186 TH9 cells depend on cystine uptake and PPAR-γ signaling to prevent unchecked lipid ROS and cell death

Abstract

TH9 cells, also known as pathogenic TH2 cells, are a subset of proinflammatory effector TH cells characterized by high levels of IL-9 expression. They share many properties with conventional TH2 cells but are distinguished by their expression of the transcription factor PPAR-γ, on which they depend for full effector function. PPAR-γ is best known for its role in controlling lipid and glucose metabolism but is increasingly implicated in type 2 inflammation. However, the role of PPAR-γ in TH9 cells remains unclear. Transcriptional profiling of human TH9 cells in presence or absence of the PPAR-γ inhibitor, GW9662, showed strong upregulation of genes involved in cystine transport and redox control of lipid peroxidation. One of the top upregulated genes was SLC7A11, which encodes a cystine/glutamate transporter. Interestingly, we found that the chemical inhibition of SLC7A11 by erastin and cystine starvation in cystine free medium leads to an increase in lipid ROS levels and cell death in TH9 cells but not in conventional TH2 cells. Moreover, PPAR-γ inhibition promotes a further increase in lipid ROS and cell death upon erastin treatment only in TH9 cells, and this effect was not associated with augmented cellular ROS or mitochondrial ROS. Importantly, the anti-oxidant N-acetylcysteine completely rescued the effect of erastin, alone or in combination with GW9662. Erastin and/or GW9662 were also able to selectively deplete the CCR8+CRTh2+ effector memory T cells isolated from allergic contact dermatitis skin biopsies, which share phenotypic and functional features with TH9 cells. These preliminary data suggest that PPAR-y plays a role in protecting pathogenic TH2 cells from unchecked lipid ROS and consecutive cell death. Our findings open up new therapeutic avenues to selectively target pathogenic TH2 cells in the treatment of allergic diseases by leveraging their particular dependency on cystine to prevent cell death from unchecked lipid ROS.