Amelioration of excess collagen IαI, fibrosis, and smooth muscle growth in TNBS-induced colitis in IGF-I(+/-) mice.
BACKGROUND
Strictures occur in ≈ 30% of patients with Crohn's disease (CD) and are characterized by intestinal smooth muscle hyperplasia, hypertrophy, and fibrosis due to excess extracellular matrix production including collagen. Insulin-like growth factor-I (IGF-I) expression is increased in smooth muscle cells of the muscularis propria in CD and in animal models of CD, including trinitrobenzene sulfonic acid (TNBS)-induced colitis. While upregulated IGF-I is conjectured to cause smooth muscle cell growth and collagen production in the inflamed intestine, its role in the development of fibrosis has not been directly demonstrated.


METHODS
Colitis was induced in IGF-I(+/-) or wildtype C57BL/6J mice by rectal administration of TNBS or ethanol vehicle. After 7 days, colonic smooth muscle cells were isolated and used to prepare RNA or protein lysates. Transcript levels of IGF-IEa, IGF binding protein (IGFBP)-3, IGFBP-5, TGF-β1, and collagen IαI were measured by quantitative reverse-transcription polymerase chain reaction (RT-PCR). Corresponding protein levels were measured by Western blot or enzyme-linked immunosorbent assay (ELISA). Fibrosis was measured using digital image analysis of Masson's trichrome-stained histologic sections.


RESULTS
In IGF-I(+/-) mice, which express significantly lower levels of IGF-I than wildtype, the response to TNBS-induced colitis: upregulation of IGF-I, IGFBP-3, IGFBP-5 muscle growth, and collagen IαI expression, the resulting collagen deposition, and fibrosis are all significantly diminished compared to C57BL/6J wildtype controls. TGF-β1 expression and its increase following TNBS administration are not altered in IGF-I(+/-) mice compared to wildtype.


CONCLUSIONS
The findings indicate that IGF-I is a key regulator in intestinal smooth muscle hyperplasia and excess collagen production that leads to fibrosis and long term to stricture formation.
Mahavadi
Sunila
S
Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia 23298-0341, USA.
Flynn
Robert S
RS
Grider
John R
JR
Qiao
Li-Ya
LY
Murthy
Karnam S
KS
Hazelgrove
Krystina B
KB
Kuemmerle
John F
JF
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002478:Cells, Cultured; D003092:Colitis / Q000139:chemically induced / Q000378:metabolism*; D024042:Collagen Type I / Q000378:metabolism*; D000090602:Collagen Type I, alpha 1 Chain; D004797:Enzyme-Linked Immunosorbent Assay; D005355:Fibrosis / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D007422:Intestines / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009130:Muscle, Smooth / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D014302:Trinitrobenzenesulfonic Acid / Q000633:toxicity
D024042:Collagen Type I; D000090602:Collagen Type I, alpha 1 Chain; D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; D012333:RNA, Messenger; D053773:Transforming Growth Factor beta1; D007334:Insulin-Like Growth Factor I; D014302:Trinitrobenzenesulfonic Acid