Implication of transcription factor FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below age 30 years. Many monogenic forms have been discovered due to comprehensive genetic testing like exome sequencing. However, disease-causing variants in known disease-associated genes only explain a proportion of cases. Here, we aim to unravel underlying molecular mechanisms of syndromic CAKUT in three unrelated multiplex families with presumed autosomal recessive inheritance. Exome sequencing in the index individuals revealed three different rare homozygous variants in FOXD2, encoding a transcription factor not previously implicated in CAKUT in humans: a frameshift in the Arabic and a missense variant each in the Turkish and the Israeli family with segregation patterns consistent with autosomal recessive inheritance. CRISPR/Cas9-derived Foxd2 knockout mice presented with a bilateral dilated kidney pelvis accompanied by atrophy of the kidney papilla and mandibular, ophthalmologic, and behavioral anomalies, recapitulating the human phenotype. In a complementary approach to study pathomechanisms of FOXD2-dysfunction-mediated developmental kidney defects, we generated CRISPR/Cas9-mediated knockout of Foxd2 in ureteric bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important for kidney/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a shift toward a stromal cell identity. Histology of Foxd2 knockout mouse kidneys confirmed increased fibrosis. Further, genome-wide association studies suggest that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. Thus, our studies help in genetic diagnostics of monogenic CAKUT and in understanding of monogenic and multifactorial kidney diseases.

Establishment of an organ culture system to maintain the structure of mouse Müllerian ducts during development

We previously showed that the anti-Müllerian hormone (AMH), infiltrating from the testis to the mesonephros reaches the cranial and middle regions of the Müllerian duct (MD) and induces their regression using an organ culture in mice. However, it is difficult to maintain structural integrity, such as the length and diameter and normal direction of elongation of the caudal region of the MD, in conventional organ culture systems. Therefore, the pathway of AMH to the caudal MD region remains uncharted. In this study, we established an organ culture method that can maintain the morphology of the caudal region of the MD. The gonad-mesonephros complex, metanephros, and urinary bladder of mouse fetuses at 12.5 dpc attached to the body trunk were cultured on agarose gels for 72 hr. The cultured caudal region of the mesonephros was elongated along the body trunk, and the course of the mesonephros was maintained in many individuals. In males, mesenchymal cells aggregated around the MD after culture. Moreover, the male MD diameter was significantly smaller than the female. Based on these results, it was concluded that the development of the MD was maintained in the present organ culture system. Using this culture system, AMH infiltration to the caudal region of the MD can be examined without the influence of AMH in the blood. This culture system is useful for clarifying the regression mechanism of the caudal region of the MD.

A single-cell time-lapse of mouse prenatal development from gastrula to birth

The house mouse (Mus musculus) is an exceptional model system, combining genetic tractability with close evolutionary affinity to humans1,2. Mouse gestation lasts only 3 weeks, during which the genome orchestrates the astonishing transformation of a single-cell zygote into a free-living pup composed of more than 500 million cells. Here, to establish a global framework for exploring mammalian development, we applied optimized single-cell combinatorial indexing3 to profile the transcriptional states of 12.4 million nuclei from 83 embryos, precisely staged at 2- to 6-hour intervals spanning late gastrulation (embryonic day 8) to birth (postnatal day 0). From these data, we annotate hundreds of cell types and explore the ontogenesis of the posterior embryo during somitogenesis and of kidney, mesenchyme, retina and early neurons. We leverage the temporal resolution and sampling depth of these whole-embryo snapshots, together with published data4-8 from earlier timepoints, to construct a rooted tree of cell-type relationships that spans the entirety of prenatal development, from zygote to birth. Throughout this tree, we systematically nominate genes encoding transcription factors and other proteins as candidate drivers of the in vivo differentiation of hundreds of cell types. Remarkably, the most marked temporal shifts in cell states are observed within one hour of birth and presumably underlie the massive physiological adaptations that must accompany the successful transition of a mammalian fetus to life outside the womb.

Engineering physiological environments to advance kidney organoid models from human pluripotent stem cells

During embryogenesis, the mammalian kidney arises because of reciprocal interactions between the ureteric bud (UB) and the metanephric mesenchyme (MM), driving UB branching and nephron induction. These morphogenetic processes involve a series of cellular rearrangements that are tightly controlled by gene regulatory networks and signaling cascades. Here, we discuss how kidney developmental studies have informed the definition of procedures to obtain kidney organoids from human pluripotent stem cells (hPSCs). Moreover, bioengineering techniques have emerged as potential solutions to externally impose controlled microenvironments for organoid generation from hPSCs. Next, we summarize some of these advances with major focus On recent works merging hPSC-derived kidney organoids (hPSC-kidney organoids) with organ-on-chip to develop robust models for drug discovery and disease modeling applications. We foresee that, in the near future, coupling of different organoid models through bioengineering approaches will help advancing to recreate organ-to-organ crosstalk to increase our understanding on kidney disease progression in the human context and search for new therapeutics.

Differential expression of epithelial and smooth muscle lineage-specific markers of metanephros in one-humped camel foetuses

The development of the metanephros in one-humped camels involves a complex series of interactions between epithelial and mesenchymal cells. As a result, there is a synchronized differentiation process of stromal, vascular and epithelial cell types during glomerulogenesis, angiogenesis and tubulogenesis. In the current work, the metanephros of camel foetuses were divided into four stages where kidneys from each stage were processed and immunoassayed, followed by quantitative analysis to determine target protein intensities throughout metanephrogenesis in the camel. This study demonstrated robust expression of α-smooth muscle actin (α-SMA) in the glomerular mesangium, as well as in interlobular and glomerular arterioles during the earlier stages of development. However, in the late stages, α-SMA expression became more localized around the blood capillaries in both the cortex and medulla. Strong expression of CD34 was observed in the immature glomerular and peritubular endothelial cells within the subcapsular zone, as well as in the glomerular, proximal tubular and distal tubular epithelium of stage one foetuses, although its expression gradually diminished with foetal maturation. The expression pattern of osteopontin was prominently observed in the distal convoluted tubules throughout all stages, however, no expression was detected in the proximal tubules, glomeruli and arterioles. E-cadherin was detected in the developing renal tubular epithelial cells but not in the glomeruli. In conclusion, this study reveals the spatiotemporal distribution of key proteins, including α-SMA, CD34, Osteopontin and E-cadherin, which play a crucial role in metanephrogenesis in camel foetuses.

Ultrasound Measurement of Fetal Kidney Length in Normal Pregnancy and its Correlation with Gestational Age

BACKGROUND

To establish a nomogram of fetal kidney length for a normal pregnancy from 20 to 41 weeks of gestational age.

METHODS

A prospective cross-sectional study was carried out in the Department of radio-diagnosis and imaging BPKIHS, Dharan. 400 kidneys of 200 fetuses between the gestational age 20 to 41 weeks were scanned. Renal measurement was performed by ultrasonography.

RESULTS

Analysis was performed on data obtained from 200 normal fetuses. Size charts for right, left and mean fetal kidney length with standard deviation were presented for each weeks of gestation from 20 weeks to 41 weeks. The difference in renal length between right and left side was statistically not significant.There was significant correlation between gestational age and fetal kidney length (r=0.947, p=0.001).

CONCLUSIONS

Fetal kidney length can be used as an adjunct parameter for estimation of gestation age.

A comparative study of cellular diversity between the Xenopus pronephric and mouse metanephric nephron

The kidney is an essential organ that ensures bodily fluid homeostasis and removes soluble waste products from the organism. Nephrons, the functional units of the kidney, comprise a blood filter, the glomerulus or glomus, and an epithelial tubule that processes the filtrate from the blood or coelom and selectively reabsorbs solutes, such as sugars, proteins, ions, and water, leaving waste products to be eliminated in the urine. Genes coding for transporters are segmentally expressed, enabling the nephron to sequentially process the filtrate. The Xenopus embryonic kidney, the pronephros, which consists of a single large nephron, has served as a valuable model to identify genes involved in nephron formation and patterning. Therefore, the developmental patterning program that generates these segments is of great interest. Prior work has defined the gene expression profiles of Xenopus nephron segments via in situ hybridization strategies, but a comprehensive understanding of the cellular makeup of the pronephric kidney remains incomplete. Here, we carried out single-cell mRNA sequencing of the functional Xenopus pronephric nephron and evaluated its cellular composition through comparative analyses with previous Xenopus studies and single-cell mRNA sequencing of the adult mouse kidney. This study reconstructs the cellular makeup of the pronephric kidney and identifies conserved cells, segments, and associated gene expression profiles. Thus, our data highlight significant conservation in podocytes, proximal and distal tubule cells, and divergence in cellular composition underlying the capacity of each nephron to remove wastes in the form of urine, while emphasizing the Xenopus pronephros as a model for physiology and disease.

Disruption of mitochondrial complex III in cap mesenchyme but not in ureteric progenitors results in defective nephrogenesis associated with amino acid deficiency

Oxidative metabolism in mitochondria regulates cellular differentiation and gene expression through intermediary metabolites and reactive oxygen species. Its role in kidney development and pathogenesis is not completely understood. Here we inactivated ubiquinone-binding protein QPC, a subunit of mitochondrial complex III, in two types of kidney progenitor cells to investigate the role of mitochondrial electron transport in kidney homeostasis. Inactivation of QPC in sine oculis-related homeobox 2 (SIX2)-expressing cap mesenchyme progenitors, which give rise to podocytes and all nephron segments except collecting ducts, resulted in perinatal death from severe kidney dysplasia. This was characterized by decreased proliferation of SIX2 progenitors and their failure to differentiate into kidney epithelium. QPC inactivation in cap mesenchyme progenitors induced activating transcription factor 4-mediated nutritional stress responses and was associated with a reduction in kidney tricarboxylic acid cycle metabolites and amino acid levels, which negatively impacted purine and pyrimidine synthesis. In contrast, QPC inactivation in ureteric tree epithelial cells, which give rise to the kidney collecting system, did not inhibit ureteric differentiation, and resulted in the development of functional kidneys that were smaller in size. Thus, our data demonstrate that mitochondrial oxidative metabolism is critical for the formation of cap mesenchyme-derived nephron segments but dispensable for formation of the kidney collecting system. Hence, our studies reveal compartment-specific needs for metabolic reprogramming during kidney development.

Acyl-CoA binding protein (ACBP) is highly expressed in the developing human kidney

OBJECTIVE

Acyl-CoA-binding protein (ACBP), also known as diazepam binding inhibitor (DBI), is a small phylogenetically conserved protein. This ancestral peptide is multifunctional, performing intracellular activities as ACBP protein or extracellular roles as DBI. Several studies showed its endless facets, including a relevant activity as appetite stimulator and as anabolic factor. High levels of ACBP have been described in erythrocytes, liver, kidney, and gut cells. The aim of this study was to analyze, at immunohistochemical level, the expression of ACBP in fetal human tissues during development, focusing on the developing kidney.

MATERIALS AND METHODS

Immunohistochemistry for ACBP was performed on 30 human fetal kidneys, from 15 fetuses of gestational age ranging from 13 to 19 weeks. At autopsy, all kidney samples were 10% formalin-fixed, routinely processed and paraffin-embedded. Five micron-thick paraffin sections were stained with Hematoxylin and Eosin and PAS stain for a morphological examination.

RESULTS

ACBP was detected in all 30 kidneys analyzed in this study. No significant changes in ACBP expression were observed at different gestational ages. Immunostaining for ACBP was restricted to the epithelium covering the renal pelvis, the papillae, the collecting tubules, and the proximal and distal tubules. On the other hand, medullary regions and in the metanephric mesenchymal stem/progenitor cells did not show any reactivity for ACBP.

CONCLUSIONS

According to our findings, ACBP should be considered as a new player in the complex field of human nephrogenesis, given that it was detected in all fetal kidneys immunostained. Its preferential localization in the renal structures derived from the Wolf duct, such as pelvis epithelium and collecting ducts, suggests a major role for ACBP in the induction of the metanephric mesenchymal cells toward the differentiation into glomerular structures. ACBP expression in proximal and distal tubules, two structures originating from the metanephric mesenchyme, indicates a further role of this protein in nephron development. In conclusion, ACBP should be added to the multiple molecules involved in human nephrogenesis.

Growth Hormone and IGF1 Actions in Kidney Development and Function

Growth hormone (GH) exerts multiple effects on different organs including the kidneys, either directly or via its main mediator, insulin-like-growth factor-1 (IGF-1). The GH/IGF1 system plays a key role in normal kidney development, glomerular hemodynamic regulation, as well as tubular water, sodium, phosphate, and calcium handling. Transgenic animal models demonstrated that GH excess (and not IGF1) may lead to hyperfiltration, albuminuria, and glomerulosclerosis. GH and IGF-1 play a significant role in the early development of diabetic nephropathy, as well as in compensatory kidney hypertrophy after unilateral nephrectomy. Chronic kidney disease (CKD) and its complications in children are associated with alterations in the GH/IGF1 axis, including growth retardation, related to a GH-resistant state, attributed to impaired kidney postreceptor GH-signaling and chronic inflammation. This may explain the safety of prolonged rhGH-treatment of short stature in CKD.

Adverse Impact of Environmental Chemicals on Developmental Origins of Kidney Disease and Hypertension

Chronic kidney disease (CKD) and hypertension are becoming a global health challenge, despite developments in pharmacotherapy. Both diseases can begin in early life by so-called "developmental origins of health and disease" (DOHaD). Environmental chemical exposure during pregnancy can affect kidney development, resulting in renal programming. Here, we focus on environmental chemicals that pregnant mothers are likely to be exposed, including dioxins, bisphenol A (BPA), phthalates, per- and polyfluoroalkyl substances (PFAS), polycyclic aromatic hydrocarbons (PAH), heavy metals, and air pollution. We summarize current human evidence and animal models that supports the link between prenatal exposure to environmental chemicals and developmental origins of kidney disease and hypertension, with an emphasis on common mechanisms. These include oxidative stress, renin-angiotensin system, reduced nephron numbers, and aryl hydrocarbon receptor signaling pathway. Urgent action is required to identify toxic chemicals in the environment, avoid harmful chemicals exposure during pregnancy and lactation, and continue to discover other potentially harmful chemicals. Innovation is also needed to identify kidney disease and hypertension in the earliest stage, as well as translating effective reprogramming interventions from animal studies into clinical practice. Toward DOHaD approach, prohibiting toxic chemical exposure and better understanding of underlying mechanisms, we have the potential to reduce global burden of kidney disease and hypertension.

The origin and role of the renal stroma

The postnatal kidney is predominantly composed of nephron epithelia with the interstitial components representing a small proportion of the final organ, except in the diseased state. This is in stark contrast to the developing organ, which arises from the mesoderm and comprises an expansive stromal population with distinct regional gene expression. In many organs, the identity and ultimate function of an epithelium is tightly regulated by the surrounding stroma during development. However, although the presence of a renal stromal stem cell population has been demonstrated, the focus has been on understanding the process of nephrogenesis whereas the role of distinct stromal components during kidney morphogenesis is less clear. In this Review, we consider what is known about the role of the stroma of the developing kidney in nephrogenesis, where these cells come from as well as their heterogeneity, and reflect on how this information may improve human kidney organoid models.

Vascular deficiencies in renal organoids and ex vivo kidney organogenesis

Chronic kidney disease (CKD) and end stage renal disease (ESRD) are increasingly frequent and devastating conditions that have driven a surge in the need for kidney transplantation. A stark shortage of organs has fueled interest in generating viable replacement tissues ex vivo for transplantation. One promising approach has been self-organizing organoids, which mimic developmental processes and yield multicellular, organ-specific tissues. However, a recognized roadblock to this approach is that many organoid cell types fail to acquire full maturity and function. Here, we comprehensively assess the vasculature in two distinct kidney organoid models as well as in explanted embryonic kidneys. Using a variety of methods, we show that while organoids can develop a wide range of kidney cell types, as previously shown, endothelial cells (ECs) initially arise but then rapidly regress over time in culture. Vasculature of cultured embryonic kidneys exhibit similar regression. By contrast, engraftment of kidney organoids under the kidney capsule results in the formation of a stable, perfused vasculature that integrates into the organoid. This work demonstrates that kidney organoids offer a promising model system to define the complexities of vascular-nephron interactions, but the establishment and maintenance of a vascular network present unique challenges when grown ex vivo.

CRKL, AIFM3, AIF, BCL2, and UBASH3A during Human Kidney Development

We aimed to investigate the spatio-temporal expression of possible CAKUT candidate genes CRKL, AIFM3, and UBASH3A, as well as AIF and BCL2 during human kidney development. Human fetal kidney tissue was stained with antibodies and analyzed by fluorescence microscopy and RT-PCR. Quantification of positive cells was assessed by calculation of area percentage and counting cells in nephron structures. Results showed statistically significant differences in the temporal expression patterns of the examined markers, depending on the investigated developmental stage. Limited but strong expression of CRKL was seen in developing kidneys, with increasing expression up to the period where the majority of nephrons are formed. Results also lead us to conclude that AIFM3 and AIF are important for promoting cell survival, but only AIFM3 is considered a CAKUT candidate gene due to the lack of AIF in nephron developmental structures. Our findings imply great importance of AIFM3 in energy production in nephrogenesis and tubular maturation. UBASH3A raw scores showed greater immunoreactivity in developing structures than mature ones which would point to a meaningful role in nephrogenesis. The fact that mRNA and proteins of CRKL, UBASH3A, and AIFM3 were detected in all phases of kidney development implies their role as renal development control genes.

The nephric mesenchyme lineage of intermediate mesoderm is derived from Tbx6-expressing derivatives of neuro-mesodermal progenitors via BMP-dependent Osr1 function

In vertebrate embryos, the kidney primordium metanephros is formed from two distinct cell lineages, Wolffian duct and metanephric mesenchyme, which were classically grouped as intermediate mesoderm. Whereas the reciprocal interactions between these two cell populations in kidney development have been studied extensively, the mechanisms generating them remain elusive. Here, we show that the mouse cell lineage that forms nephric mesenchyme develops as a subpopulation of Tbx6-expressing mesodermal precursor derivatives of neuro-mesodermal progenitors (NMPs) under the condition of bone morphogenetic protein (BMP)-signal-dependent Osr1 expression. The Osr1-expressing nephric mesenchyme precursors were confirmed as descendants of NMPs because they were labeled by Sox2 N1 enhancer-EGFP. In Tbx6 mutant embryos, nephric mesenchyme changed its fate into neural tissues, which reflected its NMP origin. In Osr1 mutant embryos, the specific region of the Tbx6-expressing mesoderm precursor, which normally expresses Osr1 and develops into the nephric mesenchyme, instead expressed the somite marker FoxC2. BMP signaling activated Osr1 expression in a region of TBX6-expressing mesoderm and elicited nephric mesenchyme development. This study suggested a new model of cell lineage segregation during gastrulation.

Prenatal diagnosis of congenital nephrotic syndrome of the Finnish type in a Chinese family

OBJECTIVE

To explore the genetic bias in a Chinese family suspected of having congenital nephrotic syndrome of the Finnish type (CNF).

CASE REPORT

We developed a prenatal genetic diagnosis in a Chinese family with CNF. A single heterozygous mutation (c.3213delG) was found in the foetus IId and we presumed that it was an asymptomatic carrier of the normal phenotype. Additionally, two compound heterozygous variants (c.3213delG and c.3478C > T) were discovered in the foetus IIe, which were inherited from the mother and father, respectively. We performed further pathological examinations after medical abortion. Kidney histopathology and immunofluorescence results were similar to those reported in previous studies.

CONCLUSION

Prenatal genetic diagnosis of CNF still requires further research to explore the pathogenicity of suspected mutations.

Single cell derived mRNA signals across human kidney tumors

Tumor cells may share some patterns of gene expression with their cell of origin, providing clues into the differentiation state and origin of cancer. Here, we study the differentiation state and cellular origin of 1300 childhood and adult kidney tumors. Using single cell mRNA reference maps of normal tissues, we quantify reference "cellular signals" in each tumor. Quantifying global differentiation, we find that childhood tumors exhibit fetal cellular signals, replacing the presumption of "fetalness" with a quantitative measure of immaturity. By contrast, in adult cancers our assessment refutes the suggestion of dedifferentiation towards a fetal state in most cases. We find an intimate connection between developmental mesenchymal populations and childhood renal tumors. We demonstrate the diagnostic potential of our approach with a case study of a cryptic renal tumor. Our findings provide a cellular definition of human renal tumors through an approach that is broadly applicable to human cancer.

Sexual Dimorphism of Corticosteroid Signaling during Kidney Development

Sexual dimorphism involves differences between biological sexes that go beyond sexual characteristics. In mammals, differences between sexes have been demonstrated regarding various biological processes, including blood pressure and predisposition to develop hypertension early in adulthood, which may rely on early events during development and in the neonatal period. Recent studies suggest that corticosteroid signaling pathways (comprising glucocorticoid and mineralocorticoid signaling pathways) have distinct tissue-specific expression and regulation during this specific temporal window in a sex-dependent manner, most notably in the kidney. This review outlines the evidence for a gender differential expression and activation of renal corticosteroid signaling pathways in the mammalian fetus and neonate, from mouse to human, that may favor mineralocorticoid signaling in females and glucocorticoid signaling in males. Determining the effects of such differences may shed light on short term and long term pathophysiological consequences, markedly for males.

A missing kidney and a hidden congenital diaphragmatic hernia

Congenital intrathoracic kidney (ITK) is a rare condition, which is usually discovered incidentally in asymptomatic children who do not need any intervention. However, it may be associated with congenital diaphragmatic hernia (CDH), in which case it requires urgent surgical intervention. We present a case of prenatally diagnosed ITK associated with a left CDH that was operated on day 5 of life. The neonate is currently well at 15 months of age.

DDRGK1, a crucial player of ufmylation system, is indispensable for autophagic degradation by regulating lysosomal function

DDRGK domain-containing protein 1 (DDRGK1) is an important component of the newly discovered ufmylation system and its absence has been reported to induce extensive endoplasmic reticulum (ER) stress. Recently, emerging evidence indicates that the ufmylation system is correlated with autophagy, although the exact mechanism remains largely unknown. To explore the regulation mechanism of DDRGK1 on autophagy, in this study, we established an immortalized mouse embryonic fibroblast (MEF) cell lines harvested from the DDRGK1F/F:ROSA26-CreERT2 mice, in which DDRGK1 depletion can be induced by 4-hydroxytamoxifen (4-OHT) treatment. Here, we show that DDRGK1 deficiency in MEFs has a dual effect on autophagy, which leads to a significant accumulation of autophagosomes. On one hand, it promotes autophagy induction by impairing mTOR signaling; on the other hand, it blocks autophagy degradation by inhibiting autophagosome-lysosome fusion. This dual effect of DDRGK1 depletion on autophagy ultimately aggravates apoptosis in MEFs. Further studies reveal that DDRGK1 loss is correlated with suppressed lysosomal function, including impaired Cathepsin D (CTSD) expression, aberrant lysosomal pH, and v-ATPase accumulation, which might be a potential trigger for impairment in autophagy process. Hence, this study confirms a crucial role of DDRGK1 as an autophagy regulator by controlling lysosomal function. It may provide a theoretical basis for the treatment strategies of various physiological diseases caused by DDRGK1 deficiency.

Renin Cells, the Kidney, and Hypertension

Renin cells are essential for survival perfected throughout evolution to ensure normal development and defend the organism against a variety of homeostatic threats. During embryonic and early postnatal life, they are progenitors that participate in the morphogenesis of the renal arterial tree. In adult life, they are capable of regenerating injured glomeruli, control blood pressure, fluid-electrolyte balance, tissue perfusion, and in turn, the delivery of oxygen and nutrients to cells. Throughout life, renin cell descendants retain the plasticity or memory to regain the renin phenotype when homeostasis is threatened. To perform all of these functions and maintain well-being, renin cells must regulate their identity and fate. Here, we review the major mechanisms that control the differentiation and fate of renin cells, the chromatin events that control the memory of the renin phenotype, and the major pathways that determine their plasticity. We also examine how chronic stimulation of renin cells alters their fate leading to the development of a severe and concentric hypertrophy of the intrarenal arteries and arterioles. Lastly, we provide examples of additional changes in renin cell fate that contribute to equally severe kidney disorders.

Impact of gestational low-protein intake on embryonic kidney microRNA expression and in nephron progenitor cells of the male fetus

BACKGROUND

Here, we have demonstrated that gestational low-protein (LP) intake offspring present lower birth weight, reduced nephron numbers, renal salt excretion, arterial hypertension, and renal failure development compared to regular protein (NP) intake rats in adulthood. We evaluated the expression of various miRNAs and predicted target genes in the kidney in gestational 17-days LP (DG-17) fetal metanephros to identify molecular pathways involved in the proliferation and differentiation of renal embryonic or fetal cells.

METHODS

Pregnant Wistar rats were classified into two groups based on protein supply during pregnancy: NP (regular protein diet, 17%) or LP diet (6%). Renal miRNA sequencing (miRNA-Seq) performed on the MiSeq platform, RT-qPCR of predicted target genes, immunohistochemistry, and morphological analysis of 17-DG NP and LP offspring were performed using previously described methods.

RESULTS

A total of 44 miRNAs, of which 19 were up and 25 downregulated, were identified in 17-DG LP fetuses compared to age-matched NP offspring. We selected 7 miRNAs involved in proliferation, differentiation, and cellular apoptosis. Our findings revealed reduced cell number and Six-2 and c-Myc immunoreactivity in metanephros cap (CM) and ureter bud (UB) in 17-DG LP fetuses. Ki-67 immunoreactivity in CM was 48% lesser in LP compared to age-matched NP fetuses. Conversely, in LP CM and UB, β-catenin was 154%, and 85% increased, respectively. Furthermore, mTOR immunoreactivity was higher in LP CM (139%) and UB (104%) compared to that in NP offspring. TGFβ-1 positive cells in the UB increased by approximately 30% in the LP offspring. Moreover, ZEB1 metanephros-stained cells increased by 30% in the LP offspring. ZEB2 immunofluorescence, although present in the entire metanephros, was similar in both experimental groups.

CONCLUSIONS

Maternal protein restriction changes the expression of miRNAs, mRNAs, and proteins involved in proliferation, differentiation, and apoptosis during renal development. Renal ontogenic dysfunction, caused by maternal protein restriction, promotes reduced reciprocal interaction between CM and UB; consequently, a programmed and expressive decrease in nephron number occurs in the fetus.

Ultrasound Measurement and Kidney Development: a Mini-Review for Nephrologists

Ultrasound (US) is a noninvasive, simple and safe imaging investigation that can be done as many times as needed. Therefore, it is the primary imaging modality for evaluating kidneys. We carried out a literature review of information about ultrasonography for clinicians, especially nephrologists. US utilization from prenatal time till adult life with various measurements including, length, width, depth, and volume was searched during 2019. US identifies 90% of fetal kidneys by 20 weeks of gestational age. Kidney weight and volume at birth are approximately only 10% of the mature kidney. Kidney growth is most rapid during the first few weeks of life, with the kidney length increasing by as much as 15-20% in full-term neonates. There is a good correlation between relative function shown by scintigraphy and relative volume estimated from sonography. The most accurate measurement of kidney size is provided by kidney volume, which is correlated with subject's height, weight, and total body area. Kidney length is the most easily reproduced. Kidney volume is a better approximation of size than length because of the shape of the kidney varies considerably, but it is technically more demanding and needs four measurements in two different planes. It has been shown that in normal adult kidneys, the sonography measurements of kidney length differ by values of between about 1 cm and 1.85 cm in 95% of the cases, irrespective of whether the measurements are performed by the same or by different sonographers. Measuring the renal parenchyma with US is a novel method to assess fetal kidney development and predict future renal function.

Variations in Laminar Arrangements of the Mesocolon and Retropancreatic Fascia: a Histological Study Using Human Fetuses Near Term

OBJECTIVE

The embryonic mesentery of the ascending and descending colons as well as the pancreas disappears due to peritoneal fusion, but there might be no or few photographic demonstrations of the intermediate morphologies during the process. The aims of this study were to characterize the morphological relationship of the interface between the renal fascia and peritoneum.

METHODS

Fourteen late-stage fetuses with crown rump lengths (CRLs) of 250-325 mm (gestational age: 30-38 weeks) were histologically examined.

RESULTS

The renal fascia, a thick or thin layer consisting of densely-distributed abundant fibers, was consistently separated from the renal capsule by a perirenal space containing fat. The transverse colon carried a typical mesocolon histologically different from the renal fascia. The ascending and descending mesocolons were irregularly divided into multiple laminae and the colic external longitudinal muscle appeared to directly contact the renal fascia. There was a spectrum of variations from multiple laminae to a single thick fascia between the pancreatic body and the left kidney or adrenal.

CONCLUSIONS

A fascial development after retroperitoneal fusion of the mesentery showed great individual and site-dependent differences in proportion of 1) a complete fusion with the renal fascia and 2) a multilaminar structure including the remnant peritoneum. These variations masked the likely stage-dependent change.

Abnormal Intestinal Anatomy in Late-stage Human Fetuses: Three Case Series

OBJECTIVE

We reported three cases of fetuses with abnormal intestinal anatomy found during our recent study of the transverse mesocolon using 20 late-stage fetuses.

CASES

The first case (CRL: 328 mm) appeared to have a duodenum and transverse colon trapped in Winslow's foramen (foramen epiploicum) and the duodenum superior portion elongated rightward. The second case (CRL: 264 mm) had a transverse colon inserted deeply into a space between the right kidney and duodenum. The third case (CRL: 276 mm) had a descending colon that ran inferiorly through a deep space between the left kidney and duodenum. Each case had a greater omentum that was shifted leftward, but this is usual. These 3 abnormalities were not evident in the anterior view during dissection of the liver, stomach, jejunum, and ileum. With underdeveloped pancreatic ducts due to unknown reason other than the internal hernia, the first case seemed to be fatal after birth. However, the second and third cases could have recovered after birth because there was no evidence of definite malrotation and because of loose attachments of the intestines to surrounding structures.

CONCLUSIONS

The intestinal morphologies described here could cause some sort of symptoms, such as abdominal pain, whose cause might be difficult to determine.

The low affinity p75 neurotrophin receptor is down-regulated in congenital anomalies of the kidney and the urinary tract: Possible involvement in early nephrogenesis

Congenital Anomalies of the Kidney and of the Urinary Tract (CAKUT) cover a broad range of disorders including abnormal kidney development caused by defective nephrogenesis. Here we explored the possible involvement of the low affinity p75 neurotrophin receptor (p75NTR) in CAKUT and nephrogenesis. In mouse, p75NTR was highly expressed in fetal kidney, located within cortical early nephrogenic bodies, and decreased rapidly after birth. In human control fetal kidney, p75NTR was also located within the early nephrogenic bodies as well as in the mature glomeruli, presumably in the mesangium. In CAKUT fetal kidneys, the kidney cortical structure and the localization of p75NTR were often disorganized, and quantification of p75NTR in amniotic fluid revealed a significant reduction in CAKUT compared to control. Finally, invalidation of p75NTR in zebrafish embryo with an antisense morpholino significantly altered pronephros development. Our results indicate that renal p75NTR is altered in CAKUT fetuses, and could participate to early nephrogenesis.

Connexin Signaling in the Juxtaglomerular Apparatus (JGA) of Developing, Postnatal Healthy and Nephrotic Human Kidneys

Our study analyzed the expression pattern of different connexins (Cxs) and renin positive cells in the juxtaglomerular apparatus (JGA) of developing, postnatal healthy human kidneys and in nephrotic syndrome of the Finnish type (CNF), by using double immunofluorescence, electron microscopy and statistical measuring. The JGA contained several cell types connected by Cxs, and consisting of macula densa, extraglomerular mesangium (EM) and juxtaglomerular cells (JC), which release renin involved in renin-angiotensin- aldosteron system (RAS) of arterial blood pressure control. During JGA development, strong Cx40 expression gradually decreased, while expression of Cx37, Cx43 and Cx45 increased, postnatally showing more equalized expression patterning. In parallel, initially dispersed renin cells localized to JGA, and greatly increased expression in postnatal kidneys. In CNF kidneys, increased levels of Cx43, Cx37 and Cx45 co-localized with accumulations of renin cells in JGA. Additionally, they reappeared in extraglomerular mesangial cells, indicating association between return to embryonic Cxs patterning and pathologically changed kidney tissue. Based on the described Cxs and renin expression patterning, we suggest involvement of Cx40 primarily in the formation of JGA in developing kidneys, while Cx37, Cx43 and Cx45 might participate in JGA signal transfer important for postnatal maintenance of kidney function and blood pressure control.

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.

3D kidney organoids for bench-to-bedside translation

The kidneys are essential organs that filter the blood, removing urinary waste while maintaining fluid and electrolyte homeostasis. Current conventional research models such as static cell cultures and animal models are insufficient to grasp the complex human in vivo situation or lack translational value. To accelerate kidney research, novel research tools are required. Recent developments have allowed the directed differentiation of induced pluripotent stem cells to generate kidney organoids. Kidney organoids resemble the human kidney in vitro and can be applied in regenerative medicine and as developmental, toxicity, and disease models. Although current studies have shown great promise, challenges remain including the immaturity, limited reproducibility, and lack of perfusable vascular and collecting duct systems. This review gives an overview of our current understanding of nephrogenesis that enabled the generation of kidney organoids. Next, the potential applications of kidney organoids are discussed followed by future perspectives. This review proposes that advancement in kidney organoid research will be facilitated through our increasing knowledge on nephrogenesis and combining promising techniques such as organ-on-a-chip models.

Role of Claudins in Renal Branching Morphogenesis

Claudins are a family of tight junction proteins that are expressed during mouse kidney development. They regulate paracellular transport of solutes along the nephron and contribute to the final composition of the urinary filtrate. To understand their roles during development, we used a protein reagent, a truncated version of the Clostridium perfringens enterotoxin (C-CPE), to specifically remove a subset of claudin family members from mouse embryonic kidney explants at embryonic day 12. We observed that treatment with C-CPE decreased the number and the complexity of ureteric bud tips that formed: there were more single and less bifid ureteric bud tips when compared to control-treated explants. In addition, C-CPE-treated explants exhibited ureteric bud tips with larger lumens when compared to control explants (p < .05). Immunofluorescent analysis revealed decreased expression and localization of Claudin-3, -4, -6, and -8 to tight junctions of ureteric bud tips following treatment with C-CPE. Interestingly, Claudin-7 showed higher expression in the basolateral membrane of the ureteric bud lineage and poor localization to the tight junctions of the ureteric bud lineage both in controls and in C-CPE-treated explants. Taken together, it appears that claudin proteins may play a role in ureteric bud branching morphogenesis through changes in lumen formation that may affect the efficiency by which ureteric buds emerge and branch.

Birth Weight and Susceptibility to Chronic Kidney Disease

The worldwide prevalence of noncommunicable diseases (NCDs) is projected to increase substantially over the next few decades. Chronic kidney disease (CKD) is a key determinant of poor health outcomes for major NCD. Genetic predisposition and environmental exposures are contributory factors, but increasingly, it is being recognized that fetal development is also an important modulator of the NCD risk. Low birth weight (LBW) and CKD affect more disadvantaged populations and ethnic minorities and, therefore, causes a disproportionate burden on the poor. Human nephron number is highly variable and may range from under half a million to almost over two million. Significant variability is already present at birth, highlighting the importance of early nephrogenesis. Nearly 60% of nephrons are developed in the third-trimester of pregnancy. Nephron numbers increase in proportion to birth weight and gestational age. This wide-variability probably contributes to individual susceptibility to develop CKD where individuals with nephron numbers on the lower side of the spectrum are those at higher risk of developing kidney dysfunction at higher rate and progress more toward end-stage CKD. This article aims at discussing LBW and the susceptibility to CKD. Furthermore, in postnatal environment, the weight gain or change at adult life increases the metabolic demand and determines the phenotypic expression of disease along with the spectrum of nephron number. Hence, a cycle of hyperfiltration mechanism of these nephrons leads to proteinuria, glomerulo- sclerosis, and progressive development of larger glomeruli, a greater risk of proteinuria and progressive CKD. Therefore, LBW offspring are at risk of developing CKD (defined as albuminuria, a reduced glomerular filtration rate, or renal failure) in later life. Furthermore, the impact of prenatal programming is expected to be compounded with age, and the association of LBW with the risk of CKD seen in younger adults may become greater with age. It would be prudent, to adopt policies of intensified life-long surveillance of LBW people, anticipating this risk.

A mutation affecting laminin alpha 5 polymerisation gives rise to a syndromic developmental disorder

Laminin alpha 5 (LAMA5) is a member of a large family of proteins that trimerise and then polymerise to form a central component of all basement membranes. Consequently, the protein plays an instrumental role in shaping the normal development of the kidney, skin, neural tube, lung and limb, and many other organs and tissues. Pathogenic mutations in some laminins have been shown to cause a range of largely syndromic conditions affecting the competency of the basement membranes to which they contribute. We report the identification of a mutation in the polymerisation domain of LAMA5 in a patient with a complex syndromic disease characterised by defects in kidney, craniofacial and limb development, and by a range of other congenital defects. Using CRISPR-generated mouse models and biochemical assays, we demonstrate the pathogenicity of this variant, showing that the change results in a failure of the polymerisation of α/β/γ laminin trimers. Comparing these in vivo phenotypes with those apparent upon gene deletion in mice provides insights into the specific functional importance of laminin polymerisation during development and tissue homeostasis.

[The kidney of the premature child: Long-term risks]

The premature newborn faces extrauterine conditions with some systems still immature, both ana tomically and physiologically. The kidney finishes developing at the end of the third trimester of pregnancy, so it is especially exposed to alter its normal development if preterm birth occurs. This si tuation may condition, among other consequences, a lower functional renal mass and microvascular changes comprising a high risk of chronic kidney disease in the long term and arterial hypertension. This article analyzes the current evidence on these risks in premature infants and offers a nephrology follow-up scheme of these children.

N-glycosylation of infectious bronchitis virus M41 spike determines receptor specificity

Infection of chicken coronavirus infectious bronchitis virus (IBV) is initiated by binding of the viral heavily N-glycosylated attachment protein spike to the alpha-2,3-linked sialic acid receptor Neu5Ac. Previously, we have shown that N-glycosylation of recombinantly expressed receptor binding domain (RBD) of the spike of IBV-M41 is of critical importance for binding to chicken trachea tissue. Here we investigated the role of N-glycosylation of the RBD on receptor specificity and virus replication in the context of the virus particle. Using our reverse genetics system we were able to generate recombinant IBVs for nine-out-of-ten individual N-glycosylation mutants. In vitro growth kinetics of these viruses were comparable to the virus containing the wild-type M41-S1. Furthermore, Neu5Ac binding by the recombinant viruses containing single N-glycosylation site knock-out mutations matched the Neu5Ac binding observed with the recombinant RBDs. Five N-glycosylation mutants lost the ability to bind Neu5Ac and gained binding to a different, yet unknown, sialylated glycan receptor on host cells. These results demonstrate that N-glycosylation of IBV is a determinant for receptor specificity.

Deficiency in the endocytic adaptor proteins PHETA1/2 impairs renal and craniofacial development

A critical barrier in the treatment of endosomal and lysosomal diseases is the lack of understanding of the in vivo functions of the putative causative genes. We addressed this by investigating a key pair of endocytic adaptor proteins, PH domain-containing endocytic trafficking adaptor 1 and 2 (PHETA1/2; also known as FAM109A/B, Ses1/2, IPIP27A/B), which interact with the protein product of OCRL, the causative gene for Lowe syndrome. Here, we conducted the first study of PHETA1/2 in vivo, utilizing the zebrafish system. We found that impairment of both zebrafish orthologs, pheta1 and pheta2, disrupted endocytosis and ciliogenesis in renal tissues. In addition, pheta1/2 mutant animals exhibited reduced jaw size and delayed chondrocyte differentiation, indicating a role in craniofacial development. Deficiency of pheta1/2 resulted in dysregulation of cathepsin K, which led to an increased abundance of type II collagen in craniofacial cartilages, a marker of immature cartilage extracellular matrix. Cathepsin K inhibition rescued the craniofacial phenotypes in the pheta1/2 double mutants. The abnormal renal and craniofacial phenotypes in the pheta1/2 mutant animals were consistent with the clinical presentation of a patient with a de novo arginine (R) to cysteine (C) variant (R6C) of PHETA1. Expressing the patient-specific variant in zebrafish exacerbated craniofacial deficits, suggesting that the R6C allele acts in a dominant-negative manner. Together, these results provide insights into the in vivo roles of PHETA1/2 and suggest that the R6C variant is contributory to the pathogenesis of disease in the patient.This article has an associated First Person interview with the first author of the paper.

Dnmt3a and Dnmt3b-Decommissioned Fetal Enhancers are Linked to Kidney Disease

BACKGROUND

Cytosine methylation is an epigenetic mark that dictates cell fate and response to stimuli. The timing and establishment of methylation logic during kidney development remains unknown. DNA methyltransferase 3a and 3b are the enzymes capable of establishing de novo methylation.

METHODS

We generated mice with genetic deletion of Dnmt3a and Dnmt3b in nephron progenitor cells (Six2CreDnmt3a/3b) and kidney tubule cells (KspCreDnmt3a/3b). We characterized KspCreDnmt3a/3b mice at baseline and after injury. Unbiased omics profiling, such as whole genome bisulfite sequencing, reduced representation bisulfite sequencing and RNA sequencing were performed on whole-kidney samples and isolated renal tubule cells.

RESULTS

KspCreDnmt3a/3b mice showed no obvious morphologic and functional alterations at baseline. Knockout animals exhibited increased resistance to cisplatin-induced kidney injury, but not to folic acid-induced fibrosis. Whole-genome bisulfite sequencing indicated that Dnmt3a and Dnmt3b play an important role in methylation of gene regulatory regions that act as fetal-specific enhancers in the developing kidney but are decommissioned in the mature kidney. Loss of Dnmt3a and Dnmt3b resulted in failure to silence developmental genes. We also found that fetal-enhancer regions methylated by Dnmt3a and Dnmt3b were enriched for kidney disease genetic risk loci. Methylation patterns of kidneys from patients with CKD showed defects similar to those in mice with Dnmt3a and Dnmt3b deletion.

CONCLUSIONS

Our results indicate a potential locus-specific convergence of genetic, epigenetic, and developmental elements in kidney disease development.

Differential role of planar cell polarity gene Vangl2 in embryonic and adult mammalian kidneys

Planar cell polarity (PCP) pathway is crucial for tissue morphogenesis. Mutations in PCP genes cause multi-organ anomalies including dysplastic kidneys. Defective PCP signaling was postulated to contribute to cystogenesis in polycystic kidney disease. This work was undertaken to elucidate the role of the key PCP gene, Vangl2, in embryonic and postnatal renal tubules and ascertain whether its loss contributes to cyst formation and defective tubular function in mature animals. We generated mice with ubiquitous and collecting duct-restricted excision of Vangl2. We analyzed renal tubules in mutant and control mice at embryonic day E17.5 and postnatal days P1, P7, P30, P90, 6- and 9-month old animals. The collecting duct functions were analyzed in young and adult mutant and control mice. Loss of Vangl2 leads to profound tubular dilatation and microcysts in embryonic kidneys. Mechanistically, these abnormalities are caused by defective convergent extension (larger tubular cross-sectional area) and apical constriction (cuboidal cell shape and a reduction of activated actomyosin at the luminal surface). However, the embryonic tubule defects were rapidly resolved by Vangl2-independent mechanisms after birth. Normal collecting duct architecture and functions were found in young and mature animals. During embryogenesis, Vangl2 controls tubular size via convergent extension and apical constriction. However, rapidly after birth, PCP-dependent control of tubular size is switched to a PCP-independent regulatory mechanism. We conclude that loss of the Vangl2 gene is dispensable for tubular elongation and maintenance postnatally. It does not lead to cyst formation and is unlikely to contribute to polycystic kidney disease.

Configuration of the extra-renal venous system in relation to the left renal vein: A cadaveric study and new proposed classification

The advent of laparoscopic live-donor nephrectomy for renal transplantation has prompted the need to define the precise anatomical relations of the left renal vein (LRV) and its tributaries. The left kidney is preferred as the greater length of the LRV facilitates implantation in the recipient. While previous studies have described variations in the LRV system, the connections between the left ascending lumbar vein (LALV) and LRV tributaries have been less well-defined. This study aims to further characterise the LALV and proposes a novel classification for its relation to other veins. Dissection of the LRV system, including the left suprarenal vein (LSV), left gonadal vein (LGV) and LALV, was performed in 38 cadavers. Their drainage points into the LRV were recorded, and measurements taken of the distances from these points to the junction of the LRV and inferior vena cava (IVC). The position of the LRV in relation to the aorta was anterior in 35 cases (92%), entirely posterior in 1 case (3%), and circumaortic in 2 cases (5%). Duplication of the LSV and LGV occurred in 6 (16%) and 10 (27%) cases respectively. A direct posterior connection between the LALV and LRV was identified in 32 (86%) cases. The drainage point of the LALV into the LRV lay between the IVC and LGV in 8 (25%) cases. In 20 cases (63%), the drainage points of the LALV and LGV were equidistant from the IVC; and in 5 cases (16%), those of the LALV and posterior branch of the LRV were equidistant from the IVC. In these two groups, the vessels shared a confluent trunk in 10 and 4 cases respectively. In 3 cases, connections were observed between all three vessels (LALV, LGV and posterior branch of LRV). No confluence trunk was shared by the LALV and LSV. These results confirm the high incidence of communicating LALVs, which represent a potentially troublesome source of operative bleeding if unrecognised. Confluent venous trunks may also present difficulties during vessel ligation prior to nephrectomy. It is suggested that a novel classification of the relation of the LALV based on these findings may assist in surgical planning and reduce complications.

Prenatal hypoxia increases susceptibility to kidney injury

Prenatal hypoxia is a gestational stressor that can result in developmental abnormalities or physiological reprogramming, and often decreases cellular capacity against secondary stress. When a developing fetus is exposed to hypoxia, blood flow is preferentially redirected to vital organs including the brain and heart over other organs including the kidney. Hypoxia-induced injury can lead to structural malformations in the kidney; however, even in the absence of structural lesions, hypoxia can physiologically reprogram the kidney leading to decreased function or increased susceptibility to injury. Our investigation in mice reveals that while prenatal hypoxia does not affect normal development of the kidneys, it primes the kidneys to have an increased susceptibility to kidney injury later in life. We found that our model does not develop structural abnormalities when prenatally exposed to modest 12% O2 as evident by normal histological characterization and gene expression analysis. Further, adult renal structure and function is comparable to mice exposed to ambient oxygen throughout nephrogenesis. However, after induction of kidney injury with a nephrotoxin (cisplatin), the offspring of mice housed in hypoxia exhibit significantly reduced renal function and proximal tubule damage following injury. We conclude that exposure to prenatal hypoxia in utero physiologically reprograms the kidneys leading to increased susceptibility to injury later in life.

Cyp26b1 is an essential regulator of distal airway epithelial differentiation during lung development

Proper organ development depends on coordinated communication between multiple cell types. Retinoic acid (RA) is an autocrine and paracrine signaling molecule essential for the development of most organs, including the lung. Despite extensive work detailing effects of RA deficiency in early lung morphogenesis, little is known about how RA regulates late gestational lung maturation. Here, we investigate the role of the RA catabolizing protein Cyp26b1 in the lung. Cyp26b1 is highly enriched in lung endothelial cells (ECs) throughout development. We find that loss of Cyp26b1 leads to reduction of alveolar type 1 cells, failure of alveolar inflation and early postnatal lethality in mouse. Furthermore, we observe expansion of distal epithelial progenitors, but no appreciable changes in proximal airways, ECs or stromal populations. Exogenous administration of RA during late gestation partially mimics these defects; however, transcriptional analyses comparing Cyp26b1-/- with RA-treated lungs reveal overlapping, but distinct, responses. These data suggest that defects observed in Cyp26b1-/- lungs are caused by both RA-dependent and RA-independent mechanisms. This work reports crucial cellular crosstalk during lung development involving Cyp26b1-expressing endothelium and identifies a novel RA modulator in lung development.

Embryonal precursors of Wilms tumor

Adult cancers often arise from premalignant clonal expansions. Whether the same is true of childhood tumors has been unclear. To investigate whether Wilms tumor (nephroblastoma; a childhood kidney cancer) develops from a premalignant background, we examined the phylogenetic relationship between tumors and corresponding normal tissues. In 14 of 23 cases studied (61%), we found premalignant clonal expansions in morphologically normal kidney tissues that preceded tumor development. These clonal expansions were defined by somatic mutations shared between tumor and normal tissues but absent from blood cells. We also found hypermethylation of the H19 locus, a known driver of Wilms tumor development, in 58% of the expansions. Phylogenetic analyses of bilateral tumors indicated that clonal expansions can evolve before the divergence of left and right kidney primordia. These findings reveal embryonal precursors from which unilateral and multifocal cancers develop.

The Effect of Preterm Birth on Renal Development and Renal Health Outcome

Preterm birth is associated with adverse renal health outcomes including hypertension, chronic kidney disease, and an increased rate of progression to end-stage renal failure. This review explores the antenatal, perinatal, and postnatal factors that affect the functional nephron mass of an individual and contribute to long-term kidney outcome. Health-care professionals have opportunities to increase their awareness of the risks to kidney health in this population. Optimizing maternal health around the time of conception and during pregnancy, providing kidney-focused supportive care in the NICU during postnatal nephrogenesis, and avoiding accelerating nephron loss throughout life may all contribute to improved long-term outcomes. There is a need for ongoing research into the long-term kidney outcomes of preterm survivors in mid-to-late adulthood as well as a need for further research into interventions that may improve ex utero nephrogenesis.

DYRK1A-related intellectual disability: a syndrome associated with congenital anomalies of the kidney and urinary tract

PURPOSE

Haploinsufficiency of DYRK1A causes a recognizable clinical syndrome. The goal of this paper is to investigate congenital anomalies of the kidney and urinary tract (CAKUT) and genital defects (GD) in patients with DYRK1A variants.

METHODS

A large database of clinical exome sequencing (ES) was queried for de novo DYRK1A variants and CAKUT/GD phenotypes were characterized. Xenopus laevis (frog) was chosen as a model organism to assess Dyrk1a's role in renal development.

RESULTS

Phenotypic details and variants of 19 patients were compiled after an initial observation that one patient with a de novo pathogenic variant in DYRK1A had GD. CAKUT/GD data were available from 15 patients, 11 of whom presented with CAKUT/GD. Studies in Xenopus embryos demonstrated that knockdown of Dyrk1a, which is expressed in forming nephrons, disrupts the development of segments of embryonic nephrons, which ultimately give rise to the entire genitourinary (GU) tract. These defects could be rescued by coinjecting wild-type human DYRK1A RNA, but not with DYRK1AR205* or DYRK1AL245R RNA.

CONCLUSION

Evidence supports routine GU screening of all individuals with de novo DYRK1A pathogenic variants to ensure optimized clinical management. Collectively, the reported clinical data and loss-of-function studies in Xenopus substantiate a novel role for DYRK1A in GU development.

Bisphenol A-induced apoptosis, oxidative stress and DNA damage in cultured rhesus monkey embryo renal epithelial Marc-145 cells

Bisphenol A (BPA) is widely used in the production of epoxy resins and polycarbonate plastics. Under harsh situations, these plastics likely desorb BPA, which then can seep into the environment. Various concentrations of BPA have been detected in most biological fluid. However, there is paucity of information on the detrimental effects of BPA and its subsequent cellular events in chronic kidney disease (CKD). Hence, in this in vitro study, we aimed to investigate the effects of BPA on renal epithelial cell activation, apoptosis, and DNA damage. Rhesus monkey embryo renal epithelial Marc-145 cells were exposed to 0, 10^-1, 10^-2, 10^-3, 10^-4, 10^-5, and 10^-6 M of BPA. Alterations in intracellular apoptosis, oxidative stress, and DNA damage were evaluated. The results showed that BPA decreased cell viability, superoxide dismutase (SOD) activity and glutathione (GSH) level, with concomitant increases in apoptosis related indices, lactate dehydrogenase (LDH) activity, reactive oxygen species (ROS) generation, thiobarbituric acid reactive substances (TBARS) content, and the rate of comet Marc-145 cells with a dose-dependent manner. The data indicated that increased oxidative stress, apoptosis and DNA damage in epithelial Marc-145 cells might play a pivotal role in the mechanism of BPA-induced nephrotoxicity.

Kidney organoids: accurate models or fortunate accidents

There are now many reports of human kidney organoids generated via the directed differentiation of human pluripotent stem cells (PSCs) based on an existing understanding of mammalian kidney organogenesis. Such kidney organoids potentially represent tractable tools for the study of normal human development and disease with improvements in scale, structure, and functional maturation potentially providing future options for renal regeneration. The utility of such organotypic models, however, will ultimately be determined by their developmental accuracy. While initially inferred from mouse models, recent transcriptional analyses of human fetal kidney have provided greater insight into nephrogenesis. In this review, we discuss how well human kidney organoids model the human fetal kidney and how the remaining differences challenge their utility.

Steroidogenic potential of human fetal kidney at early gestational age

Steroidogenic potential of the human fetal kidney (hFK) at the end of first trimester is poorly investigated. Little is known about the ontogeny of steroidogenic enzymes and activities of steroidogenic pathways in the hFK at early pregnancy. Our aim was to explore steroidogenesis and the expression of steroidogenic enzymes in the hFK at gestational weeks (GW) 9-12. Steroids in the hFK were analyzed by gas chromatography/coupled to tandem mass spectrometry. The expression of steroidogenic enzymes in the hFK at GW 9-12 was investigated by qPCR, automated Western blotting and immunohistochemistry. We observed that the hFK produced substantial amount of steroids of the Δ⁵ and Δ⁴ pathways and several steroid precursors in the biosynthesis of DHT via the backdoor pathway but not DHT itself. The levels of steroids and expression of relevant steroidogenic enzymes (e.g., CYP17A1, HSD3B1, HSD3B2, CYP11B1 and AKR1C4) we significantly higher in the hFK at GW11-12 compared to GW9. We also found the expression of sex steroid receptors (e.g., AR, ERα and ERβ) in the hFK at GW9-12. No sex-dependent differences in the levels of all identified steroids and expression of steroidogenic enzymes in the hFK from male and female fetuses were found. Altogether, our data indicate that the hFK at early pregnancy is steroidogenic organ with potential to synthesize multiple steroids that may play an important role in the formation and development of this organ in humans.

The relationship between maternal adiposity during pregnancy and fetal kidney development and kidney function in infants: the Gomeroi gaaynggal study

Maternal obesity during pregnancy has a detrimental impact on offspring renal development and function. This is pertinent to Indigenous Australians as they are twice as likely as non-Indigenous Australians to develop chronic kidney disease (CKD). The aim of this study was to examine whether there was an association between maternal adiposity and fetal kidney growth in late gestation (>28 weeks) and kidney function in infants, <2.5 years of age, from the Gomeroi gaaynggal cohort. Pre-pregnancy body mass index (BMI) was recorded at the first prenatal visit and maternal adiposity indicators (percent body fat and visceral fat area) measured at >28 weeks gestation by bioelectrical impedance analysis. Fetal kidney structure was assessed by ultrasound. Renal function indicators (urinary albumin:creatinine and protein:creatinine) were measured in infants from a spot urine collection from nappies. Multiple linear regression and multi-level mixed effects linear regression models with clustering were used to account for repeated measures of urine. 147 mother-child pairs were examined. Estimated fetal weight (EFW), but not fetal kidney size, was positively associated with maternal adiposity and pre-pregnancy BMI. When adjusted for smoking, combined kidney volume relative to EFW was negatively associated with maternal percentage body fat. Infant kidney function was not influenced by maternal adiposity and pre-pregnancy BMI (n = 84 observations). Current findings show that Indigenous babies born to obese mothers have reduced kidney size relative to EFW. We suggest that these babies are experiencing a degree of glomerular hyperfiltration in utero, and therefore are at risk of developing CKD in later life, especially if their propensity for obesity is maintained. Although no impact on renal function was observed at <2.5 years of age, long-term follow-up of offspring is required to evaluate potential later life impacts.

In vivo analysis of renal epithelial cells in zebrafish

The zebrafish kidney has been used effectively for studying kidney development, repair and disease. New gene editing capability makes it a more versatile in vivo vertebrate model system to investigate renal epithelial cells in their native environment. In this chapter we focus on dissecting gene function in basic cellular biology of renal epithelial cells, including lumen formation and cell polarity, in intact zebrafish embryos.

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.