Upregulation and spatial shift in the localization of the mannose 6-phosphate/insulin-like growth factor II receptor during radiation enteropathy development in the rat.
OBJECTIVE
Transforming growth factor beta1 (TGF-beta1) appears to play an important role in the pathogenesis of chronic radiation-induced fibrosis in the intestine and several other organs. TGF-beta1 is secreted as a non-biologically active complex and its function depends on activation. In vitro data suggest that the mannose 6-phosphate/insulin-like growth factor-beta (M6P/IGF-II) receptor is involved in the mechanism of TGF-beta1 activation. Thus, we used a rat model of radiation enteropathy to examine the potential role of the M6P/IGF-II receptor in the in vivo regulation of TGF-beta1 activity and localization.


METHODS
A scrotal hernia containing a loop of small intestine was created in male rats. The intestine in the scrotum was exposed to 0, 12, or 21 Gy single dose X-radiation. Groups of rats were euthanized 1 day and 2, 6 and 26 weeks after irradiation. Histopathologic injury was assessed with a radiation injury score (RIS). Computerized image analysis was used to identify M6P/IGF-II receptor-positive cells and to quantify extracellular matrix-associated TGF-beta1 immunoreactivity. Changes in urokinase plasminogen activator (uPA), tissue-like plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) immunoreactivity were also assessed.


RESULTS
In normal (sham-irradiated) intestine, M6P/IGF-II immunoreactivity was confined to relatively weak, but specific epithelial staining. Irradiated intestine exhibited a highly significant time- and dose-dependent increase in the number of M6P/IGF-II receptor-positive cells (P < 0.001). There was a striking spatial shift of M6P/IGF-II receptor immunoreactivity from epithelium during the early post-radiation phase to stromal cells, most notably fibroblasts during the later stages of injury. Irradiated intestine exhibited distinct co-localization of M6P/ IGF-II receptor-positive cells and extracellular matrix-associated TGF-beta1 in areas of histopathologic injury. There were highly significant associations between the number of M6P/IGF-II receptor-positive stromal cells and TGF-beta1 immunoreactivity (P < 0.001), radiation-induced fibrosis (P < 0.001) and RIS (P < 0.001). Endothelial tPA immunoreactivity decreased significantly after irradiation (P < 0.001), whereas uPA and PAI-1 immunoreactivity levels appeared to be unchanged.


CONCLUSIONS
M6P/IGF-II receptor upregulation may be a key factor in the in vivo control of TGF-beta1 activity and responsible for the tissue specificity of TGF-beta1 action after irradiation.
Wang
J
J
Department of Surgery, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
Richter
K K
KK
Sung
C C
CC
Hauer-Jensen
M
M
D000818:Animals; D015415:Biomarkers; D005109:Extracellular Matrix / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D005500:Follow-Up Studies; D007410:Intestinal Diseases / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D007421:Intestine, Small / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D008297:Male; D008360:Mannosephosphates / Q000378:metabolism*; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D011833:Radiation Injuries, Experimental / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology
D015415:Biomarkers; D008360:Mannosephosphates; D017395:Plasminogen Activator Inhibitor 1; D017527:Receptor, IGF Type 2; D016212:Transforming Growth Factor beta; C027693:mannose-6-phosphate; D010959:Tissue Plasminogen Activator