manumycin and Diabetic-Nephropathies

The activation of Ras signaling and vascular endothelial growth factor (VEGF) expression in mesangial cells is a pathogenic consequence of diabetic nephropathy. We examined the role of simvastatin in modulating Ras signaling and the expression of VEGF in mesangial cells stressed with high doses of glucose in vitro and in vivo.. For the in vitro studies, we cultured mesangial cells, with or without simvastatin or manumycin A pretreatment, in 35 mM glucose and assayed VEGF activity. For the in vivo studies, we administered simvastatin or manumycin A to streptozocin-induced diabetic rats for 28 days and dissected renal tissues for an immunohistological assessment of Ras and VEGF expression in glomerular cells.. We showed that high glucose significantly increased VEGF gene expression and Ras activation. The pretreatment with 10 microM simvastatin and inhibition of Ras activity by manumycin A significantly reversed high glucose promotion of VEGF mRNA expression. Pretreatment with simvastatin and manumycin A clearly affected the activation of Ras promoted by high glucose. Tube-like formations were abundant in high glucose-treated mesangial cells co-cultured with HUVEC. However, the simvastatin and manumycin A treatment group's down-regulated tube formation was comparable to the mesangial cells treated only with high glucose. Exogenous simvastatin and manumycin A treatment alleviated urinary albumin secretion and attenuated Ras activation and VEGF protein expression in the kidneys of diabetic rats.. Ras protein activation is a key mediator of VEGF-induced diabetic nephropathy. By inhibiting Ras activation, simvastatin modulates the high glucose-induced VEGF-mediated signaling pathway in vitro and in vivo.

Topics: Animals; Cells, Cultured; Diabetic Nephropathies; Glomerular Mesangium; Polyenes; Polyunsaturated Alkamides; ras Proteins; Rats; Signal Transduction; Simvastatin; Vascular Endothelial Growth Factor A

Although previous studies have demonstrated that diabetic nephropathy is attributable to early extracellular matrix accumulation in glomerular mesangial cells, the molecular mechanism by which high glucose induces matrix protein deposition remains not fully elucidated. Rat mesangial cells pretreated with or without inhibitors were cultured in high-glucose or advanced glycation end product (AGE) conditions. Streptozotocin-induced diabetic rats were given superoxide dismutase (SOD)-conjugated propylene glycol to scavenge superoxide. Transforming growth factor (TGF)-beta1, fibronectin expression, Ras, ERK, p38, and c-Jun activation of glomerular mesangial cells or urinary albumin secretion were assessed. Superoxide, not nitric oxide or hydrogen peroxide, mediated high glucose- and AGE-induced TGF-beta1 and fibronectin expression. Pretreatment with diphenyliodonium, not allopurinol or rotenone, reduced high-glucose and AGE augmentation of superoxide synthesis and fibronection expression. High glucose and AGEs rapidly enhanced Ras activation and progressively increased cytosolic ERK and nuclear c-Jun activation. Inhibiting Ras by manumycin A reduced the stimulatory effects of high glucose and AGEs on superoxide and fibronectin expression. SOD or PD98059 pretreatment reduced high-glucose and AGE promotion of ERK and c-Jun activation. Exogenous SOD treatment in diabetic rats significantly attenuated diabetes induction of superoxide, urinary albumin excretion, 8-hydroxy-2'-deoxyguanosine, TGF-beta1, and fibronectin immunoreactivities in renal glomerular mesangial cells. Ras induction of superoxide activated ERK-dependent fibrosis-stimulatory factor and extracellular matrix gene transcription of mesangial cells. Reduction of oxidative stress by scavenging superoxide may provide an alternative strategy for controlling diabetes-induced early renal injury.

Topics: Animals; Cytosol; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Fibronectins; Flavonoids; Free Radical Scavengers; Gene Expression; Glucose; Glycation End Products, Advanced; Kidney Glomerulus; Male; Mesangial Cells; Oxidative Stress; Polyenes; Polyunsaturated Alkamides; Proto-Oncogene Proteins c-jun; ras Proteins; Rats; Rats, Wistar; Superoxide Dismutase; Superoxides; Transforming Growth Factor beta