Dual Specificity Phosphatase 6 (DUSP6) regulates T cell responses and experimental colitis in mice

Dual specificity phosphatases (DUSPs) are a family of protein tyrosine phosphatases, many of which specifically dephosphorylate threonine and tyrosine residues on mitogen activated protein kinases (MAPKs) rendering them inactive. DUSP6, which preferentially dephosphorylates ERK1/2, has been shown to negatively regulate Th1-associated cytokine production (Gonzalez-Navajas et al., 2010). In addition to DUSP6, other DUSPs are also expressed on CD4+ T cells (e.g. DUSP1), but the role of this family of phosphatases in T cell responses and intestinal homeostasis remains unclear. In this project we aim to study the molecular mechanisms behind the TLR-dependent regulation of DUSP6 on CD4+ T cells and its influence in T cell differentiation and function. Furthermore, we aim to study the contribution of this phosphatase in T cell-mediated intestinal inflammation. We found that DUSP6 expression is upregulated in response to both TCRand TLR-dependent activation in CD4+ T cells. After TCR activation, CD4 T cells isolated from Dusp6−/− mice produced higher levels of the inflammatory cytokines IL-6 and IFNγ, but lower levels of IL-17, in comparison with CD4+ T cells from wild type (WT) mice. In addition, Dusp6−/− T cells showed increased levels of ERK1/2 and p38 phosphorylation, but not JNK. In line with the cytokine production, we found that in vitro Th1 polarization is enhanced while Th17 polarization is impaired in Dusp6−/− naïve CD4+ T cells compared to WT T cells (measured by intracellular cytokine staining and ELISA). Next, we evaluated the role of DUSP6 during chronic inflammation. Since Il10−/− mice develop spontaneous intestinal inflammation between 16 and 20 weeks of age, we examined the effect of DUSP6 deficiency on colitis in Il10−/− mice. Interestingly, Il10−/−/Dusp6−/− mice developed severe intestinal inflammation at the early age of 6 to 8 weeks. Histological evaluation of the colons showed that Il10−/−/Dusp6−/− mice have a high degree of epithelial hyperplasia and cellular infiltration. Consistent with the in vivo phenotype, we found that colonic explants from Il10−/−/Dusp6−/− mice produced elevated levels of the inflammatory cytokines IFNγ, TNFα, IL-6 and IL-2, but lower levels of IL-17, when compared to Il10−/− mice. In addition, MLN-derived CD4+ T cells from Il10−/−/Dusp6−/− mice also produced higher levels of IFNγ and lower levels of IL-17 in response to TCR activation compared to Il10−/− CD4 T cells. Moreover, TCR-dependent activation of Il10−/−/Dusp6−/− CD4 T cells resulted in increased phosphorylation of ERK1/2 and IκBα degradation. In contrast, p38 activation remained unaffected by the DUSP6 deficiency Our data indicates that DUSP6 deficiency affects CD4 T cell differentiation and inflammatory profile. In vitro, Dusp6−/− T cells have a greater propensity to differentiate along the Th1 axis while a smaller propensity to differentiate along the Th17 axis. In vivo, mice lacking DUSP6 develop exacerbated Th1-mediated colitis.