Acute murine antigen-induced arthritis is not affected by disruption of osteoblastic glucocorticoid signalling

Transgenic disruption of endogenous glucocorticoid signaling in osteoblasts does not alter long-term K/BxN serum transfer-induced arthritis

BACKGROUND

Disruption of glucocorticoid (GC) signaling in osteoblasts results in a marked attenuation of acute antibody-induced arthritis. The role of endogenous GCs in chronic inflammatory arthritis is however not fully understood. Here, we investigated the impact of endogenous GC signaling in osteoblasts on inflammation and bone integrity under chronic inflammatory arthritis by inactivating osteoblastic GC signaling in a long-term K/BxN serum transfer-induced induced arthritis (STIA) model.

METHODS

Intracellular GC signaling in osteoblasts was disrupted by transgenic (tg) overexpression of 11beta-hydroxysteroid dehydrogenase type 2 (11ß-HSD2). Inflammatory arthritis was induced in 5-week-old male tg mice and their wild type (WT) littermates by intraperitoneal (i.p.) injection of K/BxN serum while controls (CTRLs) received phosphate-buffered saline (PBS). In a first cohort, K/BxN STIA was allowed to abate until  the endpoint of 42 days (STIA). To mimic rheumatic flares, a second cohort was additionally injected on days 14 and 28 with K/BxN serum (STIA boost). Arthritis severity was assessed daily by clinical scoring and ankle size measurements. Ankle joints were assessed histopathologically. Systemic effects of inflammation on long bone metabolism were analyzed in proximal tibiae by micro-computed tomography (μCT) and histomorphometry.

RESULTS

Acute arthritis developed in both tg and WT mice (STIA and STIA boost) and peaked around day 8. While WT STIA and tg STIA mice showed a steady decline of inflammation until day 42, WT STIA boost and tg STIA boost mice exhibited an arthritic phenotype over a period of 42 days. Clinical arthritis severity did not differ significantly between WT and tg mice, neither in the STIA nor in the STIA boost cohorts. Correspondingly, histological indices of inflammation, cartilage damage, and bone erosion showed no significant difference between WT and tg mice on day 42. Histomorphometry revealed an increased bone turnover in tg CTRL and tg STIA boost compared to WT CTRL and WT STIA boost animals, respectively.

CONCLUSIONS

In contrast to the previously reported modulating effects of endogenous GC signaling in osteoblasts during acute K/BxN STIA, this effect seems to perish during the chronic inflammatory and resolution phase. These findings indicate that endogenous GC signaling in osteoblasts may mainly be relevant during acute and subacute inflammatory processes.

Standardized protocol and outcome measurements for the collagen antibody-induced arthritis mouse model

The murine collagen antibody-induced arthritis (CAIA) model resembles various features of human rheumatoid arthritis and is based on the intraperitoneal or intravenous injection of autoantibodies against type II collagen. Here, we present a standardized protocol for the intraperitoneal injection of arthritis-inducing autoantibodies in mice, followed by a description of daily arthritis assessments. We then detail the steps to harvest joint and bone tissues for histological, radiological, and molecular analyses. We highlight animal welfare and 3^R considerations for experimental arthritis studies. For complete details on the use and execution of this protocol, please refer to Maleitzke et al. (2021, 2022).

Arthritis and the role of endogenous glucocorticoids

Rheumatoid arthritis and osteoarthritis, the most common forms of arthritis, are chronic, painful, and disabling conditions. Although both diseases differ in etiology, they manifest in progressive joint destruction characterized by pathological changes in the articular cartilage, bone, and synovium. While the potent anti-inflammatory properties of therapeutic (i.e., exogenous) glucocorticoids have been heavily researched and are widely used in clinical practice, the role of endogenous glucocorticoids in arthritis susceptibility and disease progression remains poorly understood. Current evidence from mouse models suggests that local endogenous glucocorticoid signaling is upregulated by the pro-inflammatory microenvironment in rheumatoid arthritis and by aging-related mechanisms in osteoarthritis. Furthermore, these models indicate that endogenous glucocorticoid signaling in macrophages, mast cells, and chondrocytes has anti-inflammatory effects, while signaling in fibroblast-like synoviocytes, myocytes, osteoblasts, and osteocytes has pro-inflammatory actions in rheumatoid arthritis. Conversely, in osteoarthritis, endogenous glucocorticoid signaling in both osteoblasts and chondrocytes has destructive actions. Together these studies provide insights into the role of endogenous glucocorticoids in the pathogenesis of both inflammatory and degenerative joint disease.

Endogenous glucocorticoid signaling in chondrocytes attenuates joint inflammation and damage

Previous studies demonstrated that endogenous glucocorticoid signaling in osteoblasts promotes inflammation in murine immune arthritis. The current study determined whether disruption of endogenous glucocorticoid signaling in chondrocytes also modulates the course and severity of arthritis. Tamoxifen-inducible chondrocyte-targeted glucocorticoid receptor-knockout (chGRKO) mice were generated by breeding GR^flox/flox mice with tamoxifen-inducible collagen 2a1 Cre (Col2a1-CreER^T2) mice. Antigen-induced arthritis (AIA) and K/BxN serum transfer-induced arthritis (STIA) were induced in both chGRKO mice and their Cre-negative GR^flox/flox littermates [wild type (WT)]. Arthritis was assessed by measurement of joint swelling and histology of joints collected at d 14. Neutrophil activity and gene expression patterns associated with cartilage damage were also evaluated. In both arthritis models clinical (joint swelling) and histologic indices of inflammatory activity were significantly greater in chGRKO than in WT mice. The STIA model was characterized by early up-regulation of CXCR2/CXCR2 ligand gene expression in ankle tissues, and significant and selective expansion of splenic CXCR2⁺ neutrophils in chGRKO arthritic compared to WT arthritic mice. At later stages, gene expression of enzymes involved in cartilage degradation was up-regulated in chGRKO but not WT arthritic mice. Therefore, we summarize that chondrocytes actively mitigate local joint inflammation, cartilage degradation and systemic neutrophil activity via a glucocorticoid-dependent pathway.-Tu, J., Stoner, S., Fromm, P. D., Wang, T., Chen, D., Tuckermann, J., Cooper, M. S., Seibel, M. J., Zhou, H. Endogenous glucocorticoid signaling in chondrocytes attenuates joint inflammation and damage.

Preventive effects of Polygonum multiflorum on glucocorticoid-induced osteoporosis in rats

In Traditional Chinese Medicine, Polygonum multiflorum (PM) is known for its anti-aging properties. A previous study by our group showed that extracts of PM were able to prevent and treat bone loss in vivo, and the active components emodin and 2,3,5,4,-tetrahydroxystilbene-2-O-β-glucoside (TSG) promoted the osteogenic differentiation of mesenchymal stem cells in vitro. The aim of the present study was to investigate the preventive effects of PM on glucocorticoid-induced osteoporosis (GIO) in rats. A crude extract of PM was prepared with 75% ethanol, purified and enriched using a D-101 macroresin column and elution with 30% ethanol, and the material obtained was assessed by high-performance liquid chromatography. Male or female Sprague Dawley rats (n=180) were randomly divided into nine groups: Control, prednisone, prednisone plus calcitriol (CAL), prednisone plus 30% ethanolic eluate of PM [high (H), medium (M) and low (L) dose] and prednisone plus crude extract of PM (H, M and L dose). Prednisone was orally administered to the osteoporosis model rats for 21 weeks, alongside which they received PM extracts. The weight of the viscera, anterior tibial muscle and other tissues was recorded at the end of the experiment. The femur and lumbar vertebra were collected for the measurement of three-dimensional microarchitecture by micro-computed tomography scanning, assessment of biomechanical properties and determination of bone mineral density (BMD). In the 30% ethanolic eluate of the PM extract, the content of TSG and combined anthraquinone was 9.20 and 0.15%, respectively, and that in the crude extract of PM was 2.23 and 0.03%, respectively. Over 6 weeks, the weight of the rats the in prednisone group decreased (P<0.05), while the weight of rats treated with M and H doses of 30% ethanolic eluate was increased compared with that in the prednisone group (P<0.05). Rats exposed to prednisone exhibited a deteriorated bone microarchitecture, low BMD, decreased bone volume/total volume and poor biomechanical properties. Furthermore, the weight of the adrenal gland and the anterior tibial muscle was decreased. 30% ethanolic eluate of PM at M and L doses and crude extract of PM at the H dose counteracted the alterations of skeletal and other characteristics induced by prednisone in rats, as did CAL. In conclusion, extracts of PM exerted a protective effect on bone tissue in GIO rats.

Secondary osteoporosis in collagen-induced arthritis rats

Numerous studies have demonstrated that rheumatoid arthritis (RA) is often associated with bone loss; however, few experiments have focused on cancellous and cortical bone changes in rats during the process of arthritis. We have investigated bone changes in rats with collagen-induced arthritis (CIA) and have explored the characteristics of how RA induces osteoporosis by means of bone histomorphometry, bone biomechanics studies, bone mineral density studies, micro computer tomography, enzyme-linked immunosorbant assay, immunohistochemistry, and Western blot analysis. Bone mineral density of the femur and lumbar vertebrae and biomechanical properties of the femur were decreased in CIA rats. Trabecular bone volume of the tibia and lumbar vertebrae was decreased whereas bone resorption was increased in CIA rats. Bone formation of the tibial shaft in periosteal surfaces was decreased in CIA rats. Furthermore, the trabecular bone loss in CIA rats was severer at 16 weeks than at 8 weeks, as was cortical bone loss. The serum level of tumor necrosis factor α in CIA rats was increased, and the expression of dickkopf 1 and that of receptor activator of nuclear factor κB (RANKL) ligand (RANKL) in the ankle joints were also increased, but the expression of osteoprotegerin (OPG) was decreased. We conclude that CIA rats developed systemic osteoporosis, and that osteoporosis became more serious with CIA development. The mechanism may be related to the increase of bone resorption in cancellous bone cause by upregulation of the expression of DKK-1 and regulation of the RANKL/RANK/OPG signaling pathway, and the decrease of bone formation in cortical bone caused by an increase in the expression of DKK-1.

Mouse Osteoblasts Play a Crucial Role in the Immune System

This commentary highlights the article by Tu et al describing mechanisms in immune-mediated arthritis that may propel strategies to treat diseases involving the bone and immune system.