Pkd2 Deficiency in Embryonic Aqp2 + Progenitor Cells Is Sufficient to Cause Severe Polycystic Kidney Disease

SIGNIFICANCE STATEMENT

Autosomal dominant polycystic kidney disease (ADPKD) is a devastating disorder caused by mutations in polycystin 1 ( PKD1 ) and polycystin 2 ( PKD2 ). Currently, the mechanism for renal cyst formation remains unclear. Here, we provide convincing and conclusive data in mice demonstrating that Pkd2 deletion in embryonic Aqp2 + progenitor cells (AP), but not in neonate or adult Aqp2 + cells, is sufficient to cause severe polycystic kidney disease (PKD) with progressive loss of intercalated cells and complete elimination of α -intercalated cells, accurately recapitulating a newly identified cellular phenotype of patients with ADPKD. Hence, Pkd2 is a new potential regulator critical for balanced AP differentiation into, proliferation, and/or maintenance of various cell types, particularly α -intercalated cells. The Pkd2 conditional knockout mice developed in this study are valuable tools for further studies on collecting duct development and early steps in cyst formation. The finding that Pkd2 loss triggers the loss of intercalated cells is a suitable topic for further mechanistic studies.

BACKGROUND

Most cases of autosomal dominant polycystic kidney disease (ADPKD) are caused by mutations in PKD1 or PKD2. Currently, the mechanism for renal cyst formation remains unclear. Aqp2 + progenitor cells (AP) (re)generate ≥5 cell types, including principal cells and intercalated cells in the late distal convoluted tubules (DCT2), connecting tubules, and collecting ducts.

METHODS

Here, we tested whether Pkd2 deletion in AP and their derivatives at different developmental stages is sufficient to induce PKD. Aqp2Cre Pkd2f/f ( Pkd2AC ) mice were generated to disrupt Pkd2 in embryonic AP. Aqp2ECE/+Pkd2f/f ( Pkd2ECE ) mice were tamoxifen-inducted at P1 or P60 to inactivate Pkd2 in neonate or adult AP and their derivatives, respectively. All induced mice were sacrificed at P300. Immunofluorescence staining was performed to categorize and quantify cyst-lining cell types. Four other PKD mouse models and patients with ADPKD were similarly analyzed.

RESULTS

Pkd2 was highly expressed in all connecting tubules/collecting duct cell types and weakly in all other tubular segments. Pkd2AC mice had obvious cysts by P6 and developed severe PKD and died by P17. The kidneys had reduced intercalated cells and increased transitional cells. Transitional cells were negative for principal cell and intercalated cell markers examined. A complete loss of α -intercalated cells occurred by P12. Cysts extended from the distal renal segments to DCT1 and possibly to the loop of Henle, but not to the proximal tubules. The induced Pkd2ECE mice developed mild PKD. Cystic α -intercalated cells were found in the other PKD models. AQP2 + cells were found in cysts of only 13/27 ADPKD samples, which had the same cellular phenotype as Pkd2AC mice.

CONCLUSIONS

Hence, Pkd2 deletion in embryonic AP, but unlikely in neonate or adult Aqp2 + cells (principal cells and AP), was sufficient to cause severe PKD with progressive elimination of α -intercalated cells, recapitulating a newly identified cellular phenotype of patients with ADPKD. We proposed that Pkd2 is critical for balanced AP differentiation into, proliferation, and/or maintenance of cystic intercalated cells, particularly α -intercalated cells.

Urothelial progenitors in development and repair

Urothelium is a specialized multilayer epithelium that lines the urinary tract from the proximal urethra to the kidney. In addition to proliferation and differentiation during development, urothelial injury postnatally triggers a robust regenerative capacity to restore the protective barrier between the urine and tissue. Mounting evidence supports the existence of dedicated progenitor cell populations that give rise to urothelium during development and in response to injury. Understanding the cellular and molecular basis for urothelial patterning and repair will inform tissue regeneration therapies designed to ameliorate a number of structural and functional defects of the urinary tract. Here, we review the current understanding of urothelial progenitors and the signaling pathways that govern urothelial development and repair. While most published studies have focused on bladder urothelium, we also discuss literature on upper tract urothelial progenitors. Furthermore, we discuss evidence supporting existence of context-specific progenitors. This knowledge is fundamental to the development of strategies to regenerate or engineer damaged or diseased urothelium.

Abstract 5431: FGF7 peptide (FGF7p) mimetic mitigates urothelial injury from cyclophosphamide or radiation

Background: Hemorrhagic cystitis from chemical or radiation bladder injury can cause life-threatening bleeding and/or urothelial cancer. Fibroblast growth factor 7 (FGF7) blocks urothelial apoptosis induced by cyclophosphamide (CPP) or radiation, but there are limitations to its use in patients, including an inability to apply it by direct bladder infusion and the high cost due to the large size of the protein (18.8 kDa).

Purpose: We previously identified a small peptide that equaled or exceeded the mitigation effect of full length FGF2 on acute radiation syndrome. Benefits of developing a similar FGF7 biomimetic peptide include lower likelihood of inflammation, longer shelf life, higher purity, and lower cost than the full-length protein.

Methods: Based on the 3-dimensional structure of FGF2 peptide, a corresponding FGF7 peptide (FGF7p) consisting of 19 amino acids was identified and synthesized. FGF7p or vehicle was given subcutaneously (SQ) to female mice subjected to sham injury, intraperitoneal (IP) CPP or external beam radiation over the bladder. One day after injury, bladders were harvested. Slides with paraffin embedded tissues underwent H&E staining, TUNEL and immunofluorescence (IF) assays.

Results: In uninjured control mice, a 20 mg/kg threshold dose of FGF7p induced expression of phosphorylated (activated) FRS2a (pFRS2a) and pAKT in urothelium (consistent with cytoprotective effects of FGF7, albeit at a 4x higher dose than full length FGF7). Unexpectedly, FGF7p activation of urothelial FRS2a and AKT was delayed 24 hours compared to FGF7. FGF7p (20 mg/kg) or vehicle was given at 72 and 48 hours prior to CPP (150 mg/kg). One day after CPP, TUNEL staining revealed an increase in apoptotic and sloughing urothelial cells in vehicle-treated mice compared to in FGF7p-treated mice. IF for pAKT and its targets, pS6K and pBAD, revealed minimal staining in vehicle-treated mice, but strong urothelial staining for all protective markers in FGF7p-treated mice. Using the same dosing strategy, we subjected anesthetized mice to 10 Gy radiation over the bladder. One day after injury, TUNEL staining revealed many more apoptotic urothelial nuclei in control mice, than in FGF7p-treated mice.

Conclusions: FGF7p appears to block bladder urothelial apoptosis via AKT and its targets, in a similar manner to FGF7. FGF7p is 200x less expensive to make vs. FGF7 and is likely to work via direct bladder infusion (avoiding systemic side effects) due to its small size. Our future studies will clarify long term benefits of FGF7p and assess effectiveness of direct bladder infusion.

Citation Format: Sridhar Narla, Lori P. Rice, David Ostrov, Steven G. Swarts, Dietmar W. Siemann, Carlton M. Bates. FGF7 peptide (FGF7p) mimetic mitigates urothelial injury from cyclophosphamide or radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5431.

AKT Signaling Downstream of KGF Is Necessary and Sufficient for Blocking Cyclophosphamide Bladder Injury

Keratinocyte growth factor (KGF) drives phosphorylated (activated) AKT (pAKT) in bladder urothelium, which correlates with cytoprotection from cyclophosphamide. The current study determined whether: i) KGF modifies AKT targets [B-cell lymphoma protein 2-associated agonist of cell death (BAD) and mammalian target of rapamycin complex (mTORC)-1] that could block apoptosis; ii) AKT signaling is required for KGF cytoprotection; iii) direct AKT activation drives cytoprotection; iv) co-administration of KGF and an AKT inhibitor blocks urothelial cytoprotection and AKT and AKT-target activation; and v) an AKT agonist prevents cyclophosphamide-induced urothelial apoptosis. Mice were given KGF and cyclophosphamide (or sham injury), and pBAD (readout of BAD inhibition) or p-p70S6k (pS6, readout of mTORC1 signaling) was assessed. KGF induced pBAD urothelial staining and prevented cyclophosphamide-induced loss of urothelial pS6 staining (likely stabilizing mTORC1 activity). Co-administration of KGF and AKT inhibitor blocked KGF-driven urothelial cytoprotection from cyclophosphamide and prevented pAKT, pBAD, and pS6 urothelial expression. Conversely, systemic AKT agonist blocked cyclophosphamide-induced urothelial apoptosis and induced pAKT, pBAD, and pS6, similar to KGF. Thus, the KGF-AKT signaling axis appeared to phosphorylate (suppress) BAD and prevent cyclophosphamide-induced loss of mTORC1 signaling, both of which likely suppress apoptosis. Additionally, AKT signaling was required for KGF-driven cytoprotection, and direct AKT activation was sufficient for blocking apoptosis. Thus, AKT may be a therapeutic target for blocking urothelial apoptosis from cyclophosphamide.

Loss of Fibroblast Growth Factor Receptor 2 (FGFR2) Leads to Defective Bladder Urothelial Regeneration after Cyclophosphamide Injury

Cyclophosphamide may cause hemorrhagic cystitis and eventually bladder urothelial cancer. Genetic determinants for poor outcomes are unknown. We assessed actions of fibroblast growth factor receptor (FGFR) 2 in urothelium after cyclophosphamide exposure. Conditional urothelial deletion of Fgfr2 (Fgfr2KO) did not affect injury severity or proliferation of keratin 14⁺ (KRT14⁺) basal progenitors or other urothelial cells 1 day after cyclophosphamide exposure. Three days after cyclophosphamide exposure, Fgfr2KO urothelium had defective regeneration, fewer cells, larger basal cell bodies and nuclei, paradoxical increases in proliferation markers, and excessive replication stress versus controls. Fgfr2KO mice had evidence of pathologic basal cell endoreplication associated with absent phosphorylated ERK staining and decreased p53 expression versus controls. Mice with conditional deletion of Fgfr2 in urothelium enriched for KRT14⁺ cells reproduced Fgfr2KO abnormalities after cyclophosphamide exposure. Fgfr2KO urothelium had defects up to 6 months after injury versus controls, including larger basal cells and nuclei, more persistent basal and ectopic lumenal KRT14⁺ cells, and signs of metaplasia (attenuated E-cadherin staining). Mice missing one allele of Fgfr2 also had (less severe) regeneration defects and basal cell endoreplication 3 days after cyclophosphamide exposure versus controls. Thus, reduced FGFR2/ERK signaling apparently leads to abnormal urothelial repair after cyclophosphamide exposure from pathologic basal cell endoreplication. Patients with genetic variants in FGFR2 or its ligands may have increased risks of hemorrhagic cystitis or urothelial cancer from persistent and ectopic KRT14⁺ cells.

Increased rates of vesicoureteral reflux in mice from deletion of Dicer in the peri-Wolffian duct stroma

BACKGROUND

Vesicoureteral reflux (VUR), backflow of urine into the kidney, is associated with urinary tract infections and chronic kidney disease. Integrity of the vesicoureteral junction (VUJ), where reflux occurs, is determined largely by proper induction of the ureteric bud from the Wolffian duct. Induction is modulated by signals from the surrounding peri-Wolffian duct stroma. We evaluated whether miRNAs in the peri-Wolffian duct stroma are necessary for proper ureteric induction, VUJ formation, and suppression of VUR.

METHODS

We generated a mouse with loss of miRNAs in the peri-Wolffian duct stroma. We evaluated embryos for ureteric bud induction defects and expression of genes that regulate induction. We performed cystograms to assess for reflux and assessed VUJs in postnatal mice.

RESULTS

Mutant embryos had cranially displaced ureteric bud induction sites vs. controls. We observed no changes in expression of genes known to regulate induction. While mutants were early postnatal lethal, they had high rates of VUR vs. controls. Mutant VUJs that refluxed had low inserting ureters and shortened intravesicular tunnels vs. non-refluxing mice.

CONCLUSIONS

We found that miRNAs in the peri-Wolffian duct stroma are required for normal ureteric bud induction, VUJ formation, and prevention of VUR.

Keratinocyte Growth Factor Reduces Injury and Leads to Early Recovery from Cyclophosphamide Bladder Injury

Keratinocyte growth factor (KGF) improves cyclophosphamide-induced bladder injury. To understand the mechanisms, we subcutaneously administered KGF to mice 24 hours before i.p. cyclophosphamide administration, followed by histologic assays and immunostaining. In vehicle (phosphate-buffered saline)-pretreated mice, nonapoptotic superficial cell death from 2 to 6 hours and apoptosis in intermediate and basal cells from 4 to 24 hours was observed after cyclophosphamide. Despite superficial cell loss, KGF suppressed intermediate and basal cell apoptosis, likely via AKT signaling. At 6 and 24 hours after cyclophosphamide, KGF-pretreated mice also had apparent extracellular signal-regulated kinase (ERK)-driven proliferation of mostly keratin 5 (KRT5)+/KRT14- intermediate cells. At 1 to 28 days after cyclophosphamide treatment, mostly KRT14+ basal progenitor cells proliferated in response to injury, peaking at 3 days in both treatment groups; however, proliferation rates were lower in the KGF group at 3 days, consistent with less injury. Three days after injury, unlike controls, KGF-pretreated mice had regenerated superficial cells. At 10 and 28 days after cyclophosphamide treatment, KGF-pretreated mice had little proliferation and marked restoration of urothelial layers, whereas the phosphate-buffered saline group had ongoing regeneration. Administration of KGF to uninjured mice reproduced ERK-driven KRT5+/KRT14- proliferation seen in injured mice; KRT14+ cells were unaffected. KGF pretreatment blocks cyclophosphamide-induced intermediate and basal cell apoptosis, likely by phosphorylated AKT, and drives phosphorylated ERK-mediated KRT5+/KRT14- cell proliferation, leading to early urothelial regeneration.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Ift25 is not a cystic kidney disease gene but is required for early steps of kidney development

Eukaryotic cilia are assembled by intraflagellar transport (IFT) where large protein complexes called IFT particles move ciliary components from the cell body to the cilium. Defects in most IFT particle proteins disrupt ciliary assembly and cause mid gestational lethality in the mouse. IFT25 and IFT27 are unusual components of IFT-B in that they are not required for ciliary assembly and mutant mice survive to term. The mutants die shortly after birth with numerous organ defects including duplex kidneys. Completely duplex kidneys result from defects in ureteric bud formation at the earliest steps of metanephric kidney development. Ureteric bud initiation is a highly regulated process involving reciprocal signaling between the ureteric epithelium and the overlying metanephric mesenchyme with regulation by the peri-Wolffian duct stroma. The finding of duplex kidney in Ift25 and Ift27 mutants suggests functions for these genes in regulation of ureteric bud initiation. Typically the deletion of IFT genes in the kidney causes rapid cyst growth in the early postnatal period. In contrast, the loss of Ift25 results in smaller kidneys, which show only mild tubule dilations that become apparent in adulthood. The smaller kidneys appear to result from reduced branching in the developing metanephric kidney. This work indicates that IFT25 and IFT27 are important players in the early development of the kidney and suggest that duplex kidney is part of the ciliopathy spectrum.

Ectopic Phosphorylated Creb Marks Dedifferentiated Proximal Tubules in Cystic Kidney Disease

Ectopic cAMP signaling is pathologic in polycystic kidney disease; however, its spatiotemporal actions are unclear. We characterized the expression of phosphorylated Creb (p-Creb), a target and mediator of cAMP signaling, in developing and cystic kidney models. We also examined tubule-specific effects of cAMP analogs in cystogenesis in embryonic kidney explants. In wild-type mice, p-Creb marked nephron progenitors (NP), early epithelial NP derivatives, ureteric bud, and cortical stroma; p-Creb was present in differentiated thick ascending limb of Henle, collecting duct, and stroma; however, it disappeared in mature NP-derived proximal tubules. In Six2cre;Frs2αFl/Fl mice, a renal cystic model, ectopic p-Creb stained proximal tubule-derived cystic segments that lost the differentiation marker lotus tetragonolobus lectin. Furthermore, lotus tetragonolobus lectin-negative/p-Creb-positive cyst segments (re)-expressed Ncam1, Pax2, and Sox9 markers of immature nephron structures and dedifferentiated proximal tubules after acute kidney injury. These dedifferentiation markers were co-expressed with p-Creb in renal cysts in Itf88 knockout mice subjected to ischemia and Six2cre;Pkd1Fl/Fl mice, other renal cystogenesis models. 8-Br-cAMP addition to wild-type embryonic kidney explants induced proximal tubular cystogenesis and p-Creb expression; these effects were blocked by co-addition of protein kinase A inhibitor. Thus p-Creb/cAMP signaling is appropriate in NP and early nephron derivatives, but disappears in mature proximal tubules. Moreover, ectopic p-Creb expression/cAMP signaling marks dedifferentiated proximal tubular cystic segments. Furthermore, proximal tubules are predisposed to become cystic after cAMP stimulation.

Fgfr2 is integral for bladder mesenchyme patterning and function

While urothelial signals, including sonic hedgehog (Shh), drive bladder mesenchyme differentiation, it is unclear which pathways within the mesenchyme are critical for its development. Studies have shown that fibroblast growth factor receptor 2 (Fgfr2) is necessary for kidney and ureter mesenchymal development. Our objective was to determine the role of Fgfr2 in bladder mesenchyme. We used Tbx18cre mice to delete Fgfr2 in bladder mesenchyme (Fgfr2^BM-/-). We performed three-dimensional reconstructions, quantitative real-time PCR, in situ hybridization, immunolabeling, ELISAs, immunoblotting, void stain on paper, ex vivo bladder sheet assays, and in vivo decerebrated cystometry. Compared with controls, embryonic (E) day 16.5 (E16.5) Fgfr2^BM-/- bladders have thin muscle layers with reduced α-smooth muscle actin levels and thickened lamina propria with increased collagen expression that intrudes into muscle. From postnatal (P) day 1 (P1) to P30, Fgfr2^BM-/- bladders demonstrate progressive muscle loss and increased collagen expression. Postnatal Fgfr2^BM-/- bladder sheets exhibit decreased contractility and increased passive stretch tension compared with controls. In vivo cystometry revealed high baseline and threshold pressures and shortened intercontractile intervals in Fgfr2^BM-/- bladders compared with controls. Mechanistically, while Shh expression appears normal, mRNA and protein readouts of hedgehog activity are increased in E16.5 Fgfr2^BM-/- bladders compared with controls. Moreover, E16.5Fgfr2^BM-/- bladders exhibit higher levels of Cdo and Boc, hedgehog coreceptors that enhance sensitivity to Shh, than controls. Fgfr2 is critical for bladder mesenchyme patterning by virtue of its role in modulation of hedgehog signaling.

Correction: Deletion of Fibroblast Growth Factor Receptor 2 from the Peri-Wolffian Duct Stroma Leads to Ureteric Induction Abnormalities and Vesicoureteral Reflux

[This corrects the article DOI: 10.1371/journal.pone.0056062.].

Ablation of the epithelial-specific splicing factor Esrp1 results in ureteric branching defects and reduced nephron number

Background:

Abnormalities in ureteric bud (UB) branching morphogenesis lead to congenital anomalies of the kidney and reduced nephron numbers associated with chronic kidney disease (CKD) and hypertension. Previous studies showed that the epithelial fibroblast growth factor receptor 2 (Fgfr2) IIIb splice variant supports ureteric morphogenesis in response to ligands from the metanephric mesenchyme during renal organogenesis. The epithelial‐specific splicing regulator Esrp1 is required for expression of Fgfr2‐IIIb and other epithelial‐specific splice variants. Our objective was to determine whether Esrp1 is required for normal kidney development.

Results:

Ablation of Esrp1 in mice, alone or together with its paralog Esrp2, was associated with reduced kidney size and increased incidence of renal aplasia. Three‐dimensional imaging showed that embryonic Esrp1 knockout (KO) kidneys had fewer ureteric tips and reduced nephron numbers. Analysis of alternative splicing in Esrp‐null ureteric epithelial cells by RNA‐Seq confirmed a splicing switch in Fgfr2 as well as numerous other transcripts.

Conclusions:

Our findings reveal that Esrp1‐regulated splicing in ureteric epithelial cells plays an important role in renal development. Defects in Esrp1 KO kidneys likely reflect reduced and/or absent ureteric branching, leading to decreased nephron induction secondary to incorrect Fgfr2 splicing and other splicing alterations. Developmental Dynamics 245:991–1000, 2016. © 2016 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Abnormalities in Ureteric bud (UB) branching morphogenesis lead to congenital anomalies of the kidney and reduced nephron numbers associated with chronic kidney disease (CKD) and hypertension.

We investigated the consequences of ablating the epithelial‐specific splicing regulator Esrp1 on renal organogenesis and determined that Esrp1 KO mice have reduced kidney size, fewer ureteric tips, reduced nephron numbers, and increased incidence of renal aplasia.

Analysis of alternative splicing in Esrp null ureteric epithelial cells by RNA‐Seq identified numerous alterations in splicing.

These findings reveal that Esrp1 regulated splicing in ureteric epithelial cells plays an important role in the kidney and illustrate the importance of alternative splicing for normal renal organogenesis.

Lichen sclerosus

Lichen sclerosus (LS) is a chronic inflammatory disorder of the skin and mucosa, presenting to genitourinary physicians and dermatologists. It affects both sexes and all age groups. Although the exact aetiology is uncertain, genetic predisposition, infections and autoimmune factors have been implicated in its pathogenesis. Symptoms include pruritis and soreness, but asymptomatic presentations are not uncommon. The classical clinical picture is of atrophic white plaques in the anogenital region. Histopathology is specific with basal cell degeneration, upper dermal oedema, homogenization of collagen and a chronic inflammatory infiltrate. Short courses of potent topical corticosteroids form the mainstay of treatment. The condition tends to be remitting and relapsing, with spontaneous regressions reported in a few. In men, the term balanitis xerotica obliterans is sometimes used to describe late and severe LS of the penis. Scarring and progression to squamous cell carcinomas can occur in chronic LS, resulting in significant morbidity. A multi-disciplinary approach to care and the need for long-term monitoring cannot be over-emphasized.

Prorenin receptor is critical for nephron progenitors

Deficient nephrogenesis is the major factor contributing to renal hypoplasia defined as abnormally small kidneys. Nephron induction during kidney development is driven by reciprocal interactions between progenitor cells of the cap mesenchyme (CM) and the ureteric bud (UB). The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump H(+)-ATPase. Global loss of PRR is lethal in mice and PRR mutations are associated with a high blood pressure, left ventricular hypertrophy and X-linked mental retardation in humans. To circumvent lethality of the ubiquitous PRR mutation in mice and to determine the potential role of the PRR in nephrogenesis, we generated a mouse model with a conditional deletion of the PRR in Six2(+) nephron progenitors and their epithelial derivatives (Six2(PRR-/-)). Targeted ablation of PRR in Six2(+) nephron progenitors caused a marked decrease in the number of developing nephrons, small cystic kidneys and podocyte foot process effacement at birth, and early postnatal death. Reduced congenital nephron endowment resulted from premature depletion of nephron progenitor cell population due to impaired progenitor cell proliferation and loss of normal molecular inductive response to canonical Wnt/β-catenin signaling within the metanephric mesenchyme. At 2 months of age, heterozygous Six2(PRR+/-) mice exhibited focal glomerulosclerosis, decreased kidney function and massive proteinuria. Collectively, these findings demonstrate a cell-autonomous requirement for the PRR within nephron progenitors for progenitor maintenance, progression of nephrogenesis, normal kidney development and function.

Survey of genitourinary medicine specialist registrars in the United Kingdom regarding genital dermatology training

The British Association for Sexual Health and HIV Genital Dermatology Special Interest Group (SIG) conducted a survey of specialist registrar training in genital dermatology (GD) to inform future training provision provided by the group and other services. The survey shows that training in GD is variable with most trainees receiving GD training through formal lectures or ad hoc clinical teaching, with fewer trainees having access to specialist GD clinics. There is mixed confidence in diagnosis and use of topical steroids, and few trainees are independent in GD practical procedures. Many trainees feel training could be improved with requests for a formalised attachment, formal qualification and greater training in practical procedures. The GD SIG, in liaison with British Association for Sexual Health and HIV (BASHH), aims to optimise GD training for registrars. Plans for improved resources are in progress, including a practical skills course and e-learning. It is hoped this survey will also inform GD training at both local and national levels.

Fgfr2 is integral for bladder mesenchyme patterning and function

While urothelial signals, including sonic hedgehog (Shh), drive bladder mesenchyme differentiation, it is unclear which pathways within the mesenchyme are critical for its development. Studies have shown that fibroblast growth factor receptor (Fgfr)2 is necessary for kidney and ureter mesenchymal development. The objective of the present study was to determine the role of Fgfr2 in the bladder mesenchyme. We used Tbx18cre mice to delete Fgfr2 in the bladder mesenchyme (Fgfr2(BM-/-)). We performed three-dimensional reconstructions, quantitative real-time PCR, in situ hybridization, immunolabeling, ELISAs, immunoblot analysis, void stain on paper, ex vivo bladder sheet assays, and in vivo decerebrated cystometry. Compared with control bladders, embryonic day 16.5 (E16.5) Fgfr2(BM-/-) bladders had thin muscle layers with less α-smooth muscle actin and thickened lamina propria with increased collagen type Ia and IIIa that intruded into the muscle. The reciprocal changes in mutant layer thicknesses appeared partly due to a cell fate switch. From postnatal days 1 to 30, Fgfr2(BM-/-) bladders demonstrated progressive muscle loss and increased collagen expression. Postnatal Fgfr2(BM-/-) bladder sheets exhibited decreased agonist-mediated contractility and increased passive stretch tension versus control bladder sheets. Cystometry revealed high baseline and threshold pressures and shortened intercontractile intervals in Fgfr2(BM-/-) versus control bladders. Mechanistically, whereas Shh expression appeared normal, mRNA and protein readouts of hedgehog activity were increased in E16.5 Fgfr2(BM-/-) versus control bladders. Moreover, E16.5 Fgfr2(BM-/-) bladders exhibited higher levels of Cdo and Boc, hedgehog coreceptors that enhance sensitivity to Shh, compared with control bladders. In conclusion, loss of Fgfr2 in the bladder mesenchyme leads to abnormal bladder morphology and decreased compliance and contractility.

Fibroblast growth factor receptor-Frs2α signaling is critical for nephron progenitors

Previous studies using transgenic Pax3cre mice have revealed roles for fibroblast growth factor receptors (Fgfrs) and Fgfr substrate 2α (Frs2α) signaling in early metanephric mesenchyme patterning and in ureteric morphogenesis. The role of Fgfr/Frs2α signaling in nephron progenitors is unknown. Thus, we generated mouse models using BAC transgenic Six2EGFPcre (Six2cre) mediated deletion of Fgfrs and/or Frs2α in nephron progenitors. Six2cre mediated deletion of Fgfr1 or Fgfr2 alone led to no obvious kidney defects. Six2creFgfr1(flox/flox)Fgfr2(flox/flox) (Fgfr1/2(NP-/-)) mice generate a discernable kidney; however, they develop nephron progenitor depletion starting at embryonic day 12.5 (E12.5) and later demonstrate severe cystic dysplasia. To determine the role of Frs2α signaling downstream of Fgfr2 in Fgfr1/2(NP-/-) mice, we generated Six2cre(,)Fgfr1(flox/flox)Fgfr2(LR/LR) (Fgfr1(NP-/-)Fgfr2(LR/LR)) mice that have point mutations in the Frs2α binding site of Fgfr2. Like Fgfr1/2(NP-/-) mice, Fgfr1(NP-/-)Fgfr2(LR/LR) develop nephron progenitor depletion, but it does not start until E14.5 and older mice have less severe cystic dysplasia than Fgfr1/2(NP-/-) To determine the role of Frs2α alone in nephron progenitors, we generated Six2creFrs2'A(flox/flox) (Frs2a(NP-/-)) mice. Frs2a(NP-/-)mice also develop nephron progenitor depletion and renal cysts, although these occurred later and were less severe than in the other Six2cre mutant mice. The nephron progenitor loss in all Six2cre mutant lines was associated with decreased Cited1 expression and increased apoptosis versus controls. FAC-sorted nephron progenitors in Six2cre Frs2'A(flox/flox) mice demonstrated evidence of increased Notch activity versus controls, which likely drives the progenitor defects. Thus, Fgfr1 and Fgfr2 have synergistic roles in maintaining nephron progenitors; furthermore, Fgfr signaling in nephron progenitors appears to be mediated predominantly by Frs2α.

Renal blood flow and oxygenation drive nephron progenitor differentiation

During kidney development, the vasculature develops via both angiogenesis (branching from major vessels) and vasculogenesis (de novo vessel formation). The formation and perfusion of renal blood vessels are vastly understudied. In the present study, we investigated the regulatory role of renal blood flow and O2 concentration on nephron progenitor differentiation during ontogeny. To elucidate the presence of blood flow, ultrasound-guided intracardiac microinjection was performed, and FITC-tagged tomato lectin was perfused through the embryo. Kidneys were costained for the vasculature, ureteric epithelium, nephron progenitors, and nephron structures. We also analyzed nephron differentiation in normoxia compared with hypoxia. At embryonic day 13.5 (E13.5), the major vascular branches were perfused; however, smaller-caliber peripheral vessels remained unperfused. By E15.5, peripheral vessels started to be perfused as well as glomeruli. While the interior kidney vessels were perfused, the peripheral vessels (nephrogenic zone) remained unperfused. Directly adjacent and internal to the nephrogenic zone, we found differentiated nephron structures surrounded and infiltrated by perfused vessels. Furthermore, we determined that at low O2 concentration, little nephron progenitor differentiation was observed; at higher O2 concentrations, more differentiation of the nephron progenitors was induced. The formation of the developing renal vessels occurs before the onset of blood flow. Furthermore, renal blood flow and oxygenation are critical for nephron progenitor differentiation.

Pediatric kidney disease: tracking onset and improving clinical outcomes

Recent studies confirm that much of adult kidney disease may have its origins in childhood, often as a result of abnormal or suboptimal fetal kidney development. Understanding of the etiology and pathogenesis of CKD in children is rapidly evolving because of robust longitudinal clinical data, identification of monogenic mutations related to common causes of CKD, and improved knowledge of factors that influence the onset and progression of CKD. The Kidney Research National Dialogue, supported by the National Institute of Diabetes and Digestive and Kidney Diseases, asked the research and clinical communities to formulate and prioritize research objectives that would improve understanding of kidney function and diseases. This commentary outlines high-priority research objectives to assess factors associated with the predisposition to develop renal disease in children, and address the unique challenges in treating this population.

Regulation of renal phosphate transport by FGF23 is mediated by FGFR1 and FGFR4

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that acts on the proximal tubule to decrease phosphate reabsorption and serum levels of 1,25-dihydroxyvitamin D₃ [1,25(OH)₂ Vitamin D₃]. Abnormal FGF23 metabolism has been implicated in several debilitating hypophosphatemic and hyperphosphatemic disorders. The renal receptors responsible for the phosphaturic actions of FGF23 have not been elucidated. There are four fibroblast growth factor receptors (FGFR); 1-4 with "b" and "c" isoforms for receptors 1, 2, and 3. FGFR1, 3, and 4 are expressed in the mouse proximal tubule, and deletion of any one receptor did not affect serum phosphate levels, suggesting that more than one receptor is involved in mediating the phosphaturic actions of FGF23. To determine the receptors responsible for the phosphaturic actions of FGF23, we studied Fgfr1 (kidney conditional) and Fgfr4 (global) double mutant mice (Fgfr1⁻/⁻/Fgfr4⁻/⁻). Fgfr1⁻/⁻/Fgfr4⁻/⁻ mice have higher FGF23 levels than their wild-type counterparts (108.1 ± 7.3 vs. 4,953.6 ± 675.0 pg/ml; P < 0.001). Despite the elevated FGF23 levels, Fgfr1⁻/⁻/Fgfr4⁻/⁻ mice have elevated serum phosphorus levels, increased brush-border membrane vesicle (BBMV) phosphate transport, and increased Na-P(i) cotransporter 2c (NaPi-2c) protein expression compared with wild-type mice. These data are consistent with FGFR1 and FGFR4 being the critical receptors for the phosphaturic actions of FGF23.

Deletion of fibroblast growth factor receptor 2 from the peri-wolffian duct stroma leads to ureteric induction abnormalities and vesicoureteral reflux

Purpose

Pax3cre-mediated deletion of fibroblast growth factor receptor 2 (Fgfr2) broadly in renal and urinary tract mesenchyme led to ureteric bud (UB) induction defects and vesicoureteral reflux (VUR), although the mechanisms were unclear. Here, we investigated whether Fgfr2 acts specifically in peri-Wolffian duct stroma (ST) to regulate UB induction and development of VUR and the mechanisms of Fgfr2 activity.

Methods

We conditionally deleted Fgfr2 in ST (Fgfr2^ST−/−) using Tbx18cre mice. To look for ureteric bud induction defects in young embryos, we assessed length and apoptosis of common nephric ducts (CNDs). We performed 3D reconstructions and histological analyses of urinary tracts of embryos and postnatal mice and cystograms in postnatal mice to test for VUR. We performed in situ hybridization and real-time PCR in young embryos to determine mechanisms underlying UB induction defects.

Results

We confirmed that Fgfr2 is expressed in ST and that Fgfr2 was efficiently deleted in this tissue in Fgfr2^ST−/− mice at embryonic day (E) 10.5. E11.5 Fgfr2^ST−/− mice had randomized UB induction sites with approximately 1/3 arising too high and 1/3 too low from the Wolffian duct; however, apoptosis was unaltered in E12.5 mutant CNDs. While ureters were histologically normal, E15.5 Fgfr2^ST−/− mice exhibit improper ureteral insertion sites into the bladder, consistent with the ureteric induction defects. While ureter and bladder histology appeared normal, postnatal day (P) 1 mutants had high rates of VUR versus controls (75% versus 3%, p = 0.001) and occasionally other defects including renal hypoplasia and duplex systems. P1 mutant mice also had improper ureteral bladder insertion sites and shortened intravesicular tunnel lengths that correlated with VUR. E10.5 Fgfr2^ST−/− mice had decreases in Bmp4 mRNA in stromal tissues, suggesting a mechanism underlying the ureteric induction and VUR phenotypes.

Conclusion

Mutations in FGFR2 could possibly cause VUR in humans.

The accuracy and health risks of a voiding cystourethrogram after a febrile urinary tract infection

OBJECTIVE

Physicians often defer obtaining a voiding cystourethrogram (VCUG) after the diagnosis of urinary tract infection (UTI) due to concerns regarding increased health risks and inflated rates of vesicoureteral reflux (VUR). This study examines the health risks and accuracy of VCUG testing after diagnosis of a febrile UTI.

PATIENTS AND METHODS

A retrospective review was conducted of children aged 0-18 years admitted to Nationwide Children's Hospital with a febrile UTI in 1995-2000. Children were divided into two cohorts - those who had a VCUG performed within 1 week of diagnosis (early VCUG cohort) and those who had a VCUG performed more than 1 week after diagnosis (late VCUG cohort). All children were followed for an additional 5 years after hospital discharge.

RESULTS

The incidence and severity of VUR were similar in patients that underwent early and late VCUG testing. Patients who underwent early VCUG testing showed no sign of worsening illness after the test was performed. During the 5-year follow up, these patients did not have higher rates of return emergency department visits or hospital readmission compared to those who received late VCUG testing.

CONCLUSIONS

The rate of VUR detection does not increase with early VCUG testing. Early VCUG testing does not lead to increased risk of bacterial dissemination or urosepsis.

3-Dimensional morphometric analysis of murine bladder development and dysmorphogenesis

BACKGROUND

Disorders of the urinary tract represent a major cause of morbidity and impaired quality of life. To better understand the morphological events responsible for normal urinary tract development, we performed 3-D reconstructive analysis of developing mouse bladders in control, mgb-/-, and Fgfr2(Mes-/-) mice.

RESULTS

Detrusor smooth muscle differentiation initiated in the bladder dome and progressed caudally with the leading edge extending down the right posterior surface of the bladder. Gender-specific differences in detrusor smooth muscle development were observed during early embryonic development. Bladder trigone morphology transitioned from an isosceles to equilateral triangle during development due to the preferential lengthening of the urethra to ureter distance. The primary defect observed in mgb-/- bladders was a significant reduction in detrusor smooth muscle differentiation throughout development. Deviations from normal trigone morphology correlated best with VUR development in Fgfr2(Mes-/-) mice, while alterations in intravesicular tunnel length did not.

CONCLUSIONS

Multivariate morphometric analysis provides a powerful tool to quantify and assess urinary tract development.

Ureteric morphogenesis requires Fgfr1 and Fgfr2/Frs2α signaling in the metanephric mesenchyme

Conditional deletion of fibroblast growth factor receptors (Fgfrs) 1 and 2 in the metanephric mesenchyme (MM) of mice leads to a virtual absence of MM and unbranched ureteric buds that are occasionally duplex. Deletion of Fgfr2 in the MM leads to kidneys with cranially displaced ureteric buds along the Wolffian duct or duplex ureters. Mice with point mutations in Fgfr2's binding site for the docking protein Frs2α (Fgfr2(LR/LR)), however, have normal kidneys; the roles of the Fgfr2/Frs2α signaling axis in MM development and regulating the ureteric bud induction site are incompletely understood. Here, we generated mice with both Fgfr1 deleted in the MM and Fgfr2(LR/LR) point mutations (Fgfr1(Mes-/-)Fgfrf2(LR/LR)). Unlike mice lacking both Fgfr1 and Fgfr2 in the MM, these mice had no obvious MM defects but had cranially displaced or duplex ureteric buds, probably as a result of decreased Bmp4 expression. Fgfr1(Mes-/-)Fgfr2(LR/LR) mice also had subsequent defects in ureteric morphogenesis, including dilated, hyperproliferative tips and decreased branching. Ultimately, they developed progressive renal cystic dysplasia associated with abnormally oriented cell division. Furthermore, mutants had increased and ectopic expression of Ret and its downstream targets in ureteric trunks, and exhibited upregulation of Ret/Etv4/5 signaling effectors, including Met, Myb, Cxcr4, and Crlf1. These defects were associated with reduced expression of Bmp4 in mesenchymal cells near mutant ureteric bud tips. Taken together, these results demonstrate that Fgfr2/Frs2α signaling in the MM promotes Bmp4 expression, which represses Ret levels and signaling in the ureteric bud to ensure normal ureteric morphogenesis.

Role of fibroblast growth factor receptor signaling in kidney development

Fibroblast growth factor receptors (Fgfrs) are expressed throughout the developing kidney. Several early studies have shown that exogenous fibroblast growth factors (Fgfs) affect growth and maturation of the metanephric mesenchyme (MM) and ureteric bud (UB). Transgenic mice that over-express a dominant negative receptor isoform develop renal aplasia/severe dysplasia, confirming the importance of Fgfrs in renal development. Furthermore, global deletion of Fgf7, Fgf10, and Fgfr2IIIb (isoform that binds Fgf7 and Fgf10) in mice leads to small kidneys with fewer collecting ducts and nephrons. Deletion of Fgfrl1, a receptor lacking intracellular signaling domains, causes severe renal dysgenesis. Conditional targeting of Fgf8 from the MM interrupts nephron formation. Deletion of Fgfr2 from the UB results in severe ureteric branching and stromal mesenchymal defects, although loss of Frs2α (major signaling adapter for Fgfrs) in the UB causes only mild renal hypoplasia. Deletion of both Fgfr1 and Fgfr2 in the MM results in renal aplasia with defects in MM formation and initial UB elongation and branching. Loss of Fgfr2 in the MM leads to many renal and urinary tract anomalies as well as vesicoureteral reflux. Thus, Fgfr signaling is critical for patterning of virtually all renal lineages at early and later stages of development.

Chronic kidney disease after liver transplantation for acute liver failure is not associated with perioperative renal dysfunction

Renal dysfunction of acute liver failure (ALF) may have distinct pathophysiological mechanisms to hepatorenal syndrome of cirrhosis. Yet, the impact of perioperative renal function on posttransplant renal outcomes in ALF patients specifically has not been established. The aims of this study were (1) to describe the incidence and risk factors for chronic renal dysfunction following liver transplantation for ALF and (2) to compare renal outcomes with age-sex-matched patients transplanted for chronic liver disease. This was a single-center study of 101 patients transplanted for ALF. Fifty-three-and-a-half percent had pretransplant acute kidney injury and 64.9% required perioperative renal replacement therapy. After transplantation the 5-year cumulative incidence of chronic kidney disease (eGFR <60 mL/min/1.73 m²) was 41.5%. There was no association between perioperative acute kidney injury (p = 0.288) or renal replacement therapy (p = 0.134) and chronic kidney disease. Instead, the independent predictors of chronic kidney disease were older age (p = 0.019), female gender (p = 0.049), hypertension (p = 0.031), cyclosporine (p = 0.027) and nonacetaminophen-induced ALF (p = 0.039). Despite marked differences in the perioperative clinical condition and survival of patients transplanted for ALF and chronic liver disease, renal outcomes were the same. In conclusion, in patients transplanted for ALF the severity of perioperative renal injury does not predict posttransplant chronic renal dysfunction.

Role of fibroblast growth factor receptor signaling in kidney development

Fibroblast growth factor receptors (Fgfrs) consist of four signaling family members and one nonsignaling "decoy" receptor, Fgfr-like 1 (Fgfrl1), all of which are expressed in the developing kidney. Several studies have shown that exogenous fibroblast growth factors (Fgfs) affect growth and maturation of the metanephric mesenchyme (MM) and ureteric bud (UB) in cultured tissues. Transgenic and conditional knockout approaches in whole animals have shown that Fgfr1 and Fgfr2 (predominantly the IIIc isoform) in kidney mesenchyme are critical for early MM and UB formation. Conditional deletion of the ligand, Fgf8, in nephron precursors or global deletion of Fgfrl1 interrupts nephron formation. Fgfr2 (likely the IIIb isoform signaling downstream of Fgf7 and Fgf10) is critical for ureteric morphogenesis. Moreover, Fgfr2 appears to act independently of Frs2α (the major signaling adapter for Fgfrs) in regulating UB branching. Loss of Fgfr2 in the MM leads to many kidney and urinary tract anomalies, including vesicoureteral reflux. Thus Fgfr signaling is critical for patterning of virtually all renal lineages at early and later stages of development.

Fgfr1 and the IIIc isoform of Fgfr2 play critical roles in the metanephric mesenchyme mediating early inductive events in kidney development

Fibroblast growth factor receptors (Fgfrs) have critical roles in kidney development. FgfrIIIb is thought to act in epithelium, while FgfrIIIc functions in mesenchyme. We aimed to determine roles of Fgfr2IIIc in kidney development. Mice with deletion of Fgfr2IIIc (Fgfr2IIIc-/-) had normal kidneys. Combination of Fgfr2IIIc-/- with conditional deletion of Fgfr1 in metanephric mesenchyme (MM) (Fgfr1(Mes-/-)Fgfr2IIIc-/-) had small but identifiable MM at embryonic day (E) 10.5, expressing mesenchymal markers including Eya1, Six2, Pax2, and Gdnf (unlike Fgfr1/2(Mes-/-) mice that have no obvious MM). E11.5 Fgfr1(Mes-/-)Fgfr2IIIc-/- mice had rudimentary MM expressing only Eya1. Control, Fgfr2IIIc-/-, and Fgfr1(Mes-/-)Fgfr2IIIc-/- kidney mesenchymal tissues also express Fgfr2IIIb. In ureteric lineages, E10.5 Fgfr1(Mes-/-)Fgfr2IIIc-/- embryos had ureteric outgrowth (sometimes multiple buds); however, by E11.5 Gdnf absence lead to no ureteric elongation or branching (similar to Fgfr1/2(Mes-/-) mice). Beyond E12.5, Fgfr1(Mes-/-)Fgfr2IIIc-/- mice had no renal tissue. In conclusion, Fgfr2IIIc and Fgfr1 in kidney mesenchyme (together) are critical for normal early renal development.

Cell death serves as a single etiological cause of a wide spectrum of congenital urinary tract defects

PURPOSE

We genetically disrupted the wolffian duct in mice to study the affected organogenesis processes and to test the hypothesis that cell loss can be the developmental basis for a wide spectrum of congenital anomalies in the kidney and urinary tract.

MATERIALS AND METHODS

We used Hoxb7-Cre transgenic lines (HC1 and HC2) to induce diphtheria toxin production from a ROSA(DTA) allele, disrupting the wolffian duct and derivatives.

RESULTS

The first set of mutants (HC1;ROSA(DTA/+)) exhibited agenesis of the kidney, ureter and reproductive tracts. The second set of mutants (HC2;ROSA(DTA/+)) exhibited diverse defects, including renal agenesis/hypoplasia, hydronephrosis, hydroureter, ureter-vas deferens fistulas in males and ureter-oviduct/uterus fistulas in females. The phenotypic differences correspond to the degree of apoptosis induced caudal truncation of the wolffian duct, which is less severe and more variable in HC2;ROSA(DTA/+) mice. Whenever the wolffian duct failed to reach the urogenital sinus, the ureter failed to separate from the wolffian duct, suggesting that ureteral migration along the common nephric duct to the cloaca and the subsequent common nephric duct degeneration constitute the only pathway for separating the ureter and wolffian duct derivatives.

CONCLUSIONS

The diverse and severe defects observed emphasize the central role of the wolffian duct in providing progenitors and signals for urogenital development. These results also indicate that the quantitative difference in cell death induced caudal truncation of the wolffian duct can lead to a wide range of qualitatively distinct defects, and that cell death can serve as a single etiological cause of a wide spectrum of congenital kidney and urinary tract defects.

Independent roles of Fgfr2 and Frs2alpha in ureteric epithelium

Mice with conditional deletion of fibroblast growth factor receptor 2 (Fgfr2) in the ureteric bud using a Hoxb7cre line (Fgfr2(UB-/-)) develop severe ureteric branching defects; however, ureteric deletion of fibroblast growth factor receptor substrate 2α (Frs2α), a key docking protein that transmits fibroblast growth factor receptor intracellular signaling (Frs2α(UB-/-)) leads to mild ureteric defects. Mice with point mutations in the Frs2α binding site of Fgfr2 (Fgfr2(LR/LR)) have normal kidneys. The aim of this study was to determine the relationship between Fgfr2 and Frs2α in the ureteric lineage. Mice with ureteric deletion of both Fgfr2 and Frs2α (Fgfr2/Frs2α(UB-/)) were compared with Frs2α(UB-/-) and Fgfr2(UB-/-) mice. To avoid potential rescue of Fgfr1 forming heterodimers with Fgfr2(LR) alleles to recruit Frs2α, compound mutant mice were generated with ureteric deletion of Fgfr1 and with Fgfr2(LR/LR) point mutations (Fgfr1(UB-/-)Fgfr2(LR/LR)). At E13.5, three-dimensional reconstructions and histological assessment showed that, whereas Fgfr2(UB-/-) kidneys had more severe ureteric branching defects than Frs2α(UB-/-), Fgfr2(UB-/-) kidneys were indistinguishable from Fgfr2/Frs2α(UB-/-). At later stages, however, Fgfr2/Frs2α(UB-/-) kidneys were more severely affected than either Fgfr2(UB-/-) or Frs2α(UB-/-) kidneys. Taken together, although Fgfr2 and Frs2α have crucial roles in the ureteric lineage, they appear to act separately and additively.

Assessing vesicoureteral reflux in live inbred mice via ultrasound with a microbubble contrast agent

Vesicoureteral reflux (VUR) is a common pediatric anomaly linked to renal scarring and hypertension. Although there are many mouse VUR models, cystograms have previously only been performed in euthanized animals, thus preventing serial assessments for VUR in the same animal and not delineating "live" physiology. Our purpose was to develop a live murine cystogram assay that could be used serially to track reflux. We injected microbubbles via transurethral catheters into bladders of C57BL6/J and C3H/HeJ inbred mouse strains that are known to have low and high VUR rates, respectively. We performed ultrasound to visualize microbubbles in the renal pelvis to determine feasibility of the procedure. We then repeated the microbubble ultrasound using a transducer allowing for visualization of both kidneys and ureters simultaneously and for 3 dimensional (3D) reconstruction. We then performed "euthanized" cystograms on all mice for comparison. C3H/HeJ mice had a strong and persistent microbubble signal in the renal pelvis and ureters bilaterally with low-contrast infusion volumes (<100 μl) and similarly showed bilateral reflux by euthanized cystograms. With larger infused volumes (≥150 μl), C57BL6/J mice had small volumes of microbubbles in the renal pelvis that cleared quickly and did not show reflux on euthanized cystograms. Thus, using animal models of known VUR, we demonstrate the utility of contrast-enhanced ultrasound to visualize reflux in live mice.

Pathogenesis of renal injury in the megabladder mouse: a genetic model of congenital obstructive nephropathy

Congenital obstructive nephropathy (CON) is the most common cause of chronic renal failure in children often leading to end-stage renal disease. The megabladder (mgb) mouse exhibits signs of urinary tract obstruction in utero resulting in the development of hydroureteronephrosis and progressive renal failure after birth. This study examined the development of progressive renal injury in homozygous mgb mice (mgb-/-). Renal ultrasound was used to stratify the disease state of mgb-/- mice, whereas surgical rescue was performed using vesicostomy. The progression of renal injury was characterized using a series of pathogenic markers including alpha smooth muscle isoactin (α-SMA), TGF-β1, connective tissue growth factor (CTGF), E-cadherin, F4/80, Wilm's tumor (WT)-1, and paired box gene (Pax) 2. This analysis indicated that mgb-/- mice are born with pathologic changes in kidney development that progressively worsen in direct correlation with the severity of hydronephrosis. The initiation and pattern of fibrotic development observed in mgb-/- kidneys appeared distinctive from previous animal models of obstruction. These observations suggest that the mgb mouse represents a unique small animal model for the study of CON.

High incidence of vesicoureteral reflux in mice with Fgfr2 deletion in kidney mesenchyma

PURPOSE

Mice with Fgfr2 conditional deletion in metanephric mesenchyma (Fgfr2(Mes-/-)) have ureteral bud induction abnormalities. We determined whether Fgfr2(Mes-/-) mutants developed abnormally positioned ureters predisposing to vesicoureteral reflux.

MATERIALS AND METHODS

We measured common nephric duct length and assayed for apoptosis in embryonic day 11.5 mice. We performed 3-dimensional reconstruction of, and real-time polymerase chain reaction and whole mount in situ hybridization for Fgfr2 in urinary tracts in embryonic day 15.5 embryos. We also performed cystograms followed by 3-dimensional reconstruction in postnatal animals.

RESULTS

Compared with controls Fgfr2(Mes-/-) embryos had increased common nephric duct length with no difference in apoptosis, indicating cranially displaced ureteral buds. Three-dimensional reconstruction at embryonic day 15.5 showed low ureteral insertion into the bladder near the bladder neck in Fgfr2(Mes-/-) mice. Postnatal Fgfr2(Mes-/-) mutants had a high rate of vesicoureteral reflux compared with controls (47.4% vs 4.0%, p = 0.00006). In postnatal mutants with unilateral reflux the refluxing ureters inserted closer to the bladder neck than nonrefluxing ureters. External ureteral insertional angles at the outer bladder wall formed by the ureteral insertion points and the bladder neck were greater in mutant refluxing ureters than in contralateral nonrefluxing ureters or control ureters. At embryonic day 15.5 Fgfr2 was decreased in Fgfr2(Mes-/-) kidneys compared with that in controls but not statistically different in ureters or bladders.

CONCLUSIONS

Fgfr2(Mes-/-) mice have ureteral induction abnormalities associated with abnormal ureteral insertion in the bladder and subsequent vesicoureteral reflux, consistent with the Mackie and Stephens hypothesis.

Three-dimensional imaging reveals ureteric and mesenchymal defects in Fgfr2-mutant kidneys

Current techniques to morphologically characterize the processes of nephrogenesis and ureteric branching during kidney development have many limitations. Here, we used in vivo three-dimensional analysis to study renal development in mice lacking fibroblast growth factor receptor 2 in the ureteric bud (Fgfr2(UB-/-)) and in littermate controls. We found that Fgfr2(UB-/-) mice have more severe defects in ureteric branching morphogenesis than previously reported, including significantly fewer branches and tips than control mice. Furthermore, these mice had decreased ureteric volume and surface area and longer ureteric segments than control mice. We also observed previously unrecognized abnormalities in nephrogenesis, including a gradual increase in volume and surface area during maturation from renal vesicles to mature nephrons, in the mutant mice. Finally, we quantified many events of normal renal development that are either difficult or impossible to measure without this three-dimensional technique. In summary, the three-dimensional approach is a powerful and quantitative means to characterize branching morphogenesis and nephrogenesis.

Deletion of Frs2alpha from the ureteric epithelium causes renal hypoplasia

Fibroblast growth factor receptor 2 (Fgfr2) signaling is critical in maintaining ureteric branching architecture and mesenchymal stromal morphogenesis in the kidney. Fibroblast growth factor receptor substrate 2alpha (Frs2alpha) is a major docking protein for Fgfr2 with downstream targets including Ets variant (Etv) 4 and Etv5 in other systems. Furthermore, global deletion of Frs2alpha causes early embryonic lethality. The purpose of the study was to determine the role of Frs2alpha in mediating Fgfr2 signaling in the ureteric epithelium. To that end, we generated mice with conditional deletion of Frs2alpha in the ureteric epithelium (Frs2alpha(UB-/-)) and mice with point mutations in the Frs2alpha binding site of Fgfr2 (Fgfr2(LR/LR)). Frs2alpha(UB-/-) mice developed mild renal hypoplasia characterized by decreased ureteric branching morphogenesis but maintained normal overall branching architecture and had normal mesenchymal stromal development. Reduced nephron endowment in postnatal mutant mice was observed, corresponding with the reduction in branching morphogenesis. Furthermore, there were no apparent renal abnormalities in Fgfr2(LR/LR) mice. Interestingly, Etv4 and Etv5 expression was unaltered in Frs2alpha(UB-/-) mice, as was Sprouty1, an antagonist of Frs2alpha signaling. However, Ret and Wnt11 (molecules critical for ureteric branching morphogenesis) mRNA levels were lower in mutants vs. controls. Taken together, these findings suggest that Fgfr2 signals through adapter molecules other than Frs2alpha in the ureteric epithelium. Furthermore, Frs2alpha may transmit signals through other receptor kinases present in ureteric epithelium. Finally, the renal hypoplasia observed in Frs2alpha(UB-/-) mice is likely secondary to decreased Ret and Wnt11 expression.

The systemic inflammatory response syndrome is predictive of renal dysfunction in patients with non-paracetamol-induced acute liver failure

BACKGROUND

Although renal dysfunction is a common complication of acute liver failure (ALF) with significant prognostic implications, the pathophysiological mechanisms remain unclear. The current hypothesis suggests that the renal dysfunction may mirror the hepatorenal syndrome of cirrhosis. However, ALF has distinct clinical characteristics and the circulatory derangement may be more comparable with sepsis.

OBJECTIVES

To examine the relationship between the systemic inflammatory response syndrome (SIRS) and renal dysfunction in ALF, and to identify additional risk factors for renal dysfunction.

METHODS

A single-centre retrospective study of 308 patients with ALF was carried out. Renal dysfunction was defined according to the RIFLE criteria for acute kidney injury.

RESULTS

67% of patients developed renal dysfunction. On univariate analysis, renal dysfunction patients were more likely to be hypothermic (p = 0.010), had a faster heart rate (p<0.001), a higher white cell count (p = 0.001) and a lower PaCO(2) (p = 0.033). 78% of renal dysfunction patients and 53% of non-renal dysfunction patients had SIRS (p<0.001). On multivariate analysis, the risk factors for renal dysfunction were age (p = 0.024), fulfilled Kings College Hospital prognostic criteria (p<0.001), hypotension (p<0.001), paracetamol-induced ALF (p<0.001), infection (p = 0.077) and SIRS (p = 0.017). SIRS remained an independent predictor of renal dysfunction in the subgroup of patients with non-paracetamol-induced ALF (n = 91, p = 0.001). In contrast, in patients with paracetamol-induced ALF (n = 217), no relationship between SIRS and renal dysfunction was demonstrated (p = 0.373).

CONCLUSION

SIRS is strongly associated with the development of renal dysfunction in patients with non-paracetamol-induced ALF. It is proposed that the systemic inflammatory cascade plays a key role in its pathogenesis.

Management and etiology of the unilateral multicystic dysplastic kidney: a review

In children, unilateral multicystic dysplastic kidney (MCDK) is one of the most frequently identified urinary tract abnormalities. A variety of proposed etiologies has been associated with the underlying pathogenesis of MCDK. These include genetic disturbances, teratogens, in utero infections, and urinary outflow tract obstruction. From 5-43% of the time, MCDK has associated genito-urinary anomalies, both structural and functional in nature. A review of the literature reveals that involution rates are reported to be 19-73%, compensatory hypertrophy of the contralateral kidney occurs from 24-81% of the time, and estimated glomerular filtration rates (GFRs) (by the Schwartz formula) range from 86-122 ml/min per 1.73 m(2) body surface area. Most authors suggest serial ultrasonography to monitor contralateral growth, routine blood pressure monitoring, and a serum creatinine monitoring algorithm. The risk of hypertension in those with MCDKs does not appear to be greater than that of the general population, and the rates of malignant transformation of MCDK are small, if at all increased, in comparison with those in the general population. If the patient develops a urinary tract infection or has abnormalities of the contralateral kidney, shown on ultrasound, a voiding cystourethrogram is recommended. Finally, the body of literature does not support the routine surgical removal of MCDKs.

Coordinate integrin and c-Met signaling regulate Wnt gene expression during epithelial morphogenesis

Integrin receptors for the extracellular matrix and receptor tyrosine kinase growth factor receptors represent two of the major families of receptors that transduce into cells information about the surrounding environment. Wnt proteins are a major family of signaling molecules that regulate morphogenetic events. There is presently little understanding of how the expression of Wnt genes themselves is regulated. In this study, we demonstrate that alpha3beta1 integrin, a major laminin receptor involved in the development of the kidney, and c-Met, the receptor for hepatocyte growth factor, signal coordinately to regulate the expression of Wnt7b in the mouse. Wnt signals in turn appear to regulate epithelial cell survival in the papilla of the developing kidney, allowing for the elongation of epithelial tubules to form a mature papilla. Together, these results demonstrate how signals from integrins and growth factor receptors can be integrated to regulate the expression of an important family of signaling molecules so as to regulate morphogenetic events.

Role of fibroblast growth factor receptor 2 in kidney mesenchyme

Conditional deletion of murine fibroblast growth factor receptors (Fgfrs) 1 and 2 in metanephric mesenchyme leads to renal agenesis with unbranched ureteric buds; however, there are occasionally two buds per nephric duct. Our goal was to determine whether conditional deletion of Fgfr1 or Fgfr2 alone resulted in multiple ureteric bud induction sites. Although deletion of Fgfr1 alone results in no abnormalities, loss of Fgfr2 often leads to multiple ureteric buds and anomalies including renal aplasia, misshaped kidneys, partially duplicated kidneys, duplicated ureters, and obstructed hydroureter. Deletion of Fgfr2 did not change expression domains of glial cell line-derived neurotrophic factor (GDNF), Robo2, bone morphogenetic protein 4, or Sprouty1, all of which regulate ureteric bud induction. Cultured Fgfr2 mutant nephric ducts were also not more sensitive to exogenous GDNF than controls. Whole mount in situ hybridization revealed that in mutant embryos, Fgfr2 was deleted from stromal cells around the nephric duct and ureteric bud base, which correlates well with the ureteric bud induction abnormalities. Thus, Fgfr2 is critical in ensuring that there is a single ureteric bud from the nephric duct. The plethora of later stage defects in Fgfr2 conditional knockouts is reminiscent of many human cases of genetic urogenital anomalies.

Motion and dissolution of drops of sparingly soluble alcohols on water

The dissolution of liquids with low mutual solubility is typically slow. However, drops of sparingly soluble, low-density, low-surface-tension liquids often dissolve rapidly on water due to surface tension instabilities and gradients. We report observations of the motion and dissolution of drops of aliphatic alcohols of a wide range of alkyl chain lengths as they dissolve in water. The alcohol drops are rendered visible by adding small amounts of iodine or other dyes. These drops display dewetting instabilities, fragmentation, fingering, and oscillation. As the length of the alcohol carbon chain increases from n = 4 to n = 9, dissolution slows dramatically. The roles of alcohol solubility and water surface area in promoting rapid dissolution are discussed.

Transcriptional profiling of the megabladder mouse: a unique model of bladder dysmorphogenesis

Recent studies in our lab identified a mutant mouse model of obstructive nephropathy designated mgb for megabladder. Homozygotic mgb mice (mgb-/-) develop lower urinary tract obstruction in utero due to a lack of bladder smooth muscle differentiation. This defect is the result of a random transgene insertion/translocation into chromosomes 11 and 16. Transcriptional profiling identified a significantly over-expressed cluster of gene products located on the translocated fragment of chromosome 16 including urotensin II-related peptide (Urp), which was shown to be preferentially over-expressed in developing mgb-/- bladders. Pathway analysis of mgb microarray data indicated dysregulation of at least 60 gene products associated with smooth muscle development. In conclusion, the results of this study indicate that the molecular pathways controlling normal smooth muscle development are severely altered in mgb-/- bladders, and provide the first evidence that Urp may play a critical role in bladder smooth muscle development.

Role of fibroblast growth factor receptor signaling in kidney development

Fibroblast growth factor receptors (Fgfrs) are expressed in the ureteric bud and metanephric mesenchyme of the developing kidney. Furthermore, in vitro and in vivo studies have shown that exogenous fibroblast growth factors (Fgfs) increase growth and maturation of the metanephric mesenchyme and ureteric bud. Deletion of fgf7, fgf10, and fgfr2IIIb (the receptor isoform that binds Fgf7 and Fgf10) in mice lead to smaller kidneys with fewer collecting ducts and nephrons. Overexpression of a dominant negative receptor isoform in transgenic mice has revealed more striking defects including renal aplasia or severe dysplasia. Moreover, deletion of many fgf ligands and receptors in mice results in early embryonic lethality, making it difficult to determine their roles in kidney development. Recently, conditional targeting approaches revealed that deletion of fgf8 from the metanephric mesenchyme interrupts nephron formation. Furthermore, deletion of fgfr2 from the ureteric bud resulted in both ureteric bud branching and stromal mesenchymal patterning defects. Deletion of both fgfr1 and fgfr2 in the metanephric mesenchyme resulted in renal aplasia, characterized by defects in metanephric mesenchyme formation and initial ureteric bud elongation and branching. Thus, Fgfr signaling is critical for growth and patterning of all renal lineages at early and later stages of kidney development.