Structural, cellular, and molecular evaluation of bone erosion in experimental models of rheumatoid arthritis: Assessment by μCT, histology, and serum biomarkers

In Vivo Longitudinal Monitoring of Disease Progression in Inflammatory Arthritis Animal Models Using Raman Spectroscopy

Current techniques for monitoring disease progression and testing drug efficacy in animal models of inflammatory arthritis are either destructive, time-consuming, subjective, or require ionizing radiation. To accommodate this, we have developed a non-invasive and label-free optical system based on Raman spectroscopy for monitoring tissue alterations in rodent models of arthritis at the biomolecular level. To test different sampling geometries, the system was designed to collect both transmission and reflection mode spectra. Mice with collagen antibody-induced arthritis and controls were subject to in vivo Raman spectroscopy at the tibiotarsal joint every 3 days for 14 days. Raman-derived measures of bone content correlated well with micro-computed tomography bone mineral densities. This allowed for time-resolved quantitation of bone densities, which indicated gradual bone erosion in mice with arthritis. Inflammatory pannus formation, bone erosion, and bone marrow inflammation were confirmed by histological analysis. In addition, using library-based spectral decomposition, we quantified the progression of bone and soft tissue components. In general, the tissue components followed significantly different tendencies in mice developing arthritis compared to the control group in line with the histological analysis. In total, this demonstrates Raman spectroscopy as a versatile technique for monitoring alterations to both mineralized and soft tissues simultaneously in rodent models of musculoskeletal disorders. Furthermore, the technique presented herein allows for objective repeated within-animal measurements potentially refining and reducing the use of animals in research while improving the development of novel antiarthritic therapeutics.

Effects of Mild and Moderate Monoclonal Antibody Dose on Inflammation, Bone Loss, and Activation of the Central Nervous System in a Female Collagen Antibody-induced Arthritis Mouse Model

Induction of severe inflammatory arthritis in the collagen antibody-induced arthritis (CAIA) murine model causes extensive joint damage and pain-like behavior compromising analysis. While mild models are less severe, their reduced, variable penetrance makes assessment of treatment efficacy difficult. This study aimed to compare macroscopic and microscopic changes in the paws, along with central nervous system activation between a mild and moderate CAIA model. Balb/c mice (n=18) were allocated to control, mild, and moderate CAIA groups. Paw inflammation, bone volume (BV), and paw volume (PV) were assessed. Histologically, the front paws were assessed for joint inflammation, cartilage damage, and pre/osteoclast-like cells and the lumbar spinal cord and the periaqueductal gray (PAG) region of the brain for glial reactivity. A moderate CAIA dose induced (1) significantly greater local paw inflammation, inflammatory cell infiltration, and PV; (2) significantly more osteoclast-like cells on the bone surface and within the surrounding soft tissue; and (3) significantly greater glial reactivity within the PAG compared with the mild CAIA model. These findings support the use of a moderate CAIA model (higher dose of monoclonal antibodies with low-dose lipopolysaccharide) to induce more consistent histopathological features, without excessive joint destruction.

Increased chemotaxis and activity of circulatory myeloid progenitor cells may contribute to enhanced osteoclastogenesis and bone loss in the C57BL/6 mouse model of collagen-induced arthritis

Our study aimed to determine the functional activity of different osteoclast progenitor (OCP) subpopulations and signals important for their migration to bone lesions, causing local and systemic bone resorption during the course of collagen-induced arthritis in C57BL/6 mice. Arthritis was induced with chicken type II collagen (CII), and assessed by clinical scoring and detection of anti-CII antibodies. We observed decreased trabecular bone volume of axial and appendicular skeleton by histomorphometry and micro-computed tomography as well as decreased bone formation and increased bone resorption rate in arthritic mice in vivo. In the affected joints, bone loss was accompanied with severe osteitis and bone marrow hypercellularity, coinciding with the areas of active osteoclasts and bone erosions. Flow cytometry analysis showed increased frequency of putative OCP cells (CD3^- B220^- NK1.1^- CD11b^-/lo CD117⁺ CD115⁺ for bone marrow and CD3^- B220^- NK1.1^- CD11b⁺ CD115⁺ Gr-1⁺ for peripheral haematopoietic tissues), which exhibited enhanced differentiation potential in vitro. Moreover, the total CD11b⁺ population was expanded in arthritic mice as well as CD11b⁺ F4/80⁺ macrophage, CD11b⁺ NK1.1⁺ natural killer cell and CD11b⁺ CD11c⁺ myeloid dendritic cell populations in both bone marrow and peripheral blood. In addition, arthritic mice had increased expression of tumour necrosis factor-α, interleukin-6, CC chemokine ligand-2 (Ccl2) and Ccl5, with increased migration and differentiation of circulatory OCPs in response to CCL2 and, particularly, CCL5 signals. Our study characterized the frequency and functional properties of OCPs under inflammatory conditions associated with arthritis, which may help to clarify crucial molecular signals provided by immune cells to mediate systemically enhanced osteoresorption.

PPARβ/δ directs the therapeutic potential of mesenchymal stem cells in arthritis

OBJECTIVES

To define how peroxisome proliferator-activated receptor (PPAR) β/δ expression level in mesenchymal stem cells (MSCs) could predict and direct both their immunosuppressive and therapeutic properties. PPARβ/δ interacts with factors such as nuclear factor-kappa B (NF-κB) and regulates the expression of molecules including vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1. Since these molecules are critical for MSC function, we investigated the role of PPARβ/δ on MSC immunosuppressive properties.

METHODS

We either treated human MSCs (hMSCs) with the irreversible PPARβ/δ antagonist (GSK3787) or derived MSCs from mice deficient for PPARβ/δ (PPARβ/δ^-/- MSCs). We used the collagen-induced arthritis (CIA) as model of immune-mediated disorder and the MSC-immune cell coculture assays.

RESULTS

Modulation of PPARβ/δ expression in hMSCs either using GSK3787 or hMSCs from different origin reveals that MSC immunosuppressive potential is inversely correlated with Ppard expression. This was consistent with the higher capacity of PPARβ/δ^-/- MSCs to inhibit both the proliferation of T lymphocytes, in vitro, and arthritic development and progression in CIA compared with PPARβ/δ^+/+ MSCs. When primed with proinflammatory cytokines to exhibit an immunoregulatory phenotype, PPARβ/δ^-/- MSCs expressed a higher level of mediators of MSC immunosuppression including VCAM-1, ICAM-1 and nitric oxide (NO) than PPARβ/δ^+/+ MSCs. The enhanced NO₂ production by PPARβ/δ^-/- MSCs was due to the increased retention of NF-κB p65 subunit on the κB elements of the inducible nitric oxide synthase promoter resulting from PPARβ/δ silencing.

CONCLUSIONS

Our study is the first to show that the inhibition or knockdown of PPARβ/δ in MSCs primes their immunoregulatory functions. Thus, the regulation of PPARβ/δ expression provides a new strategy to generate therapeutic MSCs with a stable regulatory phenotype.

The X-Linked Inhibitor of Apoptosis Protein Inhibitor Embelin Suppresses Inflammation and Bone Erosion in Collagen Antibody Induced Arthritis Mice

Objective. To investigate the effect of Embelin, an inhibitor of X-Linked Inhibitor of Apoptosis Protein (XIAP), on inflammation and bone erosion in a collagen antibody induced arthritis (CAIA) in mice. Methods. Four groups of mice (n = 6 per group) were allocated: CAIA untreated mice, CAIA treated with Prednisolone (10 mg/kg/day), CAIA treated with low dose Embelin (30 mg/kg/day), and CAIA treated with high dose Embelin (50 mg/kg/day). Joint inflammation was evaluated using clinical paw score and histological assessments. Bone erosion was assessed using micro-CT, tartrate resistant acid phosphatase (TRAP) staining, and serum carboxy-terminal collagen crosslinks (CTX-1) ELISA. Immunohistochemistry was used to detect XIAP protein. TUNEL was performed to identify apoptotic cells. Results. Low dose, but not high dose Embelin, suppressed inflammation as reflected by lower paw scores (P < 0.05) and lower histological scores for inflammation. Low dose Embelin reduced serum CTX-1 (P < 0.05) and demonstrated lower histological score and TRAP counting, and slightly higher bone volume as compared to CAIA untreated mice. XIAP expression was not reduced but TUNEL positive cells were more abundant in Embelin treated CAIA mice. Conclusion. Low dose Embelin suppressed inflammation and serum CTX-1 in CAIA mice, indicating a potential use for Embelin to treat pathological bone loss.

Quantifying not only bone loss, but also soft tissue swelling, in a murine inflammatory arthritis model using micro-computed tomography

In rodent models of inflammatory arthritis, bone erosion has been non-invasively assessed by micro-computed tomography (micro-CT). However, non-invasive assessments of paw swelling (oedema) are still based on clinical grading by visual evaluation, or measurements by callipers, not always reliable for the tiny mouse paws. The aim of this work was to demonstrate a novel straightforward 3D micro-CT analysis protocol capable of quantifying not only joint bone erosion, but also soft tissue swelling, from the same scans, in a rodent inflammatory arthritis model. Balb/c mice were divided into two groups: collagen antibody-induced arthritis (CAIA) and CAIA treated with prednisolone, the latter reflecting an established treatment in human rheumatoid arthritis. Clinical paw scores were recorded. On day 10, front paws were assessed by micro-CT and histology. Micro-CT measurements included paw volume (bone and soft tissue together) and bone volume at the radiocarpal joint, and bone volume from the radiocarpal to the metacarpophalangeal joint. Micro-CT analysis revealed significantly lower paw volume (−36%, P < 0.01) and higher bone volume (+17%, P < 0.05) in prednisolone-treated CAIA mice compared with untreated CAIA mice. Paw volume and bone volume assessed by micro-CT correlated significantly with clinical and histological scores (|r| > 0.5, P < 0.01). Untreated CAIA mice showed significantly higher clinical scores, higher inflammation levels histologically, cartilage and bone degradation, and pannus formation, compared with treated mice (P < 0.01). The presented novel micro-CT analysis protocol enables 3D-quantification of paw swelling at the micrometre level, along with the typically assessed bone erosion, using the same images/scans, without altering the scanning procedure or using contrast agents.

Autoimmunity in 2010

There is now growing evidence that autoimmunity is the common trait connecting multiple clinical phenotypes albeit differences in tissue specificity, pathogenetic mechanisms, and therapeutic approaches cannot be overlooked. Over the past years we witnessed a constant growth of the number of publications related to autoimmune diseases in peer-reviewed journals of the immunology area. Original data referred to factors from common injury pathways (i.e. T helper 17 cells, serum autoantibodies, or vitamin D) and specific diseases such as multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis. As an example, the issue of a latitudinal gradient in the prevalence and incidence rates has been proposed for all autoimmune diseases and was recently coined as geoepidemiology to suggest new environmental triggers for tolerance breakdown. The present article is aimed at reviewing the articles that were published over the past year in the major autoimmunity and immunology journals.

IL-23 is critical for induction of arthritis, osteoclast formation, and maintenance of bone mass

The role of IL-23 in the development of arthritis and bone metabolism was studied using systemic IL-23 exposure in adult mice via hydrodynamic delivery of IL-23 minicircle DNA in vivo and in mice genetically deficient in IL-23. Systemic IL-23 exposure induced chronic arthritis, severe bone loss, and myelopoiesis in the bone marrow and spleen, which resulted in increased osteoclast differentiation and systemic bone loss. The effect of IL-23 was partly dependent on CD4(+) T cells, IL-17A, and TNF, but could not be reproduced by overexpression of IL-17A in vivo. A key role in the IL-23-induced arthritis was made by the expansion and activity of myeloid cells. Bone marrow macrophages derived from IL-23p19(-/-) mice showed a slower maturation into osteoclasts with reduced tartrate-resistant acid phosphatase-positive cells and dentine resorption capacity in in vitro osteoclastogenesis assays. This correlated with fewer multinucleated osteoclast-like cells and more trabecular bone volume and number in 26-wk-old male IL-23p19(-/-) mice compared with control animals. Collectively, our data suggest that systemic IL-23 exposure induces the expansion of a myeloid lineage osteoclast precursor, and targeting IL-23 pathway may combat inflammation-driven bone destruction as observed in rheumatoid arthritis and other autoimmune arthritides.