The 2020 Pediatric Rheumatology Symposium, originally scheduled for April 29 – May 2, was postponed due to COVID-19; therefore, abstracts were not presented as scheduled.
Session Type: Poster Breakout Session
Session Time: 5:10PM-5:40PM
Background/Purpose: MYD88 is a critical adaptor protein that connects Toll-like and IL-1 receptor signaling to activation of NF-kB. We previously reported a heterozygous de novo mutation in MYD88 (S222R) in a female pediatric patient with progressively deforming arthritis. To further investigate the contribution of MYD88 to arthritis pathogenesis, we created a novel Myd88 gene-edited (S209R ortholog) mouse using CRISPR/Cas.
Methods: In an attempt to elicit an arthritic phenotype, wild-type (WT), Myd88S209R/WT (S209R+/-), and Myd88S209R/S209R (S209R+/+) C57BL/6 mice were acutely stimulated with LPS or repeated CpG injections. We induced arthritis with collagen (CIA) in the mice to assess whether Myd88-S209R could drive differences in incidence, duration, or severity of arthritic phenotype. Arthritis was assessed via clinical scoring, caliper measurements of limb swelling, H&E staining of limb sections, and measurement of anti-collagen antibody production. Since CIA is a Th17 dependent model, draining lymph node IL-17+ and IFN-g+ T cells were measured during peak arthritis using flow cytometry. Serum IFN-g was measured by ELISA. To test the effect of Myd88-S209R on IFN-g production, which is protective in the CIA model, non-immunized splenic NK cells were stimulated ex vivo with IL-12, IL-18, or IL-12+IL-18. To bypass the role of MYD88 in collagen-antibody production, we induced arthritis with anti-collagen antibodies (CAIA) in WT, S209R+/-, and S209R+/+ mice and assessed arthritis severity as above.
Results: Myd88-S209R+ mice did not develop a spontaneous arthritic phenotype, nor with acute TLR stimulation. CIA was achievable in 83% of S209R+/+ mice, 59% of S209R+/-, and 54% of WT mice. Interestingly, this difference in incidence is sex dependent; 100% of female S209R+/+ mice developed arthritis, whereas male S209R+/+ incidence did not differ from WT. S209R+/+ mice experienced significantly worsened clinical scores, histological scores, and increased number of affected limbs relative to WT mice, and these differences were most pronounced in female mice. Serum IFN-g was nearly undetectable in all S209R+/+ mice at peak arthritis. Furthermore, S209R+/+ mice showed a deficit in IFN-g production in draining lymph node CD8+ T cells. This impaired IFN-g production was also observed in stimulated ex vivo splenic NK cells of non-immunized S209R+/+ mice. While all mice in the CAIA model developed arthritis, it persisted longer in mutant mice than in WT. Data from these experiments indicate enhancement of both the lymphocyte-dependent production of antibodies, likely influenced by lack of IFN-g, and their downstream pathogenic effects.
Conclusion: The Myd88-S209R mutation impacts the CAIA and CIA models by increasing the incidence, severity, and duration of the arthritic phenotype, likely due to a defect in IFN-g production. Recapitulating the sex bias of juvenile idiopathic arthritis, female Myd88-S209R develop a higher incidence and severity compared to males. This is the first description of a mouse model harboring the Myd88-S209R mutation, which will allow for further investigation of the mechanism(s) by which innate and adaptive immune activation through MYD88 contributes to the complex phenotype of arthritis.
To cite this abstract in AMA style:Bakshi S, Waschmann M, Lindstedt A, Rominger E, Colbert R, Sikora K. MyD88 S209R-Mediated Immune Dysregulation in Mouse Models of Arthritis [abstract]. Arthritis Rheumatol. 2020; 72 (suppl 4). https://acrabstracts.org/abstract/myd88-s209r-mediated-immune-dysregulation-in-mouse-models-of-arthritis/. Accessed October 23, 2020.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/myd88-s209r-mediated-immune-dysregulation-in-mouse-models-of-arthritis/