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

TGF-β phospho antibody array identifies altered SMAD2, PI3K/AKT/SMAD, and RAC signaling contribute to the pathogenesis of myxomatous mitral valve disease

Background

TGFβ signaling appears to contribute to the pathogenesis of myxomatous mitral valve disease (MMVD) in both dogs and humans. However, little is known about the extent of the downstream signaling changes that will then affect cell phenotype and function in both species.

Objective

Identify changes in downstream signals in the TGFβ pathway in canine MMVD and examine the effects of antagonism of one significant signal (SMAD2 was selected).

Materials and methods

Canine cultures of normal quiescent valve interstitial cells (qVICs) and disease-derived activated myofibroblasts (aVICs) (n = 6) were examined for TGFβ signaling protein expression using a commercial antibody array. Significant changes were confirmed, and additional proteins of interest downstream in the TGFβ signaling pathway and markers of cell phenotype were examined (PRAS40, S6K, elF4E IRS-1, αSMA, and VIM), using protein immunoblotting. RT-PCR examined expression of gene markers of VIC activation (ACTA2, TAGLN, and MYH10; encoding the proteins αSMA, SM22, and Smemb, respectively). Attenuation of pSMAD2 in aVICs was examined using a combination of RNA interference technology (siRNA) and the SMAD7 (antagonizes SMAD2) agonist asiaticoside.

Results

The antibody array identified significant changes (P < 0.05) in 19 proteins, of which six were phosphorylated (p). There was increased expression of pSMAD2 and pRAC1 and decreased expression of pmTOR, pERK1/2, and pAKT1. Expression of pPRAS40 and pIRS-1 was increased, as was the mTOR downstream transcription factor pS6K, with increased expression of peIF4E in aVICs, indicating negative feedback control of the PI3K/AKT/mTOR pathway. SMAD2 antagonism by siRNA and the SMAD7 agonist asiaticoside decreased detection of pSMAD by at least 50%, significantly decreased expression of the aVIC gene markers ACTA2, TAGLN, and MYH10, and pαSMA, pAKT2, and pERK1, but had no effect on pS6K, pERK2, or pVIM expression in aVICs. SMAD2 antagonism transitioned diseased aVICs to normal qVICs, while maintaining a mesenchymal phenotype (VIM+) while concurrently affecting non-canonical TGFβ signaling.

Conclusion

MMVD is associated with changes in both the canonical and non-canonical TGFβ signaling pathway. Antagonism of SMAD2 transitions diseased-activated myofibroblasts back to a normal phenotype, providing data that will inform studies on developing novel therapeutics to treat MMVD in dogs and humans.

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.

Down-regulation of connexin 43 contributes to structure and function of pulmonary artery in nicotine-administered mice

Dysregulated connexin signaling is implicated in the pathophysiology of pulmonary artery hypertension (PAH). Nicotine affects pulmonary vascular remodeling. However, the potential mechanistic link between connexin signaling and nicotine-induced pulmonary artery remodeling remains unclear. We aimed to investigate the role of connexin 43 (Cx43) in pulmonary artery remodeling in nicotine-administered C57BL/6 J wild-type (WT) and Cx43 heterozygous (Cx43^+/-) mice. Hemodynamic parameters and right ventricle pathology were assessed in the mice. Serum biochemical indices of hepatic and renal function were measured. The RT-PCR, immunofluorescence, and western blotting were conducted to evaluate Cx43 mRNA and protein levels. We performed histological staining to identify pulmonary arteries. Wire myography was used to examine contraction and relaxation responses in the pulmonary arteries. Pulmonary vascular permeability was assessed through Evans blue staining. Compared with the WT group, the Cx43^+/- group showed lower Cx43 mRNA and protein expression in the pulmonary arteries (P < 0.01). Nicotine treatment significantly increased Cx43 expression (P < 0.01) and induced morphological changes in the pulmonary arteries (P < 0.01). Our findings suggest that Cx43 plays a crucial role in pulmonary artery reactivity and permeability in mice. Furthermore, downregulation of Cx43 expression may contribute to alterations in pulmonary artery structure and function.

Electronic cigarette liquids impair metabolic cooperation and alter proteomic profiles in V79 cells

Background

Although still considered a safer alternative to classical cigarettes, growing body of work points to harmful effects of electronic cigarettes (e-cigarettes) affecting a range of cellular processes. The biological effect of e-cigarettes needs to be investigated in more detail considering their widespread use.

Methods

In this study, we treated V79 lung fibroblasts with sub-cytotoxic concentration of e-cigarette liquids, with and without nicotine. Mutagenicity was evaluated by HPRT assay, genotoxicity by comet assay and the effect on cellular communication by metabolic cooperation assay. Additionally, comprehensive proteome analysis was performed via high resolution, parallel accumulation serial fragmentation-PASEF mass spectrometry.

Results

E-cigarette liquid concentration used in this study showed no mutagenic or genotoxic effect, however it negatively impacted metabolic cooperation between V79 cells. Both e-cigarette liquids induced significant depletion in total number of proteins and impairment of mitochondrial function in treated cells. The focal adhesion proteins were upregulated, which is in accordance with the results of metabolic cooperation assay. Increased presence of posttranslational modifications (PTMs), including carbonylation and direct oxidative modifications, was observed. Data are available via ProteomeXchange with identifier PXD032071.

Conclusions

Our study revealed impairment of metabolic cooperation as well as significant proteome and PTMs alterations in V79 cells treated with e-cigarette liquid warranting future studies on e-cigarettes health impact.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02102-w.

Strategies for Improving Photodynamic Therapy Through Pharmacological Modulation of the Immediate Early Stress Response

Photodynamic therapy (PDT) is a minimally to noninvasive treatment modality that has emerged as a promising alternative to conventional cancer treatments. PDT induces hyperoxidative stress and disrupts cellular homeostasis in photosensitized cancer cells, resulting in cell death and ultimately removal of the tumor. However, various survival pathways can be activated in sublethally afflicted cancer cells following PDT. The acute stress response is one of the known survival pathways in PDT, which is activated by reactive oxygen species and signals via ASK-1 (directly) or via TNFR (indirectly). The acute stress response can activate various other survival pathways that may entail antioxidant, pro-inflammatory, angiogenic, and proteotoxic stress responses that culminate in the cancer cell's ability to cope with redox stress and oxidative damage. This review provides an overview of the immediate early stress response in the context of PDT, mechanisms of activation by PDT, and molecular intervention strategies aimed at inhibiting survival signaling and improving PDT outcome.

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.

Collagen I Modifies Connexin-43 Hemichannel Activity via Integrin α2β1 Binding in TGFβ1-Evoked Renal Tubular Epithelial Cells

Chronic Kidney Disease (CKD) is associated with sustained inflammation and progressive fibrosis, changes that have been linked to altered connexin hemichannel-mediated release of adenosine triphosphate (ATP). Kidney fibrosis develops in response to increased deposition of extracellular matrix (ECM), and up-regulation of collagen I is an early marker of renal disease. With ECM remodeling known to promote a loss of epithelial stability, in the current study we used a clonal human kidney (HK2) model of proximal tubular epithelial cells to determine if collagen I modulates changes in cell function, via connexin-43 (Cx43) hemichannel ATP release. HK2 cells were cultured on collagen I and treated with the beta 1 isoform of the pro-fibrotic cytokine transforming growth factor (TGFβ1) ± the Cx43 mimetic Peptide 5 and/or an anti-integrin α2β1 neutralizing antibody. Phase microscopy and immunocytochemistry observed changes in cell morphology and cytoskeletal reorganization, whilst immunoblotting and ELISA identified changes in protein expression and secretion. Carboxyfluorescein dye uptake and biosensing measured hemichannel activity and ATP release. A Cytoselect extracellular matrix adhesion assay assessed changes in cell-substrate interactions. Collagen I and TGFβ1 synergistically evoked increased hemichannel activity and ATP release. This was paralleled by changes to markers of tubular injury, partly mediated by integrin α2β1/integrin-like kinase signaling. The co-incubation of the hemichannel blocker Peptide 5, reduced collagen I/TGFβ1 induced alterations and inhibited a positive feedforward loop between Cx43/ATP release/collagen I. This study highlights a role for collagen I in regulating connexin-mediated hemichannel activity through integrin α2β1 signaling, ahead of establishing Peptide 5 as a potential intervention.

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.

Ischemia-reperfusion Injury in the Transplanted Lung: A Literature Review

Lung ischemia-reperfusion injury (LIRI) and primary graft dysfunction are leading causes of morbidity and mortality among lung transplant recipients. Although extensive research endeavors have been undertaken, few preventative and therapeutic treatments have emerged for clinical use. Novel strategies are still needed to improve outcomes after lung transplantation. In this review, we discuss the underlying mechanisms of transplanted LIRI, potential modifiable targets, current practices, and areas of ongoing investigation to reduce LIRI and primary graft dysfunction in lung transplant recipients.

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.