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

Abstract

Background: The role of endogenous glucocorticoids (GC) in the initiation and maintenance of rheumatoid arthritis (RA) remains unclear. We demonstrated previously that disruption of GC signalling in osteoblasts results in a profound attenuation of K/BxN serum-induced arthritis, a mouse model of RA. To determine whether or not the modulation of the inflammatory response by osteoblasts involves T cells, we studied the effects of disrupted osteoblastic GC-signalling in the T cell-dependent model of antigen-induced arthritis (AIA).

Methods: Acute arthritis was induced in pre-immunised 11-week-old male 11β-hydroxysteroid dehydrogenase type 2 transgenic (tg) mice and their wild-type (WT) littermates by intra-articular injection of methylated bovine serum albumine (mBSA) into one knee joint. Knee diameter was measured every 1-2 days until euthanasia on day 14 post injection. In a separate experiment, arthritis was maintained for 28 days by weekly reinjections of mBSA. Tissues were analysed by histology, histomorphometry and microfocal-computed tomography. Serum cytokines levels were determined by multiplex suspension array.

Results: In both short and long term experiments, arthritis developed in tg and WT mice with no significant difference between both groups. Histological indices of inflammation, cartilage damage and bone erosion were similar in tg and WT mice. Bone volume and turnover at the contralateral tibia and systemic cytokine levels were not different.

Conclusions: Acute murine AIA is not affected by a disruption in osteoblastic GC signalling. These data indicate that osteoblasts do not modulate the T cell-mediated inflammatory response via a GC-dependent pathway.

Figure 1

Clinical assessment of inflammation in arthritic mice injected with mBSA and non-arthritic control mice. Arthritic mice were injected with mBSA on day 0 (AIA) and control mice were injected with phosphate buffered saline (CTR). (A) Means and SEM for knee joint swelling from day 1 to day 14 post intra-articular injection. Knee diameter was measured every 1–2 days and knee joint swelling was calculated as the difference to the knee diameter at day 0 (before arthritis induction) for each day. A repeated-measures analysis was performed (see Materials and Methods); the P_AIA value indicates the significance of the difference in variation of knee joint swelling over time between wild-type (WT) and transgenic (TG) mice treated with mBSA. (B) Means and SEM for knee joint swelling from day 1 to day 28, post intra-articular injection and three flare-up reactions induced by intravenous mBSA injections on days 7, 14, 21 (arrows). Knee diameter was measured every 1–2 days. The P_AIA value represents the significance derived by repeated-measures analysis between WT AIA mice and transgenic AIA mice.

Figure 2

Arthritis and cartilage damage in the knee joint 14 days post intra-articular injection. (A-F) Representative histologic sections of knee joints from wild-type (WT) and transgenic mice (TG) treated with mBSA (AIA) and from non-arthritic wild-type control mice (CTR). Both inflammatory activity and cartilage damage were similar in transgenic mice and wild-type mice treated with mBSA. (A–C) Hematoxylin and eosin staining. Arrows show synovitis, joint space exudate and soft tissue inflammation. Bars = 100 μm. (D–F) Toluidine blue staining. Arrows show proteoglycan loss of articular cartilage. Bars = 100 μm. (G-H) Histopathology scores (G single, H total) in mBSA-treated mice (AIA) 14 days post injection. The knee joints of all mice were assessed as described in Materials and Methods. Bars show the mean ± SEM. Findings in arthritic wild-type AIA mice and arthritic transgenic AIA mice for single scores were compared by Mann–Whitney test. Total scores were compared between the 4 groups with adjustment for 4 parallel tests (α* = 0.0125). NS = not significant (see Figure 1 for other definitions).

Figure 3

Micro-CT and histomorphometric analysis of the contralateral proximal tibia 14 days post injection of mBSA. Bone turnover was measured at a location distant to the site of active inflammation to assess the systemic effects of joint inflammation. (A) Micro-CT. The bone volume fraction (bone volume/tissue volume (BV/TV]), trabecular number (Tb.N), trabecular separation (Tb.Sp), and trabecular thickness (Tb.Th) are shown for bones harvested. Bars show the mean ± SEM. Findings between the 4 groups were compared using the Mann–Whitney-Test with adjustment for 4 parallel tests (α* = 0.0125). NS = not significant (see Figure 1 for other definitions). (B) Histomorphometric quantification. Bone resorption, shown as osteoclast surface/bone surface (Oc.S/BS) and osteoclast number/bone surface (N.Oc/BS), respectively. Bone formation, shown as osteoblast surface/bone surface (Ob.S/BS). Bars show the mean ± SEM. Findings between the 4 groups were compared by using the Mann–Whitney test with adjustment for 4 parallel tests (α* = 0.0125). NS = not significant (see Figure 1 for other definitions).

Figure 4

Arthritis and cartilage damage in the knee joint on day 28 of prolonged arthritis. Mice received intra-articular injection on day 0 and three repeated intravenous boosts with antigen or PBS on days 7, 14, 21. (A–F) Representative histologic sections of knee joints from wild-type (WT) and transgenic (TG) mice treated with mBSA (AIA) and from non-arthritic wild-type control mice (CTR). Both inflammatory activity and cartilage damage were similar in TG and WT mice. (A–C) Haematoxylin and eosin staining. Arrows show synovitis and soft tissue inflammation. Bars = 100 μm. (D–F) Toluidine blue staining. Arrows show proteoglycan loss of articular cartilage. Bars = 100 μm. (G-H) Histopathology scores (G single, H total) in mBSA treated mice (AIA) on day 28 post intra-articular injection and three flare-up reactions. The knee joints of all mice were assessed as described in Materials and Methods. Bars show the mean ± SEM. Findings in arthritic wild-type and transgenic mice for single scores were compared by Mann–Whitney test. Total scores were compared between the 4 groups with adjustment for 4 parallel tests (α* = 0.0125). NS = not significant.