Stretch In Endothelial Cells Research Articles

Differential Expression of Adipokines in Mechanically Stretched‐ Endothelial cells

IntroductionHypertension is considered as the major risk factor for cardiovascular diseases, which are the leading cause of morbidity and mortality worldwide. This disease can develop mainly due to the mechanical forces exerted by the blood on the vessels wall. The endothelium, lining the blood vessel, responds to these hemodynamic mechanical forces such as mechanical stretch leading to endothelial dysfunction. Leptin and adiponectin (APN) are two adipokines that are known to be associated with the pathogenesis of hypertension. However, how the level of these hormones is elevated in response to mechanical stretch in endothelial cells is yet to be elucidated.AimIn the present study, we investigated the expression of leptin and adiponectin in endothelial cells exposed to mechanical stretch.MethodsImmortalized human umbilical vein endothelial cells (EA. hy926) were subjected to mechanical stretch (15%, 60 cycle/min and 1Hz) using STREX cell stretching system (STREX Inc., California, USA) for 6, 16 and 24 h. Cultured cells not subjected to stretch (static condition) where used as controls. The mRNA expression of leptin and its receptor (OB‐Rb) as well as APN and adiponectin receptor 2 (APN‐R2) were assessed at different time points using real‐time PCR.ResultsMechanical stretch induced changes in cell morphology in which the cells were elongated and aligned perpendicular to the stretch axis. Stretching of endothelial cells significantly upregulated the expression of leptin after 16 h (0.9515 ± 0.4238‐fold, n=6, p<0.05) and after 24 h (1.577 ± 0.4503‐fold, n=6, p<0.05) of stretching but without affecting the expression of its receptor (OB‐Rb). The mRNA expression of APN also increased significantly in response to 6 h stretching (0.5457 ± 0.1890‐fold, n=6, p<0.05), 16 h stretching (0.9487 ± 0.4058‐fold, n=6, p<0.05) and 24 h stretching (2.664 ± 0.3447, n=6, p<0.0001) compared to unstretched cells, however no change in the expression of APN‐R2 was observed.ConclusionOur findings suggesting that the exposure of endothelial cells to mechanical stretch can result in changes in the expression of adipokines, leptin and adiponectin, will result in better understanding of how vascular biology is affected by mechanical forces and how these molecules can modulate endothelial function in cardiovascular diseases.

The molecular mechanism of mechanotransduction in vascular homeostasis and disease

Blood vessels are constantly exposed to mechanical stimuli such as shear stress due to flow and pulsatile stretch. The extracellular matrix maintains the structural integrity of the vessel wall and coordinates with a dynamic mechanical environment to provide cues to initiate intracellular signaling pathway(s), thereby changing cellular behaviors and functions. However, the precise role of matrix-cell interactions involved in mechanotransduction during vascular homeostasis and disease development remains to be fully determined. In this review, we introduce hemodynamics forces in blood vessels and the initial sensors of mechanical stimuli, including cell-cell junctional molecules, G-protein-coupled receptors (GPCRs), multiple ion channels, and a variety of small GTPases. We then highlight the molecular mechanotransduction events in the vessel wall triggered by laminar shear stress (LSS) and disturbed shear stress (DSS) on vascular endothelial cells (ECs), and cyclic stretch in ECs and vascular smooth muscle cells (SMCs)-both of which activate several key transcription factors. Finally, we provide a recent overview of matrix-cell interactions and mechanotransduction centered on fibronectin in ECs and thrombospondin-1 in SMCs. The results of this review suggest that abnormal mechanical cues or altered responses to mechanical stimuli in EC and SMCs serve as the molecular basis of vascular diseases such as atherosclerosis, hypertension and aortic aneurysms. Collecting evidence and advancing knowledge on the mechanotransduction in the vessel wall can lead to a new direction of therapeutic interventions for vascular diseases.

Angiotensin II induces microtubule reorganization mediated by a deacetylase SIRT2 in endothelial cells

Angiotensin II has been implicated in vascular remodeling. Microtubule composed of tubulins regulates cell shape, migration and survival. Tubulin acetylation has an important role in the control of microtubule structure and microtubule-based cellular functions. In this study, angiotensin II induced disassembly and deacetylation of α-tubulin, which were blocked by pretreatment with an angiotensin II type 1 receptor blocker losartan and a sirtuin class deacetylase inhibitor sirtinol, and by depletion of a deacetylase SIRT2 using RNA interference. We investigated the involvement of SIRT2 in angiotensin II-induced endothelial cell migration using the Boyden chamber method. Angiotensin II caused a significant increase in cell migration, which was blocked by pretreatment with sirtinol and SIRT2 depletion. It has been reported that angiotensin II is involved in cytoskeletal reorganization stimulated by mechanical stretch in endothelial cells. We also demonstrated that endothelial cells subjected to a 10% uniaxial stretch showed vertical alignment to the direction of tension and tubulin deacetylation in the peripheral side of cells, in comparison with control static cells. The mechanical stretch-induced changes of microtubules were blocked by pretreatment with sirtinol and SIRT2 depletion. Immunofluorescence microscopy showed that acetylated tubulin was decreased in platelet-endothelial cell adhesion molecule-1-positive cells in the intima of the aortic walls in mice loaded with angiotensin II, in comparison with mice loaded with control vehicle. These data show that angiotensin II and mechanical stretch stimulate microtubule redistribution and deacetylation via SIRT2 in endothelial cells, suggesting the emerging role of SIRT2 in hypertension-induced vascular remodeling.

Abstract 4848: Angintensin II Stimulates Microtubule Reorganization Mediated by SIRT2 in Endothelial Cells

Angiotensin II has been implicated in the pathophysiology of vascular remodeling. Microtubule composed of tubulins regulates cell shape, migration and survival. Tubulin acetylation plays an important role in the control of microtubule structure and microtubule-based cellular functions. We studied angiotensin II-induced changes in microtubules in endothelial cells. Immunofluorescence microscopy showed that acetylated tubulin was decreased in PECAM-1-positive cells in the intima of the aortic walls in mice loaded with angiotensin II, compared to mice loaded with control vehicle. In cultured human endothelial cells in quiescence, α -tubulin-positive microtubules were acetylated and showed radial layout from microtubule-organizing center to peripheral edge of cells. Angiotensin II induced disassembly and deacetylation of α -tubulin, which were blocked by pretreatment with losartan that is an angiotensin II type 1 receptor blocker, sirtinol that is an inhibitor for sirtuin class deacetylases, and depletion of a deacetylase SIRT2 by RNA interference. We investigated the involvement of SIRT2 in angiotensin II-induced endothelial cell migration using Boyden chamber method. Angiotensin II caused a significant increase in cell migration, which was blocked by pretreatment with sirtinol and SIRT2 depletion. It has been reported that angiotensin II is involeved in cytoskeletal reorganization stimulated by mechanical stretch in endothelial cells. To investigate the effects of mechanical stretch on microtubule reorganization, cultured endothelial cells were subjected to 10% uniaxial stretch and examnied by immunofluorescence. Mechanically stretched cells showed vertical alignment to tension direction and tubulin deacetylation in peripheral side of cells, compared to control static cells. Mechanical stretch-induced changes of microtubules were blocked by pretreatment with sirtinol and SIRT2 depletion. These data suggest that angiotensin II and mechanical stretch stimulate microtubule redistribution and deacetylation via SIRT2 in endothelial cells. Further studies are necessary to elucidate the roles of SIRT2-mediated microtubule reorganization in vascular remodeling.

Cadherins, RhoA, and Rac1 Are Differentially Required for Stretch-Mediated Proliferation in Endothelial Versus Smooth Muscle Cells

Abnormal mechanical forces can trigger aberrant proliferation of endothelial and smooth muscle cells, as observed in the progression of vascular diseases such as atherosclerosis. It has been previously shown that cells can sense physical forces such as stretch through adhesions to the extracellular matrix. Here, we set out to examine whether cell-cell adhesions are also involved in transducing mechanical stretch into a proliferative response. We found that both endothelial and smooth muscle cells exhibited an increase in proliferation in response to stretch. Using micropatterning to isolate the role of cell-cell adhesion from cell-extracellular matrix adhesion, we demonstrate that endothelial cells required cell-cell contact and vascular endothelial cadherin engagement to transduce stretch into proliferative signals. In contrast, smooth muscle cells responded to stretch without contact to neighboring cells. We further show that stretch stimulated Rac1 activity in endothelial cells, whereas RhoA was activated by stretch in smooth muscle cells. Blocking Rac1 signaling by pharmacological or adenoviral reagents abrogated the proliferative response to stretch in endothelial cells but not in smooth muscle cells. Conversely, blocking RhoA completely inhibited the proliferative response in smooth muscle cells but not in endothelial cells. Together, these data suggest that vascular endothelial cadherin has an important role in mechanotransduction and that endothelial and smooth muscle cells use different mechanisms to respond to stretch.

Changes in the distribution of tyrosine phosphorylated focal proteins caused by uniaxial cyclic stretch in endothelial cells

Changes in the distribution of tyrosine phosphorylated focal proteins caused by uniaxial cyclic stretch in endothelial cells

Stretch induces upregulation of key tyrosine kinase receptors in microvascular endothelial cells

We previously demonstrated that cyclic stretch of cardiac myocytes activates paracrine signaling via vascular endothelial growth factor (VEGF) leading to angiogenesis. The present study tested the hypothesis that cyclic stretch upregulates tyrosine kinase receptors in rat coronary microvascular endothelial cells (RCMEC) and human umbilical vein endothelial cells (HUVEC). VEGF receptor-2 (Flk-1) protein levels increased in HUVEC and RCMEC in a time-dependent manner, but the increase occurred much earlier in RCMEC than in HUVEC. The enhancement of Flk-1 protein level was not inhibited by addition of VEGF neutralizing antibodies, indicating that VEGF is not involved in stretch-induced Flk-1 expression. VEGF receptor-1 (Flt-1) protein and mRNA were not changed by stretch. However, Tie-2 and Tie-1 protein levels increased in RCMEC. Angiopoietin-1 and -2, the ligands for Tie-2, increased in cardiac myocytes subjected to cyclic stretch but were not affected by stretch in endothelial cells (EC). Stretch or incubation of RCMEC with VEGF increased cell proliferation moderately, whereas stretch + VEGF had an additive effect on proliferation. Mechanical stretch induces upregulation of the key tyrosine kinase receptors Flk-1, Tie-2, and Tie-1 in vascular EC, which underlies the increase in sensitivity of EC to growth factors and, therefore, facilitates angiogenesis. These in vitro findings support the concept that stretch of cardiac myocytes and EC plays a key role in coronary angiogenesis.

A molecular mechanism for mechanical activation of endothelial cells

In this brief review, we will present evidence that platelet endothelial cell adhesion molecule-1 (PECAM-1) is a mechanoresponsive molecule. When endothelial cells (ECs) are exposed to mechanical stress, PECAM-1 is tyrosine-phosphorylated and recruits SHP-2 and Gab1 to the area of cell–cell attachment. These events are necessary for ERK activation by fluid shear stress (FSS) and cyclic stretch in endothelial cells. Both PECAM-1 tyrosine phosphorylation and ERK activation can be achieved by applying mechanical force directly on PECAM-1, suggesting that PECAM-1 is a mechanotransduction molecule.

Mechanical stretch augments PDGF receptor beta expression and protein tyrosine phosphorylation in pulmonary artery tissue and smooth muscle cells.

With regard to the mechanotransduction mechanisms of vasculature involved in hypertensive diseases, we aimed to identify tyrosine-phosphorylated proteins in pulmonary artery that responded to mechanical stress. Mechanical stretch simultaneously augmented protein-tyrosine phosphorylation in p55, p95, p105, p115, p130, p165, p180 in pulmonary artery tissue and pulmonary artery-derived smooth muscle cells (PASMC), whereas p115 and p55 were preferentially phosphorylated by the stretch in endothelial cells (PAEC). A series of experiments designed to characterize these proteins indicated that p115 and p180 were focal adhesion kinase (FAK) and platelet-derived growth factor receptor beta (PDGF-Rbeta), respectively, and that stretch augmented the surface-expression of PDGF-Rbeta in PASMC but not in PAEC. Moreover, a significant increase in the steady-state mRNA level for PDGF-Rbeta was observed in the pulmonary artery of rats with monocrotaline-induced pulmonary hypertension, where the artery should be overstretched due to increasing pulmonary arterial blood pressure. These results suggest that stretch-induced overexpression of cell-surface PDGF-Rbeta as well as augmentation of yrosine phosphorylation of proteins including FAK in PASMC might be involved in the mechanotransduction of pulmonary artery.

Involvement of stretch-activated ion channels in Ca2+ mobilization to mechanical stretch in endothelial cells

Endothelial cells are subjected to shear stresses by blood flow, normal stresses by blood pressure, and stretch by vessel expansion. These forces are known to induce secretions of several vasoactive substances probably via internal calcium mobilization (R. F. Furchgott. Circ. Res. 53: 557-573, 1983; M. J. Peach, A. L. Loeb, H. A. Singer, and J. Saye. Hypertension Dallas 7, Suppl. I: I-94-I-100, 1985). Here we report that stretching cellular membranes increased intracellular Ca2+ concentration ([Ca2+]i) in human umbilical endothelial cells cultured on silicon membranes. Upon application of a stretch pulse (3-s duration), [Ca2+]i increased rapidly and decayed slowly. The following results suggest that this increase arises from Ca2+ entry through stretch-activated (SA) channels: 1) the Ca2+ response disappeared when extracellular Ca2+ was removed; 2) gadolinium (Gd3+), a blocker for cation-selective SA channels, blocked the response but nifedipine did not; and 3) externally applied Mn2+, which is known to permeate mechanosensitive channels but not Ca2+ channels, entered the intracellular space immediately after an application of mechanical stretch. The increase in [Ca2+]i was found to consist of at least two components: an initial fast component and a delayed slower component. Ryanodine inhibited the slow component. It is suggested that stretching the membrane primarily induced extracellular Ca2+ entry through SA channels followed by Ca2+ releases from intracellular Ca2+ stores.