Th136 - The CLOCK Protein Regulates Naive CD4+ T-cell Differentiation in Mesenteric Lymph Nodes Independently of BMAL1

Abstract Text: Immune cells secrete cytokines and chemokines rhythmically in response to the circadian clock, regulating time-of-day-dependent immune cell trafficking, antigen presentation, and host responses to infections. These rhythms are driven by core clock genes, including Clock and Bmal1. However, their roles in naïve CD4 T-cell differentiation remain unclear. Our data indicate IL-17 cytokine expression by gut infiltrating T-cells is circadian regulated. Mice expressing a dominant negative Clock mutant (ClockD19) are inflamed and have more Th17 cells compared to B6 and Bmal1-/- mice. We mapped chromatin accessibility, Clock/Bmal1 binding, and the expression profiles of naive CD4+ T-cells from mesenteric lymphnodes of ClockD19 and B6 mice. Chromatin accessibility was reduced in ClockD19 T-cells, consistent with RNA-seq data indicating gene downregulation, including key circadian genes. Interestingly, ClockD19 T-cells upregulated Hes7, a key factor in Notch signaling pathway and deregulated heat shock response genes. Furthermore, ClockD19 cells upregulated Wnt signaling genes and oncoproteins like Mycl, which implicated in cell growth and Th17 differentiation. ChIP-seq analysis revealed, in wild-type mice Clock and Bmal1 bind to genes associated with cell cycle, RNA metabolism and protein folding. However, in ClockD19 mice they bind to the promoters of genes involved in IL-17 signaling. Focusing exclusively on Bmal1-bound genes does not support a role in Th17 differentiation. However, Clock appears to regulate Th17 differentiation and influence naive CD4+ T-cell fate independently of Bmal1, and mutations like ClockD19 deregulate this process, skewing differentiation toward Th17 cells. Ongoing research aims to uncover additional mechanisms by Clock/Bmal1 influence the naive CD4+ T-cells fate.