title: Obesity and intestinal epithelial deletion of the insulin receptor, but not the IGF 1 receptor, affect radiation-induced apoptosis in colon.
abstract: Current views suggest that apoptosis eliminates genetically damaged cells that may otherwise form tumors. Prior human studies link elevated insulin and reduced apoptosis to risk of colorectal adenomas. We hypothesized that hyperinsulinemia associated with obesity would lead to reduced colon epithelial cell (CEC) apoptosis after radiation and that this effect would be altered by deletion of the insulin-like growth factor (IGF) 1 receptor (IGF1R) or the insulin receptor (IR). Mice with villin-Cre-mediated IGF1R or IR deletion in CECs and floxed littermates were fed a high-fat diet to induce obesity and hyperinsulinemia or control low-fat chow. Mice were exposed to 5-Gy abdominal radiation to induce DNA damage and euthanized 4 h later for evaluation of apoptosis by localization of cleaved caspase-3. Obese mice exhibited decreased apoptosis of genetically damaged CECs. IGF1R deletion did not affect CEC apoptosis in lean or obese animals. In contrast, IR loss increased CEC apoptosis in both diet groups but did not prevent antiapoptotic effects of obesity. Levels of p53 protein were significantly reduced in CECs of obese mice with intact IR but increased in both lean and obese mice without IR. Levels of mRNAs encoding proapoptotic Perp and the cell cycle inhibitor Cdkn1b/p27 were reduced in CECs of obese mice and increased in lean mice lacking IR. Together, our studies provide novel evidence for antiapoptotic roles of obesity and IR, but not IGF1R, in colonic epithelium after DNA damage. However, neither IR nor IGF1R deletion prevented a reduction in radiation-induced CEC apoptosis during obesity and hyperinsulinemia.
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and.
authors.forename: M Agostina
authors.initials: MA
authors.lastname: Santoro
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and.
authors.forename: R Eric
authors.initials: RE
authors.lastname: Blue
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and.
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Andres
authors.affiliation: Department of Nutrition, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Amanda T
authors.initials: AT
authors.lastname: Mah
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and.
authors.forename: Laurianne
authors.initials: L
authors.lastname: Van Landeghem
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and empk@med.unc.edu.
authors.forename: P Kay
authors.initials: PK
authors.lastname: Lund
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D015153:Blotting, Western; D053148:Caspase 3; D003106:Colon / Q000378:metabolism / Q000473:pathology*; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D051379:Mice; D009765:Obesity / Q000378:metabolism*; D011833:Radiation Injuries, Experimental; D060888:Real-Time Polymerase Chain Reaction; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*
chemical_list: D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D053148:Caspase 3
keywords: apoptosis; colon; insulin receptor; insulin-like growth factor 1 receptor; obesity