LGR6 frameshift variant abrogates receptor expression on select leukocyte subsets and associates with viral infections.

The leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6) was recently identified as the cognate receptor for the pro-resolving mediator Maresin (MaR)1. To address the biological role of LGR6 in humans, we investigated the functional impact of a genetic variant in the gene encoding for LGR6, which is predicted to lead to a frameshift mutation in one of the receptor isoforms, on both receptor expression and immune cell responses. In neutrophils, monocytes, and NK cells from volunteers homozygous for this variant, we found a significant downregulation in the expression of LGR6 when compared with controls without the variant. Whereas LGR6 expression was essentially similar in monocyte-derived macrophages and CD8+ T-cells. Functionally loss of LGR6 expression was linked with a decreased ability of neutrophils and monocytes to phagocytose bacteria. We observed an increase in neutrophil chemotaxis and leukotriene B4 (LTB4) production, and increased expression of activation markers, including markers for platelet-leukocyte phagocyte heterotypic aggregates, such as CD41, in neutrophils and monocytes from the variant group. Using data from the UK Biobank we found that at a population level the rs4266947 variant which is in high linkage disequilibrium with rs74355478 was associated with a higher incidence of viral infections. Intriguingly, neutrophils, NK cells and CD8+ T-cells from volunteers with the LGR6 variant displayed altered viral responses when stimulated with Toll-like receptor (TLR)3, TLR7/TLR8 and TLR9 agonists. Together these findings shed new light on the cell type-specific regulation of LGR6 expression and the role of this receptor in directing host immune responses.

Resolvin D2 prevents vascular remodeling, hypercontractility and endothelial dysfunction in obese hypertensive mice through modulation of vascular and proinflammatory factors.

During resolution of inflammation, specialized proresolving mediators (SPMs), including resolvins, are produced to restore tissue homeostasis. We hypothesized that there might be a dysregulation of SPMs pathways in pathological vascular remodeling and that resolvin D2 (RvD2) might prevent vascular remodeling and contractile and endothelial dysfunction in a model of obesity and hypertension. In aortic samples of patients with or without abdominal aortic aneurysms (AAA), we evaluated gene expression of enzymes involved in SPMs synthesis (ALOXs), SPMs receptors and pro-inflammatory genes. In an experimental model of aortic dilation induced by high fat diet (HFD, 60%, eighteen weeks) and angiotensin II (AngII) infusion (four weeks), we studied the effect of RvD2 administration in aorta and small mesenteric arteries structure and function and markers of inflammation. In human macrophages we evaluated the effects of AngII and RvD2 in macrophages function and SPMs profile. In patients, we found positive correlations between AAA and obesity, and between AAA and expression of ALOX15, RvD2 receptor GPR18, and pro-inflammatory genes. There was an inverse correlation between the expression of aortic ALOX15 and AAA growth rate. In the mice model, RvD2 partially prevented the HFD plus AngII-induced obesity and adipose tissue inflammation, hypertension, aortic and mesenteric arteries remodeling, hypercontratility and endothelial dysfunction, and the expression of vascular proinflammatory markers and cell apoptosis. In human macrophages, RvD2 prevented AngII-induced impaired efferocytosis and switched SPMs profile. RvD2 might represent a novel protective strategy in preventing vascular damage associated to hypertension and obesity likely through effects in vascular and immune cells.

Corrigendum: Arachidonate 15-lipoxygenase-mediated production of Resolvin D5n-3 DPA abrogates pancreatic stellate cell-induced cancer cell invasion.

[This corrects the article DOI: 10.3389/fimmu.2023.1248547.].

Resolvin T4 enhances macrophage cholesterol efflux to reduce vascular disease.

While cardiovascular disease (CVD) is one of the major co-morbidities in patients with rheumatoid arthritis (RA), the mechanism(s) that contribute to CVD in patients with RA remain to be fully elucidated. Herein, we observe that plasma concentrations of 13-series resolvin (RvT)4 negatively correlate with vascular lipid load in mouse inflammatory arthritis. Administration of RvT4 to male arthritic mice fed an atherogenic diet significantly reduces atherosclerosis. Assessment of the mechanisms elicited by this mediator demonstrates that RvT4 activates cholesterol efflux in lipid laden macrophages via a Scavenger Receptor class B type 1 (SR-BI)-Neutral Cholesterol Ester Hydrolase-dependent pathway. This leads to the reprogramming of lipid laden macrophages yielding tissue protection. Pharmacological inhibition or knockdown of macrophage SR-BI reverses the vasculo-protective activities of RvT4 in vitro and in male mice in vivo. Together these findings elucidate a RvT4-SR-BI centered mechanism that orchestrates macrophage responses to limit atherosclerosis during inflammatory arthritis.

Efferocyte-Derived MCTRs Metabolically Prime Macrophages for Continual Efferocytosis via Rac1-Mediated Activation of Glycolysis.

Clearance of multiple rounds of apoptotic cells (ACs) through continual efferocytosis is critical in the maintenance of organ function, the resolution of acute inflammation, and tissue repair. To date, little is known about the nature of mechanisms and factors that govern this fundamental process. Herein, the authors reported that breakdown of ACs leads to upregulation of 12-lipoxygenase in macrophages. This enzyme converts docosahexaenoic acid to maresin conjugates in tissue regeneration (MCTRs). The levels of these autacoids are elevated at sites of high apoptotic burden in vivo and in efferocytosing macrophages in vitro. Abrogation of MCTR production using genetic approaches limits the ability of macrophages to perform continual efferocytosis both in vivo and in vitro, an effect that is rescued by add-back of MCTRs. Mechanistically, MCTR-mediated priming of macrophages for continual efferocytosis is dependent on alterations in Rac1 signalling and glycolytic metabolism. Inhibition of Rac1 abolishes the ability of MCTRs to increase glucose uptake and efferocytosis in vitro, whereas inhibition of glycolysis limits the MCTR-mediated increases in efferocytosis and tissue repair. Together, these findings demonstrate that upregulation of MCTRs by efferocytosing macrophages plays a central role in the regulation of continual efferocytosis via the autocrine and paracrine modulation of metabolic pathways.

Arachidonate 15-lipoxygenase-mediated production of Resolvin D5n-3 DPA abrogates pancreatic stellate cell-induced cancer cell invasion.

Activation of pancreatic stellate cells (PSCs) to cancer-associated fibroblasts (CAFs) is responsible for the extensive desmoplastic reaction observed in PDAC stroma: a key driver of pancreatic ductal adenocarcinoma (PDAC) chemoresistance leading to poor prognosis. Specialized pro-resolving mediators (SPMs) are prime modulators of inflammation and its resolution, traditionally thought to be produced by immune cells. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based lipid mediator profiling PSCs as well as primary human CAFs express enzymes and receptors to produce and respond to SPMs. Human PSC/CAF SPM secretion profile can be modulated by rendering these cells activated [transforming growth factor beta (TGF-ß)] or quiescent [all-trans retinoic acid (ATRA)]. ATRA-induced nuclear translocation of arachidonate-15-lipoxygenase (ALOX15) was linked to increased production of n-3 docosapentaenoic acid-derived Resolvin D5 (RvD5n-3 DPA), among other SPMs. Inhibition of RvD5n-3 DPA formation increases cancer cell invasion, whereas addback of this molecule reduced activated PSC-mediated cancer cell invasion. We also observed that circulating concentrations of RvD5n-3 DPA levels were decreased in peripheral blood of metastatic PDAC patients when compared with those measured in plasma of non-metastatic PDAC patients. Together, these findings indicate that RvD5n-3 DPA may regulate cancer-stroma cross-talk and invasion.

The Annexin-A1 mimetic RTP-026 promotes acute cardioprotection through modulation of immune cell activation.

AIMS: The cardio-protective and immuno-regulatory properties of RTP-026, a synthetic peptide that spans the Annexin-A1 (AnxA1) N-terminal region, were tested in rat acute myocardial infarction. METHODS AND RESULTS: In vitro, selective activation of formyl-peptide receptor type 2 (FPR2) by RTP-026 occurred with apparent EC50 in the 10-30 nM range. With human primary cells, RTP-026 counteracted extension of neutrophil life-span and augmented phagocytosis of fluorescent E.coli by blood myeloid cells. An in vivo model of rat acute infarction was used to quantify tissue injury and phenotype immune cells in myocardium and blood. The rat left anterior descending coronary artery was occluded and then reopened for 2-hour or 24-hour reperfusion. For the 2-hour reperfusion protocol, RTP-026 (25-500 µg/kg; given i.v. at the start of reperfusion) significantly reduced infarct size by ∼50 %, with maximal efficacy at 50 µg/kg. Analyses of cardiac immune cells showed that RTP-026 reduced neutrophil and classical monocyte recruitment to the damaged heart. In the blood, RTP-026 (50 µg/kg) attenuated activation of neutrophils and monocytes monitored through CD62L and CD54 expression. Modulation of vascular inflammation by RTP-026 was demonstrated by reduction in plasma levels of mediators like TNF-α, IL-1ß, KC, PGE2 and PGF2α⊡ For the 24-hour reperfusion protocol, RTP-026 (30 µg/kg given i.v. at 0, 3 and 6 h reperfusion) reduced necrotic myocardium by ∼40 %. CONCLUSIONS: RTP-026 modulate immune cell responses and decreases infarct size of the heart in preclinical settings. Tempering over-exuberant immune cell activation by RTP-026 is a suitable approach to translate the biology of AnxA1 for therapeutic purposes.

Stereoselective Synthesis, Pro-resolution, and Anti-inflammatory Actions of RvD5n-3 DPA.

The methyl ester of resolvin D5n-3 DPA, a lipid mediator biosynthesized from the omega-3 fatty acid n-3 docosapentaenoic acid, was stereoselectively prepared in 8% yield over 12 steps (longest linear sequence). The key steps for the introduction of the two stereogenic secondary alcohols were an organocatalyzed oxyamination and the Midland Alpine borane reduction. For the assembly of the carbon chain, the Sonogashira cross-coupling reaction and the Takai olefination were utilized. The physical properties, including retention time in liquid chromatography and tandem mass spectra, of the synthetic material were matched against material from human peripheral blood and mouse infectious exudates. Synthetic RvD5n-3 DPA, obtained just prior to biological experiments, displayed potent leukocyte-directed activities, upregulating the ability of neutrophils and macrophages to phagocytose bacteria, known as hallmark bioactions of specialized pro-resolving endogenous mediators.

Maresin 1 activates brown adipose tissue and promotes browning of white adipose tissue in mice.

OBJECTIVE: Maresin 1 (MaR1) is a docosahexaenoic acid-derived proresolving lipid mediator with insulin-sensitizing and anti-steatosis properties. Here, we aim to unravel MaR1 actions on brown adipose tissue (BAT) activation and white adipose tissue (WAT) browning. METHODS: MaR1 actions were tested in cultured murine brown adipocytes and in human mesenchymal stem cells (hMSC)-derived adipocytes. In vivo effects of MaR1 were tested in diet-induced obese (DIO) mice and lean WT and Il6 knockout (Il6-/-) mice. RESULTS: In cultured differentiated murine brown adipocytes, MaR1 reduces the expression of inflammatory genes, while stimulates glucose uptake, fatty acid utilization and oxygen consumption rate, along with the upregulation of mitochondrial mass and genes involved in mitochondrial biogenesis and function and the thermogenic program. In Leucine Rich Repeat Containing G Protein-Coupled Receptor 6 (LGR6)-depleted brown adipocytes using siRNA, the stimulatory effect of MaR1 on thermogenic genes was abrogated. In DIO mice, MaR1 promotes BAT remodeling, characterized by higher expression of genes encoding for master regulators of mitochondrial biogenesis and function and iBAT thermogenic activation, together with increased M2 macrophage markers. In addition, MaR1-treated DIO mice exhibit a better response to cold-induced BAT activation. Moreover, MaR1 induces a beige adipocyte signature in inguinal WAT of DIO mice and in hMSC-derived adipocytes. MaR1 potentiates Il6 expression in brown adipocytes and BAT of cold exposed lean WT mice. Interestingly, the thermogenic properties of MaR1 were abrogated in Il6-/- mice. CONCLUSIONS: These data reveal MaR1 as a novel agent that promotes BAT activation and WAT browning by regulating thermogenic program in adipocytes and M2 polarization of macrophages. Moreover, our data suggest that LGR6 receptor is mediating MaR1 actions on brown adipocytes, and that IL-6 is required for the thermogenic effects of MaR1.

Pro-inflammatory and pro-resolving lipid mediators of inflammation in HIV: effect of aspirin intervention.

BACKGROUND: Persons with HIV (PWH) have an increased risk of cardiovascular disease (CVD) compared to HIV-seronegative individuals (SN). Inflammation contributes to this risk but the role of lipid mediators, with central roles in inflammation, in HIV infection remain to be established; further aspirin reduces CVD risk in the general population through production of some of these anti-inflammatory lipid mediators, but they have not been studied in PWH. METHODS: We evaluated the relationship between plasma lipid mediators (i.e. 50 lipid mediators including classic eicosanoids and specialized pro-resolving mediators (SPMs)) and HIV status; and the impact of aspirin in PWH on regulating these autacoids. Plasma samples were obtained from 110 PWH receiving antiretroviral therapy (ART) from a randomized trial of aspirin (ACTG-A5331) and 107 matched SN samples (MACS-WIHS Combined Cohort). FINDINGS: PWH had lower levels of arachidonic acid-derived pro-inflammatory prostaglandins (PGs: PGE2 and PGD2) and thromboxanes (Tx: TxB2), and higher levels of select pro-resolving lipid mediators (e.g. RvD4 and MaR2n-3 DPA) compared to SN. At the interval tested, aspirin intervention was observed to reduced PGs and Tx, and while we did not observe an increase in aspirin triggered mediators, we observed the upregulation of other SPM in aspirin treated PWH, namely MaR2n-3 DPA. INTERPRETATION: Together these observations demonstrate that plasma lipid mediators profiles, some with links to systemic inflammation and CVD risk, become altered in PWH. Furthermore, aspirin intervention did not increase levels of aspirin-triggered pro-resolving lipid mediators, consistent with other reports of an impaired aspirin response in PWH. FUNDING: NIH.

Deletion of macrophage Gpr101 disrupts their phenotype and function dysregulating host immune responses in sterile and infectious inflammation.

We recently found that the G protein coupled receptor GPR101 mediates the phagocyte-directed pro-resolving activities of RvD5n-3 DPA (n-3 docosapentaenoic acid-derived Resolvin D5). Herein, we investigated the endogenous role of this pro-resolving receptor in modulating macrophage biology using a novel mouse line where the expression of Gpr101 was conditionally deleted in macrophages (MacGpr101KO). Peritoneal macrophages obtained from naïve MacGpr101KO mice displayed a marked shift in the expression of phenotypic and activation markers, including the Interleukin (IL)-10 and IL-23 receptors. Loss of Gpr101 on macrophages was also associated with a significant disruption in their cellular metabolism and a decreased ability to migrate towards the chemoattractant Mcp-1. The alterations in macrophage phenotype observed in Gpr101 deficient macrophages were maintained following inflammatory challenge. This was linked with an increased inflammatory response in the Gpr101 deficient animals and a reduced ability of phagocytes, including macrophages, to clear bacteria. Loss of Gpr101 on macrophages disrupted host pro-resolving responses to zymosan challenge with MacGpr101KO mice exhibiting significantly higher neutrophil numbers and a delay in the resolution interval when compared with control mice. These observations were linked with a marked dysregulation in peritoneal lipid mediator concentrations in Gpr101 deficient mice, with a downregulation of pro-resolving mediators including MaR2n-3 DPA, Resolvin (Rv) D3 and RvE3. Together these findings identify Gpr101 as a novel regulator of both macrophage phenotype and function, modulating key biological activities in both limiting the propagation of inflammation and expediting its resolution.

Resolvin D2 Attenuates Cardiovascular Damage in Angiotensin II-Induced Hypertension.

BACKGROUND: Resolution of inflammation is orchestrated by specialized proresolving lipid mediators (SPMs), and this would be impaired in some cardiovascular diseases. Among SPMs, resolvins (Rv) have beneficial effects in cardiovascular pathologies, but little is known about their effect on cardiovascular damage in hypertension. METHODS: Aorta, small mesenteric arteries, heart, and peritoneal macrophages were taken from C57BL/6J mice, infused or not with angiotensin II (AngII; 1.44 mg/kg/day, 14 days) in presence or absence of resolvin D2 (RvD2) (100 ng/mice, every second day) starting 1 day before or 7 days after AngII infusion. RESULTS: Enzymes and receptors involved in SPMs biosynthesis and signaling were increased in aorta or heart from AngII-infused mice. We also observed a differential regulation of SPMs in heart from these mice. Preventive treatment with RvD2 partially avoided AngII-induced hypertension and protected the heart and large and small vessels against functional and structural alterations induced by AngII. RvD2 increased the availability of vasoprotective factors, modified SPMs profile, decreased cardiovascular fibrosis, and increased the infiltration of pro-resolving macrophages. When administered in hypertensive animals with established cardiovascular damage, RvD2 partially improved cardiovascular function and structure, decreased fibrosis, reduced the infiltration of neutrophils, and shifted macrophage phenotype toward a pro-resolving phenotype. CONCLUSIONS: There is a disbalance between proinflammatory and resolution mediators in hypertension. RvD2 protects cardiovascular function and structure when administered before and after the development of hypertension by modulating vascular factors, fibrosis and inflammation. Activating resolution mechanisms by treatment with RvD2 may represent a novel therapeutic strategy for the treatment of hypertensive cardiovascular disease.

Resolution Pharmacology: Focus on Pro-Resolving Annexin A1 and Lipid Mediators for Therapeutic Innovation in Inflammation.

Chronic diseases that affect our society are made more complex by comorbidities and are poorly managed by the current pharmacology. While all present inflammatory etiopathogeneses, there is an unmet need for better clinical management of these diseases and their multiple symptoms. We discuss here an innovative approach based on the biology of the resolution of inflammation. Studying endogenous pro-resolving peptide and lipid mediators, how they are formed, and which target they interact with, can offer innovative options through augmenting the expression or function of pro-resolving pathways or mimicking their actions with novel targeted molecules. In all cases, resolution offers innovation for the treatment of the primary cause of a given disease and/or for the management of its comorbidities, ultimately improving patient quality of life. By implementing resolution pharmacology, we harness the whole physiology of inflammation, with the potential to bring a marked change in the management of inflammatory conditions.