title: Insulin-like growth factor-binding protein-3 mediates high glucose-induced apoptosis by increasing oxidative stress in proximal tubular epithelial cells.
abstract: IGF-binding protein-3 (IGFBP-3) is the major circulating carrier protein for IGF, and also acts as a potent antiproliferative agent in various cell types. Recently, IGFBP-3 was reported to mediate high glucose-induced apoptosis in mesangial cells and podocytes. In this study, we investigated the role of IGFBP-3 in high glucose-induced apoptosis in proximal tubular epithelial cells (PTEC). Expression of IGFBP-3 protein and mRNA in a porcine PTEC line (LLC-PK1 cells) was measured after exposure to either standard (5.5 mM) or high-glucose (30 mM) medium. We quantified apoptosis after treatment with small interfering RNA against IGFBP-3 (siRNA:IGFBP-3) in high-glucose medium or in cells that overexpressed IGFBP-3. Oxidative stress was measured in high-glucose medium, in the presence of siRNA:IGFBP-3, or in IGFBP-3-overexpressing cells. IGFBP-3 protein and mRNA expression in LLC-PK1 cells was higher in high-glucose medium than in standard-glucose medium. Exposure to high-glucose medium increased apoptosis, and high-glucose-induced apoptosis was abolished by siRNA:IGFBP-3. IGFBP-3 overexpression induced apoptosis in LLC-PK1 cells. Both high-glucose medium and IGFBP-3 overexpression increased reactive oxygen species, and siRNA:IGFBP-3 reduced this increase. Antioxidant treatment decreased IGFBP-3 expression and apoptosis, whereas oxidative stress from hydrogen peroxide increased IGFBP-3 expression, suggesting that oxidative stress increases IGFBP-3 expression. Our results suggest that increased IGFBP-3 expression by high glucose mediates high-glucose-induced apoptosis in PTEC. Increased oxidative stress from high glucose enhances IGFBP-3 expression, inducing apoptosis. Increased expression of IGFBP-3 by high glucose induces additional oxidative stress, which may result in amplification of hyperglycemic damage.
authors.affiliation: Department of Pediatrics, College of Medicine, CHA University, Sungnam 463-712, Korea.
authors.forename: Eun-Gyong
authors.initials: EG
authors.lastname: Yoo
authors.forename: Woo Jung
authors.initials: WJ
authors.lastname: Lee
authors.forename: Jung Hyun
authors.initials: JH
authors.lastname: Kim
authors.forename: Hyun-Wook
authors.initials: HW
authors.lastname: Chae
authors.forename: Se Eun
authors.initials: SE
authors.lastname: Hyun
authors.forename: Duk Hee
authors.initials: DH
authors.lastname: Kim
authors.forename: Ho-Seong
authors.initials: HS
authors.lastname: Kim
authors.forename: Youngman
authors.initials: Y
authors.lastname: Oh
mesh_terms: D000818:Animals; D017209:Apoptosis; D004847:Epithelial Cells / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D006943:Hyperglycemia / Q000378:metabolism / Q000473:pathology; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000502:physiology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D018374:LLC-PK1 Cells; D018384:Oxidative Stress; D013552:Swine
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D005947:Glucose