Foxp3 isoform expression and regulation of autoantibody production - PROJECT SUMMARY Systemic Lupus Erythematosus (SLE) is a multi-systemic autoimmune disease that arises from a combination of genetic factors, dysregulated immune responses and environmental triggers. SLE-like phenotypes, including elevated anti-nuclear IgG autoantibody titers, kidney nephritis, splenomegaly and reduced survival have been reported in several animal models of SLE, but few of these models require environmental factors to drive disease. Therefore, studies of causative environmental factors have used mouse models that already have lethal SLE disease prior to exposure. Consequently, they cannot be used to determine how these factors can induce flares in patients with latent SLE. Therefore, a mouse model of moderate SLE is required to appropriately replicate SLE flares that are induced by environmental triggers. Regulatory T (Treg) cells play a central role in maintaining immune system homeostasis and modulating immune responses. Foxp3 is a master regulator of Treg development and function. FOXP3 mutations in patients with IPEX (Immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome), which result in a deficiency in Tregs, result in lethal autoimmunity, similar to the disease observed in Foxp3 deficient mice. While highly conserved in both amino acid sequence and gene structure, one difference between humans and mice is that the human FOXP3 gene encodes two major alternatively spliced isoforms: a full-length version that uses all 10 exons (FOXP3FL, the only isoform in mice) and a shorter isoform lacking exon 2 (FOXP3∆E2). Recent studies have shown that Tregs from patients with some autoimmune diseases express increased levels of the ∆E2 isoform compared to those from healthy donors. Consistent with this finding, we have found that Tregs from SLE patients have increased expression of the FOXP3∆Ex2 isoform. To study the role of the ∆E2 isoform in Treg function we generated a new mouse strain with Foxp3 exon 2 deletion. Interestingly, we found that Foxp3∆E2 mice develop hallmark features of SLE, including anti-DNA and anti-nuclear autoantibodies, increased number and size of spontaneous germinal centers and kidney deposition of antibody complexes, by 4-5 weeks of age. Our central hypothesis is that expression of the ∆E2 isoform of FOXP3 leads to Treg dysfunction and loss of tolerance. To test this hypothesis we will first determine the role of Foxp3∆Ex2-expressing Tregs in germinal center function, focusing on the relationship between Tfh and Tfr cells. Next, we will assess the response to UVB light in Foxp3∆E2 mice. Finally, we will examine the expression of FOXP3∆E2 in Tregs from cohorts of SLE and MCTD patients to determine the potential role of this isoform and disease expression. These studies will provide insights into the role of Foxp3∆E2 Treg function and predisposition to SLE.
