Calcium and the replication of human vascular smooth muscle cells: studies on the activation and translocation of extracellular signal regulated kinase (ERK) and cyclin D1 expression

Stimulation of vascular smooth muscle cell proliferation by stiff matrix via the IKCa channel-dependent Ca2+ signaling

Vascular stiffening, an early and common characteristic of cardiovascular diseases (CVDs), stimulates vascular smooth muscle cell (VSMC) proliferation which reciprocally accelerates the progression of CVDs. However, the mechanisms by which extracellular matrix stiffness accompanying vascular stiffening regulates VSMC proliferation remain largely unknown. In the present study, we examined the role of the intermediate-conductance Ca²⁺ -activated K⁺  (IK_Ca ) channel in the matrix stiffness regulation of VSMC proliferation by growing A7r5 cells on soft and stiff polydimethylsiloxane substrates with stiffness close to these of arteries under physiological and pathological conditions, respectively. Stiff substrates stimulated cell proliferation and upregulated the expression of the IK_Ca channel. Stiff substrate-induced cell proliferation was suppressed by pharmacological inhibition using TRAM34, an IK_Ca channel blocker, or genetic depletion of the IK_Ca channel. In addition, stiff substrate-induced cell proliferation was also suppressed by reducing extracellular Ca²⁺ concentration using EGTA or intracellular Ca²⁺ concentration using BAPTA-AM. Moreover, stiff substrate induced activation of extracellular signal-regulated kinases (ERKs), which was inhibited by treatment with TRAM34 or BAPTA-AM. Stiff substrate-induced cell proliferation was suppressed by treatment with PD98059, an ERK inhibitor. Taken together, these results show that substrates with pathologically relevant stiffness upregulate the IK_Ca channel expression to enhance intracellular Ca²⁺ signaling and subsequent activation of the ERK signal pathway to drive cell proliferation. These findings provide a novel mechanism by which vascular stiffening regulates VSMC function.

The effects of calcium channel blockade on proliferation and differentiation of cardiac progenitor cells

Cardiogenesis depends on a tightly regulated balance between proliferation and differentiation of cardiac progenitor cells (CPCs) and their cardiomyocyte descendants. While exposure of early mouse embryos to Ca(2+) channel antagonists has been associated with abnormal cardiac morphogenesis, less is known about the consequences of Ca(2+) channel blockade on proliferation and differentiation of CPCs at the cellular level. Here we showed that at embryonic day (E) 11.5, the murine ventricles express several L-type and T-type Ca(2+) channel isoforms, and that the dihydropyridine Ca(2+) channel antagonist, nifedipine, blunts isoproterenol induced increases in intracellular Ca(2+). Nifedipine mediated Ca(2+) channel blockade was associated with a reduction in cell cycle activity of E11.5 CPCs and impaired assembly of the cardiomyocyte contractile apparatus. Furthermore, in cell transplantation experiments, systemic administration of nifedipine to adult mice receiving transplanted E11.5 ventricular cells (containing CPCs and cardiomyocytes) was associated with smaller graft sizes compared to vehicle treated control animals. These data suggest that intracellular Ca(2+) is a critical regulator of the balance between CPC proliferation and differentiation and demonstrate that interactions between pharmacological drugs and transplanted cells could have a significant impact on the effectiveness of cell based therapies for myocardial repair.

Effects of thapsigargin on the proliferation and survival of human rheumatoid arthritis synovial cells

A series of experiments have been carried out to investigate the effects of different concentrations of thapsigargin (0, 0.001, 0.1, and 1 μM) on the proliferation and survival of human rheumatoid arthritis synovial cells (MH7A). The results showed that thapsigargin can block the cell proliferation in human rheumatoid arthritis synovial cells in a time- and dose-dependent manner. Results of Hoechst staining suggested that thapsigargin may induce cell apoptosis in MH7A cells in a time- and dose-dependent manner, and the percentages of cell death reached 44.6% at thapsigargin concentration of 1 μM treated for 4 days compared to the control. The protein and mRNA levels of cyclin D1 decreased gradually with the increasing of thapsigargin concentration and treatment times. Moreover, the protein levels of mTORC1 downstream indicators pS6K and p4EBP-1 were reduced by thapsigargin treatment at different concentrations and times, which should be responsible for the reduced cyclin D1 expressions. Our results revealed that thapsigargin may effectively impair the cell proliferation and survival of MH7A cells. The present findings will help to understand the molecular mechanism of fibroblast-like synoviocytes proliferations and suggest that thapsigargin is of potential for the clinical treatment of rheumatoid arthritis.

Low nanomolar thapsigargin inhibits the replication of vascular smooth muscle cells through reversible endoplasmic reticular stress

Thapsigargin (TG), an inhibitor of Ca(2+) ATPase pumps in the endoplasmic reticulum (ER), inhibits replication of human vascular smooth muscle cell (hVSMC) at low nM concentrations. TG blocks replication of other cell types through promotion of ER stress (ERS). In order to determine whether ERS may mediate the cytostatic effect of TG in hVSMCs, the effect of TG on ERS in hVSMCs was studied by assessing markers of ERS: Immunoglobulin Heavy Chain Binding Protein (BiP), growth inhibitory transcription factor, GADD153, phosphorlylated eukaryotic initiation factor 2α (p-eIF2α) and phosphorlylated protein kinase R (p-PKR). hVSMCs derived from saphenous veins were rendered quiescent with serum-free medium for 96 h incubated with 10 nM TG at 37 °C for 24 h, then washed free of TG and incubated with 10% foetal calf serum (FCS) for a further 24 h. At selected times, BiP, GADD153, p-eIF2α, p-PKR and cyclin D1 expression was assessed. TG promoted a marked increase in BiP and GADD153, but suppressed cyclin D1 mRNA and protein expression. Under serum-free conditions p-eIF2α and p-PKR expression was not enhanced by TG. 15-24 h After removal of TG all these factors returned to levels seen in control cells. These data demonstrate that the inhibitory effect of 10nM TG on hVSMC replication is mediated through induction of ERS and associated factors that cessate replication and is reversible. These observations have implications in the aetiology and treatment of diseases that include atherogenesis, vein graft failure and restenosis.

NADPH oxidase 4 mediates upregulation of type 4 phosphodiesterases in human endothelial cells

The protective actions of prostacyclin (PGI(2) ) are mediated by cyclic AMP (cAMP) which is reduced by type 4 phosphodiesterases (PDE4) which hydrolyze cAMP. Superoxide (O2(-)) from NADPH oxidase (Nox) is associated with impaired PGI(2) bioactivity. The objective of this study, therefore, was to study the relationship between Nox and PDE4 expression in human umbilical vein endothelial cells (HUVECs). HUVECs were incubated with the thromboxane A(2) analog, U46619, 8-isoprostane F(2α) (8IP), or tumor necrosing factor alpha (TNFα) [±iloprost (a PGI(2) analog)] and the expression of PDE4A, B, C, and D and splice variants thereof assessed using Western blotting and qPCR and mRNA silencing of Nox4 and Nox5. Effects on cell replication and angiogenesis were also studied. U46619, 8IP, and TNFα increased the expression of Nox 4 and Nox 5 and all PDE4 isoforms as well as cell replication and tubule formation (index of angiogenesis), effects inhibited by mRNA silencing of Nox4 (but not Nox5) and iloprost and rolipram. These data demonstrate that upregulation of Nox4 leads to an upregulation of PDE4A, B, and D and increased hydrolysis of cAMP which in turn augments cell replication and angiogenesis. This mechanism may be central to vasculopathies associated with endothelial dysfunction since the PGI(2)-cAMP signaling axis plays a key role in mediating functions that include hemostasis and angiogenesis.

Comparison of sildenafil with strontium fructose diphosphate in improving erectile dysfunction against upregulated cavernosal NADPH oxidase, protein kinase Cε, and endothelin system in diabetic rats

Objectives

Phosphodiesterase type 5 inhibitors are potent in relieving erectile dysfunction (ED), however, they are less satisfactory in diabetic patients, probably due to the pro-inflammatory biomarkers caused by diabetes. Therefore, it was interesting to compare the effects of sildenafil with strontium fructose 1,6-diphosphate (FDP-Sr) on cavernosal vascular activity and expressions of pro-inflammatory biomarkers in diabetic rats.

Methods

Male Sprague-Dawley rats were injected with streptozocin (60 mg/kg, i.p.) to develop diabetes. The animals were diabetic for eight weeks with sildenafil (12 mg/kg per day) or FDP-Sr (200 mg/kg per day) being administered for the last four of those eight weeks.

Key findings

Sildenafil was more effective in relieving reduced vascular dilatation (relevant to ED), but less in attenuating over-expressions of NADPH oxidase p22, p47 and p67 subunits, and ETA/BR (endothelin receptor type A and type B) in the diabetic cavernosum. In contrast, FDP-Sr was less effective in improving ED, but more effective in normalizing the abnormal NADPH oxidase and ETA/BR.

Conclusions

The activated NADPH oxidase and upregulated ETAR and ETBR due to diabetic lesions played a minor or moderate role in ED. By offering extra ATP, FPD-Sr suppressed these abnormalities, however, sildenafil did not. A combined therapy of sildenafil with FDP-Sr may be more effective in relieving ED in diabetic patients through normalizing pro-inflammatory cytokines and improving the nitric oxide/cGMP pathway in the cavernosum.

Mitogen activated protein kinase at the nuclear pore complex

Mitogen activated protein (MAP) kinases control eukaryotic proliferation, and import of kinases into the nucleus through the nuclear pore complex (NPC) can influence gene expression to affect cellular growth, cell viability and homeostatic function. The NPC is a critical regulatory checkpoint for nucleocytoplasmic traffic that regulates gene expression and cell growth, and MAP kinases may be physically associated with the NPC to modulate transport. In the present study, highly enriched NPC fractions were isolated and investigated for associated kinases and/or activity. Endogenous kinase activity was identified within the NPC fraction, which phosphorylated a 30 kD nuclear pore protein. Phosphomodification of this nucleoporin, here termed Nup30, was inhibited by apigenin and PD-98059, two MAP kinase antagonists as well as with SB-202190, a pharmacological blocker of p38. Furthermore, high throughput profiling of enriched NPCs revealed constitutive presence of all members of the MAP kinase family, extracellular regulated kinases (ERK), p38 and Jun N-terminal kinase. The NPC thus contains a spectrum of associated MAP kinases that suggests an intimate role for ERK and p38 in regulation of nuclear pore function.

Interactions between calcium and reactive oxygen species in pulmonary arterial smooth muscle responses to hypoxia

In contrast to the systemic vasculature, where hypoxia causes vasodilation, pulmonary arteries constrict in response to hypoxia. The mechanisms underlying this unique response have been the subject of investigation for over 50 years, and still remain a topic of great debate. Over the last 20 years, there has emerged a general consensus that both increases in intracellular calcium concentration and changes in reactive oxygen species (ROS) generation play key roles in the pulmonary vascular response to hypoxia. Controversy exists, however, regarding whether ROS increase or decrease during hypoxia, the source of ROS, and the mechanisms by which changes in ROS might impact intracellular calcium, and vice versa. This review will discuss the mechanisms regulating [Ca2+]i and ROS in PASMCs, and the interaction between ROS and Ca2+ signaling during exposure to acute hypoxia.

Calcium channel regulation in vascular smooth muscle cells: synergistic effects of statins and calcium channel blockers

In the Anglo-Scandinavian Cardiac Outcomes Trial-Lipid Lowering Arm (ASCOT-LLA) we have reported a positive interaction between atorvastatin and amlodipine-based antihypertensive strategy in terms of the prevention of coronary events. In cellular and molecular studies on human vascular smooth muscle cells (VSMC) we have reported that transformation from a differentiated to a synthetic or dedifferentiated phenotype is associated with loss of function of L-type calcium channels and hence loss of potential responsiveness to calcium channel blockers (CCB). Statins directly inhibit cell cycle progression and dedifferentiation of VSMC due to their ability to inhibit the synthesis of isoprenoid cholesterol intermediates. We hypothesize that statins promote a more differentiated VSMC phenotype that results in upregulation of L-type calcium channels and restoration of a CCB-sensitive calcium influx pathway in VSMC, favourably affecting the balance that exists between VSMC proliferation, apoptosis and matrix metalloproteinase production with an associated increase in stability of atheromatous plaques.

High-Expression of Transforming Growth Factor β1and Phosphorylation of Extracellular Signal-Regulated Protein Kinase in Vascular Smooth Muscle Cells from Aorta and Renal Arterioles of Spontaneous Hypertension Rats

To further elucidate the molecular mechanisms involved in hypertensive vascular remodeling, an immunohistochemical technique and Western blot were applied to study phospho-extracellular signal-regulated kinase (ERK1/2) and transforming growth factor beta1 (TGF-beta1) expression in endothelial and vascular smooth muscle cell (VSMC) of the thoracic aorta and renal arterioles from SHR of different ages. Results of both the immunohistochemistry and Western blot assays showed that either the phospho-ERK1/2 at endothelium or VSMC of renal small arteries from SHR8, SHR16, and SHR20 groups and of the aorta from SHR16 and SHR20 were higher than that from control group. Comparing with that in the small arteries of the kidney, the phospho-ERK1/2 in the endothelium and in VSMC was markedly increased in the aorta, and high expression of TGF-beta1 was detected in the aorta and kidney from SHR16 and SHR20 by Western blot. These results suggested that ERK 1/2 could be activated by phosphorylation with over-expression of TGF-beta1 in the endothelium and in VSMC of aorta and renal arterioles from SHR, which might play an important role in VSMC proliferation under hypertension.

Orally administered penicillamine is a potent inhibitor of neointimal and medial thickening in porcine saphenous vein–carotid artery interposition grafts

OBJECTIVE

In patients who have undergone coronary artery bypass grafting, blood copper levels are elevated for 6 weeks after surgery. Copper is an established risk factor for cardiovascular disease and atherogenesis and promotes oxidative stress, lipid oxidation, cell proliferation, and matrix formation, all components of vein graft disease. This project therefore examined the effect of the copper chelator penicillamine on saphenous vein graft thickening in a pig model.

METHODS

Saphenous vein-carotid artery interposition grafts were carried out in Landrace pigs. Penicillamine (10 mg/kg once daily, n = 8) was administered orally incorporated into small amounts of mashed potato for 1 month (n = 8 controls). Vein grafts were then excised and fixed at 100 mm Hg, histologic sections were prepared, and morphometry and measurement of proliferating cell nuclear antigen count were carried out. In vitro studies on the effect of copper or penicillamine on human vascular smooth muscle cell replication was carried out with bromodeoxyuridine incorporation.

RESULTS

Administration of penicillamine had a potent inhibitory effect on both neointimal and medial thickness and proliferating cell nuclear antigen count but elicited a marked increase in luminal area and reduced serum copper concentrations. In vitro, copper augmented vascular smooth muscle cell proliferation, an effect blocked by penicillamine. Penicillamine alone also inhibited in vitro vascular smooth muscle cell replication.

CONCLUSION

The administration of penicillamine reduces vein graft thickening and promotes positive remodeling through negation of copper-induced cell proliferation. Copper chelators may therefore be therapeutically useful in preventing late vein graft failure in patients undergoing reconstructive arterial surgery.

Ca2+ channels and chronic hypoxia

Many chronic lung diseases are associated with prolonged exposure to alveolar hypoxia, resulting in the development of pulmonary hypertension. While the exact mechanisms underlying the pathogenesis of hypoxic pulmonary hypertension remain poorly understood, a key role for changes in Ca2+ homeostasis has emerged. Intracellular Ca2+ concentration controls a variety of pulmonary vascular cell functions, including contraction, gene expression, growth, barrier function and synthesis of vasoactive substances. Several studies indicate that prolonged exposure to hypoxia causes alterations in the expression and activity of several Ca2+ handling pathways in pulmonary arterial smooth muscle cells. In contrast, the effect of chronic hypoxia on Ca2+ homeostasis in pulmonary arterial endothelial cells is relatively unexplored. In this review, we discuss data from our laboratory and others describing the effects of prolonged hypoxia on pulmonary vascular smooth muscle and endothelial cell Ca2+ homeostasis and the various Ca2+ channels and handling pathways involved in these responses. We will also highlight future directions of investigation that might improve our understanding of the response of pulmonary vascular cells to chronic hypoxia.

Vascular endothelial growth factor stimulates a novel calcium-signaling pathway in vascular smooth muscle cells

BACKGROUND

Vascular endothelial growth factor (VEGF) is a potent vascular mitogen that selectively stimulates vascular smooth muscle cell (VSMC) migration through an unknown mechanism while having no effect on VSMC proliferation. It is known that VSMC migration and proliferation are dependent on the second messenger Ca2+ and, in particular, mitogen-stimulated Ca2+ influx. We hypothesized that the selective effect of VEGF on VSMC migration versus proliferation was a result of differential VEGF-stimulated Ca2+ signaling pathways.

METHODS

Primary cultured human aortic smooth muscle cells (VSMCs) were grown to subconfluency and assigned to the following experimental groups: no stimulation, stimulation with platelet-derived growth factor-BB (PDGF-BB) (20 ng/mL) as positive control, and stimulation with VEGF165 (40 ng/mL). Total increase in [Ca2+]cyt and intracellular calcium release was quantified with the use of a fura-2 fluorescence assay. Assays for the following receptors VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1) and PDGFR-beta were performed by immunoprecipitation, while PLCgamma1, Akt 1/2, and phospholamban B phosphorylation were assessed with Western immunoblotting.

RESULTS

VSMCs stimulated with VEGF165 exhibited no intracellular Ca2+ release, compared with a 75 +/- 30 nmol/L intracellular calcium release after PDGF-BB stimulation, (P < .02) VEGF165-stimulated VSMCs in Ca2+-containing media exhibited 192 +/- 26 nmol/L increase in [Ca2+]cyt, compared with 354 +/- 54 nmol/L increase after PDGF-BB stimulation (P < .02). VEGF165 did not phosphorylate PLCgamma1 after 1, 5, or 10 minutes of treatment. VEGF165 treatment did not result in PI3-K/Akt activation at 1-, 5-, or 10-minute time points. Calmodulin-dependent kinase II (CaMKII) was activated by both VEGF165 and PDGF-BB after 1 and 5 minutes of stimulation. The presence of the receptors VEGFR-1, VEGFR-2, and PDGFR-beta was confirmed in all experimental groups.

CONCLUSIONS

VEGF induces extracellular calcium influx but no intracellular calcium release in VSMCs. This lack of intracellular Ca2+ release stems from the inability of VEGF165 to activate the PLCgamma1 cascade and IP3 receptor-mediated Ca2+ release. The lack of PI3-K/Akt activation at these time points indicates a novel extracellular Ca2+ influx pathway sufficient to activate CaMKII. A paradigm relating extracellular Ca2+ influx to CaMKII activation and migration is suggested and may account for the selective effects of VEGF on VSMC migration.