Mast Cell Lineage Commitment and Function

Project Summary The incidence of mast cell (MC)-mediated diseases, including allergic diseases and mast cell activation syndrome (MCAS), has risen at an alarming rate in developed countries during the past several decades. MCs, which express the high-affinity receptor for IgE (FceRI), release inflammatory mediators in response to antigen crosslinking of their surface IgE/FceRI complex. A G protein-coupled receptor known as MRGPRB2, which is mainly expressed on MCs, has been discovered to be responsible for facilitating antibody-independent MC activation, including clinically important drug-induced MC activation. The role of Microphthalmia-associated transcription factor (MITF) in MC differentiation was uncovered by studying mice with various spontaneous mutations in the Mitf gene. However, because MITF is important for MC differentiation, few mature MCs develop in the absence of MITF. As a result, the role of MITF in MC lineage commitment and function is still poorly understood. Our long-term goal is to enhance understanding of the regulation of MC genes that influence allergy susceptibility and severity. This application investigates how MITF promotes the expression of MC-specific genes while simultaneously suppressing the expression of basophil-specific genes. Additionally, it will evaluate the functional deficiencies of MCs with an inducibly deleted Mitf gene. Our preliminary studies generated mice with a genetically modified Mitf gene that can be specifically deleted in fully differentiated MCs. Our findings show that deleting the Mitf gene in fully differentiated bone marrow-derived MCs (BMMCs) substantially reduces FceR1a and c-KIT expression. Importantly, Mitf-/- BMMCs also have re-expressed the gene for the basophil lineage-determining transcription factor (TF) Cebpa. In addition to these observations, our preliminary RNA-seq data revealed that MITF regulates the Mrgprb2 gene, opening a new area of investigation. Based on our preliminary findings, we hypothesize that MITF both promotes MC-specific gene expression and suppresses basophil-specific gene expression and that MITF regulates antibody-and drug-induced anaphylaxis. Aim 1 will determine whether MITF maintains MC-specific genes by promoting chromatin accessibility and by cooperating with other TFs to activate enhancers that regulate the MC-specific genes. Aim 2 will determine how MITF suppresses basophil cell fate in MCs by silencing the Cepba enhancers. Aim 3 of this study will evaluate the functional deficiencies of BMMCs with an inducibly deleted Mitf gene in IgE-mediated and IgG-mediated anaphylaxis, as well as anaphylaxis induced by the antibiotic ciprofloxacin. Results from these studies should advance our understanding of MC lineage commitment and how MITF- dependent MC transcriptional programing regulates antibody-mediated and drug-induced anaphylaxis. Decoding enhancers can help find ways to reduce the expression levels of genes involved in MC activation and anaphylaxis and thus control MC-mediated diseases by providing targets for CRISPR-based interventions.