Role of the purinergic signaling network in lung ischemia-reperfusion injury

Transient receptor potential vanilloid 4 channel inhibition attenuates lung ischemia-reperfusion injury in a porcine lung transplant model

OBJECTIVE

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel important in many physiological and pathophysiological processes, including pulmonary disease. Using a murine model, we previously demonstrated that TRPV4 mediates lung ischemia-reperfusion injury, the major cause of primary graft dysfunction after transplant. The current study tests the hypothesis that treatment with a TRPV4 inhibitor will attenuate lung ischemia-reperfusion injury in a clinically relevant porcine lung transplant model.

METHODS

A porcine left-lung transplant model was used. Animals were randomized to 2 treatment groups (n = 5/group): vehicle or GSK2193874 (selective TRPV4 inhibitor). Donor lungs underwent 30 minutes of warm ischemia and 24 hours of cold preservation before left lung allotransplantation and 4 hours of reperfusion. Vehicle or GSK2193874 (1 mg/kg) was administered to the recipient as a systemic infusion after recipient lung explant. Lung function, injury, and inflammatory biomarkers were compared.

RESULTS

After transplant, left lung oxygenation was significantly improved in the TRPV4 inhibitor group after 3 and 4 hours of reperfusion. Lung histology scores and edema were significantly improved, and neutrophil infiltration was significantly reduced in the TRPV4 inhibitor group. TRPV4 inhibitor-treated recipients had significantly reduced expression of interleukin-8, high mobility group box 1, P-selectin, and tight junction proteins (occludin, claudin-5, and zonula occludens-1) in bronchoalveolar lavage fluid as well as reduced angiopoietin-2 in plasma, all indicative of preservation of endothelial barrier function.

CONCLUSIONS

Treatment of lung transplant recipients with TRPV4 inhibitor significantly improves lung function and attenuates ischemia-reperfusion injury. Thus, selective TRPV4 inhibition may be a promising therapeutic strategy to prevent primary graft dysfunction after transplant.

Lipoxin A 4 /FPR2 signaling mitigates ferroptosis of alveolar epithelial cells via NRF2-dependent pathway during lung ischemia-reperfusion injury

BACKGROUND

Post-lung transplantation (LTx) injury can involve sterile inflammation due to ischemia-reperfusion injury (IRI). We investigated the cell-specific role of ferroptosis (excessive iron-mediated cell death) in mediating lung IRI and determined if specialized pro-resolving mediators such as Lipoxin A4 (LxA 4 ) can protect against ferroptosis in lung IRI.

METHODS

Single-cell RNA sequencing of lung tissue from post-LTx patients was analyzed. Lung IRI was evaluated in C57BL/6 (WT), formyl peptide receptor 2 knockout ( Fpr2 -/- ) and nuclear factor erythroid 2-related factor 2 knockout ( Nrf2 -/- ) mice using a hilar-ligation model with or without LxA 4 administration. Furthermore, the protective efficacy of LxA 4 was evaluated employing a murine orthotopic LTx model and in vitro studies using alveolar type II epithelial (ATII) cells.

RESULTS

Differential expression of ferroptosis-related genes was observed in post-LTx patient samples compared to healthy controls. A significant increase in the levels of oxidized lipids and reduction in the levels of intact lipids were observed in mice subjected to IRI compared to shams. Furthermore, pharmacological inhibition of ferroptosis with liproxstatin-1 mitigated lung IRI and lung dysfunction. Importantly, LxA 4 treatment attenuated pulmonary dysfunction, ferroptosis and inflammation in WT mice subjected to lung IRI, but not in Fpr2 -/- or Nrf2 -/- mice, after IRI. In the murine LTx model, LxA 4 treatment increased PaO 2 levels and attenuated lung IRI. Mechanistically, LxA 4 -mediated protection involves increase in NRF2 activation and glutathione concentration as well as decrease in MDA levels in ATII cells.

CONCLUSIONS

LxA 4 /FPR2 signaling on ATII cells mitigates ferroptosis via NRF2 activation and protects against lung IRI.

The endothelium: gatekeeper to lung ischemia-reperfusion injury

The success of lung transplantation is limited by the high rate of primary graft dysfunction due to ischemia-reperfusion injury (IRI). Lung IRI is characterized by a robust inflammatory response, lung dysfunction, endothelial barrier disruption, oxidative stress, vascular permeability, edema, and neutrophil infiltration. These events are dependent on the health of the endothelium, which is a primary target of IRI that results in pulmonary endothelial barrier dysfunction. Over the past 10 years, research has focused more on the endothelium, which is beginning to unravel the multi-factorial pathogenesis and immunologic mechanisms underlying IRI. Many important proteins, receptors, and signaling pathways that are involved in the pathogenesis of endothelial dysfunction after IR are starting to be identified and targeted as prospective therapies for lung IRI. In this review, we highlight the more significant mediators of IRI-induced endothelial dysfunction discovered over the past decade including the extracellular glycocalyx, endothelial ion channels, purinergic receptors, kinases, and integrins. While there are no definitive clinical therapies currently available to prevent lung IRI, we will discuss potential clinical strategies for targeting the endothelium for the treatment or prevention of IRI. The accruing evidence on the essential role the endothelium plays in lung IRI suggests that promising endothelial-directed treatments may be approaching the clinic soon. The application of therapies targeting the pulmonary endothelium may help to halt this rapid and potentially fatal injury.

Purinergic P2Y2 receptor-induced activation of endothelial TRPV4 channels mediates lung ischemia-reperfusion injury

Lung ischemia-reperfusion injury (IRI), characterized by inflammation, vascular permeability, and lung edema, is the major cause of primary graft dysfunction after lung transplantation. Here, we investigated the cellular mechanisms underlying lung IR-induced activation of endothelial TRPV4 channels, which play a central role in lung edema and dysfunction after IR. In a left lung hilar-ligation model of IRI in mice, we found that lung IRI increased the efflux of ATP through pannexin 1 (Panx1) channels at the endothelial cell (EC) membrane. Elevated extracellular ATP activated Ca2+ influx through endothelial TRPV4 channels downstream of purinergic P2Y2 receptor (P2Y2R) signaling. P2Y2R-dependent activation of TRPV4 channels was also observed in human and mouse pulmonary microvascular endothelium in ex vivo and in vitro models of IR. Endothelium-specific deletion of P2Y2R, TRPV4, or Panx1 in mice substantially prevented lung IRI-induced activation of endothelial TRPV4 channels and lung edema, inflammation, and dysfunction. These results identify endothelial P2Y2R as a mediator of the pathological sequelae of IRI in the lung and show that disruption of the endothelial Panx1-P2Y2R-TRPV4 signaling pathway could be a promising therapeutic strategy for preventing lung IRI after transplantation.

Differential early response of monocyte/macrophage subsets to intra-operative corticosteroid administration in lung transplantation

Introduction

Lung transplantation often results in primary and/or chronic dysfunctions that are related to early perioperative innate allo-responses where myeloid subsets play a major role. Corticosteroids are administered upon surgery as a standard-of-care but their action on the different myeloid cell subsets in that context is not known.

Methods

To address this issue, we used a cross-circulatory platform perfusing an extracorporeal lung coupled to cell mapping in the pig model, that enabled us to study the recruited cells in the allogeneic lung over 10 hours.

Results

Myeloid cells, i.e. granulocytes and monocytic cells including classical CD14pos and non-classical/intermediate CD16pos cells, were the dominantly recruited subsets, with the latter upregulating the membrane expression of MHC class II and CD80/86 molecules. Whereas corticosteroids did not reduce the different cell subset recruitment, they potently dampened the MHC class II and CD80/86 expression on monocytic cells and not on alveolar macrophages. Besides, corticosteroids induced a temporary and partial anti-inflammatory gene profile depending on cytokines and monocyte/macrophage subsets.

Discussion

This work documents the baseline effects of the standard-of-care corticosteroid treatment for early innate allo-responses. These insights will enable further optimization and improvement of lung transplantation outcomes.

Purinergic P2Y2 Receptor-Induced Activation of Endothelial TRPV4 Channels Mediates Lung Ischemia-Reperfusion Injury

Lung ischemia-reperfusion injury (IRI), characterized by inflammation, vascular permeability, and lung edema, is the major cause of primary graft dysfunction after lung transplantation. We recently reported that endothelial cell (EC) TRPV4 channels play a central role in lung edema and dysfunction after IR. However, the cellular mechanisms for lung IR-induced activation of endothelial TRPV4 channels are unknown. In a left-lung hilar ligation model of IRI in mice, we found that lung IR increases the efflux of extracellular ATP (eATP) through pannexin 1 (Panx1) channels at the EC membrane. Elevated eATP activated elementary Ca2+ influx signals through endothelial TRPV4 channels through purinergic P2Y2 receptor (P2Y2R) signaling. P2Y2R-dependent activation of TRPV4 channels was also observed in human and mouse pulmonary microvascular endothelium in ex vivo and in vitro surrogate models of lung IR. Endothelium-specific deletion of P2Y2R, TRPV4, and Panx1 in mice had substantial protective effects against lung IR-induced activation of endothelial TRPV4 channels, lung edema, inflammation, and dysfunction. These results identify endothelial P2Y2R as a novel mediator of lung edema, inflammation, and dysfunction after IR, and show that disruption of endothelial Panx1-P2Y2R-TRPV4 signaling pathway could represent a promising therapeutic strategy for preventing lung IRI after transplantation.

Altered purine metabolism at reperfusion affects clinical outcome in lung transplantation

INTRODUCTION

Lung transplantation is an established treatment for patients with end-stage lung disease. However, ischaemia reperfusion injury remains a barrier to achieving better survival outcomes. Here, we aim to investigate the metabolomic and transcriptomic profiles in human lungs before and after reperfusion, to identify mechanisms relevant to clinical outcome.

METHODS

We analysed 67 paired human lung tissue samples collected from 2008 to 2011, at the end of cold preservation and 2 hours after reperfusion. Gene expression analysis was performed with R. Pathway analysis was conducted with Ingenuity Pathway Analysis. MetaboAnalyst and OmicsNet were used for metabolomics analysis and omics data integration, respectively. Association of identified metabolites with transplant outcome was investigated with Kaplan-Meier estimate and Cox proportional hazard models.

RESULTS

Activation of energy metabolism and reduced antioxidative biochemicals were found by metabolomics. Upregulation of genes related to cytokines and inflammatory mediators, together with major signalling pathways were revealed by transcriptomics. Purine metabolism was identified as the most significantly enriched pathway at reperfusion, based on integrative analysis of the two omics data sets. Elevated expression of purine nucleoside phosphorylase (PNP) could be attributed to activation of multiple transcriptional pathways. PNP catabolised reactions were evidenced by changes in related metabolites, especially decreased levels of inosine and increased levels of uric acid. Multivariable analyses showed significant association of inosine and uric acid levels with intensive care unit length of stay and ventilation time.

CONCLUSION

Oxidative stress, especially through purine metabolism pathway, is a major metabolic event during reperfusion and may contribute to the ischaemia reperfusion injury of lung grafts.

ZNF354C Mediated by DNMT1 Ameliorates Lung Ischemia-Reperfusion Oxidative Stress Injury by Reducing TFPI Promoter Methylation to Upregulate TFPI

Background

Pulmonary ischemia reperfusion- (I/R-) induced dysfunction is a significant clinical problem after lung transplantation. In this study, we aim to explore the molecular mechanism of lung I/R injury (LIRI).

Methods

Bioinformatic analysis of gene involved in oxidative stress. A HUVEC oxygen glucose deprivation/reoxygenation (OGD/R) model and I/R mouse model were first established via I/R. The cellular proliferation, migration, reactive oxygen species (ROS), and parameters of lung injury were assessed via CCK-8, EdU staining, Transwell, cellular ROS kit, and H&E staining. We also confirmed related gene expressions and protein levels and the interaction between the tissue factor pathway inhibitor (TFPI) promotor and ZNF354C.

Results

Bioinformatic analysis results showed TFPI contributed to oxidative stress. OGD/R caused a reduction in cell viability and migration, hypermethylation of TFPI, increased ROS, and downregulation of ZNF354C, TFPI, and DNA methyltransferases (DNMTs) in HUVECs. Besides, ZNF354C could directly bind to the TFPI promoter, enhance proliferation and migration, and inhibit ROS in OGD/R-induced HUVECs by upregulating TFPI. More importantly, we discovered that 5-Aza could reduce TFPI methylation, upregulate TFPI, and enhance the binding of ZNF354C to the TFPI promoter in LIRI. Furthermore, DNMT1 silencing could induce proliferation and migration and prevent ROS in OGD/R-induced HUVECs by upregulating ZNF354C. Additionally, we verified that ZNF354C could alleviate LIRI by preventing DNA methylation in vivo.

Conclusions

ZNF354C overexpression induced proliferation and migration, as well as suppressed ROS in OGD/R-induced HUVECs, and alleviated LIRI in mice by inhibiting TFPI promoter methylation to upregulate TFPI. Therefore, ZNF354C and TFPI methylation might be promising molecular markers for LIRI therapy.

Endothelial TRPV4 channels in lung edema and injury

The alveolo-capillary barrier is relatively impermeable, and facilitates gas exchange via the large alveolar surface in the lung. Disruption of alveolo-capillary barrier leads to accumulation of edema fluid in lung injury. Studies in animal models of various forms of lung injury provide evidence that TRPV4 channels play a critical role in disruption of the alveolo-capillary barrier and pathogenesis of lung injury. TRPV4 channels from capillary endothelial cells, alveolar epithelial cells, and immune cells have been implicated in the pathogenesis of lung injury. Recent studies in endothelium-specific TRPV4 knockout mice point to a central role for endothelial TRPV4 channels in lung injury. In this chapter, we review the findings on the pathological roles of endothelial TRPV4 channels in different forms of lung injury and future directions for further investigation.

Pannexin-1 channel opening is critical for COVID-19 pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly rampaged worldwide, causing a pandemic of coronavirus disease (COVID -19), but the biology of SARS-CoV-2 remains under investigation. We demonstrate that both SARS-CoV-2 spike protein and human coronavirus 229E (hCoV-229E) or its purified S protein, one of the main viruses responsible for the common cold, induce the transient opening of Pannexin-1 (Panx-1) channels in human lung epithelial cells. However, the Panx-1 channel opening induced by SARS-CoV-2 is greater and more prolonged than hCoV-229E/S protein, resulting in an enhanced ATP, PGE₂, and IL-1β release. Analysis of lung lavages and tissues indicate that Panx-1 mRNA expression is associated with increased ATP, PGE₂, and IL-1β levels. Panx-1 channel opening induced by SARS-CoV-2 spike protein is angiotensin-converting enzyme 2 (ACE-2), endocytosis, and furin dependent. Overall, we demonstrated that Panx-1 channel is a critical contributor to SARS-CoV-2 infection and should be considered as an alternative therapy.

Endothelial Transient Receptor Potential V4 Channels Mediate Lung Ischemia-Reperfusion Injury

BACKGROUND

Lung ischemia-reperfusion injury (IRI), involving severe inflammation and edema, is a major cause of primary graft dysfunction following transplant. Activation of transient receptor potential vanilloid 4 (TRPV4) channels modulates vascular permeability. Thus, this study tests the hypothesis that endothelial TRPV4 channels mediate lung IRI.

METHODS

C57BL/6 wild-type (WT), TRPV4^-/-, tamoxifen-inducible endothelial TRPV4 knockout (TRPV4_EC^-/-), and tamoxifen-treated control (TRPV4^fl/fl) mice underwent lung IR using a left lung hilar-ligation model (n≥6 mice/group). WT mice were also treated with a TRPV4-specific inhibitor (GSK2193874; 1mg/kg) (WT+GSK219). Partial pressure of oxygen (PaO₂), edema (wet-to-dry weight ratio), compliance, neutrophil infiltration, and cytokine concentrations in bronchioalveolar lavage fluid were assessed. Pulmonary microvascular endothelial cells (PMVECs) were characterized in vitro following exposure to hypoxia-reoxygenation.

RESULTS

Compared to WT, PaO₂ following IR was significantly improved in TRPV4^-/- mice (133.1±43.9 vs 427.8±83.1 mmHg, p<0.001) and WT+GSK219 mice (133.1±43.9 vs 447.0±67.6 mmHg, p<0.001). Pulmonary edema and neutrophil infiltration were also significantly reduced after IR in TRPV4^-/- and WT+GSK219 mice versus WT. TRPV4_EC^-/- mice following IR demonstrated significantly improved oxygenation versus control (109.2±21.6 vs 405.3±41.4 mmHg, p<0.001) as well as significantly improved compliance, and significantly less edema, neutrophil infiltration and proinflammatory cytokine production (TNF-α, CXCL1, IL-17, IFN-γ). Hypoxia-reoxygenation-induced permeability and CXCL1 expression by PMVECs was significantly attenuated by TRPV4 inhibitors.

CONCLUSIONS

Endothelial TRPV4 plays a key role in vascular permeability and lung inflammation following IR. TRPV4 channels may be a promising therapeutic target to mitigate lung IRI and decrease the incidence of primary graft dysfunction following transplant. (Word Count: 249/250).