Differential regulation of gap junctions by proinflammatory mediators in vitro

Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing

Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.

Cellular Crosstalk between Endothelial and Smooth Muscle Cells in Vascular Wall Remodeling

Pathological vascular wall remodeling refers to the structural and functional changes of the vessel wall that occur in response to injury that eventually leads to cardiovascular disease (CVD). Vessel wall are composed of two major primary cells types, endothelial cells (EC) and vascular smooth muscle cells (VSMCs). The physiological communications between these two cell types (EC–VSMCs) are crucial in the development of the vasculature and in the homeostasis of mature vessels. Moreover, aberrant EC–VSMCs communication has been associated to the promotor of various disease states including vascular wall remodeling. Paracrine regulations by bioactive molecules, communication via direct contact (junctions) or information transfer via extracellular vesicles or extracellular matrix are main crosstalk mechanisms. Identification of the nature of this EC–VSMCs crosstalk may offer strategies to develop new insights for prevention and treatment of disease that curse with vascular remodeling. Here, we will review the molecular mechanisms underlying the interplay between EC and VSMCs. Additionally, we highlight the potential applicable methodologies of the co-culture systems to identify cellular and molecular mechanisms involved in pathological vascular wall remodeling, opening questions about the future research directions.

Connexins: Key Players in the Control of Vascular Plasticity and Function

Of the 21 members of the connexin family, 4 (Cx37, Cx40, Cx43, and Cx45) are expressed in the endothelium and/or smooth muscle of intact blood vessels to a variable and dynamically regulated degree. Full-length connexins oligomerize and form channel structures connecting the cytosol of adjacent cells (gap junctions) or the cytosol with the extracellular space (hemichannels). The different connexins vary mainly with regard to length and sequence of their cytosolic COOH-terminal tails. These COOH-terminal parts, which in the case of Cx43 are also translated as independent short isoforms, are involved in various cellular signaling cascades and regulate cell functions. This review focuses on channel-dependent and -independent effects of connexins in vascular cells. Channels play an essential role in coordinating and synchronizing endothelial and smooth muscle activity and in their interplay, in the control of vasomotor actions of blood vessels including endothelial cell reactivity to agonist stimulation, nitric oxide-dependent dilation, and endothelial-derived hyperpolarizing factor-type responses. Further channel-dependent and -independent roles of connexins in blood vessel function range from basic processes of vascular remodeling and angiogenesis to vascular permeability and interactions with leukocytes with the vessel wall. Together, these connexin functions constitute an often underestimated basis for the enormous plasticity of vascular morphology and function enabling the required dynamic adaptation of the vascular system to varying tissue demands.

Connexins in the control of vasomotor function

Vascular endothelial cells, as well as smooth muscle cells, show heterogeneity with regard to their receptor expression and reactivity. For the vascular wall to act as a functional unit, the various cells' responses require integration. Such an integration is not only required for a homogeneous response of the vascular wall, but also for the vasomotor behaviour of consecutive segments of the microvascular arteriolar tree. As flow resistances of individual sections are connected in series, sections require synchronization and coordination to allow effective changes of conductivity and blood flow. A prerequisite for the local coordination of individual vascular cells and different sections of an arteriolar tree is intercellular communication. Connexins are involved in a dual manner in this coordination. (i) By forming gap junctions between cells, they allow an intercellular exchange of signalling molecules and electrical currents. In particular, the spread of electrical currents allows for coordination of cell responses over longer distances. (ii) Connexins are able to interact with other proteins to form signalling complexes. In this way, they can modulate and integrate individual cells' responses also in a channel-independent manner. This review outlines mechanisms allowing the vascular connexins to exert their coordinating function and to regulate the vasomotor reactions of blood vessels both locally, and in vascular networks. Wherever possible, we focus on the vasomotor behaviour of small vessels and arterioles which are the main vessels determining vascular resistance, blood pressure and local blood flow.

Tumor-induced loss of mural Connexin 43 gap junction activity promotes endothelial proliferation

Background

Proper functional association between mural cells and endothelial cells (EC) causes EC of blood vessels to become quiescent. Mural cells on tumor vessels exhibit decreased attachment to EC, which allows vessels to be unstable and proliferative. The mechanisms by which tumors prevent proper association between mural cells and EC are not well understood. Since gap junctions (GJ) play an important role in cell-cell contact and communication, we investigated whether loss of GJ plays a role in tumor-induced mural cell dissociation.

Methods

Mural cell regulation of endothelial proliferation was assessed by direct co-culture assays of fluorescently labeled cells quantified by flow cytometry or plate reader. Gap junction function was assessed by parachute assay. Connexin 43 (Cx43) protein in mural cells exposed to conditioned media from cancer cells was assessed by Western and confocal microscopy; mRNA levels were assessed by quantitative real-time PCR. Expression vectors or siRNA were utilized to overexpress or knock down Cx43. Tumor growth and angiogenesis was assessed in mouse hosts deficient for Cx43.

Results

Using parachute dye transfer assay, we demonstrate that media conditioned by MDA-MB-231 breast cancer cells diminishes GJ communication between mural cells (vascular smooth muscle cells, vSMC) and EC. Both protein and mRNA of the GJ component Connexin 43 (Cx43) are downregulated in mural cells by tumor-conditioned media; media from non-tumorigenic MCF10A cells had no effect. Loss of GJ communication by Cx43 siRNA knockdown, treatment with blocking peptide, or exposure to tumor-conditioned media diminishes the ability of mural cells to inhibit EC proliferation in co-culture assays, while overexpression of Cx43 in vSMC restores GJ and endothelial inhibition. Breast tumor cells implanted into mice heterozygous for Cx43 show no changes in tumor growth, but exhibit significantly increased tumor vascularization determined by CD31 staining, along with decreased mural cell support detected by NG2 staining.

Conclusions

Our data indicate that i) functional Cx43 is required for mural cell-induced endothelial quiescence, and ii) downregulation of Cx43 GJ by tumors frees endothelium to respond to angiogenic cues. These data define a novel and important role for maintained Cx43 function in regulation of vessel quiescence, and suggest its loss may contribute to pathological tumor angiogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1420-9) contains supplementary material, which is available to authorized users.

Oral squamous cell carcinoma in a patient with keratitis-ichthyosis-deafness syndrome: a rare case

Keratitis-ichthyosis-deafness (KID) syndrome is a rare form of ectodermal dysplasia with significant visual and auditory impairment. Pathogenesis involves a mutation in the GJB2 gene, which encodes connexin-26, a protein in the epithelial gap junctions thought to be involved in the differentiation of ectodermally derived tissues. Affected patients are also at increased risk for the epithelial malignancies. To our knowledge, nearly 100 cases of KID syndrome, including 19 with squamous cell carcinoma (SCC) complications, have been reported worldwide. We report here a patient with KID syndrome who developed an ulcerative oral lesion causing him significant discomfort; he was subsequently diagnosed with oral SCC. We review the clinical presentation and symptomatology, including those affecting the oral cavity for this syndrome and highlight the importance of multidisciplinary collaboration and life-long screening aimed at prevention of the evolving complications.

NO, via its target Cx37, modulates calcium signal propagation selectively at myoendothelial gap junctions

BACKGROUND

Gap junctional calcium signal propagation (transfer of calcium or a calcium releasing messenger via gap junctions) between vascular cells has been shown to be involved in the control of vascular tone. We have shown before that nitric oxide (NO) inhibits gap junctional communication in HeLa cells exclusively expressing connexin 37 (HeLa-Cx37) but not in HeLa-Cx40 or HeLa-Cx43. Here we studied the effect of NO on the gap junctional calcium signal propagation in endothelial cells which, in addition to Cx37, also express Cx40 and Cx43. Furthermore, we analyzed the impact of NO on intermuscle and on myoendothelial gap junction-dependent calcium signal propagation. Since specific effects of NO at one of these three junctional areas (interendothelial/ myoendothelial/ intermuscle) may depend on a differential membrane localization of the connexins, we also studied the distribution of the vascular connexins in small resistance arteries.

RESULTS

In endothelial (HUVEC) or smooth muscle cells (HUVSMC) alone, NO did not affect gap junctional Ca2+ signal propagation as assessed by analyzing the spread of Ca2+ signals after mechanical stimulation of a single cell. In contrast, at myoendothelial junctions, it decreased Ca2+ signal propagation in both directions by about 60% (co-cultures of HUVEC and HUVSMC). This resulted in a longer maintenance of calcium elevation at the endothelial side and a faster calcium signal propagation at the smooth muscle side, respectively. Immunohistochemical stainings (confocal and two-photon-microscopy) of cells in co-cultures or of small arteries revealed that Cx37 expression was relatively higher in endothelial cells adjoining smooth muscle (culture) or in potential areas of myoendothelial junctions (arteries). Accordingly, Cx37 - in contrast to Cx40 - was not only expressed on the endothelial surface of small arteries but also in deeper layers (corresponding to the internal elastic lamina IEL). Holes of the IEL where myoendothelial contacts can only occur, stained significantly more frequently for Cx37 and Cx43 than for Cx40 (endothelium) or Cx45 (smooth muscle).

CONCLUSION

NO modulates the calcium signal propagation specifically between endothelial and smooth muscle cells. The effect is due to an augmented distribution of Cx37 towards myoendothelial contact areas and potentially counteracts endothelial Ca2+ signal loss from endothelial to smooth muscle cells. This targeted effect of NO may optimize calcium dependent endothelial vasomotor function.

Role of the JNK signaling pathway in downregulation of connexin43 by TNF-α in human corneal fibroblasts

PURPOSE/AIM

Proinflammatory cytokines such as tumor necrosis factor (TNF)-α contribute to corneal inflammation. Corneal stromal fibroblasts are connected to each other via gap junctions. We have now examined the role of mitogen-activated protein kinase (MAPK) signaling pathways in TNF-α-induced downregulation of the gap junction protein connexin43 (Cx43) in human corneal fibroblasts.

MATERIALS AND METHODS

Cultured human corneal fibroblasts were exposed to TNF-α in the absence or presence of inhibitors of MAPK signaling pathways. Expression of Cx43 was evaluated by immunofluorescence and immunoblot analyses. Gap-junctional intercellular communication (GJIC) was measured with a dye-coupling assay.

RESULTS

TNF-α reduced the abundance of Cx43 in human corneal fibroblasts (as revealed by immunoblot analysis) as well as induced the loss of specific staining for this protein (as revealed by immunofluorescence analysis). These effects of TNF-α were attenuated by an inhibitor of c-Jun NH₂-terminal kinase (JNK inhibitor II) but not by inhibitors of signaling by extracellular signal-regulated kinase (PD98059) or by p38 MAPK (SB203580). JNK inhibitor II also attenuated the inhibitory effect of TNF-α on GJIC.

CONCLUSIONS

The inhibitory effects of TNF-α on Cx43 expression and GJIC in human corneal fibroblasts are mediated, at least in part, by the JNK signaling pathway, which therefore likely plays a role in corneal inflammation.

Pericytes on the tumor vasculature: jekyll or hyde?

The induction of tumor vasculature, known as the 'angiogenic switch', is a rate-limiting step in tumor progression. Normal blood vessels are composed of two distinct cell types: endothelial cells which form the channel through which blood flows, and mural cells, the pericytes and smooth muscle cells which serve to support and stabilize the endothelium. Most functional studies have focused on the responses of endothelial cells to pro-angiogenic stimuli; however, there is mounting evidence that the supporting mural cells, particularly pericytes, may play key regulatory roles in both promoting vessel growth as well as terminating vessel growth to generate a mature, quiescent vasculature. Tumor vessels are characterized by numerous structural and functional abnormalities, including altered association between endothelial cells and pericytes. These dysfunctional, unstable vessels contribute to hypoxia, interstitial fluid pressure, and enhanced susceptibility to metastatic invasion. Increasing evidence points to the pericyte as a critical regulator of endothelial activation and subsequent vessel development, stability, and function. Here we discuss both the stimulatory and inhibitory effects of pericytes on the vasculature and the possible utilization of vessel normalization as a therapeutic strategy to combat cancer.

Modulation of connexin signaling by bacterial pathogens and their toxins

Inherent to their pivotal tasks in the maintenance of cellular homeostasis, gap junctions, connexin hemichannels, and pannexin hemichannels are frequently involved in the dysregulation of this critical balance. The present paper specifically focuses on their roles in bacterial infection and disease. In particular, the reported biological outcome of clinically important bacteria including Escherichia coli, Shigella flexneri, Yersinia enterocolitica, Helicobacter pylori, Bordetella pertussis, Aggregatibacter actinomycetemcomitans, Pseudomonas aeruginosa, Citrobacter rodentium, Clostridium species, Streptococcus pneumoniae, and Staphylococcus aureus and their toxic products on connexin- and pannexin-related signaling in host cells is reviewed. Particular attention is paid to the underlying molecular mechanisms of these effects as well as to the actual biological relevance of these findings.

Blastocyst-mediated induction of endometrial connexins: an inflammatory response?

As a prerequisite for successful embryo implantation in mammals, before implantation ovarian hormones regulate the transformation of the endometrium into the receptive phase. During the implantation process, gene expression in the receptive endometrium is additionally modulated by the presence of a blastocyst. During this complex differentiation process, in humans as well as in rodents, gap junction connexin 26 (Cx26) is suppressed in the uterine epithelium and Cx43 is suppressed in the endometrial stromal cells during the receptive phase. In rodents, a blastocyst-mediated induction of Cx26 takes place locally in the uterine epithelial cells of the implantation chamber surrounding the blastocyst, followed by an increase in Cx43 in the cells of the developing decidua. The Cx26 induction is dependent on the presence of a blastocyst and occurs even before adhesion and invasion of the trophoblast takes place. The signal cascades involved in this blastocyst-mediated connexin induction are still elusive. The process of implantation is considered as a proinflammatory response, and inflammatory factors have been shown to be involved in the implantation process. In fact, Cx26 expression can be induced in the receptive rat endometrium by mediators of the inflammatory cascade including prostaglandin-F2α and IL1β by an ER-independent pathway similar to the blastocyst-mediated connexin induction at the time of implantation. Thus, in the receptive endometrium induction of connexin expression may also be induced by mediators of the inflammatory signaling cascade, and the implantation-related induction of intercellular communication may in part be due to an inflammatory response.

Role of connexins in microvascular dysfunction during inflammation

In arterioles, a locally initiated diameter change can propagate rapidly along the vessel length (arteriolar conducted response), thus contributing to arteriolar hemodynamic resistance. The response is underpinned by electrical coupling along the arteriolar endothelial layer. Connexins (Cx; constituents of gap junctions) are required for this coupling. This review addresses the effect of acute systemic inflammation (sepsis) on arteriolar conduction and interendothelial electrical coupling. Lipopolysaccharide (LPS; an initiating factor in sepsis) and polymicrobial sepsis (24 h model) attenuate conducted vasoconstriction in mice. In cultured microvascular endothelial cells harvested from rat and mouse skeletal muscle, LPS reduces both conducted hyperpolarization–depolarization along capillary-like structures and electrical coupling along confluent cell monolayers. LPS also tyrosine-phosphorylates Cx43 and serine-dephosphorylates Cx40. Since LPS-reduced coupling is Cx40- but not Cx43-dependent, only Cx40 dephosphorylation may be consequential. Nitric oxide (NO) overproduction is critical in advanced sepsis, since the removal of this overproduction prevents the attenuated conduction. Consistently, (i) exogenous NO in cultured cells reduces coupling in a Cx37-dependent manner, and (ii) the septic microvasculature in vivo shows no Cx40 phenotype. A complex role emerges for endothelial connexins in sepsis. Initially, LPS may reduce interendothelial coupling and arteriolar conduction by targeting Cx40, whereas NO overproduction in advanced sepsis reduces coupling and conduction by targeting Cx37 instead.

Germline mosaicism in keratitis-ichthyosis-deafness syndrome: pre-natal diagnosis in a familial lethal form

Keratitis-ichthyosis-deafness (KID) syndrome is an autosomal dominant congenital ectodermal defect characterized by the association of skin lesions, hearing loss and keratitis. Most of the cases appear to be sporadic. KID syndrome is mostly related to mutations of GJB2 gene encoding connexin-26. Recently, a lethal form of the disease during the first year of life has been reported in two unrelated Caucasian patients. This rare lethal form is caused by the G45E mutation of GJB2 gene. We here report the first pre-natal molecular genetic diagnosis of the lethal form of KID syndrome relating to a G45E mutation. In the same family, the occurrence of this condition in three other siblings born to African non-consanguineous healthy parents lead to perform pre-natal diagnosis for this last pregnancy. Molecular analysis confirms the diagnosis of the lethal form of KID for the fetus. These results establish the role of germline mosaicism in KID syndrome and warrant careful genetic counseling. Furthermore, analysis of our cases and the literature allowed us to define a characteristic severe neonatal phenotype including facial dysmorphy, severe cornification with massive focal hyperkeratosis of the skin with erythroderma, dystrophic nails, complete atrichia and absence of foreskin.

Essential role of nitric oxide in sepsis-induced impairment of endothelium-derived hyperpolarizing factor-mediated relaxation in rat pulmonary artery

Both endothelial nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) are important vasodilators in pulmonary circulation. Sepsis is known to impair endothelium-dependent dilation in the pulmonary vasculature, but the mechanisms are incompletely understood. We have examined the relative contribution of EDHF/NO to the attenuated endothelium-dependent relaxation of pulmonary artery in sepsis, and the role of inducible nitric oxide synthase (iNOS)-derived NO in this mechanism. Sepsis was induced in male adult Wistar rats by caecal ligation and puncture. At 18h after surgery, left and right branches of pulmonary arteries were isolated for tension recording, NO/cyclic guanosine monophosphate (cGMP) measurements, mRNA and protein expressions. Despite a marked decrease in the arterial endothelial nitric oxide synthase (eNOS) mRNA and phosphorylated-eNOS (p-eNOS) protein expressions in sepsis, endothelium-dependent relaxation to acetylcholine (ACh) mediated by NO, acetylcholine-stimulated NO release and tissue cGMP levels were moderately inhibited. Sepsis however abolished the N(G)-Nitro-l-arginine methyl ester (L-NAME)/indomethacin-resistant arterial relaxation (EDHF response) to acetylcholine in this vessel. In vitro treatment of the arterial rings from septic rats with 1400W, a selective inhibitor of iNOS restored the EDHF response, but had no effect on the acetylcholine-induced relaxation mediated by endothelial NO. The functional role of iNOS-derived NO in impairing EDHF-mediated relaxation was coincident with an increased basal NO production, iNOS mRNA and protein expressions in the rat pulmonary artery. In conclusion, the loss of the EDHF response may be primarily responsible for the endothelial dysfunction in sepsis, and its restoration by a selective iNOS inhibitor may improve pulmonary vasodilation.

C-reactive protein, sodium azide, and endothelial connexin43 gap junctions

We investigated the effect of C-reactive protein (CRP) and sodium azide (NaN(3)) on endothelial Cx43 gap junctions. Human aortic endothelial cells (HAEC) were treated with (a) detoxified CRP, (b) detoxified dialyzed CRP, (c) detoxified dialyzed CRP plus NaN(3), (d) NaN(3), or (e) dialyzed NaN(3). The concentration of CRP in all preparations was fixed to 25 microg/ml and that of NaN(3) in the preparations of (c) to (e) was equivalent to that contained in the 25 microg/ml CRP purchased commercially. The results showed that both the expression of Cx43 protein and gap junctional communication function post-48-h incubation were reduced and inhibited by the detoxified CRP, NaN(3), or detoxified dialyzed CRP plus NaN(3), but not by the detoxified dialyzed CRP or dialyzed NaN(3). Reverse transcription-polymerase chain reaction analysis of cells treated for 72 h also showed a pattern of transcriptional regulation essentially the same as that for the proteins. We concluded that CRP does not have a significant effect on Cx43 gap junctions of HAEC, but NaN(3) inhibited the viability of cells and downregulate their junctions.

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.

Sharing the burden: antigen transport and firebreaks in immune responses

Communication between cells is crucial for immune responses. An important means of communication during viral infections is the presentation of viral antigen on the surface of an infected cell. Recently, it has been shown that antigen can be shared between infected and uninfected cells through gap junctions, connexin-based channels, that allow the transport of small molecules. The uninfected cell receiving antigen can present it on its surface. Cells presenting viral antigen are detected and killed by cytotoxic T lymphocytes. The killing of uninfected cells can lead to increased immunopathology. However, the immune response might also profit from killing those uninfected bystander cells. One benefit might be the removal of future 'virus factories'. Another benefit might be through the creation of 'firebreaks', areas void of target cells, which increase the diffusion time of free virions, making their clearance more likely. Here, we use theoretical models and simulations to explore how the mechanism of gap junction-mediated antigen transport (GMAT) affects the dynamics of the virus and immune response. We show that under the assumption of a well-mixed system, GMAT leads to increased immunopathology, which always outweighs the benefit of reduced virus production due to the removal of future virus factories. By contrast, a spatially explicit model leads to quite different results. Here we find that the firebreak mechanism reduces both viral load and immunopathology. Our study thus shows the potential benefits of GMAT and illustrates how spatial effects may be crucial for the quantitative understanding of infection dynamics and immune responses.

Irsogladine maleate counters the interleukin-1 beta-induced suppression in gap-junctional intercellular communication but does not affect the interleukin-1 beta-induced zonula occludens protein-1 levels in human gingival epithelial cells

BACKGROUND AND OBJECTIVE

Irsogladine maleate counters gap junctional intercellular communication reduction induced by interleukin-8 or Actinobacillus actinomycetemcomitans in cultured human gingival epithelial cells. Interleukin-1 beta is involved in periodontal disease. Little is known, however, about the effect of interleukin-1 beta on intercellular junctional complexes in human gingival epithelial cells. Furthermore, irsogladine maleate may affect the actions of interleukin-1 beta. In this study, we examined how interleukin-1 beta affected gap junctional intercellular communication, connexin 43 and zonula occludens protein-1, and how irsogladine maleate modulated the interleukin-1 beta-induced changes in the intercellular junctional complexes in human gingival epithelial cells.

MATERIAL AND METHODS

Human gingival epithelial cells were exposed to interleukin-1 beta, with or without irsogladine maleate. Connexin 43 and zonula occludens protein-1 were examined at mRNA and protein levels by real-time polymerase chain reaction and western blotting, respectively. Gap junctional intercellular communication was determined using the dye transfer method. The expression of zonula occludens protein-1 was also confirmed by immunofluorescence.

RESULTS

Interleukin-1 beta decreased connexin 43 mRNA levels, but increased zonula occludens protein-1 mRNA levels. Irsogladine maleate countered the interleukin-1 beta-induced reduction in gap junctional intercellular communication and connexin 43 levels. However, irsogladine maleate did not influence the increased zonula occludens protein-1 levels.

CONCLUSION

The effect of interleukin-1 beta on gap junctional intercellular communication and tight junctions of human gingival epithelial cells is different. The recovery of gap junctional intercellular communication by irsogladine maleate in the gingival epithelium may be a normal process in gingival epithelial homeostasis.

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.

Cisplatin cytotoxicity of auditory cells requires secretions of proinflammatory cytokines via activation of ERK and NF-kappaB

The ototoxicity of cisplatin, a widely used chemotherapeutic agent, involves a number of mechanisms, including perturbation of redox status, increase in lipid peroxidation, and formation of DNA adducts. In this study, we demonstrate that cisplatin increased the early immediate release and de novo synthesis of proinflammatory cytokines, including TNF-alpha, IL-1beta, and IL-6, through the activation of ERK and NF-kappaB in HEI-OC1 cells, which are conditionally immortalized cochlear cells that express hair cell markers. Both neutralization of proinflammatory cytokines and pharmacologic inhibition of ERK significantly attenuated the death of HEI-OC1 auditory cells caused by cisplatin and proinflammatory cytokines. We also observed a significant increase in the protein and mRNA levels of proinflammatory cytokines in both serum and cochleae of cisplatin-injected rats, which was suppressed by intraperitoneal injection of etanercept, an inhibitor of TNF-alpha. Immunohistochemical studies revealed that TNF-alpha expression was mainly located in the spiral ligament, spiral limbus, and the organ of Corti in the cochleae of cisplatin-injected rats. NF-kappaB protein expression, which overlapped with terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling-positive signal, was very strong in specific regions of the cochleae, including the organ of Corti, spiral ligament, and stria vascularis. These results indicate that proinflammatory cytokines, especially TNF-alpha, play a central role in the pathophysiology of sensory hair cell damage caused by cisplatin.

Lipopolysaccharide reduces electrical coupling in microvascular endothelial cells by targeting connexin40 in a tyrosine-, ERK1/2-, PKA-, and PKC-dependent manner

Electrical coupling along the endothelium is central in the arteriolar conducted response and in control of vascular resistance. It has been shown that exposure of endothelium to lipopolysaccharide (LPS, an initiating factor in sepsis) reduces intercellular communication in vitro and in vivo. The molecular basis for this reduction is not known. We examined the effect of LPS on electrical coupling in monolayers of cultured mouse microvascular endothelial cells (MMEC) derived from the mouse hindlimb skeletal muscle. To assess coupling, we measured the spread of electrical current injected into the monolayer and computed the monolayer intercellular resistance (inverse measure of coupling). LPS (10 microg/ml, 1 h) reduced coupling (i.e., increased resistance) in MMEC isolated from wild-type, connexin37 (Cx37) null and Cx43(G60S) (nonfunctional mutant) mice, but not in MMEC derived from Cx40 null mice. LPS also activated JNK1/2, p38 and ERK1/2 MAP kinases. Pretreatment of WT monolayers with ERK1/2 inhibitor U0126 (20 microM, 1 h) prevented the LPS-induced decrease in coupling, while inhibition of JNK1/2 with SP600125 (20 microM, 1 h) and p38 with a p38 inhibitor (10 nM, 1 h) had no effect. Furthermore, inhibition of tyrosine kinases with PP-2 (10 nM, 1 h), activation of PKA by 8-bromo-cAMP (1 mM, 5 min), and activation of PKC by bryostatin-2 (10 nM, 1 h) also prevented the reduction in coupling. We propose that LPS reduces inter-endothelial electrical coupling via tyrosine-, ERK1/2-, PKA-, and PKC-dependent signaling that targets Cx40. We suggest that this mechanism contributes to compromised arteriolar function following LPS exposure.

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.

Endogenous and exogenous NO attenuates conduction of vasoconstrictions along arterioles in the microcirculation

Vascular coordination in the microcirculation depends on gap junctional intercellular communication (GJIC), which is reflected by the conduction of locally initiated vasomotor responses. However, little is known about the regulation of GJIC in vivo. We hypothesized that endothelial NO regulates GJIC and therefore studied whether conduction of constrictions and dilations along the vessel wall is modulated by modifying the level of microcirculatory NO. Arterioles were focally stimulated using high K(+) or acetylcholine in the cremaster muscle in situ, and diameter changes were assessed at the local and remote upstream sites by intravital microscopy. Local stimulation with K(+) initiated a constriction that conducted along the arteriole with diminishing amplitude (length constant lambda: 371 +/- 42 mum). After N(omega)-nitro-l-arginine (l-NNA), lambda increased to 507 +/- 30 mum, indicating that GJIC is attenuated by endogenous NO. Exogenous NO, but not adenosine, reduced lambda after l-NNA in a reversible, concentration-dependent, and mainly cGMP-dependent manner as assessed by inhibition of soluble guanylate cyclase. In endothelial NO synthase-deficient mice, lambda was 530 +/- 80 mum and thus similar to that in wild-type mice after l-NNA. Exogenous NO likewise reduced lambda in these mice. The effects of NO were comparable to those of wild-type animals in Cx40-deficient mice, which excludes Cx40 as a specific target of NO. In contrast to constrictions, the amplitude of conducted dilations on acetylcholine did not diminish up to 1,300 mum and were not altered by l-NNA or exogenous NO. We conclude that endogenously released NO attenuates the conduction of vasoconstrictions most likely due to a modulation of gap junctional conductivity. We suggest that this effect is specific for smooth muscle cells, which probably transmit constricting signals, and involves connexins other than Cx40. This mechanism may support the dilatory potency of NO by preventing the conduction of remote vasoconstrictions into areas with basal or activated NO release.

Connexins: new genes in atherosclerosis

Atherosclerosis, the main cause of death and disability in adult populations of industrialized societies, is a multifactorial progressive process involving a variety of pathogenic mechanisms. Our current view on the pathogenesis of the disease implies complex patterns of interactions between a dysfunctional endothelium, leukocytes, and activated smooth muscle cells in which cytokines and growth factors are known to play a crucial role. Apart from paracrine cell-to-cell signalling, a role for gap junction-mediated intercellular communication in the development of the disease has been recently suggested. Gap junction channels result from the docking of two hemichannels or connexons, formed by the hexameric assembly of connexins, and directly connect the cytoplasm of adjacent cells. In this review, we summarize existing evidence implicating connexins in atherosclerosis. Indeed, the expression pattern of vascular connexins is altered during atherosclerotic plaque formation. In addition, changes in connexin expression or gap junctional communication have been observed in vascular cells in vitro by disturbances in blood flow, cholesterol, inflammatory cytokines, and growth factors. Furthermore, genetically modifying connexin expression affects the course of the atherosclerotic process in mouse models of the disease. Finally, the involvement of connexins in treatment of atherosclerotic disease will be discussed.

Gap junctional communication in tissue inflammation and repair

Local injury induces a complex orchestrated response to stimulate healing of injured tissues, cellular regeneration and phagocytosis. Practically, inflammation is defined as a defense process whereby fluid and white blood cells accumulate at a site of injury. The balance of cytokines, chemokines, and growth factors is likely to play a key role in regulating important cell functions such as migration, proliferation, and matrix synthesis during the process of inflammation. Hence, the initiation, maintenance, and resolution of innate responses depend upon cellular communication. A process similar to tissue repair and subsequent scarring is found in a variety of fibrotic diseases. This may occur in a single organ such as liver, kidneys, pancreas, lung, skin, and heart, but fibrosis may also have a more generalized distribution such as in atherosclerosis. The purpose of this review is to summarize recent advances on the contribution of gap junction-mediated intercellular communication in the modulation of the inflammatory response and tissue repair.

Nitric oxide specifically reduces the permeability of Cx37-containing gap junctions to small molecules

Gap junction intercellular communication (GJIC) plays a significant role in the vascular system. Regulation of GJIC is a dynamic process, with alterations in connexin (Cx) protein expression and post-translational modification as contributing mechanisms. We hypothesized that the endothelial autacoid nitric oxide (NO) would reduce dye coupling in human umbilical vein endothelial cells (HUVECs). In our subsequent experiments, we sought to isolate the specific Cx isoform(s) targeted by NO or NO-activated signaling pathways. Since HUVEC cells variably express three Cx (Cx37, Cx40, and Cx43), this latter aim required the use of transfected HeLa cells (HeLaCx37, HeLaCx43), which do not express Cx proteins in their wild type form. Dye coupling was measured by injecting fluorescent dye (e.g., Alexa Fluor 488) into a single cell and determining the number of stained adjacent cells. Application of the NO donor SNAP (2 microM, 20 min) reduced dye coupling in HUVEC by 30%. In HeLa cells, SNAP did not reduce dye transfer of cells expressing Cx43, but decreased the dye transfer from Cx37-expressing cells to Cx43-expressing cells by 76%. The effect of SNAP on dye coupling was not mediated via cGMP. In contrast to its effect on dye coupling, SNAP had no effect on electrical coupling, measured by a double patch clamp in whole cell mode. Our results demonstrate that NO inhibits the intercellular transfer of small molecules by a specific influence on Cx37, suggesting a potential role of NO in controlling certain aspects of vascular GJIC.

Decreased intercellular communication and connexin expression in mouse aortic endothelium during lipopolysaccharide-induced inflammation

The role of gap junctional intercellular communication during inflammatory processes is not well understood. In particular, changes in the expression and function of vascular endothelial connexins (gap junction proteins) in response to inflammatory agents has not been fully investigated. In this study, we used intercellular dye transfer methods to assess interendothelial communication in aortic segments isolated from mice treated with or without intraperitoneal lipopolysaccharide (LPS), a potent inflammatory mediator. LPS treatment resulted in a 49% decrease in endothelial dye coupling 18 h after injection. Western blots indicated that LPS treatment also caused a reduction in endothelial connexin40 (Cx40) levels to 33% of control levels. Connexin37 (Cx37) levels decreased only slightly after LPS treatment to 79% of control levels. We also examined endothelial communication in aortic segments isolated from Cx37-/- and Cx40-/- mice. LPS treatment caused a significantly greater decrease in dye transfer in endothelium isolated from Cx37-/- animals compared with endothelium from Cx40-/- animals (71 vs. 26% decrease). LPS injection caused a reduction in Cx40 levels in Cx37-/- endothelium, whereas LPS actually increased Cx37 levels in Cx40-/- endothelium. These results suggest that LPS mediates changes in endothelial gap junction-mediated communication, at least in part, through modulation of Cx40 and Cx37 levels.

Plasma membrane channels formed by connexins: their regulation and functions

Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.

Gap-junctional coupling between neutrophils and endothelial cells: a novel modulator of transendothelial migration

Communication between leukocytes and endothelial cells is crucial for inflammatory reactions. Paracrine cross-talk and outside-in signaling (via adhesion molecules) have been characterized as communication pathways to date. As leukocytes and endothelial cells express connexins, we considered intercellular communication via gap junctions an intriguing additional concept. We found that gap-junctional coupling between neutrophils and endothelium occurred in a time-dependent, bidirectional manner and was facilitated by adhesion. After blockade of connexins, transmigration of neutrophils through the endothelial layer was enhanced, and the barrier function of cell monolayers was reduced during transmigration. Tumor necrosis factor alpha decreased coupling. In the presence of connexins, transmigration of neutrophils did not alter permeability. Thus, neutrophils couple to endothelium via gap junctions, functionally modulating transmigration and leakiness. Gap-junctional coupling may be a novel way of leukocyte-endothelial communication.

Missense mutations in GJB2 encoding connexin-26 cause the ectodermal dysplasia keratitis-ichthyosis-deafness syndrome

Keratitis-ichthyosis-deafness syndrome (KID) is a rare ectodermal dysplasia characterized by vascularizing keratitis, profound sensorineural hearing loss (SNHL), and progressive erythrokeratoderma, a clinical triad that indicates a failure in development and differentiation of multiple stratifying epithelia. Here, we provide compelling evidence that KID is caused by heterozygous missense mutations in the connexin-26 gene, GJB2. In each of 10 patients with KID, we identified a point mutation leading to substitution of conserved residues in the cytoplasmic amino terminus or first extracellular domain of Cx26. One of these mutations was detected in six unrelated sporadic case subjects and also segregated in one family with vertical transmission of KID. These results indicate the presence of a common, recurrent mutation and establish its autosomal dominant nature. Cx26 and the closely related Cx30 showed differential expression in epidermal, adnexal, and corneal epithelia but were not significantly altered in lesional skin. However, mutant Cx26 was incapable of inducing intercellular coupling in vitro, which indicates its functional impairment. Our data reveal striking genotype-phenotype correlations and demonstrate that dominant GJB2 mutations can disturb the gap junction system of one or several ectodermal epithelia, thereby producing multiple phenotypes: nonsyndromic SNHL, syndromic SNHL with palmoplantar keratoderma, and KID. Decreased host defense and increased carcinogenic potential in KID illustrate that gap junction communication plays not only a crucial role in epithelial homeostasis and differentiation but also in immune response and epidermal carcinogenesis.

Clinical implications of inflammatory cytokines in the cochlea: a technical note

HYPOTHESIS

Establishing the presence of critical cellular stress response components in cochlear cells can contribute to a better understanding of cochlear cell biology and pathology.

BACKGROUND

Inflammatory cytokines and related proteins play critical roles in a variety of cellular processes, but to date, little is known about the identity and cellular localization of these compounds within the ear. Cytokines are autocrine, which means that cells that produce them have corresponding surface receptors. The presence of these receptors makes the cells vulnerable to disruption by circulating or local sources of cytokines and related ligands. Such disruptions may explain previously poorly understood cochlear pathologies.

METHODS

The messenger RNA precursors that encode inflammatory cytokines and related proteins are identified in the inner ear by using reverse transcriptase-polymerase chain reaction. Cochlear cells that contain the corresponding proteins are identified by immunostaining.

RESULTS

Messenger RNA for interleukin-1alpha, tumor necrosis factor alpha, NFkappaB P65 and P50, and IkappaBalpha was found in cochlear tissue. Cells that immunostained most conspicuously for cytokine production are Type I fibrocytes and root cells located within the spiral ligament.

CONCLUSION

Production of inflammatory cytokines by the above-mentioned cells indicates that they are vulnerable to disruption by extra-cochlear sources of cytokines and associated ligands. These cells play critical roles in cochlear function, and their disruption could induce hearing loss. These findings suggest that systemic or local production of inflammatory ligands may play roles in a number of causes of deafness, including immune mediated hearing loss, sudden hearing loss, and sensorineural hearing loss associated with otosclerosis, otitis media, and bacterial meningitis.

Cancer: the role of extracellular disease

Invasive carcinoma originates from the epithelial cells lining the lumen of an organ. It is often preceded by metaplasia, dysplasia or carcinoma in situ. The purpose of this review is to suggest that this disease of the epithelium may be, in part, the result of underlying tissue-based disorganization. Human cancer is frequently associated with pre-existing tissue disease. For example, hepatocellular carcinoma usually occurs in patients with a macronodular cirrhotic liver. Most lung cancers arise among patients with chronic lung disease (bronchitis, emphysema, and chronic infection). Mechanical forces appear to play a major role in regulating normal and cancer cell growth. The loss of cell polarity by neoplastic cells, coupled to an otherwise normal growth rate is enough to explain the cancer star-shaped pattern. By changing the plane of cell division, tumor cells may escape physical constraints from surrounding cells and divide. Loss of cell polarity and the resulting cell proliferation appears to be a consequence of either tissue-based disorganization (chronic inflammation, fibrosis) or of direct carcinogenic insult. The multiple mutations frequently described in cancer may be, in part, secondary to physical stress and not primary events. Several animal and clinical trials have shown that tissue disruption (i.e. radiation-induced fibrosis or liver cirrhosis) can be successfully treated. It is possible that treatment targeted at tissue disruption would delay or reduce cancer incidence regardless of the precise biological mechanism of carcinogenesis.

Gene monitoring of surface-activated monocytes in circulating whole blood using duplex RT-PCR

Previous studies have shown that blood-contacting materials activate blood monocytes. The aim of this study is to evaluate a highly sensitive technique for detecting changes at the mRNA level in circulating monocytes and to find suitable "gene markers" for assessing the hemocompatibility of biomaterials. Human blood was recirculated in a modified Chandler Loop formed of test tubes. Five groups of biomaterials were compared. Monocytes were separated by using magnetic beads, and gene expression analyses were performed using RT-PCR. We investigated the mRNA expression of stress proteins (hsp70) and inflammatory markers (IL-1alpha, IL-1beta, IL-6, TNF-alpha). mRNAs for cytokines were highly upregulated in LPS-stimulated monocytes. Hsp70 transcripts were upregulated after heat shock but were not influenced by treatment with LPS. The gene expression of the cytokines was affected by various biomaterials. The intensity of the inflammatory response increased in the following order: heparin coatings (PVC) < uncoated PVC < silicone, polypeptide-coated PVC. No change was seen in the expression of the hsp70 genes. An inhibitory effect of systemic heparin on surface-activated monocytes was observed for the mRNA expression of the cytokines. The recirculation of human blood in an in vitro model in combination with the immunomagnetic separation of monocytes and the Duplex RT-PCR method is a powerful tool for getting reliable results. Our data demonstrate that hsp70 genes cannot be recommended for short-term, biomaterial-induced mRNA expression studies. Conversely, mRNAs for IL-1alpha, IL-1beta, IL-6, and TNF-alpha were expressed in a material-dependent manner. Thus our model provides an effective tool for assessing the hemocompatibility of biomaterials before their clinical application and it also can serve as a safety control during the industrial manufacturing process. This method can be applied to various blood cell populations and numerous gene expression studies and may enable a more fundamental understanding of the biologic processes involved in blood-material interactions.

Regulation of gap junctional communication by a pro-inflammatory cytokine in cystic fibrosis transmembrane conductance regulator-expressing but not cystic fibrosis airway cells

Airway inflammation is orchestrated by cell-cell interactions involving soluble mediators and cell adhesion molecules. Alterations in the coordination of the multicellular process of inflammation may play a major role in the chronic lung disease state of cystic fibrosis (CF). The aim of this study was to determine whether direct cell-cell interactions via gap junctional communication is affected during the inflammatory response of the airway epithelium. We have examined the strength of intercellular communication and the activation of nuclear factor-kappaB (NF-kappaB) in normal (non-CF) and CF human airway cell lines stimulated with tumor necrosis factor-alpha (TNF-alpha). TNF-alpha induced maximal translocation of NF-kappaB into the nucleus of non-CF as well as CF airway cells within 20 minutes. In non-CF cells, TNF-alpha progressively decreased the extent of intercellular communication. In contrast, gap junctional communication between CF cells exposed to TNF-alpha remained unaltered. CF results from mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Interestingly, transfer of wild-type CFTR into CF cells by adenovirus-mediated infection was associated with the recovery of TNF-alpha-induced uncoupling. These results suggest that expression of functional CFTR is necessary for regulation of gap junctional communication by TNF-alpha. Gap junction channels close during the inflammatory response, therefore limiting the intercellular diffusion of signaling molecules, and thereby the recruitment of neighboring cells. Defects in this mechanism may contribute to the excessive inflammatory response of CF airway epithelium.

Suicide gene therapy: possible applications in haematopoietic disorders

Although the treatment results for some forms of haematologic malignancies are excellent, especially for the childhood acute leukaemias, there is still a significant fraction of patients that will not benefit from the therapy available today. The identification of new techniques, such as gene therapy, may therefore be of great importance for future therapeutic applications. Suicide gene therapy is one of several gene therapeutic approaches to treat cancer. A suicide gene is a gene encoding a protein, frequently an enzyme, that in itself is nontoxic to the genetically modified cell. However, when a cell is exposed to a specific nontoxic prodrug, this is selectively converted by the gene product into toxic metabolites that kill the cell. The suicide gene most commonly employed, both in experimental and a clinical settings, is herpes simplex thymidine kinase (HSVtk). Some suicide gene products also induce a so-called 'bystander effect', i.e. a toxic effect on adjacent nongene modified tumour cells and sometimes also on more distant tumour cells. The bystander effect is most evident in tumour cells that have a high number of gap junctions, cellular channels build up by proteins called connexins. Many tumours, amongst them many haematological ones, have a low number of gap junctions. Therefore, it is important to develop gap junction independent drug delivery systems. Suicide gene technology may also be used for the ex vivo purging of tumour cells in bone marrow or peripheral blood stem cell autografts or for inactivation of effector cells, such as antitumour T donor lymphocytes in allogeneic transplantation to prevent severe graft versus host reactions. New constructs, e.g. combining suicide genes and immune response enhancing genes or suicide genes and connexin inducing genes may further improve the value of suicide gene therapy.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Endotoxin increases intercellular resistance in microvascular endothelial cells by a tyrosine kinase pathway

Gap junction communication between microvascular endothelial cells has been proposed to contribute to the coordination of microvascular function. Septic shock may attenuate microvascular cell-to-cell communication. We hypothesized that lipopolysaccharide (LPS) attenuates communication between microvascular endothelial cells derived from rat hindlimb skeletal muscle. Endothelial cells grown in monolayers expressed mRNA for connexin 37, 40, and 43. The expression of connexin 43 protein was confirmed, but connexin 40 protein was not detected by immunocytochemistry or immunoblot analysis. Intercellular resistance between cells of the monolayer, calculated using a Bessel function model, was increased from 3.3 to 5.3 MOmega by LPS. The effect was seen after 1 h of exposure and required a minimum concentration of 10 ng/ml. Intercellular resistance returned to normal 1 h following removal of LPS. Neither the response to LPS, nor its reversal, was blocked by the protein synthesis inhibitor cycloheximide (10 microg/ml). Pretreatment of monolayers with the tyrosine kinase inhibitors PP-2 (10 nM), lavendustin-C (1 microM), and geldanamycin (200 nM) prevented this LPS response; geldanamycin was also able to reverse the response. Inhibitors of MAP kinases, PD 98059 (5 microM) and SB 202190 (5 microM), and PKC (500 nM bisindolylmaleimide I) were unable to block the LPS response. We propose that LPS attenuates cell-to-cell communication through a signaling pathway that is tyrosine kinase dependent.

Blockade of connexin 43 expression by stable transfection of antisense cDNA in cultured vascular smooth muscle cells

Gap junctional communication is involved in embryogenesis, cell growth control, and coordinated contraction of cardiac myocytes. It has been hypothesized that gap junctions coordinate responses of vascular cells to constrictor or dilator stimulation. Three connexin (Cx) proteins, 37, 40, and 43, are found in the vasculature. Cx43 gap junctions are widely distributed along the vascular tree, although a precise physiologic role in vascular function is unknown because of a lack of specific functional inhibitors and of suitable animal models. To investigate the role of Cx43 in intercellular communication among vascular smooth muscle (VSM) cells, we selectively modified the expression of the Cx43 gene using antisense cDNA stable transfections in culture. Results show that in cells stably transfected with antisense Cx43 cDNA, gene expression of Cx43 could be reduced to 20% of that observed in vector-transfected cells. In spite of the mRNA and protein reduction, the antisense Cx43 cDNA-transfected cells did not show a significant reduction in dye transfer or a difference in cell growth rate as compared with control. These results suggest either that the residual amount of Cx43 protein is sufficient for dye transfer and growth control or that the dye transfer in these cells can be mediated by Cx40 or other connexin proteins. Therefore, more potent approaches, such as dominant negative and gene knockout, are required to fully block gap junctional communication in VSM cells.

Intercellular communication in the immune system: differential expression of connexin40 and 43, and perturbation of gap junction channel functions in peripheral blood and tonsil human lymphocyte subpopulations

The distribution and function of connexins (integral membrane proteins assembled into gap junction intercellular communication channels) were studied in human lymphocyte subpopulations. The expression of mRNA encoding connexins in peripheral blood and tonsil-derived T, B and natural killer (NK) lymphocytes was examined. Connexin43 (Cx43) mRNA was expressed in peripheral blood and tonsil lymphocytes, but Cx40 mRNA expression was confined to tonsil-derived T and B lymphocytes; Cx26, Cx32, Cx37 and Cx45 were not detected by reverse transcription-polymerase chain reaction (RT-PCR). Western blot analysis also demonstrated the presence of Cx40 and Cx43 proteins in T and B lymphocytes in a manner coincidental to the mRNA detection. Stimulation in vitro of T and B lymphocytes with phytohaemagglutinin (PHA) and lipopolysaccharide (LPS), respectively, increased Cx40 and Cx43 protein expression. Flow cytometric analysis, using antibodies to extracellular loop amino acid sequences of connexins, confirmed the surface expression of connexins in all lymphocyte subpopulations. Assembly of connexins into gap junctions providing direct intercellular channels linking attached lymphocytes was demonstrated by using a dye transfer technique. The exchange of dye between lymphocytes was inhibited by a connexin extracellular loop mimetic peptide and alpha-glycyrrhetinic acid, two reagents that restrict intercellular communication across gap junctions. Dye coupling occurred between homologous and heterologous co-cultures of T and B lymphocytes, and was not influenced by their stimulation with PHA and LPS. The connexin mimetic peptide caused a significant decrease in the in vitro synthesis of immunoglobulin M (IgM) by T- and B-lymphocyte co-cultured populations in the presence or absence of stimulation by PHA. The results identify connexins as important cell surface components that modulate immune processes.

Gap junctions in cells of the immune system: structure, regulation and possible functional roles

Gap junction channels are sites of cytoplasmic communication between contacting cells. In vertebrates, they consist of protein subunits denoted connexins (Cxs) which are encoded by a gene family. According to their Cx composition, gap junction channels show different gating and permeability properties that define which ions and small molecules permeate them. Differences in Cx primary sequences suggest that channels composed of different Cxs are regulated differentially by intracellular pathways under specific physiological conditions. Functional roles of gap junction channels could be defined by the relative importance of permeant substances, resulting in coordination of electrical and/or metabolic cellular responses. Cells of the native and specific immune systems establish transient homo- and heterocellular contacts at various steps of the immune response. Morphological and functional studies reported during the last three decades have revealed that many intercellular contacts between cells in the immune response present gap junctions or "gap junction-like" structures. Partial characterization of the molecular composition of some of these plasma membrane structures and regulatory mechanisms that control them have been published recently. Studies designed to elucidate their physiological roles suggest that they might permit coordination of cellular events which favor the effective and timely response of the immune system.

Gap junction modulation by extracellular signaling molecules: the thymus model

Gap junctions are intercellular channels which connect adjacent cells and allow direct exchange of molecules of low molecular weight between them. Such a communication has been described as fundamental in many systems due to its importance in coordination, proliferation and differentiation. Recently, it has been shown that gap junctional intercellular communication (GJIC) can be modulated by several extracellular soluble factors such as classical hormones, neurotransmitters, interleukins, growth factors and some paracrine substances. Herein, we discuss some aspects of the general modulation of GJIC by extracellular messenger molecules and more particularly the regulation of such communication in the thymus gland. Additionally, we discuss recent data concerning the study of different neuropeptides and hormones in the modulation of GJIC in thymic epithelial cells. We also suggest that the thymus may be viewed as a model to study the modulation of gap junction communication by different extracellular messengers involved in non-classical circuits, since this organ is under bidirectional neuroimmunoendocrine control.

Inhibition of endothelial cell migration, intercellular communication, and vascular tube formation by thromboxane A(2)

The eicosanoid thromboxane A(2) (TXA(2)) is released by activated platelets, monocytes, and the vessel wall and interacts with high affinity receptors expressed in several tissues including endothelium. Whether TXA(2) might alter endothelial migration and tube formation, two determinants of angiogenesis, is unknown. Thus, we investigated the effect of the TXA(2) mimetic [1S-(1alpha, 2beta(5Z),3alpha(1E,3R), 4alpha]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-o xab icyclo- [2.2.1]heptan-2-yl]-5'-heptenoic acid (IBOP) on human endothelial cell (HEC) migration and angiogenesis in vitro. IBOP stimulation inhibited HEC migration by 50% and in vitro capillary formation by 75%. These effects of IBOP were time- and concentration-dependent with an IC(50) of 25 nM. IBOP did not affect integrin expression or cytoskeletal morphology of HEC. Since gap junction-mediated intercellular communication increases in migrating HEC, we determined whether IBOP might inhibit coupling or connexin expression in HEC. IBOP reduced the passage of microinjected dyes between HEC by 50%, and the effects of IBOP on migration and tube formation were mimicked by the gap junction inhibitor 18beta-glycyrrhetinic acid (1 microM) with a similar time course and efficacy. IBOP (24 h) did not affect the expression or phosphorylation of connexin 43 in whole HEC lysates. Immunohistologic examination of HEC suggested that IBOP may impair functional coupling by altering the cellular distribution of gap junctions, leading to increased connexin 43 internalization. Thus, this finding that TXA(2) mimetics can prevent HEC migration and tube formation, possibly by impairing intercellular communication, suggests that antagonizing TXA(2) signaling might enhance vascularization of ischemic tissue.

Biphasic response to gut manipulation and temporal correlation of cellular infiltrates and muscle dysfunction in rat

BACKGROUND

Surgical manipulation of the intestine results in the massive movement of leukocytes into the intestinal muscularis at 24 hours. This is associated with muscle inhibition. The aim of this study was to temporally associate leukocyte extravasation with ileus after surgical manipulation.

METHODS

Rats underwent a simple manipulation of the small bowel and were killed at various times (0, 0.25, 0.5, 1, 3, 6, 12, and 24 hours) postoperatively. Jejunal circular-muscle contractile activity was assessed in a standard organ bath. Both extravasating and resident leukocytes were immunohistochemically stained in muscularis whole mounts.

RESULTS

Contractile activity was significantly reduced immediately after surgery, but rapidly returned to control levels at 3 hours. After recovery, muscle function decreased at 12 and 24 hours (41% and 81%, respectively). The resident muscularis macrophage network demonstrated cellular activation 1 hour postoperatively. The number of leukocytes increased over time (neutrophils, 67.5-fold; monocytes, 98.2-fold; and mast cells, 47-fold at 24 hours).

CONCLUSIONS

The functional results demonstrate a biphasic response in the suppression of muscle activity after surgical manipulation. Regression analysis (r2 = 0.998) of the temporal development of leukocyte infiltration and the protracted phase of muscle inhibition provides evidence for a correlation between cellular inflammation and postoperative dysmotility.