The transcription factor Nrf2 - modulation of Foxp3$^{+}$ regulatory T cells and implications in Juvenile Idiopathic Arthritis

Klemm, Patricia; Pradel, Gabriele (Thesis advisor); Tenbrock, Klaus (Thesis advisor); Fabry, Marlies (Thesis advisor); Zimmer-Bensch, Geraldine Marion (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Oxidative stress, defined as the imbalanced production of oxidizing species and antioxidants in favor of the first, is implicated in a wide range of diseases including autoimmunity, chronic inflammatory diseases as well as cancer. Antioxidant systems, that detoxify excess reactive species generated during oxidative stress, are tightly regulated. Nuclear factor erythroid 2-related factor (Nrf2) is the key transcription factor inducing the expression of genes involved in the antioxidant stress response. Nrf2 is constantly ubiquitinylated and degraded in the proteasome, a process that is directly controlled by the redox sensitive E3 ubiquitin ligase Kelch-like ECH-associated protein 1(Keap1). Under conditions of oxidative stress, Keap1 releases Nrf2, which subsequently translocates to the nucleus and induces the transcription of its target genes. T cells are confronted with oxidative stress in several diseases of chronic inflammation and autoimmunity and presumably also in Juvenile Idiopathic Arthritis (JIA), the most common rheumatic disease in children. Increased amounts of oxidized products as well as deficits in the antioxidant machinery have been described in JIA patients. Additionally, it is known that reactive oxygen species critically contribute to cartilage destruction in rheumatoid arthritis. Forkhead box P3 (Foxp3)-positive regulatory T cells (Tregs), which are essential in the suppression of exaggerated immune responses against self- or harmless antigens and are critically involved in immune homeostasis, seem unable to suppress the overactivated T cells in the affected joints of JIA patients. Currently, it is unclear, how oxidative stress and particularly Nrf2 signaling modulate Foxp3+ T cells under homeostatic conditions and inflammatory autoimmunity. In this thesis, it could be shown that activation of Nrf2 in Foxp3-expressing cells induces early postnatal lethality and elicits an inflammatory autoimmune response in Foxp3creKeapfl mice, with lymphocyte infiltrates in the lung, increased percentages of interferon γ (IFNγ) producing CD4+ T cells, effector and central memory T cells as well as activated B cells. Furthermore, Tregs of Foxp3creKeapfl mice show a lineage instability with decreased Foxp3 expression, altered proliferation and differentiation and metabolic changes including mammalian target of rapamycin (mTOR) pathway activation and increased glucose uptake. These effects are mostly reproducible in bone marrow (BM) chimaeras and thus point towards Treg cell-intrinsic mechanisms. Additionally, it was shown that synovial fluid (SF) of JIA patients increases oxidative stress in human CD4+ T cells and seems to dampen Nrf2. Furthermore, SF increased the percentages of Tregs, CD4+ T cell proliferation and altered CD4+ T cell metabolism. The data presented here uncover a so far underacknowledged negative role of Nrf2 for the stability and homeostasis of Foxp3+ regulatory T cells. Furthermore, the experiments with synovial fluid mononuclear cells (SFMCs) and SF of JIA patients point towards a dysregulated Nrf2 activation that might contribute to disease development or progression in JIA patients. As reactive species not only contribute to oxidative stress but also serve important signaling functions in T cells e.g. during T cell activation, the tight regulation of Nrf2 seems to be essential for the generation of appropriate immune responses.