Immunohistochemical localization of thrombomodulin in the stratified epithelium of the rat is restricted to the keratinizing epidermis

Loss of Arnt (Hif1β) in mouse epidermis triggers dermal angiogenesis, blood vessel dilation and clotting defects

Targeted ablation of Aryl hydrocarbon receptor nuclear translocator (Arnt) in the mouse epidermis results in severe abnormalities in dermal vasculature reminiscent of petechia induced in human skin by anticoagulants or certain genetic disorders. Lack of Arnt leads to downregulation of Egln3/Phd3 hydroxylase and concomitant hypoxia-independent stabilization of hypoxia-induced factor 1α (Hif1α) along with compensatory induction of Arnt2. Ectopic induction of Arnt2 results in its heterodimerization with stabilized Hif1α and is associated with activation of genes coding for secreted proteins implicated in control of angiogenesis, coagulation, vasodilation and blood vessel permeability such as S100a8/S100a9, S100a10, Serpine1, Defb3, Socs3, Cxcl1 and Thbd. Since ARNT and ARNT2 heterodimers with HIF1α are known to have different (yet overlapping) downstream targets our findings suggest that loss of Arnt in the epidermis activates an aberrant paracrine regulatory pathway responsible for dermal vascular phenotype in K14-Arnt KO mice. This assumption is supported by a significant decline of von Willebrand factor in dermal vasculature of these mice where Arnt level remains normal. Given the essential role of ARNT in the adaptive response to environmental stress and striking similarity between skin vascular phenotype in K14-Arnt KO mice and specific vascular features of tumour stroma and psoriatic skin, we believe that further characterization of Arnt-dependent epidermal-dermal signalling may provide insight into the role of macro- and micro-environmental factors in control of skin vasculature and in pathogenesis of environmentally modulated skin disorders.

Localization of thrombomodulin in pericryptal fibroblasts of the rat duodenum

Thrombomodulin (TM) contributes to the inactivation of thrombin which activates protein C, a major anticoagulant and anti-inflammatory protein. This report describes the distribution and localization of TM in the rat duodenum by light and electron microscopic immunohistochemistry. In addition to the endothelium of the entire vasculature, TM was found on the non-vascular structures, cellular networks of pericryptal fibroblasts surrounding the bases of the glandular crypts. TM was localized on the plasma membrane of the pericryptal fibroblasts which existed in the pericryptal spaces between the basal lamina of the epithelium and the collagenous sheets around the base of the crypt. TM-immunoreactive pericryptal fibroblasts were stellate-shaped cells and contacted with each other by their cytoplasmic processes forming an anastomosing syncytium around the base of the crypt. In contrast to pericryptal fibroblasts, TM was not localized in subepithelial fibroblasts in the villi or smooth muscle cells in the lamina muscularis mucosae and the muscularis. The functional significance of TM in pericryptal fibroblasts is discussed.

Protein C and thrombomodulin in human acute lung injury

Decreased circulating protein C and increased circulating thrombomodulin are markers of the prothrombotic, antifibrinolytic state associated with poor outcomes in sepsis but have not been measured in patients with ALI (acute lung injury)/ARDS (acute respiratory distress syndrome). We measured circulating and intra-alveolar protein C and thrombomodulin in 45 patients with ALI/ARDS from septic and nonseptic causes and correlated the levels with clinical outcomes. Plasma protein C levels were lower in ALI/ARDS compared with normal. Lower levels of protein C were associated with worse clinical outcomes, including death, fewer ventilator-free days, and more nonpulmonary organ failures, even when only patients without sepsis were analyzed. Levels of thrombomodulin in pulmonary edema fluid from ALI/ARDS patients were >10-fold higher than normal plasma and 2-fold higher than ALI/ARDS plasma. Higher edema fluid thrombomodulin levels were associated with worse clinical outcomes. The higher levels in edema fluid compared with plasma suggest local release of soluble thrombomodulin in the lung, possibly from a lung epithelial source. To determine whether lung epithelial cells can release thrombomodulin, A549 cells and primary isolates of human alveolar type II cells were exposed to H2O2 or inflammatory cytokines. Both epithelial cell types released thrombomodulin into the media. In summary, the protein C system is markedly disrupted in patients with ALI/ARDS from both septic and nonseptic causes. The protein C system may be a potential therapeutic target in patients with ALI/ARDS.