Date of Award
Fall 2022
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Immunobiology
First Advisor
Lucas, Carrie
Abstract
Inborn errors of immunity provide a unique lens through which broader biological and immunological mechanisms can be elucidated. While inborn errors of immunity constitute a range of manifestations, monogenic autoinflammatory diseases offer insights into the regulation of classically protective inflammation. Inflammation is mediated by many different cell types and complex factors that must carefully regulate initiation, duration, and magnitude of a given response. Autoinflammation occurs when there is no clear trigger and often results in a sustained and potentially pathogenic response. We have discovered a novel monogenic disease, Deficiency of ELF4 X-Linked (DEX), caused by the deficiency of the transcription factor ELF4 that results in chronic autoinflammation. Since ELF4 is an X-linked gene, DEX patients were all young males who presented with inflammatory bowel disease (IBD)-like symptoms including fever, gastrointestinal inflammation, and oral ulcers. While several functions for Elf4 had previously been defined in mice, this was the first report of a human deficiency of ELF4 which further elucidated the most physiologically relevant roles, including suppression of Th17 cells. We established three novel mouse models to study deficiency of Elf4 including a complete knockout mouse (Elf4 KO), W250S to recapitulate the human variant W251S, and Elf4 floxed mice to analyze cell-specific changes. Utilizing DEX patient samples and corresponding mouse models, we first defined functional and transcriptional changes in Elf4-deficient Th17 cells. Importantly, we discovered that Elf4 carries out transcriptional and epigenetic regulation in the naïve CD4 cell state that serves to suppress inflammatory CD4 T cell subset differentiation. Naïve CD4 T cells serve as the precursors for several T-helper subset lineages, including Th1, Th2, Th17, and Treg cells. We discovered that Th1 cells, another important inflammatory CD4 cell subset particularly relevant for mucosal/gastrointestinal inflammation, similarly present with a hyperinflammatory phenotype through increased IFNγ production. We established that Th1 responses are elevated in vitro, in vivo, and in situ. Since Elf4 KO mice do not present with any spontaneous disease at baseline, we utilized several mouse models of colitis to recapitulate gastrointestinal inflammation observed in DEX patients which revealed increased numbers of Th1 and Th17 cells in relevant tissues, including the colon and mesenteric lymph nodes. These data suggest that Elf4 regulates the inflammatory capacity of CD4 T cells. In addition, we further defined one potential mechanism through which Elf4 may regulate inflammatory cytokine production. Combining transcriptional data from RNA-seq and genomic binding locations from CUT&RUN in naïve CD4 T cells, we established that Elf4 likely directly regulates expression of cJun and cFos, which heterodimerize to form the AP-1 transcription factor that was been well characterized in inflammation. Both genes are bound by Elf4 in their promoter region and have increased expression in naïve CD4 T cells. Effector CD4 T cells isolated from WT and Elf4 KO mice showed increased numbers of IFNγ+ cJun and cFos-expressing cells. Furthermore, we were able to reverse this phenotype by treating Th1 and Th17 cells with the JNK inhibitor SP600125, observing a reduction of IFNγ and IL-17A, respectively. We also utilized motif enrichment analysis to predict that Elf4 may cooperate with another transcription factor, such as Sp1, to carry out this regulation. Regulation of cFos and cJun by Elf4 likely represents one of many ways in which Elf4 regulates the inflammatory capacity of CD4 T cells. More broadly, we believe that Elf4 may function as a pioneer factor in naïve CD4 T cells to maintain a suppressive cell state through diverse mechanisms that are disrupted in the absence of Elf4, leading to autoinflammation. Collectively, these findings define physiologically relevant roles of Elf4 in the regulation of inflammatory CD4 T cells. This contributes to our understanding of fundamental immunological regulation of Elf4, which can further be leveraged to inform design of more specific and efficacious therapies for IBD and Th1/Th17-mediated inflammatory diseases.
Recommended Citation
Bucklin, Molly Lynn, "Elf4 transcriptionally regulates the inflammatory capacity of CD4 T cells" (2022). Yale Graduate School of Arts and Sciences Dissertations. 832.
https://elischolar.library.yale.edu/gsas_dissertations/832
