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Insulin deficiency induces rat renal mesangial cell dysfunction via activation of IGF-1/IGF-1R pathway.

ABSTRACT: Diabetic nephropathy is one of the major complications of diabetes and the major cause of end-stage renal disease. In this study we investigated the insulin deficiency (ID) induced changes in renal mesangial cells (MCs) and in the kidney of STZ-induced diabetic rats.Cultured rat renal MCs were incubated in ID media. Cell proliferation was analyzed using BrdU incorporation assay. The expression of insulin receptor (IR), insulin-like growth factor-1 receptor (IGF-1R), phosphorylated IGF-1R, fibronectin, and collagen IV was determined with Western blot analysis. STZ-induced diabetic rats were treated with an IGF-1R antagonist picropodophyllin (PPP, 20 mg·kg(-1)·d(-1), po) for 8 weeks. After the rats were euthanized, plasma and kidneys were collected. IGF-1 levels in renal cortex were measured with RT-PCR or ELISA. The morphological changes in the kidneys were also examined.Incubation in ID media significantly increased cell proliferation, the synthesis of fibronectin and collagen IV, and the expression of IGF-1 and IGF-1R and phosphorylated IGF-1R in renal MCs. Pretreatment of the cells with PPP (50 nmol/L) blocked ID-induced increases in cell proliferation and the synthesis of fibronectin and collagen IV; knockdown of IGF-1R showed a similar effect as PPP did. In contrast, treatment of the cells with IGF-1 (50 ng/mL) exacerbated ID-induced increases in cell proliferation. In the kidneys of diabetic rats, the expression of IGF-1, IGF-1R and phosphorylated IGF-1R were significantly elevated. Treatment of diabetic rats with PPP did not lower the blood glucose levels, but significantly suppressed the expression of TGF-β, fibronectin and collagen IV in the kidneys, the plasma levels of urinary nitrogen and creatinine, and the urinary protein excretion.Insulin deficiency increases the expression of IGF-1 and IGF-1R in renal MCs and the kidney of diabetic rats, which contributes to the development of diabetic nephropathy.

SUBMITTER: Kong YL

PROVIDER: S-EPMC4753370 | biostudies-other | 2016 Feb

REPOSITORIES: biostudies-other

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Project description:Prior studies implicate type 1 IGF receptor (IGF-1R) in mediating chemo-resistance. Here, we investigated whether IGF-1R influences response to temozolomide (TMZ), which generates DNA adducts that are removed by O6-methylguanine-DNA methyltransferase (MGMT), or persist causing replication-associated double-strand breaks (DSBs). Initial assessment in 10 melanoma cell lines revealed that TMZ resistance correlated with MGMT expression (r = 0.79, p = 0.009), and in MGMT-proficient cell lines, with phospho-IGF-1R (r = 0.81, p = 0.038), suggesting that TMZ resistance associates with IGF-1R activation. Next, effects of IGF-1R inhibitors (IGF-1Ri) AZ3801 and linsitinib (OSI-906) were tested on TMZ-sensitivity, cell cycle progression and DSB induction. IGF-1Ri sensitized BRAF wild-type and mutant melanoma cells to TMZ in vitro, an effect that was independent of MGMT. Cells harboring wild-type p53 were more sensitive to IGF-1Ri, and showed schedule-dependent chemo-sensitization that was most effective when IGF-1Ri followed TMZ. This sequence sensitized to clinically-achievable TMZ concentrations and enhanced TMZ-induced apoptosis. Simultaneous or prior IGF-1Ri caused less effective chemo-sensitization, associated with increased G1 population and reduced accumulation of TMZ-induced DSBs. Clinically relevant sequential (TMZ ? IGF-1Ri) treatment was tested in mice bearing A375M (V600E BRAF, wild-type p53) melanoma xenografts, achieving peak plasma/tumor IGF-1Ri levels comparable to clinical Cmax, and inducing extensive intratumoral apoptosis. TMZ or IGF-1Ri caused minor inhibition of tumor growth (gradient reduction 13%, 25% respectively), while combination treatment caused supra-additive growth delay (72%) that was significantly different from control (p < 0.01), TMZ (p < 0.01) and IGF-1Ri (p < 0.05) groups. These data highlight the importance of scheduling when combining IGF-1Ri and other targeted agents with drugs that induce replication-associated DNA damage.

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Insulin deficiency induces rat renal mesangial cell dysfunction via activation of IGF-1/IGF-1R pathway.

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