Low nephron number results in an increased risk of developing hypertension and chronic kidney disease. Intrauterine growth restriction is associated with a nephron deficit in humans, and is commonly caused by placental insufficiency, which results in fetal hypoxia. The underlying mechanisms by which hypoxia impacts kidney development are poorly understood. microRNA‐210 is the most consistently induced microRNA in hypoxia and is known to promote cell survival in a hypoxic environment. In this study, the role of microRNA‐210 in kidney development was evaluated using a global microRNA‐210 knockout mouse. A male‐specific 35% nephron deficit in microRNA‐210 knockout mice was observed. Wnt/β‐catenin signaling, a pathway crucial for nephron differentiation, was misregulated in male kidneys with increased expression of the canonical Wnt target lymphoid enhancer binding factor 1. This coincided with increased expression of caspase‐8‐associated protein 2, a known microRNA‐210 target and apoptosis signal transducer. Together, these data are consistent with a sex‐specific requirement for microRNA‐210 in kidney development.
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 versus 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 versus controls. Mutant VUJs that refluxed had low inserting ureters and shortened intravesicular tunnels versus 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.
IntroductionTransient hyperphosphatasemia (TH) is a rare benign condition of elevated serum alkaline phosphatase (AP) levels seen in healthy children. TH has been reported to occur in pediatric solid organ transplants, including kidney transplant patients. Little is known about TH in pediatric kidney transplant patients. ObjectiveTo evaluate the incidence and natural history of TH in pediatric kidney transplant patients. MethodsA retrospective chart review of patients < 18 years of age who underwent kidney transplantation at the University of Pittsburgh Medical Center (UPMC) Children's Hospital of Pittsburgh between 2008 and 2019 was performed to identify patients with TH, defined as an AP level greater than 1,000 IU/L. Exclusion criteria included repeat kidney transplants or kidney transplant as part of a multiorgan transplant. ResultsOne hundred seventy-six patients underwent a solitary kidney transplant, of which 87 were less than 12 years of age. Eleven patients (6.5%) were found to have TH, all of whom were < 12 years of age (12.8%) (median age: 5 years; range: 1 -11 years). The median AP level prior to transplant was 183 IU/L (range: 104 -309 IU/L) and the median peak AP was > 2,300 IU/L (range: 1,227 -4,912 IU/L). The median time from a kidney transplant to the diagnosis of TH was 0.6 years (range: 0.3 to 7.7 years). The median length of time that TH persisted was 0.5 years (range: 0.2 to 0.9 years). The median estimated glomerular filtration rate (GFR) at the time of diagnosis of TH was 84 mL/min/1.73m 2 per the bedside Schwartz equation (range: 45 to 152 mL/min/1.73m 2 ). One patient had variable AP levels over nine months prior to resolution; the other 10 patients had a solitary peak of AP prior to resolution. No patient required treatment of elevated AP levels and the TH resolved spontaneously without intervention. No patients had significant abnormalities of markers of metabolic bone disease or were on active vitamin D, calcium, or phosphorus supplements. Two patients reported bone pain, and one patient was found to have avascular necrosis of the hip. ConclusionsTH is a relatively common finding following a pediatric kidney transplant in pre-pubertal children less than 12 years of age. It primarily occurs in the first year following a kidney transplant and usually resolves without recurrence within one year of onset.
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