Functional dry powders of connexin-containing extracellular vesicles.

Extracellular vesicles (EVs) have emerged as a promising drug delivery system. Connectosomes are a specialized type of EVs that contain connexins in their membranes. Connexin is a surface transmembrane protein that forms connexin hemichannels. When a connexin hemichannel on a connectosome docks with another connexin hemichannel of a target cell, they form a gap junction that allows direct intracellular delivery of therapeutic cargos from within the connectosome to the cytoplasm of the recipient cell. In the present study, we tested the feasibility of converting connectosomes into dry powders by (thin-film) freeze-drying to enable their potential storage in temperatures higher than the recommended -80 °C, while maintaining their activity. Connectosomes were isolated from a genetically engineered HeLa cell line that overexpressing connexin-43 subunit protein tagged with red fluorescence protein. To facilitate the testing of the function of the connectosomes, they were loaded with calcein green dye. Calcein green-loaded connectosomes were thin-film freeze-dried with trehalose alone or trehalose and a polyvinylpyrrolidone polymer as lyoprotectant(s) to produce amorphous powders with high glass transition temperatures (>100 °C). Thin-film freeze-drying did not significantly change the morphology and structure of the connectosomes, nor their particle size distribution. Based on data from confocal microscopy, flow cytometry, and fluorescence spectrometry, the connexin hemichannels in the connectosomes reconstituted from the thin-film freeze-dried powder remained functional, allowing the passage of calcein green through the hemichannels and the release of the calcein green from the connectosomes when the channels were opened by chelating calcium in the reconstituted medium. The function of connectosomes was assessed after one month storage at different temperatures. The connexin hemichannels in connectosomes in liquid lost their function when stored at -19.5 ± 2.2 °C or 6.0 ± 0.5 °C for a month, while those in dry powder form remained functional under the same storage conditions. Finally, using doxorubicin-loaded connectosomes, we showed that the connectosomes reconstituted from thin-film freeze-dried powder remained pharmacologically active. These findings demonstrate that (thin-film) freeze-drying represents a viable method to prepare stable and functional powders of EVs that contain connexins in their membranes.

Novel insight into astrocyte-mediated gliotransmission modulates the synaptic plasticity in major depressive disorder.

Major depressive disorder (MDD) is a form of glial cell-based synaptic dysfunction disease in which glial cells interact closely with neuronal synapses and perform synaptic information processing. Glial cells, particularly astrocytes, are active components of the brain and are responsible for synaptic activity through the release gliotransmitters. A reduced density of astrocytes and astrocyte dysfunction have both been identified the brains of patients with MDD. Furthermore, gliotransmission, i.e., active information transfer mediated by gliotransmitters between astrocytes and neurons, is thought to be involved in the pathogenesis of MDD. However, the mechanism by which astrocyte-mediated gliotransmission contributes to depression remains unknown. This review therefore summarizes the alterations in astrocytes in MDD, including astrocyte marker, connexin 43 (Cx43) expression, Cx43 gap junctions, and Cx43 hemichannels, and describes the regulatory mechanisms of astrocytes involved in synaptic plasticity. Additionally, we investigate the mechanisms acting of the glutamatergic, gamma-aminobutyric acidergic, and purinergic systems that modulate synaptic function and the antidepressant mechanisms of the related receptor antagonists. Further, we summarize the roles of glutamate, gamma-aminobutyric acid, d-serine, and adenosine triphosphate in depression, providing a basis for the identification of diagnostic and therapeutic targets for MDD.

Brugada Phenotype Following a Cocaine Overdose.

Brugada syndrome is a rare cardiac condition characterized by distinctive electrocardiogram patterns, predisposing individuals to fatal arrhythmias. While primarily linked to a loss-of-function mutation in the SCN5A gene, acquired forms of the syndrome have been associated with various factors, including drug use. We present a case of a 31-year-old female who presented to the emergency department unresponsive following cocaine use and developed type 1 Brugada ECG patterns alongside an incomplete right bundle branch block in V1-V3, ST elevations with biphasic waves, and diffuse repolarization abnormalities with J point deviations while in the intensive care unit. This study aimed to discuss the complexity of managing drug-induced Brugada-like findings and highlights the need for further research into the mechanisms underlying cocaine-induced cardiac effects. We aimed to discuss potential mechanisms for the impact of cocaine as its role as a sodium channel blocker and its potential effects on connexin 43 in the context of Brugada syndrome. This study also reinforced the importance of differentiating between true Brugada syndrome and other similar ECG changes for appropriate care management.

Characterizing ER Retention Defects of PDZ Binding Deficient Cx36 Mutants Using Confocal Microscopy.

Overexpression of proteins in transiently transfected cells is a simple way to study basic transport mechanisms and the underlying protein-protein interactions. While expression systems have obvious drawbacks compared to in vivo experiments, they allow a quick assessment of more conserved functions, for instance, ER export or sorting of proteins in the Golgi. In a previous study, our group described the formation of ER-derived removal vesicles for the gap junction protein Cx36 in transfected HEK293T cells. These removal vesicles, termed "whorls" because of their concentric structure, were formed by Cx36 channels that failed to escape the ER. In this article, we describe an imaging protocol that can be used to determine these ER retention defects for Cx36 expressed in cultured cells. The protocol we provide here employs regular confocal microscopy, which allows for sufficient resolution to reveal the characteristic shape of ER whorls.

Impacts of exposure to and subsequent discontinuation of clozapine on tripartite synaptic transmission.

BACKGROUND AND PURPOSE: Clozapine is an effective antipsychotic for treatment-resistant schizophrenia, but its discontinuation leads to discontinuation syndrome/catatonia complicated by benzodiazepine-resistance and rhabdomyolysis. EXPERIMENTAL APPROACH: This study determined time-dependent effects of exposure and subsequent discontinuation of clozapine on expression of connexin43, 5-HT receptors, intracellular L-ß-aminoisobutyrate (L-BAIBA) and 2nd-messengers and signalling of AMPK, PP2A and Akt in cultured astrocytes and rat frontal cortex. KEY RESULTS: Intracellular L-BAIBA levels increased during clozapine exposure but immediately recovered after discontinuation. Both exposure to clozapine and L-BAIBA increased connexin43 and signalling of AMPK/Akt time-dependently, but reduced PP2A signalling, 5-HT receptor expression and IP3 level. These changes recovered within 2 weeks after discontinuation, while 5-HT receptors and IP3 transiently increased during the recovery process. L-BAIBA activated AMPK signalling, leading to attenuated PP2A signalling. Astroglial D-serine release was increased by clozapine exposure but continued to increase within 1 week after discontinuation via activation of IP3 receptor function. CONCLUSION AND IMPLICATIONS: Clozapine discontinuation restored PP2A signalling due to decreased L-BAIBA, increased 5-HT receptor expression via probably enhanced 5-HT receptor recycling, but increased astroglial D-serine release persisted by transiently activated IP3 receptors via transiently increased IP3 level. Decreased L-BAIBA caused by clozapine discontinuation is, at least partially, involved in the transiently increased 5-HT receptor and astroglial D-serine release.

Sigma-1 receptor targeting inhibits connexin 43 based intercellular communication in chronic neuropathic pain.

BACKGROUND AND OBJECTIVE: Neuropathic pain is a chronic condition characterized by aberrant signaling within the somatosensory system, affecting millions of people worldwide with limited treatment options. Herein, we aim at investigating the potential of a sigma-1 receptor (σ1R) antagonist in managing neuropathic pain. METHODS: A Chronic Constriction Injury (CCI) model was used to induce neuropathic pain. The potential of (+)-MR200 was evaluated following daily subcutaneous injections of the compound. Its mechanism of action was confirmed by administration of a well-known σ1R agonist, PRE084. RESULTS: (+)-MR200 demonstrated efficacy in protecting neurons from damage and alleviating pain hypersensitivity in CCI model. Our results suggest that (+)-MR200 reduced the activation of astrocytes and microglia, cells known to contribute to the neuroinflammatory process, suggesting that (+)-MR200 may not only address pain symptoms but also tackle the underlying cellular mechanism involved. Furthermore, (+)-MR200 treatment normalized levels of the gap junction (GJ)-forming protein connexin 43 (Cx43), suggesting a reduction in harmful intercellular communication that could fuel the chronicity of pain. CONCLUSIONS: This approach could offer a neuroprotective strategy for managing neuropathic pain, addressing both pain symptoms and cellular processes driving the condition. Understanding the dynamics of σ1R expression and function in neuropathic pain is crucial for clinical intervention.

Hyperhomocysteine promotes cataract development through mTOR-mediated inhibition of autophagy and connexins expression.

AIM: Hyperhomocysteine has been recognized as an independent risk factor of multiple diseases, including several eye diseases. In this study, we aim to investigate whether increased homocysteine (Hcy) is related to cataracts, and to explore whether dysregulation of mTOR-mediated autophagy and connexin expression are underlying mechanisms. METHOD: We first developed a method of liquid chromatography tandem mass spectrometry to accurately measure serum concentrations of Hcy in 287 cataract patients and 334 healthy controls. Next, we treated human lens epithelial (HLC-B3) cells with Hcy at different concentrations and durations, and then analyzed expression of autophagy-related markers and connexins, as well as phosphorylated mTOR (p-mTOR) in these cells by Western blotting. Formation of autophagic vacuoles and intracellular Ca2+ in the Hcy-treated cells were observed by fluorescence microscopy. Further, we performed a rescue experiment in the Hcy-treated HLC-B3 cells by pre-incubation with rapamycin, an mTOR inhibitor. RESULTS: The serum levels of Hcy in patients with cataracts were significantly increased compared to those in healthy controls. In cultured HLC-B3 cells, expression of autophagy related markers (LC3B and Beclin1) and connexins (Cx43 and Cx50) was inhibited by Hcy treatment in a dose- and duration-dependent manner. Accumulation of Ca2+ in the Hcy-treated lens epithelial cells was observed as a consequence of reduced connexin expression. Meanwhile, expression of p-mTOR increased, representing up-regulation of the mTOR pathway. Importantly, inhibition of autophagy and connexin expression due to hyperhomocysteine was rescued via mTOR suppression by pretreatment with rapamycin in HLC-B3 cells. CONCLUSION: Our results demonstrate that hyperhomocysteine might promote cataract development through two mTOR-mediated pathways in the lens epithelial cells: 1) dysregulation of autophagy and 2) accumulation of intracellular calcium via decreased connexin expression.

Connexin 43 Modulation in Human Chondrocytes, Osteoblasts and Cartilage Explants: Implications for Inflammatory Joint Disorders.

Connexin 43 (Cx43) is crucial for the development and homeostasis of the musculoskeletal system, where it plays multifaceted roles, including intercellular communication, transcriptional regulation and influencing osteogenesis and chondrogenesis. Here, we investigated Cx43 modulation mediated by inflammatory stimuli involved in osteoarthritis, i.e., 10 ng/mL Tumor Necrosis Factor alpha (TNFα) and/or 1 ng/mL Interleukin-1 beta (IL-1ß), in primary chondrocytes (CH) and osteoblasts (OB). Additionally, we explored the impact of synovial fluids from osteoarthritis patients in CH and cartilage explants, providing a more physio-pathological context. The effect of TNFα on Cx43 expression in cartilage explants was also assessed. TNFα downregulated Cx43 levels both in CH and OB (-73% and -32%, respectively), while IL-1ß showed inconclusive effects. The reduction in Cx43 levels was associated with a significant downregulation of the coding gene GJA1 expression in OB only (-65%). The engagement of proteasome in TNFα-induced effects, already known in CH, was also observed in OB. TNFα treatment significantly decreased Cx43 expression also in cartilage explants. Of note, Cx43 expression was halved by synovial fluid in both CH and cartilage explants. This study unveils the regulation of Cx43 in diverse musculoskeletal cell types under various stimuli and in different contexts, providing insights into its modulation in inflammatory joint disorders.

Determinants of vascular impairment in type 1 diabetes-impact of sex and connexin 37 gene polymorphism: A cross-sectional study.

BACKGROUND: The associations of risk factors with vascular impairment in type 1 diabetes patients seem more complex than that in type 2 diabetes patients. Therefore, we analyzed the associations between traditional and novel cardiovascular risk factors and vascular parameters in individuals with T1D and modifications of these associations according to sex and genetic factors. METHODS: In a cross-sectional study, we analyzed the association of risk factors in T1D individuals younger than 65 years using vascular parameters, such as ankle brachial index (ABI) and toe brachial index (TBI), duplex ultrasound, measuring the presence of plaques in carotid and femoral arteries (Belcaro score) and intima media thickness of carotid arteries (CIMT). We also used photoplethysmography, which measured the interbranch index expressed as the Oliva-Roztocil index (ORI), and analyzed renal parameters, such as urine albumin/creatinine ratio (uACR) and glomerular filtration rate (GFR). We evaluated these associations using multivariate regression analysis, including interactions with sex and the gene for connexin 37 (Cx37) polymorphism (rs1764391). RESULTS: In 235 men and 227 women (mean age 43.6 ± 13.6 years; mean duration of diabetes 22.1 ± 11.3 years), pulse pressure was strongly associated with unfavorable values of most of the vascular parameters under study (ABI, TBI, Belcaro scores, uACR and ORI), whereas plasma lipids, represented by remnant cholesterol (cholesterol - LDL-HDL cholesterol), the atherogenic index of plasma (log (triglycerides/HDL cholesterol) and Lp(a), were associated primarily with renal impairment (uACR, GFR and lipoprotein (a)). Plasma non-HDL cholesterol was not associated with any vascular parameter under study. In contrast to pulse pressure, the associations of lipid factors with kidney and vascular parameters were modified by sex and the Cx37 gene. CONCLUSION: In addition to known information, easily obtainable risk factor, such as pulse pressure, should be considered in individuals with T1D irrespective of sex and genetic background. The associations of plasma lipids with kidney function are complex and associated with sex and genetic factors. The decision of whether pulse pressure, remnant lipoproteins, Lp(a) and other determinants of vascular damage should become treatment targets in T1D should be based on the results of future clinical trials.

Empagliflozin mitigates ponatinib-induced cardiotoxicity by restoring the connexin 43-autophagy pathway.

BACKGROUND: Empagliflozin (EMPA), a selective sodium-glucose cotransporter type 2 (SGLT2) inhibitor, has been shown to reduce major adverse cardiovascular events in patients with heart failure of different etiologies, although the underlying mechanism still remains unclear. Ponatinib (PON) is a multi-tyrosine kinase inhibitor successfully used against myeloid leukemia and other human malignancies, but its cardiotoxicity remains worrisome. Cardiac connexins (Cxs) are both substrates and regulators of autophagy and responsible for proper heart function. Alteration in connexin expression and localization have been described in patients with heart failure. AIMS: To assess whether EMPA can mitigate PON-induced cardiac dysfunction by restoring the connexin 43-autophagy pathway. METHODS AND RESULTS: Male C57BL/6 mice, randomized into four treatment groups (CNTRL, PON, EMPA, PON+EMPA) for 28 days, showed increased autophagy, decreased Cx43 expression as well as Cx43 lateralization, and attenuated systo-diastolic cardiac dysfunction after treatment with EMPA and PON compared with PON alone. Compared with CNTRL (DMSO), cardiomyocyte-differentiated H9c2 (dH9c2) cells treated with PON showed significantly reduced cell viability to approximately 20 %, decreased autophagy, increased cell senescence and reduced DNA binding activity of serum response factor (SRF) to serum response elements (SRE), which were paralleled by reduction in cardiac actin expression. Moreover, PON induced a significant increase of Cx43 protein and its S368-phosphorylated form (pS368-Cx43), as well as their displacement from the plasma membrane to the perinuclear and nuclear cellular region. All these effects were reverted by EMPA. CONCLUSION: EMPA attenuates PON-induced cardiotoxicity by reducing senescence, enhancing the SRE-SRF binding and restoring the connexin 43-autophagy pathway. This effect may pave the way to use of SGLT2 inhibitors in attenuating tyrosine-kinase inhibitor cardiotoxicity.

Chronic dietary exposure to glyphosate-induced connexin 43 autophagic degradation contributes to blood-testis barrier disruption in roosters.

Glyphosate (GLY) is the most universally used herbicide worldwide and its application has caused extensive pollution to the ecological environment. Increasing evidence has revealed the multi-organ toxicity of GLY in different species, but its male reproductive toxicity in avian species remains unknown. Thus, in vivo and in vitro studies were conducted to clarify this issue. Data firstly showed that chronic GLY exposure caused testicular pathological damage. Intriguingly, we identified and verified a marked down-regulation gap junction gene Connexin 43 (Cx43) in GLY-exposed rooster testis by transcriptome analysis. Cx43 generated by Sertoli cells acts as a key component of blood-testis barrier (BTB). To further investigate the cause of GLY-induced downregulation of Cx43 to disrupt BTB, we found that autophagy activation is revealed in GLY-exposed rooster testis and primary avian Sertoli cells. Moreover, GLY-induced Cx43 downregulation was significantly alleviated by ATG5 knockdown or CQ administration, respectively, demonstrating that GLY-induced autophagy activation contributed to Cx43 degradation. Mechanistically, GLY-induced autophagy activation and resultant Cx43 degradation was due to its direct interaction with ER-α. In summary, these findings demonstrate that chronic GLY exposure activates autophagy to induce Cx43 degradation, which causes BTB damage and resultant reproductive toxicity in roosters.

Corrigendum: Ginsenoside Rg1 ameliorates neuroinflammation via suppression of connexin43 ubiquitination to attenuate depression.

[This corrects the article DOI: 10.3389/fphar.2021.709019.].

Multiple approaches for the evaluation of connexin-43 expression and function in macrophages.

Connexins are essential gap junction proteins that play pivotal roles in intercellular communication in various organs of mammals. Connexin-43 (Cx43) is expressed in various components of the immune system, and there is extensive evidence of its participation in inflammation responses. The involvement of Cx43 in macrophage functionality involves the purinergic signaling pathway. Macrophages contribute to defenses against inflammatory reactions such as bacterial sepsis and peritonitis. Several assays can identify the presence and activity of Cx43 in macrophages. Real-time polymerase chain reaction (PCR) can measure the relative mRNA expression of Cx43, whereas western blotting can detect protein expression levels. Using immunofluorescence assays, it is possible to analyze the expression and observe the localization of Cx43 in cells or tissues. Moreover, connexin-mediated gap junction intercellular communication can be evaluated using functional assays such as microinjection of fluorescent dyes or scrape loading-dye transfer. The use of selective inhibitors contributes to this understanding and reinforces the role of connexins in various processes. Here, we discuss these methods to evaluate Cx43 and macrophage gap junctions.

The effects of inflammation on connexin 43 in chronic Chagas disease cardiomyopathy.

Background: Cardiac arrhythmias are the main cause of sudden death due to Chronic Chagasic Cardiomyopathy (CCC). Here we investigated alterations in connexin 43 (Cx43) expression and phosphorylation in cardiomyocytes as well as associations with cardiac arrhythmias in CCC. Methods: C57Bl/6 mice infected with Trypanosoma cruzi underwent cardiac evaluations at 6 and 12 months after infection via treadmill testing and EKG. Histopathology, cytokine gene expression, and distribution of total Cx43 and its phosphorylated forms Cx43S368 and Cx43S325/328/330 were investigated. Human heart samples obtained from subjects with CCC were submitted to immunofluorescence analysis. In vitro simulation of a pro-inflammatory microenvironment (IL-1ß, TNF, and IFN-γ) was performed in H9c2 cells and iPSC-derived cardiomyocytes to evaluate Cx43 distribution, action potential duration, and Lucifer Yellow dye transfer. Results: Mice chronically infected with T. cruzi exhibited impaired cardiac function associated with increased inflammation, fibrosis and upregulated IL-1ß, TNF, and IFN-γ gene expression. Confocal microscopy revealed altered total Cx43, Cx43S368 and Cx43S325/328/330 localization and phosphorylation patterns in CCC, with dispersed staining outside the intercalated disc areas, i.e., in lateral membranes and the cytoplasm. Reduced co-localization of total Cx43 and N-cadherin was observed in the intercalated discs of CCC mouse hearts compared to controls. Similar results were obtained in human CCC heart samples, which showed Cx43 distribution outside the intercalated discs. Stimulation of human iPSC-derived cardiomyocytes or H9c2 cells with IL-1ß, TNF, and IFN-γ induced alterations in Cx43 localization, reduced action potential duration and dye transfer between adjacent cells. Conclusion: Heart inflammation in CCC affects the distribution and phosphorylation pattern of Cx43, which may contribute to the generation of conduction disturbances in Chagas disease.

Hemichannels contribute to mitochondrial Ca2+ and morphology alterations evoked by ethanol in astrocytes.

Alcohol, a toxic and psychoactive substance with addictive properties, severely impacts life quality, leading to significant health, societal, and economic consequences. Its rapid passage across the blood-brain barrier directly affects different brain cells, including astrocytes. Our recent findings revealed the involvement of pannexin-1 (Panx1) and connexin-43 (Cx43) hemichannels in ethanol-induced astrocyte dysfunction and death. However, whether ethanol influences mitochondrial function and morphology in astrocytes, and the potential role of hemichannels in this process remains poorly understood. Here, we found that ethanol reduced basal mitochondrial Ca2+ but exacerbated thapsigargin-induced mitochondrial Ca2+ dynamics in a concentration-dependent manner, as evidenced by Rhod-2 time-lapse recordings. Similarly, ethanol-treated astrocytes displayed increased mitochondrial superoxide production, as indicated by MitoSox labeling. These effects coincided with reduced mitochondrial membrane potential and increased mitochondrial fragmentation, as determined by MitoRed CMXRos and MitoGreen quantification, respectively. Crucially, inhibiting both Cx43 and Panx1 hemichannels effectively prevented all ethanol-induced mitochondrial abnormalities in astrocytes. We speculate that exacerbated hemichannel activity evoked by ethanol may impair intracellular Ca2+ homeostasis, stressing mitochondrial Ca2+ with potentially damaging consequences for mitochondrial fusion and fission dynamics and astroglial bioenergetics.

Patterns of connexin36 and eGFP reporter expression among motoneurons in spinal sexually dimorphic motor nuclei in mouse.

BACKGROUND: Sexually dimorphic spinal motoneurons (MNs) in the dorsomedial nucleus (DMN) and dorsolateral nucleus (DLN) as well as those in the cremaster nucleus are involved in reproductive behaviours, and the cremaster nucleus additionally contributes to testicular thermoregulation. It has been reported that MNs in DMN and DLN are extensively linked by gap junctions forming electrical synapses composed of connexin36 (Cx36) and there is evidence that subpopulation of MNs in the cremaster nucleus are also electrically coupled by these synapses. METHODOLOGY: We used immunofluorescence methods to detect enhanced green fluorescent protein (eGFP) reporter for Cx36 expression in these motor nuclei. RESULTS: We document in male mice that about half the MNs in each of DMN and DLN express eGFP, while the remaining half do not. Further, we found that the eGFP+ vs. eGFP- subsets of MNs in each of these motor nuclei innervate different target muscles; eGFP+ MNs in DMN and DLN project to sexually dimorphic bulbocavernosus and ischiocavernosus muscles, while the eGFP- subsets project to sexually non-dimorphic anal and external urethral sphincter muscles. Similarly, eGFP+ vs. eGFP- cremaster MNs were found to project to anatomically distinct portions of the cremaster muscle. By immunofluorescence, nearly all motoneurons in both DMN and DLN displayed punctate labelling for Cx36, including at eGFP+/eGFP+, eGFP+/eGFP- and eGFP-/eGFP- cell appositions. CONCLUSIONS: Most if not all motoneurons in DMN and DLN are electrically coupled, including sexually dimorphic and non-dimorphic motoneurons with each other, despite absence of eGFP reporter in the non-dimorphic populations in these nuclei that have selective projections to sexually non-dimorphic target muscles.

Chlorpromazine overcomes temozolomide resistance in glioblastoma by inhibiting Cx43 and essential DNA repair pathways.

BACKGROUND: In the fight against GBM, drug repurposing emerges as a viable and time-saving approach to explore new treatment options. Chlorpromazine, an old antipsychotic medication, has recently arisen as a promising candidate for repositioning in GBM therapy in addition to temozolomide, the first-line standard of care. We previously demonstrated the antitumor efficacy of chlorpromazine and its synergistic effects with temozolomide in suppressing GBM cell malignant features in vitro. This prompted us to accomplish a Phase II clinical trial to evaluate the efficacy and safety of adding chlorpromazine to temozolomide in GBM patients with unmethylated MGMT gene promoter. In this in vitro study, we investigate the potential role of chlorpromazine in overcoming temozolomide resistance. METHODS: In our experimental set, we analyzed Connexin-43 expression at both the transcriptional and protein levels in control- and chlorpromazine-treated GBM cells. DNA damage and subsequent repair were assessed by immunofluorescence of γ-H2AX and Reverse-Phase Protein microArrays in chlorpromazine treated GBM cell lines. To elucidate the relationship between DNA repair systems and chemoresistance, we analyzed a signature of DNA repair genes in GBM cells after treatment with chlorpromazine, temozolomide and Connexin-43 downregulation. RESULTS: Chlorpromazine treatment significantly downregulated connexin-43 expression in GBM cells, consequently compromising connexin-dependent cellular resilience, and ultimately contributing to cell death. In line with this, we observed concordant post-translational modifications of molecular determinants involved in DNA damage and repair pathways. Our evaluation of DNA repair genes revealed that temozolomide elicited an increase, while chlorpromazine, as well as connexin-43 silencing, a decrease in DNA repair gene expression in GBM cells. CONCLUSIONS: Chlorpromazine potentiates the cytotoxic effects of the alkylating agent temozolomide through a mechanism involving downregulation of Cx43 expression and disruption of the cell cycle arrest essential for DNA repair processes. This finding suggests that chlorpromazine may be a potential therapeutic strategy to overcome TMZ resistance in GBM cells by inhibiting their DNA repair mechanisms.

Connexin 30 locally controls actin cytoskeleton and mechanical remodeling in motile astrocytes.

During brain maturation, astrocytes establish complex morphologies unveiling intense structural plasticity. Connexin 30 (Cx30), a gap-junction channel-forming protein expressed postnatally, dynamically regulates during development astrocyte morphological properties by controlling ramification and extension of fine processes. However, the underlying mechanisms remain unexplored. Here, we found in vitro that Cx30 interacts with the actin cytoskeleton in astrocytes and inhibits its structural reorganization and dynamics during cell migration. This translates into an alteration of local physical surface properties, as assessed by correlative imaging using stimulated emission depletion (STED) super resolution imaging and atomic force microscopy (AFM). Specifically, Cx30 impaired astrocyte cell surface topology and cortical stiffness in motile astrocytes. As Cx30 alters actin organization, dynamics, and membrane physical properties, we assessed whether it controls astrocyte migration. We found that Cx30 reduced persistence and directionality of migrating astrocytes. Altogether, these data reveal Cx30 as a brake for astrocyte structural and mechanical plasticity.

The components of an electrical synapse as revealed by expansion microscopy of a single synaptic contact.

Most nervous systems combine both transmitter-mediated and direct cell-cell communication, known as 'chemical' and 'electrical' synapses, respectively. Chemical synapses can be identified by their multiple structural components. Electrical synapses are, on the other hand, generally defined by the presence of a 'gap junction' (a cluster of intercellular channels) between two neuronal processes. However, while gap junctions provide the communicating mechanism, it is unknown whether electrical transmission requires the contribution of additional cellular structures. We investigated this question at identifiable single synaptic contacts on the zebrafish Mauthner cells, at which gap junctions coexist with specializations for neurotransmitter release and where the contact unequivocally defines the anatomical limits of a synapse. Expansion microscopy of these single contacts revealed a detailed map of the incidence and spatial distribution of proteins pertaining to various synaptic structures. Multiple gap junctions of variable size were identified by the presence of their molecular components. Remarkably, most of the synaptic contact's surface was occupied by interleaving gap junctions and components of adherens junctions, suggesting a close functional association between these two structures. In contrast, glutamate receptors were confined to small peripheral portions of the contact, indicating that most of the synaptic area functions as an electrical synapse. Thus, our results revealed the overarching organization of an electrical synapse that operates with not one, but multiple gap junctions, in close association with structural and signaling molecules known to be components of adherens junctions. The relationship between these intercellular structures will aid in establishing the boundaries of electrical synapses found throughout animal connectomes and provide insight into the structural organization and functional diversity of electrical synapses.

Neurons communicate with each other through specialized structures known as synapses. At chemical synapses, the cells do not physically interact as they rely instead on molecules called neurotransmitters to pass along signals. At electrical synapses, however, neurons are directly connected via gap junctions, which are clusters of intercellular channels that allow ions and other small compounds to move from one cell to another. Both electrical and chemical synapses play critical roles in neural circuits, and both exhibit some amount of plasticity ­ they weaken or strengthen depending on how often they are used, an important feature for the brain to adapt to the needs of the environment. Yet the structure and molecular organization of electrical synapses have remained poorly understood compared to their chemical counterparts. In response, Cárdenas-García, Ijaz and Pereda took advantage of a new approach known as expansion microscopy to examine the electrical synapse that connects neurons bringing sound information to a pair of unusually large neurons in the brain of most bony fish. With this method, a biological sample is prepared in such a way that its size increases, but the relative position of its components is preserved. This allows scientists to better observe structures that would otherwise be too difficult to capture using traditional microscopy techniques. Experiments in larval zebrafish revealed that contrary to previous assumptions, the electrical synapse was formed of not one but multiple gap junctions of various sizes closely associated with a range of structural and signaling molecules typically found in adherens junctions (a type of structure that physically links cells together). The team suggests that these molecular actors could work to ensure that the multiple gap junctions act in concert at the synapse. Overall, these findings offer a new perspective on how electrical synapses are organized and regulated, which refines our understanding of how the nervous system functions both in health and in disease.

Integrative analyses identified gap junction beta-2 as a prognostic biomarker and therapeutic target for breast cancer.

Background: Increasing evidence has shown that connexins are involved in the regulation of tumor development, immune escape, and drug resistance. This study investigated the gene expression patterns, prognostic values, and potential mechanisms of connexins in breast cancer. Methods: We conducted a comprehensive analysis of connexins using public gene and protein expression databases and clinical samples from our institution. Connexin mRNA expressions in breast cancer and matched normal tissues were compared, and multiomics studies were performed. Results: Gap junction beta-2 mRNA was overexpressed in breast cancers of different pathological types and molecular subtypes, and its high expression was associated with poor prognosis. The tumor membrane of the gap junction beta-2 mutated group was positive, and the corresponding protein was expressed. Somatic mutation and copy number variation of gap junction beta-2 are rare in breast cancer. The gap junction beta-2 transcription level in the p110α subunit of the phosphoinositide 3-kinase mutant subgroup was higher than that in the wild-type subgroup. Gap junction beta-2 was associated with the phosphoinositide 3-kinase-Akt signaling pathway, extracellular matrix-receptor interaction, focal adhesion, and proteoglycans in cancer. Furthermore, gap junction beta-2 overexpression may be associated with phosphoinositide 3-kinase and histone deacetylase inhibitor resistance, and its expression level correlated with infiltrating CD8+ T cells, macrophages, neutrophils, and dendritic cells. Conclusions: Gap junction beta-2 may be a promising therapeutic target for targeted therapy and immunotherapy and may be used to predict breast cancer prognosis.