Induction of polyploidy in cultures of neonatal rat aortic smooth muscle cells

PCSK9 (Proprotein Convertase Subtilisin/Kexin Type 9) Triggers Vascular Smooth Muscle Cell Senescence and Apoptosis: Implication of Its Direct Role in Degenerative Vascular Disease

OBJECTIVE

PCSK9 (proprotein convertase subtilisin/kexin type 9) plays a critical role in cholesterol metabolism via the PCSK9-LDLR (low-density lipoprotein receptor) axis in the liver; however, evidence indicates that PCSK9 directly contributes to the pathogenesis of various diseases through mechanisms independent of its LDL-cholesterol regulation. The objective of this study was to determine how PCSK9 directly acts on vascular smooth muscle cells (SMCs), contributing to degenerative vascular disease. Approach and Results: We first examined the effects of PCSK9 on cultured human aortic SMCs. Overexpression of PCSK9 downregulated the expression of ApoER2 (apolipoprotein E receptor 2), a known target of PCSK9. Treatment with soluble recombinant human ApoER2 or the DNA synthesis inhibitor, hydroxyurea, inhibited PCSK9-induced polyploidization and other cellular responses of human SMCs. Treatment with antibodies against ApoER2 resulted in similar effects to those observed with PCSK9 overexpression. Inducible, SMC-specific knockout of Pcsk9 accelerated neointima formation in mouse carotid arteries and reduced age-related arterial stiffness. PCSK9 was expressed in SMCs of human atherosclerotic lesions and abundant in the "shoulder" regions of vulnerable atherosclerotic plaques. PCSK9 was also expressed in SMCs of abdominal aortic aneurysm, which was inversely related to the expression of smooth muscle α-actin.

CONCLUSIONS

Our findings demonstrate that PCSK9 inhibits proliferation and induces polyploidization, senescence, and apoptosis, which may be relevant to various degenerative vascular diseases.

A differentiated Ca2+ signalling phenotype has minimal impact on myocardin expression in an automated differentiation assay using A7r5 cells

Vascular smooth muscle cells are unusual in that differentiated, contractile cells possess the capacity to "de-differentiate" into a synthetic phenotype that is characterized by being replicative, secretory, and migratory. One aspect of this phenotypic modulation is a shift from voltage-gated Ca²⁺ signalling in electrically coupled, differentiated cells to increased dependence on store-operated Ca²⁺ entry and sarcoplasmic reticulum Ca²⁺ release in synthetic cells. Conversely, an increased voltage-gated Ca²⁺ entry is seen when proliferating A7r5 smooth muscle cells quiesce. We asked whether this change in Ca²⁺ signalling was linked to changes in the expression of the phenotype-regulating transcriptional co-activator myocardin or α-smooth muscle actin, using correlative epifluorescence Ca²⁺ imaging and immunocytochemistry. Cells were cultured in growth media (DMEM, 10% serum, 25 mM glucose) or differentiation media (DMEM, 1% serum, 5 mM glucose). Coinciding with growth arrest, A7r5 cells became electrically coupled, and spontaneous Ca²⁺ signalling showed increasing dependence on L-type voltage-gated Ca²⁺ channels that were blocked with nifedipine (5 μM). These synchronized oscillations were modulated by ryanodine receptors, based on their sensitivity to dantrolene (5 μM). Actively growing cultures had spontaneous Ca²⁺ transients that were insensitive to nifedipine and dantrolene but were blocked by inhibition of the sarco-endoplasmic reticulum ATPase with cyclopiazonic acid (10 μM). In cells treated with differentiation media, myocardin and αSMA immunoreactivity increased prior to changes in the Ca²⁺ signalling phenotype, while chronic inhibition of voltage-gated Ca²⁺ entry modestly increased immunoreactivity of myocardin. Stepwise regression analyses suggested that changes in myocardin expression had a weak relationship with Ca²⁺ signalling synchronicity, but not frequency or amplitude. In conclusion, we report a 96-well assay and analytical pipeline to study the link between Ca²⁺ signalling and smooth muscle differentiation. This assay showed that changes in the expression of two molecular differentiation markers (myocardin and αSMA) tended to precede changes in the Ca²⁺ signalling phenotype.

Smooth Muscle Diversity in Arterial Wound Repair*

Repair of arterial injury results in formation of a new structure, a neointima, that causes luminal narrowing. Smooth muscle cell (SMC) properties required for neointima formation are also found in nascent SMCs of developing blood vessels in the embryo (e.g., proliferation, extracellular matrix synthesis, cell migration). We isolated 2 distinct types of SMC from aortic media of newborn rats that were distinguished by cell shape, secretion of platelet-derived growth factor (PDGF) and insulin-like growth factor-1 (IGF-1), and expression of PDGF-B and PDGF α-receptor genes. These two SMC types did not interconvert over many cell generations in vitro. Adult rat aorta yields only one SMC type, suggesting that the “pup” SMC variant is developmentally regulated. However, SMC with the “pup” phenotype reappear in the adult artery wall during neointima formation after balloon catheter injury. These observations raise the possibility that SMC proliferation and arterial remodeling during development, repair and disease of the artery wall might depend upon a SMC subpopulation with special properties.

Best practices for naming, receiving, and managing cells in culture

One of the first considerations in using an existing cell line or establishing a new a cell line is the detailed proactive planning of all phases of the cell line management. It is necessary to have a well-trained practitioner in best practices in cell culture who has experience in receiving a new cell line into the laboratory, the correct and appropriate use of a cell line name, the preparation of cell banks, microscopic observation of cells in culture, growth optimization, cell count, cell subcultivation, as well as detailed protocols on how to expand and store cells. Indeed, the practitioner should best manage all activities of cell culture by ensuring that the appropriate certified facilities, equipment, and validated supplies and reagents are in place.

FAM3B mediates high glucose-induced vascular smooth muscle cell proliferation and migration via inhibition of miR-322-5p

The proliferation and migration of vascular smooth muscle cells (VSMCs) play an essential role during the development of cardiovascular diseases (CVDs). While many factors potentially contribute to the abnormal activation of VSMCs, hyperglycemia is generally believed to be a major causative factor. On the other hand, FAM3B (named PANDER for its secretory form) is a uniquely structured protein strongly expressed within and secreted from the endocrine pancreas. FAM3B is co-secreted with insulin from the β-cell upon glucose stimulation and regulates glucose homeostasis. In the present study, we sought to determine the roles of FAM3B in the regulation of VSMC physiology, especially under the hyperglycemic condition. We found that FAM3B expression was induced by hyperglycemia both in vivo and in vitro. FAM3B knockdown inhibited, whereas FAM3B overexpression accelerated VSMC proliferation and migration. At the molecular level, FAM3B inhibited miR-322-5p expression, and enforced expression of miR-322-5p antagonized FAM3B-induced VSMC proliferation and migration, suggesting that FAM3B facilitated VSMC pathological activation via miR-322-5p. Taken together, FAM3B mediates high glucose-induced VSMC proliferation and migration via inhibition of miR-322-5p. Thus, FAM3B may therefore serve as a novel therapeutic target for diabetes-related CVDs.

Evodiamine inhibits PDGF‑BB‑induced proliferation of rat vascular smooth muscle cells through the suppression of cell cycle progression and oxidative stress

Vascular smooth muscle cell (VSMC) proliferation is a key event in the development of in-stent restenosis. Evodiamine is an indole alkaloid extracted from the Chinese medicine, evodia, and has been shown to inhibit tumor cell proliferation and protect the cardiovascular system. However, whether evodiamine affects VSMC proliferation remains to be elucidated. Therefore, the present study examined the effects and the mechanisms of action of evodiamine on the proliferation of rat VSMCs. The cells were treated with evodiamine alone or in combination with platelet-derived growth factor-BB (PDGF-BB) stimulation. It was found that evodiamine inhibited PDGF-BB-induced VSMC proliferation in a dose-dependent manner, without inducing cell death. Evodiamine also retarded cell cycle progression, evidenced by the suppression of the expression of cell cycle-promoting cyclin proteins and cyclin-dependent kinases. In addition, evodiamine attenuated the PDGF-BB-induced phosphorylation of mitogen-activated protein kinases p38 and extracellular signal-regulated kinases 1/2, however, it had no effect on the phosphorylation of Akt. Evodiamine also inhibited the increase of reactive oxygen species generation and upregulated the mRNA expression levels of genes encoding antioxidant enzymes. These findings provide important insights into the mechanisms underlying the vasoprotective actions of evodiamine and suggest that it may be a useful therapeutic agent for the treatment of vascular occlusive disease.

Thymoquinone Inhibits Angiotensin II-Induced Proliferation and Migration of Vascular Smooth Muscle Cells Through the AMPK/PPARγ/PGC-1α Pathway

The proliferation and migration of vascular smooth muscle cells (VSMCs) play crucial roles in the pathogenesis of diabetes and its complications. Thymoquinone (TQ) is the primary bioactive component of Nigella sativa L. seed oil, which exhibits antihyperglycemic effect in diabetic rats, but its role in VSMC proliferation and migration has not been investigated. The results of MTT assay and flow cytometry assay indicated that TQ dose-dependently inhibited angiotensin II (Ang II)-induced VSMCs' cell cycle progression, as well as cyclin D1 expression, whereas p21 expression was altered conversely. TQ dose-dependently suppressed Ang II-induced VSMC migration accompanied by reduced MMP-9 expression. In addition, we observed the elevated reactive oxygen species (ROS) generation and NADPH oxidase activity and reduced superoxide dismutase activity in Ang II-treated VSMCs, which were dose-dependently reversed by TQ. Western blot analysis indicated that TQ dose-dependently restored Ang II-inhibited expression of p-AMPK, PPARγ, and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) proteins. Furthermore, adenosine monophosphate-activated protein kinase (AMPK) inhibitor Compound C and PGC-1α siRNA transfection abrogated the activation of TQ on Ang II-inhibited AMPK/PPARγ/PGC-1α signaling, but abolished the inhibitory effects of TQ on Ang II-induced VSMC proliferation and migration, as well as ROS generation. Taken together, these results demonstrated that TQ inhibited Ang II-induced VSMC proliferation and migration through the AMPK/PPARγ/PGC-1α pathway.

Imperatorin derivative OW1 inhibits the upregulation of TGF-β and MMP-2 in renovascular hypertension-induced cardiac remodeling

Chronic hypertension induces vascular and cardiac remodeling. OW1 is a novel imperatorin derivative that was previously reported to inhibit vascular remodeling and improve kidney function affected by hypertension. In the present study, the effect of OW1 on the cardiac remodeling induced by hypertension was investigated. OW1 inhibited vascular smooth muscle cell (VSMC) proliferation and the phenotypic modulation of VSMCs induced by angiotensin II (Ang II). The OW1-induced vasodilatation of rat cardiac arteries was evaluated in vitro. Renovascular hypertensive rats were developed using the two-kidney one-clip method and treated with OW1 (40 or 80 mg/kg/day) or nifedipine (30 mg/kg per day) for 5 weeks. OW1 markedly reduced the systolic and diastolic blood pressure compared with that in the hypertension group or the respective baseline value during the first week. OW1 also reduced cardiac weight, and the concentrations of Ang II, aldosterone and transforming growth factor-β1 (TGF-β1). Histological examination demonstrated that OW1 exerted an inhibitory effect on vascular and cardiac remodeling. These inhibitory effects were associated with decreased cardiac levels of Ang II, matrix metalloproteinase-2 and TGF-β₁ in the hypertensive rats. In summary, OW1 exhibited a clear antihypertensive effect. More importantly, it inhibited vascular and cardiovascular remodeling, which may reduce the risk of hypertension-induced cardiovascular diseases. These results have potential implications in the development of new antihypertensive drugs.

Evodiamine Attenuates PDGF-BB-Induced Migration of Rat Vascular Smooth Muscle Cells through Activating PPARγ

The uncontrolled migration of vascular smooth muscle cells (VSMCs) into the intima is a critical process in the development of atherosclerosis. Evodiamine, an indole alkaloid extracted from the Chinese medicine evodia, has been shown to inhibit tumor cell invasion and protect the cardiovascular system, but its effects on VSMCs remain unknown. In the present study, we investigated the inhibitory effects of evodiamine on the platelet-derived growth factor-BB (PDGF-BB)-induced VSMC migration using wound healing and transwell assays, and assessed its role in decreasing the protein levels of matrix metalloproteinases and cell adhesion molecules. More importantly, we found that evodiamine activated the expression and nuclear translocation of peroxisome proliferator-activated receptor γ (PPARγ). Inhibition of PPARγ activity by using its antagonist T0070907 and its specific siRNA oligonucleotides significantly attenuated the inhibitory effects of evodiamine on VSMC migration. Taken together, our results indicate a promising anti-atherogenic effect of evodiamine through attenuation of VSMC migration by activating PPARγ.

Hyperlipidaemia impairs the circadian clock and physiological homeostasis of vascular smooth muscle cells via the suppression of Smarcd1

Many mammalian physiological processes show diurnal oscillation and are controlled by a circadian clock. Disruption of the circadian clock has been implicated in the pathogenesis of cardiovascular disorders, but the mechanism through which clock and vessel function are integrated is unclear. Here we show that the rhythmicity of key clock genes and Smarcd1, a member of the SWI/SNF chromatin remodelling complex family, is suppressed in the layer of vascular smooth muscle cells (VSMCs) of the thoracic aorta of hyperlipidaemic rats fed a high-fat diet (HFD). Smarcd1 stimulates the transcription of clock genes, notably bmal1, through co-activation of the nuclear orphan receptor RORα in VSMCs. The co-activation of Smarcd1 and RORα is dependent on the mediation of PGC-1α, a transcriptional co-activator. Pathophysiologically, Smarcd1 inhibits VSMC proliferation and migration by blocking cell cycle re-entry and via the activation of kinase signalling pathways. Our results demonstrate that Smarcd1 is a critical node integrating the circadian clock and VSMC physiological homeostasis.

Lithium chloride inhibits vascular smooth muscle cell proliferation and migration and alleviates injury-induced neointimal hyperplasia via induction of PGC-1α

The proliferation and migration of vascular smooth muscle cells (VSMCs) contributes importantly to the development of in-stent restenosis. Lithium has recently been shown to have beneficial effects on the cardiovascular system, but its actions in VSMCs and the direct molecular target responsible for its action remains unknown. On the other hand, PGC-1α is a transcriptional coactivator which negatively regulates the pathological activation of VSMCs. Therefore, the purpose of the present study is to determine if lithium chloride (LiCl) retards VSMC proliferation and migration and if PGC-1α mediates the effects of lithium on VSMCs. We found that pretreatment of LiCl increased PGC-1α protein expression and nuclear translocation in a dose-dependent manner. MTT and EdU incorporation assays indicated that LiCl inhibited serum-induced VSMC proliferation. Similarly, deceleration of VSMC migration was confirmed by wound healing and transwell assays. LiCl also suppressed ROS generation and cell cycle progression. At the molecular level, LiCl reduced the protein expression levels or phosphorylation of key regulators involved in the cell cycle re-entry, adhesion, inflammation and motility. In addition, in vivo administration of LiCl alleviated the pathophysiological changes in balloon injury-induced neointima hyperplasia. More importantly, knockdown of PGC-1α by siRNA significantly attenuated the beneficial effects of LiCl on VSMCs both in vitro and in vivo. Taken together, our results suggest that LiCl has great potentials in the prevention and treatment of cardiovascular diseases related to VSMC abnormal proliferation and migration. In addition, PGC-1α may serve as a promising drug target to regulate cardiovascular physiological homeostasis.

Tunicamycin inhibits PDGF-BB-induced proliferation and migration of vascular smooth muscle cells through induction of HO-1

The abnormal proliferation and migration of vascular smooth muscle cell (VSMC), which is triggered by various external stimuli, contributes importantly to the pathogenesis of atherosclerosis and restenosis. Recent studies indicate that the endoplasmic reticulum (ER) stress is intensively involved in the pathophysiological changes of VSMCs by various stimuli. However, the direct effects of ER stress on VSMC proliferation and migration remain unknown. In this study, we found that pretreatment with tunicamycin (Tm), an ER stress inducer, significantly inhibited platelet-derived growth factor (PDGF)-BB-induced VSMC proliferation and migration in a dose-dependent manner without causing significant apoptosis. Tm stimulated the expression of the antioxidant gene heme oxygenase-1 (HO-1) both at the transcriptional and translational levels, while reducing phosphorylation and activation of mitogen-activated protein (MAP) kinases. The negative regulative effects of Tm were associated with a decrease in cyclins and cyclin-dependent kinases (CDKs) activation. More importantly, HO-1 siRNA partially abolished the beneficial effects of Tm on VSMCs. These results indicate that Tm-induced ER stress provides protection against the abnormal VSMC activation by PDGF-BB, which may be mediated by the induction of HO-1 and blockade of cell cycle reentry.

Naringenin inhibits TNF-α induced VSMC proliferation and migration via induction of HO-1

Vascular smooth muscle cell (VSMC) proliferation and migration, which is triggered by various inflammatory stimuli, contributes importantly to the pathogenesis of atherosclerosis and restenosis. Naringenin is a citrus flavonoid with both lipid-lowering and insulin-like properties. Here, we investigated whether naringenin affects TNF-α-induced VSMC proliferation and migration and if so, whether heme oxygenase-1 (HO-1) is involved. Rat VSMCs were treated with naringenin alone or in combination of TNF-α stimulation. We found that naringenin induced HO-1 mRNA and protein levels, as well as its activity, in VSMCs. Naringenin inhibited TNF-α-induced VSMC proliferation and migration in a dose-dependent manner. Mechanistic study demonstrated that naringenin prevented ERK/MAPK and Akt phosphorylation while left p38 MAPK and JNK unchanged. Naringenin also blocked the increase of ROS generation induced by TNF-α. More importantly, the specific HO-1 inhibitor ZnPP IX or HO-1 siRNA partially abolished the beneficial effects of naringenin on VSMCs. These results suggest that naringenin may serve as a novel drug in the treatment of these pathologies by inducing HO-1 expression/activity and subsequently decreasing VSMC proliferation and migration.

Effect of PGC-1α on proliferation, migration, and transdifferentiation of rat vascular smooth muscle cells induced by high glucose

We assessed the role of PGC-1α (PPARγ coactivator-1 alpha) in glucose-induced proliferation, migration, and inflammatory gene expression of vascular smooth muscle cells (VSMCs). We carried out phagocytosis studies to assess the role of PGC-1α in transdifferentiation of VSMCs by flow cytometry. We found that high glucose stimulated proliferation, migration and inflammatory gene expression of VSMCs, but overexpression of PGC-1α attenuated the effects of glucose. In addition, overexpression of PGC-1α decreased mRNA and protein level of VSMCs-related genes, and induced macrophage-related gene expression, as well as phagocytosis of VSMCs. Therefore, PGC-1α inhibited glucose-induced proliferation, migration and inflammatory gene expression of VSMCs, which are key features in the pathology of atherosclerosis. More importantly, PGC-1α transdifferentiated VSMCs to a macrophage-like state. Such transdifferentiation possibly increased the portion of VSMCs-derived foam cells in the plaque and favored plaque stability.

The inhibitory effect of dexamethasone on platelet-derived growth factor-induced vascular smooth muscle cell migration through up-regulating PGC-1α expression

Dexamethasone has been shown to inhibit vascular smooth muscle cell (VSMC) migration, which is required for preventing restenosis. However, the mechanism underlying effect of dexamethasone remains unknown. We have previously demonstrated that peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 alpha (PGC-1α) can inhibit VSMC migration and proliferation. Here, we investigated the role of PGC-1α in dexamethasone-reduced VSMC migration and explored the possible mechanism. We first examined PGC-1α expression in cultured rat aortic VSMCs. The results revealed that incubation of VSMCs with dexamethasone could significantly elevate PGC-1α mRNA expression. In contrast, platelet-derived growth factor (PDGF) decreased PGC-1α expression while stimulating VSMC migration. Mechanistic study showed that suppression of PGC-1α by small interfering RNA strongly abrogated the inhibitory effect of dexamethasone on VSMC migration, whereas overexpression of PGC-1α had the opposite effect. Furthermore, an analysis of MAPK signal pathways showed that dexamethasone inhibited ERK and p38 MAPK phosphorylation in VSMCs. Overexpression of PGC-1α decreased both basal and PDGF-induced p38 MAPK phosphorylation, but it had no effect on ERK phosphorylation. Finally, inhibition of PPARγ activation by a PPARγ antagonist GW9662 abolished the suppressive effects of PGC-1α on p38 MAPK phosphorylation and VSMC migration. These effects of PGC-1α were enhanced by a PPARγ agonist troglitazone. Collectively, our data indicated for the first time that one of the anti-migrated mechanisms of dexamethasone is due to the induction of PGC-1α expression. PGC-1α suppresses PDGF-induced VSMC migration through PPARγ coactivation and, consequently, p38 MAPK inhibition.

Celastrol attenuates hypertension-induced inflammation and oxidative stress in vascular smooth muscle cells via induction of heme oxygenase-1

BACKGROUND

The aim of this study was to investigate the potential beneficial effects of celastrol, a compound with anti-inflammatory and antioxidant properties, on vascular smooth muscle cells (VSMCs) under hypertensive conditions.

METHODS

Hypertension was induced in rats by fructose feeding. Hypertensive rats were injected with celastrol, and systolic blood pressure (SBP) and diastolic BP (DBP) were monitored by the tail-cuff method. Insulin sensitivity in animals was measured by glucose tolerance test (GTT). Serum levels of inflammatory cytokines were determined by enzyme-linked immunosorbent assay. Real-time reverse transcription-PCR and western blot were applied to quantify mRNA and protein levels in tissues and primary cultured VSMCs. Generation of reactive oxygen species (ROS) was measured using lucigenin chemiluminescence for tissue homogenates and dichlorodihydrofluorescein diacetate staining for VSMC cells.

RESULTS

Celastrol decreased both SBP and DBP while improving insulin sensitivity in fructose-induced hypertensive rats. Celastrol also inhibited vascular and cardiac hypertrophy. Hypertension augmented circulating and mRNA levels of inflammatory cytokines, and celastrol treatment suppressed their induction. Celastrol also blocked activation of extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) and Akt signaling both in vivo and in vitro. More importantly, celastrol increased heme oxygenase-1 (HO-1) expression and activity, whereas zinc protoporphyrin 9 (ZnPP9), a HO-1 inhibitor, partially abolished the beneficial effects of celastrol on hypertensive rats and VSMCs. Finally, ROS generation in tissue homogenates and in VSMCs was reduced by celastrol.

CONCLUSIONS

These findings suggest that celastrol attenuates hypertension-induced inflammation and oxidative stress in VSMCs via HO-1 induction, and this compound may therefore serve as a novel drug to treat hypertension.

17beta-estradiol inhibits oleic acid-induced rat VSMC proliferation and migration by restoring PGC-1alpha expression

Estrogen shows a vasoprotective role through inhibiting the proliferation and migration of vascular smooth muscle cells (VSMCs). The mechanism underlying the effect of estrogen, however, is not completely understood. Here, we explored the role of peroxisome proliferator-activated receptor-gamma (PPARgamma) coactivator-1alpha (PGC-1alpha) in estrogen-mediated vasoprotection. Firstly, we showed that oleic acid (OA) decreased PGC-1alpha expression while stimulating VSMC proliferation and migration. In contrast, administration of VSMCs with 17beta-estradiol (E(2), 1 or 10nM) significantly restored OA-decreased PGC-1alpha expression, treatment with 10nM E(2) almost completely abolished OA-induced VSMC proliferation and migration. Secondly, by using PGC-1alpha siRNA, the inhibitory effect of E(2) on VSMC growth is strongly reduced via suppressing PGC-1alpha expression, indicating that E(2) may exert its role through restoring PGC-1alpha. Finally, E(2) (10nM) treatment inhibits OA-induced extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, however, suppression of PGC-1alpha expression abolishes this inhibitory effect of E(2). Our findings demonstrate for the first time that in OA-stimulated rat VSMCs, treatment with E(2) (1 or 10nM) diminishes VSMC proliferation and migration via restoring OA-decreased PGC-1alpha expression. This observation offers a novel molecular basis of the vasoprotective effect of estrogen.

PGC-1α attenuates neointimal formation via inhibition of vascular smooth muscle cell migration in the injured rat carotid artery

Oxidative stress contributes significantly to the migration of vascular smooth muscle cells (VSMCs), the major pathogenic process of vascular diseases, but the mechanism remains unclear. In the present study, we explored the role of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a major regulator of mitochondrial biogenesis and energy balance, in VSMC migration in vitro and in vivo. Overexpression of PGC-1α in cultured VSMCs led to a 74.5% reduction of migration activity and mitochondrial ROS generation by the increased expression of antioxidative proteins such as SOD-2 in the mitochondria. The knockdown of PGC-1α by specific small interfering (si)RNA markedly augmented VSMC migration activity and greatly reduced mitochondrial antioxidative protein expression. Furthermore, knockdown of SOD-2 expression by siRNA greatly reversed the inhibitory effect of PGC-1α overexpression on VSMC migration. In a rat carotid balloon injury model, adenovirus-mediated overexpression of PGC-1α greatly reduced neointimal formation (ratio of intima to media: 0.78 ± 0.09 vs. 1.45 ± 0.18 in the adenovirus + green fluorescent protein gene- transfected group). Moreover, the expression of SOD-2 was significantly increased in vivo in local vessels after injury in the PGC-1α-overexpressing group. These data strongly suggest that PGC-1α inhibits VSMC migration and neointimal formation after vascular injury in rats, mainly by upregulating the expression of the mitochondrial antioxidant enzyme SOD-2.

PGC-1alpha inhibits oleic acid induced proliferation and migration of rat vascular smooth muscle cells

Background

Oleic acid (OA) stimulates vascular smooth muscle cell (VSMC) proliferation and migration. The precise mechanism is still unclear. We sought to investigate the effects of peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 alpha (PGC-1α) on OA-induced VSMC proliferation and migration.

Principal Findings

Oleate and palmitate, the most abundant monounsaturated fatty acid and saturated fatty acid in plasma, respectively, differently affect the mRNA and protein levels of PGC-1α in VSMCs. OA treatment resulted in a reduction of PGC-1α expression, which may be responsible for the increase in VSMC proliferation and migration caused by this fatty acid. In fact, overexpression of PGC-1α prevented OA-induced VSMC proliferation and migration while suppression of PGC-1α by siRNA enhanced the effects of OA. In contrast, palmitic acid (PA) treatment led to opposite effects. This saturated fatty acid induced PGC-1α expression and prevented OA-induced VSMC proliferation and migration. Mechanistic study demonstrated that the effects of PGC-1α on VSMC proliferation and migration result from its capacity to prevent ERK phosphorylation.

Conclusions

OA and PA regulate PGC-1α expression in VSMCs differentially. OA stimulates VSMC proliferation and migration via suppression of PGC-1α expression while PA reverses the effects of OA by inducing PGC-1α expression. Upregulation of PGC-1α in VSMCs provides a potential novel strategy in preventing atherosclerosis.

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.

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

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

IGF-binding protein-4 expression and IGF-binding protein-4 protease activity are regulated coordinately in smooth muscle during postnatal development and after vascular injury

Recent studies support a critical role for the paracrine IGF/IGF-binding protein system in the regulation of vascular smooth muscle cell growth. In this study we have explored the hypothesis that the abundance of individual IGF-binding proteins in smooth muscle is subject to regulation during postnatal life and in response to injury. IGF-binding protein-2 was the predominant binding protein secreted by neonatal rat vascular smooth muscle cells, whereas IGF-binding protein-4 was most prevalent in adult vascular smooth muscle cells coincident with increased IGF-binding protein-4 protease activity. After arterial injury, IGF-binding protein-4 mRNA increased, associated with greater IGF-binding protein-4 proteolytic activity, resulting in stable steady state levels of the IGF-binding protein-4 protein. Expression of pregnancy-associated plasma protein A mRNA, recently identified as an IGF-binding protein-4 protease, was expressed at higher levels in adult than neonatal vascular smooth muscle cell lines, but did not change significantly after arterial injury. The peak of immunoreactive pregnancy-associated plasma protein A from hydrophobic interaction chromatography fractions of smooth muscle cell-conditioned medium coincided, but did not fully overlap, with the fractions containing maximal IGF-binding protein-4 protease activity. In conclusion, our data point to a developmental switch from IGF-binding protein-2 to IGF-binding protein-4 in vascular smooth muscle cells postnatally. Moreover, IGF-binding protein-4 expression is coregulated with IGF-binding protein-4 protease activity, suggesting that biosynthesis and degradation of this binding protein are coordinated events important for regulating biological activity of IGF-I.

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.

Vascular smooth muscle cells spontaneously adopt a skeletal muscle phenotype: a unique Myf5(-)/MyoD(+) myogenic program

Smooth and skeletal muscle tissues are composed of distinct cell types that express related but distinct isoforms of the structural genes used for contraction. These two muscle cell types are also believed to have distinct embryological origins. Nevertheless, the phenomenon of a phenotypic switch from smooth to skeletal muscle has been demonstrated in several in vivo studies. This switch has been minimally analyzed at the cellular level, and the mechanism driving it is unknown. We used immunofluorescence and RT-PCR to demonstrate the expression of the skeletal muscle-specific regulatory genes MyoD and myogenin, and of several skeletal muscle-specific structural genes in cultures of the established rat smooth muscle cell lines PAC1, A10, and A7r5. The skeletal muscle regulatory gene Myf5 was not detected in these three cell lines. We further isolated clonal sublines from PAC1 cultures that homogeneously express smooth muscle characteristics at low density and undergo a coordinated increase in skeletal muscle-specific gene expression at high density. In some of these PAC1 sublines, this process culminates in the high-frequency formation of myotubes. As in the PAC1 parental line, Myf5 was not expressed in the PAC1 sublines. We show that the PAC1 sublines that undergo a more robust transition into the skeletal muscle phenotype also express significantly higher levels of the insulin-like growth factor (IGF1 and IGF2) genes and of FGF receptor 4 (FGFR4) gene. Our results suggest that MyoD expression in itself is not a sufficient condition to promote a coordinated program of skeletal myogenesis in the smooth muscle cells. Insulin administered at a high concentration to PAC1 cell populations with a poor capacity to undergo skeletal muscle differentiation enhances the number of cells displaying the skeletal muscle differentiated phenotype. The findings raise the possibility that the IGF signaling system is involved in the phenotypic switch from smooth to skeletal muscle. The gene expression program described here can now be used to investigate the mechanisms that may underlie the propensity of certain smooth muscle cells to adopt a skeletal muscle identity.(J Histochem Cytochem 48:1173-1193, 2000)

Human endothelial cell life extension by telomerase expression

Normal human endothelial cells, like other somatic cells in culture, divide a limited number of times before entering a nondividing state called replicative senescence. Expression of the catalytic component of human telomerase, human telomerase reverse transcriptase (hTERT), extends the life span of human fibroblasts and retinal pigment epithelial cells beyond senescence without causing neoplastic transformation (Bodnar, A. G., Ouellette, M., Frolkis, M., Holt, S. E., Chiu, C. P., Morin, G. B., Harley, C. B., Shay, J. W., Lichtsteiner, S., and Wright, W. E. (1998) Science 279, 349-352; Jiang, X., Jimenez, G., Chang, E., Frolkis, M., Kusler, B., Sage, M., Beeche, M., Bodnar, A., Wahl, G., Tlsty, T., and Chiu, C.-P. (1999) Nat. Genet. 21, 111-114). Here, we show that both human large vessel and microvascular endothelial cells also bypass replicative senescence after introduction of hTERT. For the first time, we report that hTERT expression in these life-extended vascular cells does not affect their differentiated and functional phenotype and that these cells maintain their angiogenic potential in vitro. Furthermore, hTERT(+) microvascular endothelial cells have normal karyotype, and hTERT(+) endothelial cell strains do not exhibit a transformed phenotype. Relative to parental cells at senescence, hTERT-expressing endothelial cells exhibit resistance to induction of apoptosis by a variety of different conditions. Such characteristics are highly desirable for designing vascular transplantation and gene therapy delivery systems in vivo.

Dexamethasone suppresses vascular smooth muscle cell proliferation

BACKGROUND

Experimental studies in vivo have demonstrated that dexamethasone inhibits neointimal hyperplasia following arterial injury. The mechanisms of this inhibition have not been clearly defined. Our objective was to test the hypothesis that dexamethasone directly suppresses smooth muscle cell (SMC) proliferation by inhibiting cell cycle progression and the expression of key cell cycle-dependent genes.

METHODS

Cultured rat aortic SMC were treated with incremental concentrations of dexamethasone and cell number was determined after 72 h. To determine if dexamethasone inhibited cell cycle progression, cells were synchronized, then restimulated to enter the cell cycle, and treated with or without dexamethasone. DNA synthesis was determined 24 h after restimulation by measuring [3H]thymidine incorporation. To define the point of action of dexamethasone in the cell cycle, synchronized SMC were treated with dexamethasone (10(-7) M) at various time points after entry into the cell cycle. Flow cytometry and Northern blots were performed to examine cell cycle progression and the expression of smooth muscle cell cycle-dependent genes c-fos, c-myc, and thymidine kinase (TK).

RESULTS

Dexamethasone treatment induced a concentration-dependent inhibition of SMC proliferation and DNA synthesis. The cell cycle progression of synchronized SMC from G1 into S phase was inhibited by dexamethasone, even when added as late as 16 h after restimulation. The expression of TK was suppressed by dexamethasone, while c-fos and c-myc were not affected.

CONCLUSIONS

Dexamethasone inhibits the proliferation of SMC in a concentration-dependent fashion. This inhibition is associated with a block in cell cycle progression late in G1 phase of the cell cycle. Consistent with this finding, dexamethasone does not alter the expression of the early cell cycle-dependent genes c-fos and c-myc, but significantly inhibits the expression of TK, a marker of late G1 phase.

Transcription factor nuclear factor kappaB regulates the inducible expression of the human B1 receptor gene in inflammation

Expression of the bradykinin B1 receptor gene is up-regulated in vascular smooth muscle cells (VSMCs) in response to a variety of inflammatory stimuli. We isolated the 5'-flanking region of the human bradykinin B1 receptor gene and examined its promoter activity by transient transfection analysis. This region (-2582 to +34) showed promoter activity inducible by lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-alpha), and interleukin-1beta (IL-1beta) in VSMCs. Further deletion analysis revealed that constructs containing 111 base pairs of 5'-flanking sequence were sufficient for transcriptional induction. Mutagenesis of a nuclear factor kappaB (NF-kappaB)-like site at -64 to -55 abolished most of the LPS, TNF-alpha, and IL-1beta inducibility, whereas a mutation of a cyclic AMP response element at -50 to -43 markedly reduced the basal promoter activity, and a mutation of the activator protein 1 (AP-1) site at -78 to -72 had minimal effects. Nuclear extracts from LPS, TNF-alpha, and IL-1beta-treated VSMCs, IL-1beta-treated human hepatoma HepG2, and human lung fibroblast IMR-90 cells showed strong inducible binding activity to the NF-kappaB-like site by gel shift assays. These results demonstrated that NF-kappaB-like nuclear factor was involved in the inducible expression of the human bradykinin B1 receptor gene during inflammatory processes.

Improved retroviral transduction efficiency of vascular cells in vitro and in vivo during clinically relevant incubation periods using centrifugation to increase viral titers

Vascular cells are an important target for gene transfer because of their potential to deliver gene products both locally and systemically. Direct retroviral gene transfer to vascular cells in vivo has been limited by inefficient rates of transduction. We hypothesized that vascular cell transduction efficiency (TE), during short retroviral incubation periods, is significantly improved in vitro and in vivo using centrifugation to increase viral titer. Furthermore, we hypothesized a linear relationship between concentration of viable viral particles (measured as colony-forming units (CFUs)/cell) and retroviral TE during short incubation periods. Cultured rat pulmonary artery endothelial cells (RPAECs), rat aortic smooth muscle cells (RSMCs), and human iliac artery endothelial cells (HIAECs) demonstrated a strong correlation between TE and high concentrations of virus (> 100 CFU/cell) during retroviral incubation periods of 10 to 60 minutes. High titers, and thereby high concentrations, were achieved by centrifugation and resuspension in a fraction of the original volume. Titers was consistently increased tenfold, for a twentyfold increase in concentration by volume. A 20-minute incubation with a Moloney murine leukemia-derived retroviral vector coding for human placental alkaline phosphatase, pLJhpAP, at a concentration of 1150 CFU/cell yielded TEs of 10.6% +/- 0.7%, 40.4% +/- 1.6%, and 15.1% +/- 2.0% for RPAECs, RSMCs, and HIAECs, respectively. A similar effect was shown using the Moloney murine leukemia-derived MFGlacZ retroviral vector, coding for Escherichia coli beta-galactosidase. Increased titer and concentration had no effect on target cell viability, as shown by trypan blue exclusion. Although RSMCs had the most cells transduced in a given incubation period (p < 0.05), RPAECs had the highest replication rate (p < 0.05), suggesting the importance of factors other than cell cycle on retroviral TEs during short, clinically relevant incubation periods. In subsequent in vivo experiments, gene transfer was achieved in the rat carotid artery during a 20-minute incubation period infusing the concentrated pLJhpAP retrovirus after carotid balloon injury. Rats infused with virus 2 days after balloon injury exhibited hpAP activity (0 to 10 cells/section/rat) in the neointima of five out of six rats. Rats infused 4 days after balloon injury exhibited hpAP activity (0 to 25 cells/section/rat) in the media and adventitia of five out of five rats. Control rats that received the balloon injury alone or the balloon injury and unconcentrated retrovirus exhibited zero hpAP activity. We conclude that the TE of retroviral-mediated gene transfer to vascular cells in vitro and in vivo can be improved during short, clinically relevant incubation periods using centrifugation to increase retroviral titer, and thereby concentration of viable viral particles.

Dual cell cycle-specific mechanisms mediate the antimitogenic effects of nitric oxide in vascular smooth muscle cells

OBJECTIVE

To determine the cell cycle specificity and intracellular mechanisms involved in inhibition by nitric oxide (NO) of vascular smooth muscle cell mitogenesis.

METHODS

Cultured rat aortic smooth muscle cells were synchronized by serum withdrawal, treated with the NO donor S-nitroso-N-acetylpenicillamine and the cyclic GMP analog 8-Br-cGMP at various times during cell cycle progression, and DNA synthesis measured during the S phase. Two additional NO donors, 5-nitroso-glutathione and diethylamine NONOate, were used to confirm the inhibition of DNA synthesis by S-nitroso-N-acetylpenicillamine, and the ability of two antagonists of free NO to reverse the effects of NO donors was also evaluated. Bypass of ribonucleotide reductase by use of exogenous deoxynucleosides was attempted to determine whether inhibition of this S-phase enzyme was the mechanism by which NO inhibited DNA synthesis during the S phase.

RESULTS

Vascular smooth muscle cell mitogenesis was inhibited by cyclic GMP (cGMP) up to late G1 phase of the cell cycle, which corresponded to the point of greatest sensitivity to exogenous NO. In contrast to cGMP, three different NO donors inhibited DNA synthesis when added to cells synchronized in S phase, beyond the restriction point of cell cycle control in late G1 phase. This S-phase inhibition was reversible by removal of the NO donor or addition of two NO antagonists and was not observed with non-NO analogs of the donors. Inhibition by NO donors in S phase was neither reversed by the guanylate cyclase inhibitor methylene blue nor mimicked by exogenous cGMP. The S-phase inhibition by all three NO donors was reversed partially by bypass of ribonucleotide reductase, establishing this enzyme as an S-phase target of NO.

CONCLUSIONS

These findings demonstrate that NO inhibits smooth muscle mitogenesis by cGMP-dependent and -independent mechanisms acting at distinct points in the cell cycle. NO is the first endogenous substance to have been shown to inhibit mitogenesis beyond the restriction point in late G1 phase, suggesting that it plays a role in regulation of cells that have lost normal mechanisms of G1 growth control, such as the hyperproliferative smooth muscle cells noted in hypertension and restenosis.

Induction by staurosporine of nitric oxide synthase expression in vascular smooth muscle cells: role of NF-kappa B, CREB and C/EBP beta

1. The effect of different protein kinase inhibitors on the expression of the inducible isoform of nitric oxide (NO) synthase (iNOS) was investigated in cultured vascular smooth muscle cells (VSMC) isolated from the rat aorta. 2. The non-selective protein kinase C (PKC) inhibitor, staurosporine, but not the more selective PKC inhibitors, calphostin C and Ro 31-8820, or the tyrosine kinase inhibitors, genistein and erbstatin analogue (erbstatin A), elicited a distinct (up to six fold) up-regulation of iNOS gene expression in these cells, as demonstrated by a parallel increase in iNOS mRNA and protein abundance as well as an accumulation of nitrite (NO2-) in the conditioned medium. Actinomycin D and cycloheximide inhibited the effect of staurosporine, suggesting an involvement of both DNA transcription and de nova protein synthesis. 3. Staurosporine also synergistically potentiated the stimulating effect of interleukin-1 beta (IL-1 beta), but not that of the adenylyl cyclase activator, forskolin, on NO2- production and iNOS protein abundance. Staurosporine, on the other hand, had no effect on the IL-1 beta-mediated increase in iNOS mRNA abundance. The effect of staurosporine on both basal and IL-1 beta-stimulated NO2- production was concentration-dependent with an apparent maximum at 3 nM. Among the other protein kinase inhibitors tested, only calphostin C also enhanced the stimulant effect of IL-1 beta approximately two fold, while genistein, erbstatin A and Ro 31-8220 inhibited rather than potentiated it. 4. Staurosporine did not influence basal activity of the transcription factors CREB and nuclear factor kappa B (NF-kappa B), but increased that of C/EBP. Moreover, staurosporine significantly augmented the activation of C/EBP by IL-1 beta and forskolin. 5. These findings suggest that in cultured VSMC a staurosporine-sensitive protein kinase exists, which is unlikely to be related to PKC, that prevents iNOS gene expression presumably by suppressing basal C/EBP activity. They also indicate that NF-kappa B and a member of the C/EBP family of transcription factors, presumably C/EBP beta, act synergistically under basal conditions and possibly also following exposure to IL-1 beta in the up-regulation of iNOS gene expression in these cells. Targeting of the activation of C/EBP beta may thus represent an interesting approach to interfere selectively with the cytokine-induced over-production of NO in acute and chronic inflammatory conditions.

Effect of cyclic GMP-dependent vasodilators on the expression of inducible nitric oxide synthase in vascular smooth muscle cells: role of cyclic AMP

1. In the present study we examined whether interleukin-1 beta (IL-1 beta) increases the activity of adenylyl cyclase in vascular smooth muscle cells and determined its role in the cytokine-induced expression of the inducible nitric oxide synthase (iNOS) and activation of nuclear transcription factor-kappa B (NF-kappa B). In addition the interaction between cyclic AMP- and cyclic GMP-elevating agonists on the IL-1 beta-stimulated expression of iNOS was examined. 2. Exposure of vascular smooth muscle cells to IL-1 beta stimulated the formation of cyclic AMP but not of cyclic GMP. The intracellular level of cyclic AMP reached a maximum within 1 h and then gradually declined over the next 5 h. This IL-1 beta (60 u ml-1)-stimulated formation of cyclic AMP was modest (about 3 fold at 60 u ml-1 for 1 h) compared to that evoked by isoprenaline (about 9 fold at 3 x 10(-6) M for 2 min). 3. The IL-1 beta (60 u ml-1 for 24 h)-stimulated accumulation of nitrite, which was taken as an index of NO production, was concentration-dependently increased by preferential inhibitors of cyclic AMP-dependent phosphodiesterases (rolipram and trequinsin). This effect was reproduced by a specific activator of the cyclic AMP-dependent protein kinase(s) A, Sp-8-CPT-cAMPS (10(-4) M) but was prevented by a specific inhibitor of cyclic AMP-dependent protein kinase(s) A, Rp-8-CPT-cAMPS (10(-4) M). These compounds alone [rolipram (10(-6) M), trequinsin (3 x 10(-6) M) and Sp-8-CPT-cAMPS (10(-4) M)] slightly but significantly increased the release of nitric oxide while Rp-8-CPT-cAMPS elicited no such effect. 4. Inducible NOS protein was expressed in IL-1 beta (30 u ml-1, 24 h)-stimulated smooth muscle cells as assessed by Western blot analysis. The level of iNOS protein was markedly increased in smooth muscle cells which had been exposed to IL-1 beta in combination with either rolipram (3 x 10(-6) M) or Sp-8-CPT-cAMPS (10(-4) M) but was reduced in those exposed to IL-1 beta and Rp-8-CPT-cAMPS (10(-4) M). A weak expression of iNOS protein was found in smooth muscle cells which had been exposed to either Sp-8-CPT-cAMPS or rolipram alone for 24 h while Rp-8-CPT-cAMPS elicited no such effect. 5. Exposure of smooth muscle cells to IL-1 beta (30 u ml-1) for 30 min increased the level of NF-kappa B-DNA complexes in nuclear extracts as detected by electrophoretic mobility shift assay. Similar levels of NF-kappa B-DNA complexes were found in cells which had been exposed to IL-1 beta in combination with either Sp-8-CPT-cAMPS (10(-4) M), trequinsin (10(-6) M) or rolipram (10(-6) M). None of the modulators alone affected the basal level of NF-kappa B binding activity. 6. NO-donors [sodium nitroprusside (SNP) 10(-4) M; dinitrosyl-iron-di-L-cysteine-complex (DNIC), 10(-4) M; 3-morpholino-sydnonimine (SIN-1), 10(-4) M] and atrial natriuretic factor (10(-6) M) significantly increased the IL-1 beta (30 or 60 u ml-1, 24 h)-stimulated expression of iNOS protein and activity as assessed indirectly by the conversion of oxyhaemoglobin to methaemoglobin. In the absence of IL-1 beta, SNP (10(-4) M, 24 h) but not the other cyclic GMP-dependent vasodilators caused a modest expression of iNOS protein. No such effect was found in smooth muscle cells exposed to SNP in combination with Rp-8-CPT-cAMPS (10(-4) M) while an increased level of iNOS protein was found in those exposed to SNP in combination with either Sp-8-CPT-cAMPS (10(-4) M) or rolipram (3 x 10(-6) M). 7. Exposure of vascular smooth muscle cells to either S-nitroso-L-cysteine (Cys-SNO, 10(-4) M), SNP (10(-4) M) or SIN-1 (10(-4) M) for 35 min affected minimally the basal activation of NF-kappa B but abolished that evoked by IL-1 beta (30 u ml-1 added during the last 30 min). However, addition of Cys-SNO following the stimulation with IL-1 beta (during the last 5 min of the 30 min exposure period) reduced the level of NF-kappa B-DNA complexes only slightly. 8. These data indicate that the cyclic AMP-dependent pathway plays a decisi

Antioxidants differentially affect nuclear factor kappa B-mediated nitric oxide synthase expression in vascular smooth muscle cells

Increased 'oxidative stress' resulting in the activation of nuclear factor kappa B (NF-kappa B) is thought to play a crucial role in the cytokine-mediated expression of the inducible isoform of nitric oxide synthase (iNOS) in different cell types. Therefore, the effects of four different antioxidants, carbocromen, chrysin, 3,4-dichloroisocoumarin (DCI) and N-acetylserotonin (NAS), on iNOS expression were investigated in vascular smooth muscle cells (VSMC). All antioxidants strongly reduced the phorbol ester-stimulating superoxide anion formation in native VSMC. Carbocromen (200 microM) and chrysin (50 microM) had no effect, while NAS (1 mM) abolished the increase in nitrine production and iNOS protein abundance in cultured VSMC exposed to interleukin-1 beta (IL-1 beta, 60 U/ml) or the adenyl cyclase activator forskolin (10 microM). DCI also revealed a marked inhibitory effect in IL-1 beta-stimulated VSMC, but was less effective in cells treated with forskolin. DCI, but not NAS, also suppressed the activation of NF-kappa B in VSMC exposed to IL-1 beta, while no significant NF-kappa B activation was detected in forskolin-treated cells. These findings demonstrate that antioxidants differentially affect iNOS expression in VSMC both at the transcriptional level by preventing the activation of NF-kappa B and at the post-transcriptional level, presumably by promoting iNOS mRNA or protein degradation. They also suggest that reactive oxygen intermediates do not play a role in the activation of NF-kappa B by IL-1 beta in VSMC, and that transcription factors other than NF-kappa B mediate the induction of iNOS expression by elevating the intracellular concentration of cyclic AMP.

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.

Telomere length and replicative aging in human vascular tissues

Because repeated injury of the endothelium and subsequent turnover of intimal and medial cells have been implicated in atherosclerosis, we examined telomere length, a marker of somatic cell turnover, in cells from these tissues. Telomere lengths were assessed by Southern analysis of terminal restriction fragments (TRFs) generated by HinfI/Rsa I digestion of human genomic DNA. Mean TRF length decreased as a function of population doublings in human endothelial cell cultures from umbilical veins, iliac arteries, and iliac veins. When endothelial cells were examined for mean TRF length as a function of donor age, there was a significantly greater rate of decrease for cells from iliac arteries than from iliac veins (102 bp/yr vs. 47 bp/yr, respectively, P < 0.05), consistent with higher hemodynamic stress and increased cell turnover in arteries. Moreover, the rate of telomere loss as a function of donor age was greater in the intimal DNA of iliac arteries compared to that of the internal thoracic arteries (147 bp/yr vs. 87 bp/yr, respectively, P < 0.05), a region of the arterial tree subject to less hemodynamic stress. This indicates that the effect is not tissue specific. DNA from the medial tissue of the iliac and internal thoracic arteries showed no significant difference in the rates of decrease, suggesting that chronic stress leading to cellular senescence is more pronounced in the intima than in the media. These observations extend the use of telomere size as a marker for the replicative history of cells and are consistent with a role for focal replicative senescence in cardiovascular diseases.

Inhibition by N-acetyl-5-hydroxytryptamine of nitric oxide synthase expression in cultured cells and in the anaesthetized rat

1. Induction of the calcium-independent isoform of nitric oxide (NO) synthase (iNOS) in various cell types has been implicated in the circulatory failure in experimental models of septic shock. Tetrahydrobiopterin (BH4) appears to be an essential co-factor for NO formation and therefore an inhibition of its biosynthesis represents a feasible therapeutic target. We have investigated the effects of an inhibitor of BH4 synthesis, N-acetyl-5-hydroxytryptamine (N-acetylserotonin, NAS), on the expression of iNOS in cultured macrophages and smooth muscle cells in vitro, and on the hypotensive response to bacterial lipopolysaccharide (LPS) in the anaesthetized rat in vivo. 2. NAS (0.01-5 mM) caused a concentration-dependent inhibition of the accumulation of nitrite in the conditioned medium of LPS/interferon-gamma (IFN gamma)-stimulated RAW 264.7 macrophages and interleukin-1 beta (IL-1 beta)-activated vascular smooth muscle cells (VSMC). This effect was paralleled by a similar decrease in the iNOS protein content of these cells, as determined by immunoblot analysis. 3. Pretreatment of RAW 264.7 macrophages with the BH4 precursor, dihydrobiopterin (BH2, 0.1 mM) did not restore nitrite formation in the presence of NAS (1 mM). 4. Intravenous administration of NAS (1 mg kg-1 min-1 for 30 min) in anaesthetized rats significantly reduced the fall in mean arterial blood pressure, restored the pressor response to noradrenaline (1 micrograms kg-1), and ameliorated the increase in plasma nitrite following exposure to LPS (10 mg kg-1). 5. NAS pretreatment also attenuated iNOS activity in lung homogenates, as determined by the conversion of radiolabelled L-arginine to L-citrulline, and partially restored the constrictor effect of noradrenaline in aortic rings isolated from LPS-treated rats. Moreover, NAS significantly reduced the rise in the plasma concentration of tumour necrosis factor alpha (TNFalpha) in response to LPS.6. These findings suggest that NAS inhibits the expression rather than the activity of iNOS in cultured macrophages and smooth muscle cells. This effect of NAS appears to be independent of the availability of BH4, but may be related to an attenuation of the release of TNFalpha following LPS administration, as shown in the anaesthetized rat. This mechanism may also account for the beneficial haemodynamic effect of NAS in our experimental model of endotoxaemia.

cAMP- and rapamycin-sensitive regulation of the association of eukaryotic initiation factor 4E and the translational regulator PHAS-I in aortic smooth muscle cells

Incubating rat aortic smooth muscle cells with either platelet-derived growth factor BB (PDGF) or insulin-like growth factor I (IGF-I) increased the phosphorylation of PHAS-I, an inhibitor of the mRNA cap binding protein, eukaryotic initiation factor (eIF) 4E. Phosphorylation of PHAS-I promoted dissociation of the PHAS-I-eIF-4E complex, an effect that could partly explain the stimulation of protein synthesis by the two growth factors. Increasing cAMP with forskolin decreased PHAS-I phosphorylation and markedly increased the amount of eIF-4E bound to PHAS-I, effects consistent with an action of cAMP to inhibit protein synthesis. Both PDGF and IGF-I activated p70S6K, but only PDGF increased mitogen-activated protein kinase activity. Forskolin decreased by 50% the effect of PDGF on increasing p70S6K, and forskolin abolished the effect of IGF-I on the kinase. The effects of PDGF and IGF-I on increasing PHAS-I phosphorylation, on dissociating the PHAS-I-eIF-4E complex, and on increasing p70S6K were abolished by rapamycin. The results indicate that IGF-I and PDGF increase PHAS-I phosphorylation in smooth muscle cells by the same rapamycin-sensitive pathway that leads to activation of p70S6K.

Characterization of the stable L-arginine-derived relaxing factor released from cytokine-stimulated vascular smooth muscle cells as an NG-hydroxyl-L-arginine-nitric oxide adduct

The nature of an L-arginine-derived relaxing factor released from vascular smooth muscle cells cultured on microcarrier beads and stimulated for 20 h with interleukin 1 beta was investigated. Unlike the unstable relaxation elicited by authentic nitric oxide (NO) in a cascade superfusion bioassay system, the effluate from vascular smooth muscle cells induced a stable relaxation that was susceptible to inhibition by oxyhemoglobin. Three putative endogenous NO carriers mimicked this stable relaxing effect: S-nitroso-L-cysteine, low molecular weight dinitrosyl-iron complexes (DNICs), and the adduct of NG-hydroxy-L-arginine (HOArg) with NO. Inactivation of S-nitroso-L-cysteine by Hg2+ ions or trapping of DNICs with agarose-bound bovine serum albumin abolished their relaxing effects, whereas that of the vascular smooth muscle cell effluate remained unaffected. In addition, neither S-nitrosothiols nor DNICs were detectable in the effluate from these cells, as judged by UV and electron spin resonance (ESR) spectroscopy. The HOArg-NO adduct was instantaneously generated upon reaction of HOArg with authentic NO under bioassay conditions. Its pharmacological profile was indistinguishable from that of the vascular smooth muscle cell effluate, as judged by comparative bioassay with different vascular and nonvascular smooth muscle preparations. Moreover, up to 100 nM HOArg was detected in the effluate from interleukin 1 beta-stimulated vascular smooth muscle cells, suggesting that sufficient amounts of HOArg are released from these cells to spontaneously generate the HOArg-NO adduct. This intercellular NO carrier probably accounts for the stable L-arginine-derived relaxing factor released from cytokine-stimulated vascular smooth muscle cells and also from other NO-producing cells, such as macrophages and neutrophils.

Expression of basic fibroblast growth factor and fibroblast growth factor receptor genes in cultured rat aortic smooth muscle cells

Basic fibroblast growth factor (bFGF) exerts a differential effect on DNA synthesis, bFGF mRNA synthesis, and expression of FGF-receptor genes by cultured smooth muscle cells from aortae of newborn and adult rats (used as a model in atherosclerosis research). Cells from adult animals, are more sensitive to bFGF, and bFGF triggers its own mRNA synthesis. Moreover, the level of the transcript of the FGFR-1 gene (coding for the most abundant FGF-receptor in smooth muscle cells) is higher in smooth muscle cells from adult rats. In contrast, the FGFR-3 gene only is expressed in smooth muscle cells from newborn rats. Crosslinking of [125I]bFGF to its receptor showed 130 kDa and 160 kDa complexes both in newborn and adult smooth muscle cells.

The adhesive and migratory effects of osteopontin are mediated via distinct cell surface integrins. Role of alpha v beta 3 in smooth muscle cell migration to osteopontin in vitro

Osteopontin is an arginine-glycine-aspartate containing acidic glycoprotein postulated to mediate adhesion, migration, and biomineralization in diverse tissues. The mechanisms explaining this multifunctionality are not well understood, although it is known that one osteopontin receptor is the alpha v beta 3 integrin. In this work, we studied human smooth muscle cells varying in alpha v beta 3 levels to identify additional osteopontin receptors. We report that, in addition to alpha v beta 3, both alpha v beta 5 and alpha v beta 1 are osteopontin receptors. Moreover, the presence or absence of alpha v beta 3 on the cell surface altered the adhesive and migratory responses of smooth muscle cells to osteopontin. Adhesion of alpha v beta 3-deficient cell populations to osteopontin was only half that of cells containing alpha v beta 3, and migration toward an osteopontin gradient in the Boyden chamber was dependent on cell surface alpha v beta 3. Although alpha v beta 3-deficient smooth muscle cells were unable to migrate to osteopontin, they did migrate significantly in response to vitronectin and fibronectin. These findings represent the first description of alpha v beta 5 and alpha v beta 1 as osteopontin receptors and suggest that, while adhesion to osteopontin is supported by integrins containing beta 1, beta 3, and beta 5, migration in response to osteopontin appears to depend on alpha v beta 3. Thus, interaction with distinct receptors is one mechanism by which osteopontin may initiate multiple functions.

Different electrical responses to vasoactive agonists in morphologically distinct smooth muscle cell types

Vascular smooth muscle cells (SMCs) in the blood vessel wall are frequently heterogeneous in nature, differing in their gross morphology, size, and shape, subcellular organelles, cytoskeleton, and contractile protein composition. In adult rat arterial vessels, two populations of SMCs have been shown to predominate: elongated bipolar cells, representing the majority of cells, and epithelial-like SMCs. We examined the ionic responses of these two types of SMCs, isolated by multiple subculture, to vasoactive stimuli. Elevations in intracellular Na+ and Ca2+ were measured with SBFI and fura 2, respectively, and changes in membrane potential were measured using the potential-sensitive fluorescent probe bis-oxonol. The resting membrane potential of the elongated bipolar cells was less negative than that of the epithelial-like SMCs. Exposure of the elongated SMCs to endothelin 1, alpha-thrombin, or arginine vasopressin induced elevations in [Ca2+]i and [Na+]i and membrane depolarization. Depolarization occurred because of entry of both Na+ and Ca2+, and pharmacological blockade of Cl- or K+ channels did not attenuate the depolarization. In contrast, when [Ca2+]i was elevated by the same agonists in the epithelial-like SMCs there was a pronounced hyperpolarization that appeared to be the consequence of enhanced activity of charybdotoxin-sensitive Ca(2+)-activated K+ channels because it was abolished by charybdotoxin (20 nmol/L), partially attenuated by tetraethylammonium chloride (10 mmol/L), and unaffected by apamin (1 mumol/L), glibenclamide (1 mumol/L), or 4-aminopyridine (5 mmol/L). Chelation of [Ca2+]i also abolished the hyperpolarization; instead, a small depolarization was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Smooth muscle cells (SMCs) of rabbit aorta undergo marked changes in myosin isoform content during development. Analysis of nonmuscle myosin composition at the protein level has permitted the identification of three phases in the SMC differentiation process: fetal, postnatal, and adult. Using monoclonal antibodies specific for smooth muscle and nonmuscle myosins and extra domain A of fibronectin as well as cDNA probes for platelet-derived growth factors (PDGF) and various procollagens, we have evaluated the differentiation pattern of aortic SMCs in two-kidney, one-clip hypertensive rabbits. Morphometric and bromo-deoxyuridine studies indicate that hypertrophy of aortic media along with intimal thickening occurring in hypertensive animals is due to SMC hyperplasia. Western blotting experiments performed on aortic specimens from hypertensive animals with antimyosin antibodies revealed the appearance of a myosin isoform pattern of the "immature" type. Immunofluorescence tests showed that these cells are localized in the thickened intima or distributed in the underlying media (sparsely or in groups). Similarly, the fibronectin variant showing the extra domain A, peculiar to "phenotypically modulated" SMCs, appeared in intimal thickening, and its expression followed the time course of nonmuscle myosin expression. Counting of postnatal-type SMCs in the aortic media revealed that this cell population increases markedly with hypertension (2- up to 15-fold at 4 months) and then declines to near control level in 8-month hypertensive rabbits. Diminution of postnatal-type SMCs at later stages of hypertension was temporally correlated with the slowing down of aortic wall hypertrophy. Average levels of mRNAs, as determined by densitometric analysis in aortas from 1- and 2.5-month hypertensive rabbits, showed an increased expression for PDGF beta receptor (up to twofold), procollagen type I (alpha 1, threefold), procollagen type III (alpha 1, twofold), and fibronectin (up to threefold) compared with controls. Conversely, the steady-state levels of mRNAs for PDGF (A and B chain), PDGF alpha receptor, TGF-beta 1, and procollagen type IV (alpha 1) did not increase significantly. These results provide evidence that in adult renovascular hypertensive rabbits, the hyperplastic growth of aortic SMCs is accompanied by the expansion of an "immature" cell phenotype characteristic of the early stages of development.

Osteopontin promotes vascular cell adhesion and spreading and is chemotactic for smooth muscle cells in vitro

Osteopontin is an Arg-Gly-Asp-containing acidic phosphoprotein recently shown to be upregulated in vascular smooth muscle during rat arterial neointima formation and in human atherosclerotic plaques. Functional studies showed that osteopontin promoted adhesion of both cultured aortic endothelial cells and aortic smooth muscle cells. Adhesion of vascular cells to osteopontin was dose dependent and half maximal when solutions containing 7 and 30 nmol/L osteopontin were used to coat wells for endothelial and smooth muscle cells, respectively. Smooth muscle cells adherent to osteopontin were spread after 60 minutes, whereas endothelial cells remained round, although flattened, at this time point but were spread at 90 minutes. Cell spreading on osteopontin was accompanied by the formation of focal adhesion plaques. A newly developed anti-osteopontin antibody completely inhibited adhesion of both cell types to osteopontin but not to fibronectin or vitronectin. In addition, the peptide GRGDSP blocked adhesion to osteopontin, suggesting that integrins mediate Arg-Gly-Asp-dependent adhesion. Indeed, an antibody against the alpha v beta 3 integrin neutralized adhesion of both endothelium and smooth muscle cells to osteopontin by approximately 50%, demonstrating that alpha v beta 3 is one osteopontin receptor on vascular cells. Osteopontin also promoted the migration of smooth muscle cells in a Boyden-type chamber, with half-maximal effects observed at 77 nmol/L osteopontin. Checkerboard analysis demonstrated that this stimulus was chemotactic in nature. Our findings suggest that osteopontin may be functionally important as an adhesive and chemotactic molecule for vascular cells, particularly when levels of osteopontin are dramatically increased, as is the case after arterial angioplasty and in atherosclerotic plaques.

Expression of elastin, smooth muscle alpha-actin, and c-jun as a function of the embryonic lineage of vascular smooth muscle cells

In the avian embryo, vascular smooth muscle cells (VSMC) in the aortic arch (elastic) arteries originate in the neural crest, whereas other VSMC develop from local mesoderm. These two lineages have been shown previously to be significantly different in the timing and expression of the smooth muscle phenotype and in their respective abilities to produce an orderly elastic matrix. Two differing kinds of VSMC also have been shown in mammals. In the experimental absence of neural crest (NC) in the avian embryo, the matrix is spatially disordered. The molecular basis of the difference between the normal NC-VSMC and the surrogate mesodermal (MDM)-VSMC has not previously been investigated. In this study the expression of vascular smooth muscle alpha-actin, tropoelastin, c-fos and c-jun were examined via immunoblotting, immunohistochemistry, Northern blot, and/or transcription run-on assays. Control avian VSMC of NC origin were compared with experimental MDM-derived VSMC that populate the cardiac outflow after surgical ablation of the NC. The results show that, when they are grown under identical conditions in vitro or freshly removed from an embryonic vessel, surrogate MDM-VSMC express about 10 times more alpha-actin and tropoelastin than the normal NC-VSMC; and MDM-VSMC express up to 15 times more c-jun, whereas c-fos was not different. These results show profound heterogeneity in the regulation of VSMC-specific genes that is based in the embryonic lineage of the cells.

Regulation of platelet-derived growth factor ligand and receptor gene expression by alpha-thrombin in vascular smooth muscle cells

Since the expression of genes for platelet-derived growth factor (PDGF)-A and PDGF beta-receptor are reciprocally regulated in vascular wall cells after balloon injury, we have investigated the ability of specific vasoactive molecules or growth factors to reproduce the injury pattern of gene expression in cultured rat smooth muscle cells (SMCs) and assessed the effect of inactivating alpha-thrombin on injury-induced expression of PDGF-A mRNA by vascular wall cells in vivo. The molecules investigated, to which vascular SMCs may be locally exposed after mechanical injury, included vasoactive factors (alpha- and beta-adrenergic agonists, serotonin, histamine, angiotensin II, and endothelin) and growth factors (PDGF-AA, PDGF-BB, basic fibroblast growth factor, insulin-like growth factor, epidermal growth factor, and alpha-thrombin). In cultured rat SMCs, only alpha-thrombin (0.1-100 nM), among these compounds, produced the pattern of transiently increased PDGF-A and decreased PDGF beta-receptor mRNA. PDGF-B chain mRNA levels remained undetectable in these cultured SMCs. The dependence of these changes in gene expression on the proteolytic activity of alpha-thrombin was shown by the interruption of altered gene expression or DNA synthesis after incubating the cultured SMCs with covalently inactivated alpha-thrombin using D-Phe-Pro-Arg chloromethyl ketone, a synthetic direct active-site irreversible inhibitor of alpha-thrombin. Continuous intravenous infusion of this synthetic antithrombin into baboons for 6 hours (100 nmol/kg per minute maintaining constant plasma levels of 3.0 +/- 0.5 microns/ml) after inducing balloon-catheter arterial injury also prevented the threefold increase in expression of PDGF-A mRNA characteristically exhibited by untreated mechanically injured vessels.(ABSTRACT TRUNCATED AT 250 WORDS)