title: Deficiency of microvascular thrombomodulin and up-regulation of protease-activated receptor-1 in irradiated rat intestine: possible link between endothelial dysfunction and chronic radiation fibrosis.
abstract: Microvascular injury is believed to be mechanistically involved in radiation fibrosis, but direct molecular links between endothelial dysfunction and radiation fibrosis have not been established in vivo. We examined radiation-induced changes in endothelial thrombomodulin (TM) and protease-activated receptor-1 (PAR-1) in irradiated intestine, and their relationship to structural, cellular, and molecular aspects of radiation injury. Rat small intestine was locally exposed to fractionated X-radiation. Structural injury was assessed 24 hours and 2, 6, and 26 weeks after the last radiation fraction using quantitative histology and morphometry. TM, neutrophils, transforming growth factor-beta, and collagens I and III were assessed by quantitative immunohistochemistry. PAR-1 protein was localized immunohistochemically, and cells expressing TM or PAR-1 transcript were identified by in situ hybridization. Steady-state PAR-1 mRNA levels in intestinal smooth muscle were determined using laser capture microdissection and competitive reverse transcriptase-polymerase chain reaction. Radiation caused a sustained, dose-dependent decrease in microvascular TM. The number of TM-positive vessels correlated with all parameters of radiation enteropathy and, after adjusting for radiation dose and observation time in a statistical model, remained independently associated with neutrophil infiltration, intestinal wall thickening, and collagen I accumulation. PAR-1 immunoreactivity and transcript increased in vascular and intestinal smooth muscle cells in irradiated intestine. PAR-1 mRNA increased twofold in irradiated intestinal smooth muscle. Intestinal irradiation up-regulates PAR-1 and causes a dose-dependent, sustained deficiency of microvascular TM that is independently associated with the severity of radiation toxicity. Interventions aimed at preserving or restoring endothelial TM or blocking PAR-1 should be explored as strategies to increase the therapeutic ratio in clinical radiation therapy.
authors.affiliation: Department of Surgery, University of Arkansas for Medical Sciences and Central Arkansas Veterans Healthcare System, Little Rock, Arkansas 72205, USA.
authors.forename: Junru
authors.initials: J
authors.lastname: Wang
authors.forename: Huaien
authors.initials: H
authors.lastname: Zheng
authors.forename: Xuemei
authors.initials: X
authors.lastname: Ou
authors.forename: Louis M
authors.initials: LM
authors.lastname: Fink
authors.forename: Martin
authors.initials: M
authors.lastname: Hauer-Jensen
mesh_terms: D000818:Animals; D002908:Chronic Disease; D004727:Endothelium / Q000503:physiopathology; D005355:Fibrosis; D017403:In Situ Hybridization; D007410:Intestinal Diseases / Q000503:physiopathology*; D007422:Intestines / Q000528:radiation effects*; D008297:Male; D008833:Microcirculation; D012333:RNA, Messenger / Q000378:metabolism; D011833:Radiation Injuries, Experimental / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000096:biosynthesis*; D018180:Thrombomodulin / Q000172:deficiency*; D015854:Up-Regulation
chemical_list: D012333:RNA, Messenger; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; D018180:Thrombomodulin