Chronic signaling via the metabolic checkpoint kinase mTORC1 induces macrophage granuloma formation and marks sarcoidosis progression.

The aggregation of hypertrophic macrophages constitutes the basis of all granulomatous diseases, such as tuberculosis or sarcoidosis, and is decisive for disease pathogenesis. However, macrophage-intrinsic pathways driving granuloma initiation and maintenance remain elusive. We found that activation of the metabolic checkpoint kinase mTORC1 in macrophages by deletion of the gene encoding tuberous sclerosis 2 (Tsc2) was sufficient to induce hypertrophy and proliferation, resulting in excessive granuloma formation in vivo. TSC2-deficient macrophages formed mTORC1-dependent granulomatous structures in vitro and showed constitutive proliferation that was mediated by the neo-expression of cyclin-dependent kinase 4 (CDK4). Moreover, mTORC1 promoted metabolic reprogramming via CDK4 toward increased glycolysis while simultaneously inhibiting NF-κB signaling and apoptosis. Inhibition of mTORC1 induced apoptosis and completely resolved granulomas in myeloid TSC2-deficient mice. In human sarcoidosis patients, mTORC1 activation, macrophage proliferation and glycolysis were identified as hallmarks that correlated with clinical disease progression. Collectively, TSC2 maintains macrophage quiescence and prevents mTORC1-dependent granulomatous disease with clinical implications for sarcoidosis.

Bona fide dendritic cells are pivotal precursors for osteoclasts.

OBJECTIVES: Osteoclasts (OCs) are myeloid-derived multinucleated cells uniquely able to degrade bone. However, the exact nature of their myeloid precursors is not yet defined. METHODS: CD11c-diphtheria toxin receptor (CD11cDTR) transgenic mice were treated with diphtheria toxin (DT) or phosphate buffered saline (PBS) during serum transfer arthritis (STA) and human tumour necrosis factor transgenic (hTNFtg) arthritis and scored clinically and histologically. We measured cytokines in synovitis by quantitative polymerase chain reaction (qPCR). We performed ovariectomy in CD11cDTR mice treated with PBS or DT. We analysed CD11cDTR, CD11c-Cre/CX3CR1-STOP-DTR and Zbtb46-DTR-treated mice with DT using histomorphometry and OC of CD11c and Zbtb46 fate reporter mice by fluorescent imaging. We sorted murine and human OC precursors and stimulated them with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL) to generate OCs. RESULTS: Targeting CD11c+ cells in vivo in models of inflammatory arthritis (STA and hTNFtg) ameliorates arthritis by reducing inflammatory bone destruction and OC generation. Targeting CD11c-expressing cells in unchallenged mice removes all OCs in their long bones. OCs do not seem to be derived from CD11c+ cells expressing CX3CR1+, but from Zbtb46+conventional dendritic cells (cDCs) as all OCs in Zbtb46-Tomato fate reporter mice are Tomato+. In line, administration of DT in Zbtb46-DTR mice depletes all OCs in long bones. Finally, human CD1c-expressing cDCs readily differentiated into bone resorbing OCs. CONCLUSION: Taken together, we identify DCs as important OC precursors in bone homeostasis and inflammation, which might open new avenues for therapeutic interventions in OC-mediated diseases.

Itaconate is a metabolic regulator of bone formation in homeostasis and arthritis.

OBJECTIVES: Bone remodelling is a highly dynamic process dependent on the precise coordination of osteoblasts and haematopoietic-cell derived osteoclasts. Changes in core metabolic pathways during osteoclastogenesis, however, are largely unexplored and it is unknown whether and how these processes are involved in bone homeostasis. METHODS: We metabolically and transcriptionally profiled cells during osteoclast and osteoblast generation. Individual gene expression was characterised by quantitative PCR and western blot. Osteoblast function was assessed by Alizarin red staining. immunoresponsive gene 1 (Irg1)-deficient mice were used in various inflammatory or non-inflammatory models of bone loss. Tissue gene expression was analysed by RNA in situ hybridisation. RESULTS: We show that during differentiation preosteoclasts rearrange their tricarboxylic acid cycle, a process crucially depending on both glucose and glutamine. This rearrangement is characterised by the induction of Irg1 and production of itaconate, which accumulates intracellularly and extracellularly. While the IRG1-itaconate axis is dispensable for osteoclast generation in vitro and in vivo, we demonstrate that itaconate stimulates osteoblasts by accelerating osteogenic differentiation in both human and murine cells. This enhanced osteogenic differentiation is accompanied by reduced proliferation and altered metabolism. Additionally, supplementation of itaconate increases bone formation by boosting osteoblast activity in mice. Conversely, Irg1-deficient mice exhibit decreased bone mass and have reduced osteoproliferative lesions in experimental arthritis. CONCLUSION: In summary, we identify itaconate, generated as a result of the metabolic rewiring during osteoclast differentiation, as a previously unrecognised regulator of osteoblasts.

TNFR2 is critical for TNF-induced rheumatoid arthritis fibroblast-like synoviocyte inflammation.

OBJECTIVES: TNF-induced activation of fibroblast-like synoviocytes (FLS) is a critical determinant for synovial inflammation and joint destruction in RA. The detrimental role of TNF-receptor 1 (TNFR1) has thoroughly been characterized. The contributions of TNFR2, however, are largely unknown. This study was performed to delineate the role of TNFR2 in human FLS activation. METHODS: TNFR2 expression in synovial tissue samples was determined by immunohistochemistry. Expression of TNFR2 was silenced using RNAi or CRISPR/Cas9 technologies. Global transcriptional changes were determined by RNA-seq. QPCR, ELISA and immunoblotting were used to validate RNA-seq results and to uncover pathways operating downstream of TNFR2 in FLS. RESULTS: TNFR2 expression was increased in RA when compared with OA synovial tissues. In particular, RA-FLS demonstrated higher levels of TNFR2 when compared with OA-FLS. TNFR2 expression in RA-FLS correlated with RA disease activity, synovial T- and B-cell infiltration. TNF and IL1ß were identified as inflammatory mediators that upregulate TNFR2 in RA-FLS. Silencing of TNFR2 in RA-FLS markedly diminished the TNF-induced expression of inflammatory cytokines and chemokines, including CXCR3-binding chemokines and the B-cell activating factor TNFSF13B. Immunobiochemical analyses revealed that TNFR2-mediated expression of inflammatory mediators critically depends on STAT1. CONCLUSION: Our results define a critical role for TNFR2 in FLS-driven inflammation and unfold its participation in the unresolved course of synovial inflammation in RA.

'SMASH' recommendations for standardised microscopic arthritis scoring of histological sections from inflammatory arthritis animal models.

Animal models for inflammatory arthritides such as rheumatoid arthritis (RA) and psoriatic arthritis are widely accepted and frequently used to identify pathological mechanisms and validate novel therapeutic strategies. Unfortunately, many publications reporting on these animal studies lack detailed description and appropriate assessment of the distinct histopathological features of arthritis: joint inflammation, cartilage damage and bone erosion. Therefore, the European consortium BeTheCure, consisting of 38 academic and industrial partners from 15 countries, set as goal to standardise the histological evaluation of joint sections from animal models of inflammatory arthritis. The consensual approach of a task force including 16 academic and industrial scientists as well as laboratory technicians has resulted in the development of the Standardised Microscopic Arthritis Scoring of Histological sections ('SMASH') recommendations for a standardised processing and microscopic scoring of the characteristic histopathological features of arthritis, exemplified by four different rodent models for arthritis: murine collagen-induced arthritis, collagen-antibody-induced arthritis, human tumour necrosis factor transgenic Tg197 mice and rat pristane-induced arthritis, applicable to any other inflammatory arthritis model. Through standardisation, the SMASH recommendations are designed to improve and maximise the information derived from in vivo arthritis experiments and to promote reproducibility and transparent reporting on such studies. In this manuscript, we will discuss and provide recommendations for analysis of histological joint sections: identification of the regions of interest, sample preparation, staining procedures and quantitative scoring methods. In conclusion, awareness of the different features of the arthritis pathology in animal models of inflammatory arthritis is of utmost importance for reliable research outcome, and the standardised histological processing and scoring methods in these SMASH recommendations will help increase uniformity and reproducibility in preclinical research on inflammatory arthritis.

Histone deacetylase 1 (HDAC1): A key player of T cell-mediated arthritis.

Rheumatoid Arthritis (RA) represents a chronic T cell-mediated inflammatory autoimmune disease. Studies have shown that epigenetic mechanisms contribute to the pathogenesis of RA. Histone deacetylases (HDACs) represent one important group of epigenetic regulators. However, the role of individual HDAC members for the pathogenesis of arthritis is still unknown. In this study we demonstrate that mice with a T cell-specific deletion of HDAC1 (HDAC1-cKO) are resistant to the development of Collagen-induced arthritis (CIA), whereas the antibody response to collagen type II was undisturbed, indicating an unaltered T cell-mediated B cell activation. The inflammatory cytokines IL-17 and IL-6 were significantly decreased in sera of HDAC1-cKO mice. IL-6 treated HDAC1-deficient CD4+ T cells showed an impaired upregulation of CCR6. Selective inhibition of class I HDACs with the HDAC inhibitor MS-275 under Th17-skewing conditions inhibited the upregulation of chemokine receptor 6 (CCR6) in mouse and human CD4+ T cells. Accordingly, analysis of human RNA-sequencing (RNA-seq) data and histological analysis of synovial tissue samples from human RA patients revealed the existence of CD4+CCR6+ cells with enhanced HDAC1 expression. Our data indicate a key role for HDAC1 for the pathogenesis of CIA and suggest that HDAC1 and other class I HDACs might be promising targets of selective HDAC inhibitors (HDACi) for the treatment of RA.

FOXO3 is involved in the tumor necrosis factor-driven inflammatory response in fibroblast-like synoviocytes.

Fibroblast-like synoviocytes (FLS) are major contributors to joint inflammation in rheumatoid arthritis (RA). Forkhead box O 3 (FOXO3) perturbations in immune cells are increasingly linked to RA pathogenesis. Here, we show that FOXO3 is distinctly inactivated/phosphorylated in the FLS of rheumatoid synovitis. In vitro, stimulation of FLS with tumor necrosis factor-alpha α (TNFα) induced a rapid and sustained inactivation of FOXO3. mRNA profiling revealed that the inactivation of FOXO3 is important for the sustained pro-inflammatory interferon response to TNFα (CXCL9, CXCL10, CXCL11, and TNFSF18). Mechanistically, our studies demonstrate that the inactivation of FOXO3 results from TNF-induced downregulation of phosphoinositide-3-kinase-interacting protein 1 (PIK3IP1). Thus, we identified FOXO3 and its modulator PIK3IP1 as a critical regulatory circuit for the inflammatory response of the resident mesenchymal cells to TNFα and contribute insight into how the synovial tissue brings about chronic inflammation that is driven by TNFα.

CCR6 controls autoimmune but not innate immunity-driven experimental arthritis.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease, characterized by synovial infiltration of various inflammatory cells. Chemokines are involved in controlling the recruitment of different cell types into the synovial membrane. The role of CCR6 in the development of arthritis so far remains unclear. In this study, we investigated the role of CCR6 in the pathogenesis of arthritis using three different murine arthritis models. Compared to WT animals, CCR6-/- mice developed less clinical signs of arthritis in the collagen-induced arthritis model but not in the K/BxN serum transfer arthritis model and in the human tumour necrosis factor transgenic arthritis model, suggesting a defect in adaptive effector functions but intact innate effector functions in the development of arthritis in CCR6-/- animals. In line with this, anti-collagen antibody levels were significantly reduced in CCR6-/- mice compared with WT mice. Moreover, we demonstrate enhanced osteoclastogenesis in vitro in CCR6-/- mice compared with WT mice. However, we did not detect differences in bone mass under steady state conditions in vivo between WT and CCR6-deficient mice. These data suggest that CCR6 is crucially involved in adaptive but not in innate immunity-driven arthritis. CCR6 or its chemokine ligand CCL20 might represent a possible new target for the treatment of RA.

The involvement of Toll-like receptor 9 in the pathogenesis of erosive autoimmune arthritis.

Endogenous nucleic acids and their receptors may be involved in the initiation of systemic autoimmune diseases including rheumatoid arthritis (RA). As the role of the DNA sensing Toll-like receptor (TLR) 9 in RA is unclear, we aimed to investigate its involvement in the pathogenesis of autoimmune arthritis using three different experimental models of RA. The data obtained revealed involvement of TLR9 in the T cell-dependent phase of inflammatory arthritis. In rats with pristane-induced arthritis (PIA), TLR9 inhibition before disease onset reduced arthritis significantly and almost completely abolished bone erosion. Accordingly, serum levels of IL-6, α-1-acid-glycoprotein and rheumatoid factor were reduced. Moreover, in TLR9-/- mice, streptococcal cell wall (SCW)-induced arthritis was reduced in the T cell-dependent phase, whereas T cell-independent serum-transfer arthritis was not affected. Remarkably, while TLR7 expression did not change during in vitro osteoclastogenesis, TLR9 expression was higher in precursor cells than in mature osteoclasts and partial inhibition of osteoclastogenesis was achieved only by the TLR9 antagonist. These results demonstrate a pivotal role for TLR9 in the T cell-dependent phases of inflammatory arthritis and additionally suggest some role during osteoclastogenesis. Hence, endogenous DNA seems to be crucially involved in the pathophysiology of inflammatory autoimmune arthritis.

Non-classical monocytes as mediators of tissue destruction in arthritis.

OBJECTIVES: Bone destruction in rheumatoid arthritis is mediated by osteoclasts (OC), which are derived from precursor cells of the myeloid lineage. The role of the two monocyte subsets, classical monocytes (expressing CD115, Ly6C and CCR2) and non-classical monocytes (which are CD115 positive, but low in Ly6C and CCR2), in serving as precursors for OC in arthritis is still elusive. METHODS: We investigated CCR2-/- mice, which lack circulating classical monocytes, crossed into hTNFtg mice for the extent of joint damage. We analysed monocyte subsets in hTNFtg and K/BxN serum transfer arthritis by flow cytometry. We sorted monocyte subsets and analysed their potential to differentiate into OC and their transcriptional response in response to RANKL by RNA sequencing. With these data, we performed a gene ontology enrichment analysis and gene set enrichment analysis. RESULTS: We show that in hTNFtg arthritis local bone erosion and OC generation are even enhanced in the absence of CCR2. We further show the numbers of non-classical monocytes in blood are elevated and are significantly correlated with histological signs of joint destruction. Sorted non-classical monocytes display an increased capacity to differentiate into OCs. This is associated with an increased expression of signal transduction components of RANK, most importantly TRAF6, leading to an increased responsiveness to RANKL. CONCLUSION: Therefore, non-classical monocytes are pivotal cells in arthritis tissue damage and a possible target for therapeutically intervention for the prevention of inflammatory joint damage.

Targeted inhibition of Janus kinases abates interfon gamma-induced invasive behaviour of fibroblast-like synoviocytes.

Objectives: The aim was to explore the function of the T-cell cytokine IFNγ for mesenchymal tissue remodelling in RA and to determine whether IFNγ signalling controls the invasive potential of fibroblast-like synoviocytes (FLS). Methods: To assess architectural responses, FLS were cultured in three-dimensional micromasses. FLS motility was analysed in migration and invasion assays. Signalling events relevant to cellular motility were defined by western blots. Baricitinib and small interfering RNA pools were used to suppress Janus kinase (JAK) functions. Results: Histological analyses of micromasses revealed unique effects of IFNγ on FLS shape and tissue organization. This was consistent with accelerated migration upon IFNγ stimulation. Given that cell shape and cell motility are under the control of the focal adhesion kinase (FAK), we next analysed its activity. Indeed, IFNγ stimulation induced the phosphorylation of FAK-Y925, a phosphosite implicated in FAK-mediated cell migration. Small interfering RNA knockdown of JAK2, but not JAK1, substantially abrogated FAK activation by IFNγ. Correspondingly, IFNγ-induced FAK activation and invasion of FLS was abrogated by the JAK inhibitor, baricitinib. Conclusion: Our study contributes insight into the synovial response to IFNγ and reveals JAK2 as a potential therapeutic target for FLS-mediated joint destruction in arthritis, especially in RA.

MicroRNA-146a governs fibroblast activation and joint pathology in arthritis.

Synovial fibroblasts are key cells orchestrating the inflammatory response in arthritis. Here we demonstrate that loss of miR-146a, a key epigenetic regulator of the innate immune response, leads to increased joint destruction in a TNF-driven model of arthritis by specifically regulating the behavior of synovial fibroblasts. Absence of miR-146a in synovial fibroblasts display a highly deregulated gene expression pattern and enhanced proliferation in vitro and in vivo. Deficiency of miR-146a induces deregulation of tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6) in synovial fibroblasts, leading to increased proliferation. In addition, loss of miR-146a shifts the metabolic state of fibroblasts towards glycolysis and augments the ability of synovial fibroblasts to support the generation of osteoclasts by controlling the balance of osteoclastogenic regulatory factors receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG). Bone marrow transplantation experiments confirmed the importance of miR-146a in the radioresistant mesenchymal compartment for the control of arthritis severity, in particular for inflammatory joint destruction. This study therefore identifies microRNA-146a as an important local epigenetic regulator of the inflammatory response in arthritis. It is a central element of an anti-inflammatory feedback loop in resident synovial fibroblasts, who are orchestrating the inflammatory response in chronic arthritis. MiR-146a restricts their activation, thereby preventing excessive tissue damage during arthritis.

Loss of Phosphatase and Tensin Homolog in APCs Impedes Th17-Mediated Autoimmune Encephalomyelitis.

The PI3K signaling cascade in APCs has been recognized as an essential pathway to initiate, maintain, and resolve immune responses. In this study, we demonstrate that a cell type-specific loss of the PI3K antagonist phosphatase and tensin homolog (PTEN) in myeloid cells renders APCs toward a regulatory phenotype. APCs deficient for PTEN exhibit reduced activation of p38 MAPK and reduced expression of T cell-polarizing cytokines. Furthermore, PTEN deficiency leads to upregulation of markers for alternative activation, such as Arginase 1, with concomitant downregulation of inducible NO synthase in APCs in vitro and in vivo. As a result, T cell polarization was dysfunctional in PTEN(-/-) APCs, in particular affecting the Th17 cell subset. Intriguingly, mice with cell type-specific deletions of PTEN-targeting APCs were protected from experimental autoimmune encephalomyelitis, which was accompanied by a pronounced reduction of IL-17- and IL-22-producing autoreactive T cells and reduced CNS influx of classically activated monocytes/macrophages. These observations support the notion that activation of the PI3K signaling cascade promotes regulatory APC properties and suppresses pathogenic T cell polarization, thereby reducing the clinical symptoms and pathology of experimental autoimmune encephalomyelitis.

The MAPK-Activated Kinase MK2 Attenuates Dendritic Cell-Mediated Th1 Differentiation and Autoimmune Encephalomyelitis.

Dendritic cell (DC)-mediated inflammation induced via TLRs is promoted by MAPK-activated protein kinase (MK)-2, a substrate of p38 MAPK. In this study we show an opposing role of MK2, by which it consolidates immune regulatory functions in DCs through modulation of p38, ERK1/2-MAPK, and STAT3 signaling. During primary TLR/p38 signaling, MK2 mediates the inhibition of p38 activation and positively cross-regulates ERK1/2 activity, leading to a reduction of IL-12 and IL-1α/ß secretion. Consequently, MK2 impairs secondary autocrine IL-1α signaling in DCs, which further decreases the IL-1α/p38 but increases the anti-inflammatory IL-10/STAT3 signaling route. Therefore, the blockade of MK2 activity enables human and murine DCs to strengthen proinflammatory effector mechanisms by promoting IL-1α-mediated Th1 effector functions in vitro. Furthermore, MK2-deficient DCs trigger Th1 differentiation and Ag-specific cytotoxicity in vivo. Finally, wild-type mice immunized with LPS in the presence of an MK2 inhibitor strongly accumulate Th1 cells in their lymph nodes. These observations correlate with a severe clinical course in DC-specific MK2 knockout mice compared with wild-type littermates upon induction of experimental autoimmune encephalitis. Our data suggest that MK2 exerts a profound anti-inflammatory effect that prevents DCs from prolonging excessive Th1 effector T cell functions and autoimmunity.

Loss of phosphatase and tensin homolog (PTEN) in myeloid cells controls inflammatory bone destruction by regulating the osteoclastogenic potential of myeloid cells.

OBJECTIVE: Local bone destruction in rheumatic diseases, which often leads to disability and severely reduced quality of life, is almost exclusively mediated by osteoclasts. Therefore, it is important to understand pathways regulating the generation of osteoclasts. Here, we analysed the impact of the Phosphoinositide-3-Kinase (PI3K)/Phosphatase and tensin homolog (PTEN) axis on osteoclast generation and bone biology under basal and inflammatory conditions. METHODS: We analysed osteoclastogenesis of wildtype (wt) and PTEN(-/-) cells in vitro and in vivo, pit resorption and qPCR of osteoclasts in vitro. Mice with a myeloid cell-specific deletion of PTEN and wt littermate mice were investigated by bone histomorphometry and clinical and histological assessment in the human tumour necrosis factor (TNF)-transgenic (hTNFtg) arthritis model. RESULTS: We show that myeloid-specific PTEN(-/-) mice display increased osteoclastogenesis in vitro and in vivo compared to wt mice. Loss of PTEN did not affect the generation or survival of osteoclast precursor cells. However, PTEN deficiency greatly enhanced receptor activator of nuclear factor κ-B ligand (RANKL)-induced expression of the master transcription factor of osteoclastogenesis, nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), resulting in markedly increased terminal differentiation of osteoclasts in vitro. We also observed increased osteoclastogenesis under inflammatory conditions in the hTNFtg mouse model of arthritis, where hTNFtg/myeloid-specific PTEN(-/-) mice displayed enhanced local bone destruction as well as osteoclast formation in the inflamed joints. The extent of synovial inflammation, however, as well as recruitment of osteoclast precursor cells was not different between wt and myeloid-specific PTEN(-/-) mice. CONCLUSIONS: These data demonstrate that loss of PTEN and, therefore, sustained PI3-Kinase signalling in myeloid cells especially, elevates the osteoclastogenic potential of myeloid cells, leading to enhanced inflammatory local bone destruction. Therefore, although our study allows no direct translational conclusion since we used a conditional knockout approach, the therapeutic targeting of the PI3-Kinase pathway may be of benefit in preventing structural joint damage.

FHL2 regulates the resolution of tissue damage in chronic inflammatory arthritis.

OBJECTIVE: We analysed the role of the adaptor molecule four-and-a-half Lin11, Isl-1 & Mec-3 (LIM) domain protein 2 (FHL2) in the activation of fibroblast-like synoviocytes in human rheumatoid arthritis (RA) and tumour necrosis factor α (TNFα)-dependent animal models of the disease. METHODS: Synovial tissues of patients with RA and osteoarthritis (OA) as well as hind paw sections from arthritic human TNFα transgenic (hTNFtg) mice and synovial fibroblasts from these were analysed. The effects of cytokines on the expression of FHL2 and disease-relevant matrixmetalloproteases (MMPs) were determined. Analyses of human tissue specimens from patients treated with anti-TNFα as well as anti-TNFα treatment of hTNFtg mice were performed to substantiate the TNFα effects on FHL2 levels. FHL2(-/-) mice and hTNFtg mice (with constitutive or inducible transgene expression) were crossbred to generate TNFα overexpressing FHL2-deficient animals. Signalling pathways were analysed in cells from these mice and in human cells after knock down of FHL2 by western blot. RESULTS: FHL2 levels were higher in RA than in OA and in hTNFtg than in wild-type mice. Surprisingly, while transforming growth factor (TGF)ß-induced FHL2 expression, TNFα suppressed FHL2. In vivo, anti-TNFα treatment led to higher FHL2 levels both in RA patients and hTNFtg mice. The loss of FHL2 increased joint destruction in hTNFtg mice, which was accompanied by elevated MMP-13. In vitro, TNFα-mediated MMP-13 was significantly higher in FHL2(-/-) cells and after knock down of FHL2, which was caused by prolonged p38 MAPK activation. CONCLUSIONS: These data suggest that FHL2 serves as a protective factor and that, rather than promoting the pathology, the upregulation of FHL2 in RA occurs in frame of a regenerative attempt.

Interphalangeal Osteoarthritis Radiographic Simplified (iOARS) score: a radiographic method to detect osteoarthritis of the interphalangeal finger joints based on its histopathological alterations.

OBJECTIVE: To develop a radiographic score for assessment of hand osteoarthritis (OA) that is based on histopathological alterations of the distal (DIP) and proximal (PIP) interphalangeal joints. METHODS: DIP and PIP joints were obtained from corpses (n=40). Plain radiographies of these joints were taken. Joint samples were prepared for histological analysis; cartilage damage was graded according to the Mankin scoring system. A 2×2 Fisher's exact test was applied to define those radiographic features most likely to be associated with histological alterations. Receiver operating characteristic curves were analysed to determine radiographic thresholds. Intraclass correlation coefficients (ICC) estimated intra- and inter-reader variability. Spearman's correlation was applied to examine the relationship between our score and histopathological changes. Differences between groups were determined by a Student's t test. RESULTS: The Interphalangeal Osteoarthritis Radiographic Simplified (iOARS) score is presented. The score is based on histopathological changes of DIP and PIP joints and follows a simple dichotomy whether OA is present or not. The iOARS score relies on three equally ranked radiographic features (osteophytes, joint space narrowing and subchondral sclerosis). For both DIP and PIP joints, the presence of one x-ray features reflects interphalangeal OA. Sensitivity and specificity for DIP joints were 92.3% and 90.9%, respectively, and 75% and 100% for PIP joints. All readers were able to reproduce their own readings in DIP and PIP joints after 4 weeks. The overall agreement between the three readers was good; ICCs ranged from 0.945 to 0.586. Additionally, outcomes of the iOARS score in a hand OA cohort revealed a higher prevalence of interphalangeal joint OA compared with the Kellgren and Lawrence score. CONCLUSIONS: The iOARS score is uniquely based on histopathological alterations of the interphalangeal joints in order to reliably determine OA of the DIP and PIP joints radiographically. Its high specificity and sensitivity together with the dichotomous approach renders the iOARS score reliable, fast to perform and easy to apply. This tool may not only be valuable in daily clinical practice but also in clinical and epidemiological trials.

Tumor necrosis factor-inhibiting therapy preferentially targets bone destruction but not synovial inflammation in a tumor necrosis factor-driven model of rheumatoid arthritis.

OBJECTIVE: To investigate how tumor necrosis factor (TNF)-inhibiting therapy affects bone destruction and inflammation in a TNF-driven mouse model of rheumatoid arthritis. METHODS: In order to evaluate the influence of TNF on osteoclastogenesis in vitro, different concentrations of TNF were added to spleen cell-derived monocytes in the absence or presence of different concentrations of RANKL. In addition, the effects of TNF inhibition on osteoclast precursors as well as local bone destruction in vivo were assessed by treating TNF-transgenic mice with different doses of adalimumab. RESULTS: TNF stimulated osteoclastogenesis mainly by increasing the number of osteoclast precursor cells in vitro. This TNF effect was independent of the presence of RANKL. In the hTNF-transgenic mouse model of destructive arthritis, low-dose TNF-inhibiting therapy with adalimumab had no effect on synovial inflammation but significantly inhibited local bone destruction and the generation of osteoclasts. This inhibition was accompanied by a reduction in the number of c-Fms-positive osteoclast precursor cells in the bone marrow and a reduction of the osteoclast precursor pools in the blood and inflamed synovial membrane of hTNF-transgenic mice. CONCLUSION: Low-dose TNF-inhibiting therapy significantly reduces bone erosions by reducing the number of circulating and joint-invading osteoclast precursors. This effect is uncoupled from its antiinflammatory action.

Amino Acids Fueling Fibroblast-Like Synoviocyte Activation and Arthritis By Regulating Chemokine Expression and Leukocyte Migration.

OBJECTIVE: We analyzed the impact of amino acid (AA) availability on the inflammatory response in arthritis. METHODS: We stimulated rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLSs) with tumor necrosis factor (TNF) in the presence or absence of proteinogenic AAs and measured their response by QuantSeq 3' messenger RNA sequencing, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay. Signal transduction events were determined by Western blot. We performed K/BxN serum transfer arthritis in mice receiving a normal and a low-protein diet and analyzed arthritis clinically and histologically. RESULTS: Deprivation of AAs decreased the expression of a specific subset of genes, including the chemokines CXCL10, CCL2, and CCL5 in TNF-stimulated FLSs. Mechanistically, the presence of AAs was required for the TNF-induced activation of an interferon regulatory factor 1 (IRF1)-STAT1 signaling circuit that drives the expression of chemotactic factors. The expression of IRF1 and the IRF1-dependent gene set in FLSs was highly correlated with the presence of inflammatory cells in human RA, emphasizing the important role of this AA-dependent pathway in inflammatory cell recruitment to the synovial tissue. Finally, we show that mice receiving a low-protein diet expressed less IRF1 in the inflamed synovium and consequently developed reduced clinical and histologic signs of arthritis. CONCLUSION: AA deprivation reduces the severity of arthritis by suppressing the expression of IRF1-STAT1-driven chemokines, which are crucial for leukocyte recruitment to the arthritic joint. Overall, our study provides novel insights into critical determinants of inflammatory arthritis and may pave the way for dietary intervention trials in RA.

Histopathological correlation supports the use of x-rays in the diagnosis of hand osteoarthritis.

OBJECTIVE: To correlate histopathological and radiographic features of distal and proximal interphalangeal (DIP and PIP) joints in order to test whether the use of an x-ray examination would be beneficial to the classification/diagnosis process of hand osteoarthritis (OA). METHODS: DIP and PIP joints were obtained from post mortem specimens (n=40). Plain x-rays of the DIP and PIP joints were taken and radiographic OA was determined by the Kellgren and Lawrence classification. Individual radiographic features were scored according to the method described by Altman. Joint samples were prepared for histological analysis; cartilage damage was graded according to the Mankin scoring system. Spearman's correlation was applied to examine the relationship between histological and radiographical changes. Differences between groups (bony swelling vs no bony swelling) were determined by Student t test. RESULTS: A highly significant correlation was found between histological (Mankin score) and radiographic (Kellgren/Lawrence score) changes in the investigated DIP (r(s)=0.87, p<0.0001) and PIP (r(s)=0.79, p<0.0001) joints. A subgroup of patients (37.5% for DIP and 18.8% for PIP joints) showed advanced radiographic changes (Kellgren/Lawrence score ≥2) in joints without clinical bony swelling. Histologically, the mean Mankin scores accounted for 11±1.66 for DIP and 9.67±2.4 for PIP joints. CONCLUSION: On the basis of histopathological changes of DIP and PIP joints, this investigation demonstrates the validity of x-ray examinations and supports the use of plain radiography in the diagnosis of hand OA and in the classification of hand OA in clinical trials.