Spontaneous arthritis and ankylosis in male DBA/1 mice: further evidence for a role of behavioral factors in "stress-induced arthritis"

Abstract

Background: Ageing male DBA/1 mice spontaneously develop arthritis in the hind paws. We and others have demonstrated that this model shares striking features with human spondyloarthritis, in particular entheseal involvement, progressive ankylosis but also dactylitis. Here, we report on our recent experience with this model highlighting how changes in the animal facility affect the development of the disease.

Findings: Ageing male DBA/1 mice from different litters were caged together (6 mice per cage) at the age of 10 weeks. The mice were checked twice a week for clinical signs of arthritis. Disease severity was assessed in further detail post-mortem by scoring for histomorphological characteristics. DBA/1 mice spontaneously develop macroscopically detectable arthritis, presenting as joint swelling or toe stiffness. Standard settings with open cages lead to an almost 100% incidence by the age of 26 weeks. The introduction of larger cages and filter tops reducing exposure to other cages dramatically affected incidence. Other negative factors include excess bedding material reducing the impact of walking and running. Switching back to the original conditions resulted again in a high incidence, further optimized by sensory exposure to female mice. We also showed that the related DBA/2 strain is sensitive to the disease.

Conclusions: Changing environmental factors in the housing conditions of DBA/1 mice severely affects the spontaneous development of arthritis. This points out that the model is very sensitive to external stress and sensory factors that are likely affecting the behavior of the male mice and that the model needs to be optimized in different situations.

Figure 1

Entheseal endochondral bone formation in male DBA/1 paws. (A) H&E staining of a DBA/1 hind paw showing new cartilage and bone formation which originates from the enthesis. In (B), Toluidine blue staining of chondrogenic differentiation which occurs on both the proximal and distal side of the joint, resulting in ankylosis and loss of function of the joint. A’ and B’ showing higher magnifications of boxed areas in A and B, respectively. Scale bars: 500 μm in A and B, 125 μm in A’ and B’.

Figure 2

Bone formation in the interphalangeal joint of male DBA/1 hind paw as assessed by X-ray micro-computed tomography (μCT). μCT imaging of the hindpaw forefeet of a 17 week old DBA/1 mouse shows new bone formation in the proximal interphalangeal joint of the 5th toe and late stage onychoperiostitis of the 4th toe. The mouse bones were visualized ex vivo using Skyscan 1172 μCT system and related SkyScan software (Kontich, Belgium). The scanning parameters were 5 μm pixel size, 50 kV, 200 uA, 0.5 mm Al filter. Data images acquired at multiple viewing angles were reconstructed to generate a full 3D representation of the hind paw.

Figure 3

Comparison of the development of spontaneous arthritis in male DBA/1 and DBA/2 mice. Cumulative incidence (A) and clinical severity (B) of arthritis in male DBA/1 and DBA/2 mice. (B) Data are shown as mean + SEM; n = 15 or 12 mice per group. (C) Representative microscopic image of late stage endochondral bone formation in an arthritic DBA/2 hind paw. C’ shows a higher magnification of boxed area in C. Scale bars: 500 μm in C, 125 μm in C’.

Figure 4

Changing housing conditions affects the development of spontaneous arthritis in DBA/1 mice. Cumulative incidence (A) and clinical severity (B) of arthritis in male DBA/1 mice before (black line) and after (dotted line) changing environmental factors in the animal facility. (B) Data are shown as mean + SEM; n = 32 in both groups until week 17; n = 23 and 12 from week 18 until end in the ‘after’ and ‘before’ group respectively).