Background/Purpose: Genome-wide association studies have linked polymorphisms in the PTPN2 locus to rheumatoid arthritis (RA). PTPN2 encodes the tyrosine phosphatase TC-PTP, an important regulator of cytokine signaling. Disease-associated variants of PTPN2 result in a partial loss of expression. To model the functional genetics of PTPN2 in mice, we studied the effect of PTPN2 haploinsufficiency in the SKG mouse, a spontaneous CD4⁺ T-cell-driven model of autoimmune arthritis.

Methods: Development of spontaneous and/or mannan-induced arthritis was evaluated in SKG mice. CD4⁺ T-cells isolated from SKG mice were transferred to RAG2^-/- mice. Clinical scoring of arthritis was followed by histological and micro-CT analysis. Flow cytometry was used to assess T-cell development and T-cell effector populations. Gene expression was analyzed using qPCR. Statistical differences were calculated using the Mann-Whitney or un-paired T tests.

Results: Haploinsufficiency of PTPN2 caused increased severity of spontaneous (P=0.003) and mannan-induced (P=0.007) arthritis in SKG mice, with high expression of TNF (P=0.056), IL-1b (P=0.020), IL-6 (P=0.026) and RANKL (P=0.007) in arthritic joints. PTPN2^+/- mice showed an increased presence of ectopic lymphoid-like structures within arthritic joints, correlating with an increased expression of Cxcl13 (P=0.035). Increased susceptibility to arthritis could be transferred to RAG2^-/- mice by PTPN2^+/- CD4⁺ T-cells (P=0.011 vs PTPN2^+/+ CD4⁺ T-cells). Next we generated a novel C57BL/6 mouse carrying the SKG mutation and the H2^d haplotype (B6.H2^d.SKG), which showed similar arthritis development as BALB/c SKG mice. B6.H2^d.SKG carrying T-cell specific haploinsufficiency of PTPN2 (Lck-Cre⁺.PTPN2^{floxed/wild type}) developed increased severity of arthritis (P=0.002) when compared to WT mice. Further investigation into the effect of PTPN2 haploinsufficiency in T-cell function revealed no alterations in thymocyte development or selection; however, PTPN2^+/- SKG mice had an increased accumulation of Th17 cells (P=0.027) in arthritic joints which correlated to an increased sensitivity to IL-6 stimulation in PTPN2^+/- CD4+ T-cells.

Conclusion: Haploinsufficiency of human RA-associated PTPN2 mediates autoimmune arthritis in mice by rendering CD4⁺ T-cells more susceptible to IL-6 stimulation and promoting expansion of pathogenic Th17 cells in arthritic joints. We validate our newly generated B6.H2^d.SKG model as a novel powerful tool for mechanistic studies of RA pathogenesis.

« Back to 2016 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/functional-genetics-of-ptpn2-in-rheumatoid-arthritis-haploinsufficiency-of-ptpn2-promotes-severity-of-th17-cell-mediated-autoimmune-arthritis/