Abnormal Kidney Development Research Articles

Translational strategies to uncover the etiology of congenital anomalies of the kidney and urinary tract.

While up to 50% of children requiring kidney replacement therapy have congenital anomalies of the kidney and urinary tract (CAKUT), they represent only a fraction of the total patient population with CAKUT. The extreme variability in clinical outcome underlines the fundamental need to devise personalized clinical management strategies for individuals with CAKUT. Better understanding of the pathophysiology of abnormal kidney and urinary tract development provides a framework for precise diagnoses and prognostication of patients, the identification of biomarkers and disease modifiers, and, thus, the development of personalized strategies for treatment. In this review, we provide a state-of-the-art overview of the currently known genetic causes, including rare variants in kidney and urinary tract development genes, genomic disorders, and common variants that have been attributed to CAKUT. Furthermore, we discuss the impact of environmental factors and their interactions with developmental genes in kidney and urinary tract malformations. Finally, we present multi-angle translational modalities to validate candidate genes and environmental factors and shed light on future strategies to better understand the molecular underpinnings of CAKUT.

#2289 Pregnancy outcomes in patients with congenital abnormality of the urinary tract: experience of a tertiary Portuguese center

Abstract Background and Aims Congenital abnormalities of the urinary tract (CAKUT) represent a broad range of disorders that occur due to abnormal kidney development. Maternal, obstetric, and perinatal outcome in pregnant woman with CAKUT have not been extensively evaluated, although small series report an increased incidence of urinary tract infections (UTI) and obstructive uropathy. Method Retrospective analysis of maternal, obstetric, and perinatal outcomes in pregnant patients with CAKUT (including genetic cystic kidney disease) that were surveilled in our tertiary center by a nephro-obstetric team between 2011 and June 2023. Information was obtained from medical records. Results We evaluated 47 gestations in 41 patients, with mean age of 31 ± 5 years [17-40], 89% were Caucasian, 11% black; 40% were nulliparous, 36% had hypertension (HT) and 42% a previous history of UTI. Regarding CAKUT specificity, 17/41 patients had genetic cystic diseases, 10/41 ureteropelvic junction obstruction (UPJ), 4/41 duplicate collecting system, 5/41 vesicourethral reflux, 2/41 ectopic kidney, 3/41 renal hypoplasia. Genetic testing was done before, during or after pregnancy in 2/4/4 patients, respectively. Teratogenic therapy exposure occurred in 25% of gestations. Most patients were CKD stage 1 (33/41), with 2/4/1/1 with patients in CKD stage 2/3/4/5, respectively. Mean baseline SCr was 0.99 ± 0.8 mg/dL [0.4-4.6] and mean proteinuria was 194 ± 357 mg/g [22-1500]. Renal function (RF) deterioration occurred in 9/47 (19%) women due to pre-eclampsia (PE), pregnancy hyperfiltration (PH) and hydronephrosis in 3/3/3 patients, respectively. Urologic intervention was needed in 2 patients due to hydronephrosis, and one of the patients required transient dialysis. All patients fully recovered RF except for the 1 CKD stage 3 patients that had partial RF recovery. De novo and worsening proteinuria occurred in 7/47 gestations due to PE (3/7) and PH (4/7). De novo or aggravation of HTN occurred in 25% gestations, UTI in 19% and PE in 6% gestations. Regarding fetal outcomes, mean duration of gestation was 38 ± 2 weeks [32-41] and mean birth weight 2910 ± 634 g [1360-4600]. There was 1 miscarriage and 1 medical termination of pregnancy at 17 weeks (neural tube defect). Cesarean was performed in (8/47, 17%) gestations and 10/47 (17%) newborns were admitted to the neonatal care unit (NICU) mainly due to prematurity, sepsis and feeding intolerance. Conclusion Our cohort of CAKUT patients was very heterogenous and only 19.5% had CKD stage 2-5. Still, we found a significant incidence of maternal, obstetric, and perinatal complications, namely HT UTI, PE, and the need for NICU. UPJ obstruction can evolve with RF deterioration and the need for intervention during pregnancy. This study underlines the importance of the management of these patients by a multidisciplinary team.

Impact of preterm birth on kidney health and development.

Preterm birth, defined as birth before the gestational age of 37 weeks, affects 11% of the newborns worldwide. While extensive research has focused on the immediate complications associated with prematurity, emerging evidence suggests a link between prematurity and the development of kidney disease later in life. It has been demonstrated that the normal course of kidney development is interrupted in infants born prematurely, causing an overall decrease in functional nephrons. Yet, the pathogenesis leading to the alterations in kidney development and the subsequent pathophysiological consequences causing kidney disease on the long-term are incompletely understood. In the present review, we discuss the current knowledge on nephrogenesis and how this process is affected in prematurity. We further discuss the epidemiological evidence and experimental data demonstrating the increased risk of kidney disease in these individuals and highlight important knowledge gaps. Importantly, understanding the intricate interplay between prematurity, abnormal kidney development, and the long-term risk of kidney disease is crucial for implementing effective preventive and therapeutic strategies.

Single-Cell Gene Expression Analysis in Patients with Medullary Sponge Kidney and a Retrospective Study.

To establish better diagnosis thinking and provide advanced understanding of MSK, the CT imaging features, clinical characteristics, and the expression of suspected genes in the kidney spatiotemporal immune zonation and fetal renal development were investigated. 17 patients with MSK hospitalized in our hospital were selected as our research subjects. Human Phenotype Ontology, MalaCards: The Human Disease Database, GeneCards: The Human Gene Database, Human Protein Atlas, and Single Cell Expression Atlas were used to analyze this disease. In our 17 patients, the incidence of MSK tended to be the same in male and female, and the onset age of MSK was probably 31-50 years old. The top one related disease of MSK was nephrocalcinosis and the most frequent phenotype related to MSK was nephrolithiasis. In addition, the expression of HNF1B, CLCN5, GDNF, ATP6V0A4, ATP6V1B1, LAMA2, RET, ACAN, and ABCC8 has been implicated in both human kidney immune zonation and fetal kidney development. HNF1B, CLCN5, GDNF, ATP6V0A4, ATP6V1B1, LAMA2, RET, ACAN, and ABCC8 could be independent indicators for the diagnosis and preventive intervention of MSK patients, and abnormal kidney development due to mutations in key genes was the underlying cause of MSK.

Clinical and pathological investigation of oligomeganephronia.

Oligomeganephronia (OMN) is a rare congenital anomaly involving the kidney and urinary tract, characterized by decreased number and compensatory hypertrophy of the nephron. It is caused by abnormal kidney development during the embryonic period, especially in patients with low birth weight; however, the actual etiology and clinical features remain unknown. We aim to reveal the clinical and pathological characteristics, treatment, and outcome. Ten patients diagnosed with OMN between 2013 and 2020 were retrospectively investigated. The data were presented as the median ± interquartile range, and statistical significance was set at p < 0.05. The age at diagnosis was 14.1years, the male-to-female ratio was 6:4, and only four cases were born with low birth weight. The estimated glomerular filtration rate (eGFR) was 62.2mL/min/1.73 m2. The glomerulus diameter of OMN patients was significantly larger (217 vs. 154µm, p < 0.001) in OMN patients, and the number of glomeruli of OMN patients was lower (0.89 vs. 2.05/mm2, p < 0.001) than the control group. Eight of the ten cases were identified by urinary screening. Nine patients were treated with renin-angiotensin system (RAS) inhibitors, following which proteinuria successfully decreased or disappeared. Their median eGFR was also stable, 53.3mL/min/1.73 m2. As few symptoms can lead to OMN discovery, most patients were found during urine screening at school. Kidney dysfunction was observed in all patients at the time of kidney biopsy. Proteinuria has been significantly reduced and the decline rate of eGFR might be improved by RAS inhibitors. "A higher resolution version of the Graphical abstract is available as Supplementary information".

Post-translational modifications by SIRT3 de-2-hydroxyisobutyrylase activity regulate glycolysis and enable nephrogenesis

Abnormal kidney development leads to lower nephron number, predisposing to renal diseases in adulthood. In embryonic kidneys, nephron endowment is dictated by the availability of nephron progenitors, whose self-renewal and differentiation require a relatively repressed chromatin state. More recently, NAD+-dependent deacetylase sirtuins (SIRTs) have emerged as possible regulators that link epigenetic processes to the metabolism. Here, we discovered a novel role for the NAD+-dependent deacylase SIRT3 in kidney development. In the embryonic kidney, SIRT3 was highly expressed only as a short isoform, with nuclear and extra-nuclear localisation. The nuclear SIRT3 did not act as deacetylase but exerted de-2-hydroxyisobutyrylase activity on lysine residues of histone proteins. Extra-nuclear SIRT3 regulated lysine 2-hydroxyisobutyrylation (Khib) levels of phosphofructokinase (PFK) and Sirt3 deficiency increased PFK Khib levels, inducing a glycolysis boost. This altered Khib landscape in Sirt3−/− metanephroi was associated with decreased nephron progenitors, impaired nephrogenesis and a reduced number of nephrons. These data describe an unprecedented role of SIRT3 in controlling early renal development through the regulation of epigenetics and metabolic processes.

Identification of limb-specific Lmx1b auto-regulatory modules with Nail-patella syndrome pathogenicity

LMX1B haploinsufficiency causes Nail-patella syndrome (NPS; MIM 161200), characterized by nail dysplasia, absent/hypoplastic patellae, chronic kidney disease, and glaucoma. Accordingly in mice, Lmx1b has been shown to play crucial roles in the development of the limb, kidney and eye. Although one functional allele of Lmx1b appears adequate for development, Lmx1b null mice display ventral-ventral distal limbs with abnormal kidney, eye and cerebellar development, more disruptive, but fully concordant with NPS. In Lmx1b functional knockouts (KOs), Lmx1b transcription in the limb is decreased nearly 6-fold, indicating autoregulation. Herein, we report on two conserved Lmx1b-associated cis-regulatory modules (LARM1 and LARM2) that are bound by Lmx1b, amplify Lmx1b expression with unique spatial modularity in the limb, and are necessary for Lmx1b-mediated limb dorsalization. These enhancers, being conserved across vertebrates (including coelacanth, but not other fish species), and required for normal locomotion, provide a unique opportunity to study the role of dorsalization in the fin to limb transition. We also report on two NPS patient families with normal LMX1B coding sequence, but with loss-of-function variations in the LARM1/2 region, stressing the role of regulatory modules in disease pathogenesis.

Gene Ontology Enrichment Analysis of Renal Agenesis: Improving Prenatal Molecular Diagnosis

Uni- or bilateral renal agenesis (RA) is a commonly occurring major congenital anomaly impacting fetal and neonatal outcomes. Since the etiology is highly heterogeneous, our aim was to provide a logically structured approach by highlighting the genes in which variants have been identified to be associated with RA and to define the pathways involved in this type of abnormal kidney development. We used Phenolyzer to collect a list of all the genes known as causative for RA. Using ClueGO gene enrichment analysis, we classified the relationship between these genes and the biological processes defined by gene ontology. We identified 287 genes and 69 groups of enriched biological processes. About 50% included pathways directly related to the development of urogenital organ tissues. Several ciliary, axis specification, hindgut development, and endocrine pathways were enriched, which may relate to different clinical presentations of RA. Our gene ontology enrichment analysis shows that genes representing distinct biological pathways are significantly enriched. This knowledge will lead to an improved molecular diagnosis in clinical care when applying genome-wide sequencing approaches. The findings will also allow to further study the biological pathways involved in RA and to identify novel candidate genes and pathways.

Canonical Wnt/Beta-Catenin Signaling Network as Emerging Signaling Cascade for Therapeutic Intervention in Chronic Renal Disease.

The socio-economic burden of renal disease is enormous due to the unavailability of effective treatment to cure it. High risk patients have only two costly options in chronic renal disease, dialysis and renal replacement therapy (RRT). RRT has limitations of the organ donor, and ethical concerns are also associated with it. The Wnt/beta-catenin pathway is highly conserved and active during embryogenesis in early life but suppressed in adults. Animal studies suggested that knockdown of Wnt protein led to abnormal kidney development at birth. In the adult kidney, Wnt/beta-- catenin pathway activation led to tissue repair after acute injury, but sustained activation is harmful and involved in renal fibrosis. Recently, Wnt/beta-catenin signaling cascade has emerged as a potential pathway involved in adult renal diseases and is considered an attractive therapeutic target for developing effective therapeutic intervention. Precise information about the involvement of specific types of Wnt/beta-catenin pathway components in adult renal disease using cutting-edge molecular techniques will help develop novel therapies for renal diseases. Future studies will determine Wnt/beta-catenin signaling proteins' effectiveness and safety as a treatment option for renal disorders.

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

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

P0060COMBINED NOVEL PBX1 AND RET VARIANTS IN AN ADULT WITH SYNDROMIC RENAL HYPOPLASIA: A CASE REPORT

Abstract Background and Aims Congenital abnormalities of the kidney and urinary tract (CAKUT) represent the main cause of pediatric end-stage renal disease with vast pheno- and genotypic heterogeneity. However, its contribution to adult chronic kidney disease (CKD) is less well characterized. We here report on an adult who underwent genetic testing for previously unrecognized CAKUT. Method Phenotypic characterization of a family with mild syndromic form of kidney hypoplasia. Panel-based genetic analysis for CAKUT associated genes in DNA from peripheral blood cells, oral mucosa, and urinary cells. Results A 20-year-old male presented with bilateral hypoplastic kidneys, first diagnosed with nocturnal enuresis at the age of ten. For CKD stage 2 (eGFR 72ml/min/1.73m), hypertension, and moderate albuminuria (300mg/d) he was treated with Ramipril. Additionally, facial dysmorphism with low-set microtia, slight micrognathia, and slightly impaired intelligence was apparent. Bilateral audiograms did not reveal any hearing impairment. His father showed slightly reduced kidney size without any laboratory anomalies or extrarenal symptoms. Further family history including his mother and three half siblings presented unremarkable. Genetic analysis revealed the following two variants: First, a novel heterozygous truncating variant, absent from patient and population databases, was found in PBX1 c.992C&amp;gt;A p.Ser331* (NM_002585.3). As this variant was detected in 25% of NGS reads, we tested for potential mosaicism by direct sequencing in DNA obtained from oral mucosa and urinary epithelia. While the latter showed no PBX1 variation, mucosa cells revealed the mutated allele in 50% of reads. Segregation analysis of the father showed PBX1 wild-type. The mother was not available for genetic testing. Additionally, we identified a novel heterozygous splice site variant in RET: c.1760-5C&amp;gt;A (NM_020975.4), absent from both patient and population databases. This substitution is predicted to affect splicing at the acceptor site of exon 10. Sanger sequencing demonstrated paternal inheritance. Conclusion Pathogenic PBX1 variants were recently associated with CAKUTHED (Congenital Abnormalities of the Kidney and Urinary Tract with or without Hearing loss, abnormal Ears, or Developmental delay) syndrome (Heidet 2017), characterized by highly variable phenotypes. PBX1 encodes a homeodomain transcription factor taking part in transcriptional regulation during embryonic development. Functional studies suggest disturbed PBX1-dependent transactivation ability and altered nuclear translocation, resulting in abnormal interactions between PBX1 proteins and cofactors (Slavotinek 2017). Prevailing PBX1 expression in embryonic compared to adult kidneys support an important function in development (Le Tanno 2017). An aberrant splicing effect of the identified RET variant is supported by the fact that the father, who carries the same variant but PBX1 wild-type, has slightly reduced kidneys. Associations between abnormal kidney development and alterations of RET were first described in stillborn fetuses with renal agenesis (Skinner 2008), but also in patients with vesicoureteral reflux (Yang 2008). RET encodes for a receptor tyrosine-protein kinase, which while binding ligands such as GDNF (glial cell-line derived neurotrophic factor) is involved in signaling pathways and plays an important part during organ development. Particularly, the RET/GDNF signaling pathway plays a crucial role during development of the kidneys (Costantini 2010). Functional analyses indicate an altered phosphorylation status of RET as possible causative mechanism. To the best of our knowledge, this case is the first to report on combined PBX1 and RET gene variants associated with mild syndromic renal hypoplasia, likely mitigated by genetic mosaicism.

Fetal renal parenchyma: Evaluation of a novel ultrasound measurement to assess kidney development

Introduction Abnormal fetal growth can adversely impact renal development and is associated with increased risks of developing hypertension and chronic kidney disease later in life. A non-invasive, sensitive method of assessing normal and abnormal fetal kidney development is required. We hypothesise that the fetal renal parenchymal thickness could be used to evaluate the development of the fetal kidneys and provide an indirect estimate of fetal nephron number. This study uses antenatal ultrasound to assess fetal renal parenchymal growth and blood flow to determine if these are affected by abnormal fetal growth. Methods A longitudinal, observational study was conducted at the Townsville Hospital, Townsville, Australia between May 2017 to December 2018. Mixed risk women with an accurately dated, singleton pregnancy underwent a pregnancy ultrasound scan at least every four weeks between 16 and 40 weeks gestation. Renal parenchymal thickness and echogenicity, renal volume, fetal growth biometries, amniotic fluid measurements, renal artery Doppler and other fetal Dopplers were assessed in appropriately grown, fetal growth restriction or large for gestational age fetuses. Results 155 participants were recruited, with 7 participants excluded due to fetal abnormalities. Mixed effects modelling was used so that variations between gestational ages within fetuses and between fetuses was considered. A reference graph was developed for normal fetal renal parenchymal growth. In growth restricted fetuses the renal parenchymal thickness was found to be significantly less when compared to the parenchymal thickness of appropriately grown fetuses. Conclusions Measurement of the renal parenchymal thickness is an innovative method to evaluate the development of the fetal kidneys. This new chart of fetal renal parenchymal thickness may be useful for the diagnosis of nephropathologies and the identification of infants at risk of kidney disease. Fetal growth restriction was found to adversely affect the renal parenchymal growth. This suggests growth restricted fetuses are born with fewer nephrons and are therefore likely to be more susceptible to hypertension and early onset kidney disease later in life.

Cellular and molecular determinants of normal and abnormal kidney development.

Kidneys are bilateral organs required to maintain homeostasis in the body through the regulation of fluid composition and the excretion of metabolic waste products. The initial steps in organ development are characterized by cellular interactions which regulate both the position and number of kidneys formed. Once established, further development is driven by orchestrated interactions between progenitor cell populations which serve to establish both nephrons-the functional unit of the organ which filters the blood-and the complex ramified collecting duct system which transports urine to the bladder. The delicate balance involved in these processes is reflected in the emerging family of genetic or environmental factors which, when perturbed, give rise to defects in organ development or function later in life. This article is categorized under: Vertebrate Organogenesis > From a Tubular Primordium: Branched Birth Defects > Organ Anomalies.

Gene-targeted deletion in mice of the Ets-1 transcription factor, a candidate gene in the Jacobsen syndrome kidney "critical region," causes abnormal kidney development.

Ets-1 is a member of the Ets family of transcription factors and has critical roles in multiple biological functions. Structural kidney defects occur at an increased frequency in Jacobsen syndrome (OMIM #147791), a rare chromosomal disorder caused by deletions in distal 11q, implicating at least one causal gene in distal 11q. In this study, we define an 8.1 Mb "critical region" for kidney defects in Jacobsen syndrome, which spans ~50 genes. We demonstrate that gene-targeted deletion of Ets-1 in mice results in some of the most common congenital kidney defects occurring in Jacobsen syndrome, including: duplicated kidney, hypoplastic kidney, and dilated renal pelvis and calyces. Taken together, our results implicate Ets-1 in normal mammalian kidney development and, potentially, in the pathogenesis of some of the most common types of human structural kidney defects.

Effect of bariatric surgery on urinary sphingolipids in adolescents with severe obesity

BackgroundUntreated severe obesity of adolescents is associated with abnormal kidney function and development of chronic kidney disease. Lipotoxicity due to lipid accumulation in glomeruli might be an important mechanism in the progression of kidney disease in obesity. ObjectiveTo assess subclinical glomerular injury by measuring urinary sphingolipids in adolescents with severe obesity before and after weight loss surgery. We hypothesized that the levels of urinary sphingolipids would be elevated at baseline and improve after weight reduction. SettingCincinnati Children’s Hospital Medical Center, University of Cincinnati. MethodsTen adolescents undergoing bariatric surgery with no microalbuminuria and normal kidney function were selected. Urinary sphingolipids (ceramides, glycosphingolipids, and sphingomyelins) were quantified using ultra performance liquid chromatography electrospray ionization tandem mass spectrometry at baseline and 1 year postoperatively. The levels of sphingolipids were compared with lean and moderately obese controls. ResultsParticipants with severe obesity had a mean baseline body mass index of 50 kg/m2 that decreased to 36 kg/m2 at 1 year postsurgery (28% reduction). Almost all urinary ceramides, glycosphingolipids, and sphingomyelin species were significantly elevated in participants with severe obesity compared with controls at baseline (P<.01). One year after weight loss surgery, levels of urinary sphingolipids improved but were still significantly elevated compared with controls. ConclusionsOur study indicates that severe obesity is associated with increased urinary excretion of sphingolipids despite the absence of microalbuminuria or decreased kidney function. Urinary sphingolipids may therefore represent a marker of early (subclinical) glomerular injury in adolescents with severe obesity.

The renal parenchyma—evaluation of a novel ultrasound measurement to assess fetal renal development: protocol for an observational longitudinal study

IntroductionDisorders of fetal growth, such as intrauterine growth restriction (IUGR) and large for gestational age (LGA), have been found to have a profound effect on the development of the fetal...

Impact of maternal cigarette smoke exposure on brain and kidney health outcomes in female offspring.

Increased oxidative stress in the brain can lead to increased sympathetic tone that may further induce kidney dysfunction. Previously we have shown that maternal cigarette smoke exposure (SE) leads to significantly increased oxidative stress and inflammation in both brain and kidney, as well as reduced brain and kidney mitochondrial activity. This is closely associated with significant kidney underdevelopment and abnormal function in adulthood in the male offspring. This study aimed to investigate the impact of maternal SE on brain and kidney health in the female offspring. In this study, the mouse dams were exposed to two cigarettes, twice daily for 6weeks prior to gestation, during pregnancy and lactation. Brains and kidneys from the female offspring were collected at 20days (P20) and 13weeks (W13) and were subject to further analysis. We found that mRNA expression of brain inflammatory markers interleukin-1 receptor and Toll-like receptor 4 were significantly increased in the SE offspring at both P20 and W13. Their brain mitochondrial activity markers were however increased at W13 with increased antioxidant activity. Kidney development and function in the female SE offspring were not different from the control offspring. We concluded that although brain inflammatory markers were upregulated in the SE female offspring, they were protected from some of the indicators of brain oxidative stress, such as endogenous antioxidant and mitochondrial dysfunction, as well as abnormal kidney development and function in adulthood.

Control of mitochondrial function and cell growth by the atypical cadherin Fat1

Mitochondrial products such as ATP, reactive oxygen species, and aspartate are key regulators of cellular metabolism and growth. Abnormal mitochondrial function compromises integrated growth-related processes such as development and tissue repair, as well as homeostatic mechanisms that counteract ageing and neurodegeneration, cardiovascular disease, and cancer. Physiologic mechanisms that control mitochondrial activity in such settings remain incompletely understood. Here we show that the atypical Fat1 cadherin acts as a molecular 'brake' on mitochondrial respiration that regulates vascular smooth muscle cell (SMC) proliferation after arterial injury. Fragments of Fat1 accumulate in SMC mitochondria, and the Fat1 intracellular domain interacts with multiple mitochondrial proteins, including critical factors associated with the inner mitochondrial membrane. SMCs lacking Fat1 (Fat1KO) grow faster, consume more oxygen for ATP production, and contain more aspartate. Notably, expression in Fat1KO cells of a modified Fat1 intracellular domain that localizes exclusively to mitochondria largely normalizes oxygen consumption, and the growth advantage of these cells can be suppressed by inhibition of mitochondrial respiration, which suggest that a Fat1-mediated growth control mechanism is intrinsic to mitochondria. Consistent with this idea, Fat1 species associate with multiple respiratory complexes, and Fat1 deletion both increases the activity of complexes I and II and promotes the formation of complex-I-containing supercomplexes. In vivo, Fat1 is expressed in injured human and mouse arteries, and inactivation of SMC Fat1 in mice potentiates the response to vascular damage, with markedly increased medial hyperplasia and neointimal growth, and evidence of higher SMC mitochondrial respiration. These studies suggest that Fat1 controls mitochondrial activity to restrain cell growth during the reparative, proliferative state induced by vascular injury. Given recent reports linking Fat1 to cancer, abnormal kidney and muscle development, and neuropsychiatric disease, this Fat1 function may have importance in other settings of altered cell growth and metabolism.

Kidney epithelium specific deletion of kelch-like ECH-associated protein 1 (Keap1) causes hydronephrosis in mice.

BackgroundTranscription factor Nrf2 protects from experimental acute kidney injury (AKI) and is promising to limit progression in human chronic kidney disease (CKD) by upregulating multiple antioxidant genes. We recently demonstrated that deletion of Keap1, the endogenous inhibitor of Nrf2, in T lymphocytes significantly protects from AKI. In this study, we investigated the effect of Keap1 deletion on Nrf2 mediated antioxidant response in the renal tubular epithelial cells.MethodsWe deleted Keap1 exon 2 and 3 in the renal tubular epithelial cells by crossing Ksp-Cre mice with Keap1 floxed (Keap1f/f) mice. Deletion of Keap1 gene in the kidney epithelial cells of Ksp-Keap1-/- mice and its effect on Nrf2 target gene expression was performed using PCR and real-time PCR respectively. Histological evaluation was performed on H&E stained sections. Complete blood count, serum and urine analysis were performed to assess systemic effects of defective kidney development. Student’s T test was used to determine statistical difference between the groups.ResultsKsp-Cre resulted in the deletion of Keap1 exon 2 and 3 and subsequent upregulation of Nrf2 target genes, Nqo1, Gclm and Gclc in the kidney epithelial cells of Ksp-Keap1-/- mice at baseline. Renal epithelial cell specific deletion of Keap1 in Ksp-Keap1-/- mice caused marked renal pelvic expansion and significant compression of medullary parenchyma consistent with hydronephrosis in both (3 month-old) males and females. Kidneys from 6 month-old Ksp-Keap1-/- mice showed progressive hydronephrosis. Hematological, biochemical and urinary analysis showed significantly higher red blood cell count (p = 0.04), hemoglobin (p = 0.01), hematocrit (p = 0.02), mean cell volume (p = 0.02) and mean cell hemoglobin concentration (p = 0.003) in Ksp-Keap1-/- mice in comparison to Keap1f/f mice.ConclusionsThese unexpected findings demonstrate that Keap1 deletion in renal tubular epithelial cells results in an abnormal kidney development consistent with hydronephrosis and reveals a novel Keap1 mediated signaling pathway in renal development.

Dynamin Binding Protein (Tuba) Deficiency Inhibits Ciliogenesis and Nephrogenesis in Vitro and in Vivo

Dysfunction of renal primary cilia leads to polycystic kidney disease. We previously showed that the exocyst, a protein trafficking complex, is essential for ciliogenesis and regulated by multiple Rho and Rab family GTPases, such as Cdc42. Cdc42 deficiency resulted in a disruption of renal ciliogenesis and a polycystic kidney disease phenotype in zebrafish and mice. Here we investigate the role of Dynamin binding protein (also known as Tuba), a Cdc42-specific guanine nucleotide exchange factor, in ciliogenesis and nephrogenesis using Tuba knockdown Madin-Darby canine kidney cells and tuba knockdown in zebrafish. Tuba depletion resulted in an absence of cilia, with impaired apical polarization and inhibition of hepatocyte growth factor-induced tubulogenesis in Tuba knockdown Madin-Darby canine kidney cell cysts cultured in a collagen gel. In zebrafish, tuba was expressed in multiple ciliated organs, and, accordingly, tuba start and splice site morphants showed various ciliary mutant phenotypes in these organs. Co-injection of tuba and cdc42 morpholinos at low doses, which alone had no effect, resulted in genetic synergy and led to abnormal kidney development with highly disorganized pronephric duct cilia. Morpholinos targeting two other guanine nucleotide exchange factors not known to be in the Cdc42/ciliogenesis pathway and a scrambled control morpholino showed no phenotypic effect. Given the molecular nature of Cdc42 and Tuba, our data strongly suggest that tuba and cdc42 act in the same ciliogenesis pathway. Our study demonstrates that Tuba deficiency causes an abnormal renal ciliary and morphogenetic phenotype. Tuba most likely plays a critical role in ciliogenesis and nephrogenesis by regulating Cdc42 activity.