Kidney Defects Research Articles

A Point Mutation in p190A RhoGAP Affects Ciliogenesis and Leads to Glomerulocystic Kidney Defects.

Rho family GTPases act as molecular switches regulating actin cytoskeleton dynamics. Attenuation of their signaling capacity is provided by GTPase-activating proteins (GAPs), including p190A, that promote the intrinsic GTPase activity of Rho proteins. In the current study we have performed a small-scale ENU mutagenesis screen and identified a novel loss of function allele of the p190A gene Arhgap35, which introduces a Leu1396 to Gln substitution in the GAP domain. This results in decreased GAP activity for the prototypical Rho-family members, RhoA and Rac1, likely due to disrupted ordering of the Rho binding surface. Consequently, Arhgap35-deficient animals exhibit hypoplastic and glomerulocystic kidneys. Investigation into the cystic phenotype shows that p190A is required for appropriate primary cilium formation in renal nephrons. P190A specifically localizes to the base of the cilia to permit axoneme elongation, which requires a functional GAP domain. Pharmacological manipulations further reveal that inhibition of either Rho kinase (ROCK) or F-actin polymerization is able to rescue the ciliogenesis defects observed upon loss of p190A activity. We propose a model in which p190A acts as a modulator of Rho GTPases in a localized area around the cilia to permit the dynamic actin rearrangement required for cilia elongation. Together, our results establish an unexpected link between Rho GTPase regulation, ciliogenesis and glomerulocystic kidney disease.

Acquired Mutations Link Congenital Heart Disease, Neurodevelopmental Disorders

Back to table of contents Previous article Next article Clinical and Research NewsFull AccessAcquired Mutations Link Congenital Heart Disease, Neurodevelopmental DisordersNick ZagorskiNick ZagorskiSearch for more papers by this authorPublished Online:4 Feb 2016https://doi.org/10.1176/appi.pn.2016.1b16AbstractAbout 20 percent of children with severe congenital heart disease have an excess of mutations that are also commonly found in children with developmental problems such as autism.A study published December 4 in Science suggests that neurodevelopmental abnormalities in children with congenital heart disease may arise from the acquisition of harmful de novo gene mutations. These are not inherited but rather spontaneously occur during fetal development. These abnormalities include cognitive, motor, social, and language impairments.Michelle Massi“Finding this strong association between the developing heart and brain was a bit surprising, for while the heart and brain are both complex organs, they do separate early in the development process,” said study coauthor Jonathan Kaltman, M.D., who is the administrator of the National Heart, Lung, and Blood Institute’s (NHLBI) Bench to Bassinet Program, which funded this study.“At the same time, it makes sense clinically, given that there are several inherited disorders such as Down’s syndrome or DiGeorge syndrome, which feature both cardiac and neurological problems.”Investigators from the NHLBI’s Pediatric Cardiac Genomics Consortium used a technique known as exome sequencing to scan all the protein-encoding regions of the genome in over 1,200 affected family trios (a child with congenital heart disease [CHD] and his or her parents) along with 900 control trios without CHD.They uncovered almost 400 potentially harmful de novo mutations that significantly contribute to the risk of co-occurring CHD and neurodevelopmental disorders.While an excess number of these harmful mutations were found in only 2 percent of patients who had isolated CHD, the prevalence rose in children with more complications. The mutations were present in about 10 percent of patients who also had neurodevelopmental disorders or other extracardiac congenital anomalies (such as limb or kidney defects), and 20 percent of patients who had both.When the researchers compared the genetic data from children with CHD and children with neurodevelopmental disorders but no heart problems, they found 85 mutations were present in both groups—more than twice as many as would be expected by random chance.“These findings show enough statistical risk of developing neurodevelopmental disabilities when these particular gene mutations are present that we might consider developing a genetic test for patients with CHD,” Kaltman told Psychiatric News. Such a test could help to identify high-risk children for early interventions that might help to limit developmental delays and improve functioning, he said.In addition to the NHLBI, this study was supported in part by the National Human Genome Research Institute, the Howard Hughes Medical Institute, and Simons Foundation for Autism Research. ■An abstract of “De Novo Mutations in Congenital Heart Disease With Neurodevelopmental and Other Congenital Anomalies” can be accessed here. ISSUES NewArchived

ER stress and basement membrane defects combine to cause glomerular and tubular renal disease resulting from Col4a1 mutations in mice.

ABSTRACTCollagen IV is a major component of basement membranes, and mutations in COL4A1, which encodes collagen IV alpha chain 1, cause a multisystemic disease encompassing cerebrovascular, eye and kidney defects. However, COL4A1 renal disease remains poorly characterized and its pathomolecular mechanisms are unknown. We show that Col4a1 mutations in mice cause hypotension and renal disease, including proteinuria and defects in Bowman's capsule and the glomerular basement membrane, indicating a role for Col4a1 in glomerular filtration. Impaired sodium reabsorption in the loop of Henle and distal nephron despite elevated aldosterone levels indicates that tubular defects contribute to the hypotension, highlighting a novel role for the basement membrane in vascular homeostasis by modulation of the tubular response to aldosterone. Col4a1 mutations also cause diabetes insipidus, whereby the tubular defects lead to polyuria associated with medullary atrophy and a subsequent reduction in the ability to upregulate aquaporin 2 and concentrate urine. Moreover, haematuria, haemorrhage and vascular basement membrane defects confirm an important vascular component. Interestingly, although structural and compositional basement membrane defects occurred in the glomerulus and Bowman's capsule, no tubular basement membrane defects were detected. By contrast, medullary atrophy was associated with chronic ER stress, providing evidence for cell-type-dependent molecular mechanisms of Col4a1 mutations. These data show that both basement membrane defects and ER stress contribute to Col4a1 renal disease, which has important implications for the development of treatment strategies for collagenopathies.

SGLT2 Inhibitors: Glucotoxicity and Tumorigenesis Downstream the Renal Proximal Tubule?

At present, diabetes mellitus is the main cause of end-stage renal disease. Effective glycaemic management is the most powerful tool to delay the establishment of diabetic complications, such as diabetic kidney disease. Together with reducing blood glucose levels, new anti-diabetic agents are expected not only to control the progression but also to restore known defects of the diabetic kidney. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are promising anti-diabetic agents that reduce hyperglycaemia by impairing glucose reabsorption in proximal tubule of the kidney and increasing glucosuria. SGLT2 inhibitors have shown to reduce glucotoxicity in isolated proximal tubule cells and also to attenuate expression of markers of overall kidney damage in experimental animal models of diabetes, but the actual renoprotective effect for downstream nephron segments is still unknown and deserves further attention. Here, we briefly discuss possible undesired effects of enhanced glucosuria and albuminuria in nephron segments beyond the proximal tubule after SGLT2 inhibitor treatment, offering new lines of research to further understand the renoprotective action of these anti-diabetic agents. Strategies blocking glucose reabsorption by renal proximal tubule epithelial cells (RPTEC) may be protective for RPTEC, but downstream nephron segments will still be exposed to high glucose and albumin levels through the luminal face. The actual effect of constant enhanced glucosuria over distal nephron segments remains to be established. J. Cell. Physiol. 231: 1635-1637, 2016. © 2015 Wiley Periodicals, Inc.

A New Sliding-Loop Technique in Renorrhaphy for Partial Nephrectomy: A Feasibility Study in a Porcine Model.

We developed a sliding-loop technique that narrowed both sides of the parenchyma in a porcine model and compared it with the conventional sliding-clip technique. Three pigs (30-40 kg) were reused following another experiment conducted by the same researchers. Bilateral kidneys were harvested within 30 minutes after euthanasia. Two partial nephrectomies per kidney were performed on opposite surfaces. All kidney defects were of the same size (diameter of 2.5-3 cm with a depth of 1.0-1.5 cm). The sliding-clip technique and sliding-loop technique were performed separately. In the sliding-loop technique, we created a 1-cm loop at the end of a Vicryl and placed a tetrafluoroethylene polymer pledget in front of the knots passing through the needle. The needle then crossed the loop after passing through the renal parenchyma. A Weck clip was placed and slid on one side to tighten the suture. Tightening was controlled with an equivalent force using a digital push-pull gauge. Three stitches were placed at each renorrhaphy site. The distance between repaired renal surfaces was measured at 5 different points (3 suture sites and 2 middle sites between sutures). The results of the 2 techniques were compared by using the independent t test. The mean distance between renal surfaces was significantly narrower in the sliding-loop technique than in the conventional technique (1.80 ± 1.08 mm vs 5.28 ± 2.46 mm, P < .001). In the porcine model, the sliding-loop technique more effectively closed the partial nephrectomy defects compared with the conventional sliding-clip technique.

In vivo Modeling Implicates APOL1 in Nephropathy: Evidence for Dominant Negative Effects and Epistasis under Anemic Stress.

African Americans have a disproportionate risk for developing nephropathy. This disparity has been attributed to coding variants (G1 and G2) in apolipoprotein L1 (APOL1); however, there is little functional evidence supporting the role of this protein in renal function. Here, we combined genetics and in vivo modeling to examine the role of apol1 in glomerular development and pronephric filtration and to test the pathogenic potential of APOL1 G1 and G2. Translational suppression or CRISPR/Cas9 genome editing of apol1 in zebrafish embryos results in podocyte loss and glomerular filtration defects. Complementation of apol1 morphants with wild-type human APOL1 mRNA rescues these defects. However, the APOL1 G1 risk allele does not ameliorate defects caused by apol1 suppression and the pathogenicity is conferred by the cis effect of both individual variants of the G1 risk haplotype (I384M/S342G). In vivo complementation studies of the G2 risk allele also indicate that the variant is deleterious to protein function. Moreover, APOL1 G2, but not G1, expression alone promotes developmental kidney defects, suggesting a possible dominant-negative effect of the altered protein. In sickle cell disease (SCD) patients, we reported previously a genetic interaction between APOL1 and MYH9. Testing this interaction in vivo by co-suppressing both transcripts yielded no additive effects. However, upon genetic or chemical induction of anemia, we observed a significantly exacerbated nephropathy phenotype. Furthermore, concordant with the genetic interaction observed in SCD patients, APOL1 G2 reduces myh9 expression in vivo, suggesting a possible interaction between the altered APOL1 and myh9. Our data indicate a critical role for APOL1 in renal function that is compromised by nephropathy-risk encoding variants. Moreover, our interaction studies indicate that the MYH9 locus is also relevant to the phenotype in a stressed microenvironment and suggest that consideration of the context-dependent functions of both proteins will be required to develop therapeutic paradigms.

Dysmorphologic assessment in 115 Mayer-Rokitansky-Küster-Hauser patients.

Mayer-Rokitansky-Küster-Hauser (MRKH) patients are characterized by congenital aplasia of the uterus and the upper part of the vagina, with normal secondary sexual characteristics. This disorders affects one in 4000-5000 females and it is classified as typical, type I or isolated, and as atypical, type II, manifesting additional malformations. To date, no specific study has addressed the question of facial features in MRKH patients. The aim of this study is to perform a dysmorphological assessment of a large cohort of patients. We studied 115 women referred to our center from 2008 to 2012. Seventy-two percentage (83/115) of our patients showed isolated uterovaginal aplasia (MRKH type I); 32/115 (28%) had other abnormalities including kidney and cardiac defects, skeletal anomalies, and hearing impairment. Auxologic investigations comprised measurements of height, weight, BMI, head circumference, arm span, span to height ratio, hand length, middle finger length, foot length, inner and outer intercanthal distance, and auricle length. All patients had normal measurements, except for the outer canthal distance-inner canthal distance ratio, which was consistent with elongated eyelids. Women with MRKH syndromes do not present a typical facial feature and a dysmorphological examination of all patients seems unnecessary. However, a multidisciplinary approach is useful with respect to explaining the etiology, interpreting test results, and counseling.

Kidney adysplasia and variable hydronephrosis, a new mutation affecting the odd-skipped related 1 gene in the mouse, causes variable defects in kidney development and hydronephrosis.

Many genes, including odd-skipped related 1 (Osr1), are involved in regulation of mammalian kidney development. We describe here a new recessive mutation (kidney adysplasia and variable hydronephrosis, kavh) in the mouse that leads to downregulation of Osr1 transcript, causing several kidney defects: agenesis, hypoplasia, and hydronephrosis with variable age of onset. The mutation is closely associated with a reciprocal translocation, T(12;17)4Rk, whose Chromosome 12 breakpoint is upstream from Osr1. The kavh/kavh mutant provides a model to study kidney development and test therapies for hydronephrosis.

Emanuel Syndrome (Es): New Case-Report and Review of the Literature/ Емануел Синдром (Es): Презентација На Нов Случај И Преглед На Литературата

Abstract Multiple congenital anomalies and craniofacial dysmorphism are characterizing the so-called Emanuel or supernumerary der(22)t(11;22) syndrome (OMIM609029). Mental and developmental retardation are major clinical features. The der(22) may arise from a parental balanced t(11;22)(q23;q11.2) or can be created de novo. Here we present a 2 years old boy with normal prenatal history, cyanotic at delivery and with ear anomalies, a preauricular tag, high-arched palate and micrognathia. There were neither microcephaly, nor heart or kidney defects. Psychological and motor testing at the age of 2 years confirmed significant mental and developmental delay. In addition, the child had seizures and an abnormal electroencephalogram. Cytogenetic and molecular analyses revealed a karyotype 47,XY,+der(22)t(11;22)(q23;q11.2). As parents refused further tests it could not be determined if the der(22) arose de novo or was parentally derived. Overall the present report should alert physician to offer cytogenetic and/or molecular diagnostics in comparable cases.

Structural and Functional Study of d-Glucuronyl C5-epimerase

Heparan sulfate (HS) is a glycosaminoglycan present on the cell surface and in the extracellular matrix, which interacts with diverse signal molecules and is essential for many physiological processes including embryonic development, cell growth, inflammation, and blood coagulation. D-glucuronyl C5-epimerase (Glce) is a crucial enzyme in HS synthesis, converting D-glucuronic acid to L-iduronic acid to increase HS flexibility. This modification of HS is important for protein ligand recognition. We have determined the crystal structures of Glce in apo-form (unliganded) and in complex with heparin hexasaccharide (product of Glce following O-sulfation), both in a stable dimer conformation. A Glce dimer contains two catalytic sites, each at a positively charged cleft in C-terminal α-helical domains binding one negatively charged hexasaccharide. Based on the structural and mutagenesis studies, three tyrosine residues, Tyr(468), Tyr(528), and Tyr(546), in the active site were found to be crucial for the enzymatic activity. The complex structure also reveals the mechanism of product inhibition (i.e. 2-O- and 6-O-sulfation of HS keeps the C5 carbon of L-iduronic acid away from the active-site tyrosine residues). Our structural and functional data advance understanding of the key modification in HS biosynthesis.

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. Six2creFgfr1flox/floxFgfr2flox/flox (Fgfr1/2NP−/−) 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 Fgfr1/2NP−/− mice, we generated Six2cre,Fgfr1flox/floxFgfr2LR/LR (Fgfr1NP−/−Fgfr2LR/LR) mice that have point mutations in the Frs2α binding site of Fgfr2. Like Fgfr1/2NP−/− mice, Fgfr1NP−/−Fgfr2LR/LR develop nephron progenitor depletion, but it does not start until E14.5 and older mice have less severe cystic dysplasia than Fgfr1/2NP−/− To determine the role of Frs2α alone in nephron progenitors, we generated Six2creFrs2′Aflox/flox (Frs2aNP−/−) mice. Frs2aNP−/−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′Aflox/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.

A role for the extracellular matrix component hyaluronan in kidney dysfunction during ACE-inhibitor fetopathy.

Despite data showing that inhibitors of the renin-angiotensin system increase the risks of fetal morbidity and dysfunctionality later in life, their use during pregnancy has increased. The fetopathy induced by angiotensin converting enzyme (ACE) inhibitors is characterized by anuria, hypotension and growth restriction, but can also be associated with pulmonary hypoplasia. In the kidney, this fetopathy includes atrophy of the medulla, reduced number of glomeruli, developmental lesions of tubules and vessels, tubulointerstitial inflammation and extracellular matrix accumulation. Although angiotensin II (Ang II) inhibition during nephrogenesis interferes with normal growth and development, this review will focus on effects of the heavily accumulated matrix component hyaluronan (HA). An important mechanism of HA accumulation during nephrogenesis is disruption of its normal reduction as a consequence of lack of Ang II activation of hyaluronidase. Hyaluronan has very large water-attracting properties and is pro-inflammatory when fragmented. The ensuing inflammation and interstitial oedema affect kidney function. Hyaluronan is colocalized with CD44 overexpression and infiltrating immune cells. These properties make HA a plausible contributor to the observed structural and functional kidney defects associated with the fetopathy. Available data support an involvement of HA in kidney dysfunction of the foetus and during adulthood due to the physico-chemical characteristics of HA. No clinical treatment for HA accumulation exists. Treatment with the HA-degrading enzyme hyaluronidase and an HA synthesis inhibitor has been tested successfully in experimental models in the kidney, heart and pancreas. Reduced HA accumulation to reduce interstitial oedema and inflammation may improve organ function, but this concept needs to be tested in a controlled study before causal relationships can be established.

Evidence for a Dominant Negative Effect Conferred By the APOL1 G2 Sickle Cell Nephropathy Risk Allele in an in Vivo Model

BACKGROUND: Sickle cell disease (SCD) patients have a heterogeneous clinical course, and as patient survival has improved, end-organ damage has become an emergent clinical priority. End stage renal disease (ESRD), occurring in 5-18% of SCD patients, is a particular concern, because it is a major risk factor for early mortality (Platt et al. 1994). Detection of SCD nephropathy (SCDN) relies on relatively late-stage markers, namely proteinuria and reduced glomerular filtration rate (GFR). Consequently, at-risk SCD patients are not identified prior to end-organ damage. In non-SCD nephropathy, ESRD risk among African American individuals has been attributed to coding variants (termed G1 and G2) in apolipoprotein L1 (APOL1). The G1 allele consists of two nonsynonymous variants in perfect LD, rs73885319 and rs60910145 (encoding S384G and I384M), while the G2 variant consists of a six base pair deletion removing amino acids N388 and Y389 (~21% and ~13% allelic frequency in African Americans for G1 and G2, respectively). We demonstrated that these variants in APOL1 are strong predictors of risk for proteinuria in SCD (Ashley-Koch et al. 2011). Here, we use zebrafish as an in vivo model to both examine the role of apol1 in glomerular development and pronephric filtration and also to test the effects of APOL1 G1 and G2 expression in the developing kidney.METHODS: A morpholino (MO) was designed by Gene Tools, LLC (Philomath, OR) to target the translation initiation site of zebrafish apol1. APOL1 G1 and G2 allelic constructs were synthesized from a wild-type (WT) APOL1 human open reading frame clone (GenBank: BC112943) using site-directed mutagenesis (Stratagene, QuikChange II), subsequently transcribed (mMESSAGE mMACHINE®, Life Technologies) into capped mRNA and co-injected with apol1-MO into zebrafish embryos. To assay glomerular filtration, 70 kDa FITC-conjugated dextran was injected into the cardiac venous sinus of 48 hour post-fertilization embryos. The eye vasculature of individual fish was imaged at two, 12, and 36 hours after dextran injection. The average fluorescence intensity was measured across the eye, and changes in intensity relative to the 2-hour post-injection measurements were calculated for comparison. Electron microscopy sections of five days post-fertilization embryos were cut on a Leica-Reichert Ultracut E ultramicrotome, and semi-thin sections (1.0μm) were stained and examined on a Phillips CM12 electron microscope.RESULTS: As we showed previously (Anderson et al., ASH 2013), MO-induced suppression of apol1 in zebrafish embryos results in pericardial edema, glomerular filtration defects, and extensive podocyte loss. Importantly, complementation of apol1 morphants with WT human APOL1 mRNA rescues the observed kidney defects. However, we now show that neither APOL1 G1 nor G2 risk alleles ameliorate defects caused by apol1 suppression. Notably, injection of APOL1 G2 alone results in renal defects, as indicated by increased dextran clearance and the presence of microvillus protrusions in the urinary space. Injection of APOL1 G1 alone, however, does not induce noticeable kidney dysfunction. Furthermore, when APOL1 G2 injected embryos were titrated with increasing concentrations of human APOL1 WT mRNA, we observed a significant reduction of edema formation in developing embryos, suggesting a possible dominant-negative effect of the altered protein.CONCLUSIONS: Unlike the WT APOL1 mRNA, neither the APOL1 G1 or G2 risk alleles could rescue kidney dysfunction due to knockdown of apol1 in zebrafish embryos, suggesting that these SCDN risk alleles impact the normal function of APOL1 in the kidney. Furthermore, development of edema with concomitant defects in glomerular ultrastructure in zebrafish embryos injected with APOL1 G2 mRNA alone suggest that this allele may act in a dominant-negative manner to induce kidney defects. Interestingly, it has been shown that APOL1 may cause toxic renal effects through programmed cell death pathways leading to glomerulosclerosis (Wan et al. 2008). Thus, apol1 suppression could result in the dysregulation of autophagic pathways, causing podocyte malformation and thereby affecting the susceptibility of the pronephros to glomerular injury. In summary, these data provide essential insight into the biological mechanisms by which APOL1 variants confer disease risk in human SCDN and other nondiabetic nephropathies. DisclosuresNo relevant conflicts of interest to declare.

Congenital hepatic fibrosis in the Franches-Montagnes horse is associated with the polycystic kidney and hepatic disease 1 (PKHD1) gene.

Congenital hepatic fibrosis has been described as a lethal disease with monogenic autosomal recessive inheritance in the Swiss Franches-Montagnes horse breed. We performed a genome-wide association study with 5 cases and 12 controls and detected an association on chromosome 20. Subsequent homozygosity mapping defined a critical interval of 952 kb harboring 10 annotated genes and loci including the polycystic kidney and hepatic disease 1 (autosomal recessive) gene (PKHD1). PKHD1 represents an excellent functional candidate as variants in this gene were identified in human patients with autosomal recessive polycystic kidney and hepatic disease (ARPKD) as well as several mouse and rat mutants. Whereas most pathogenic PKHD1 variants lead to polycystic defects in kidney and liver, a small subset of the human ARPKD patients have only liver symptoms, similar to our horses with congenital hepatic fibrosis. The PKHD1 gene is one of the largest genes in the genome with multiple alternative transcripts that have not yet been fully characterized.We sequenced the genomes of an affected foal and 46 control horses to establish a comprehensive list of variants in the critical interval. We identified two missense variants in the PKHD1 gene which were strongly, but not perfectly associated with congenital hepatic fibrosis. We speculate that reduced penetrance and/or potential epistatic interactions with hypothetical modifier genes may explain the imperfect association of the detected PKHD1 variants. Our data thus indicate that horses with congenital hepatic fibrosis represent an interesting large animal model for the liver-restricted subtype of human ARPKD.

Of Heart & Kidneys: Hands-On Activities for Demonstrating Organ Function & Repair.

A major challenge in teaching organ development and disease is deconstructing a complex choreography of molecular and cellular changes over time into a linear stepwise process for students. As an entry toward learning developmental concepts, I propose two inexpensive hands-on activities to help facilitate learning of (1) how to identify defects in heart and kidneys and (2) what evolutionarily conserved strategies from organ development can be applied to understand how to repair these defects. The ease of assembling these activities, combined with traffic flow as a metaphor for physiological function of heart and kidneys, provides students the opportunity to explore and discover biological concepts in organ formation and disease.

Deficiency of the planar cell polarity protein Vangl2 in podocytes affects glomerular morphogenesis and increases susceptibility to injury.

The planar cell polarity (PCP) signaling pathway is crucial for tissue morphogenesis. Van Gogh-like protein 2 (Vangl2) is central in the PCP pathway; in mice, Vangl2 loss is embryonically lethal because of neural tube defects, and mutations in Vangl2 are associated with human neural tube defects. In the kidney, PCP signaling may be important for tubular morphogenesis and organization of glomerular epithelial cells (podocytes) along the glomerular basement membrane. Podocyte cell protrusions (foot processes) are critical for glomerular permselectivity; loss of foot process architecture results in proteinuria and FSGS. Previously, we showed a profound effect of PCP signaling on podocyte shape, actin rearrangement, cell motility, and nephrin endocytosis. To test our hypothesis that the PCP pathway is involved in glomerular development and function and circumvent lethality of the ubiquitous Vangl2 mutation in the Looptail mouse, we generated a mouse model with a podocyte-specific ablation of the Vangl2 gene. We report here that podocyte-specific deletion of Vangl2 leads to glomerular maturation defects in fetal kidneys. In adult mice, we detected significantly smaller glomeruli, but it did not affect glomerular permselectivity in aging animals. However, in the context of glomerular injury induced by injection of antiglomerular basement membrane antibody, deletion of Vangl2 resulted in exacerbation of injury and accelerated progression to chronic segmental and global glomerular sclerosis. Our results indicate that Vangl2 function in podocytes is important for glomerular development and protects against glomerular injury in adult animals.

Standardized, systemic phenotypic analysis of Slc12a1I299F mutant mice.

BackgroundType I Bartter syndrome is a recessive human nephropathy caused by loss-of-function mutations in the SLC12A1 gene coding for the Na+-K+-2Cl− cotransporter NKCC2. We recently established the mutant mouse line Slc12a1I299F exhibiting kidney defects highly similar to the late-onset manifestation of this hereditary human disease. Besides the kidney defects, low blood pressure and osteopenia were revealed in the homozygous mutant mice which were also described in humans. Beside its strong expression in the kidney, NKCC2 has been also shown to be expressed in other tissues in rodents i.e. the gastrointestinal tract, pancreatic beta cells, and specific compartments of the ear, nasal tissue and eye.ResultsTo examine if, besides kidney defects, further organ systems and/or metabolic pathways are affected by the Slc12a1I299F mutation as primary or secondary effects, we describe a standardized, systemic phenotypic analysis of the mutant mouse line Slc12a1I299F in the German Mouse Clinic. Slc12a1I299F homozygous mutant mice and Slc12a1I299F heterozygous mutant littermates as controls were tested at the age of 4–6 months. Beside the already published changes in blood pressure and bone metabolism, a significantly lower body weight and fat content were found as new phenotypes for Slc12a1I299F homozygous mutant mice. Small additional effects included a mild erythropenic anemia in homozygous mutant males as well as a slight hyperalgesia in homozygous mutant females. For other functions, such as immunology, lung function and neurology, no distinct alterations were observed.ConclusionsIn this systemic analysis no clear primary effects of the Slc12a1I299F mutation appeared for the organs other than the kidneys where Slc12a1 expression has been described. On the other hand, long-term effects additional and/or secondary to the kidney lesions might also appear in humans harboring SLC12A1 mutations.

A mouse Col4a4 mutation causing Alport glomerulosclerosis with abnormal collagen α3α4α5(IV) trimers

A spontaneous mutation termed bilateral wasting kidneys (bwk) was identified in a colony of NONcNZO recombinant inbred mice. These mice exhibit a rapid increase of urinary albumin at an early age associated with glomerulosclerosis, interstitial nephritis, and tubular atrophy. The mutation was mapped to a location on Chromosome 1 containing the Col4a3 and Col4a4 genes, for which mutations in the human orthologs cause the hereditary nephritis Alport syndrome. DNA sequencing identified a G to A mutation in the conserved GT splice donor of Col4a4 intron 30, resulting in skipping of exon 30 but maintaining the mRNA reading frame. Protein analyses showed that mutant collagen α3α4α5(IV) trimers were secreted and incorporated into the glomerular basement membrane (GBM), but levels were low, and GBM lesions typical of Alport syndrome were observed. Moving the mutation into the more renal damage-prone DBA/2J and 129S1/SvImJ backgrounds revealed differences in albuminuria and its rate of increase, suggesting an interaction between the Col4a4 mutation and modifier genes. This novel mouse model of Alport syndrome is the only one shown to accumulate abnormal collagen α3α4α5(IV) in the GBM, as also found in a subset of Alport patients. These mice will be valuable for testing potential therapies, for understanding abnormal collagen IV structure and assembly, for gaining better insights into the mechanisms leading to Alport syndrome and to the variability in the age of onset and associated phenotypes.

Early B-cell factor 1 is an essential transcription factor for postnatal glomerular maturation

The coordination of multiple cytokines and transcription factors with their downstream signaling pathways have been shown to be integral to nephron maturation. Here we present a completely novel role for the helix-loop-helix transcription factor Early B cell Factor 1 (Ebf1), originally identified for B cell maturation, for the proper maturation of glomerular cells from mesenchymal progenitors. The expression of Ebf1 was both spatially and temporally regulated within the developing cortex and glomeruli. Using Ebf1-null mice we then identified biochemical, metabolic, and histological abnormalities in renal development that arose in the absence of this transcription factor. In the Ebf1 knockout mice the developed kidneys show thinned cortices and reduced glomerular maturation. The glomeruli showed abnormal vascularization and severely effaced podocytes. The mice exhibited early albuminuria and elevated blood urea nitrogen levels. Moreover, the GFR was reduced over 66 percent and the expression of podocyte-derived VEGF-A was decreased compared to wild type control mice. Thus, Ebf1 has a significant and novel role in glomerular development, podocyte maturation, and the maintenance of kidney integrity and function.

Whole exome analysis identifies dominant COL4A1 mutations in patients with complex ocular phenotypes involving microphthalmia

Anophthalmia/microphthalmia (A/M) is a developmental ocular malformation defined as complete absence or reduction in size of the eye. A/M is a heterogenous disorder with numerous causative genes identified; however, about half the cases lack a molecular diagnosis. We undertook whole exome sequencing in an A/M family with two affected siblings, two unaffected siblings, and unaffected parents; the ocular phenotype was isolated with only mild developmental delay/learning difficulties reported and a normal brain magnetic resonance imaging (MRI) in the proband at 16 months. No pathogenic mutations were identified in 71 known A/M genes. Further analysis identified a shared heterozygous mutation in COL4A1, c.2317G>A, p.(Gly773Arg) that was not seen in the unaffected parents and siblings. Analysis of 24 unrelated A/M exomes identified a novel c.2122G>A, p.(Gly708Arg) mutation in an additional patient with unilateral microphthalmia, bilateral microcornea and Peters anomaly; the mutation was absent in the unaffected mother and the unaffected father was not available. Mutations in COL4A1 have been linked to a spectrum of human disorders; the most consistent feature is cerebrovascular disease with variable ocular anomalies, kidney and muscle defects. This study expands the spectrum of COL4A1 phenotypes and indicates screening in patients with A/M regardless of MRI findings or presumed inheritance pattern.