Biomedical subjects

Fuad N Ziyadeh

Publications and source records attributed to Fuad N Ziyadeh.

22 records · Page 2Linked to original sources

PubMed2002

Effects of high glucose and TGF-beta1 on the expression of collagen IV and vascular endothelial growth factor in mouse podocytes.

UNLABELLED: Effects of high glucose and TGF-beta1 on the expression of collagen IV and vascular endothelial growth factor in mouse podocytes. BACKGROUND: The podocyte takes center stage in the pathogenesis of glomerular basement membrane (GBM) thickening and proteinuria in diabetic glomerulopathy. In part, GBM thickening may occur when the podocyte synthesizes increased amounts of collagen IV. Proteinuria may develop if the podocyte secretes excessive amounts of vascular endothelial growth factor (VEGF), which may increase the glomerular permeability to macromolecules. The augmented production of collagen IV and VEGF may be caused by metabolic mediators of diabetes such as hyperglycemia and transforming growth factor-beta (TGF-beta). METHODS: The effects of high glucose and exogenous TGF-beta1 were examined on a mouse podocyte cell line that retains its differentiated phenotype. The gene expression and protein production of certain alpha chains of collagen IV, the major isoforms of VEGF, and components of the TGF-beta system were assayed. An inhibitor of TGF-beta signaling was used to determine whether some of the high glucose effects might be mediated by the TGF-beta system. RESULTS: Compared with normal glucose (5.5 mmol/L), high glucose (HG, 25 mmol/L) for 14 days stimulated [3H]-proline incorporation, a measure of collagen production, by 1.8-fold, and exogenous TGF-beta1 (2 ng/mL) for 24 hours stimulated proline incorporation by 2.4-fold. Northern analysis showed that exposure to HG for 14 days increased the mRNA level of alpha1(IV) collagen by 51% and alpha5(IV) by 90%, whereas treatment with TGF-beta1 (2 ng/mL) for 24 hours decreased the mRNA level of alpha1(IV) by 36% and alpha5(IV) by 40%. Consistent with these effects on mRNA expression, Western blotting showed that HG increased alpha1(IV) protein by 44% and alpha5(IV) by 28%, while TGF-beta1 decreased alpha1(IV) protein by 29% and alpha5(IV) by 7%. In contrast to their opposing actions on alpha1 and alpha5(IV), both HG and exogenous TGF-beta1 increased alpha3(IV) collagen and VEGF, with TGF-beta1 having the greater effect. An inhibitor of the TGF-beta type I receptor (ALK5) was able to prevent the stimulation of alpha3(IV) and VEGF proteins by HG. Unlike in other renal cell types, HG did not increase TGF-beta1 mRNA or protein in the podocyte, but HG did induce the expression of the ligand-binding TGF-beta type II receptor (TbetaRII). Because HG had up-regulated TbetaRII after two weeks, the addition of physiological-dose TGF-beta1 (0.010 ng/mL) for 24 hours stimulated the production of alpha3(IV) and VEGF proteins to a greater extent in high than in normal glucose. Up-regulation of TbetaRII in the podocyte was corroborated by immunohistochemistry of the kidney cortex in the db/db mouse, a model of type 2 diabetes. CONCLUSIONS: High glucose and exogenous TGF-beta1 exert disparate effects on the expression of alpha1 and alpha5(IV) collagen. However, high glucose and TGF-beta1 coordinately induce the production of alpha3(IV) collagen and VEGF in the podocyte. The HG-induced increases in alpha3(IV) collagen and VEGF proteins are mediated by the TGF-beta system. By increasing the expression of TbetaRII, high glucose may augment the response of the podocyte to ambient levels of TGF-beta1.

Activin Receptors, Type I↗

PubMed2002

Leptin and renal disease.

Leptin is a small peptide hormone that is mainly, but not exclusively, produced in adipose tissue. The circulating leptin concentration therefore directly reflects the amount of body fat. Leptin was identified through positional cloning of the obese (ob) gene, which is mutated in the massively obese ob/ob mouse, and it has a pivotal role in regulating food intake and energy expenditure. It binds to the so-called long receptor (Ob-Rb) in the hypothalamus and regulates food intake through the release of other neurotransmitters. Moreover, leptin exerts several other important metabolic effects on peripheral tissue, including modification of insulin action, induction of angiogenesis, and modulation of the immune system. As a small peptide, leptin is cleared principally by the kidney. Not surprisingly, serum leptin concentrations are increased in patients with chronic renal failure and those undergoing maintenance dialysis. Whether the hyperleptinemia of chronic renal failure contributes to some uremic manifestations, such as anorexia and weight loss, requires additional investigation. The kidney expresses abundant concentrations of the truncated isoform of the leptin receptor Ob-Ra, but only a small amount of the full-length receptor Ob-Rb. We recently discovered that leptin has direct effects on renal pathophysiological characteristics. Both cultured glomerular endothelial cells and mesangial cells obtained from the diabetic db/db mouse possess the Ob-Ra receptor, but whether biological effects of leptin are transduced through this receptor remains unknown. In glomerular endothelial cells, leptin stimulates cellular proliferation, transforming growth factor-beta1 (TGF-beta1) synthesis, and type IV collagen production. Conversely, in mesangial cells, leptin upregulates synthesis of the TGF-beta type II receptor, but not TGF-beta1, and stimulates glucose transport and type I collagen production through signal transduction pathways involving phosphatidylinositol-3-kinase. These data suggest that leptin triggers a paracrine interaction in which glomerular endothelial cells secrete TGF-beta, to which sensitized mesangial cells may respond. Both cell types increase their expression of extracellular matrix in response to leptin. Infusion of leptin into normal rats for 3 weeks fosters the development of focal glomerulosclerosis and proteinuria. Additional previously described direct and indirect effects of leptin on the kidney include natriuresis, increased sympathetic nervous activity, and stimulation of reactive oxygen species. These findings collectively suggest that the kidney is not only a site of leptin metabolism, but also a target organ for leptin action in pathophysiological states.

Animals↗

PubMed2002

Regulation of inducible class II MHC, costimulatory molecules, and cytokine expression in TGF-beta1 knockout renal epithelial cells: effect of exogenous TGF-beta1.

As reports of mice genetically deficient for TGF-beta1 demonstrated aberrant renal class II MHC expression, we investigated inducible class II MHC expression on renal tubular epithelial cells derived from TGF-beta1 knockout (-/-) and wild-type (+/+) mice. IFN-gamma markedly upregulated class II MHC (I-A(b)) expression in both (-/-) and (+/+) tubular epithelial cells. Coincubation studies of (+/+) and (-/-) tubular epithelial cells with IFN-gamma+LPS, or pretreatment of these cells with TGF-beta1, revealed inhibition of IFN-gamma-induced I-A(b) mRNA and cell surface expression that occurred via a decrease in class II transactivator gene expression in both (+/+) and (-/-) tubular epithelial cells. In addition, ICAM-1 was constitutively expressed on both (+/+) and (-/-) tubular epithelial cells and was upregulated by IFN-gamma or IFN-gamma+LPS. ICAM-1 expression in (+/+) and (-/-) tubular epithelial cells, however, was decreased by TGF-beta1. Parallel analysis evaluating B7-1 expression detected low levels of B7-1 in unstimulated (+/+) and (-/-) tubular epithelial cells that were increased by IFN-gamma, LPS, and IFN-gamma+LPS. IFN-gamma+LPS-mediated upregulation of B7-1 was also blocked by pretreatment with TGF-beta1. Cytokine analysis detected significantly higher levels of TNF-alpha and MIP-1alpha mRNA in all treated (-/-) preparations than in (+/+) tubular epithelial cell controls. These studies demonstrate normal patterns of class II MHC, ICAM-1, and B7 expression in TGF-beta1 (-/-) tubular epithelial cells in response to IFN-gamma, LPS, and TGF-beta1. Upregulated cytokine expression at baseline and in response to proinflammatory mediators is apparent in (-/-) tubular epithelial cells, however, and suggests that dysregulation of cytokine expression in inflammatory responses may be a primary event in multifocal inflammation observed in TGF-beta1-deficient animals.

Animals↗

PubMed2000

Extracellular signal-regulated kinase mediates stimulation of TGF-beta1 and matrix by high glucose in mesangial cells.

High ambient glucose exerts its injurious effects on renal cells through nonenzymatic and enzymatic pathways, including altered signal transduction and upregulation of the transforming growth factor-beta (TGF-beta) system. Extracellular signal-regulated kinase (ERK), a member of the mitogen-activated protein kinase (MAPK) cascade, is activated in mesangial cells cultured in high glucose and in glomeruli of diabetic rats. However, the biologic consequences of ERK activation in the kidney have not been investigated. To clarify the role of ERK activation, mouse mesangial cells were exposed to normal (5.5 mM) or high (25 mM) glucose with or without addition of PD98059, a specific inhibitor of MAPK/ERK kinase (MEK), an upstream kinase activator of ERK. Cells that were exposed to high glucose exhibited significant increases in ERK activity, TGF-beta1 expression (total protein, mRNA levels, and promoter activity), [(3)H]-proline uptake, and alpha1(I) collagen and fibronectin mRNA levels. Treatment with PD98059 (up to 25 microM) significantly inhibited these parameters. In contrast, 25 microM PD98059 had no significant effect on any of the parameters measured in cells that were exposed to normal glucose. Overexpression of MAPK phosphatase CL 100 prevented TGF-beta1 promoter activation by high glucose, confirming the involvement of the MEK-ERK pathway in response to high glucose. The conclusion is that activation of ERK in mesangial cells is responsible for high-glucose-induced stimulation of TGF-beta1 and contributes to the increased extracellular matrix expression.

Animals↗