Thrombomodulin (TM) is an endothelial anticoagulant cofactor that promotes thrombin-mediated formation of activated protein C (APC). We have found that the N-terminal lectin-like domain (D1) of TM has unique antiinflammatory properties. TM, via D1, binds high-mobility group-B1 DNA-binding protein (HMGB1), a factor closely associated with necrotic cell damage following its release from the nucleus, thereby preventing in vitro leukocyte activation, in vivo UV irradiation-induced cutaneous inflammation, and in vivo lipopolysaccharide-induced lethality. Our data also demonstrate antiinflammatory properties of a peptide spanning D1 of TM and suggest its therapeutic potential. These findings highlight a novel mechanism, i.e., sequestration of mediators, through which an endothelial cofactor, TM, suppresses inflammation quite distinctly from its anticoagulant cofactor activity, thereby preventing the interaction of these mediators with cell surface receptors on effector cells in the vasculature.

Thrombomodulin (TM) is an endothelial anticoagulant cofactor that promotes thrombin-mediated formation of activated protein C (APC). We have found that the N-terminal lectin-like domain (D1) of TM has unique antiinflammatory properties. TM, via D1, binds high-mobility group-B1 DNA-binding protein (HMGB1), a factor closely associated with necrotic cell damage following its release from the nucleus, thereby preventing in vitro leukocyte activation, in vivo UV irradiation-induced cutaneous inflammation, and in vivo lipopolysaccharide-induced lethality. Our data also demonstrate antiinflammatory properties of a peptide spanning D1 of TM and suggest its therapeutic potential. These findings highlight a novel mechanism, i.e., sequestration of mediators, through which an endothelial cofactor, TM, suppresses inflammation quite distinctly from its anticoagulant cofactor activity, thereby preventing the interaction of these mediators with cell surface receptors on effector cells in the vasculature.

Platelet-derived growth factor receptors (PDGFRs) belong to the same kinase group as c-Kit receptor tyrosine kinase that is specifically expressed in the interstitial cells of Cajal (ICC) in the gastrointestinal tract. In this study, we examined PDGFRalpha immunoreactivity in the murine gastrointestinal tract. PDGFRalpha-immunopositive (PDGFRalpha-ip) cells were observed in the musculature in all parts of the gastrointestinal tract. Although PDGFRalpha-ip cells were distinct from ICC and neurons, these cells were closely associated with intramuscular ICC and enteric nerve fibers. In the myenteric layer, PDGFRalpha-ip cells formed a cellular network with their ramified processes and encompassed myenteric ganglia. Numerous PDGFRalpha-ip cells were observed in the subserosal plane and showed a multipolar shape. The distribution pattern of the PDGFRalpha-ip cells in the ICC-deficient W(v)/W(v) mutant mice was the same as that in normal mice. PDGFRalpha-ip cells that showed intense immunoreactivity of SK3 potassium channel were considered to correspond to fibroblast-like cells or non-Cajal interstitial cells. Our observations suggest that PDGFRalpha-ip cells are basic cellular elements throughout the gastrointestinal musculature and are involved in the gastrointestinal functions.

Recent studies have demonstrated that intramuscular interstitial cells of Cajal (ICC) are preferential targets for neurotransmission in the stomach. Terminals of enteric motor neurones also form tight, synaptic-like contacts with ICC in the small intestine and colon, but little is known about the role of these cells in neurotransmission. ICC at the deep muscular plexus (ICC-DMP) of the small intestine express neurokinin 1 receptors (NK1R) and internalize these receptors in response to exogenous substance P. We used NK1R internalization as an assay of functional innervation of ICC-DMP in the murine small intestine. Under basal conditions NK1R-like immunoreactivity (NK1R-LI) was mainly observed in ICC-DMP (519 cells counted, 100% were positive) and myenteric neurones. ICC-DMP were closely apposed to substance P-containing nerve fibres. Of 338 ICC-DMP examined, 65% were closely associated with at least one substance P-positive nerve fibre, 32% were associated with at least two, 2% were associated with more than two nerve fibres and 1% with none. After electrical field stimulation (EFS, 10 Hz; 1 min) NK1R-LI was internalized in more than 80% of ICC-DMP, as compared to 10% of cells before EFS. Internalization of NK1R was not observed in myenteric ICC or smooth muscle cells in response to nerve stimulation. Internalization of NK1R-LI was blocked by the specific NK1 receptor antagonist WIN 62577 (1 microm) and by tetrodotoxin (0.3 microm), suggesting that internalization resulted from stimulation of receptors with neurally released neurokinins. These data suggest that ICC-DMP are primary targets for neurokinins released from enteric motor neurones in the intestine.

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