ABSTRACT
Partial resection of the small intestine results in compensatory proliferation and adaptation in the remaining small intestinal mucosa. The molecular mechanisms governing the proliferative response are not known, nor has the timing of events associated with proliferation been adequately defined, particularly during the period just after resection. We designed experiments to characterize early (within 24 h) proliferative events associated with proximal intestinal resection and sought to determine the cell type that first responds to proliferative stimuli. Twenty-one day old male Sprague-Dawley rats underwent a 70% proximal intestinal resection or transection (control). Poly(A) RNA was isolated from the distal (ileal) remnants. Northern blots showed a marked induction of the immediate early genes zif-268, nup-475, and c-myc 1-3 h following resection, but not following transection. Immunohistochemical analysis of c-myc expression in ileal crypt epithelial cells showed a biphasic induction that was most marked 6 h after resection and less prominent 24 h after resection. Immunostaining with 5-bromodeoxyuridine (5-BrdU) was restricted to ileal crypt nuclei and was maximal 24 h after resection. All these events were observed in the absence of nutrient intake. Taken together, these data show that a potent nutrient-independent stimulus for intestinal epithelial cell proliferation occurs within minutes of partial small intestinal resection and that the first targets of this stimulus are crypt epithelial cells in the residual intestine.
Subject(s)
Immediate-Early Proteins , Intestinal Mucosa/cytology , Intestine, Small/surgery , Animals , Blotting, Northern , Bromodeoxyuridine/analysis , Cell Division , DNA/biosynthesis , DNA-Binding Proteins/genetics , Early Growth Response Protein 1 , Gene Expression , Genes, myc , Immunohistochemistry , Intestinal Mucosa/metabolism , Intestine, Small/cytology , Intestine, Small/metabolism , Male , Proteins/genetics , RNA/isolation & purification , RNA, Messenger/metabolism , Rats , Rats, Sprague-Dawley , Transcription Factors/genetics , Tristetraprolin , Zinc FingersABSTRACT
BACKGROUND: The transforming growth factor beta (TGF-beta) proteins are key regulators of cellular growth and differentiation. Previous studies have shown that TGF-beta 1 is a potent growth inhibitor of cultured jejunal epithelial cells. The reported distribution of TGF-beta 1 messenger RNA (mRNA) expression along the intestinal villus has been controversial. The purpose of the current study is to determine the loci of TGF-beta protein expression in the normal small intestine and colon. METHODS: Intestinal localization of TGF-beta isoform mRNA and protein was examined by Northern blot analysis and immunohistochemistry using isoform specific reagents. RESULTS: TGF-beta 1, TGF-beta 2, and TGF-beta 3 mRNA were found in homogenates from the intact mouse jejunum and colon. The three isoforms colocalized in these tissues. Expression in the small intestinal epithelium was most prominent in cells located on the villus tip, and no staining was detected in the crypt. Occasional lymphocytes in the lamina propria were immunopositive, and all layers of the muscularis were moderately stained. This pattern was seen in all regions of the small intestine. The surface epithelium of the colon was intensely immunopositive, whereas cells in the glands were only weakly stained. CONCLUSIONS: TGF-beta molecules may serve overlapping functions in the intestinal tract, and expression in the epithelium may function to arrest growth of cells emerging from the crypt and induce or maintain the terminally differentiated state.
