Age-related alteration of gap junction distribution and connexin expression in rat aortic endothelium

Connexins 30 and 43 expression changes in relation to age-related hearing loss

Age-related hearing loss (ARHL), also known as presbycusis, is the number one communication disorder for aging adults. Connexin proteins are essential for intercellular communication throughout the human body, including the cochlea. Mutations in connexin genes have been linked to human syndromic and nonsyndromic deafness; thus, we hypothesize that changes in connexin gene and protein expression with age are involved in the etiology of ARHL. Here, connexin gene and protein expression changes for CBA/CaJ mice at different ages were examined, and correlations were analyzed between the changes in expression levels and functional hearing measures, such as ABRs and DPOAEs. Moreover, we investigated potential treatment options for ARHL. Results showed significant downregulation of Cx30 and Cx43 gene expression and significant correlations between the degree of hearing loss and the changes in gene expression for both genes. Moreover, dose-dependent treatments utilizing cochlear cell lines showed that aldosterone hormone therapy significantly increased Cx expression. In vivo mouse treatments with aldosterone also showed protective effects on connexin expression in aging mice. Based on these functionally relevant findings, next steps can include more investigations of the mechanisms related to connexin family gap junction protein expression changes during ARHL; and expand knowledge of clinically-relevant treatment options by knowing what specific members of the Cx family and related inter-cellular proteins should be targeted therapeutically.

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.

Mechanobiology of Microvascular Function and Structure in Health and Disease: Focus on the Coronary Circulation

The coronary microvasculature plays a key role in regulating the tight coupling between myocardial perfusion and myocardial oxygen demand across a wide range of cardiac activity. Short-term regulation of coronary blood flow in response to metabolic stimuli is achieved via adjustment of vascular diameter in different segments of the microvasculature in conjunction with mechanical forces eliciting myogenic and flow-mediated vasodilation. In contrast, chronic adjustments in flow regulation also involve microvascular structural modifications, termed remodeling. Vascular remodeling encompasses changes in microvascular diameter and/or density being largely modulated by mechanical forces acting on the endothelium and vascular smooth muscle cells. Whereas in recent years, substantial knowledge has been gathered regarding the molecular mechanisms controlling microvascular tone and how these are altered in various diseases, the structural adaptations in response to pathologic situations are less well understood. In this article, we review the factors involved in coronary microvascular functional and structural alterations in obstructive and non-obstructive coronary artery disease and the molecular mechanisms involved therein with a focus on mechanobiology. Cardiovascular risk factors including metabolic dysregulation, hypercholesterolemia, hypertension and aging have been shown to induce microvascular (endothelial) dysfunction and vascular remodeling. Additionally, alterations in biomechanical forces produced by a coronary artery stenosis are associated with microvascular functional and structural alterations. Future studies should be directed at further unraveling the mechanisms underlying the coronary microvascular functional and structural alterations in disease; a deeper understanding of these mechanisms is critical for the identification of potential new targets for the treatment of ischemic heart disease.

Connexins in Cancer: Jekyll or Hyde?

The expression, localization, and function of connexins, the protein subunits that comprise gap junctions, are often altered in cancer. In addition to cell-cell coupling through gap junction channels, connexins also form hemichannels that allow communication between the cell and the extracellular space and perform non-junctional intracellular activities. Historically, connexins have been considered tumor suppressors; however, they can also serve tumor-promoting functions in some contexts. Here, we review the literature surrounding connexins in cancer cells in terms of specific connexin functions and propose that connexins function upstream of most, if not all, of the hallmarks of cancer. The development of advanced connexin targeting approaches remains an opportunity for the field to further interrogate the role of connexins in cancer phenotypes, particularly through the use of in vivo models. More specific modulators of connexin function will both help elucidate the functions of connexins in cancer and advance connexin-specific therapies in the clinic.

Connexin43 is Dispensable for Early Stage Human Mesenchymal Stem Cell Adipogenic Differentiation But is Protective against Cell Senescence

In the last couple of decades, there has been a growing optimism surrounding the potential transformative use of human mesenchymal stem cells (MSCs) and human-induced pluripotent stem cells (iPSCs) for regenerative medicine and disease treatment. In order for this to occur, it is first essential to understand the mechanisms underpinning their cell-fate specification, which includes cell signaling via gap junctional intercellular communication. Here, we investigated the role of the prototypical gap junction protein, connexin43 (Cx43), in governing the differentiation of iPSCs into MSCs and MSC differentiation along the adipogenic lineage. We found that control iPSCs, as well as iPSCs derived from oculodentodigital dysplasia patient fibroblasts harboring a GJA1 (Cx43) gene mutation, successfully and efficiently differentiated into LipidTox and perilipin-positive cells, indicating cell differentiation along the adipogenic lineage. Furthermore, the complete CRISPR-Cas9 ablation of Cx43 from iPSCs did not prevent their differentiation into bona fide MSCs or pre-adipocytes, strongly suggesting that even though Cx43 expression is upregulated during adipogenesis, it is expendable. Interestingly, late passage Cx43-ablated MSCs senesced more quickly than control cells, resulting in failure to properly differentiate in vitro. We conclude that despite being upregulated during adipogenesis, Cx43 plays no detectable role in the early stages of human iPSC-derived MSC adipogenic differentiation. However, Cx43 may play a more impactful role in protecting MSCs from premature senescence.

Single and fractionated ionizing radiation induce alterations in endothelial connexin expression and channel function

Radiotherapy is an effective treatment for most tumor types. However, emerging evidence indicates an increased risk for atherosclerosis after ionizing radiation exposure, initiated by endothelial cell dysfunction. Interestingly, endothelial cells express connexin (Cx) proteins that are reported to exert proatherogenic as well as atheroprotective effects. Furthermore, Cxs form channels, gap junctions and hemichannels, that are involved in bystander signaling that leads to indirect radiation effects in non-exposed cells. We here aimed to investigate the consequences of endothelial cell irradiation on Cx expression and channel function. Telomerase immortalized human Coronary Artery/Microvascular Endothelial cells were exposed to single and fractionated X-rays. Several biological endpoints were investigated at different time points after exposure: Cx gene and protein expression, gap junctional dye coupling and hemichannel function. We demonstrate that single and fractionated irradiation induce upregulation of proatherogenic Cx43 and downregulation of atheroprotective Cx40 gene and protein levels in a dose-dependent manner. Single and fractionated irradiation furthermore increased gap junctional communication and induced hemichannel opening. Our findings indicate alterations in Cx expression that are typically observed in endothelial cells covering atherosclerotic plaques. The observed radiation-induced increase in Cx channel function may promote bystander signaling thereby exacerbating endothelial cell damage and atherogenesis.

Transition From Phasic to Tonic Contractility in Airway Smooth Muscle After Birth: An Experimental and Computational Modeling Study

Fetal airway smooth muscle (ASM) exhibits phasic contractile behavior, which transitions to a more sustained "tonic" contraction after birth. The timing and underlying mechanisms of ASM transition from a phasic to a tonic contractile phenotype are yet to be established. We characterized phasic ASM contraction in preterm (128 day gestation), term (~150 day gestation), 1-4 month, 1 yr, and adult sheep (5yr). Spontaneous phasic activity was measured in bronchial segments as amplitude, frequency, and intensity. The mechanism of phasic ASM contraction was investigated further with a computational model of ASM force development and lumen narrowing. The computational model comprised a two-dimensional cylindrical geometry of a network of contractile units and the activation of neighboring cells was dependent on the strength of coupling between cells. As expected, phasic contractions were most prominent in fetal airways and decreased with advancing age, to a level similar to the level in the 1-4 month lambs. Computational predictions demonstrated phasic contraction through the generation of a wave of activation events, the magnitude of which is determined by the number of active cells and the strength of cell-cell interactions. Decreases in phasic contraction with advancing age were simulated by reducing cell-cell coupling. Results show that phasic activity is suppressed rapidly after birth, then sustained at a lower intensity from the preweaning phase until adulthood in an ovine developmental model. Cell-cell coupling is proposed as a key determinant of phasic ASM contraction and if reduced could explain the observed maturational changes.

Proinflammatory Arterial Stiffness Syndrome: A Signature of Large Arterial Aging

Age-associated structural and functional remodeling of the arterial wall produces a productive environment for the initiation and progression of hypertension and atherosclerosis. Chronic aging stress induces low-grade proinflammatory signaling and causes cellular proinflammation in arterial walls, which triggers the structural phenotypic shifts characterized by endothelial dysfunction, diffuse intimal-medial thickening, and arterial stiffening. Microscopically, aged arteries exhibit an increase in arterial cell senescence, proliferation, invasion, matrix deposition, elastin fragmentation, calcification, and amyloidosis. These characteristic cellular and matrix alterations not only develop with aging but can also be induced in young animals under experimental proinflammatory stimulation. Interestingly, these changes can also be attenuated in old animals by reducing low-grade inflammatory signaling. Thus, mitigating age-associated proinflammation and arterial phenotype shifts is a potential approach to retard arterial aging and prevent the epidemic of hypertension and atherosclerosis in the elderly.

Joint diseases: from connexins to gap junctions

Connexons form the basis of hemichannels and gap junctions. They are composed of six tetraspan proteins called connexins. Connexons can function as individual hemichannels, releasing cytosolic factors (such as ATP) into the pericellular environment. Alternatively, two hemichannel connexons from neighbouring cells can come together to form gap junctions, membrane-spanning channels that facilitate cell-cell communication by enabling signalling molecules of approximately 1 kDa to pass from one cell to an adjacent cell. Connexins are expressed in joint tissues including bone, cartilage, skeletal muscle and the synovium. Indicative of their importance as gap junction components, connexins are also known as gap junction proteins, but individual connexin proteins are gaining recognition for their channel-independent roles, which include scaffolding and signalling functions. Considerable evidence indicates that connexons contribute to the function of bone and muscle, but less is known about the function of connexons in other joint tissues. However, the implication that connexins and gap junctional channels might be involved in joint disease, including age-related bone loss, osteoarthritis and rheumatoid arthritis, emphasizes the need for further research into these areas and highlights the therapeutic potential of connexins.

Levels of Gap Junction Proteins in Coronary Arterioles and Aorta of Hamsters Exposed to the Cold and During Hibernation and Arousal

There are marked changes in vascular dynamics during prolonged periods in the cold, entrance into hibernation, and arousal to euthermy. Cell-to-cell communication through gap junction channels plays a pivotal role in the control of vasomotor function. Multiple gap junction proteins are expressed in blood vessels, including connexins 37 (Cx37), 40 (Cx40), 43 (Cx43), and 45 (Cx45). Using immunolabeling techniques combined with confocal microscopy, we quantitated the levels of these connexins in coronary arterioles and the thoracic aorta of the golden hamster in four physiological conditions: normal control animals at euthermy; cold-exposed animals (before entrance into hibernation); during hibernation; and after 2-hr arousal from hibernation. In all groups, Cx37 was localized between endothelial cells of the aorta and Cx40 was observed between endothelial cells of coronary arterioles and the aorta. Cx43 was confined to smooth muscle cells of the aorta. Labeling for Cx45 was detected in the endothelium of the ascending aorta. The expression of Cx37 was significantly reduced in cold-exposed, hibernating, and aroused animals. Immunolabeling for Cx40 was increased in the coronary arteriolar endothelium of the cold-exposed group compared with normal controls, hibernating, and aroused animals, perhaps to facilitate intercellular communication during the prolonged circulatory changes to vascular dynamics required to maintain core temperature during cold adaptation. Cx40 expression was unchanged in the aorta. Cx43 immunoexpression in the aorta remained constant under all conditions examined. These changes in connexin expression did not occur during the rapid circulatory changes associated with arousal from hibernation.

Changes of junctions of endothelial cells in coronary sclerosis: A review

Atherosclerosis, the major cause of cardiovascular diseases, has been a leading contributor to morbidity and mortality in the United States and it has been on the rise globally. Endothelial cell-cell junctions are critical for vascular integrity and maintenance of vascular function. Endothelial cell junctions dysfunction is the onset step of future coronary events and coronary artery disease.

The Stress-Response MAP Kinase Signaling in Cardiac Arrhythmias

Stress-response kinases, the mitogen-activated protein kinases (MAPKs) are activated in response to the challenge of a myriad of stressors. c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERKs), and p38 MAPKs are the predominant members of the MAPK family in the heart. Extensive studies have revealed critical roles of activated MAPKs in the processes of cardiac injury and heart failure and many other cardiovascular diseases. Recently, emerging evidence suggests that MAPKs also promote the development of cardiac arrhythmias. Thus, understanding the functional impact of MAPKs in the heart could shed new light on the development of novel therapeutic approaches to improve cardiac function and prevent arrhythmia development in the patients. This review will summarize the recent findings on the role of MAPKs in cardiac remodeling and arrhythmia development and point to the critical need of future studies to further elucidate the fundamental mechanisms of MAPK activation and arrhythmia development in the heart.

Association between 1019C/T polymorphism in the connexin 37 gene and essential hypertension

OBJECTIVE

To investigate the association between the CX 37 1019C/T polymorphism and the susceptibility to essential hypertension (EH).

METHODS

A total of 1126 cases of EH were diagnosed in the People's Hospital of Wuxi City, China. A control group consisted of 874 healthy people, i.e., non-EH patients. All cases were genotyped by DNA sequencing.

RESULTS

Polymorphism C1019T on the Connexin37 gene was found in the whole population. The distribution of three genotype frequencies in both groups was in accordance with the Hardy-Weinberg equilibrium. The frequency of the CX37C allele was higher in EH patients (57.4% vs. 42.1%, χ(2)=92.5, P<0.01) compared to the control group. The frequency of C carriers (CC+TC) was 80.5% in EH patients compared to 66.7% in the control (χ(2)=49.0, P<0.01). EH risk was significantly increased in carriers of C the allele (CC+TC) over that in the TT homozygote (OR=2.06, 95% CI: 1.68 ∼ 2.52). Subsequent stratified analyses demonstrate that a significant difference exists in the frequency of C carriers between male EH patients and controls (79.2% vs. 69.1%, χ(2)=13.4, P<0.01) and in female EH patients and the control group (81.8% vs. 64.4%, χ(2)=38.7, P<0.01). The carriers of the C allele had higher EH risk compared with the TT homozygote without sex differences (male: OR=1.71, 95% CI: 1.28 ∼ 2.27; female: OR=2.48, 95%CI: 1.85 ∼ 3.31).

CONCLUSION

The C allele in the CX37 gene might be associated with the susceptibility to EH in population of Wuxi, China.

Lipopolysaccharide exposure during pregnancy leads to aortic dysfunction in offspring rats

BACKGROUND

Prenatal exposure to Lipopolysaccharide (LPS) produces hypertension in adult offspring rats. The present study was to explore the effects of prenatal inflammation on morphological and functional changes in the aorta from offspring rats and to further assess its susceptibility to cardiovascular diseases.

METHODS AND RESULTS

Pregnant rats were treated intraperitoneally on gestation Days 8, 10 and 12 with saline, LPS (0.79 mg/kg), or pyrrolidine dithiocarbamate (PDTC, 100 mg/kg)+LPS, respectively. Aortic ring reactivity and histopathological alteration were analyzed in offspring at the age of 12 weeks. The detections of connexin (Cx) 37, Cx40, Cx43, and Cx45, including immunofluorescent patterns, protein levels and mRNA expression in the aorta, were performed as well. Furthermore, the expressions of Nuclear factor (NF)-κB (p65), IκBα, phospho-IκBα and IκBβ were determined. The results showed that prenatal LPS exposure leads to morphological abnormalities and impaired aortic reactivity in offspring. Prenatal LPS exposure also decreased the protein and mRNA expression of Cx37 in the aorta from offspring rats. NF-κB and phospho-IκBα levels were both increased, IκBα level, however, was decreased in the aorta of offspring from the maternal LPS exposure compared to the controls. Simultaneously, PDTC treatment markedly reversed the action of LPS.

CONCLUSIONS

Decreased expression of Cx37 contributed to the aortic dysfunction of prenatal LPS exposure offspring, which should be associated with NF-κB activation.

Age-related impairment of conducted dilation in human coronary arterioles

Conducted vasodilation is essential to coordinate vascular resistance along distances to ensure adequate tissue perfusion. We hypothesized that conducted vasodilation of coronary resistance arteries declines with age. Coronary arterioles were dissected from right atrial appendage of patients (n = 27) undergoing cardiac surgery. Arterioles (~100 μm) were cannulated and pressurized (80 mmHg), and developed spontaneous myogenic tone. Conducted vasodilation was initiated by locally administering the endothelium-dependent agonist bradykinin (BK; 100 μM) ejected from a glass micropipette (~3 μm tip opening, positioned in close proximity to the vessel wall). Diameter changes were measured at local and upstream sites (500 and 1,000 μm from the stimulus) with videomicroscopy. Local administration of BK elicited vasodilation, the magnitude of which increased with the duration of stimulus (69 ± 6, 81 ± 6, 90 ± 2%, after 1, 3, and 5 × 100 ms, respectively). BK-induced dilation remained substantial at upstream sites (500 μm: 53 ± 7%; 1,000 μm: 46 ± 9%). The gap junction uncoupler carbenoxolone or 18-α-glycyrrhetinic acid did not affect local responses, but diminished conducted vasodilation. Inhibitors of small/intermediate conductance calcium-activated potassium channels (SKCa/IKCa), apamin and TRAM34, reduced dilations both at local and remote sites. We found that conducted dilation, but not the local response, was significantly reduced in older (≥64 yr) patients. The nitric oxide (NO) synthesis inhibitor N(ω)-nitro-l-arginine methyl ester did not affect local responses, but markedly reduced conducted dilation in younger (<64 yr) individuals. Collectively, we show that human coronary arterioles exhibit SKCa/IKCa-mediated hyperpolarization spread through gap junctions, which contributes to conducted vasodilation initiated by focal application of BK. We demonstrate that conducted dilation declines with age, likely due to reduced NO availability, which plays a permissive role in propagating longitudinal vasomotor signaling.

Polymorphism in endothelial connexin40 enhances sensitivity to intraluminal pressure and increases arterial stiffness

OBJECTIVE

To determine whether impairment of endothelial connexin40 (Cx40), an effect that can occur in hypertension and aging, contributes to the arterial dysfunction and stiffening in these conditions.

APPROACH AND RESULTS

A new transgenic mouse strain, expressing a mutant Cx40, (Cx40T202S), specifically in the vascular endothelium, has been developed and characterized. This mutation produces nonfunctional hemichannels, whereas gap junctions containing the mutant are electrically, but not chemically, patent. Mesenteric resistance arteries from Cx40T202S mice showed increased sensitivity of the myogenic response to intraluminal pressure in vitro, compared with wild-type mice, whereas transgenic mice overexpressing native Cx40 (Cx40Tg) showed reduced sensitivity. In control and Cx40Tg mice, the sensitivity to pressure of myogenic constriction was modulated by both NO and endothelium-derived hyperpolarization; however, the endothelium-derived hyperpolarization component was absent in Cx40T202S arteries. Analysis of passive mechanical properties revealed that arterial stiffness was enhanced in vessels from Cx40T202S mice, but not in wild-type or Cx40Tg mice.

CONCLUSIONS

Introduction of a mutant form of Cx40 in the endogenous endothelial Cx40 population prevents endothelium-derived hyperpolarization activation during myogenic constriction, enhancing sensitivity to intraluminal pressure and increasing arterial stiffness. We conclude that genetic polymorphisms in endothelial Cx40 can contribute to the pathogenesis of arterial disease.

Regulation of cardiovascular connexins by mechanical forces and junctions

Connexins form a family of transmembrane proteins that consists of 20 members in humans and 21 members in mice. Six connexins assemble into a connexon that can function as a hemichannel or connexon that can dock to a connexon expressed by a neighbouring cell, thereby forming a gap junction channel. Such intercellular channels synchronize responses in multicellular organisms through direct exchange of ions, small metabolites, and other second messenger molecules between the cytoplasms of adjacent cells. Multiple connexins are expressed in the cardiovascular system. These connexins not only experience the different biomechanical forces within this system, but may also act as effector proteins in co-ordinating responses within groups of cells towards these forces. This review discusses recent insights regarding regulation of cardiovascular connexins by mechanical forces and junctions. It specifically addresses effects of (i) shear stress on endothelial connexins, (ii) hypertension on vascular connexins, and (iii) changes in afterload and the composition of myocardial mechanical junctions on cardiac connexins.

Association between C1019T polymorphism of the connexin37 gene and coronary heart disease in patients with in-stent restenosis

Studies have shown that a C1019T polymorphism of the gene encoding the gap junction protein connexin37 is associated with coronary artery disease (CAD). The aim of the present study was to explore the association between the C1019T polymorphism in the connexin37 gene and CAD patients with in-stent restenosis (ISR). A total of 532 patients who had undergone coronary stenting and coronary angiography at least three months after the procedure were divided according to a clinical diagnosis standard into two groups which were ISR (n=67) and no in-stent restenosis (NISR; n=465) groups. A further 501 healthy individuals were controls. The subjects were genotyped by DNA sequencing. The results demonstrated the following: i) connexin37 gene 1019 sites in the population were distributed by polymorphism into three genetic types (CC, TC and TT types). The distribution frequency of the healthy control, ISR and NISR groups conformed to the Hardy-Weinberg genetic balance rule; ii) in comparison with the healthy controls, the frequency of the connexin37 C allele was higher in the CAD patients (57.05% vs. 41.32%; OR, 1.89; 95% CI, 1.58–2.25; P<0.01). The frequency of the C carriers (CC+TC) was 65.47% in the healthy controls, vs. 79.32% in CAD patients (P<0.01). The CAD risk was significantly increased in the carriers of the C allele (CC+TC) compared with TT homozygotes (OR, 2.03; 95% CI, 1.53–2.80; P<0.01). Stratified analysis demonstrated that a significant difference existed in the frequency of C carriers between the male CAD patients and healthy controls (79.63% vs. 72.45%; OR, 1.48; 95% CI, 1.06–2.09, P=0.02), as well as in the female CAD patients (78.00% vs. 51.50%; OR, 3.34; 95% CI, 1.90–5.86; P<0.01). In the female and male CAD patients, the frequency of the connexin37 C allele was higher than in the healthy controls (male: χ²=12.67, P<0.01; female: χ²=50.20, P<0.01); iii) compared with the NISR group, the frequencies of the connexin37 C allele and C carriers (CC+TC) were significantly higher in the ISR group (frequency of C allele: 72.39% vs. 54.84%; P<0.01; frequency of C carriers: 89.55% vs. 77.85%; P=0.03). Compared with TT homozygotes, the restenosis risk was significantly increased in the carriers of the C allele (CC+TC; OR, 2.44; 95% CI, 1.08–5.50). Subsequent stratified analysis revealed that the frequency of the C allele was significantly higher in the male ISR group than in the male NISR group (78.57% vs. 52.66%; OR, 3.30; 95% CI, 2.05–5.29; P<0.01). The restenosis risk was ∼four-fold higher in the C carriers (CC+TC) than in the TT homozygotes (OR, 3.74; 95% CI, 1.32–10.64). However in the female population, there was no difference in the ISR risk between the carriers of the C allele (CC+TC) and the TT homozygotes (P=0.70). In summary, the C allele of the connexin37 gene is not only is associated with the susceptibility to CAD, but also associated with restenosis following coronary stenting in the population studied herein, particularly the male population.

Age-related changes in gap junctional intercellular communication in osteoblastic cells

Aging demonstrates deleterious effects upon the skeleton which can predispose an individual to osteoporosis and related fractures. Despite the well-documented evidence that aging decreases bone formation, there remains little understanding whereby cellular aging alters skeletal homeostasis. We, and others, have previously demonstrated that gap junctions--membrane-spanning channels that allow direct cell-to-cell conductance of small signaling molecules--are critically involved in osteoblast differentiation and skeletal homeostasis. We examined whether the capacity of rat osteoblastic cells to form gap junctions and respond to known modulators of gap junction intercellular communication (GJIC) was dependent on the age of the animal from which they were isolated. We observed no effect of age upon osteoblastic Cx43 mRNA, protein or GJIC. We also examined age-related changes in PTH-stimulated GJIC. PTH demonstrated age-dependent effects upon GJIC: Osteoblastic cells from young rats increased GJIC in response to PTH, whereas there was no change in GJIC in response to PTH in osteoblastic cells from mature or old rats. PTH-stimulated GJIC occurred independently of changes in Cx43 mRNA or protein expression. Cholera toxin significantly increased GJIC in osteoblastic cells from young rats compared to those from mature and old rats. These data demonstrate an age-related impairment in the capacity of osteoblastic cells to generate functional gap junctions in response to PTH, and suggest that an age-related defect in G protein-coupled adenylate cyclase activity at least partially contributes to decreased PTH-stimulated GJIC.

Central arterial aging and the epidemic of systolic hypertension and atherosclerosis

The structure and function of central arteries change throughout the lifetime of humans and animals. Since atherosclerosis and hypertension are prevalent in epidemic proportion among older persons, it is reasonable to hypothesize that specific mechanisms that underlie the arterial substrate that has been altered by an "aging process" are intimately linked to arterial diseases. Indeed, recent studies reveal a profile of arterial cell and matrix properties that emerges with advancing age within the grossly normal appearing aortic wall of both animals and humans. This profile is proinflammatory, and is manifested by intimal infiltration of fetal cells, increased production of angiotensin II (Ang II)-signaling pathway molecules, eg, matrix metalloproteases (MMPs), and monocyte chemoattractant protein (MCP-1), transforming growth factor B1 (TGF-beta1), enhanced activation of MMPs, TGF-beta, and NADPH oxidase, and reduced nitric oxide (NO) bioavailability. This profile is similar to that induced at younger ages in experimental animal models of hypertension or atherosclerosis. In humans, this proinflammatory state, which occurs in the absence of lipid deposition, appears to be attributable to aging, per se. Other well known human risk factors, eg, altered lipid metabolism, smoking, and lack of exercise, interact with this arterial substrate that is altered by aging and render the aging human artery fertile soil for facilitation of the initiation and progression of arterial diseases. Therapies to reduce or retard this age-associated proinflammatory state within the grossly appearing arterial wall central arteries, in addition to slowing arterial aging, per se, may have a substantial impact on the quintessential age-associated arterial diseases of our society.

Inducible coexpression of connexin37 or connexin40 with connexin43 selectively affects intercellular molecular transfer

Many tissues express multiple gap junction proteins, or connexins (Cx); for example, Cx43, Cx40, and Cx37 are coexpressed in vascular cells. This study was undertaken to elucidate the consequences of coexpression of Cx40 or Cx37 with Cx43 at different ratios. EcR-293 cells (which endogenously produce Cx43) were transfected with ecdysone-inducible plasmids encoding Cx37 or Cx40. Immmunoblotting showed a ponasterone dose-dependent induction of Cx37 or Cx40 while constant levels of Cx43 were maintained. The coexpressed connexins colocalized at appositional membranes. Double whole-cell patch clamp recordings showed no significant change in total junctional conductances in cells treated with 0, 0.5, or 4 μM ponasterone; however, they did show a diversity of unitary channel sizes consistent with the induced connexin expression. In cells with induced expression of either Cx40 or Cx37, intercellular transfer of microinjected Lucifer yellow was reduced, but transfer of NBD-TMA (2-(4-nitro-2,1,3-benzoxadiol-7-yl)[aminoethyl]trimethylammonium) was not affected. In cocultures containing uninduced EcR cells together with cells induced to coexpress Cx37 or Cx40, Lucifer yellow transfer was observed only between the cells expressing Cx43 alone. These data show that induced expression of either Cx37 or Cx40 in Cx43-expressing cells can selectively alter the intercellular exchange of some molecules without affecting the transfer of others.

Loss of anti-arrhythmic effect of vagal nerve stimulation on ischemia-induced ventricular tachyarrhythmia in aged rats

Reduced vagal activity is associated with increased risk for life-threatening arrhythmia during myocardial ischemia (MI); conversely, the increase in vagal tone may provide protective effect against ventricular arrhythmias. In fact, vagal nerve stimulation (VNS) exerted an anti-arrhythmic effect by preserving connexin 43 (Cx43), a gap junction protein in ventricles, in a rat model of MI. We investigated the effects of VNS on ventricular tachyarrhythmia during acute MI and the expression of Cx43 in aged rats. Both adult (3-4 months) and aged (≥ 24 months) male rats were subjected to ischemia of 30 min. VNS was applied before ischemia either alone or in combination with atropine (0.5 mg/kg) or carbenoxolone, a gap junction inhibitor (10 mg/kg). During the 30-min ischemia, the incidence of ventricular tachycardia (VT) or ventricular fibrillation (VF) was higher in aged rats compared with adult rats. VNS significantly suppressed VT and VF in adult rats and these effects were eliminated by atropine or carbenoxolone. In contrast, VNS did not suppress VT and VF in the aged rats. Moreover, ischemia did not change the expression levels of total Cx43 protein in adult and aged rat ventricles. However, the expression level of total Cx43 protein was two times lower in sham-operated aged rats than that in sham-operated adult rats. Thus, in aged rats, loss of anti-arrhythmic effect of VNS is associated with reduced expression of Cx43 protein. These findings suggest that Cx43 may be an important target for inhibiting ischemia-induced VT in adult patients but not in aged patients.

Sex- and age-related changes in connexin 43 expression in normal rat bladder

Purpose

Gap junctions are intercellular channels to facilitate electrical and metabolic communication between adjacent cells. Connexin 43 is the most predominant type of connexin expressed on rat detrusor muscle cells. We investigated the connexin 43 expressions in various age groups of either sex in normal rats.

Methods

Eighty Sprague-Dawley rats were used for analysis. Each group was quantified by 8 rats at 1 week, 2 weeks, 1 month, 3 months, and 6 months of age in either sex. In each animal, bladder was removed without any kind of intervention and fresh-frozen in liquid nitrogen. Total RNA extraction was done with easy-BLUE total RNA extraction kit. Reverse transcription polymerase chain reaction was done for connexin 43 and glyceraldehyde-3-phosphate dehydrogenase as an internal control using ImProm-II Reverse Transcription System.

Results

In female rats, no age-related change was detected in connexin 43 expressions. In male rats, connexin expression at 3 months of age showed significant decrease compared with 1 week, 2 weeks, and 6 months of age (P<0.05). When connexin expression at the same age in male and female were compared, only 3 months group in male showed significant decrease than the same age group in female.

Conclusions

Our data suggest that the expressions of connexin 43 mRNA in normal detrusor muscle cell showed age-related changes especially in male rats. Although it is difficult to interpret these findings at this stage, age should be considered as a possible compounding factor affecting connexin 43 expressions in male rats.

The ageing cardiovascular system

The increase in the ageing population has generated much interest and research into what constitutes normal ageing. By identifying normal ageing processes it is hoped it will be possible to distinguish risk factors for the development of abnormal or premature ageing.

This review discusses biological, structural and mechanical changes in the cardiovascular system with ageing that are thought to increase the risk of cardiovascular disease with ageing. Contributory factors are thought to be genetic and lifestyle related. Measurements of biological as opposed to chronological ageing such as vascular stiffness are explored as a possible useful predictor of cardiovascular morbidity and mortality, indicating its possible utilization as a non-invasive screening tool in older people.

The identification of those at risk of cardiovascular disease and modification of risk factors may minimize interactions of the ageing process and therefore reduce the incidence of cardiovascular disease within the UK population.

Down-regulation of connexin43 gap junction by serum deprivation in human endothelial cells was improved by (-)-Epigallocatechin gallate via ERK MAP kinase pathway

Intercellular communication through gap junctions (GJIC) plays an essential role in maintaining the functional integrity of vascular endothelium. Despite emerging evidence suggests that (-)-Epigallocatechin gallate (EGCG) may improve endothelial function. However, its effect on Cx43 gap junction in endothelial cells remains unexplored. Here we investigated the effect of EGCG on connexin43 (Cx43) gap junction in endothelial cells. The levels of Cx43 protein in human umbilical vein endothelial cells (HUVECs) cultured under serum-deprivation 48 h decreased about 50%, accompanied by decreased GJIC. This reduction can be reversed by treatments with EGCG. In addition, EGCG activated ERK, P38, and JNK mitogen-activated protein kinases (MAPKs), which were supposed to participate in the regulation of Cx43. A MEK inhibitor PD98059, but not SB203580 (a p38 kinase inhibitor) or SP600125 (a JNK kinase inhibitor), abolished the effects of EGCG on Cx43 expression and GJIC. Moreover, although both Akt and eNOS phosphorylation were time-dependently augmented by EGCG, neither PI3K inhibitor LY294002 nor eNOS inhibitor L-NAME blocked the effects of EGCG on Cx43 gap junctions. Thus, EGCG attenuated Cx43 down-regulation and impaired GJIC induced by serum deprivation, ERK MAPK Signal transduction pathway appears to be involved in these processes.

Differential endothelial gap junction expression in venous vessels exposed to different hemodynamics

After being anastomosed with the artery, vein graft is exposed to abruptly increased hemodynamic stresses. These hemodynamic stresses may change the profile of endothelial gap junction expression as demonstrated in the artery, which may subsequently play active roles in physiological adaptation or pathophysiological changes of the vein grafts. We investigated the endothelial expression of gap junction in the venous vessels exposed to different hemodynamic stresses. Immunocytochemical analysis of the endothelial Cx expression was performed by observing the whole mounts of inferior vena cava (IVC) of aortocaval fistula (ACF) rats or IVC-banded ACF rats using confocal microscope. Immunocytochemical analysis demonstrated that in the endothelium of the native vein, the gap-junctional spot numbers (GJSNs) and the total gap-junctional areas (TGJAs) of Cx40 and Cx43 were lower than those of the thoracic aorta and that Cx37 was hardly detectable. In the IVCs of ACF rats, which were demonstrated to be exposed to a hemodynamic condition of high flow velocity and low pressure, the GJSNs and the TGJAs of all three Cxs were increased. In the IVCs of IVC-banded ACF rats, which were exposed to a hemodynamic condition of high pressure and low flow velocity, the GJSNs and the TGJAs of Cx37 increased markedly and those of Cx40 and Cx43 remained without significant changes. In conclusion, the endothelial expressions of gap junctions in the native veins were lower than those of the arteries. When exposed to different hemodynamic stresses, the gap junctions were expressed in specific patterns.

Deletion of the FHL2 gene attenuates the formation of atherosclerotic lesions after a cholesterol-enriched diet

AIMS

FHL2, a member of the four and a half LIM domain (FHL) family of proteins, may play an important role in the circulatory system and in particular atherosclerosis.

MAIN METHODS

To investigate the role of FHL2 in atherogenesis, FHL2-null and wild-type control male mice were fed either a normal chow (NC) or a cholesterol-enriched diet (CED).

KEY FINDINGS

At 3 months post CED, aortic atherosclerotic plaques were observed in both control and FHL2-null mice. Lesions in control mice increased dramatically by 6 months of CED. In contrast, lesion size did not increase during this time in CED-fed FHL2-null mice. Relative to control mice on a normal chow of diet (NCD), control mice on a CED exhibited lower circulating nitric oxide (NO) levels, and decreased expression of connexin37 (Cx37) and Cx40 in aortic endothelium. In contrast, FHL2-null mice on a CED maintained similar levels of circulating NO as FHL2-null mice fed a NCD. Cxs levels in aortic endothelium of FHL2-null mutants on a NCD were lower relative to control mice on a NCD, and did not decrease with CED.

SIGNIFICANCE

Our data demonstrate a role for FHL2 in atherogenesis, the regulation of circular NO release, and expression of gap junctions within aortic endothelium.

Asymmetric dimethylarginine damages connexin43-mediated endothelial gap junction intercellular communication

Asymmetric dimethylarginine (ADMA), a major endogenous inhibitor of nitric oxide synthase, is recently defined as a novel atherogenic factor. Communication via gap junction (GJIC) is involved in the regulation of a variety of endothelial activities, such as cell differentiation and senescence. The aim of this study is to explore the effects of ADMA on connexin43 (Cx43) mediated endothelial GJIC. Lysophosphatidylcholine (LPC) caused the downregulation of Cx43 expression and GJIC dysfunction in cultured human umbilical vein endothelial cells (HUVECs), which were significantly ameliorated by decreasing ADMA accumulation. Furthermore, we found that ADMA (10 µmol·L–1, 24 h) markedly downregulated Cx43 expression and damaged GJIC function in HUVECs. ADMA also increased production of intracellular reactive oxygen species (ROS) and induced phosphorylation of p38 MAPK. Furthermore, the inhibitory effect of ADMA on Cx43-mediated GJIC could be attenuated by NADPH oxidase inhibitor diphenyleneiodonium and apocynin as well as p38 MAPK inhibitor SB203580, respectively. In conclusion, our present results suggest that ADMA inhibits endothelial GJIC function via downregulating Cx43 expression, which suggesting a novel mechanism linking between elevated ADMA level and progression of atherosclerosis.

Shear Stress and Cyclic Circumferential Stretch, But Not Pressure, Alter Connexin43 Expression in Endothelial Cells

Hemodynamic forces play a critical role in atherogenesis, as evidenced by the focal pattern of development of atherosclerotic lesions. Whereas disturbed flow in the branches and curved regions of large arteries is proatherogenic, laminar flow in the straight parts of vessels is atheroprotective. In addition, hypertension and age-related changes in arterial stiffness are important risk factors of the disease. Hemodynamic forces induce various changes in the structure and function of vascular endothelium, many of which reflect alterations in gene expression. Endothelial cells are linked by gap junctions, which facilitate the propagation of electrical and chemical signals along the vascular wall. Using an in vitro perfusion system, we investigated the effects of pulsed unidirectional and oscillatory flows in combination with different levels of hydrostatic pressure and circumferential stretch on the expression of Cx43 in endothelial cells. Our results show that shear stress and circumferential stretch, but not pressure, modulate the expression of Cx43. In view of the distribution of this protein along the vascular tree, our findings provide new insights into the role of mechanical forces on gap junctional communication in regions prone to the development of atherosclerosis.

Arterial aging and subclinical arterial disease are fundamentally intertwined at macroscopic and molecular levels

The structure and function of arteries change throughout a lifetime. Age is the dominant risk factor for hypertension, coronary heart disease, congestive heart failure, and stroke. The cellular/molecular proinflammatory alterations that underlie arterial aging are novel putative candidates to be targeted by interventions aimed at attenuating arterial aging as a major risk factor for cardiovascular diseases. This review provides a landscape of central arterial aging and age-disease interactions, integrating perspectives that range from humans to molecules, with the goal that future therapies for cardiovascular diseases, such as hypertension, also will target the prevention or amelioration of unsuccessful arterial aging.

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.

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.

Diabetes reduces aortic endothelial gap junctions in ApoE-deficient mice: simvastatin exacerbates the reduction

We examined the endothelial gap junctions in diabetic hyperlipidemic mice. Male apolipoprotein E (apoE)-deficient mice were made diabetic by streptozotocin. Three weeks later, the animals were treated with simvastatin for 2 weeks. The expression of aortic gap junctions in the non-diabetic (n=10), untreated diabetic (n=10), and simvastatin-treated diabetic animals (n=6) was analyzed. There was a >4-fold increase in serum cholesterol level and >50% increase in plaque areas in the diabetic mice, regardless of simvastatin treatment. Western blotting of aortae showed reduced expression of connexin37 (Cx37) and Cx40 in the diabetic mice, which were further decreased in the simvastatin-treated diabetic mice. Immunoconfocal microscopy showed that endothelial gap junctions made of Cx37 and Cx40 were both reduced in the untreated diabetic mice compared with the non-diabetic mice (decrease: Cx37, 41%; Cx40, 42%; both p<0.01). The reduction was greater in the simvastatin-treated mice (decrease in treated diabetic vs non-diabetic: Cx37, 61%; Cx40, 79%; both p<0.01; decrease in treated diabetic vs untreated diabetic: Cx37, 34%; Cx40, 63%; both p<0.01). Cx37 and Cx40 were decreased in the endothelium of plaque surface. Cx43 appeared in the medial layer and inner layer of the intima. All three connexins were rarely expressed in monocytes/macrophages inside the plaques. In conclusion, in apoE-deficient mice, streptozotocin-induced diabetes is associated with downregulation of endothelial Cx37 and Cx40 gap junctions. Short-term treatment with simvastatin exacerbates the downregulation.

Perineuronal satellite cells in mouse spinal ganglia express the gap junction protein connexin43 throughout life with decline in old age

Satellite glial cells that envelope the bodies of sensory neurons in spinal ganglia are connected to each other by gap junctions and exhibit dye coupling. These junctions may endow perineuronal satellite cells with the coordination necessary for the efficient performance of functions such as buffering of K(+) in the perineuronal microenvironment, provision of metabolic support to ganglionic neurons, and neuroprotection. Our knowledge of gap junctions has increased considerably in recent years, but little information is available on the connexins that form these junctions in spinal ganglia. In the present study we set out to determine whether the perineuronal satellite cells of mouse spinal ganglia express the connexins that are mainly present in neuroglial cells (Cx32 and Cx43). In young (3 months) mice, PCR showed the presence of both Cx32 and Cx43 transcripts. By immunocytochemistry, we localized Cx32 to axon-ensheathing Schwann cells, but not to other parts of the ganglion. We found Cx43 positivity in the perineuronal satellite cells, which were identified by their immunoreactivity to S100 protein and to glutamine synthetase. PCR showed Cx43 transcripts also in the spinal ganglia of adult (8 months) and old (24 months) animals. Cx43 immunostaining was present in satellite cells surrounding all nerve cell bodies, irrespective of size. The mean number of Cx43-immunoreactive puncta was significantly lower in the perineuronal satellite cells of aged mice compared to young and adult animals. This latter finding is consistent with observations in non-nervous tissues, and the hypothesis that a prominent decrease in Cx43 is a marker of senescence.

The influence of smoking and homocysteine on subclinical atherosclerosis is modified by the connexin37 C1019T polymorphism - The Cardiovascular Risk in Young Finns Study

BACKGROUND

A polymorphism C1019T on the connexin37 (Cx37) gene has been found to associate with coronary artery disease. There are conflicting results on which allele confers risk, and the possibility of interactions between the polymorphism and risk factors has been raised. In this study, we examined interactions between the Cx37 polymorphism and common risk factors and their associations to early vascular parameters of atherosclerosis: carotid artery intima-media thickness (IMT), and carotid artery compliance (CAC) and brachial artery flow mediated dilatation (FMD).

METHODS

A population of 1440 healthy young adults from the Cardiovascular Risk in Young Finns Study was studied. The subjects were genotyped and their cardiovascular risk factor and ultrasound data gathered in 2001 were used for the statistical analyses.

RESULTS

In the whole population, homocysteine in subjects with the TT genotype was found to be associated with higher FMD values (p for interaction 0.038) and remained so in three different adjusted models (p for interaction 0.022-0.038). In women with the CC genotype, smoking was found to be associated with higher FMD values and the smoking-by-genotype interaction remained significant in three adjusted models (p for interaction 0.001-0.041). In women with TT genotype, the effect of smoking was opposite, i.e., FMD values for smokers were lower compared to non-smokers. In men, physical activity interacted with Cx37 on CAC in the CT and TT genotypes (p for interaction 0.011). No significant interactions were found to predict IMT.

CONCLUSIONS

The effect of smoking and homocysteine levels on arterial endothelial functions and elasticity were modified by the allelic variation of the Cx37 gene. These data suggest that variation in the connexin gene may modify effects risk factors have on vascular function.

Associations between connexin37 gene polymorphism and markers of subclinical atherosclerosis: the Cardiovascular Risk in Young Finns study

OBJECTIVE

Connexin37 (cx37) C1019T polymorphism has been shown to associate with coronary artery disease in different populations. We investigated whether this polymorphism associates with carotid artery intima-media thickness (IMT), carotid artery compliance (CAC) and brachial artery flow mediated dilatation (FMD) - i.e., early ultrasound markers of subclinical atherosclerosis - in a clinically healthy population of young Finnish adults.

METHODS AND RESULTS

1440 individuals from the Cardiovascular Risk in Young Finns study were genotyped and studied using cardiovascular risk factor and ultrasound data obtained in 2001. In linear regression models, no significant association between the cx37 polymorphism and carotid IMT, CAC or brachial artery FMD (ANOVA, p=0.159, 0.151 and 0.547), respectively, was found in the whole population or in women and men separately.

CONCLUSIONS

The connexin37 C1019T polymorphism is not related with markers of subclinical atherosclerosis in young adults.

Endothelial gap junctions are down-regulated by arsenic trioxide

We investigated the effect of As(2)O(3), an anti-cancer drug, on endothelial gap junctions. Human aortic endothelial cells (HAEC) were treated with As(2)O(3) at 1, 10, 100, and 1000 ng/ml and the cells were examined to evaluate the expression of connexin43 (Cx43) and to assess gap-junction communication. Endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) were measured to assess for endothelial dysfunction. Male Sprague-Dawley rats were given intravenous As(2)O(3) (200 mug/kg/day) or saline for 4 weeks, after which aortic endothelial gap junctions, eNOS, and circulating NO levels were evaluated. We found that HAEC Cx43 transcripts and gap junctions were reduced and gap-junction communication was attenuated by As(2)O(3). This decrease of Cx43 gap junctions was prevented by the addition of protease inhibitors. At a dose of 100 ng/ml of As(2)O(3), eNOS was reduced at 48 h, but NO was markedly reduced by 1 h. In animals treated with As(2)O(3), endothelial gap junctions comprising Cx37, Cx40, or Cx43 were all reduced in amount, while eNOS and circulating NO levels remained unchanged. In both in vitro and in vivo rat experiments, endothelial gap junctions were consistently reduced by As(2)O(3), unlike the response of eNOS and NO, which were decreased in cells but not in the rat aortic endothelium. The reduction in Cx43 involved both down-regulation at the transcriptional level and increased degradation. These findings indicate that gap-junction communication in the vascular endothelium is inhibited by treatment with As(2)O(3).

Loss of ischemic preconditioning's cardioprotection in aged mouse hearts is associated with reduced gap junctional and mitochondrial levels of connexin 43

Connexin 43 (Cx43) is localized at left ventricular (LV) gap junctions and in cardiomyocyte mitochondria. A genetically induced reduction of Cx43 as well as blockade of mitochondrial Cx43 import abolishes the infarct size (IS) reduction by ischemic preconditioning (IP). With progressing age, Cx43 content in ventricular and atrial tissue homogenates is reduced. We now investigated whether or not 1) the mitochondrial Cx43 content is reduced in aged mice hearts and 2) IS reduction by IP is lost in aged mice hearts in vivo. Confirming previous results, sarcolemmal Cx43 content was reduced in aged (>13 mo) compared with young (<3 mo) C57Bl/6 mice hearts, whereas the expression levels of protein kinase C epsilon and endothelial nitric oxide synthase remained unchanged. Also in mitochondria isolated from aged mice LV myocardium, Western blot analysis indicated a 40% decrease in Cx43 content compared with mitochondria isolated from young mice hearts. In young mice hearts, IP by one cycle of 10 min ischemia and 10 min reperfusion reduced IS (% of area at risk) following 30 min regional ischemia and 120 min reperfusion from 67.7 +/- 3.3 (n = 17) to 34.2 +/- 6.6 (n = 5, P < 0.05). In contrast, IP's cardioprotection was lost in aged mice hearts, since IS in nonpreconditioned (57.5 +/- 4.0, n = 10) and preconditioned hearts (65.4 +/- 6.3, n = 8, P = not significant) was not different. In conclusion, mitochondrial Cx43 content is decreased in aged mouse hearts. The reduced levels of Cx43 may contribute to the age-related loss of cardioprotection by IP.

Spatial separation of endothelial small- and intermediate-conductance calcium-activated potassium channels (K(Ca)) and connexins: possible relationship to vasodilator function?

Activation of endothelial cell small- (S) and intermediate- (I) conductance calcium-activated potassium channels (K(Ca)) and current or molecular transfer via myoendothelial gap junctions underlies endothelium-derived hyperpolarization leading to vasodilation. The mechanism underlying the K(Ca) component of vasodilator activity and the characteristics of gap junctions are targets for the selective control of vascular function. In the rat mesenteric artery, where myoendothelial gap junctions and connexin (Cx) 40 are critical for the transmission of the endothelial cell hyperpolarization to the smooth muscle, SK(Ca) and IK(Ca) provide different facets of the endothelium-derived hyperpolarization response, being critical for the hyperpolarization and repolarization phases, respectively. The present study addressed the question of whether this functional separation of responses may be related to the spatial localization of the associated channels? The distribution of endothelial SK(Ca) and IK(Ca) and Cx subtype(s) were examined in the rat mesenteric artery using conventional confocal and high-resolution ultrastructural immunohistochemistry. At the internal elastic lamina-smooth muscle cell interface at internal elastic lamina holes (as potential myoendothelial gap junction sites), strong punctate IK(Ca), Cx37 and Cx40 expression was present. SK(Ca), Cx37, Cx40 and Cx43 were localized to adjacent endothelial cell gap junctions. High-resolution immunohistochemistry demonstrated IK(Ca) and Cx37-conjugated gold to myoendothelial gap junction-associated endothelial cell projections. Clear co-localization of K(Ca) and Cxs suggests a causal relationship between their activity and the previously described differential functional activation of SK(Ca) and IK(Ca). Such precise localizations may represent a selective target for control of vasodilator function and vascular tone.

Comparison of endothelial cells grown on different stent materials

We compared the behavior of endothelial cells grown on stent materials. Human umbilical vein endothelial cells (HUVEC) were seeded (200 or 800 cells/mm(2)) onto different metallic sheets, including 316 stainless steel (low carbon; 316LSS), nitinol, and 316LSS coated with TiN or TiO(2). Cells seeded onto tissue culture-treated polystyrene dish coated with gelatin were used as controls. Forty-eight hours later, the cells were examined by Western blotting, immunofluorescence microscopy, and scanning electron microscopy (SEM). The results showed that for either seeding values, the levels of cellularity on TiN and TiO(2) are comparable or higher, and those on 316LSS and nitinol are lower compared to the controls (p < 0.05). SEM demonstrated that cells are well-attached on the metallic surface with various amount of cellular processes. In metals seeded with 800 cells/mm(2), Western blotting showed that the overlying cells expressed less amounts of endothelial nitric oxide synthase (eNOS), Von Willebrand factor (VWF), and connexin43 protein compared to the controls (p < 0.05). Immunofluorescence microscopy confirmed the results of immunoblotting. In conclusion, stent materials affect HUVEC's growth and protein expression profile. Down-regulation of eNOS, VWF, and connexin43 gap junctions is a common phenomenon in the cells growing on the examined metallic materials, suggesting the existence of endothelial dysfunction in the arterial segments containing the stents made of such materials.

Specific impairment of endothelium-derived hyperpolarizing factor-type relaxation in mesenteric arteries from streptozotocin-induced diabetic mice

We hypothesized that the contribution made by endothelium-derived hyperpolarizing factor (EDHF) to acetylcholine (ACh)-induced endothelium-dependent relaxation (EDR) might be altered in mesenteric arteries from streptozotocin (STZ)-induced diabetic mice. In endothelium-intact preparations, the ACh-induced EDR (but not the sodium nitroprusside-induced relaxation) was weaker in the STZ group than in age-matched controls. Indomethacin (10 muM) had no significant effect on EDR in either group, indicating that cyclooxygenase products, including prostacyclin, are not involved. This indomethacin-resistant EDR was weaker in the STZ group than in the controls. To isolate the EDHF-resistant component of EDR, charybdotoxin (100 nM) and apamin (100 nM) were present in the bath solution throughout the next experiment. This EDHF-resistant relaxation did not differ significantly between the two groups. On the other hand, the EDHF-mediated relaxation was significantly weaker in the STZ group than in the controls, and it was completely blocked by lysophosphatidylcholine (LPC, 10 microM) in each group. The eNOS protein expression was similar between the two groups. These results suggest that (a) the endothelial dysfunction present in mesenteric arteries from type 1 diabetic mice is largely attributable to reduced EDHF signaling, and (b) LPC may be involved in this attenuation of EDHF-mediated relaxation.

Downregulation of connexin 43 expression by high glucose induces senescence in glomerular mesangial cells

Connexin 43 (Cx43) plays an important role in cell differentiation and growth control, but whether it can be regulated by high glucose and whether it can mediate in glomerular mesangial cells (GMC) the phenotype alterations that are induced by high glucose still remain to be explored. In this study, RNA interference and gene transfer techniques were used to knock down and overexpress Cx43 gene in rat GMC to determine the contribution of Cx43 to GMC senescence that was induced by high glucose. The results show that high glucose (30 mM) not only downregulated Cx43 mRNA and protein expression (P<0.05) but also increased the percentage of senescence-associated beta-galactosidase (SA-beta-gal) stained cells and expression of p21cip1 and p27kip1 (P<0.05), indicating that high glucose promoted rat GMC senescence. Knocking down Cx43 gene expression significantly increased the percentage of SA-beta-gal stained cells and p27kip1 and p21cip1 expression in GMC (P<0.05), whereas overexpression of Cx43 significantly decreased the percentage of SA-beta-gal stained cells (P<0.05). These results demonstrate for the first time that downregulation of Cx43 expression by high glucose promotes the senescence of GMC, which may be involved in the pathogenesis of diabetic nephropathy.

Flow regulates intercellular communication in HAEC by assembling functional Cx40 and Cx37 gap junctional channels

Direct cell-to-cell transfer of ions and small signaling molecules via gap junctions plays a key role in vessel wall homeostasis. Vascular endothelial gap junctional channels are formed by the connexin (Cx) proteins Cx37, Cx40, and Cx43. The mechanisms regulating connexin expression and assembly into functional channels have not been fully identified. We investigated the dynamic regulation of endothelial gap junctional intercellular communication (GJIC) by fluid flow and the participation of each vascular connexin in functional human endothelial gap junctions in vitro. Human aortic endothelial cells (HAEC) were exposed for 5, 16, and 24 h to physiological flows in a parallel-plate flow chamber. Connexin protein expression and localization were evaluated by immunocytochemistry, and functional GJIC was evaluated by dye injection. Connexin-mimetic peptide inhibitors were used to assess the specific connexin composition of functional channels. HAEC monolayers in culture exhibited baseline functional communication at a striking low level despite abundant expression of Cx43 and Cx40 localized at cell-to-cell appositions. Upon exposure to flow, GJIC by dye spread demonstrated a significant time-dependent increase from baseline levels, reaching 7.5-fold in 24 h. Inhibition studies revealed that this response was mediated primarily by Cx40, with lesser contributions of the other two vascular connexins assembled into functional homotypic and/or heterotypic channels. This is the first study to demonstrate that flow simultaneously and differentially regulates expression of the Cx37, Cx40, and Cx43 proteins and their involvement in the augmentation of intercellular communication by dye transfer in human endothelial cells in vitro.

Association between C1019T polymorphism of connexin37 and acute myocardial infarction: a study in patients from Sicily

During atherogenesis, a critical role is played by intercellular communication via gap junctions, cell membrane channels linking the cytoplasmic compartments of adjacent cells. The component protein subunits of these channels, called connexin (Cx), belong to a multigene family. Cx37 is involved in growth, regeneration after injury and ageing of the endothelial cells, suggesting its role in atherosclerosis. The C1019 single nucleotide polymorphism (SNP) of Cx37 gene was associated with thickening of the carotid intima in Swedish men and was also associated with coronary artery disease in a Taiwanese population. On the other hand, in two more recent studies performed in male Japanese population, T1019 Cx37 SNP has shown to be a risk factor for acute myocardial infarction (AMI). In the light of these discrepant results, we have studied the frequency of this SNP in a very homogeneous cohort of young male people affected by AMI. We analysed 97 male Sicilian patients (mean age 40, age range 20-46) and 196 healthy male controls (mean age 39, age range 20-55) for C1019T of the Cx37. The 1019T SNP was significantly increased in the patients compared to the controls (43.8% vs. 34.4%; p=0.03 by chi2 test with Yates' correction; odds ratio (OR) 1.5, (1.0-2.1) 95% confidence interval (CI)). The present case control study performed in a homogeneous Caucasoid population confirms the Japanese results that T SNP of Cx37 gene is involved in AMI phenotype, demonstrating the consistency of the association across past studies and across different populations. The differences between patients and controls are significant but relatively small with an odd ratio risk of 1.5. However, as AMI is a multifactorial disease, any single mutation will only provide a small or modest contribution to risk, also depending on interaction with other genes and/or a particular environment.

Down-regulating effect of nicotine on connexin43 gap junctions in human umbilical vein endothelial cells is attenuated by statins

We investigated the effect of nicotine on connexin43 (Cx43) expression and gap-junctional communication in human umbilical vein endothelial cells (HUVEC). We also evaluated whether the effect requires activation of acetyl choline receptors sensitive to nicotine (nAChRs) and is altered by statins. The results showed that expression of Cx43 protein is reduced by nicotine in a dose-dependent manner (6 x 10(-4) M nicotine vs control, 33% reduction, p < 0.01), though Cx43 mRNA is up-regulated (6 x 10(-4) M nicotine vs control, 36% increase, p < 0.01). Concomitantly, the communication function, determined by fluorescence recovery after photobleaching, is decreased (6 x 10(-4) M nicotine vs control, 38% reduction, p < 0.05). Such a down-regulation of Cx43 gap junctions by nicotine disappears in the presence of the nAChRs antagonist, dihydro-beta-erythroidine, and protease inhibitors leupeptin plus N-acetyl-Leu-Leu-Norleu-al (ALLN). Similarly, the effect of nicotine is attenuated by statins, including fluvastatin, lovastatin, pravastatin, and simvastatin, even at the presence of mevalonate. We concluded that i) nicotine down-regulates Cx43 expression and gap-junctional communication in HUVEC via post-transcriptional modification, which involves enhancement of Cx43 proteolysis; ii) the effect of nicotine is mediated via activation of nAChRs; and iii) the effect of nicotine is attenuated by statins through mechanisms outside the hypolipidemic pathway.

Arteriolar network architecture and vasomotor function with ageing in mouse gluteus maximus muscle

Physical diminishes with ageing, but little is known of how the microvascular supply to skeletal muscle fibres is affected. To test the hypothesis that ageing alters blood flow control, we investigated network architecture and vasomotor responses of arterioles in the gluteus maximus muscle of young (2-3 months), adult (12-14 months) and old (18-20 months) C57BL6 male mice (n = 83) (Young, Adult and Old, respectively). Microvascular casts revealed that the total number, length and surface area of arteriolar segments (diameter, 10-50 microm) were not significantly different across age-groups. However, for arterioles with diameter of 30 microm, tortuosity and branch angles increased with age (P < 0.05). In anaesthetized mice, second-order (2A) distributing arterioles had similar resting (17 +/- 1 microm) and maximal (37 +/- 1 microm) diameters and similar responsiveness to cumulative (10(-10)-10(-4) M) superfusion of acetylcholine or phenylephrine. With superfusate oxygen level raised from 0 to 21%, 2A arteriolar constriction in Young (11 +/- 1 microm) was greater (P < 0.05) than Adult and Old (5 +/- 1 microm). Observed 1 mm upstream from microiontophoresis of ACh (1 microA, 1 s), conducted vasodilatation was 10 +/- 1 microm in Young, 17 +/- 1 microm in Adult and 6 +/- 1 microm in Old (P < 0.05). With muscle contractions (2, 4 and 8 Hz; 30 s) arteriolar diameter increased similarly across age-groups (6 +/- 1, 11 +/- 1 and 18 +/- 1 microm, respectively). Muscle mass and active tension were similar across age-groups yet postcontraction vasodilatation recovered more rapidly in Old versus Adult and Young (P < 0.05). With arteriolar network architecture maintained during ageing, the impairment in conducted vasodilatation and attenuation of postcontraction vasodilatation may compromise exercise tolerance.

Reduced expression of endothelial connexin37 and connexin40 in hyperlipidemic mice: recovery of connexin37 after 7-day simvastatin treatment

OBJECTIVE

We sought to clarify the response of endothelial connexins to hyperlipidemia and lipid-lowering therapy.

METHODS AND RESULTS

Aortic endothelial gap junctions were analyzed by en face immunoconfocal microscopy and electron microscopy in C57BL/6 mice subjected to the following regimens: (1) normal chow (NC) for 3 months (3 mo), (2) NC for 9 mo, (3) NC for 3 mo, followed by a cholesterol-enriched diet (CED) for 6 mo, (4) NC for 3 mo and CED for 6 mo, with simvastatin in the final week, and (5) (in apoprotein E [apoE]-deficient mice) NC and examined at 3 mo and 7 to 9 mo. In wild-type mice, connexin37 (Cx37) and Cx40 were markedly downregulated in the CED-fed animals compared with those fed NC (CED vs 9-mo NC, 77% reduction in Cx37 and 65% reduction in Cx40; both P<0.01). After simvastatin treatment, Cx40 remained depressed, but Cx37 recovered to 94% of the level found in non-cholesterol-fed animals (P<0.01). Electron microscopy demonstrated that gap junctions were smaller in animals fed the CED compared with those given simvastatin and with controls fed NC (P<0.01). Endothelial connexins were rare in the atherosclerotic plaques of apoE-deficient mice.

CONCLUSIONS

Mouse aortic endothelial gap junctions and connexins are downregulated during long-term hyperlipidemia. Short-term treatment with simvastatin leads to recovery of Cx37 expression but not Cx40 expression.

Decreased intercellular dye-transfer and downregulation of non-ablated connexins in aortic endothelium deficient in connexin37 or connexin40

Vascular endothelial cells are coupled by gap junctions that permit cell-to-cell transfer of small molecules, including signals that may be important for vasomotor responses. Connexin37 (Cx37) and connexin40 (Cx40) are the predominant gap-junction proteins present in mouse endothelium. We examined the effect of eliminating Cx37, Cx40, or both, on interendothelial communication in mouse aorta. Intercellular transfer of biocytin and [2-(4-nitro-2,1,3-benzoxadiazol-7-yl)aminoethyl]trimethylammonium (NBD-TMA) was used to assess gap-junction-mediated coupling. Ablation of Cx40 generally had a greater effect on dye-transfer than ablation of Cx37. The effect of Cx40 ablation on dye-transfer was age dependent. There was a 27-fold reduction in biocytin transfer in embryonic Cx40-/- aortic endothelium, a much larger change than in aortas of 6-7-week-old Cx40-/- animals, which showed a 3.5-fold reduction. By contrast, there was no reduction in biocytin transfer in embryonic Cx37-/- endothelium. Embryonic aortas lacking both Cx37 and Cx40 showed a complete loss of endothelial dye-transfer. Surprisingly, elimination of Cx40 resulted in up to a 17-fold drop in endothelial Cx37 on western blots, whereas deletion of Cx37 reduced endothelial Cx40 up to 4.2-fold. By contrast, in the medial layer, both Cx37 and Cx43 increased approximately fourfold in Cx40-/- aortas. Declines in non-ablated endothelial connexins were not mediated by changes in connexin mRNA levels, suggesting a post-transcriptional effect. Our results indicate that Cx37 and Cx40 are the only functional connexins expressed in mouse aortic endothelium and are collectively crucial for endothelial communication. Furthermore, Cx37 and Cx40 are codependent on each other for optimal expression in vascular endothelium.