Renal-specific oxidoreductase biphasic expression under high glucose ambience during fetal versus neonatal development

Effects of Environmental Conditions on Nephron Number: Modeling Maternal Disease and Epigenetic Regulation in Renal Development

A growing body of evidence suggests that low nephron numbers at birth can increase the risk of chronic kidney disease or hypertension later in life. Environmental stressors, such as maternal malnutrition, medication and smoking, can influence renal size at birth. Using metanephric organ cultures to model single-variable environmental conditions, models of maternal disease were evaluated for patterns of developmental impairment. While hyperthermia had limited effects on renal development, fetal iron deficiency was associated with severe impairment of renal growth and nephrogenesis with an all-proximal phenotype. Culturing kidney explants under high glucose conditions led to cellular and transcriptomic changes resembling human diabetic nephropathy. Short-term high glucose culture conditions were sufficient for long-term alterations in DNA methylation-associated epigenetic memory. Finally, the role of epigenetic modifiers in renal development was tested using a small compound library. Among the selected epigenetic inhibitors, various compounds elicited an effect on renal growth, such as HDAC (entinostat, TH39), histone demethylase (deferasirox, deferoxamine) and histone methyltransferase (cyproheptadine) inhibitors. Thus, metanephric organ cultures provide a valuable system for studying metabolic conditions and a tool for screening for epigenetic modifiers in renal development.

Catalase prevents maternal diabetes-induced perinatal programming via the Nrf2-HO-1 defense system

We investigated whether overexpression of catalase (CAT) in renal proximal tubular cells (RPTCs) could prevent the programming of hypertension and kidney disease in the offspring of dams with maternal diabetes. Male offspring of nondiabetic and diabetic dams from two transgenic (Tg) lines (Hoxb7-green fluorescent protein [GFP]-Tg [controls] and Hoxb7/CAT-GFP-Tg, which overexpress CAT in RPTCs) were studied from the prenatal period into adulthood. Nephrogenesis, systolic blood pressure, renal hyperfiltration, kidney injury, and reactive oxygen species (ROS) generation were assessed. Gene expression of transforming growth factor-β1 (TGF-β1), nuclear factor erythroid 2p45-related factor-2 (Nrf2), and heme oxygenase-1 (HO-1) was tested in both in vitro and in vivo studies. Renal dysmorphogenesis was observed in offspring of Hoxb7-GFP-Tg dams with severe maternal diabetes; the affected male offspring displayed higher renal ROS generation and developed hypertension and renal hyperfiltration as well as renal injury with heightened TGF-β1 expression in adulthood. These changes were ameliorated in male offspring of diabetic Hoxb7/CAT-GFP-Tg dams via the Nrf2-HO-1 defense system. CAT promoted Nrf2 nuclear translocation and HO-1 gene expression, seen in both in vitro and in vivo studies. In conclusion, CAT overexpression in the RPTCs ameliorated maternal diabetes-induced perinatal programming, mediated, at least in part, by triggering the Nrf2-HO-1 defense system.

The role of reactive oxygen species in apoptosis of the diabetic kidney

Increased levels of reactive oxygen species (ROS) by hyperglycemia can induce apoptosis of renal cells and diabetic nephropathy. The redox balance in the renal cell seems, therefore, of the utmost importance. ROS-mediated apoptosis may be further aggravated by an inadequate cytoprotective response against ROS. When there are insufficient cytoprotective and ROS scavenging molecules, ROS lead to considerable cellular damage and to a point of no return in apoptosis. Induction of cytoprotective proteins may prevent or attenuate apoptosis, renal cell injury, and finally diabetic nephropathy. Here, we discuss some mechanisms of apoptosis and several strategies that have been probed to ameliorate, or to prevent apoptosis in the diabetic kidney.

Transcription factors in the pathogenesis of diabetic nephropathy

Approximately a third of patients with diabetes develop diabetic kidney disease, and diabetes is the leading cause of end-stage renal disease in most developed countries. Hyperglycaemia is known to activate genes that ultimately lead to extracellular matrix accumulation, the hallmark of diabetic nephropathy. Several transcription factors have been implicated in glucose-mediated expression of genes involved in diabetic nephropathy. This review focuses on the transcription factors upstream stimulatory factors 1 and 2 (USF1 and 2), activator protein 1 (AP-1), nuclear factor (NF)-kappaB, cAMP-response-element-binding protein (CREB), nuclear factor of activated T cells (NFAT), and stimulating protein 1 (Sp1). In response to high glucose, several of these transcription factors regulate the gene encoding the profibrotic cytokine transforming growth factor beta, as well as genes for a range of other proteins implicated in inflammation and extracellular matrix turnover, including thrombospondin 1, the chemokine CCL2, osteopontin, fibronectin, decorin, plasminogen activator inhibitor 1 and aldose reductase. Identifying the molecular mechanisms by which diabetic nephropathy occurs has important clinical implications as therapies can then be tailored to target those at risk. Strategies to specifically target transcription factor activation and function may be employed to halt the progression of diabetic nephropathy.

Maternal diabetes modulates renal morphogenesis in offspring

Maternal diabetes leads to an adverse in utero environment, but whether maternal diabetes impairs nephrogenesis is unknown. Diabetes was induced with streptozotocin in pregnant Hoxb7-green fluorescence protein mice at embryonic day 13, and the offspring were examined at several time points after birth. Compared with offspring of nondiabetic controls, offspring of diabetic mice had lower body weight, body size, kidney weight, and nephron number. The observed renal dysmorphogenesis may be the result of increased apoptosis, because immunohistochemical analysis revealed significantly more apoptotic podocytes as well as increased active caspase-3 immunostaining in the renal tubules compared with control mice. Regarding potential mediators of these differences, offspring of diabetic mice had increased expression of intrarenal angiotensinogen and renin mRNA, upregulation of NF-kappaB isoforms p50 and p65, and activation of the NF-kappaB pathway. In conclusion, maternal diabetes impairs nephrogenesis, possibly via enhanced intrarenal activation of the renin-angiotensin system and NF-kappaB signaling.

Pax-2 and N-myc regulate epithelial cell proliferation and apoptosis in a positive autocrine feedback loop

Both paired homeo box-2 (Pax-2) and N-myc genes play pivotal roles in renal morphogenesis via their effects on cell proliferation and differentiation, but whether and how they interact have not been addressed. In the present study, we investigated such a potential interaction using embryonic renal cells in vitro. Mouse embryonic mesenchymal (MK4) cells stably transfected with Pax-2 cDNA in sense (+) or antisense (-) orientation were used for experiments. Pax-2 promoter activity was monitored by luciferase assay. Reactive oxygen species (ROS) generation, cell proliferation, and cell apoptosis were evaluated. We found that Pax-2 and N-myc gene expression were upregulated and downregulated in Pax-2 (+) and Pax-2 (-) stable transformants, respectively. ROS generation and apoptosis were significantly reduced both in Pax-2 (+) transformants compared with Pax-2 (-) transformants and in naïve MK4 cells cultured in either normal- (5 mM) or high-glucose (25 mM) medium. Transient transfection of N-myc cDNA into Pax-2 (-) stable transformants restored Pax-2 gene expression and prevented ROS generation induced by high glucose. Our data demonstrate that Pax-2 gene overexpression prevents hyperglycemia-induced apoptosis, and N-myc appears to provide a positive autocrine feedback on Pax-2 gene expression in embryonic mesenchymal cells.

Reactive oxygen species in the presence of high glucose alter ureteric bud morphogenesis

Renal malformations are a major cause of childhood renal failure. During the development of the kidney, ureteric bud (UB) branching morphogenesis is critical for normal nephrogenesis. These studies investigated whether renal UB branching morphogenesis is altered by a high ambient glucose environment and studied underlying mechanism(s). Kidney explants that were isolated from different periods of gestation (embryonic days 12 to 18) from Hoxb7-green fluorescence protein mice were cultured for 24 h in either normal d-glucose (5 mM) or high d-glucose (25 mM) medium with or without various inhibitors. Alterations in renal morphogenesis were assessed by fluorescence microscopy. Paired-homeobox 2 (Pax-2) gene expression was determined by real-time quantitative PCR, Western blotting, and immunohistology. The results revealed that high d-glucose (25 mM) specifically stimulates UB branching morphogenesis via Pax-2 gene expression, whereas other glucose analogs, such as d-mannitol, l-glucose, and 2-deoxy-d-glucose, had no effect. The stimulatory effect of high glucose on UB branching was blocked in the presence of catalase and inhibitors of NADPH oxidase, mitochondrial electron transport chain complex I, and Akt signaling. Moreover, in in vivo studies, it seems that high glucose induces, via Pax-2 (mainly localized in UB), acceleration of UB branching but not nephron formation. Taken together, these data demonstrate that high glucose alters UB branching morphogenesis. This occurs, at least in part, via reactive oxygen species generation, activation of Akt signaling, and upregulation of Pax-2 gene expression.

Reactive oxygen species and nuclear factor-kappa B pathway mediate high glucose-induced Pax-2 gene expression in mouse embryonic mesenchymal epithelial cells and kidney explants

Diabetic mellitus confers a major risk of congenital malformations, and is associated with diabetic embryopathy, affecting multiple organs including the kidney. The DNA paired box-2 (Pax-2) gene is essential in nephrogenesis. We investigated whether high glucose alters Pax-2 gene expression and aimed to delineate its underlying mechanism(s) of action using both in vitro (mouse embryonic mesenchymal epithelial cells (MK4) and ex vivo (kidney explant from Hoxb7-green florescent protein (GFP) mice) approaches. Pax-2 gene expression was determined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunofluorescent staining. A fusion gene containing the full-length 5'-flanking region of the human Pax-2 promoter linked to a luciferase reporter gene, pGL-2/hPax-2, was transfected into MK4 cells with or without dominant negative IkappaBalpha (DN IkappaBalpha) cotransfection. Fusion gene expression level was quantified by cellular luciferase activity. Reactive oxygen species (ROS) generation was measured by lucigenin assay. Embryonic kidneys from Hoxb7-GFP mice were cultured ex vivo. High D(+) glucose (25 mM), compared to normal glucose (5 mM), specifically induced Pax-2 gene expression in MK4 cells and kidney explants. High glucose-induced Pax-2 gene expression is mediated, at least in part, via ROS generation and activation of the nuclear factor kappa B signaling pathway, but not via protein kinase C, p38 mitogen-activated protein kinase (MAPK), and p44/42 MAPK signaling.

Modulation of renal-specific oxidoreductase/myo-inositol oxygenase by high-glucose ambience

Biological properties of renal-specific oxidoreductase (RSOR), characteristics of its promoter, and underlying mechanisms regulating its expression in diabetes were analyzed. RSOR expression, normally confined to the renal cortex, was markedly increased and extended into the outer medullary tubules in db/db mice, a model of type 2 diabetes. Exposure of LLCPK cells to d-glucose resulted in a dose-dependent increase in RSOR expression and its enzymatic activity. The latter was related to one of the glycolytic enzymes, myo-inositol oxygenase. The increase in activity was in proportion to serum glucose concentration. The RSOR expression also increased in cells treated with various organic osmolytes, e.g., sorbitol, myoinositol, and glycerolphosphoryl-choline and H(2)O(2). Basal promoter activity was confined to -1,252 bp upstream of ATG, and it increased with the treatment of high glucose and osmolytes. EMSAs indicated an increased binding activity with osmotic-, carbohydrate-, and oxidant-response elements in cells treated with high glucose and was abolished by competitors. Supershifts, detected by anti-nuclear factor of activated T cells, and carbohydrate-response-element-binding protein established the binding specificity. Nuclear factor of activated T cells tonicity-enhancer-binding protein and carbohydrate-response-element-binding protein had increased nuclear expression in cells treated with high glucose. The activity of osmotic-response element exhibited a unique alternate binding pattern, as yet unreported in osmoregulatory genes. Data indicate that RSOR activity is modulated by diverse mechanisms, and it is endowed with dual properties to channel glucose intermediaries, characteristic of hepatic aldehyde reductases, and to maintain osmoregulation, a function of renal medullary genes, e.g., aldose reductase, in diabetes.