Delayed onset of smooth muscle cell differentiation leads to hydroureter formation in mice with conditional loss of the zinc finger transcription factor gene Gata2 in the ureteric mesenchyme

Ureter development and associated congenital anomalies

Malformations of the ureter are among the most common birth defects in humans. Although some of these anomalies are asymptomatic, others are clinically relevant, causing perinatal lethality or progressing to kidney failure in childhood. The genetic causes and developmental aetiology of ureteral anomalies are difficult to study in humans; however, embryological and genetic analyses in the mouse have provided insights into the complex developmental programmes that govern ureter formation from simple tissue primordia, and the pathological consequences that result from disruption of these programmes. Abnormalities in the formation of the nephric duct and ureteric bud lead to changes in the number of ureters (and kidneys), whereas the formation of ectopic ureteric buds, failure of the nephric duct to target the cloaca or failure of the distal ureter to mature underlie vesicoureteral reflux, ureter ectopia, ureterocoele and subsequent hydroureter. Alterations in ureter specification, early growth or cyto-differentiation programmes have now also been associated with various forms of perinatal hydroureter and hydronephrosis as a consequence of functional obstruction. The characterization of cellular processes and molecular drivers of ureterogenesis in the mouse may not only aid understanding of the aetiology of human ureteral anomalies, improve prognostication and benefit the development of therapeutic strategies, but may also prove important for efforts to generate a bioartificial organ.

Crucial roles of mesenchymal Gata2 in murine epididymal development

Androgens drive the morphogenesis and differentiation of the Wolffian duct (WD) into the epididymis, an essential organ for male reproduction, by binding to the androgen receptor (AR). However, it remains unclear whether other transcriptional programs operate beyond the central androgen/AR signaling in promoting WD development. We discovered that mesenchyme-specific deletion of the transcription factor Gata2 resulted in defective epididymal coiling in the corpus and caudal regions. The defective coiling in the absence of mesenchymal Gata2 did not result from androgen signaling deficiency, as there were no abnormalities in testicular morphology, androgen production, or AR/Ar expression, and dihydrotestosterone supplementation did not restore epididymal coiling in cultured WDs. Instead, Gata2 deletion reduced the expression of the mesenchyme-derived factor Inhba and epithelial proliferation, both of which play critical roles in epididymal coiling. The epididymal defect persisted into adulthood, with the uncoiled corpus and caudal epididymis exhibiting abnormal epithelial morphology and lumen environments, resulting in an unfavorable environment for sperm storage. Our results demonstrate the androgen-independent role of mesenchymal GATA2 in promoting epididymal development through Inhba induction and highlight the importance of proper fetal development in male reproduction.

Expression and localization of HSD17B13 along mouse urinary tract

17β-Hydroxysteroid dehydrogenase-13 (HSD17B13), a newly identified lipid droplet-associated protein, plays an important role in the development of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Emerging evidence demonstrates that NASH is an independent risk factor for chronic kidney disease, which is frequently accompanied by renal lipid accumulation. In addition, the HSD17B13 rs72613567 variant is associated with lower levels of albuminuria in patients with biopsy-proven NAFLD. At present, the role of HSD17B13 in lipid accumulation in the kidney is unclear. This study utilized bioinformatic and immunostaining approaches to examine the expression and localization of HSD17B13 along the mouse urinary tract. We found that HSD17B13 is constitutively expressed in the kidney, ureter, and urinary bladder. Our findings reveal for the first time, to our knowledge, the precise localization of HSD17B13 in the mouse urinary system, providing a basis for further studying the pathogenesis of HSD17B13 in various renal and urological diseases.NEW & NOTEWORTHY HSD17B13, a lipid droplet-associated protein, is crucial in nonalcoholic fatty liver disease (NAFLD) development. NAFLD also independently raises chronic kidney disease (CKD) risk, often with renal lipid buildup. However, HSD17B13's role in CKD-related lipid accumulation is unclear. This study makes the first effort to examine HSD17B13 expression and localization along the urinary system, providing a basis for exploring its physiological and pathophysiological roles in the kidney and urinary tract.

Crucial Roles of the Mesenchymal Androgen Receptor in Wolffian Duct Development

Wolffian duct (WD) maintenance and differentiation is predominantly driven by the androgen action, which is mediated by the androgen receptor (AR). It is well established that the mesenchyme indicates the fate and differentiation of epithelial cells. However, in vivo developmental requirement of mesenchymal AR in WD development is still undefined. By designing a mesenchyme-specific Ar knockout (ARcKO), we discovered that the loss of mesenchymal Ar led to the bilateral or unilateral degeneration of caudal WDs and cystic formation at the cranial WDs. Ex vivo culture of ARcKO WDs invariably resulted in bilateral defects, suggesting that some factor(s) originating from surrounding tissues in vivo might promote WD survival and growth even in the absence of mesenchymal Ar. Mechanistically, we found cell proliferation was significantly reduced in both epithelial and mesenchymal compartments; but cell apoptosis was not affected. Transcriptomic analysis by RNA sequencing of E14.5 mesonephroi revealed 131 differentially expressed genes. Multiple downregulated genes (Top2a, Wnt9b, Lama2, and Lamc2) were associated with morphological and cellular changes in ARcKO male embryos (ie, reduced cell proliferation and decreased number of epithelial cells). Mesenchymal differentiation into smooth muscle cells that are critical for morphogenesis was also impaired in ARcKO male embryos. Taken together, our results demonstrate the crucial roles of the mesenchymal AR in WD maintenance and morphogenesis in mice.

The genetics and pathogenesis of CAKUT

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

Mesenchymal FGFR1 and FGFR2 control patterning of the ureteric mesenchyme by balancing SHH and BMP4 signaling

The coordinated development of the mesenchymal and epithelial progenitors of the murine ureter depends on a complex interplay of diverse signaling activities. We have recently shown that epithelial FGFR2 signaling regulates stratification and differentiation of the epithelial compartment by enhancing epithelial Shh expression, and mesenchymal SHH and BMP4 activity. Here, we show that FGFR1 and FGFR2 expression in the mesenchymal primordium impinges on the SHH/BMP4 signaling axis to regulate mesenchymal patterning and differentiation. Mouse embryos with conditional loss of Fgfr1 and Fgfr2 in the ureteric mesenchyme exhibited reduced mesenchymal proliferation and prematurely activated lamina propria formation at the expense of the smooth muscle cell program. They also manifested hydroureter at birth. Molecular profiling detected increased SHH, WNT and retinoic acid signaling, whereas BMP4 signaling in the mesenchyme was reduced. Pharmacological activation of SHH signaling in combination with inhibition of BMP4 signaling recapitulated the cellular changes in explant cultures of wild-type ureters. Additional experiments suggest that mesenchymal FGFR1 and FGFR2 act as a sink for FGF ligands to dampen activation of Shh and BMP receptor gene expression by epithelial FGFR2 signaling.

GATA6 is a crucial factor for Myocd expression in the visceral smooth muscle cell differentiation program of the murine ureter

Smooth muscle cells (SMCs) are a crucial component of the mesenchymal wall of the ureter, as they account for the efficient removal of the urine from the renal pelvis to the bladder by means of their contractile activity. Here, we show that the zinc-finger transcription factor gene Gata6 is expressed in mesenchymal precursors of ureteric SMCs under the control of BMP4 signaling. Mice with a conditional loss of Gata6 in these precursors exhibit a delayed onset and reduced level of SMC differentiation and peristaltic activity, as well as dilatation of the ureter and renal pelvis (hydroureternephrosis) at birth and at postnatal stages. Molecular profiling revealed a delayed and reduced expression of the myogenic driver gene Myocd, but the activation of signaling pathways and transcription factors previously implicated in activation of the visceral SMC program in the ureter was unchanged. Additional gain-of-function experiments suggest that GATA6 cooperates with FOXF1 in Myocd activation and SMC differentiation, possibly as pioneer and lineage-determining factors, respectively.

Notch signaling is a novel regulator of visceral smooth muscle cell differentiation in the murine ureter

The contractile phenotype of smooth muscle cells (SMCs) is transcriptionally controlled by a complex of the DNA-binding protein SRF and the transcriptional co-activator MYOCD. The pathways that activate expression of Myocd and of SMC structural genes in mesenchymal progenitors are diverse, reflecting different intrinsic and extrinsic signaling inputs. Taking the ureter as a model, we analyzed whether Notch signaling, a pathway previously implicated in vascular SMC development, also affects visceral SMC differentiation. We show that mice with a conditional deletion of the unique Notch mediator RBPJ in the undifferentiated ureteric mesenchyme exhibit altered ureter peristalsis with a delayed onset, and decreased contraction frequency and intensity at fetal stages. They also develop hydroureter 2 weeks after birth. Notch signaling is required for precise temporal activation of Myocd expression and, independently, for expression of a group of late SMC structural genes. Based on additional expression analyses, we suggest that a mesenchymal JAG1-NOTCH2/NOTCH3 module regulates visceral SMC differentiation in the ureter in a biphasic and bimodal manner, and that its molecular function differs from that in the vascular system.

FGFR2 signaling enhances the SHH-BMP4 signaling axis in early ureter development

The patterned array of basal, intermediate and superficial cells in the urothelium of the mature ureter arises from uncommitted epithelial progenitors of the distal ureteric bud. Urothelial development requires signaling input from surrounding mesenchymal cells, which, in turn, depend on cues from the epithelial primordium to form a layered fibro-muscular wall. Here, we have identified FGFR2 as a crucial component in this reciprocal signaling crosstalk in the murine ureter. Loss of Fgfr2 in the ureteric epithelium led to reduced proliferation, stratification, intermediate and basal cell differentiation in this tissue, and affected cell survival and smooth muscle cell differentiation in the surrounding mesenchyme. Loss of Fgfr2 impacted negatively on epithelial expression of Shh and its mesenchymal effector gene Bmp4. Activation of SHH or BMP4 signaling largely rescued the cellular defects of mutant ureters in explant cultures. Conversely, inhibition of SHH or BMP signaling in wild-type ureters recapitulated the mutant phenotype in a dose-dependent manner. Our study suggests that FGF signals from the mesenchyme enhance, via epithelial FGFR2, the SHH-BMP4 signaling axis to drive urothelial and mesenchymal development in the early ureter.

Inflammation-like changes in the urothelium of Lifr-deficient mice and LIFR-haploinsufficient humans with urinary tract anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of end-stage kidney disease in children. While the genetic aberrations underlying CAKUT pathogenesis are increasingly being elucidated, their consequences on a cellular and molecular level commonly remain unclear. Recently, we reported rare heterozygous deleterious LIFR variants in 3.3% of CAKUT patients, including a novel de novo frameshift variant, identified by whole-exome sequencing, in a patient with severe bilateral CAKUT. We also demonstrated CAKUT phenotypes in Lifr-/- and Lifr+/- mice, including a narrowed ureteric lumen due to muscular hypertrophy and a thickened urothelium. Here, we show that both in the ureter and bladder of Lifr-/- and Lifr+/- embryos, differentiation of the three urothelial cell types (basal, intermediate and superficial cells) occurs normally but that the turnover of superficial cells is elevated due to increased proliferation, enhanced differentiation from their progenitor cells (intermediate cells) and, importantly, shedding into the ureteric lumen. Microarray-based analysis of genome-wide transcriptional changes in Lifr-/- versus Lifr+/+ ureters identified gene networks associated with an antimicrobial inflammatory response. Finally, in a reverse phenotyping effort, significantly more superficial cells were detected in the urine of CAKUT patients with versus without LIFR variants indicating conserved LIFR-dependent urinary tract changes in the murine and human context. Our data suggest that LIFR signaling is required in the epithelium of the urinary tract to suppress an antimicrobial response under homeostatic conditions and that genetically induced inflammation-like changes underlie CAKUT pathogenesis in Lifr deficiency and LIFR haploinsufficiency.

Development and Carcinogenesis: Roles of GATA Factors in the Sympathoadrenal and Urogenital Systems

The GATA family of transcription factors consists of six proteins (GATA1-6) that control a variety of physiological and pathological processes. In particular, GATA2 and GATA3 are coexpressed in a number of tissues, including in the urogenital and sympathoadrenal systems, in which both factors participate in the developmental process and tissue maintenance. Furthermore, accumulating studies have demonstrated that GATA2 and GATA3 are involved in distinct types of inherited diseases as well as carcinogenesis in diverse tissues. This review summarizes our current knowledge of how GATA2 and GATA3 participate in the transcriptional regulatory circuitry during the development of the sympathoadrenal and urogenital systems, and how their dysregulation results in the carcinogenesis of neuroblastoma, renal urothelial, and gynecologic cancers.