Isolation and characterization of clonal vascular smooth muscle cell lines from spontaneously hypertensive and normotensive rat aortas

Characterization of clonal vascular smooth muscle cell lines derived from young and old Fischer 344 rats

A significant finding with aging humans (and aging animal models) is that blood vessels lose their ability to respond to beta-adrenergic receptor stimuli. Therefore, they produce less cyclic adenosine monophosphate (cAMP) and have decreased vasorelaxation with advancing age. This change likely contributes to hypertension, insufficient blood flow, and atherosclerosis. Our goal was to develop a vascular smooth muscle cell culture model that replicates the molecular and biochemical changes observed in blood vessels with advancing age. A clonal selection strategy was used to produce cell lines from 2-, 6-, 12-, and 24-month-old male Fischer 344 rat aortae. Cultures were validated as smooth muscle cells with immunocytochemistry positive for α-actin and negative for von Willebrand factor VIII. Positive staining for G protein-coupled receptor kinase 2 indicated presence of this adrenergic receptor regulator. A total of n = 5 clones from n = 7 animals for each age group were initially analyzed for cAMP accumulation under three conditions: basal, isoproterenol stimulated, and forskolin stimulated. Results found that at passage 3, there was a significant reduction in cAMP accumulation to isoproterenol. However, this reduction disappeared by passage 6. Secondary analysis segregated clones into phenotypic age groups independent of donor animal age. Segregation identified n = 3 clones per group. At passage 3, the age-related change in the beta-adrenergic change was magnified. However, even with segregation, the adrenergic response was lost by passage 6. Our results show that early passaged clonal vascular smooth muscle cell cultures maintain their aging, adrenergic phenotype. Two separate strategies to identify age-representative phenotypes into later passage were unsuccessful.

Angiotensin II-induced aortic ring constriction is mediated by phosphatidylinositol 3-kinase/L-type calcium channel signaling pathway

Angiotensin II (AngII) is a crucial hormone that affects vasoconstriction and exerts hypertrophic effects on vascular smooth muscle cells. Here, we showed that phosphatidylinositol 3-kinase-dependent calcium mobilization plays pivotal roles in AngII-induced vascular constriction. Stimulation of rat aortic vascular smooth muscle cell (RASMC)-embedded collagen gel with AngII rapidly induced contraction. AngII-induced collagen gel contraction was blocked by pretreatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002) whereas ERK inhibitor (PD98059) was not effective. AngII-induced collagen gel contraction was significantly blocked by extracellular calcium depletion by EGTA or by nifedipine which is an L-type calcium channel blocker. In addition, AngII-induced calcium mobilization was also blocked by nifedipine and EGTA, whereas intracellular calcium store-depletion by thapsigargin was not effective. Finally, pretreatment of rat aortic ring with LY294002 and nifedipine significantly reduced AngII-induced constriction. Given these results, we suggest that PI3K-dependent activation of L-type calcium channels might be involved in AngII-induced vascular constriction.

CYP26 Inhibitor R115866 Increases Retinoid Signaling in Intimal Smooth Muscle Cells

OBJECTIVE

Intimal smooth muscle cells (SMCs) are dedifferentiated SMCs that have a powerful ability to proliferate and migrate. This cell-type is responsible for the development of intimal hyperplasia after vascular angioplasty. Retinoids, especially all-trans retinoid acid, are known to regulate many processes activated at sites of vascular injury, including modulation of SMC phenotype and inhibition of SMC proliferation. Intracellular levels of active retinoids are under firm control. A key enzyme is the all-trans retinoic acid-degrading enzyme cytochrome p450 isoform 26 (CYP26). Thus, an alternative approach to exogenous retinoid administration could be to increase the intracellular level of all-trans retinoic acid by blocking CYP26-mediated degradation of retinoids.

METHODS AND RESULTS

Vascular intimal and medial SMCs expressed CYP26A1 and B1 mRNA. Although medial cells remained unaffected, treatment with the CYP26-inhibitor R115866 significantly increased cellular levels of all-trans retinoic acid in intimal SMCs. The increased levels of all-trans retinoic acid induced retinoid-regulated genes and decreased mitogenesis.

CONCLUSIONS

Blocking of the CYP26-mediated catabolism mimics the effects of exogenously administrated active retinoids on intimal SMCs. Therefore, CYP26-inhibitors offer a potential new therapeutic approach to vascular proliferative disorders.

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.

A decrease in the amount and function of the stimulatory GTP-binding protein in the small resistance arteries of spontaneously hypertensive rats

We investigated the concentration of stimulatory GTP-binding protein (Gs protein) in the peripheral resistance arteries of spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and renovascular hypertensive rats (RHR). Changes in the function of Gs protein in SHR and WKY were also investigated by microcannulation techniques. The localization and abundance of Gs protein were determined immunohistochemically in 4-, 10- and 20-week-old SHR and age-matched WKY (control), as well as in RHR. Sections of the cremaster artery were stained with polyclonal antibodies to Gs protein. The concentration of Gs protein-like immunoreactivity in the cremaster artery was significantly lower in SHR at 4, 10, and 20 weeks of age, relative to that in age-matched WKY. In contrast, no significant differences were detected in the abundance of Gs between RHR and control rats. The dilatory response by isoproterenol in the presence of beta1-adrenoceptor blocker was lower in 4- and 10-week-old SHR than in age-matched WKY. The dilatory response by cholera toxin was also lower in SHR than in WKY for these two age groups. These results indicated that the amount and function of Gs protein in the peripheral resistance vessels in SHR was reduced. Since this change occurred before the onset of hypertension and no changes were seen in the secondary hypertensive rats, this change was not a secondary change due to hypertension. The impaired receptor-Gs protein-mediated signal transduction in the peripheral resistance arteries may be one of the possible mechanisms responsible for the pathogenesis of hypertension in SHR.

Cell volume and rate of proliferation, but not protein expression pattern, distinguish pup/intimal smooth muscle cells from subcultured adult smooth muscle cells

Smooth muscle cells from neonatal rats and from injured blood vessels grow with a characteristic cobblestone morphology that distinguishes them from adult smooth muscle cells. This has led to the proposition that there are two distinct types of smooth muscle cells with different proliferative capacity. Here we systematically compare the properties of subcultured adult smooth muscle cells in culture and clonal lines of cobblestone smooth muscle cells from both neonatal rats and injured vessels. The cobblestone smooth muscle cells have a significantly smaller average cell volume, estimated using two different flow cytometry measurements. However, the two types of smooth muscle cells have indistinguishable protein expression patterns when the levels of more than 20 different proteins (including cytoskeletal proteins, matrix proteins, cytokines, cytokine receptors, adhesion molecules and enzymes) are measured by quantitative immunofluorescence. Furthermore, in contrast to previous observations, we demonstrate that both types of smooth muscle cells secrete a powerful mitogenic activity. The higher cell density achieved by the cobblestone smooth muscle cells in culture was responsible for the earlier reports that this mitogenic activity was secreted only by cobblestone smooth muscle cells. We conclude that many of the differences seen between cobblestone smooth muscle cells and adult smooth muscle cells in vitro (proliferation rate, morphology, protein expression pattern, secretion of mitogenic activity) could be attributable to a stable difference in the median cell volume of the cultures.

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.

Kallikrein gene delivery inhibits vascular smooth muscle cell growth and neointima formation in the rat artery after balloon angioplasty

Tissue kallikrein cleaves kininogen substrate to produce vasoactive kinin peptides that have been implicated in the proliferation of vascular smooth muscle cells (VSMCs). To explore potential roles of the kallikrein-kinin system in vascular biology, we evaluated the effects of adenovirus-mediated human kallikrein gene delivery on the growth of primary cultured VSMCs and in balloon-injured rat artery in vivo. Kallikrein gene transfer into cultured rat VSMCs resulted in time-dependent secretion of recombinant human tissue kallikrein and inhibition of cell proliferation. Balloon angioplasty reduced endogenous rat tissue kallikrein mRNA and protein levels at the injured site. In rats that received adenovirus-mediated human kallikrein gene delivery, we observed a 39% reduction in intima/media ratio at the injured vessel after delivery compared with that of rats that received control virus (n=8, P<0.01). Icatibant, a specific bradykinin B(2) receptor antagonist, blocked the protective effect and reversed the intima/media ratio to that of the control rats (n=5, P<0.01). After gene delivery, human kallikrein mRNA was identified at the injured vessel and a 3-fold increase occurred in kininogenase activity. cAMP and cGMP levels in balloon-injured aorta increased significantly at 4, 7, and 14 days after kallikrein gene delivery, but icatibant abolished the increase. These results provide new insights into the role of the vascular kallikrein-kinin system and have significant implications for gene therapy to treat restenosis or atherosclerosis.

A decrease in the amount and function of inhibitory GTP-binding protein in the resistance small artery from spontaneously hypertensive rats

The inhibitory GTP-binding protein (Gi protein) plays an important role in regulation of vascular tone. Many studies have implicated the role of Gi protein in conduit vessels. However, the physiological role of Gi protein in the control of peripheral microvascular tone in hypertension has not been established yet. Therefore, we investigated the concentration of Gi protein in the peripheral resistance arteries and aorta in the spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY) and renovascular hypertensive rats (RHR), using immunohistochemical methods semiquantitatively. Changes in the function of Gi protein in relation to alpha2-adrenoceptor were also investigated by microcannulation techniques. We have shown that the amount of alpha2 subunits of Gi protein in the cremaster small artery was significantly lower in SHR aged 4 weeks and older than in age-matched WKY and that there were no significant differences between RHR and WKY. We also demonstrated that the function of Gi protein in relation to alpha2-adrenoceptor was already lower in SHR before the onset of hypertension. The quantitative and functional decline in Gi protein in the smooth muscle cells of peripheral small arteries were observed in SHR even before the onset of hypertension, whereas rats with secondary hypertension did not exhibit this finding.

AE anion exchanger mRNA and protein expression in vascular smooth muscle cells, aorta, and renal microvessels

Intracellular pH (pHi) is an important regulator of vascular smooth muscle cell (VSMC) tone, contractility, and intracellular Ca2+ concentration. Among the multiple transport processes that regulate VSMC pHi, Na(+)-independent Cl-/HCO3- exchange is the major process that acidifies VSMCs in response to an alkaline load. Here, we characterize, in native and cultured VSMCs, the expression of the AE family of band 3-related anion exchangers, the best studied of these Cl-/HCO3- exchangers. A 4.2-kb AE2 mRNA was present in aorta and in all cultured VSMCs tested. Cultured VSMCs and aorta both expressed a approximately 165-kDa AE2 polypeptide, but a approximately 115-kDa polypeptide was the major AE2-related protein in aorta. AE3 mRNA levels in VSMCs and in arterial tissue were significantly lower than those for AE2, but AE3 or related polypeptides were readily detected by immunoblot and immunolocalization experiments. The approximately 125-kDa AE3 polypeptide was present in an immortalized aortic VSMC line, but the predominant AE3 epitope in aorta and most cultured cells was associated with a polypeptide of M(r) approximately 80 kDa. These data demonstrate the expression in native arteries and in VSMCs of products of the AE2 and AE3 genes, which may contribute to Na(+)-independent Cl-/HCO3- exchange activity in these tissues and cells.

Establishment and characterization of a conditionally immortalized smooth muscle/myometrial-like cell line

A novel smooth muscle/myometrial-like cell line, SMU1-10, has been generated from the uterus of a H-2Kb-tsA58 transgenic mouse carrying a thermolabile SV40 large T-antigen gene. These cells grow continuously when maintained at the permissive temperature (33 degrees C) for the SV40 large T-antigen but stop dividing when placed at the non-permissive temperature (39 degrees C) and ultimately die within 3 weeks. All of the SMU1-10 cells produce smooth muscle alpha-actin (SMAA) at both 33 degrees C and 39 degrees C. A subset of the cells also contain smooth muscle gamma-actin (SMGA), a hallmark of smooth muscle differentiation, and the fraction of cells staining for this actin increases from about 1% when maintained for three days at 33 degrees C to as much as 30% at 39 degrees C over the same length of time. However, the appearance of SMGA in SMU1-10 cells appears to be regulated mainly at a post-transcriptional level since in situ hybridization indicates that all cells contain SMGA mRNA at both 33 degrees C and 39 degrees C. SMU1-10 cultures also contain smooth muscle myosin heavy chain (SM-MHC) and SM22 alpha, both of which are only found in smooth muscle of the adult mouse. Three additional smooth muscle (myometrium)-related markers, connexin 43, the thromboxane A2 receptor, and the progesterone receptor also are present in these cells. At the nonpermissive temperature for SV40 large T-antigen, the both level of SMGA mRNA and the number of cells staining for this actin are significantly increased in the presence of progesterone, a process that is similar to the upregulation of SMGA in the myometrium late in pregnancy. Overall, SMU1-10 cells provides a potentially useful in vitro model system to study smooth muscle/myometrial differentiation.

Modulation of intercellular communication between smooth muscle cells by growth factors and cytokines

We recently reported that tumor necrosis factor alpha is able to cause a dose-dependent and persistent reduction in gap junctional intercellular communication between primary human smooth muscle cells. In order to study whether this observed persistent reduction in gap junctional intercellular communication is a unique feature for tumor necrosis factor alpha, the present study focuses on the effects of other growth factors and cytokines on gap junctional intercellular communication. Platelet-derived growth factor AA and BB (PDGF-AA, PDGF-BB), basic fibroblast growth factor (bFGF), interleukin-6 and interferon-gamma were able to modulate gap junctional intercellular communication between primary human smooth muscle cells in vitro. However, our results demonstrate that the magnitude and nature of the observed effects are growth factor- and cytokine-specific. PDGF-AA, PDGF-BB and interleukin-6 caused a transient reduction in gap junctional intercellular communication, while bFGF induced a transient increase in gap junctional intercellular communication. Interferon-gamma was shown to be capable of causing a persistent reduction in gap junctional intercellular communication. In addition, PDGF-AA, PDGF-BB, bFGF, interleukin-6, interferon-gamma and tumor necrosis factor alpha all stimulated smooth muscle cell proliferation. These observations suggest a more complex relationship between modulation of gap junctional intercellular communication and cell proliferation than current hypotheses imply. The implications of the observed effects of growth factors and cytokines on gap junctional intercellular communication between smooth muscle cells in relation to the process of atherosclerosis is discussed.

Distinct rat aortic smooth muscle cells differ in versican/PG-M expression

Smooth muscle cells (SMCs) with distinct phenotypes are present in blood vessels, and distinct culture types appear when SMCs are maintained in vitro. For example, cultured SMCs from rat adult media grow as bipolar cells, which differ in gene expression from the predominantly cobblestone-shaped SMCs from rat pup aortas and rat neointimas that we call pi SMCs. Since proteoglycans are present at different concentrations in the normal intima and media and are elevated in atherosclerotic plaque, we sought to determine whether pi and adult medial SMC types synthesize different or unique proteoglycans that are characteristic of each phenotype. [35S]sulfate-labeled proteoglycans were purified by ion-exchange chromatography. An adult medial SMC line synthesized a large proteoglycan (0.2 Kav on Sepharose CL-2B) that was not detectable in a pi SMC line. Digestion of this proteoglycan with chondroitin ABC lyase revealed three core glycoproteins of 330, 370, and 450 kD. By Western blot analysis, the two smallest of these reacted with two antibodies to the human fibroblast proteoglycan versican. RNAs hybridizing to versican probes were found only in adult medial-type SMCs, including an adult medial type clone from pup aorta, by Northern blot analysis. Both SMC types synthesize RNAs that hybridize to probes for other proteoglycans, such as perlecan, biglycan, and decorin. We conclude that rat pi SMC cultures, unlike monkey, human, and rat adult medial SMC cultures, express little or no versican. This difference in expression may be responsible for the different morphologies and growth properties of the two cell types.

Restricted expression of homeobox genes distinguishes fetal from adult human smooth muscle cells

Smooth muscle cell plasticity is considered a prerequisite for atherosclerosis and restenosis following angioplasty and bypass surgery. Identification of transcription factors that specify one smooth muscle cell phenotype over another therefore may be of major importance in understanding the molecular basis of these vascular disorders. Homeobox genes exemplify one class of transcription factors that could govern smooth muscle cell phenotypic diversity. Accordingly, we screened adult and fetal human smooth muscle cell cDNA libraries with a degenerate oligonucleotide corresponding to a highly conserved region of the homeodomain with the idea that homeobox genes, if present, would display a smooth muscle cell phenotype-dependent pattern of expression. No homeobox genes were detected in the adult human smooth muscle cell library; however, five nonparalogous homeobox genes were uncovered from the fetal library (HoxA5, HoxA11, HoxB1, HoxB7, and HoxC9). Northern blotting of adult and fetal tissues revealed low and restricted expression of all five homeobox genes. No significant differences in transcripts of HoxA5, HoxA11, and HoxB1 were detected between adult or fetal human smooth muscle cells in culture. HoxB7 and HoxC9, however, showed preferential mRNA expression in fetal human smooth muscle cells that appeared to correlate with the age of the donor. This phenotype-dependent expression of homeobox genes was also noted in rat pup versus adult smooth muscle cells. While similar differences in gene expression have been reported between subsets of smooth muscle cells from rat vessels of different-aged animals or clones of rat smooth muscle, our findings represent a demonstration of a transcription factor distinguishing two human smooth muscle cell phenotypes.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

Measurement of Ca2+ pump-mediated efflux in hypertension

Ca2+ homeostasis has been a prominent research area in the study of hypertension. There is convincing evidence that hypertension in spontaneously hypertensive rats is characterized by enhanced Ca2+ influx in various cell types. It is, however, still unclear whether hypertension is associated with reduced or enhanced Ca2+ efflux. Reduced Ca2+ efflux would augment the effects of enhanced Ca2+ influx. However, enhanced Ca2+ extrusion may occur as an adaptive process to minimize the effects of Ca2+ overload. This question remains unanswered because of inconsistent results obtained using a variety of experimental techniques. In this article we have reviewed the research findings and discuss existing and possible new techniques to assess Ca2+ efflux in hypertension, with particular attention to vascular smooth muscle. We have focused mainly on studies using the spontaneously hypertensive rat and discuss its appropriateness as a model for essential hypertension.

Identification and characterization of a novel angiotensin binding site in cultured vascular smooth muscle cells that is specific for the hexapeptide (3-8) fragment of angiotensin II, angiotensin IV

This study demonstrates the existence of a previously unrecognized class of angiotensin binding sites on vascular smooth muscle that exhibit high affinity and specificity for the hexapeptide (3-8) fragment of angiotensin II (AngIV). Binding of [125I]AngIV is saturable, reversible and describes a pharmacologic profile that is distinct and separate from the classic AT1 or AT2 angiotensin receptors. Saturation binding studies utilizing cultured vascular smooth muscle cells obtained from bovine aorta (BVSM) revealed that [125I]AngIV bound to a single high affinity site with an associated Hill coefficient of 0.99 +/- 0.003, exhibiting a KD = 1.85 +/- 0.45 nM and a corresponding Bmax = 960 +/- 100 fmol mg-1 protein. Competition binding curves in BVSM demonstrated the following rank order effectiveness: AngIV > AngII(3-7) >> AngIII > Sar1,Ile8 AngII > AngII > AngII(1-7) > AngII(4-8), DuP 753, PD123177. The presence of the non-hydrolyzable GTP analog GTP gamma S, had no effect on [125I]AngIV binding affinity in BVSM. The presence of this novel angiotensin binding site on smooth muscle in high concentration suggests the possibility that this system may play an important, yet unrecognized role in vascular control.

Development and characterization of a cloned rat pulmonary arterial smooth muscle cell line that maintains differentiated properties through multiple subcultures

BACKGROUND

Pulmonary hypertension is associated with abnormal pulmonary arterial contractility and growth. The mechanisms for these abnormalities are largely unknown. To study these processes, we sought to develop an in vitro system. Even though cultured aortic and pulmonary artery smooth muscle cells (SMCs) have been of considerable value in studying smooth muscle biology, one drawback of this system has been that these cells often lose differentiated properties in an unpredictable manner when they are passaged in culture. In addition, there appear to be significant differences in physiological and pathological responses between the systemic and pulmonary circulations, many of which could be directly related to the smooth muscle. We therefore established a cloned population of rat pulmonary arterial SMCs (PASMCs) that maintain differentiated properties through multiple subcultures.

METHODS AND RESULTS

PASMCs were obtained initially by enzymatic dissociation from pulmonary arteries of adult Sprague-Dawley rats. From these cells, clones were isolated. The cloned cells retained expression of functional surface receptors for angiotensin II, norepinephrine, and alpha-thrombin and high levels of the smooth muscle isoforms of alpha-actin, myosin heavy chain, myosin regulatory light chain, and alpha-tropomyosin mRNAs even after multiple passages. The cells could also be transfected and processed exogenous transcripts in a smooth muscle-specific fashion.

CONCLUSIONS

These cloned PASMCs retain many differentiated characteristics and should be valuable for future studies of pulmonary vascular smooth muscle cell biology.