Replacement of connexin 43 by connexin 32 in a knock-in mice model attenuates aortic endothelium-derived hyperpolarizing factor-mediated relaxation

Previous studies demonstrated that intercellular communication through endothelial, smooth muscle or myoendothelial connexin channels contributes to the control of vascular tone. At least four connexin types are present in the arterial wall. The aim of the present work was to assess the role played by connexin 43 (Cx43)-formed gap junctions on vessel function. Aortic reactivity to noradrenaline, acetylcholine and sodium nitroprusside, and endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations, were analysed in a Cx43KI32 mouse model in which the coding region of Cx43 was replaced by that of connexin 32 (Cx32). Aortic rings were placed in organ baths containing a Krebs solution oxygenated at 37 degrees C (pH 7.4). Confocal images of aortic rings confirmed connexin substitution in mutant mice. In control conditions, replacement of Cx43 by Cx32 in homozygous mutant mice did not modify endothelium-independent contractile responses to noradrenaline, or relaxations in response to sodium nitroprusside (endothelium independent) or acetylcholine (endothelium dependent). However, residual endothelium-dependent relaxations in response to acetylcholine after nitric oxide synthase and cyclooxygenase inhibition (EDHF type) were significantly reduced in homozygous Cx43KI32 mice (maximal effect values: 4.86 +/- 0.37% of noradrenaline precontraction versus 7.06 +/- 0.31% in wild-type, n = 8, P < 0.05). This attenuation was mimicked by treatment of rings from wild-type animals with the connexin-mimetic peptide (37,43)Gap27 (5 x 10(-6)m). In conclusion, replacement of Cx43 by Cx32 attenuates EDHF-mediated relaxations in mice aortic rings, suggesting that they are, at least in part, dependent on Cx43-formed gap junctions. In contrast, aortic responses to tested endothelium-independent agonists were not modified in knock-in animals.

Limiting transport steps and novel interactions of Connexin-43 along the secretory pathway

Connexins are four-transmembrane-domain proteins expressed in all vertebrates which form permeable gap junction channels that connect cells. Here, we analysed Connexin-43 (Cx43) transport to the plasma membrane and studied the effects of small GTPases acting along the secretory pathway. We show that both GTP- and GDP-restricted Sar1 prevents exit of Cx43 from the endoplasmic reticulum (ER), but only GTP-restricted Sar1 arrests Cx43 in COP II-coated ER exit sites and accumulates 14-3-3 proteins in the ER fraction. FRET-FLIM data confirm that already in ER exit sites Cx43 exists in oligomeric form, suggesting an in vivo role for 14-3-3 in Cx43 oligomerization. Exit of Cx43 from the ER can be blocked by other factors—such as expression of the β subunit of the COP I coat or p50/dynamitin that acts on the microtubule-based dynein motor complex. GTP-restricted Arf1 blocks Cx43 in the Golgi. Lastly, we show that GTP-restricted Arf6 removes Cx43 gap junction plaques from the cell–cell interface and targets them to degradation. These data provide a molecular explanation of how small GTPases act to regulate Cx43 transport through the secretory pathway, facilitating or abolishing cell–cell communication through gap junctions.

Regulation of gap junctional charge selectivity in cells coexpressing connexin 40 and connexin 43

Expression of connexin 40 (Cx40) and Cx43 in cardiovascular tissues varies as a function of age, injury, and development with unknown consequences on the selectivity of junctional communication and its acute regulation. We investigated the PKC-dependent regulation of charge selectivity in junctions composed of Cx43, Cx40, or both by simultaneous assessment of junctional permeance rate constants (B(dye)) for dyes of similar size but opposite charge, N,N,N-trimethyl-2-[methyl-(7-nitro-2,1,3-benzoxadiol-4-yl)amino]ethanaminium (NBD-M-TMA; +1) and Alexa 350 (-1). The ratio of dye rate constants (B(NBD-M-TMA)/B(Alexa 350)) indicated that Cx40 junctions are cation selective (10.7 +/- 0.5), whereas Cx43 junction are nonselective (1.22 +/- 0.14). In coexpressing cells, a broad range of junctional selectivities was observed with mean cation selectivity increasing as the Cx40 to Cx43 expression ratio increased. PKC activation reduced or eliminated dye permeability of Cx43 junctions without altering their charge selectivity, had no effect on either permeability or charge selectivity of Cx40 junctions, and significantly increased the cation selectivity of junctions formed by coexpressing cells (approaching charge selectivity of Cx40 junctions). Junctions composed of Cx43 truncated at residue 257 (Cx43tr) were also not charge selective, but when Cx43tr was coexpressed with Cx40, a broad range of junctional selectivities that was unaffected by PKC activation was observed. Thus, whereas the charge selectivities of homomeric/homotypic Cx43 and Cx40 junctions appear invariant, the selectivities of junctions formed by cells coexpressing Cx40 and Cx43 vary considerably, reflecting both their relative expression levels and phosphorylation-dependent regulation. Such regulation could represent a mechanism by which coexpressing cells such as vascular endothelium and atrial cells regulate acutely the selective intercellular communication mediated by their gap junctions.

Reduction of electrical coupling between microvascular endothelial cells by NO depends on connexin37

We have previously shown that increased nitric oxide (NO) production in sepsis impairs arteriolar-conducted vasoconstriction cGMP independently and that the gap junction protein connexin (Cx) 37 is required for this conducted response. In the present study, we hypothesized that NO impairs interendothelial electrical coupling in sepsis by targeting Cx37. We examined the effect of exogenous NO on coupling in monolayers of cultured microvascular endothelial cells derived from the hindlimb skeletal muscle of wild-type (WT), Cx37 null, Cx40 null, and Cx43(G60S) (nonfunctional mutant) mice. To assess coupling, we measured the spread of electrical current injected in the monolayer and calculated the monolayer intercellular resistance (inverse measure of coupling). The NO donor 2,2'-(hydroxynitrosohydrazino)bis-ethanamine (DETA) rapidly and reversibly reduced coupling in cells from WT mice, cGMP independently. NO scavenger HbO(2) did not affect baseline coupling, but it eliminated DETA-induced reduction in coupling. Reduced coupling in response to DETA was also seen in cells from Cx40 null and Cx43(G60S) mice, but not in cells from Cx37 null mice. DETA did not alter the expression of Cx37, Cx40, and Cx43 in WT cells analyzed by immunoblotting and immunofluorescence. Furthermore, neither the peroxynitrite scavenger 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III), superoxide scavenger Mn(III)tetrakis(4-benzoic acid)porphyrin chloride, nor preloading of WT cells with the antioxidant ascorbate affected this reduction. We conclude that NO-induced reduction of electrical coupling between microvascular endothelial cells depends on Cx37 and propose that NO in sepsis impairs arteriolar-conducted vasoconstriction by targeting Cx37 within the arteriolar wall.

Connexin 43, a new therapeutic target for cardiovascular diseases

Junctional channels (JC) play essential roles in the normal function of the cardiovascular system, mediating the spread of the electrical impulse that triggers synchronized contraction of the cardiac chambers and contributing to the coordination of activities between cells of the arterial wall. In mammalian hearts, cells most prominently express JC built of Connexin40 (Cx40), Cx43 and Cx45, of which Cx43 is the predominant intercellular gap junction protein. Changes in cardiovascular Cx gene expression during development or in response to (patho)physiological signals are expected to be a crucial factor in normal cardiac development and functions, and several cardiac diseases, such as atrial fibrillation, hypertrophy, heart failure, atherosclerosis, etc. Although the underlying molecular mechanisms have not yet been elucidated, recent research has found a variety of novel potential therapies related to Cx43 that can help to learn more about the mechanism of those cardiovascular diseases and the signaling pathway.

Connexin mimetic peptides improve cell migration rates of human epidermal keratinocytes and dermal fibroblasts in vitro

Nonhealing cutaneous wounds, a major cause of morbidity and mortality, are difficult to treat. Recent studies suggest that significant increases in skin wound-healing rates occur by altering gap junction intercellular communication (GJIC). As migration of keratinocytes and fibroblasts is an important feature of wound healing, this study investigated whether migration rates in cultured normal human epidermal keratinocytes and dermal fibroblasts could be altered by modulating GJIC via connexin mimetic peptides. First, HeLa cells stably transfected with connexin43 (Cx43), Cx40, or Cx26 were used as a model to determine connexin specificity and the doses of connexin mimetic peptides required to attenuate GJIC. Gap26 and Gap26M inhibited GJIC dose dependently and were nonconnexin specific, whereas Gap27 was Cx43-selective. Skin keratinocytes and fibroblasts expressed a variety of connexins, with Cx43 predominating. Cx43 protein expression was reduced at leading edges 3 hours after scraping confluent monolayers, resolving at 24 hours. Gap26M and Gap27 significantly increased migration rates across scrapes in keratinocytes and fibroblasts by blocking gap junction functionality. GJIC inhibition can thus directly influence keratinocyte and fibroblast migration. Furthermore, our results support the therapeutic potential of connexin mimetic peptides to aid wound closure, and provide a simple approach to screening new agents.

[Distribution of connexin 43 and interstitial cells of Cajal in bowels of children with Hirschsprung's disease]

OBJECTIVE

To investigate the distribution of connexin 43 (Cx43) and interstitial cells of Cajal (ICC) in bowels of children with Hirschsprung's disease (HD) and explore their roles in the pathogenesis of HD.

METHODS

Forty-two children with HD diagnosed by histopathology (33 males and 9 females) aged from 2 months to 10 years were enrolled. Expression of Cx43 and ICC in the bowels was detected using immunohistochemistry. These cases were all sporadic, including 30 cases of common type and 12 cases of short segment type. Five samples from the children with intussusception (aged from 1 month to 8 years) were used as controls.

RESULTS

Cx43 and ICC were not expressed in the muscle layers of the aganglionic segment in children with HD, which was significantly different from the Cx43 and ICC expression in the ganglionic segment of HD patients and the control bowels. Moderate expression of Cx43 and ICC were observed in the migratory segment, which was significantly different from that in the ganglionic and aganglionic segments in patients with HD. Moderate or strong expression of Cx43 and ICC was observed in the circular muscle and the region between the circular and longitudinal layer in the ganglionic segment from patients with HD. There were no significant differences in the Cx43 and ICC expression between the ganglionic segment of HD patients and control bowels.

CONCLUSIONS

The absence of Cx43 and ICC expression in the aganglionic bowel and the destruction of the gap junction may induce the dysfunctions of intercellular substance exchange and communication transmission, which might partly be responsible for the pathogenesis of HD.

Cell-cell communication in the osteoblast/osteocyte lineage

Skeletal development (bone modeling) and its maintenance in post-natal life in response to local and systemic stimuli (bone remodeling) require coordinated activity among osteoblasts (bone forming cells), osteocytes (cells embedded in bone) and osteoclasts (bone resorbing cells), in order to meet the needs of structural integrity, mechanical competence and maintenance of mineral homeostasis. One mechanism of cell-cell interaction is via direct cell-cell communication via gap junctions. These are transmembrane channels that allow continuity of cytoplasms between communicating cells. The biologic importance of connexin43 (Cx43), the most abundant gap junction protein in the skeleton is demonstrated by the skeletal malformations present in oculodentodigital dysplasia (ODDD), a disease linked to Cx43 gene (GJA1) mutations, and by the low bone mass and osteoblast dysfunction in Gja1 ablated mice. The presence of Cx43 is required for osteoblast differentiation and function, and by forming either gap junctions or "hemichannels" Cx43 allows participation of cell networks to responses to extracellular stimuli, via propagation of specific signals converging upon connexin sensitive transcriptional units. Hence, Cx43 is involved in skeletal responsiveness to anabolic signals, as those provided by parathyroid hormone and physical load, the latter function probably involving osteocyte-osteoblast communication.

Neonatal rat cardiomyocytes show characteristics of nonhomotypic gap junction channels

Neonatal rat cardiomyocytes mainly coexpress the connexins Cx40, Cx43, and to a small amount Cx45, leading to potential formation of mixed (heteromeric/heterotypic) gap junction channels. Using the dual-voltage clamp technique with switching clamp circuits, the authors investigated voltage sensitivity of gap junction channels between cell pairs of Cx40, Cx43, and Cx45 stably transfected HeLa cells and compared those data to data obtained from cell pairs of cultured neonatal rat cardiomyocytes. In accordance to previously published data, the relationship between normalized conductance and transjunctional voltage (g/V(j)) was quasisymmetrical for the transfected HeLa cells, indicating homotypic gap junction channels. Boltzmann curves fitted to data obtained from neonatal rat cardiomyocyte pairs expressing both Cx40 and Cx43 showed an asymmetrical inactivation pattern, which cannot be explained by the presence of pure populations of homotypic gap junction channels of either isoform. In conclusion the authors assume the additional presence of heterotypic and possibly even heteromeric gap junction channels in neonatal rat cardiomyocytes.

Electrical remodeling contributes to complex tachyarrhythmias in connexin43-deficient mouse hearts

Loss of connexin43 (Cx43) gap junction channels in the heart results in a marked increase in the incidence of spontaneous and inducible polymorphic ventricular tachyarrhythmias (PVTs). The mechanisms resulting in this phenotype remain unclear. We hypothesized that uncoupling promotes regional ion channel remodeling, thereby increasing electrical heterogeneity and facilitating the development of PVT. In isolated-perfused control hearts, programmed electrical stimulation elicited infrequent monomorphic ventricular tachyarrhythmias (MVT), and dominant frequencies (DFs) during MVT were similar in the right ventricle (RV) and left ventricle (LV). Moreover, conduction properties, action potential durations (APDs), and repolarizing current densities were similar in RV and LV myocytes. In contrast, PVT was common in Cx43 conditional knockout (OCKO) hearts, and arrhythmias were characterized by significantly higher DFs in the RV compared to the LV. APDs in OCKO myocytes were significantly shorter than those from chamber-matched controls, with RV OCKO myocytes being most affected. APD shortening was associated with higher levels of sustained current in myocytes from both chambers as well as higher levels of the inward rectifier current only in RV myocytes. Thus, alterations in cell-cell coupling lead to regional changes in potassium current expression, which in this case facilitates the development of reentrant arrhythmias. We propose a new mechanistic link between electrical uncoupling and ion channel remodeling. These findings may be relevant not only in cardiac tissue but also to other organ systems where gap junction remodeling is known to occur.

A new role for extracellular Ca2+ in gap-junction remodeling: studies in humans and rats

We wanted to elucidate whether extracellular calcium may regulate the expression of the cardiac gap-junction proteins connexin 40 and connexin43. In the free wall of the left atria of 126 cardiac surgery patients with either sinus rhythm (SR) or chronic atrial fibrillation (AF), we determined the expression of the cardiac gap-junction proteins Cx43 and Cx40 by Western blot and immunohistology. For deeper investigation, we incubated cultured neonatal rat cardiomyocytes at 2 or 4 mM Ca(++) for 24 h and determined intercellular coupling, Cx40, Cx43 protein and mRNA expression, protein trafficking and sensitivity to verapamil (10-100 nM), cyclosporin A (1 microM),and BMS605401 (100 nM), a specific inhibitor of Ca(2+)-sensing receptor (CaSR). We found in patients that both Cx are up-regulated in AF in the left atrium (by 100-200%). Interestingly, Cx40 was mainly up-regulated, if total serum calcium was >or=2.2 mM, while Cx43 was independent from extracellular [Ca(++)]. In cultured cells, 4 mM Ca(++)-exposure lead to up-regulation of Cx40, but not Cx43. We found enhanced Cx40 in the plasma membrane and reduced Cx40 in the Golgi apparatus. The membrane Cx40 up-regulation resulted in enhanced gap-junction intercellular coupling with a shift in the Boltzmann fit of voltage-dependent inactivation indicating a higher contribution of Cx40 as revealed by dual whole cell voltage clamp experiments. BMS605401 could prevent all Ca(2+)-induced changes. Moreover, cyclosporin A completely abolished the Ca(2+)-induced changes, while verapamil was ineffective. We conclude that extracellular calcium (24 h exposure) seems to up-regulate Cx40 but not Cx43.

[Influence of connexin 43 gene knockout on the analgesic effect of acupuncture in visceral pain mice]

OBJECTIVE

To explore the possible central and peripheral mechanisms of connexin 43 gene knockout in acupuncture analgesia.

METHODS

Fifty-four wide type (WT) mice and 54 connexin 43 gene knockout (heterozygote, HT) mice were randomly divided into WT control group, WT model group, WT acupuncture group, HT control group, HT model group and HT acupuncture group (n = 18/group). Visceral pain model was established by intraperitoneal injection of 0.6% acetic acid (0. 1 mL/10 g). "Zhongwan" (CV 12) and bilateral "Zusanli" (ST 36) were punctured with filiform needles and stimulated for 30 min by manipulating the needle for 30 s every 5 min. The latency and the number of body-writhing response were observed and the contents of beta-endorphin (beta-EP) in hypothalamus and serum prostaglandin E2 (PGE2) were detected with radioimmunoassay (RIA).

RESULTS

There was no significant difference in the latency and the number of body-writhing response, and contents of hypothalamic beta-EP and serum PGE2 between HT and WT control groups (P > 0.05). Compared with the corresponding control groups, the latency of body-writhing in WT model and HT model groups shortened significantly and the number of body- writhing increased considerably in two model groups (P < 0.01). While in comparison with WT model group, the latency of body-writhing prolonged significantly and the number of body-writhing decreased apparently in WT acupuncture group (P < 0.01); but no marked differences were found between HT model and HT acupuncture groups in these two indexes (P > 0.05). Compared with the corresponding control groups, the contents of both beta-EP and PGE2 increased obviously in WT model and HT model groups (P < 0.05). In comparison with WT model group, beta-EP levels in WT acupuncture group increased further significantly (P < 0.05), and serum PGE2 in WT acupuncture group decreased obviously (P < 0.05); but no significant changes were found between HT model and HT acupuncture groups in beta-EP and PGE2 levels (P > 0.05).

CONCLUSION

Acupuncture has a marked antinociceptive effect in WT mice with visceral pain, which may be related to its effects in increasing hypothalamic beta-EP and decreasing serum PGE2; while in connexin 43 gene knockout mice, all the above-mentioned effects of acupuncture are eliminated, indicating an important role of connexin 43 in the analgesic effect of acupuncture.

Role of Connexin 43 in Sertoli Cells of Testis

Connexin 43 (CX43, also known as GJA1) is the predominant testicular gap-junction protein. In the seminiferous epithelium, gap junctions occur between adjacent Sertoli cells and between Sertoli and germ cells. The specific role of CX43 in Sertoli cell has been difficult to study because of the neonatal lethality of the Cx43 global knockout. Recently two laboratories have independently developed a Sertoli cell conditional Cx43 knockout using Cre-loxP methodology. These have allowed the role of CX43 in Sertoli cells to be determined while circumventing lethal abnormalities in organs such as the heart seen in Cx43 global knockouts. In this review the focus is on the insights into the role of CX43 in Sertoli cells derived from these new model systems. Results indicate that CX43 is essential for cessation of proliferation and normal maturation in Sertoli cells. In addition, CX43 in Sertoli cells is required for spermatogenesis, but not early germ cell proliferation. These model systems show that CX43 is important in Sertoli cell development, and will be useful in further studies of its role in Sertoli cell and testis biology.

Connexin43 enhances glioma invasion by a mechanism involving the carboxy terminus

Gliomas are particularly difficult to cure owing largely to their invasive nature. The neoplastic changes of astrocytes which give rise to these tumors frequently include a reduction of connexin43 (Cx43), the most abundant connexin isoform expressed in astrocytes. Cx43 is a subunit of gap junctions (GJ), intercellular channels which directly link the cytosol of adjacent cells and allow the regulated passage of ions and small molecules. To examine the role of Cx43 in glioma motility, we identified two variant C6 cell lines which endogenously express high (C6-H) or low (C6-L) levels of Cx43. In wound healing and transwell assays, C6-H cells were more motile than C6-L cells. To deduce whether Cx43 mediated these differences, assays were conducted on C6-H cells retrovirally transduced with Cx43 shRNA. Coincident with the stable knockdown of endogenous Cx43, a decrease in motility and invasion was observed. Gap junctional intercellular communication was also decreased, however motility assays conducted in the presence of GJ inhibitors did not reveal significant differences in cell motility. C6 cells transfected with full length or C-terminal truncated Cx43 (Cx43DeltaCT) were subjected to the aforementioned motility assays to expose alternate mechanisms of Cx43-mediated motility. Cells expressing full length Cx43 exhibited increased motility while cells expressing Cx43DeltaCT did not. This report, the first in which RNAi has been employed to reduce Cx43 expression in gliomas, indicates that the downregulation of Cx43 decreases motility of C6 cells. Furthermore, it is the first report to suggest that the Cx43 CT plays an important role in glioma motility.

Connexin 43 in ischemic pre- and postconditioning

Connexin 43 (Cx43) is the predominant protein forming gap junctions and non-junctional hemichannels in ventricular myocardium, but Cx43 is also localized at the inner membrane of cardiomyocyte mitochondria. In cardiomyocytes, Cx43 is involved in the formation of reactive oxygen species, which are central to the signal transduction cascade of ischemic preconditioning's protection. Accordingly, genetically-induced or age-related loss of Cx43 abolishes infarct size reduction by ischemic preconditioning. Similarly, mitochondrial import inhibition of Cx43 completely blocks infarct size reduction by pharmacological preconditioning with diazoxide. In contrast to its importance for preconditioning-induced cardioprotection, Cx43 is not important for infarct size reduction by ischemic postconditioning. In summary, Cx43--especially Cx43 localized in mitochondria--appears to be one key element of the signal transduction cascade of the protection by preconditioning.

Abnormal connexin expression underlies delayed wound healing in diabetic skin

OBJECTIVE

Dynamically regulated expression of the gap junction protein connexin (Cx)43 plays pivotal roles in wound healing. Cx43 is normally downregulated and Cx26 upregulated in keratinocytes at the edge of the wound as they adopt a migratory phenotype. We have examined the dynamics of Cx expression during wound healing in diabetic rats, which is known to be slow.

RESEARCH DESIGN AND METHODS

We induced diabetes with streptozotocin and examined Cx expression and communication in intact and healing skin.

RESULTS

We found that diabetes decreased Cx43 and Cx26 protein and communication in the intact epidermis and increased Cx43 protein and communication in the intact dermis. Diabetes also altered the dynamic changes of Cxs associated with wound healing. Within 24 h, Cx43 was upregulated in a thickened bulb of keratinocytes at the wound edge (rather than downregulated as in controls, which formed a thin process of migratory cells). Cx43 decline was delayed until 48 h, when reepithelialization began. Although Cx26 was upregulated as normal after wounding in diabetic skin, its distribution at the wound edge was abnormal, being more widespread. Application of Cx43-specific antisense gel to diabetic wounds prevented the abnormal upregulation of Cx43 and doubled the rate of reepithelialization, which exceeded control levels.

CONCLUSIONS

Cx expression in diabetic skin is abnormal, as is the dynamic response of Cx43 to injury, which may underlie the delayed healing of diabetic wounds. Preventing the upregulation of Cx43 in diabetic wounds significantly improves the rate of healing and clearly has potential therapeutic value.

[Influence of acupuncture on the immune function of immunosuppressive Cx43 knockout mice]

OBJECTIVE

To observe the influence of acupuncture on the immune function in immunosuppressive Cx43 knockout mice so as to explore the relationship between connexin 43 (Cx43) and acupuncture signal transmission.

METHODS

Eighteen male Cx43 knockout mice (Cx43 + / -, 8-9 weeks old) and eighteen wide-type mice (Cx43 + / + ) were divided into normal group, model group and acupuncture group randomly, with 6 cases in each. The immunosuppressive mice model was established by intraperitoneal injection of Cyclophosphamide. Mice in acupuncture group were treated with manual acupuncture of "Zusanli" (ST 36) and "Guanyuan" (CV 4), once daily for 7 days. Spleen index, thymus index, number of leukocytes in the peripheral blood were calculated and the percentage of T lymphocyte subpopulation was detected by using flow cytometry.

RESULTS

Compared with normal control group, the spleen index, thymus index and leukocyte number of model group in both Cx43 + / + mice and Cx43 + / - mice were obviously lower (P < 0.05, 0.01), while in Cx43 + / + mice and in comparison with model group, the spleen index, thymus index and leukocyte number of acupuncture group were significantly higher (P < 0.05, 0.01) and no significant differences were found between acupuncture group and control group (P > 0.05). But in Cx43 + / - mice , no obvious differences were found between acupuncture and model groups in the aforementioned 3 indexes (P > 0.05), showing a disappearance of the effect of acupuncture in raising immune function after Cx43 knockout. There were no obvious differences between two control groups and between two model groups in the 3 indexes of Cx43 + / + mice and Cx43 + / - mice. The immune function of Cx43 + / + mice was obviously stronger than that of Cx43 + / - mice in acupuncture group.

CONCLUSION

Knockout of Cx43 gene inhibits the effect of acupuncture in reinforcing mouse immunity, suggesting an important role of Cx43 in the transmission of acupuncture signals for adjusting immunity function.

Connexin Levels Regulate Keratinocyte Differentiation in the Epidermis

To understand the role of connexin43 (Cx43) in epidermal differentiation, we reduced Cx43 levels by RNA-mediated interference knockdown and impaired its functional status by overexpressing loss-of-function Cx43 mutants associated with the human disease oculodentodigital dysplasia (ODDD) in rat epidermal keratinocytes. When Cx43 expression was knocked down by 50-75%, there was a coordinate 55-65% reduction in Cx26 level, gap junction-based dye coupling was reduced by 60%, and transepithelial resistance decreased. Importantly, the overall growth and differentiation of Cx43 knockdown organotypic epidermis was severely impaired as revealed by alterations in the levels of the differentiation markers loricrin and involucrin and by reductions in vital and cornified layer thicknesses. Conversely, although the expression of Cx43 mutants reduced the coupling status of rat epidermal keratinocytes by approximately 80% without altering the levels of endogenous Cx43 or Cx26, their ability to differentiate was not altered. In addition, we used a mouse model of ODDD and found that newborn mice harboring the loss-of-function Cx43(G60S) mutant had slightly reduced Cx43 levels, whereas Cx26 levels, epidermis differentiation, and barrier function remained unaltered. This properly differentiated epidermis was maintained even when Cx43 and Cx26 levels decreased by more than 70% in 3-week-old mutant mice. Our studies indicate that Cx43 and Cx26 collectively co-regulate epidermal differentiation from basal keratinocytes but play a more minimal role in the maintenance of established epidermis. Altogether, these studies provide an explanation as to why the vast majority of ODDD patients, where Cx43 function is highly compromised, do not suffer from skin disease.

Modulation of membrane channel currents by gap junction protein mimetic peptides: size matters

Connexin mimetic peptides are widely used to assess the contribution of nonjunctional connexin channels in several processes, including ATP release. These peptides are derived from various connexin sequences and have been shown to attenuate processes downstream of the putative channel activity. Yet so far, no documentation of effects of peptides on connexin channels has been presented. We tested several connexin and pannexin mimetic peptides and observed attenuation of channel currents that is not compatible with sequence specific actions of the peptides. Connexin mimetic peptides inhibited pannexin channel currents but not the currents of the channel formed by connexins from which the sequence was derived. Pannexin mimetic peptides did inhibit pannexin channel currents but also the channels formed by connexin 46. The same pattern of effects was observed for dye transfer, except that the inhibition levels were more pronounced than for the currents. The channel inhibition by peptides shares commonalities with channel effects of polyethylene glycol (PEG), suggesting a steric block as a mechanism. PEG accessibility is in the size range expected for the pore of innexin gap junction channels, consistent with a functional relatedness of innexin and pannexin channels.

Connexin 43 confers resistance to hydrogen peroxide-mediated apoptosis

The current study aimed to understand the anti-apoptotic effect of overexpressed gap junction forming protein connexin (Cx) 43 in C6 glioma cells. C6 cells exposed to hydrogen peroxide (H2O2) or staurosporine demonstrated morphological and biochemical changes consistent with apoptosis, whereas C6 cells expressing Cx43 demonstrated relative resistance to H2O2, but not to staurosporine. This selective protection against H2O2 was due to inhibition of caspase-3 activation in Cx43 expressing cells. siRNA knockdown experiments in rat primary astrocytes confirmed the presence of endogenous Cx43-mediated anti-apoptotic effect. Cx43 interacts with the upstream apoptosis signal-regulating kinase 1 known to mediate H2O2-induced apoptosis providing a possible mechanism for protection. These findings provided new evidence for regulation of the mitogen activated protein kinase pathway and apoptosis by Cx43 implicating this protein in intracellular signaling beyond its role as a gap junction forming protein on the plasma membrane.

Possible involvement of different connexin43 domains in plasma membrane permeabilization induced by ischemia-reperfusion

In vitro and in vivo studies support the involvement of connexin 43-based cell-cell channels and hemichannels in cell death propagation induced by ischemia-reperfusion. In this context, open connexin hemichannels in the plasma membrane have been proposed to act as accelerators of cell death. Progress on the mechanisms underlying the cell permeabilization induced by ischemia-reperfusion reveals the involvement of several factors leading to an augmented open probability and increased number of hemichannels on the cell surface. While open probability can be increased by a reduction in extracellular concentration of divalent cations and changes in covalent modifications of connexin 43 (oxidation and phosphorylation), increase in number of hemichannels requires an elevation of the intracellular free Ca(2+) concentration. Reversal of connexin 43 redox changes and membrane permeabilization can be induced by intracellular, but not extracellular, reducing agents, suggesting a cytoplasmic localization of the redox sensor(s). In agreement, hemichannels formed by connexin 45, which lacks cytoplasmic cysteines, or by connexin 43 with its C-terminal domain truncated to remove its cysteines are insensitive to reducing agents. Although further studies are required for a precise localization of the redox sensor of connexin 43 hemichannels, modulation of the redox potential is proposed as a target for the design of pharmacological tools to reduce cell death induced by ischemia-reperfusion in connexin 43-expressing cells.

A sertoli cell-specific knockout of connexin43 prevents initiation of spermatogenesis

The predominant testicular gap junctional protein connexin43 (cx43) is located between neighboring Sertoli cells (SCs) and between SCs and germ cells. It is assumed to be involved in testicular development, cell differentiation, initiation, and maintenance of spermatogenesis with alterations of its expression being correlated with various testicular disorders. Because total disruption of the cx43 gene leads to perinatal death, we generated a conditional cx43 knockout (KO) mouse using the Cre/loxP recombination system, which lacks the cx43 gene solely in SCs (SCCx43KO), to evaluate the SC-specific functions of cx43 on spermatogenesis in vivo. Adult SCCx43KO(-/-) mice showed normal testis descent and development of the urogenital tract, but testis size and weight were drastically lower compared with heterozygous and wild-type littermates. Histological analysis and quantitation of mRNA expression of germ cell-specific marker genes revealed a significant reduction in the number of spermatogonia but increased SC numbers/tubule with only a few tubules left showing normal spermatogenesis. Thus, SC-specific deletion of cx43 mostly resulted in an arrest of spermatogenesis at the level of spermatogonia or SC-only syndrome and in intratubular SC clusters. Our data demonstrate for the first time that cx43 expression in SCs is an absolute requirement for normal testicular development and spermatogenesis.

Inhibition of connexin 43 expression and function in cultured rat dental pulp cells by antisense oligonucleotide

Connexins are gap-junction proteins forming hexameric structures in the plasma membranes of adjacent cells, thereby creating intercellular channels. Connexin 43 (CX43) is expressed in pulp tissue. However, its function in dental pulp tissue has yet to be fully investigated. We have employed antisense oligonucleotides (AS) against rat CX43 to study the role of CX43 in dental pulp cells. Cultured dental pulp cells were treated with AS or sense (S) oligonucleotides. The number of cells in the AS-treated groups was approximately 1.3-fold that in the S-treated controls. Growth rates were significantly different between the AS- and S-treated groups at 48 h (P < 0.01). An alkaline phosphatase assay revealed that AS-treated pulp cells dramatically decreased at 48 h after AS incorporation, whereas S-treated pulp cells showed no marked changes. Western blot analysis revealed that heat-shock protein 25 was highly expressed in S-treated cells but was only weakly expressed in AS-treated cells at 48 h. Furthermore, AS-treated cells highly expressed CX45, whereas S-treated cells exhibited high expression of CX32. These results suggest that CX43 is involved in cell growth, mineralization, and differentiation to odontoblasts in rat pulp cells, and that CX43 plays the opposite role to that of CX45.