Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

Antibody-activation of connexin hemichannels in bone osteocytes with ATP release suppresses breast cancer and osteosarcoma malignancy

Bone tissue represents the most frequent site of cancer metastasis. We developed a hemichannel-activating antibody, Cx43-M2. Cx43-M2, directly targeting osteocytes in situ, activates osteocytic hemichannels and elevates extracellular ATP, thereby inhibiting the growth and migration of cultured breast and osteosarcoma cancer cells. Cx43-M2 significantly decreases breast cancer metastasis, osteosarcoma growth, and osteolytic activity, while improving survival rates in mice. The antibody's inhibition of breast cancer and osteosarcoma is dose dependent in both mouse and human cancer metastatic models. Furthermore, Cx43-M2 enhances anti-tumor immunity by increasing the population and activation of tumor-infiltrating immune-promoting effector T lymphocytes, while reducing immune-suppressive regulatory T cells. Our results suggest that the Cx43-M2 antibody, by activating Cx43 hemichannels and facilitating ATP release and purinergic signaling, transforms the cancer microenvironment from a supportive to a suppressive state. Collectively, our study underscores the potential of Cx43-M2 as a therapeutic for treating breast cancer bone metastasis and osteosarcoma.

Mapping the Anti-Cancer Activity of α-Connexin Carboxyl-Terminal (aCT1) Peptide in Resistant HER2+ Breast Cancer

Connexin 43 (Cx43) is a protein encoded by the GJA1 gene and is a component of cell membrane structures called gap junctions, which facilitate intercellular communication. Prior evidence indicates that elevated GJA1 expression in the HER2-positive (HER2+) subtype of breast cancer is associated with poor prognosis. Prior evidence also suggests that HER2+ breast cancers that have become refractory to HER2-targeted agents have a loss of Cx43 gap junction intercellular communication (GJIC). In this study, a Cx43-targeted agent called alpha-connexin carboxyl-terminal peptide (aCT1) is examined to determine whether GJIC can be rescued in refractory HER2+ breast cancer cells. A proposed mechanism of action for aCT1 is binding to the tight junction protein Zonal Occludens-1 (ZO-1). However, the true scope of activity for aCT1 has not been explored. In this study, mass spectrometry proteomic analysis is used to determine the breadth of aCT1-interacting proteins. The NanoString nCounter Breast Cancer 360 panel is also used to examine the effect of aCT1 on cancer signaling in HER2+ breast cancer cells. Findings from this study show a dynamic range of binding partners for aCT1, many of which regulate gene expression and RNA biology. nCounter analysis shows that a number of pathways are significantly impacted by aCT1, including upregulation of apoptotic factors, leading to the prediction and demonstration that aCT1 can boost the cell death effects of cisplatin and lapatinib in HER2+ breast cancer cells that have become resistant to HER2-targeted agents.

Evaluation of Tyrosine Kinase Inhibitors Loaded Injectable Hydrogels for Improving Connexin43 Gap Junction Intercellular Communication

Myocardial infarction (MI) is one of the leading causes of death in the developed world, and the loss of cardiomyocytes plays a critical role in the pathogenesis of heart failure. Implicated in this process is a decrease in gap junction intercellular communication due to remodeling of Connexin43 (Cx43). We previously identified that intraperitoneal injection of the Pyk2 inhibitor PF4618433 reduced infarct size, maintained Cx43 at the intercalated disc in left ventricle hypertrophic myocytes, and improved cardiac function in an MI animal model of heart failure. With the emergence of injectable hydrogels as a therapeutic toward the regeneration of cardiac tissue after MI, here, we provide proof of concept that the release of tyrosine kinase inhibitors from hydrogels could have beneficial effects on cardiomyocytes. We developed an injectable hydrogel consisting of thiolated hyaluronic acid and P123-maleimide micelles that can incorporate PF4618433 as well as the Src inhibitor Saracatinib and achieved sustained release (of note, Src activates Pyk2). Using neonatal rat ventricular myocytes in the presence of a phorbol ester, endothelin-1, or phenylephrine to stimulate cardiac hypertrophy, the release of PF4618433 from the hydrogel had the same ability to decrease Cx43 tyrosine phosphorylation and maintain Cx43 localization at the plasma membrane as when directly added to the growth media. Additional beneficial effects included decreases in apoptosis, the hypertrophic marker atrial natriuretic peptide (ANP), and serine kinases upregulated in hypertrophy. Finally, the presence of both PF4618433 and Saracatinib further decreased the level of ANP and apoptosis than each inhibitor alone, suggesting that a combinatorial approach may be most beneficial. These findings provide the groundwork to test if tyrosine kinase inhibitor release from hydrogels will have a beneficial effect in an animal model of MI-induced heart failure.

Purification, Reconstitution, and Functional Analysis of Connexin Hemichannels

Connexins are the proteins that form the gap junction channels that are essential for cell-to-cell communication. These channels are formed by head-to-head docking of hemichannels (each from one of two adjacent cells). Free "undocked" hemichannels at the plasma membrane are mostly closed, although they are still important under physiological conditions. However, abnormal and sustained increase in hemichannel activity due to connexin mutations or acquired conditions can produce or contribute to cell damage. For example, mutations of Cx26, a connexin isoform, can increase hemichannel activity and cause deafness. Studies using purified isolated systems under well-controlled conditions are essential for a full understanding of molecular mechanisms of hemichannel function under normal conditions and in disease, and here, we present methodology for the expression, purification, and functional analysis of hemichannels formed by Cx26.

Estradiol and 3β-diol protect female cortical astrocytes by regulating connexin 43 Gap Junctions

While estrogens have been described to protect or preserve neuronal function in the face of insults such as oxidative stress, the prevailing mechanistic model would suggest that these steroids exert direct effects on the neurons. However, there is growing evidence that glial cells, such as astrocytes, are key cellular mediators of protection. Noting that connexin 43 (Cx43), a protein highly expressed in astrocytes, plays a key role in mediating inter-cellular communication, we hypothesized that Cx43 is a target of estradiol (E2), and the estrogenic metabolite of DHT, 3β-diol. Additionally, we sought to determine if either or both of these hormones attenuate oxidative stress-induced cytotoxicity by eliciting a reduction in Cx43 expression or inhibition of Cx43 channel permeability. Using primary cortical astrocytes, we found that E2 and 3β-diol were each protective against the mixed metabolic/oxidative insult, iodoacetic acid (IAA). Moreover, these effects were blocked by estrogen receptor antagonists. However, E2 and 3β-diol did not alter Cx43 mRNA levels in astrocytes but did inhibit IAA-induced Cx43 gap junction opening/permeability. Taken together, these data implicate astrocyte Cx43 gap junction as an understudied mediator of the cytoprotective effects of estrogens in the brain. Given the wide breadth of disease states associated with Cx43 function/dysfunction, further understanding the relationship between gonadal steroids and Cx43 channels may contribute to a better understanding of the biological basis for sex differences in various diseases.

MLKL regulates Cx43 ubiquitinational degradation and mediates neuronal necroptosis in ipsilateral thalamus after focal cortical infarction

Necroptosis is known to play an important role in the pathophysiology of cerebral ischemia; however, its role in the occurrence of secondary thalamic injury after focal cerebral infarction and the mechanism about how mixed lineage kinase domain-like (MLKL) executes necroptosis in this pathophysiology are still unclear. In this study, Sprague-Dawley rats were subjected to distal branch of middle cerebral artery occlusion (dMCAO). The expression of MLKL, connexin 43 (Cx43) and Von Hippel-Lindau (VHL) in vitro and in vivo were assessed by Western blot. Bioinformatic methods were used to predict the potential binding sites where MLKL interacted with Cx43, and the ubiquitination degradation of Cx43 regulated by VHL. The interactions among MLKL, Cx43, VHL, and Ubiquitin were assessed by immunoprecipitation. Dye uptake assay were used to examine the Cx43 hemichannels. Intracellular Ca2+ concentration was measured using Fluo-4 AM. Overexpression and site-directed mutagenesis studies were used to study the mechanisms by which MLKL regulates Cx43 ubiquitinational degradation to mediate neuronal necroptosis. We found that MLKL and Cx43 were upregulated in the ventral posterolateral nucleus (VPN) of the ipsilateral thalamus after dMCAO. In the in vitro experiments MLKL and Cx43 were upregulated after TSZ-mediated necroptosis in SH-SY5Y cells. The interaction between MLKL and Cx43 inhibited the K48-linked ubiquitination of Cx43 in necroptotic SH-SY5Y cells. VHL is an E3 ubiquitin ligase for Cx43, and MLKL competes with VHL for binding to Cx43. Interaction of MLKL Ser454 with Cx43 can trigger the opening of Cx43 hemichannels, causing increased intracellular Ca2+, and cell necroptosis. This innovative study at animal models, cellular, and molecular levels is anticipated to clarify the roles of MLKL and Cx43 in thalamic damage after focal cortical infarction. Our findings may help identify novel targets for neurological recovery after cortical infarction.

Muscle mitochondrial transplantation can rescue and maintain cellular homeostasis

Mitochondria control cellular functions through their metabolic role. Recent research that has gained considerable attention is their ability to transfer between cells. This has the potential of improving cellular functions in pathological or energy-deficit conditions, but little is known about the role of mitochondrial transfer in sustaining cellular homeostasis. Few studies have investigated the potential of skeletal muscle as a source of healthy mitochondria that can be transferred to other cell types. Thus, we isolated intermyofibrillar mitochondria from murine skeletal muscle and incubated them with host cells. We observed dose- and time-dependent increases in mitochondrial incorporation into myoblasts. This resulted in elongated mitochondrial networks and an enhancement of bioenergetic profile of the host cells. Mitochondrial donation also rejuvenated the functional capacities of the myoblasts when respiration efficiency and lysosomal function were inhibited by complex I inhibitor rotenone and bafilomycin A, respectively. Mitochondrial transfer was accomplished via tunneling nanotubes, extracellular vesicles, gap junctions, and by macropinocytosis internalization. Murine muscle mitochondria were also effectively transferred to human fibroblast cells having mitochondrial DNA mutations, resulting in augmented mitochondrial dynamics and metabolic functions. This improved cell function by diminishing reactive oxygen species (ROS) emission in the diseased cells. Our findings suggest that mitochondria from donor skeletal muscle can be integrated in both healthy and functionally compromised host cells leading to mitochondrial structural refinement and respiratory boost. This mitochondrial trafficking and bioenergetic reprogramming to maintain and revitalize tissue homeostasis could be a useful therapeutic strategy in treating diseases.NEW & NOTEWORTHY In our study, we have shown the potential of mouse skeletal muscle intermyofibrillar mitochondria to be transplanted in myoblasts and human fibroblast cells having mitochondrial DNA mutations. This resulted in an augmentation of mitochondrial dynamics and enhancement of bioenergetic profile in the host cells. Our findings suggest that mitochondria from donor skeletal muscle can be integrated into both healthy and functionally compromised host cells leading to mitochondrial structural refinement and respiratory boost.

Fibroblasts - the cellular choreographers of wound healing

Injuries to our skin trigger a cascade of spatially- and temporally-synchronized healing processes. During such endogenous wound repair, the role of fibroblasts is multifaceted, ranging from the activation and recruitment of innate immune cells through the synthesis and deposition of scar tissue to the conveyor belt-like transport of fascial connective tissue into wounds. A comprehensive understanding of fibroblast diversity and versatility in the healing machinery may help to decipher wound pathologies whilst laying the foundation for novel treatment modalities. In this review, we portray the diversity of fibroblasts and delineate their unique wound healing functions. In addition, we discuss future directions through a clinical-translational lens.

Downregulation of cardiac PIASy inhibits Cx43 SUMOylation and ameliorates ventricular arrhythmias in a rat model of myocardial ischemia/reperfusion injury

BACKGROUND

Dysfunction of the gap junction channel protein connexin 43 (Cx43) contributes to myocardial ischemia/reperfusion (I/R)-induced ventricular arrhythmias. Cx43 can be regulated by small ubiquitin-like modifier (SUMO) modification. Protein inhibitor of activated STAT Y (PIASy) is an E3 SUMO ligase for its target proteins. However, whether Cx43 is a target protein of PIASy and whether Cx43 SUMOylation plays a role in I/R-induced arrhythmias are largely unknown.

METHODS

Male Sprague-Dawley rats were infected with PIASy short hairpin ribonucleic acid (shRNA) using recombinant adeno-associated virus subtype 9 (rAAV9). Two weeks later, the rats were subjected to 45 min of left coronary artery occlusion followed by 2 h reperfusion. Electrocardiogram was recorded to assess arrhythmias. Rat ventricular tissues were collected for molecular biological measurements.

RESULTS

Following 45 min of ischemia, QRS duration and QTc intervals statistically significantly increased, but these values decreased after transfecting PIASy shRNA. PIASy downregulation ameliorated ventricular arrhythmias induced by myocardial I/R, as evidenced by the decreased incidence of ventricular tachycardia and ventricular fibrillation, and reduced arrythmia score. In addition, myocardial I/R statistically significantly induced PIASy expression and Cx43 SUMOylation, accompanied by reduced Cx43 phosphorylation and plakophilin 2 (PKP2) expression. Moreover, PIASy downregulation remarkably reduced Cx43 SUMOylation, accompanied by increased Cx43 phosphorylation and PKP2 expression after I/R.

CONCLUSION

PIASy downregulation inhibited Cx43 SUMOylation and increased PKP2 expression, thereby improving ventricular arrhythmias in ischemic/reperfused rats heart.

Integrated proteomics and phosphoproteomics profiling reveals the cardioprotective mechanism of bioactive compounds derived from Salvia miltiorrhiza Burge

BACKGROUND

Natural products are an important source for discovering novel drugs due to their various pharmacological activities. Salvia miltiorrhiza Burge (Danshen) has been shown to have promising therapeutic potential in the management of heart diseases, making it a candidate for cardiovascular drug discovery. Currently, there is limited quantitative analysis of the phosphorylation levels of Danshen-derived natural products on a proteome-wide, which may bias the study of their mechanisms of action.

PURPOSE

This study aimed to evaluate the global signaling perturbation induced by Danshen-derived bioactive compounds and their potential relationship with myocardial ischemia/reperfusion (IR) injury therapy.

STUDY DESIGN

We employed quantitative proteome and phosphoproteome analysis to identify dysregulated signaling in IR injury hearts from mice. We compared changes induced by Danshen-derived compounds based on IR-associated phospho-events, using an integrative approach that maps relative abundance of proteins and phosphorylation sites.

METHODS

Isobaric chemical tandem mass tags (TMT) labeled multiplexing strategy was used to generate unbiased quantitative proteomics and phosphoproteomics data. Highly accurate and precise TMT quantitation was performed using the Orbitrap Fusion Tribrid Mass Spectrometer with synchronous precursor selection MS3 detection mode. Mass spectrometric raw files were analyzed with MaxQuant (2.0.1.0) and statistical and bioinformatics analysis was conducted with Perseus (1.6.15).

RESULTS

We quantified 3661 proteins and over 11,000 phosphosites in impaired heart tissue of the IR mice model, expanding our knowledge of signaling pathways and other biological processes disrupted in IR injury. Next, 1548 and 5545 differently expressed proteins and phosphosites were identified by quantifying the proteome and phosphoproteome of H9c2 cells treated by five Danshen bioactive compounds respectively. Results revealed the vast differences in abilities of five Danshen-derived bioactive compounds to regulate phosphorylation modifications in cardiomyocytes, with dihydrotanshinone I (DHT) showing potential for protecting against IR injury by modulating the AMPK/mTOR signaling pathway.

CONCLUSIONS

This study provides a new strategy for analyzing drug/natural product-regulated phosphorylation modification levels on a proteome-wide scale, leading to a better understanding of cell signaling pathways and downstream phenotypic responses.

Mitochondrial connexin43 and mitochondrial KATP channels modulate triggered arrhythmias in mouse ventricular muscle

Connexin43 (Cx43) exits as hemichannels in the inner mitochondrial membrane. We examined how mitochondrial Cx43 and mitochondrial K_ATP channels affect the occurrence of triggered arrhythmias. To generate cardiac-specific Cx43-deficient (cCx43^-/-) mice, Cx43^flox/flox mice were crossed with α-MHC (Myh6)-cre^+/- mice. The resulting offspring, Cx43^flox/flox/Myh6-cre^+/- mice (cCx43^-/- mice) and their littermates (cCx43^+/+ mice), were used. Trabeculae were dissected from the right ventricles of mouse hearts. Cardiomyocytes were enzymatically isolated from the ventricles of mouse hearts. Force was measured with a strain gauge in trabeculae (22°C). To assess arrhythmia susceptibility, the minimal extracellular Ca²⁺ concentration ([Ca²⁺]_o,min), at which arrhythmias were induced by electrical stimulation, was determined in trabeculae. ROS production was estimated with 2',7'-dichlorofluorescein (DCF), mitochondrial membrane potential with tetramethylrhodamine methyl ester (TMRM), and Ca²⁺ spark frequency with fluo-4 and confocal microscopy in cardiomyocytes. ROS production within the mitochondria was estimated with MitoSoxRed and mitochondrial Ca²⁺ with rhod-2 in trabeculae. Diazoxide was used to activate mitochondrial K_ATP. Most of cCx43^-/- mice died suddenly within 8 weeks. Cx43 was present in the inner mitochondrial membrane in cCx43^+/+ mice but not in cCx43^-/- mice. In cCx43^-/- mice, the [Ca²⁺]_o,min was lower, and Ca²⁺ spark frequency, the slope of DCF fluorescence intensity, MitoSoxRed fluorescence, and rhod-2 fluorescence were higher. TMRM fluorescence was more decreased in cCx43^-/- mice. Most of these changes were suppressed by diazoxide. In addition, in cCx43^-/- mice, antioxidant peptide SS-31 and N-acetyl-L-cysteine increased the [Ca²⁺]_o,min. These results suggest that Cx43 deficiency activates Ca²⁺ leak from the SR, probably due to depolarization of mitochondrial membrane potential, an increase in mitochondrial Ca²⁺, and an increase in ROS production, thereby causing triggered arrhythmias, and that Cx43 hemichannel deficiency may be compensated by activation of mitochondrial K_ATP channels in mouse hearts.

LRP6-mediated phosphorylation of connexin43 in myocardial infarction

Ventricular tachycardia (VT) and ventricular fibrillation are most causes of early death in patients with acute myocardial infarction (AMI). Conditional cardiac-specific low-density lipoprotein receptor-related protein 6 (LRP6)-knockout mice with connexin 43 (Cx43) reduction triggered the lethal ventricular arrhythmias. Thus, it is necessary for exploring whether LRP6 and its upstream genes circRNA1615 mediate the phosphorylation of Cx43 in VT of AMI. Here, we showed that circRNA1615 regulated the expression of LRP6 mRNA through sponge adsorption of miR-152-3p. Importantly, LRP6 interference fragments aggravated hypoxia injury of Cx43, while overexpression of LRP6 improved the phosphorylation of Cx43. Subsequently, interference with G-protein alpha subunit (Gα_s) downstream of LRP6 further inhibited the phosphorylation of Cx43, along with increasing VT. Our results demonstrated that LRP6 upstream genes circRNA1615 controlled the damage effect and VT in AMI, and LRP6 mediated the phosphorylation of Cx43 via Gα_s which played a role in VT of AMI.

Qilong Capsule Alleviated MPTP-Induced Neuronal Defects by Inhibiting Apoptosis, Regulating Autophagy in Zebrafish Embryo Model

Qilong capsule (QLC) originates from the famous "Buyang Huanwu decoction" prescription. It is representative of drugs used in China during recovery from stroke, but its neuroprotective mechanism of action remains obscure. HPLC was used to evaluate the similarity of 10 batches of QLC samples. Then we used a zebrafish model to study the neuroprotective effect of QLC. At 24 hpf, embryos were treated with QLC and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and zebrafish were observed the neuronal length and the number of apoptotic cells in the brain at 72 hpf. At 120 hpf, we conduct zebrafish behavioural tests. We then also used qPCR to detect the expression of genes related to autophagy and apoptosis. The results showed that QLC significantly reduced the damage of dopaminergic neurons, the number of apoptotic cells in the brain, and alleviated motor disturbances induced by MPTP. We found that the mechanism of QLC activity involved decreased neuron cell death by inhibiting mitochondrial apoptosis and autophagy, promoting autophagy, degradation of alpha-synuclein, and neuron cell growth, and rescuing the function of neurons damaged by MPTP. The results indicated that QLC protected against MPTP-induced neuron injury and provided pharmacological evidence for clinical use of QLC.

Mitochondria on the move: Horizontal mitochondrial transfer in disease and health

Mammalian genes were long thought to be constrained within somatic cells in most cell types. This concept was challenged recently when cellular organelles including mitochondria were shown to move between mammalian cells in culture via cytoplasmic bridges. Recent research in animals indicates transfer of mitochondria in cancer and during lung injury in vivo, with considerable functional consequences. Since these pioneering discoveries, many studies have confirmed horizontal mitochondrial transfer (HMT) in vivo, and its functional characteristics and consequences have been described. Additional support for this phenomenon has come from phylogenetic studies. Apparently, mitochondrial trafficking between cells occurs more frequently than previously thought and contributes to diverse processes including bioenergetic crosstalk and homeostasis, disease treatment and recovery, and development of resistance to cancer therapy. Here we highlight current knowledge of HMT between cells, focusing primarily on in vivo systems, and contend that this process is not only (patho)physiologically relevant, but also can be exploited for the design of novel therapeutic approaches.

Engineering a conduction-consistent cardiac patch with rGO/PLCL electrospun nanofibrous membranes and human iPSC-derived cardiomyocytes

The healthy human heart has special directional arrangement of cardiomyocytes and a unique electrical conduction system, which is critical for the maintenance of effective contractions. The precise arrangement of cardiomyocytes (CMs) along with conduction consistency between CMs is essential for enhancing the physiological accuracy of in vitro cardiac model systems. Here, we prepared aligned electrospun rGO/PLCL membranes using electrospinning technology to mimic the natural heart structure. The physical, chemical and biocompatible properties of the membranes were rigorously tested. We next assembled human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) on electrospun rGO/PLCL membranes in order to construct a myocardial muscle patch. The conduction consistency of cardiomyocytes on the patches were carefully recorded. We found that cells cultivated on the electrospun rGO/PLCL fibers presented with an ordered and arranged structure, excellent mechanical properties, oxidation resistance and effective guidance. The addition of rGO was found to be beneficial for the maturation and synchronous electrical conductivity of hiPSC-CMs within the cardiac patch. This study verified the possibility of using conduction-consistent cardiac patches to enhance drug screening and disease modeling applications. Implementation of such a system could one day lead to in vivo cardiac repair applications.

Co-axial fibrous scaffolds integrating with carbon fiber promote cardiac tissue regeneration post myocardial infarction

Myocardium is an excitable tissue with electrical conductivity and mechanical strength. In this work, carbon fibers (CFs) and co-axial fibrous mesh were integrated which combined the high modulus and excellent electrical conductivity of CFs and the fibrous and porous structures of the electrospun fibers. The scaffold was fabricated by simply integrating coaxial electrospun fibers and carbon fibers through a freeze-drying procedure. It was shown that the integration of carbon fibers have the conductivity and Young's modulus of the fibrous mesh increased significantly, meanwhile, upregulated the expression of CX43, α-actinin, RhoA of the neonatal rat primary cardiomyocytes and primary human umbilical vein endothelial cells (HUVECs), and promoted the secretion of VEGF of HUVECs. Moreover, the cardiomyocytes grown on the scaffolds increased the ability of HUVECs migration. When implanted to the injury area post myocardial infraction, the scaffolds were able to effectively enhance the tissue regeneration and new vessel formation, which rescued the heart dysfunction induced by the myocardial infraction, evidenced by the results of echocardiography and histochemical analysis. In conclusion, the composite scaffolds could promote the myocardium regeneration and function's recovery by enhancing cardiomyocytes maturation and angiogenesis and establishing the crosstalk between the cardiomyocytes and the vascular endothelial cells.

Connexins in endothelial cells as a therapeutic target for solid organ transplantation

Connexins are a class of membrane proteins widely distributed throughout the body and have various functions based on their location and levels of expression. More specifically, connexin proteins expressed in endothelial cells (ECs) have unique roles in maintaining EC barrier integrity and function-a highly regulated process that is critical for pro-inflammatory and pro-coagulant reactions. In this minireview, we discuss the regulatory influence connexin proteins have in maintaining EC barrier integrity and their role in ischemia-reperfusion injury as it relates to organ transplantation. It is evident that certain isoforms of the connexin protein family are uniquely positioned to have far-reaching effects on preserving organ function; however, there is still much to be learned of their roles in transplant immunology and the application of this knowledge to the development of targeted therapeutics.

Glycated serum albumin decreases connexin 43 phosphorylation in the corpus cavernosum

Background

Glycated serum albumin (GSA) is an early glycosylation product that participates in diabetic vascular complications. This study examined the role of GSA in early damage to the corpus cavernosum and the involved mechanisms.

Methods

Nine 8-week-old male Sprague-Dawley (SD) rats (250-300 g) were divided into the control (saline vehicle, n=3) and GSA (200 µg/kg, n=6) groups. The corpus cavernosum tissues were harvested. Phosphorylated and non-phosphorylated connexin 43 (Cx43), endothelial nitric oxide synthase (eNOS), phosphatidylinositol 3-kinase (PI3K), and serine-threonine kinase (Akt) were tested by immunohistochemistry and western blotting. Human umbilical vein endothelial cells (HUVECs) overexpressing Cx43 were used to analyze the Cx43 phosphorylation sites (S368, S262, Y265, S255, and S279/282) using western blotting.

Results

The expression of phosphorylated Cx43 in the penis was significantly lower in GSA-treated rats than in controls. The expression levels of p-Cx43, p-eNOS, p-PI3K, and p-Akt were significantly decreased in HUVECs exposed to GSA in dose- and time-dependent manners. The most significant impact on all four proteins was observed with 1 µg/mL of GSA for 12 h. Phosphorylation at the S368, S262, Y265, S255, and S279/282 sites of Cx43 was downregulated by GSA, and S368 was the most significantly suppressed phosphorylation site compared with the other sites.

Conclusions

GSA decreases the expression of p-Cx43 in the corpus cavernosum of rats. This effect might be also related to the decreased phosphorylation of p-eNOS, p-PI3K, and p-Akt, as well as by the downregulation of phosphorylation at the S368 site.

Contraction Band Necrosis with Dephosphorylated Connexin 43 in Rat Myocardium after Daily Cocaine Administration

Contraction band necrosis (CBN) is a common abnormality found in the myocardium of cocaine abusers, but is rarely reported in experimental models of cocaine abuse. Connexin 43 (Cx43) is essential for cardiac intercellular communication and the propagation of CBN. Under stress or injury, cardiac Cx43 is dephosphorylated, which is related to cardiomyocyte dysfunction and pathogenesis, whereas adiponectin exerts beneficial effects in the myocardium. In this study, we explore the effects of cocaine on cardiac Cx43 in vivo. Rats were administered cocaine via the tail vein at 20 mg/kg/day for 14 days, and showed widespread CBN, microfocal myocarditis and myocardial fibrosis, corresponding to a dysfunction of cardiac mitochondria under increased oxidative stress. The increase in dephosphorylated cardiac Cx43 and its negative correlation with the myocardial distribution of CBN after cocaine administration were determined. In addition, apoptosis and necroptosis, as well as increased adiponectin levels, were observed in the myocardium after cocaine exposure. Accordingly, we found altered profiles of cardiac Cx43, CBN and its negative correlation with dephosphorylated cardiac Cx43, and the possible involvement of adiponectin in the myocardium after 14 days of cocaine administration. The latter might play a protective role in the cardiotoxicity of cocaine. The current findings would be beneficial for establishing novel therapeutic strategies in cocaine-induced cardiac consequences.

Connexin 43: insights into candidate pathological mechanisms of depression and its implications in antidepressant therapy

Major depressive disorder (MDD), a chronic and recurrent disease characterized by anhedonia, pessimism or even suicidal thought, remains a major chronic mental concern worldwide. Connexin 43 (Cx43) is the most abundant connexin expressed in astrocytes and forms the gap junction channels (GJCs) between astrocytes, the most abundant and functional glial cells in the brain. Astrocytes regulate neurons' synaptic strength and function by expressing receptors and regulating various neurotransmitters. Astrocyte dysfunction causes synaptic abnormalities, which are related to various mood disorders, e.g., depression. Increasing evidence suggests a crucial role of Cx43 in the pathogenesis of depression. Depression down-regulates Cx43 expression in humans and rats, and dysfunction of Cx43 also induces depressive behaviors in rats and mice. Recently Cx43 has received considerable critical attention and is highly implicated in the onset of depression. However, the pathological mechanisms of depression-like behavior associated with Cx43 still remain ambiguous. In this review we summarize the recent progress regarding the underlying mechanisms of Cx43 in the etiology of depression-like behaviors including gliotransmission, metabolic disorders, and neuroinflammation. We also discuss the effects of antidepressants (monoamine antidepressants and ketamine) on Cx43. The clarity of the candidate pathological mechanisms of depression-like behaviors associated with Cx43 and its potential pharmacological roles for antidepressants will benefit the exploration of a novel antidepressant target.

Amphiphilic aminoglycosides: Modifications that revive old natural product antibiotics

Widely-used Streptomyces-derived antibacterial aminoglycosides have encountered challenges because of antibiotic resistance and toxicity. Today, they are largely relegated to medicinal topical applications. However, chemical modification to amphiphilic aminoglycosides can revive their efficacy against bacterial pathogens and expand their targets to other pathogenic microbes and disorders associated with hyperactive connexin hemichannels. For example, amphiphilic versions of neomycin and neamine are not subject to resistance and have expanded antibacterial spectra, and amphiphilic kanamycins are effective antifungals and have promising therapeutic uses as connexin hemichannel inhibitors. With further research and discoveries aimed at improved formulations and delivery, amphiphilic aminoglycosides may achieve new horizons in pharmacopeia and agriculture for Streptomyces aminoglycosides beyond just serving as topical antibacterials.

Cardiac-specific overexpression of Claudin-5 exerts protection against myocardial ischemia and reperfusion injury

Claudin-5 has recently attracted increasing attention by its potential as a novel treatment target in the early stage of heart failure. However, whether Claudin-5 produces beneficial effects on myocardial ischemia and reperfusion (IR) injury has not been elucidated yet. In this study, we identified reduced levels of Claudin-5 in the hearts of mice subjected to acute myocardial IR injury and murine HL-1 cardiomyocytes subjected to hypoxia and reoxygenation (HR). We then constructed cardiac-specific Cldn5-overexpressing mice using an adeno-associated virus (AAV9) vector and demonstrated that Cldn5 overexpression ameliorated cardiac dysfunction and myocardial damage in mice subjected to myocardial IR injury. Moreover, Cldn5 overexpression attenuated myocardial oxidative stress (DHE and protein levels of Nrf2, HO-1, and NQO1), inflammatory response (levels of MPO, F4/80, Ly6C, and circulating inflammatory cells), mitochondrial dysfunction (protein levels of PGC-1α, NRF1, and TFAM), endoplasmic reticulum stress (protein levels of GRP78, ATF6, and CHOP and p-PERK), energy metabolism disorder (p-AMPK and ACC), and apoptosis (TUNEL assay and protein levels of Bax and Bcl2) in mice subjected to myocardial IR. Next, we generated Cldn5 knockdown cells by lentiviral shRNA and observed that Cldn5 knockdown inhibited cell viability and affected the expression or activation of these IR-related signalings in HL-1 cardiomyocytes subjected to HR. Mechanistically, SIRT1 was proved to be involved in regulating the expression of Claudin-5 by co-immunoprecipitation analysis and Sirt1 knockdown experiments. Our data demonstrated that targeting Claudin-5 may represent a promising approach for preventing and treating acute myocardial IR injury.

Connexin 43 hyper-phosphorylation at serine 282 triggers apoptosis in rat cardiomyocytes via activation of mitochondrial apoptotic pathway

Cx43 is the major connexin in ventricular gap junctions, and plays a pivotal role in control of electrical and metabolic communication among adjacent cardiomyocytes. We previously found that Cx43 dephosphorylation at serine 282 (pS282) caused cardiomyocyte apoptosis, which is involved in cardiac ischemia/reperfusion injury. In this study we investigated whether Cx43-S282 hyper-phosphorylation could protect cardiomyocytes against apoptosis. Adenovirus carrying rat full length Cx43 gene (Cx43-wt) or a mutant gene at S282 substituted with aspartic acid (S282D) were transfected into neonatal rat ventricular myocytes (NRVMs) or injected into rat ventricular wall. Rat abdominal aorta constriction model (AAC) was used to assess Cx43-S282 phosphorylation status. We showed that Cx43 phosphorylation at S282 was increased over 2-times compared to Cx43-wt cells at 24 h after transfection, while pS262 and pS368 were unaltered. S282D-transfected cells displayed enhanced gap junctional communication, and increased basal intracellular Ca²⁺ concentration and spontaneous Ca²⁺ transients compared to Cx43-wt cells. However, spontaneous apoptosis appeared in NRVMs transfected with S282D for 34 h. Rat ventricular myocardium transfected with S282D in vivo also exhibited apoptotic responses, including increased Bax/Bcl-xL ratio, cytochrome c release as well as caspase-3 and caspase-9 activities, while factor-associated suicide (Fas)/Fas-associated death domain expression and caspase-8 activity remained unaltered. In addition, AAC-induced hypertrophic ventricles had apoptotic injury with Cx43-S282 hyper-phosphorylation compared with Sham ventricles. In conclusion, Cx43 hyper-phosphorylation at S282, as dephosphorylation, also triggers cardiomyocyte apoptosis, but through activation of mitochondrial apoptosis pathway, providing a fine-tuned Cx43-S282 phosphorylation range required for the maintenance of cardiomyocyte function and survival.

Connexins and angiogenesis: Functional aspects, pathogenesis, and emerging therapies (Review)

Connexins (Cxs) play key roles in cellular communication. By facilitating metabolite exchange or interfering with distinct signaling pathways, Cxs affect cell homeostasis, proliferation, and differentiation. Variations in the activity and expression of Cxs have been linked to numerous clinical conditions including carcinomas, cardiac disorders, and wound healing. Recent discoveries on the association between Cxs and angiogenesis have sparked interest in Cx-mediated angiogenesis due to its essential functions in tissue formation, wound repair, tumor growth, and metastasis. It is now widely recognized that understanding the association between Cxs and angiogenesis may aid in the development of new targeted therapies for angiogenic diseases. The aim of the present review was to provide a comprehensive overview of Cxs and Cx-mediated angiogenesis, with a focus on therapeutic implications.

Dapagliflozin Improves Diabetic Cardiomyopathy by Modulating the Akt/mTOR Signaling Pathway

Background

Dapagliflozin can significantly improve heart failure, and Cx43 is one of the molecular mechanisms of heart failure. This study investigated the effect of dapagliflozin on Cx43 and Akt/mTOR signaling pathway in ventricular myocytes.

Methods

A rat model of type 2 diabetes mellitus was established by high-fat diet combined with streptozotocin, and the animals were treated randomly with dapagliflozin. The morphological changes of the myocardium were observed by hematoxylin eosin staining, and the expression and distribution of Cx43 in ventricular myocytes were detected by immunohistochemistry. And Western blot determined the expressions of Cx43, Akt, mTOR, p62, and LC3 proteins in rat myocardium.

Results

Compared with the normal control group, the heart rate of diabetic rats decreased significantly (p < 0.05), QRS wave of ECG widened, and QT interval prolonged (p < 0.05). Dapagliflozin treatment in diabetic rats resulted in improvements in these ECG indexes (p < 0.05) with early administration group obtaining greater efficacy than the late administration group (p < 0.05). In the normal control group, the cardiomyocytes were arranged orderly, and the expression of Cx43 was dense, uniform, and regular, which was higher than that in the intercalated disc. In the diabetic control model group, the cardiomyocytes were enlarged and presented disorderly with detection of Cx43 in the cytoplasm. Early use of dapagliflozin better improved these myocardial tissue lesions. Of note, as diabetic rats exhibited decreased expression of Cx43, Akt, and mTOR (p < 0.05), increased p62 expression (p < 0.05), and decreased LC3-II/I ratio (p < 0.05), administration of dapagliflozin partially reversed the expression of the above proteins (p < 0.05) with greater improvement in the early administration group compared with the late administration group (p < 0.05).

Conclusions

Dapagliflozin increases the expression of Cx43 in cardiomyocytes of diabetic rats and thereby alleviates heart failure partly through regulating the Akt/mTOR signaling pathway.

Connexin 43 overexpression induces lung cancer angiogenesis in vitro following phosphorylation at Ser279 in its C‑terminus

Blocking angiogenesis can inhibit tumor growth and metastasis. However, the mechanism underlying regulation of lung cancer angiogenesis remains unclear. The gap junction protein connexin 43 (Cx43) is implicated in angiogenesis. The aim of the present study was to determine the role of Cx43 in angiogenesis in vitro and its signaling pathways. Human pulmonary microvascular endothelial cells were transfected with Cx43-targeting siRNA or Cx43-overexpressing recombinant plasmid vector. Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to determine Cx43, zonula occludens-1 (ZO-1), E-cadherin, β-catenin, von Willebrand factor (vWF), and plasminogen activator inhibitor-1 (PAI-1) mRNA and protein expression levels, respectively. Tyr265, Ser279, Ser368, and Ser373 phosphorylation levels in the C-terminus of Cx43 and intracellular and membranal Cx43 contents were determined using western blotting. Additionally, immunofluorescence, tube formation, Cell Counting Kit-8, and Transwell migration assays were performed. The results revealed that compared with that in the control samples, Cx43, ZO-1, E-cadherin, β-catenin, vWF, and PAI-1 mRNA and protein expression were significantly increased in the Cx43 overexpression group and significantly decreased in the Cx43-knockdown group. Moreover, the phosphorylation level of Ser279 as well as cell proliferation and migration rates were markedly increased in the Cx43 overexpression group, and tube formation revealed that the potential of angiogenesis was also increased. Conversely, in the Cx43-knockdown group, the phosphorylation level of Ser279 and cell proliferation and migration rates were reduced, and the potential of angiogenesis was greatly impaired. Under Cx43 overexpression, membranal Cx43 content was significantly increased, whereas under Cx43 knockdown, it was significantly reduced. Therefore, Cx43 overexpression could induce pulmonary angiogenesis in vitro by promoting cell proliferation and migration and activating ZO-1, E-cadherin, β-catenin, vWF, and PAI-1. This may be achieved by promoting phosphorylation and activation of the intracellular signal site Ser279 at the C-terminus of Cx43.

Connexin 43 in Mitochondria: What Do We Really Know About Its Function?

Connexins are known for their ability to mediate cell-cell communication via gap junctions and also form hemichannels that pass ions and molecules over the plasma membrane when open. Connexins have also been detected within mitochondria, with mitochondrial connexin 43 (Cx43) being the best studied to date. In this review, we discuss evidence for Cx43 presence in mitochondria of cell lines, primary cells and organs and summarize data on its localization, import and phosphorylation status. We further highlight the influence of Cx43 on mitochondrial function in terms of respiration, opening of the mitochondrial permeability transition pore and formation of reactive oxygen species, and also address the presence of a truncated form of Cx43 termed Gja1-20k. Finally, the role of mitochondrial Cx43 in pathological conditions, particularly in the heart, is discussed.

Activating Connexin43 gap junctions primes adipose tissue for therapeutic intervention

Adipose tissue is a promising target for treating obesity and metabolic diseases. However, pharmacological agents usually fail to effectively engage adipocytes due to their extraordinarily large size and insufficient vascularization, especially in obese subjects. We have previously shown that during cold exposure, connexin43 (Cx43) gap junctions are induced and activated to connect neighboring adipocytes to share limited sympathetic neuronal input amongst multiple cells. We reason the same mechanism may be leveraged to improve the efficacy of various pharmacological agents that target adipose tissue. Using an adipose tissue-specific Cx43 overexpression mouse model, we demonstrate effectiveness in connecting adipocytes to augment metabolic efficacy of the β 3-adrenergic receptor agonist Mirabegron and FGF21. Additionally, combing those molecules with the Cx43 gap junction channel activator danegaptide shows a similar enhanced efficacy. In light of these findings, we propose a model in which connecting adipocytes via Cx43 gap junction channels primes adipose tissue to pharmacological agents designed to engage it. Thus, Cx43 gap junction activators hold great potential for combination with additional agents targeting adipose tissue.

MicroRNA-155 inhibition attenuates myocardial infarction-induced connexin 43 degradation in cardiomyocytes by reducing pro-inflammatory macrophage activation

BACKGROUND

Degradation of pro-inflammatory macrophage-mediated connexin 43 (Cx43) plays an important role in post-myocardial infarction (MI) arrhythmogenesis, microRNA (miR)-155 produced by macrophages has been shown to mediate post-MI effects. We hypothesized that miR-155 inhibition attenuated MI-induced Cx43 degradation by reducing pro-inflammatory macrophage activation.

METHODS

MI was induced by permanent ligation of the left anterior descending coronary artery in male C57BL/6 mice. Lipopolysaccharide (LPS)-stimulated mice bone marrow-derived macrophages (BMDMs) and hypoxia-induced neonatal rat cardiomyocytes (NRCMs) were used in vitro models. qRT-PCR, Western-blot and immunofluorescence were used to analyze relevant indicators.

RESULTS

The expression levels of miR-155, interleukin-1 beta (IL-1β), and matrix metalloproteinase (MMP)7 were higher in MI mice and LPS-treated BMDMs than in the sham/control groups, treatment with a miR-155 antagomir reversed these effects. Moreover, miR-155 inhibition reduced ventricular arrhythmias incidence and improved cardiac function in MI mice. Cx43 expression was decreased in MI mice and hypoxia-exposed NRCMs, and hypoxia-induced Cx43 degradation in NRCMs was reduced by application of conditioned medium from LPS-induced BMDMs treated with the miR-155 antagomir, but increased by conditioned medium from BMDMs treated with a miR-155 agomir. Importantly, NRCMs cultured in conditioned medium from LPS-induced BMDMs transfected with small interfering RNA against IL-1β and MMP7 showed decreased hypoxia-mediated Cx43 degradation, and this effect also was diminished by BMDM treatment with the miR-155 agomir. Additionally, siRNA-mediated suppressor of cytokine signaling 1 (SOCS1) knockdown in LPS-induced BMDMs promoted Cx43 degradation in hypoxia-exposed NRCMs, and the effect was reduced by the miR-155 inhibition.

CONCLUSIONS

MiR-155 inhibition attenuated post-MI Cx43 degradation by reducing macrophage-mediated IL-1β and MMP7 expression through the SOCS1/nuclear factor-κB pathway.

Pre-transplantation of Bone Marrow Mesenchymal Stem Cells Amplifies the Therapeutic Effect of Ultrasound-Targeted Microbubble Destruction-Mediated Localized Combined Gene Therapy in Post-Myocardial Infarction Heart Failure Rats

Although stem cell transplantation and single-gene therapy have been intensively discussed separately as treatments for myocardial infarction (MI) hearts and have exhibited ideal therapeutic efficiency in animal models, clinical trials turned out to be disappointing. Here, we deliver sarcoplasmic reticulum Ca²⁺-ATPase 2a (SERCA2a) and connexin 43 (Cx43) genes simultaneously via an ultrasound-targeted microbubble destruction (UTMD) approach to chronic MI hearts that have been pre-treated with bone marrow mesenchymal stem cells (BMSCs) to amplify cardiac repair. First, biotinylated microbubbles (BMBs) were fabricated, and biotinylated recombinant adenoviruses carrying the SERCA2a or Cx43 gene were conjugated to the surface of self-assembled BMBs to form SERCA2a-BMBs, Cx43-BMBs or dual gene-loaded BMBs. Then, the general characteristics of these bubbles, including particle size, concentration, contrast signal and gene loading capacity, were examined. Second, a rat myocardial infarction model was created by ligating the left anterior descending coronary artery and injecting BMSCs into the infarct and border zones. Four weeks later, co-delivery of SERCA2a and Cx43 genes to the infarcted heart were delivered together to the infarcted heart using the UTMD approach. Cardiac mechano-electrical function was determined 4 wk after gene transfection, and the infarcted hearts were collected for myocardial infarct size measurement and detection of expression of SERCA2a, Cx43 and cardiac-specific markers. Finally, to validate the role of BMSC transplantation, MI rats transplanted or not with BMSCs were transfected with SERCA2a and Cx43, and the cardiac mechano-electrical function of these two groups of rats was recorded and compared. General characteristics of the self-assembled gene-loaded BMBs were qualified, and the gene loading rate was satisfactory. The self-assembled gene-loaded BMBs were in microscale and exhibit satisfactory dual-gene loading capacity. High transfection efficiency was achieved under ultrasound irradiation in vitro. In addition, rats in which SERCA2a and Cx43 were overexpressed simultaneously had the best contractile function and electrical stability among all experimental groups. Immunofluorescence assay revealed that the levels of SERCA2a and/or Cx43 proteins were significantly elevated, especially in the border zone. Moreover, compared with rats that did not receive BMSCs, rats pre-treated with BMSCs have better mechano-electrical function after transfection with SERCA2a and Cx43. Collectively, we report a promising cardiac repair strategy for post-MI hearts that exploits the providential advantages of stem cell therapy and UTMD-mediated localized co-delivery of specific genes.

GJA1-20k and Mitochondrial Dynamics

Connexin 43 (Cx43) is the primary gap junction protein of mammalian heart ventricles and is encoded by the gene Gja1 which has a single coding exon and therefore cannot be spliced. We previously identified that Gja1 mRNA undergoes endogenous internal translation initiated at one of several internal AUG (M) start codons, generating N-terminal truncated protein isoforms that retain the C-terminus distal to the start site. GJA1-20k, whose translation initiates at mRNA M213, is usually the most abundant isoform in cells and greatly increases after ischemic and metabolic stress. GJA1-20k consists of a small segment of the last transmembrane domain and the complete C-terminus tail of Cx43, with a total size of about 20 kDa. The original role identified for GJA1-20k is as an essential subunit that facilitates the trafficking of full-length Cx43 hexameric hemichannels to cell-cell contacts, generating traditional gap junctions between adjacent cells facilitating, in cardiac muscle, efficient spread of electrical excitation. GJA1-20k deficient mice (generated by a M213L substitution in Gja1) suffer poor electrical coupling between cardiomycytes and arrhythmogenic sudden death two to 4 weeks after their birth. We recently identified that exogenous GJA1-20k expression also mimics the effect of ischemic preconditioning in mouse heart. Furthermore, GJA1-20k localizes to the mitochondrial outer membrane and induces a protective and DRP1 independent form of mitochondrial fission, preserving ATP production and generating less reactive oxygen species (ROS) under metabolic stress, providing powerful protection of myocardium to ischemic insult. In this manuscript, we focus on the detailed roles of GJA1-20k in mitochondria, and its interaction with the actin cytoskeleton.

TGF-β2 increases cell-cell communication in chondrocytes via p-Smad3 signalling

Connexin 43 (Cx43)-mediated gap junction intercellular communication (GJIC) plays a crucial role in the pathology and physiology of joint tissues. Transforming growth factor-β2 (TGF-β2), one of the potent regulatory factors in chondrocytes, plays a key role in the regulation of cell cycle and development of joint diseases. However, it is still unknown how TGF-β2 mediates GJIC in chondrocytes. The aim of this study was to explore the potential mechanism by which TGF-β2 regulates GJIC in chondrocytes. CCK-8 assays and scratch assays were performed to define the role of TGF-β2 on cell proliferation and migration. The scrape loading/dye transfer assay and scanning electron microscopy (SEM) were used to verify the effect of TGF-β2 on GJIC between chondrocytes. qPCR was performed to analyse the expression of genes in the gap junction protein family in chondrocytes. The expression of the Cx43 protein and phosphorylated Smad3 (p-Smad3) was evaluated by western blot assay. Immunofluorescence staining was used to explore p-Smad3 signalling pathway activation and Cx43 distribution. From these experiments, we found that the Cx43 protein was the most highly expressed member of the gap junction protein family in chondrocytes. We also found that TGF-β2 facilitated cell-to-cell communication in chondrocytes by upregulating Cx43 expression in chondrocytes. Finally, we found that TGF-β2 activated Smad3 signalling and promoted the nuclear aggregation of p-Smad3. Inhibition experiments by SIS3 also confirmed that TGF-β2-mediated GJIC through p-Smad3 signalling. For the first time, this study confirmed that TGF-β2 could regulate the formation of Cx43-mediated GJIC in chondrocytes via the canonical p-Smad3 signalling pathway.

CAPE-pNO2 ameliorates diabetic brain injury through modulating Alzheimer's disease key proteins, oxidation, inflammation and autophagy via a Nrf2-dependent pathway

AIMS

CAPE-pNO₂, an active derivative of caffeic acid phenethyl ester, has been verified to exert protection of diabetic cardiomyopathy and diabetic nephropathy. The present study aims to explore the brain protection effects and potential mechanisms of CAPE-pNO₂ on streptozotocin-induced diabetic brain injury in vivo and in vitro.

MAIN METHODS

Biochemical indexes including triglyceride, total cholesterol, superoxide dismutase and malondialdehyde contents were detected. The histopathological structure of hippocampus and cerebral cortex were determined. Immunofluorescence and immunoblot methods were used to assess expression of oxidative stress, inflammation and autophagy pathway-related proteins of diabetic brain in vivo. Alzheimer's disease (AD)-associated key proteins were also checked in vivo. DCFH-DA assay, immunofluorescence and immunoblot methods were applied to verify the master role of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in vitro.

KEY FINDINGS

First, CAPE-pNO₂ could rescue the diabetic brain atrophy and diminish CA1 and CA3 cells of hippocampus and cerebral cortex. Second, CAPE-pNO₂ could decrease Aβ and p-tau (S396) expression through anti-oxidation, anti-inflammation and autophagy induction in vivo. Last, CAPE-pNO₂ could down-regulate p-tau (S396) expression through Nrf2-related anti-oxidation mechanisms in vitro.

SIGNIFICANCE

CAPE-pNO₂ may exert brain protection via Nrf2-dependent way in diabetes. Additionally, Nrf2 was capable of regulating p-tau (S396) expression that is critical to AD.

Protein phosphatase 2A in the healthy and failing heart: New insights and therapeutic opportunities

Protein phosphatases have emerged as critical regulators of phosphoprotein homeostasis in settings of health and disease. Protein phosphatase 2A (PP2A) encompasses a large subfamily of enzymes that remove phosphate groups from serine/threonine residues within phosphoproteins. The heterogeneity in PP2A structure, which arises from the grouping of different catalytic, scaffolding and regulatory subunit isoforms, creates distinct populations of catalytically active enzymes (i.e. holoenzymes) that localise to different parts of the cell. This structural complexity, combined with other regulatory mechanisms, such as interaction of PP2A heterotrimers with accessory proteins and post-translational modification of the catalytic and/or regulatory subunits, enables PP2A holoenzymes to target phosphoprotein substrates in a highly specific manner. In this review, we summarise the roles of PP2A in cardiac physiology and disease. PP2A modulates numerous processes that are vital for heart function including calcium handling, contractility, β-adrenergic signalling, metabolism and transcription. Dysregulation of PP2A has been observed in human cardiac disease settings, including heart failure and atrial fibrillation. Efforts are underway, particularly in the cancer field, to develop therapeutics targeting PP2A activity. The development of small molecule activators of PP2A (SMAPs) and other compounds that selectively target specific PP2A holoenzymes (e.g. PP2A/B56α and PP2A/B56ε) will improve understanding of the function of different PP2A species in the heart, and may lead to the development of therapeutics for normalising aberrant protein phosphorylation in settings of cardiac remodelling and dysfunction.

Remote limb ischaemic conditioning produces cardioprotection in rats with testicular ischaemia-reperfusion injury

NEW FINDINGS

What is the central question of this study? Can remote limb ischaemic conditioning produce cardioprotection in rats with testicular ischaemia-reperfusion injury? What is the main finding and its importance? Testicular ischaemia-reperfusion (TI/R)-injured rats were predisposed to myocardial reperfusion-induced atrioventricular block. Remote limb ischaemia preconditioning and postconditioning protected TI/R hearts against ischaemia-provoked ventricular arrhythmia and ultimately reduced the incidence of sudden cardiac death, with a possible role of c-Jun N-terminal kinase inhibition and connexin 43 activation.

ABSTRACT

Remote ischaemic conditioning can protect hearts against arrhythmia. Testicular ischaemia-reperfusion (TI/R) injury is associated with electrocardiographic abnormalities. We investigated the effect of remote limb ischaemia preconditioning (RIPre) and postconditioning (RIPost) on arrhythmogenesis in TI/R rats, and determined the potential role of c-Jun N-terminal kinase (JNK)/connexin 43 (Cx43) signalling. Rats were randomized to sham-operated, control, TI/R, RIPre and RIPost groups. TI/R rats were more predisposed to myocardial reperfusion-induced atrioventricular block (AVB). RIPre and RIPost reduced the incidence of sudden cardiac death (SCD) or AVB, and duration of ventricular tachyarrhythmias during myocardial reperfusion. RIPre and RIPost decreased myocardial I/R-induced phosphorylation level of JNK, while preserving myocardial Cx43 expression in TI/R rats. Taken together, TI/R rats were predisposed to myocardial reperfusion-induced AVB. RIPre and RIPost protected TI/R hearts against ischaemia-provoked ventricular arrhythmia and ultimately reduced the incidence of SCD by suppressing JNK activation and restoring Cx43 expression.

Majonoside-R2 Postconditioning Protects Cardiomyocytes Against Hypoxia/Reoxygenation Injury by Attenuating the Expression of HIF1α and Activating RISK Pathway

Reoxygenation of hypoxic cardiac myocytes can paradoxically induce myocardial injury and affect the recovery processes. Pharmacological postconditioning is an efficient strategy used in clinical practice that protects cardiomyocytes from hypoxia/reoxygenation (HR) injury. Natural products or foods have been known to possess effective cardioprotective properties. Majonoside-R2 (MR2) is a dominant saponin component of Vietnamese ginseng that has several biological effects. In this study, we evaluated the protective effect of MR2 on HR-stimulated cardiomyocytes and investigated the related molecular mechanisms. H9C2 cardiomyocytes were exposed to HR conditions with or without MR2 supplementation. Samples from experimental groups were used to analyze the expression of apoptosis- and activating reperfusion injury salvage kinase (RISK)-related factors in response to HR injury by using enzyme-linked immunosorbent assay, real-time polymerase chain reaction, and Western blotting. Post-treatment, MR2 enhanced cell viability under HR conditions. We found that MR2 suppressed the expression of hypoxia-inducible factor 1-alpha (HIF1α) and transforming growth factor beta 1 (TGFβ1), modulated Akt/GSK3ß/cAMP response element-binding signaling, and regulated gene expression related to apoptosis (B cell lymphoma-extra-large [Bcl-xl], Bcl-2 homologous killer [Bak], Bcl-2 associated X [Bax], and connexin 43 [Cnx43]). Thus, the present findings demonstrate that MR2 protects cardiomyocytes against HR injury by suppressing the expression of HIF1α and activating the RISK pathway.

Roles of Exosomes in Cardiac Fibroblast Activation and Fibrosis

Alterations in the accumulation and composition of the extracellular matrix are part of the normal tissue repair process. During fibrosis, this process becomes dysregulated and excessive extracellular matrix alters the biomechanical properties and function of tissues involved. Historically fibrosis was thought to be progressive and irreversible; however, studies suggest that fibrosis is a dynamic process whose progression can be stopped and even reversed. This realization has led to an enhanced pursuit of therapeutic agents targeting fibrosis and extracellular matrix-producing cells. In many organs, fibroblasts are the primary cells that produce the extracellular matrix. In response to diverse mechanical and biochemical stimuli, these cells are activated or transdifferentiate into specialized cells termed myofibroblasts that have an enhanced capacity to produce extracellular matrix. It is clear that interactions between diverse cells of the heart are able to modulate fibroblast activation and fibrosis. Exosomes are a form of extracellular vesicle that play an important role in intercellular communication via the cargo that they deliver to target cells. While relatively recently discovered, exosomes have been demonstrated to play important positive and negative roles in the regulation of fibroblast activation and tissue fibrosis. These roles as well as efforts to engineer exosomes as therapeutic tools will be discussed.

Estrogen alleviates hepatocyte necroptosis depending on GPER in hepatic ischemia reperfusion injury

Hepatic ischemia reperfusion injury (IRI) occurs in liver transplantation, complex liver resection, and hemorrhagic shock, which causes donor organ shortage and hepatic damage. The burst of reactive oxygen species (ROS) during reperfusion leads to cell apoptosis and necroptosis. It has been reported that estrogen could attenuate hepatic IRI. G protein estrogen receptor (GPER) mediates estrogen effects via nonclassic receptor systems. Here, we investigate whether estrogen protecting liver from hepatic IRI depends on GPER and the influence of GPER activation on hepatocyte necroptosis. We proved that estrogen had a protective effect on both hepatocyte hypoxia re-oxygen (H/R) challenge and mouse hepatic ischemia reperfusion model. However, the application of GPER specific antagonist G15 before estrogen inhibited this beneficial effect. The results of mitochondria functional measurement revealed that estrogen improved hepatocyte mitochondria function by activating GPER, which might benefit from the increased expression of connexin 43 (Cx43) in mitochondria. To investigate the relationship between GPER activation and necroptosis, we used caspase-3/7 inhibitor benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-chloromethylketone (Z-DEVD-FMK) to eliminate the interference of apoptosis. Estrogen showed a protective effect on hepatic IRI after using Z-DEVD-FMK, which could be suppressed by G15. GPER activation decreased the level of receptor interacting protein kinase (RIPK) 3, phosphorylated (p-) RIPK1, and p-mixed lineage kinase domain-like (MLKL). The co-immunoprecipitation result indicated that GPER could bind with RIPK3. GPER is indispensable in estrogen protecting liver from IRI. GPER activation attenuates hepatocyte necroptosis by decreasing the level of RIPK3, p-RIPK1, and p-MLKL.

Mesenchymal stem cells seeded onto nanofiber scaffold for myocardial regeneration

Cardiac disease is the leading cause of mortality and disability worldwide. We investigated the role of undifferentiated adipose tissue-derived mesenchymal stem cells (ADMSC) alone and ADMSC seeded onto the electro-spun nanofibers (NF) for reconstructing damaged cardiac tissue in isoprenaline-induced myocardial infarction (MI) in rats. ADMSC were sorted by morphological appearance and by detection of cluster of differentiation (CD) surface antigens. The therapeutic potential of ADMSC for treating MI was evaluated by electrocardiogram (ECG), biochemical analysis, molecular genetic analysis and histological examination. Treatment of MI-challenged rats with ADMSC improved ECG findings, which were corroborated by significant decreases in serum lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) enzyme activities together with reduced serum troponin T (cTnT) and connexin 43 (Cx43) levels. MI model rats treated with ADMSC exhibited a significant increase in serum alpha sarcomeric actin (Actn) and GATA binding protein 4 (GATA4), and NK2 homeobox 5 (NKX2.5) gene expression was decreased following treatment with ADMSC. ADMSC also ameliorated damage to cardiac tissue. The effects of ADMSC seeded onto NF were superior to those of ADMSC alone. ADMSC may be useful for mitigation of MI.

Novel antidepressant mechanism of ginsenoside Rg1: Regulating biosynthesis and degradation of connexin43

ETHNOPHARMACOLOGICAL RELEVANCE

Panax ginseng C. A. Meyer is a valuable medicinal herb and "alternative" remedy for the prevention and treatment of depression. Dysfunction of connexin43 (Cx43)-gap junction in astrocytes is predisposed to the precipitation of depression. Ginsenoside Rg1 (Rg1), the main bioactive constituent extracted from ginseng, is efficacious in the management of depression by upregulating the content of Cx43. Our previous results indicated that pretreatment with Rg1 significantly improved Cx43-gap junction in corticosterone (CORT)-treated astrocytes. However, the antidepressant mechanism underlying how Rg1 upregulates Cx43-gap junction in astrocytes hasn't been proposed.

AIM OF THE STUDY

To dissect the mechanisms of Rg1 controlling Cx43 levels in primary astrocytes.

METHODS

We examined the changes of the level of Cx43 mRNA, the degradation of Cx43, as well as the ubiquitin-proteasomal and autophagy-lysosomal degradation pathways of Cx43 followed by Rg1 prior to CORT in rat primary astrocytes isolated from prefrontal cortex and hippocampus. Furthermore, the recognized method of scrape loading/dye transfer was performed to detect Cx43-gap junctional function, an essencial indicator of the antidepressant effect.

RESULTS

Pretreatment with Rg1 could reverse CORT-induced downregulation of Cx43 biosynthesis, acceleration of Cx43 degradation, and upregulation of two Cx43 degradation pathways in primary astrocytes.

CONCLUSION

The findings in the present study provide the first evidence highlighting that Rg1 increases Cx43 protein levels through the upregulation of Cx43 mRNA and downregulation of Cx43 degradation, which may be attributed to the effect of Rg1 on the ubiquitin-proteasomal and autophagy-lysosomal degradation pathways of Cx43.

Protective mitochondrial fission induced by stress-responsive protein GJA1-20k

The Connexin43 gap junction gene GJA1 has one coding exon, but its mRNA undergoes internal translation to generate N-terminal truncated isoforms of Connexin43 with the predominant isoform being only 20 kDa in size (GJA1-20k). Endogenous GJA1-20k protein is not membrane bound and has been found to increase in response to ischemic stress, localize to mitochondria, and mimic ischemic preconditioning protection in the heart. However, it is not known how GJA1-20k benefits mitochondria to provide this protection. Here, using human cells and mice, we identify that GJA1-20k polymerizes actin around mitochondria which induces focal constriction sites. Mitochondrial fission events occur within about 45 s of GJA1-20k recruitment of actin. Interestingly, GJA1-20k mediated fission is independent of canonical Dynamin-Related Protein 1 (DRP1). We find that GJA1-20k-induced smaller mitochondria have decreased reactive oxygen species (ROS) generation and, in hearts, provide potent protection against ischemia-reperfusion injury. The results indicate that stress responsive internally translated GJA1-20k stabilizes polymerized actin filaments to stimulate non-canonical mitochondrial fission which limits ischemic-reperfusion induced myocardial infarction.

Serine-threonine protein phosphatase regulation of Cx43 dephosphorylation in arrhythmogenic disorders

Regulation of cell-to-cell communication in the heart by the gap junction protein Connexin43 (Cx43) involves modulation of Cx43 phosphorylation state by protein kinases, and dephosphorylation by protein phosphatases. Dephosphorylation of Cx43 has been associated with impaired intercellular coupling and enhanced arrhythmogenesis in various pathologic states. While there has been extensive study of the protein kinases acting on Cx43, there has been limited studies of the protein phosphatases that may underlie Cx43 dephosphorylation. The focus of this review is to introduce serine-threonine protein phosphatase regulation of Cx43 phosphorylation state and cell-to-cell communication, and its impact on arrhythmogenesis in the setting of chronic heart failure and myocardial ischemia, as well as on atrial fibrillation. We also discuss the therapeutic potential of modulating protein phosphatases to treat arrhythmias in these clinical settings.

Mechanisms of Connexin Regulating Peptides

Gap junctions (GJ) and connexins play integral roles in cellular physiology and have been found to be involved in multiple pathophysiological states from cancer to cardiovascular disease. Studies over the last 60 years have demonstrated the utility of altering GJ signaling pathways in experimental models, which has led to them being attractive targets for therapeutic intervention. A number of different mechanisms have been proposed to regulate GJ signaling, including channel blocking, enhancing channel open state, and disrupting protein-protein interactions. The primary mechanism for this has been through the design of numerous peptides as therapeutics, that are either currently in early development or are in various stages of clinical trials. Despite over 25 years of research into connexin targeting peptides, the overall mechanisms of action are still poorly understood. In this overview, we discuss published connexin targeting peptides, their reported mechanisms of action, and the potential for these molecules in the treatment of disease.

Mesenchymal Stem/Stromal Cell Therapy in Blood-Brain Barrier Preservation Following Ischemia: Molecular Mechanisms and Prospects

Ischemic stroke is the leading cause of mortality and long-term disability worldwide. Disruption of the blood-brain barrier (BBB) is a prominent pathophysiological mechanism, responsible for a series of subsequent inflammatory cascades that exacerbate the damage to brain tissue. However, the benefit of recanalization is limited in most patients because of the narrow therapeutic time window. Recently, mesenchymal stem cells (MSCs) have been assessed as excellent candidates for cell-based therapy in cerebral ischemia, including neuroinflammatory alleviation, angiogenesis and neurogenesis promotion through their paracrine actions. In addition, accumulating evidence on how MSC therapy preserves BBB integrity after stroke may open up novel therapeutic targets for treating cerebrovascular diseases. In this review, we focus on the molecular mechanisms of MSC-based therapy in the ischemia-induced prevention of BBB compromise. Currently, therapeutic effects of MSCs for stroke are primarily based on the fundamental pathogenesis of BBB breakdown, such as attenuating leukocyte infiltration, matrix metalloproteinase (MMP) regulation, antioxidant, anti-inflammation, stabilizing morphology and crosstalk between cellular components of the BBB. We also discuss prospective studies to improve the effectiveness of MSC therapy through enhanced migration into defined brain regions of stem cells. Targeted therapy is a promising new direction and is being prioritized for extensive research.

The Cx43 Carboxyl-Terminal Mimetic Peptide αCT1 Protects Endothelial Barrier Function in a ZO1 Binding-Competent Manner

The Cx43 carboxyl-terminus (CT) mimetic peptide, αCT1, originally designed to bind to Zonula Occludens 1 (ZO1) and thereby inhibit Cx43/ZO1 interaction, was used as a tool to probe the role of Cx43/ZO1 association in regulation of epithelial/endothelial barrier function. Using both in vitro and ex vivo methods of barrier function measurement, including Electric Cell-Substrate Impedance Sensing (ECIS), a TRITC-dextran Transwell permeability assay, and a FITC-dextran cardiovascular leakage protocol involving Langendorff-perfused mouse hearts, αCT1 was found to protect the endothelium from thrombin-induced breakdown in cell-cell contacts. Barrier protection was accompanied by significant remodeling of the F-actin cytoskeleton, characterized by a redistribution of F-actin away from the cytoplasmic and nuclear regions of the cell, towards the endothelial cell periphery, in association with alterations in cellular chiral orientation distribution. In line with observations of increased cortical F-actin, αCT1 upregulated cell-cell border localization of endothelial VE-cadherin, the tight junction protein Zonula Occludens 1 (ZO1), and the Gap Junction Protein (GJ) Connexin43 (Cx43). A ZO1 binding-incompetent variant of αCT1, αCT1-I, indicated that these effects on barrier function and barrier-associated proteins, were likely associated with Cx43 CT sequences retaining ability to interact with ZO1. These results implicate the Cx43 CT and its interaction with ZO1, in the regulation of endothelial barrier function, while revealing the therapeutic potential of αCT1 in the treatment of vascular edema.

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.

Propofol Mediated Protection of the Brain From Ischemia/Reperfusion Injury Through the Regulation of Microglial Connexin 43

Cerebral ischemia/reperfusion (I/R) injury is a serious condition that leads to increased apoptosis of microglial and neurons in the brain. In this study, we identified that Cx43 expression level is significantly increased in the microglial cells during I/R injury. Using an in vitro model (hypoxia/reoxygenation-H/R injury), we observed that H/R injury leads to an increase in activation of microglial cells and increase in levels of pro-inflammatory markers such as IL-1β, IL-6, and TNF-α. Additionally, we could also observe significant increase in phosphorylation of Cx43 and Cav3.2 levels. To assess the role of H/R injured microglial cells on neuronal population, we cultured the neurons with conditioned media (MCS) from H/R injured microglial cells. Interestingly, we observed that microglial H/R injury significantly decreased Map2 expression and affected neuronal morphology. Further, we aimed to assess the effects of propofol on cerebral H/R injury, and observed that 40 μM propofol significantly decreased Cx43, Cx43 phosphorylation, and CaV3.2 levels. Additionally, propofol decreased apoptosis and increased Map2 expression levels in H/R injured neurons. Using silencing experiments, we confirmed that siCx43 could significantly improve the propofol's rescue after H/R injury in both microglia and neurons. We further developed an in vivo MCAO (middle cerebral artery occlusion) rat model to understand the effect of propofol in I/R injury. Interestingly, propofol treatment and downregulation of Cx43 significantly decreased the infract volume and apoptosis in these MCAO rats. Thus, this study clearly establishes that propofol protects the brain against I/R injury through the downregulation of Cx43 in microglial cells.

Astroglial Connexins in Neurodegenerative Diseases

Astrocytes play a crucial role in the maintenance of the normal functions of the Central Nervous System (CNS). During the pathogenesis of neurodegenerative diseases, astrocytes undergo morphological and functional remodeling, a process called reactive astrogliosis, in response to the insults to the CNS. One of the key aspects of the reactive astrocytes is the change in the expression and function of connexins. Connexins are channel proteins that highly expressed in astrocytes, forming gap junction channels and hemichannels, allowing diffusional trafficking of small molecules. Alterations of astrocytic connexin expression and function found in neurodegenerative diseases have been shown to affect the disease progression by changing neuronal function and survival. In this review, we will summarize the role of astroglial connexins in neurodegenerative diseases including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Also, we will discuss why targeting connexins can be a plausible therapeutic strategy to manage these neurodegenerative diseases.

Effects of Hypothermic Hypoxia/Reoxygenation Fibroblast Culture Medium Containing Sevoflurane on Cardiomyocytes

We established a model of hypothermic hypoxia/reoxygenation injury of fibroblasts, simulated the process of ischemia/reperfusion injury during cardiopulmonary bypass, and studied the effects of cardiac fibroblasts on cardiomyocyte activity, connexin 43 (Cx43), and calmodulin kinase II (CaMKII) expression. Furthermore, the effects of sevoflurane-treated fibroblast culture medium on cardiac activity, Cx43 protein, and CaMKII expression were observed. The results showed that the fibroblast culture medium damaged by hypothermic hypoxia/reoxygenation could reduce the beating frequency of cardiomyocytes, increase the mortality of cardiomyocytes, decrease the relative expression of Cx43, and increase the relative expression of CaMKII. However, sevoflurane containing hypothermic hypoxia/reoxygenation injury fibroblast culture medium can increase the beating frequency of cardiomyocytes, reduce the mortality of cardiomyocytes, increase the relative expression of Cx43 protein, and decrease the relative expression of CaMKII. The results suggest that the antiarrhythmic effects of sevoflurane on the expression of Cx43 and CaMKII are related to fibroblasts.

A role of connexin 43 on the drug-induced liver, kidney, and gastrointestinal tract toxicity with associated signaling pathways

Drug-induced organ toxicity/injury, especially in the liver, kidney, and gastrointestinal tract, is a systematic disorder that causes oxidative stress formation and inflammation resulting in cell death and organ failure. Current therapies target reactive oxygen species (ROS) scavenging and inhibit inflammatory factors in organ injury to restore the functions and temporary relief. Organ cell function and tissue homeostasis are maintained through gap junction intercellular communication, regulating connexin hemichannels. Mis-regulation of such connexin, especially connexin (Cx) 43, affects a comprehensive process, including cell differentiation, inflammation, and cell death. Aim to describe knowledge about the importance of connexin role and insights therapeutic targeting. Cx43 misregulation has been implicated in recent decades in various diseases. Moreover, in recent years there is increasing evidence that Cx43 is involved in the toxicity process, including hepatic, renal, and gastrointestinal disorders. Cx43 has the potential to initiate the immune system to cause cell death, which has been activated in the acceleration of apoptosis, necroptosis, and autophagy signaling pathway. So far, therapies targeting Cx43 have been under inspection and are subjected to clinical trial phases. This review elucidates the role of Cx43 in drug-induced vital organ injury, and recent reports compromise its function in the major signaling pathways.