Mechanisms of genetic variants in TH2 autoimmunity

PROJECT SUMMARY Monogenic autoimmune diseases, while rare, offer a unique opportunity to develop models that enable a more mechanistic understanding of the disease process, in particular, if the mutation is in the coding region and the penetrance is high. We have identified a family, in which father and two daughters have Immunoglobulin G4- related disease (IgG4-RD) while the mother is healthy. Exome sequencing identified shared mutations in the E3 ubiquitin ligase UBR4 (Cys4179Ter) and the transcription factor IKZF1 (IKAROS, Arg183His) genes in affected family members. IgG4-RD is a systemic autoimmune disease manifesting as a fibrosing inflammation of major salivary glands, orbits, pancreas, and retroperitoneal soft tissue, frequently associated with elevated serum IgG4 and IgE, increased peripheral eosinophilia and high rates of atopy/allergies. The pathogenesis of the disease is essentially unknown. IKZF1 is a gene that has been associated with a variety of autoimmune manifestations, without that pathogenetic pathways have been identified. Specifically, loss of function mutations cause immune deficiencies combined with tissue inflammation, while IKZF1 haplotypes have been associated with SLE and other autoimmune diseases in GWAS studies. The IKZF1 mutation identified here is unique in that it is a gain- of-function (GOF) due to increasing DNA binding affinity. We propose that an understanding of the effect of the GOF effects and their interaction with the proteome changes due UBR4 haploinsufficiency provides an opportunity to define mechanisms that lead to defective tolerance and excessive TH2 polarization. We propose a two-pronged approach. In Aims 1 and 2, we will build on our preliminary data that UBR4 haploinsufficiency increases CD45 expression while GOF IKAROS increases FYN transcription. Aim 1 will determine whether UBR4 and IKFZ1 GOF gene variants increase TCR signaling and break tolerance by upregulating CD45 and FYN. Aim 2 will examine the model that FYN drives TH2 polarization by phosphorylating ITCH2 and preventing the degradation of JunB. In these aims, we use a combination of human in vitro and mouse in vivo studies. Therapeutic implications will be examined in models of allergic airway inflammation by pharmacological depletion of IKAROS, as recently done for human SLE. In addition to these hypothesis-driven studies based on a large body of preliminary data, we propose to continue an unbiased screening of the proteomic and transcriptomic changes due to the gene variants to identify molecules that can be built into the current model. Aim 3 will determine whether the biomarkers developed from studying this digenic disease have broader implications for non-familial IgG4-RD disease as well as for other diseases that are characterized by an unopposed TH2 immunity.