Clinical Outcomes of Acutely Ill Children According to Cycle Threshold Values of Respiratory Viruses Detected by Multiplex PCR Testing.

In this cohort study of 800 children attending a pediatric emergency department at Oulu University Hospital, Finland with fever or respiratory symptoms, the cycle threshold values of point-of-care multiplex polymerase chain reaction testing for respiratory viruses were not associated with hospitalization, respiratory support, or need for intensive care.

Severe hospital-acquired hyponatremia in acutely ill children receiving moderately hypotonic fluids.

BACKGROUND: Hypotonic fluids have been associated with hospital-acquired hyponatremia. The incidence of life-threatening severe hyponatremia associated with hypotonic fluids has not been evaluated. METHODS: This was a population-based cohort study of 46,518 acutely ill children 15 years of age or under who visited the pediatric emergency department (ED) at Oulu University Hospital, Finland, between 2007 and 2017. We retrieved all electrolyte measurements from the comprehensive electronic laboratory system and reviewed medical records for all patients with severe hyponatremia. RESULTS: The overall occurrence of severe hyponatremia (serum sodium < 125 mmol/L) was found in 27 out of 46,518 acutely ill children (0.06%, 95% confidence interval 0.04-0.08%). After admission, severe hyponatremia developed in seven of 6,984 children receiving moderately hypotonic fluid therapy (0.1%, 95% confidence interval 0.04-0.2%), usually within 8 h of admission. All children who developed severe hyponatremia during hospitalization were severely ill. CONCLUSION: In this register-based cohort study of children presenting to the ED, severe hyponatremia developed in one of 998 acutely ill children receiving moderately hypotonic fluid therapy. A higher resolution version of the Graphical abstract is available as Supplementary information.

CD146(+) cells are essential for kidney vasculature development.

The kidney vasculature is critical for renal function, but its developmental assembly mechanisms remain poorly understood and models for studying its assembly dynamics are limited. Here, we tested whether the embryonic kidney contains endothelial cells (ECs) that are heterogeneous with respect to VEGFR2/Flk1/KDR, CD31/PECAM, and CD146/MCAM markers. Tie1Cre;R26R(YFP)-based fate mapping with a time-lapse in embryonic kidney organ culture successfully depicted the dynamics of kidney vasculature development and the correlation of the process with the CD31(+) EC network. Depletion of Tie1(+) or CD31(+) ECs from embryonic kidneys, with either Tie1Cre-induced diphtheria toxin susceptibility or cell surface marker-based sorting in a novel dissociation and reaggregation technology, illustrated substantial EC network regeneration. Depletion of the CD146(+) cells abolished this EC regeneration. Fate mapping of green fluorescent protein (GFP)-marked CD146(+)/CD31(-) cells indicated that they became CD31(+) cells, which took part in EC structures with CD31(+) wild-type ECs. EC network development depends on VEGF signaling, and VEGF and erythropoietin are expressed in the embryonic kidney even in the absence of any external hypoxic stimulus. Thus, the ex vivo embryonic kidney culture models adopted here provided novel ways for targeting renal EC development and demonstrated that CD146(+) cells are critical for kidney vasculature development.

Functional genetic targeting of embryonic kidney progenitor cells ex vivo.

The embryonic mammalian metanephric mesenchyme (MM) is a unique tissue because it is competent to generate the nephrons in response to Wnt signaling. An ex vivo culture in which the MM is separated from the ureteric bud (UB), the natural inducer, can be used as a classic tubule induction model for studying nephrogenesis. However, technological restrictions currently prevent using this model to study the molecular genetic details before or during tubule induction. Using nephron segment-specific markers, we now show that tubule induction in the MM ex vivo also leads to the assembly of highly segmented nephrons. This induction capacity was reconstituted when MM tissue was dissociated into a cell suspension and then reaggregated (drMM) in the presence of human recombinant bone morphogenetic protein 7/human recombinant fibroblast growth factor 2 for 24 hours before induction. Growth factor-treated drMM also recovered the capacity for organogenesis when recombined with the UB. Cell tracking and time-lapse imaging of chimeric drMM cultures indicated that the nephron is not derived from a single progenitor cell. Furthermore, viral vector-mediated transduction of green fluorescent protein was much more efficient in dissociated MM cells than in intact mesenchyme, and the nephrogenic competence of transduced drMM progenitor cells was preserved. Moreover, drMM cells transduced with viral vectors mediating Lhx1 knockdown were excluded from the nephric tubules, whereas cells transduced with control vectors were incorporated. In summary, these techniques allow reproducible cellular and molecular examinations of the mechanisms behind nephrogenesis and kidney organogenesis in an ex vivo organ culture/organoid setting.

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.

Coordination of kidney organogenesis by Wnt signaling.

Several Wnt proteins are expressed in the embryonic kidney during various stages of development. Gene knockout models and ex vivo studies have provided strong evidence that Wnt-mediated signals are essential in renal ontogeny. Perhaps the most critical factors, Wnt9b and Wnt4, function during the early phase when the cap mesenchyme is induced to undergo morphogenesis into a nephron. Wnt11 controls early ureteric bud branching and contributes to the final kidney size. In addition to its inductive role, later on Wnt9b plays a significant role in the convergent extension of the tubular epithelial cells, while Wnt4 signaling controls smooth muscle cell fates in the medulla. Wnt7b has a specific function together with its likely antagonist Dkk1 in controlling the morphogenesis of the renal medulla. The signal-transduction mechanisms of the Wnts in kidney ontogeny have not been resolved, but studies characterizing the downstream signaling pathways are emerging. Aberrant Wnt signaling may lead to kidney diseases ranging from fatal kidney agenesis to more benign phenotypes. Wnt-mediated signaling regulates several critical aspects of kidney development from the early inductive stages to later steps of tubular epithelial maturation.

In vitro induction of nephrogenesis in mouse metanephric mesenchyme with lithium introduction and ureteric bud recombination.

The organ culture setup of embryonic kidney has served as a model of nephrogenesis for several decades. In vitro culture of the mouse metanephric mesenchyme enables easy manipulation and analysis of the tissue and provides information of cellular interactions, morphogenesis, cell differentiation, and molecular biology of the developmental process. The advantages of the tissue culture method include enhanced representativeness of situation in living organism compared to cell culture assays and less demanding and time-consuming possibilities to experimental work compared with in vivo research.