Cytoskeleton of rat aortic smooth muscle cells. Normal conditions and experimental intimal thickening

The organization of actin, vimentin, and desmin in smooth muscle cells of rat aortic media and intima under normal conditions and 15 or 75 days after endothelial injury has been studied by means of electron microscopy, indirect immunofluorescence, densitometric analysis of sodium dodecyl sulfate-polyacrylamide gels, isoelectric focusing, and bidimensional gels. In the normal aortic media, practically all smooth muscle cells contain vimentin, and about 50% of them contain, in addition, desmin; upon analysis of actin isotypes by bidimensional gels, smooth muscle cells show a predominance of alpha-actin, some beta-actin, and very little gamma-actin. Fifteen days after endothelial injury, cells that have migrated into the intima contain decreased amounts of actin and desmin and increased amounts of vimentin compared with normal medial smooth muscle cells. Moreover, beta-actin becomes the predominant actin isotype and significant amounts of gamma-actin appear, whereas alpha-actin decreases. Seventy-five days after endothelial injury, regenerated endothelial cells have repaired the injury. Intimal smooth muscle cells are less numerous than 15 days after injury, and the organization of their cytoskeletal elements has reverted almost to normal conditions. At both 15 and 75 days after endothelial injury, no significant changes of cytoskeletal elements are seen in the aortic media underlying intimal thickenings.     

Phenotypic variants of the smooth-muscle cells in an atheromatous plaque of the human aorta

The authors investigated the expression of cytoskeletal proteins and the ultrastructure of cells in normal intima and atheromatous plaque of human aorta. It has been established, using double immunofluorescent method and a set of antibodies that intimal smooth muscle cells /SMC/ of normal aorta express myosin, vimentin, alpha-actin and actin but not desmin. In seven out of 28 atherosclerotic plaques the cells contained desmin and all other SMC cytoskeletal proteins were found. These cells had the ultrastructural features of SMC, i.e. well-developed endoplasmic reticulum and Golgi apparatus. Besides, some cells in 13 atherosclerotic plaques proved to be myosin-, alpha-actin- and desmin-negative. The cells were stained with monoclonal antibodies specific to SMC but not with macrophage-specific antibody. Ultrastructurally, the cytoplasm of the cells was filled with rough endoplasmic reticulum and a developed Golgi complex, but a certain portion of the cells retained basal lamina and myofilament bundles. The peculiarities of cytoskeletal protein in expression and ultrastructure of cells in human aortic atherosclerotic plaques may be explained by a phenotypic modulation of vascular SMC.     

Heterogeneity of smooth muscle cells in atheromatous plaque of human aorta.

This study was undertaken to investigate the expression of cytoskeletal proteins and the ultrastructure of cells in normal intima and atheromatous plaque of human aorta. It has been established, using double-labeling immunofluorescence, that smooth muscle cells (SMC) in normal aortic intima contain myosin, vimentin, and alpha-actin but do not react with antibodies against desmin. In contrast, 7 of 28 atherosclerotic plaques contained many cells expressing desmin in addition to the other cytoskeletal proteins characteristic of normal intima SMC. These cells were localized predominantly in the plaque cap and had the ultrastructural features of modulated SMC, ie, well-developed endoplasmic reticulum and Golgi apparatus. Besides, some cells in the 13 atherosclerotic plaques proved to be myosin, alpha actin, and desmin negative but contained vimentin and actin as revealed by fluorescent phalloidin. These cells were found in the immediate proximity of atheromatous material and reacted with a monoclonal antibody specific to SMC surface protein (11G10) but not with monoclonal anti-muscle actin (HHF35) and anti-macrophage (HAM56) antibodies. Electron microscopy of this plaque zone revealed that the cytoplasm of these cells was filled with rough endoplasmic reticulum and a developed Golgi complex. At the same time, a certain proportion of cells in this region retained morphologic features of differentiated SMC such as the presence of a basal lamina and myofilament bundles. The revealed peculiarities of cytoskeletal protein expression and the ultrastructure of cells in human aortic atherosclerotic plaques may be explained by a phenotypic modulation of vascular SMC.     

Cytoskeletal features of immature pulmonary vascular smooth muscle cells: the influence of pulmonary hypertension on normal development

Using an immunohistochemical technique, the development of the cytoskeletal proteins desmin, vimentin, and actin (using alpha isotype and non-isotype specific antibodies) was assessed using a semi-quantitative grading system in the pulmonary vascular smooth muscle of nine normal pigs and 19 normal humans at different ages, and in 13 children with pulmonary hypertensive congenital heart disease. In the normal of both species, immunostaining for vimentin decreased after birth and then increased gradually while immunostaining for desmin and alpha actin increased steadily with age. In pulmonary hypertension, immunostaining for alpha actin and vimentin showed an accelerated increase at between 2 and 8 months. Also, the media showed regional differences in immunostaining which preceded the development of intimal proliferation. The inner media showed less immunoreactivity for all cytoskeletal proteins studied than did the outer media. Within areas of intimal proliferation many cells were immunonegative. These results suggest that the cytoskeletal features of medial smooth muscle cells are remodelled in the normal infant; that this process is altered from at least 2 months in the pulmonary hypertensive infant; and that the smooth muscle cells immediately beneath the internal elastic lamina are remodelled before migrating to form intimal proliferation. Changes in cytoskeletal composition can be related to the previously described postnatal maturation of pulmonary vascular smooth muscle cells.     

Cytoskeletal features of normal and atheromatous human arterial smooth muscle cells

The distribution of actin, vimentin, desmin, and tropomyosin was studied in the media of the human aorta and femoral and coronary arteries, as well as in atheromatous plaques from the same arteries, by means of immunofluorescence, densitometric analysis of sodium dodecylsulfate-polyacrylamide gel electrophoresis, and bidimensional gel electrophoresis. The proportions of desmin-containing cells varied in the media of different arteries; 4 per cent of the cells in the aorta, 11 per cent in the coronary artery, and 37 per cent in the femoral artery contained desmin. In fibrous atheromatous plaques, independently of the artery, desmin-containing cells were almost absent, but they reappeared in complicated lesions. The content of vimentin per smooth muscle cell increased in fibrous atheromatous plaques, whereas the content of actin and tropomyosin was less than in normal media. Moreover, the alpha-actin predominance observed in the media was transformed to beta-actin predominance in the atheromatous plaques. These cytoskeletal changes provide new, possibly useful, biochemical markers for the characterization of smooth muscle cells during early and advanced phases of atheroma formation.     

Actin isoform synthesis and mRNA levels in quiescent and proliferating rat aortic smooth muscle cells in vivo and in vitro

The relative levels of actin isoform synthesis in rat aortic smooth muscle cells (SMC) have been studied in vivo and in culture by means of [35S]methionine incorporation. They have been compared to the functional levels of actin isoform mRNAs, assayed by translation of total cell RNA in a reticulocyte lysate or, in some cases, to the actin isoform RNA content, assayed by Northern-blot hybridization to a total actin cRNA probe. In normal media and in freshly isolated SMC, the relative levels of actin isoform synthesis and the actin mRNA translation products show a remarkable similarity, but differ from the proportions of actin isoforms present in a total cell extract (Gabbiani G, Kocher O, Bloom WS, Vandekerckhove J, Weber K: Actin expression in smooth muscle cells of rat aortic intimal thickening, human atheromatous plaque, and cultured rat aortic media. J Clin Invest 73:148, 1984); (Skalli O, Bloom WS, Ropraz P, Azzarone B, Gabbiani G: Cytoskeletal remodeling of rat aortic smooth muscle cells in vitro: relationship to culture conditions and analogies to in vivo situations. J Submicrosc Cytol, in press 1986). This suggests that different actin isoforms have different stabilities. Fifteen days after balloon induced endothelial denudation in vivo, and after being placed in culture, SMC show a decrease in the proportions of alpha-actin synthesis and alpha-actin mRNA levels with a corresponding increase in these parameters for beta- and lambda-actins. The proportions of actin isoform synthesis and actin mRNA translation products in intimal SMC revert to normal values 60 days after balloon induced endothelial denudation, when the aorta is reendothelialized; however, in culture decreased alpha-actin synthesis and mRNA level persist up to the fifth passage (P5). These changes may be helpful for the understanding of SMC adaptation mechanisms during arterial development and atheromatous plaque formation.     

Ultrastructural changes in re-endothelialized and non-endothelialized rabbit aortic neo-intima following re-injury with a balloon catheter.

The response by normal rabbit aortas to the removal of the endothelium with a balloon catheter, was compared to the response to the removal of regenerated endothelium from rabbit aortas that had been previously de-endothelialized. De-endothelialization results in the formation of a neo-intima. Thrombus formation following a second balloon catheter injury was compared among injured neo-intima that had been re-endothelialized, non-re-endothelialized neo-intima, and the subendothelium of normal vessels following a single injury. Rabbit aortas were examined by scanning electron microscopy of full circumference segments of the aorta and by transmission electron microscopy. Thirty minutes after a single de-endothelialization injury with a balloon catheter the luminal surface is covered by a monolayer of platelets adhering to the subendothelial connective tissues. Two weeks later there is neo-intimal formation and endothelial regeneration around branch vessel orifices. The remainder of the luminal surface is composed of smooth muscle cells (SMC). A balloon catheter injury to a vessel injured 2 weeks previously results in fibrin formation and platelet-fibrin microthrombi on the aortic intimal surface. The response of the aortic wall to re-injury does not seem to be related to the prior existence of endothelium. Both single and repeated injuries result in a distribution of formed elements which may depend, in part, on haemodynamic factors.     

Ultrastructural changes in re-endothelialized and non-endothelialized rabbit aortic neo-intima following re-injury with a balloon catheter

The response by normal rabbit aortas to the removal of the endothelium with a balloon catheter, was compared to the response to the removal of regenerated endothelium from rabbit aortas that had been previously de-endothelialized. De-endothelialization results in the formation of a neo-intima. Thrombus formation following a second balloon catheter injury was compared among injured neo-intima that had been re-endothelialized, non-re-endothelialized neo-intima, and the subendothelium of normal vessels following a single injury. Rabbit aortas were examined by scanning electron microscopy of full circumference segments of the aorta and by transmission electron microscopy. Thirty minutes after a single de-endothelialization injury with a balloon catheter the luminal surface is covered by a monolayer of platelets adhering to the subendothelial connective tissues. Two weeks later there is neo-intimal formation and endothelial regeneration around branch vessel orifices. The remainder of the luminal surface is composed of smooth muscle cells (SMC). A balloon catheter injury to a vessel injured 2 weeks previously results in fibrin formation and platelet-fibrin microthrombi on the aortic intimal surface. The response of the aortic wall to re-injury does not seem to be related to the prior existence of endothelium. Both single and repeated injuries result in a distribution of formed elements which may depend, in part, on haemodynamic factors.     

Regrowth of arterial endothelium. Denudation with minimal trauma leads to complete endothelial cell regrowth

Endothelial regeneration in the rat carotid artery was investigated using two different techniques of denudation. With balloon catheter denudation, medial cell death occurred, and endothelial regrowth stopped after several weeks, leaving a large area devoid of endothelium. After denudation with a new technique that removed the endothelium without damaging the media complete endothelial regrowth was achieved. Acutely after this denudation, large platelet thrombi were present on the subendothelial surface of vessels denuded with the filament loop. In contrast, balloon catheter denuded arteries showed only a platelet monolayer on their luminal surface. Within the first few weeks after denudation with either technique the regenerating endothelial cells stained strongly for basic fibroblast growth factor. At later times when replication of endothelium had stopped, the balloon catheter denuded vessels did not stain with this antibody. After filament denudation endothelial cell replication remained high until regrowth was complete and intensive staining was observed in the regenerating endothelial cells at all times. No differences were seen in staining of smooth muscle cells for transforming growth factor-beta and fibronectin in either set of denuded vessels. Both groups showed transforming growth factor-beta to be located in the developing intima and especially on the apical surface of luminal smooth muscle cells. The surface of these luminal smooth muscle cells also stained with antibody to fibronectin. These data demonstrate that total regrowth of endothelium can occur over large denuded areas despite the presence of transforming growth factor-beta and fibronectin on these surfaces. Furthermore the ability of these endothelial cells to proliferate would appear to be dependent on the presence of basic fibroblast growth factor and on the severity of the trauma induced by denudation.     

A morphologic and permeability study of luminal smooth muscle cells after arterial injury in the rat.

In the carotid air drying model of arterial endothelial injury in the stressed rat, endothelium does not always regenerate over the zone of intimal thickening; instead, a layer of modified smooth muscle cells appears to form a temporary luminal surface. We examined the properties of these luminal smooth muscle cells in injured right carotid arteries from stressed rats at intervals up to 2 months by light, scanning electron, and transmission electron microscopy. Before perfusion fixation, selected animals were given injections of Evans blue dye, ferritin, or horseradish peroxidase. Unlike adjacent endothelium, the luminal smooth muscle cells most closely resembled neighboring intimal smooth muscle cells, lacked morphologic characteristics of normal endothelium, and did not stain with rabbit antibody to rat factor viii. Unlike normal mature endothelium, this layer did not exclude horseradish peroxidase, Evans blue, or ferritin. These data demonstrate that a nonthrombogenic layer composed of modified smooth muscle cells can appear at the luminal surface of a zone of injury-induced myointimal thickening; however, this layer does not form a permeability barrier to large molecules.     

Endothelial regeneration. V. Inhibition of endothelial regrowth in arteries of rat and rabbit

Endothelium was removed from the carotid artery of both rat and rabbit using a 2F balloon catheter. The regrowth of endothelium progressed from either end of the vessels but had stopped after 2 weeks in the rabbit and 6 weeks in the rat. Total outgrowth along the vessel was 3 mm in the rabbit and approximately 10 mm in the rat, and by 12 weeks a large zone of the vessel was still devoid of endothelium. Autoradiographic data showed that 12 weeks after the injury endothelial cell replication was reduced to background values. When these vessels were reinjured with a nylon catheter, endothelial cell replication was initiated and the wound rehealed, but these cells did not progress further into the denuded region. Morphologic examination of arteries 12 weeks after balloon denudation showed that endothelial cells, abutting the luminal smooth muscle cells, were larger and not aligned with flow. The luminal smooth muscle cells formed a loose junction with the leading edge of the endothelium and exhibited an extracellular material on their luminal aspect. These results demonstrate that endothelial regeneration will stop before cellular regrowth is complete and that cell senescence is not responsible. The presence of smooth muscle cells on the luminal surface appears to be related to this inhibition of growth.     

Kinetics of cellular proliferation after arterial injury. II. Inhibition of smooth muscle growth by heparin

Heparin inhibits intimal thickening after arterial injury. Whether this effect is due to inhibition of medial smooth muscle cell (SMC) migration, SMC proliferation in the intima, or synthesis and deposition of connective tissue has not been evident. In this study we have investigated these possibilities in a rat carotid balloon injury model. Heparin (0.3 mg/kg/hour) was administered intravenously by means of osmotic pumps to experimental animals, and controls received lactated Ringer's solution. Smooth muscle proliferation (thymidine index), intimal smooth muscle accumulation, and endothelial regeneration were measured at intervals between 0 and 28 days. Total smooth muscle growth as determined biochemically at 14 days was markedly inhibited by heparin if the pumps were placed 24 hours before or at the time of injury and less so if inserted 48 or 96 hours after injury. SMC thymidine indices were maximal in the media at 4 days and in the intima at 7 days for injured arteries of both heparin-treated and control rats; at each time point SMC proliferation and intimal thickening were less in heparin-treated rats. The volume of connective tissue in the intima was the same in both groups at 28 days. Medial SMC migration into the intima was diminished by heparin treatment, but endothelial regeneration was not affected. These results support the hypothesis that heparin is a specific inhibitor of SMC migration and proliferation and is most effective if started before SMC enter S-phase.     

Rabbit ductus arteriosus during development: Anatomical structure and smooth muscle cell composition

The anatomical structure as well as the smooth muscle cell (SMC¹) composition of the ductus arteriosus (DA) were studied in rabbits ranging in age from 29 days of gestation to 20 days after birth. Computerassisted, three-dimensional reconstructions of hematoxylin-eosin stained serial cryosections from ductus arteriosus-aorta (DA-AO) junctures revealed that DA in animals near term is separated from the aorta by a “septumlike” structure that is continuous with the aortic wall. Two days after birth, obliteration of DA is almost complete, and a small “pocketlike” cavity appears in the pre-existing site in which DA merged into the aorta. This small cavity in the aortic arch was still evident in the large majority of animals examined even 20 days after birth, as also demonstrated by scanning electron microscopy. At this time period DA consisted of a central, fibrotic region surrounded by several layers of SMC (the ligamentum arteriosum, LA) and ended within the aortic media just above the small cavity, forming a round “scar.” Vascular SMC composition of DA during closure was examined by means of indirect and double immunofluorescence procedures, using a panel of monoclonal antibodies against some cytoskeletal and cytocontractile proteins (vimentin, desmin, smooth muscle (SM), and nonmuscle (NM) myosinisoforms). “Intimal cushions” were particularly evident from 5 hr after birth and were found to be desmin-negative, homogenously reactive for vimentin and NM myosin, and heterogeneously stained with anti-SM myosin antibody. In SMC subjacent to the “intimal cushions,” distribution of vimentin and SM myosin was homogeneous, whereas the one of desmin and NM myosin content was heterogeneous. The cytoskeletal and cytocontractile protein content displayed by SMC during the closure of DA is similar to that of “intimal thickening” found in some pathological conditions of the arterial wall in adult rabbits. Completation of DA closure (day 2) was accompanied by the disappearance of cellular heterogeneity in myosin isoform distribution in both the “intimal cushions” and the underlying media. These results give new insights into: (1) the structure of DA-AO juncture, which can be relevant to the physiology of blood circulation in the fetus, and (2) the phenotypic similarity of vascular SMC populations involved in the formation of “intimal cushions” and “intimal thickening”.     

Kinetics of cellular proliferation after arterial injury. III. Endothelial and smooth muscle growth in chronically denuded vessels

The healing of injured rat carotid chronically denuded of endothelium was studied at late times after balloon injury. One year after injury the endothelial layer was not fully regenerated and had ceased proliferating. The denuded areas of these vessels were covered with luminal smooth muscle cells which strongly resembled endothelium but did not stain with factor VIII.R.Ag antibody. These cells were actively proliferating and formed a surface which was weakly thrombogenic. Indium-111 platelet studies showed that over 24 hours there was a slight but significant adherence of platelets to the denuded surface. Luminal smooth muscle cell proliferation was matched by cell loss and did not produce further intimal thickening or an increase in total cell number. These results demonstrate that damaged conduit arteries can exist in a stable state without endothelium and do not develop thrombosis even after prolonged periods of time.     

A nonantibiotic chemically modified tetracycline (CMT-3) inhibits intimal thickening

Recent research has shown that the tetracycline antibiotics are pluripotent drugs that inhibit the activity of matrix metalloproteinases (MMPs) and affect many cellular functions including proliferation, migration, and matrix remodeling. We have shown that doxycycline inhibits MMP activity and intimal thickening after injury of the rat carotid artery, however we do not know whether these effects are because of the antibiotic, anti-MMP, or other actions of doxycycline. Recently, chemically modified tetracyclines have been synthesized that lack antibiotic activity but retain anti-MMP activity (CMT-3), or lack both antibiotic and anti-MMP activity (CMT-5). In the current study we have assessed the effects of treatment with CMT-3 or CMT-5 on intimal thickening after balloon catheter injury of the rat carotid artery. Rats were treated by oral gavage with 15 mg/kg/day CMT-3 or CMT-5. CMT-3 significantly reduced smooth muscle cell (SMC) proliferation in both the medial and intimal layers of the injured rat carotid artery compared to CMT-5. Furthermore, CMT-3 inhibited SMC migration from the media to the intima by 86% at 4 days after injury. CMT-3 also decreased MMP-2 activity. Finally, we found that CMT-3 treatment resulted in a significant reduction in intimal cross-sectional area from 0.23 +/- 0.01 mm(2) in the CMT-5 control group to 0.19 +/- 0.01 mm(2). There was also a reduction in elastin and collagen accumulation within the intima. We conclude that CMT-3 attenuated intimal thickening after arterial injury by inhibiting SMC proliferation, migration and MMP activity, and accumulation of extracellular matrix. The inhibitory effects of CMT-3 were independent of the antibiotic properties, but were dependent on the anti-MMP activity of the tetracycline family.     

Endothelial regeneration. VIII. Interaction of smooth muscle cells with endothelial regrowth

This study examined the ability of arterial endothelial cells to repopulate arterial grafts which were devoid of luminal smooth muscle cells and in arterial grafts which had an established pseudoendothelium comprised of smooth muscle cells. These studies were designed to explore the hypothesis that smooth muscle cells when forming a pseudoendothelium can retard endothelial cell regrowth. Segments of denuded glutaraldehyde-fixed carotid arteries and of viable autologous carotid arteries with a pseudoendothelium of smooth muscle cells were implanted end to end into the rabbit carotid arteries and left for 6 or 12 weeks. Endothelial outgrowth onto these arterial grafts was extremely limited (approximately 3 mm) regardless of the preparation and was equal to that observed in a carotid artery denuded of endothelium with a balloon catheter. Endothelial cell replication was significantly elevated in these implanted carotid segments at all times studied with the majority of the replicating cells not located at the leading edge of endothelium. The location of these cells suggests this replication was not associated with regrowth. Finally, the ability of denuded arteries to support endothelial cell adherence was tested in vitro by plating [3H]thymidine bovine endothelial cells on segments of excised arteries which had been denuded of endothelium for 2 and 12 weeks. No difference in plating efficiency was observed. These studies suggest that the presence of smooth muscle cells on the luminal surface of denuded arteries was not responsible for the cessation of endothelial regrowth.     

Thrombospondin deposition in rat carotid artery injury.

The balloon catheter injury model was used to determine the relative contributions of vascular smooth muscle cells (SMC) and platelets to thrombospondin (TSP) antigen deposition in the artery wall. Rat carotid arteries were denuded of endothelium, exposing the thrombogenic subendothelial extracellular matrix (ECM) to the circulation. Rats were killed after 1 hour, or 5, 10, or 20 days. Thrombospondin antigen deposition in the injured arteries was assessed using a specific polyclonal antiserum raised in rabbit against rat platelet TSP and a sensitive silver-enhanced immunogold staining method. Faint immunostaining for TSP antigen was detected, associated mostly with cells, in the media of the carotid artery of the nonoperated controls. One hour after balloon catheter injury, however, prominent cell-associated immunostaining was evident in the media; extracellular matrix staining was negligible. At this time, large foci of immunostaining were present on the lumenal surface of the vessel. Intimal proliferation was evident on most stained sections of tissue taken 5 days after balloon injury. Thrombospondin antigen immunostaining was markedly increased compared to nonoperated controls in all sections, regardless of the degree of intimal thickening. Thrombospondin immunostaining remained associated with cells in the neointima and media; extracellular matrix staining remained negligible. Ten days after endothelial injury, immunostaining for TSP antigen was detected in all layers of the artery, but was greater in the neointima and media. Reaction product was still associated only with cells. Thrombospondin antigen levels, as detected by this procedure, remained high in the injured tissue through 10 days of observation but appeared less prominent 20 days after injury. At this time extracellular matrix staining was obvious and cell-associated staining was reduced. These data support the hypotheses that thrombospondin (TSP) expression by vascular smooth muscle cells is an early response to injury and that the primary source of TSP antigen in injured artery is the vascular smooth muscle cells (SMC). These results support data derived from in vitro studies of TSP secretion.     

Angiotensin-converting enzyme inhibitor versus angiotensin II, AT1 receptor antagonist. Effects on smooth muscle cell migration and proliferation after balloon catheter injury.

The angiotensin-converting enzyme (ACE) inhibitor, benazeprilat and the angiotensin II (Ang II), AT1-specific receptor antagonist, DuP753, were compared for their effects on intimal lesion formation as well as smooth muscle cell (SMC) proliferation and migration in Sprague Dawley rats after carotid balloon injury. Both the ACE inhibitor (benazeprilat, 3 mg/kg/day) and the AT1 antagonist (DuP 753, 10 mg/kg/day) significantly reduced intimal lesion formation after balloon injury (by 35% and 49%, respectively). Medial SMC proliferation after injury was reduced 53% by the AT1 antagonist; however, the ACE inhibitor had no effect on SMC proliferation. SMC migration was reduced 94% by the AT1 antagonist and 68% by the ACE inhibitor. These data demonstrate the importance of Ang II in SMC proliferation and migration after balloon injury. They also demonstrate that in the balloon injury model, the ACE inhibitor reduced intimal lesion size by inhibiting SMC migration alone without affecting SMC proliferation. A more pronounced reduction in lesion size was obtained after AT1 antagonism, however, when both SMC migration and proliferation were inhibited.     

Role of the cytoskeleton in flow (shear stress)-induced dilation and remodeling in resistance arteries

Cytoskeletal proteins determine cell shape and integrity and membrane-bound structures connected to extracellular components allow tissue integrity. These structural elements have an active role in the interaction of blood vessels with their environment. Shear stress due to blood flow is the most important force stimulating the endothelium. The role of cytoskeletal proteins in endothelial responses to flow has been studied in resistance arteries using pharmacological tools and transgenic models. Shear stress activates extracellular “flow sensing” elements associated with a thick glycocalyx communicating the signal to membrane-bound complexes (integrins and/or dystrophin-dystroglycans) and to eNOS through a pathway involving the intermediate filament vimentin, the microtubule network and actin. When blood flow increases chronically the endothelium triggers diameter enlargement and medial hypertrophy. This is facilitated by the genetic absence of the intermediate filaments, vimentin and desmin suggesting that these elements oppose the process.