Expression and role of connexin-based gap junctions in pulmonary inflammatory diseases

Dynamics of Endothelial Cell Diversity and Plasticity in Health and Disease

Endothelial cells (ECs) are vital structural units of the cardiovascular system possessing two principal distinctive properties: heterogeneity and plasticity. Endothelial heterogeneity is defined by differences in tissue-specific endothelial phenotypes and their high predisposition to modification along the length of the vascular bed. This aspect of heterogeneity is closely associated with plasticity, the ability of ECs to adapt to environmental cues through the mobilization of genetic, molecular, and structural alterations. The specific endothelial cytoarchitectonics facilitate a quick structural cell reorganization and, furthermore, easy adaptation to the extrinsic and intrinsic environmental stimuli, known as the epigenetic landscape. ECs, as universally distributed and ubiquitous cells of the human body, play a role that extends far beyond their structural function in the cardiovascular system. They play a crucial role in terms of barrier function, cell-to-cell communication, and a myriad of physiological and pathologic processes. These include development, ontogenesis, disease initiation, and progression, as well as growth, regeneration, and repair. Despite substantial progress in the understanding of endothelial cell biology, the role of ECs in healthy conditions and pathologies remains a fascinating area of exploration. This review aims to summarize knowledge and concepts in endothelial biology. It focuses on the development and functional characteristics of endothelial cells in health and pathological conditions, with a particular emphasis on endothelial phenotypic and functional heterogeneity.

NGF increases Connexin-43 expression and function in pulmonary arterial smooth muscle cells to induce pulmonary artery hyperreactivity

AIMS

Pulmonary hypertension (PH) is characterised by an increase in pulmonary arterial pressure, ultimately leading to right ventricular failure and death. We have previously shown that nerve growth factor (NGF) plays a critical role in PH. Our objectives here were to determine whether NGF controls Connexin-43 (Cx43) expression and function in the pulmonary arterial smooth muscle, and whether this mechanism contributes to NGF-induced pulmonary artery hyperreactivity.

METHODS AND RESULTS

NGF activates its TrkA receptor to increase Cx43 expression, phosphorylation, and localization at the plasma membrane in human pulmonary arterial smooth muscle cells, thus leading to enhanced activity of Cx43-dependent GAP junctions as shown by Lucifer Yellow dye assay transfer and fluorescence recovery after photobleaching -FRAP- experiments. Using both in vitro pharmacological and in vivo SiRNA approaches, we demonstrate that NGF-dependent increase in Cx43 expression and activity in the rat pulmonary circulation causes pulmonary artery hyperreactivity. We also show that, in a rat model of PH induced by chronic hypoxia, in vivo blockade of NGF or of its TrkA receptor significantly reduces Cx43 increased pulmonary arterial expression induced by chronic hypoxia and displays preventive effects on pulmonary arterial pressure increase and right heart hypertrophy.

CONCLUSIONS

Modulation of Cx43 by NGF in pulmonary arterial smooth muscle cells contributes to NGF-induced alterations of pulmonary artery reactivity. Since NGF and its TrkA receptor play a role in vivo in Cx43 increased expression in PH induced by chronic hypoxia, these NGF/Cx43-dependent mechanisms may therefore play a significant role in human PH pathophysiology.

Intercellular Communication in Airway Epithelial Cell Regeneration: Potential Roles of Connexins and Pannexins

Connexins and pannexins are transmembrane proteins that can form direct (gap junctions) or indirect (connexons, pannexons) intercellular communication channels. By propagating ions, metabolites, sugars, nucleotides, miRNAs, and/or second messengers, they participate in a variety of physiological functions, such as tissue homeostasis and host defense. There is solid evidence supporting a role for intercellular signaling in various pulmonary inflammatory diseases where alteration of connexin/pannexin channel functional expression occurs, thus leading to abnormal intercellular communication pathways and contributing to pathophysiological aspects, such as innate immune defense and remodeling. The integrity of the airway epithelium, which is the first line of defense against invading microbes, is established and maintained by a repair mechanism that involves processes such as proliferation, migration, and differentiation. Here, we briefly summarize current knowledge on the contribution of connexins and pannexins to necessary processes of tissue repair and speculate on their possible involvement in the shaping of the airway epithelium integrity.

Exosomal miRNAs contribute to coal dust particle-induced pulmonary fibrosis in rats

Coal workers' pneumoconiosis (CWP) is a fatal occupational disease caused by inhalation of coal dust particles, which leads to progressive pulmonary fibrosis. Recently, as new signal carriers for intercellular communication, exosomal miRNAs have been validated in the pathogenesis of multiple diseases. However, the research on exosomal miRNAs in CWP is still in the preliminary stage. Here, using miRNA sequencing, exosomal miRNA profiles in bronchoalveolar lavage fluid (BALF) from rats with pulmonary fibrosis induced by coal dust particles were analyzed, and the underlying biological function of putative target genes was explored by GO term analysis and KEGG pathway enrichment analysis. According to the results, intratracheal instillation of coal dust particles can alter the exosomal miRNAs expression in the BALF of rats. Further bioinformatics analysis provided some clues to reveal their function in pathological process of pneumoconiosis. More importantly, we identified 4 differentially expressed exosomal miRNAs (miRNA-21-5p, miRNA-29a-3p, miRNA-26a-5p, and miRNA-34a-5p) by qRT‑PCR and further verified the temporal changes in the expression of these exosomal miRNAs in animal models from 2 weeks to 16 weeks postexposure. In addition, we conducted a preliminary study on Smad7 as a potential target of miRNA-21-5p and found that exosomal miRNA 21-5p/Smad7 may contribute to the pulmonary fibrosis induced by coal dust particles. Our study confirmed the contribution of exosomal miRNAs to coal dust particle-induced pulmonary fibrosis and provided new insights into the pathogenesis of CWP.

Connexins may play a critical role in cigarette smoke-induced pulmonary hypertension

Pulmonary hypertension (PH) is a chronic progressive disease characterized by pulmonary vasoconstriction and remodeling. It causes a gradual increase in pulmonary vascular resistance leading to right-sided heart failure, and may be fatal. Chronic exposure to cigarette smoke (CS) is an essential risk factor for PH group 3; however, smoking continues to be prevalent and smoking cessation is reported to be difficult. A majority of smokers exhibit PH, which leads to a concomitant increase in the risk of mortality. The current treatments for PH group 3 focus on vasodilation and long-term oxygen supplementation, and fail to stop or reverse PH-associated continuous vascular remodeling. Recent studies have suggested that pulmonary vascular endothelial dysfunction induced by CS exposure may be an initial event in the natural history of PH, which in turn may be associated with abnormal alterations in connexin (Cx) expression. The relationship between Cx and CS-induced PH development has not yet been directly investigated. Therefore, this review will describe the roles of CS and Cx in the development of PH and discuss the related downstream pathways. We also discuss the possible role of Cx in CS-induced PH. It is hoped that this review may provide new perspectives for early intervention.

Mechanisms of SARS-CoV-2 and Male Infertility: Could Connexin and Pannexin Play a Role?

The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on male infertility has lately received significant attention. SARS-CoV-2, the virus that causes coronavirus disease (COVID-19) in humans, has been shown to impose adverse effects on both the structural components and function of the testis, which potentially impact spermatogenesis. These adverse effects are partially explained by fever, systemic inflammation, oxidative stress, and an increased immune response leading to impaired blood-testis barrier. It has been well established that efficient cellular communication via gap junctions or functional channels is required for tissue homeostasis. Connexins and pannexins are two protein families that mediate autocrine and paracrine signaling between the cells and the extracellular environment. These channel-forming proteins have been shown to play a role in coordinating cellular communication in the testis and epididymis. Despite their role in maintaining a proper male reproductive milieu, their function is disrupted under pathological conditions. The involvement of these channels has been well documented in several physiological and pathological conditions and their designated function in infectious diseases. However, their role in COVID-19 and their meaningful contribution to male infertility remains to be elucidated. Therefore, this review highlights the multivariate pathophysiological mechanisms of SARS-CoV-2 involvement in male reproduction. It also aims to shed light on the role of connexin and pannexin channels in disease progression, emphasizing their unexplored role and regulation of SARS-CoV-2 pathophysiology. Finally, we hypothesize the possible involvement of connexins and pannexins in SARS-CoV-2 inducing male infertility to assist future research ideas targeting therapeutic approaches.

The Role of Extracellular Vesicles in Idiopathic Pulmonary Fibrosis Progression: An Approach on Their Therapeutics Potential

Idiopathic pulmonary fibrosis (IPF) is a fibrosing interstitial lung disease of unknown etiology. Different types of cells are involved in fibrogenesis, which is persistently physical and molecular stimulation, either directly or by interacting with bioactive molecules and extracellular vesicles (EVs). Current evidence suggests that EVs play an essential role in IPF development. EVs are released by a variety of cells, including fibroblasts, epithelial cells, and alveolar macrophages. In addition, EVs can transport bioactive molecules, such as lipids, proteins, and nucleic acids, which play a pivotal role in cellular communication. Several proposed mechanisms show that an acceptor cell can capture, absorb, or interact with EVs through direct fusion with the plasma membrane, ligand–receptor interaction, and endocytotic process, modifying the target cell. During fibrogenesis, the release of EVs is deregulated, increases the EVs amount, and the cargo content is modified. This alteration is closely associated with the maintenance of the fibrotic microenvironment. This review summarizes the current data on the participation of EVs secreted by the cells playing a critical role in IPF pathogenesis.

Vitexin restores lung homeostasis by targeting vicious loop between inflammatory aggravation and autophagy mediated via multiple redox cascade and myeloid cells alteration in experimental allergic asthma

BACKGROUND

Allergic asthma is one of the leading respiratory diseases with complex pathology. Attributes of vitexin, a trihydroxyflavone, has been studied to alleviate Th2 cytokines response in allergic asthma. However, its efficacy and underlying mechanism in mitigating allergic asthma particularly mediated by oxi-inflammatory stress, autophagy and apoptosis, yet to be delineated.

PURPOSE

Present study aimed to decipher efficacy and governing molecular mechanism of vitexin in mitigating allergic asthma particularly mediated by vicious loop of oxi-inflammatory stress, autophagy and apoptosis.

METHODS

To ascertain this, OVA-LPS induced mice model was used and protective attributes of vitexin for different mediators, pathological facets and sensing pathways of allergic asthma were evaluated.

RESULTS

Vitexin treatment remarkably inhibited OVA-LPS induced inflammatory cell infiltration, mast cell activation, alveolar collapse, congestion, fibrosis in lung architecture. These results were accompanied by suppression of immune cells hyperactivation, mucus secretion, goblet cell proliferation, persistent inflammation which were affirmed by alleviation in levels of IgE, Th1/Th2/Th17, IL-4/IFN-γ, chemokines, endopeptidases (MMP-1, MMP-13), oxidative effectors with concomitant increase in IL-15, IL-10, MMP-9 and MMP-3. Additionally, noticeable decline in p-connexin 43, p-c-Fos, TGF-β, Smad2/3/4, Caspase9/3, LC3A/B expression and upregulation in beclin-1, p62 co-localization and Bcl2/Bax indicate reversal of lung vascular permeability, mast cell degranulation, fibrosis, apoptosis, autophagosome impairment. Subsequent allergic inflammatory cascades analysis revealed p-NF-κB, p-PI3K, p-Akt, p-p38, p-Stat3, GATA3 upregulation and p-PTEN downregulation in sensitized mice, which were decisively counteracted by vitexin. In silico studies signified target specificity of vitexin with these proteins. Suppression in myeloid cells activation and enhancements of Tregs demonstrated immunomodulatory potential of vitexin in allergic airways.

CONCLUSION

Collectively, to our knowledge, this is the first report that confers vitexin meditated multi-faceted protective attribute in mitigation of allergic asthma that could be linked to its suppressive effects on vicious cycle of pathological process particularly regulated via oxi-inflammation, autophagy and apoptosis. Thus, signify vitexin as safe therapeutic strategy.

Rising trends towards the development of oral herbal male contraceptive: an insight review

Background

Acknowledging population control to be an essential step for global health promotes wide research study in the area of male contraception. Although there are a great number of synthetic contraceptives available in the market, they have plenty of adverse effects. Different potential strategies for male contraception were investigated over a long period time consisting of hormonal, chemical, and immunological interventions, although these methods showed good antifertility results with low failure rates relative to condoms.

Main text

This review is based upon the concept of herbal contraceptives which are an effective method for controlling the fertility of animals and humans. This review has highlighted herbal medicinal plants and plant extracts which have been reported to possess significant antifertility action in males. The review considers those plants which are used traditionally for their spermicidal and antispermatogenic activities and imbalance essential hormones for fertility purposes and plants with reported animal studies as well as some with human studies for antifertility effect along with their doses, chemical constituents, and mechanism of action of the antifertility effect of the plants. This review also explains the phases of sperm formation, hormone production, and the mechanism of male contraceptives.

Conclusion

As far as the relevance of the current review is discussed, it might be quite useful in generating monographs on plants and recommendations on their use. A lot of the plant species listed here might appear promising as effective alternative oral fertility-regulating agents in males. Therefore, significant research into the chemical and biological properties of such less-explored plants is still needed to determine their contraceptive efficacy and also to possibly define their toxic effects so that these ingredients can be utilized with confidence to regulate male fertility. The new inventions in this field are necessary to concentrate on modern, more potent drugs with less harmful content and that are self-administrable, less costly, and entirely reversible.

Impact of a Gap Junction Protein Alpha 4 Variant on Clinical Disease Phenotype in F508del Homozygous Patients With Cystic Fibrosis

Background

Lung disease phenotype varies widely even in the F508del (homozygous) genotype. Leukocyte-driven inflammation is important for pulmonary disease pathogenesis in cystic fibrosis (CF). Blood cytokines correlate negatively with pulmonary function in F508del homozygous patients, and gap junction proteins (GJA) might be related to the influx of blood cells into the lung and influence disease course. We aimed to assess the relationship between GJA1/GJA4 genotypes and the clinical disease phenotype.

Methods

One-hundred-and-sixteen homozygous F508del patients (mean age 27 years, m/f 66/50) were recruited from the CF centers of Bonn, Frankfurt, and Amsterdam. Sequence analysis was performed for GJA1 and GJA4. The clinical disease course was assessed over 3 years using pulmonary function tests, body mass index, Pseudomonas aeruginosa colonization, diabetes mellitus, survival to end-stage lung disease, blood and sputum inflammatory markers.

Results

Sequence analysis revealed one clinically relevant single nucleotide polymorphism. In this GJA4 variant (rs41266431), homozygous G variant carriers (n = 84/116; 72.4%) had poorer pulmonary function (FVC% pred: mean 78/86, p < 0.040) and survival to end-stage lung disease was lower (p < 0.029). The frequency of P. aeruginosa colonization was not influenced by the genotype, but in those chronically colonized, those with the G/G genotype had reduced pulmonary function (FVC% pred: mean 67/80, p < 0.049). Serum interleukin-8 (median: 12.4/6.7 pg/ml, p < 0.052) and sputum leukocytes (2305/437.5 pg/ml, p < 0.025) were higher for the G/G genotype.

Conclusions

In carriers of the A allele (27.6%) the GJA4 variant is associated with significantly better protection against end-stage lung disease and superior pulmonary function test results in F508del homozygous patients. This SNP has the potential of a modifier gene for phenotyping severity of CF lung disease, in addition to the CFTR genotype.

Clinical Trial Registration

The study was registered with ClinicalTrials.gov, number NCT04242420, retrospectively on January 24th, 2020.

Effects of Connexin 32-Mediated Lung Inflammation Resolution During Liver Ischemia Reperfusion

BACKGROUND

Hepatic ischemia reperfusion (HIR) leads to a lung inflammatory response and subsequent pulmonary barrier dysfunction. The gap junction communication protein connexin 32 (Cx32), which is widely expressed in the lungs, participates in intercellular signaling. This study determined whether the communication protein Cx32 could affect pulmonary inflammation caused by HIR.

METHODS

Mice were randomly allocated into four groups (n = 8/group): (i) Cx32+/+ sham group; (ii) Cx32+/+ HIR model group; (iii) Cx32-/- sham group; and (iv) Cx32-/- HIR model group. Twenty-four hours after surgery, lung tissues were collected for bright field microscopy, western blot (Cx32, JAK2, p-JAK2, STAT3, p-STAT3), and immunofluorescence (ZO-1, 8-OHDG) analyses. The collected bronchoalveolar fluid was tested for levels of interleukin-6 (IL-6), matrix metalloproteinase 12 (MMP-12), and antitrypsin (α1-AT). Lung mmu-miR-26a/b expression was detected using a PCR assay.

RESULTS

Increased expression of Cx32 mRNA and protein was noted in the lungs after HIR. Cx32 deletion significantly aggravated pulmonary function from acute lung injury induced by HIR. In addition, Cx32 deletion decreased the protein level of ZO-1 (pulmonary function) and increased the level of the oxidative stress marker 8-OHDG in the lungs. Moreover, in the Cx32-/- HIR model group, the levels of IL-6 and MMP-12 in bronchoalveolar lavage fluid were significantly increased leading to activation of the JAK2/STAT3 pathway, and decreased α1-AT levels. Furthermore, we found mmu-miR-26a/b was significantly downregulated in the Cx32-/- HIR model group.

CONCLUSION

HIR leads to acute lung inflammatory injury. Cx32 deletion aggravates hepatic-derived lung inflammation, partly through blocking the transferring of mmu-miR-26a/b and leading to IL-6-related JAK2/STAT3 pathway activation.

Airborne PAHs inhibit gap junctional intercellular communication and activate MAPKs in human bronchial epithelial cell line

Inhalation exposures to polycyclic aromatic hydrocarbons (PAHs) have been associated with various adverse health effects, including chronic lung diseases and cancer. Using human bronchial epithelial cell line HBE1, we investigated the effects of structurally different PAHs on tissue homeostatic processes, namely gap junctional intercellular communication (GJIC) and MAPKs activity. Rapid (<1 h) and sustained (up to 24 h) inhibition of GJIC was induced by low/middle molecular weight (MW) PAHs, particularly by those with a bay- or bay-like region (1- and 9-methylanthracene, fluoranthene), but also by fluorene and pyrene. In contrast, linear low MW (anthracene, 2-methylanthracene) or higher MW (chrysene) PAHs did not affect GJIC. Fluoranthene, 1- and 9-methylanthracene induced strong and sustained activation of MAPK ERK1/2, whereas MAPK p38 was activated rather nonspecifically by all tested PAHs. Low/middle MW PAHs can disrupt tissue homeostasis in human airway epithelium via structure-dependent nongenotoxic mechanisms, which can contribute to their human health hazards.

Early Mechanistic Events Induced by Low Molecular Weight Polycyclic Aromatic Hydrocarbons in Mouse Lung Epithelial Cells: A Role for Eicosanoid Signaling

Low molecular weight polycyclic aromatic hydrocarbons (LMW PAHs; < 206.3 g/mol) are under regulated environmental contaminants (eg, secondhand smoke) that lead to gap junction dysregulation, p38 MAPK activation, and increased mRNA production of inflammatory mediators, such as cytokines and cyclooxygenase (COX2), in lung epithelial cells. However, the early mechanisms involving lipid signaling through the arachidonic acid pathway and subsequent eicosanoid production leading to these downstream events are not known. Common human exposures are to mixtures of LMW PAHs, thus C10 cells (a mouse lung epithelial cell line) were exposed to a representative binary PAH mixture, 1-methylanthracene (1-MeA) and fluoranthene (Flthn), for 30 min-24 h with and without p38 and cytosolic phospholipase A2 (cPLA2) inhibitors. Cytosolic phospholipase A2 inhibition reversed PAH-induced phospho-p38 MAPK activation and gap junction dysregulation at 30 min. A significant biphasic increase in cPLA2 protein was observed at 30 min, 2, and 4 h, as well as COX2 protein at 2 and 8 h. Untargeted metabolomics demonstrated a similar trend with significantly changing metabolites at 30 min and 4 h of exposure relative to 1 h; a "cPLA2-like" subset of metabolites within the biphasic response were predominately phospholipids. Targeted metabolomics showed several eicosanoids (eg, prostaglandin D2 (PGD2), PGE2α) were significantly increased at 4, 8, and 12 h following exposure to the binary PAH mixture and this effect was p38-dependent. Finally, PAH metabolism was not observed until after 8 h. These results indicate an early lipid signaling mechanism of LMW PAH toxicity in lung epithelial cells due to parent PAH compounds.

Connexin-43 is a promising target for pulmonary hypertension due to hypoxaemic lung disease

The mechanisms underlying pulmonary hypertension (PH) are complex and multifactorial, and involve different cell types that are interconnected through gap junctional channels. Although connexin (Cx)-43 is the most abundant gap junction protein in the heart and lungs, and critically governs intercellular signalling communication, its contribution to PH remains unknown. The focus of the present study is thus to evaluate Cx43 as a potential new target in PH.Expressions of Cx37, Cx40 and Cx43 were studied in lung specimens from patients with idiopathic pulmonary arterial hypertension (IPAH) or PH associated with chronic hypoxaemic lung diseases (chronic hypoxia-induced pulmonary hypertension (CH-PH)). Heterozygous Cx43 knockdown CD1 (Cx43^+/-) and wild-type littermate (Cx43^+/+) mice at 12 weeks of age were randomly divided into two groups, one of which was maintained in room air and the other exposed to hypoxia (10% oxygen) for 3 weeks. We evaluated pulmonary haemodynamics, remodelling processes in cardiac tissues and pulmonary arteries (PAs), lung inflammation and PA vasoreactivity.Cx43 levels were increased in PAs from CH-PH patients and decreased in PAs from IPAH patients; however, no difference in Cx37 or Cx40 levels was noted. Upon hypoxia treatment, the Cx43^+/- mice were partially protected against CH-PH when compared to Cx43^+/+ mice, with reduced pulmonary arterial muscularisation and inflammatory infiltration. Interestingly, the adaptive changes in cardiac remodelling in Cx43^+/- mice were not affected. PA contraction due to endothelin-1 (ET-1) was increased in Cx43^+/- mice under normoxic and hypoxic conditions.Taken together, these results indicate that targeting Cx43 may have beneficial therapeutic effects in PH without affecting compensatory cardiac hypertrophy.

Improved multiparametric scrape loading-dye transfer assay for a simultaneous high-throughput analysis of gap junctional intercellular communication, cell density and viability

Gap junctional intercellular communication (GJIC) is a vital cellular process required for maintenance of tissue homeostasis. In vitro assessment of GJIC represents valuable phenotypic endpoint that could be effectively utilized as an integral component in modern toxicity testing, drug screening or biomedical in vitro research. However, currently available methods for quantifying GJIC with higher-throughputs typically require specialized equipment, proprietary software and/or genetically engineered cell models. To overcome these limitations, we present here an innovative adaptation of traditional, fluorescence microscopy-based scrape loading-dye transfer (SL-DT) assay, which has been optimized to simultaneously evaluate GJIC, cell density and viability. This multiparametric method was demonstrated to be suitable for various multiwell microplate formats, which facilitates an automatized image acquisition. The assay workflow is further assisted by an open source-based software tools for batch image processing, analysis and evaluation of GJIC, cell density and viability. Our results suggest that this approach provides a simple, fast, versatile and cost effective way for in vitro high-throughput assessment of GJIC and other related phenotypic cellular events, which could be included into in vitro screening and assessment of pharmacologically and toxicologically relevant compounds.

Effects of Mesenchymal Stem Cell Coculture on Human Lung Small Airway Epithelial Cells

Mesenchymal stem cells (MSCs) and their secreted extracellular vesicles have been used effectively in different lung disease animal models and clinical trials. Their specific beneficial effects, the potential differences between MSCs derived from different organs, and interactions between MSC products and target cells still need to be studied further. Therefore, we investigated the effects of secreted products of human MSCs derived from the bone marrow and adipose tissue on human lung small airway epithelial (AE) cells in vitro. AE cells were cocultured with MSCs in inserts that allowed the free exchange of medium but did not allow direct cell-to-cell contact. We examined the effects on AE cell viability, proliferation, cell numbers, expression of AE cell-specific genes, and CD54 (intercellular adhesion molecule 1 (ICAM1)) surface positivity, as well as the secretion/uptake of growth factors relevant for AE cell. We found that coculture increased the viability of AE cells. The majority of AE cells expressed CD54 on their surface, but the percentage of cells being positive for CD54 did not increase in coculture. However, ICAM1 gene expression was increased in coculture. Also, we observed increased gene expression of mucin (MUC1), a lung-enriched cell surface glycoprotein. These observed effects were the same between bone marrow and adipose tissue MSCs. However, MSCs derived from adipose tissue reduced angiopoietin concentrations in coculture, whereas those from the bone marrow did not. Conclusively, MSCs influenced AE cells positively by increasing their viability and affecting gene expression, with some effects being specific for the tissue origin of MSCs.

Carbenoxolone decreases monocrotaline‑induced pulmonary inflammation and pulmonary arteriolar remodeling in rats by decreasing the expression of connexins in T lymphocytes

The adaptive immune response mediated by T lymphocytes is a well-established factor in the pathogenesis of pulmonary inflammation. Changes in the expression of various connexins (Cxs) or disruption of connexin-mediated cellular communication in T lymphocytes contribute to inflammation or tissue remodeling. The aim of the present study was to investigate the potential therapeutic value of blocking Cxs in a monocrotaline (MCT)-induced pulmonary inflammation rat model. Carbenoxolone (CBX) was used to inhibit connexin-mediated cellular communication. An MCT rat model was established by intraperitoneal (i.p.) injection of a single dose of MCT (60 mg/kg), and CBX treatment (20 µg/kg/day, i.p.) was initiated on the day following MCT treatment for 28 days. Vehicle-treated male Sprague-Dawley rats were used as the negative control. The MCT rat model was evaluated by measuring the pulmonary artery flow acceleration time and right ventricular hypertrophy index (RVHI). Histopathological features of the lung tissues and pulmonary arteriolar remodeling were assessed. The proportions of T lymphocyte subtypes, Cx40/cx43 expression in the T cell subtypes and the cytokine levels in the plasma and the lung tissues were also analyzed. Pharmacological inhibition of Cxs using CBX attenuated MCT-induced right ventricular hypertrophy, pulmonary arteriolar remodeling, lung fibrosis and inflammatory cell infiltration by decreasing the RVHI, pulmonary arterial wall thickening, collagen deposition and pro-inflammatory cytokines production as well as CD3⁺ and CD4⁺ T cell accumulation in lung tissues of MCT-treated rats. Furthermore, flow cytometry analysis revealed that CBX may inhibit MCT-induced Cx40 and Cx43 expression in CD4⁺ and CD8⁺ T lymphocytes in lung tissues. The present study provides evidence that pharmacological inhibition of Cxs may attenuate MCT-induced pulmonary arteriolar remodeling and pulmonary inflammatory response, at least in part, by decreasing Cx expression. The results highlight the critical role of Cxs in T lymphocytes in the MCT-induced pulmonary inflammatory response and that targeting of Cxs may be a potential therapeutic method for treating pulmonary inflammatory diseases.

Pannexin-1 channels on endothelial cells mediate vascular inflammation during lung ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury (IRI), which involves inflammation, vascular permeability, and edema, remains a major challenge after lung transplantation. Pannexin-1 (Panx1) channels modulate cellular ATP release during inflammation. This study tests the hypothesis that endothelial Panx1 is a key mediator of vascular inflammation and edema after I/R and that IRI can be blocked by Panx1 antagonism. A murine hilar ligation model of IRI was used whereby left lungs underwent 1 h of ischemia and 2 h of reperfusion. Treatment of wild-type mice with Panx1 inhibitors (carbenoxolone or probenecid) significantly attenuated I/R-induced pulmonary dysfunction, edema, cytokine production, and neutrophil infiltration versus vehicle-treated mice. In addition, VE-Cad-CreERT2+/Panx1fl/fl mice (tamoxifen-inducible deletion of Panx1 in vascular endothelium) treated with tamoxifen were significantly protected from IRI (reduced dysfunction, endothelial permeability, edema, proinflammatory cytokines, and neutrophil infiltration) versus vehicle-treated mice. Furthermore, extracellular ATP levels in bronchoalveolar lavage fluid is Panx1-mediated after I/R as it was markedly attenuated by Panx1 antagonism in wild-type mice and by endothelial-specific Panx1 deficiency. Panx1 gene expression in lungs after I/R was also significantly elevated compared with sham. In vitro experiments demonstrated that TNF-α and/or hypoxia-reoxygenation induced ATP release from lung microvascular endothelial cells, which was attenuated by Panx1 inhibitors. This study is the first, to our knowledge, to demonstrate that endothelial Panx1 plays a key role in mediating vascular permeability, inflammation, edema, leukocyte infiltration, and lung dysfunction after I/R. Pharmacological antagonism of Panx1 activity may be a novel therapeutic strategy to prevent IRI and primary graft dysfunction after lung transplantation.

Multifaceted Roles of Connexin 43 in Stem Cell Niches

Purpose of Review

Considerable progress has been made in the field of stem cell research; nonetheless, the use of stem cells for regenerative medicine therapies, for either endogenous tissue repair or cellular grafts post injury, remains a challenge. To better understand how to maintain stem cell potential in vivo and promote differentiation ex vivo, it is fundamentally important to elucidate the interactions between stem cells and their surrounding partners within their distinct niches.

Recent Findings

Among the vast array of proteins depicted as mediators for cell-to-cell interactions, connexin-comprised gap junctions play pivotal roles in the regulation of stem cell fate both in vivo and in vitro.

Summary

This review summarizes and illustrates the current knowledge regarding the multifaceted roles of Cx43, specifically, in various stem cell niches.

Rapid Communication: Subclinical bovine respiratory disease - loci and pathogens associated with lung lesions in feedlot cattle

Bovine respiratory disease (BRD) is an economically important disease of feedlot cattle that is caused by viral and bacterial pathogen members of the BRD complex. Many cases of subclinical BRD go untreated and are not detected until slaughter, when lung lesions are identified. The objectives of this study were to identify which BRD pathogens were associated with the presence of lung lesions at harvest and to identify genomic loci that were associated with susceptibility to lung lesions as defined by consolidation of the lung and/or the presence of fibrin tissue. Steers from a Colorado feedlot (n = 920) were tested for the presence of viral and bacterial pathogens using deep pharyngeal and mid-nasal swabs collected on entry into the study. Pathogen profiles were compared between cattle with or without lung consolidation (LC), fibrin tissue in the lung (FT), a combination of LC and FT in the same lung (lung lesions [LL]), and hyperinflated lungs (HIF) at harvest. Genotyping was conducted using the Illumina BovineHD BeadChip. Genomewide association analyses (GWAA) were conducted using EMMAX (efficient mixed-model association eXpedited), and pseudoheritabilities were estimated. The pathogen profile comparisons revealed that LC (P = 0.01, odds ratio [OR] = 3.37) and LL cattle (P = 0.04, OR = 4.58) were more likely to be infected with bovine herpes virus-1 and that HIF cattle were more likely to be infected with Mycoplasma spp. (P = 0.04, OR = 4.33). Pseudoheritability estimates were 0.25 for LC, 0.00 for FT, 0.28 for LL, and 0.13 for HIF. Because pseudoheritability for FT was estimated to be 0, GWAA results for FT were not reported. There were 4 QTL that were moderately associated (P < 1 × 10⁻⁵) with only LC, 2 that were associated with only LL, and 1 that was associated with LC and LL. Loci associated with HIF included 12 that were moderately associated and 3 that were strongly associated (uncorrected P < 5 × 10−7). A 24-kb region surrounding significant lead SNP was investigated to identify positional candidate genes. Many positional candidate genes underlying or flanking the detected QTL have been associated with signal transduction, cell adhesion, or gap junctions, which have functional relevance to the maintenance of lung health. The identification of pathogens and QTL associated with the presence of lung abnormalities in cattle exhibiting subclinical BRD allows the identification of loci that may not be detected through manifestation of clinical disease alone.

The role of connexin and pannexin containing channels in the innate and acquired immune response

Connexin (Cx) and pannexin (Panx) containing channels - gap junctions (GJs) and hemichannels (HCs) - are present in virtually all cells and tissues. Currently, the role of these channels under physiological conditions is well defined. However, their role in the immune response and pathological conditions has only recently been explored. Data from several laboratories demonstrates that infectious agents, including HIV, have evolved to take advantage of GJs and HCs to improve viral/bacterial replication, enhance inflammation, and help spread toxicity into neighboring areas. In the current review, we discuss the role of Cx and Panx containing channels in immune activation and the pathogenesis of several infectious diseases. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

The role of gap junctions in inflammatory and neoplastic disorders (Review)

Gap junctions are intercellular channels made of connexin proteins, mediating both electrical and biochemical signals between cells. The ability of gap junction proteins to regulate immune responses, cell proliferation, migration, apoptosis and carcinogenesis makes them attractive therapeutic targets for treating inflammatory and neoplastic disorders in different organ systems. Alterations in gap junction profile and expression levels are observed in hyperproliferative skin disorders, lymphatic vessel diseases, inflammatory lung diseases, liver injury and neoplastic disorders. It is now recognized that the therapeutic effects mediated by traditional pharmacological agents are dependent upon gap junction communication and may even act by influencing gap junction expression or function. Novel strategies for modulating the function or expression of connexins, such as the use of synthetic mimetic peptides and siRNA technology are considered.