Phenotype-dependent response of cultured aortic smooth muscle to serum mitogens

Proliferative heterogeneity of vascular smooth muscle cells and its alteration by injury

This study was designed to explore the question of whether the population of morphologically similar smooth muscle cells (SMC) in the vessel wall is functionally homogeneous or heterogeneous with respect to their proliferative response to injury. Using time-lapse video recording we measured interdivision times (IDT) of primary SMC clones, sibling pairs, and mother/daughter pairs. SMC from in vivo undisturbed vessels displayed an interclonal and intraclonal heterogeneity with a wide range in IDT. In vivo balloon injury resulted in a population with homogeneously short IDT. While 80% of IDT of SMC from injured vessels were shorter than 14 h, only slightly more than half of IDT of cells from undisturbed vessels fell into this category. Longitudinal analysis of mother/daughter pairs confirmed the presence of a heterogeneous population of SMC in the undisturbed vessel wall. In vivo balloon injury not only shortened the IDT of the majority of cells, but the shorter IDT persisted much longer than in the case of the undisturbed vessel. We suggest that a morphologically homogeneous SMC population in the aorta can now be subdivided into several groups of functionally different SMC with respect to their proliferative response to injury.

A smooth muscle-specific monoclonal antibody recognizes smooth muscle actin isozymes

Injection of chicken gizzard actin into BALB/c mice resulted in the isolation of a smooth muscle-specific monoclonal antibody designated CGA7. When assayed on methanol-Carnoy's fixed, paraffin-embedded tissue, it bound to smooth muscle cells and myoepithelial cells, but failed to decorate striated muscle, endothelium, connective tissue, epithelium, or nerve. CGA7 recognized microfilament bundles in early passage cultures of rat aortic smooth muscle cells and human leiomyosarcoma cells but did not react with human fibroblasts. In Western blot experiments, CGA7 detected actin from chicken gizzard and monkey ileum, but not skeletal muscle or fibroblast actin. Immunoblots performed on two-dimensional gels demonstrated that CGA7 recognizes gamma-actin from chicken gizzard and alpha- and gamma-actin from rat colon muscularis. This antibody was an excellent tissue-specific smooth muscle marker.

Adult human arterial smooth muscle cells in primary culture. Modulation from contractile to synthetic phenotype

Smooth muscle cells were isolated enzymatically from adult human arteries, grown in primary culture in medium containing 10% whole blood serum, and studied by transmission electron microscopy and [3H]thymidine autoradiography. In the intact arterial wall and directly after isolation, each smooth muscle cell had a nucleus with a wide peripheral zone of condensed chromatin and a cytoplasm dominated by myofilament bundles with associated dense bodies. After 1-2 days of culture, the cells had attached to the substrate and started to spread out. At the same time, a characteristic fine-structural modification took place. It included nuclear enlargement, dispersion of the chromatin and formation of large nucleoli. Moreover, myofilament bundles disappeared and an extensive rough endoplasmic reticulum and a large Golgi complex were organized in the cytoplasm. This morphological transformation of the cells was completed in 3-4 days. It was accompanied by initiation of DNA replication and mitosis. The observations demonstrate that adult human arterial smooth muscle cells, when cultivated in vitro, pass through a phenotypic modulation of the same type as arterial smooth muscle cells from experimental animals. This modulation gives the cells morphological and functional properties resembling those of the modified smooth muscle cells found in fibroproliferative lesions of atherosclerosis. Further studies of the regulation of smooth muscle phenotype and growth may provide important clues for a better understanding of the pathogenesis of atherosclerosis.

Glycoprotein 115, a glycoprotein isolated from chick blood vessels, is widely distributed in connective tissue

An extracellular glycoprotein (gp 115) with an apparent Mr = 115,000 isolated from chick aortas (Bressan, G. M., I. Castellani, A. Colombatti, and D. Volpin, 1983, J. Biol. Chem., 258:13262-13267), was used to immunize mice. The antisera were shown to specifically recognize gp 115 by numerous criteria: a major band around Mr = 115,000 plus minor bands of lower Mr were visible by immunoblotting on aorta extracts, and a similar pattern was observed with a monoclonal antibody; no cross-reactivity was detected by radioimmunobinding with other extracellular proteins, namely, fibronectin, laminin, and collagen types I, III, IV, V, and VI. Antigen distribution on frozen tissue sections from newborn chicks was investigated by using affinity-purified antibody. Strong immunoreactivity was always found in blood vessels. In the digestive tract, the fluorescent staining was localized both at the level of muscular layers and in the stromal matrix of the villi. Within skeletal muscle and myocardium, staining was associated with large connective tissue bundles and the matrix around each muscle fiber. Intense fluorescence was observed in the kidney, in smooth muscle cells rich areas of parabronchi, and within the portal space and along liver sinusoids. The antigen was not detected at the epidermal-dermal junction; immunoreactivity in the dermis was present as a diffuse fibrillar pattern. That the antigen detected by immunofluorescence in the various organs was indeed gp 115 was demonstrated by immunoblotting analysis: as in aorta extracts, a major band around Mr = 115,000 was detected in several tissues. Antibody-reacting material was also incorporated into the extracellular matrix produced by embryo smooth muscle cells grown in vitro and was organized as a meshwork of fine fibrils.

Beta-adrenergic stimulation inhibits calcium efflux and alters the morphology of cultured arterial muscle cells

Beta-adrenoreceptor stimulation with isoproterenol (IP) rapidly and reversibly rounded and arborized smooth muscle cells (SMC) cultured from rat aorta. The arborized SMC remained firmly attached to the substratum via a network of long, dendritelike processes. Arborization of the SMC correlated closely with increases in cellular cAMP produced by IP and a variety of other compounds. The intracellular calcium antagonist 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8) also rounded and arborized the SMC. Antitubulin compounds potently blocked arborized by IP, dibutyryl cAMP, and TMB-8. The release of cell-bound 45Ca2+ was followed in the presence and absence of IP. IP strikingly increased the amount of 45Ca2+ that remained cell bound between 20 and 120 min. Propranolol and colchicine prevented IP from inhibiting the release of cell-bound 45Ca2+. These results suggest that the modulation of Ca2+ transport is involved in the arborization of cultured SMC by cAMP.

Phenotype modulation in primary cultures of arterial smooth-muscle cells

The effects of prostaglandin E1 (PGE1) on the phenotypic state of enzymatically isolated arterial smooth-muscle cells in primary culture were studied by transmission electron microscopy, thymidine autoradiography, and cell counting. Early in culture (day 0-2), PGE1 stimulated conversion of the cells from contractile (less euchromatic nucleus and cytoplasm dominated by myofilament bundles) to synthetic state (more euchromatic nucleus and cytoplasm dominated by cisternae of rough endoplasmic reticulum and a large Golgi complex). The rate of entrance of the cells into DNA synthesis and mitosis was also increased at this time. Later on (day 3-6), when the majority of the cells had entered synthetic state, PGE1 inhibited DNA synthesis and cellular proliferation. These observations indicate that the effect of prostaglandins on arterial smooth muscle is dual in nature and dependent on the state of differentiation of the cells.

Myosin in cultured vascular smooth muscle cells: immunofluorescence and immunochemical studies of alterations in antigenic expression

Vascular smooth muscle cells (VSMC) in the rat mesenteric artery show specific immunofluorescent staining with antisera against purified human uterine myosin (ASMM) but not human platelet myosin (APM). However, in primary cultures produced by enzymatic dissociation of this vessel, VSMC stain specifically with both ASMM and APM within 5 h after plating and throughout growth to confluence (4-10 d). In confluent cultures, APM staining remains bright while ASMM staining is reduced in intensity in most cells. In contrast, cellular myosin content, determined by quantitative SDS PAGE, is comparable in confluent and growing cultures. Immunoprecipitation of high salt extracts of cultured VSMC with ASMM and APM yields myosins with the same mobilities on SDS PAGE. When serial, exhaustive precipitations are performed with one antiserum, followed by reprecipitation with the other, myosin in subconfluent and confluent VSMC cultures is exhaustively precipitated by either antiserum, thus indicating complete immunological cross-reactivity. These results might be explained by synthesis of a new myosin isoform reactive with both ASMM and APM. However, the development of APM staining in cultured VSMC did not require protein synthesis. Therefore, it is more likely that the changes in immunofluorescent staining observed in vitro reflect conformational alterations, perhaps related to cytoskeletal rearrangements. These changes in myosin antigenic expression may be relevant to the problem of VSMC phenotypic modulation both in vitro and in vivo.

Growth properties and composition of cytoskeletal and cytocontractile proteins in aortic cells isolated and cultured from normal and atherosclerotic rabbits

Aortic intima-medias of normal and cholesterol-fed rabbits were studied with EM and cells were isolated by enzyme digestion. The composition of cytoskeletal and cytocontractile proteins was determined with SDS-PAGE and the primary growth and thymidine incorporation rates were assessed after seeding the cells into tissue culture flasks. Ultrastructurally, the SMCs in the thickened atherosclerotic intima differed from the contractile medial SMCs in containing lipid vacuoles, enlarged endoplasmic reticulum and a reduced number of myofilaments, thus showing characteristics of dedifferentiated SMCs. In SDS-PAGE, freshly isolated cells from the atherosclerotic intima-medias had a lower content of myosin and actin, and a higher proportion of vimentin and desmin than SMCs from normal aortas. Enzyme-isolated SMCs from normal aortas did not start to grow and incorporate radioactive thymidine until 5-6 days after seeding, whereas those from atherosclerotic aortas did so within 2 days. After a week in culture, SMCs from both sources resembled each other, and had decreased contents of myosin and actin, and increased concentrations of vimentin in comparison to freshly isolated normal SMCs. The present results indicate (a) that morphological dedifferentiation of SMCs in aortic lesions of cholesterol-fed rabbits is associated with an increased proportion of the proteins of the intermediate filaments and a decrease in those of the thin and thick myofilaments as determined with SDS-PAGE, and (b) that similar changes take place when normal SMCs are cultured in vitro. The results also suggest (c) that enzyme-isolated atherosclerotic SMCs proliferate in a primary culture without the lag period that normal SMCs apparently require for dedifferentiation.

Platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a basic (pI congruent to 10) 30 000 molecular weight protein circulating in normal blood sequestered within the platelet alpha-granules. It binds with high affinity (Kd = 10(-11) M) to a specific cell-surface receptor found on many connective tissue cell types in culture. It is active in stimulating the metabolism and multiplication of connective tissue cells at very low concentrations (ED50 = 10(-11) M). It is likely that PDGF is released from platelets at sites of vascular damage and that it contributes toward the cell proliferation and connective tissue formation seen in healing wounds and in arteriosclerotic lesions. PDGF which does not bind to responsive cells at the wound site is largely inactivated by a plasma binding protein and is rapidly cleared from the circulation.

Glucocorticoids stimulate collagen and noncollagen protein synthesis in cultured vascular smooth muscle cells

The effect of glucocorticoids on collagen synthesis was examined in cultured bovine aortic smooth muscle (BASM) cells. BASM cells treated with 0.1 microM dexamethasone during their proliferative phase (11 d) were labeled with [3H]proline for 24 h, and the acid-precipitable material was incubated with bacterial collagenase. Dexamethasone produced an approximate twofold increase in the incorporation of proline into collagenase-digestible protein (CDP) and noncollagen protein (NCP) in the cell layer and medium. The stimulation was present in both primary mass cultures and cloned BASM. An increase in CDP and NCP was detected at 0.1 nM, while maximal stimulation occurred at 0.1 microM. Only cells exposed to dexamethasone during their log phase of growth (1-6 d after plating) showed the increase in CDP and NCP when labeled 11 d after plating. The stimulatory effect was observed in BASM cells treated with the natural bovine glucocorticoid, cortisol, dexamethasone, and testosterone, but was absent in cells treated with aldosterone, corticosterone, cholesterol, 17 beta-estradiol, and progesterone. The increase in CDP and NCP was absent in cells treated with the inactive glucocorticoid, epicortisol, and totally abolished by the antagonist, 17 alpha-hydroxyprogesterone, suggesting that the response was mediated by specific cytoplasmic glucocorticoid receptors. Dexamethasone-treated BASM cells showed a 4.5-fold increase in the specific activity of intracellular proline, which was the result of a twofold increase in the uptake of proline and depletion of the total proline pool. After normalizing for specific activity, dexamethasone produced a 2.4- and 2.8-fold increase in the rate of collagen and NCP synthesis, respectively. Cells treated with dexamethasone secreted 1.7-fold more collagen protein in 24 h compared to control cultures. The BASM cells secreted 70% Type I and 30% Type III collagen into the media as assessed by two-dimensional gel electrophoresis. The ratio of these two types was not altered by dexamethasone. The results of the present study demonstrate that glucocorticoids can act directly on vascular smooth muscle cells to increase the synthesis and secretion of collagen and NCP.

Phenotype modulation in primary cultures of arterial smooth muscle cells. On the role of platelet-derived growth factor

Smooth muscle cells were isolated from adult rat aorta by collagenase digestion, grown in primary culture in the presence of 10% whole blood serum (WBS), and studied by quantitative electron microscopy and thymidine autoradiography in order to correlate cellular fine structure and proliferation. On day 2-4, the cells passed through a structural transition from contractile to synthetic state. In the former they were characterized by predominance of cytoplasmic microfilament bundles and in the latter by an extensive rough endoplasmic reticulum (RER) and a large Golgi complex. The disappearance of the microfilament bundles was accompanied by a transient increase in lysosomal volume density but no signs of bulk autophagy. This suggests that microfilaments were disassembled into subunit proteins and that lysosomes were engaged in adjusting the pool of free subunits into a new equilibrium. RER cisternae grew out from the nuclear envelope and successively spread throughout the cytoplasm. Stacks of Golgi cisternae were organized in a circumscribed juxtanuclear region. The structural modulation occurred also in medium containing 10% plasma-derived serum (PDS). Its onset was delayed by addition of antibodies (50 micrograms/ml) against platelet-derived growth factor (PDGF) to 10% WBS-medium and speeded up by addition of purified PDGF (25 ng/ml) to 10% PDS-medium. Otherwise, the kinetics of the structural modulation was the same in all experimental groups. The observations could not be explained by overgrowth of contaminating fibroblasts since (1) successive steps in the process were clearly evident, (2) the cells surrounded themselves by an incomplete basement membrane, a characteristic feature of smooth muscle, and (3) mitomycin C blocked cell growth but not conversion from contractile to synthetic state. After 3-4 days of culture in 10% WBS-medium, active DNA synthesis and cellular proliferation were initiated as determined autoradiographically and by cell counting. Electron microscopic autoradiography showed that all cells were morphologically in the synthetic state at the time of entrance into S-phase. Initially, the cells grew at a lower rate in the presence of PDGF antibodies but after 5-6 days of culture attained a rate similar to that in the controls. No distinct proliferation was obtained in 10% PDS-medium unless purified PDGF (10 ng/ml) was added during the first days of culture. The results suggest that the structural modulation of the smooth muscle is an absolute but not sufficient prerequisite for cellular proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)

Glucocorticoid inhibition of vascular smooth muscle cell proliferation: influence of homologous extracellular matrix and serum mitogens

We examined the influence of glucocorticoid hormones on the proliferation of cultured adult bovine aortic smooth muscle cells (BASM) using both primary mass cultures and a cloned strain. Cloned BASM cells maintained on plastic culture dishes were inhibited by approximately 40% by dexamethasone treatment but showed no inhibition when grown of homologous extracellular matrix (ECM) coated dishes. Dexamethasone inhibited growth of primary cultures by 73% on plastic and by 45% on ECM. The inhibitory effect was specific for the glucocorticoids, dexamethasone, corticosterone, and cortisol and was not observed with progesterone, aldosterone, estradiol or 17-alpha OH progesterone. In cloned cells, the abolition of glucocorticoid inhibition by ECM was independent of seeding density and serum concentration. The inhibition on plastic was dependent on serum concentrations greater than 1% and resulted in both a slow rate of proliferation and a lower saturation density. A specific subset of peptides detected on two-dimensional gels was induced by glucocorticoids under growth inhibitory conditions but was not induced when the cells were grown on ECM. Primary cultures grown on ECM and exposed to Dulbecco's modified Eagle's Medium (DME) containing high density lipoprotein and transferrin grew at 40% of the rate observed for cultures exposed to DME with 10% serum. Both conditions showed growth inhibition of 70% in the presence of dexamethasone. The addition of epidermal and platelet-derived growth factors in DME containing high density lipoprotein and transferrin to cells grown on ECM resulted in growth rates comparable to that observed with cultures exposed to 10% serum and were inhibited 45% by dexamethasone. These results suggest that glucocorticoids inhibit smooth muscle proliferation by decreasing the sensitivity of the cells to mitogenic stimulation by high density lipoprotein when the cells are maintained on a homologous substrate.

Vascular smooth muscle cell hypertrophy and hyperploidy in the Goldblatt hypertensive rat

Our major objective in this study was to examine the hypothesis that the aortic smooth muscle cell hypertrophy and hyperploidy observed in previous studies of spontaneously hypertensive rats is not peculiar to that model, but also occurs in Sprague-Dawley rats made hypertensive by a Goldblatt procedure (two-kidney, one-clip model). Flow microfluorometric and microdensitometric analysis of smooth muscle cell DNA content showed a significant increase in the frequency of tetraploid smooth muscle cells from 5.6 +/- 0.9% in controls to 14.6 +/- 1.94% in hypertensives 1 month after Goldblatt surgery. Neither differences in ploidy nor elevation in blood pressure were apparent 2 weeks after surgery. The frequency of polyploid smooth muscle cells increased with age, duration of hypertension, and level of blood pressure. Analysis of the interrelationship between smooth muscle cell ploidy and hypertrophy in 5-month post-surgery Goldblatts by cytospectrophotometric measurements of the protein and DNA content of individual smooth muscle cells showed that tetraploid and octaploid cells from Goldblatt rats had 64% and 129% greater protein mass, respectively, than diploid cells. In addition, the mean protein mass of smooth muscle cells from Goldblatts was approximately 100% greater than that of normotensive controls, with each of the ploidy classes in Goldblatts having a higher frequency and mass than the corresponding cells in controls. Estimates of cell number per centimeter aortic length, based on measurements of average DNA/cell and total aortic medial DNA, showed no difference between hypertensives and controls. Furthermore, the rate of accumulation of polyploid cells could account for the increased frequency of cells undergoing DNA synthesis as measured by [3H]thymidine autoradiography. Thus, smooth muscle cell hypertrophy, not hyperplasia, was responsible for the increased mass of smooth muscle in aortas of Goldblatt hypertensive rats compared with normotensive controls, and this smooth muscle cell hypertrophy was accompanied by an increase in DNA ploidy.

Structural alterations in fibronectin correlated with morphological changes in smooth muscle cells

Nontransformed cultures of vascular smooth muscle cells proliferate until they form a confluent sheet of cells. Subsequently, the cells become reorganized to form multicellular nodules that are loosely attached to the substrate. The formation of nodules is facilitated by the addition of medium conditioned by nodular cultures. Nodulation is inhibited by the addition of fibronectin. Fibronectins derived from monolayer culture conditioned medium or from plasma are maximally effective while fibronectin isolated from nodular cell conditioned medium is inactive. Analysis by NaDodSO4-polyacrylamide gel electrophoresis reveals that the nodular cell fibronectin has a molecular weight that is about 20-30 kd less than that of monolayer cell fibronectin. Further, nodular cell conditioned medium contains an activity that can convert both plasma fibronectin and monolayer cell fibronectin to the lower molecular weight correlated with the loss of biological activity.

Lipid accumulation in arterial smooth muscle cells. Influence of phenotype

Isolated smooth muscle cells from the adult pig and rabbit aorta in primary culture undergo a spontaneous change in phenotype from a contractile to a synthetic state over 6-8 days, losing their capacity to contract and gaining the capacity to divide. The change in smooth muscle phenotype to the synthetic state is accompanied by distinct changes in the cells' ability to metabolize LDL, with the rate of degradation of 125I-labelled LDL decreasing to about one fifth of the level in contractile state cells. This does not appear to be due to changes in the number or affinity of LDL receptors since saturable binding of LDL is unaltered. The specific activities of the lysosomal enzymes acid phosphatase and N-acetyl-beta-glucosaminidase increase with change to the synthetic state as do cytochrome c oxidase (mitochondria) and NADPH-dependent cytochrome c reductase (endoplasmic reticulum). In contrast there is a slight but not significant decrease in the specific activity of the lysosomal enzyme acid cholesteryl esterase of rabbit smooth muscle cells and a significant decrease in the activity of pig cells with change in phenotype to the synthetic state. Significantly more [3H]cholesteryl oleate is recovered in synthetic state than in contractile state cells following incubation with 20 micrograms/ml unlabelled LDL and [3H]sodium oleate. Morphologically there is no difference in the number of lipid droplets in contractile and synthetic state cells after incubation in 5% normolipemic serum, but in cells grown in 10% hyperlipemic serum for 4 days synthetic state cells become almost completely filled with lipid droplets while contractile state cells are unaffected. Lipid accumulation also occurs selectively in vivo in synthetic as compared with contractile state smooth muscle cells within intimal fibromuscular thickenings induced by de-endothelialization of the carotid artery of cholesterol-fed rabbits. We suggest that accumulation of lipid in smooth muscle cells of atherosclerotic plaques is related to reduced catabolism of LDL following smooth muscle phenotypic change from the contractile to synthetic state.

Organizational behavior of human umbilical vein endothelial cells

Culture conditions that favor rapid multiplication of human umbilical vein endothelial cells (HUV-EC) also support long-term serial propagation of the cells. This is routinely achieved when HUV-EC are grown in Medium 199 (M-199) supplemented with fetal bovine serum (FBS) and endothelial cell growth factor (ECGF), on a human fibronectin (HFN) matrix. The HUV-EC can shift from a proliferative to an organized state when the in vitro conditions are changed from those favoring low density proliferation to those supporting high density survival. When ECGF and HFN are omitted, cultures fail to achieve confluence beyond the first or second passage: the preconfluent cultures organize into tubular structures after 4-6 wk. Some tubes become grossly visible and float in the culture medium, remaining tethered to the plastic dish at either end of the tube. On an ultrastructural level, the tubes consist of cells, held together by junctional complexes, arranged so as to form a lumen. The smallest lumens are formed by one cell folding over to form a junction with itself. The cells contain Weibel-Palade bodies and factor VIII-related antigen. The lumens contain granular, fibrillar and amorphous debris. Predigesting the HFN matrix with trypsin (10 min, 37 degrees C) or plasmin significantly accelerates tube formation. Thrombin and plasminogen activator had no apparent effect. Disruption of the largest tubes with trypsin/EDTA permits the cells to revert to a proliferative state if plated on HFN, in M-199, FBS, and ECGF. These observations indicate that culture conditions that do not favor proliferation permit attainment of a state of nonterminal differentiation (organization) by the endothelial cell. Furthermore, proteolytic modification of the HFN matrix may play an important role in endothelial organization.

Fibronectin inhibits morphological changes in cultures of vascular smooth muscle cells

In culture, vascular smooth muscle cells proliferate until they form a confluent sheet of cells. At that time the morphology of the culture becomes altered and the cells form multilayered regions that eventually develop into nodular aggregations. We now demonstrate that the transition from monolayer culture to nodular culture is influenced by the presence of components in conditioned media. The development of nodules is enhanced by conditioned medium made from nodular cultures but is either inhibited or unaffected by monolayer culture-conditioned medium. Examination of the two types of conditioned media using NaDodSO4- polyacrylamide gels reveals many similarities and one major difference. Nodular-conditioned medium contains a prominent 42 kilodalton polypeptide which is not present in monolayer-conditioned medium. Further, we demonstrate that although both nodular and monolayer cultures produce fibronectin the transition to nodular culture does not occur in the presence of exogeneously added plasma fibronectin.

Smooth muscle and endothelial cell function in the pathogenesis of atherosclerosis

Although clinical studies have been very useful in identifying factors that accelerate the development of atherosclerotic vascular disease, the pathogenesis of the vascular lesions remains unknown. Studies carried out in the last 10 years have shown that smooth muscle and endothelial cells of the vascular wall play a very important role in atherogenesis. It has become apparent that these cells are very active metabolically during the initiation and subsequent growth of the plaques, and that the materials that these cells produce and secrete are important in the composition and growth of the plaques. In addition, there are important interactions at the vessel wall-blood interface that involve endothelial cells, hemodynamic forces and many constituents of the blood, including platelets, lipoproteins, coagulation factors, fibrinolytic agents and leukocytes. In this article the numerous functions of both smooth muscle and endothelial cells are discussed and the effects of known atherogenic agents on these cellular functions are reviewed. Emphasis is placed on the important interactions that take place both within the vessel wall and at the vessel wall-blood interface. Understanding of the regulation of smooth muscle and endothelial cell function during the development and subsequent growth of fibrofatty plaques may be useful in designing appropriate therapeutic interventions to control atherosclerotic disease.

Functional angiotensin II receptors in cultured vascular smooth muscle cells

To study cellular mechanisms influencing vascular reactivity, vascular smooth muscle cells (VSMC) were obtained by enzymatic dissociation of the rat mesenteric artery, a highly reactive, resistance-type blood vessel, and established in primary culture. Cellular binding sites for the vasoconstrictor hormone angiotensin II (AII) were identified and characterized using the radioligand 125I-angiotensin II. Freshly isolated VSMC, and VSMC maintained in primary culture for up to 3 wk, exhibited rapid, saturable, and specific 125I-AII binding similar to that seen with homogenates of the intact rat mesenteric artery. In 7-d primary cultures, Scatchard analysis indicated a single class of high-affinity binding sites with an equilibrium dissociation constant (Kd) of 2.8 +/- 0.2 nM and a total binding capacity of 81.5 +/- 5.0 fmol/mg protein (equivalent to 4.5 x 10(4) sites per cell). Angiotensin analogues and antagonists inhibited 125I-AII binding to cultured VSMC in a potency series similar to that observed for the vascular AII receptor in vivo. Nanomolar concentrations of native AII elicited a rapid, reversible, contractile response, in a variable proportion of cells, that was inhibited by pretreatment with the competitive antagonist Sar1,Ile8-AII. Transmission electron microscopy showed an apparent loss of thick (12-18 nm Diam) myofilaments and increased synthetic activity, but these manifestations of phenotypic modulation were not correlated with loss of 125I-AII binding sites or hormonal responsiveness. Primary cultures of enzymatically dissociated rat mesenteric artery VSMC thus may provide a useful in vitro system to study cellular mechanisms involved in receptor activation-response coupling, receptor regulation, and the maintenance of differentiation in vascular smooth muscle.

Phenotypic modulation of the canine prostate after long-term treatment with androgens and estrogens

Fine structural alterations of the canine prostate induced by long-term treatment of castrated adult animals with estrogens and/or androgens and also in combination with antiandrogens and/or antiestrogens for six months have been studied with particular respect to their topographic location within the gland. Three major patterns of structural responses of the epithelium have been distinguished: squamous metaplasia, atrophy, and hypertrophy, while in stroma, regression, hypertrophy, or sclerosis were observed. In addition to cellular alterations of stromal fibrocytes and smooth muscle cells, characteristic changes in the arrangement, distribution, and pattern of the different stromal elements occurred. General squamous metaplasia of the epithelium and regressive alterations of stromal cells were most obvious in animals treated with estradiol plus androstanediol. Atrophy of the epithelium and stromal sclerosis were the salient features of antiandrogen-treated castrated animals, while hypertrophy or hyperplasia of both the epithelium and stroma was a major finding in androstanediol-substituted castrated animals. Combined treatment caused rather heterogeneous structural patterns seemingly dependent on the location within the gland. The results indicate that the prostatic epithelial cells dispose of a broad variety of structural reaction patterns that, in case of combined hormonal treatment, are expressed in a manner typical for their locations within the ductal system of the gland. However, with the exception of combined treatment with estradiol, tamoxifen, and androstanediol of castrated dogs, none of the experimental protocols used induced a morphologic response of the gland comparable to that seen in human benign prostatic hyperplasia. The canine prostate therefore is of rather limited value as a model for human BPH.

Metabolic changes in modified smooth muscle cells of rabbit carotid arteries

In the common carotid artery of rabbits, intimal myocyte proliferations were induced by daily repeated local electrical stimulation of the vessel wall in combination with a cholesterol containing diet given for 4 weeks. Some biochemical parameters of the morphologically modified intimal smooth muscle cells were studied and compared with those of samples obtained from nonstimulated tunica media of the contralateral carotid artery. The results show that in relation to dry weight both alkali extractable protein and DNA content of the proliferates are increased to about 125%. In the proliferates, the in-vivo tissue concentrations of glucose and glycogen are only 50-70% of the normal values, whereas the concentration of lactate is increased to about 160%. In-vitro incubation experiments of excised tissues samples from the intimal proliferates and normal media indicate that under an optimal supply of substrates the glucose uptake and lactate production of the proliferates are increased to 140% and 150%, respectively. This results provides evidence for an increased capacity of glycolysis in the proliferates, which in vivo may lead to a decrease in glucose concentration and to an increased concentration of lactate. This investigation shows that modified smooth muscle cells proliferating in the arterial intima exhibit an activated metabolism as seen in other models of arteriosclerosis.

What controls smooth muscle phenotype?

Enzyme-dispersed smooth muscle cells from the adult pig aortic media in the first few days of primary culture are in the contractile phenotype and do not divide when challenged with 5% WBS. After 6--8 days the isolated cells spontaneously undergo a change in phenotype where contraction cannot be stimulated and the cells respond to mitogens in WBS by logarithmic growth. The change in phenotype is reversible if the cells are seeded sufficiently densely (5 x 10(4) to 1 x 10(5)/ml) that a confluent monolayer results after less than 1 week of proliferation, but is irreversible if the cells are seeded sparsely (1 x 10(3) to 5 x 10(3)/ml) and take more than 2 weeks of proliferation to reach confluence. When the cells are seeded so densely (10(6)/ml) that a confluent monolayer is present from day 1, the cells do not undergo a change in phenotype but remain indefinitely in the contractile state. The spontaneous modulation of phenotype of isolated smooth muscle cells can be inhibited by a confluent monolayer of contractile smooth muscle or endothelial cells in co-culture with the sparsely seeded smooth muscle such that the two cell layers are not in contact but bathed by the same nutrient medium. Smooth muscle modulation can also be inhibited by a factor extracted from pig and rabbit aortic tissue, and its effects mimicked by commercially available sodium heparin at 50 units/ml.

Smooth muscle phenotypic modulation: role in atherogenesis

Observations in vivo and in vitro demonstrate: 1) smooth muscle cells are capable of more than one function and can alter their phenotype/state accordingly (modulation); 2) in the majority of cases before a smooth muscle can divide it must modulate from a contractile to a synthetic phenotype; 3) modulation is reversible; 4) however, if synthetic state smooth muscle which has been stimulated to divide achieves approximately nine cell doublings before being inhibited by confluence it appears unable to return to the contractile state; 5) smooth muscle cells in the synthetic state respond almost immediately to serum mitogens and have an altered ability to metabolize low density lipoprotein compared with those in the contractile state 6) diffuse intimal thickenings and intimal cushions at branch points form from the media apparently as a result of adaptation of the vessel wall to growth and development and are sites of predilection for the formation of atherosclerotic plaques. The "smooth muscle metabolic reactivity" hypothesis of atherogenesis suggests that due to the large number of smooth muscle cell doublings which occur in the formation of diffuse intimal thickenings and intimal cushions at branch points a number of these cells are permanently in the synthetic state. This confers upon these cells a selective proliferative advantage and an altered ability to metabolize lipoproteins - both essential ingredients in atherogenesis.