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

Connexin 43 Affects Pulmonary Artery Reactivity via Changes in Nitric Oxide Production and Influences Proliferative and Migratory Responses in Mouse Pulmonary Artery Fibroblasts

Pulmonary hypertension (PH) is a complex condition characterized by pulmonary artery constriction and vascular remodeling. Connexin 43 (Cx43), involved in cellular communication, may play a role in PH development. Cx43 heterozygous (Cx43+/-) mice show partial protection against hypoxia-induced pulmonary remodeling, with prior research highlighting its role in rat pulmonary artery fibroblast (PAF) proliferation and migration. However, inhibiting Cx43 may compromise nitric oxide (NO)-mediated vascular relaxation. This study evaluated the effects of Cx43 on mouse PAF (MPAF) proliferation, migration, NO-dependent and independent pulmonary vascular relaxation, and NO synthesis. Proliferation and migration were assessed in Cx43+/- MPAFs under normoxic and hypoxic conditions. Vascular responses were analyzed in intra-lobar pulmonary artery rings with acetylcholine (ACh), SNAP, and U46619, while NO production was measured in lung tissue. Both genetic knockdown and pharmacological inhibition of Cx43 significantly reduced serum-induced proliferation but not migration under normoxia, while 37,43Gap27 inhibited hypoxia-induced proliferation and migration. The effects of genetic knockdown and pharmacological inhibition of Cx43 on vascular reactivity were also investigated. NO-dependent and independent relaxations and NO production were reduced in Cx43+/- mice by 37,43Gap27. In conclusion, while Cx43 inhibition may protect against PAF proliferation and migration, it could also impair pulmonary vascular relaxation, at least in part through a reduction in NO signaling. Further studies are needed to fully understand the mechanisms by which Cx43 influences NO signaling.

1,8-Cineole reduces pulmonary vascular remodelling in pulmonary arterial hypertension by restoring intercellular communication and inhibiting angiogenesis

BACKGROUND

Pulmonary Arterial Hypertension (PAH) is characterized by pulmonary vascular remodelling, often associated with disruption of BMPR2/Smad1/5 and BMPR2/PPAR-γ signalling pathways that ultimately lead to right ventricle failure. Disruption of intercellular junctions and communication and a pro-angiogenic environment are also characteristic features of PAH. Although, current therapies improve pulmonary vascular tone, they fail to tackle other key pathological features that could prevent disease progression. In this scenario, aromatic plants emerge as promising sources of bioactive compounds, with 1,8-cineole standing out due to its hypotensive properties and cardioprotective effect in PAH.

PURPOSE

The present study aims to explore for the first time the effect of 1,8-cineole in pulmonary vascular remodelling associated with PAH.

METHODS

Resorting to the monocrotaline (MCT)-induced PAH animal model, the effect of 1,8-cineole on vascular remodelling including interstitial collagen accumulation, smooth muscle cell proliferation and protein levels of BMPR2 pathway-related proteins, was assessed by microscopy and western blot (WB) analysis. The integrity of gap junctions, pulmonary surfactant, mitochondrial structure and endothelial cell barrier were evaluated by transmission electron microscopy, confocal microscopy and WB analysis. Furthermore, the effect of 1,8-cineole on angiogenesis was determined on pulmonary artery endothelial cells (PAEC) submitted to hypoxia using the scratch wound and Matrigel angiogenesis assays, and the number of sprouts on isolated healthy and diseased pulmonary artery rings, treated with the compound, enabled the validation of these effects.

RESULTS

1,8-Cineole mitigated PAH-associated derailment of both BMPR2/Smad1/5 and BMPR2/PPAR-γ pathways and concomitantly reduced interstitial fibrosis and the arterial medial layer thickness in pulmonary arteries. The compound restored gap junction, lung surfactant and mitochondrial integrity and preserved endothelial barrier integrity. Furthermore, 1,8-cineole exerted an anti-angiogenic effect, by impairing the formation of vessel-like structures in PAEC and sprouting formation in isolated pulmonary arteries.

CONCLUSION

The present study brings new insights about the mechanisms whereby 1,8-cineole impacts pulmonary vascular remodelling and demonstrates the potential of 1,8-cineole as a therapeutic strategy to hamper PAH progression.

Cx43 Regulates Nicotine-Induced Proliferation and Migration of Distal Pulmonary Artery Smooth Muscle Cells by the ERK1/2 Signaling Pathway

Pulmonary hypertension is a progressive disease associated with remodeling of the pulmonary vasculature. Excessive proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) play important roles in nicotine-induced vascular injury. Connexin 43 (Cx43) is involved in intracellular communication and regulation of the pulmonary vasculature. However, the role of Cx43 and the potential mechanisms in PASMCs proliferation and migration induced by nicotine remains not very clear. In this study, we used both in vitro and in vivo models to explore the crucial role of Cx43 in pulmonary artery remodeling in nicotine treatment Tagln-Cre; Cx43+/+ and Cx43 heterozygous (Tagln-Cre; Cx43flox/+) or Cx43 Homozygous (Tagln-Cre; Cx43flox/flox) deletion mice, and further explore the mechanism. We found that nicotine exposure led to modifications in the morphology and ultrastructure of pulmonary arteries in Tagln-Cre; Cx43+/+ mice. Nicotine increased the Cx43 expression of pulmonary arteries and promoted the proliferation and migration of PASMCs of Tagln-Cre; Cx43+/+ mice in a concentration-dependent manner by promoting ERK1/2 phosphorylation. Compared with the Tagln-Cre; Cx43+/+ mice, the Tagln-Cre; Cx43flox/+ mice were protected against increased ERK1/2 phosphorylation induced by nicotine. These results demonstrated that the downregulation of Cx43 reduced nicotine-induced proliferation and migration of distal PASMCs by inhibiting ERK1/2 phosphorylation.

From basic scientific research to the development of new drugs for pulmonary arterial hypertension: insights from activin-targeting agents

Pulmonary arterial hypertension (PAH) is a severe disorder of the pulmonary vasculature leading to right ventricular failure. This pulmonary vascular remodelling leads to increased pulmonary vascular resistance and high pulmonary arterial pressures. Despite the development of new therapies, many patients continue to experience significant morbidity and mortality. This review offers a comprehensive overview of the current understanding of PAH pathophysiology, with a focus on key mechanisms that contribute to pulmonary endothelial cell dysfunction and the pathological accumulation of pulmonary artery smooth muscle cells, mesenchymal cells and inflammatory cells in the walls of remodelled small pulmonary vessels, three processes central to the progression of PAH. In particular, it highlights recent developments in targeting the activin signalling pathway, a novel therapeutic approach that shows promise in modulating these pathological processes. The review also addresses the ongoing challenges in translating preclinical findings into effective clinical treatments, emphasising the importance of integrating human data with preclinical models and adopting innovative strategies to bridge the gap between research and clinical practice.

Connexin 25 maintains self-renewal and functions of airway basal cells for airway regeneration

BACKGROUND

The formation of stem cell clones enables close contact of stem cells inside. The gap junctions in such clone spheres establish a microenvironment that allows frequent intercellular communication to maintain self-renewal and functions of stem cells. Nevertheless, the essential gap junction protein for molecular signaling in clones is poorly known.

METHODS

Primary human airway basal cells (hBCs) were isolated from brushing samples through bronchoscopy and then cultured. A tightly focused femtosecond laser was used to excite the local Ca2+ in an individual cell to initiate an internal Ca2+ wave in a clone to screen gap junction proteins. Immunoflourescence staining and clonogenicity assay were used to evaluate self-renewal and functions. RNA and protein levels were assessed by PCR and Western blot. Air-liquid interface assay was conducted to evaluate the differentiation potential. A Naphthalene injury mouse model was used to assess the regeneration potential.

RESULTS

Herein, we identify Connexin 25 (Cx25) dominates intercellular Ca2+ communications in clones of hBCs in vitro to maintain the self-renewal and pluripotency of them. The self-renewal and in vitro differentiation functions and in vivo regeneration potential of hBCs in an airway damage model are both regulated by Cx25. The abnormal expression of Cx25 is validated in several diseases including IPF, Covid-19 and bronchiectasis.

CONCLUSION

Cx25 is essential for hBC clones in maintaining self-renewal and functions of hBCs via gap junctions.

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.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Pulmonary Vascular Remodeling in Pulmonary Hypertension

Pulmonary vascular remodeling is the critical structural alteration and pathological feature in pulmonary hypertension (PH) and involves changes in the intima, media and adventitia. Pulmonary vascular remodeling consists of the proliferation and phenotypic transformation of pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells (PASMCs) of the middle membranous pulmonary artery, as well as complex interactions involving external layer pulmonary artery fibroblasts (PAFs) and extracellular matrix (ECM). Inflammatory mechanisms, apoptosis and other factors in the vascular wall are influenced by different mechanisms that likely act in concert to drive disease progression. This article reviews these pathological changes and highlights some pathogenetic mechanisms involved in the remodeling process.

Hypertension Induces Pro-arrhythmic Cardiac Connexome Disorders: Protective Effects of Treatment

Prolonged population aging and unhealthy lifestyles contribute to the progressive prevalence of arterial hypertension. This is accompanied by low-grade inflammation and over time results in heart dysfunction and failure. Hypertension-induced myocardial structural and ion channel remodeling facilitates the development of both atrial and ventricular fibrillation, and these increase the risk of stroke and sudden death. Herein, we elucidate hypertension-induced impairment of "connexome" cardiomyocyte junctions. This complex ensures cell-to-cell adhesion and coupling for electrical and molecular signal propagation. Connexome dysfunction can be a key factor in promoting the occurrence of both cardiac arrhythmias and heart failure. However, the available literature indicates that arterial hypertension treatment can hamper myocardial structural remodeling, hypertrophy and/or fibrosis, and preserve connexome function. This suggests the pleiotropic effects of antihypertensive agents, including anti-inflammatory. Therefore, further research is required to identify specific molecular targets and pathways that will protect connexomes, and it is also necessary to develop new approaches to maintain heart function in patients suffering from primary or pulmonary arterial hypertension.

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.

New Insights into Pulmonary Hypertension: A Role for Connexin-Mediated Signalling

Pulmonary hypertension is a serious clinical condition characterised by increased pulmonary arterial pressure. This can lead to right ventricular failure which can be fatal. Connexins are gap junction-forming membrane proteins which serve to exchange small molecules of less than 1 kD between cells. Connexins can also form hemi-channels connecting the intracellular and extracellular environments. Hemi-channels can mediate adenosine triphosphate release and are involved in autocrine and paracrine signalling. Recently, our group and others have identified evidence that connexin-mediated signalling may be involved in the pathogenesis of pulmonary hypertension. In this review, we discuss the evidence that dysregulated connexin-mediated signalling is associated with pulmonary hypertension.

HIF-1α promotes the proliferation and migration of pulmonary arterial smooth muscle cells via activation of Cx43

The proliferation of pulmonary artery smooth muscle cells (PASMCs) is an important cause of pulmonary vascular remodelling in hypoxia-induced pulmonary hypertension (HPH). However, its underlying mechanism has not been well elucidated. Connexin 43 (Cx43) plays crucial roles in vascular smooth muscle cell proliferation in various cardiovascular diseases. Here, the male Sprague-Dawley (SD) rats were exposed to hypoxia (10% O₂ ) for 21 days to induce rat HPH model. PASMCs were treated with CoCl₂ (200 µM) for 24 h to establish the HPH cell model. It was found that hypoxia up-regulated the expression of Cx43 and phosphorylation of Cx43 at Ser 368 in rat pulmonary arteries and PASMCs, and stimulated the proliferation and migration of PASMCs. HIF-1α inhibitor echinomycin attenuated the CoCl₂ -induced Cx43 expression and phosphorylation of Cx43 at Ser 368 in PASMCs. The interaction between HIF-1α and Cx43 promotor was also identified using chromatin immunoprecipitation assay. Moreover, Cx43 specific blocker (^37,43 Gap27) or knockdown of Cx43 efficiently alleviated the proliferation and migration of PASMCs under chemically induced hypoxia. Therefore, the results above suggest that HIF-1α, as an upstream regulator, promotes the expression of Cx43, and the HIF-1α/Cx43 axis regulates the proliferation and migration of PASMCs in HPH.

Construction and analysis of the abnormal lncRNA-miRNA-mRNA network in hypoxic pulmonary hypertension

The incidence of hypoxic pulmonary hypertension (HPH) is increasing. Accumulating evidence suggests that long noncoding RNAs (lncRNAs) play an important role in HPH, but the functions and mechanism have yet to be fully elucidated. In the present study, we established a HPH rat model with 8 h of hypoxia exposure (10% O2) per day for 21 days. High-throughput sequencing identified 60 differentially expressed (DE) lncRNAs, 20 DE miRNAs and 695 DE mRNAs in rat lung tissue. qRT-PCR verified the accuracy of the results. The DE mRNAs were significantly enriched in immune response, inflammatory response, leukocyte migration, cell cycle, cellular response to interleukin-1, IL-17 signalling pathway, cytokine-cytokine receptor interaction and Toll-like receptor signalling pathway. According to the theory of competing endogenous RNA (ceRNA) networks, lncRNA-miRNA-mRNA network was constructed by Cytoscape software, 16 miRNAs and 144 mRNAs. The results suggested that seven DE lncRNAs (Ly6l, AABR07038849.2, AABR07069008.2, AABR07064873.1, AABR07001382.1, AABR07068161.1 and AABR07060341.2) may serve as molecular sponges of the corresponding miRNAs and play a major role in HPH.

Importance of Cx43 for Right Ventricular Function

In the heart, connexins form gap junctions, hemichannels, and are also present within mitochondria, with connexin 43 (Cx43) being the most prominent connexin in the ventricles. Whereas the role of Cx43 is well established for the healthy and diseased left ventricle, less is known about the importance of Cx43 for the development of right ventricular (RV) dysfunction. The present article focusses on the importance of Cx43 for the developing heart. Furthermore, we discuss the expression and localization of Cx43 in the diseased RV, i.e., in the tetralogy of Fallot and in pulmonary hypertension, in which the RV is affected, and RV hypertrophy and failure occur. We will also introduce other Cx molecules that are expressed in RV and surrounding tissues and have been reported to be involved in RV pathophysiology. Finally, we highlight therapeutic strategies aiming to improve RV function in pulmonary hypertension that are associated with alterations of Cx43 expression and function.

Chronic Hypoxia Decreases Endothelial Connexin 40, Attenuates Endothelium-Dependent Hyperpolarization-Mediated Relaxation in Small Distal Pulmonary Arteries, and Leads to Pulmonary Hypertension

Background Abnormal endothelial function in the lungs is implicated in the development of pulmonary hypertension; however, there is little information about the difference of endothelial function between small distal pulmonary artery (PA) and large proximal PA and their contribution to the development of pulmonary hypertension. Herein, we investigate endothelium-dependent relaxation in different orders of PAs and examine the molecular mechanisms by which chronic hypoxia attenuates endothelium-dependent pulmonary vasodilation, leading to pulmonary hypertension. Methods and Results Endothelium-dependent relaxation in large proximal PAs (second order) was primarily caused by releasing NO from the endothelium, whereas endothelium-dependent hyperpolarization (EDH)-mediated vasodilation was prominent in small distal PAs (fourth-fifth order). Chronic hypoxia abolished EDH-mediated relaxation in small distal PAs without affecting smooth muscle-dependent relaxation. RNA-sequencing data revealed that, among genes related to EDH, the levels of Cx37, Cx40, Cx43, and IK were altered in mouse pulmonary endothelial cells isolated from chronically hypoxic mice in comparison to mouse pulmonary endothelial cells from normoxic control mice. The protein levels were significantly lower for connexin 40 (Cx40) and higher for connexin 37 in mouse pulmonary endothelial cells from hypoxic mice than normoxic mice. Cx40 knockout mice exhibited significant attenuation of EDH-mediated relaxation and marked increase in right ventricular systolic pressure. Interestingly, chronic hypoxia led to a further increase in right ventricular systolic pressure in Cx40 knockout mice without altering EDH-mediated relaxation. Furthermore, overexpression of Cx40 significantly decreased right ventricular systolic pressure in chronically hypoxic mice. Conclusions These data suggest that chronic hypoxia-induced downregulation of endothelial Cx40 results in impaired EDH-mediated relaxation in small distal PAs and contributes to the development of pulmonary hypertension.

Connexin 43 plays a role in proliferation and migration of pulmonary arterial fibroblasts in response to hypoxia

Pulmonary hypertension (PH) is a disease associated with vasoconstriction and remodelling of the pulmonary vasculature. Pulmonary artery fibroblasts (PAFs) play an important role in hypoxic-induced remodelling. Connexin 43 (Cx43) is involved in cellular communication and regulation of the pulmonary vasculature. Using both in vitro and in vivo models of PH, the aims of this study were to (i) investigate the role of Cx43 in hypoxic-induced proliferation and migration of rat PAFs (rPAFs) and rat pulmonary artery smooth muscle cells (rPASMCs) and (ii) determine whether Cx43 expression is dysregulated in the rat sugen5416/hypoxic model of PH. The role of Cx43 in hypoxic-induced proliferation and migration was investigated using Gap27 (a pharmacological inhibitor of Cx43) or genetic knockdown of Cx43 using siRNA. Cx43 protein expression was increased by hypoxia in rPAFs but not rPASMCs. Hypoxic exposure, in the presence of serum, resulted in an increase in proliferation of rPAFs but not rPASMCs. Hypoxic exposure caused migration of rPAFs but not rPASMCs. Phosphorylation of p38 mitogen-activated protein kinase (MAPK) and ERK1/2 were increased by hypoxia in rPAFs. The effects of hypoxia on proliferation, migration and MAPK phosphorylation in rPAFs were attenuated in the presence of Gap27 or Cx43 siRNA. Cx43 protein expression was increased in sugen5416/hypoxic rat lung; this increased expression was not observed in sugen5416/hypoxic rats treated with the MAPK pathway inhibitor GS-444217. In conclusion, Cx43 is involved in the proliferation and migration of rPAFs in response to hypoxia via the MAPK signalling pathway.