Leonard Bell

Effect of platelet factors on migration of cultured bovine aortic endothelial and smooth muscle cells.

Endothelial cell (EC) injury and the response of EC and smooth muscle cells (SMCs) to injury contribute to the pathophysiology in patients with vascular disease and atherosclerosis. Since platelets have been suggested to play an important role in modulating vascular injury, the present study was undertaken to examine the influence and mechanism of action of individual platelet factors on bovine aortic EC and SMC migration using an in vitro wound assay system. Serotonin decreased EC proliferation and reduced EC migration 21 ± 1% (p <0.005), which was attenuated by imipramine. Transforming growth factor-β reduced EC proliferation and decreased EC migration 52 ± 3% (p <0.005). Norepinephrine increased EC proliferation but decreased EC migration 26 ± 2% (p < 0.005), which was abolished by phenoxybenzamine. Histamine increased EC proliferation but reduced EC migration 29 ± 2% (p < .005), which was attenuated by diphenhydramine. Platelet-derived growth factor decreased EC proliferation and decreased EC migration 40 ± 2% (p <0.005). In contrast, serotonin increased SMC proliferation and increased SMC migration 31 ± 2% (p <0.005), which was abolished by ketanserin. Transforming growth factor-β increased SMC migration 35 ± 5% (p <0.005). Norepinephrine increased SMC proliferation and increased SMC migration 43 ± 4% (p <0.005), which was abolished by propranolol. Histamine increased SMC proliferation and increased SMC migration 38 ± 3% (p <0.005), which was abolished by cimetidine. Platelet-derived growth factor increased SMC proliferation and increased SMC migration 40 ± 3% (p <0.005). Changes in migration were unaffected by growth-arresting treatment. Hence, these individual platelet factors inhibit EC migration and augment SMC migration via specific receptors and independent of proliferation changes. These results suggest mechanisms in which platelet factors may contribute to blood vessel injury in vivo.

Autocrine angiotensin system regulation of bovine aortic endothelial cell migration and plasminogen activator involves modulation of proto-oncogene pp60c-src expression.

Rapid endothelial cell migration and inhibition of thrombosis are critical for the resolution of denudation injuries to the vessel wall. Inhibition of the endothelial cell autocrine angiotensin system, with either the angiotensin-converting enzyme inhibitor lisinopril or the angiotensin II receptor antagonist sar1, ile8-angiotensin II, leads to increased endothelial cell migration and urokinase-like plasminogen activator (u-PA) activity (Bell, L., and J. A. Madri. 1990. Am. J. Pathol. 137:7-12). Inhibition of the autocrine angiotensin system with the converting-enzyme inhibitor or the receptor antagonist also leads to increased expression of the proto-oncogene c-src: pp60c-src mRNA increased 7-11-fold, c-src protein 3-fold, and c-src kinase activity 2-3-fold. Endothelial cell expression of c-src was constitutively elevated after stable infection with a retroviral vector containing the c-src coding sequence. Constitutively increased c-src kinase activity reconstituted the increases in migration and u-PA observed with angiotensin system interruption. Antisera to bovine u-PA blocked the increase in migration associated with increased c-src expression. These data suggest that increases in endothelial cell migration and plasminogen activator after angiotensin system inhibition are at least partially pp60c-src mediated. Elevated c-src expression with angiotensin system inhibition may act to enhance intimal wound closure and to reduce luminal thrombogenicity in vivo.

Interactions of Vascular Cells with Transforming Growth Factors-βa

The vascular system is lined by mitotically quiescent endothelial cells, which in addition to having a broad range of metabolic activities, provide a non-thrombogenic surface for blood flow. Beneath the endothelium, smooth muscle cells are found in the media of large vessels and pericytes are found in close association with the endothelial cells of various microvascular beds. These smooth muscle cells play major roles in the maintenance of the connective tissues of the vessel wall and in the control of vascular tone.’ Vascular cells (endothelial, pericyte, and smooth muscle) have been found to respond to injury in specific ways, depending upon the vascular bed and the cell type(s) injured. For example, following denudation injury evoked by angioplasty, endarterectomy, or autologous or synthetic grafting, large vessel endothelial cells bordering the affected area will exhibit rapid sheet migration over the exposed extracelMar matrix and proliferate in an attempt to reconstitute the normal continuous endothelial cell lining?.3 Medial smooth muscle cells of large and medium-sized vessels respond to vessel injury by migrating into the intima, where they proliferate and synthesize matrix components, which may result in the formation of a thickened intima that narrows the vessel lumen? In contrast, following soft tissue injury or in response to a variety of angiogenic factors, microvascular endothelial cells respond by freeing themselves from the constraints of their investing basement membranes and migrating and proliferating in the surrounding three-dimensional interstitial stroma and ultimately forming new microvessels? The role of pericytes (smooth muscle cell analogs found surrounding microvessels following new vessel formation) in the response to injury has been less well-studied and their origin(s) (endothelial, undifferentiated mesenchymalfibroblastic, or vascular smooth muscle cell) is still a matter of

The Interactions of Vascular Cells with Solid Phase (Matrix) and Soluble Factors

The vessel wall is composed of heterogeneous cell populations residing in a variety of vascular beds. Each cell type has different functions and morphologies but all of them have a role in the repair process following vascular injury. Responses to injury vary depending upon the type and extent of the injury and the vascular bed affected. The sheet migration and proliferation exhibited by large vessel endothelial cells is in striking contrast to the migration through soft tissues and tube formation exhibited by microvascular endothelial cells in response to injury. Vascular smooth muscle cells respond to injury by migrating into the intima, proliferating and synthesizing matrix, causing intimal thickening. The response to injury by vascular cells appears to be modulated, in part, by the composition and organization of the surrounding matrix and the various platelet factors and cytokines found at sites of injury. Furthermore, evidence has been accrued in culture, suggesting that solid phase (matrix) and soluble factors modulate each others effects on local vascular cell populations following injury.

Interactions of Matrix Components and Soluble Factors in Vascular Responses to Injury

The vascular system is lined by mitotically quiescent but metabolically active endothelial cells, which in addition to having a broad range of metabolic activities, provide a nonthrombogenic surface for blood flow. Beneath the endothelium, smooth muscle cells are found in the media of large vessels, and pericytes are found in close association with the endothelial cells of microvascular beds. The smooth muscle cells (pericytes) are thought to play major roles in maintaining vessel wall integrity, being responsible for the maintenance to the connective tissues of the vessel wall and in the control of vascular tone.8 Vascular cells (large and small vessel derived endothelial, pericyte, and smooth muscle cells) have been found to respond to injury in specific ways, depending upon the vascular bed and the cell type(s) injured. For example, following denudation injury evoked by angioplasty, endarterectomy or autologous or synthetic grafting, large vessel endothelial cells bordering the affected area will exhibit rapid sheet migration over the exposed extracellular matrix and proliferate in an attempt to reconstitute the normal continuous endothelial cell lining.15,20 The medial smooth muscle cells of large and medium-sized vessels respond to vessel injury by migrating into the intima, where they proliferate and synthesize matrix components, which results in the formation of a thickened intima which narrows the vessel lumen.34 In contrast, following soft tissue injury or in response to a variety of angiogenic factors, microvascular endothelial cells respond by freeing themselves from the constraints of their investing basement membranes. Following this, they migrate and proliferate in the surrounding three-dimensional interstitial stroma and ultimately form new microvessels.17

The role of the splanchnic circulation in the regulation of total intravascular volume during alpha adrenergic receptor stimulation

Previous studies have not defined the contribution of the splanchnic circulation to the total intravascular volume change associated with selective alpha adrenergic receptor stimulation. Since the splanchnic circulation is responsible for the total volume changes associated with other types of selective autonomic receptor stimulation, the present study was undertaken to examine the influence of alpha adrenergic receptor stimulation on splanchnic intravascular volume, the hemodynamic mechanism responsible for the splanchnic volume change, and the contribution of the splanchnic volume change to the change in total volume. In 35 anesthetized dogs, blood from the vena cavae was drained into an extracorporeal reservoir and returned to the right atrium at a constant rate so that changes in total intravascular volume could be measured as reciprocal changes in reservoir volume. Phenylephrine infusion (100 μg/min) for 20 min in 28 dogs was associated with a decrease in total volume of 64±17 (SEM) ml (P<0.0001). The response was abolished by either alpha adrenergic blockade or evisceration but was not attenuated by beta adrenergic blockade, sinoaortic baroreceptor denervation, ganglionic blockade, or splenectomy. In 5 animals with separate splanchnic perfusion and drainage, total and splanchnic volumes decreased 59±8 ml (P<0.0001) and 317±20 ml (P<0.0001), respectively, while transhepatic vascular resistance increased 17±4 cm H2O·min/l (P<0.0001). These responses were abolished after alpha adrenergic blockade. Thus, splanchnic volume decreases with alpha adrenergic receptor stimulation, despite an increase in hepatic resistance to splanchnic, venous outflow. The splanchnic volume decrement is entirely responsible for the total volume decrement.