Chronic Stress and Gonadectomy Affect the Expression of Cx37, Cx40 and Cx43 in the Spinal Cord

The study aimed to determine whether the exposure to chronic stress and/or performance of gonadectomy might lead to disturbance in the expression of connexin (Cx) 37, 40 and 43 in the spinal cord (SC), as a potential explanation for sex differences in stress-related chronic pain conditions. After the rats were sham-operated or gonadectomized, three 10-day sessions of sham or chronic stress were applied. Immunohistochemistry and transmission electron microscopy (TEM) were used to examine Cx localization and expression in the SC. The gonadectomy resulted in an increase of Cx37 expression in the dorsal horn (DH) of the female rats, but chronic stress suppressed the effects of castration. In male rats, only the combined effects of castration and chronic stress increased Cx37 expression. The influence of chronic stress on the DH Cx40 expression was inversely evident after the castration: increased in the ovariectomized female rats, while decreased in the orchidectomized male rats. We did not find any effect of chronic stress and castration, alone or together, on Cx43 expression in the DH, but the percentage of Cx43 overlapping the astrocyte marker glial fibrillary acidic protein (gfap) increased in the male stressed group after the castration. In conclusion, the association of the chronic stress with sex hormone depletion results in disturbances of the SC Cx expression and might be a possible mechanism of disturbed pain perception after chronic stress exposure.

Modulation of Vascular Smooth Muscle Cell Multiplication, Apoptosis, and Inflammatory Damage by miR-21 in Coronary Heart Disease

This study is aimed at exploring the role and potential molecular mechanism of microRNA-21 (miR-21) in coronary heart disease (CHD). RT-qPCR analysis was conducted to detect the expression of miR-21, Sprouty 1 (SPRY1), and connexin 43 (CX43). The protein expression of SPRY1 and CX43 was measured by western blot. ELISA was performed for measuring inflammatory factors, including intercellular adhesion molecule-1 (ICAM-1) and interleukin-1 beta (IL-1β). The target relationship between miR-21 and SPRY1 was determined by dual-luciferase reporter assay. Cell multiplication and apoptosis were detected using CCK-8 assay and flow cytometry analysis, respectively. Our results indicated that miR-21, CX43, and the level of inflammatory cytokines including ICAM-1 and IL-1β were upregulated, while SPRY1 was downregulated in blood samples from CHD patients compared with the controls. Besides, miR-21 directly targeted SRPY-1. miR-21 could suppress SPRY1 expression and enhance CX43 expression in VSMCs. Moreover, miR-21 accelerated cell multiplication and attenuated cell apoptosis in VSMCs. Collectively, these findings suggested that miR-21 could effectively elevate VSMC multiplication and repress apoptosis by targeting SPRY1 in CHD, providing a potential target for therapeutic strategy of CHD.

Molecular Indicators of Biomaterials Osteoinductivity - Cell Migration, BMP Production and Signalling Turns a Key

In this work we dissected the osteoinductive properties of selected, PLGA-based scaffolds enriched with gel-derived bioactive glasses (SBGs) of either binary SiO2-CaO or ternary SiO2-CaO-P2O5 system, differing in CaO/SiO2 ratio (i.e. high -or low-calcium SBGs). To assess the inherent ability of the scaffolds to induce osteogenesis of human bone marrow stromal cells (BMSC), the study was designed to avoid any osteogenic stimuli beyond the putative osteogenic SBG component of the studied scaffolds. The bioactivity and porosity of scaffolds were confirmed by SBF test and porosimetry. Condition media (CM) from BMSC-loaded scaffolds exhibited increased Ca and decreased P content corresponding to SBGs CaO/SiO2 ratio, whereas Si content was relatively stable and overall lower in CM from scaffolds containing binary SBGs. CM from cell-loaded scaffolds containing high-calcium, binary SBGs promoted migration of BMSC and BMP-response in reporter osteoblast cell line. BMSC culture on these scaffolds or the ones containing ternary, low-calcium SBGs resulted in the activation of BMP-related signaling and expression of several osteogenic markers. Ectopic bone formation was induced by scaffolds containing binary SBGs, but high-calcium ones produced significantly more osteoid. Scaffolds containing ternary SBGs negatively influenced the expression of osteogenic transcription factors and Cx43, involved in cell-cell interactions. High-calcium scaffolds stimulated overall higher Cx43 expression. We believe the initial cell-cell communication may be crucial to induce and maintain osteogenesis and high BMP signaling on the studied scaffolds. The presented scaffolds’ biological properties may also constitute new helpful markers to predict osteoinductive potential of other bioactive implant materials. Graphical Abstract

Advances of Traditional Chinese Medicine Regulating Connexin43 in the Prevention and Treatment of Myocardial Infarction

Gap junctions are the main form of interaction between cardiomyocytes, through which the electrochemical activities between cardiomyocytes can be synchronized to maintain the normal function of the heart. Connexins are the basis of gap junctions. Changes in the expression, structural changes (e.g., phosphorylation and dephosphorylation), and distribution of connexins can affect the normal electrophysiological activities of the heart. Myocardial infarction (MI) and concurrent arrhythmia, shock, or heart failure can endanger life. The structural and functional damage of connexin (Cx) 43 in cardiomyocytes is a central part of the pathological progression of MI and is one of the main pathological mechanisms of arrhythmia after MI. Therefore, increasing Cx43 expression has become one of the main measures to prevent MI. Also, intervention in Cx43 expression can improve the structural and electrical remodeling of the myocardium to improve MI prognosis. Here, research progress of Cx43 in MI and its prevention and treatment using Traditional Chinese Medicine formulations is reviewed.

Effects of an Atypical Antipsychotic, Zotepine, on Astroglial L-Glutamate Release through Hemichannels: Exploring the Mechanism of Mood-Stabilising Antipsychotic Actions and Antipsychotic-Induced Convulsion

Accumulating neuropsychopharmacological evidence has suggested that functional abnormalities of astroglial transmission and protein kinase B (Akt) contribute to the pathophysiology and/or pathomechanisms of several neuropsychiatric disorders, such as epilepsy, schizophrenia, affective disorders and antipsychotic-induced convulsions. Therefore, to explore the pathophysiology of mood-stabilising antipsychotics and the proconvulsive actions of atypical antipsychotics, the present study determined the effects of a mood-stabilising, atypical, antipsychotic agent, zotepine (ZTP), on astroglial L-glutamate release and the expression of connexin43 (Cx43) protein in cortical, primary, cultured astrocytes using ultra-high-pressure liquid chromatography and capillary immunoblotting systems. Both acute and subchronic administrations of therapeutically relevant concentrations of ZTP did not affect astroglial L-glutamate release or Cx43 expression in plasma membranes; however, chronic administration of a therapeutically relevant concentration of ZTP increased astroglial L-glutamate release and Cx43 expression in the plasma membrane. Subchronic administrations of a supratherapeutic concentration of ZTP enhanced astroglial L-glutamate release and Cx43 expression in the plasma membrane, whereas acute administration of a supratherapeutic concentration of ZTP enhanced astroglial L-glutamate release without affecting Cx43 expression. These stimulatory effects of ZTP on astroglial L-glutamate release through activated hemichannels and Cx43 trafficking to the astroglial plasma membrane were suppressed by the Akt inhibitor. These results suggest that ZTP enhances astroglial L-glutamate release in a concentration-dependent and time-dependent manner due to the enhanced function of astroglial hemichannels, probably via activation of Akt signalling. Therefore, the enhanced astroglial L-glutamatergic transmission induced by ZTP is, at least partially, involved in the mood-stabilising antipsychotic and proconvulsive actions of ZTP.

Upregulation of Cx43 Expression Under Stretch Condition is Mediated by TGF Beta1 and Cytoskeletal Network

Many physiological and pathophysiological processes in cells or tissues are involving mechanical stretch, which is inducing gap junction gene expression and cytokine TGF beta changes. However, the underlying mechanisms of gap junction gene expression changes remain unknown. Here, we showed that the expression of Cx43 at mRNA and protein level in Human umbilical-vein endothelial cells (HUVECs) is significantly increased after 24 h stretch stimulation, and TGF beta1, but not TGF beta2 expression is also upregulated. Administration of TGF betal into HUVECs without stretch also induced upregulation of Cx43 mRNA and protein expression. While simultaneously administration of TGF beta1 with SB431542, a specific inhibitor of TGF beta1 receptor, blocked the Cx43 protein upregulation by TGF beta1. Further, the increase of Cx43 protein expression under stretch condition can be partially blocked by SB431542; moreover, it also can be partially blocked by simultaneously administration of anti-TGF beta1 monoclonal neutralization antibody. Importantly, the stretch induced upregulation of Cx43 can be blocked by administration of actin and microtubule inhibitors, while NEDD4, a key element in mediating Cx43 protein ubiquitination and degradation, is not changed under stretch condition. Therefore, we conclude that upregulation of Cx43 expression under 24 h stretch condition is mediated by TGF beta1 via TGF beta1 receptor signaling pathway, and it also involves the actin and microtubule cytoskeletal network.

PDGF-AA promotes cell-to-cell communication in osteocytes through PI3K/Akt signaling pathway

Osteocytes are the main sensitive cells in bone remodeling due to their potent functional cell processes from the mineralized bone matrix to the bone surface and the bone marrow. Neighboring osteocytes communicate with each other by these cell processes to achieve molecular exchange through gap junction channels. Platelet-derived growth factor-AA (PDGF-AA) has been reported to enhance bone tissue remodeling by promoting cell proliferation, migration, and autocrine secretion in osteoid cell linage. However, the effect of PDGF-AA on intercellular communication between osteocytes is still unclear. In the present study, we elucidated that PDGF-AA could enhance the formation of dendritic processes of osteocytes and the gap junctional intercellular communication by promoting the expression of connexin43 (Cx43). This modulation process was mainly dependent on the activation of phosphorylation of Akt protein by phosphatidylinositol 3-kinase (PI3K)/Akt (also known as protein kinase B, PKB) signaling. Inhibition of PI3K/Akt signaling decreased the Cx43 expression induced by PDGF-AA. These results establish a bridge between PDGF-AA and cell–cell communication in osteocytes, which could help us understand the molecular exchange between bone cells and fracture healing.

Distinct Effects of Escitalopram and Vortioxetine on Astroglial L-Glutamate Release Associated with Connexin43

It has been established that enhancement of serotonergic transmission contributes to improvement of major depression; however, several post-mortem studies and experimental depression rodent models suggest that functional abnormalities of astrocytes play important roles in the pathomechanisms/pathophysiology of mood disorders. Direct effects of serotonin (5-HT) transporter inhibiting antidepressants on astroglial transmission systems has never been assessed in this context. Therefore, to explore the effects of antidepressants on transmission associated with astrocytes, the present study determined the effects of the selective 5-HT transporter inhibitor, escitalopram, and the 5-HT partial agonist reuptake inhibitor, vortioxetine, on astroglial L-glutamate release through activated hemichannels, and the expression of connexin43 (Cx43), type 1A (5-HT1AR) and type 7 (5-HT7R) 5-HT receptor subtypes, and extracellular signal-regulated kinase (ERK) in astrocytes using primary cultured rat cortical astrocytes in a 5-HT-free environment. Both escitalopram and 5-HT1AR antagonist (WAY100635) did not affect basal astroglial L-glutamate release or L-glutamate release through activated hemichannels. Subchronic (for seven days) administrations of vortioxetine and the 5-HT7R inverse agonist (SB269970) suppressed both basal L-glutamate release and L-glutamate release through activated hemichannels, whereas 5-HT1AR agonist (BP554) inhibited L-glutamate release through activated hemichannels, but did not affect basal L-glutamate release. In particular, WAY100635 did not affect the inhibitory effects of vortioxetine on L-glutamate release. Subchronic administration of vortioxetine, BP554 and SB269970 downregulated 5-HT1AR, 5-HT7R and phosphorylated ERK in the plasma membrane fraction, but escitalopram and WAY100635 did not affect them. Subchronic administration of SB269970 decreased Cx43 expression in the plasma membrane but did not affect the cytosol; however, subchronic administration of BP554 increased Cx43 expression in the cytosol but did not affect the plasma membrane. Subchronic vortioxetine administration increased Cx43 expression in the cytosol and decreased it in the plasma membrane. WAY100635 prevented an increased Cx43 expression in the cytosol induced by vortioxetine without affecting the reduced Cx43 expression in the plasma membrane. These results suggest that 5-HT1AR downregulation probably increases Cx43 synthesis, but 5-HT7R downregulation suppresses Cx43 trafficking to the plasma membrane. These results also suggest that the subchronic administration of therapeutic-relevant concentrations of vortioxetine inhibits both astroglial L-glutamate and Cx43 expression in the plasma membrane via 5-HT7R downregulation but enhances Cx43 synthesis in the cytosol via 5-HT1AR downregulation. This combination of the downregulation of 5-HT1AR, 5-HT7R and Cx43 in the astroglial plasma membrane induced by subchronic vortioxetine administration suggest that astrocytes is possibly involved in the pathophysiology of depression.

Connexin 43 and Sonic Hedgehog Pathway Interplay in Glioblastoma Cell Proliferation and Migration

Glioblastoma (GBM) represents the most common primary brain tumor within the adult population. Current therapeutic options are still limited by high rate of recurrences and signalling axes that promote GBM aggressiveness. The contribution of gap junctions (GJs) to tumor growth and progression has been proven by experimental evidence. Concomitantly, tumor microenvironment has received increasing interest as a critical process in dysregulation and homeostatic escape, finding a close link between molecular mechanisms involved in connexin 43 (CX43)-based intercellular communication and tumorigenesis. Moreover, evidence has come to suggest a crucial role of sonic hedgehog (SHH) signalling pathway in GBM proliferation, cell fate and differentiation. Herein, we used two human GBM cell lines, modulating SHH signalling and CX43-based intercellular communication in in vitro models using proliferation and migration assays. Our evidence suggests that modulation of the SHH effector smoothened (SMO), by using a known agonist (i.e., purmorphamine) and a known antagonist (i.e., cyclopamine), affects the CX43 expression levels and therefore the related functions. Moreover, SMO activation also increased cell proliferation and migration. Importantly, inhibition of CX43 channels was able to prevent SMO-induced effects. SHH pathway and CX43 interplay acts inducing tumorigenic program and supporting cell migration, likely representing druggable targets to develop new therapeutic strategies for GBM.

Modulation of Rac1/PAK1/connexin43-Mediated ATP Release from Astrocytes Contributes to Retinal Ganglion Cell Survival in Experimental Glaucoma

Background: Connexin43 (Cx43) is one of major gap junction proteins in glial cells. Mutation in the gap junction protein alpha 1 gene of Cx43 has been detected in human glaucomatous retinas, suggestive of involvement of Cx43 in pathogenesis of glaucoma. However, the role of Cx43 in glaucoma has not been clearly elucidated. Methods: A mouse model of chronic ocular hypertension (COH) was produced by injecting magnetic microbeads into the eye anterior chamber. To explore the role of Rac1 in regulating Cx43 function, Rac1 conditional knockout in astrocytes was generated by subretinal injection of AAV-GFAP-Cre in Rac1flox/flox mice. The hemichannel activity was assayed by ethidium bromide uptake. The level and source of ATP were assayed by a commercial ATP assay kit, ATP sensors and removing microglia. Results: In this study, we showed that Cx43 were mainly expressed in retinal astrocytes. Intraocular pressure (IOP) elevation induced astrocyte activation, as evidenced by increased expressions of c-Fos and glial fibrillary acidic protein (GFAP), which results in downregulation of Cx43 and changes of Cx43 phosphorylation at Ser373 and Ser368 sites. In the optic nerve head of COH mice, Cx43 expression in Gap43 (an activity-dependent plasticity protein) positive astrocytes was reduced. In COH retinas, Rac1, a member of the Rho family, was activated, which was consistent with the decrease of Cx43 expression in a time course. Pharmacological inhibition of Rac1 inhibited the activity of its downstream molecule PAK1, and reversed the reduction of Cx43 expression and astrocyte activation induced by IOP elevation. Co-immunoprecipitation experiments further demonstrated the interactions between Cx43 and active Rac1 or p-PAK1. Inhibition of Rac1 or conditional knockout of Rac1 in macroglial cells increased the ATP release through Cx43 hemichannels in astrocytes of COH retinas. Additionally, Rac1 deletion in astrocytes upregulated the expression of adenosine A3 receptor in retinal ganglion cells (RGCs) and promoted RGC survival, at least at early stage of IOP elevation through activating adenosine receptors.Conclusions: Our results showed that Rac1 in astrocytes regulated glaucomatous RGC survival through Cx43-mediated ATP release. These findings suggest that modulation of Rac1/PAK1/Cx43 pathway in astrocytes may be a potential strategy of neuroprotection in glaucoma.