Increased connexin43 expression in human saphenous veins in culture is associated with intimal hyperplasia

Connexin and Pannexin Large-Pore Channels in Microcirculation and Neurovascular Coupling Function

Microcirculation homeostasis depends on several channels permeable to ions and/or small molecules that facilitate the regulation of the vasomotor tone, hyperpermeability, the blood–brain barrier, and the neurovascular coupling function. Connexin (Cxs) and Pannexin (Panxs) large-pore channel proteins are implicated in several aspects of vascular physiology. The permeation of ions (i.e., Ca²⁺) and key metabolites (ATP, prostaglandins, D-serine, etc.) through Cxs (i.e., gap junction channels or hemichannels) and Panxs proteins plays a vital role in intercellular communication and maintaining vascular homeostasis. Therefore, dysregulation or genetic pathologies associated with these channels promote deleterious tissue consequences. This review provides an overview of current knowledge concerning the physiological role of these large-pore molecule channels in microcirculation (arterioles, capillaries, venules) and in the neurovascular coupling function.

Connexin 43 Expression in Cutaneous Biopsies of Lupus Erythematosus

INTRODUCTION

Gap junctions are channels between adjacent cells formed by connexins (Cxs). Cxs also form hemichannels that connect the cell with its extracellular milieu. These channels allow the transport of ions, metabolites, and small molecules; therefore, Cxs, and more specifically, connexin (Cx) 43 has been demonstrated to be in control of several crucial events such as inflammation and cell death.

MATERIAL AND METHODS

We examined the immunostaining of Cx43 in the endothelia of the cutaneous blood vessels of biopsies from 28 patients with several variants of lupus erythematosus.

RESULTS

In 19 cases (67.86%), staining of more than half of the dermal vessels including both vessels of the papillary and of the reticular dermis was identified. Only in 4 cases (14.28%), less than 25% of the vessels in the biopsy showed expression of the marker.

CONCLUSIONS

Our results suggest a role of Cx43 in regulating the endothelial activity in lupus erythematosus, which also opens a door for targeted therapeutic options.

The important role of connexin 43 in subarachnoid hemorrhage-induced cerebral vasospasm

Background

Gap junctions are involved in the development of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH). However, the specific roles and regulatory functions of related connexin isoforms remain unknown. The aim of this study was to investigate the importance of connexin 43 (Cx43) in CVS and determine whether Cx43 alterations are modulated via the protein kinase C (PKC) signaling transduction pathway.

Methods

Oxyhemoglobin (OxyHb)-induced smooth muscle cells of basilar arterial and second-injection model in rat were used as CVS models in vitro and in vivo. In addition, dye transfer assays were used for gap junction-mediated intercellular communication (GJIC) observation in vitro and delayed cerebral ischemia (DCI) was observed in vivo by perfusion-weighted imaging (PWI) and intravital fluorescence microscopy.

Results

Increase in Cx43 mediated the development of SAH-induced CVS was found in both in vitro and in vivo CVS models. Enhanced GJIC was observed in vitro CVS model, this effect and increased Cx43 were reversed by preincubation with specific PKC inhibitors (chelerythrine or GF 109203X). DCI was observed in vivo on day 7 after SAH. However, DCI was attenuated by pretreatment with Cx43 siRNA or PKC inhibitors, and the increased Cx43 expression in vivo was also reversed by Cx43 siRNA or PKC inhibitors.

Conclusions

These data provide strong evidence that Cx43 plays an important role in CVS and indicate that changes in Cx43 expression may be mediated by the PKC pathway. The current findings suggest that Cx43 and the PKC pathway are novel targets for developing treatments for SAH-induced CVS.

Hydrogen sulfide-releasing peptide hydrogel limits the development of intimal hyperplasia in human vein segments

Currently available interventions for vascular occlusive diseases suffer from high failure rates due to re-occlusive vascular wall adaptations, a process called intimal hyperplasia (IH). Naturally occurring hydrogen sulfide (H2S) works as a vasculoprotective gasotransmitter in vivo. However, given its reactive and hazardous nature, H2S is difficult to administer systemically. Here, we developed a hydrogel capable of localized slow release of precise amounts of H2S and tested its benefits on IH. The H2S-releasing hydrogel was prepared from a short peptide attached to an S-aroylthiooxime H2S donor. Upon dissolution in aqueous buffer, the peptide self-assembled into nanofibers, which formed a gel in the presence of calcium. This new hydrogel delivered H2S over the course of several hours, in contrast with fast-releasing NaHS. The H2S-releasing peptide/gel inhibited proliferation and migration of primary human vascular smooth muscle cells (VSMCs), while promoting proliferation and migration of human umbilical endothelial cells (ECs). Both NaHS and the H2S-releasing gel limited IH in human great saphenous vein segments obtained from vascular patients undergoing bypass surgery, with the H2S-releasing gel showing efficacy at a 5x lower dose than NaHS. These results suggest local perivascular H2S release as a new strategy to limit VSMC proliferation and IH while promoting EC proliferation, hence re-endothelialization. STATEMENT OF SIGNIFICANCE: Arterial occlusive disease is the leading cause of death in Western countries, yet current therapies suffer from high failure rates due to intimal hyperplasia (IH), a thickening of the vascular wall leading to secondary vessel occlusion. Hydrogen sulfide (H2S) is a gasotransmitter with vasculoprotective properties. Here we designed and synthesized a peptide-based H2S-releasing hydrogel and found that local application of the gel reduced IH in human vein segments obtained from patients undergoing bypass surgery. This work provides the first evidence of H2S efficacy against IH in human tissue, and the results show that the gel is more effective than NaHS, a common instantaneous H2S donor.

The effect of Telmisartan on the expression of connexin43 and neointimal hyperplasia in a rabbit iliac artery restenosis model

We established a rabbit iliac artery restenosis model to explore the impact of Telmisartan on the expression of Connexin43 (Cx43) and neointimal hyperplasia. Thirty New Zealand white rabbits were randomly divided into three groups: control group (n = 10), restenosis group (n = 10), and Telmisartan group (n = 10). The restenosis model was established by high-cholesterol diet combined with double-balloon injury of iliac arteries. In addition, Telmisartan at 5 mg/(kg day) was administered to the rabbits of Telmisartan group on the second day after the second balloon injury. All rabbits were killed at the end of the experiment followed by institution policy. Before sacrifice, blood samples were obtained to test serum angiotensinII (AngII). Iliac arteries were isolated for morphological analysis and determining the expression of Cx43 by HE staining, immunohistochemical analysis, reverse transcription-polymerase chain reaction (RT-PCR), and Western Blotting analysis. Then, the local AngII levels of arteries were measured by radioimmunoassay. As compared with controls, the expression of Cx43 mRNA (0.98 ± 0.08) vs. (1.27 ± 0.17), P < 0.01), and Cx43 protein [(0.75 ± 0.08) vs. (0.90 ± 0.08), P < 0.05] of restenosis group were increased, which were significantly higher than those of Telmisartan group [Cx43 mRNA: (1.27 ± 0.17) vs. (1.00 ± 0.20), P < 0.01; Cx43 protein: (0.90 ± 0.08) vs. (0.82 ± 0.05), P < 0.05]. Furthermore, The intima thickness [(266.12 ± 70.27) vs. (2.85 ± 0.19) μm, P < 0.01] and the local AngII [(115.6 ± 15.7) vs. (90.1 ± 7.7), P < 0.05] of restenosis group were raised when compared with controls. Telmisartan group exhibited thinner intima compared with restenosis group [(68.22 ± 24.37) vs. (266.12 ± 70.27), P < 0.01]. However, the local AngII levels between these two groups were approximate. In addition, the plasma concentration of AngII was not significantly different among three groups. In conclusion, Telmisartan can inhibit the expression of connexin43 and neointimal hyperplasia in iliac artery restenosis model.

Perfusion Tissue Culture Initiates Differential Remodeling of Internal Thoracic Arteries, Radial Arteries, and Saphenous Veins

Adaptive remodeling processes are essential to the maintenance and viability of coronary artery bypass grafts where clinical outcomes depend strongly on the tissue source. In this investigation, we utilized an ex vivo perfusion bioreactor to culture porcine analogs of common human bypass grafts: the internal thoracic artery (ITA), the radial artery (RA), and the great saphenous vein (GSV), and then evaluated samples acutely (6 h) and chronically (7 days) under in situ or coronary-like perfusion conditions. Although morphologically similar, primary cells harvested from the ITA illustrated lower intimal and medial, but not adventitial, cell proliferation rates than those from the RA or GSV. Basal gene expression levels were similar in all vessels, with only COL3A1, SERPINE1, FN1, and TGFB1 being differentially expressed prior to culture; however, over half of all genes were affected nominally by the culturing process. When exposed to coronary-like conditions, RAs and GSVs experienced pathological remodeling not present in ITAs or when vessels were studied in situ. Many of the remodeling genes perturbed at 6 h were restored after 7 days (COL3A1, FN1, MMP2, and TIMP1) while others (SERPINE1, TGFB1, and VCAM1) were not. The findings elucidate the potential mechanisms of graft failure and highlight strategies to encourage healthy ex vivo pregraft conditioning.

Connexin37 reduces smooth muscle cell proliferation and intimal hyperplasia in a mouse model of carotid artery ligation

AIMS

Intimal hyperplasia (IH) is an abnormal response to vessel injury characterized by the dedifferentiation, migration, and proliferation of quiescent vascular smooth muscle cells (VSMC) to form a neointima layer. Vascular connexins (Cx) are involved in the pathophysiology of various vascular diseases, and Cx43, the main Cx expressed in VSMC, has been shown to promote VSMC proliferation and IH. The aim of this study was to investigate the participation of another Cx, namely Cx37, in the formation of the neointima layer.

METHODS AND RESULTS

Wild-type (WT) and Cx37-deficient (Cx37-/-) C57BL/6J mice were subjected to carotid artery ligation (CAL), a model of vessel injury and IH. The neointima developed linearly in WT until 28 days post surgery. In contrast, the neointima layer was almost absent 14 days after surgery in Cx37-/- mice, and twice as more developed after 28 days compared to WT mice. This large neointima formation correlated with a two-fold increase in cell proliferation in the media and neointima regions between 14 and 28 days in Cx37-/- mice compared to WT mice. The CAL triggered Cx43 overexpression in the media and neointima layers of ligated carotids in WT mice, and selectively up-regulated Cx37 expression in the media layer, but not in the neointima layer. The de novo expression of Cx37 in human primary VSMC reduced cell proliferation and P-Akt levels, in association with lower Cx43 levels, whereas Cx43 overexpression increased P-Akt levels.

CONCLUSION

The presence of Cx37 in the media layer of injured arteries restrains VSMC proliferation and limits the development of IH, presumably by interfering with the pro-proliferative effect of Cx43 and the Akt pathway.

TNF‑α regulates apoptosis of human vascular smooth muscle cells through gap junctions

Inflammatory cytokines are released by immune cells and are able to induce vascular smooth muscle cells (VSMCs) to undergo apoptosis, causing atherosclerotic plaque rupture. Changes in the expression levels of connexins (Cxs) have been demonstrated in VSMCs to be involved in the pathogenesis of atherosclerotic progression. The present study examined the effect of tumor necrosis factor‑α (TNF‑α) on Cx43 expression levels and apoptosis in human VSMCs. Overexpression of Cx43 plasmids notably stimulated VSMC proliferation. TNF‑α directly inhibited Cx43 expression levels in a dose‑ and time‑dependent manner in VSMCs, however this was blocked by c‑Jun N‑terminal kinase inhibitor. TNF‑α also increased caspase‑3 activity and apoptosis of VSMCs through the inhibition of Cx43. These data suggested that TNF‑α induced the apoptosis of VMSCs and prompted the destabilization of atherosclerotic plaques by downregulating Cx43.

Determinants of Cx43 Channel Gating and Permeation: The Amino Terminus

Separate connexin domains partake in proposed gating mechanisms of gap junction channels. The amino-terminus (NT) domains, which contribute to voltage sensing, may line the channel's cytoplasmic-facing funnel surface, stabilize the channel's overall structure through interactions with the transmembrane domains and each other, and integrate to form a compound particle to gate the channel closed. Interactions of the carboxyl-terminus (CT) and cytoplasmic loop (CL) domains underlie voltage- and low pH-triggered channel closure. To elucidate potential cooperation of these gating mechanisms, we replaced the Cx43NT with the Cx37NT (chimera Cx43(∗)NT37), leaving the remainder of the Cx43 sequence, including the CT and CL, unchanged. Compared to wild-type Cx43 (Cx43WT), Cx43(∗)NT37 junctions exhibited several functional alterations: extreme resistance to halothane- and acidification-induced uncoupling, absence of voltage-dependent fast inactivation, longer channel open times, larger unitary channel conductances, low junctional dye permeability/permselectivity, and an overall cation selectivity more typical of Cx37WT than Cx43WT junctions. Together, these results suggest a cohesive model of channel function wherein: 1) channel conductance and size selectivity are largely determined by pore diameter, whereas charge selectivity results from the NT domains, and 2) transition between fully open and (multiple) closed states involves global changes in structure of the pore-forming domains transduced by interactions of the pore-forming domains with either the NT, CT, or both, with the NT domains forming the gate of the completely closed channel.

Connexin43 Inhibition Prevents Human Vein Grafts Intimal Hyperplasia

Venous bypass grafts often fail following arterial implantation due to excessive smooth muscle cells (VSMC) proliferation and consequent intimal hyperplasia (IH). Intercellular communication mediated by Connexins (Cx) regulates differentiation, growth and proliferation in various cell types. Microarray analysis of vein grafts in a model of bilateral rabbit jugular vein graft revealed Cx43 as an early upregulated gene. Additional experiments conducted using an ex-vivo human saphenous veins perfusion system (EVPS) confirmed that Cx43 was rapidly increased in human veins subjected ex-vivo to arterial hemodynamics. Cx43 knock-down by RNA interference, or adenoviral-mediated overexpression, respectively inhibited or stimulated the proliferation of primary human VSMC in vitro. Furthermore, Cx blockade with carbenoxolone or the specific Cx43 inhibitory peptide ⁴³gap26 prevented the burst in myointimal proliferation and IH formation in human saphenous veins. Our data demonstrated that Cx43 controls proliferation and the formation of IH after arterial engraftment.

Arterial levels of oxygen stimulate intimal hyperplasia in human saphenous veins via a ROS-dependent mechanism

Saphenous veins used as arterial grafts are exposed to arterial levels of oxygen partial pressure (pO₂), which are much greater than what they experience in their native environment. The object of this study is to determine the impact of exposing human saphenous veins to arterial pO₂. Saphenous veins and left internal mammary arteries from consenting patients undergoing coronary artery bypass grafting were cultured ex vivo for 2 weeks in the presence of arterial or venous pO₂ using an established organ culture model. Saphenous veins cultured with arterial pO₂ developed intimal hyperplasia as evidenced by 2.8-fold greater intimal area and 5.8-fold increase in cell proliferation compared to those freshly isolated. Saphenous veins cultured at venous pO₂ or internal mammary arteries cultured at arterial pO₂ did not develop intimal hyperplasia. Intimal hyperplasia was accompanied by two markers of elevated reactive oxygen species (ROS): increased dihydroethidium associated fluorescence (4-fold, p<0.05) and increased levels of the lipid peroxidation product, 4-hydroxynonenal (10-fold, p<0.05). A functional role of the increased ROS saphenous veins exposed to arterial pO₂ is suggested by the observation that chronic exposure to tiron, a ROS scavenger, during the two-week culture period, blocked intimal hyperplasia. Electron paramagnetic resonance based oximetry revealed that the pO₂ in the wall of the vessel tracked that of the atmosphere with a ~30 mmHg offset, thus the cells in the vessel wall were directly exposed to variations in pO₂. Monolayer cultures of smooth muscle cells isolated from saphenous veins exhibited increased proliferation when exposed to arterial pO₂ relative to those cultured at venous pO₂. This increased proliferation was blocked by tiron. Taken together, these data suggest that exposure of human SV to arterial pO₂ stimulates IH via a ROS-dependent pathway.

Procedure for human saphenous veins ex vivo perfusion and external reinforcement

The mainstay of contemporary therapies for extensive occlusive arterial disease is venous bypass graft. However, its durability is threatened by intimal hyperplasia (IH) that eventually leads to vessel occlusion and graft failure. Mechanical forces, particularly low shear stress and high wall tension, are thought to initiate and to sustain these cellular and molecular changes, but their exact contribution remains to be unraveled. To selectively evaluate the role of pressure and shear stress on the biology of IH, an ex vivo perfusion system (EVPS) was created to perfuse segments of human saphenous veins under arterial regimen (high shear stress and high pressure). Further technical innovations allowed the simultaneous perfusion of two segments from the same vein, one reinforced with an external mesh. Veins were harvested using a no-touch technique and immediately transferred to the laboratory for assembly in the EVPS. One segment of the freshly isolated vein was not perfused (control, day 0). The two others segments were perfused for up to 7 days, one being completely sheltered with a 4 mm (diameter) external mesh. The pressure, flow velocity, and pulse rate were continuously monitored and adjusted to mimic the hemodynamic conditions prevailing in the femoral artery. Upon completion of the perfusion, veins were dismounted and used for histological and molecular analysis. Under ex vivo conditions, high pressure perfusion (arterial, mean = 100 mm Hg) is sufficient to generate IH and remodeling of human veins. These alterations are reduced in the presence of an external polyester mesh.

Regulation of cellular communication by signaling microdomains in the blood vessel wall

It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.

Atorvastatin-loaded hydrogel affects the smooth muscle cells of human veins

Intimal hyperplasia (IH) is the major cause of stenosis of vein grafts. Drugs such as statins prevent stenosis, but their systemic administration has limited effects. We developed a hyaluronic acid hydrogel matrix, which ensures a controlled release of atorvastatin (ATV) at the site of injury. The release kinetics demonstrated that 100% of ATV was released over 10 hours, independent of the loading concentration of the hydrogel. We investigated the effects of such a delivery on primary vascular smooth muscle cells isolated from human veins. ATV decreased the proliferation, migration, and passage of human smooth muscle cells (HSMCs) across a matrix barrier in a similar dose-dependent (5-10 µM) and time-dependent manner (24-72 hours), whether the drug was directly added to the culture medium or released from the hydrogel. Expression analysis of genes known to be involved in the development of IH demonstrated that the transcripts of both the gap junction protein connexin43 (Cx43) and plasminogen activator inhibitor-1 (PAI-1) were decreased after a 24-48-hour exposure to the hydrogel loaded with ATV, whereas the transcripts of the heme oxygenase (HO-1) and the inhibitor of tissue plasminogen activator were increased. At the protein level, Cx43, PAI-1, and metalloproteinase-9 expression were decreased, whereas HO-1 was upregulated in the presence of ATV. The data demonstrate that ATV released from a hydrogel has effects on HSMCs similar to the drug being freely dissolved in the environment.

Biological and biophysical properties of vascular connexin channels

Intercellular channels formed by connexin proteins play a pivotal role in the direct movement of ions and larger cytoplasmic solutes between vascular endothelial cells, between vascular smooth muscle cells, and between endothelial and smooth muscle cells. Multiple genetic and epigenetic factors modulate connexin expression levels and/or channel function, including cell-type-independent and cell-type-specific transcription factors, posttranslational modifications, and localized membrane targeting. Additionally, differences in protein-protein interactions, including those between connexins, significantly contribute to both vascular homeostasis and disease progression. The biophysical properties of the connexin channels identified in the vasculature, those formed by Cx37, Cx40, Cx43 and/or Cx45 proteins, are discussed in this chapter in the physiological and pathophysiological context of vessel function.

Endothelial injury induces vascular smooth muscle cell proliferation in highly localized regions of a direct contact co-culture system

Though previous studies have indicated a relationship between the proliferation of endothelial cells and vascular smooth muscle cells (VSMCs) in co-culture, the results have been contradictory and the signaling mechanism poorly understood. In this transmembrane co-culture study, VSMCs and endothelial cells were grown to confluence on opposite sides of a microporous membrane to mimic the intima/media border of vessels. The endothelial layer was injured, and then cultured for 3 days, resulting in partial re-endothelialization. VSMC proliferation across from the injured/partially recovered endothelial region was significantly higher than across from the de-endothelialized region (a sevenfold increase) and the uninjured region (a threefold increase). ELISA indicated that PDGF, which was undetectable in uninjured co-culture and homotypic controls, increased after injury and the addition of a piperazinyl-quinazoline carboxamide PDGF receptor inhibitor blocked VSMC proliferation across from the injured/partially recovered region. We conclude that co-culture signaling initiated by endothelial cell injury locally stimulates VSMC proliferation and that this signaling could be mediated by PDGF-BB.

Activin-A in myometrium: characterization of the actions on myometrial cells

Activin is a pleiotropic growth factor with a broad pattern of tissue distribution that includes reproductive tissues. Although direct actions of activin have been described in gonadal and uterine tissues, actions in the myometrium have not been defined. In this study we have characterized the responsiveness of uterine tissue and myometrial cell lines to activin-A. Uterine tissue and two myometrial cell lines, PHM1 (pregnant human myometrial 1) and hTERT HM (telomerase reverse transcriptase-infected human myometrial) respond to activin-A as measured by phosphorylation of Smad-2. Those cell lines express a full complement of activin receptors, as well as activin beta(A) subunit and follistatin. Activin inhibited proliferation of PHM1 and human telomerase reverse transcriptase-infected human myometrial cell line cells, with more extensive growth inhibition observed in PHM1s. In PHM1s, activin-A decreased oxytocin receptor and HoxA-10 mRNA expression but did not alter total progesterone receptor, cyclooxygenase-2 (Cox-2), and connexin 43 mRNA expression levels. Furthermore, treatment of PHM1 myometrial cells with activin-A attenuated oxytocin and thromboxaneA2 induced intracellular Ca(2+) accumulation. In conclusion, myometrial cells are activin sensitive, and activin-A can regulate myometrial cell functions.

Involvement of connexin 43 in angiotensin II-induced migration and proliferation of saphenous vein smooth muscle cells via the MAPK-AP-1 signaling pathway

Proliferation and migration of vascular smooth muscle cells (VSMCs) lead to intimal thickening and influence the long-term patency of venous graft post coronary arterial bypass graft. There is increasing evidence that connexins are involved in the development of intimal hyperplasia and restenosis. We assessed connexin 43 (Cx43) expression and its role in angiotensin II-induced proliferation and migration of smooth muscle cells and the signal pathways involved in human saphenous vein bypass conduits. Angiotensin II significantly increased gap junctional intercellular communication and induced the expression of Cx43 in human saphenous vein SMCs in a dose- and time-dependent manner through angiotensin II type 1 receptor. The effect of angiotensin II was blocked by siRNA of ERK 1/2, p38 MAPK and JNK, respectively. Overexpression of Cx43 markedly increased the proliferation of saphenous vein SMCs. However, siRNA for Cx43 inhibited angiotensin II-induced proliferation, cyclin E expression and migration of human saphenous vein SMCs. In dual-luciferase reporter assay, angiotensin II markedly activated AP-1 transcription factor, which was significantly attenuated by a dominant-negative AP-1 (A-Fos) with subsequent inhibition of angiotensin II-induced transcriptional expression of Cx43. These data demonstrate the role of Cx43 in the proliferation and migration of human saphenous vein SMCs and angiotensin II-induced Cx43 expression via mitogen-activated protein kinases (MAPK)-AP-1 signaling pathway.

Roles of Gap Junctions and Connexins in Non-Neoplastic Pathological Processes in which Cell Proliferation Is Involved

Cell proliferation is an important process for reproduction, growth and renewal of living cells and occurs in several situations during life. Cell proliferation is present in all the steps of carcinogenesis, initiation, promotion and progression. Gap junctions are the only specialization of cell membranes that allows communication between adjacent cells. They are known to contribute to tissue homeostasis and are composed of transmembrane proteins called "connexins." These junctions are also known to be involved in cell proliferation control. The roles of gap junctions and connexins in cell proliferation are complex and still under investigation. Since pioneer studies by Loewenstein, it is known that neoplastic cells lack communicating junctions. They do not communicate with their neighbors or with non-neoplastic cells from the surrounding area. There are many studies and review articles dedicated to neoplastic tissues. The aim of this review is to present evidence on the roles of gap junctions and connexins in non-neoplastic processes in which cell proliferation is involved.

Angiotensin II and IGF-1 regulate connexin43 expression via ERK and p38 signaling pathways in vascular smooth muscle cells of coronary artery bypass conduits

BACKGROUND

Changes in connexin expression have been found in vascular smooth muscle cells (VSMCs) during the progression of atherosclerotic lesion and intimal hyperplasia. It is our hypothesis that increased connexin43 expression following stimulation of VSMCs with Ang II and IGF-1 contributes to more proliferation in saphenous vein (SV) than in the internal mammary artery (IMA).

MATERIALS AND METHOD

Using immunohistochemistry, Western blot, and reverse-transcription polymerase chain reaction, we assessed the effect of Ang II and IGF-1 stimulation on connexin43 expression and the signaling pathways involved in VSMCs of SV and IMA.

RESULTS

Immunostaining demonstrated strong expression of connexin43 in SV compared with IMA after stimulation with Ang II and IGF-1. Ang II up-regulated the expression of connexin43 in VSMCs of SV in a dose- and time-dependent manner. This was inhibited by p38 and ERK MAP kinase inhibitors, SB203580 and PD98059, respectively. In the VSMCs of IMA, the connexin43 expression was markedly low and maintained at a reduced level even after 3 h stimulation. IGF-1 dose-dependently induced mRNA expression of connexin43 in the VSMCs of SV, which was blocked by PD98059. However, in VSMCs of IMA there was no significant effect of IGF-1 on the connexin43 mRNA expression.

CONCLUSION

These data suggest that connexin43 expression can be influenced by Ang II and IGF-1 through ERK and p38 pathways and may contribute to the pathogenesis of vein graft disease following coronary artery bypass grafting.

The role of myoendothelial gap junctions in the formation of arterial aneurysms: the hypothesis of "connexin 43:40 stoichiometry"

Heterocellular myoendothelial gap junctions (MEGJs) are essential in coordinating and regulating vasomotion. Little is known about their potential role in disease states. We discuss how alteration in the Cx 43:40 expression ratio at the level of MEGJs may begin a chain of reactions in the arterial wall resulting in an aneurysm formation. In this model, we assumed that aneurysm is a chronic arterial disease associated with medial degeneration and intimal hyperplasia. It also was assumed that MEGJs are composed of Cx43 and Cx40 in different stoichiometry and that the characteristic of a given junction is in the favor of its most abundantly expressed constituent. The hypothesis of Cx 43:40 stoichiometry indicates that impaired MEGJs may play a role in the pathogenesis of arterial aneurysms. Cx43 upregulation and Cx40 downregulation (increased Cx 43:40 stoichiometry) may induce a cascade of inflammatory, electrical, metabolic and proliferative derangements in the arterial wall, which finally lead to the matrix degradation, intimal hyperplasia, endothelial-medial dissociation and loss of endothelium-dependent hyperpolarizing currents, irregular vasomotion, impaired growth factor activation, and arterial sympathetic deprivation. The final consequence of these alterations is aneurysm formation.

Glucose represses connexin36 in insulin-secreting cells

The gap-junction protein connexin36 (Cx36) contributes to control the functions of insulin-producing cells. In this study, we investigated whether the expression of Cx36 is regulated by glucose in insulin-producing cells. Glucose caused a significant reduction of Cx36 in insulin-secreting cell lines and freshly isolated pancreatic rat islets. This decrease appeared at the mRNA and the protein levels in a dose- and time-dependent manner. 2-Deoxyglucose partially reproduced the effect of glucose, whereas glucosamine, 3-O-methyl-D-glucose and leucine were ineffective. Moreover, KCl-induced depolarization of beta-cells had no effect on Cx36 expression, indicating that glucose metabolism and ATP production are not mandatory for glucose-induced Cx36 downregulation. Forskolin mimicked the repression of Cx36 by glucose. Glucose or forskolin effects on Cx36 expression were not suppressed by the L-type Ca(2+)-channel blocker nifedipine but were fully blunted by the cAMP-dependent protein kinase (PKA) inhibitor H89. A 4 kb fragment of the human Cx36 promoter was identified and sequenced. Reporter-gene activity driven by various Cx36 promoter fragments indicated that Cx36 repression requires the presence of a highly conserved cAMP responsive element (CRE). Electrophoretic-mobility-shift assays revealed that, in the presence of a high glucose concentration, the binding activity of the repressor CRE-modulator 1 (CREM-1) is enhanced. Taken together, these data provide evidence that glucose represses the expression of Cx36 through the cAMP-PKA pathway, which activates a member of the CRE binding protein family.