Search Results (9)

Background: Connexins (Cx) are a family of transmembrane proteins that form gap junctions and connexin hemichannels (HCs), enabling direct intercellular communication within the nervous system. Connexin 43 (Cx43), the principal astrocytic connexin, exhibits a context-dependent dual role: under physiological conditions it maintains tissue homeostasis and metabolic support, whereas under pathological conditions excessive activation of Cx43 hemichannels promotes neuroinflammation, excitotoxicity, blood–brain barrier disruption, and secondary neural tissue damage. Other connexin isoforms also contribute to the pathogenesis of neurological and psychiatric disorders through alterations in neuronal synchronization, glial signaling, and myelin integrity. Objective: To systematize current evidence on the role of key connexin isoforms in acute nervous system injuries—including stroke, traumatic brain injury, spinal cord injury, and peripheral nerve injury—as well as chronic disorders such as neurodegenerative diseases, epilepsy, and psychiatric disorders, with particular emphasis on the functional duality of connexin channels and the therapeutic potential of their selective modulation. Methods: A systematic literature search was conducted in the PubMed, Scopus, and Web of Science databases in accordance with the PRISMA framework and the PRISMA Extension for Scoping Reviews guidelines. The review included data from experimental models, postmortem brain studies, genetic association analyses, and pharmacological intervention studies. The retrieved studies were screened, assessed for eligibility, and integrated using a qualitative narrative synthesis approach. Results: In acute neural injuries, hyperactivation of Cx43 hemichannels amplifies inflammatory signaling, edema formation, and neuronal death, whereas selective HCs inhibitors reduce lesion volume and improve functional outcomes in experimental models. Connexin 36 (Cx36) contributes to cortical spreading depolarization and seizure propagation, while Connexin 32 (Cx32) and Connexin 47 (Cx47) are critically involved in oligodendrocyte function and white-matter demyelination. In PNI, Cx43 upregulation contributes to neuropathic pain, whereas mutations in Cx32 cause hereditary demyelinating neuropathies. In neurodegenerative diseases—including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis—Cx43 hemichannel activity promotes neuroinflammation and pathological protein accumulation, while reduced Cx32/Cx47 expression disrupts metabolic support of axons. In psychiatric disorders such as major depressive disorder, bipolar disorder, and schizophrenia, decreased astrocytic connexin expression (Cx43 and Cx30) has been associated with impaired glial–neuronal communication and cognitive–emotional dysfunction. In epilepsy, increased Cx43/Cx30 expression contributes to neuronal hypersynchronization and blood–brain barrier dysfunction, whereas selective hemichannel blockade suppresses seizure activity. Conclusions: Cx—particularly Cx43—occupies a central position in the molecular mechanisms of secondary neural injury and network dysfunction. The dual functional properties of gap junctions and hemichannels determine their context-dependent effects across neurological and psychiatric diseases. Selective inhibition of pathological HCs activity shows significant neuroprotective and anticonvulsant potential and represents a promising direction for the development of targeted therapeutic strategies. Further studies are required to determine optimal therapeutic time windows, tissue-specific effects, and the long-term safety of Cx modulation. Full article

In this review we propose the hypothesis that an energy-dissipating process precedes the continuous stimulation of insulin secretion by glucose. This process is mediated by connexin 36 hemichannels (Cx36H), or Cx36 connexons. Cx36H oligomers are expressed at the plasma membrane, and their gating activity (opening) is activated by plasma membrane depolarization after the closure of K⁺ATP channels by glucose (>5 mM) metabolism. This initial depolarization (1st step) might be responsible for the first phase of insulin secretion, with the subsequent opening of Cx36H increasing β-cell plasma membrane permeability, allowing for the efflux of metabolites (less than 1KD) (GABA, adenine nucleotides) and K⁺ (2nd step). This provokes a breakdown of oxidative glucose metabolism and the repolarization of the plasma membrane. As the extracellular glucose concentration increases further (>>5 mM), it exerts a progressive inhibition effect on Cx36H opening, allowing for the continuous stimulation of insulin secretion (3d step, second phase,). The glucose feature of regulating Cx36H closing with sigmoidal kinetics (8 mM IC₅₀ and around 20 mM at maximum) has been confirmed in mouse Cx36 connexin expression in Xenopus oocytes and in mouse islets stimulated by a range of glucose concentrations in the presence of 70 mM KCl. This gating activity was also inhibited by some non-metabolized glucose analogs. Glucose inhibition of Cx3H opening might not only contribute to making the insulin secretory response more specific for glucose but might also play a role in the pulsatility of sustained insulin secretion. Cx36H opening also offers the opportunity to potentiate the secretory effect in vivo by, permeant or not, metabolic stimuli. Confirmation of this novel physiological role for Cx36H in β-cells would place them as new susceptibility locus for type 1 and type 2 diabetes, whose physiological implication in the mechanism of insulin secretion regulation should be evaluated by in vivo studies in diabetic patients. Full article

Endometriosis is a complicated condition characterized by inflammation, low oocyte quality, and decreased uterus receptivity, associated with fertility issues. This study aims to better understand the reduced pregnancy outcome in endometriosis by analyzing both the granulosa cells (GCs) and the follicular fluids (FFs) obtained during the assisted reproductive technology (ART)-related oocyte pick-up. Seventy patients, approaching our ART Center with the diagnosis of infertility for Age-Idiopathic Factor (AIF) (n = 36), endometriosis (ENDO) (n = 23), or male factor (MF) (n = 11), were enrolled in this study. GCs from each group were separately analyzed for morphology, replication, and expression of Connexin-43 and Follicle-Stimulating Hormone Receptor (FSHR) by microscopy, flow cytometry, and immunocytochemistry. Results show that FF in a culture medium allowed GCs to survive and replicate. Upon culturing GCs from each group with ENDO follicular fluid, increases were observed in both population doublings and in the development of fibroblast-like and muscle-like morphologies. Despite undergoing morphological changes, GCs consistently expressed FSHR. However, exposure to ENDO follicular fluid led to an upregulation of Connexin-43 expression across all GC groups. These findings suggest that in endometriosis, FF contains unidentified factors that can induce aberrant replication, morphological differentiation, and overexpression of Connexin-43, potentially contributing to follicular dysfunction. Full article

Appropriate glucose-stimulated insulin secretion (GSIS) by pancreatic β-cells is an essential component of blood glucose homeostasis. Configuration of β-cells as 3D pseudoislets (PI) improves the GSIS response compared to 2D monolayer (ML) culture. The aim of this study was to determine the underlying mechanisms. MIN6 β-cells were grown as ML or PI for 5 days. Human islets were isolated from patients without diabetes. Function was assessed by GSIS and metabolic capacity using the Seahorse bioanalyser. Connexin 36 was downregulated using inducible shRNA. Culturing MIN6 as PI improved GSIS. MIN6 PI showed higher glucose-stimulated oxygen consumption (OCR) and extracellular acidification (ECAR) rates. Further analysis showed the higher ECAR was, at least in part, a consequence of increased glycolysis. Intact human islets also showed glucose-stimulated increases in both OCR and ECAR rates, although the latter was smaller in magnitude compared to MIN6 PI. The higher rates of glucose-stimulated ATP production in MIN6 PI were consistent with increased enzyme activity of key glycolytic and TCA cycle enzymes. There was no impact of connexin 36 knockdown on GSIS or ATP production. Configuration of β-cells as PI improves GSIS by increasing the metabolic capacity of the cells, allowing higher ATP production in response to glucose. Full article

Birdsong is a precisely timed animal behavior. The connectivity of song premotor neural networks has been proposed to underlie the temporal patterns of neuronal activity that control vocal muscle movements during singing. Although the connectivity of premotor nuclei via chemical synapses has been characterized, electrical synapses and their molecular identity remain unexplored. We show with in situ hybridizations that GJD2 mRNA, coding for the major channel-forming electrical synapse protein in mammals, connexin 36, is expressed in the two nuclei that control song production, HVC and RA from canaries and zebra finches. In canaries’ HVC, GJD2 mRNA is extensively expressed in GABAergic and only a fraction of glutamatergic cells. By contrast, in RA, GJD2 mRNA expression is widespread in glutamatergic and GABAergic neurons. Remarkably, GJD2 expression is similar in song nuclei and their respective embedding brain regions, revealing the widespread expression of GJD2 in the avian brain. Inspection of a single-cell sequencing database from zebra and Bengalese finches generalizes the distributions of electrical synapses across cell types and song nuclei that we found in HVC and RA from canaries, reveals a differential GJD2 mRNA expression in HVC glutamatergic subtypes and its transient increase along the neurogenic lineage. We propose that songbirds are a suitable model to investigate the contribution of electrical synapses to motor skill learning and production. Full article

Calmodulin binding is a nearly universal property of gap junction proteins, imparting a calcium-dependent uncoupling behavior that can serve in an emergency to decouple a stressed cell from its neighbors. However, gap junctions that function as electrical synapses within networks of neurons routinely encounter large fluctuations in local cytoplasmic calcium concentration; frequent uncoupling would be impractical and counterproductive. We have studied the properties and functional consequences of calmodulin binding to the electrical synapse protein Connexin 35 (Cx35 or gjd2b), homologous to mammalian Connexin 36 (Cx36 or gjd2). We find that specializations in Cx35 calmodulin binding sites make it relatively impervious to moderately high levels of cytoplasmic calcium. Calmodulin binding to a site in the C-terminus causes uncoupling when calcium reaches low micromolar concentrations, a behavior prevented by mutations that eliminate calmodulin binding. However, milder stimuli promote calcium/calmodulin-dependent protein kinase II activity that potentiates coupling without interference from calmodulin binding. A second calmodulin binding site in the end of the Cx35 cytoplasmic loop, homologous to a calmodulin binding site present in many connexins, binds calmodulin with very low affinity and stoichiometry. Together, the calmodulin binding sites cause Cx35 to uncouple only at extreme levels of intracellular calcium. Full article

The gap junctional protein connexin 36 (Cx36) has been co-purified with the lipid raft protein caveolin-1 (Cav-1). The relevance of an interaction between the two proteins is unknown. In this study, we explored the significance of Cav-1 interaction in the context of intracellular and membrane transport of Cx36. Coimmunoprecipitation assays and Förster resonance energy transfer analysis (FRET) were used to confirm the interaction between the two proteins in the Neuro 2a cell line. We found that the Cx36 and Cav-1 interaction was dependent on the intracellular calcium levels. By employing different microscopy techniques, we demonstrated that Cav-1 enhances the vesicular transport of Cx36. Pharmacological interventions coupled with cell surface biotinylation assays and FRET analysis revealed that Cav-1 regulates membrane localization of Cx36. Our data indicate that the interaction between Cx36 and Cav-1 plays a role in the internalization of Cx36 by a caveolin-dependent pathway. Full article

Gap junction (GJ) channels and their connexins (Cxs) are complex proteins that have essential functions in cell communication processes in the central nervous system (CNS). Neurons, astrocytes, oligodendrocytes, and microglial cells express an extraordinary repertory of Cxs that are important for cell to cell communication and diffusion of metabolites, ions, neurotransmitters, and gliotransmitters. GJs and Cxs not only contribute to the normal function of the CNS but also the pathological progress of several diseases, such as cancer and neurodegenerative diseases. Besides, they have important roles in mediating neuroprotection by internal or external molecules. However, regulation of Cx expression by epigenetic mechanisms has not been fully elucidated. In this review, we provide an overview of the known mechanisms that regulate the expression of the most abundant Cxs in the central nervous system, Cx30, Cx36, and Cx43, and their role in brain cancer, CNS disorders, and neuroprotection. Initially, we focus on describing the Cx gene structure and how this is regulated by epigenetic mechanisms. Then, the posttranslational modifications that mediate the activity and stability of Cxs are reviewed. Finally, the role of GJs and Cxs in glioblastoma, Alzheimer’s, Parkinson’s, and Huntington’s diseases, and neuroprotection are analyzed with the aim of shedding light in the possibility of using Cx regulators as potential therapeutic molecules. Full article

This review highlights the most important discovery in the reticular activating system in the last 10 years, the manifestation of gamma band activity in cells of the reticular activating system (RAS), especially in the pedunculopontine nucleus, which is in charge of waking and rapid eye movement (REM) sleep. The identification of different cell groups manifesting P/Q-type Ca²⁺ channels that control waking vs. those that manifest N-type channels that control REM sleep provides novel avenues for the differential control of waking vs. REM sleep. Recent discoveries on the development of this system can help explain the developmental decrease in REM sleep and the basic rest-activity cycle. Full article