title: Cellular sources of transforming growth factor-beta isoforms in early and chronic radiation enteropathy.
abstract: The three mammalian transforming growth factor (TGF)-beta isoforms (TGF-beta1, TGF-beta2, and TGF-beta3) differ in their putative roles in radiation-induced fibrosis in intestine and other organs. Furthermore, tissue specificity of TGF-beta action may result from temporal or spatial changes in production and/or activation. The present study examined shifts in the cell types expressing TGF-beta mRNA relative to TGF-beta immunoreactivity and histopathological injury during radiation enteropathy development. A 4-cm loop of rat small intestine was locally exposed to O, 12, or 21-Gy single doses of x-irradiation. Sham-irradiated and irradiated intestine were procured 2 and 26 weeks after irradiation. Cells expressing the TGF-beta1, TGF-beta2, or TGF-beta3 transcripts were identified by in situ hybridization with digoxigenin-labeled riboprobes. Intestinal wall TGF-beta immunoreactivity was measured using computerized image analysis, and structural radiation injury was assessed by quantitative histopathology. Normal intestinal epithelium expressed transcripts for all three TGF-beta isoforms. Two weeks after irradiation, regenerating crypts, inflammatory cells, smooth muscle cells, and mesothelium exhibited increased TGF-beta1 expression and, to a lesser degree, TGF-beta2 and TGF-beta3 expression. Twenty-six weeks after irradiation, TGF-beta2 and TGF-beta3 expression had returned to normal. In contrast, TGF-beta1 expression remained elevated in smooth muscle, mesothelium, endothelium, and fibroblasts in regions of chronic fibrosis. Extracellular matrix-associated TGF-beta1 immunoreactivity was significantly increased at both observation times, whereas, TGF-beta2 and TGF-beta3 immunoreactivity exhibited minimal postradiation changes. Intestinal radiation injury is associated with overexpression of all three TGF-beta isoforms in regenerating epithelium. Radiation enteropathy was also associated with sustained shifts in the cellular sources of TGF-beta1 from epithelial cells to cells involved in the pathogenesis of chronic fibrosis. TGF-beta2 and TGF-beta3 did not exhibit consistent long-term changes. TGF-beta1 appears to be the predominant isoform in radiation enteropathy and may be more important in the mechanisms of chronicity than TGF-beta2 and TGF-beta3.
authors.affiliation: Department of Surgery, University of Arkansas for Medical Sciences, Little Rock, USA.
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: H
authors.initials: H
authors.lastname: Zheng
authors.forename: C C
authors.initials: CC
authors.lastname: Sung
authors.forename: K K
authors.initials: KK
authors.lastname: Richter
authors.forename: M
authors.initials: M
authors.lastname: Hauer-Jensen
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000032:analysis; D004307:Dose-Response Relationship, Radiation; D005109:Extracellular Matrix / Q000378:metabolism; D017403:In Situ Hybridization; D007410:Intestinal Diseases / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000473:pathology / Q000528:radiation effects*; D008297:Male; D016376:Oligonucleotides, Antisense / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011833:Radiation Injuries, Experimental / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta