Cultured aortic smooth muscle cells from newborn and adult rats show distinct cytoskeletal features

Easy recognition and high autoimmune hepatitis specificity of smooth muscle antibodies giving an actin microfilament immunofluorescent pattern on embryonal vascular smooth muscle cells

Smooth muscle antibodies (SMA) with anti-microfilament actin (MF-SMA) specificity are regarded as highly specific markers of type 1 autoimmune hepatitis (AIH-1) but their recognition relying on immunofluorescence of vessel, glomeruli, and tubules (SMA-VGT pattern) in rodent kidney tissue, is restricted by operator-dependent interpretation. A gold standard method for their identification is not available. We assessed and compared the diagnostic accuracy for AIH-1 of an embryonal aorta vascular smooth muscle (VSM) cell line-based assay with those of the rodent tissue-based assay for the detection of MF-SMA pattern in AIH-1 patients and controls. Sera from 138 AIH-1 patients and 295 controls (105 primary biliary cholangitis, 40 primary sclerosing cholangitis, 50 chronic viral hepatitis, 20 alcohol-related liver disease, 40 steatotic liver disease, and 40 healthy controls) were assayed for MF-SMA and SMA-VGT using VSM-based and rodent tissue-based assays, respectively. MF-SMA and SMA-VGT were found in 96 (70%) and 87 (63%) AIH-1 patients, and 2 controls (P < 0.0001). Compared with SMA-VGT, MF-SMA showed similar specificity (99%), higher sensitivity (70% vs 63%, P = ns) and likelihood ratio for a positive test (70 vs 65). Nine (7%) AIH-1 patients were MF-SMA positive despite being SMA-VGT negative. Overall agreement between SMA-VGT and MF-SMA was 87% (kappa coefficient 0.870, [0.789-0.952]). MF-SMA were associated with higher serum γ-globulin [26 (12-55) vs 20 g/l (13-34), P < 0.005] and immunoglobulin G (IgG) levels [3155 (1296-7344) vs 2050 mg/dl (1377-3357), P < 0.002]. The easily recognizable IFL MF-SMA pattern on VSM cells strongly correlated with SMA-VGT and has an equally high specificity for AIH-1. Confirmation of these results in other laboratories would support the clinical application of the VSM cell-based assay for reliable detection of AIH-specific SMA.

Genetic ablation of smooth muscle KIR2.1 is inconsequential to the function of mouse cerebral arteries

Cerebral blood flow is a finely tuned process dependent on coordinated changes in arterial tone. These changes are strongly tied to smooth muscle membrane potential and inwardly rectifying K⁺ (K_IR) channels are thought to be a key determinant. To elucidate the role of K_IR2.1 in cerebral arterial tone development, this study examined the electrical and functional properties of cells, vessels and living tissue from tamoxifen-induced smooth muscle cell (SMC)-specific K_IR2.1 knockout mice. Patch-clamp electrophysiology revealed a robust Ba²⁺-sensitive inwardly rectifying K⁺ current in cerebral arterial myocytes irrespective of K_IR2.1 knockout. Immunolabeling clarified that K_IR2.1 expression was low in SMCs while K_IR2.2 labeling was remarkably abundant at the membrane. In alignment with these observations, pressure myography revealed that the myogenic response and K⁺-induced dilation were intact in cerebral arteries post knockout. At the whole organ level, this translated to a maintenance of brain perfusion in SMC K_IR2.1^-/- mice, as assessed with arterial spin-labeling MRI. We confirmed these findings in superior epigastric arteries and implicated K_IR2.2 as more functionally relevant in SMCs. Together, these results suggest that subunits other than K_IR2.1 play a significant role in setting native current in SMCs and driving arterial tone.

Dual origins of the Northwest Chinese Kyrgyz: the admixture of Bronze age Siberian and Medieval Niru'un Mongolian Y chromosomes

The Kyrgyz are a trans-border ethnic group, mainly living in Kyrgyzstan. Previous genetic investigations of Central Asian populations have repeatedly investigated the Central Asian Kyrgyz. However, from the standpoint of human evolution and genetic diversity, Northwest Chinese Kyrgyz is one of the more poorly studied populations. In this study, we analyzed the non-recombining portion of the Y-chromosome from 298 male Kyrgyz samples from Xinjiang Uygur Autonomous Region in northwestern China, using a high-resolution analysis of 108 biallelic markers and 17 or 24 STRs. First, via a Y-SNP-based PCA plot, Northwest Chinese Kyrgyz tended to cluster with other Kyrgyz population and are located in the West Asian and Central Asian group. Second, we found that the Northwest Chinese Kyrgyz display a high proportion of Y-lineage R1a1a1b2a2a-Z2125, related to Bronze Age Siberian, and followed by Y-lineage C2b1a3a1-F3796, related to Medieval Niru'un Mongols, such as Uissun tribe from Kazakhs. In these two dominant lineages, two unique recent descent clusters have been detected via NETWORK analysis, respectively, but they have nearly the same TMRCA ages (about 13th-14th centuries). This finding once again shows that the expansions of Mongol Empire had a striking effect on the Central Asian gene pool.

Sudden coronary death in the young: Evidence of contractile phenotype of smooth muscle cells in the culprit atherosclerotic plaque

BACKGROUND

Culprit coronary atherosclerotic plaques (APs) from young sudden cardiac death (SCD) victims are mostly non-atheromatous, i.e., consisting of proliferative smooth muscle cells (SMCs). Coronary vasospasm has been advocated to explain plaque instability in the absence of thrombosis. Our aim was to characterize the SMC phenotype in the intima and media of coronary arteries from young SCD victims.

METHODS AND RESULTS

A total of 38 coronary artery segments were studied: (a) 18 APs from young (≤40 years old) SCD patients, (b) 9 APs from old (>40 years old) SCD patients, (c) 11 non-atherosclerotic coronary arteries from young patients (≤40 years old). Markers of differentiated SMCs such as α-smooth muscle actin (α-SMA), smooth muscle myosin heavy chains (SMMHCs), and heavy-caldesmon (h-CaD), were assessed in intima and media by immunohistochemistry and quantified morphometrically. In the intima, their expression was higher in non-atherosclerotic arteries (44.37 ± 3.03% for α-SMA, 14.21 ± 2.01% for SMMHCs, 8.90 ± 1.33% for h-CaD) and APs from young SCD victims (38.95 ± 2.29% for α-SMA, 11.92 ± 1.92% for SMMHCs, 8.93 ± 1.12% for h-CaD) compared with old patients (22.01 ± 3.56% for α-SMA, 6.39 ± 0.7% for SMMHCs, 3.00 ± 0.57% for h-CaD; all P statistically significant). The media of non-atherosclerotic arteries and APs from young SCD victims exhibited strong positivity for the differentiation markers unlike that of old patients.

CONCLUSIONS

SMCs of coronary APs as well as from the underlying media from young SCD victims exhibit strong contractile phenotype. In the setting of critical stenosis, both intima and media SMC contractility might contribute to transient coronary spasm leading to myocardial ischemia and SCD.

CFTR protects against vascular inflammation and atherogenesis in apolipoprotein E-deficient mice

Atherosclerosis is a chronic inflammatory disease of the vascular wall. Dysfunction of cystic fibrosis transmembrane conductance regulator (CFTR) has been shown to result in inflammatory responses in cystic fibrosis (CF) patients. However, little is known about the role of CFTR in vascular inflammation and atherogenesis. Our results showed that CFTR was dominantly expressed in macrophages of atherosclerotic plaque and reduced in aorta and aortic sinus from atherosclerotic apolipoprotein E-deficient (apoE^−/−) mice. In vivo administration of adenovirus encoding CFTR (Ad-CFTR) with apoE^−/− mice fed on high-fat diet (HFD) improved plaque stability by decreasing lipid accumulation and necrotic area and increasing smooth muscle cell content and collagen. The Ad-CFTR-treated mice also displayed reduced proinflammatory cytokines levels in aorta and peritoneal macrophages, whereas the anti-inflammatory M2 macrophage markers were increased. Confocal microscopy revealed that the infiltration of T lymphocytes, neutrophils, and macrophages in aortic sinus was markedly attenuated in Ad-CFTR-treated apoE^−/− mice. Moreover, in vitro experiments showed that overexpression of CFTR inhibited ox-LDL-induced the migration of peritoneal macrophages. Finally, it was observed that CFTR up-regulation suppressed NFκB and MAPKs activity induced by ox-LDL. Inhibition of JNK or ERK abrogated CFTR down-regulation induced NFκB activation, whereas NFκB inhibitor had no effect on JNK or ERK activation. Taken together, these results demonstrate that CFTR prevents inflammation and atherogenesis via inhibition of NFκB and MAPKs activation. Our data suggest that CFTR may present a potential therapeutic target for the treatment of vascular inflammation and development of atherosclerotic disease.

Effects of p53-knockout in vascular smooth muscle cells on atherosclerosis in mice

In vitro and in vivo evidence has indicated that the tumor suppressor, p53, may play a significant role in the regulation of atherosclerotic plaque formation. In vivo studies using global knockout mice models, however, have generated inconclusive results that do not address the roles of p53 in various cell types involved in atherosclerosis. In this study, we have specifically ablated p53 in vascular smooth muscle cells (VSMC) in the ApoE^-/- mouse model to investigate the roles of p53 in VSMC in atherosclerotic plaque formation and stability. We found that p53 deficiency in VSMC alone did not affect the overall size of atherosclerotic lesions. However, there was a significant increase in the number of p53^-/- VSMC in the fibrous caps of atherosclerotic plaques in the early stages of plaque development. Loss of p53 results in migration of VSMC at a faster rate using wound healing assays and augments PDGF-induced formation of circular dorsal ruffles (CDR), known to be involved in cell migration and internalization of surface receptors. Furthermore, aortic VSMC from ApoE^-/- /p53^-/- mice produce significantly more podosomes and are more invasive. We conclude that p53^-/- VSMC are enriched in the fibrous caps of lesions at early stages of plaque formation, which is caused in part by an increase in VSMC migration and invasion as shown by p53^-/- VSMC in culture having significantly higher rates of migration and producing more CDRs and invasive podosomes.

Mechanisms of angiogenesis in a Curculigoside A-treated rat model of cerebral ischemia and reperfusion injury

Curculigoside A has shown protective effects against rat cortical neuron damage in vivo. However, the molecular mechanisms through which Curculigoside A affords this protection are unclear. In the present study, we sought to elucidate the mechanisms of angiogenesis in rat aortic endothelial cells (RAEC), rat aortic smooth muscle cells (RASMC) as well as a rat model of cerebral ischemia and reperfusion injury following treatment with Curculigoside A. We examined the role of Curculigoside A on RAEC and RASMC proliferation, migration, and tube formation in vitro and in a cerebral ischemia and reperfusion injury rat model. We used the recombinant Dickkopf (DKK)-1 protein, a Wnt/β-catenin inhibitor, and the recombinant WIF-1 protein, a Wnt5a antagonist to determine mechanisms. In addition, we measured leakage of the blood-brain barrier (BBB) and tested for angiogenesis associated proteins. Our data suggest that Curculigoside A induces angiogenesis in vitro by increasing proliferation, migration and tube formation in RAEC and RASMC. The increase in Curculigoside A-induced proliferation and tube formation was counteracted by DKK-1 and WIF-1. Curculigoside A increased expression of VEGF, p-VEGFR, p-CREB, Egr-3, VCAM-1, Ang1 and Tie2 while prohibiting BBB leakage in cerebral ischemia and reperfusion injured rats. However, Cyclosporine A, a CREB inhibitor, reduced the expression of p-CREB, Egr-3, VCAM-1, Ang1 and Tie2. These data suggest that Curculigoside A induces cell proliferation and angiogenesis through the Wnt5a/β-catenin and VEGF/CREB/Egr-3/VCAM-1 signaling axis and promotes maturation and stability of new blood vessels via increasing Ang1 and Tie-2 expression.

Astaxanthin induces angiogenesis through Wnt/β-catenin signaling pathway

OBJECTIVE

In the present study, we sought to elucidate whether astaxanthin contributes to induce angiogenesis and its mechanisms.

MATERIALS AND METHODS

To this end, we examined the role of astaxanthin on human brain microvascular endothelial cell line (HBMEC) and rat aortic smooth muscle cell (RASMC) proliferation, invasion and tube formation in vitro. For study of mechanism, the Wnt/β-catenin signaling pathway inhibitor IWR-1-endo was used. HMBECs and RASMCs proliferation were tested by cell counting. Scratch adhesion test was used to assess the ability of invasion. A matrigel tube formation assay was performed to test capillary tube formation ability. The Wnt/β-catenin pathway activation in HMBECs and RASMCs were tested by Western blot.

RESULTS

Our data suggested that astaxanthin induces angiogenesis by increasing proliferation, invasion and tube formation in vitro. Wnt and β-catenin expression were increased by astaxanthin and counteracted by IWR-1-endo in HMBECs and RASMCs. Tube formation was increased by astaxanthin and counteracted by IWR-1-endo.

CONCLUSIONS

It may be suggested that astaxanthin induces angiogenesis in vitro via a programmed Wnt/β-catenin signaling pathway.

p53 Down regulates PDGF-induced formation of circular dorsal ruffles in rat aortic smooth muscle cells

The tumor suppressor, p53, negatively regulates cell migration and invasion in addition to its role in apoptosis, cell cycle regulation and senescence. Here, we study the roles of p53 in PDGF-induced circular dorsal ruffle (CDR) formation in rat aortic smooth muscle (RASM) cells. In primary and immortalized RASM cells, up-regulation of p53 expression or increase in activity with doxorubicin inhibits CDR formation. In contrast, shRNA-knockdown of p53 or inhibition of its activity with pifithrin α promotes CDR formation. p53 acts by up-regulating PTEN expression, which antagonizes Rac and Cdc42 activation. Both lipid and protein phosphatase activities of PTEN are required for maximal suppression of CDR, but the lipid activity clearly plays the dominant role. N-WASP, the downstream effector of Cdc42, is the major positive contributor to CDR formation in RASM, and is an indirect target of p53. The Rac effector, WAVE2, appears to also play a minor role, while WAVE1 has no significant effect in CDR formation. In sum, we propose that p53 suppresses PDGF-induced CDR formation in RASM cells by upregulating PTEN leading mainly to the inhibition of the Cdc42-N-WASP pathway.

Embryonic rat vascular smooth muscle cells revisited - a model for neonatal, neointimal SMC or differentiated vascular stem cells?

BACKGROUND

The A10 and A7r5 cell lines derived from the thoracic aorta of embryonic rat are widely used as models of non-differentiated, neonatal and neointimal vascular smooth muscle cells in culture. The recent discovery of resident multipotent vascular stem cells within the vessel wall has necessitated the identity and origin of these vascular cells be revisited. In this context, we examined A10 and A7r5 cell lines to establish the similarities and differences between these cell lines and multipotent vascular stem cells isolated from adult rat aortas by determining their differentiation state, stem cell marker expression and their multipotency potential in vitro.

METHODS

Vascular smooth muscle cell differentiation markers (alpha-actin, myosin heavy chain, calponin) and stem cell marker expression (Sox10, Sox17 and S100β) were assessed using immunocytochemistry, confocal microscopy, FACS analysis and real-time quantitative PCR.

RESULTS

Both A10 and A7r5 expressed vascular smooth muscle differentiation, markers, smooth muscle alpha - actin, smooth muscle myosin heavy chain and calponin. In parallel analysis, multipotent vascular stem cells isolated from rat aortic explants were immunocytochemically myosin heavy chain negative but positive for the neural stem cell markers Sox10+, a neural crest marker, Sox17+ the endoderm marker, and the glia marker, S100β+. This multipotent vascular stem cell marker profile was detected in both embryonic vascular cell lines in addition to the adventitial progenitor stem cell marker, stem cell antigen-1, Sca1+. Serum deprivation resulted in a significant increase in stem cell and smooth muscle cell differentiation marker expression, when compared to serum treated cells. Both cell types exhibited weak multipotency following adipocyte inductive stimulation. Moreover, Notch signaling blockade following γ-secretase inhibition with DAPT enhanced the expression of both vascular smooth muscle and stem cell markers.

CONCLUSIONS

We conclude that A10 and A7r5 cells share similar neural stem cell markers to both multipotent vascular stem cells and adventitial progenitors that are indicative of neointimal stem-derived smooth muscle cells. This may have important implications for their use in examining vascular contractile and proliferative phenotypes in vitro.

Studies of the cellular uptake of hydrogel nanospheres and microspheres by phagocytes, vascular endothelial cells, and smooth muscle cells

Intensive research efforts have been placed on the development of nanospheres for targeted drug delivery for treating a variety of diseases, including coronary restenosis, cancer, and inflammatory reactions. Although most of these drug-bearing spheres are delivered via intravenous administration, little is known about the effect of sphere physical characteristics on the responses of vascular and blood cells. To find the answer, this work was aimed to investigate the cellular uptake of nanosized (100 nm) and microsized hydrogel spheres (1 microm) made of poly(N-isopropylacrylamide) by vascular cells and phagocytes under various flow conditions in vitro. We found that the cellular uptake of nanospheres depended on incubation times and sphere concentrations as well as on the introduced shear stress levels of the medium. Measurements of the intracellular-released fluorescence and confocal fluorescence microscopy revealed that nanospheres were internalized by endothelial cells and smooth muscle cells more than microspheres, whereas microspheres were rapidly taken up by phagocytes, especially at high concentration. Our results strongly suggest that hydrogel nanospheres are more effective as an intravascular delivery system compared to microspheres in the terms of vascular cellular uptake and biocompatibility.

Calponin control of cerebrovascular reactivity: therapeutic implications in brain trauma

Calponin (Cp) is an actin-binding protein first characterized in chicken gizzard smooth muscle (SM). This review discusses the role of Cp in mediating SM contraction, the biochemical process by which Cp facilitates SM contraction and the function of Cp in the brain. Recent work on the role of Cp in pathological states with emphasis on traumatic brain injury is also discussed. Based on past and present data, the case is presented for targeting Cp for novel genetic and pharmacological therapies aimed at improving outcome following traumatic brain injury (TBI).

Preparation of primary cultured mesenteric artery smooth muscle cells for fluorescent imaging and physiological studies

In this protocol, we describe a method for isolation and culture of smooth muscle cells derived from the adult rat (or mouse) superior mesenteric artery. Arterial myocytes are obtained by enzymatic dissociation and established in primary culture. The cultured cells retain expression of smooth muscle-specific alpha-actin and physiological responses to agonists. Cultured arterial myocytes (prepared from wild-type or transgenic animals) provide a useful model for studying the regulation of a wide range of vascular smooth muscle responses at the cellular and subcellular levels. Plasmids, RNA interference and antisense oligodeoxynucleotides can be readily introduced into the cells to alter protein expression. Fluorescent dyes can also be introduced to visualize a variety of activities, some of which may be specific to vascular smooth muscle cells. This protocol requires about 3 h on each of 2 consecutive days to complete.

Formation of extracellular matrix-digesting invadopodia by primary aortic smooth muscle cells

Invasion of the subendothelial space by vascular smooth muscle cells (VSMCs) contributes to the development and progression of diverse cardiovascular diseases. In this report we show that the expression of activated versions of Src, Cdc42 and Rac1, or a kinase-dead but open form of the p21-activated kinase (PAK1), induces primary rat aorta VSMCs to form extracellular matrix-degrading actin-rich protrusions that are morphologically similar to the invadopodia formed by highly invasive tumor cells. The matrix-degrading structures are enriched in known markers for invadopodia, including cortactin and tyrosine-phosphorylated cortactin and contain the matrix metalloproteinases MMP-9 and MT1-MMP and the urokinase plasminogen activator receptor (uPAR). In contrast to other cell types, invadopodia formation in VSMCs is only weakly supported by the phorbol ester PBDu. Invadopodia formation by Src was dependent on Cdc42, Rac, and ERK, but not on p38 MAPK. Invadopodia formation induced by kinase-dead PAK1 required Src and ERK activity and a direct interaction with the exchange factor PIX. VSMCs embedded in a three-dimensional collagen matrix formed actin- and cortactin-rich extensions that penetrated through holes in the matrix, suggesting that invadopodia-like structures are formed in a three-dimensional environment.

Counter-regulatory function of protein tyrosine phosphatase 1B in platelet-derived growth factor- or fibroblast growth factor-induced motility and proliferation of cultured smooth muscle cells and in neointima formation

OBJECTIVE

We have previously reported that vascular injury or treatment of cultured vascular smooth muscle cells with platelet-derived growth factor-BB (PDGF-BB) or fibroblast growth factor-2 (FGF2) increases the levels of protein tyrosine phosphatase (PTP)1B. The current study was designed to test the hypothesis that PTP1B attenuates PDGF- or FGF-induced motility and proliferation of cultured cells, as well as neointima formation in injured rat carotid arteries.

METHODS AND RESULTS

Treatment of cultured cells with adenovirus expressing PTP1B decreased PDGF-BB- or FGF2-induced cell motility and blocked PDGF-BB- or FGF2-induced proliferation, whereas expression of dominant negative PTP1B (C215S-PTP1B) uncovered the motogenic effect of subthreshold levels of PDGF-BB or FGF2, increased neointimal and medial cell proliferation, and induced neointimal enlargement after balloon injury. The inhibitory effect of PTP1B directed against PDGF in cultured cells was associated with dephosphorylation of the PDGFbeta receptor.

CONCLUSIONS

PTP1B suppresses cell proliferation and motility in cultured smooth muscle cells treated with PDGF-BB or FGF2, and the phosphatase plays a counter-regulatory role in vascular injury-induced cell proliferation and neointima formation. Taken together with previous studies indicating increased PTP1B levels in cells treated with growth factors, the current findings are the first to report the existence of an inhibitory feedback loop involving PDGF or FGF, and PTP1B in blood vessels.

Heparin recovers AT1 receptor and its intracellular signal transduction in cultured vascular smooth muscle cells

Although vascular smooth muscle cells (VSMCs) are widely used in cardiovascular research, their phenotypic change under various culture conditions is problematic to evaluate the experimental results obtained. The levels of angiotensin (Ang) type 1/2 (AT1/AT2) receptors as well as contractile and structural proteins are degraded through culture passages. The present study demonstrated that heparin recovered Ang receptors and differentiation markers, such as desmin, SM-22 and smooth muscle alpha-actin in VSMCs at the ninth passage. Heparin also potenciated Ang II-induced activation for ERK1/2 and p38. These results suggest a potential value of heparin-treated VSMCs as the model for analysis of Ang-mediated signal transduction under physiological condition.

Modulation of smooth muscle cell proliferation and migration: role of smooth muscle cell heterogeneity

Proliferation and migration of smooth muscle cells (SMCs) from the media towards the intima are key events in atherosclerosis and restenosis. During these processes, SMC undergo phenotypic modulations leading to SMC dedifferentiation. The identification and characterization of factors controlling these phenotypic changes are crucial in order to prevent the formation of intimal thickening. One of the questions which presently remains open, is to know whether any SMCs of the media are capable of accumulating into the intima or whether only a predisposed medial SMC subpopulation is involved in this process. The latter hypothesis implies that arterial SMCs are phenotypically heterogenous. In this chapter, we will describe the distinct SMC phenotypes identified in arteries of various species, including humans. Their role in the formation of intimal thickening will be discussed.

Functional regulation of tissue plasminogen activator on the surface of vascular smooth muscle cells by the type-II transmembrane protein p63 (CKAP4)

We have demonstrated that tissue plasminogen activator (tPA) binds specifically to human vascular smooth muscle cells (VSMC) in a functionally relevant manner, both increasing plasminogen activation and decreasing tPA inhibition (Ellis, V., and Whawell, S. A. (1997) Blood 90, 2312-2322; Werner, F., Razzaq, T. M., and Ellis, V. (1999) J. Biol. Chem. 274, 21555-21561). To further understand this system we have now identified and characterized the protein responsible for this binding. Rat VSMC were surface-labeled with 125I, and cell lysates were subjected to an affinity chromatography scheme based on the previously identified tPA binding characteristics. A single radiolabeled protein of 63 kDa bound specifically and was eluted at low pH. This protein was isolated from large scale preparations of VSMC and unambiguously identified as the rat homologue of the human type-II transmembrane protein p63 (CKAP4) by matrix-assisted laser desorption ionization and nano-electrospray tandem mass spectrometry of tryptic fragments. In confirmation of this, a monoclonal antibody raised against authentic human p63 recognized the isolated protein in Western blotting. Immunofluorescence microscopy demonstrated that p63 was located principally in the endoplasmic reticulum but was also detected in significant quantities on the surface of human VSMC. In support of the hypothesis that p63 is the functional tPA binding site on VSMC, an anti-p63 monoclonal antibody was found to block tPA binding. Furthermore, heterologous expression of an N-terminally truncated mutant of p63, which targets exclusively to the plasma membrane, led to an increase in tPA-catalyzed plasminogen activation. Therefore, p63 on the surface of VSMC may contribute to the functional regulation of the plasminogen activation system in the vessel wall.

Arterial smooth muscle cell heterogeneity: implications for atherosclerosis and restenosis development

During atheromatous plaque formation or restenosis after angioplasty, smooth muscle cells (SMCs) migrate from the media toward the intima, where they proliferate and undergo phenotypic changes. The mechanisms that regulate these phenomena and, in particular, the phenotypic modulation of intimal SMCs have been the subject of numerous studies and much debate during recent years. One view is that any SMCs present in the media could undergo phenotypic modulation. Alternatively, the seminal observation of Benditt and Benditt that human atheromatous plaques have the features of a monoclonal or an oligoclonal lesion has led to the hypothesis that a predisposed, medial SMC subpopulation could play a crucial role in the production of intimal thickening. The presence of a distinct SMC population in the arterial wall implies that under normal conditions, SMCs are phenotypically heterogeneous. The concept of SMC heterogeneity is gaining wider acceptance, as shown by the increasing number of publications on this subject. In this review, we discuss the in vitro studies that demonstrate the presence of distinct SMC subpopulations in arteries of various species, including humans. Their specific features and their regulation will be highlighted. Finally, the relevance of an atheroma-prone phenotype to intimal thickening formation will be discussed.

Nitric oxide-induced inhibition of aortic smooth muscle cell motility: role of PTP-PEST and adaptor proteins p130cas and Crk

Vascular injury increases nitric oxide (NO) levels, and this effect may play a counterregulatory role in neointima formation, by decreasing vascular smooth muscle cell motility. However, the mechanisms underlying this effect are not well established. We tested the hypothesis that NO decreases cell motility by increasing the activity of a protein tyrosine phosphatase (PTP), PTP-PEST, in cultured rat aortic smooth muscle cells. Two NO donors increased the activity of PTP-PEST. A cGMP analog mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked it, indicating that elevated cGMP is both necessary and sufficient to induce PTP-PEST activity. Overexpression of wild-type PTP-PEST induced antimotogenesis, whereas expression of dominant negative PTP-PEST blocked the antimotogenic effect of NO, indicating that increased PTP-PEST activity is both sufficient and necessary to explain the effect of NO. Overexpression of PTP-PEST mimicked NO-induced dephosphorylation of adapter protein p130cas, whereas dominant negative PTP-PEST blocked the effect of NO, indicating that upregulation of PTP-PEST is both necessary and sufficient to explain NO-induced p130cas dephosphorylation. Expression of a substrate domain-deleted p130cas decreased motogenesis, whereas overexpression of wild-type p130cas blocked the antimotogenic effect of NO, indicating the functional importance of p130cas dephosphorylation. NO induced dissociation of the Cas-Crk complex, an effect that was mimicked by overexpression of PTP-PEST and opposed by expression of dominant negative PTP-PEST. Our results indicate that NO decreases aortic smooth muscle cell motility via a cGMP-mediated mechanism, involving upregulation of PTP-PEST, in turn inducing dephosphorylation of p130cas, and likely involving Cas-Crk dissociation as a downstream event.

Nitric oxide-induced motility in aortic smooth muscle cells: role of protein tyrosine phosphatase SHP-2 and GTP-binding protein Rho

We have previously reported that SHP-2 upregulation is necessary for NO-stimulated motility in differentiated rat aortic smooth muscle cells. We now test the hypothesis that upregulation of SHP-2 is necessary and sufficient to stimulate cell motility. Overexpression of SHP-2 via recombinant adenoviral vector stimulated motility to the same extent as NO, whereas the expression of C463S-SHP-2, the dominant-negative SHP-2 allele, blocked the motogenic effect of NO. On the basis of previous studies, we next tested the hypothesis that NO decreases RhoA activity and that this event is necessary and sufficient to explain NO-induced motogenesis. We found that NO decreased RhoA activity in a concentration-dependent manner. Moreover, a dominant-negative SHP-2 allele, DSH2, blocked the NO-induced inhibition of RhoA activity, indicating that upregulation of SHP-2 is necessary for this event. Expression of G14V-RhoA, the constitutively active RhoA allele, decreased cell motility and blocked the motogenic effect of NO, whereas the expression of T19N-RhoA, the dominant-negative RhoA allele, increased cell motility to an extent similar to that induced by NO. Dominant-negative RhoA reversed the effect of dominant-negative SHP-2, indicating that RhoA functions downstream from SHP-2. To investigate events downstream from RhoA, we treated cells with fasudil, a selective Rho kinase inhibitor, and found that it increased cell motility. These results indicate that upregulation of SHP-2, leading to downregulation of RhoA, which is followed by decreased Rho kinase activity, is a sequence of events necessary and sufficient to explain NO-induced cell motility in differentiated aortic smooth muscle cells. The results may be of relevance to in vivo events such as neointimal formation, angiogenesis, and vasculogenesis.

NO attenuates insulin signaling and motility in aortic smooth muscle cells via protein tyrosine phosphatase 1B-mediated mechanism

OBJECTIVE

Hyperinsulinemia is a significant risk factor for the pathogenesis of vascular disease. Protein tyrosine phosphatase 1B (PTP1B) has been recognized as a modulator of insulin signaling in nonvascular cells, and we have recently reported that NO increases the activity of PTP1B in rat vascular smooth muscle cells. In the present study, we tested the hypothesis that NO attenuates insulin-stimulated cell motility via a PTP1B-mediated mechanism involving downregulation of insulin signal transduction.

METHODS AND RESULTS

Treatment of primary aortic smooth muscle cells from newborn rats with the NO donor S-nitroso-N-acetylpenicillamine reduced cell motility, tyrosine phosphorylation levels of insulin receptor beta subunit and insulin receptor substrate-1, and extracellular signal-regulated kinase activity. Overexpression of wild-type PTP1B via an adenoviral vector blocked the capacity of insulin to stimulate cell motility and insulin receptor phosphorylation, whereas expression of a dominant-negative mutant of PTP1B attenuated the capacity of NO to decrease cell motility.

CONCLUSIONS

Our findings indicate that activation of PTP1B is necessary and sufficient to account for the capacity of NO to decrease insulin-stimulated signal transduction and cell motility in cultured aortic smooth muscle cells. The results could explain the capacity of NO to oppose neointima formation in states of hyperinsulinemia.

Advances towards understanding heart valve response to injury

BACKGROUND

Composed of endocardial endothelial, valvular interstitial, cardiac muscle, and smooth muscle cells (SMC), heart valves are prone to various pathologic conditions the morphology of which has been well described. The morphology of diseased valves suggest that the "response to injury" process occurs in these valves, and is associated with an accumulation of interstitial cells and matrix, valvular inflammation and calcification, conditions that lead to dysfunction. The purpose of this study is to describe the current knowledge of the regulation of the valvular "response to injury" process, since we feel that this paradigm is essential to understanding valve disease.

METHODS

The pertinent literature relating to the cell and molecular biology of valvular repair, and specifically interstitial cell function in valve repair, is reviewed.

RESULTS

The cell and molecular biology of valve interstitial cells are poorly understood. Molecules regulating some of the aspects of the "response to injury" process have been studied, however, the signal transduction pathways, gene activation, and interactions of bioactive molecules with each other, with cells, and with the matrix have not been characterized. Initial studies identify the cell and molecular biology of interstitial cells to be an important area of research. Agents that have been studied include nitric oxide (NO) and FGF-2 and several matrix-related proteins including osteopontin. The present review suggests several directions for future study and a working model of valvular repair is presented.

DISCUSSION

The regulation of the "response to injury" process in the human heart valve is still largely unknown. The cell and molecular events and processes that occur in heart valve function and repair remain poorly understood. These events and processes are vital to our understanding of the pathobiology of heart valve disease, and to the successful design of tissue engineered replacement valves.

Requirement of protein tyrosine phosphatase SHP2 for NO-stimulated vascular smooth muscle cell motility

We have previously reported that nitric oxide (NO) increases the motility of differentiated cultured primary aortic smooth muscle cells from adult rats. There is little information on the role of protein tyrosine phosphatases in vascular biology. One such phosphatase, Src homology 2 phosphatase 2 (SHP2), is essential for motility. We tested the hypothesis that NO increases SHP2 levels via a cGMP-mediated mechanism and that this effect is necessary for NO-stimulated cell motility. Here we report that two different NO donors increased SHP2 protein levels and enzyme activity. This effect was mimicked by several cGMP agonists and blocked by an inhibitor of guanylyl cyclase. Specific decrease of SHP2 protein levels via the use of antisense oligodeoxynucleotides (ODNs), but not several control ODNs attenuated the motogenic effect of NO, which indicates the involvement of SHP2 in NO-elicited motogenesis. S-nitroso-N-acetylpenicillamine failed to increase SHP2 protein levels in subcultured aortic smooth muscle cells. This provides a potential explanation for the lack of effect of NO on cell motility in dedifferentiated subcultured cells. These results support the hypothesis that NO-elicited upregulation of SHP2 via a cGMP-mediated pathway is necessary for NO-induced motogenesis in differentiated aortic smooth muscle cells.

Age-related decrease of protein kinase G activation in vascular smooth muscle cells

Protein kinase G-I (PKG-I) activation is essential for vascular relaxation; however, its quantitative analysis in intact cells has been difficult. To overcome this difficulty, a monoclonal antibody, VASP-16C2, was recently developed that detects phosphorylated serine residue 239 of vasodilator-stimulated phosphoprotein (VASP), a substrate of PKG-I. In this study, we used this antibody to examine (i) possible functional differences between the alpha and beta isoforms of PKG-I, (ii) ability of cAMP to activate PKG-I, as compared to cGMP, the principal PKG-I-activating cyclic nucleotide, and (iii) time course and levels of PKG-I activation in vascular smooth muscle cells (VSMC) of young and old rats. We created COS-7 cell clones that overexpressed PKG-Ialpha or PKG-Ibeta, treated them with cAMP or cGMP, and analyzed their cell lysates for reactivity with VASP-16C2. The results showed that PKG-Ialpha phosphorylated VASP at a higher level than PKG-Ibeta, and cAMP was slightly weaker than cGMP in PKG-I activation. VSMC of young rats responded to cAMP or cGMP stimulation in a dose-dependent manner with increasing levels of PKG-I activation. The response was detected within 10 min and continued for at least 24 h. In contrast, VSMC of old rats showed no PKG-I activation during the first hour of cAMP or cGMP stimulation and, at 24 h these cells showed only low-level PKG-I activation. We propose that the reduced PKG-I activation may explain why vascular relaxation is decreased in older individuals.

Cultured arterial smooth muscle cells maintain distinct phenotypes when implanted into carotid artery

Cultured arterial smooth muscle cells (SMCs) with distinct phenotypic features have been described by several laboratories; however, it is not presently known whether this phenotypic heterogeneity can be maintained within an in vivo environment. To answer this question, we have seeded into the intima of denuded rat carotid artery 2 SMC populations with well-established distinct biological features, ie, spindle-shaped, not growing in the absence of serum, and well differentiated versus epithelioid, growing in the absence of serum, and relatively undifferentiated, derived from the aortic media of newborn rats (aged 4 days) and old rats (aged >18 months), respectively. We show that these 2 populations maintain their distinct biochemical features (ie, expression of alpha-smooth muscle actin, smooth muscle myosin heavy chains, and cellular retinol binding protein-1) in the in vivo environment. The old rat media-derived SMCs continue to produce cellular retinol binding protein-1 but little alpha-smooth muscle actin and smooth muscle myosin heavy chains, whereas the newborn rat media-derived SMCs continue to express alpha-smooth muscle actin and smooth muscle myosin heavy chains but no cellular retinol binding protein-1. Our results reinforce the notion of arterial SMC phenotypic heterogeneity and suggest that in our model, heterogeneity is controlled genetically and not by the local environment.

Adventitial remodeling after angioplasty is associated with expression of tenascin mRNA by adventitial myofibroblasts

OBJECTIVES

The purpose of this study was to determine the temporospatial expression of tenascin-C (TnC) in balloon-injured rat and porcine arteries.

BACKGROUND

Recent studies suggest that cell migration, in addition to cell proliferation, is a critical component of neointima formation after vascular injury. We have previously shown that adventitial myofibroblasts synthesize growth factors that contribute to the formation of neointima after arterial injury. We have also shown that the extracellular matrix protein, TnC, regulates cell migration. Consequently, we investigated the temporospatial expression of TnC by myofibroblasts after vascular injury.

METHODS

In situ hybridization and immunohistochemistry were used to investigate the temporospatial expression of TnC in injured arteries. Northern and Western blots were used to determine the in vitro expression of TnC.

RESULTS

In situ hybridization revealed that the major site of TnC expression early after vascular injury was the adventitial myofibroblasts. Immunohistochemical staining demonstrated that TnC expression began in adventitial myofibroblasts three days after injury. Tenascin-C expression, however, did not persist in this region. Rather, it moved progressively across the vascular wall toward the luminal surface. By one week, TnC expression reached the developing neointima. In vitro, myofibroblasts did not express TnC mRNA under basal conditions. In contrast, angiotensin II and PDGF-BB, factors that have been implicated in remodeling of balloon-injured arteries, markedly upregulated TnC mRNA.

CONCLUSIONS

Tenascin-C is expressed in response to balloon injury. Tenascin-C expression begins with adventitial myofibroblasts. Over a period of 7 to 14 days, expression moves progressively across the vessel wall to the neointima. We hypothesize that adventitial myofibroblasts are actively involved in the formation of neointima and that TnC facilitates migration of these cells during adventitial remodeling.

Smooth muscle cells of injured rat and rabbit arteries in culture: contractile and cytoskeletal proteins

The aim of this study is to determine whether subpopulations of smooth muscle cells (SMC), as distinguished by variations in contractile and cytoskeletal proteins, appear in the neointima at different times after vascular injury, and/or whether subpopulations develop during serial passaging of these cells. Rat aortae and rabbit carotid arteries were injured with a 2F Fogarty balloon catheter and cultures established from the resulting neointima and the media 2, 6, 12, 16 and 24 weeks later. Cultures were examined at passages 1-5 and subpopulations of SMC categorised by intensity of staining for each protein by immunohistochemistry. Two populations of SMC with different staining intensities ('++', '+') were observed for each of the following proteins: alpha-SM actin, SM-myosin, desmin and vimentin. Populations without these proteins were also found. Changes in the percentages of cells expressing these proteins were transitory, indicating that the populations were not limited to a particular tissue (neointima or media), time after injury or passage number. One exception was found in rabbit cultures where the number of desmin-expressing cells quickly decreased with both time after injury and time in culture. Subpopulations of SMC were found at all times after injury in the media and neointima of rat and rabbit arteries, and after multiple passage of these cells. There was no pattern of development of one population suggesting that either no subpopulation has a proliferative or migratory advantage over others, or that only one population exists that is capable of diverse phenotypic changes.

Nicotine induces platelet-derived growth factor release and cytoskeletal alteration in aortic smooth muscle cells

BACKGROUND

Cigarette smoking is implicated in atherosclerotic plaque formation, but the role of nicotine in this process is not completely understood. The release of platelet-derived growth factor (PDGF) by the bovine aortic smooth muscle cell (SMC) after nicotine administration at a concentration similar to that ingested by active and passive smokers and the role of PDGF in SMC cytoskeletal modification were studied.

METHODS

SMC, harvested with enzymatic digestion from calf aorta, were stimulated in a serum-free medium for 72 hours with (-)-nicotine (from 6 x 10(-4) mol/L to 6 x 10(-8) mol/L). The release of PDGF was assessed by inhibition antibody-binding assay and confirmed by Western blotting. Mitogenic activity of nicotine on SMCs was also determined. The SMC cytoskeleton was studied with specific antibodies anti-alpha-actin fibers, anti-vimentin, and anti-beta-tubulin, and the modification induced by PDGF was assessed by blocking PDGF activity with specific antibodies.

RESULTS

The greatest PDGF release (1.24 +/- 0.14 ng/10(4) cells vs control 0.43 +/- 0.07 ng/10(4) cells) was noted at a (-)-nicotine concentration of 6 x 10(-7) mol/L (P < .001). The addition of monoclonal antibody anti-PDGF decreased the tritiated thymidine uptake of SMCs exposed to (-)-nicotine compared with the control (29% vs 5%-P < .001). SMCs exposed to (-)-nicotine concentration of 6 x 10(-7) mol/L and 6 x 10(-8) mol/L had a significant alteration in the expression of alpha-actin fibers, vimentin, and beta-tubulin compared with control. The administration of antibody anti-PDGF in the culture medium reversed cytoskeletal alteration.

CONCLUSIONS

Nicotine enhanced the release of platelet-derived growth, which in turn caused an alteration in cytoskeletal organization.

Augmented expression of inducible NO synthase in vascular smooth muscle cells during aging is associated with enhanced NF-kappaB activation

Vascular smooth muscle cells (SMCs) are important targets for endothelium-derived nitric oxide (NO), but this production is attenuated in injured and diseased arteries and during aging. However, SMCs can produce NO themselves by expressing an inducible form of NO synthase (iNOS) under inflammatory conditions and in the repair process after arterial injury. We examined iNOS expression in SMCs derived from the aortic media of newborn, young adult, and old rats. Our results show that SMCs from newborn rats cannot produce significant amounts of NO on stimulation with interferon-gamma plus lipopolysaccharide or interleukin-1beta. In contrast, SMCs from old rats exhibit markedly enhanced iNOS activity. The difference in iNOS activity between the newborn and the old SMCs was closely correlated with levels of iNOS protein, mRNA, and gene promoter activity. Similarly, intercellular adhesion molecule-1 (ICAM-1) was also expressed more abundantly in the old than in the newborn SMCs in response to cytokines. Both iNOS and ICAM-1 are transcriptionally regulated by nuclear factor kappaB (NF-kappaB). Our data demonstrate an intense transactivation of NF-kappaB in old SMCs on tumor necrosis factor-alpha stimulation but only a weak one in newborn SMCs. The difference in the NF-kappaB activation could be explained by a much faster and more extensive IkappaBalpha degradation in old than in newborn SMCs. These data indicate that the capability to respond to proinflammatory stimuli by activating NF-kappaB differs between SMCs at different stages of development. This results in differential capability to express NF-kappaB-dependent genes such as iNOS and ICAM-1, which could have implications for host defense and the pathogenesis of vascular diseases.

Age dependence of smooth muscle myosin expression by cultured rat aortic smooth muscle cells

Vascular smooth muscle cells (SMC) in vivo are highly heterogeneous phenotypically, particularly during development and in the adult during periods of remodeling. Much remains to be learned, however, regarding regulation of the SMC phenotype at the gene level. Here, we studied smooth muscle myosin heavy chain (SMMHC) expression at the transcriptional and mRNA levels in SMC cultured from newborn, adult, and old animals, which express different patterns of differentiation markers. We also examined regulation of SMMHC gene expression by TGF-beta, a cytokine known to be involved in the differentiation process. The activity of SMMHC promoter constructs, the expression of which is smooth-muscle-specific, was greatest in SMC from newborn animals and least in cells from old animals. Thus, differences in the degree of differentiation of SMC from these three sources may at least in part be due to transcriptional events. SMC from the three animal sources each contained mRNAs for the SM-1A and SM-2A tail but not those for the SM-1B and SM-2B head isoforms. Total SMMHC mRNA levels reflected similar differences as found at the transcriptional level. SM-2A mRNA as a proportion of total SMMHC mRNA was greatest in SMC from newborn animals, consistent with their higher degree of differentiation. TGF-beta up-regulated both transcription and mRNA levels but did not change the proportions of SMMHC mRNAs. Though the levels of transcriptional activity and mRNA were widely different in untreated cells, the degree of TGF-beta stimulation was approximately the same in all cases.

Inverse relationship between connexin43 and desmin expression in cultured porcine aortic smooth muscle cells

Our previous work has shown that in vascular tissues the elastic medial regions express high levels of the gap junctional protein, connexin43, but low levels of desmin, while the muscular medial regions express low levels of connexin43 but high levels of desmin. It is uncertain, however, whether this regional difference at the tissue level extends down to the level of the individual cell, or reflects an averaged relationship of groups of cells of different connexin43 and desmin expression. The present study has addressed this question using cultured porcine aortic smooth muscle cells. Immunoconfocal microscopic analysis of single-labeled cells showed that while smooth muscle alpha-actin, calponin and vimentin were positively labeled in the majority of medial smooth muscle cells both in intact porcine aorta and corresponding cultured cells, desmin and connexin43 labeling was highly heterogeneous. In the cultured cells, 0.3-0.5% of cells were found to be desmin-positive, and quantitative analysis after double labeling for desmin and connexin43 revealed that the desmin-positive cells were smaller, and contained significantly lower numbers and smaller sizes of connexin43 gap-junctional spots than did desmin-negative cells. Our findings demonstrate that an inverse expression pattern of connexin43 and desmin holds true at the level of the individual cell. This suggests a close relationship between intrinsic phenotypic control and the regulation of connexin43 expression in the arterial smooth muscle cell.

Cultured porcine coronary artery smooth muscle cells. A new model with advanced differentiation

Arterial intimal thickening after endothelial injury induced in rodents has proven to be a relatively unreliable model of restenosis for testing clinically useful compounds. The same has been found for cultured rat or rabbit vascular smooth muscle cells (SMCs). To test alternative possibilities, we have studied several differentiation features of porcine coronary artery SMCs, cultured up to the 5th passage after enzymatic digestion of the media. The effects of heparin, transforming growth factor (TGF)-beta1 or TGF-beta2, and all-trans-retinoic acid (tRA) on proliferation, migration, and differentiation of these cells also were examined. Porcine arterial SMCs in culture not only express high levels of alpha-smooth muscle (SM) actin but, contrary to rodent SMCs, also maintain an appreciable expression of SM myosin heavy chain isoforms 1 and 2, desmin, and smoothelin, a recently described late differentiation marker of vascular SMCs. We demonstrate for the first time that smoothelin is colocalized with alpha-SM actin in these cells. Finally, we show that in the porcine model, heparin is more potent than TGF-beta1 or TGF-beta2 and tRA in terms of inhibition of proliferation and migration and of increasing the expression of differentiation markers. This model should be a useful complement to in vivo studies of SMC differentiation and of pathological situations such as restenosis and atheromatosis.

Effect of pentoxifylline on early proliferation and phenotypic modulation of fibrogenic cells in two rat models of liver fibrosis and on cultured hepatic stellate cells

BACKGROUND/AIMS

During liver fibrosis, different fibroblastic cells, i.e. hepatic stellate cells (HSCs) or portal fibroblasts, are involved in the development of lesions, and acquire myofibroblastic differentiation. We investigated, in the rat, whether pentoxifylline can influence the early phase of fibrogenesis in two animal models of fibrosis induced by either carbon tetrachloride (CCl4) plus acetone (given twice) or bile duct ligation.

METHODS

The fibroproliferative response and myofibroblastic phenotypic modulation were evaluated by PCNA and alpha-smooth muscle (alpha-SM) actin immunohistochemistry, respectively, in livers taken 24 h after the last CCl4 treatment or 72 h after bile duct ligation. Desmin expression was also measured, and inflammation was evaluated by ED-1 staining. Furthermore, proliferation and alpha-SM actin expression were studied in cultured HSCs after pentoxifylline treatment.

RESULTS

In the CCl4-acetone groups, pretreatment with pentoxifylline decreased the proliferative response and expression of alpha-SM actin in the HSCs. Similarly, pentoxifylline reduced the proliferation and myofibroblastic differentiation of portal fibroblasts after bile duct ligation. Pentoxifylline reduced ED-1 expression, particularly in the CCl4 model, where there was significant inflammation. In cultured pentoxifylline-treated HSCs, both proliferation and alpha-SM actin expression were decreased.

CONCLUSIONS

In both animal models of fibrosis, during the early stages of tissue injury, pentoxifylline was able to reduce fibroproliferation and myofibroblastic differentiation and to reduce hepatocellular damage and the inflammatory response, particularly in the toxin-induced model. In culture, alpha-SM actin expression decreased in both growing and quiescent HSCs treated with pentoxifylline, indicating that the drug may also exert a direct effect on hepatic fibrogenic cells.

The cytoskeleton of the vertebrate smooth muscle cell

Smooth muscle cells possess a structural lattice composed of two primary parts: the 'cytoskeleton' that pervades the cytoplasm and the 'membrane skeleton' that provides anchorage for the cytoskeleton and contractile apparatus at the cell surface. The cytoskeleton contains two major components: first, a complement of actin filaments that links the cytoplasmic dense bodies at equispaced intervals in longitudinal fibrils; and second, a network of desmin intermediate filaments that co-distributes with the cytoskeletal actin. The actin filaments of the contractile apparatus are presumed to interface with the cytoskeleton at the cytoplasmic dense bodies and with the longitudinal rib-like arrays of dense plaques of the membrane skeleton that couple to the extracellular matrix. The present report focuses attention on the functional role of intermediate filaments and on the molecular domain structure of the protein calponin, which is found both in the cytoskeleton and the contractile apparatus. New information about the role of intermediate filaments in smooth muscle has come from studies of transgenic mice in which desmin expression has been ablated. These have shown that while desmin is dispensable for normal development and viability its absence has significant consequences for the mechanical properties of muscle tissue. Thus, the visceral smooth muscles develop only 40% of the normal contractile force and the maximal shortening velocity is reduced by 25-40%. Intermediate filaments therefore play an active role in force transmission and do not contribute solely to cell shape maintenance, as has hitherto been presumed. Recent studies on calponin have revealed a second actin binding domain at the C-terminus of the molecule and have also pinpointed an N-terminal domain that shares homology with a growing family of actin binding and signalling molecules. How these newly identified features of calponin relate to its function in vivo remains to be established.

Plasminogen activator expression in rat arterial smooth muscle cells depends on their phenotype and is modulated by cytokines

Cultured rat aortic smooth muscle cells (SMCs) exhibit at least 2 phenotypic variants: (1) a spindle-shaped phenotype, obtained from normal adult media, and (2) an epithelioid phenotype, obtained from intimal thickening 15 days after endothelial injury. Both phenotypes can be cloned from each location, with normal media yielding a majority of spindle-shaped clones and intimal thickening yielding a majority of epithelioid clones. These findings suggest that intimal thickening develops essentially from a subpopulation of medial SMCs exhibiting epithelioid features in vitro. Using zymographic and Northern blot analyses, we have studied plasminogen activator (PA) expression by these SMCs. Our results show that epithelioid SMCs, cultured as whole SMC populations or as clones, display higher PA activity than do spindle-shaped SMCs, irrespective of their origin. This is mainly due to differences in the expression of tissue PA and, to a lesser extent, urokinase PA and is accompanied by a decrease in PA inhibitor 1. Tissue PA activity is increased by basic fibroblast growth factor and platelet-derived growth factor-BB, particularly in epithelioid SMCs. Taken together, these results indicate that SMCs are heterogeneous with respect to their proteolytic profile, at least as far as the PA system is concerned. Proteolytic activity of the different SMC populations is modulated by cytokines that play a role in intimal thickening. Our results are in agreement with the suggestion that epithelioid SMCs are mainly responsible for intimal thickening.

Smooth muscle cell heterogeneity: patterns of gene expression in vascular smooth muscle cells in vitro and in vivo

Early morphological and biochemical studies indicated that vascular smooth muscle cells (VSMCs) exhibited two distinct phenotypes and that a change from the contractile to the synthetic phenotype was a prerequisite for progression of vascular disease. More recently, it has become evident that these phenotypes probably represent the extremes of a spectrum of phenotypes that may coexist in the vessel wall, which are dictated by their environment and functional requirements and which reflect differing patterns of gene expression. Therefore, knowledge of the key factors that regulate these patterns of gene expression is likely to lead to the ability to manipulate VSMC phenotype. However, before such factors can be identified, the relationship between VSMC gene expression and VSMC phenotype must first be established. We therefore undertook a differential screen of cDNA from VSMCs in vitro to provide a bank of gene markers that could be used under a variety of circumstances to define VSMC phenotype in terms of the pattern of genes expressed. Using this approach, we have found that the pattern of gene expression that occurs during neointima formation in the balloon-injured rat carotid artery is very similar to that seen at a specific period in the developing aorta of the early neonate and is characterized by coexpression of genes for both contractile and matrix proteins. Furthermore, recent studies have shown that VSMCs isolated at different stages of aortic development can stably maintain different phenotypic characteristics in cell culture. The use of these cells in transfection experiments with SM-specific promoter-chloramphenicol acetyltransferase reporter constructs may enable us to determine what regulates the pattern of gene expression in different VSMC phenotypes. Such studies may ultimately lead to the identification of transcription factors responsible for determining VSMC phenotype and may therefore provide targets for therapy aimed at manipulating VSMC gene expression in vascular disease.

A comparative molecular analysis of four rat smooth muscle cell lines

Transcriptional regulation of smooth muscle cell (SMC) differentiation is a rapidly growing area of interest that has relevance for understanding intimal disease. Despite the wealth of data accumulating in vitro, however, no study has compared the cell-specific marker profile, transfectability, promoter activity, and growth characteristics among several SMC culture systems. Accordingly, we performed a comprehensive analysis of the marker profile, growth properties, transfectability, and SMC promoter activity in four rat SMC lines (A7r5, adult and pup aortic, and PAC1). Despite alterations in chromosomal number and structure, A7r5, adult aortic, and PAC1 cells express all SMC markers studied including SM alpha-actin, SM calponin, SM22, tropoelastin, and to a lesser extent, SM myosin heavy chain (SMMHC). In contrast, pup aortic cells express very low or undetectable levels of all the above markers except tropoelastin. Adult aortic, pup, and PAC1 cells display similar growth curves and levels of proto-oncogene transcripts, whereas those in the A7r5 line are comparatively less. All cell lines studied except pup cells show expression of SMC differentiation genes during active growth, indicating that growth and differentiation are not mutually exclusive in cultured smooth muscle. Transfection studies reveal dramatic differences in DNA uptake and SMC-restricted promoter activity between cell lines. Collectively, these results provide detailed information relating to SMC molecular biology in culture that should facilitate the selection of a cell line for studying the transcriptional regulatory mechanisms underlying SMC differentiation.

Overexpression of inducible nitric oxide synthase by neointimal smooth muscle cells

The formation of a neointima represents an important repair mechanism in response to vascular injury. It is associated with the expression of a specific set of genes by the intimal smooth muscle cells. Recently, expression of the inducible isoform of NO synthase (iNOS) has been identified in injured arteries during neointimal formation, suggesting that intimal SMCs have a unique mechanism for regulating NO production. Therefore, we have analyzed the expression of iNOS in intimal SMCs. Although first expressed in the media within 1 day after injury, iNOS was confined to neointimal smooth muscle cells at 1 to 2 weeks after injury. Isolated intimal SMCs were found to consistently reexpress iNOS in reaction to proinflammatory mediators. This was associated with a 5- to 8-fold higher output of NO in comparison with SMCs derived from the media of uninjured arteries. Western blot and Northern blot analyses likewise revealed that the high production of NO by intimal SMCs was due to overexpression of iNOS. Moreover, the same stimuli induced a higher transcriptional activity in intimal than in medial SMCs, as detected by transfection of a reporter gene under the iNOS promoter. Induction of iNOS led to a reduced proliferation in both medial and intimal SMCs. This inhibitory effect was, however, less pronounced in intimal than in medial SMCs. Similarly, intimal cells were less sensitive to NO-induced inhibition of mitochondrial respiration. When SMC clones were analyzed, there was no correlation between iNOS expression and growth pattern, suggesting that iNOS expression is independent of the morphological phenotype of SMCs. Together, our data show that the intimal SMC is the main iNOS-expressing cell type in the injured artery, that it responds more vividly to iNOS-inducing cytokines because of a more efficient activation of the iNOS promoter, and that it is more resistant to the actions of NO compared with medial SMCs. Intimal production of NO via the inducible pathway may be important for the restoration of vascular homeostasis after injury.

Intracellular thiol redox status affects rat cytomegalovirus infection of vascular cells

There is increasing evidence for cytomegalovirus (CMV) induced vascular pathology during acute infection in the immunocompromised host. Inflammation is involved in such processes, which is frequently associated with increased levels of oxidative mediators and reduced anti-oxidant protection. A relation between viral infection and oxidative stress has been recognized for human immunodeficiency virus and herpes simplex virus-1 infections, but little is known in this respect for CMV infections. We investigated if there is a relation between CMV infection of vascular cells and the intracellular redox status using an in vitro rat model. We measured intracellular glutathione levels and rat CMV (RCMV) permissiveness of rat heart endothelial cell lines (RHEC), rat smooth muscle cells (RSMC), and compared these with fully CMV-permissive rat fibroblasts (REF and Rat 2). In addition, the effects of the anti-oxidant N-acetylcysteine (NAC) and the glutathione synthesis inhibitor buthionine sulfoximide (BSO) on CMV permissiveness and replication were investigated in these cell lines. Finally, we investigated infection of vascular cells under inflammatory conditions in an in vivo rat model for acute CMV infection. The results show a very high endogenous glutathione level in RHEC compared to REF, Rat 2 cells and RSMC. This is associated with a low CMV permissiveness in RHEC as opposed to full permissiveness in REF, Rat 2 cells and RSMC in vitro. In addition, modulation of the intracellular thiol redox status affected CMV infection and replication only in RHEC, but not in RSMC and Rat 2 cells. During acute infection in vivo under immunosuppressed conditions rat endothelial cells first become activated and subsequently infected leading to vascular damage and pathology. This study suggests that a high endogenous thiol redox status may contribute to the apparent barrier function of endothelial cells with respect of CMV infection and that oxidative stress may facilitate CMV infection of the vascular wall.

Differentiation of smooth muscle cells in human blood vessels as defined by smoothelin, a novel marker for the contractile phenotype

Smoothelin is a constituent of the cytoskeleton specific for smooth muscle cells (SMCs) in a broad range of species. It has been postulated that smoothelin represents a marker of highly differentiated, contractile SMCs. Here, we present data on the presence of smoothelin in the human vascular system that support this hypothesis. For this purpose, smoothelin distribution was studied (1) during vasculogenesis of the placenta, (2) in normal adult blood vessels, and (3) in atherosclerotic lesions. Smoothelin was first observed in placental tissue at approximately week 10 to 11 of gestation. In full-term placenta, it was found in the SMCs of vessels in the large stem villi and in the chorionic plate. Furthermore, it was present in the fetal arteries of smaller stem villi, but it was not found in the veins. In adult blood vessels, a small population of aortic (approximately 10%) and large muscular artery (approximately 30% to 50%) SMCs was positive for smoothelin. In general, smoothelin and desmin were coexpressed in the same SMCs, but expression of desmin appeared to be less abundant. However, the majority of SMCs in these blood vessels were smoothelin- and desmin negative but expressed vimentin, whereas alpha-smooth muscle actin (alpha-SMA) was present in all SMCs. The SMCs in the media of small muscular arteries were positive for smoothelin and desmin (> 95%), whereas the vimentin-positive SMC type was scarce. Smoothelin was absent in capillaries, pericytic venules, and small veins but was occasionally observed in the SMCs of large veins. Thus, the distribution of smoothelin in the SMCs of the vascular system appears to be limited to blood vessels that are capable of pulsatile contraction. In atherosclerotic femoral arteries, smoothelin-positive cells were detected in the media, the atheromatous plaque, and the intimal thickening. Smoothelin-positive cells were present primarily at the luminal portion of advanced lesions. The presence of a considerable number of such smoothelin-positive cells at that location may indicate that these plaques are no longer expanding.

Differential expression of nonmuscle myosin II isoforms in human atherosclerotic plaque

Intimal proliferation and functional changes involving vascular smooth muscle cells are key events in the development of atherosclerosis, including restenosis after percutaneous transluminal angioplasty. Nonmuscle myosin (NMM) is required for cytokinesis and has been shown in cultures of vascular smooth muscle cells to undergo changes of isoform expression depending on the stage of proliferation and differentiation. The purpose of this study was to examine the differential expression of the two most recently identified nonmuscle myosin heavy chain isoform II (NMMHC-II) isoforms A and B in atherosclerotic plaque. Primary atherosclerotic and restenotic atherectomy specimens and non-atherosclerotic controls, were analyzed by Western Blot analysis, immunohistochemistry and in situ hybridization. Nonmuscle myosin heavy chain isoform IIA (NMMHC-IIA) was equally expressed in all types of tissue specimens both at the protein and mRNA levels. In contrast, NMMHC-IIB protein was found in restenotic specimens and normal artery but was at very low levels in primary atherosclerotic plaque. By in situ hybridization NMMHC-IIB mRNA levels were significantly greater in restenotic versus primary atherosclerotic lesions. NMMHC-IIB expression is associated with vascular restenosis but is downregulated in stable atherosclerotic lesions, whereas NMMHC-IIA is expressed in both. These results indicate that these new myosin isoforms have different functions and should be regarded separately with respect to smooth muscle proliferation and restenosis. They should prove to be useful molecular markers for the study of atherosclerosis and restenosis.

Transfected muscle and non-muscle actins are differentially sorted by cultured smooth muscle and non-muscle cells

We have analyzed by immunolabeling the fate of exogenous epitope-tagged actin isoforms introduced into cultured smooth muscle and non-muscle (i.e. endothelial and epithelial) cells by transfecting the corresponding cDNAs in transient expression assays. Exogenous muscle actins did not produce obvious shape changes in transfected cells. In smooth muscle cells, transfected striated and smooth muscle actins were preferentially recruited into stress fibers. In non-muscle cells, exogenous striated muscle actins were rarely incorporated into stress fibers but remained scattered within the cytoplasm and frequently appeared organized in long crystal-like inclusions. Transfected smooth muscle actins were incorporated into stress fibers of epithelial cells but not of endothelial cells. Exogenous non-muscle actins induced alterations of cell architecture and shape. All cell types transfected by non-muscle actin cDNAs showed an irregular shape and a poorly developed network of stress fibers. beta- and gamma-cytoplasmic actins transfected into muscle and non-muscle cells were dispersed throughout the cytoplasm, often accumulated at the cell periphery and rarely incorporated into stress fibers. These results show that isoactins are differently sorted: not only muscle and non-muscle actins are differentially distributed within the cell but also, according to the cell type, striated and smooth muscle actins can be discriminated for. Our observations support the assumption of isoactin functional diversity.

The integrin very late antigen-4 is expressed in human smooth muscle cell. Involvement of alpha 4 and vascular cell adhesion molecule-1 during smooth muscle cell differentiation

Vascular cell adhesion molecule-1 (VCAM-1) and its counterreceptor, the integrin very late antigen-4 (VLA-4), have recently been identified in smooth muscle cells during intimal thickening in humans and in newly forming vessels during ontogeny in mice, respectively. We examined the coexpression of VCAM-1 and the alpha 4 integrin subunit in human smooth muscle cells. The expression of VCAM-1 and alpha 4 subunit were studied during development of the aorta. In the 10-week-old human fetal aorta, VCAM-1 and alpha 4 were strongly expressed in smooth muscle cells. Their expression was dramatically reduced within the 24th week of gestation and disappeared in the adult aortic media. However, smooth muscle cells from intimal atherosclerotic thickening of adult aorta reexpressed both VCAM-1 and alpha 4. In a culture model mimicking smooth muscle differentiation, VCAM-1 mRNA and protein and alpha 4 integrin protein were coexpressed with smooth muscle-specific variants of cytoskeletal and contractile proteins, smooth muscle myosin heavy chain, caldesmon heavy chain, and desmin. Treatment with antibodies against VCAM-1 or alpha 4 integrin subunit interfered with the mRNA induction of smooth muscle-specific markers of differentiation. These results in vitro, associated with the transitory expression of VCAM-1 and VLA-4 during vascular ontogeny and the atherosclerosis process, point to a possible role of VCAM-1 and VLA-4 in the induction of smooth muscle differentiation.

Apoptosis during wound healing, fibrocontractive diseases and vascular wall injury

Following injury, tissue repair involves inflammation, granulation tissue formation and scar constitution. Granulation tissue develops from the connective tissue surrounding the damaged or missing area and contains mainly small vessels, inflammatory cells, fibroblasts and myofibroblasts. As the wound closes and evolves into a scar, there is a striking decrease in cellularity, including disappearance of typical myofibroblasts. The question arises as to what process is responsible for granulation tissue cell disappearance. Our results (in cutaneous wounds) and results of other laboratories (particularly in lungs and kidney) suggest that apoptosis is the mechanism responsible for the evolution of granulation tissue into a scar. During excessive scarring (hypertrophic scar or fibrosis), it is conceivable that the process of apoptosis cannot take place. After experimental endothelial injury in an artery, accumulation of smooth muscle cells participates in the formation of intimal thickening. Apoptotic features have been observed in cells of intimal thickening and also within human atherosclerotic plaques. In the case of atherosclerosis, apoptosis could be detrimental: since smooth muscle cells participate in plaque stability, apoptosis could lead to weakening and rupture of the plaque. These results underline the fact that both increased cell survival or excessive cell death can be associated with pathological disorders. Specific therapies devised to enhance or decrease the susceptibility of individual cell types to apoptosis development could modify the evolution of a variety of human diseases.

Mechanical strain increases smooth muscle and decreases nonmuscle myosin expression in rat vascular smooth muscle cells

The effect of cyclic (1-Hz) mechanical strain on expression of myosin heavy chain isoforms was examined in neonatal rat vascular smooth muscle cells cultured on silicone elastomer plates. Myosin heavy chain isoforms were identified by immunoblot using antibodies recognizing (1) smooth muscle myosin heavy chain isoforms SM-1 and SM-2, (2) SM-1 exclusively, and (3) nonmuscle myosin heavy chains A and B. In response to 36 to 72 hours of strain, SM-1 and SM-2 increased by fourfold to sixfold, whereas nonmuscle myosin A decreased to 30% of control. Nonmuscle myosin B was unaffected by strain. SM-1 mRNA increased by twofold to threefold after 12 hours of strain but decreased toward control levels thereafter. SM-2 mRNA was only barely detectable. Nonmuscle myosin A mRNA decreased to 50% of control after 3 hours of strain and then returned to the control level. Since these cells secrete platelet-derived growth factor (PDGF) in response to strain, we assessed the effects of PDGF on myosin isoform expression. Exogenous PDGF (10 ng/mL) decreased SM-1 expression by 35% and increased nonmuscle myosin expression twofold, opposite the effect of strain. In cells exposed to strain with neutralizing antibodies to PDGF-AB, the strain-induced increase in SM-1 was enhanced 10-fold, and nonmuscle myosin A was reduced to 40% of control. Finally, the effect of extracellular matrix on transduction of the strain signal was studied. Forty-eight hours of cyclic strain increased SM-1 by twofold in cells cultured on collagen type 1 and threefold in cells cultured on laminin. In fibronectin-cultured cells, strain elicited no increase in SM-1. Thus, mechanical strain, sensed through specific interactions with the matrix, can alter myosin isoform expression toward that found in a more differentiated state.