Extended Interval Aminoglycoside Treatment for Klebsiella Pneumoniae Endocarditis in an Extremely Low Birth Weight Neonate

Infective endocarditis (IE) in neonates is associated with high mortality and incidence has been increasing over the past two decades. The majority of very low birth weight infants will be treated with at least one nephrotoxic medication during their hospital course. Over one-quarter of very low birth weight neonates exposed to gentamicin may develop acute kidney injury (AKI); this is particularly worrisome as AKI is an independent factor associated with increased neonatal mortality and increased length of stay. AKI during periods of neonatal nephrogenesis, which continues until 34–36 weeks postmenstrual age, may also have serious effects on the long-term nephron development which subsequently puts infants at risk of chronic kidney disease. Extended interval (EI) aminoglycoside (AMG) dosing has been used for decades in adult populations and has proven to reduce AKI while being at least as effective as traditional dosing, although there is limited published research for using an EI AMG in endocarditis in adults or pediatric patients. We describe an extremely low birth weight neonate, born preterm at 24 weeks gestation treated for Klebsiella pneumoniae IE that required AMG therapy who also had concurrent AKI. We utilized EI AMG combination therapy for treatment of Klebsiella pneumoniae endocarditis with good outcome and encourage others to report their experiences to improve our knowledge of EI AMG in this population.

Esrrγa regulates nephron development and ciliogenesis by controlling prostaglandin synthesis and cooperation with Ppargc1a

Cilia are essential for the ontogeny and function of many tissues, including the kidney. In mammals, Esrrγ has been previously established as a significant determinant of renal health, with decreased expression linked to age related dysfunction, cyst formation, and kidney disease. Here, we report that the Esrrγ vertebrate ortholog estrogen related receptor gamma a (esrrγa) is essential for proper cell fate choice within kidney functional units (nephrons) as well as ciliogenesis. Deficiency of esrrγa resulted in nephrons with alterations in proximodistal segmentation and a decreased multiciliated epithelial cell populace. Surprisingly, esrrγa deficiency disrupted renal ciliogenesis and caused a similar abrogation within the developing node and otic vesicle—all defects that occurred independently of changes in cell polarity or basal body organization. These phenotypes were consistent with interruptions in prostaglandin signaling, and we found that ciliogenesis was rescued in esrrγa deficient embryos with exogenous PGE2 or through overexpression of the cyclooxygenase enzyme Ptgs1. Through genetic interaction studies, we found that peroxisome proliferator–activated receptor gamma, coactivator 1 alpha (ppargc1a), which acts upstream of Ptgs1–mediated prostaglandin synthesis, has a synergistic relationship with esrrγa in the ciliogenic pathway. These data position Esrrγa as a novel link between ciliogenesis and nephrogenesis through regulation of prostaglandin signaling and cooperation with Ppargc1a, and highlight Esrrγa as a potential new therapeutic target for ciliopathies.

Slit2-Robo Signaling Promotes Glomerular Vascularization and Nephron Development

BackgroundKidney function requires continuous blood filtration by glomerular capillaries. Disruption of glomerular vascular development or maintenance contributes to the pathogenesis of kidney diseases, but the signaling events regulating renal endothelium development remain incompletely understood. Here, we discovered a novel role of Slit2-Robo signaling in glomerular vascularization. Slit2 is a secreted polypeptide that binds to transmembrane Robo receptors and regulates axon guidance as well as ureteric bud branching and angiogenesis.MethodsWe performed Slit2-alkaline phosphatase binding to kidney cryosections from mice with or without tamoxifen-inducible Slit2 or Robo1 and -2 deletions, and we characterized the phenotypes using immunohistochemistry, electron microscopy, and functional intravenous dye perfusion analysis.ResultsOnly the glomerular endothelium, but no other renal endothelial compartment, responded to Slit2 in the developing kidney vasculature. Induced Slit2 gene deletion or Slit2 ligand trap at birth affected nephrogenesis and inhibited vascularization of developing glomeruli by reducing endothelial proliferation and migration, leading to defective cortical glomerular perfusion and abnormal podocyte differentiation. Global and endothelial-specific Robo deletion showed that both endothelial and epithelial Robo receptors contributed to glomerular vascularization.ConclusionsOur study provides new insights into the signaling pathways involved in glomerular vascular development and identifies Slit2 as a potential tool to enhance glomerular angiogenesis.

The Expression of Transcription Factors in Fetal Lamb Kidney

(1) Background: Renal development involves frequent expression and loss of transcription factors, resulting in the activation of genes. Wilms’ tumor 1 (WT1), hepatocyte nuclear factor-1-beta (HNF1β), and paired box genes 2 and 8 (Pax2 and Pax8) play an important role in renal development. With this in vivo study, we examined the period and location of expression of these factors in renal development. (2) Methods: Fetal lamb kidneys (50 days from gestation to term) and adult ewe kidneys were evaluated by hematoxylin and eosin staining. Serial sections were subjected to immunohistochemistry for WT1, HNF1β, Pax2, and Pax8. (3) Results: Pax2, Pax8, and HNF1β expression was observed in the ureteric bud and collecting duct epithelial cells. We observed expression of WT1 alone in metanephric mesenchymal cells, glomerular epithelial cells, and interstitial cells in the medullary rays and Pax8 and HNF1β expression in tubular epithelial cells. WT1 was highly expressed in cells more proximal to the medulla in renal vesicles and in C- and S-shaped bodies. Pax2 was expressed in the middle and peripheral regions, and HNF1β in cells in the region in the middle of these. (4) Conclusions: WT1 is involved in nephron development. Pax2, Pax8, and HNF1β are involved in nephron maturation and the formation of peripheral collecting ducts from the Wolffian duct.

TrkC Is Essential for Nephron Function and Trans-Activates Igf1R Signaling

BackgroundInjury to kidney podocytes often results in chronic glomerular disease and consecutive nephron malfunction. For most glomerular diseases, targeted therapies are lacking. Thus, it is important to identify novel signaling pathways contributing to glomerular disease. Neurotrophic tyrosine kinase receptor 3 (TrkC) is expressed in podocytes and the protein transmits signals to the podocyte actin cytoskeleton.MethodsNephron-specific TrkC knockout (TrkC-KO) and nephron-specific TrkC-overexpressing (TrkC-OE) mice were generated to dissect the role of TrkC in nephron development and maintenance.ResultsBoth TrkC-KO and TrkC-OE mice exhibited enlarged glomeruli, mesangial proliferation, basement membrane thickening, albuminuria, podocyte loss, and aspects of FSGS during aging. Igf1 receptor (Igf1R)–associated gene expression was dysregulated in TrkC-KO mouse glomeruli. Phosphoproteins associated with insulin, erb-b2 receptor tyrosine kinase (Erbb), and Toll-like receptor signaling were enriched in lysates of podocytes treated with the TrkC ligand neurotrophin-3 (Nt-3). Activation of TrkC by Nt-3 resulted in phosphorylation of the Igf1R on activating tyrosine residues in podocytes. Igf1R phosphorylation was increased in TrkC-OE mouse kidneys while it was decreased in TrkC-KO kidneys. Furthermore, TrkC expression was elevated in glomerular tissue of patients with diabetic kidney disease compared with control glomerular tissue.ConclusionsOur results show that TrkC is essential for maintaining glomerular integrity. Furthermore, TrkC modulates Igf-related signaling in podocytes.

Cell-Cell Adhesion During Nephron Development Is Driven by Wnt/PCP Formin Daam1

SUMMARYE-cadherin junctions facilitate the assembly and disassembly of cell-cell contacts that drive development and homeostasis of epithelial tissues. The stability of E-cadherin-based junctions highly depends on their attachment to the actin cytoskeleton, but little is known about how the assembly of junctional actin filaments is regulated. Formins are a conserved group of proteins responsible for the formation and elongation of filamentous actin (F-actin). In this study, using Xenopus embryonic kidney and Madin-Darby canine kidney (MDCK) cells, we investigate the role of the Wnt/ planar cell polarity (PCP) formin protein Daam1 (Dishevelled-associated activator of morphogenesis 1) in regulating E-cadherin based intercellular adhesion. Using live imaging we show that Daam1 localizes to newly formed cell-cell contacts in the developing nephron. Furthermore, analyses of junctional F-actin upon Daam1 depletion indicate a decrease in microfilament localization and their slowed turnover. We also show that Daam1 is necessary for efficient and timely localization of junctional E-cadherin, which is mediated by Daam1’s formin homology domain 2 (FH2). Finally, we establish that Daam1 signaling is essential for promoting organized movement of renal cells. This study demonstrates that Daam1 formin junctional activity is critical for epithelial tissue organization.

Nephron Progenitor Maintenance Is Controlled through Fibroblast Growth Factors and Sprouty1 Interaction

BackgroundNephron progenitor cells (NPCs) give rise to all segments of functional nephrons and are of great interest due to their potential as a source for novel treatment strategies for kidney disease. Fibroblast growth factor (FGF) signaling plays pivotal roles in generating and maintaining NPCs during kidney development, but little is known about the molecule(s) regulating FGF signaling during nephron development. Sprouty 1 (SPRY1) is an antagonist of receptor tyrosine kinases. Although SPRY1 antagonizes Ret-GDNF signaling, which modulates renal branching, its role in NPCs is not known.MethodsSpry1, Fgf9, and Fgf20 compound mutant animals were used to evaluate kidney phenotypes in mice to understand whether SPRY1 modulates FGF signaling in NPCs and whether FGF8 functions with FGF9 and FGF20 in maintaining NPCs.ResultsLoss of one copy of Spry1 counters effects of the loss of Fgf9 and Fgf20, rescuing bilateral renal agenesis premature NPC differentiation, NPC proliferation, and cell death defects. In the absence of SPRY1, FGF9, and FGF20, another FGF ligand, FGF8, promotes nephrogenesis. Deleting both Fgf8 and Fgf20 results in kidney agenesis, defects in NPC proliferation, and cell death. Deleting one copy of Fgf8 reversed the effect of deleting one copy of Spry1, which rescued the renal agenesis due to loss of Fgf9 and Fgf20.ConclusionsSPRY1 expressed in NPCs modulates the activity of FGF signaling and regulates NPC stemness. These findings indicate the importance of the balance between positive and negative signals during NPC maintenance.

Conserved and Divergent Molecular and Anatomic Features of Human and Mouse Nephron Patterning

The nephron is the functional unit of the kidney, but the mechanism of nephron formation during human development is unclear. We conducted a detailed analysis of nephron development in humans and mice by immunolabeling, and we compared human and mouse nephron patterning to describe conserved and divergent features. We created protein localization maps that highlight the emerging patterns along the proximal–distal axis of the developing nephron and benchmark expectations for localization of functionally important transcription factors, which revealed unanticipated cellular diversity. Moreover, we identified a novel nephron subdomain marked by Wnt4 expression that we fate-mapped to the proximal mature nephron. Significant conservation was observed between human and mouse patterning. We also determined the time at which markers for mature nephron cell types first emerge—critical data for the renal organoid field. These findings have conceptual implications for the evolutionary processes driving the diversity of mammalian organ systems. Furthermore, these findings provide practical insights beyond those gained with mouse and rat models that will guide in vitro efforts to harness the developmental programs necessary to build human kidney structures.