Obesity and metabolic syndrome are associated with glomerulosclerosis and proteinuria, but the mechanisms are not known. The purpose of this study was to determine if there is altered renal lipid metabolism and increased expression of sterol regulatory elementbinding proteins (SREBPs) in a model of diet-induced obesity. C57BL/6J mice that were fed a high fat, 60 kcal % saturated (lard) fat diet (HFD) developed obesity, hyperglycemia, and hyperinsulinemia compared with those that were fed a low fat, 10 kcal % fat diet (LFD). In contrast, A/J mice were resistant when fed the same diet. C57BL/6J mice with HFD exhibited significantly higher levels of renal SREBP-1 and SREBP-2 expression than those mice with LFD, whereas in A/J mice there were no changes with the same treatment. The increases in SREBP-1 and SREBP-2 expression in C57BL/6J mice resulted in renal accumulation of triglyceride and cholesterol. There were also significant increases in the renal expression of plasminogen activator inhibitor-1 (PAI-1), vascular endothelial growth factor (VEGF), type IV collagen, and fibronectin, resulting in glomerulosclerosis and proteinuria. To determine a role for SREBPs per se in modulating renal lipid metabolism and glomerulosclerosis we performed studies in SREBP-1c ؊/؊ mice. In contrast to control mice, in the SREBP-1c ؊/؊ mice with HFD the accumulation of triglyceride was prevented, as well as the increases in PAI-1, VEGF, type IV collagen, and fibronectin expression. Our results therefore suggest that diet-induced obesity causes increased renal lipid accumulation and glomerulosclerosis in C57BL/6J mice via an SREBP-1c-dependent pathway.Obesity is a known risk factor for cardiovascular disease (1) and type-2 diabetes mellitus (2) and has been proposed to play a role in the pathogenesis of diabetic nephropathy (3). Obesity is one of the defining criteria of the metabolic syndrome as proposed by the National Cholesterol Education Program Adult Treatment Panel III (4) and the World Health Organization (5). The metabolic syndrome, which is characterized by the concurrent existence of obesity, dyslipidemia, hyperglycemia, hyperinsulinemia, and hypertension, has been shown to be a strong and independent risk factor for cardiovascular, and all cause mortality (6, 7) as well as the development of microalbuminuria and chronic kidney disease (8).Obesity is considered a major generator of metabolic syndrome (9). Early in the course of obesity-initiated metabolic syndrome, structural and functional changes similar to diabetic kidney disease occur (10). These changes include glomerular hyperfiltration, glomerular basement membrane thickening, mesangial cell proliferation, mesangial matrix thickening, and expansion of Bowman's capsule (10) and are considered precursors to more severe renal injury. Severe obesity has been associated with the eventual development of focal and segmental glomerulosclerosis (11). Although incompletely understood, several hemodynamic, hormonal, and metabolic factors have been proposed to contribute to t...

Diabetic kidney disease has been associated with the presence of lipid deposits, but the mechanisms for the lipid accumulation have not been fully determined. In the present study, we found that db/db mice on the FVB genetic background with loss-of-function mutation of the leptin receptor (FVB-Lepr db mice or FVB db/db ) develop severe diabetic nephropathy, including glomerulosclerosis, tubulointerstitial fibrosis, increased expression of type IV collagen and fibronectin, and proteinuria, which is associated with increased renal mRNA abundance of transforming growth factor-␤, plasminogen activator inhibitor-1, and vascular endothelial growth factor. Electron microscopy demonstrates increases in glomerular basement membrane thickness and foot process (podocyte) length. We found that there is a marked increase in neutral lipid deposits in glomeruli and tubules by oil red O staining and biochemical analysis for cholesterol and triglycerides. We also detected a significant increase in the renal expression of adipocyte differentiation-related protein (adipophilin), a marker of cytoplasmic lipid droplets. We examined the expression of sterol regulatory element-binding protein (SREBP)-1 and -2, transcriptional factors that play an important role in the regulation of fatty acid, triglyceride, and cholesterol synthesis. We found significant increases in SREBP-1 and -2 protein levels in nuclear extracts from the kidneys of FVB db/db mice, with increases in the mRNA abundance of acetyl-CoA carboxylase, fatty acid synthase, and 3-hydroxy-3-methylglutaryl-CoA reductase, which mediates the increase in renal triglyceride and cholesterol content. Our results indicate that in FVB db/db mice, renal triglyceride and cholesterol accumulation is mediated by increased activity of SREBP-1 and -2. Based on our previous results with transgenic mice overexpressing SREBP-1 in the kidney, we propose that increased expression of SREBPs plays an important role in causing renal lipid accumulation, glomerulosclerosis, tubulointerstitial fibrosis, and proteinuria in mice with type 2 diabetes.

Background-The noninvasive, tissue-specific delivery of therapeutic agents to the heart would be a valuable clinical tool.This study addressed the hypothesis that albumin-coated microbubbles could be used to effectively deliver an adenoviral transgene to rat myocardium by ultrasound-mediated microbubble destruction. Methods and Results-Recombinant adenovirus containing ␤-galactosidase and driven by a constitutive promoter was attached to the surface of albumin-coated, perfluoropropane-filled microbubbles. These bubbles were infused into the jugular vein of rats with or without simultaneous echocardiography. Additional controls included ultrasound of microbubbles that did not contain virus, virus alone, and virus plus ultrasound. One group underwent ultrasoundmediated destruction of microbubbles followed by adenovirus infusion. Rats were killed after 4 days and examined for ␤-galactosidase expression. The hearts of all rats that underwent ultrasound-mediated destruction of microbubbles containing virus showed nuclear staining with 5-bromo-4-chloro-3-indolyl-␤-D-galactopyranoside substrate, indicating expression of the transgene. None of the control animals showed myocardial expression of the ␤-galactosidase transgene. By quantitative analysis, ␤-galactosidase activity was 10-fold higher in the treated group than in controls (PϽ0.0001). Conclusions-Ultrasound-mediated destruction of albumin-coated microbubbles is a promising method for the delivery of bioactive agents to the heart.

In Akita and OVE26 mice, two genetic models of type 1 diabetes, diabetic nephropathy is characterized by mesangial expansion and loss of podocytes, resulting in glomerulosclerosis and proteinuria, and is associated with increased expression of profibrotic growth factors, proinflammatory cytokines, and increased oxidative stress. We have also found significant increases in renal triglyceride and cholesterol content. The increase in renal triglyceride content is associated with 1) increased expression of sterol regulatory element-binding protein (

Leptin is an adipocyte-derived hormone with potent weight reducing effects. Genetically obese rodents with mutations of leptin or the leptin receptor are defective in leptin signaling and develop morbid obesity and diabetes. Interestingly, the levels of both leptin mRNA and protein are increased by up to 20-fold in these animals, suggesting the existence of a feedback mechanism controlling the amount of leptin in circulation. In this report, we attempted to determine whether the up-regulation of circulating leptin in Zucker Diabetic Fatty rats, which are nonresponsive to leptin due to a receptor point mutation, is entirely due to increased expression of leptin. We demonstrate that the high level of circulating leptin in these rats is attributable to at least two factors: increased leptin expression by the adipose tissue and delayed clearance of leptin from circulation due to binding to its soluble receptor. The latter conclusion was supported by three lines of evidence: 1) The soluble leptin receptor is up-regulated by about 20-fold in Zucker Diabetic Fatty rats; 2) Adenovirus-mediated overexpression of the soluble leptin receptor results in a similar -fold increase of circulating leptin; 3) In ob/ob mice, which have no endogenous leptin, exogenously administered leptin reaches a higher level when the soluble leptin receptor is overexpressed. The weightreducing effect of leptin is enhanced in C57Bl/6 ob/ob mice with overexpression of the soluble leptin receptor. Soluble leptin receptor may be a significant factor determining the amount of total leptin in circulation.Leptin is an adipocyte-derived hormone of 167 amino acids (1). It has potent weight-reducing effects in vivo (2-4). In ob/ob mice, the gene encoding leptin is mutated, resulting in morbid obesity and associated abnormalities, including hyperphagia, hypothermia, diabetes, and infertility.The leptin receptor, OB-R, 1 is a member of the cytokine receptor family (5). It is encoded by the diabetes (db) gene, mutation of which also results in morbid obesity and other abnormalities similar to that in ob/ob mice. OB-R is alternatively spliced into at least five transcripts from a single gene. These transcripts encode proteins that are called the long (OBRb), short (OB-Ra, -c, and -d), and soluble (OB-Re) forms of the leptin receptor. With the exception of the soluble leptin receptor, receptor isoforms differ from each other by the alternative use of a unique terminal coding exon (6). OB-Rb is essential in mediating leptin's weight-reducing and other biological effects (6, 7).OB-R is expressed in both the nervous system and peripheral tissues. The relative levels of expression of different receptor isoforms vary among different tissues, providing a possible mechanism of regulating leptin's biological activity at various leptin target sites (8). OB-Rb is enriched in the hypothalamus, the site of leptin's action on food intake and body weight. Leptin activation of OB-Rb within this brain region results in the inhibition of neuropeptide Y/agouti-related protein ...