Sarah Price

Bone: Evidence for local effects of LRP5 on bone mass

The question of how LRP5 (LDL receptor-related protein 5) exerts its effects on bone formation has come under debate. New findings published by Cui et al. in Nature Medicine support a local role for LRP5 signaling in bone. LRP5 was first implicated in the regulation of bone mass through studies of two human genetic diseases: heterozygous missense mutations in LRP5 were shown to produce a dominantly inherited high bone mass (HBM) phenotype, whereas loss-of-function LRP5 mutations were shown to cause osteoporosis-pseudoglioma syndrome (OPPG), which is associated with low bone mass. “What excited the bone research community was that LRP5 appeared to function in the Wnt signaling pathway, which had previously not been implicated in regulating bone strength,” says Matthew Warman, one of the authors of the Nature Medicine paper. Data from other lines of investigation supported a direct role for Wnt signaling in bone mass accrual; however, direct proof that LRP5 functioned locally in bone cells or that it was a transducer of Wnt signaling in bone cells was lacking. It has since been hypothezised that, surprisingly, LRP5 influences bone formation not through its role as a Wnt co-receptor on osteoblasts, but indirectly, via its effects on the production of serotonin (5-hydroxytryptophan) in the gut. Cui et al. sought to independently test this serotonin hypothesis and also determine where and how LRP5 functioned to regulate bone mass. Instead of confirming a serotonin-based mechanisms, however, their data suggest that LRP5 functions locally in bone cells. The researchers were able to determine the site of Lrp5 function in mouse models by generating conditional alleles that could be activated or inactivated in different cell types, in animals of different ages or in cells at different stages of differentiation. This approach BONE

Experimental arthritis: Dermal fibroblasts have MSC-like immunosuppressive effects in vivo

Experimental arthritis: Dermal fibroblasts have MSC-like immunosuppressive effects in vivo

Immunology: Therapy influences response to flu vaccine

The outbreak of the H1N1 influenza virus in 2009 led to the development and use of novel adjuvanted vaccines, and provided an opportunity to assess the safety of and humoral response to these vaccines in patients with autoimmune rheumatic diseases. The H1N1 study group of Geneva University Hospitals prospectively studied 173 patients with rheumatic diseases and 138 healthy controls who received two doses or one dose, respectively, of the ASO3adjuvanted influenza A/09/H1N1 vaccine, in line with Swiss recommendations. “A significant vaccine antibody response was detected in both patients and healthy controls,” reports Cem Gabay, who led the study. “However, patients required two vaccine doses to reach serum antibody levels similar to those achieved in the control group after one dose.” Primary antibody responses to the vaccine were influenced by an individual’s increasing age and by type of immunosuppressive treatment, but not by the nature of their underlying disease. IMMUNOLOGY

Pain: Resolvins show promise for treating inflammatory pain

resolvins, a recently discovered family of endogenous omega-3 fatty-acid-derived mediators with potent immunoregulatory effects, could be novel analgesics for the treatment of inflammatory pain. the term ‘resolvins’ was coined to denote that these resolution phase interaction products stimulate the resolution of inflammation, an active process that returns inflamed tissues to a normal state following the acute inflammatory response. new research shows that these compounds also have the potential to attenuate inflammatory pain. in mice, resolvins were shown to modulate pain by regulating both peripheral and spinal sensitization and hyperalgesia. these findings may well be of particular importance given the well-known limitations of agents commonly used to treat inflammatory pain such as opioids and cyclo-oxygenase (CoX) inhibitors. the study that produced these findings was a joint effort between two laboratories in the Department of anesthesiology, Perioperative and Pain medicine of Brigham & women’s Hospital and Harvard medical school. lead investigators ru-rong Ji, associate Director of the Pain research Center, and Charles serhan, Director of the Center for experimental therapeutics and reperfusion injury, hope this is the first of many such collaborations. “Dr serhan’s lab discovered these lipid mediators and has demonstrated the dual anti-inflammatory and proresolution role of resolvins,” explains Ji, “and my lab has been working on inflammatory pain mechanisms for many years, so it made perfect sense for these two labs in the same department to collaborate to test the effects of resolvins in mouse models of inflammatory pain.” the investigators used mouse models of acute, mid-term and persistent inflammatory pain induced by formalin, carrageenan and complete Freund’s adjuvant, respectively. to determine the peripheral and central actions of resolvins on pain in these models, the synthetic resolvins rve1 and rvD1 were injected peripherally, into the foot pad, or centrally, into the spinal cord. investigations of the peripheral role of resolvins demonstrated that they can attenuate inflammatory pain through anti-inflammatory actions including reducing edema, neutrophil infiltration, and proinflammatory cytokine expression. Centrally, resolvins were shown to further attenuate inflammatory pain by blocking synaptic plasticity in the spinal cord. notably, resolvins were shown to effectively reduce pain at very low doses, 1–10 ng, which are much lower than those required for morphine and CoX2 inhibitors. in addition, resolvins did not affect basal pain thresholds, suggesting that they have a ‘normalizing’ effect on pain. exploring the potential mechanisms of resolvin-induced inhibition of inflammatory pain, the researchers showed that spinal administration of rve1 reduced heat hyperalgesia and spontaneous pain by blocking capsaicin receptor (trPv1) and tumor necrosis factor (tnF) signaling in dorsal root ganglion neurons and spinal presynaptic terminals. in addition, they demonstrated that pretreatment with rve1 reduces another feature of inflammatory pain, mechanical allodynia. in electrophysiological studies, rve1 was shown to block trPv1-induced and tnF-induced excitatory postsynaptic current increases and tnF-evoked n-methyl-d-aspartic acid receptor (nmDa-r) hyperactivity in spinal dorsal horn neurons. the investigators suggest that rve1 might resolve inflammatory pain by inhibition of the extracellular signal-regulated kinase (erK) signaling pathway, which mediates glutamate release in presynaptic terminals in response to stimulation by tnF and trPv1 activation and also mediates nmDa-r activation in postsynaptic dorsal horn neurons, a mechanism involved in central sensitization. the researchers plan to extend their study of resolvins to other models of chronic pain, such as neuropathic pain models after nerve injury.

Bone: novel microRNA expressed in osteoblasts promotes bone formation.

in a study published in The Journal of Clinical Investigation, li et al. demonstrated in st2 stromal cells that mir-2861 promotes osteogenic differentiation induced by bone morphogenetic protein 2 (BmP2). overexpression of mir-2861 increased levels of amP activity, osteocalcin secretion, and bone nodule formation in cultures. in addition, expression of runtrelated transcription factor 2 (runX2) protein, but not Runx2 messenger rna bone

Connective tissue diseases: Small-molecule inhibitor of MIF protects lupus-prone mice from kidney disease

Connective tissue diseases: Small-molecule inhibitor of MIF protects lupus-prone mice from kidney disease

Rheumatoid arthritis: Monitoring serum concentration of infliximab might improve RA disease control

Rheumatoid arthritis: Monitoring serum concentration of infliximab might improve RA disease control

Connective tissue diseases: Activated platelets as a target for SLE therapy?

Activated platelets as a target for SLE therapy? New research linking platelet activation, immune complexes (iCs) and interferon (iFn)-α in the pathogenesis of systemic lupus erythematosus (sle) could provide support for the use of antiplatelet strategies as adjuvant therapy for the disease. Previous research has shown that levels of soluble CD154 (sCD154) are elevated in the sera of patients with sle, and that these levels correlate with disease activity. “However,” points out Pierre Duffau, lead author of the paper reporting the findings in Science Translational Medicine, “the origin of the sCD154 remained somewhat of a mystery.” the investigators hypothesized that the source could be CD154 released from the surface of activated platelets, and that plateletderived CD154 could drive sle disease activity through the iFn-α system. in ex vivo experiments, they confirmed that platelets isolated from patients with active sle are activated, as characterized by overexpression of CD154, and that CD154 levels correlated with disease severity. in addition, platelets isolated from healthy controls exposed to sera from patients with sle were activated in a dosedependent fashion. notably, this activation could be inhibited by prior incubation with an anti-CD32 antibody or by depleting the sle sera of igG; by contrast, blocking iFn-α, CD154 or interleukin-6 had no such inhibitory effect. western blot analysis showed that igG was found in platelet lysates from patients with sle but was “barely detectable” in those with rheumatoid arthritis or in healthy individuals. together, the findings pointed to the platelets being activated by iCs through a CD32-dependent mechanism. But what about the consequences of platelet activation in sle? Duffau et al. used flow cytometry and confocal microscopy to demonstrate that activated platelets aggregate with circulating antigen-presenting cells—including monocytes and plasmacytoid dendritic cells (pDCs; a major source of type i iFn in sle). in addition, incubating purified pDCs with iCs alone induced some iFn production, but the simultaneous presence of activated platelets increased the level of production several times over. the addition of CD154+ l-cells to the pDC–iC culture also induced an increase in iFn-α secretion, whereas co-culture of pDCs, iCs and activated platelets with an anti-CD40 antibody attenuated the increase, highlighting a role for the CD154–CD40 pathway in potentiating iFn-α production. to target the mechanisms of platelet activation in vivo, the authors turned to the nZBxnZw(F1) and mrl/lpr mouse models of lupus. similar to the mechanisms of platelet activation in human disease, nZBxnZw(F1) mice show elevated serum levels of sCD154 and occurrence of platelet–DC aggregates, and sera from these mice activate normal platelets, leading to increased production of iFn-α by stimulated pDCs. Platelet depletion reduced inflammatory infiltrates and signs of glomerulonephritis in these mice. By contrast, the kidneys of animals transfused with activated platelets had increased iC deposits and inflammatory infiltrates. similarly, daily administration of clopidogrel, an inhibitor of platelet activation, improved disease measures and overall survival in nZBxnZw(F1) and mrl/lpr mice. “the findings provide a link between CD154 and iFn-α, two important cytokines in the pathogenesis of sle,” says Duffau, “and strongly highlight antiplatelet treatment as a valuable therapy for lupus.” lars ronnblom of uppsala university agrees that platelets undoubtedly have a role in sle pathogenesis, but maintains that their role in the iFn response remains far from certain. as an example, he points out, type i iFn exacerbates disease in nZBxnZw(F1) mice and ameliorates disease in the mlr/lpr model, whereas inhibition of platelets improved disease severity in both these models in the study by Duffau et al. “a more direct experiment would be to take an sle patient with an iFn-α signature, administer clopidogrel to block platelets in vivo, and see if the iFn signature decreases or disappears,” suggests ronnblom. George tsokos of Harvard medical school commends the report for bringing together several findings that were known to researchers in the field, although he too suggests that the full story of platelet activation in sle could yet prove more complex than outlined in this paper. nonetheless, tsokos agrees that the results confirm the need to include antiplatelet strategies in the treatment of patients with sle: “i think there is sufficient evidence to try platelet inhibitors or platelet depletion as an adjuvant treatment in patients with sle, particularly those with lupus nephritis.” Duffau et al. plan to undertake a clinical trial of clopidogrel in patients with sle. “lupus patients are prone to premature cardiovascular disease, which is a leading cause of mortality,” says Duffau. “thus, a long-term antiplatelet strategy may affect not only the immune aspects of lupus pathogenesis but also cardiovascular problems related to the disease.”

Therapy: A role for TIARP in TNF-dependent arthritis

tumor necrosis factor (tnF) agonists are widely used in the treatment of rheumatoid arthritis (ra), but the mechanisms of action of these agents remain poorly understood. new research suggests that tnF-alpha-induced adipose-related protein (tiarP) has an important role in inflammatory arthritis in both mice and humans through the regulation of proinflammatory cytokines. expression of the transmembrane protein tiarP in adipocytes has previously been shown to be regulated by both tnF and interleukin-6. to characterize the role of tiarP in inflammatory arthritis, the investigators studied mice with glucose-6-phosphate isomerase (GPi)-induced arthritis—a model of tnF-dependent arthritis. “we have recently demonstrated a therapy

Rheumatoid arthritis: Statins have immunomodulatory and clinical effects in RA.

Studies in patients with cardiovascular disease have shown that statins regulate the inflammatory response and affect T-cell subsets; however, evidence for the value of this approach to the treatment of patients with rheumatoid arthritis (RA) is lacking. To test their hypothesis that statins have clinical benefits in this setting, related to their effects on regulatory T (TREG) cells, Xiang Cheng and colleagues treated 55 patients with RA with a 12-week course of atorvastatin. Compared with those who did not undergo treatment with the drug, patients with RA who received atorvastatin 20 mg per day showed improved clinical outcomes and reduced serum levels of lipids and inflammatory markers after 12 weeks of therapy: improvements were observed in levels of both LDL and total cholesterol, erythrocyte sedimentation rate, levels of C-reactive protein and 28-joint disease activity score. RHEUMATOID ARTHRITIS