Elevated tissue expression of thrombomodulatory factors correlates with acute symptomatic carotid plaque phenotype.

OBJECTIVES: Thrombomodulatory factors have been implicated in plaque instability. The aim was to examine the relationship between thrombomodulatory gene expression, timing of clinical events and plaque histology. DESIGN OF STUDY: Plaques were obtained from 40 consecutive patients undergoing carotid endarterectomy and divided into three groups (group 1, early symptomatic, within 1 month; group 2, late symptomatic, 1-6 months and group 3, asymptomatic). Total RNA was isolated to determine the expression of tissue plasminogen activator (t-PA), urokinase plasminogen activator (u-PA), plasminogen activator inhibitor-1 (PAI-1), tissue factor (TF), tissue factor pathway inhibitor (TFPI), thrombomodulin (TM), CD68 and vascular endothelial-cadherin (VE-Cadherin). RESULTS: Expression of t-PA, PAI-1, TF, TFPI, TM, CD68 and VE-cadherin were significantly increased in the early symptomatic group (p=0.019, 0.028, 0.018, 0.025, 0.038, 0.016 and 0.027 respectively), but the level of gene expression in the late symptomatic group was indistinguishable from the asymptomatic group. The incidence of plaque rupture and intraplaque haemorrhage was significantly increased in the early symptomatic groups (58% versus 18%/18% group 2/3, and 55% versus 6%/9% respectively, p<0.05 for both). CONCLUSIONS: Expression of thrombomodulatory genes is increased in unstable plaques, though levels after 1 month are comparable to asymptomatic plaques. This transient rise may influence plaque instability, and rapid resolution mirrors the clinical reduction in risk of further thrombo-embolic events.

Inducible expression of human endoglin during inflammation and wound healing in vivo.

OBJECTIVE: Because angiogenesis and inflammation are intimately associated and endoglin is required for angiogenesis, we wished to determine whether it also plays a role in inflammation. METHODS: Using an immunohistochemical approach, we examined spatial and temporal changes in endoglin expression during inflammation and angiogenesis. RESULTS: We found low levels of endoglin expression in quiescent endothelium in a range of normal adult human tissues. However, constitutive levels of expression are higher in dermal capillaries surrounding hair follicles and in alveolar capillaries as well as in the high endothelial cells of lymph tissue. During inflammatory disease, endoglin expression is strongly upregulated and is consistently associated with an infiltrate of inflammatory cells. For the first time, we have determined the relative changes in endoglin expression from the normal quiescent state through the inflammatory changes and angiogenesis that occur during dermal wound healing in vivo using a timed human wound healing model. Endoglin expression increases rapidly, reaching a peak of expression co-incident with maximal T cell infiltrate and persisting at an elevated level for at least 28 days in both activated and proliferating endothelial cells. CONCLUSION: Enhanced endoglin expression is not limited to angiogenesis, it is also associated with inflammation.

Endoglin, an ancillary TGFbeta receptor, is required for extraembryonic angiogenesis and plays a key role in heart development.

Endoglin (CD105) is expressed on the surface of endothelial and haematopoietic cells in mammals and binds TGFbeta isoforms 1 and 3 in combination with the signaling complex of TGFbeta receptors types I and II. Endoglin expression increases during angiogenesis, wound healing, and inflammation, all of which are associated with TGFbeta signaling and alterations in vascular structure. The importance of endoglin for normal vascular architecture is further indicated by the association of mutations in the endoglin gene with the inherited disorder Hereditary Haemorrhagic Telangiectasia Type 1 (HHT1), a disease characterised by bleeding from vascular malformations. In order to study the role of endoglin in vivo in more detail and to work toward developing an animal model of HHT1, we have derived mice that carry a targeted nonsense mutation in the endoglin gene. Studies on these mice have revealed that endoglin is essential for early development. Embryos homozygous for the endoglin mutation fail to progress beyond 10.5 days postcoitum and fail to form mature blood vessels in the yolk sac. This phenotype is remarkably similar to that of the TGFbeta1 and the TGFbeta receptor II knockout mice, indicating that endoglin is needed in vivo for TGFbeta1 signaling during extraembryonic vascular development. In addition, we have observed cardiac defects in homozygous endoglin-deficient embryos, suggesting endoglin also plays a role in cardiogenesis. We anticipate that heterozygous mice will ultimately serve as a useful disease model for HHT1, as some individuals have dilated and fragile blood vessels similar to vascular malformations seen in HHT patients.