A Novel Role for ZEB2 as a Lineage Fidelity Checkpoint in Human Cd4+ T Cells

Abstract

Autoimmune diseases are a broad range of more than eighty related disorders, affecting up to 5% of the population. The incidence of autoimmune disease is increasing worldwide. It is a disease where the body's immune system fails to recognize its own cells and tissues as “self”. Instead, immune cells attack these healthy cells and tissues as if they were foreign or invading pathogens. One of the key immune cell populations implicated in this immune attack is CD4+ T cells. The CD4+ T cell lineage consists of a number of phenotypically and functionally distinct subsets. In particular there are two functionally distinct compartments in CD4, namely T regulatory cells (Treg) and T conventional cells (Tconv), and the function of each is potentially altered in autoimmune disease. My PhD project has investigated the role of a transcription factor, ZEB2 in shaping the function of human CD4+ T cells. Little is known about the role of ZEB2 in CD4+ T cells and therefore elucidating its role in CD4+ T cells and identifying the transcriptional landscape controlled by ZEB2 has the potential to highlight novel targets for autoimmune disease diagnosis and therapy. ZEB2 is a zinc-finger transcription factor known to play a major role in early embryogenesis and in tumour metastasis. ZEB2 has an established role in the cancer metastasis of several cancers but its role in the immune system has only fairly recently been explored. Interestingly, ZEB2, is directly induced by T-bet (T helper 1 master transcription factor) in mouse NK cells and CD8+ T cells, and therefore I speculated that T-bet may be implicated in the regulation of ZEB2 in CD4+ T cells where T-bet is the defining transcription factor for Th1 cells. My PhD project identifies which CD4+ T cell subsets ZEB2 is expressed in. I show that ZEB2 is expressed highly in Tconv effector memory subsets, indicating its role in the effector compartment of CD4+ T cells. Further investigation indicated that ZEB2 was found predominantly in Th1 effector memory (EM) cells. ZEB2 was expressed at very low levels in the other Tconv helper lineages, suggesting a unique effector role of ZEB2 in Th1 where T-bet is highly expressed and FOXP3 is absent. However, the regulation of ZEB2 is clearly more complex, since in some CD4+ T cell subsets with high T-bet, for instance Th1/17, there is not necessarily high ZEB2, suggesting ZEB2 is not regulated by T-bet alone. In order to specifically define the role of ZEB2 in Th1 EM cells, I deleted ZEB2 and analysed global changes in gene expression by RNA-seq. RNA-seq analysis showed that 222 genes were differentially expressed between WT and ZEB2-deleted Th1 EM, and pathway analysis of the gene profile indicates a potential role for ZEB2 in regulating inflammatory cytokines, repressing cytotoxic responses, enhancing motility and increasing survival in high stress environments. ZEB2 is also shown to regulate effector memory and central memory genes important for Th1 effector memory differentiation. Hence, ZEB2 is important in maintaining the function and fidelity of a Th1 effector memory cell in the steady state, and indirectly or directly maintaining IFNγ expression. Th1 cells preferentially produce IFNγ and IL-2 and are the principal regulators of type 1 immunity (Th1 response), which eradicates intracellular pathogens including viruses. Unravelling the role of ZEB2 in the complex relationships between the Th1 and Treg lineages and subsets may provide critical insight into the disruption of immune homeostasis that leads to autoimmune disease including inflammatory bowel disease (IBD), and may suggest novel therapeutic targets for autoimmune diseases.