The Role of TFE3 and TFEB in the Differentiation of CD4+ T cells and the Development of Autoimmunity

Abstract

Our laboratory discovered that CD40L is a critical target gene for the transcription factors TFE3 and TFEB. It is expressed by murine and human activated CD4+ T cells and is a ligand for CD40, which is expressed by B cells. Both CD40L and CD40 play critical roles in humoral immune responses. However, in autoimmune diseases, such as Systemic Lupus Erythematosus (SLE), aberrant overexpression of CD40L by CD4+ self-reactive T cells is implicated in the maintenance and survival of self-reactive B cells, resulting in production of disease-causing autoantibodies. There is also evidence that TFE3 plays a role in TGFβ target gene expression, such as the TGFβ pathway inhibitor Smad7, but its role in TGFβ signaling in T cells is not know. TGFβ is critically important for the development of pro-inflammatory Th17 cells and anti-inflammatory inducible T regulatory cells (iTregs), both of which play a prominent role in a spectrum of autoimmune diseases. In Aim 1 of this thesis, the role of transcription factors, TFE3 and TFEB, in TGFβ-mediated differentiation of CD4+ T cells into Tregs (CD4+/FoxP3+) and Th17 (CD4+/Rorγt+) cells. Specifically, I investigated whether CD4+ T cells that lacked TFE3, TFEB or both were able to differentiate into Th1, Th2, Th17, and iTregs, as measured by linage-specific cytokine production (IFNγ, IL-4, IL-17, IL-10, IL-2) and the expression of lineage-transcription transcription factors (T-bet, Gata-3, Rorγt, FoxP3). This was accomplished by comparing cells from unimmunized wild type mice to those from mice that expressed (via a transgene) a trans dominant negative (TDN) inhibitor of TFE3 and TFEB only in T cells, mice homozygous for a null allele of TFE3, and mice that carried a conditional null allele of TFEB in only T cells. These analyses employed flow cytometry, ELISA, and RT-qPCR. In Aim 2, the importance of TFE3 and TFEB in the regulation of CD4+ self-reactive T cell-dependent autoantibody production and renal disease was evaluated in C57BL/6 Faslpr/lpr mouse model of lupus-like disease. Manifestations of autoimmunity, such as impaired renal function (proteinuria) caused by glomerular autoimmune complex deposition, secondary lymphoid organ hyperplasia, abnormal lymphocyte populations and autoantibody production, were measured comparing control, Faslpr/lpr, and Faslpr/lpr/TDN+ mice. It was demonstrated (1) TFE3, but not TFEB, is required for induction of the subset of T regulatory cells known as inducible T regulatory cells (iTregs) and that TGFβ-dependent induction of FosP3, the master transcription factor of T regulatory cells, was impaired. Subsequent chromatin immunoprecipitation analyses and reporter gene assays using the FosP3 gene enhancer and promoter showed that TFE3 directly binds to and activates the TGFβ-responsive CNS1 enhancer. (2) Inactivation of TFE3 and TFEB by the TDN results in decreased production of a subset of a subset of autoantibodies associated with nephritis, and amelioration of renal damage characteristic of SLE.