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Inflammatory responses require mobilization of innate immune cells from the bone marrow. The functionality of this process depends on the state of the bone marrow microenvironment. We therefore hypothesized that molecular changes in osteoblasts, which are essential stromal cells of the bone marrow microenvironment, influence the inflammatory response. Here, we show that osteoblast-specific expression of the AP-1 transcription factor Fra-2 (Fra-2Obtet) induced a systemic inflammatory state with infiltration of neutrophils and pro-inflammatory macrophages into the spleen and liver as well as increased levels of pro-inflammatory cytokines, such as IL-1β, IL-6 and GM-CSF. By in vivo inhibition of osteopontin (OPN) in Fra-2Obtet mice, we demonstrate that this process was dependent on OPN expression, which mediates alterations of the bone marrow niche. Furthermore, in a murine lung injury model, Fra-2Ob-tet mice show increased inflammatory responses and more severe disease features. Our findings demonstrate for the first time that molecular changes in osteoblasts influence the susceptibility to inflammation by altering evasion of innate immune cells from the bone marrow space. [ABSTRACT FROM AUTHOR]

Infections with different helminth species have been observed to ameliorate a variety of chronic inflammatory diseases. Herein, we show that the natural murine helminth species,Heligmosomoides polygyrus bakeri(Hp) is capable of attenuating disease severity in two different inflammatory arthritis models. Furthermore, we show that excretory–secretory (ES) products from Hp directly suppress osteoclast differentiationin vitro. Taken together, these results demonstrate that helminth infections can dampen autoimmune diseases and highlight a previously unrecognized and important role for ES products, by directly impacting on bone destruction. [ABSTRACT FROM PUBLISHER]

The aim of this study was the registration of digitized thin 2D sections of mouse vertebrae and tibiae used for histomorphometry of trabecular bone structure into 3D micro computed tomography (μCT) datasets of the samples from which the sections were prepared. Intensity-based and segmentation-based registrations (SegRegs) of 2D sections and 3D μCT datasets were applied. As the 2D sections were deformed during their preparation, affine registration for the vertebrae was used instead of rigid registration. Tibiae sections were additionally cut on the distal end, which subsequently undergone more deformation so that elastic registration was necessary. The Jaccard distance was used as registration quality measure. The quality of intensity-based registrations and SegRegs was practically equal, although precision errors of the elastic registration of segmentation masks in tibiae were lower, while those in vertebrae were lower for the intensity-based registration. Results of SegReg significantly depended on the segmentation of the μCT datasets. Accuracy errors were reduced from approximately 64% to 42% when applying affine instead of rigid transformations for the vertebrae and from about 43% to 24% when using B-spline instead of rigid transformations for the tibiae. Accuracy errors can also be caused by the difference in spatial resolution between the thin sections (pixel size: 7.25 μm) and the μCT data (voxel size: 15 μm). In the vertebrae, average deformations amounted to a 6.7% shortening along the direction of sectioning and a 4% extension along the perpendicular direction corresponding to 0.13–0.17 mm. Maximum offsets in the mouse tibiae were 0.16 mm on average. [ABSTRACT FROM AUTHOR]

The presence of a solid tumor is the result of a complex balance between rejection, tolerance and regeneration in which the interactions of tumor cells with cells of the host immune system contribute strongly to the final outcome. Here we report on a model where lethally UVB-irradiated cells cause accelerated growth of viable tumor cells in vitro and in allogeneic immune competent mice. UVB-irradiated tumor cells alone did not form tumors and failed to induce tolerance for a second challenge with the same allogeneic tumor. Our data show an important role for dying cells in promoting accelerated tumor cell growth of a small number of viable tumor cells in a large inoculum of UVB-irradiated tumor cells. This occurs when viable and dying/dead tumor cells are in close proximity, suggesting that mobile factors contribute to growth promotion. The anti-inflammatory and growth promoting properties of apoptotic cells are based on several independent effects. UVB-irradiated apoptotic cells directly release a growth promoting activity and clearance by macrophages of apoptotic cells is accompanied by the secretion of IL10, TGFß, and PGE2. Growth promotion is even observed with dying heterologous cells implying a conserved mechanism. Future experiments should focus on the effects of dying tumor cells generated in vivo on the outgrowth of surviving tumor cells which is prone to have implications for cancer therapy. [ABSTRACT FROM AUTHOR]

Rapid clearance of apoptotic cells, frequently referred to as efferocytosis, is crucial for the maintenance of tissue homeostasis and the prevention of autoimmunity. The common model of apoptotic cell clearance involves a system of released 'Find me' and exposed 'Eat me' signals on apoptotic cells, detected and recognized by matching receptors on macrophages or dendritic cells (DC), referred to as the phagocytic synapse. Osteoclasts share the monocyte lineage with these professional mononuclear phagocytes, thus raising the question if, in addition to bone resorption, osteoclasts can act as scavengers for apoptotic cells. Our qPCR data clearly show that osteoclasts express most of the genes required for dying cell clearance at mRNA levels similar to or even higher than those observed in M1-macrophages, M2-macrophages or DC. Our microscopical analyses reveal that osteoclasts in fact can bind and/or engulf apoptotic cells in an essentially serum-independent fashion. Together with our data on the abundance of the respective mRNAs, these results identify the vitronectin receptor (integrin ανβ3)/milk fat globule-EGF factor 8 protein (MFG-E8) axis, the scavenger receptors (CD36, CD68 and class A macrophage scavenger receptor (SR-A)), the complement/complement receptor axis, the Mer/Tyro3/Protein S axis, and the phosphatidylserine (PS) receptor brain-specific angiogenesis inhibitor 1 (BAI1) as the most promising candidates to be involved in osteoclast-mediated efferocytosis. [ABSTRACT FROM AUTHOR]

Patients with Systemic Lupus Erythematosus (SLE) carry an increased risk for the development of coronary artery disease (CAD). The R131 allele of the Fc gamma receptor IIa (FcγRIIa) is associated with SLE incidence and disease severity but also with CAD. Compared to stable angina pectoris (SAP) the unstable angina (UAP), as a manifestation of destabilizing CAD, is associated with increased risk of persistent instability, myocardial infarction, and death. Identification of clinically relevant determinants for unstable angina promises reduction of UAP-associated mortality in patients with SLE. We conducted a clinical study among 553 consecutive patients with stable angina pectoris ( n = 330) and unstable angina pectoris ( n = 223). All patients were genotyped for a frequent functional variant at position 131 of the mature FcγRIIa. UAP, but not SAP was significantly associated with the R/R131 genotype ( P < 0.001). In troponin-negative patients with angina carrying the R/R131 genotype the odds ratio for suffering from UAP was 4.02 (95% confidence interval, 2.52-6.41) compared to those with non-R/R131 genotypes. In a multivariable analysis, the R/R131 genotype independently predicted the risk for development of UAP in a model adjusted for classical atherogenic risk factors. Our data imply that risk stratification of SLE- and other high risk patients with troponin-negative angina could be significantly improved by FcγRIIa genotyping. [ABSTRACT FROM AUTHOR]

Deficiencies in the recognition and engulfment of apoptotic cells have been reported in patients with systemic lupus erythematosus (SLE). If dying cells are not promptly cleared, they undergo secondary necrosis and release nuclear autoantigens. Secondarily necrotic cell-derived material (SNEC) can be generated in vitro employing various methods. SNEC generated by either methods shows similar DNA content, light scatter characteristics, and binding pattern of dead and dying cell ligands and is readily recognized by autoantibodies (AAb) of many patients with SLE. In whole blood, AAb opsonize SNEC and foster its uptake by blood-borne non-professional phagocytes. We observed a significant secretion of the inflammatory cytokines IL-8 and TNF-α by phagocytes which had engulfed different types of opsonized SNEC. Phagocytosis of SNEC and the subsequent production of inflammatory cytokines were strongly influenced by the presence of DNA in this prey, since DNase I treatment reduced both the uptake of SNEC and the induction of IL-8 and TNF-α production. In conclusion, the proinflammatory phagocytosis by circulating phagocytes of IgG-opsonized cellular remnants fosters systemic inflammation in SLE. [ABSTRACT FROM AUTHOR]

Churg-Strauss syndrome (CSS) is a rare systemic necrotizing vasculitis associated with granuloma formation and severe blood and tissue eosinophilia. CSS occurs almost exclusively in patients with asthma. Its pathogenesis remains largely unknown, as triggering factors for CSS development have not been identified so far. AAb, such as anti-neutrophil cytoplasmic autoantibodies, are found in less than half of patients and possibly constitute a subtype of CSS with different clinical behaviour. On a cellular level, CSS is characterized by a strong Th2-type immune response. Th2-associated cytokines such as IL-4, IL-13 and IL-5 may precipitate the severe eosinophilia in CSS, while migration of Eos to inflammatory sites is possibly mediated by eotaxin-3. This review summarizes recent advances in the knowledge on epidemiology, clinical features, and pathogenesis of CSS. [ABSTRACT FROM AUTHOR]

Cytokine expression in the inflamed synovial membrane of patients with rheumatoid arthritis and other forms of chronic inflammatory arthritis and other forms of chronic inflammatory arthritis leads to formation of osteoclasts. These cells are primarily involved in the resorption of mineralized cartilage and bone and thus participate in joint damage in the course of chronic arthritides. Osteoclastogenesis in the synovial membrane is driven by cytokines such as RANKL, MCSF but also classical proinflammatory mediators such as TNF, IL-1 and IL-6. Inhibition of osteoclast formation has proven as an effective approach to inhibit structural damage in experimental arthritis and preliminary data suggest that such approaches are also effective in human RA. [ABSTRACT FROM AUTHOR]

Inflammatory joint disease typically provokes progressive cartilage damage. The proliferative synovial inflammatory tissue directly invades the cartilage and induces the expression and activation of degrading enzymes such as matrix metalloproteases (MMPs) and aggrecanases. However, also chondrocyte apoptosis has been observed in cartilage samples of inflamed joints. It remains unclear whether this is a secondary phenomenon due to cartilage damage or a primary event initiated by the synovial inflammation. To determine the presence or absence of chondrocyte death in experimental arthritis, we longitudinally assessed proteoglycan depletion and chondrocyte apoptosis in paw sections from human tumor necrosis factor transgenic (hTNFtg) mice and wild-type littermates. Whereas, wild-type mice showed no signs of cartilage damage, hTNFtg mice exhibited progressive proteoglycan loss starting at clinical onset of arthritis. However, we already found the first apoptotic chondrocytes well before cartilage matrix breakdown occurred indicating that chondrocyte death can be induced before matrix resorption. Chondrocyte death could constantly be observed until late stages of arthritis causing a continuous increase in the number of empty cartilage lacunae. As apoptotic cells in cartilage cannot be cleared by phagocytes due to their spatial isolation in the avascular lacunae of cartilage, having no contact to professional or amateur phagocytes. The dying cells are compelled to undergo a "lonely death" inevitable ending up in secondary necrosis giving rise to perpetuation of a pro-inflammatory cascade. These data indicate that chondrocyte death may play a primary role in inflammatory arthritis fuelling cartilage inflammation and damage due to secondary necrosis. [ABSTRACT FROM AUTHOR]

Owing to the common coincidence of osteoporosis and vascular disease, pathophysiological links between both disorders have long been sought. The osteoprotegerin (OPG)/receptor activator of NF-κB (RANK)/receptor activator of NF-κB ligand (RANKL) cytokine network, a key regulatory system in bone homeostasis, has been implicated recently in vascular calcification, changes in matrix composition and diabetic macroangiopathy, aortic aneurysm development, heart failure and, most importantly, advanced atherosclerosis, plaque destabilization and manifestation of cardiovascular diseases. The concept of an active role of RANKL and OPG in vascular pathophysiology is intriguing and is gaining increasing support from both epidemiological and basic research. OPG serum level is considered to be a stable and reliable indicator of the overall activity of the OPG/RANK/RANKL axis and may find application as a biomarker of vascular risk and prognosis. RANKL in turn may be a suitable target for novel therapies. Pharmacological strategies for specific interference with the OPG/RANK/RANKL axis are currently being developed and evaluated in osteoporosis therapy. [ABSTRACT FROM AUTHOR]

Accumulation in tissues of post-apoptotic cells is a feature frequently observed in patients with systemic lupus erythematosus and in murine models of systemic autoimmune diseases. One of the endogenous danger molecules released by secondarily necrotic cells is monosodium urate (MSU), which is already established to be the causative agent of gout. Here, we show that MSU is taken up by eosinophils, neutrophils and monocytes in a process involving (a) heat-labile serum factor(s) and divalent cations. The uptake induces the release of the pro-inflammatory cytokines IL-1β/IL-18/TNFα and IL-6/IL-8 by monocytes and PMN, respectively. [ABSTRACT FROM AUTHOR]

The phagocytosis of apo cells in patients with systemic lupus erythematosus (SLE) has been shown to be impaired. Recognition and engulfment of dying cells are mediated by molecules and receptors that are also involved in cell adhesion. Therefore, we analysed the adhesion capabilities of MoMa from patients with SLE. We employed a colorimetric assay to quantify the adhesion of MoMa to various substrates. In addition, we evaluated the morphological characteristics of the MΦ adhesion cultures by phase contrast microscopy. We have observed various morphologic characteristics depending on the adhesive substrate. The typical spindle shaped MoMa adhered to plastic and a bigger and rounder formed MoMa adhered to immunoglobulin (Ig) coated surfaces. Quantitatively, adhesion to plastic was significantly decreased in some SLE patients. Those patients showing a defective adhesion to plastic simultaneously showed an enhanced adhesion to Ig coated surfaces. These findings suggest that there is an alteration in the integrin and/or FcγR mediated stimulation of MoMa from SLE patients and this alteration may be associated with the impaired clearance of apo cells seen in this disease. [ABSTRACT FROM AUTHOR]

CRP is an important inflammatory marker, however, CRP levels are relatively low in patients with SLE. In addition patients with SLE often display low activities and serum levels for DNase I and complement, respectively. Here we show that DNase I treatment of nec PBMC increased their binding of CRP. Consequently, reduced DNase I activity in patients with SLE may contribute to the impaired opsonisation by CRP of dead cells, exacerbating the clearance defect in SLE of apo and nec cells. [ABSTRACT FROM AUTHOR]

The architectural chromosomal protein high-mobility group box 1 protein (HMGB1) acts as an alarmin when released from cells. It is involved in the pathogenesis of inflammatory and autoimmune diseases. HMGB1 can undergo post-translational modifications including oxidation. However, the mechanisms and functional relevance of HMGB1 oxidation are not yet understood. Increased concentrations of reactive oxygen species (ROS) have been reported during apoptosis and necrosis. Hence, we investigated the oxidative status of HMGB1 in dead cells. Immunoblot analyses under reducing and non-reducing conditions revealed that HMGB1 is oxidized in dead cells. Moreover, tagging of oxidized cysteine residues by a maleimide moiety linked to polyethylene glycol showed that HMGB1 passively released from primary and secondary necrotic cells was predominantly oxidized. Also HMGB1 in plasma of patients with systemic lupus was reversibly oxidized. In conclusion, HMGB1 undergoes reversible oxidative modifications at cysteine residues during cell death, which may modulate its biological properties. [ABSTRACT FROM AUTHOR]

Uric acid (UA) is identified as a danger signal released from dying cells. It precipitates in sodium-rich extracellular fluid and in potassium-rich intracellular fluid as monosodium urate (MSU) and monopotassium urate (MPU), respectively. Here, we examined the structural and functional features of these crystals. In contrast to MPU MSU crystals induced reactive oxygen species production and release of pro-inflammatory cytokines in whole blood ex vivo assays. These results show that the cation of urate crystals determines the response of innate immune cells, indicating that the micromilieu at the site of crystal formation is important for their inflammatory potential. [ABSTRACT FROM AUTHOR]

Although 12/15-lipoxygenase (12/15-LO) has been implicated as negative regulator of systemic bone mass in mice and humans, the underlying mechanisms remain elusive. Here, we show that 12/15-LO is a positive regulator of osteoclast (OC) development. Enzymatic inhibition as well as genetic ablation of 12/15-LO significantly impaired osteoclastogenesis. Conversely, addition of the 12/15-LO-derived eicosanoids 12- and 15-HETE augmented differentiation of precursors into fully matured OCs. Together these data point towards a crucial role of 12/15-LO in the regulation of OC development. Therefore, 12/15-LO and its human homologue 15-LO may display novel targets for the treatment of diseases such as osteoporosis and rheumatoid arthritis. [ABSTRACT FROM AUTHOR]