Hyperplastic growth of aortic smooth muscle cells in renovascular hypertensive rabbits is characterized by the expansion of an immature cell phenotype

Identification of platelet-derived growth factor C as a mediator of both renal fibrosis and hypertension

Platelet-derived growth factors (PDGF) have been implicated in kidney disease progression. We previously found that PDGF-C is upregulated at sites of renal fibrosis and that antagonism of PDGF-C reduces fibrosis in the unilateral ureteral obstruction model. We studied the role of PDGF-C in collagen 4A3^-/- ("Alport") mice, a model of progressive renal fibrosis with greater relevance to human kidney disease. Alport mice were crossbred with PDGF-C^-/- mice or administered a neutralizing PDGF-C antibody. Both PDGF-C deficiency and neutralization reduced serum creatinine and blood urea nitrogen levels and mitigated glomerular injury, renal fibrosis, and renal inflammation. Unexpectedly, systolic blood pressure was also reduced in both Alport and wild-type mice treated with a neutralizing PDGF-C antibody. Neutralization of PDGF-C reduced arterial wall thickness in the renal cortex of Alport mice. Aortic rings isolated from anti-PDGF-C-treated wildtype mice exhibited reduced tension and faster relaxation than those of untreated mice. In vitro, PDGF-C upregulated angiotensinogen in aortic tissue and in primary hepatocytes and induced nuclear factor κB (NFκB)/p65-binding to the angiotensinogen promoter in hepatocytes. Neutralization of PDGF-C suppressed transcript expression of angiotensinogen in Alport mice and angiotensin II receptor type 1 in Alport and wildtype mice. Finally, administration of neutralizing PDGF-C antibodies ameliorated angiotensin II-induced hypertension in healthy mice. Thus, in addition to its key role in mediating renal fibrosis, we identified PDGF-C as a mediator of hypertension via effects on renal vasculature and on the renin-angiotensin system. The contribution to both renal fibrosis and hypertension render PDGF-C an attractive target in progressive kidney disease.

The transition of smooth muscle cells from a contractile to a migratory, phagocytic phenotype: direct demonstration of phenotypic modulation

Key points

Smooth muscle cell (SMC) phenotypic conversion from a contractile to a migratory phenotype is proposed to underlie cardiovascular disease but its contribution to vascular remodelling and even its existence have recently been questioned.

Tracking the fate of individual SMCs is difficult as no specific markers of migratory SMCs exist.

This study used a novel, prolonged time‐lapse imaging approach to continuously track the behaviour of unambiguously identified, fully differentiated SMCs.

In response to serum, highly‐elongated, contractile SMCs initially rounded up, before spreading and migrating and these migratory cells displayed clear phagocytic activity.

This study provides a direct demonstration of the transition of fully contractile SMCs to a non‐contractile, migratory phenotype with phagocytic capacity that may act as a macrophage‐like cell.

Abstract

Atherosclerotic plaques are populated with smooth muscle cells (SMCs) and macrophages. SMCs are thought to accumulate in plaques because fully differentiated, contractile SMCs reprogramme into a ‘synthetic’ migratory phenotype, so‐called phenotypic modulation, whilst plaque macrophages are thought to derive from blood‐borne myeloid cells. Recently, these views have been challenged, with reports that SMC phenotypic modulation may not occur during vascular remodelling and that plaque macrophages may not be of haematopoietic origin. Following the fate of SMCs is complicated by the lack of specific markers for the migratory phenotype and direct demonstrations of phenotypic modulation are lacking. Therefore, we employed long‐term, high‐resolution, time‐lapse microscopy to track the fate of unambiguously identified, fully‐differentiated, contractile SMCs in response to the growth factors present in serum. Phenotypic modulation was clearly observed. The highly elongated, contractile SMCs initially rounded up, for 1–3 days, before spreading outwards. Once spread, the SMCs became motile and displayed dynamic cell‐cell communication behaviours. Significantly, they also displayed clear evidence of phagocytic activity. This macrophage‐like behaviour was confirmed by their internalisation of 1 μm fluorescent latex beads. However, migratory SMCs did not uptake acetylated low‐density lipoprotein or express the classic macrophage marker CD68. These results directly demonstrate that SMCs may rapidly undergo phenotypic modulation and develop phagocytic capabilities. Resident SMCs may provide a potential source of macrophages in vascular remodelling.

Smooth muscle cell (SMC) phenotypic conversion from a contractile to a migratory phenotype is proposed to underlie cardiovascular disease but its contribution to vascular remodelling and even its existence have recently been questioned.

Tracking the fate of individual SMCs is difficult as no specific markers of migratory SMCs exist.

This study used a novel, prolonged time‐lapse imaging approach to continuously track the behaviour of unambiguously identified, fully differentiated SMCs.

In response to serum, highly‐elongated, contractile SMCs initially rounded up, before spreading and migrating and these migratory cells displayed clear phagocytic activity.

This study provides a direct demonstration of the transition of fully contractile SMCs to a non‐contractile, migratory phenotype with phagocytic capacity that may act as a macrophage‐like cell.

Intrauterine growth restriction promotes vascular remodelling following carotid artery ligation in rats

Epidemiological studies revealed an association between IUGR (intrauterine growth restriction) and an increased risk of developing CVDs (cardiovascular diseases), such as atherosclerosis or hypertension, in later life. Whether or not IUGR contributes to the development of atherosclerotic lesions, however, is unclear. We tested the hypothesis that IUGR aggravates experimentally induced vascular remodelling. IUGR was induced in rats by maternal protein restriction during pregnancy (8% protein diet). To detect possible differences in the development of vascular injury, a model of carotid artery ligation to induce vascular remodelling was applied in 8-week-old intrauterine-growth-restricted and control rat offspring. Histological and immunohistochemical analyses were performed in the ligated and non-ligated carotid arteries 8 weeks after ligation. IUGR alone neither caused overt histological changes nor significant dedifferentiation of VSMCs (vascular smooth muscle cells). After carotid artery ligation, however, neointima formation, media thickness and media/lumen ratio were significantly increased in rats after IUGR compared with controls. Moreover, dedifferentiation of VSMCs and collagen deposition in the media were more prominent in ligated carotids from rats after IUGR compared with ligated carotids from control rats. We conclude that IUGR aggravates atherosclerotic vascular remodelling induced by a second injury later in life.

Redox signaling, vascular function, and hypertension

Accumulating evidence supports the importance of redox signaling in the pathogenesis and progression of hypertension. Redox signaling is implicated in many different physiological and pathological processes in the vasculature. High blood pressure is in part determined by elevated total peripheral vascular resistance, which is ascribed to dysregulation of vasomotor function and structural remodeling of blood vessels. Aberrant redox signaling, usually induced by excessive production of reactive oxygen species (ROS) and/or by decreases in antioxidant activity, can induce alteration of vascular function. ROS increase vascular tone by influencing the regulatory role of endothelium and by direct effects on the contractility of vascular smooth muscle. ROS contribute to vascular remodeling by influencing phenotype modulation of vascular smooth muscle cells, aberrant growth and death of vascular cells, cell migration, and extracellular matrix (ECM) reorganization. Thus, there are diverse roles of the vascular redox system in hypertension, suggesting that the complexity of redox signaling in distinct spatial spectrums should be considered for a better understanding of hypertension.

Time courses of growth and remodeling of porcine aortic media during hypertension: a quantitative immunohistochemical examination

Arteries undergo marked structural and functional changes in human and experimental hypertension that generally involve smooth muscle cell (SMC) hypertrophy/hyperplasia as well as abnormal extracellular matrix turnover. In this study we examined time courses of changes in SMC activity and matrix protein content in a novel mini-pig aortic coarctation model. Cell proliferation was evaluated by immunostaining of Ki-67, apoptosis was assessed by TUNEL, and phenotypic changes were monitored by immunostaining three SMC contractile markers (caldesmon, calponin, and smoothelin). Changes in medial collagen and elastin were examined by picrosirius red and Verhoeff-van Gieson staining, respectively. LabVIEW-based image analysis routines were developed to objectively and efficiently quantify the (immuno)histochemical results. We found that significant cell proliferation and matrix production occurred in the early stages of this coarctation model and then declined gradually; the SMCs also tended to exhibit a less contractile phenotype following these cellular and extracellular changes. Specifically, different aspects of the phenotypic changes associated with hypertension occurred at different rates: cell proliferation and collagen production occurred early and peaked by 2 weeks, whereas changes in contractile protein expression continued to decrease over the entire 8-week study period. Temporal changes found in this study emphasize the importance of simultaneously tracing time courses of SMC growth and differentiation as well as matrix protein production and content. SMCs are multifunctional, and caution must be used to not overdefine phenotype. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Absence of vascular remodelling in a high angiotensin-II state (Bartter's and Gitelman's syndromes): implications for angiotensin II signalling pathways

BACKGROUND

Angiotensin II (Ang II) is a powerful proinflammatory cytokine and growth factor that activates NF-kappaB, as well as NAD(P)H oxidase, and thus is a key factor for the induction and progression of cardiovascular diseases. Our previous studies have shown high Ang II and high blood pressure-driven proatherogenic remodelling in an animal model. To further explore Ang II in proatherogenic vascular remodelling independent of blood pressure, we used Bartter's/Gitelman's syndrome (BS/GS) patients given their elevated plasma Ang II, yet normo/hypotension, because extensive mechanistic studies in these patients suggest they are a good model to explore Ang II-mediated signalling.

METHODS

The study evaluated BS/GS patients for nitric oxide-dependent (FMD) and -independent vasodilation and intima-media thickness (IMT) of the carotid arteries compared with healthy subjects and essential hypertensive patients.

RESULTS

The results showed the absence of IMT growth in BS/GS patients as cumulative mean-IMT and mean maximum-IMT levels in BS/GS did not differ from normotensives: 0.58 +/- 0.09 mm versus 0.60 +/- 0.09 and 0.67 +/- 0.09 versus 0.70 +/- 0.13 respectively, P = ns, but were significantly lower compared with hypertensive patients: 0.69 +/- 0.13, P < 0.046 and 0.85 +/- 0.19, P < 0.018, respectively. FMD was increased in BS/GS versus hypertensives or normotensive controls (10.8 +/- 2.7% versus 6.5 +/- 2.3 and 8.7 +/- 1.9, P < 0.002 respectively) while endothelium-independent dilation did not differ (10.2 +/- 3.6% versus 7.2 +/- 1.9 and 8.2 +/- 3.3, P = ns) between groups.

CONCLUSIONS

Our study in BS/GS provides to our knowledge the first clinical data that point to a direct proatherogenic role for Ang II. However, because the data are derived from findings in BS/GS and therefore are indirect, further studies in this and other models using more direct approaches should be pursued to demonstrate a direct proatherogenic effect of Ang II as well as further studies on Ang II type 2 receptor (AT2R) signalling that the spectrum of findings of this and other studies indicate as involved in the lack of vascular remodelling.

Effects of PPAR-γ ligands on vascular smooth muscle marker expression in hypertensive and normal arteries

Having previously demonstrated that glucose transporter-4 (GLUT4) expression was reduced in aortas and carotid arteries of deoxycorticosterone acetate (DOCA) salt-hypertensive rats, we hypothesized that troglitazone (TG), through activation of peroxisome proliferator-activated receptor-γ (PPAR-γ), would stabilize GLUT4 expression and possibly preserve the differentiated phenotype in vascular smooth muscle cells. In DOCA salt-hypertensive rats treated with TG (100 mg/day), there was a significant ( P < 0.001) decrease in systolic blood pressure (BP; 149.9 ± 4.4 mmHg) compared with the untreated DOCA salt-hypertensive rats (202.2 ± 10.34 mmHg). Separate trials with rosiglitazone (RS; 3 mg/day) demonstrated a significant ( P < 0.001) decrease in BP (DOCA salt, 164.2 ± 9.8 vs. DOCA-RS, 124.9 ± 3.7 mmHg) comparable to that with TG. Expression of GLUT4, h-caldesmon, and smooth muscle myosin heavy chain SM2 was significantly decreased in aortas of DOCA salt-hypertensive rats and was reversed by TG to levels similar to those in aortas of sham-treated rats. TG (50 μM) induced GLUT4 and h-caldesmon expression in 24-h culture of explanted carotid arteries of DOCA salt-hypertensive rats, and the endogenous PPAR-γ ligand 15-deoxy-Δ12–14-prostaglandin J2 (PGJ2; 20 μM) and TG (50 μM) similarly increased GLUT4, h-caldesmon, and SM2 protein expression in explanted aortas. The expression of activated, phosphorylated Akt was increased by PGJ2 and TG with no significant effect on total Akt levels. Inhibition of phosphorylated Akt expression using the phosphatidylinositol 3-kinase inhibitor LY-294002 (16 μM) abrogated the increased expression of h-caldesmon and SM2. These data demonstrate that PPAR-γ agonists maintain or induce expression of markers of the contractile phenotype independently of their effects on hypertension, and that this effect may be mediated through activation of phosphatidylinositol 3-kinase/Akt.

Chronic all-trans retinoic acid treatment prevents medial thickening of intramyocardial and intrarenal arteries in spontaneously hypertensive rats

There are in vitro data linking all-trans retinoic acid (atRA) with inhibition of hypertrophy and hyperplasia in cardiomyocytes, vascular smooth muscle cells, and fibroblasts. In the present study, we tested the hypothesis that chronic treatment with atRA may blunt the process of myocardial remodeling in spontaneously hypertensive rats (SHR). Four-week-old male SHR were treated with atRA (5 or 10 mg.kg-1.day-1) given daily for 3 mo by gavage; age- and sex-matched Wistar-Kyoto rats (WKY) and placebo-treated SHR served as controls. At the end of the treatment period, cardiac geometry and function were assessed by Doppler echocardiography. Histological examination and RIA were performed to evaluate medial thickening of intramyocardial and renal arteries, perivascular and interstitial collagen content, and atrial natriuretic peptide (ANP) and IGF-I in the heart, respectively. The novel finding of the present study is that atRA prevented hypertrophy of intramyocardial and intrarenal arteries and ventricular fibrosis. However, atRA treatment did not lower blood pressure or left ventricular weight and left ventricular weight-to-body weight ratio in SHR. atRA did not change cardiac geometry and function as assessed by Doppler echocardiography. atRA showed no influence on either ANP or IGF-I levels. In conclusion, the present study suggests that chronic atRA treatment prevents medial thickening of intramyocardial and intrarenal arteries and ventricular fibrosis during the development of hypertension. Left ventricular hypertrophy and cardiac geometry and function are not changed by atRA treatment.

Mechanically altered embryonic chicken endothelial cells change their phenotype to an epithelioid phenotype

Monolayers of retracted endothelial cells exhibiting wounds or zones denuded of cells were obtained from aortic explants from 10- to 12-day-old chicken embryos. Using time-lapse videomicroscopy, we investigated the sequence of events that occurred both during and after closure of the monolayer wounds. Such wound closure (re-endothelialization process) occurred 4-12 hr after removing the explants, depending on wound width and presence of serum. The cells from along the wound edges appeared to move toward one another. We suggest an important role for bFGF and TGFbeta-2 and -3 during this process. Twenty-five hours after removal there were still some areas of retracted cells, and many of the cells displayed a weak von Willebrand's Factor (vWf) immunoreactivity. Surprisingly, after 63-65 hr many of the endothelial cells had become epithelioid in shape and the vWf immunoreactivity appeared increased. This epithelioid phenotype is currently considered typical of cultured vascular non-muscle-like cells and intimal thickening cells. By 5-7 days, the vast majority of cells in the monolayer had acquired an epithelioid morphology, showing a cobblestone appearance. These cells were significantly smaller than polygonal cells. Most importantly, they showed strong vWf immunoreactivity. At the edge of the monolayers we found that the majority of the cells had become epithelioid. Some of them detached from their neighbors and became round in shape and acquired mesenchymal characteristics, some expressing smooth muscle alpha-actin (SM alpha-actin). These findings demonstrate not only that embryonic endothelial cells that are transiently mechanically altered may change their phenotype to an epithelioid phenotype, but also that these cells may eventually transdifferentiate into mesenchymal cells expressing SM alpha-actin. Since some aspects of endothelial cell behavior have been shown to be regulated by locally released growth factors such as TGFbeta and FGF, we also investigated TGFbeta-2 and -3 and bFGF expression. Presence of TGFbeta-2 and -3 and bFGF-immunoreactive epithelioid and mesenchymal cells indicates that these growth factors may be involved in the changes described.

Familial combined hyperlipidemia plasma stimulates protein secretion by HepG2 cells: identification of fibronectin in the differential secretion proteome

The aim of this study was to evaluate whether soluble factors in plasma of familial combined hyperlipidemia (FCHL) patients affect hepatic protein secretion. Cultured human hepatocytes, i.e., HepG2 cells, were incubated with fasting plasma (20%, v/v, in DMEM) from untreated FCHL patients or normolipidemic controls. Overall protein secretion was 10-15% higher after incubation with FCHL plasma. This was specifically caused by an increase in four secreted proteins, with estimated sizes of 240, 180, 120, and <40 kD (P < 0.001, P < 0.006, P < 0.002, P < 0.02, respectively). The 240 kD protein in the secretion proteome was identified as fibronectin by mass spectrometry. Plasma fibronectin concentrations were elevated in FCHL patients, confirming biological relevance of these data. Overall protein secretion by HepG2 cells correlated with concentrations of triglycerides (r = 0.61, P < 0.001) in the applied plasma samples. VLDL+IDL isolated from FCHL patients, induced a higher protein secretion than lipoproteins isolated from controls (P < 0.001). Remarkably, secretion of apoB, the structural protein of VLDL, was stimulated to a similar extent by FCHL and control plasma. FCHL plasma did not induce excess secretion of apoB by HepG2 cells compared with control plasma. FCHL plasma did stimulate secretion of several distinct hepatic proteins, among which fibronectin was identified.

Cell phenotype as a target of drug therapy in chronic inflammatory diseases

Many diseases share common pathological changes which could in principle be targets for new drugs. Vascular leakage of plasma and migration of cells into perivascular tissues are common to chronic inflammatory diseases such as asthma, atherosclerosis, arthritis, and proliferative nephropathy as well as some non-inflammatory proliferative disorders such as diabetes mellitus. Individual components of plasma have been shown to stimulate cellular proliferation, matrix deposition and phenotypic change, leading to tissue-damaging structural changes. Whereas most anti-inflammatory drugs either downregulate expression of inflammatory mediators or inhibit their actions on cells, there are alternate potential therapeutic strategies described here based on moderating vascular leakage or its consequences in chronic diseases. The hypothesis is that drugs that can modify a cell's phenotype could be used to limit structural changes which accompany inflammation and thus reduce permanent debility resulting from these diseases. Such drugs include the differentiating agents being developed for cancer therapy.

Hypoxia induces cell-specific changes in gene expression in vascular wall cells: implications for pulmonary hypertension

Mammals respond to reduced oxygen concentrations (hypoxia) in many different ways at the systemic, local, cellular and molecular levels. Within the pulmonary circulation, exposure to chronic hypoxia has been demonstrated to illicit increases in pulmonary artery pressure as well as dramatic structural changes in both large and small vessels. It has become increasingly clear that the response to hypoxia in vivo is differentially regulated at the level of specific cell types within the vessel wall. For instance, in large pulmonary blood vessels there is now convincing evidence to suggest that the medial layer is made up of many different subpopulations of smooth muscle cells. In response to hypoxia there are remarkable differences in the proliferative and matrix producing responses of these cells to the hypoxic environment. Some cell populations proliferate and increase matrix protein synthesis, while in other cell populations no apparent change in the proliferative or differentiation state of the cell takes place. In more peripheral vessels, the predominant proliferative changes in response to hypoxia in the pulmonary circulation occur in the adventitial layer rather than in the medial layer. Here again, specific increases in proliferation and matrix protein synthesis take place. Accumulating evidence suggests that the unique responses exhibited by specific cell types of hypoxia in vivo can be modeled in vitro. We have isolated, in culture, specific medial cell populations which demonstrate significant increases in proliferation in response to hypoxia, and others which exhibit no change or, in fact, a decrease in proliferation under hypoxic conditions. We have also isolated and cloned several unique populations of adventitial fibroblasts. There is good evidence that only certain fibroblast populations are capable of responding to hypoxia with an increase in proliferation. We have begun to elucidate the signaling pathways which are activated in those cell populations that exhibit proliferative responses to hypoxia. We show that hypoxia, in the absence of serum or mitogens, specifically activates select members of the protein kinase C isozyme family, as well as members of the mitogen-activated protein kinase (MAPK) family of proteins. This selective activation appears to take place in response to hypoxia only in those cells exhibiting a proliferative response, and antagonists of this pathway inhibit the response. Thus, there appear to be cells within each organ that demonstrate unique responses to hypoxia. A better understanding of why these cells exist and how they specifically transduce hypoxia-mediated signals will lead to a better understanding of how the changes in the pulmonary circulation take place under conditions of chronic hypoxia.

Oestrogen-dependent expression of the SM2 smooth muscle-type myosin isoform in rabbit myometrium

Ovarectomized rabbits displayed a decreased SM1 to SM2 ratio of smooth muscle-type myosin heavy chain isoforms compared to unoperated, virgin females which was reversed after 17beta-oestradiol administration to a value similar to that of control animals. When this steroid was given to sexually immature animals or to adult virgin rabbits, SM2 expression was not induced, as also happened with proliferating myometrial smooth muscle cells grown in vitro. In growing rabbit, the 17beta-oestradiol administration induced the formation of the circular and the longitudinal muscle layers, characteristics of sexually competent females. The SM2 isoform was up-regulated during postnatal development and the SM1 to SM2 ratio changed during pregnancy and post-partum period but not with human gonadotropin treatment which increases the level of circulating progesterone. Immunofluorescence staining of adult myometrium with anti-SM2 antibody indicated that this isoform is localized to the longitudinal layer exclusively and, in contrast to the circular layer, its expression was independent of oestrogen level. Difference in oestrogen sensitivity between the two layers was also detected for the expression of the intermediate filament protein vimentin and the thin filament protein calponin. Changes of SM2 expression in the myometrium correlated with variations in the oestrogen receptor density as also confirmed by decreased SM2 content/oestrogen receptor density in the circular layer when ovarectomized females were treated with the oestrogen antagonist ICI 182,780. Our results indicate that: (1) a specific distribution of myosin heavy chain exists within rabbit myometrium, and (2) SM2 myosin expression in this smooth muscle is under oestrogen control.

Inflammatory cytokines cause coronary arteriosclerosis-like changes and alterations in the smooth-muscle phenotypes in pigs

We recently developed a porcine model in which chronic, local treatment with interleukin-1 beta (IL-1 beta) causes coronary arteriosclerosis-like changes and hyperconstrictive responses. This study was designed to examine whether or not other major inflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha) might also cause similar coronary responses and whether those responses are associated with alterations in the smooth-muscle phenotypes. A segment of the porcine coronary artery was aseptically wrapped with cotton mesh, absorbing IL-1 beta, TNF-alpha, and IL-1 alpha. Two weeks after the operation, coronary arteriography showed the development of mild stenotic lesions at the cytokine-treated sites, where hyperconstrictive responses were repeatedly induced by intracoronary serotonin or histamine. Histologically mild intimal thickening was noted at those cytokine-treated sites. Immunostaining and immunoblotting demonstrated that all three myosin heavy chain isoforms, SM1, SM2 (smooth-muscle type), and SMemb (nonmuscle type), were noted in the normal coronary segments, whereas in the segments treated with inflammatory cytokines, SM1 and SM2 were markedly reduced, and only SMemb was noted. These results indicate that inflammatory cytokines all have a similar ability to induce coronary arteriosclerosis-like changes and hyperconstrictive responses, which are associated with alterations in smooth-muscle phenotypes toward dedifferentiation.

Homologous serum increases fibronectin expression and cell adhesion in airway smooth muscle cells

This study describes altered patterns of growth and upregulation of fibronectin expression of cultured canine airway smooth muscle cells grown in homologous serum, which provides a model of the vascular leakage occurring in asthma, compared to fetal bovine serum (FBS). Cells were incubated in increasing concentrations of serum (2.5-40%) for 72 hours. Both homologous serum and FBS caused cellular proliferation which reached a maximum increase at 2.5-5% serum concentration. Differences in the cellular responses to the two types of sera were noted at higher concentrations of sera. At a concentration of 40% FBS, airway smooth muscle cells increased in number by 307 +/- 16% (n = 5) compared to serum-free control cells, whereas in canine serum the increase in growth was significantly smaller, 239 +/- 25% (n = 7) (P < 0.05). Airway fibrocytes similarity treated increased in number by 256 +/- 43% (n = 3) in 40% FBS, but exhibited a reduction in cell number to 80 +/- 10% (n = 3) of controls in 40% homologous serum (P < 0.05). Smooth muscle cells demonstrated a dose-dependent increase in fibronectin expression when grown in homologous serum but not in FBS, suggesting phenotypic change occurred in these cells when exposed to homologous serum. These data suggest that the leakage of plasma in the asthmatic airway may trigger phenotypic change in both airway smooth muscle cells and airway fibrocytes leading to cellular proliferation and expression of extracellular matrix molecules. These in vitro changes are consistent with the histological findings in clinical asthma.

Regulation and interactions of transforming growth factor-beta with cardiovascular cells: implications for development and disease

1. Transforming growth factors-beta (TGF-beta) are multifunctional proteins that regulate cell growth, differentiation, migration and extracellular matrix production and have an important role in embryonic development and tissue remodelling. 2. The diverse biological actions of TGF-beta are elicited following their interaction with type I and type II TGF-beta receptors, both of which are transmembrane serine/threonine kinases, suggesting an important role for protein phosphorylation in the mechanism of action of these cytokines on the growth of cells and their extracellular environment. 3. Alterations in TGF-beta gene expression and action in various cell types associated with the cardiovascular system may contribute to the pathophysiology of a number of diseases, such as hypertension, atherosclerosis and restenosis, as well as the development of cardiac abnormalities.

Correlation between the presence of an immature smooth muscle cell population in tunica media and the development of atherosclerotic lesion. A study on different-sized rabbit arteries from cholesterol-fed and Watanabe heritable hyperlipemic rabbits

Mapping the distribution of an immature smooth muscle cell (SMC) subpopulation in large- and small-sized arterial vessels was carried out in normocholesterolemic rabbits and compared with the mapping atherosclerotic lesions in endogenously (Watanabe heritable hyperlipemic, WHHL) and exogenously derived (cholesterol-fed, CT) hypercholesterolemic rabbits. This cell subset is identified by a specific myosin isoform content and displays an intermediate degree of differentiation between fetal- and adult-type SMC. Monoclonal anti-myosin antibodies, immunofluorescence procedures, and different arterial segments of a rabbit vessel tree, i.e. from aorta to dental pulp (common carotid, external carotid, lingual, facial, maxillary, inferior alveolar arteries, and dental branches of alveolar arteries) were studied. WHHL of different ages (3 to 12 months), and two different concentrations of CT (2% and 0.2%) in the diet for 3 and 12 months, respectively, were used. The results of the present study indicate that: (1) using a diet with a higher percentage of CT (rabbits fed 2% CT-diet for 3 months) there is maximum expansion of atherosclerotic lesions from the aorta up to the maxillary artery; (2) localization of atherosclerotic lesions with a lower CT content in the diet is dependent on the duration of feeding and may involve the aorta up to the external carotid artery; (3) the development of the atherosclerotic lesion in hypercholesterolemic rabbit is strictly related to the appearance of an intermediate SMC subtype; (4) atherosclerotic lesions occur only in those arterial sites which, in corresponding normocholesterolemic rabbit, contain intermediate-type SMC; and (5) no differences can be found in the distribution of SMC subpopulations present in the lesions from WHHL, CT-fed animals, or at various arterial levels, whereas some discrepancies can be shown in aortic atherogenesis.

Hypoxia selectively induces proliferation in a specific subpopulation of smooth muscle cells in the bovine neonatal pulmonary arterial media

Medial thickening of the pulmonary arterial wall, secondary to smooth muscle cell (SMC) hyperplasia, is commonly observed in neonatal hypoxic pulmonary hypertension. Because recent studies have demonstrated the existence of multiple phenotypically distinct SMC populations within the arterial media, we hypothesized that these SMC subpopulations would differ in their proliferative responses to hypoxic pulmonary hypertension and thus contribute in selective ways to the vascular remodeling process. Expression of meta-vinculin, a muscle-specific cytoskeletal protein, has been shown to reliably distinguish two unique SMC subpopulations within the bovine pulmonary arterial media. Therefore, to assess the proliferative responses of phenotypically distinct SMC subpopulations in the setting of neonatal pulmonary hypertension, we performed double immunofluorescence staining on pulmonary artery cryosections from control and hypertensive calves with antibodies against meta-vinculin and the proliferation-associated nuclear antigen, Ki-67. We found that, although neonatal pulmonary hypertension caused significant increases in overall cell replication, proliferation occurred almost exclusively in one, the meta-vinculin-negative SMC population, but not the other SMC population expressing meta-vinculin. We also examined fetal pulmonary arteries, where proliferative rates were high and meta-vinculin expression again reliably distinguished two SMC subpopulations. In contrast to the hypertensive neonate, we found in the fetus that the relative proliferative rates of both SMC subpopulations were equal, thus suggesting the existence of different mechanisms controlling proliferation and expression of cytoskeletal proteins in the fetus and neonate. We conclude that phenotypically distinct SMC populations in the bovine arterial media exhibit specific and selective proliferative responses to neonatal pulmonary hypertension. Distinct SMC subpopulations may, thus, contribute in unique ways to vascular homeostasis under both normal and pathologic conditions.