Regulation of connexin expression after balloon injury: possible mechanisms for antiproliferative effect of statins

Beneficial effect of simvastatin on human umbilical vein endothelial cells gap junctions induced by TNF-α

Although simvastatin has been shown to inhibit vascular permeability, which might be amplified via gap junction intercellular communication (GJIC), the underlying mechanism of action remains unclear. In the present study, we investigated the effects and mechanisms of simvastatin on endothelial cells GJIC. Specifically, human umbilical vein endothelial cells (HUVECs) were stimulated with TNF-α (10 ng/mL) alone or in combination with simvastatin (5 µM), and their effects on vascular endothelial cell GJIC tested via the scrape loading/dye transfer (SL/DT) assay. Next, we performed immunofluorescence, real-time PCR and western blot assays to analyze expression of Cx37, Cx40 and Cx43 in HUVECs. Results showed that GJIC activity in HUVECs was markedly elevated in HUVECs treated with TNF-α in combination with simvastatin. In addition, simvastatin treatment significantly upregulated expression of Cx37 and Cx40 but downregulated Cx43 mRNAs and proteins. Taken together, these marked changes indicated that simvastatin exerts its regulatory effects on gap junction function by upregulating Cx37 and Cx40 and downregulating Cx43 expression.

Connexins in Cardiovascular and Neurovascular Health and Disease: Pharmacological Implications

Connexins are ubiquitous channel forming proteins that assemble as plasma membrane hemichannels and as intercellular gap junction channels that directly connect cells. In the heart, gap junction channels electrically connect myocytes and specialized conductive tissues to coordinate the atrial and ventricular contraction/relaxation cycles and pump function. In blood vessels, these channels facilitate long-distance endothelial cell communication, synchronize smooth muscle cell contraction, and support endothelial-smooth muscle cell communication. In the central nervous system they form cellular syncytia and coordinate neural function. Gap junction channels are normally open and hemichannels are normally closed, but pathologic conditions may restrict gap junction communication and promote hemichannel opening, thereby disturbing a delicate cellular communication balance. Until recently, most connexin-targeting agents exhibited little specificity and several off-target effects. Recent work with peptide-based approaches has demonstrated improved specificity and opened avenues for a more rational approach toward independently modulating the function of gap junctions and hemichannels. We here review the role of connexins and their channels in cardiovascular and neurovascular health and disease, focusing on crucial regulatory aspects and identification of potential targets to modify their function. We conclude that peptide-based investigations have raised several new opportunities for interfering with connexins and their channels that may soon allow preservation of gap junction communication, inhibition of hemichannel opening, and mitigation of inflammatory signaling.

Yiqihuoxuejiedu Formula Restrains Vascular Remodeling by Reducing the Inflammation Reaction and Cx43 Expression in the Adventitia after Balloon Injury

Vascular remodeling is closely related to hypertension, atherosclerosis, and restenosis after PCI. Considerable evidence indicates that the activation and proliferation of adventitial fibroblasts play key roles in vessel injury. The inflammatory response and high expression of connexins contribute to adventitial remodeling. Therefore, reducing inflammation reaction and connexins expression in adventitia may become a new target to prevent vascular remodeling. Yiqihuoxuejiedu formula, composed of TCM therapeutic principle of supplementing qi, activating blood and detoxification, can inhibit restenosis after intimal injury. To further investigate the effect of Yiqihuoxuejiedu formula on inflammation and connexins, we established a carotid artery injury model. In model rats, hyperplasia in the intima was mild but obvious in the adventitia; CRP heightened; expressions of MCP-1, CD68, and Cx43 increased. Yiqihuoxuejiedu formula relieved intimal hyperplasia and adventitial area, obviously diminished the expressions of CD68 and Cx43 in the adventitia, and reduced CRP but did not lower MCP-1. These results indicated that Yiqihuoxuejiedu formula inhibited vascular remodeling especially adventitial hyperplasia by reducing the inflammation reaction including lowering macrophages infiltration and systemic nonspecific inflammatory response and also restraining gap junction connexins leading to less communication among cells. This study provides new ideas and methods for the prevention and treatment of vascular remodeling.

Lentivirus-mediated RNAi knockdown of the gap junction protein, Cx43, attenuates the development of vascular restenosis following balloon injury

Percutaneous coronary intervention [PCI or percutaneous transluminal coronary angioplasty (PTCA)] has been developed into a mature interventional treatment for atherosclerotic cardiovascular disease. However, the long-term therapeutic effect is compromised by the high incidence of vascular restenosis following angioplasty, and the underlying mechanisms of vascular restenosis have not yet been fully elucidated. In the present study, we investigated the role of the gap junction (GJ) protein, connexin 43 (Cx43), in the development of vascular restenosis. To establish vascular restenosis, rat carotid arteries were subjected to balloon angioplasty injury. At 0, 7, 14 and 2 days following balloon injury, the arteries were removed, and the intimal/medial area of the vessels was measured to evaluate the degree of restenosis. We found that the intimal area gradually increased following balloon injury. Intimal hyperplasia and restenosis were particularly evident at 14 and 28 days after injury. In addition, the mRNA and protein expression of Cx43 was temporarily decreased at 7 days, and subsequently increased at 14 and 28 days following balloon injury, as shown by RT-PCR and western blot analysis. To determine the involvement of Cx43 in vascular restenosis, the lentivirus vector expressing shRNA targeting Cx43, Cx43-RNAi-LV, was used to silence Cx43 in the rat carotid arteries. The knockdown of Cx43 effectively attenuated the development of intimal hyperplasia and vascular restenosis following balloon injury. Thus, our data indicate the vital role of the GJ protein, Cx43, in the development of vascular restenosis, and provide new insight into the pathogenesis of vascular reste-nosis. Cx43 may prove to be a novel potential pharmacological target for the prevention of vascular restenosis following PCI.

Inhibition of neointimal hyperplasia in rats treated with atorvastatin after carotid artery injury may be mainly associated with down-regulation of survivin and Fas expression

CONTEXT

Atorvastatin is a member of the drug class known as statins, which is used for lowering blood cholesterol.

OBJECTIVE

The present study investigates the effect and mechanism of atorvastatin on neointimal hyperplasia after carotid artery injury (CAI) of rat.

MATERIALS AND METHODS

Fifty male rats were randomly divided into four groups: control group, sham-operated group, model group, and atorvastatin treatment group. The treatment group was fed with atorvastatin (10 mg/kg) with gastro-gavage at 5 p.m. every day for 28 d after surgery. The control group, model group, and sham-operated group were fed with the same volume of distilled water instead. The proliferations of intimal and medial layers were evaluated by hematoxylin & eosin (H&E) staining. The apoptosis of vascular smooth muscle cells (VSMCs) was determined by terminal deoxynucleotidyl transferased UTP nick end labeling (TUNEL) staining. Plasma concentrations of survivin and sFas were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Atorvastatin reduced neointimal formation and increased apoptosis of VSMCs in neointima. VSMCs apoptosis emerged at 3 d (8.42 ± 0.449 μm) and the intimal proliferation peaked by the end of 14 d (41.58 ± 1.64 μm). The plasma levels of survivin and sFas were gradually increased with the neointimal hyperplasia and increasingly decreased after atorvastatin treatment. The plasma levels of survivin and sFas in rats were elevated at 3 d (464.80 ± 105.27 pg/ml and 3256.00 ± 478.20 pg/ml, respectively), reached the peak of survivin at 14 d (1089.20 ± 232.32 pg/ml) and sFas at 7 d (4362.00 ± 639.92 pg/ml) and decreased at 28 d (562.00 ± 90.11 pg/ml and 2148.00 ± 257.14 pg/ml, respectively) in the model group. Compared with the model group, the atorvastatin treatment group has significantly less neointimal hyperplasia and more apoptosis of VSMCs.

CONCLUSIONS

Atorvastatin can inhibit neointimal hyperplasia and promote SMCs apoptosis in neointimal layers, which may be mainly associated with down-regulation of survivin and Fas expression after CAI of rat.

Multiple roles of connexins in atherosclerosis- and restenosis-induced vascular remodelling

Endothelial dysfunction is the initial step in atherosclerotic plaque development in large- and medium-sized arteries. This progressive disease, which starts during childhood, is characterized by the accumulation of lipids, macrophages, neutrophils, T lymphocytes and smooth muscle cells in the intima of the vessels. Erosion and rupture of the atherosclerotic plaque may induce myocardial infarction and cerebrovascular accidents, which are responsible for a large percentage of sudden deaths. The most common treatment for atherosclerosis is angioplasty and stent implantation, but these surgical interventions favour a vascular reaction called restenosis and the associated de-endothelialization increases the risk of thrombosis. This review provides an overview of the role of connexins, a large family of transmembrane proteins, in vascular remodelling associated with atherosclerosis and restenosis. The connexins expressed in the vascular wall are Cx37, Cx40, Cx43 and Cx45; their expressions vary with vascular territory and species. Connexins form hemichannels or gap junction channels, allowing the exchange of ions and small metabolites between the cytosol and extracellular space or between neighbouring cells, respectively. Connexins have important roles in vascular physiology; they support radial and longitudinal cell-to-cell communication in the vascular wall, and significant changes in their expression patterns have been described during atherosclerosis and restenosis.

Phenotypic transformation of smooth muscle in vasospasm after aneurysmal subarachnoid hemorrhage

Differentiated smooth muscle cells (SMC) control vasoconstriction and vasodilation, but they can undergo transformation, proliferate, secret cytokines, and migrate into the subendotherial layer with adverse consequences. In this review, we discuss the phenotypic transformation of SMC in cerebral vasospasm after subarachnoid hemorrhage. Phenotypic transformation starts with an insult as caused by aneurysm rupture: Elevation of intracranial and blood pressure, secretion of norepinephrine, and mechanical force on an artery are factors that can cause aneurysm. The phenotypic transformation of SMC is accelerated by inflammation, thrombin, and growth factors. A wide variety of cytokines (e.g., interleukin (IL)-1β, IL-33, matrix metalloproteinases, nitric oxidase synthases, endothelins, thromboxane A2, mitogen-activated protein kinase, platelet-derived vascular growth factors, and vascular endothelial factor) all play roles in cerebral vasospasm (CVS). We summarize the correlations between various factors and the phenotypic transformation of SMC. A new target of this study is the transient receptor potential channel in CVS. Statin together with fasdil prevents phenotypic transformation of SMC in an animal model. Clazosentan prevents CVS and improves outcome in aneurysmal subarachnoid hemorrhage in a dose-dependent manner. Clinical trials of cilostazol for the prevention of phenotypic transformation of SMC have been reported, along with requisite experimental evidence. To conquer CVS in its complexity, we will ultimately need to elucidate its general, underlying mechanism.

Human Connexin Channel Specificity of Classical and New Gap Junction Inhibitors

Connexins are transmembrane proteins involved in gap junction intercellular communication. They present cell- and tissue-specific expression, with own electric and metabolic coupling specificities. These proteins are involved in numerous physiological processes in the brain and among them neuronal synchronization and trafficking of glucose. Such proteins are also described as being misregulated in various pathologies in the central nervous system. Thus, connexin blockers have been proposed as pharmacological tools to dissect these implications. However, such approaches lack accurate characterization of known inhibitors toward gap junction isoform specificity. In addition, those compounds are limited to few chemical classes and exhibit other activities, for example, an anti-inflammatory effect. The aims of this study were to evaluate the selectivity of described inhibitors and to enrich this pharmacopeia by new chemical classes. In this study, we present the specificity of published inhibitors toward several connexin isoforms expressed in the brain. Furthermore, after a screening of compounds using cellular models, we identified seven new inhibitors, with high functional reversibility and different relative selectivity toward isoforms. They constitute new chemical classes of connexin modulators completing those previously described. These new inhibitors might also provide new insights in understanding numerous pathophysiological processes involving gap junctions.

MAPK phosphorylation of connexin 43 promotes binding of cyclin E and smooth muscle cell proliferation

RATIONALE

Dedifferentiation of vascular smooth muscle cells (VSMC) leading to a proliferative cell phenotype significantly contributes to the development of atherosclerosis. Mitogen-activated protein kinase (MAPK) phosphorylation of proteins including connexin 43 (Cx43) has been associated with VSMC proliferation in atherosclerosis.

OBJECTIVE

To investigate whether MAPK phosphorylation of Cx43 is directly involved in VSMC proliferation.

METHODS AND RESULTS

We show in vivo that MAPK-phosphorylated Cx43 forms complexes with the cell cycle control proteins cyclin E and cyclin-dependent kinase 2 (CDK2) in carotids of apolipoprotein-E receptor null (ApoE(-/-)) mice and in C57Bl/6 mice treated with platelet-derived growth factor-BB (PDGF). We tested the involvement of Cx43 MAPK phosphorylation in vitro using constructs for full-length Cx43 (Cx43) or the Cx43 C-terminus (Cx43(CT)) and produced null phosphorylation Ser>Ala (Cx43(MK4A)/Cx43(CTMK4A)) and phospho-mimetic Ser>Asp (Cx43(MK4D)/Cx43(CTMK4D)) mutations. Coimmunoprecipitation studies in primary VSMC isolated from Cx43 wild-type (Cx43(+/+)) and Cx43 null (Cx43(-/-)) mice and analytic size exclusion studies of purified proteins identify that interactions between cyclin E and Cx43 requires Cx43 MAPK phosphorylation. We further demonstrate that Cx43 MAPK phosphorylation is required for PDGF-mediated VSMC proliferation. Finally, using a novel knock-in mouse containing Cx43-MK4A mutation, we show in vivo that interactions between Cx43 and cyclin E are lost and VSMC proliferation does not occur after treatment of carotids with PDGF and that neointima formation is significantly reduced in carotids after injury.

CONCLUSIONS

We identify MAPK-phosphorylated Cx43 as a novel interacting partner of cyclin E in VSMC and show that this interaction is critical for VSMC proliferation. This novel interaction may be important in the development of atherosclerotic lesions.

Lovastatin inhibits gap junctional communication in cultured aortic smooth muscle cells

BACKGROUND

Gap junctions, which serve as intercellular channels that allow the passage of ions and other small molecules between neighboring cells, play an important role in vital functions, including the regulation of cell growth, differentiation, and development. Statins, the 3-hydroxy-3-methylglutaryl-coenzymeA (HMG-CoA) reductase inhibitors, have been shown to inhibit the migration and proliferation of smooth muscle cells (SMCs) leading to an antiproliferative effect. Recent studies have shown that statins can reduce gap junction protein connexin43 (Cx43) expression both in vivo and in vitro. However, little work has been done on the effects of statins on gap junctional intercellular communication (GJIC). We hypothesized in this study that lovastatin inhibits vascular smooth muscle cells (VSMCs) migration through the inhibition of the GJIC.

METHODS

Rat aortic SMCs (RASMCs) were exposed to lovastatin. Vascular smooth muscle cells migration was then assessed with a Transwell migration assay. Gap junctional intercellular communication was determined by using fluorescence recovery after photobleaching (FRAP) analysis, which was performed with a laser-scanning confocal microscope.

RESULTS

The migration of the cultured RASMCs were detected by Transwell system. Cell migration was dose-dependently inhibited with lovastatin. Compared with that in the control (110 ± 26), the number of migrated SMCs was significantly reduced to 72 ± 24 (P < .05), 62 ± 18 (P < .01), and 58 ± 19 (P < .01) at the concentration of 0.4, 2, and 10 umol/L, per field. The rate of fluorescence recovery (R) at 5 minutes after photobleaching was adopted as the functional index of GJIC. The R- value of cells exposed to lovastatin 10 umol/L for 48 hours was 24.38% ± 4.84%, whereas the cells in the control group had an R- value of 36.11% ± 10.53%, demonstrating that the GJIC of RASMCs was significantly inhibited by lovastatin (P < .01). Smaller concentrations of lovastatin 0.08 umol/L did not change gap junction coupling (P > .05).

CONCLUSIONS

These results suggest that lovastatin inhibits migration in a dose-dependent manner by attenuating JIC. Suppression of gap junction function could add another explanation of statin-induced antiproliferative effect.

Intercellular Communication in Atherosclerosis

Cell-to-cell communication is a process necessary for physiological tissue homeostasis and appears often altered during disease. Gap junction channels, formed by connexins, allow the direct intercellular communication between adjacent cells. After a brief review of the pathophysiology of atherosclerosis, we will discuss the role of connexins throughout the different stages of the disease.

Connexins in vascular physiology and pathology

Cellular interaction in blood vessels is maintained by multiple communication pathways, including gap junctions. They consist of intercellular channels ensuring direct interaction between endothelial and smooth muscle cells and the synchronization of their behavior along the vascular wall. Gap-junction channels arise from the docking of two hemichannels or connexons, formed by the assembly of six connexins, and achieve direct cellular communication by allowing the transport of small metabolites, second messengers, and ions between two adjacent cells. Physiologic variations in connexin expression are observed along the vascular tree, with most common connexins being Cx37, Cx40, and Cx43. Changes in the level of expression of connexins have been correlated to the development of vascular disease, such as hypertension, atherosclerosis, or restenosis. Recent studies on connexin-deficient mice highlighted key roles of these communication pathways in the development of these pathologies and confirmed the need for targeted pharmacologic approaches for their prevention and treatment. The aim of this issue is to review the current knowledge on the implication of gap junctions in vascular function and most common cardiovascular diseases.

Targeting connexin 43 prevents platelet-derived growth factor-BB-induced phenotypic change in porcine coronary artery smooth muscle cells

We previously reported that reducing the expression of the gap junction protein connexin (Cx)43 in mice restricts intimal thickening formation after acute vascular injury by limiting the inflammatory response and the proliferation and migration of smooth muscle cells (SMCs) toward the damaged site. SMC populations isolated from porcine coronary artery exhibit distinct phenotypes: spindle-shaped (S) and rhomboid (R). S-SMCs are predominant in the normal media, whereas R-SMCs are recovered in higher proportion from stent-induced intimal thickening, suggesting that they participate in the restenotic process. Here, we further investigate the relationship between connexin expression and SMC phenotypes using porcine coronary artery SMCs. Cx40 was highly expressed in normal media of porcine coronary artery in vivo, whereas Cx43 was barely detectable. In contrast, Cx40 was downregulated and Cx43 was markedly upregulated in stent-induced intimal thickening. In vitro, S-SMCs expressed Cx40 and Cx43. In R-SMCs, Cx43 expression was increased and Cx40 was absent. We confirmed that S-SMCs treated with platelet-derived growth factor-BB acquire an R phenotype. This was accompanied by an upregulation of Cx43 and a loss of Cx40. Importantly, platelet-derived growth factor-BB-induced S-to-R phenotypic change was prevented by a reduction of Cx43 expression with antisense, ie, S-SMCs retained their typical elongated appearance and the expression of alpha-smooth muscle actin, a well-known SMC differentiation marker, whereas the expression of S100A4, a typical marker of R-SMCs, was prevented. In conclusion, limiting Cx43 expression in S-SMCs prevents platelet-derived growth factor-BB-induced S-to-R modulation. This suggests that Cx43 may be an additional target for local delivery strategies aimed at reducing restenosis.

Beneficial effects of statins on the microcirculation during sepsis: the role of nitric oxide

This review describes the laboratory evidence and microvascular mechanisms responsible for the beneficial effects of statins in sepsis. During sepsis, changes occur within the microcirculation including alterations in arteriolar tone influencing blood pressure, adaptations to endothelial cell integrity causing leakage of proteins and macromolecules, and adhesion and migration of leucocytes through the vascular endothelium. Statins are widely used as cholesterol-lowering agents, but appear to have anti-inflammatory actions during sepsis. We have discussed the effects of statins on specific pathological processed within the microcirculation and focused on the role of nitric oxide (NO). The main mechanism by which statins appear to be an effective treatment for sepsis is increased expression of endothelial nitric oxide synthase (eNOS), in conjunction with down-regulation of inducible nitric oxide synthase. Combined, this results in an increase in physiological concentrations of NO, thus restoring endothelial function. Laboratory studies have therefore suggested that enhancement of eNOS activity during sepsis may lead to restoration of microvascular tone, maintenance of microvascular integrity, and inhibition of cell adhesion molecules. However, other mechanisms independent of lipid-lowering effects, including antioxidant activity and alterations in the development of vascular atherosclerosis, may also contribute to the beneficial effects of statins. We have also addressed the influence on the effects of statins of lipid solubility and pre- and pro-phylactic administration.

Reduced Connexin43 Expression Limits Neointima Formation After Balloon Distension Injury in Hypercholesterolemic Mice

Background— Reducing the expression of the gap junction protein connexin43 (Cx43) inhibits the progression of atherosclerosis, a chronic inflammatory disease. Furthermore, acute vascular injury induced by percutaneous coronary interventions is associated with increased Cx43 expression in neointimal smooth muscle cells (SMCs). However, the relevance of Cx43 after acute vascular injury remains unclear.

Methods and Results— To investigate whether reducing Cx43 expression would affect neointima formation in vivo, we subjected hypercholesterolemic Cx43 +/− LDL receptor–deficient (LDLR −/− ) mice and Cx43 +/+ LDLR −/− control littermates to carotid balloon distension injury, which induced marked endothelial denudation and activation of medial SMCs. We observed decreased macrophage infiltration in Cx43 +/− LDLR −/− mice 7 days after injury. Similarly, peritoneal macrophages isolated from Cx43 +/− LDLR −/− mice showed reduced migration in vitro compared with Cx43 +/+ LDLR −/− macrophages. Interestingly, Cx43 +/− LDLR −/− macrophages also displayed decreased chemotactic activity for SMCs. In addition, we observed less SMC infiltration and proliferation in Cx43 +/− LDLR −/− mice 7 and 14 days after balloon angioplasty. Likewise, Cx43 +/− LDLR −/− SMCs showed decreased proliferation and migration in vitro compared with Cx43 +/+ LDLR −/− cells. All these events resulted in a reduction of neointimal thickening after vascular injury in Cx43 +/− LDLR −/− mice.

Conclusions— The present study shows for the first time that reducing Cx43 limits neointima formation after acute vascular injury by decreasing the inflammatory response and reducing SMC migration and proliferation. Thus, decreasing Cx43 expression may offer a novel therapeutic strategy for reducing restenosis after percutaneous coronary intervention.

Short-term atorvastatin treatment does not modify neointimal morphology but reduces MMP-2 expression in normocholesterolemic rabbit stented arteries

The aim of our study was to explore some potential pleïotropic effects of atorvastatin, after stenting in the iliac arteries of normocholesterolemic rabbits. On day 0, 27 rabbits underwent stent implantation and were randomized into either the control group (standard chow, CTRL, n = 15) or the atorvastatin group (10 mg/kg/d per os, Ator, n = 12). On day 30, the stented arteries were harvested for histomorphometry and neointimal analysis [macrophages, matrix metalloproteinases (MMP-2), tissue inhibitor of metalloproteinase-2, vascular smooth muscle cells, and collagen]. Atorvastatin did not induce significant histomorphometric and inflammatory modifications but reduced neointimal expression of MMP-2 with no modification of tissue inhibitor of metalloproteinase-2, and also induced higher neointimal collagen content (Ator vs. CTRL: MMP-2: 0.05 +/- 0.03 vs. 0.70 +/- 0.20, P < 0.01; collagen: 17.0+/-0.7%/mm vs. 12.0 +/- 1.2%/mm(2) P < 0.01). Atorvastatin treatment also induced a significant decrease in neointimal vascular smooth muscle cells and cellular density (respectively: 2.0 +/- 0.2 vs. 1.4 +/- 0.2, P < 0.05; 5406 +/- 241 nuclei/mm(2) vs. 4402 +/- 163 nuclei/mm(2), P < 0.001). Our study provides new insights into the field of MMP response to stenting and the effects of statin therapy, which could have important implications in the field of in-stent restenosis.