Insulin-like Growth Factor-I Governs Submucosal Growth and Thickness in the Newborn Mouse Ileum

Spontaneous intestinal perforations in extremely premature infants are associated with glucocorticoid-induced thinning of the ileal bowel wall. We have previously demonstrated that insulin-like growth factor-1 (IGF-1) is abundant within the submucosa of the newborn mouse ileum but is diminished by glucocorticoid exposure, concomitant with bowel wall thinning. These findings prompted us to hypothesize that IGF-I governs submucosal growth during neonatal gut development and that diminished IGF-I abundance results in submucosal thinning. Heterozygous IGF-I knockout, wild type and homozygous IGF-I over-expresser newborn mice were euthanized at 3 d of life. Additionally, wild type newborn mice received daily dexamethasone (DEX) (1µg/gm/d) or vehicle control on days of life 1 and 2 and were also euthanized at 3 d of life. Their ileums were harvested, fixed and the resulting sections were processed in parallel for IGF-I immunohistochemistry and morphometric measurements of submucosal thickness and bowel diameter. Immunolocalization of IGF-I in each genotype was also compared with that seen in DEX-treated and control mice euthanized at the same time of life. IGF-I heterozygous knockouts had diminished submucosal IGF-I immunolocalization (similar to that seen in DEX-treated newborn mice) whereas homozygous IGF-I over-expressers exceeded that seen within wild type mice. IGF-I genotype and submucosal abundance was positively correlated with ileal submucosal thickness. DEX treatment of newborn mice diminished IGF-I and caused significant thinning of the submucosa compared with controls. Submucosal growth and thickness in the neonatal mouse ileum is governed by IGF-I and is diminished by dexamethasone treatment.