MCTR3 reprograms arthritic monocytes to upregulate Arginase-1 and exert pro-resolving and tissue-protective functions in experimental arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a progressive degenerative disorder that leads to joint destruction. Available treatments only target the inflammatory component with minimal impact on joint repair. We recently uncovered a previously unappreciated family of pro-resolving mediators, the maresin conjugate in tissue regeneration (MCTR), that display both immunoregulatory and tissue-protective activities. Thus, we queried whether the production of these autacoids is disrupted in RA patients and whether they can be useful in treating joint inflammation and promoting joint repair.

METHODS

Using a highly phenotyped RA cohort we evaluated plasma MCTR concentrations and correlated these to clinical markers of disease activity. To evaluate the immunoregulatory and tissue reparative activities we employed both in vivo models of arthritis and organ culture models.

FINDINGS

Herein, we observed that plasma MCTR3 concentrations were negatively correlated with joint disease activity and severity in RA patients. Evaluation of the mechanisms engaged by this mediator in arthritic mice demonstrated that MCTR3 reprograms monocytes to confer enduring joint protective properties. Single cell transcriptomic profiling and flow cytometric evaluation of macrophages from mice treated with MCTR3-reprogrammed monocytes revealed a role for Arginase-1 (Arg-1) in mediating their joint reparative and pro-resolving activities. Arg-1 inhibition reversed both the anti-arthritic and tissue reparative actions of MCTR3-reprogrammed monocytes.

INTERPRETATION

Our findings demonstrate that circulating MCTR3 levels are negatively correlated with disease in RA. When administered to mice in vivo, MCTR3 displayed both anti-inflammatory and joint reparative activities, protecting both cartilage and bone in murine arthritis. These activities were, at least in part, mediated via the reprogramming of mononuclear phagocyte responses.

FUNDING

This work was supported by funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant no: 677542) and the Barts Charity (grant no: MGU0343) to J.D. J.D. is also supported by a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (grant 107613/Z/15/Z).

Alpha-1-antitrypsin reduces inflammation and exerts chondroprotection in arthritis

While new treatments have been developed to control joint disease in rheumatoid arthritis, they are partially effective and do not promote structural repair of cartilage. Following an initial identification of α-1-Antitrypsin (AAT) during the resolution phase of acute inflammation, we report here the properties of this protein in the context of cartilage protection, joint inflammation, and associated pain behavior. Intra-articular and systemic administration of AAT reversed joint inflammation, nociception, and cartilage degradation in the KBxN serum and neutrophil elastase models of arthritis. Ex vivo analyses of arthritic joints revealed that AAT promoted transcription of col2a1, acan, and sox9 and downregulated mmp13 and adamts5 gene expression. In vitro studies using human chondrocytes revealed that SERPINA1 transfection and rAAT protein promoted chondrogenic differentiation through activation of PKA-dependent CREB signaling and inhibition of Wnt/β-catenin pathways. Thus, AAT is endowed with anti-inflammatory, analgesic, and chondroprotective properties that are partially inter-related. We propose that AAT could be developed for new therapeutic strategies to reduce arthritic pain and repair damaged cartilage.

Blood pro-resolving mediators are linked with synovial pathology and are predictive of DMARD responsiveness in rheumatoid arthritis

Biomarkers are needed for predicting the effectiveness of disease modifying antirheumatic drugs (DMARDs). Here, using functional lipid mediator profiling and deeply phenotyped patients with early rheumatoid arthritis (RA), we observe that peripheral blood  specialized pro-resolving mediator (SPM) concentrations are linked with both DMARD responsiveness and disease pathotype. Machine learning analysis demonstrates that baseline plasma concentrations of resolvin D4, 10S, 17S-dihydroxy-docosapentaenoic acid, 15R-Lipoxin (LX)A4 and n-3 docosapentaenoic-derived Maresin 1 are predictive of DMARD responsiveness at 6 months. Assessment of circulating SPM concentrations 6-months after treatment initiation establishes that differences between responders and non-responders are maintained, with a decrease in SPM concentrations in patients resistant to DMARD therapy. These findings elucidate the potential utility of  plasma SPM concentrations as biomarkers of DMARD responsiveness in RA.

The GPR40 Agonist GW9508 Enhances Neutrophil Function to Aid Bacterial Clearance During E. coli Infections

G-protein-coupled receptor 40 (GPR40) is known to play a role in the regulation of fatty acids, insulin secretion, and inflammation. However, the function of this receptor in human neutrophils, one of the first leukocytes to arrive at the site of infection, remains to be fully elucidated. In the present study, we demonstrate that GPR40 is upregulated on activated human neutrophils and investigated the functional effects upon treatment with a selective agonist; GW9508. Interestingly, GPR40 expression was up-regulated after neutrophil stimulation with platelet-activating factor (10 nM) or leukotriene B₄ (LTB₄, 10 nM) suggesting potential regulatory roles for this receptor during inflammation. Indeed, GW9508 (1 and 10 μM) increased neutrophil chemotaxis in response to the chemokine IL-8 (30 ng/ml) and enhanced phagocytosis of Escherichia coli by approximately 50% when tested at 0.1 and 1 μM. These results were translated in vivo whereby administration of GW9508 (10 mg/kg, i.p.) during E. coli infections resulted in elevated peritoneal leukocyte infiltration with a higher phagocytic capacity. Importantly, GW9508 administration also modulated the lipid mediator profile, with increased levels of the pro-resolving mediators resolvin D3 and lipoxins. In conclusion, GPR40 is expressed by activated neutrophils and plays an important host protective role to aid clearance of bacterial infections.

Enriched Marine Oil Supplements Increase Peripheral Blood Specialized Pro-Resolving Mediators Concentrations and Reprogram Host Immune Responses: A Randomized Double-Blind Placebo-Controlled Study

RATIONALE

Specialized pro-resolving mediators (SPM-lipoxins, resolvins, protectins, and maresins) are produced via the enzymatic conversion of essential fatty acids, including the omega-3 fatty acids docosahexaenoic acid and n-3 docosapentaenoic acid. These mediators exert potent leukocyte directed actions and control vascular inflammation. Supplementation of animals and humans with essential fatty acids, in particular omega-3 fatty acids, exerts protective actions reducing vascular and systemic inflammation. Of note, the mechanism(s) activated by these supplements in exerting their protective actions remain poorly understood.

OBJECTIVE

Given that essential fatty acids are precursors in the biosynthesises of SPM, the aim of the present study was to establish the relationship between supplementation and peripheral SPM concentrations. We also investigated the relationship between changes in plasma SPM concentrations and peripheral blood platelet and leukocyte responses.

METHODS AND RESULTS

Healthy volunteers were enrolled in a double-blinded, placebo-controlled, crossover study, and peripheral blood was collected at baseline, 2, 4, 6, and 24 hours post administration of placebo or one of 3 doses of an enriched marine oil supplement. Assessment of plasma SPM concentrations using lipid mediator profiling demonstrated a time- and dose-dependent increase in peripheral blood SPM concentration. Supplementation also led to a regulation of peripheral blood cell responses. Here we found a dose-dependent increase in neutrophil and monocyte phagocytosis of bacteria and a decrease in the diurnal activation of leukocytes and platelets, as measured by a reduction in adhesion molecule expression. In addition, transcriptomic analysis of peripheral blood cells demonstrated a marked change in transcript levels of immune and metabolic genes 24 hours post supplementation when compared with placebo.

CONCLUSIONS

Together, these findings demonstrate that supplementation with an enriched marine oil leads to an increase in peripheral blood SPM concentrations and reprograms peripheral blood cells, indicating a role for SPM in mediating the immune-directed actions of this supplement.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT03347006.

PDn-3 DPA Pathway Regulates Human Monocyte Differentiation and Macrophage Function

Macrophages are central in orchestrating the clearance of apoptotic cells and cellular debris during inflammation, with the mechanism(s) regulating this process remaining of interest. Herein, we found that the n-3 docosapentaenoic acid-derived protectin (PD_{n-3 DPA}) biosynthetic pathway regulated the differentiation of human monocytes, altering macrophage phenotype, efferocytosis, and bacterial phagocytosis. Using lipid mediator profiling, human primary cells and recombinant enzymes we found that human 15-lipoxygenases initiate the PD_{n-3 DPA} pathway catalyzing the formation of an allylic epoxide. The complete stereochemistry of this epoxide was determined using stereocontrolled total organic synthesis as 16S,17S-epoxy-7Z,10Z,12E,14E,19Z-docosapentaenoic acid (16S,17S-ePD_{n-3 DPA}). This intermediate was enzymatically converted by epoxide hydrolases to PD1_{n-3 DPA} and PD2_{n-3 DPA}, with epoxide hydrolase 2 converting 16S,17S-ePD_{n-3 DPA} to PD2_{n-3 DPA} in human monocytes. Taken together these results establish the PD_{n-3 DPA} biosynthetic pathway in human monocytes and macrophages and its role in regulating macrophage resolution responses.

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PD_{n-3 DPA} regulates human monocyte-derived macrophage differentiation and function

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Evidence for the formation and complete stereochemistry of 16S,17S-ePD_{n-3 DPA}

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EPHX2 converts 16S,17S-ePD_{n-3 DPA} to PD2_{n-3 DPA} in human monocytes

Impaired Production and Diurnal Regulation of Vascular RvDn-3 DPA Increase Systemic Inflammation and Cardiovascular Disease

RATIONALE

Diurnal mechanisms are central to regulating host responses. Recent studies uncovered a novel family of mediators termed as specialized proresolving mediators that terminate inflammation without interfering with the immune response.

OBJECTIVE

Herein, we investigated the diurnal regulation of specialized proresolving mediators in humans and their role in controlling peripheral blood leukocyte and platelet activation.

METHODS AND RESULTS

Using lipid mediator profiling and healthy volunteers, we found that plasma concentrations of n-3 docosapentaenoic acid-derived D-series resolvins (RvD_{n-3 DPA}) were regulated in a diurnal manner. The production and regulation of these mediators was markedly altered in patients at risk of myocardial infarct. These changes were associated with decreased 5-lipoxygenase expression and activity, as well as increased systemic adenosine concentrations. We also found a significant negative correlation between plasma RvD_{n-3 DPA} and markers of platelet, monocyte, and neutrophil activation, including CD63 and CD11b. Incubation of RvD_{n-3 DPA} with peripheral blood from healthy volunteers and patients with cardiovascular disease significantly and dose-dependently decreased platelet and leukocyte activation. Furthermore, administration of RvD5_{n-3 DPA} to ApoE^-/- (apolipoprotein E deficient) mice significantly reduced platelet-leukocyte aggregates, vascular thromboxane B₂ concentrations, and aortic lesions.

CONCLUSIONS

These results demonstrate that peripheral blood RvD_{n-3 DPA} are diurnally regulated in humans, and dysregulation in the production of these mediators may lead to cardiovascular disease.

13-Series resolvins mediate the leukocyte-platelet actions of atorvastatin and pravastatin in inflammatory arthritis

Rheumatoid arthritis is an inflammatory condition characterized by overzealous inflammation that leads to joint damage and is associated with an increased incidence of cardiovascular disease. Statins are frontline therapeutics for patients with cardiovascular disease and exert beneficial actions in rheumatoid arthritis. The mechanism that mediates the beneficial actions of statins in rheumatoid arthritis remains of interest. In the present study, we found that the administration of 2 clinically relevant statins—atorvastatin (0.2 mg/kg) or pravastatin (0.2 mg/kg)—to mice during inflammatory arthritis up-regulated systemic and tissue amounts of a novel family of proresolving mediators, termed 13-series resolvins (RvTs), and significantly reduced joint disease. Of note, administration of simvastatin (0.2 mg/kg) did not significantly up-regulate RvTs or reduce joint inflammation. We also found that atorvastatin and pravastatin each reduced systemic leukocyte activation, including platelet-monocyte aggregates (∼25–60%). These statins decreased neutrophil trafficking to the joint as well as joint monocyte and macrophage numbers. Atorvastatin and pravastatin produced significant reductions (∼30–50%) in expression of CD11b and major histocompatibility complex class II on both monocytes and monocyte-derived macrophages in joints. Administration of an inhibitor to cyclooxygenase-2, the initiating enzyme in the RvT pathway, reversed the protective actions of these statins on both joint and systemic inflammation. Together, these findings provide evidence for the role of RvTs in mediating the protective actions of atorvastatin and pravastatin in reducing local and vascular inflammation, and suggest that RvTs may be useful in measuring the anti-inflammatory actions of statins.—Walker, M. E., Souza, P. R., Colas, R. A., Dalli, J. 13-Series resolvins mediate the leukocyte-platelet actions of atorvastatin and pravastatin in inflammatory arthritis.

Galectin-3-null mice display defective neutrophil clearance during acute inflammation

Expression of galectin-3 by exudated neutrophils drives neutrophil apoptosis and clearance in a model of self-resolving peritonitis.

Galectin-3 has been associated with a plethora of proinflammatory functions because of its ability, among others, to promote neutrophil activation and because of the reduction in neutrophil recruitment in models of infection in Gal-3-null mice. Conversely, it has also been linked to resolution of inflammation through its actions as an opsonin and its ability to promote efferocytosis of apoptotic neutrophils. Using a self-resolving model of peritonitis, we have addressed the modulation and role of Gal-3 in acute inflammation. We have shown that Gal-3 expression is increased in neutrophils that travel to the inflamed peritoneum and that cellular localization of this lectin is modulated during the course of the inflammatory response. Furthermore, neutrophil recruitment to the inflamed peritoneum is increased in Gal-3–null mice during the course of the response, and that correlates with reduced numbers of monocytes/macrophages in the cavities of those mice, as well as reduced apoptosis and efferocytosis of Gal-3–null neutrophils. These data indicate a role for endogenous Gal-3 in neutrophil clearance during acute inflammation.

Neutrophil-derived microvesicles enter cartilage and protect the joint in inflammatory arthritis

Microvesicles (MVs) are emerging as a new mechanism of intercellular communication by transferring cellular lipid and protein components to target cells, yet their function in disease is only now being explored. We found that neutrophil-derived MVs were increased in concentration in synovial fluid from rheumatoid arthritis patients compared to paired plasma. Synovial MVs overexpressed the proresolving, anti-inflammatory protein annexin A1 (AnxA1). Mice deficient in TMEM16F, a lipid scramblase required for microvesiculation, exhibited exacerbated cartilage damage when subjected to inflammatory arthritis. To determine the function of MVs in inflammatory arthritis, toward the possibility of MV-based therapeutics, we examined the role of immune cell-derived MVs in rodent models and in human primary chondrocytes. In vitro, exogenous neutrophil-derived AnxA1(+) MVs activated anabolic gene expression in chondrocytes, leading to extracellular matrix accumulation and cartilage protection through the reduction in stress-adaptive homeostatic mediators interleukin-8 and prostaglandin E2. In vivo, intra-articular injection of AnxA1(+) MV lessened cartilage degradation caused by inflammatory arthritis. Arthritic mice receiving adoptive transfer of whole neutrophils displayed abundant MVs within cartilage matrix and revealed that MVs, but not neutrophils themselves, can penetrate cartilage. Mechanistic studies support a model whereby MV-associated AnxA1 interacts with its receptor FPR2 (formyl peptide receptor 2)/ALX, increasing transforming growth factor-β production by chondrocytes, ultimately leading to cartilage protection. We envisage that MVs, either directly or loaded with therapeutics, can be harnessed as a unique therapeutic strategy for protection in diseases associated with cartilage degeneration.

Implications for eicosapentaenoic acid- and docosahexaenoic acid-derived resolvins as therapeutics for arthritis

Omega-3 polyunsaturated fatty acids are essential for health and are known to possess anti-inflammatory properties, improving cardiovascular health as well as benefiting inflammatory diseases. Indeed, dietary supplementation with omega-3 polyunsaturated fatty acids has proved efficacious in reducing joint pain, morning stiffness and nonsteroidal anti-inflammatory drugs usage in rheumatoid arthritis patients. However, the mechanisms by which omega-3 polyunsaturated fatty acids exert their beneficial effects have not been fully explored. Seminal discoveries by Serhan and colleagues have unveiled a novel class of bioactive lipid mediators that are enzymatically biosynthesized in vivo from omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), termed resolvins, protectins and maresins. These bioactive pro-resolving lipid mediators provide further rationale for the beneficial effects of fish-oil enriched diets. These endogenous lipid mediators are spatiotemporally biosynthesized to actively regulate resolution by acting on specific G protein-coupled receptors (GPCRs) to initiate anti-inflammatory and pro-resolving signals that terminate inflammation. In this review, we will discuss the mechanism of actions of these molecules, including their analgesic and bone-sparing properties making them ideal therapeutic agonists for the treatment of inflammatory diseases such as rheumatoid arthritis.