Inhibition of Connexin43 hemichannels with Gap19 protects cerebral ischemia/reperfusion injury via the JAK2/STAT3 pathway in mice. Brain Res Bull. 2019;146:124-135. [PMID: 30593877 DOI: 10.1016/j.brainresbull.2018.12.009]

Effect of connexin 43 in LPS/IL-4-induced macrophage M1/M2 polarization: An observational study

Lipopolysaccharide (LPS) and interleukin-4 (IL-4) play important roles in inducing M1 and M2 macrophage polarization. Studies have shown that LPS can promote the polarization of macrophages to M1-type and produce many pro-inflammatory cytokines, while IL-4 can promote the polarization of macrophages to M2-type and produce many anti-inflammatory cytokines. Moreover, Connexin 43 (Cx43) is widely expressed in macrophages and has various regulatory functions. However, whether Cx43 is involved in the regulation of macrophage M1/M2 polarization has not been fully studied. This study examined the role of Cx43 and M2 polarization markers using Western blot, immunofluorescence, flow cytometry. Cx43 overexpression was induced using Cx43 overexpressing lentivirus. The statistical software SPSS 20.0 (IBM Corp.) and GraphPad Prism 8.0 (GraphPad Software, La Jolla, CA, United States) were used to analyze the results. P values < .05 were considered to indicate statistically significant differences. Our results showed that LPS promotes the polarization of macrophages to M1-type, which is accompanied by an increase in Cx43 expression from 0 to 24 hours. Moreover, the application of the Cx43-specific blockers Gap19 and Gap26 reduces the expression of macrophage M1-type polarization markers. Thus, the expression of Cx43 increases first, and then, due to the initiation of intracellular autophagy during LPS-induced macrophage M1 polarization. Cx43 is degraded and the expression of Cx43 decreases from 24 hours to 48 hours. IL-4 decreases the expression of Cx43 from 24 hours to 48 hours and promotes the transformation of macrophages to M2-type. The application of Cx43 overexpression lentivirus leads to a reduction in the expression of M2 polarization markers. IL-4-induced M2 polarization of macrophages inhibits cell autophagy, reducing Cx43 degradation and leading to an increase in Cx43 from 24 hours to 48 hours. Thus, Cx43 expression in M2-type polarization experiences a reduction at first and then an increase from 24 hours to 48 hours. The direction of macrophage polarization can be controlled by regulating the expression of Cx43, thus providing a theoretical basis for treating atherosclerosis, tumors, and other diseases associated with macrophage polarization.

Enriched environment alleviates neurological deficits via downregulation of Cx43 after experimental stroke

While it has been demonstrated that enriched environment (EE) can protect against cerebral ischemia/reperfusion (I/R) injury, the underlying mechanism remains largely unknown. Connexin 43 (Cx43) is a key component of gap junctions, which may mediate cell-to-cell communication in neural cells. This study aimed to investigate the neuroprotective effects of EE against cerebral I/R injury in rats by modulating Cx43. A rat model of cerebral I/R injury was established by middle cerebral artery occlusion (MCAO)/reperfusion. Rats were randomly divided into the sham, MCAO, MCAO + EE, MCAO + Gap19, and MCAO + EE + Gap19 groups. The modified neurological severity score test and Morris water maze assay were used to assess neurological deficits. The infarct volume was measured using triphenyltetrazolium chloride (TTC) staining. Neuronal survival was detected by immunofluorescence. The indices of oxidative stress were determined using ELISA, and the reactive oxygen species levels were determined using a dihydroethidium probe. Cx43 and inflammation-related protein expression levels were also measured using western blotting and immunohistochemistry. EE and Gap19 treatment significantly improved neurological deficits, reduced infarct volumes, attenuated neuronal injury, and suppressed inflammatory cytokine expression and oxidative stress. Furthermore, EE and Gap19 treatment notably downregulated the expression of Cx43 and the inflammation-related pathway TLR4/MyD88/NF-κB in the ischemic penumbra. Gap19, a Cx43 inhibitor, markedly enhanced the neuroprotective effects of EE in rats with cerebral I/R injury. EE treatment protects against cerebral I/R injury in rats via Cx43 downregulation. Our findings may shed light on the mechanism underlying the protective efficacy of EE.

The potential roles of stress-induced phosphoprotein 1 and connexin 43 in rats with reperfusion arrhythmia

OBJECTIVE

Connexin 43 (Cx43) is a critical gene for maintaining myocardial homeostasis. Interestingly, Cx43 and stress-induced phosphoprotein 1 (STIP1) were recorded to be lowly expressed in ischemia/reperfusion (I/R). However, their impacts on reperfusion arrhythmia (RA) remain to be explored. Our study aimed to find out the related underlying mechanisms.

METHODS

After the establishment of an isolated heart model through Langendorff perfusion, the heart rate, conduction activation time, conduction velocity, and conduction direction of the left ventricle were evaluated, along with the apoptotic rate detection in the collected myocardial tissues. After the construction of a hypoxia/reoxygenation (H/R)-induced cellular model, cell apoptosis, intercellular communication, cell viability, and the content of reactive oxygen species, superoxide dismutase, malondialdehyde, and lactic dehydrogenase were measured. The expression of Cx43 and STIP1 was determined in both rat heart and cell models. The bindings of STIP3 and Cx43 to  heat shock protein 90 (HSP90) and heat shock protein 70 (HSP70) were verified.

RESULTS

Relative to the corresponding controls, Cx43 and STIP1 were decreased in myocardial tissues of RA rats and H/R-stimulated H9C2 cells, where Cx43-binding HSP70 and HSP90 were respectively increased and decreased, and ubiquitination level of Cx43 was enhanced. STIP1 overexpression promoted protein expression of Cx43, intercellular communication, and cell viability, and reduced cell apoptosis and oxidative stress in H/R-stimulated H9C2 cells.

CONCLUSION

STIP1 promoted Cx43 expression to improve intercellular communication and reduce oxidative stress in H/R-stimulated H9C2 cells.

Spatial and temporal mapping of neuron-microglia interaction modes in acute ischemic stroke

Ischemic stroke (IS) is a major cause of morbidity and mortality worldwide, accounting for 75-80% of all strokes. Under conditions of ischemia and hypoxia, neurons suffer damage or death, leading to a series of secondary immune reactions. Microglia, the earliest activated immune cells, can exert neurotoxic or neuroprotective effects on neurons through secretion of factors. There exists a complex interaction between neurons and microglia during this process. Moreover, the interaction between them becomes even more complex due to differences in the infarct area and reperfusion time. This review first elaborates on the differences in neuronal death modes between the ischemic core and penumbra, and then introduces the differences in microglial markers across different infarct areas with varying reperfusion time, indicating distinct functions. Finally, we focus on exploring the interaction modes between neurons and microglia in order to precisely target beneficial interactions and inhibit harmful ones, thus providing new therapeutic strategies for the treatment of IS.

Preclinical Characterization of Pharmacologic NAD+ Boosting as a Promising Therapeutic Approach in Rheumatoid Arthritis

OBJECTIVE

We analyzed NAD+ metabolism in patients with rheumatoid arthritis (RA), its association with disease activity and clinical outcomes of RA, and the therapeutic potential of pharmacologic NAD+ boosting.

METHODS

Our study included 253 participants. In the first cohort, comprising 153 RA patients and 56 healthy donors, we assessed NAD+ levels and NAD+ -related gene pathways. We analyzed 92 inflammatory molecules by proximity extension assay. In the second cohort, comprising 44 RA patients starting anti-tumor necrosis factor (anti-TNF) drugs, we evaluated changes in NAD+ levels and their association with clinical response after 3 months. Mechanistic studies were performed ex vivo on peripheral blood mononuclear cells (PBMCs) from patients with RA to test the beneficial effects of NAD+ boosters, such as nicotinamide and nicotinamide riboside.

RESULTS

Reduced NAD+ levels were found in RA samples, in line with altered activity and expression of genes involved in NAD+ consumption (sirtuins, poly[ADP-ribose] polymerase, CD38), transport (connexin 43), and biosynthesis (NAMPT, NMNATs). Unsupervised clustering analysis identified a group of RA patients with the highest inflammatory profile, the lowest NAD+ levels, and the highest disease activity (as shown by the Disease Activity Score in 28 joints). NAD+ levels were modulated by anti-TNF therapy in parallel with the clinical response. In vitro studies using PBMCs from RA patients showed that nicotinamide riboside and nicotinamide increased NAD+ levels via NAMPT and NMNAT and reduced their prooxidative, proapoptotic, and proinflammatory status.

CONCLUSION

RA patients display altered NAD+ metabolism, directly linked to their inflammatory and disease activity status, which was reverted by anti-TNF therapy. The preclinical beneficial effects of NAD+ boosters, as shown in leukocytes from RA patients, along with their proven clinical safety, might pave the way for the development of clinical trials using these compounds.

CircRIMS promotes cerebral ischemia-reperfusion injury through increasing apoptosis and targeting the miR-96-5p/JAK/STAT1 axis

OBJECTIVE

This study aims to explore the function of circRIMS in cerebral ischemia/reperfusion (CIR) and its regulatory mechanism.

METHOD

The expression of the circRIMS was examined in GEO chip data and validated by qRT-PCR analysis. A middle cerebral artery occlusion/repression (MCAO/R) model was developed using C57BL/6J mice. Starbase and circinteractome were employed to identify the target miRNA and mRNA. The result was confirmed by dual-luciferase reporter assay, and biotinylated RNA-pulldown assay. The cell viability and apoptosis were confirmed through CCK-8 and flow cytometry assay.

RESULTS

This study revealed that circRIMS expression was upregulated in MCAO mice model and OGD/RX-simulated cell model. Knockdown circRIMS demonstrated the functional of circRIMS in increasing cell viability, reducing apoptosis, LDH activity and inflammatory factors secretion in OGD/RX-simulated CIR injury in vitro. Additionally, miR-96-5p was identified as a target of circRIMS, while the STAT1 gene is a downstream gene of miR-96-5p, and JAK was also considered to be a downstream gene of the JAK-STAT pathway. Furthermore, inhibition of miR-96-5p or overexpression of STAT1 promoted the progression of CIR injury by elevating apoptosis, reducing cell viability, and increasing the secretion of inflammatory cytokines.

CONCLUSION

CircRIMS contributes to the progression of CIR injury via regulating miR-96-5p/JAK/STAT1 axis.

A new perspective on hippocampal synaptic plasticity and post-stroke depression

Post-stroke depression, a common complication after stroke, severely affects the recovery and quality of life of patients with stroke. Owing to its complex mechanisms, post-stroke depression treatment remains highly challenging. Hippocampal synaptic plasticity is one of the key factors leading to post-stroke depression; however, the precise molecular mechanisms remain unclear. Numerous studies have found that neurotrophic factors, protein kinases and neurotransmitters influence depressive behaviour by modulating hippocampal synaptic plasticity. This review further elaborates on the role of hippocampal synaptic plasticity in post-stroke depression by summarizing recent research and analysing possible molecular mechanisms. Evidence for the correlation between hippocampal mechanisms and post-stroke depression helps to better understand the pathological process of post-stroke depression and improve its treatment.

Connexin 43 Promotes Neurogenesis via Regulating Aquaporin-4 after Cerebral Ischemia

We aimed to test the effects of connexin43 (Cx43) on ischemic neurogenesis and examined whether it was dependent on aquaporin-4 (AQP4). We detected the expression of Cx43 and AQP4 in the ipsilateral subventricular zone (SVZ) and peri-infarct cortex after middle cerebral artery occlusion (MCAO). Also, we examined neurogenesis in the above regions via co-labeling of 5-bromo-2-deoxyuridine (BrdU)/neuronal nuclear antigen (NeuN) and BrdU/doublecortin (DCX). The effects of Cx43 and AQP4 were investigated by using two transgenic animals: heterozygous Cx43 (Cx43±) mice and AQP4 knockout (AQP4-/-) mice, and connexin mimetic peptide (CMP), a selective Cx43 blocker. We demonstrated AQP4 and Cx43 were co-expressed in the astrocytes after MCAO and the expression was highly increased in ipsilateral SVZ and peri-infarct cortex. Cx43± mice had larger infarction volumes and worse neurological function. Both BrdU/NeuN and BrdU/DCX co-labeled cells in the two regions were reduced in Cx43± and AQP4-/- mice compared to wild-type (WT) mice, suggesting Cx43 and AQP4 participated in neurogenesis of neural stem cells. Moreover, CMP decreased AQP4 expression and inhibited neurogenesis in WT mice, while the latter failed to be observed in AQP4-/- mice. Besides, higher levels of IL-1β and TNF-α were detected in the SVZ and peri-infarct cortex of AQP4-/- and Cx43± mice than those in WT mice. In conclusion, our data suggest that Cx43 elicits neuroprotective effects after cerebral ischemia through promoting neurogenesis in the SVZ to regenerate the injured neurons, which is AQP4 dependent and associated with down-regulation of inflammatory cytokines IL-1β and TNF-α.

Tetramethylpyrazine promotes stroke recovery by inducing the restoration of neurovascular unit and transformation of A1/A2 reactive astrocytes

2,3,5,6-Tetramethylpyrazine (TMP) as an active ingredient extracted from a traditional Chinese herbal medicine Ligusticum chuanxiong Hort. has been proved to penetrate blood-brain barrier (BBB) and show neuroprotective effects on cerebral ischemia. However, whether TMP could regulate astrocytic reactivity to facilitate neurovascular restoration in the subacute ischemic stroke needs to be urgently verified. In this research, permanent occlusion of the middle cerebral artery (MCAO) model was conducted and TMP (10, 20, 40 mg/kg) was intraperitoneally administrated to rats once daily for 2 weeks. Neurological function was evaluated by motor deficit score (MDS). Magnetic resonance imaging (MRI) was implemented to analyze tissue injury and cerebral blood flow (CBF). Magnetic resonance angiography (MRA) was applied to exhibit vascular signals. Transmission electron microscopy (TEM) was performed to detect the neurovascular unit (NVU) ultrastructure. Haematoxylin and eosin (HE) staining was utilized to evaluate cerebral histopathological lesions. The neurogenesis, angiogenesis, A1/A2 reactivity, aquaporin 4 (AQP4) and connexin 43 (Cx43) of astrocytes were observed with immunofluorescent staining. Then FGF2/PI3K/AKT signals were measured by western blot. Findings revealed TMP ameliorated neurological functional recovery, preserved NVU integrity, and enhanced endogenous neurogenesis and angiogenesis of rats with subacute ischemia. Shifting A1 to A2 reactivity, suppressing excessive AQP4 and Cx43 expression of astrocytes, and activating FGF2/PI3K/AKT pathway might be potential mechanisms of promoting neurovascular restoration with TMP after ischemic stroke.

Upregulation of retinal VEGF and connexin 43 in murine nonarteritic anterior ischemic optic neuropathy induced with 577 nm laser

Nonarteritic anterior ischemic optic neuropathy (NAION) is a common acute optic neuropathy and cause of irreversible vision loss in those older than 50 years of age. There is currently no effective treatment for NAION and the biological mechanisms leading to neuronal loss are not fully understood. Promising novel targets include glial cells activation and intercellular communication mediated by molecules such as gap junction protein Connexin 43 (Cx43), which modulate neuronal fate in central nervous system disorders. In this study, we investigated retinal glial changes and neuronal loss following a novel NAION animal model using a 577 nm yellow laser. We induced unilateral photochemical thrombosis using rose bengal at the optic nerve head vasculature in adult C57BL/6 mice using a 577 nm laser and performed morphometric analysis of the retinal structure using serial in vivo optical coherence tomography (OCT) and histology for glial and neuronal markers. One day after experimental NAION, in acute phase, OCT imaging revealed peripapillary thickening of the retinal ganglion cell complex (GCC, baseline: 79.5 ± 1.0 μm, n = 8; NAION: 93.0 ± 2.5 μm, n = 8, P < 0.01) and total retina (baseline: 202.9 ± 2.4 μm, n = 8; NAION: 228.1 ± 6.8 μm, n = 8, P < 0.01). Twenty-one days after ischemia, at a chronic phase, there was significant GCC thinning (baseline 78.3 ± 2.1 μm, n = 6; NAION: 72.2 ± 1.9 μm, n = 5, P < 0.05), mimicking human disease. Examination of molecular changes in the retina one day after ischemia revealed that NAION induced a significant increase in retinal VEGF levels (control: 2319 ± 195, n = 5; NAION: 4549 ± 683 gray mean value, n = 5, P < 0.05), which highly correlated with retinal thickness (r = 0.89, P < 0.05). NAION also led to significant increase in mRNA level for Cx43 (Gj1a) at day 1 (control: 1.291 ± 0.38; NAION: 3.360 ± 0.58 puncta/mm2, n = 5, P < 0.05), but not of glial fibrillary acidic protein (Gfap) at the same time (control: 2,800 ± 0.59; NAION: 4,690 ± 0.90 puncta/mm2 n = 5, P = 0.19). Retinal ganglion cell loss at day 21 was confirmed by a 30% decrease in Brn3a+ cells (control: 2,844 ± 235; NAION: 2,001 ± 264 cells/mm2, n = 4, P < 0.05). We described a novel protocol of NAION induction by photochemical thrombosis using a 577 nm laser, leading to retinal edema and VEGF increase at day 1 and RGCs loss at day 21 after injury, consistent with the pathophysiology of human NAION. Early changes in glial cells intercommunication revealed by increased Cx43+ gap junctions are consistent with a retinal glial role in mediating cell-to-cell signaling after an ischemic insult. Our study demonstrates an early glial response in a novel NAION animal model and reveals glial intercommunication molecules such as Cx43 as a promising therapeutic target in acute NAION.

Unravelling Contributions of Astrocytic Connexin 43 to the Functional Activity of Brain Neuron-Glial Networks under Hypoxic State In Vitro

Brain hypoxia remains an Achilles' heel for public health that must be urgently addressed. Hypoxic damage affects both neurons and glial cells, particularly astrocytes, which are in close dynamic bi-directional communication, and are organized in plastic and tightly regulated networks. However, astroglial networks have received limited attention regarding their influence on the adaptive functional rearrangements of neural networks to oxygen deficiency. Herein, against the background of astrocytic Cx43 gap junction blockade by the selective blocker Gap19, we evaluated the features of spontaneous calcium activity and network characteristics of cells in primary cultures of the cerebral cortex, as well as the expression levels of metabotropic glutamate receptors 2 (mGluR2) and 5 (mGluR5) in the early and late periods after simulated hypoxia in vitro. We showed that, under normoxic conditions, blockade of Cx43 leads to an increase in the expression of metabotropic glutamate receptors mGluR2 and mGluR5 and long-term modulation of spontaneous calcium activity in primary cortical cultures, primarily expressed in the restructuring of the functional architectonics of neuron-glial networks through reducing the level of correlation between cells in the network and the percentage of existing correlated connections between cells. Blocking Cx43 during hypoxic injury has a pronounced neuroprotective effect. Together with the increased expression of mGluR5 receptors, a decrease in mGluR2 expression to the physiological level was found, which suggests the triggering of alternative molecular mechanisms of cell adaptation to hypoxia. Importantly, the blockade of Cx43 in hypoxic damage contributed to the maintenance of both the main parameters of the spontaneous calcium activity of primary cortical cultures and the functional architectonics of neuron-glial networks while maintaining the profile of calcium oscillations and calcium signal communications between cells at a highly correlated level. Our results demonstrate the crucial importance of astrocytic networks in functional brain adaptation to hypoxic damage and could be a promising target for the development of rational anti-hypoxic therapy.

GJA1/CX43 High Expression Levels in the Cervical Spinal Cord of ALS Patients Correlate to Microglia-Mediated Neuroinflammatory Profile

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting motoneurons (MNs) with a fatal outcome. The typical degeneration of cortico-spinal, spinal, and bulbar MNs, observed in post-mortem biopsies, is associated with the activation of neuroimmune cells. GJA1, a member of the connexins (Cxs) gene family, encodes for connexin 43 (Cx43), a core gap junctions (GJs)- and hemichannels (HCs)-forming protein, involved in cell death, proliferation, and differentiation. Recently, Cx43 expression was found to play a role in ALS pathogenesis. Here, we used microarray and RNA-seq datasets from the NCBI of the spinal cord of control (NDC) and ALS patients, which were stratified according to the GJA1 gene expression. Genes that positively or negatively correlated to GJA1 expression were used to perform a genomic deconvolution analysis (GDA) using neuroimmune signatures. Expression analysis revealed a significantly higher GJA1 expression in the MNs of ALS patients as compared to NDC. Gene deconvolution analysis revealed that positively correlated genes were associated with microglia activation, whereas negatively correlated genes were associated with neuronal activation profiles. Moreover, gene ontology analysis, performed on genes characterizing either microglia or neuronal signature, indicated immune activation or neurogenesis as main biological processes. Finally, using a synthetic analysis of drugs able to revert the GJA1 transcriptomic signatures, we found a specific drug profile for ALS patients with high GJA1 expression levels, composed of amlodipine, sertraline, and prednisolone. In conclusion, our exploratory study suggests GJA1 as a new neuro-immunological gene correlated to microglial cellular profile in the spinal cord of ALS patients. Further studies are warranted to confirm these results and to evaluate the therapeutic potential of drugs able to revert typical GJA1/CX43 signature in ALS patients

Connexins Signatures of the Neurovascular Unit and Their Physio-Pathological Functions

Central nervous system (CNS) homeostasis is closely linked to the delicate balance of the microenvironment in which different cellular components of the neurovascular unit (NVU) coexist. Intercellular communication plays a pivotal role in exchanges of signaling molecules and mediators essential for survival functions, as well as in the removal of disturbing elements that can lead to related pathologies. The specific signatures of connexins (Cxs), proteins which form either gap junctions (GJs) or hemichannels (HCs), represent the biological substrate of the pathophysiological balance. Connexin 43 (Cx43) is undoubtedly one of the most important factors in glia–neuro–vascular crosstalk. Herein, Cxs signatures of every NVU component are highlighted and their critical influence on functional processes in healthy and pathological conditions of nervous microenvironment is reviewed.

Connexins, Pannexins and Gap Junctions in Perinatal Brain Injury

Perinatal brain injury secondary to hypoxia-ischemia and/or infection/inflammation remains a major cause of disability. Therapeutic hypothermia significantly improves outcomes, but in randomized controlled trials nearly half of infants still died or survived with disability, showing that additional interventions are needed. There is growing evidence that brain injury spreads over time from injured to previously uninjured regions of the brain. At least in part, this spread is related to opening of connexin hemichannels and pannexin channels, both of which are large conductance membrane channels found in many brain cells. Opening of these membrane channels releases adenosine triphosphate (ATP), and other neuroactive molecules, into the extracellular space. ATP has an important role in normal signaling, but pathologically can trigger the assembly of the multi-protein inflammasome complex. The inflammasome complex promotes activation of inflammatory caspases, and release of inflammatory cytokines. Overall, the connexin hemichannel appears to play a primary role in propagation of injury and chronic disease, and connexin hemichannel blockade has been shown to be neuroprotective in multiple animal models. Thus, there is potential for some blockers of connexin or pannexin channels to be developed into targeted interventions that could be used in conjunction with or separate to therapeutic hypothermia.

Long non-coding RNA lincRNA-erythroid prosurvival (EPS) alleviates cerebral ischemia/reperfusion injury by maintaining high-temperature requirement protein A1 (Htra1) stability through recruiting heterogeneous nuclear ribonucleoprotein L (HNRNPL)

This study aimed at investigating the role and mechanism of lincRNA-EPS (erythroid prosurvival) in cerebral ischemia/reperfusion (CIR) injury. The results showed that the overexpression of lincRNA-EPS was able to reduce the levels of interleukin-6, tumor necrosis factor-alpha and interleukin-1β stimulated in the OGD-treated Neuro-2a (N-2a) cells. The levels of reactive oxygen species and malondialdehyde were enhanced while the superoxide dismutase levels were reduced by oxygen and glucose deprivation (OGD) treatment, in which the lincRNA-EPS overexpression could reverse this effect in the cells. LincRNA-EPS interacted with high-temperature requirement protein A1 (Htra1) and heterogeneous nuclear ribonucleoprotein L (HNRNPL), and their depletion inhibited the Htra1 mRNA stability in N-2a cells. HNRNPL knockdown blocked lincRNA-EPS overexpression-induced Htra1 expression in the cells. The depletion of Htra1 could rescue lincRNA-EPS overexpression-mediated N-2a cell injury, inflammation, and oxidative stress induced by OGD. Functionally, lincRNA-EPS alleviates CIR injury of the middle cerebral artery occlusion/reperfusion mice in vivo. In conclusion, lincRNA-EPS attenuates CIR injury by maintaining Htra1 stability through recruiting HNRNPL.

Gomisin J attenuates cerebral ischemia/reperfusion injury by inducing anti-apoptotic, anti-inflammatory, and antioxidant effects in rats

Ischemic stroke is one of the leading causes of morbidity and mortality in humans. Cerebral ischemia-reperfusion (CIR) injury serves as a leading cause of stroke. Schisandra chinensis is a well-known Chinese traditional medicine. In this study, we explored the role of Gomisin J (GJ), a compound of S. chinensis, in CIR using a middle cerebral artery occlusion/reperfusion rat model and the possible mechanisms. We identified that GJ reduced neurological scores, cerebral infarction, and water content in the I/R rat brain. Importantly, GJ rescued I/R treatment-reduced neuron survival in the hippocampus, inhibited apoptosis of ischemic tissues in I/R rats, increased B-cell lymphoma-extra-large (Bcl-XL) expression, and reduced the levels of cleaved caspase-3, Bax, cyclooxygenase-2, nuclear factor kappa-B, and nitric oxide in I/R rat brain tissues. Furthermore, GJ treatment enhanced nuclear factor E2 related factor 2 (Nrf2) translocation, heme oxygenase-1 (HO-1) expression, superoxide dismutase and glutathione peroxidase activities, and glutathione level. Overall, GJ treatment GJ attenuates CIR injury by inducing anti-apoptotic, antioxidant, and anti-inflammatory effects in vivo.

The Role of Connexin Hemichannels in Inflammatory Diseases

The connexin protein family consists of approximately 20 members, and is well recognized as the structural unit of the gap junction channels that perforate the plasma membranes of coupled cells and, thereby, mediate intercellular communication. Gap junctions are assembled by two preexisting hemichannels on the membranes of apposing cells. Non-junctional connexin hemichannels (CxHC) provide a conduit between the cell interior and the extracellular milieu, and are believed to be in a protectively closed state under physiological conditions. The development and characterization of the peptide mimetics of the amino acid sequences of connexins have resulted in the development of a panel of blockers with a higher selectivity for CxHC, which have become important tools for defining the role of CxHC in various biological processes. It is increasingly clear that CxHC can be induced to open by pathogen-associated molecular patterns. The opening of CxHC facilitates the release of damage-associated molecular patterns, a class of endogenous molecules that are critical for the pathogenesis of inflammatory diseases. The blockade of CxHC leads to attenuated inflammation, reduced tissue injury and improved organ function in human and animal models of about thirty inflammatory diseases and disorders. These findings demonstrate that CxHC may contribute to the intensification of inflammation, and serve as a common target in the treatments of various inflammatory diseases. In this review, we provide an update on the progress in the understanding of CxHC, with a focus on the role of these channels in inflammatory diseases.

Connexin 43: A Target for the Treatment of Inflammation in Secondary Complications of the Kidney and Eye in Diabetes

Of increasing prevalence, diabetes is characterised by elevated blood glucose and chronic inflammation that precedes the onset of multiple secondary complications, including those of the kidney and the eye. As the leading cause of end stage renal disease and blindness in the working population, more than ever is there a demand to develop clinical interventions which can both delay and prevent disease progression. Connexins are membrane bound proteins that can form pores (hemichannels) in the cell membrane. Gated by cellular stress and injury, they open under pathophysiological conditions and in doing so release 'danger signals' including adenosine triphosphate into the extracellular environment. Linked to sterile inflammation via activation of the nod-like receptor protein 3 inflammasome, targeting aberrant hemichannel activity and the release of these danger signals has met with favourable outcomes in multiple models of disease, including secondary complications of diabetes. In this review, we provide a comprehensive update on those studies which document a role for aberrant connexin hemichannel activity in the pathogenesis of both diabetic eye and kidney disease, ahead of evaluating the efficacy of blocking connexin-43 specific hemichannels in these target tissues on tissue health and function.

Gap Junctional Coupling Between Retinal Astrocytes Exacerbates Neuronal Damage in Ischemia-Reperfusion Injury

Purpose

Retinal astrocytes abundantly express connexin 43 (Cx43), a transmembrane protein that forms gap junction (GJ) channels and unopposed hemichannels. While it is well established that Cx43 is upregulated in retinal injuries, it is unclear whether astrocytic Cx43 plays a role in retinal ganglion cell (RGC) loss associated with injury. Here, we investigated the effect of astrocyte-specific deletion of Cx43 (Cx43KO) and channel inhibitors on RGC loss in retinal ischemia/reperfusion (I/R) injury and assessed changes in expression and GJ channel and hemichannel function that occur in I/R injury. The effect of Cx43 deletion on neural function in the uninjured retina was also assessed.

Methods

Cx43 expression, astrocyte density and morphology, and RGC death in wild-type and Cx43KO mice after I/R injury were determined using immunohistochemistry and Western blotting. Visual function was assessed using ERG recordings. GJ coupling and hemichannel activity were evaluated using tracer coupling and uptake studies, respectively.

Results

Loss of RGCs in I/R injury was accompanied by an increase of Cx43 expression in astrocytes. Functional studies indicated that I/R injury augmented astrocytic GJ coupling but not Cx43 hemichannel activity. Importantly, deletion of astrocytic Cx43 improved neuronal survival in acute ischemia but did not affect RGC function in the absence of injury. In support, pharmacologic inhibition of GJ coupling provided neuroprotection in I/R injury.

Conclusions

The increase in Cx43 expression and GJ coupling during acute I/R injury exacerbates RGC loss. Inhibition of astrocytic Cx43 channels might represent a useful strategy to promote RGC survival in pathologic conditions.

Astroglial Hemichannels and Pannexons: The Hidden Link between Maternal Inflammation and Neurological Disorders

Maternal inflammation during pregnancy causes later-in-life alterations of the offspring’s brain structure and function. These abnormalities increase the risk of developing several psychiatric and neurological disorders, including schizophrenia, intellectual disability, bipolar disorder, autism spectrum disorder, microcephaly, and cerebral palsy. Here, we discuss how astrocytes might contribute to postnatal brain dysfunction following maternal inflammation, focusing on the signaling mediated by two families of plasma membrane channels: hemi-channels and pannexons. [Ca²⁺]_i imbalance linked to the opening of astrocytic hemichannels and pannexons could disturb essential functions that sustain astrocytic survival and astrocyte-to-neuron support, including energy and redox homeostasis, uptake of K⁺ and glutamate, and the delivery of neurotrophic factors and energy-rich metabolites. Both phenomena could make neurons more susceptible to the harmful effect of prenatal inflammation and the experience of a second immune challenge during adulthood. On the other hand, maternal inflammation could cause excitotoxicity by producing the release of high amounts of gliotransmitters via astrocytic hemichannels/pannexons, eliciting further neuronal damage. Understanding how hemichannels and pannexons participate in maternal inflammation-induced brain abnormalities could be critical for developing pharmacological therapies against neurological disorders observed in the offspring.

Over-activated hemichannels: A possible therapeutic target for human diseases

In our body, all the cells are constantly sharing chemical and electrical information with other cells. This intercellular communication allows them to respond in a concerted way to changes in the extracellular milieu. Connexins are transmembrane proteins that have the particularity of forming two types of channels; hemichannels and gap junction channels. Under normal conditions, hemichannels allow the controlled release of signaling molecules to the extracellular milieu. However, under certain pathological conditions, over-activated hemichannels can induce and/or exacerbate symptoms. In the last decade, great efforts have been put into developing new tools that can modulate these over-activated hemichannels. Small molecules, antibodies and mimetic peptides have shown a potential for the treatment of human diseases. In this review, we summarize recent findings in the field of hemichannel modulation via specific tools, and how these tools could improve patient outcome in certain pathological conditions.

RNA Localization and Local Translation in Glia in Neurological and Neurodegenerative Diseases: Lessons from Neurons

Cell polarity is crucial for almost every cell in our body to establish distinct structural and functional domains. Polarized cells have an asymmetrical morphology and therefore their proteins need to be asymmetrically distributed to support their function. Subcellular protein distribution is typically achieved by localization peptides within the protein sequence. However, protein delivery to distinct cellular compartments can rely, not only on the transport of the protein itself but also on the transport of the mRNA that is then translated at target sites. This phenomenon is known as local protein synthesis. Local protein synthesis relies on the transport of mRNAs to subcellular domains and their translation to proteins at target sites by the also localized translation machinery. Neurons and glia specially depend upon the accurate subcellular distribution of their proteome to fulfil their polarized functions. In this sense, local protein synthesis has revealed itself as a crucial mechanism that regulates proper protein homeostasis in subcellular compartments. Thus, deregulation of mRNA transport and/or of localized translation can lead to neurological and neurodegenerative diseases. Local translation has been more extensively studied in neurons than in glia. In this review article, we will summarize the state-of-the art research on local protein synthesis in neuronal function and dysfunction, and we will discuss the possibility that local translation in glia and deregulation thereof contributes to neurological and neurodegenerative diseases.

Circular RNA TTC3 regulates cerebral ischemia-reperfusion injury and neural stem cells by miR-372-3p/TLR4 axis in cerebral infarction

Background

Stroke serves as a prevalent cerebrovascular disorder with severe cerebral ischemia/reperfusion (CIR) injury, in which neural stem cells (NSCs) play critical roles in the recovery of cerebral function. Circular RNAs (circRNAs) have been widely found to participate in stroke and NSC modulation. However, the role of circRNA TTC3 (circTTC3) in the regulation of CIR injury and NSCs remains elusive. Here, we aimed to explore the impact of circTTC3 on CIR injury and NSCs.

Methods

The middle cerebral artery occlusion/repression (MCAO/R) model was established in C57BL/6J mice. The primary astrocytes were isolated from the cerebellum from C57BL/6J mice. The primary NSCs were obtained from rat embryos. The effect of circTTC3 on CIR injury and NSCs was analyzed by TTC staining, qPCR, Western blot, LDH colorimetric kits, MTT assays, Annexin V-FITC Apoptosis Detection Kit, luciferase reporter gene assays, and others in the system.

Results

Significantly, the expression of circTTC3 was elevated in the MCAO/R mice and oxygen and glucose deprivation (OGD)-treated astrocytes. The depletion of circTTC3 attenuated cerebral infarction, neurological score, and brain water content. The OGD treatment induced apoptosis and the levels of lactate dehydrogenase (LDH) in the astrocytes, in which circTTC3 depletion reduced this phenotype in the system. Moreover, the depletion of circTTC3 promoted the proliferation and upregulated the nestin and β-tubulin III expression in NSCs. Mechanically, circTTC3 was able to sponge miR-372-3p, and miR-372-3p can target Toll-like receptor 4 (TLR4) in NSCs. The miR-372-3p inhibitor or TLR4 overexpression could reverse circTTC3 depletion-mediated astrocyte OGD injury and NSC regulation.

Conclusion

Thus, we conclude that circTTC3 regulates CIR injury and NSCs by the miR-372-3p/TLR4 axis in cerebral infarction. Our finding presents new insight into the mechanism by which circTTC3 modulates CIR injury and NSC dysfunction. CircTTC3, miR-372-3p, and TLR4 may serve as potential targets for the treatment of CIR injury during stroke.

Knockdown of long non-coding RNA RMRP protects cerebral ischemia-reperfusion injury via the microRNA-613/ATG3 axis and the JAK2/STAT3 pathway

Cerebral ischemia-reperfusion (I/R) injury can induce the mitophagy of neurons in the ischemic brain. Long non-coding RNAs (lncRNAs) play an important role in the pathogenesis of various injuries, especially in cerebral I/R injury. The purpose of this study is to investigate the molecular mechanism of lncRNA RNA component of mitochondrial RNA processing endoribonuclease (RMRP) in cerebral I/R injury. The middle cerebral artery occlusion (MCAO) mouse model was established. Neurological deficit score, pathological structure, infarcted area, neuron number, cell apoptosis, and coagulation ability of MCAO mice were evaluated. The expressions of RMRP, microRNA (miR)-613, and ATG3 in MCAO mice were detected. The binding relationships among miR-613, RMRP, and ATG3 were predicted and verified. Neuro 2A (N2a) cells were treated with oxygen-glucose deprivation/reperfusion (OGD/R) to simulate I/R injury. Cell viability and apoptosis assays were performed. The effects of miR-613, ATG3, and RMRP on I/R injury were verified by functional rescue experiments. JAK2/STAT3 phosphorylation level was detected. We found significantly upregulated RMRP and ATG3, and downregulated miR-613 expressions in MCAO mice. RMRP could escalate ATG3 mRNA expression through miR-613. RMRP knockdown promoted viability and inhibited apoptosis of OGD/R-treated N2a cells, which could be reversed by miR-613 inhibition or ATG3 overexpression. RMRP overexpression inhibited the activation of JAK2/STAT3 signaling pathway. We demonstrated that lncRNA RMRP competitively bound to miR-613, leading to the increase of ATG3 expression and the inhibition the JAK2/STAT3 pathway, thus promoting cerebral I/R injury in mice.

MicroRNA-26b-5p alleviates cerebral ischemia-reperfusion injury in rats via inhibiting the N-myc/PTEN axis by downregulating KLF10 expression

MicroRNAs plays important role in cerebral ischemia-reperfusion (CIR). However, the role of miR-26b-5p in CIR injury remains unclear. PC12 cells were treated with oxygen-glucose deprivation (OGD) for 0 h, 2 h, 4 h, 6 h, and then reoxygenated for 24 h to construct an in vitro I/R model. Then, miR-26b-5p mimic, small interfering RNA of KLF10 and KLF10 overexpression plasmid were transfected into cells respectively for mechanism study. Our results showed that miR-26b-5p was downregulated in OGD/R-induced PC12 cells. After overexpression of miR-26b-5p, cell proliferation ability was enhanced, apoptosis, ROS and inflammatory mediators were inhibited. Bioinformatics analysis indicated that miR-26b-5p was directly bound to the 3' UTR of KLF10, and downregulated the expression of KLF10. KLF10 was upregulated in OGD/R cells, and transfection with si-KLF10 promoted cell proliferation and reduced apoptosis, NO concentration and inflammatory factor secretion. Moreover, pcDNA-KLF10 reversed the inhibitory effects of miR-26b-5p mimic on apoptosis, NO content and inflammatory factor secretion, as well as the downregulation of N-myc and PTEN expression. Meanwhile, I/R rat models were constructed and divided into sham operation group (femoral artery isolation only), model group (middle cerebral artery occlusion model of rats was prepared by thread embolization), treatment group (200 µL of miR-26b-5p mimic was injected into the brain of model rats). We observed that the infarct size of brain tissue was reduced, KLF10 expression was downregulated, and apoptosis and inflammatory response were reduced. These results suggest that miR-26b-5p had protective effects on CIRI and it may be a potential treatment target.

Effect of Quercetin-Loaded Mesoporous Silica Nanoparticles on Myocardial Ischemia-Reperfusion Injury in Rats and Its Mechanism

BACKGROUND

Quercetin has potential value in treating cardiovascular diseases, but it is not suitable for clinical application due to its own water solubility. The limitation of quercetin can be distinctly ameliorated by delivering it with nanocarriers.

OBJECTIVE

To determine the effect of quercetin-loaded mesoporous silica nanoparticles (Q-MSNs) on myocardial ischemia-reperfusion injury in rats and its mechanism.

METHODS

Q-MSNs were synthesized, and the morphology of Q-MSNs and MSNs was characterized by transmission electron microscopy and dynamic light scattering technique, respectively. Healthy rats were enrolled and randomly divided into a sham operation control group, an ischemia-reperfusion (IR) group, an IR+Q group, an IR+Q-MSNs group, and an MSNs group (each n = 10). Rats in the sham operation group were not treated with ischemia reperfusion, but given normal perfusion meantime. Rats in the sham operation control group, IR group, and MSNs group were given normal saline for 10 days before ischemia reperfusion, and rats in the IR+Q group and IR+Q-MSNs group were given drugs by gavage for 10 days before ischemia reperfusion. Primary myocardial cells were sampled from SD neonatal rats to construct hypoxia/reoxygenation myocardial cell models. The myocardial cells were assigned to a control group, IR group, quercetin (Q) group, Q-MSNs group, and MSNs group. Except for the control group, all the other groups were treated with hypoxia/reoxygenation. Cells in the Q group were treated with quercetin (10 μM, 20 μM, 40 μM) for 24 h in advance and then treated with measures to cause hypoxia-reoxygenation injury. Cells in the Q-MSNs group were treated with the same concentration of loaded quercetin and the same method used for the Q group. The myocardial apoptosis, myocardial infarction, ventricular remodeling, hemodynamic indexes, physiological and biochemical indexes, and JAK2/STAT3 pathway expression of each group were detected, and the apoptosis, viability, oxidative stress, and JAK2/STAT3 pathway expression of primary myocardial cells in each group were also detected.

RESULTS

Quercetin significantly activated the JAK2/STAT3 pathway in vivo and in vitro, and MSNs intensified the activation. Compared with quercetin, Q-MSNs were more effective in inhibiting cell apoptosis and oxidative stress, reducing myocardial infarction size, improving ventricular remodeling and cardiac function-related biochemical indexes, and promoting the recovery of cardiac blood flow.

CONCLUSION

Q-MSNs can significantly enhance the activation effect of quercetin on JAK2/STAT3 pathway, thus enhancing its protection on the heart of MIRI rats.

Desflurane protects against liver ischemia/reperfusion injury via regulating miR-135b-5p

BACKGROUND

A number of anesthetics have protective effect against ischemia-reperfusion (I/R) injury, including desflurane. But the function and molecular mechanism of desflurane in liver I/R injury have not been fully understood. The aim of this study was to investigate the effect of desflurane on liver I/R injury and further investigated the molecular mechanisms involving in miR-135b-5p.

METHODS

The models of liver I/R injury in rats were established, and received desflurane treatment throughout the injury. Serum alanine transaminase (ALT) and aspartate transaminase (AST) were measured and compared between groups. H/R-induced cell model in L02 was established, and were treated with desflurane before hypoxia. Quantitative real-time polymerase chain reaction was performed to determine the expression of miR-135b-5p in different groups. The cell apoptosis was detected using flow cytometry assay. Western blot was used for the measurement of protein levels.

RESULTS

I/R significantly increased serum levels of ALT and AST in rats, which were reversed by desflurane treatment. Desflurane also significantly attenuated the increase of cell apoptosis induced by I/R in both vivo and vitro. MiR-135b-5p significantly reversed the protective effect of desflurane against liver I/R injury. Additionally, Janus protein tyrosine kinase (JAK)2 was shown to be a target gene of miR-135b-5p, and miR-135b-5p overexpression significantly decreased the protein levels of p-JAK2, JAK2, p-STAT3.

CONCLUSION

Desflurane attenuated liver I/R injury through regulating miR-135b-5p, and JAK2 was the target gene of mIR-135b-5p. These findings provide references for further development of therapeutic strategies in liver injury.

Astroglial connexins in epileptogenesis

The astroglial network connected through gap junctions assembling from connexins physiologically balances the concentrations of ions and neurotransmitters around neurons. Astrocytic dysfunction has been associated with many neurological disorders including epilepsy. Dissociated gap junctions result in the increased activity of connexin hemichannels which triggers brain pathophysiological changes. Previous studies in patients and animal models of epilepsy indicate that the reduced gap junction coupling from assembled connexin hemichannels in the astrocytes may play an important role in epileptogenesis. This abnormal cell-to-cell communication is now emerging as an important feature of brain pathologies and being considered as a novel therapeutic target for controlling epileptogenesis. In particular, candidate drugs with ability of inhibition of connexin hemichannel activity and enhancement of gap junction formation in astrocytes should be explored to prevent epileptogenesis and control epilepsy.

Neuroprotective potential of imatinib in global ischemia-reperfusion-induced cerebral injury: possible role of Janus-activated kinase 2/signal transducer and activator of transcription 3 and connexin 43

The present study was aimed to explore the neuroprotective role of imatinib in global ischemia-reperfusion-induced cerebral injury along with possible mechanisms. Global ischemia was induced in mice by bilateral carotid artery occlusion for 20 min, which was followed by reperfusion for 24 h by restoring the blood flow to the brain. The extent of cerebral injury was assessed after 24 h of global ischemia by measuring the locomotor activity (actophotometer test), motor coordination (inclined beam walking test), neurological severity score, learning and memory (object recognition test) and cerebral infarction (triphenyl tetrazolium chloride stain). Ischemia-reperfusion injury produced significant cerebral infarction, impaired the behavioral parameters and decreased the expression of connexin 43 and phosphorylated signal transducer and activator of transcription 3 (p-STAT3) in the brain. A single dose administration of imatinib (20 and 40 mg/kg) attenuated ischemia-reperfusion-induced behavioral deficits and the extent of cerebral infarction along with the restoration of connexin 43 and p-STAT3 levels. However, administration of AG490, a selective Janus-activated kinase 2 (JAK2)/STAT3 inhibitor, abolished the neuroprotective actions of imatinib and decreased the expression of connexin 43 and p-STAT3. It is concluded that imatinib has the potential of attenuating global ischemia-reperfusion-induced cerebral injury, which may be possibly attributed to activation of JAK2/STAT3 signaling pathway along with the increase in the expression of connexin 43.

Targeting connexin 43 provides anti-inflammatory effects after intracerebral hemorrhage injury by regulating YAP signaling

Background

In the central nervous system (CNS), connexin 43 (Cx43) is mainly expressed in astrocytes and regulates astrocytic network homeostasis. Similar to Cx43 overexpression, abnormal excessive opening of Cx43 hemichannels (Cx43Hcs) on reactive astrocytes aggravates the inflammatory response and cell death in CNS pathologies. However, the role of excessive Cx43Hc opening in intracerebral hemorrhage (ICH) injury is not clear.

Methods

Hemin stimulation in primary cells and collagenase IV injection in C57BL/6J (B6) mice were used as ICH models in vitro and in vivo. After ICH injury, the Cx43 mimetic peptide Gap19 was used for treatment. Ethidium bromide (EtBr) uptake assays were used to measure the opening of Cx43Hcs. Western blotting and immunofluorescence were used to measure protein expression. qRT-PCR and ELISA were used to determine the levels of cytokines. Coimmunoprecipitation (Co-IP) and the Duolink in situ proximity ligation assay (PLA) were applied to measure the association between proteins.

Results

In this study, Cx43 expression upregulation and excessive Cx43Hc opening was observed in mice after ICH injury. Delayed treatment with Gap19 significantly alleviated hematoma volume and neurological deficits after ICH injury. In addition, Gap19 decreased inflammatory cytokine levels in the tissue surrounding the hematoma and decreased reactive astrogliosis after ICH injury in vitro and in vivo. Intriguingly, Cx43 transcriptional activity and expression in astrocytes were significantly increased after hemin stimulation in culture. However, Gap19 treatment downregulated astrocytic Cx43 expression through the ubiquitin-proteasome pathway without affecting Cx43 transcription. Additionally, our data showed that Gap19 increased Yes-associated protein (YAP) nuclear translocation. This subsequently upregulated SOCS1 and SOCS3 expression and then inhibited the TLR4-NFκB and JAK2-STAT3 pathways in hemin-stimulated astrocytes. Finally, the YAP inhibitor, verteporfin (VP), reversed the anti-inflammatory effect of Gap19 in vitro and almost completely blocked its protective effects in vivo after ICH injury.

Conclusions

This study provides new insight into potential treatment strategies for ICH injury involving astroglial Cx43 and Cx43Hcs. Suppression of abnormal astroglial Cx43 expression and Cx43Hc opening by Gap19 has anti-inflammatory and neuroprotective effects after ICH injury.

Astrocytes in the regulation of cerebrovascular functions

Astrocytes are the most numerous type of neuroglia in the brain and have a predominant influence on the cerebrovascular system; they control perivascular homeostasis, the integrity of the blood-brain barrier, the dialogue with the peripheral immune system, the transfer of metabolites from the blood, and blood vessel contractility in response to neuronal activity. These regulatory processes occur in a specialized interface composed of perivascular astrocyte extensions that almost completely cover the cerebral blood vessels. Scientists have only recently started to study how this interface is formed and how it influences cerebrovascular functions. Here, we review the literature on the astrocytes' role in the regulation of the cerebrovascular system. We cover the anatomy and development of the gliovascular interface, the known gliovascular functions, and molecular factors, the latter's implication in certain pathophysiological situations, and recent cutting-edge experimental tools developed to examine the astrocytes' role at the vascular interface. Finally, we highlight some open questions in this field of research.

Synaptic Plasticity After Focal Cerebral Ischemia Was Attenuated by Gap26 but Enhanced by GAP-134

Objective: Synaptic plasticity is critical for neurorehabilitation after focal cerebral ischemia. Connexin 43 (Cx43), the main component of the gap junction, has been shown to be pivotal for synaptic plasticity. The objective of this study was to investigate the role of the Cx43 inhibitor (Gap26) and gap junction modifier (GAP-134) in neurorehabilitation and to study their contribution to synaptic plasticity after focal ischemia. Methods: Time course expression of both total and phosphorylated Cx43 (p-Cx43) were detected by western blotting at 3, 7, and 14 d after focal ischemia. Gap26 and GAP-134 were administered starting from 3 d post focal ischemia. Neurological performances were evaluated by balance beam walking test and Y-maze test at 1, 3, and 7 d. Golgi staining and transmission electron microscope (TEM) detection were conducted at 7 d for observing dendritic spine numbers and synaptic ultrastructure, respectively. Immunofluorescent staining was used at 7 d for detection of synaptic plasticity markers, including synaptophysin (SYN) and growth-associated protein-43 (GAP-43). Results: Expression levels of both total Cx43 and p-Cx43 were increased after focal cerebral ischemia, peaking at 7 d. Compared with the MCAO group, Gap26 worsened the neurological behavior and decreased the dendritic spine number while GAP-134 improved the neurobehavior and increased the number of dendritic spines. Moreover, Gap26 further destroyed the synaptic structure, concomitant with downregulated SYN and GAP-43, whereas GAP-134 alleviated synaptic destruction and upregulated SYN and GAP-43. Conclusion: These findings suggested that Cx43 or the gap junction was involved in synaptic plasticity, thereby promoting neural recovery after ischemic stroke. Treatments enhancing gap junctions may be potential promising therapeutic measures for neurorehabilitation after ischemic stroke.

Role of the neurovascular unit in the process of cerebral ischemic injury

Cerebral ischemic injury exhibits both high morbidity and mortality worldwide. Traditional research of the pathogenesis of cerebral ischemic injury has focused on separate analyses of the involved cell types. In recent years, the neurovascular unit (NVU) mechanism of cerebral ischemic injury has been proposed in modern medicine. Hence, more effective strategies for the treatment of cerebral ischemic injury may be provided through comprehensive analysis of brain cells and the extracellular matrix. However, recent studies that have investigated the function of the NVU in cerebral ischemic injury have been insufficient. In addition, the metabolism and energy conversion of the NVU depend on interactions among multiple cell types, which make it difficult to identify the unique contribution of each cell type. Therefore, in the present review, we comprehensively summarize the regulatory effects and recovery mechanisms of four major cell types (i.e., astrocytes, microglia, brain-microvascular endothelial cells, and neurons) in the NVU under cerebral ischemic injury, as well as discuss the interactions among these cell types in the NVU. Furthermore, we discuss the common signaling pathways and signaling factors that mediate cerebral ischemic injury in the NVU, which may help to provide a theoretical basis for the comprehensive elucidation of cerebral ischemic injury.

Glial Connexins and Pannexins in the Healthy and Diseased Brain

Over the past several decades a large amount of data have established that glial cells, the main cell population in the brain, dynamically interact with neurons and thus impact their activity and survival. One typical feature of glia is their marked expression of several connexins, the membrane proteins forming intercellular gap junction channels and hemichannels. Pannexins, which have a tetraspan membrane topology as connexins, are also detected in glial cells. Here, we review the evidence that connexin and pannexin channels are actively involved in dynamic and metabolic neuroglial interactions in physiological as well as in pathological situations. These features of neuroglial interactions open the way to identify novel non-neuronal aspects that allow for a better understanding of behavior and information processing performed by neurons. This will also complement the "neurocentric" view by facilitating the development of glia-targeted therapeutic strategies in brain disease.

Connexin43 Hemichannel Targeting With TAT-Gap19 Alleviates Radiation-Induced Endothelial Cell Damage

BACKGROUND

Emerging evidence indicates an excess risk of late occurring cardiovascular diseases, especially atherosclerosis, after thoracic cancer radiotherapy. Ionizing radiation (IR) induces cellular effects which may induce endothelial cell dysfunction, an early marker for atherosclerosis. In addition, intercellular communication through channels composed of transmembrane connexin proteins (Cxs), i.e. Gap junctions (direct cell-cell coupling) and hemichannels (paracrine release/uptake pathway) can modulate radiation-induced responses and therefore the atherosclerotic process. However, the role of endothelial hemichannel in IR-induced atherosclerosis has never been described before.

MATERIALS AND METHODS

Telomerase-immortalized human Coronary Artery/Microvascular Endothelial cells (TICAE/TIME) were exposed to X-rays (0.1 and 5 Gy). Production of reactive oxygen species (ROS), DNA damage, cell death, inflammatory responses, and senescence were assessed with or without applying a Cx43 hemichannel blocker (TAT-Gap19).

RESULTS

We report here that IR induces an increase in oxidative stress, cell death, inflammatory responses (IL-8, IL-1β, VCAM-1, MCP-1, and Endothelin-1) and premature cellular senescence in TICAE and TIME cells. These effects are significantly reduced in the presence of the Cx43 hemichannel-targeting peptide TAT-Gap19.

CONCLUSION

Our findings suggest that endothelial Cx43 hemichannels contribute to various IR-induced processes, such as ROS, cell death, inflammation, and senescence, resulting in an increase in endothelial cell damage, which could be protected by blocking these hemichannels. Thus, targeting Cx43 hemichannels may potentially exert radioprotective effects.

Danegaptide Enhances Astrocyte Gap Junctional Coupling and Reduces Ischemic Reperfusion Brain Injury in Mice

Ischemic stroke is a complex and devastating event characterized by cell death resulting from a transient or permanent arterial occlusion. Astrocytic connexin43 (Cx43) gap junction (GJ) proteins have been reported to impact neuronal survival in ischemic conditions. Consequently, Cx43 could be a potential target for therapeutic approaches to stroke. We examined the effect of danegaptide (ZP1609), an antiarrhythmic dipeptide that specifically enhances GJ conductance, in two different rodent stroke models. In this study, danegaptide increased astrocytic Cx43 coupling with no significant effects on Cx43 hemichannel activity, in vitro. Using matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI IMS) the presence of danegaptide within brain tissue sections were detected one hour after reperfusion indicating successful transport of the dipeptide across the blood brain barrier. Furthermore, administration of danegaptide in a novel mouse brain ischemia/reperfusion model showed significant decrease in infarct volume. Taken together, this study provides evidence for the therapeutic potential of danegaptide in ischemia/reperfusion stroke.

Azithromycin Affords Neuroprotection in Rat Undergone Transient Focal Cerebral Ischemia

Repurposing existing drugs represents a promising approach for successful development of acute stroke therapies. In this context, the macrolide antibiotic azithromycin has been shown to exert neuroprotection in mice due to its immunomodulatory properties. Here, we have demonstrated that acute administration of a single dose of azithromycin upon reperfusion produces a dose-dependent (ED₅₀ = 1.40 mg/kg; 95% CI = 0.48-4.03) reduction of ischemic brain damage measured 22 h after transient (2 h) middle cerebral artery occlusion (MCAo) in adult male rats. Neuroprotection by azithromycin (150 mg/kg, i.p., upon reperfusion) was associated with a significant elevation of signal transducer and activator of transcription 3 (STAT3) phosphorylation in astrocytes and neurons of the peri-ischemic motor cortex as detected after 2 and 22 h of reperfusion. By contrast, in the core region of the striatum, drug administration resulted in a dramatic elevation of STAT3 phosphorylation only after 22 h of reperfusion, being the signal mainly ascribed to infiltrating leukocytes displaying an M2 phenotype. These early molecular events were associated with a long-lasting neuroprotection, since a single dose of azithromycin reduced brain infarct damage and neurological deficit measured up to 7 days of reperfusion. These data, together with the evidence that azithromycin was effective in a clinically relevant time-window (i.e., when administered after 4.5 h of MCAo), provide robust preclinical evidence to support the importance of developing azithromycin as an effective acute therapy for ischemic stroke.

Beneficial and Detrimental Remodeling of Glial Connexin and Pannexin Functions in Rodent Models of Nervous System Diseases

A variety of glial cell functions are supported by connexin and pannexin proteins. These functions include the modulation of synaptic gain, the control of excitability through regulation of the ion and neurotransmitter composition of the extracellular milieu and the promotion of neuronal survival. Connexins and pannexins support these functions through diverse molecular mechanisms, including channel and non-channel functions. The former comprise the formation of gap junction-mediated networks supported by connexin intercellular channels and the formation of pore-like membrane structures or hemichannels formed by both connexins and pannexins. Non-channel functions involve adhesion properties and the participation in signaling intracellular cascades. Pathological conditions of the nervous system such as ischemia, neurodegeneration, pathogen infection, trauma and tumors are characterized by distinctive remodeling of connexin expression and function. However, whether these changes can be interpreted as part of the pathogenesis, or as beneficial compensatory effects, remains under debate. Here we review the available evidence addressing this matter with a special emphasis in mouse models with selective manipulation of glial connexin and pannexin proteins in vivo. We postulate that the beneficial vs. detrimental effects of glial connexin remodeling in pathological conditions depend on the impact of remodeling on the different connexin and pannexin channel and non-channel functions, on the characteristics of the inflammatory environment and on the type of interaction among glial cells types.

The Opening of Connexin 43 Hemichannels Alters Hippocampal Astrocyte Function and Neuronal Survival in Prenatally LPS-Exposed Adult Offspring

Clinical evidence has revealed that children born from mothers exposed to viral and bacterial pathogens during pregnancy are more likely to suffer various neurological disorders including schizophrenia, autism bipolar disorder, major depression, epilepsy, and cerebral palsy. Despite that most research has centered on the impact of prenatal inflammation in neurons and microglia, the potential modifications of astrocytes and neuron-astrocyte communication have received less scrutiny. Here, we evaluated whether prenatally LPS-exposed offspring display alterations in the opening of astrocyte hemichannels and pannexons in the hippocampus, together with changes in neuroinflammation, intracellular Ca²⁺ and nitric oxide (NO) signaling, gliotransmitter release, cell arborization, and neuronal survival. Ethidium uptake recordings revealed that prenatal LPS exposure enhances the opening of astrocyte Cx43 hemichannels and Panx1 channels in the hippocampus of adult offspring mice. This enhanced channel activity occurred by a mechanism involving a microglia-dependent production of IL-1β/TNF-α and the stimulation of p38 MAP kinase/iNOS/[Ca²⁺]_i-mediated signaling and purinergic/glutamatergic pathways. Noteworthy, the activity of Cx43 hemichannels affected the release of glutamate, [Ca²⁺]_i handling, and morphology of astrocytes, whereas also disturbed neuronal function, including the dendritic arbor and spine density, as well as survival. We speculate that excitotoxic levels of glutamate triggered by the activation of Cx43 hemichannels may contribute to hippocampal neurotoxicity and damage in prenatally LPS-exposed offspring. Therefore, the understanding of how astrocyte-neuron crosstalk is an auspicious avenue toward the development of broad treatments for several neurological disorders observed in children born to women who had a severe infection during gestation.

How does Helicobacter pylori cause gastric cancer through connexins: An opinion review

Helicobacter pylori (H. pylori) is a Gram-negative bacterium with a number of virulence factors, such as cytotoxin-associated gene A, vacuolating cytotoxin A, its pathogenicity island, and lipopolysaccharide, which cause gastrointestinal diseases. Connexins function in gap junctional homeostasis, and their downregulation is closely related to gastric carcinogenesis. Investigations into H. pylori infection and the fine-tuning of connexins in cells or tissues have been reported in previous studies. Therefore, in this review, the potential mechanisms of H. pylori-induced gastric cancer through connexins are summarized in detail.

Kappa opioid receptor agonists improve postoperative cognitive dysfunction in rats via the JAK2/STAT3 signaling pathway

Postoperative cognitive dysfunction (POCD) is a common and well‑known complication following surgery, particularly cardiopulmonary bypass (CPB) surgery. There are currently no suitable treatments for POCD, which is associated with increased illness and mortality rates. The present study aimed to identify a novel treatment for POCD. The protective effect of kappa opioid receptor (KOR) agonists on POCD in rats following CPB was determined and the regulatory mechanism of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway was examined. The rats were randomly divided into five groups: Sham operation (Sham group), CPB operation (CPB group), KOR agonist + CPB (K group), KOR agonist + norbinaltorphimine (nor‑BNI) + CPB (NK group), and KOR agonist + JAK2‑STAT3 specific pathway inhibitor + CPB (AG group). A water maze test and neurological function scores were used to evaluate POCD. Hematoxylin and eosin staining was used to observe hippocampal neurons. ELISA was used to detect the levels of inflammatory factors, oxidative stress factors and brain injury markers. Immunofluorescence was used to visualize the neurons. TUNEL staining and western blotting were used to detect neuronal apoptosis, and western blotting was also used to detect JAK2/STAT3 pathway‑related proteins. The KOR agonists significantly improved POCD. S‑100β and NSE detection revealed that KOR agonists alleviated brain damage in CPB rats, and this result was reversed by KOR antagonists. The KOR agonists led to a significantly reduced inflammatory response and oxidative stress, as determined by ELISA detection, and attenuated hippocampal neuronal apoptosis, as revealed by TUNEL staining and western blotting, compared with the results in the CPB group. Finally, the KOR agonists inhibited the expression levels of phosphorylated (p‑)JAK2 and p‑STAT3, rather than total JAK2 and STAT3, compared with levels in the CPB group. Taken together, KOR agonists improved POCD in rats with CPB by inhibiting the JAK2/STAT3 signaling pathway.

Echinocystic acid, a natural plant extract, alleviates cerebral ischemia/reperfusion injury via inhibiting the JNK signaling pathway

Echinocystic acid (EA) was found to possess antiviral, anti-inflammatory and antioxidation activities. A recent study showed the antiapoptotic effects of EA on acute myocardial infarction. In this study, we demonstrated the potential neuroprotective effects of EA on cerebral ischemia/reperfusion (I/R) injury in mice. Intraperitoneal injection of EA 1 h before ischemia significantly reduced the cerebral infarct volume and neurological deficit after 60 min of ischemia and 24 h of reperfusion. The neuroprotective effects of EA occurred in a dose-dependent manner. Then, we explored the mechanisms of neuroprotection by EA. This compound exerted antiapoptotic activity by upregulating the level of Bcl-2 and simultaneously downregulating the levels of cleaved caspase-3 and Bax. Furthermore, EA also possessed anti-inflammatory activity and prevented the excessive phosphorylation of NF-κB (p-P65) and the increase in IL-1β and IL-6 levels. Finally, our data indicated that EA treatment decreased the level of phosphorylated JNK in vivo, and the JNK activator anisomycin (AN) reversed the neuroprotective effects of EA, indicating that the JNK pathway is involved in the antiapoptotic and anti-inflammatory mechanisms of EA. In summary, our findings suggest that EA provides neuroprotective effects through its antiapoptotic and anti-inflammatory activities by inhibiting the JNK signaling pathway in cerebral I/R injury. Due to its safety and lack of toxicity, EA is a potential candidate for the treatment of ischemic stroke in future clinical trials.