Preeclampsia is a pregnancy-specific hypertensive syndrome that causes substantial maternal and fetal morbidity and mortality. Maternal endothelial dysfunction mediated by excess placenta-derived soluble VEGF receptor 1 (sVEGFR1 or sFlt1) is emerging as a prominent component in disease pathogenesis. We report a novel placenta-derived soluble TGF-beta coreceptor, endoglin (sEng), which is elevated in the sera of preeclamptic individuals, correlates with disease severity and falls after delivery. sEng inhibits formation of capillary tubes in vitro and induces vascular permeability and hypertension in vivo. Its effects in pregnant rats are amplified by coadministration of sFlt1, leading to severe preeclampsia including the HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome and restriction of fetal growth. sEng impairs binding of TGF-beta1 to its receptors and downstream signaling including effects on activation of eNOS and vasodilation, suggesting that sEng leads to dysregulated TGF-beta signaling in the vasculature. Our results suggest that sEng may act in concert with sFlt1 to induce severe preeclampsia.

Abstract-Decreased endothelial NO synthase (eNOS)-derived NO bioavailability and impaired vasomotor control are crucial factors in cardiovascular disease pathogenesis. Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a vascular disorder associated with ENDOGLIN (ENG) haploinsufficiency and characterized by venous dilatations, focal loss of capillaries, and arteriovenous malformations (AVMs). We report that resistance arteries from Eng ϩ/Ϫ mice display an eNOS-dependent enhancement in endothelium-dependent dilatation and impairment in the myogenic response, despite reduced eNOS levels. We have found that eNOS is significantly reduced in endoglin-deficient endothelial cells because of decreased eNOS protein half-life. We demonstrate that endoglin can reside in caveolae and associate with eNOS, suggesting a stabilizing function of endoglin for eNOS. After Ca 2ϩ -induced activation, endoglin-deficient endothelial cells have reduced eNOS/Hsp90 association, produce less NO, and generate more eNOS-derived superoxide (O 2 Ϫ ), indicating that endoglin also facilitates eNOS/Hsp90 interactions and is an important regulator in the coupling of eNOS activity. Treatment with an O 2 Ϫ scavenger reverses the vasomotor abnormalities in Eng ϩ/Ϫ arteries, suggesting that uncoupled eNOS and resulting impaired myogenic response represent early events in HHT1 pathogenesis and that the use of antioxidants may provide a novel therapeutic modality. Key Words: endothelium Ⅲ superoxide Ⅲ vascular disease Ⅲ vascular tone Ⅲ vasodilatation R esistance arteries normally contract in response to increases in perfusion pressure. This reflex, referred to as the myogenic response (MR), plays an important role in the local regulation of vascular tone and blood flow. By limiting the transmission of excessive hemodynamic forces to downstream capillaries and venules, the arterial MR also preserves the structural integrity of the microcirculation. 1 Although the MR is an intrinsic property of vascular smooth muscle, it is modulated by endothelium-derived vasoactive factors, most notably NO. 2 In the vasculature, endothelial NO synthase (eNOS) produces NO in response to humoral and mechanical stimuli via location-specific and dynamic interactions with its various allosteric regulators, including caveolin-1 (Cav-1) and Hsp90. 3-5 Impaired vasomotor control attributable to decreased eNOS-derived NO bioavailability is suggested to be a crucial factor in cardiovascular disease pathogenesis. Moreover, a mathematical model of microcirculatory hemodynamics predicts that a loss of vasomotor control may cause arteriovenous malformations (AVMs). 6 Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a vascular disorder characterized by AVMs. This autosomal dominant disorder is associated with endoglin (ENG) haploinsufficiency 7 and vascular abnormalities ranging from venous dilatations to focal loss of capillaries leading to AVMs. 8 Endoglin (Eng) is a 180-kD glycoprotein expressed on endothelial cells, 9 acting as an ancillary receptor for several transf...

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.

Endothelial and epithelial barrier disruptions are detected via local decrease in cellular tension, which are coupled to reactive oxygen species–dependent self-restorative actin remodeling dynamics.

We tested the hypothesis that induction of neuronal NO synthase (nNOS) impairs vascular smooth muscle contractility after hypoxia. nNOS protein was increased in aorta, mesenteric arterioles, pulmonary arteries, brain, and diaphragm from rats exposed to 8% O 2 for 48 hours and in human aortic SMCs after hypoxic incubation (1% O 2 ). Ca 2+ -dependent NO synthase activity was increased in endothelium-denuded aortic segments from hypoxia-exposed rats. N G -nitro-l-arginine methyl ester enhanced the contractile responses of endothelium-denuded aortic rings and mesenteric arterioles from hypoxia-exposed but not normoxic rats (P < 0.05). The hypoxia-inducible mRNA transcript expressed by human cells was found to contain a novel 5′-untranslated region, consistent with activation of transcription in the genomic region contiguous with exon 2. Translational efficiency of this transcript is markedly increased compared with previously described human nNOS mRNAs. Transgenic mice possessing a lacZ reporter construct under control of these genomic sequences demonstrated expression of the construct after exposure to hypoxia (8% O 2 , 48 hours) in the aorta, mesenteric arterioles, renal papilla, and brain. These results reveal a novel human nNOS promoter that confers the ability to rapidly upregulate nNOS expression in response to hypoxia with a functionally significant effect on vascular smooth muscle contraction.

The goal of this study was to determine whether hypoxia alters expression of endothelial nitric oxide synthase (eNOS) in the systemic circulation. Rats breathed either air or 10% oxygen for 12 hours, 48 hours, or 7 days. Thoracic aortas were excised and either mounted in organ bath myographs or frozen in liquid nitrogen for later extraction of protein and RNA. eNOS protein (Western blotting) was decreased (20% of normoxic control) after 12 hours, 48 hours, and 7 days of hypoxia. eNOS mRNA (ribonuclease protection assay) was similarly reduced. Acetylcholine (10(-4) mol/L) reversed phenylephrine (10(-5) mol/L) preconstriction by 53.3+/-5.6% in aortic rings from normoxic rats and 26.1+/-4.8% in rings from rats exposed to hypoxia for 48 hours (P<0.05), with comparable impairment of relaxation by the calcium ionophore A23187 (10(-5) mol/L). Responses to diethylamine nitric oxide and 8-bromo-cGMP were unaffected. Aortic cGMP levels after incubation with acetylcholine (10(-6) mol/L) averaged 14.0+/-1.8 fmol/mg in rings from normoxic rats compared with 8.7+/-1.0 fmol/mg in rings from hypoxic rats (P<0. 05). Similarly, nitrate concentration (by capillary electrophoresis) in the media in which the rings were incubated was reduced in the hypoxic group (5.6+/-0.23 micromol/L for hypoxic rats and 7.8+/-0.7 micromol/L for normoxic rats). Impaired endothelial NO release may handicap the vascular responses that defend vital organ function during hypoxia.

Background and Purpose-Hereditary hemorrhagic telangiectasia type 1 (HHT1) is an autosomal dominant vascular dysplasia caused by mutations in the endoglin gene and characterized by dilated vessels and arteriovenous malformations (AVMs). To understand the etiology of this disorder, we evaluated the cerebral vasculature of endoglin heterozygous (Eng ϩ/Ϫ ) mice, which represent the only animal model of HHT1. Methods-The cerebral vasculature of Eng ϩ/Ϫ and Eng ϩ/ϩ mice from C57BL/6 (B6) and 129/Ola (129) strains with a differential susceptibility to HHT1 was studied with corrosion casting. Casts were observed by scanning electron microscopy to detect malformations and evaluate arterial diameters and orientation of endothelial nuclei. Measurements were taken to assess relative constriction at arteriolar branching points and downstream relative dilatation. Results-Three of 10 Engϩ/Ϫ mice demonstrated abnormal vascular findings including AVMs, while none of 15 Eng

Objective-Loss-of-function mutations in genes coding for transforming growth factor-␤/bone morphogenetic protein receptors and changes in nitric oxide) bioavailability are associated with hereditary hemorrhagic telangiectasia and some forms of pulmonary arterial hypertension. How these abnormalities lead to seemingly disparate pulmonary pathologies remains unknown. Endoglin (Eng), a transforming growth factor-␤ coreceptor, is mutated in hereditary hemorrhagic telangiectasia and involved in regulating endothelial NO• synthase (eNOS)-derived NO • production and oxidative stress. Because some patients with pulmonary arterial hypertension harbor ENG mutations leading to haplo insufficiency, we investigated the pulmonary vasculature of Eng ϩ/Ϫ mice and the potential contribution of abnormal eNOS activation to pulmonary arterial hypertension. Methods and Results-Hemodynamic, histological, and biochemical assessments and x-ray micro-CT imaging of adult Eng ϩ/Ϫ mice indicated signs of pulmonary arterial hypertension including increased right ventricular systolic pressure, degeneration of the distal pulmonary vasculature, and muscularization of small arteries. These findings were absent in 3-week-old Eng ϩ/Ϫ mice and were attributable to constitutively uncoupled eNOS activity in the pulmonary circulation, as evidenced by reduced eNOS/heat shock protein 90 association and increased eNOS-derived superoxide () production in a BH 4 -independent manner. These changes render eNOS unresponsive to regulation by transforming growth factor-␤/bone morphogenetic protein and underlie the signs of pulmonary arterial hypertension that were prevented by Tempol. Conclusion-Adult Engϩ/Ϫ mice acquire signs of pulmonary arterial hypertension that are attributable to uncoupled eNOS activity and increasedϪ production, which can be prevented by antioxidant treatment. Eng links transforming growth factor/bone morphogenetic protein receptors to the eNOS activation complex, and its reduction in the pulmonary vasculature leads to increased oxidative stress and pulmonary arterial hypertension. Key Words: Alk-1 Ⅲ endoglin Ⅲ free radicals Ⅲ nitric oxide Ⅲ pulmonary arterial hypertension Ⅲ transforming growth factor E ndoglin (Eng; CD105) is a an ancillary receptor for several transforming growth factor (TGF)-␤ superfamily ligands, including bone morphogenetic proteins (BMP). 1 It is predominantly expressed on vascular endothelial cells 2 and found in both TGF-␤ and BMP receptor complexes, 1,3 where it modulates TGF-␤1/␤3 4 and BMP9/10 effects, 5 respectively, via its physical association with the activin-like kinase receptor-1 (ACVLR1) gene product, ALK1. Eng-null mice die at mid-gestation with impaired angiogenesis and severe cardiac defects. 6,7 Whereas Eng ϩ/Ϫ mice have a normal lifespan, they display abnormal systemic vascular autoregulatory functions related to endothelial nitric oxide synthase (eNOS) activity. 8 Mutations in the endoglin (ENG) and activin-like kinase 1 receptor (ACVLR1) genes lead to haploinsufficiency and are the underlying ca...