The number of fetal nephron progenitor cells limits ureteric branching and adult nephron endowment

Motor learning is regulated by postnatal GDNF levels in Purkinje cells

Purkinje cells (PCs), the sole output neurons of the cerebellar cortex, are crucial for cerebellum-dependent motor learning. In cerebellar ataxia, reduction in motor function and learning associates with decreased spontaneous activity of PCs. Thus, understanding what molecules regulate PCs activity is important. Previously, we demonstrated that a ubiquitous 2-fold increase of endogenous glial cell line-derived neurotrophic factor (GDNF) improves motor function in adult mice and motor learning and coordination in aged mice. However, since GDNF impacts many organ systems the underlying mechanism remained elusive. Here we utilize GDNF Hypermorphic, conditional GDNF Hypermorphic and conditional knock-out mouse models to reveal that up to a 2-fold increase in endogenous GDNF, specifically in PCs postnatally, is sufficient to enhance motor learning. We find that improved motor learning associates with increased glutamatergic input to PCs and with elevated spontaneous firing rate of PCs, opposite to cerebellar ataxia where reduction in motor function and learning associates with decreased spontaneous activity of PCs. Analysis of the human cerebellum revealed that normal interindividual variation in GDNF expression levels falls in the same variation range as studied in the mouse models, suggesting that interindividual variation in PC GDNF levels may contribute to interindividual variation in PC function. Collectively, our findings reveal how a relatively small change in postnatal GDNF expression level within the physiological range in one cell type, the PCs, affects motor learning. Thus, drugs enhancing postnatal GDNF expression in PCs or cerebellar GDNF signaling may have potential in treating cerebellar ataxias, making an interesting topic for future studies.

Absent, Small, or Homeotic 2-Like-Mediated H3K4 Methylation and Nephrogenesis

Key Points

Deficits in nephron numbers are associated with higher risk of adult-onset kidney disease seen in congenital anomalies of the kidney and urinary tract. Mouse model experiments suggested that absent, small, or homeotic 2-like was vital for kidney development by activating cell cycle genes through histone methylation. Our findings identified absent, small, or homeotic 2-like–regulated genes as a potential target for treating congenital anomalies of the kidney and urinary tract.

Background

Many congenital anomalies of the kidney and urinary tract involve deficits in the number of nephrons, which are associated with a higher risk of hypertension and CKD later in life. Prior work has implicated histone modifications in regulating kidney lineage–specific gene transcription and nephron endowment. Our earlier study suggested that absent, small, or homeotic 2-like (ASH2L), a core subunit of the H3K4 methyltransferase complex, plays a role in ureteric bud morphogenesis during mammalian kidney development. However, the potential involvement of ASH2L in nephron formation remains an open question.

Methods

To investigate the role of ASH2L in nephron development, we inactivated Ash2l specifically in nephron progenitor cells by crossing Six2 -e(Kozak-GFPCre-Wpre-polyA)1 mice with Ash2l fl/fl mice. We used RNA sequencing combined with Cleavage Under Targets and Tagmentation sequencing to screen for gene and epigenomic changes, which were further verified by rescue experiments conducted on ex vivo culture explants.

Results

Inactivating ASH2L in nephron progenitor cells disrupted H3K4 trimethylation establishment at promoters of genes controlling nephron progenitor cell stemness, differentiation, and cell cycle, inhibiting their progression through the cell cycle and differentiation into epithelial cell types needed to form nephrons. Inhibition of the TGF-β /suppressor of mothers against decapentaplegic signaling pathway partially rescued the dysplastic phenotype of the mutants.

Conclusions

ASH2L-mediated H3K4 methylation was identified as a novel epigenetic regulator of kidney development. Downregulation of ASH2L expression or H3K4 trimethylation may be linked to congenital anomalies of the kidney and urinary tract.

Methylseq, single-nuclei RNAseq, and discovery proteomics identify pathways associated with nephron-deficit CKD in the HSRA rat model

Low nephron numbers are associated with an increased risk of developing chronic kidney disease (CKD) and hypertension, which are significant global health problems. To investigate the impact of nephron deficiency, our laboratory developed a novel inbred rat model (HSRA rat). In this model, ∼75% of offspring are born with a single kidney (HSRA-S), compared with two-kidney littermates (HSRA-C). HSRA-S rats show impaired kidney development, resulting in ∼20% fewer nephrons. Our previous data and current findings demonstrate that nephron deficit (failure of one kidney to form and altered development in the remaining kidney) predisposes HSRA-S to CKD late in life (with increased proteinuria by 18 mo of age in HSRA-S = 51 ± 3.4 vs. HSRA-C = 8 ± 1.5 mg/24 h). To understand early molecular mechanisms contributing to the increased predisposition to CKD, Methylseq using reduced representation bisulfite sequencing, single-nuclei (sn)RNAseq, and discovery proteomics were performed in kidneys of 4-wk-old HSRA rats. Methylation analysis revealed a small number of differences, including five differentially methylated cytosines and six differentially methylated regions between groups. The snRNAseq analysis identified differentially expressed genes in most kidney cell types, with several hundred genes dysregulated depending on the analysis method (Seurat vs. DESeq2). Notably, many genes are involved in kidney development. Discovery proteomic analysis identified 366 differentially expressed proteins. A key finding was dysregulation of Deptor/DEPTOR and Amdhd2/AMDHD2 across omics layers, suggesting a potential role in compensatory mechanisms or the genetic basis of altered kidney development. Further understanding of these mechanisms may guide interventions to preserve nephron health and slow kidney disease progression.NEW & NOTEWORTHY The HSRA rat is a novel model of nephron deficiency and provides a unique opportunity to study the association between nephron number and chronic kidney disease (CKD). Previous work characterized the impact of age, hypertension, and diabetes on the development of CKD in HSRA animals. This study examined early changes in epigenetics, cell-type specific transcriptome, and proteomic changes in the kidney that likely predispose the model to CKD with age.

Cystic fibrosis-related kidney disease-emerging morbidity and disease modifier

Cystic fibrosis (CF) is a life-shortening multisystem disease resulting from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, causing the most devastating phenotypes in the airway and pancreas. Significant advances in treatment for CF lung disease, including the expanded use of high-efficiency modulator therapies (HEMT) such as Trikafta, have dramatically increased both quality of life and life expectancy for people with CF (PwCF). With these advances, long-term extrapulmonary manifestations are more frequently recognized. Pseudo-Barter syndrome, acute kidney injury (AKI) induced by medications or dehydration, amyloidosis, nephrolithiasis, and IgA and diabetic nephropathies have been previously reported in PwCF. Newer data suggest that chronic kidney disease (CKD) is a new morbidity in the aging CF population, affecting 19% of people over age 55. CKD carries a high risk of premature death from cardiovascular complications. Studies suggest that CFTR dysfunction increases kidneys' vulnerability to injury caused by the downstream effects of CF. Improving the mutant CFTR function by HEMT may help to tease apart the kidney responses resulting from extrinsic factors and those intrinsically related to the CFTR gene mutations. Additionally, given the novelty of HEMT approaches, the potential off-target effects of their long-term use are currently unknown. We review the evolving kidney complications in PwCF and propose the term CF-related kidney disease. We hope this review will increase awareness about the changing phenotype of kidney dysfunction in PwCF and help prevent morbidity related to this condition.

Mesenchymal GDNF promotes intestinal enterochromaffin cell differentiation

Enteroendocrine cells (EECs) differentiate and mature to form functionally distinct populations upon migration along the intestinal crypt-villus axis, but how niche signals affect this process is poorly understood. Here, we identify expression of Glial cell line-derived neurotrophic factor (GDNF) in the intestinal subepithelial myofibroblasts (SEMFs), while the GDNF receptor RET was expressed in a subset of EECs, suggesting GDNF-mediated regulation. Indeed, GDNF-RET signaling induced increased expression of EEC genes including Tph1, encoding for the rate-limiting enzyme for 5-hydroxytryptamine (5-HT, serotonin) biosynthesis, and increased the frequency of 5-HT+ enterochromaffin cells (ECs) in mouse organoid culture experiments and in vivo. Moreover, expression of the 5-HT receptor Htr4 was enriched in Lgr5+ intestinal stem cells (ISCs) and 5-HT reduced the ISC clonogenicity. In summary, our results show that GDNF-RET signaling regulate EEC differentiation, and suggest 5-HT as a potential niche factor regulating Lgr5+ ISC activity, with potential implications in intestinal regeneration.

Microplastics exposure disrupts nephrogenesis and induces renal toxicity in human iPSC-derived kidney organoids

Microplastics (MPs) have emerged as a pervasive environmental pollutant of global concern. Their detection within the human placenta and fetal organs has prompted apprehension regarding the potential hazards of MPs during early organogenesis. The kidney, a vital multifunctional organ, is susceptible to damage from MPs in adulthood. However, the precise adverse effects of MP exposure on human nephrogenesis remain ambiguous due to the absence of a suitable model. Here, we explore the potential impact of MPs on early kidney development utilizing human kidney organoids in vitro. Human kidney organoids were subjected to polystyrene-MPs (PS-MPs, 1 μm) during the nephron progenitor cell (NPC) stage, a critical phase in early kidney development and patterning. We delineate the effects of PS-MPs on various stages of nephrogenesis, including NPC, renal vesicle, and comma-shaped body, through sequential examination of kidney organoids. PS-MPs were observed to adhere to the surface of cells during the NPC stage and accumulate within glomerulus-like structures within kidney organoids. Moreover, both short- and long-term exposure to PS-MPs resulted in diminished organoid size and aberrant nephron structure. PS-MP exposure heightened reactive oxygen species (ROS) production, leading to NPC apoptosis during early kidney development. Increased apoptosis, diminished cell viability, and NPC reduction likely contribute to the observed organoid size reduction under PS-MP treatment. Transcriptomic analysis at both NPC and endpoint stages revealed downregulation of Notch signaling, resulting in compromised proximal and distal tubular structures, thereby disrupting normal nephron patterning following PS-MP exposure. Our findings highlight the significant disruptive impact of PS-MPs on human kidney development, offering new insights into the mechanisms underlying PS-MP-induced nephron toxicity.

Jamming of nephron-forming niches in the developing mouse kidney creates cyclical mechanical stresses

Urinary collecting tubules form during kidney embryogenesis through the branching of the ureteric bud epithelium. A travelling mesenchyme niche of nephron progenitor cells caps each branching ureteric bud tip. These 'tip domain' niches pack more closely over developmental time and their number relates to nephron endowment at birth. Yet, how the crowded tissue environment impacts niche number and cell decision-making remains unclear. Here, through experiments and mathematical modelling, we show that niche packing conforms to physical limitations imposed by kidney curvature. We relate packing geometries to rigidity theory to predict a stiffening transition starting at embryonic day 15 in the mouse, validated by micromechanical analysis. Using a method to estimate tip domain 'ages' relative to their most recent branch events, we find that new niches overcome mechanical resistance as they branch and displace neighbours. This creates rhythmic mechanical stress in the niche. These findings expand our understanding of kidney development and inform engineering strategies for synthetic regenerative tissues.

Expression pattern of Runt-related transcription factor (RUNX) family members and the role of RUNX1 during kidney development

Runt-related transcription factor (RUNX) family members play critical roles in the development of multiple organs. Mammalian RUNX family members, consisting of RUNX1, RUNX2, and RUNX3, have distinct tissue-specific expression and function. In this study, we examined the spatiotemporal expression patterns of RUNX family members in developing kidneys and analyzed the role of RUNX1 during kidney development. In the developing mouse kidney, RUNX1 protein was strongly expressed in the ureteric bud (UB) tip and weakly expressed in the distal segment of the renal vesicle (RV), comma-shaped body (CSB), and S-shaped body (SSB). In contrast, RUNX2 protein was restricted to the stroma, and RUNX3 protein was only expressed in immune cells. We also analyzed the expression of RUNX family members in the cynomolgus monkey kidney. We found that expression patterns of RUNX2 and RUNX3 were conserved between rodents and primates, whereas RUNX1 was only expressed in the UB tip, not in the RV, CSB, or SSB of cynomolgus monkeys, suggesting a species differences. We further evaluated the roles of RUNX1 using two different conditional knockout mice: Runx1f/f:HoxB7-Cre and Runx1f/f:R26-CreERT2 and found no abnormalities in the kidney. Our findings showed that RUNX1, which is mainly expressed in the UB tip, is not essential for kidney development.

Collagen XVIII regulates extracellular matrix integrity in the developing nephrons and impacts nephron progenitor cell behavior

Renal development is a complex process in which two major processes, tubular branching and nephron development, regulate each other reciprocally. Our previous findings have indicated that collagen XVIII (ColXVIII), an extracellular matrix protein, affects the renal branching morphogenesis. We investigate here the role of ColXVIII in nephron formation and the behavior of nephron progenitor cells (NPCs) using isoform-specific ColXVIII knockout mice. The results show that the short ColXVIII isoform predominates in the early epithelialized nephron structures whereas the two longer isoforms are expressed only in the later phases of glomerular formation. Meanwhile, electron microscopy showed that the ColXVIII mutant embryonic kidneys have ultrastructural defects at least from embryonic day 16.5 onwards. Similar structural defects had previously been observed in adult ColXVIII-deficient mice, indicating a congenital origin. The lack of ColXVIII led to a reduced NPC population in which changes in NPC proliferation and maintenance and in macrophage influx were perceived to play a role. The changes in NPC behavior in turn led to notably reduced overall nephron formation. In conclusion, the results show that ColXVIII has multiple roles in renal development, both in ureteric branching and in NPC behavior.

Highly parallel production of designer organoids by mosaic patterning of progenitors

Organoids derived from human stem cells are a promising approach for disease modeling, regenerative medicine, and fundamental research. However, organoid variability and limited control over morphological outcomes remain as challenges. One open question is the extent to which engineering control over culture conditions can guide organoids to specific compositions. Here, we extend a DNA "velcro" cell patterning approach, precisely controlling the number and ratio of human induced pluripotent stem cell-derived progenitors contributing to nephron progenitor (NP) organoids and mosaic NP/ureteric bud (UB) tip cell organoids within arrays of microwells. We demonstrate long-term control over organoid size and morphology, decoupled from geometric constraints. We then show emergent trends in organoid tissue proportions that depend on initial progenitor cell composition. These include higher nephron and stromal cell representation in mosaic NP/UB organoids vs. NP-only organoids and a "goldilocks" initial cell ratio in mosaic organoids that optimizes the formation of proximal tubule structures.

Early-life exposures and long-term health: adverse gestational environments and the programming of offspring renal and vascular disease

According to the Developmental Origins of Health and Disease hypothesis, exposure to certain environmental influences during early life may be a key determinant of fetal development and short- and long-term offspring health. Indeed, adverse conditions encountered during the fetal, perinatal, and early childhood stages can alter normal development and growth, as well as put the offspring at elevated risk of developing long-term health conditions in adulthood, including chronic kidney disease and cardiovascular diseases. Of relevance in understanding the mechanistic basis of these long-term health conditions are previous findings showing low glomerular number in human intrauterine growth restriction and low birth weight-indicators of a suboptimal intrauterine environment. In different animal models, the main suboptimal intrauterine conditions studied relate to maternal dietary manipulations, poor micronutrient intake, prenatal ethanol exposure, maternal diabetes, glucocorticoid and chemical exposure, hypoxia, and placental insufficiency. These studies have demonstrated changes in kidney structure, glomerular endowment, and expression of key genes and signaling pathways controlling endocrine, excretion, and filtration function of the offspring. This review aims to summarize those studies to uncover the effects and mechanisms by which adverse gestational environments impact offspring renal and vascular health in adulthood. This is important for identifying agents and interventions that can prevent and mitigate the long-term consequences of an adverse intrauterine environment on the subsequent generation.NEW & NOTEWORTHY Human data and experimental animal data show that suboptimal environments during fetal development increase the risk of renal and vascular diseases in adult-life. This is related to permanent changes in kidney structure, function, and expression of genes and signaling pathways controlling filtration, excretion, and endocrine function. Uncovering the mechanisms by which offspring renal development and function is impacted is important for identifying ways to mitigate the development of diseases that strain health care services worldwide.

Striatal GDNF Neurons Chemoattract RET-Positive Dopamine Axons at Seven Times Farther Distance Than Medium Spiny Neurons

Glial cell line-derived neurotrophic factor (GDNF) is among the strongest dopamine neuron function- and survival-promoting factors known. Due to this reason, it has clinical relevance in dopamine disorders such as Parkinson's disease and schizophrenia. In the striatum, GDNF is exclusively expressed in interneurons, which make up only about 0.6% of striatal cells. Despite clinical significance, histological analysis of striatal GDNF system arborization and relevance to incoming dopamine axons, which bear its receptor RET, has remained enigmatic. This is mainly due to the lack of antibodies able to visualize GDNF- and RET-positive cellular processes; here, we overcome this problem by using knock-in marker alleles. We find that GDNF neurons chemoattract RET+ axons at least seven times farther in distance than medium spiny neurons (MSNs), which make up 95% of striatal neurons. Furthermore, we provide evidence that tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, is enriched towards GDNF neurons in the dopamine axons. Finally, we find that GDNF neuron arborizations occupy approximately only twelve times less striatal volume than 135 times more abundant MSNs. Collectively, our results improve our understanding of how endogenous GDNF affects striatal dopamine system function.

The Molecular Basis of the Augmented Cardiovascular Risk in Offspring of Mothers with Hypertensive Disorders of Pregnancy

The review examines the impact of maternal preeclampsia (PE) on the cardiometabolic and cardiovascular health of offspring. PE, a hypertensive disorder of pregnancy, is responsible for 2 to 8% of pregnancy-related complications. It significantly contributes to adverse outcomes for their infants, affecting the time of birth, the birth weight, and cardiometabolic risk factors such as blood pressure, body mass index (BMI), abdominal obesity, lipid profiles, glucose, and insulin. Exposure to PE in utero predisposes offspring to an increased risk of cardiometabolic diseases (CMD) and cardiovascular diseases (CVD) through mechanisms that are not fully understood. The incidence of CMD and CVD is constantly increasing, whereas CVD is the main cause of morbidity and mortality globally. A complex interplay of genes, environment, and developmental programming is a plausible explanation for the development of endothelial dysfunction, which leads to atherosclerosis and CVD. The underlying molecular mechanisms are angiogenic imbalance, inflammation, alterations in the renin-angiotensin-aldosterone system (RAAS), endothelium-derived components, serotonin dysregulation, oxidative stress, and activation of both the hypothalamic-pituitary-adrenal axis and hypothalamic-pituitary-gonadal axis. Moreover, the potential role of epigenetic factors, such as DNA methylation and microRNAs as mediators of these effects is emphasized, suggesting avenues for future research and therapeutic interventions.

Electrophysiological Properties of Proprioception-Related Neurons in the Intermediate Thoracolumbar Spinal Cord

Proprioception, the sense of limb and body position, is required to produce accurate and precise movements. Proprioceptive sensory neurons transmit muscle length and tension information to the spinal cord. The function of excitatory neurons in the intermediate spinal cord, which receive this proprioceptive information, remains poorly understood. Using genetic labeling strategies and patch-clamp techniques in acute spinal cord preparations in mice, we set out to uncover how two sets of spinal neurons, Clarke's column (CC) and Atoh1-lineage neurons, respond to electrical activity and how their inputs are organized. Both sets of neurons are located in close proximity in laminae V-VII of the thoracolumbar spinal cord and have been described to receive proprioceptive signals. We find that a majority of CC neurons have a tonic-firing type and express a distinctive hyperpolarization-activated current (Ih). Atoh1-lineage neurons, which cluster into two spatially distinct populations, are mostly a fading-firing type and display similar electrophysiological properties to each other, possibly due to their common developmental lineage. Finally, we find that CC neurons respond to stimulation of lumbar dorsal roots, consistent with prior knowledge that CC neurons receive hindlimb proprioceptive information. In contrast, using a combination of electrical stimulation, optogenetic stimulation, and transsynaptic rabies virus tracing, we find that Atoh1-lineage neurons receive heterogeneous, predominantly local thoracic inputs that include parvalbumin-lineage sensory afferents and local interneuron presynaptic inputs. Altogether, we find that CC and Atoh1-lineage neurons have distinct membrane properties and sensory input organization, representing different subcircuit modes of proprioceptive information processing.

Recent advances in host-focused molecular tools for investigating host-gut microbiome interactions

Microbial communities in the human gut play a significant role in regulating host gene expression, influencing a variety of biological processes. To understand the molecular mechanisms underlying host-microbe interactions, tools that can dissect signaling networks are required. In this review, we discuss recent advances in molecular tools used to study this interplay, with a focus on those that explore how the microbiome regulates host gene expression. These tools include CRISPR-based whole-body genetic tools for deciphering host-specific genes involved in the interaction process, Cre-loxP based tissue/cell-specific gene editing approaches, and in vitro models of host-derived organoids. Overall, the application of these molecular tools is revolutionizing our understanding of how host-microbiome interactions contribute to health and disease, paving the way for improved therapies and interventions that target microbial influences on the host.

Impact of preterm birth on kidney health and development

Preterm birth, defined as birth before the gestational age of 37 weeks, affects 11% of the newborns worldwide. While extensive research has focused on the immediate complications associated with prematurity, emerging evidence suggests a link between prematurity and the development of kidney disease later in life. It has been demonstrated that the normal course of kidney development is interrupted in infants born prematurely, causing an overall decrease in functional nephrons. Yet, the pathogenesis leading to the alterations in kidney development and the subsequent pathophysiological consequences causing kidney disease on the long-term are incompletely understood. In the present review, we discuss the current knowledge on nephrogenesis and how this process is affected in prematurity. We further discuss the epidemiological evidence and experimental data demonstrating the increased risk of kidney disease in these individuals and highlight important knowledge gaps. Importantly, understanding the intricate interplay between prematurity, abnormal kidney development, and the long-term risk of kidney disease is crucial for implementing effective preventive and therapeutic strategies.

Highly-parallel production of designer organoids by mosaic patterning of progenitors

Human organoids are a promising approach for disease modeling and regenerative medicine. However, organoid variability and limited control over morphological outcomes remain significant challenges. Here we extend a DNA 'velcro' cell patterning approach, precisely controlling the number and ratio of human stem cell-derived progenitors contributing to nephron and mosaic nephron/ureteric bud organoids within arrays of microwells. We demonstrate long-term control over organoid size and morphology, decoupled from geometric constraints.

Deletion of NuRD component Mta2 in nephron progenitor cells causes developmentally programmed FSGS

Low nephron endowment at birth is a risk factor for chronic kidney disease. The prevalence of this condition is increasing due to higher survival rates of preterm infants and children with multi- organ birth defect syndromes that affect the kidney and urinary tract. We created a mouse model of congenital low nephron number due to deletion of Mta2 in nephron progenitor cells. Mta2 is a core component of the Nucleosome Remodeling and Deacetylase (NuRD) chromatin remodeling complex. These mice developed albuminuria at 4 weeks of age followed by focal segmental glomerulosclerosis (FSGS) at 8 weeks, with progressive kidney injury and fibrosis. Our studies reveal that altered mitochondrial metabolism in the post-natal period leads to accumulation of neutral lipids in glomeruli at 4 weeks of age followed by reduced mitochondrial oxygen consumption. We found that NuRD cooperated with Zbtb7a/7b to regulate a large number of metabolic genes required for fatty acid oxidation and oxidative phosphorylation. Analysis of human kidney tissue also supported a role for reduced mitochondrial lipid metabolism and ZBTB7A/7B in FSGS and CKD. We propose that an inability to meet the physiological and metabolic demands of post-natal somatic growth of the kidney promotes the transition to CKD in the setting of glomerular hypertrophy due to low nephron endowment.

The developing murine kidney actively negotiates geometric packing conflicts to avoid defects

The physiological functions of several organs rely on branched epithelial tubule networks bearing specialized structures for secretion, gas exchange, or filtration. Little is known about conflicts in development between building enough tubules for adequate function and geometric constraints imposed by organ size. We show that the mouse embryonic kidney epithelium negotiates a physical packing conflict between increasing tubule tip numbers through branching and limited organ surface area. Through imaging of whole kidney explants, combined with computational and soft material modeling of tubule families, we identify six possible geometric packing phases, including two defective ones. Experiments in explants show that a radially oriented tension on tubule families is necessary and sufficient for them to switch to a vertical packing arrangement that increases surface tip density while avoiding defects. These results reveal developmental contingencies in response to physical limitations and create a framework for classifying congenital kidney defects.

Regulation of nephron progenitor cell lifespan and nephron endowment

Low nephron number - resulting, for example, from prematurity or developmental anomalies - is a risk factor for the development of hypertension, chronic kidney disease and kidney failure. Considerable interest therefore exists in the mechanisms that regulate nephron endowment and contribute to the premature cessation of nephrogenesis following preterm birth. The cessation of nephrogenesis in utero or shortly after birth is synchronized across multiple niches in all mammals, and is coupled with the exhaustion of nephron progenitor cells. Consequently, no nephrons are formed after the cessation of developmental nephrogenesis, and lifelong renal function therefore depends on the complement of nephrons generated during gestation. In humans, a tenfold variation in nephron endowment between individuals contributes to differences in susceptibility to kidney disease; however, the mechanisms underlying this variation are not yet clear. Salient advances in our understanding of environmental inputs, and of intrinsic molecular mechanisms that contribute to the regulation of cessation timing or nephron progenitor cell exhaustion, have the potential to inform interventions to enhance nephron endowment and improve lifelong kidney health for susceptible individuals.

Physiology assays in human kidney organoids

Kidney organoids derived from human pluripotent stem cells constitute a novel model of disease, development, and regenerative therapy. Organoids are human, experimentally accessible, high throughput, and enable reconstitution of tissue-scale biology in a petri dish. Although gene expression patterns in organoid cells have been analyzed extensively, less is known about the functionality of these structures. Here, we review assays of physiological function in human kidney organoids, including best practices for quality control, and future applications. Tubular structures in organoids accumulate specific molecules through active transport, including dextran and organic anions, and swell with fluid in response to cAMP stimulation. When engrafted into animal models in vivo, organoids form vascularized glomerulus-like structures capable of size-selective filtration. Organoids exhibit metabolic, endocrine, injury, and infection phenotypes, although their specificity is not yet fully clear. To properly interpret organoid physiology assays, it is important to incorporate appropriate negative and positive controls, statistical methods, data presentation, molecular mechanisms, and clinical data sets. Improvements in organoid perfusion, patterning, and maturation are needed to enable branching morphogenesis, urine production, and renal replacement. Reconstituting renal physiology with kidney organoids is a new field with potential to provide fresh insights into classical phenomena.

Critical windows of perinatal particulate matter (PM2.5) exposure and preadolescent kidney function

Air pollution exposure, especially particulate matter ≤2.5 μm in diameter (PM2.5), is associated with poorer kidney function in adults and children. Perinatal exposure may occur during susceptible periods of nephron development. We used distributed lag nonlinear models (DLNMs) to examine time-varying associations between early life daily PM2.5 exposure (periconceptional through age 8 years) and kidney parameters in preadolescent children aged 8-10 years. Participants included 427 mother-child dyads enrolled in the PROGRESS birth cohort study based in Mexico City. Daily PM2.5 exposure was estimated at each participant's residence using a validated satellite-based spatio-temporal model. Kidney function parameters included estimated glomerular filtration rate (eGFR), serum cystatin C, and blood urea nitrogen (BUN). Models were adjusted for child's age, sex and body mass index (BMI) z-score, as well as maternal education, indoor smoking report and seasonality (prenatal models were additionally adjusted for average first year of life PM2.5 exposure). We also tested for sex-specific effects. Average perinatal PM2.5 was 22.7 μg/m3 and ranged 16.4-29.3 μg/m3. Early pregnancy PM2.5 exposures were associated with higher eGFR in preadolescence. Specifically, we found that PM2.5 exposure between weeks 1-18 of gestation was associated with increased preadolescent eGFR, whereas exposure in the first 14 months of life after birth were associated with decreased eGFR. Specifically, a 5 μg/m3 increase in PM2.5 during the detected prenatal window was associated with a cumulative increase in eGFR of 4.44 mL/min/1.732 (95%CI: 1.37, 7.52), and during the postnatal window we report a cumulative eGFR decrease of -10.36 mL/min/1.732 (95%CI: -17.68, -3.04). We identified perinatal windows of susceptibility to PM2.5 exposure with preadolescent kidney function parameters. Follow-up investigating PM2.5 exposure with peripubertal kidney function trajectories and risk of kidney disease in adulthood will be critical.

Chromatin accessibility and microRNA expression in nephron progenitor cells during kidney development

Mammalian nephrons originate from a population of nephron progenitor cells, and changes in these cells' transcriptomes contribute to the cessation of nephrogenesis, an important determinant of nephron number. To characterize microRNA (miRNA) expression and identify putative cis-regulatory regions, we collected nephron progenitor cells from mouse kidneys at embryonic day 14.5 and postnatal day zero and assayed small RNA expression and transposase-accessible chromatin. We detect expression of 1104 miRNA (114 with expression changes), and 46,374 chromatin accessible regions (2103 with changes in accessibility). Genome-wide, our data highlight processes like cellular differentiation, cell migration, extracellular matrix interactions, and developmental signaling pathways. Furthermore, they identify new candidate cis-regulatory elements for Eya1 and Pax8, both genes with a role in nephron progenitor cell differentiation. Finally, we associate expression-changing miRNAs, including let-7-5p, miR-125b-5p, miR-181a-2-3p, and miR-9-3p, with candidate cis-regulatory elements and target genes. These analyses highlight new putative cis-regulatory loci for miRNA in nephron progenitors.

Post-translational modifications by SIRT3 de-2-hydroxyisobutyrylase activity regulate glycolysis and enable nephrogenesis

Abnormal kidney development leads to lower nephron number, predisposing to renal diseases in adulthood. In embryonic kidneys, nephron endowment is dictated by the availability of nephron progenitors, whose self-renewal and differentiation require a relatively repressed chromatin state. More recently, NAD⁺-dependent deacetylase sirtuins (SIRTs) have emerged as possible regulators that link epigenetic processes to the metabolism. Here, we discovered a novel role for the NAD⁺-dependent deacylase SIRT3 in kidney development. In the embryonic kidney, SIRT3 was highly expressed only as a short isoform, with nuclear and extra-nuclear localisation. The nuclear SIRT3 did not act as deacetylase but exerted de-2-hydroxyisobutyrylase activity on lysine residues of histone proteins. Extra-nuclear SIRT3 regulated lysine 2-hydroxyisobutyrylation (Khib) levels of phosphofructokinase (PFK) and Sirt3 deficiency increased PFK Khib levels, inducing a glycolysis boost. This altered Khib landscape in Sirt3^−/− metanephroi was associated with decreased nephron progenitors, impaired nephrogenesis and a reduced number of nephrons. These data describe an unprecedented role of SIRT3 in controlling early renal development through the regulation of epigenetics and metabolic processes.

Structural and functional changes in the kidney caused by adverse fetal and neonatal environments

Health and disease risk in the adulthood are known to be affected by the early developmental environment. Kidney diseases are one of these diseases, and kidneys are altered both structurally and functionally by adverse pre- and perinatal events. The most known structural change is low nephron number seen in subjects born low birth weight and/or preterm. In various animal models of intrauterine growth restriction (IUGR), one of the causes of low birth weight, the mechanism of low nephron number was investigated. While apoptosis of metanephric mesenchyme has been suggested to be the cause, I showed that suppression of ureteric branching, global DNA methylation, and caspase-3 activity also contributes to the mechanism. Other structural changes caused by adverse fetal and neonatal environments include peritubular and glomerular capillary rarefaction and low podocyte endowment. These are aggravated by postnatal development of focal glomerulosclerosis and tubulointerstitial fibrosis that result from low nephron number. Functional changes can be seen in tubules, endothelium, renin-angiotensin system, sympathetic nervous system, oxidative stress, and others. As an example, I reported that aggravated nitrosative stress in a rat IUGR model resulted in more severe tubular necrosis and tubulointerstitial fibrosis after unilateral ureteral obstruction. The mechanism of various functional changes needs to be clarified but may be explained by epigenetic modifications.

Deciphering the minimal quantity of mouse primary cells to undergo nephrogenesis ex vivo

BACKGROUND

Tissue organoids derived from primary cells have high potential for studying organ development and diseases in numerous organs. They recreate the morphological structure and mimic the functions of given organ while being compact in size, easy to produce, and suitable for use in various experimental setups.

RESULTS

In this study we established the number of cells that form mouse kidney rudiments at E11.5, and generated renal organoids of various sizes from the mouse primary cells of the metanephric mesenchyme (MM). We investigated the ability of renal organoids to undergo nephrogenesis upon Wnt/ β-catenin pathway-mediated tubule induction with a GSK-3 inhibitor (BIO) or by initiation through the ureteric bud (UB). We found that 5000 cells of MM cells are necessary to successfully form renal organoids with well-structured nephrons as judged by fluorescent microscopy, transmission electron microscopy (TEM), and quantitative Polymerase Chain Reaction (qPCR). These mouse organoids also recapitulated renal secretion function in the proximal tubules.

CONCLUSIONS

We show that a significant decrease of cells used to generate renal mouse organoids in a dissociation/re-aggregation assay, does not interfere with development, and goes toward 3Rs. This enables generation of more experimental samples with one mouse litter, limiting the number of animals used for studies.

Postnatal prolongation of mammalian nephrogenesis by excess fetal GDNF

Nephron endowment, defined during the fetal period, dictates renal and related cardiovascular health throughout life. We show here that, despite its negative effects on kidney growth, genetic increase of GDNF prolongs the nephrogenic program beyond its normal cessation. Multi-stage mechanistic analysis revealed that excess GDNF maintains nephron progenitors and nephrogenesis through increased expression of its secreted targets and augmented WNT signaling, leading to a two-part effect on nephron progenitor maintenance. Abnormally high GDNF in embryonic kidneys upregulates its known targets but also Wnt9b and Axin2, with concomitant deceleration of nephron progenitor proliferation. Decline of GDNF levels in postnatal kidneys normalizes the ureteric bud and creates a permissive environment for continuation of the nephrogenic program, as demonstrated by morphologically and molecularly normal postnatal nephron progenitor self-renewal and differentiation. These results establish that excess GDNF has a bi-phasic effect on nephron progenitors in mice, which can faithfully respond to GDNF dosage manipulation during the fetal and postnatal period. Our results suggest that sensing the signaling activity level is an important mechanism through which GDNF and other molecules contribute to nephron progenitor lifespan specification.

Summary: Dosage of neurotropic factor GDNF regulates nephron progenitors and in utero growth factor augmentation can extend postnatal lifespan and differentiation of nephron progenitors.

Ret signaling in ureteric bud epithelial cells controls cell movements, cell clustering and bud formation

Ret signaling promotes branching morphogenesis during kidney development, but the underlying cellular mechanisms remain unclear. While Ret-expressing progenitor cells proliferate at the ureteric bud tips, some of these cells exit the tips to generate the elongating collecting ducts, and in the process turn off Ret. Genetic ablation of Ret in tip cells promotes their exit, suggesting that Ret is required for cell rearrangements that maintain the tip compartments. Here, we examine the behaviors of ureteric bud cells that are genetically forced to maintain Ret expression. These cells move to the nascent tips, and remain there during many cycles of branching; this tip-seeking behavior may require positional signals from the mesenchyme, as it occurs in whole kidneys but not in epithelial ureteric bud organoids. In organoids, cells forced to express Ret display a striking self-organizing behavior, attracting each other to form dense clusters within the epithelium, which then evaginate to form new buds. The ability of forced Ret expression to promote these events suggests that similar Ret-dependent cell behaviors play an important role in normal branching morphogenesis.

Development of the metanephric kidney

The kidney plays an integral role in filtering the blood-removing metabolic by-products from the body and regulating blood pressure. This requires the establishment of large numbers of efficient and specialized blood filtering units (nephrons) that incorporate a system for vascular exchange and nutrient reabsorption as well as a collecting duct system to remove waste (urine) from the body. Kidney development is a dynamic process which generates these structures through a delicately balanced program of self-renewal and commitment of nephron progenitor cells that inhabit a constantly evolving cellular niche at the tips of a branching ureteric "tree." The former cells build the nephrons and the latter the collecting duct system. Maintaining these processes across fetal development is critical for establishing the normal "endowment" of nephrons in the kidney and perturbations to this process are associated both with mutations in integral genes and with alterations to the fetal environment.

Embryonic Kidney Development, Stem Cells and the Origin of Wilms Tumor

The adult mammalian kidney is a poorly regenerating organ that lacks the stem cells that could replenish functional homeostasis similarly to, e.g., skin or the hematopoietic system. Unlike a mature kidney, the embryonic kidney hosts at least three types of lineage-specific stem cells that give rise to (a) a ureter and collecting duct system, (b) nephrons, and (c) mesangial cells together with connective tissue of the stroma. Extensive interest has been raised towards these embryonic progenitor cells, which are normally lost before birth in humans but remain part of the undifferentiated nephrogenic rests in the pediatric renal cancer Wilms tumor. Here, we discuss the current understanding of kidney-specific embryonic progenitor regulation in the innate environment of the developing kidney and the types of disruptions in their balanced regulation that lead to the formation of Wilms tumor.

Branching morphogenesis as a driver of renal development

Branching morphogenesis is an integral developmental mechanism central to the formation of a range of organs including the kidney, lung, pancreas and mammary gland. The ramified networks of epithelial tubules it establishes are critical for the processes of secretion, excretion and exchange mediated by these tissues. In the kidney, branching serves to establish the collecting duct system that transports urine from the nephrons into the renal pelvis, ureter and finally the bladder. Generally speaking, the formation of these networks in different organs begins with the specification and differentiation of simple bud-like organ anlage, which then undergo a process of elaboration, typically by bifurcation. This process is often governed by the interaction of progenitor cells at the tips of the epithelia with neighboring mesenchymal cell populations which direct the branching process and which often themselves differentiate to form part of the adult organ. In the kidney, the tips of ureteric bud elaborate through a dynamic cell signaling relationship with overlying nephron progenitor cell populations. These cells sequentially commit to differentiation and the resulting nephrons reintegrate with the ureteric epithelium as development progresses. This review will describe recent advances in understanding the how the elaboration of the ureteric bud is patterned and consider the extent to which this process is shared with other organs.

The core SWI/SNF catalytic subunit Brg1 regulates nephron progenitor cell proliferation and differentiation

Chromatin-remodeling complexes play critical roles in establishing gene expression patterns in response to developmental signals. How these epigenetic regulators determine the fate of progenitor cells during development of specific organs is not well understood. We found that genetic deletion of Brg1 (Smarca4), the core enzymatic protein in SWI/SNF, in nephron progenitor cells leads to severe renal hypoplasia. Nephron progenitor cells were depleted in Six2-Cre, Brg1^flx/flx mice due to reduced cell proliferation. This defect in self-renewal, together with impaired differentiation resulted in a profound nephron deficit in Brg1 mutant kidneys. Sall1, a transcription factor that is required for expansion and maintenance of nephron progenitors, associates with SWI/SNF. Brg1 and Sall1 bind promoters of many progenitor cell genes and regulate expression of key targets that promote their proliferation.

Deletion of hypoxia-responsive microRNA-210 results in a sex-specific decrease in nephron number

Low nephron number results in an increased risk of developing hypertension and chronic kidney disease. Intrauterine growth restriction is associated with a nephron deficit in humans, and is commonly caused by placental insufficiency, which results in fetal hypoxia. The underlying mechanisms by which hypoxia impacts kidney development are poorly understood. microRNA-210 is the most consistently induced microRNA in hypoxia and is known to promote cell survival in a hypoxic environment. In this study, the role of microRNA-210 in kidney development was evaluated using a global microRNA-210 knockout mouse. A male-specific 35% nephron deficit in microRNA-210 knockout mice was observed. Wnt/β-catenin signaling, a pathway crucial for nephron differentiation, was misregulated in male kidneys with increased expression of the canonical Wnt target lymphoid enhancer binding factor 1. This coincided with increased expression of caspase-8-associated protein 2, a known microRNA-210 target and apoptosis signal transducer. Together, these data are consistent with a sex-specific requirement for microRNA-210 in kidney development.

Mouse Models of Congenital Kidney Anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects, which cause the majority of chronic kidney diseases in children. CAKUT covers a wide range of malformations that derive from deficiencies in embryonic kidney and lower urinary tract development, including renal aplasia, hypodysplasia, hypoplasia, ectopia, and different forms of ureter abnormalities. The majority of the genetic causes of CAKUT remain unknown. Research on mutant mice has identified multiple genes that critically regulate renal differentiation. The data generated from this research have served as an excellent resource to identify the genetic bases of human kidney defects and have led to significantly improved diagnostics. Furthermore, genetic data from human CAKUT studies have also revealed novel genes regulating kidney differentiation.

In utero exposure to maternal diabetes impairs nephron progenitor differentiation

The incidence of diabetes mellitus has significantly increased among women of childbearing age, and it has been shown that prenatal exposure to maternal diabetes increases the risk of associated congenital anomalies of the kidney. Congenital anomalies of the kidney are among the leading causes of chronic kidney disease in children. To better understand the effect of maternal diabetes on kidney development, we analyzed wild-type offspring (DM_Exp) of diabetic Ins2+/C96Y mice (Akita mice). DM_Exp mice at postnatal day 34 have a reduction of ~20% in the total nephron number compared with controls, using the gold standard physical dissector/fractionator method. At the molecular level, the expression of the nephron progenitor markers sine oculis homeobox homolog 2 and Cited1 was increased in DM_Exp kidneys at postnatal day 2. Conversely, the number of early developing nephrons was diminished in DM_Exp kidneys. This was associated with decreased expression of the intracellular domain of Notch1 and the canonical Wnt target lymphoid enhancer binding factor 1. Together, these data suggest that the diabetic intrauterine environment impairs the differentiation of nephron progenitors into nephrons, possibly by perturbing the Notch and Wnt/β-catenin signaling pathways.

Von Hippel-Lindau Acts as a Metabolic Switch Controlling Nephron Progenitor Differentiation

BACKGROUND

Nephron progenitors, the cell population that give rise to the functional unit of the kidney, are metabolically active and self-renew under glycolytic conditions. A switch from glycolysis to mitochondrial respiration drives these cells toward differentiation, but the mechanisms that control this switch are poorly defined. Studies have demonstrated that kidney formation is highly dependent on oxygen concentration, which is largely regulated by von Hippel-Lindau (VHL; a protein component of a ubiquitin ligase complex) and hypoxia-inducible factors (a family of transcription factors activated by hypoxia).

METHODS

To explore VHL as a regulator defining nephron progenitor self-renewal versus differentiation, we bred Six2-TGCtg mice with VHLlox/lox mice to generate mice with a conditional deletion of VHL from Six2+ nephron progenitors. We used histologic, immunofluorescence, RNA sequencing, and metabolic assays to characterize kidneys from these mice and controls during development and up to postnatal day 21.

RESULTS

By embryonic day 15.5, kidneys of nephron progenitor cell-specific VHL knockout mice begin to exhibit reduced maturation of nephron progenitors. Compared with controls, VHL knockout kidneys are smaller and developmentally delayed by postnatal day 1, and have about half the number of glomeruli at postnatal day 21. VHL knockout nephron progenitors also exhibit persistent Six2 and Wt1 expression, as well as decreased mitochondrial respiration and prolonged reliance on glycolysis.

CONCLUSIONS

Our findings identify a novel role for VHL in mediating nephron progenitor differentiation through metabolic regulation, and suggest that VHL is required for normal kidney development.

MAPK/ERK Signaling in Regulation of Renal Differentiation

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects derived from abnormalities in renal differentiation during embryogenesis. CAKUT is the major cause of end-stage renal disease and chronic kidney diseases in children, but its genetic causes remain largely unresolved. Here we discuss advances in the understanding of how mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) activity contributes to the regulation of ureteric bud branching morphogenesis, which dictates the final size, shape, and nephron number of the kidney. Recent studies also demonstrate that the MAPK/ERK pathway is directly involved in nephrogenesis, regulating both the maintenance and differentiation of the nephrogenic mesenchyme. Interestingly, aberrant MAPK/ERK signaling is linked to many cancers, and recent studies suggest it also plays a role in the most common pediatric renal cancer, Wilms' tumor.

Loss of miR-17~92 results in dysregulation of Cftr in nephron progenitors

We have previously demonstrated that loss of miR-17~92 in nephron progenitors in a mouse model results in renal hypodysplasia and chronic kidney disease. Clinically, decreased congenital nephron endowment because of renal hypodysplasia is associated with an increased risk of hypertension and chronic kidney disease, and this is at least partly dependent on the self-renewal of nephron progenitors. Here, we present evidence for a novel molecular mechanism regulating the self-renewal of nephron progenitors and congenital nephron endowment by the highly conserved miR-17~92 cluster. Whole transcriptome sequencing revealed that nephron progenitors lacking this cluster demonstrated increased Cftr expression. We showed that one member of the cluster, miR-19b, is sufficient to repress Cftr expression in vitro and that perturbation of Cftr activity in nephron progenitors results in impaired proliferation. Together, these data suggest that miR-19b regulates Cftr expression in nephron progenitors, with this interaction playing a role in appropriate nephron progenitor self-renewal during kidney development to generate normal nephron endowment.

Mouse Cre-LoxP system: general principles to determine tissue-specific roles of target genes

Genetically engineered mouse models are commonly preferred for studying the human disease due to genetic and pathophysiological similarities between mice and humans. In particular, Cre-loxP system is widely used as an integral experimental tool for generating the conditional. This system has enabled researchers to investigate genes of interest in a tissue/cell (spatial control) and/or time (temporal control) specific manner. A various tissue-specific Cre-driver mouse lines have been generated to date, and new Cre lines are still being developed. This review provides a brief overview of Cre-loxP system and a few commonly used promoters for expression of tissue-specific Cre recombinase. Also, we finally introduce some available links to the Web sites that provides detailed information about Cre mouse lines including their characterization.

Small non-coding RNA expression in mouse nephrogenic mesenchymal progenitors

MicroRNAs (miRNAs) are small non-coding RNAs that are essential for the regulation of gene expression and play critical roles in human health and disease. Here we present comprehensive miRNA profiling data for mouse nephrogenic mesenchymal progenitors, a population of cells enriched for nephron progenitors that give rise to most cell-types of the nephron, the functional unit of the kidney. We describe a miRNA expression in nephrogenic mesenchymal progenitors, with 162 miRNAs differentially expressed in progenitors when compared to whole kidney. We also annotated 49 novel miRNAs in the developing kidney and experimentally validated 4 of them. Our data are available as a public resource, so that it can be integrated into future studies and analyzed in the context of other functional and epigenomic data in kidney development. Specifically, it will be useful in the effort to shed light on molecular mechanisms underlying processes essential for normal kidney development, like nephron progenitor specification, self-renewal and differentiation.

Regulation of Renal Differentiation by Trophic Factors

Classically, trophic factors are considered as proteins which support neurons in their growth, survival, and differentiation. However, most neurotrophic factors also have important functions outside of the nervous system. Especially essential renal growth and differentiation regulators are glial cell line-derived neurotrophic factor (GDNF), bone morphogenetic proteins (BMPs), and fibroblast growth factors (FGFs). Here we discuss how trophic factor-induced signaling contributes to the control of ureteric bud (UB) branching morphogenesis and to maintenance and differentiation of nephrogenic mesenchyme in embryonic kidney. The review includes recent advances in trophic factor functions during the guidance of branching morphogenesis and self-renewal versus differentiation decisions, both of which dictate the control of kidney size and nephron number. Creative utilization of current information may help better recapitulate renal differentiation in vitro, but it is obvious that significantly more basic knowledge is needed for development of regeneration-based renal therapies.

The Lhx1-Ldb1 complex interacts with Furry to regulate microRNA expression during pronephric kidney development

The molecular events driving specification of the kidney have been well characterized. However, how the initial kidney field size is established, patterned, and proportioned is not well characterized. Lhx1 is a transcription factor expressed in pronephric progenitors and is required for specification of the kidney, but few Lhx1 interacting proteins or downstream targets have been identified. By tandem-affinity purification, we isolated FRY like transcriptional coactivator (Fryl), one of two paralogous genes, fryl and furry (fry), have been described in vertebrates. Both proteins were found to interact with the Ldb1-Lhx1 complex, but our studies focused on Lhx1/Fry functional roles, as they are expressed in overlapping domains. We found that Xenopus embryos depleted of fry exhibit loss of pronephric mesoderm, phenocopying the Lhx1-depleted animals. In addition, we demonstrated a synergism between Fry and Lhx1, identified candidate microRNAs regulated by the pair, and confirmed these microRNA clusters influence specification of the kidney. Therefore, our data shows that a constitutively-active Ldb1-Lhx1 complex interacts with a broadly expressed microRNA repressor, Fry, to establish the kidney field.

Regenerative potential of induced pluripotent stem cells derived from patients undergoing haemodialysis in kidney regeneration

Kidney regeneration from pluripotent stem cells is receiving a lot of attention because limited treatments are currently available for chronic kidney disease (CKD). It has been shown that uremic state in CKD is toxic to somatic stem/progenitor cells, such as endothelial progenitor and mesenchymal stem cells, affecting their differentiation and angiogenic potential. Recent studies reported that specific abnormalities caused by the non-inherited disease are often retained in induced pluripotent stem cell (iPSC)-derived products obtained from patients. Thus, it is indispensable to first assess whether iPSCs derived from patients with CKD due to non-inherited disease (CKD-iPSCs) have the ability to generate kidneys. In this study, we generated iPSCs from patients undergoing haemodialysis due to diabetes nephropathy and glomerulonephritis (HD-iPSCs) as representatives of CKD-iPSCs or from healthy controls (HC-iPSCs). HD-iPSCs differentiated into nephron progenitor cells (NPCs) with similar efficiency to HC-iPSCs. Additionally, HD-iPSC-derived NPCs expressed comparable levels of NPC markers and differentiated into vascularised glomeruli upon transplantation into mice, as HC-iPSC-derived NPCs. Our results indicate the potential of HD-iPSCs as a feasible cell source for kidney regeneration. This is the first study paving the way for CKD patient-stem cell-derived kidney regeneration, emphasising the potential of CKD-iPSCs.

Single-cell analysis of progenitor cell dynamics and lineage specification in the human fetal kidney

The mammalian kidney develops through reciprocal interactions between the ureteric bud and the metanephric mesenchyme to give rise to the entire collecting system and the nephrons. Most of our knowledge of the developmental regulators driving this process arises from the study of gene expression and functional genetics in mice and other animal models. In order to shed light on human kidney development, we have used single-cell transcriptomics to characterize gene expression in different cell populations, and to study individual cell dynamics and lineage trajectories during development. Single-cell transcriptome analyses of 6414 cells from five individual specimens identified 11 initial clusters of specific renal cell types as defined by their gene expression profile. Further subclustering identifies progenitors, and mature and intermediate stages of differentiation for several renal lineages. Other lineages identified include mesangium, stroma, endothelial and immune cells. Novel markers for these cell types were revealed in the analysis, as were components of key signaling pathways driving renal development in animal models. Altogether, we provide a comprehensive and dynamic gene expression profile of the developing human kidney at the single-cell level.

Summary: New markers for specific cell types in the developing human kidney are identified and computational approaches infer developmental trajectories and interrogate the complex network of signaling pathways and cellular transitions.

Nephron progenitor cell commitment: Striking the right balance

The filtering component of the kidney, the nephron, arises from a single progenitor population. These nephron progenitor cells (NPCs) both self-renew and differentiate throughout the course of kidney development ensuring sufficient nephron endowment. An appropriate balance of these processes must be struck as deficiencies in nephron numbers are associated with hypertension and kidney disease. This review will discuss the mechanisms and molecules supporting NPC maintenance and differentiation. A focus on recent work will highlight new molecular insights into NPC regulation and their dynamic behavior in both space and time.