Although vascular development is normal in Eng(+/-) mice, angiogenic abnormalities were observed in the adult mice and their isolated endothelial cells. These results suggest that a normal level of endoglin is required for full angiogenic activity.

TGFβ regulates cellular processes by binding to type I and type II TGFβ receptors (TβRI and TβRII, respectively). In addition to these signaling receptors, endoglin is an accessory TGFβ receptor that regulates TGFβ signaling. Although there are two different alternatively spliced isoforms of endoglin, L-endoglin (L, long) and S-endoglin (S, short), little is known about the effects of S-endoglin isoform on TGFβ signaling. Here, we have analyzed the TGFβ1 signaling pathways and the effects of L- and S-endoglin in endoglin-deficient L6E9 cells. We found that TGFβ activates two distinct TβRI-Smad signaling pathways: ALK1-Smad1-Id1 and ALK5-Smad2-PAI1, in these cells. Interestingly, L-endoglin enhanced the ALK1-Id1 pathway, while S-endoglin promoted the ALK5-PAI1 route. These effects on signaling are supported by biological effects on TGFβ1-induced collagen I expression and inhibition of cell proliferation. Thus, while L-endoglin decreased TGFβ1-induced collagen I and CTGF expression and increased TGFβ1-induced proliferation, S-endoglin strongly increased TGFβ1-induced collagen I and CTGF expression, and reduced TGFβ1-induced cell proliferation.

The circulatory system is walled off by different cell types, including vascular mural cells and podocytes. The interaction and interplay between endothelial cells (ECs) and mural cells, such as vascular smooth muscle cells or pericytes, play a pivotal role in vascular biology. Endoglin is an RGD-containing counter-receptor for β1 integrins and is highly expressed by ECs during angiogenesis. We find that the adhesion between vascular ECs and mural cells is enhanced by integrin activators and inhibited upon suppression of membrane endoglin or β1-integrin, as well as by addition of soluble endoglin (SolEng), anti-integrin α5β1 antibody or an RGD peptide. Analysis of different endoglin mutants, allowed the mapping of the endoglin RGD motif as involved in the adhesion process. In Eng+/− mice, a model for hereditary hemorrhagic telangectasia type 1, endoglin haploinsufficiency induces a pericyte-dependent increase in vascular permeability. Also, transgenic mice overexpressing SolEng, an animal model for preeclampsia, show podocyturia, suggesting that SolEng is responsible for podocytes detachment from glomerular capillaries. These results suggest a critical role for endoglin in integrin-mediated adhesion of mural cells and provide a better understanding on the mechanisms of vessel maturation in normal physiology as well as in pathologies such as preeclampsia or hereditary hemorrhagic telangiectasia.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-015-2099-4) contains supplementary material, which is available to authorized users.

We have generated mouse transgenic lineages for C3G (tgC3G) and C3GΔCat (tgC3GΔCat, C3G mutant lacking the GEF domain), where the transgenes are expressed under the control of the megakaryocyte and platelet specific PF4 (platelet factor 4) gene promoter. Transgenic platelet activity has been analyzed through in vivo and in vitro approaches, including bleeding time, aggregation assays and flow cytometry. Both transgenes are expressed (RNA and protein) in purified platelets and megakaryocytes and do not modify the number of platelets in peripheral blood. Transgenic C3G animals showed bleeding times significantly shorter than control animals, while tgC3GΔCat mice presented a remarkable bleeding diathesis as compared to their control siblings. Accordingly, platelets from tgC3G mice showed stronger activation in response to platelet agonists such as thrombin, PMA, ADP or collagen than control platelets, while those from tgC3GΔCat animals had a lower response. In addition, we present data indicating that C3G is a mediator in the PKC pathway leading to Rap1 activation. Remarkably, a significant percentage of tgC3G mice presented a higher level of neutrophils than their control siblings. These results indicate that C3G plays an important role in platelet clotting through a mechanism involving its GEF activity and suggest that it might be also involved in neutrophil development.

Following arterial occlusion, blood vessels respond by forming a new network of functional capillaries (angiogenesis), by re-organizing pre-existing capillaries through the recruitment of smooth muscle cells to generate new arteries (arteriogenesis) and by growing and remodeling pre-existing collateral arterioles into physiologically relevant arteries (collateral development). All these processes result in the recovery of organ perfusion. The importance of endoglin in post-occlusion reperfusion is sustained by several observations: i) endoglin expression is increased in vessels showing active angiogenesis/remodeling; ii) genetic endoglin haploinsufficiency in humans causes deficient angiogenesis; and iii) the reduction of endoglin expression by gene disruption or the administration of endoglin-neutralizing antibodies reduces angiogenesis and revascularization. However, the precise role of endoglin in the several processes associated with revascularization has not been completely elucidated and, in some cases, the function ascribed to endoglin by different authors is controversial. The purpose of this review is to organize in a critical way the information available for the role of endoglin in several phenomena (angiogenesis, arteriogenesis, and collateral development) associated with post-ischemic revascularization.

Abstract-The endoglin heterozygous (Eng ϩ/Ϫ ) mouse, which serves as a model of hereditary hemorrhagic telangiectasia (HHT), was shown to express reduced levels of endothelial NO synthase (eNOS) with impaired activity. Because of intricate changes in vasomotor function in the Eng ϩ/Ϫ mice and the potential interactions between the NO-and prostaglandin-producing pathways, we assessed the expression and function of cyclooxygenase (COX) isoforms. A specific upregulation of COX-2 in the vascular endothelium and increased urinary excretion of prostaglandin E 2 were observed in the Eng ϩ/Ϫ mice. Specific COX-2 inhibition with parecoxib transiently increased arterial pressure in Engbut not in Eng ϩ/ϩ mice. Transfection of endoglin in L6E9 myoblasts, shown previously to stimulate eNOS expression, led to downregulation of COX-2 with no change in COX-1. In addition, COX-2 promoter activity and protein levels were inversely correlated with endoglin levels, in doxycyclin-inducible endothelial cells. Chronic NO synthesis inhibition with N -nitro-L-arginine methyl ester induced a marked increase in COX-2 only in the normal Eng ϩ/ϩ mice. N -nitro-L-arginine methyl ester also increased COX-2 expression and promoter activity in doxycyclin-inducible endoglin expressing endothelial cells, but not in control cells. The level of COX-2 expression following transforming growth factor-␤1 treatment was less in endoglin than in mock transfected L6E9 myoblasts and was higher in human endothelial cells silenced for endoglin expression. Our results indicate that endoglin is involved in the regulation of COX-2 activity. Furthermore, reduced endoglin levels and associated impaired NO production may be responsible, at least in part, for augmented COX-2 expression and activity in the

Endoglin is a proliferation-associated and hypoxia-inducible protein expressed in endothelial cells. The levels of soluble circulating endoglin and their prognostic significance in patients with acute myocardial infarction (AMI) are not known. In this observational prospective study serum endoglin levels were measured by ELISA in 183 AMI patients upon admission to hospital and 48 hrs later and in 72 healthy controls. Endoglin levels in AMI patients on admission were significantly lower than in healthy controls (4.25 ± 0.99 ng/ml versus 4.59 ± 0.87 ng/ml; P= 0.013), and decreased further in the first 48 hours (3.65 ± 0.76 ng/ml, P < 0.001). Upon follow-up (median 319 days), patients who died had a significantly greater decrease in serum endoglin level over the first 48 hrs than those who survived (1.03 ± 0.91 versus 0.54 ± 0.55 ng/ml; P= 0.025). Endoglin decrease was an independent predictor of short-term (30 days) (hazard ratio 2.33;95% CI = 1.27–4.23; P= 0.006) cardiovascular mortality, and also predicts overall cardiovascular mortality during the follow-up (median 319 days) in AMI patients (hazard ratio 2.13;95% CI = 1.20–3.78; P= 0.01). In conclusion, early changes in serum endoglin may predict mortality after AMI.

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