Tamsin M. Lindstrom

Low-grade inflammation as a key mediator of the pathogenesis of osteoarthritis

Osteoarthritis (OA) has long been viewed as a degenerative disease of cartilage, but accumulating evidence indicates that inflammation has a critical role in its pathogenesis. Furthermore, we now appreciate that OA pathogenesis involves not only breakdown of cartilage, but also remodelling of the underlying bone, formation of ectopic bone, hypertrophy of the joint capsule, and inflammation of the synovial lining. That is, OA is a disorder of the joint as a whole, with inflammation driving many pathologic changes. The inflammation in OA is distinct from that in rheumatoid arthritis and other autoimmune diseases: it is chronic, comparatively low-grade, and mediated primarily by the innate immune system. Current treatments for OA only control the symptoms, and none has been FDA-approved for the prevention or slowing of disease progression. However, increasing insight into the inflammatory underpinnings of OA holds promise for the development of new, disease-modifying therapies. Indeed, several anti-inflammatory therapies have shown promise in animal models of OA. Further work is needed to identify effective inhibitors of the low-grade inflammation in OA, and to determine whether therapies that target this inflammation can prevent or slow the development and progression of the disease.

The Cyclopentenone 15-Deoxy-Δ12,14-Prostaglandin J2 Delays Lipopolysaccharide-Induced Preterm Delivery and Reduces Mortality in the Newborn Mouse

Intrauterine infection is a common trigger for preterm birth and is also a risk factor for the subsequent development of neurodevelopmental abnormalities in the neonate. Bacterial lipopolysaccharide (LPS) binds to toll-like receptor-4 (TLR-4) to activate proinflammatory signaling pathways, which are implicated in both preterm delivery and antenatal brain injury. The transcription factor nuclear factor-kappaB (NF-kappaB) is a key player in the orchestration of the inflammatory response and has a central role in parturition. Here we show that intrauterine administration of TLR-4-specific LPS to pregnant mice results in the activation of NF-kappaB in the maternal uterus and the fetal brain, up-regulation of proinflammatory proteins cyclooxygenase-2, chemokine ligand 1, ChemoKine (C-C motif) ligand 2, and cytosolic phospholipase A(2) in myometrium, and induction of preterm delivery. 15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is an antiinflammatory prostaglandin that plays a role in promoting the resolution of inflammation. We report that coadministration of 15d-PGJ(2) and LPS to pregnant mice delays LPS-induced preterm delivery and confers protection from LPS-induced fetal mortality. This is associated with inhibition of myometrial NF-kappaB, cytosolic phospholipase A(2), and c-Jun N-terminal kinase activation, and of inflammatory protein synthesis. Therefore 15d-PGJ(2) has anti-inflammatory effects via inhibition of multiple aspects of inflammation-driven TRL-4 signaling pathway. Thus, 15d-PGJ(2) or compounds with similar antiinflammatory functions may have potential as therapeutic agents in the management of preterm labor with the added advantage of preventing detrimental effects to the fetus that may result from infection/inflammation.

Rheumatoid Arthritis: A Role for Immunosenescence?

Aging is accompanied by a progressive decline in the integrity of the immune system, a process known as immunosenescence. Pathological features typical of immune dysfunction in older adults, encompassing dysregulation of innate and adaptive immune responses, characterize rheumatoid arthritis (RA), an autoimmune disease whose incidence increases with age. Recent evidence suggests that certain features of immunosenescence, such as the decrease in T‐cell generation and diversity, may contribute to the development of RA. Thus, physiological immunosenescence may render older adults susceptible to RA, and premature immunosenescence may contribute to the development of RA in young adults. In addition, other features of immunosenescence may result from the chronic immune stimulation that occurs in RA and lead to worsening of the disease. This article reviews the immunopathological features common to aging and RA and discusses the mechanisms by which immunosenescence may contribute to the development or progression of RA.

Barcode-enabled sequencing of plasmablast antibody repertoires in rheumatoid arthritis.

A hallmark of rheumatoid arthritis (RA) is the production of autoantibodies, including anti–citrullinated protein antibodies (ACPAs). Nevertheless, the specific targets of these autoantibodies remain incompletely defined. During an immune response, B cells specific for the inciting antigen(s) are activated and differentiate into plasmablasts, which are released into the blood. We undertook this study to sequence the plasmablast antibody repertoire to define the targets of the active immune response in RA.

Plasma carboxypeptidase B downregulates inflammatory responses in autoimmune arthritis

The immune and coagulation systems are both implicated in the pathogenesis of rheumatoid arthritis (RA). Plasma carboxypeptidase B (CPB), which is activated by the thrombin/thrombomodulin complex, plays a procoagulant role during fibrin clot formation. However, an antiinflammatory role for CPB is suggested by the recent observation that CPB can cleave proinflammatory mediators, such as C5a, bradykinin, and osteopontin. Here, we show that CPB plays a central role in downregulating C5a-mediated inflammatory responses in autoimmune arthritis. CPB deficiency exacerbated inflammatory arthritis in a mouse model of RA, and cleavage of C5a by CPB suppressed the ability of C5a to recruit immune cells in vivo. In human patients with RA, genotyping of nonsynonymous SNPs in the CPB-encoding gene revealed that the allele encoding a CPB variant with longer half-life was associated with a lower risk of developing radiographically severe RA. Functionally, this CPB variant was more effective at abrogating the proinflammatory properties of C5a. Additionally, expression of both CPB and C5a in synovial fluid was higher in patients with RA than in those with osteoarthritis. These findings suggest that CPB plays a critical role in dampening local, C5a-mediated inflammation and represents a molecular link between inflammation and coagulation in autoimmune arthritis.

c-Fms-mediated differentiation and priming of monocyte lineage cells play a central role in autoimmune arthritis

IntroductionTyrosine kinases are key mediators of multiple signaling pathways implicated in rheumatoid arthritis (RA). We previously demonstrated that imatinib mesylate--a Food and Drug Administration (FDA)-approved, antineoplastic drug that potently inhibits the tyrosine kinases Abl, c-Kit, platelet-derived growth factor receptor (PDGFR), and c-Fms--ameliorates murine autoimmune arthritis. However, which of the imatinib-targeted kinases is the principal culprit in disease pathogenesis remains unknown. Here we examine the role of c-Fms in autoimmune arthritis.MethodsWe tested the therapeutic efficacy of orally administered imatinib or GW2580, a small molecule that specifically inhibits c-Fms, in three mouse models of RA: collagen-induced arthritis (CIA), anti-collagen antibody-induced arthritis (CAIA), and K/BxN serum transfer-induced arthritis (K/BxN). Efficacy was evaluated by visual scoring of arthritis severity, paw thickness measurements, and histological analysis. We assessed the in vivo effects of imatinib and GW2580 on macrophage infiltration of synovial joints in CIA, and their in vitro effects on macrophage and osteoclast differentiation, and on osteoclast-mediated bone resorption. Further, we determined the effects of imatinib and GW2580 on the ability of macrophage colony-stimulating factor (M-CSF; the ligand for c-Fms) to prime bone marrow-derived macrophages to produce tumor necrosis factor (TNF) upon subsequent Fc receptor ligation. Finally, we measured M-CSF levels in synovial fluid from patients with RA, osteoarthritis (OA), or psoriatic arthritis (PsA), and levels of total and phosphorylated c-Fms in synovial tissue from patients with RA.ResultsGW2580 was as efficacious as imatinib in reducing arthritis severity in CIA, CAIA, and K/BxN models of RA. Specific inhibition of c-Fms abrogated (i) infiltration of macrophages into synovial joints of arthritic mice; (ii) differentiation of monocytes into macrophages and osteoclasts; (iii) osteoclast-mediated bone resorption; and (iv) priming of macrophages to produce TNF upon Fc receptor stimulation, an important trigger of synovitis in RA. Expression and activation of c-Fms in RA synovium were high, and levels of M-CSF were higher in RA synovial fluid than in OA or PsA synovial fluid.ConclusionsThese results suggest that c-Fms plays a central role in the pathogenesis of RA by mediating the differentiation and priming of monocyte lineage cells. Therapeutic targeting of c-Fms could provide benefit in RA.

NF-κB regulates a cassette of immune/inflammatory genes in human pregnant myometrium at term

The onset of human labour resembles inflammation with increased synthesis of prostaglandins and cytokines. There is evidence from rodent models for an important role for nuclear factor‐κB (NF‐κB) activity in myometrium which both up‐regulates contraction‐associated proteins and antagonizes the relaxatory effects of progesterone. Here we show that in the human, although there are no differences in expression of NF‐κB p65, or IκB‐α between upper‐ or lower‐segment myometrium or before or after labour, there is nuclear localization of serine‐256‐phospho‐p65 and serine‐536‐phospho‐p65 in both upper‐ and lower‐segment myometrium both before and after the onset of labour at term. This shows that NF‐κB is active in both upper and lower segment prior to the onset of labour at term. To identify the range of genes regulated by NF‐κB we overexpressed p65 in myocytes in culture. This led to NF‐κB activation identical to that seen following interleukin (IL)‐1β stimulation, including phosphorylation and nuclear translocation of p65 and p50. cDNA microarray analysis showed that NF‐κB increased expression of 38 genes principally related to immunity and inflammation. IL‐1β stimulation also resulted in an increase in the expression of the same genes. Transfection with siRNA against p65 abolished the response to IL‐1β proving a central role for NF‐κB. We conclude that NF‐κB is active in myocytes in both the upper and lower segment of the uterus prior to the onset of labour at term and principally regulates a group of immune/inflammation associated genes, demonstrating that myocytes can act as immune as well as contractile cells.

Tyrosine kinases as targets for the treatment of rheumatoid arthritis

As critical regulators of numerous cell signaling pathways, tyrosine kinases are implicated in the pathogenesis of several diseases, including rheumatoid arthritis (RA). In the absence of disease, synoviocytes produce factors that provide nutrition and lubrication for the surrounding cartilage tissue; few cellular infiltrates are seen in the synovium. In RA, however, macrophages, neutrophils, T cells and B cells infiltrate the synovium and produce cytokines, chemokines and degradative enzymes that promote inflammation and joint destruction. In addition, the synovial lining expands owing to the proliferation of synoviocytes and infiltration of inflammatory cells to form a pannus, which invades the surrounding bone and cartilage. Many of these cell responses are regulated by tyrosine kinases that operate in specific signaling pathways, and inhibition of a number of these kinases might be expected to provide benefit in RA.

Identification of anticitrullinated protein antibody reactivities in a subset of anti-CCP-negative rheumatoid arthritis: association with cigarette smoking and HLA-DRB1 ‘shared epitope’ alleles

Introduction A hallmark of rheumatoid arthritis (RA) is the development of autoantibodies targeting proteins that contain citrulline. Anticitrullinated protein antibodies (ACPAs) are currently detected by the commercial cyclic citrullinated peptide (CCP) assay, which uses a mix of cyclised citrullinated peptides as an artificial mimic of the true antigen(s). To increase the sensitivity of ACPA detection and dissect ACPA specificities, we developed a multiplex assay that profiles ACPAs by measuring their reactivity to the citrullinated peptides and proteins derived from RA joint tissue. Methods We created a bead-based, citrullinated antigen array to profile ACPAs. This custom array contains 16 citrullinated peptides and proteins detected in RA synovial tissues. We used the array to profile ACPAs in sera from a cohort of patients with RA and other non-inflammatory arthritides, as well as sera from an independent cohort of RA patients for whom data were available on carriage of HLA-DRB1 ‘shared epitope’ (SE) alleles and history of cigarette smoking. Results Our multiplex assay showed that at least 10% of RA patients who tested negative in the commercial CCP assay possessed ACPAs. Carriage of HLA-DRB1 SE alleles and a history of cigarette smoking were associated with an increase in ACPA reactivity—in anti-CCP+ RA and in a subset of anti-CCP− RA. Conclusions Our multiplex assay can identify ACPA-positive RA patients missed by the commercial CCP assay, thus enabling greater diagnostic sensitivity. Further, our findings suggest that cigarette smoking and possession of HLA-DRB1 SE alleles contribute to the development of ACPAs in anti-CCP− RA.

Identification of Naturally Occurring Fatty Acids of the Myelin Sheath That Resolve Neuroinflammation

Myelin fatty acids resolve neuroinflammation. Eliminating Excess In tough economic times, businesses trim the fat by cutting superfluous spending. The immune system also has ways to regulate excess, such as feedback mechanisms that prevent autoimmunity. In patients with multiple sclerosis (MS), these protective mechanisms fail: The immune system attacks peripheral nerves, resulting in demyelination and a decrease in the ability of axons to carry physiological signals. Researchers have identified autoantibodies to many of the lipids that make up the myelin sheath of nerve cells, and these target lipids are believed to serve as pathogenic antigens for autoimmune encephalomyelitis—an inflammation of the brain and spinal cord seen in MS patients. However, new work by Ho et al. shows that some fat shouldn’t be trimmed; indeed, certain fatty acids of the myelin sheath actually serve to resolve neuroinflammation in a therapeutic mouse model of MS, experimental autoimmune encephalomyelitis (EAE). With lipid antigen microarrays and mass spectrometry, the authors identified targets of the autoimmune response in the brains of patients with MS and then used these lipid antigens to immunize mice with clinical EAE symptoms. Some of the phospholipids tested suppressed activation of and induced apoptosis in autoreactive T cells, ameliorating disease in the EAE mice, an effect that was mediated by the lipids’ fatty acid side chains. These data suggest that some phospholipids are natural anti-inflammatory compounds composed of fatty acids that trim the fat—in this case, excessive behavior by the immune system. Lipids constitute 70% of the myelin sheath, and autoantibodies against lipids may contribute to the demyelination that characterizes multiple sclerosis (MS). We used lipid antigen microarrays and lipid mass spectrometry to identify bona fide lipid targets of the autoimmune response in MS brain, and an animal model of MS to explore the role of the identified lipids in autoimmune demyelination. We found that autoantibodies in MS target a phosphate group in phosphatidylserine and oxidized phosphatidylcholine derivatives. Administration of these lipids ameliorated experimental autoimmune encephalomyelitis by suppressing activation and inducing apoptosis of autoreactive T cells, effects mediated by the lipids’ saturated fatty acid side chains. Thus, phospholipids represent a natural anti-inflammatory class of compounds that have potential as therapeutics for MS.