NFkB dynamics in the stimulus specificity of trained immunity

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PROJECT SUMMARY / ABSTRACT Cells of the innate immune system such as monocytes and macrophages can be reprogrammed by their environmental context. Stimuli in the environment, such as cytokines and pathogen-associated molecules, can dramatically alter cellular phenotype. This phenomenon, termed “trained immunity,” is driven by epigenetic changes to the enhancer repertoire. Upon stimulation, transcription factors such as NFκB can bind to closed chromatin regions, open the chromatin, and facilitate histone modification, activating previously silent regulatory DNA elements called latent enhancers. These epigenetically reprogrammed innate immune cells respond differently to subsequent stimulation and alter host responses to infectious diseases. Interestingly, the effects of trained immunity are variable. In some cases, trained immunity primes the host to produce an increased inflammatory response upon secondary stimulation, but in other cases it diminishes the inflammatory response. Whether reprogrammed monocytes produce increased or diminished inflammatory responses depends on what stimulus forms the memory. That is, the effects of trained immunity are stimulus- specific. However, the mechanisms that account for this stimulus-specificity are unclear, and understanding these mechanisms will be critical for harnessing the therapeutic potential of trained immunity. The central hypothesis of this grant is that different dynamic features of NFκB activity contribute to the stimulus- specificity of trained immunity. NFκB is a ubiquitous transcription factor that is considered the master regulator of inflammatory gene expression. Although nearly all pathogens and cytokines activate NFκB, they do so with varying dynamics. In particular, some stimuli induce an oscillatory pattern of activity, while others induce a non- oscillatory pattern of activity. We have shown that non-oscillatory NFκB results in more de novo enhancers than oscillatory NFκB using a mouse model in which NFκB oscillations are perturbed. Aim 1 of this proposal characterizes the stimulus-specificity of training in vivo and tests the hypothesis that trained immunity produced by different NFκB dynamics differentially alters host response to secondary infection with Candida albicans. Aim 2 investigates the mechanisms by which NFκB dynamics-dependent enhancers regulate gene expression. This mentored career development award will support the training of a promising junior faculty member at UCLA. The specific training objectives are to acquire expertise in 1) bioinformatics, 2) mouse models of infection, 3) immune profiling of tissue samples, and 4) the field of innate immune memory. Training will occur through mentorship by senior faculty members, coursework, seminars, and international conferences. The goal of this career development award is to establish the principal investigator as an independent physician-scientist, ultimately producing diagnostic and therapeutic tools for immune-mediated complications of infectious diseases.