ApoE deficiency exacerbates the development and sustainment of a semi-chronic K/BxN serum transfer-induced arthritis model

An update of murine models and their methodologies in immune-mediated joint damage and pain research

Murine models have played an indispensable role in the understanding of rheumatic and musculoskeletal disorders (RMD), elucidating the genetic, endocrine and biomechanical pathways involved in joint pathology and associated pain. To date, the available models in RMD can be classified as induced or spontaneous, both incorporating transgenic alternatives that improve specific insights. It is worth noting that the selection of the most appropriate model together with the evaluation of their specific characteristics and technical capabilities are crucial when designing the experiments. Furthermore, it is also imperative to consistently adhere to the ethical standards concerning animal experimentation. Recognizing the inherent limitation that any model can entirely encapsulates the complexity of the pathophysiology of these conditions, the aim of this review is to provide an updated overview on the methodology of current murine models in major arthropathies and their immune-mediated pathways, addressing to basic, translational and pharmacological research in joint damage and pain.

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.

The effect of HLA-DRB1*04:01 on a mouse model of atherosclerosis

Objectives

HLA-DRB1 is associated with an increased risk of cardiovascular disease in patients with rheumatoid arthritis (RA). This study aimed to determine the effect of HLA-DRB1 on atherosclerotic cardiovascular disease (ASCVD) using a novel mouse model.

Methods

Mice transgenic for HLA-DRB1*04:01 (DR4tg) were crossed with low density lipoprotein receptor knock-out (Ldlr^-/-) mice that develop atherosclerosis when fed a high fat, high cholesterol (HFHC) diet. Male and female DR4tgLdlr^-/- (n = 48), Ldlr^-/- (n = 24), DR4tg (n = 24), and C57Bl/6 (B6) background (n = 24) mice were fed HFHC or regular diet (RD) for 12 weeks. Blood samples were analyzed for serum lipoproteins using a colorimetric assay. C-reactive protein (CRP) and oxidized LDL (OxLDL) were measured using ELISA. Atherosclerosis in the aortas was assessed using the lipid stain, Sudan IV. The presence of citrulline in atherosclerotic plaque was determined by immunohistochemistry.

Results

Sera low-density lipoprotein cholesterol (LDL-C) levels were higher in HFHC-fed Ldlr^-/- versus DR4tgLdlr^-/--; p = 0.0056, but the aortic plaque burden and degree of citrullination in the plaque were similar for these two strains. The ratio of pro-atherogenic OxLDL to LDL levels was higher in DR4tgLdlr^-/- than Ldlr^-/-mice; p = 0.0017. All mice had an increase in CRP when fed a HFHC diet, most pronounced for DR4tgLdlr^-/-; p = 0.0009. There were no significant sex differences for DR4tgLdlr^-/- mice; however, male Ldlr^-/- mice had worse atherosclerosis. B6 and DR4tg mice did not have significant elevations in serum cholesterol levels and did not develop atherosclerosis.

Conclusions

Expression of HLA-DRB1 resulted in an elevation of OxLDL and a reduction in the male bias for atherosclerosis, mimicking what is observed in RA.

Occurrences and Functions of Ly6Chi and Ly6Clo Macrophages in Health and Disease

Macrophages originating from the yolk sac or bone marrow play essential roles in tissue homeostasis and disease. Bone marrow-derived monocytes differentiate into Ly6C^hi and Ly6C^lo macrophages according to the differential expression of the surface marker protein Ly6C. Ly6C^hi and Ly6C^lo cells possess diverse functions and transcriptional profiles and can accelerate the disease process or support tissue repair and reconstruction. In this review, we discuss the basic biology of Ly6C^hi and Ly6C^lo macrophages, including their origin, differentiation, and phenotypic switching, and the diverse functions of Ly6C^hi and Ly6C^lo macrophages in homeostasis and disease, including in injury, chronic inflammation, wound repair, autoimmune disease, and cancer. Furthermore, we clarify the differences between Ly6C^hi and Ly6C^lo macrophages and their connections with traditional M1 and M2 macrophages. We also summarize the limitations and perspectives for Ly6C^hi and Ly6C^lo macrophages. Overall, continued efforts to understand these cells may provide therapeutic approaches for disease treatment.

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).

Loss of the WNT9a ligand aggravates the rheumatoid arthritis-like symptoms in hTNF transgenic mice

Agonists and antagonists of the canonical Wnt signaling pathway are modulators of pathological aspects of rheumatoid arthritis (RA). Their activity is primarily modifying bone loss and bone formation, as shown in animal models of RA. More recently, modulation of Wnt signaling by the antagonist Sclerostin has also been shown to influence soft-tissue-associated inflammatory aspects of the disease pointing towards a role of Wnt signaling in soft-tissue inflammation as well. Yet, nothing is known experimentally about the role of Wnt ligands in RA. Here we provide evidence that altering Wnt signaling at the level of a ligand affects all aspects of the rheumatoid arthritic disease. WNT9a levels are increased in the pannus tissue of RA patients, and stimulation of synovial fibroblasts (SFB) with tumor necrosis factor (TNF) leads to increased transcription of Wnt9a. Loss of Wnt9a in a chronic TNF-dependent RA mouse model results in an aggravation of disease progression with enhanced pannus formation and joint destruction. Yet, loss of its activity in the acute K/BxN serum-transfer induced arthritis (STIA) mouse model, which is independent of TNF signaling, has no effect on disease severity or progression. Thus, suggesting a specific role for WNT9a in TNF-triggered RA. In synovial fibroblasts, WNT9a can activate the canonical Wnt/β-catenin pathway, but it can also activate P38- and downregulate NFκB signaling. Based on in vitro data, we propose that loss of Wnt9a creates a slight proinflammatory and procatabolic environment that boosts the TNF-mediated inflammatory response.

High LDL levels lessen bone destruction during antigen-induced arthritis by inhibiting osteoclast formation and function

Rheumatoid arthritis (RA) is a chronic inflammatory disease, characterized by severe joint inflammation and bone destruction as the result of increased numbers and activity of osteoclasts. RA is often associated with metabolic syndrome, whereby elevated levels of LDL are oxidized into oxLDL, which might affect osteoclastogenesis. In this study, we induced antigen-induced arthritis (AIA) in Apoe^-/- mice, which spontaneously develop high LDL levels, to investigate the effects of high LDL/oxLDL levels on osteoclast differentiation and bone destruction. Whereas basal levels of bone resorption were comparable between naive WT and Apoe^-/- mice, induction of AIA resulted in a significant reduction of bone destruction in Apoe^-/- mice as compared to WT controls. In line with that, the TRAP⁺ area on the cortical bone was significantly decreased. The absence of Apoe did affect neither the numbers of CD11b⁺Ly6C^high and CD11b^-/Ly6C^high osteoclast precursors (OCPs) in the BM of naïve mice nor their in vitro osteoclastogenic potential as indicated by comparable mRNA expression of osteoclast markers. Addition of oxLDL, but not LDL, to pre-osteoclasts from day 3 and mature osteoclasts from day 6 of osteoclastogenesis strongly reduced the number of TRAP⁺ osteoclasts and their resorptive capacity. This coincided with a decreased expression of various osteoclast markers. Interestingly, oxLDL significantly lowered the expression of osteoclast-associated receptor (Oscar) and the DNAX adaptor protein-12 encoding gene Tyrobp, which regulate the immunoreceptor tyrosine-based activation motif (ITAM) co-stimulation pathway that is strongly involved in osteoclastogenesis. Collectively, our findings suggest that under inflammatory conditions in the joint, high LDL levels lessen bone destruction during AIA, probably by formation of oxLDL that inhibits osteoclast formation and activity through modulation of the ITAM-signaling.

The Microbial Metabolite Trimethylamine N-Oxide Links Vascular Dysfunctions and the Autoimmune Disease Rheumatoid Arthritis

Diet and microbiota each have a direct impact on many chronic, inflammatory, and metabolic diseases. As the field develops, a new perspective is emerging. The effects of diet may depend on the microbiota composition of the intestine. A diet that is rich in choline, red meat, dairy, or egg may promote the growth, or change the composition, of microbial species. The microbiota, in turn, may produce metabolites that increase the risk of cardiovascular disease. This article reviews our current understanding of the effects of the molecule trimethylamine-N-oxide (TMAO) obtained from food or produced by the microbiota. We review the mechanisms of actions of TMAO, and studies that associate it with cardiovascular and chronic kidney diseases. We introduce a novel concept: TMAO is one among a group of selective uremic toxins that may rise to high levels in the circulation or accumulate in various organs. Based on this information, we evaluate how TMAO may harm, by exacerbating inflammation, or may protect, by attenuating amyloid formation, in autoimmune diseases such as rheumatoid arthritis.

Genetic deficiency of Wnt5a diminishes disease severity in a murine model of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation of the joints, leading to bone erosion and joint dysfunction. Despite the recent successes of disease-modifying anti-rheumatic drugs (DMARDs), there is still clinical need for understanding the development and molecular etiology of RA. Wnts are developmental morphogens whose roles in adult pathology are poorly characterized. Wnt5a is a member of the non-canonical family of Wnts that modulates a wide range of cell processes, including differentiation, migration, and inflammation. Wnt5a has been implicated as a possible contributor to arthritis and it is upregulated in synovial fibroblasts from RA patients.

METHODS

We investigated the role of endogenous Wnt5a in RA. Tamoxifen-inducible, Wnt5a knockout (Wnt5a cKO) mice and littermate controls were monitored for arthritis development and joint pathology using the K/BxN serum transfer-induced arthritis (STIA) model. To explore a role of Wnt5a in osteoclast fusion, bone marrow-derived monocytes (BMDMs) were differentiated in vitro.

RESULTS

Wnt5a cKO mice were resistant to arthritis development compared to control littermates as assessed by ankle thickness and histologic measurements. Some parameters of inflammation were reduced in the Wnt5a cKO mice, including the extent of polymononuclear cell infiltration and extra-articular inflammation. Wnt5a cKO mice also exhibited less cartilage destruction and a reduction in osteoclast activity with concomitant reduction in tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), macrophage colony-stimulating factor (MCSF), matrix metalloproteinase (MMP)2 and MMP9 in the arthritic joints. Treatment of BMDMs with Wnt5a enhanced osteoclast fusion and increased the expression of dendrocyte-expressed seven transmembrane protein (DCSTAMP) and MMP9, that are necessary for osteoclast formation and activity.

CONCLUSIONS

These data suggest that Wnt5a modulates the development of arthritis by promoting inflammation and osteoclast fusion, and provide the first mouse genetic evidence of a role for endogenous Wnt5a in autoimmune disease.

Modulation of autoimmune arthritis severity in mice by apolipoprotein E (ApoE) and cholesterol

Apolipoprotein E (ApoE) deficiency promoted an exacerbation of autoimmune arthritis in mice by inducing proinflammatory immune responses. In this study we analysed the contribution of hypercholesterolaemia and/or the absence of ApoE anti-inflammatory properties, unrelated to its function in the control of cholesterol metabolism, towards the acceleration of arthritis in these mutant animals. The induction and severity of collagen type II-induced arthritis (CIA) were compared for B10.RIII wild-type (WT), B10.RIII.ApoE^+/- , B10.RIII.ApoE^-/- and B10.RIII.low-density lipoprotein receptor (LDLR^-/- ) mice with different concentrations of circulating ApoE and cholesterol. A 50-70% reduction in serum levels of ApoE was observed in heterozygous B10.RIII.ApoE^+/- mice in comparison to B10.RIII.WT, although both strains of mice exhibited similar circulating lipid profiles. This ApoE reduction was associated with an increased CIA severity that remained lower than in homozygous B10.RIII.ApoE^-/- mice. An important rise in circulating ApoE concentration was observed in hypercholesterolaemic B10.RIII.LDLR^-/- mice fed with a normal chow diet, and both parameters increased further with an atherogenic hypercholesterolaemic diet. However, the severity of CIA in B10.RIII.LDLR^-/- mice was similar to that of B10.RIII.WT controls. In conclusion, by comparing the evolution of CIA between several strains of mutant mice with different levels of serum ApoE and cholesterol, our results demonstrate that both hypercholesterolaemia and ApoE regulate the intensity of in-vivo systemic autoimmune responses.