Influence of Different Levels of Lipoic Acid Synthase Gene Expression on Diabetic Nephropathy.

Oxidative stress is implicated in the pathogenesis of diabetic nephropathy (DN) but outcomes of many clinical trials are controversial. To define the role of antioxidants in kidney protection during the development of diabetic nephropathy, we have generated a novel genetic antioxidant mouse model with over- or under-expression of lipoic acid synthase gene (Lias). These models have been mated with Ins2Akita/+ mice, a type I diabetic mouse model. We compare the major pathologic changes and oxidative stress status in two new strains of the mice with controls. Our results show that Ins2Akita/+ mice with under-expressed Lias gene, exhibit higher oxidative stress and more severe DN features (albuminuria, glomerular basement membrane thickening and mesangial matrix expansion). In contrast, Ins2Akita/+ mice with highly-expressed Lias gene display lower oxidative stress and less DN pathologic changes. Our study demonstrates that strengthening endogenous antioxidant capacity could be an effective strategy for prevention and treatment of DN.

Tuberous Sclerosis and Bilateral Renal Angiomyolipomas: A Case Report and Literature Review of Emerging Treatment Strategies.

Tuberous sclerosis complex is a rare multisystemic genetic disorder associated with the development of benign hamartomas. Angiomyolipomas are one such characteristic finding that may be seen in 55-80% of tuberous sclerosis complex patients. While being normally asymptomatic, they can also cause significant morbidity and mortality. We present the case of a patient with tuberous sclerosis complex and recently discovered bilateral renal angiomyolipomas, admitted for hematuria who underwent left renal artery embolization; however, worsening renal function necessitated subsequent nephrectomy. Despite still being mainstays of treatment, invasive interventions are now being recommended for specific patient populations as demonstrated in our case. Emerging strategies targeting the PI3K/AKT/mTOR pathway have been shown to reduce the size of angiomyolipomas and are now used to treat asymptomatic cases >3 cm. Our review discusses these treatment options with the intention of increasing awareness of current recommendations and hopefully leading to increased application of these novel therapies that will reduce the need for invasive interventions.

Acute tubular necrosis (ATN) presenting with an unusually prolonged period of marked polyuria heralded by an abrupt oliguric phase.

A 50-year-old African-American man presented with acute tubular necrosis (ATN) secondary to hypotension from non-typhoid Salmonella gastroenteritis and bacteraemia. The oliguric phase lasted only 24 h followed by prolonged polyuria for 20 days, with urine output in excess of 16 L/day at maximum. As indexed in PubMed this is only the second published case of this nature since 1974, in which an abrupt oliguric phase of 24 h or less heralded prolonged polyuria in ATN. The diagnosis is challenging as fractional excretion of sodium early in the clinical course and rapid normalisation of serum creatinine with intravenous fluids (IVF) may point towards prerenal azotaemia resulting in a premature discharge from hospital. Patients with an abrupt oliguric phase may suffer a secondary renal insult from the profound fluid loss that is to follow and may need inpatient monitoring with supplemental IVF to prevent deleterious outcomes.

Acute Kidney Injury due to Crescentic Glomerulonephritis in a Patient with Polycystic Kidney Disease.

Polycystic kidney disease is an inherited condition, characterized by the development of cysts in the kidney, as well as in other organs. Patients with polycystic kidney can suffer from the same causes of acute kidney injury as the general population. Nephritic syndrome is an uncommon cause of acute kidney injury in the general population and less common in patients with polycystic kidney disease. We report the second case of crescentic glomerulonephritis, causing acute kidney injury, in a patient with polycystic kidney disease.

Connective tissue growth factor (CTGF) expression modulates response to high glucose.

Connective tissue growth factor (CTGF) is an important mediator of fibrosis; emerging evidence link changes in plasma and urinary CTGF levels to diabetic kidney disease. To further ascertain the role of CTGF in responses to high glucose, we assessed the consequence of 4 months of streptozotocin-induced diabetes in wild type (+/+) and CTGF heterozygous (+/-) mice. Subsequently, we studied the influence of glucose on gene expression and protein in mice embryonic fibroblasts (MEF) cells derived from wildtype and heterozygous mice. At study initiation, plasma glucose, creatinine, triglyceride and cholesterol levels were similar between non-diabetic CTGF+/+ and CTGF+/- mice. In the diabetic state, plasma glucose levels were increased in CTGF+/+ and CTGF+/- mice (28.2 3.3 mmol/L vs 27.0 3.1 mmol/L), plasma triglyceride levels were lower in CTGF+/- mice than in CTGF+/+ (0.7 0.2 mmol/L vs 0.5 0.1 mmol/L, p<0.05), but cholesterol was essentially unchanged in both groups. Plasma creatinine was higher in diabetic CTGF+/+ group (11.7±1.2 vs 7.9±0.6 µmol/L p<0.01), while urinary albumin excretion and mesangial expansion were reduced in diabetic CTGF+/- animals. Cortices from diabetic mice (both CTGF +/+ and CTGF +/-) manifested higher expression of CTGF and thrombospondin 1 (TSP1). Expression of nephrin was reduced in CTGF +/+ animals; this reduction was attenuated in CTGF+/- group. In cultured MEF from CTGF+/+ mice, glucose (25 mM) increased expression of pro-collagens 1, IV and XVIII as well as fibronectin and thrombospondin 1 (TSP1). In contrast, activation of these genes by high glucose was attenuated in CTGF+/- MEF. We conclude that induction of Ctgf mediates expression of extracellular matrix proteins in diabetic kidney. Thus, genetic variability in CTGF expression directly modulates the severity of diabetic nephropathy.

GLUT1 regulation of the pro-sclerotic mediators of diabetic nephropathy.

Diabetic glomerulosclerosis is characterized by accumulation of extracellular matrix proteins, mesangial expansion, and tubulointerstitial fibrosis. Hyperglycemia accelerates development of the disease, a direct result of increased intracellular glucose availability. The facilitative glucose transporter GLUT1 mediates mesangial cell glucose flux which leads to activation of signaling cascades favoring glomerulosclerosis, including pathways mediated by angiotensin II (Ang II), transforming growth factor ß (TGF-ß), connective tissue growth factor (CTGF), and vascular endothelial growth factor (VEGF). Ang II has both hemodynamic and metabolic effects directly inducing GLUT1 and/or matrix protein synthesis through diacyl glycerol (DAG) or protein kinase C (PKC) induction, mesangial cell stretch, and/or through transactivation of the epidermal growth factor receptor, the platelet-derived growth factor receptor, and the insulin-like growth factor-1 receptor, all of which may stimulate GLUT1 synthesis via an ERK-mediated pathway. Conversely, inhibition of Ang II effects suppresses GLUT1 and cellular glucose uptake. GLUT1-mediated glucose flux leads to metabolism of glucose via glycolysis, with induction of DAG, PKC, TGF-ß1, CTGF and VEGF. VEGF in turn triggers both GLUT1 and matrix synthesis. New roles for GLUT1-mTOR and GLUT1-mechano-growth factor interactions in diabetic glomerulosclerosis have also recently been suggested. Recent mouse models confirmed roles for GLUT1 in vivo in stimulating glomerular growth factor expression, growth factor receptors and development of glomerulosclerosis. GLUT1 may therefore act in concert with cytokines and growth factors to induce diabetic glomerulosclerosis. Further clarification of the pathways involved may prove useful for the therapy of diabetic nephropathy. New directions for investigation are discussed.

Reduced expression of lipoic acid synthase accelerates diabetic nephropathy.

Oxidative stress contributes to the pathogenesis of diabetic nephropathy. In mitochondria, lipoic acid synthase produces α-lipoic acid, an antioxidant and an essential cofactor in α-ketoacid dehydrogenase complexes, which participate in glucose oxidation and ATP generation. Administration of lipoic acid abrogates diabetic nephropathy in animal models, but whether lower production of endogenous lipoic acid promotes diabetic nephropathy is unknown. Here, we crossed mice heterozygous for lipoic acid synthase deficiency (Lias(+/-)) with Ins2(Akita/+) mice, a well characterized model of type 1 diabetes. Double mutant mice had more overt diabetic nephropathy, including microalbuminuria, glomerular basement thickening, mesangial matrix expansion, and hypertension, compared with Lias(+/+)Ins2(Akita/+) controls. We also identified proximal tubules as a major site for generation of superoxide anions during diabetic nephropathy. Mitochondria in proximal tubular cells were particularly sensitive to damage in diabetic mice with reduced lipoic acid production. These results suggest that lipoic acid synthase deficiency increases oxidative stress and accelerates the development of diabetic nephropathy.

α-Lipoic acid protects diabetic apolipoprotein E-deficient mice from nephropathy.

AIM: Both hyperglycemia and hyperlipidemia increase oxidative stress and contribute to the development of diabetic nephropathy (DN). We investigated the effects of α-lipoic acid, a natural antioxidant and a cofactor in the multienzyme complexes, on the development of DN in diabetic apolipoprotein E-deficient mice. METHODS: Twelve-week-old male apoE-/- mice on C57BL/6J genetic background were made diabetic with injections of streptozotocin (STZ). STZ-treated diabetic apoE-/- mice and non-diabetic control were fed with a synthetic high-fat (HF) diet with or without lipoic acid (LA) supplementation. Multiple parameters including plasma glucose, cholesterol, oxidative stress markers, cytokines, and kidney cortex gene expression, and glomerular morphology were evaluated. RESULTS: LA supplementation markedly protected the ß cells, reduced cholesterol levels, and attenuated albuminuria and glomerular mesangial expansion in the diabetic mice. Renoprotection by LA was equally effective regardless of whether the dietary supplementation was started 4 weeks before, simultaneously with, or 4 weeks after the induction of diabetes by STZ. LA supplementation significantly improved DN and oxidative stress in the diabetic mice. Severity of albuminuria was positively correlated with level of thiobarbituric acid reactive substances (TBARs) in the kidney (r(2)=0.62, P<.05). Diabetes significantly changed the kidney expression of Rage, Sod2, Tgfb1 and Ctgf, Pdp2, nephrin, and Lias. LA supplementation corrected these changes except that it further suppressed the expression of the Lias gene coding for lipoic acid synthase. CONCLUSIONS: Our data indicate that LA supplementation effectively attenuates the development and progression of DN through its antioxidant effect as well as enhances glucose oxidation.

Influence of glucosamine on glomerular mesangial cell turnover: implications for hyperglycemia and hexosamine pathway flux.

Cells exposed to high glucose may undergo hypertrophy, proliferation, and apoptosis, but the role of hexosamine flux in mediating these effects has not been fully elucidated. Accordingly, we studied the effects of glucose and glucosamine on rat glomerular mesangial cells (MC) turnover. Compared with physiological glucose (5.6 mM), treatment with high glucose (25 mM) for 24 h stimulated MC proliferation, an effect that was mimicked by exposure to low concentrations of glucosamine (0.05 mM). The percentage of cells in G(0)/G(1) phase of the cell cycle was reduced with a concomitant increase of the number of cells in G(2)/M phase. Proliferating cell nuclear antigen, phosphorylated mammalian target of rapamycin [phospho-mTOR (Ser(2448))], and total regulatory-associated protein of mTOR were increased by high glucose and glucosamine treatment. Inhibition of glutamine:fructose-6-phosphate amidotransferase (GFAT), the rate-limiting enzyme for hexosamine flux, with 6-diazo-5-oxonorleucine (10 muM) and of mTOR with rapamycin both attenuated glucose-mediated MC proliferation. Higher glucosamine concentrations (0.25-10 mM) caused MC apoptosis after 48 h, and, in addition, GFAT overexpression also increased MC apoptosis (TdT-dUTP nick end-labeling-positive cells: 3.8 +/- 0.3 vs. 1.1 +/- 0.2% for empty vector; P < 0.05). Hence, hexosamine flux is an important determinant of MC proliferation and apoptosis. The proliferative response to high glucose and hexosamine flux is rapamycin-sensitive, suggesting that this effect is associated with signaling through rapamycin-sensitive mTOR complex 1 (mTORC1).

Homocysteine-induced macrophage inflammatory protein-2 production by glomerular mesangial cells is mediated by PI3 Kinase and p38 MAPK.

BACKGROUND: Homocysteine (Hcy) and inflammatory cytokines have been linked to adverse outcomes in persons with cardiovascular and kidney diseases and recent reports suggest that cytokine-mediated inflammatory infiltrates may be an important contributor to the pathogenesis the aforementioned diseases. Although some reports suggest that Hcy directly influences inflammatory cytokine production, this proposition has not been supported by data from other studies. The objective of the current study was to a) utilize an in vitro cellular model to identify cytokines that may be affected by Hcy and b) examine the role of mitogen activated protein kinase (MAPK) and phosphatidyl inositol 3- (PI3) Kinase in Hcy modulated cytokine production. METHODS: Primary rat glomerular mesangial cells (MC, passage 8 to 15), isolated by standard sieving methodology, were exposed to Hcy (15, 50 or 100 muM) with L-cysteine (L-Cys; 100 muM) serving as a control. An antibody array was used to identify cytokines that were modulated when MCs were exposed to Hcy. Gene expression was assessed by quantitative RT-PCR, while western blotting analysis was used to assess cellular protein levels in the presence and absence of inhibitors of MAPK and PI3 Kinase. Finally, leukocyte adhesion assay was used to examine the effect of Hcy on leukocyte adhesion to glomerular MCs that were maintained in media without, and with, kinase inhibitors. RESULTS: We identified macrophage inflammatory protein 2 (MIP-2) as a key cytokine that manifested increases in both protein and mRNA following exposure of glomerular MC to pathophysiologic Hcy levels (50 muM). Further analyses revealed that Hcy-induced MIP-2 was dependent on activation of p38 MAPK and PI3 kinase. MIP-2 enhanced leukocyte adhesion to MC and this MIP-2-enhanced leukocyte adhesion was also dependent on activation of p38 MAPK and PI3K. Finally, we demonstrate that leukocyte adhesion to MC is specifically inhibited by anit-MIP2 antibody. CONCLUSION: The data suggest that Hcy participates in inflammatory cytokines production by glomerular MC and that Hcy-induced MIP-2 mediates leukocyte adhesion to MC.

Kidney cysts, pancreatic cysts, and biliary disease in a mouse model of autosomal recessive polycystic kidney disease.

Mutations in PKHD1 cause autosomal recessive polycystic kidney disease (ARPKD). We produced a mouse model of ARPKD by replacing exons 1-3 of Pkhd1 with a lacZ reporter gene utilizing homologous recombination. This approach yielded heterozygous Pkhd1 (lacZ/+) mice, that expressed beta-galactosidase in tissues where Pkhd1 is normally expressed, and homozygous Pkhd1 (lacZ/lacZ) knockout mice. Heterozygous Pkhd1 (lacZ/+) mice expressed beta-galactosidase in the kidney, liver, and pancreas. Homozygous Pkhd1 (lacZ/lacZ) mice lacked Pkhd1 expression and developed progressive renal cystic disease involving the proximal tubules, collecting ducts, and glomeruli. In the liver, inactivation of Pkhd1 resulted in dilatation of the bile ducts and periportal fibrosis. Dilatation of pancreatic exocrine ducts was uniformly seen in Pkhd1 (lacZ/lacZ ) mice, with pancreatic cysts arising less frequently. The expression of beta-galactosidase, Pkd1, and Pkd2 was reduced in the kidneys of Pkhd1 (lacZ/lacZ ) mice compared with wild-type littermates, but no changes in blood urea nitrogen (BUN) or liver function tests were observed. Collectively, these results indicate that deletion of exons 1-3 leads to loss of Pkhd1 expression and results in kidney cysts, pancreatic cysts, and biliary ductal plate malformations. The Pkhd1 (lacZ/lacZ ) mouse represents a new orthologous animal model for studying the pathogenesis of kidney cysts and biliary dysgenesis that characterize human ARPKD.

Lifelong genetic minipumps.

Most physiologists working with animals are familiar with osmotic minipumps. These surgically implanted devices can, for a limited period, administer a reagent at a constant predetermined rate that is unaffected by concurrent procedures. The investigator can then test the physiological effects of other treatments knowing that the animals' homeostatic responses will not be able to alter the dose of the pumped reagent. To develop the genetic equivalent of a lifelong minipump, simply inherited as an autosomal dominant, we here combine three of our previously described strategies, genetic clamping, single-copy chosen-site integration, and modification of untranslated regions (UTRs). As a test of the procedure, we have generated a series of intrinsically useful animals having genetic minipumps secreting renin ectopically from the liver at levels controlled by the investigator but not subject to homeostatic changes. To achieve the different dosage levels of these genetic minipumps, we altered the UTRs of a renin transgene driven by an albumin promoter and inserted it into the genome as a single copy at the ApoA1/ApoC3 locus, a locus that is strongly expressed in the liver. The resulting mice express plasma renin over ranges from near physiological to eightfold wild type and develop graded cardiovascular and kidney disease consequent to their different levels of ectopically secreted renin. The procedure and DNA constructs we describe can be used to generate genetic minipumps for controlling plasma levels of a wide variety of secreted protein products.

Cardiac hypertrophy and sudden death in mice with a genetically clamped renin transgene.

Several mouse models have already proved valuable for investigating hypertrophic responses to cardiac stress. Here, we characterize one caused by a well defined single copy transgene, RenTgMK, that genetically clamps plasma renin and thence angiotensin II at high levels. All of the transgenic males develop concentric cardiac hypertrophy with fibrosis but without dilatation. Over half die suddenly aged 6-8 months. Telemetry showed disturbances in diurnal rhythms a few days before death and, later, electrocardiographic disturbances comparable to those in humans with congestive heart failure. Expression of seven hypertrophy-related genes in this and two categorically different models (lack of atrial natriuretic peptide receptor A; overexpression of calsequestrin) were compared. Statistical analyses show that ventricular expressions of the genes coding for atrial natriuretic peptide, beta myosin heavy chain, medium chain acyl-CoA dehydrogenase, and adrenomedullin correlate equally well with the degree of hypertrophy, although their ranges of expression are, respectively, 50-, 30-, 10-, and 3-fold.

A genetically clamped renin transgene for the induction of hypertension.

Experimental analysis of the effects of individual components of complex mammalian systems is frequently impeded by compensatory adjustments that animals make to achieve homeostasis. We here introduce a genetic procedure for eliminating this type of impediment, by using as an example the development and testing of a transgene for "genetically clamping" the expression of renin, the major homeostatically responding component of the renin-angiotensin system, one of the most important regulators of blood pressure. To obtain a renin transgene whose expression is genetically clamped at a constant level, we have used single-copy chosen-site gene targeting to insert into a liver-specific locus a single copy of a modified mouse renin transgene driven by a liver-specific promoter/enhancer. The resulting transgene expresses renin ectopically at a constant high level in the liver and leads to elevated plasma levels of prorenin and active renin. The transgenic mice display high blood pressure, enhanced thirst, high urine output, proteinuria, and kidney damage. Treatment with the angiotensin II type I receptor antagonist, losartan, reduces the hypertension, albuminuria, and kidney damage, but does not affect expression of the transgene. This genetically clamped renin transgene can be used in models in which hypertension and its complications need to be investigated in a high prorenin/renin environment that is not subject to homeostatic compensations by the animal when other factors are changed.

Flux through the hexosamine pathway is a determinant of nuclear factor kappaB- dependent promoter activation.

The hexosamine pathway may mediate some of the toxic effects of glucose. We hypothesized that flux through this pathway might regulate the activity of nuclear factor kappaB (NF-kappaB)-dependent genes in mesangial cells (MCs). In MCs, RT-PCR revealed that high glucose (30 mmol/l) and glucosamine (1 mmol/l) increased mRNA levels for vascular cell adhesion molecule 1 (VCAM-1) and increased the activity of an NF-kappaB enhancer by 1.5- and 2-fold, respectively. Overexpression of glutamine:fructose-6-phosphate amidotransferase (GFAT), the rate-limiting enzyme for flux through the hexosamine pathway, led to a 2.2-fold increase in NF-kappaB enhancer activity; the combination of GFAT overexpression and high glucose increased activity 2.8-fold, and these increases were prevented by 40 micromol/l O-diazoacetyl-L-serine (azaserine) or 6-diazo-5-oxonorleucine. High glucose, glucosamine, and GFAT overexpression increased binding of MC nuclear proteins to NF-kappaB consensus sequences. Immunoblotting revealed that the p65 subunit of NF-kappaB was O-glycosylated in MC cultured in physiologic glucose and that significant enhancement occurred with high glucose and glucosamine. Both glucose and glucosamine dose-dependently increased human VCAM-1 promoter activity. In addition, GFAT overexpression activated the VCAM-1 promoter (2.25-fold), with further augmentation by high glucose and abrogation by inhibitors of GFAT, NF-kappaB, and O-glycosylation. Inactivation of the two NF-kappaB sites in the VCAM-1 promoter abolished its response to high glucose, glucosamine, and GFAT overexpression. These results suggest that increased flux through the hexosamine pathway leads to NF-kappaB-dependent promoter activation in MCs.