PECAM-1 and caveolae form the mechanosensing complex necessary for NOX2 activation and angiogenic signaling with stopped flow in pulmonary endothelium

Abstract

AB, Chatterjee S. PECAM-1 and caveolae form the mechanosensing complex necessary for NOX2 activation and angiogenic signaling with stopped flow in pulmonary endothelium. Am J Physiol Lung Cell Mol Physiol 305: L805-L818, 2013. First published September 27, 2013 doi:10.1152/ajplung.00123.2013.-We showed that stop of flow triggers a mechanosignaling cascade that leads to the generation of reactive oxygen species (ROS); however, a mechanosensor coupled to the cytoskeleton that could potentially transduce flow stimulus has not been identified. We showed a role for KATP channel, caveolae (caveolin-1), and NADPH oxidase 2 (NOX2) in ROS production with stop of flow. Based on reports of a mechanosensory complex that includes platelet endothelial cell adhesion molecule-1 (PECAM-1) and initiates signaling with mechanical force, we hypothesized that PECAM-1 could serve as a mechanosensor in sensing disruption of flow. Using lungs in situ, we observed that ROS production with stop of flow was significantly reduced in PECAM-1 Ϫ/Ϫ lungs compared with lungs from wild-type (WT) mice. Lack of PECAM-1 did not affect NOX2 activation machinery or the caveolin-1 expression or caveolae number in the pulmonary endothelium. Stop of flow in vitro triggered an increase in angiogenic potential of WT pulmonary microvascular endothelial cells (PMVEC) but not of PECAM-1 Ϫ/Ϫ PMVEC. Obstruction of flow in lungs in vivo showed that the neutrophil infiltration as observed in WT mice was significantly lowered in PECAM-1 Ϫ/Ϫ mice. With stop of flow, WT lungs showed higher expression of the angiogenic marker VEGF compared with untreated (sham) and PECAM-1 Ϫ/Ϫ lungs. Thus PECAM-1 (and caveolae) are parts of the mechanosensing machinery that generates superoxide with loss of shear; the resultant ROS potentially drives neutrophil influx and acts as an angiogenic signal. mechanotransduction; stop of flow; pulmonary endothelium; PECAM; K atp (Kir6.2) channel; NOX2; angiogenic potential CELLS SENSE THE PHYSICAL STIMULUS in their environment and translate these physical forces into biochemical signals (20, 37). Sensing and responding to a physical force require specialized structures and machinery that can engage in signal transduction (12,23,42).In the vascular system, with a highly distributed network of blood vessels, mechanical forces arising from blood flow initiate signaling that helps maintain vascular structure and function. Indeed, shear associated with blood flow is sensed by the endothelium and the resultant signaling regulates normal vascular physiology (such as embryonic morphogenesis and organization of the vascular tree) while irregular or abnormal shear can lead to vascular dysfunction and disease (19,27). Thus the mechanosignaling that accompanies various shear profiles and patterns, regular or aberrant, governs susceptibility to atherosclerosis, by inducing athero-protective or atheroprone phenotypes in endothelial cells (10,22). It thus becomes important to understand the link among the mechanical force, the shear sensing machinery and...

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“…Interestingly, both PECAM-1 and glypican-1 have been independently shown to be expressed in caveolin-1-containing membrane fractions (43,44), with the latter believed to be involved in shear-induced NO production through a glypican-caveolae-endothelial nitric-oxide synthase mechanism (45). Additionally, it has been recently reported that PECAM-1 and caveolin-1 form a mechanosensing complex that is necessary for NAPDH oxide 2 (NOX2) and angiogenic signaling in pulmonary endothelial cells in response to abrupt cessation of flow (44). Therefore, it is not inconceivable that a subset of PECAM-1 forms a functionally distinct mechanosensitive caveolar complex together with glypican-1.…”

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“…After extensive further study, we found that the source of ROS with ischemia was the endothelium, and the mechanism was related to altered mechanotransduction, namely the cessation of the normal shear forces applied to the pulmonary endothelial cells by the pulmonary blood flow (3,71,75). Additional studies showed that shear in pulmonary endothelium is sensed by caveolae and is somehow related to endothelial platelet-endothelial adhesion molecule (PECAM) (61,63 pulmonary endothelial ATP-sensitive K ϩ channels in the open configuration, contributing to the endothelial cell transmembrane potential; cessation of flow leads to ATP-sensitive K ϩ channel closure, endothelial cell membrane depolarization, and activation of NOX2 with subsequent O 2 ·Ϫ generation (4,14,16) (Fig. 3).…”

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