Type 1 diabetes (T1D) results from a breakdown in immune tolerance that progresses to the destruction of the insulin producing beta cells of the pancreatic islets. A large number of genetic and environmental factors contribute to the incidence of disease. One of the strongest non-MHC genetic risk factors is a single nucleotide polymorphism in the gene that encodes the tyrosine phosphatase non-receptor type 22, PTPN22, that results in a single amino acid change in the protein, R620W. PTPN22 is expressed in many bone marrow derived cells, including lymphocytes and myeloid derived cells. Although R620W increases the risk of many autoimmune diseases associated with production of autoantibodies, including T1D, rheumatoid arthritis, systemic lupus erythematosus, Graves disease, vitiligo, and others, little is know about how it enhances disease. In part, this is because it functions in many different types of cells that affect the immune system. In order to produce a mouse model that can be used to identify its mechanism of action, we used Crispr/Cas9 genome editing to introduce the mouse ortholog of the pro-autoimmune allele of PTPN22 (619W) into the non- obese diabetes (NOD) mouse that spontaneously develops T1D. NOD mice harboring this mutation demonstrate accelerated production of anti-insulin antibodies and accelerated T1D of higher penetrance, which is the same phenotype exhibited by humans expressing R620W. This proposal will use the 619W NOD model to reveal the mechanism responsible for enhanced disease by pursuing the following specific aims:
Aim1 will identify immune cells in which endogenous expression of 619W enhances IAA production and T1D. This entails adoptive transfer experiments to produce mice expressing the 619W mutation of PTPN22 in key immune cells.
Aim 2 will explore the mechanistic basis for enhanced IAA and T1D in 619W mice. The types of immune cells identified under Aim 1 will be probed to identify genes affected in their level of expression by allelic difference at 619. Genes and pathways will be identified by either RNAseq or by analyzing gene expression at the single cell level. Candidate genes will be tested for function by altering level of expression with shRNAs delivered by retroviral vectors.
Aim 3 will examine tolerance of insulin specific B lymphocytes in R619W mice.
Aim 4 will use TCR transgenic mice and single cell expression analysis to examine the fate of islet antigen specific T cells as they become activated in either 619W or 619R expressing mice. Successful completion of these studies will have relevance to development of treatments that may prevent the many different autoimmune disease associated with PTPN22.
The risk of many autoimmune diseases, including type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, Graves disease, vitiligo, and others, is enhanced by the presence of a specific form of a gene that in expressed in many different cells of the immune system, PTPN22. In order to better understand the basis for this increase in disease association, and to identify molecules that may be targeted by drugs to prevent disease, we have produced a mouse model expressing this form of the enzyme and now propose to determine how it increases type 1 diabetes.
