Protein kinase C pathway and proliferative responses of aged and young rat vascular smooth muscle cells

Modulation of binding to vascular endothelial growth factor and receptor by heparin derived oligosaccharide

We investigated the mechanism of heparin-derived oligosaccharide on the proliferation of vascular smooth muscle cell (VSMC) induced by vascular endothelial growth factor (VEGF). Expression levels of VEGFR 1 and VEGFR 2 were examined by RT-PCR, and the corresponding protein expression levels were detected by Western blotting and immunocytochemistry. Western blotting was taken to identify the expression levels of mechanism proteins. The binding of VEGF and VEGFR 2 was measured by co-IP. Besides, HS competition assay was to detect the ability of HDO to compete with Heparin for VEGF165. HDO showed an inhibitory effect on the expression of VEGFR1/2 proteins and PKC, MAPK, PI3K/Akt pathways. In addition, HDO affected the binding of VEGF-VEGFR, which may be one of the most important mechanisms of HDO suppress the cell proliferation induced by growth factors. Thus HDO showed the ability as a VEGF antagonist.

Arterial ageing: from endothelial dysfunction to vascular calcification

Complex structural and functional changes occur in the arterial system with advancing age. The aged artery is characterized by changes in microRNA expression patterns, autophagy, smooth muscle cell migration and proliferation, and arterial calcification with progressively increased mechanical vessel rigidity and stiffness. With age the vascular smooth muscle cells modify their phenotype from contractile to 'synthetic' determining the development of intimal thickening as early as the second decade of life as an adaptive response to forces acting on the arterial wall. The increased permeability observed in intimal thickening could represent the substrate on which low-level atherosclerotic stimuli can promote the development of advanced atherosclerotic lesions. In elderly patients the atherosclerotic plaques tend to be larger with increased vascular stenosis. In these plaques there is a progressive accumulation of both lipids and collagen and a decrease of inflammation. Similarly the plaques from elderly patients show more calcification as compared with those from younger patients. The coronary artery calcium score is a well-established marker of adverse cardiovascular outcomes. The presence of diffuse calcification in a severely stenotic segment probably induces changes in mechanical properties and shear stress of the arterial wall favouring the rupture of a vulnerable lesion in a less stenotic adjacent segment. Oxidative stress and inflammation appear to be the two primary pathological mechanisms of ageing-related endothelial dysfunction even in the absence of clinical disease. Arterial ageing is no longer considered an inexorable process. Only a better understanding of the link between ageing and vascular dysfunction can lead to significant advances in both preventative and therapeutic treatments with the aim that in the future vascular ageing may be halted or even reversed.

Efficacy of female rat models in translational cardiovascular aging research

Cardiovascular disease is the leading cause of death in women in the United States. Aging is a primary risk factor for the development of cardiovascular disease as well as cardiovascular-related morbidity and mortality. Aging is a universal process that all humans undergo; however, research in aging is limited by cost and time constraints. Therefore, most research in aging has been done in primates and rodents; however it is unknown how well the effects of aging in rat models translate into humans. To compound the complication of aging gender has also been indicated as a risk factor for various cardiovascular diseases. This review addresses the systemic pathophysiology of the cardiovascular system associated with aging and gender for aging research with regard to the applicability of rat derived data for translational application to human aging.

Effect of heparin-derived oligosaccharide on vascular smooth muscle cell proliferation and the signal transduction mechanisms involved

PURPOSE

In this study, the effect of heparin-derived oligosaccharide (HDO) on vascular endothelial growth factor (VEGF) induced vascular smooth muscle cell (VSMC) proliferation and the signal transduction mechanisms involved were investigated.

METHODS

MTT assays were used to measure VSMC proliferation, flow cytometry to analyze cell cycle distribution, RT-PCR for detection of gene transcript levels, and cell-based ELISA, Western blotting and immunocytochemical methods to detect the expression of PKC-α, ERK 1/2, p-ERK 1/2, Akt, p-Akt, p-PDK1 and p-GSK-3β.

RESULTS

HDO at concentrations of 0.01, 0.1 and 1 μmol·L(-1) dose-dependently inhibited VEGF-induced VSMC proliferation with inhibition indices of 6.8 %, 13.1 % and 28.9 %, respectively. Similar concentrations of HDO dose-dependently decreased the percentage of VEGF-induced cells in S phase to 3.6 %, 3.4 %, and 5.4 %, while increasing that of cells arrested in the G0/G1 phase to 80 %, 82 % and 83.6 %. HDO at 0.01, 0.1 or 1 μmol·L(-1) inhibited VEGF-induced PKC-α mRNA expression, with inhibition indices of 9.2 %, 16.1 % and 54.0 %. HDO at 0.1 or 1 μmol·L(-1) inhibited VEGF-induced proto-oncogene mRNA expression, with inhibition indices of 5.2 % and 6.6 % for c-jun, 8.8 % and 11.6 % for c-myc, and 6.5 % and 11.9 % for c-fos, respectively. Additionally, treatment with 0.01, 0.1 or 1 μmol·L(-1) HDO, inhibited VEGF-induced expression of some proliferation related proteins with inhibition indices of 33.2 %, 56.3 % and 77.0 % for PKC-α, 33.7 %, 38.7 % and 53.2 % for p-Akt, 3.5 %, 24.2 % and 49.3 % for p-ERK 1/2, 39.2 %, 71.8 % and 80.7 % for p-PDK 1 and 41.4 %, 89.4 % and 92.4 % for p-GSK-3β, respectively. The results showed that HDO inhibited PKC-α, c-jun, c-fos and c-myc mRNA transcription, and also down-regulated phosphorylation levels of ERK 1/2 and Akt.

CONCLUSION

Our study demonstrates that HDO inhibits transcription of proliferation-related proto-oncogenes and arrests G1/S transition through inhibition of the PKC, MAPK and Akt/PI3K pathways in association with inhibition of VSMC proliferation. This altered molecular signature may explain one mechanism of HDO-mediated inhibition of VSMC proliferation.

Independent beta-arrestin2 and Gq/protein kinase Czeta pathways for ERK stimulated by angiotensin type 1A receptors in vascular smooth muscle cells converge on transactivation of the epidermal growth factor receptor

Recent studies in receptor-transfected cell lines have demonstrated that extracellular signal-regulated kinase (ERK) activation by angiotensin type 1A receptor and other G protein-coupled receptors can be mediated by both G protein-dependent and β-arrestin-dependent mechanisms. However, few studies have explored these mechanisms in primary cultured cells expressing endogenous levels of receptors. Accordingly, here we utilized the β-arrestin biased agonist for the angiotensin type 1A receptor, SII-angiotensin (SII), and RNA interference techniques to investigate angiotensin II (ANG)-activated β-arrestin-mediated mitogenic signaling pathways in rat vascular smooth muscle cells. Both ANG and SII induced DNA synthesis via the ERK activation cascade. Even though SII cannot induce calcium influx (G protein activation) after receptor stimulation, it does cause ERK activation, although less robustly than ANG. Activation by both ligands is diminished by depletion of β-arrestin2 by small interfering RNA, although the effect is more complete with SII. ERK activation at early time points but not later time points is strongly inhibited by those protein kinase C inhibitors that can block protein kinase Cζ. Moreover, ANG- and SII-mediated ERK activation require transactivation of the epidermal growth factor receptor via metalloprotease 2/9 and Src kinase. β-Arrestin2 facilitates ANG and SII stimulation of Src-mediated phosphorylation of Tyr-845 on the EGFR, a known site for Src phosphorylation. These studies delineate a convergent mechanism by which G protein-dependent and β-arrestin-dependent pathways can independently mediate ERK-dependent transactivation of the EGFR in vascular smooth muscle cells thus controlling cellular proliferative responses.

ANG II-stimulated DNA synthesis is mediated by ANG II receptor-dependent Ca2+/PKC as well as EGF receptor-dependent PI3K/Akt/mTOR/p70S6K1 signal pathways in mouse embryonic stem cells

Effect of angiotensin II (ANG II) on mouse embryonic stem (ES) cell proliferation was examined. ANG II increased [(3)H] thymidine incorporation in a time- (>4 h) and dose- (>10(-9) M) dependent manner. The ANG II-induced increase in [(3)H] thymidine incorporation was blocked by inhibition of ANG II type 1 (AT(1)) receptor but not by ANG II type 2 (AT(2)) receptor, and AT(1) receptor was expressed. ANG II increased inositol phosphates formation and [Ca(2+)](i), and translocated PKC alpha, delta, and zeta to the membrane fraction. Consequently, the inhibition of PLC/PKC suppressed ANG II-induced increase in [(3)H] thymidine incorporation. The inhibition of EGF receptor kinase or tyrosine kinase prevented ANG II-induced increase in [(3)H] thymidine incorporation. ANG II phosphorylated EGF receptor and increased Akt, mTOR, and p70S6K1 phosphorylation blocked by AG 1478 (EGF receptor kinase blocker). ANG II-induced increase in [(3)H] thymidine incorporation was blocked by the inhibition of p44/42 MAPKs but not by p38 MAPK inhibition. Indeed, ANG II phosphorylated p44/42 MAPKs, which was prevented by the inhibition of the PKC and AT(1) receptor. ANG II increased c-fos, c-jun, and c-myc levels. ANG II also increased the protein levels of cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 2, and CDK4 but decreased the p21(cip1/waf1) and p27(kip1), CDK inhibitory proteins. These proteins were blocked by the inhibition of AT(1) receptor, PLC/PKC, p44/42 MAPKs, EGF receptor, or tyrosine kinase. In conclusion, ANG II-stimulated DNA synthesis is mediated by ANG II receptor-dependent Ca(2+)/PKC and EGF receptor-dependent PI3K/Akt/mTOR/p70S6K1 signal pathways in mouse ES cells.

Taurine suppresses platelet-derived growth factor (PDGF) BB-induced PDGF-β receptor phosphorylation by protein tyrosine phosphatase-mediated dephosphorylation in vascular smooth muscle cells

In atherosclerosis, abnormal vascular smooth muscle cell (VSMC) proliferation plays an important role to form fibroproliferative lesions and platelet-derived growth factor (PDGF)-BB is one of the most potent chemoattractants and proliferative factors for VSMCs. Taurine, sulfur-containing beta-amino acid, has been considered to prevent the development of atherosclerosis, although the molecular mechanism remains obscure. Previously, we demonstrated that taurine significantly suppressed PDGF-BB-induced cell proliferation, DNA synthesis, immediate-early gene expressions and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in VSMCs. The present study was aimed at elucidating the precise molecular mechanism of taurine in PDGF-BB signaling pathway. We showed that taurine significantly suppressed PDGF-BB-induced phosphorylation of PDGF-beta receptor and activation of its downstream signaling molecules such as Ras, MAPK/ERK kinase (MEK)1/2 and Akt. Because taurine did not attenuate phorbol 12-myristate 13-acetate (PMA)-induced PDGF-beta receptor-independent ERK1/2 phosphorylation, we further investigated the suppressive mechanism of taurine in PDGF-beta receptor level. Although taurine did not directly affect PDGF receptor autophosphorylation in vitro, taurine promoted PDGF-beta receptor dephosphorylation and restored PDGF-BB-induced suppression of protein tyrosine phosphatase (PTPase) activity. Taken together, we propose that taurine could prevent or delay the progression of atherosclerosis by PTPase-mediated suppression of PDGF-beta receptor phosphorylation, and by decreasing the activation of its downstream signaling molecules in VSMCs.

Role of Ras/PKCζ/MEK/ERK1/2 signaling pathway in angiotensin II-induced vascular smooth muscle cell proliferation

The role of protein kinase C (PKC) and its cross talk with extracellular signal-regulated kinase (ERK) cascade in angiotensin II (AngII)-elicited vascular smooth muscle cell (VSMC) proliferation are still unclear. In this study, the PKC pathway of AngII to activate ERK1/2 and induce cell proliferation was investigated in rat aortic smooth muscle cells. The proliferation of VSMCs was tested by [3H]-thymidine incorporation assay. Phosphorylated and non-phosphorylated PKCzeta, ERK1/2, Elk-1, and mitogen-activated ERK-activating kinase (MEK) were estimated by Western blot analysis. The interactions of signal molecules were examined by immunoprecipitation. AngII-induced VSMC proliferation and activation of ERK1/2 and nuclear transcription factor Elk-1 were all down-regulated by PKC non-specific inhibitor (staurosporine) and PKCzeta pseudosubstrate inhibitor (PS-PKCzeta). Dominant negative Ras transfection into VSMCs decreased AngII-induced PKCzeta and ERK1/2 phosphorylation. AngII stimulated the association of PKCzeta with Ras. AngII-induced MEK phosphorylation was inhibited by PKCzeta pseudosubstrate inhibitor and the PKCzeta-MEK complex was detected by immunoprecipitation. These results suggest that PKCzeta isoform is involved in VSMC proliferation and Elk-1 activation. AngII can activate ERK1/2 by Ras/PKCzeta/MEK pathway, which may be one of the important signal transduction pathways in AngII-induced VSMC proliferation.

Aging exacerbates neointimal formation, and increases proliferation and reduces susceptibility to apoptosis of vascular smooth muscle cells in mice

OBJECTIVES

In response to injury, aging mediates exaggerated neointimal formation, the pathologic hallmark of obliterative vascular diseases. We assessed the development of neointima in a model of mechanical vascular injury in aging mice (18 months old) and young mice (2 months old). To investigate the mechanisms by which aging affects neointimal formation, we also carried out a set of in vitro studies to characterize the biologic properties of vascular smooth muscle cells (VSMCs) derived from aging and young mice.

METHODS

Aging and young mice were subjected to wire injury to the carotid artery. Four weeks later injured arteries were harvested, and neointimal formation was histologically assessed. The profiles of angiogenesis-related genes between aortic VSMCs derived from aging and young mice were compared with complementary DNA arrays. Expression of platelet-derived growth factor receptor-alpha (PDGFR-alpha) and proliferation in response to platelet-derived growth factor-BB (PDGF-BB) by VSMCs were assessed. Susceptibility to apoptosis in aging and young VSMCs in response to nitric oxide and serum starvation was investigated. In addition, the level of apoptosis in neointimal VSMCs (by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay) was compared between aging and young animals.

RESULTS

When compared with young mice, aging mice exhibited exaggerated neointimal formation (intima-media ratio, 1.17 +/- 0.57 vs 0.49 +/- 0.16; P < .0001). Aging VSMCs expressed higher levels of PDGFR-alpha (12.0% +/- 2.7% vs 3.2 +/- 0.67%; P = .034) and greater proliferative response (4-fold increase) to PDGF-BB, compared with young VSMCs. However, aging VSMCs were less susceptible to apoptosis when subjected to serum starvation (75% less) and exposure to nitric oxide (50% less). Furthermore, there was more apoptosis in the neointima of young arteries than in their aging counterparts (8.75% +/- 3.3% vs 2.8% +/- 1.9; P = .021).

CONCLUSIONS

Age-dependent increases in PDGFR-alpha may alter VSMC proliferation, and when coupled with resistance to apoptosis could contribute to exaggerated neointima formation in aging animals. Of significance, our findings in the mouse will enable application of abundant molecular tools afforded by this species to further dissect the mechanisms of exaggerated neointimal formation associated with aging.

CLINICAL RELEVANCE

Neointimal formation is the pathologic hallmark of obliterative vascular diseases, including primary atherosclerosis, post stent restenosis, graft occlusion after vascular bypass procedures, and transplant allograft vasculopathy. Aging is an independent risk factor for development of cardiovascular diseases, and aging exaggerates neointimal formation after vascular injury. Understanding the mechanisms responsible for this phenomenon may facilitate prevention or provide new therapies for vascular occlusive diseases, which are so prevalent in the aging population. Our ability to reproduce the model in the mouse will no doubt facilitate such understanding.

Role of p44/p42 MAP kinase in the age-dependent increase in vascular smooth muscle cell proliferation and neointimal formation

OBJECTIVE

Age-dependent increase in vascular smooth muscle cell (VSMC) proliferation is thought to contribute to the pathology of atherosclerotic diseases. In this study, we investigated the role of mitogen-activated protein kinases (MAPKs) on VSMC proliferation and neointimal formation in the context of aging.

METHODS AND RESULTS

VSMCs were isolated from the aorta of young and old rabbits. The proliferative index after serum stimulation was significantly increased in old versus young VSMCs. This was associated with a significant and specific age-dependent increase in p44/p42 MAPK activation. Treatment with MEK inhibitor PD98059 successfully inhibited p44/p42 MAPK activities and VSMC proliferation. These results were confirmed in vivo using a model of balloon injury in rabbit iliac arteries. p44/p42 MAPK activities were rapidly induced by angioplasty in young and old animals. However, the levels of p44/p42 MAPK activities achieved in arteries of old rabbits were significantly higher than those of young rabbits. This was associated with a higher cellular proliferative index and a significant increase in neointimal formation in old animals. Local delivery of PD98059 in old rabbits successfully inhibited p44/p42 MAPK activities after angioplasty, which led to a significant reduction in cellular proliferation and neointimal formation in treated animals.

CONCLUSIONS

Our study suggests for the first time that increased p44/p42 MAPK activation contributes to augmented VSMC proliferation and neointimal formation with aging. p44/p42 MAPK inhibition could represent a novel therapeutic avenue against atherosclerotic diseases.

Effect of vitamin E and probucol on dietary cholesterol-induced atherosclerosis in rabbits

The preventive effect of vitamin E and Probucol against atherosclerosis in rabbits were compared. Atherosclerosis was induced by a 2% cholesterol-containing vitamin E-poor diet (5-10 ppm). Six groups of five rabbits each were studied. Group I (control) was fed on a vitamin E-poor diet. The other groups had the following supplements: group II, 50 mg/kg vitamin E i.m.; group III, 2% cholesterol; group IV, 2% cholesterol plus 50 mg/kg vitamin E i.m., group V, 2% cholesterol plus 1% Probucol; group VI, 2% cholesterol + 1% Probucol plus 50 mg/kg vitamin E i.m. After 4 weeks, aortas were removed and analyzed by light and scanning electron microscopy for atherosclerotic lesions. Samples of the media were analyzed for protein kinase C activity. The aortas of cholesterol-fed rabbits showed typical atherosclerotic lesions, detected by microscopic examination, their media smooth muscle cells exhibited an increase in protein kinase C activity. Vitamin E fully prevented cholesterol-induced atherosclerotic lesions and the induction of protein kinase C activity. Probucol was not effective in preventing either cholesterol-induced atherosclerotic lesions or the induction of protein kinase C activity. These results show that the protective effect of vitamin E against hypercholesterolemic atherosclerosis is not produced by an other antioxidant such as Probucol, and therefore, may not be linked to the antioxidant properties of this vitamin. The effects observed at the level of smooth muscle cells ex vivo suggest an involvement of signal transduction events in the protective effect of vitamin E against atherosclerosis.

Mevalonate deprivation impairs IGF-I/insulin signaling in human vascular smooth muscle cells

3-Hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase inhibitors (statins) are therapeutically used to lower plasma cholesterol levels. In addition, these drugs can block vascular smooth muscle cell (VSMC) proliferation. The present study addressed the question whether the inhibitory effect of lovastatin on premitotic DNA synthesis correlates with a downregulation of c-fos mRNA levels, a marker of signaling efficiency, in human SMC. Here we show that in human SMC exposed to individual growth factors (platelet-derived growth factor, epidermal growth factor, alpha-thrombin, insulin, insulin-like growth factor I (IGF-I)) and human serum, the maximal [3H]thymidine incorporation and c-fos mRNA expression are closely correlated. Only alpha-thrombin elicited overexpression of c-fos as compared with its effect on [3H]thymidine incorporation. Lovastatin efficiently inhibited [3H]thymidine uptake promoted by all mitogens tested (76-87%); however, it significantly inhibited upregulation of c-fos mRNA levels induced only by insulin (33-67%, P < 0.05) and IGF-I (31 57%, P < 0.05). This inhibition was overcome by mevalonate and geranylgeraniol, and partially by farnesol. c-fos mRNA expression induced by 4-beta-phorbol-12-myristate-13-acetate, an activator of protein kinase C, was insensitive to lovastatin treatment. Thus, in human vascular SMC, lovastatin impairs premitotic DNA synthesis induced by growth factors, but only c-fos expression promoted by insulin and IGF-I. These data indicate that statin-sensitive and -insensitive pathways seem to be involved in the regulation of c-fos in the response of human SMC to proliferative stimuli, and suggest a prominent role of isoprenylated proteins in the activation of VSMC through the IGF-I/insulin dependent pathways.

Effects of protein kinase C alpha overexpression on A7r5 smooth muscle cell proliferation and differentiation

Smooth muscle cell differentiation and proliferation are increasingly seen to be intimately tied to the etiology of atherosclerosis and hypertension. To determine the role of PKC alpha in the regulation of smooth muscle cell differentiation and proliferation, the rat embryonic smooth muscle cell line A7r5 was transfected with an expression vector containing the full-length PKC alpha cDNA. Neomycin-resistant clones which exhibited increased PKC alpha levels compared to wild-type cells were selected. The A7r5 cells overexpressing PKC alpha had altered morphology and decreased growth rates compared to wild-type cells and cells transfected only with the neomycin resistance gene. Electrophoretic mobility shift assays showed that nuclear extracts from overexpressing clones gave a different pattern of protein-DNA binding to an AP-1 consensus oligonucleotide compared to wild-type cells. In contrast to the growth characteristics of these clones, their levels of cell differentiation marker proteins such as vinculin and desmin were not affected by PKC alpha overexpression. Moreover, the smooth muscle-specific differentiation marker alpha-actin was markedly reduced, while beta-actin levels were found to remain unchanged. Northern blot analysis confirmed that alpha-actin downregulation occurred at the RNA level. Western blot analysis revealed that A7r5 cells have five different PKC isoforms and that these isoform protein levels were not changed by PKC alpha overexpression. These findings suggest that PKC alpha regulates growth and differentiation of A7r5 smooth muscle cells and that these changes might result from altered expression/function of AP-1 transcription factors.

Alpha-tocopherol as a modulator of smooth muscle cell proliferation

The effects of alpha-tocopherol and beta-tocopherol have been studied in rat and human aortic smooth muscle cells. Alpha-tocopherol, but not beta-tocopherol, inhibited smooth muscle cell proliferation and protein kinase C in a dose-dependent manner, at concentrations ranging from 10 to 50 microM. Beta-tocopherol added simultaneously with alpha-tocopherol prevented both proliferation and protein kinase C inhibition. Protein kinase C inhibition was cell cycle-dependent and it was prevented by okadaic acid, a protein phosphatase inhibitor. Protein kinase C activity measured from aortas of cholesterol-fed rabbits was also inhibited by alpha-tocopherol. By using protein kinase C (PKC) isoform-specific inhibitors and immunoprecipitation reactions it was found that PKC-alpha was selectively inhibited by alpha-tocopherol. Further, an activation of protein phosphatase 2A by alpha-tocopherol was found, which caused PKC-alpha dephosphorylation and inhibition. Ultimately, this cascade of events at the level of cell signal transduction leads to the inhibition of smooth muscle cell proliferation.

Dietary cholesterol-induced changes of protein kinase C and the effect of vitamin E in rabbit aortic smooth muscle cells

The changes occuring in smooth muscle cells during the development of atherosclerosis in rabbits fed 2% cholesterol and the effect of vitamin E treatment were investigated. Ex-vivo smooth muscle cells obtained from the aorta of cholesterol-fed rabbits exhibited a 2-fold increase of protein kinase C expression and activity. The cholesterol induced changes in protein kinase C were equally present in the membrane bound and cytosolic fraction of the enzyme. The amount of a control protein alpha-actin was not affected in smooth muscle cell by the high cholesterol diet treatment, indicating that protein kinase C increase was specific. The increase of protein kinase C expression and activity was not significantly affected by vitamin E treatment although a constant trend was noted. The data are discussed in the light of previous smooth muscle cell in vitro experiments.

Insulin increases distinct species of 1,2-diacylglycerol in isolated perfused rat heart

Insulin and glucose increase the synthesis of 1,2-diacylglycerol (1,2-DAG), the physiological activator of protein kinase C (PKC) in a variety of tissues and cells. The effects of insulin and glucose on the abundance and fatty acid composition of 1,2-DAG were investigated in isolated perfused rat hearts with the use of capillary gas chromatography and 1,2-dipentadecanoin as an internal standard. A high concentration of insulin (25 mU/ mL) significantly increased cardiac contractility and reduced coronary flow. In addition, perfusion with 25 mU/mL insulin induced significant increases of 18.2% and 26.4% in 1,2-DAG mass after 5 and 30 minutes, respectively, in the presence of 8.6 mmol/L glucose, whereas there was no increase in 1,2-DAG with 2.5 mU/mL insulin. Analysis of the fatty acid composition of 1,2-DAG showed that only species containing specific fatty acids (16:0, 18:1, and 18:2) were increased in response to insulin. In contrast, an increase in glucose concentration in the perfusion medium from 3 to 17 mmol/L had no effect on the total mass or fatty acid composition of 1,2-DAG, cardiac contractility, or coronary flow. Addition of a high insulin concentration to the high-glucose medium increased the abundance of 1,2-DAG containing 16:0, 18:1, and 18:2 fatty acids, as well as cardiac contractility. It is concluded that the effect of insulin on cardiac contractility may be related to the associated increase in 1,2-DAG abundance.

Age-related changes affecting atherosclerotic risk. Potential for pharmacological intervention

The incidence of cardiovascular diseases that are related to the atherosclerotic process increases exponentially with age. Organ lesions, the clinical manifestation of atherosclerotic disease, are late events due to complications in the plaque (ulceration, thrombosis, calcification) which are the result of an increased vulnerability to disruption of a previously stable plaque. The higher incidence of age-related clinical events could be explained by a rising sensitivity of plaques to destabilising factors, both parietal and humoral. The increased probability that a plaque in an elderly patient will became vulnerable could be related to those destabilising factors that significantly increase with aging, such as advanced glycation end-products. For these reasons, it seems most important that the analysis of these age-related destabilising factors, rather than those factors that promote the development of early atherosclerotic plaques, should be undertaken. Taking the point of view of a pharmacological intervention, this should eventually lead to a more complete understanding of this process.

Potentiation of PDGF-induced growth responses in coronary artery smooth muscle cells by thromboxane

Mitogenic effects of TXA2 in vascular smooth muscle cells are discussed to be dependent on the age of the donor organism. The present study investigates the contribution of TXA2 on PDGF-induced proliferation of bovine coronary artery smooth muscle cells (BCA-SMC) isolated from adult animals. Radioligand binding studies revealed high affinity TXA2 binding sites (Kd = 1.6 nM) in these cells. TXA2-mimetics alone showed no proliferative effect in BCA-SMC, assessed by [3H]thymidine incorporation. However, PDGF-stimulated proliferation was potentiated two-fold receptor-dependently by TXA2-mimetics. Thus, vasoconstrictory eicosanoids released from activated platelets might aggravate proliferation of vascular smooth muscle cells at sites of vessel injury in the adult organism.

A dialysis culture system for the study of the production and modulation of growth-regulatory molecules: studies using the P388D1 macrophage cell line

P388D1 macrophage-like cells have previously been shown to produce both mitogenic and inhibitory regulators of porcine smooth muscle cell (pSMC) growth. The mitogenic activity was shown to have a molecular mass of &gt; 10 kDa while the inhibitory activity was in the range of 2–6 kDa. In the present study, we present a novel dialysis culture system where P388D1 cells were grown in dialysis membranes with a 12 kDa cut-off which allowed continuous production of fractions of the culture medium. Using pSMC as target cells, mitogenic activity was found to be retained by the dialysis membrane while the low molecular mass inhibitory activity passed freely through the membrane. The effect of the macrophage-activators phorbol myristate acetate (PMA), concanavalin A (ConA) and interferon-gamma in combination with lipopolysaccharide (IFN gamma/LPS) were investigated in the dialysis culture system. PMA, ConA and IFN gamma/LPS were found to enhance the production of mitogenic activity by P388D1 cells. PMA also increased the production of growth-inhibitory activity, while ConA abolished inhibitor production and IFN gamma/LPS had no effect on the amount of inhibitory activity produced by P388D1 cells. The experiments show that the balance of production of mitogenic and inhibitory activities by macrophages can be modulated by agents that alter the state of activation of the cells. This could be of profound significance in the influence of macrophages on smooth muscle cell growth during the development of atherosclerosis.