Effects of Oxidative Stress on Intestinal Type I Insulin-Like Growth Factor Receptor Expression

Abstract

Introduction Oxidative stress activates multiple signaling transduction pathways, including the phosphatidylinositol 3-kinase (PI3-K), in an injured intestine as occurs in necrotizing enterocolitis (NEC). We have previously shown that hydrogen peroxide (H₂O₂)-induced PI3-K activation is significantly enhanced with exogenous insulin-like growth factor (IGF)-1 in intestinal epithelial cells. However, the effects of oxidative stress on IGF receptor type I (IGF-IR) activation and expression in the neonatal intestine during NEC are unknown.

Material and Methods Intestinal sections from neonates undergoing bowel resections (control = 3, NEC = 20) were analyzed for IGF-IR expression. NEC was induced in newborn mouse pups using hypoxia and hyperosmolar feeds, and distal small bowel segments were analyzed for IGF-IR expression (control = 3, NEC = 7). H₂O₂ was used to induce oxidative stress in rat (RIE-1) and fetal human (FHs74 Int) intestinal epithelial cells. Phosphorylation of IGF-IR, Akt, a downstream effector of PI3-K, and IGF-IR levels were determined by Western blotting. Flow cytometry, immunofluorescence, immunohistochemistry, IGF-IR tyrosine phosphorylation array, cell death enzyme-linked immunosorbent assay, and Western blotting were used to determine the IGF-IR expression.

Results An increased IGF-IR expression was noted in intestinal sections from NEC as well as murine model of NEC. H₂O₂ treatment rapidly activated IGF-IR and increased the expression in RIE-1 and FHs74 Int cells. Inhibition of IGF-IR resulted in significant RIE-1 cell apoptosis during oxidative stress. IGF-IR tyrosine phosphorylation array showed the recruitment of several key SH2 domain-containing proteins and oncogenes to the IGF-IR tyrosine kinase domain in H₂O₂-treated RIE-1 cells.

Conclusion IGF-IR-mediated activation of intracellular signaling may play a critical role during oxidative stress-induced apoptosis in NEC.

Keywords

phosphatidylinositol 3-kinase/Akt - insulin-like growth factor type I receptor - oxidative stress - intestinal injury

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