Automated processing of series of micro-CT scans

For some applications of high-resolution X-ray Tomography (micro-CT) scanning, a large set of similar samples is to be analyzed in order to obtain statistically significant results. The complete process, including the micro-CT scan itself, the reconstruction and the analysis is almost identical for every sample. However, in a typical workflow every step is manually performed for every individual sample. This could be optimised by automation of this process, which results in less human intervention and thus a smaller cost and a lower risk to human error. We developed a reliable method to semi-automatically scan several stacked samples and automatically reconstruct the resulting series of data sets. The reconstruction step includes the manual reconstruction of one data set in order to optimize the reconstruction parameters, which can then be used for the rest of the batch. In future work, the automatic handling of the next step in the micro-CT workflow, 3D analysis, will also be improved

Running promotes chronicity of arthritis by local modulation of complement activators and impairing T regulatory feedback loops

Objectives: The mechanisms driving onset of joint inflammation in arthritides such as rheumatoid arthritis and spondyloarthritis and the conversion to disease chronicity are poorly understood. We hypothesised mechanostrain could play an instrumental role herein by engaging local and/or systemic pathways, thereby attenuating disease course and outcome. Methods: The development of collagen antibody-induced arthritis (CAIA) in C57BL/6 mice was evaluated both clinically and histologically under different loading regimens: control, voluntary running or hindpaw unloading. Bone surface porosity was quantified by high-resolution mu-CT. Gene expression analyses were conducted by microarrays and qPCR on microdissected entheses, murine and human synovial tissues (both normal and inflamed). Serum cytokines and chemokines were measured by ELISA. The influence of complement activation and T regulatory (Treg) cell function on the induction and resolution phase of disease was studied by respectively pharmacological modulation and conditional Treg depletion. Results: Voluntary running strongly impacts the course of arthritis by impairing the resolution phase of CAIA, leading to more persistent inflammation and bone surface porosity. Mechanical strain induced local complement activation, increased danger-associated molecular pattern expression, activating Fc gamma receptors as well as changes in fibroblast phenotype. Interestingly, complement C5a receptor blockade inhibited the enhanced joint pathology caused by voluntary running. Moreover, Treg depletion led to a loss of disease resolution in CAIA mice, which was not observed under voluntary running conditions. Conclusions: Running promotes onset and chronicity of arthritis by local upregulation of complement activators and hampering regulatory T cell feedback loops

Tendon and ligament mechanical loading in the pathogenesis of inflammatory arthritis

Mechanical loading is an important factor in the development of tendon and ligament disorders. In this Review, the authors discuss the evidence for the known role of mechanical loading in tendinopathy and its potential role in inflammatory arthritis. Mechanical loading is an important factor in musculoskeletal health and disease. Tendons and ligaments require physiological levels of mechanical loading to develop and maintain their tissue architecture, a process that is achieved at the cellular level through mechanotransduction-mediated fine tuning of the extracellular matrix by tendon and ligament stromal cells. Pathological levels of force represent a biological (mechanical) stress that elicits an immune system-mediated tissue repair pathway in tendons and ligaments. The biomechanics and mechanobiology of tendons and ligaments form the basis for understanding how such tissues sense and respond to mechanical force, and the anatomical extent of several mechanical stress-related disorders in tendons and ligaments overlaps with that of chronic inflammatory arthritis in joints. The role of mechanical stress in 'overuse' injuries, such as tendinopathy, has long been known, but mechanical stress is now also emerging as a possible trigger for some forms of chronic inflammatory arthritis, including spondyloarthritis and rheumatoid arthritis. Thus, seemingly diverse diseases of the musculoskeletal system might have similar mechanisms of immunopathogenesis owing to conserved responses to mechanical stress

Mechanical strain determines the site-specific direction of inflammation and tissue damage in arthritis

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The expression of virulence genes increases membrane permeability and sensitivity to envelope stress in Salmonella Typhimurium.

Virulence gene expression can represent a substantial fitness cost to pathogenic bacteria. In the model entero-pathogen Salmonella Typhimurium (S.Tm), such cost favors emergence of attenuated variants during infections that harbor mutations in transcriptional activators of virulence genes (e.g., hilD and hilC). Therefore, understanding the cost of virulence and how it relates to virulence regulation could allow the identification and modulation of ecological factors to drive the evolution of S.Tm toward attenuation. In this study, investigations of membrane status and stress resistance demonstrate that the wild-type (WT) expression level of virulence factors embedded in the envelope increases membrane permeability and sensitizes S.Tm to membrane stress. This is independent from a previously described growth defect associated with virulence gene expression in S.Tm. Pretreating the bacteria with sublethal stress inhibited virulence expression and increased stress resistance. This trade-off between virulence and stress resistance could explain the repression of virulence expression in response to harsh environments in S.Tm. Moreover, we show that virulence-associated stress sensitivity is a burden during infection in mice, contributing to the inherent instability of S.Tm virulence. As most bacterial pathogens critically rely on deploying virulence factors in their membrane, our findings could have a broad impact toward the development of antivirulence strategies

ELMO1 signaling is a promoter of osteoclast function and bone loss

Osteoporosis affects millions worldwide and is often caused by osteoclast induced bone loss. Here, we identify the cytoplasmic protein ELMO1 as an important 'signaling node' in osteoclasts. We note that ELMO1 SNPs associate with bone abnormalities in humans, and that ELMO1 deletion in mice reduces bone loss in four in vivo models: osteoprotegerin deficiency, ovariectomy, and two types of inflammatory arthritis. Our transcriptomic analyses coupled with CRISPR/Cas9 genetic deletion identify Elmo1 associated regulators of osteoclast function, including cathepsin G and myeloperoxidase. Further, we define the 'ELMO1 interactome' in osteoclasts via proteomics and reveal proteins required for bone degradation. ELMO1 also contributes to osteoclast sealing zone on bone-like surfaces and distribution of osteoclast-specific proteases. Finally, a 3D structure-based ELMO1 inhibitory peptide reduces bone resorption in wild type osteoclasts. Collectively, we identify ELMO1 as a signaling hub that regulates osteoclast function and bone loss, with relevance to osteoporosis and arthritis. Osteoporosis and bone fractures affect millions of patients worldwide and are often due to increased bone resorption. Here the authors identify the cytoplasmic protein ELMO1 as an important 'signaling node' promoting the bone resorption function of osteoclasts

Distinct immune modulatory roles of regulatory T cells in gut versus joint inflammation in TNF-driven spondyloarthritis

Objectives: Gut and joint inflammation commonly co-occur in spondyloarthritis (SpA) which strongly restricts therapeutic modalities. The immunobiology underlying differences between gut and joint immune regulation, however, is poorly understood. We therefore assessed the immunoregulatory role of CD4+FOXP3+ regulatory T (Treg) cells in a model of Crohn's-like ileitis and concomitant arthritis. Methods: RNA-sequencing and flow cytometry was performed on inflamed gut and joint samples and tissue-derived Tregs from tumour necrosis factor (TNF)∆ARE mice. In situ hybridisation of TNF and its receptors (TNFR) was applied to human SpA gut biopsies. Soluble TNFR (sTNFR) levels were measured in serum of mice and patients with SpA and controls. Treg function was explored by in vitro cocultures and in vivo by conditional Treg depletion. Results: Chronic TNF exposure induced several TNF superfamily (TNFSF) members (4-1BBL, TWEAK and TRAIL) in synovium and ileum in a site-specific manner. Elevated TNFR2 messenger RNA levels were noted in TNF∆ARE/+ mice leading to increased sTNFR2 release. Likewise, sTNFR2 levels were higher in patients with SpA with gut inflammation and distinct from inflammatory and healthy controls. Tregs accumulated at both gut and joints of TNF∆ARE mice, yet their TNFR2 expression and suppressive function was significantly lower in synovium versus ileum. In line herewith, synovial and intestinal Tregs displayed a distinct transcriptional profile with tissue-restricted TNFSF receptor and p38MAPK gene expression. Conclusions: These data point to profound differences in immune-regulation between Crohn's ileitis and peripheral arthritis. Whereas Tregs control ileitis they fail to dampen joint inflammation. Synovial resident Tregs are particularly maladapted to chronic TNF exposure