy/interstitial fibrosis and a higher Lee's classification. Serum SHH concentration was found to be an independent predictor of severe intrarenal arteriolosclerosis in IgAN subjects after correction using multivariate analysis.

CONCLUSION

In this study, serum SHH levels were found to be significantly lower in patients with IgAN than in healthy subjects. Serum SHH may serve as a noninvasive biomarker of intrarenal arteriolosclerosis in patients with IgAN.

Hedgehog signalling in Foxd1+ embryonic kidney stromal progenitors controls nephron formation via Cxcl12 and Wnt5a

Congenital anomalies of the kidney and urinary tract (CAKUT) are characterised by a spectrum of structural and histologic abnormalities and are the major cause of childhood kidney failure. During kidney morphogenesis, the formation of a critical number of nephrons is an embryonic process supported, in part, by signalling between nephrogenic precursors and Foxd1-positive stromal progenitor cells. Low nephron number and abnormal patterning of the stroma are signature pathological features among CAKUT phenotypes with decreased kidney function. Despite their critical contribution to CAKUT pathogenesis, the mechanisms that underlie a low nephron number and the functional contribution of a disorganised renal stroma to nephron number are both poorly defined. Here, we identify a primary pathogenic role for increased Hedgehog signalling in embryonic renal stroma in the genesis of congenital low nephron number. Pharmacologic activation of Hedgehog (Hh) signalling in human kidney organoid tissue decreased the number of nephrons and generated excess stroma. The mechanisms underlying these pathogenic effects were delineated in genetic mouse models in which Hh signalling was constitutively activated in a cell lineage-specific manner. Cre-mediated excision of Ptch1 in Foxd1+ stromal progenitor cells, but not in Six2+ nephrogenic precursor cells, generated kidney malformation, identifying the stroma as a driver of low nephron number. Single-cell RNA sequencing analysis identified Cxcl12 and Wnt5a as downstream targets of increased stromal Hh signalling, findings supported by analysis in human kidney organoids. In vivo deficiency of Cxcl12 or Wnt5a in mice with increased stromal Hh signalling improved nephron endowment. These results demonstrate that dysregulated Hh signalling in embryonic renal stromal cells inhibits nephron formation in a manner dependent on Cxcl12 and Wnt5a. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Spatial-linked alignment tool (SLAT) for aligning heterogenous slices

Spatially resolved omics technologies reveal the spatial organization of cells in various biological systems. Here we propose SLAT (Spatially-Linked Alignment Tool), a graph-based algorithm for efficient and effective alignment of spatial slices. Adopting a graph adversarial matching strategy, SLAT is the first algorithm capable of aligning heterogenous spatial data across distinct technologies and modalities. Systematic benchmarks demonstrate SLAT's superior precision, robustness, and speed over existing state-of-the-arts. Applications to multiple real-world datasets further show SLAT's utility in enhancing cell-typing resolution, integrating multiple modalities for regulatory inference, and mapping fine-scale spatial-temporal changes during development. The full SLAT package is available at https://github.com/gao-lab/SLAT .

The genetics and pathogenesis of CAKUT

Congenital anomalies of the kidney and urinary tract (CAKUT) comprise a large variety of malformations that arise from defective kidney or urinary tract development and frequently lead to kidney failure. The clinical spectrum ranges from severe malformations, such as renal agenesis, to potentially milder manifestations, such as vesicoureteral reflux. Almost 50% of cases of chronic kidney disease that manifest within the first three decades of life are caused by CAKUT. Evidence suggests that a large number of CAKUT are genetic in origin. To date, mutations in ~54 genes have been identified as monogenic causes of CAKUT, contributing to 12-20% of the aetiology of the disease. Pathogenic copy number variants have also been shown to cause CAKUT and can be detected in 4-11% of patients. Furthermore, environmental and epigenetic factors can increase the risk of CAKUT. The discovery of novel CAKUT-causing genes is challenging owing to variable expressivity, incomplete penetrance and variable genotype-phenotype correlation. However, such a discovery could ultimately lead to improvements in the accurate molecular genetic diagnosis, assessment of prognosis and multidisciplinary clinical management of patients with CAKUT, potentially including personalized therapeutic approaches.

OCT4 induces long-lived dedifferentiated kidney progenitors poised to redifferentiate in 3D kidney spheroids

Upscaling of kidney epithelial cells is crucial for renal regenerative medicine. Nonetheless, the adult kidney lacks a distinct stem cell hierarchy, limiting the ability to long-term propagate clonal populations of primary cells that retain renal identity. Toward this goal, we tested the paradigm of shifting the balance between differentiation and stemness in the kidney by introducing a single pluripotency factor, OCT4. Here we show that ectopic expression of OCT4 in human adult kidney epithelial cells (hKEpC) induces the cells to dedifferentiate, stably proliferate, and clonally emerge over many generations. Control hKEpC dedifferentiate, assume fibroblastic morphology, and completely lose clonogenic capacity. Analysis of gene expression and histone methylation patterns revealed that OCT4 represses the HNF1B gene module, which is critical for kidney epithelial differentiation, and concomitantly activates stemness-related pathways. OCT4-hKEpC can be long-term expanded in the dedifferentiated state that is primed for renal differentiation. Thus, when expanded OCT4-hKEpC are grown as kidney spheroids (OCT4-kSPH), they reactivate the HNF1B gene signature, redifferentiate, and efficiently generate renal structures in vivo. Hence, changes occurring in the cellular state of hKEpC following OCT4 induction, long-term propagation, and 3D aggregation afford rapid scale-up technology of primary renal tissue-forming cells.

Protein arginine methyltransferases in renal development, injury, repair, and fibrosis

Protein arginine methyltransferases (PRMTs) methylate a range of histone and non-histone substrates and participate in multiple biological processes by regulating gene transcription and post-translational modifications. To date, most studies on PRMTs have focused on their roles in tumors and in the physiological and pathological conditions of other organs. Emerging evidence indicates that PRMTs are expressed in the kidney and contribute to renal development, injury, repair, and fibrosis. In this review, we summarize the role and the mechanisms of PRMTs in regulating these renal processes and provide a perspective for future clinical applications.

Selected renal cells harbor nephrogenic potential

Selected renal cells (SRCs), a renal epithelial cell-enriched platform, are being advanced as an autologous cell-based therapy for the treatment of chronic kidney disease. However, the mechanism underlying its renal reparative and restorative effects remains to be fully elucidated. In this study, we coupled knowledgebase data with empirical findings to demonstrate that genes differentially expressed by SRCs form interactomes within tubules and glomeruli and mediate a suite of renal developmental activities including epithelial cell differentiation, renal vasculature development, and glomerular and nephron development. In culture, SRCs form organoids which self-assemble into tubules in the presence of a scaffold. Implanted into the kidneys of subtotally nephrectomized rats, SRCs are associated with comma- and S-shaped body cell formation and glomerular development, and improvement in renal filtration indices and renal microarchitecture. These data suggest that SRCs harbor nephrogenic potential, which may explain, at least in part, their therapeutic activity.

Disease Modeling with Kidney Organoids

Kidney diseases often lack optimal treatments, causing millions of deaths each year. Thus, developing appropriate model systems to study human kidney disease is of utmost importance. Some of the most promising human kidney models are organoids or small organ-resembling tissue collectives, derived from human-induced pluripotent stem cells (hiPSCs). However, they are more akin to a first-trimester fetal kidney than an adult kidney. Therefore, new strategies are needed to advance their maturity. They have great potential for disease modeling and eventually auxiliary therapy if they can reach the maturity of an adult kidney. In this review, we will discuss the current state of kidney organoids in terms of their similarity to the human kidney and use as a disease modeling system thus far. We will then discuss potential pathways to advance the maturity of kidney organoids to match an adult kidney for more accurate human disease modeling.

Decellularization of porcine kidney with submicellar concentrations of SDS results in the retention of ECM proteins required for the adhesion and maintenance of human adult renal epithelial cells

When decellularizing kidneys, it is important to maintain the integrity of the acellular extracellular matrix (ECM), including associated adhesion proteins and growth factors that allow recellularized cells to adhere and migrate according to ECM specificity. Kidney decellularization requires the ionic detergent sodium dodecyl sulfate (SDS); however, this results in a loss of ECM proteins important for cell adherence, migration, and growth, particularly glycosaminoglycan (GAG)-associated proteins. Here, we demonstrate that using submicellar concentrations of SDS results in a greater retention of structural proteins, GAGs, growth factors, and cytokines. When porcine kidney ECM scaffolds were recellularized using human adult primary renal epithelial cells (RECs), the ECM promoted cell survival and the uniform distribution of cells throughout the ECM. Cells maintained the expression of mature renal epithelial markers but did not organize on the ECM, indicating that mature cells are unable to migrate to specific locations on ECM scaffolds.

Translational insights into mechanisms and preventive strategies after renal injury in neonates

Adverse perinatal circumstances can cause acute kidney injury (AKI) and contribute to chronic kidney disease (CKD). Accumulating evidence indicate that a wide spectrum of perinatal conditions interferes with normal kidney development and ultimately leads to aberrant kidney structure and function later in life. The present review addresses the lack of mechanistic knowledge with regard to perinatal origins of CKD and provides a comprehensive overview of pre- and peri-natal insults, including genetic predisposition, suboptimal nutritional supply, obesity and maternal metabolic disorders as well as placental insufficiency leading to intrauterine growth restriction (IUGR), prematurity, infections, inflammatory processes, and the need for life-saving treatments (e.g. oxygen supplementation, mechanical ventilation, medications) in neonates. Finally, we discuss future preventive, therapeutic, and regenerative directions. In summary, this review highlights the perinatal vulnerability of the kidney and the early origins of increased susceptibility toward AKI and CKD during postnatal life. Promotion of kidney health and prevention of disease require the understanding of perinatal injury in order to optimize perinatal micro- and macro-environments and enable normal kidney development.

The developmental origins of health and chronic kidney disease: Current status and practices in Japan

The concept of the developmental origins of health and disease (DOHaD) views unfavorable perinatal circumstances as contributing to the development of diseases in later life. It is well known that such unfavorable circumstances play an important role as a risk factor for chronic kidney disease (CKD) in infants born with prematurity. Low birthweight (LBW) is believed to be a potential contributor to CKD in adulthood. Preterm and/or LBW infants are born with incomplete nephrogenesis. As a result, the number of nephrons is low. The poor intrauterine environment also causes epigenetic changes that adversely affect postnatal renal function. After birth, hyperfiltration of individual nephrons due to low nephron numbers causes proteinuria and secondary glomerulosclerosis. Furthermore, the risk of CKD increases as renal damage takes a second hit from exposure to nephrotoxic substances and acquired insults such as acute kidney injury after birth among infants in neonatal intensive care. Meanwhile, unfortunately, recent studies have shown that the number of nephrons in healthy Japanese individuals is approximately two-thirds lower than that in previous reports. This means that Japanese premature infants are clearly at a high risk of developing CKD in later life. Recently, several DOHaD-related CKD studies from Japanese researchers have been reported. Here, we summarize the relevance of CKD in conjunction with DOHaD and review recent studies that have examined the impact of the upward LBW trend in Japan on renal health.

Expression of collagen type IV in human kidney during prenatal development

Background/Aim. Type IV collagen belongs to the group of nonfibrillar collagens and is an important component of the basement membranes, where it accounts for approximately 50% of its structural elements. The aim of the study was to describe the expression and distribution of collagen type IV in the embryonic and fetal metanephric kidney and to determine the volume density of collagen type IV in kidney tissue in each trimester of development. Methods. The material consisted of 19 human embryos/fetuses, in the gestational age from 8th to 37th week. Kidney tissue specimens were routinely processed to paraffin molds, stained immunohistochemically using polyclonal anti-collagen IV antibody and counterstained with Mayer hematoxylin and eosin. Stained slides were examined using a light microscope, and images of the selected areas under different lens magnification were captured with a digital camera. Volume density of collagen type IV was determined using ImageJ 1.48v and a plugin of the software, which inserted a grid system with 336 points. For the data comparison, the One-Way Analysis of Variance (ANOVA) was used. Results. Strong collagen IV immunopositivity was seen in all specimens, with a distribution in the basement membranes of urinary bud, parietal leaf of Bowman?s capsule, glomerular basement membrane, basement membrane of interstitial blood vessels, and basement membranes of nephron tubules and collecting ducts. No statistically significant difference in the volume density of type IV collagen was found among the different trimesters of the embryonic and fetal development. Conclusion. The synthesis and secretion of collagen type IV simultaneously follow the development of nephron structures, collecting system and blood vessels. The volume density of collagen type IV remains constant throughout all the trimesters of metanephric kidney development, indicating that it plays a crucial role in the normal development of nephron and collecting system structures, as well as in maintaining the normal kidney function.

The mutual patterning between the developing nephron and its covering tissues-valid reasons to rethink the search for traces left by impaired nephrogenesis

Background

The impairment of nephrogenesis can cause the termination of nephron formation in preterm and low birth weight babies. This leads to oligonephropathy with severe health consequences in later life. Although many clinical parameters are known, surprisingly little information is available regarding the initial damage on the developing nephron. Equally astounding, the first morphological data regarding the specifics of nephron formation in the nephrogenic zone of the fetal human kidney during late gestation has only been published within the past few years. In this context, it was observed that each stage of nephron anlage is surrounded by a specific set of tissues. Although highly relevant for the normal progress of nephron formation, the mutual patterning has not been systematically described.

Results

To contribute, the different stages of nephron anlage in the nephrogenic zone of the fetal human kidney during late gestation were screened by the optical microscope and documented by images. Following this, magnifications (28 × 18 cm) were produced to trace the contours of the developing nephron and its covering tissues. The resulting sketches, almost true to scale, were scanned, edited, and processed by a design program. As a base, first the individual position, size, and shape of the nephrogenic niche, pretubular aggregate, renal vesicles, comma- and S-shaped bodies are presented. Secondly, their structural relations to the renal capsule, collecting duct ampulla, perforating radiate artery, and expanding interstitium are shown. Third of all, the focus is on less considered configurations, such as site-specific approximation, local distancing, punctual adhesion, integration, separation, delamination, formation of congruent and divergent surfaces, and folding and opening of interstitial clefts.

Conclusions

The present contribution illuminates the mutual patterning between the developing nephron and its covering tissues. It is indispensable to know about the microanatomical relations, in order to identify whether the noxae impairing nephrogenesis targets only the developing nephron or also its covering tissues as interacting and controlling instances.

Analysis of alternative polyadenylation from single-cell RNA-seq using scDaPars reveals cell subpopulations invisible to gene expression

Alternative polyadenylation (APA) is a major mechanism of post-transcriptional regulation in various cellular processes including cell proliferation and differentiation, but the APA heterogeneity among single cells remains largely unknown. Single-cell RNA sequencing (scRNA-seq) has been extensively used to define cell subpopulations at the transcription level. Yet, most scRNA-seq data have not been analyzed in an "APA-aware" manner. Here, we introduce scDaPars (Dynamic Analysis of Alternative PolyAdenylation from Single-cell RNA-seq), a bioinformatics algorithm to accurately quantify APA events at both single-cell and single-gene resolution using either 3' end (10x Chromium) or full-length (Smart-seq2) scRNA-seq data. Validations in both real and simulated data indicate that scDaPars can robustly recover missing APA events caused by the low amounts of mRNA sequenced in single cells. When applied to cancer and human endoderm differentiation data, scDaPars not only revealed cell type-specific APA regulation but also identified cell subpopulations that are otherwise invisible to conventional gene expression analysis. Thus, scDaPars will enable us to understand cellular heterogeneity at the post-transcriptional APA level.

Identification of candidate PAX2-regulated genes implicated in human kidney development

PAX2 is a transcription factor essential for kidney development and the main causative gene for renal coloboma syndrome (RCS). The mechanisms of PAX2 action during kidney development have been evaluated in mice but not in humans. This is a critical gap in knowledge since important differences have been reported in kidney development in the two species. In the present study, we hypothesized that key human PAX2-dependent kidney development genes are differentially expressed in nephron progenitor cells from induced pluripotent stem cells (iPSCs) in patients with RCS relative to healthy individuals. Cap analysis of gene expression revealed 189 candidate promoters and 71 candidate enhancers that were differentially activated by PAX2 in this system in three patients with RCS with PAX2 mutations. By comparing this list with the list of candidate Pax2-regulated mouse kidney development genes obtained from the Functional Annotation of the Mouse/Mammalian (FANTOM) database, we prioritized 17 genes. Furthermore, we ranked three genes-PBX1, POSTN, and ITGA9-as the top candidates based on closely aligned expression kinetics with PAX2 in the iPSC culture system and susceptibility to suppression by a Pax2 inhibitor in cultured mouse embryonic kidney explants. Identification of these genes may provide important information to clarify the pathogenesis of RCS, human kidney development, and kidney regeneration.

The Role of PAX2 in Neurodevelopment and Disease

In developmental biology, transcription factors are involved in regulating the process of neural development, controlling the differentiation of nerve cells, and affecting the normal functioning of neural circuits. Transcription factors regulate the expression of multiple genes at the same time and have become a key gene category that is recognized to be disrupted in neurodevelopmental disorders such as autism spectrum disorders. This paper briefly introduces the expression and role of PAX2 in neurodevelopment and discusses the neurodevelopmental disorders associated with Pax2 mutations and its possible mechanism. Firstly, mutations in the human Pax2 gene are associated with abnormalities in multiple systems which can result in neurodevelopmental disorders such as intellectual disability, epilepsy and autism spectrum disorders. Secondly, the structure of Pax2 gene and PAX2 protein, as well as the function of Pax2 gene in neural development, was discussed. Finally, a diagram of the PAX2 protein regulatory network was made and a possible molecular mechanism of Pax2 mutations leading to neurodevelopmental disorders from the perspectives of developmental process and protein function was proposed.

El-Hattab A, Dua Puri R, Rocha ME, Merdzanic R, Paknia O, Beetz C, Rolfs A, Bertoli-Avella AM, Bauer P, Verma IC. Biallelic Pathogenic GFRA1 Variants Cause Autosomal Recessive Bilateral Renal Agenesis

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) are one of the most common malformations identified in the fetal stage. Bilateral renal agenesis (BRA) represents the most severe and fatal form of CAKUT. Only three genes have been confirmed to have a causal role in humans (ITGA8, GREB1L, and FGF20).

METHODS

Genome sequencing within a diagnostic setting and combined data repository analysis identified a novel gene.

RESULTS

Two patients presented with BRA, detected during the prenatal period, without additional recognizable malformations. They had parental consanguinity and similarly affected, deceased siblings, suggesting autosomal recessive inheritance. Evaluation of homozygous regions in patient 1 identified a novel, nonsense variant in GFRA1 (NM_001348097.1:c.676C>T, p.[Arg226*]). We identified 184 patients in our repository with renal agenesis and analyzed their exome/genome data. Of these 184 samples, 36 were from patients who presented with isolated renal agenesis. Two of them had loss-of-function variants in GFRA1. The second patient was homozygous for a frameshift variant (NM_001348097.1:c.1294delA, p.[Thr432Profs*13]). The GFRA1 gene encodes a receptor on the Wolffian duct that regulates ureteric bud outgrowth in the development of a functional renal system, and has a putative role in the pathogenesis of Hirschsprung disease.

CONCLUSIONS

These findings strongly support the causal role of GFRA1-inactivating variants for an autosomal recessive, nonsyndromic form of BRA. This knowledge will enable early genetic diagnosis and better genetic counseling for families with BRA.

Wnt signaling in kidney: the initiator or terminator?

The kidney is a key organ in the human body that excretes toxins and sustains the water-electrolyte balance. During embryonic development and disease progression, the kidney undergoes enormous changes in macrostructure, accompanied by a variety of microstructural histological changes, such as glomerular formation and sclerosis, tubule elongation and atrophy, interstitial establishment, and fibrosis progression. All of these rely on the frequent occurrence of cell death and growth. Notably, to overcome disease, some cells regenerate through self-repair or progenitor cell differentiation. However, the signaling mechanisms underlying kidney development and regeneration have not been elucidated. Recently, Wnt signaling has been noted to play an important role. Although it is a well-known developmental signal, the role of Wnt signaling in kidney development and regeneration is not well recognized. In this review, we review the role of Wnt signaling in kidney embryonic development, tissue repair, cell division, and progenitor cell differentiation after injury. Moreover, we briefly highlight advances in our understanding of the pathogenic mechanisms of Wnt signaling in mediating cellular senescence in kidney parenchymal and stem cells, an irreversible arrest of cell proliferation blocking tissue repair and regeneration. We also highlight the therapeutic targets of Wnt signaling in kidney diseases and provide important clues for clinical strategies.

The struggle to equilibrate outer and inner milieus: Renal evolution revisited

The journey of life, from primordial protoplasm to a complex vertebrate form, is a tale of survival against incessant alterations in climate, surface topography, food chain, and chemistry of the external environment. Kidneys present with an ensemble embodiment of the adaptations devised by diverse life-forms to cope with such challenges and maintain a chemical equilibrium of water and solutes, both in and outside the body. This minireview revisits renal evolution utilizing the classic: From Fish to Philosopher; the story of our internal environment, by Prof. Homer W. Smith (1895-1962) as a template. Prof. Smith's views exemplified the invention of glomeruli, or its abolishment, as a mechanism to filter water. Moreover, with the need to preserve water, as in reptiles, the loop of Henle was introduced to concentrate urine. When compared to smaller mammals, the larger ones, albeit having loops of Henle of similar lengths, demonstrated a distinct packing of the nephrons in kidneys. Moreover, the renal portal system degenerated in mammals, while still present in other vertebrates. This account will present with a critique of the current concepts of renal evolution while examining how various other factors, including the ones that we know more about now, such as genetic factors, synchronize to achieve renal development. Finally, it will try to assess the validity of ideas laid by Prof. Smith with the knowledge that we possess now, and understand the complex architecture that evolution has imprinted on the kidneys during its struggle to survive over epochs.

Preterm birth and neonatal acute kidney injury: implications on adolescent and adult outcomes

As a result of preterm birth, immature kidneys are exposed to interventions in the NICU that promote survival, but are nephrotoxic. Furthermore, the duration of renal development may be truncated in these vulnerable neonates. Immaturity and nephrotoxic exposures predispose preterm newborns to acute kidney injury (AKI), particularly in the low birth weight and extremely preterm gestational age groups. Several studies have associated preterm birth as a risk factor for future chronic kidney disease (CKD). However, only a few publications have investigated the impact of neonatal AKI on CKD development. Here, we will review the evidence linking preterm birth and AKI in the NICU to CKD and highlight the knowledge gaps and opportunities for future research. For neonatal intensive care studies, we propose the inclusion of AKI as an important short-term morbidity outcome and CKD findings such as a reduced glomerular filtration rate in the assessment of long-term outcomes.

Congenital Unilateral Renal Aplasia in a Cynomolgus Monkey (Macaca fascicularis) With Investigation Into Potential Pathogenesis

We describe and characterize unilateral renal aplasia in a cynomolgus monkey (Macaca fascicularis) from a chronic toxicology study adding to the limited histopathology reports of congenital renal anomalies in macaques. In the current case, the affected kidney was macroscopically small and characterized microscopically by a thin cortex with an underdeveloped medulla and an absent papilla. The remnant medulla lacked a corticomedullary junction and contained only a few irregular collecting duct-like structures. The cortex had extensive interstitial mature collagen deposition with fibromuscular collar formation around Bowman's capsules. Due to parenchymal collapse, mature glomeruli were condensed together with occasional atrophic and sclerotic glomeruli. The majority of the cortical tubules were poorly differentiated with only small islands of fully developed cortical tubules present. Histochemical and immunohistochemical stains were utilized to demonstrate key diagnostic features of this congenital defect, to assist with differentiating it from renal dysplasia, and to provide potential mechanistic pathways. Immunostaining (S100, paired box gene 2 [PAX2], aquaporins) of the medulla was compatible with incomplete maturation associated with aplasia, while the immunostaining profile for the cortex (vimentin, calbindin, PAX2-positive cortical tubules, and smooth muscle actin-positive fibromuscular collars) was most compatible with dedifferentiation secondary to degenerative changes.

Recapitulating kidney development in vitro by priming and differentiating mouse embryonic stem cells in monolayers

In order to harness the potential of pluripotent stem cells, we need to understand how to differentiate them to our target cell types. Here, we developed a protocol to differentiate mouse embryonic stem cells (ESCs) to renal progenitors in a step-wise manner. Microarrays were used to track the transcriptional changes at each stage of differentiation and we observed that genes associated with metanephros, ureteric bud, and blood vessel development were significantly upregulated as the cells differentiated towards renal progenitors. Priming the ESCs and optimizing seeding cell density and growth factor concentrations helped improve differentiation efficiency. Organoids were used to determine the developmental potential of the renal progenitor cells. Aggregated renal progenitors gave rise to organoids consisting of LTL+/E-cadherin+ proximal tubules, cytokeratin+ ureteric bud-derived tubules, and extracellular matrix proteins secreted by the cells themselves. Over-expression of key kidney developmental genes, Pax2, Six1, Eya1, and Hox11 paralogs, during differentiation did not improve differentiation efficiency. Altogether, we developed a protocol to differentiate mouse ESCs in a manner that recapitulates embryonic kidney development and showed that precise gene regulation is essential for proper differentiation to occur.

Cellular and Molecular Mechanisms of Kidney Development: From the Embryo to the Kidney Organoid

Development of the metanephric kidney is strongly dependent on complex signaling pathways and cell-cell communication between at least four major progenitor cell populations (ureteric bud, nephron, stromal, and endothelial progenitors) in the nephrogenic zone. In recent years, the improvement of human-PSC-derived kidney organoids has opened new avenues of research on kidney development, physiology, and diseases. Moreover, the kidney organoids provide a three-dimensional (3D) in vitro model for the study of cell-cell and cell-matrix interactions in the developing kidney. In vitro re-creation of a higher-order and vascularized kidney with all of its complexity is a challenging issue; however, some progress has been made in the past decade. This review focuses on major signaling pathways and transcription factors that have been identified which coordinate cell fate determination required for kidney development. We discuss how an extensive knowledge of these complex biological mechanisms translated into the dish, thus allowed the establishment of 3D human-PSC-derived kidney organoids.

Bifurcation analysis of a modular model of embryonic kidney development

Many biological processes show switching behaviors in response to parameter changes. Although numerous surveys have been conducted on bifurcations in biological systems, they commonly focus on over-represented parts of signaling cascades, known as motifs, ignoring the multi-motif structure of biological systems and the communication links between these building blocks. In this paper, a method is proposed which partitions molecular interactions to modules based on a control theory point of view. The modules are defined so that downstream effect of one module is a regulator for its neighboring modules. Communication links between these modules are then considered as bifurcation parameters to reveal change in steady state status of each module. As a case-study, we generated a molecular interaction map of signaling molecules during the development of mammalian embryonic kidneys. The whole system was divided to modules, where each module is defined as a group of interacting molecules that result in expression of a vital downstream regulator. Bifurcation analysis was then performed on these modules by considering the communication signals as bifurcation parameters. Two-parameter bifurcation analysis was then performed to assess the effects of simultaneous input signals on each module behavior. In the case where a module had more than two inputs, a series of two parameter bifurcation diagrams were calculated each corresponding to different values of the third parameter. We detected multi-stability for RET protein as a key regulator for fate determination. This finding is in agreement with experimental data indicating that ureteric bud cells are bi-potential, able to form tip or trunk of the bud based on their RET activity level. Our findings also indicate that Glial cell-derived neurotrophic factor (GDNF), a known potent regulator of kidney development, exerts its fate-determination function on cell placement through destruction of saddle node bifurcation points in RET steady states and confining RET activity level to high activity in ureteric bud tip. In conclusion, embryonic cells usually show a huge decision making potential; the proposed modular modeling of the system in association with bifurcation analysis provides a quantitative holistic view of organ development.

Expression of NADPH oxidase and production of reactive oxygen species contribute to ureteric bud branching and nephrogenesis

Ureteric bud branching and nephrogenesis are performed through large-scale proliferation and apoptosis events during renal development. Reactive oxygen species (ROS), produced by NADPH oxidase, may contribute to cell behaviors, including proliferation and apoptosis. We investigated the role of NADPH oxidase expression and ROS production in developing kidneys. Immunohistochemistry revealed that NADPH oxidase componentswere expressed on epithelial cells in ureteric bud branches, as well as on immature glomerular cells and epithelial cells in nephrogenic zones. ROS production, detected by dihydroethidium assay, was strongly observed in ureteric bud branches and nephrogenic zones, corresponding with NADPH oxidase localization. Organ culture of E14 kidneys revealed that the inhibition of NADPH oxidase significantly reduced the number of ureteric bud branches and tips, consistent with reduced ROS production. This was associated with reduced expression of phosphorylated ERK1/2 and increased expression of cleaved caspase-3. Organ culture of E18 kidneys showed that the inhibition of NADPH oxidase reduced nephrogenic zone size, accompanied by reduced ROS production, fewer proliferating cell nuclear antigen-positive cells, lower p-ERK1/2 expression, and increased expression of cleaved caspase-3. These results demonstrate that ROS produced by NADPH oxidase might play an important role in ureteric bud branching and nephrogenesis by regulating proliferation and apoptosis. J.Med. Invest. 66 :93-98, February, 2019.

miR-194 regulates the proliferation and migration via targeting Hnf1β in mouse metanephric mesenchyme cells

Hepatocyte nuclear factor-1β (Hnf1β) is associated with early embryogenesis failure, renal cysts, and/or diabetes. However, factors regulating Hnf1β expression in metanephric mesenchyme cells remain poorly understood. Here, we analyzed the modulation relationship of Hnf1β and miR-194 in mouse metanephric mesenchyme (MM) cells. Bioinformatics analysis, luciferase assay and semi-quantitative real-time (qPCR), western blotting, 5-ethynyl-2'-deoxyuridine cell proliferation assay, wound healing assay, and flow cytometry were employed to detect the function of miR-194 by targeting on Hnf1β in mouse MM cells. Bioinformatic prediction revealed one conserved binding site (CAGTATT) of miR-194 on Hnf1β 3'-UTR and luciferase reporter assay suggested that this is an effective target site of miR-194, and mutating CAGTATT with CGTACTT had no effects on luciferase activity compared with control. Overexpression of miR-194 decreased Hnf1β mRNA and protein level in mouse MM cells. In addition, miR-194-decreased cell proliferation and miR-194-promoted cell apoptosis and migration were reversed by overexpression of Hnf1β coding region. In addition, Hnf1β-upregulated genes were decreased in miR-194 overexpression cells and rescued in miR-194 and Hnf1β CDS region co-overexpression cells. Our findings explored one new regulator of Hnf1β and revealed the function of their regulation in cell proliferation, migration, and apoptosis in mouse metanephric mesenchyme cells. For strict regulation of Hnf1β in kidney development, these findings provide theoretical guidance for kidney development study and kidney disease therapy.

Conditional ablation of the prorenin receptor in nephron progenitor cells results in developmental programming of hypertension

Nephron induction during kidney development is driven by reciprocal interactions between progenitor cells (NPCs) of the cap mesenchyme (CM) and the ureteric bud (UB). The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump V‐ATPase. Previously, we demonstrated that conditional ablation of the PRR in Six2⁺NPCs in mice (Six2^PRR−/−) causes early neonatal death. Here, we identified genes that are regulated by PRR in Six2⁺NPCs FACS‐isolated from Six2^PRR−/− and control kidneys on embryonic day E15.5 using whole‐genome expression analysis. Seven genes with expression in CM cells previously shown to direct kidney development, including Notch1, β‐catenin, Lef1, Lhx1, Jag1, and p53, were downregulated. The functional groups within the downregulated gene set included genes involved in embryonic and cellular development, renal regeneration, cellular assembly and organization, cell morphology, death and survival. Double‐transgenic Six2^PRR−/−/BatGal⁺ mice, a reporter strain for β‐catenin transcriptional activity, showed decreased β‐catenin activity in the UB in vivo. Reduced PRR gene dosage in heterozygous Six2^PRR+/− mice was associated with decreased glomerular number, segmental thickening of the glomerular basement membrane with focal podocyte foot process effacement, development of hypertension and increased soluble PRR (sPRR) levels in the urine at 2 months of age. Together, these data demonstrate that NPC PRR performs essential functions during nephrogenesis via control of hierarchy of genes that regulate critical cellular processes. Both reduced nephron endowment and augmented urine sPRR likely contribute to programming of hypertension in Six2^PRR+/− mice.

A Novel Hybrid Cytokine IL233 Mediates regeneration following Doxorubicin-Induced Nephrotoxic Injury

Kidney injury, whether due to ischemic insults or chemotherapeutic agents, is exacerbated by inflammation, whereas Tregs are protective. We recently showed that IL-2 and IL-33, especially as a hybrid cytokine (IL233 - bearing IL-2 and IL-33 activities in one molecule), potentiated Tregs and group 2 innate lymphoid cells (ILC2) to prevent renal injury. Recent studies have indicated a reparative function for Tregs and ILC2. Here, using doxorubicin-induced nephrotoxic renal injury model, we investigated whether IL233 administration either before, late or very late after renal injury can restore kidney structure and function. We found that IL233 treatment even 2-weeks post-doxorubicin completely restored kidney function accompanied with an increase Treg and ILC2 in lymphoid and renal compartments, augmented anti-inflammatory cytokines and attenuated proinflammatory cytokine levels. IL233 treated mice had reduced inflammation, kidney injury (Score values - saline: 3.34 ± 0.334; IL233 pre: 0.42 ± 0.162; IL233 24 hrs: 1.34 ± 0.43; IL233 1 week: 1.2 ± 0.41; IL233 2 week: 0.47 ± 0.37; IL233 24 hrs + PC61: 3.5 ± 0.74) and fibrosis in all treatment regimen as compared to saline controls. Importantly, mice treated with IL233 displayed a reparative program in the kidneys, as evidenced by increased expression of genes for renal progenitor-cells and nephron segments. Our findings present the first evidence of an immunoregulatory cytokine, IL233, which could be a potent therapeutic strategy that augments Treg and ILC2 to not only inhibit renal injury, but also promote regeneration.

Wilms' Tumor Protein 1 and Enzymatic Oxidation of 5-Methylcytosine in Brain Tumors: Potential Perspectives

The patterns of 5-methylcytosine (5mC) and its oxidized derivatives, 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxylcytosine (5caC) are reportedly altered in a range of cancers. Likewise, Wilms' Tumor protein 1 (WT1), a transcription factor essential for urogenital, epicardium, and kidney development exhibits aberrant expression in multiple tumors. Interestingly, WT1 directly interacts with TET proteins that catalyze the enzymatic oxidation of 5mC and exhibits high affinity for 5caC-containing DNA substrates in vitro. Here we review recent developments in the fields of Tet-dependent 5mC oxidation and WT1 biology and explore potential perspectives for studying the interplay between TETs and WT1 in brain tumors.

TGF-β Family Signaling in Ductal Differentiation and Branching Morphogenesis

Epithelial cells contribute to the development of various vital organs by generating tubular and/or glandular architectures. The fully developed forms of ductal organs depend on processes of branching morphogenesis, whereby frequency, total number, and complexity of the branching tissue define the final architecture in the organ. Some ductal tissues, like the mammary gland during pregnancy and lactation, disintegrate and regenerate through periodic cycles. Differentiation of branched epithelia is driven by antagonistic actions of parallel growth factor systems that mediate epithelial-mesenchymal communication. Transforming growth factor-β (TGF-β) family members and their extracellular antagonists are prominently involved in both normal and disease-associated (e.g., malignant or fibrotic) ductal tissue patterning. Here, we discuss collective knowledge that permeates the roles of TGF-β family members in the control of the ductal tissues in the vertebrate body.

Adhesion GPCRs in Kidney Development and Disease

Chronic kidney disease (CKD) represents the fastest growing pathology worldwide with a prevalence of >10% in many countries. In addition, kidney cancer represents 5% of all new diagnosed cancers. As currently no effective therapies exist to restore kidney function after CKD- as well as cancer-induced renal damage, it is important to elucidate new regulators of kidney development and disease as new therapeutic targets. G protein-coupled receptors (GPCRs) represent the most successful class of pharmaceutical targets. In recent years adhesion GPCRs (aGPCRs), the second largest GPCR family, gained significant attention as they are present on almost all mammalian cells, are associated to a plethora of diseases and regulate important cellular processes. aGPCRs regulate for example cell polarity, mitotic spindle orientation, cell migration, and cell aggregation; all processes that play important roles in kidney development and/or disease. Moreover, polycystin-1, a major regulator of kidney development and disease, contains a GAIN domain, which is otherwise only found in aGPCRs. In this review, we assess the potential of aGPCRs as therapeutic targets for kidney disease. For this purpose we have summarized the available literature and analyzed data from the databases The Human Protein Atlas, EURExpress, Nephroseq, FireBrowse, cBioPortal for Cancer Genomics and the National Cancer Institute Genomic Data Commons data portal (NCIGDC). Our data indicate that most aGPCRs are expressed in different spatio-temporal patterns during kidney development and that altered aGPCR expression is associated with a variety of kidney diseases including CKD, diabetic nephropathy, lupus nephritis as well as renal cell carcinoma. We conclude that aGPCRs present a promising new class of therapeutic targets and/or might be useful as diagnostic markers in kidney disease.

Concepts for a therapeutic prolongation of nephrogenesis in preterm and low-birth-weight babies must correspond to structural-functional properties in the nephrogenic zone

Numerous investigations are dealing with anlage of the mammalian kidney and primary development of nephrons. However, only few information is available about the last steps in kidney development leading at birth to a downregulation of morphogen activity in the nephrogenic zone and to a loss of stem cell niches aligned beyond the organ capsule. Surprisingly, these natural changes in the developmental program display similarities to processes occurring in the kidneys of preterm and low-birth-weight babies. Although those babies are born at a time with a principally intact nephrogenic zone and active niches, a high proportion of them suffers on impairment of nephrogenesis resulting in oligonephropathy, formation of atypical glomeruli, and immaturity of parenchyma. The setting points out that up to date not identified noxae in the nephrogenic zone hamper primary steps of parenchyma development. In this situation, a possible therapeutic aim is to prolong nephrogenesis by medications. However, actual data provide information that administration of drugs is problematic due to an unexpectedly complex microanatomy of the nephrogenic zone, in niches so far not considered textured extracellular matrix and peculiar contacts between mesenchymal cell projections and epithelial stem cells via tunneling nanotubes. Thus, it remains to be figured out whether disturbance of morphogen signaling altered synthesis of extracellular matrix, disturbed cell-to-cell contacts, or modified interstitial fluid impair nephrogenic activity. Due to most unanswered questions, search for eligible drugs prolonging nephrogenesis and their reliable administration is a special challenge for the future.

Novel Insights into the Pathogenesis of Monogenic Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidneys and urinary tract (CAKUT) comprise a large spectrum of congenital malformations ranging from severe manifestations, such as renal agenesis, to potentially milder conditions, such as vesicoureteral reflux. CAKUT causes approximately 40% of ESRD that manifests within the first three decades of life. Several lines of evidence indicate that CAKUT is often caused by recessive or dominant mutations in single (monogenic) genes. To date, approximately 40 monogenic genes are known to cause CAKUT if mutated, explaining 5%-20% of patients. However, hundreds of different monogenic CAKUT genes probably exist. The discovery of novel CAKUT-causing genes remains challenging because of this pronounced heterogeneity, variable expressivity, and incomplete penetrance. We here give an overview of known genetic causes for human CAKUT and shed light on distinct renal morphogenetic pathways that were identified as relevant for CAKUT in mice and humans.

Genetics of vesicoureteral reflux and congenital anomalies of the kidney and urinary tract

The definition of congenital anomalies of the kidney and urinary tract (CAKUT) is the disease of structural malformations in the kidney and/or urinary tract containing vesicoureteral reflux (VUR). These anomalies can cause pediatric chronic kidney disease. However, the pathogenesis of CAKUT is not well understood, because identifying the genetic architecture of CAKUT is difficult due to the phenotypic heterogeneity and multifactorial genetic penetrance. We describe the current genetic basis and mechanisms of CAKUT including VUR via approaching the steps and signaling pathways of kidney developmental processes. We also focus on the newly developed strategies and challenges to fully address the role of the associated genes in the pathogenesis of the disease.

TβRII Regulates the Proliferation of Metanephric Mesenchyme Cells through Six2 In Vitro

The transforming growth factor-β (TGFβ) family signaling pathways play an important role in regulatory cellular networks and exert specific effects on developmental programs during embryo development. However, the function of TGFβ signaling pathways on the early kidney development remains unclear. In this work, we aim to detect the underlying role of TGFβ type II receptor (TβRII) in vitro, which has a similar expression pattern as the crucial regulator Six2 during early kidney development. Firstly, the 5-ethynyl-2′-deoxyuridine (EdU) assay showed knock down of TβRII significantly decreased the proliferation ratio of metanephric mesenchyme (MM) cells. Additionally, real-time Polymerase Chain Reaction (PCR) and Western blot together with immunofluorescence determined that the mRNA and protein levels of Six2 declined after TβRII knock down. Also, Six2 was observed to be able to partially rescue the proliferation phenotype caused by the depletion of TβRII. Moreover, bioinformatics analysis and luciferase assay indicated Smad3 could transcriptionally target Six2. Further, the EdU assay showed that Smad3 could also rescue the inhibition of proliferation caused by the knock down of TβRII. Taken together, these findings delineate the important function of the TGFβ signaling pathway in the early development of kidney and TβRII was shown to be able to promote the expression of Six2 through Smad3 mediating transcriptional regulation and in turn activate the proliferation of MM cells.

Genetics of Congenital Anomalies of the Kidney and Urinary Tract: The Current State of Play

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most frequent form of malformation at birth and represent the cause of 40–50% of pediatric and 7% of adult end-stage renal disease worldwide. The pathogenesis of CAKUT is based on the disturbance of normal nephrogenesis, secondary to environmental and genetic causes. Often CAKUT is the first clinical manifestation of a complex systemic disease, so an early molecular diagnosis can help the physician identify other subtle clinical manifestations, significantly affecting the management and prognosis of patients. The number of sporadic CAKUT cases explained by highly penetrant mutations in a single gene may have been overestimated over the years and a genetic diagnosis is missed in most cases, hence the importance of identifying new genetic approaches which can help unraveling the vast majority of unexplained CAKUT cases. The aim of our review is to clarify the current state of play and the future perspectives of the genetic bases of CAKUT.

Renal dysplasia characterized by prominent cartilaginous metaplasia lesions in VACTERL association: A case report

BACKGROUND

Renal dysplasia is the most important cause of end-stage renal disease in children. The histopathological characteristic of dysplasia is primitive tubules with fibromuscular disorganization. Renal dysplasia often includes metaplastic cartilage. Metaplastic cartilage in renal dysplasia has been explained as occurring secondary to vesicoureteral reflux (VUR). Additionally, renal dysplasia is observed in renal dysplasia-associated syndromes, which are combinations of multiple developmental malformations and include VACTERL association.

CASE PRESENTATION

We observed the following multiple developmental malformations in a 108-day-old male infant during a nephrectomy: a nonfunctioning right kidney with VUR, hemidiaphragmatic eventration, a ventricular septal defect (VSD) with tetralogy of Fallot in the heart, cryptorchidism, and hyperdactylia. These developmental anomalies satisfied the diagnostic criteria for VACTERL association. A surgical specimen of the right nonfunctioning kidney revealed prominent cartilaginous metaplasia in the renal dysplasia with VUR. The densities of the ectopic cartilaginous lesions in this nonfunctioning kidney were extraordinarily high compared with other renal dysplasia cases. Giemsa banding of his genome produced normal results. The patient has not undergone further detailed genomic investigation.

CONCLUSION

This case might be a novel type of VACTERL association, that is, renal dysplasia combined with prominent cartilaginous metaplasia, tetralogy of Fallot and VSD of the heart, hemidiaphragmatic eventration, and hyperdactylia.

Maternal determinants of renal mass and function in the fetus and neonate

The impact of adverse maternal and early gestational issues, ranging from maternal-fetal interactions all the way through to premature birth, are recognized as having influence on the subsequent development of chronic diseases later in life. The development of chronic kidney disease (CKD) as a direct result of early life renal injury or a sequela of diseases such as hypertension or diabetes is a good model example of the potential impact that early life events may have on renal development and lifelong function. The global monetary and human resource cost of CKD is exorbitant. Socio-economic factors, along with other factors (genetic and environmental) may significantly influence the timing and display of phenotypic expression in fetuses and neonates at risk for developing CKD, yet very few of these factors are studied or well understood. In general our focus has been directed at treatment once CKD is established. This strategy has been and remains short-sighted and costly. Earlier understanding of the intrauterine determinants of renal mass development (i.e. environmental "biomes", poor maternal-fetal health, socio-economic factors impacting early life events, diet, access to value based health care and educational opportunities on disease evolution) may allow us an opportunity for earlier intervention. This article aims to provide some foundation for improved understanding of the maternal determinants of renal mass and function in the fetus and neonate.

Nephron number, hypertension, and CKD: physiological and genetic insight from humans and animal models

The kidneys play a vital role in the excretion of waste products and the regulation of electrolytes, maintenance of acid-base balance, regulation of blood pressure, and production of several hormones. Any alteration in the structure of the nephron (basic functional unit of the kidney) can have a major impact on the kidney's ability to work efficiently. Progressive decline in kidney function can lead to serious illness and ultimately death if not treated by dialysis or transplantation. While there have been numerous studies that implicate lower nephron numbers as being an important factor in influencing susceptibility to developing hypertension and chronic kidney disease, a direct association has been difficult to establish because of three main limitations: 1) the large variation in nephron number observed in the human population; 2) no established reliable noninvasive methods to determine nephron complement; and 3) to date, nephron measurements have been done after death, which doesn't adequately account for potential loss of nephrons with age or disease. In this review, we will provide an overview of kidney structure/function, discuss the current literature for both humans and other species linking nephron deficiency and cardio-renal complications, as well as describe the major molecular signaling factors involved in nephrogenesis that modulate variation in nephron number. As more detailed knowledge about the molecular determinants of nephron development and the role of nephron endowment in the cardio-renal system is obtained, it will hopefully provide clinicians the ability to accurately identify people at risk to develop CKD/hypertension and lead to a shift in patient care from disease treatment to prevention.

Stem cell therapy: An emerging modality in glomerular diseases

The kidney has been considered a highly terminally differentiated organ with low proliferative potential and thus unlikely to undergo regeneration. Glomerular disease progresses to end-stage renal disease (ESRD), which requires dialysis or renal transplantation for better quality of life for patients with ESRD. Because of the shortage of implantable kidneys and complications such as immune rejection, septicemia and toxicity of immunosuppression, kidney transplantation remains a challenge. Therapeutic options available for glomerular disease include symptomatic treatment and strategies to delay progression. In an attempt to develop innovative treatments by promoting the limited capability of regeneration and repair after kidney injury and overcome the progressive pathological process that is uncontrolled with conventional treatment modalities, stem cell-based therapy has emerged as novel intervention due to its ability to inhibit inflammation and promote regeneration. Recent developments in cell therapy have demonstrated promising therapeutic outcomes in terms of restoration of renal structure and function. This review focuses on stem cell therapy approaches for the treatment of glomerular disease, including the various cell sources used and recent advances in preclinical and clinical studies.

Genetic Syndromes Affecting Kidney Development

Renal anomalies are common birth defects that may manifest as a wide spectrum of anomalies from hydronephrosis (dilation of the renal pelvis and calyces) to renal aplasia (complete absence of the kidney(s)). Aneuploidies and mosaicisms are the most common syndromes associated with CAKUT. Syndromes with single gene and renal developmental defects are less common but have facilitated insight into the mechanism of renal and other organ development. Analysis of underlying genetic mutations with transgenic and mutant mice has also led to advances in our understanding of mechanisms of renal development.

Epigenetics of Renal Development and Disease

An understanding of epigenetics is indispensable to our understanding of gene regulation under normal and pathological states. This knowledge will help with designing better therapeutic approaches in regenerative tissue medicine. Epigenetics allows us to parse out the mechanisms by which transcriptional regulators gain access to specific gene loci thereby imprinting epigenetic information affecting chromatin function. This epigenetic memory forms the basis of cell lineage specification in multicellular organisms. Post-translational modifications to DNA and histones in the nucleosome core form characteristic epigenetic codes which are distinct for self-renewing and primed progenitor cell populations. Studies of chromatin modifiers and modifications in renal development and disease have been gaining momentum. Both congenital and adult renal diseases have a gene-environment component, which involves alterations to the epigenetic information imprinted during development. This epigenetic memory must be characterized to establish optimal treatment of both acute and chronic renal diseases.

Sonic hedgehog protein regulates fibroblast growth factor 8 expression in metanephric explant culture from BALB/c mice: Possible mechanisms associated with renal morphogenesis

The sonic hedgehog (SHH) morphogen regulates cell differentiation and controls a number of genes during renal morphogenesis. To date, the effects of SHH on fibroblast growth factors (Fgfs) in embryonic kidney development remain unclear. In the present study, explants of BALB/c mouse embryonic kidney tissues were used to investigate the role of exogenous SHH on Fgf8 and Fgf10 expression levels ex vivo. Ureteric bud branches and epithelial metanephric derivatives were used to determine the renal morphogenesis with Dolichos biflorus agglutinin or hematoxylin‑eosin staining. mRNA expression levels were determined using reverse transcription‑quantitative polymerase chain reaction, while the protein expression levels were examined using immunohistochemistry and western blot analysis. During the initial stages of metanephric development, low levels of SHH, Fgf8, and Fgf10 expression were observed, which were found to increase significantly during more advanced stages of metanephric development. In addition, exogenous SHH protein treatment increased the number of ureteric bud branches and enhanced the formation of nephrons. Exogenous SHH reduced the Fgf8 mRNA and protein expression levels, whereas cyclopamine (an SHH‑smoothened receptor inhibitor) interfered with SHH‑mediated downregulation of Fgf8 expression. By contrast, exogenous SHH protein was not found to modulate Fgf10 mRNA and protein expression levels. In conclusion, these results indicate that the modulatory effects of SHH on BALB/c mouse metanephric explant cultures may involve the regulation of Fgf8 expression but not Fgf10 expression, which provides evidence for the functional role of Fgf proteins in renal morphogenesis.

Zeb1 Is a Potential Regulator of Six2 in the Proliferation, Apoptosis and Migration of Metanephric Mesenchyme Cells

Nephron progenitor cells surround around the ureteric bud tips (UB) and inductively interact with the UB to originate nephrons, the basic units of renal function. This process is determined by the internal balance between self-renewal and consumption of the nephron progenitor cells, which is depending on the complicated regulation networks. It has been reported that Zeb1 regulates the proliferation of mesenchymal cells in mouse embryos. However, the role of Zeb1 in nephrons generation is not clear, especially in metanephric mesenchyme (MM). Here, we detected cell proliferation, apoptosis and migration in MM cells by EdU assay, flow cytometry assay and wound healing assay, respectively. Meanwhile, Western and RT-PCR were used to measure the expression level of Zeb1 and Six2 in MM cells and developing kidney. Besides, the dual-luciferase assay was conducted to study the molecular relationship between Zeb1 and Six2. We found that knock-down of Zeb1 decreased cell proliferation, migration and promoted cell apoptosis in MM cells and Zeb1 overexpression leaded to the opposite data. Western-blot and RT-PCR results showed that knock-down of Zeb1 decreased the expression of Six2 in MM cells and Zeb1 overexpression contributed to the opposite results. Similarly, Zeb1 promoted Six2 promoter reporter activity in luciferase assays. However, double knock-down of Zeb1 and Six2 did not enhance the apoptosis of MM cells compared with control cells. Nevertheless, double silence of Zeb1 and Six2 repressed cell proliferation. In addition, we also found that Zeb1 and Six2 had an identical pattern in distinct developing phases of embryonic kidney. These results indicated that there may exist a complicated regulation network between Six2 and Zeb1. Together, we demonstrate Zeb1 promotes proliferation and apoptosis and inhibits the migration of MM cells, in association with Six2.

Genetics of Vesicoureteral Reflux

Vesicoureteral reflux (VUR) is the retrograde passage of urine from the bladder to the upper urinary tract. It is the most common congenital urological anomaly affecting 1-2% of children and 30-40% of patients with urinary tract infections. VUR is a major risk factor for pyelonephritic scarring and chronic renal failure in children. It is the result of a shortened intravesical ureter with an enlarged or malpositioned ureteric orifice. An ectopic embryonal ureteric budding development is implicated in the pathogenesis of VUR, which is a complex genetic developmental disorder. Many genes are involved in the ureteric budding formation and subsequently in the urinary tract and kidney development. Previous studies demonstrate an heterogeneous genetic pattern of VUR. In fact no single major locus or gene for primary VUR has been identified. It is likely that different forms of VUR with different genetic determinantes are present. Moreover genetic studies of syndromes with associated VUR have revealed several possible candidate genes involved in the pathogenesis of VUR and related urinary tract malformations. Mutations in genes essential for urinary tract morphogenesis are linked to numerous congenital syndromes, and in most of those VUR is a feature. The Authors provide an overview of the developmental processes leading to the VUR. The different genes and signaling pathways controlling the embryonal urinary tract development are analyzed. A better understanding of VUR genetic bases could improve the management of this condition in children.