Protein phosphatase 6 (Pp6) is crucial for regulatory T cell function and stability in autoimmunity

Regulatory T (T-reg) cells constitute a dynamic population that is critical in autoimmunity. T-reg cell therapies for autoimmune diseases are mainly focused on enhancing their suppressive activities. However, recent studies demonstrated that certain inflammatory conditions induce T-reg cell instability with diminished FoxP3 expression and convert them into pathogenic effector cells. Therefore, the identification of novel targets crucial to both T-reg cell function and plasticity is of vital importance to the development of therapeutic approaches in autoimmunity. In this study, we found that conditional Pp6 knockout (cKO) in T-reg cells led to spontaneous autoinflammation, immune cell activation, and diminished levels of FoxP3 in CD4(+) T cells in mice. Loss of Pp6 in T-reg cells exacerbated two classical mouse models of T-reg-related autoinflammation. Mechanistically, Pp6 deficiency increased CpG motif methylation of the FoxP3 locus by dephosphorylating Dnmt1 and enhancing Akt phosphorylation at Ser473/Thr308, leading to impaired FoxP3 expression in T-reg cells. In summary, our study proposes Pp6 as a critical positive regulator of FoxP3 that acts by decreasing DNA methylation of the FoxP3 gene enhancer and inhibiting Akt signaling, thus maintaining T-reg cell stability and preventing autoimmune diseases. Copyright (C) 2021, Chongqing Medical University. Production and hosting by Elsevier B.V.

Automated summary

Our study reveals that loss of Pp6 in T-reg cells leads to spontaneous autoinflammation and decreased FoxP3 levels, exacerbating T-reg-related autoinflammation in mice. Mechanistically, Pp6 deficiency affects DNA methylation and Akt signaling, resulting in impaired FoxP3 expression in T-reg cells.