Hnf1beta and nephron segmentation

Navigating the multifaceted intricacies of the Na+-Cl- cotransporter, a highly regulated key effector in the control of hydromineral homeostasis

The Na+-Cl- cotransporter (NCC; SLC12A3) is a highly regulated integral membrane protein that is known to exist as three splice variants in primates. Its primary role in the kidney is to mediate the cosymport of Na+ and Cl- across the apical membrane of the distal convoluted tubule. Through this role and the involvement of other ion transport systems, NCC allows the systemic circulation to reclaim a fraction of the ultrafiltered Na+, K+, Cl-, and Mg+ loads in exchange for Ca2+ and [Formula: see text]. The physiological relevance of the Na+-Cl- cotransport mechanism in humans is illustrated by several abnormalities that result from NCC inactivation through the administration of thiazides or in the setting of hereditary disorders. The purpose of the present review is to discuss the molecular mechanisms and overall roles of Na+-Cl- cotransport as the main topics of interest. On reading the narrative proposed, one will realize that the knowledge gained in regard to these themes will continue to progress unrelentingly no matter how refined it has now become.

Great potential of renal progenitor cells in kidney: From the development to clinic

The mammalian renal organ represents a pinnacle of complexity, housing functional filtering units known as nephrons. During embryogenesis, the depletion of niches containing renal progenitor cells (RPCs) and the subsequent incapacity of adult kidneys to generate new nephrons have prompted the formulation of protocols aimed at isolating residual RPCs from mature kidneys and inducing their generation from diverse cell sources, notably pluripotent stem cells. Recent strides in the realm of regenerative medicine and the repair of tissues using stem cells have unveiled critical signaling pathways essential for the maintenance and generation of human RPCs in vitro. These findings have ushered in a new era for exploring novel strategies for renal protection. The present investigation delves into potential transcription factors and signaling cascades implicated in the realm of renal progenitor cells, focusing on their protection and differentiation. The discourse herein elucidates contemporary research endeavors dedicated to the acquisition of progenitor cells, offering crucial insights into the developmental mechanisms of these cells within the renal milieu and paving the way for the formulation of innovative treatment modalities.

The Landscape of HNF1B Deficiency: A Syndrome Not Yet Fully Explored

The hepatocyte nuclear factor 1β (HNF1B) gene is involved in the development of specialized epithelia of several organs during the early and late phases of embryogenesis, performing its function mainly by regulating the cell cycle and apoptosis pathways. The first pathogenic variant of HNF1B (namely, R177X) was reported in 1997 and is associated with the maturity-onset diabetes of the young. Since then, more than 230 different HNF1B variants have been reported, revealing a multifaceted syndrome with complex and heterogenous genetic, pathologic, and clinical profiles, mainly affecting the pediatric population. The pancreas and kidneys are the most frequently affected organs, resulting in diabetes, renal cysts, and a decrease in renal function, leading, in 2001, to the definition of HNF1B deficiency syndrome, including renal cysts and diabetes. However, several other organs and systems have since emerged as being affected by HNF1B defect, while diabetes and renal cysts are not always present. Especially, liver involvement has generally been overlooked but recently emerged as particularly relevant (mostly showing chronically elevated liver enzymes) and with a putative relation with tumor development, thus requiring a more granular analysis. Nowadays, HNF1B-associated disease has been recognized as a clinical entity with a broader and more variable multisystem phenotype, but the reasons for the phenotypic heterogeneity are still poorly understood. In this review, we aimed to describe the multifaceted nature of HNF1B deficiency in the pediatric and adult populations: we analyzed the genetic, phenotypic, and clinical features of this complex and misdiagnosed syndrome, covering the most frequent, unusual, and recently identified traits.

Tumor-suppressive activity of Hnf1β in Wilms' tumor

Hepatocyte nuclear factor 1β (HNF1β) is a transcription factor belonging to the HNF-1 family and has been implicated in a number of cancers, but its role in Wilms' tumor (nephroblastoma) has not been addressed. Here, we compared its expression between Wilms' tumor patient kidney tissue and adjacent tissue based on the Oncomine database ( www.oncomine.com ). Cell proliferation, apoptosis, migration, and HNF1β expression level were analyzed in Wilms' tumor-derived G401 cells. Using a variety of mouse tissues (lung, heart, kidney, etc.), we found that HNF1β is the highest expression in the kidneys. Oncomine analysis further demonstrated that HNF1β has a lower expression in Wilms' tumor tissue than in paracancerous tissues. Overexpression of HNF1β decreased cell proliferation and migration, but promoted cell apoptosis. Knockdown of HNF1β produced the opposite results. These results indicated that HNF1β may play important roles in kidney development and function, and its activation may negatively regulate Wilms' tumor progression.

Role of epigenetic mechanisms in cisplatin-induced toxicity

Cisplatin (CDDP) is a highly effective antineoplastic agent, widely used in the treatment of various malignant tumors. However, its major problems are side effects associated to toxicity. Considerable inter-individual differences have been reported for CDDP-induced toxicity due to genetic and epigenetic factors. Genetic causes are well described; however, epigenetic modifications are not fully addressed. In the last few years, many evidences were found linking microRNA to the development of CDDP-mediated toxicity, particularly nephrotoxicity. In this review, we described how genetic and epigenetic modifications can be important determinants for the development of toxicity in patients treated with CDDP, and how these alterations may be interesting biomarkers for monitoring toxicity induced by CDDP. Considering the validation in different studies, we suggest that miR-34a, -146b, -378a, -192, and -193 represent an attractive study group to evaluate potential biomarkers to detect CDDP-related nephrotoxicity.

A novel mechanism of gland formation in zebrafish involving transdifferentiation of renal epithelial cells and live cell extrusion

Transdifferentiation is the poorly understood phenomenon whereby a terminally differentiated cell acquires a completely new identity. Here, we describe a rare example of a naturally occurring transdifferentiation event in zebrafish in which kidney distal tubule epithelial cells are converted into an endocrine gland known as the Corpuscles of Stannius (CS). We find that this process requires Notch signalling and is associated with the cytoplasmic sequestration of the Hnf1b transcription factor, a master-regulator of renal tubule fate. A deficiency in the Irx3b transcription factor results in ectopic transdifferentiation of distal tubule cells to a CS identity but in a Notch-dependent fashion. Using live-cell imaging we show that CS cells undergo apical constriction en masse and are then extruded from the tubule to form a distinct organ. This system provides a valuable new model to understand the molecular and morphological basis of transdifferentiation and will advance efforts to exploit this rare phenomenon therapeutically.

EF-hand domain containing 2 (Efhc2) is crucial for distal segmentation of pronephros in zebrafish

Background

The blood filtering organ in zebrafish embryos is the pronephros, which consists of two functional nephrons. Segmentation of a nephron into different domains is essential for its function and is well conserved among vertebrates. Zebrafish has been extensively used as a model to understand nephron segmentation during development. Here, we have identified EF-hand domain containing 2 (Efhc2) as a novel component of genetic programme regulating nephron segmentation in zebrafish. Human EFHC2 is a protein with one predicted calcium-binding EF-hand motif and three DM10 domains, whose function is unknown. EFHC2 has been implicated in several brain-related genetic diseases like Turner syndrome and juvenile myoclonic epilepsy. However, there is limited information on its normal physiological function.

Results

efhc2 mRNA is primarily expressed in the pronephros of zebrafish embryos. Other sites of expression include olfactory placode, notochord, otic vesicle, epiphysis and neuromast cells. Morpholino antisense oligonucleotide-mediated knock-down of Efhc2 resulted in defects in pronephros development and function in zebrafish embryos. Efhc2 knock-down leads to expansion of distal early segment of pronephros, whereas, the corpuscle of stannius and distal late segments were reduced. The number of multi-ciliated cells (MCC) that are present in a salt-and-pepper fashion throughout the middle of each nephron and vital for fluid flow were also reduced. It is known that retinoic acid (RA) signaling regulates pronephros segmentation in vertebrates and we show that Efhc2 function is crucial for nephron segmentation in zebrafish. Our data suggests that RA and Efhc2 function independent of each other in pronephros segmentation. However, Efhc2 and RA synergistically regulate MCC development.

Conclusion

In this study, we have identified Efhc2 as a regulator of segmentation of the distal part of nephron and pronephros function during zebrafish development.

Electronic supplementary material

The online version of this article (10.1186/s13578-018-0253-z) contains supplementary material, which is available to authorized users.

MicroRNA-375 Is Induced in Cisplatin Nephrotoxicity to Repress Hepatocyte Nuclear Factor 1-β

Nephrotoxicity is a major adverse effect of cisplatin-mediated chemotherapy in cancer patients. The pathogenesis of cisplatin-induced nephrotoxicity remains largely unclear, making it difficult to design effective renoprotective approaches. Here, we have examined the role of microRNAs (miRNAs) in cisplatin-induced nephrotoxicity. We show that cisplatin nephrotoxicity was not affected by overall depletion of both beneficial and detrimental miRNAs from kidney proximal tubular cells in mice in which the miRNA-generating enzyme Dicer had been conditionally knocked out. To identify miRNAs involved in cisplatin nephrotoxicity, we used microarray analysis to profile miRNA expression and identified 47 up-regulated microRNAs and 20 down-regulated microRNAs in kidney cortical tissues. One up-regulated miRNA was miR-375, whose expression was also induced in cisplatin-treated renal tubular cells. Interestingly, inhibition of miR-375 decreased cisplatin-induced apoptosis, suggesting that miR-375 is a cell-damaging or pro-apoptotic agent. Blockade of P53 or NF-κB attenuated cisplatin-induced miR-375 expression, supporting a role of P53 and NF-κB in miR-375 induction. We also identified hepatocyte nuclear factor 1 homeobox B (HNF-1β) as a key downstream target of miR-375. Of note, we further demonstrated that HNF-1β protected renal cells against cisplatin-induced apoptosis. Together, these results suggest that upon cisplatin exposure, P53 and NF-κB collaboratively induce miR-375 expression, which, in turn, represses HNF-1β activity, resulting in renal tubular cell apoptosis and nephrotoxicity.

HNF1B-associated clinical phenotypes: the kidney and beyond

Mutations in HNF1B, the gene encoding hepatocyte nuclear factor 1β are the most commonly identified genetic cause of renal malformations. HNF1B was first identified as a disease gene for diabetes (MODY5) in 1997, and its involvement in renal disease was subsequently noted through clinical observations in pedigrees affected by MODY5. Since then, a whole spectrum of associated phenotypes have been reported, including genital malformations, autism, epilepsy, gout, hypomagnesaemia, primary hyperparathyroidism, liver and intestinal abnormalities and a rare form of kidney cancer. The most commonly identified mutation, in approximately 50 % of patients, is an entire gene deletion occurring in the context of a 17q12 chromosomal microdeletion that also includes several other genes. Some of the associated phenotypes, especially the neurologic ones, appear to occur only in the context of this microdeletion and thus may not be directly linked to HNF1B. Here we review the spectrum of associated phenotypes and discuss potential implications for clinical management.

Zebrafish kidney development

The kidney of the zebrafish shares many features with other vertebrate kidneys including the human kidney. Similar cell types and shared developmental and patterning mechanisms make the zebrafish pronephros a valuable model for kidney organogenesis. Here we review recent advances in studies of zebrafish pronephric development and provide experimental protocols to analyze kidney cell types and structures, measure nephron function, live image kidney cells in vivo, and probe mechanisms of kidney regeneration after injury.

Development of the Mammalian Kidney

The basic unit of kidney function is the nephron. In the mouse, around 14,000 nephrons form in a 10-day period extending into early neonatal life, while the human fetus forms the adult complement of nephrons in a 32-week period completed prior to birth. This review discusses our current understanding of mammalian nephrogenesis: the contributing cell types and the regulatory processes at play. A conceptual developmental framework has emerged for the mouse kidney. This framework is now guiding studies of human kidney development enabled in part by in vitro systems of pluripotent stem cell-seeded nephrogenesis. A near future goal will be to translate our developmental knowledge-base to the productive engineering of new kidney structures for regenerative medicine.

Nephron Patterning: Lessons from Xenopus, Zebrafish, and Mouse Studies

The nephron is the basic structural and functional unit of the vertebrate kidney. To ensure kidney functions, the nephrons possess a highly segmental organization where each segment is specialized for the secretion and reabsorption of particular solutes. During embryogenesis, nephron progenitors undergo a mesenchymal-to-epithelial transition (MET) and acquire different segment-specific cell fates along the proximo-distal axis of the nephron. Even if the morphological changes occurring during nephrogenesis are characterized, the regulatory networks driving nephron segmentation are still poorly understood. Interestingly, several studies have shown that the pronephric nephrons in Xenopus and zebrafish are segmented in a similar fashion as the mouse metanephric nephrons. Here we review functional and molecular aspects of nephron segmentation with a particular interest on the signaling molecules and transcription factors recently implicated in kidney development in these three different vertebrate model organisms. A complete understanding of the mechanisms underlying nephrogenesis in different model organisms will provide novel insights on the etiology of several human renal diseases.

Criteria for HNF1B analysis in patients with congenital abnormalities of kidney and urinary tract

BACKGROUND

Congenital anomalies of kidneys and urinary tract (CAKUT) are the most predominant developmental disorders comprising ∼20-30% of all anomalies identified in the prenatal period. Mutations in hepatocyte nuclear factor 1-beta (HNF-1β) involved in the development of kidneys, liver, pancreas and urogenital tract are currently the most frequent monogenetic cause of CAKUT found in 10-30% of patients depending on screening policy and study design. We aimed to validate criteria for analysis of HNF1B in a prospective cohort of paediatric and adult CAKUT patients.

METHODS

We included CAKUT patients diagnosed in our paediatric and adult nephrology departments from January 2010 until April 2013 based on predefined screening criteria. Subjects presenting with at least one major renal criterion or one minor renal criterion combined with one or more extra-renal criteria in the personal history or a familial history of renal or extra-renal manifestations were considered eligible.

RESULTS

We prospectively screened 205 patients and detected HNF1B mutations in 10% [n = 20, 12 children, median age 4.2 (range 0-13.1) years and 8 adults, median age 34.8 (range 16.6-62) years]. We observed that bilateral renal anomaly, renal cysts from unknown origin, a combination of two major renal anomalies and hypomagnesaemia were predictive for finding HNF1B mutations (P < 0.001; P < 0.001; P = 0.004; P = 0.008, respectively).

CONCLUSIONS

We demonstrated that HNF1B mutations are responsible for ∼10% of CAKUT cases, both in children and in adults. Based on our results we propose adapted criteria for HNF1B analysis to reduce the screening costs without missing affected patients. These criteria should be reaffirmed in a larger validation cohort.

Grouper tshβ promoter-driven transgenic zebrafish marks proximal kidney tubule development

Kidney tubule plays a critical role in recovering or secreting solutes, but the detailed morphogenesis remains unclear. Our previous studies have found that grouper tshβ (gtshβ) is also expressed in kidney, however, the distribution significance is still unknown. To understand the gtshβ role and kidney tubule morphogenesis, here, we have generated a transgenic zebrafish line Tg(gtshβ:GFP) with green fluorescent protein driven by the gtshβ promoter. Similar to the endogenous tshβ in zebrafish or in grouper, the gtshβ promoter-driven GFP is expressed in pituitary and kidney, and the developing details of proximal kidney tubule are marked in the transgenic zebrafish line. The gfp initially transcribes at 16 hours post fertilization (hpf) above the dorsal mesentery, and partially co-localizes with pronephric tubular markers slc20a1a and cdh17. Significantly, the GFP specifically localizes in proximal pronephric segments during embryogenesis and resides at kidney duct epithelium in adult fish. To test whether the gtshβ promoter-driven GFP may serve as a readout signal of the tubular development, we have treated the embryos with retinoic acid signaing (RA) reagents, in which exogenous RA addition results in a distal extension of the proximal segments, while RA inhibition induces a weakness and shortness of the proximal segments. Therefore, this transgenic line provides a useful tool for genetic or chemical analysis of kidney tubule.