Endoglin (CD105), a transmembrane protein of the transforming growth factor ␤ superfamily, plays a crucial role in angiogenesis. Mutations in endoglin result in the vascular defect known as hereditary hemorrhagic telangiectasia (HHT1). The soluble form of endoglin was suggested to contribute to the pathogenesis of preeclampsia. To obtain further insight into its function, we cloned, expressed, purified, and characterized the extracellular domain (ECD) of mouse and human endoglin fused to an immunoglobulin Fc domain. We found that mouse and human endoglin ECD-Fc bound directly, specifically, and with high affinity to bone morphogenetic proteins 9 and 10 (BMP9 and BMP10) in surface plasmon resonance (Biacore) and cell-based assays. We performed a function mapping analysis of the different domains of endoglin by examining their contributions to the selectivity and biological activity of the protein. Endoglin (CD105) is a homodimeric glycosylated cell-surface protein of 180 kDa previously identified as a co-receptor belonging to the TGF␤ superfamily (1). Several lines of evidence support an important role of endoglin in cardiovascular development and vascular remodeling (2). Loss-of-function mutations in endoglin are implicated in the vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1), 3 which is a bleeding disorder characterized by arteriovenous malformations in the brain, lungs, and liver and is attributed to haploinsufficiency (3-5). Homozygous endoglin knock-out mice die during early gestation due to the lack of development of normal mature blood vessels (6). Adult endoglin heterozygous mice (7-8) or mice with a conditional mutation in the endoglin gene (9) exhibited similar angiogenic abnormalities and were used as animal models for HHT1. Mutations in the endoglin gene found in numerous HHT1 patients are localized most exclusively in the extracellular domain (4). The specific role of endoglin in the vascular dysplasia observed in HHT patients is not known, but it is likely to be related to the role of TGF␤ family signaling in angiogenesis (2, 10). Interestingly, another form of HHT, known as HHT2, which is also characterized by the presence of telangiectases as well as arteriovenous malformations in brain, lungs and liver, results from the loss of TGF␤ type I receptor ALK1 (11), which suggests an interrelatedness between endoglin and ALK1 and possibly involvement of the same ligand(s) in the mechanism of action of both molecules.A soluble form of endoglin has been observed in the serum of patients with different types of solid malignancies (12) and of pregnant women suffering from preeclampsia, a disease leading to vascular permeability (13), hypertension, and placental abruption (14). This soluble form, which reportedly results from partial shedding of the membrane-bound form of endoglin by the matrix metalloproteinase 14 (MT1-MMP) (15), a phenomenon also observed for the other type III receptor betaglycan (16), has been proposed to act as a scavenger or trap for circulating TGF␤ family liga...

Background-Disruption of the balance between matrix metalloproteinases (MMP) and MMP inhibitors (TIMPs) within a myocardial infarct (MI) contributes to left ventricular wall thinning and changes in regional stiffness at the MI region. This study tested the hypothesis that a targeted regional approach through localized high-frequency stimulation (LHFS) using low-amplitude electric pulses instituted within a formed MI scar would alter MMP/TIMP levels and prevent MI thinning. Methods and Results-At 3 weeks after MI, pigs were randomized for LHFS (nϭ7; 240 bpm, 0.8 V, 0.05-ms pulses) or were left unstimulated (UNSTIM; nϭ10

seven normal volunteers (group 1) and six patients with pulmonary hypertension of diverse etiology (group 2) using catheter-tip micromanometers. In group 1 subjects, inspiratory widening of this interval was found to average 27.2 msec, of which 7.6 ± 2.7 msec (1 SD) or 27 + 7% was due to a decrease in the Q-A2 interval. The major contribution of Q-P2 interval prolongation was divided into two components: a) Q-O was measured from the onset of the QRS to the onset of the rapid descent of the right ventricular (RV) negative dp/dt, which was felt to reflect the duration of RV electromechanical systole, b) O-P2 or Q-P2 -Q-0. Increase in the Q-O interval accounted for only 7.7 ± 5.0 msec or 28 ± 12% of the total IA. The major single component of IA was the increase in O-P2 which averaged 11.9 ± 3.0 msec. Five of six group 2 patients demonstrated significant respiratory change in Q-P2 intervals. In contrast to group 1 subjects, however, this was accomplished primarily via increases in the duration of RV electromechanical systole. The O-P2 interval is felt to primarily reflect the impedance characteristics of the pulmonary vascular bed. It is concluded that physiologic splitting of the second heart sound in normal subjects is most probably due to an inspiratory decrease in impedance of the pulmonary bed rather than the traditional explanation of prolongation of RV systole secondary to an increase in venous return. When the normal impedance characteristics of this bed are lost, as in pulmonary hypertension, IA must occur primarily via increases in the duration of RV systole. The inspiratory delay from the conclusion of RV systole to the occurrence of P2 is attributed to the inertiance of the RV stroke mass.

Increased matrix metalloproteinase (MMP) abundance occurs with adverse left ventricular (LV) remodeling in a number of cardiac disease states, including those induced by long-standing arrhythmias. However, whether regionally contained aberrant electrical activation of the LV, with consequent dyskinesia, alters interstitial MMP activation remained unknown. Electrical activation of the LV of pigs (n ϭ 10, 30 -35 kg) was achieved by pacing (150 beats/min) at left atrial and LV sites such that normal atrioventricular activation (60 min) was followed by regional early LV activation for 60 min within 1.5 cm of the paced site and restoration of normal atrioventricular pacing for 120 min. Regional shortening (piezoelectric crystals) and interstitial MMP activity (microdialysis with MMP fluorogenic substrate) at the LV pacing site and a remote LV site were monitored at 30-min intervals. During aberrant electrical stimulation, interstitial MMP activity at the paced site was increased (122 Ϯ 4%) compared with the remote region (100%, P Ͻ 0.05). Restoration of atrioventricular pacing after the 60-min period of aberrant electrical activation normalized segmental shortening (8.5 Ϯ 0.4%), but MMP activity remained elevated (121 Ϯ 6%, P Ͻ 0.05). This study demonstrates that despite the restoration of mechanical function, disturbances in electrical conduction, in and of itself, can cause acute increases in regional in vivo MMP activation and, therefore, contribute to myocardial remodeling. myocardium; interstitium ACUTE AS WELL AS CHRONIC ACTIVATION of matrix metalloproteinases (MMPs) within the myocardium can disrupt the integrity of the extracellular matrix (ECM) and, consequently, affect interstitial protein content, stability, and bioactive signaling pathways (9,14,19). Mechanical stimuli, such as abnormal myocardial stress and strain patterns, can also result in MMP induction (8,12,20). In this context, Garcia et al. (11) demonstrated that acute arrhythmias can disrupt electrical activation pathways and, therefore, induce alterations in the stretch/ contraction patterns of the myocardium and serve as a primary impetus for MMP activation and a potential nidus for stimuli to propagate a remodeling process. For example, previous studies (1, 22) have shown that short-duration disruption of electrical conduction induced in the atria can progress to the development of a sustained arrhythmia with associated remodeling of the myocardium. However, whether and to what degree an increase in MMP induction as a result of acute changes in electrical activation persist after the restoration of normal conduction patterns remain unknown. Therefore, the present study was designed to test the hypothesis that short-term (i.e., acute) alterations in the electrical activation of the myocardium would cause in vivo MMP activation and that the restoration of electrical conduction would normalize interstitial MMP activity. METHODS Instrumentation. Animals were treated and cared for in accordance with the National Institutes of Health Guide for the C...