Resolution of post-lung transplant ischemia-reperfusion injury is modulated via Resolvin D1-FPR2 and Maresin 1-LGR6 signaling

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.

Maresin 1 Activates LGR6 to Alleviate Neuroinflammation via the CREB/JMJD3/IRF4 Pathway in a Rat Model of Subarachnoid Hemorrhage

Neuroinflammation is an early event of brain injury after subarachnoid hemorrhage (SAH). Whether the macrophage mediators in resolving inflammation 1 (MaR1) is involved in SAH pathogenesis is unknown. In this study, 205 male Sprague-Dawley rats were subjected to SAH via endovascular perforation in the experimental and control groups. MaR1 was dosed intranasally at 1 h after SAH, with LGR6 siRNA and KG-501, GSK-J4 administered to determine the signaling pathway. Neurobehavioral, histological and biochemical data were obtained from the animal groups with designated treatments. The results showed: (i) The leucine-rich repeat containing G protein-coupled receptor 6 (LGR6) was decreased after SAH and reached to the lowest level at 24 h after SAH. Jumonji d3 (JMJD3) protein levels tended to increase and peaked at 24 h after SAH. LGR6 and JMJD3 expression were co-localized with microglia. (ii) MaR1 administration mitigated short-term neurological deficits, brain edema and long-term neurobehavioral performance after SAH, and attenuated microglial activation and neutrophil infiltration. (iii) Knockdown of LGR6, inhibition of CREB phosphorylation or JMJD3 activity abolished the anti-neuroinflammatory effect of MaR1 on the expression of CREB, CBP, JMJD3, IRF4, IRF5, IL-1β, IL-6 and IL-10, thus prevented microglial activation and neutrophil infiltration. Together, the results show that MaR1 can activate LGR6 and affect CREB/JMJD3/IRF4 signaling to attenuate neuroinflammation after SAH, pointing to a potential pharmacological utility in this disorder.

Nanoparticle targeting of neutrophil glycolysis prevents lung ischemia-reperfusion injury

Neutrophils exacerbate pulmonary ischemia-reperfusion injury (IRI) resulting in poor short and long-term outcomes for lung transplant recipients. Glycolysis powers neutrophil activation, but it remains unclear if neutrophil-specific targeting of this pathway will inhibit IRI. Lipid nanoparticles containing the glycolysis flux inhibitor 2-deoxyglucose (2-DG) were conjugated to neutrophil-specific Ly6G antibodies (NP-Ly6G[2-DG]). Intravenously administered NP-Ly6G(2-DG) to mice exhibited high specificity for circulating neutrophils. NP-Ly6G(2-DG)-treated neutrophils were unable to adapt to hypoglycemic conditions of the lung airspace environment as evident by the loss of demand-induced glycolysis, reductions in glycogen and ATP content, and an increased vulnerability to apoptosis. NP-Ly6G(2-DG) treatment inhibited pulmonary IRI following hilar occlusion and orthotopic lung transplantation. IRI protection was associated with less airspace neutrophil extracellular trap generation, reduced intragraft neutrophilia, and enhanced alveolar macrophage efferocytotic clearance of neutrophils. Collectively, our data show that pharmacologically targeting glycolysis in neutrophils inhibits their activation and survival leading to reduced pulmonary IRI.

Targeting Macrophages in Organ Transplantation: A Step Toward Personalized Medicine

Organ transplantation remains the most optimal strategy for patients with end-stage organ failure. However, prevailing methods of immunosuppression are marred by adverse side effects, and allograft rejection remains common. It is imperative to identify and comprehensively characterize the cell types involved in allograft rejection, and develop therapies with greater specificity. There is increasing recognition that processes mediating allograft rejection are the result of interactions between innate and adaptive immune cells. Macrophages are heterogeneous innate immune cells with diverse functions that contribute to ischemia-reperfusion injury, acute rejection, and chronic rejection. Macrophages are inflammatory cells capable of innate allorecognition that strengthen their responses to secondary exposures over time via "trained immunity." However, macrophages also adopt immunoregulatory phenotypes and may promote allograft tolerance. In this review, we discuss the roles of macrophages in rejection and tolerance, and detail how macrophage plasticity and polarization influence transplantation outcomes. A comprehensive understanding of macrophages in transplant will guide future personalized approaches to therapies aimed at facilitating tolerance or mitigating the rejection process.

Advances in lung ischemia/reperfusion injury: unraveling the role of innate immunity

BACKGROUND

Lung ischemia/reperfusion injury (LIRI) is a common occurrence in clinical practice and represents a significant complication following pulmonary transplantation and various diseases. At the core of pulmonary ischemia/reperfusion injury lies sterile inflammation, where the innate immune response plays a pivotal role. This review aims to investigate recent advancements in comprehending the role of innate immunity in LIRI.

METHODS

A computer-based online search was performed using the PubMed database and Web of Science database for published articles concerning lung ischemia/reperfusion injury, cell death, damage-associated molecular pattern molecules (DAMPs), innate immune cells, innate immunity, inflammation.

RESULTS

During the process of lung ischemia/reperfusion, cellular injury even death can occur. When cells are injured or undergo cell death, endogenous ligands known as DAMPs are released. These molecules can be recognized and bound by pattern recognition receptors (PRRs), leading to the recruitment and activation of innate immune cells. Subsequently, a cascade of inflammatory responses is triggered, ultimately exacerbating pulmonary injury. These steps are complex and interrelated rather than being in a linear relationship. In recent years, significant progress has been made in understanding the immunological mechanisms of LIRI, involving novel types of cell death, the ability of receptors other than PRRs to recognize DAMPs, and a more detailed mechanism of action of innate immune cells in ischemia/reperfusion injury (IRI), laying the groundwork for the development of novel diagnostic and therapeutic approaches.

CONCLUSIONS

Various immune components of the innate immune system play critical roles in lung injury after ischemia/reperfusion. Preventing cell death and the release of DAMPs, interrupting DAMPs receptor interactions, disrupting intracellular inflammatory signaling pathways, and minimizing immune cell recruitment are essential for lung protection in LIRI.

Maresin-1 ameliorates hypertensive vascular remodeling through its receptor LGR6

Hypertensive vascular remodeling is defined as the changes in vascular function and structure induced by persistent hypertension. Maresin-1 (MaR1), one of metabolites from Omega-3 fatty acids, has been reported to promote inflammation resolution in several inflammatory diseases. This study aims to investigate the effect of MaR1 on hypertensive vascular remodeling. Here, we found serum MaR1 levels were reduced in hypertensive patients and was negatively correlated with systolic blood pressure (SBP). The treatment of MaR1 reduced the elevation of blood pressure and alleviated vascular remodeling in the angiotensin II (AngII)-infused mouse model. In addition, MaR1-treated vascular smooth muscle cells (VSMCs) exhibited reduced excessive proliferation, migration, and phenotype switching, as well as impaired pyroptosis. However, the knockout of the receptor of MaR1, leucine-rich repeat-containing G protein-coupled receptor 6 (LGR6), was seen to aggravate pathological vascular remodeling, which could not be reversed by additional MaR1 treatment. The mechanisms by which MaR1 regulates vascular remodeling through LGR6 involves the Ca2+/calmodulin-dependent protein kinase II/nuclear factor erythroid 2-related factor 2/heme oxygenase-1 signaling pathway. Overall, supplementing MaR1 may be a novel therapeutic strategy for the prevention and treatment of hypertension.

MerTK-dependent efferocytosis by monocytic-MDSCs mediates resolution of post-lung transplant injury

Rationale

Patients with end stage lung diseases require lung transplantation (LTx) that can be impeded by ischemia-reperfusion injury (IRI) leading to subsequent chronic lung allograft dysfunction (CLAD) and inadequate outcomes.

Objectives

We examined the undefined role of MerTK (receptor Mer tyrosine kinase) on monocytic myeloid-derived suppressor cells (M-MDSCs) in efferocytosis (phagocytosis of apoptotic cells) to facilitate resolution of lung IRI.

Methods

Single-cell RNA sequencing of lung tissue and BAL from post-LTx patients was analyzed. Murine lung hilar ligation and allogeneic orthotopic LTx models of IRI were used with Balb/c (WT), cebpb -/- (MDSC-deficient), Mertk -/- or MerTK-CR (cleavage resistant) mice. Lung function, IRI (inflammatory cytokine and myeloperoxidase expression, immunohistology for neutrophil infiltration), and flow cytometry of lung tissue for efferocytosis of apoptotic neutrophils were assessed in mice.

Measurements and Main Results

A significant downregulation in MerTK-related efferocytosis genes in M-MDSC populations of CLAD patients compared to healthy subjects was observed. In the murine IRI model, significant increase in M-MDSCs, MerTK expression and efferocytosis was observed in WT mice during resolution phase that was absent in cebpb -/- Land Mertk -/- mice. Adoptive transfer of M-MDSCs in cebpb -/- mice significantly attenuated lung dysfunction, and inflammation leading to resolution of IRI. Additionally, in a preclinical murine orthotopic LTx model, increases in M-MDSCs were associated with resolution of lung IRI in the transplant recipients. In vitro studies demonstrated the ability of M-MDSCs to efferocytose apoptotic neutrophils in a MerTK-dependent manner.

Conclusions

Our results suggest that MerTK-dependent efferocytosis by M-MDSCs can significantly contribute to the resolution of post-LTx IRI.

Specialized pro-resolving mediators in vascular inflammation and atherosclerotic cardiovascular disease

Timely resolution of the acute inflammatory response (or inflammation resolution) is an active, highly coordinated process that is essential to optimal health. Inflammation resolution is regulated by specific endogenous signalling molecules that function as 'stop signals' to terminate the inflammatory response when it is no longer needed; to actively promote healing, regeneration and tissue repair; and to limit pain. Specialized pro-resolving mediators are a superfamily of signalling molecules that initiate anti-inflammatory and pro-resolving actions. Without an effective and timely resolution response, inflammation can become chronic, a pathological state that is associated with many widely occurring human diseases, including atherosclerotic cardiovascular disease. Uncovering the mechanisms of inflammation resolution failure in cardiovascular diseases and identifying useful biomarkers for non-resolving inflammation are unmet needs. In this Review, we discuss the accumulating evidence that supports the role of non-resolving inflammation in atherosclerosis and the use of specialized pro-resolving mediators as therapeutic tools for the treatment of atherosclerotic cardiovascular disease. We highlight open questions about therapeutic strategies and mechanisms of disease to provide a framework for future studies on the prevention and treatment of atherosclerosis.

Resolvin D2 and its receptor GPR18 in cardiovascular and metabolic diseases: A promising biomarker and therapeutic target

Accumulating evidence suggests that inflammation plays an important role in the pathophysiology of the initiation and progression of cardiovascular and metabolic diseases (CVMDs). Anti-inflammation strategies and those that promote inflammation resolution have gradually become potential therapeutic approaches for CVMDs. Resolvin D2 (RvD2), a specialized pro-resolving mediator, exerts anti-inflammatory and pro-resolution effects through its receptor GPR18, a G protein-coupled receptor. Recently, the RvD2/GPR18 axis has received more attention due to its protective role in CVMDs, including atherosclerosis, hypertension, ischaemiareperfusion, and diabetes. Here, we introduce basic information about RvD2 and GPR18, summarize their roles in different immune cells, and review the therapeutic potential of the RvD2/GPR18 axis in CVMDs. In summary, RvD2 and its receptor GPR18 play an important role in the occurrence and development of CVMDs and are potential biomarkers and therapeutic targets.

Resolvins and cysteinyl-containing pro-resolving mediators activate resolution of infectious inflammation and tissue regeneration

This review is a synopsis of the main points from the opening presentation by the authors in the Resolution of Inflammation session at the 8th European Workshop on Lipid Mediators held at the Karolinska Institute, Stockholm, Sweden, June 29th, 2022. Specialized pro-resolving mediators (SPM) promote tissue regeneration, control infections and resolution of inflammation. These include resolvins, protectins, maresins and the newly identified conjugates in tissue regeneration (CTRs). We reported mechanisms of CTRs in activating primordial regeneration pathways in planaria using RNA-sequencing. Also, the 4S,5S-epoxy-resolvin intermediate in the biosynthesis of resolvin D3 and resolvin D4 was prepared by total organic synthesis. Human neutrophils convert this to resolvin D3 and resolvin D4, while human M2 macrophages transformed this labile epoxide intermediate to resolvin D4 and a novel cysteinyl-resolvin that is a potent isomer of RCTR1. The novel cysteinyl-resolvin significantly accelerates tissue regeneration with planaria and inhibits human granuloma formation.

Resolution medicine in cancer, infection, pain and inflammation: are we on track to address the next Pandemic?

Uncontrolled inflammation giving rise to excessive tissue inflammation can lead to chronic inflammation that enhances tissue destruction, amplifying many chronic human pathologies. Normally the acute inflammatory response is protective and should be self-limited returning tissues to functional homeostasis with endogenous programmed resolution via leukocyte vasculature cell-cell interactions and crosstalk that biosynthesize pro-resolving mediators. When failed resolution takes place, as with the use of NSAIDs, tissues undergo chronic inflammation and fibrosis. Herein, we discuss these mechanisms and the role of specialized proresolving mediators, the resolvins, protectins and maresins produced from essential omega-3 fatty acids EPA and DHA, and their contributions via their cognate cell surface receptors, to the resolution response. Harnessing these pathways and their cellular mechanisms can help in providing new therapeutic approaches to many human diseases, infections, organ protection and trauma via resolution medicine to enhance the body's own resilience to challenge.