Mechanisms Controlling Thymic, Homeostasis, Involution, and Rebound

点击翻译按钮获取中文摘要

Overall Project The long-term objective of this Program Project is to perform a systematic analysis of the cellular and molecular mechanisms regulating thymic epithelial cell (TEC) homeostasis and the role of TECs in the involution of the adult thymus. The thymus is the primary lymphoid organ responsible for the generation of functional T cells, and is therefore critical for generation and maintenance of adaptive immunity. It is also one of the first organs to undergo significant agerelated organ degeneration, termed thymic involution. Thymic involution results in a dramatic 5'0 goal of identifying the cellular and molecular mechanisms resulting in the failure of TEC maintenance in thymic involution. The approaches used are all grounded in the central idea that the mechanisms that regulate fetal thymus development and TEC differentiation provide a conceptual framework for understanding thymic aging and regeneration. The individual projects in the P01 will take overlapping and complementary approaches to test these hypotheses that combine the unique expertise, experimental tools, and institutional resources of the investigators. CD= understood and/or controversial. Understanding the relative contributions of the mechanisms underlying this process would have significant implications for improving human health. The proposed Program Project is designed to identify mechanisms and pathways that can be exploited for induction of thymic rebound and/or prevention of involution, focused on the role of changes in TECs. The two projects will test two central hypotheses: 1)that failure to maintain postnatal thymic epithelial cell homeostasis is a causative mechanism in thymic involution; and 2) that down regulation of Foxnl, a pivotal regulator of TEC development and maintenance, is a primary molecular mechanism in thymic involution. These hypotheses will be addressed through three major Program objectives which will investigate: a) the lineage relationships of TEC subsets in the postnatal thymus; b) the molecular mechanisms driving TEC homeostasis; and c) whether these mechanisms are causal for involution. The scientific projects share the common Qua? c-"� drop in the production of new T cells, and is a significant contributing factor in immune senescence. Despite the importance of this subject for human health, the molecular mechanisms that operate in the postnatal thymus and mediate thymic homeostasis and involution are largely unknown. As a result, many aspects of thymic involution are poorly `<'O �_o (gyp 02, off- (.c -r- d-0 -00 n�) -a) (=0 o:� O.5 Q�' Erika Schwabe Assistant rants Officer Modified Project Summary/Abstract Section ... Project I thymus is also unknown. �<c0M5* 3v�3' �'.m W�� overcome thymic involution. This project will thus address one of the central hypotheses of the Program Project, that failure to maintain postnatal TEC homeostasis is a causative mechanism in thymic involution. C/) BCD homeostatic maintenance of the postnatal thymic stroma and will test whether de-repressing Wnt signaling can 3t,5 approaches to evaluate the role of Foxnl and the Wnt signaling pathway in molecular regulation of o-0 --"0- In this project, we will test the overall hypothesis that changes in the molecular mechanisms that control TESC/TEPC maintenance during postnatal thymus homeostasis contribute to thymic involution, by testing whether postnatal TESC/TEPC do not express Foxnl; and determining if modulation of Wnt signaling in specific subsets of postnatal TECs will affect TEC homeostasis and involution. These aims will use genetic .-. `�_ and in TESC/TEPC maintenance and/or function, is unknown. The Wnt signaling pathway has also been strongly implicated in regulation of TEC differentiation, at least in fetal stages, but any role in the postnatal w-0 The cellular mechanism that maintains the postnatal thymic epithelial (TE) compartment is currently unknown. Precedent from other organs suggests two possible models: the TE may be maintained by a stem/progenitor cell mechanism, as in the intestine, or by mitosis of terminally differentiated cells, as in the liver. Some recent data have been interpreted to support a stem cell mechanism, however, the results from these studies would be consistent with either of the above scenarios. Unequivocal discrimination between these possibilities is important, since development of effective strategies aimed at thymus regeneration will depend on a clear understanding of the target cell population(s) for therapeutic intervention. Previous work from the Blackburn laboratory and others has identified several candidate cell populations as containing potential stem/progenitors in the postnatal thymus. Just as candidate cell populations have been identified, molecular candidates for regulating the postnatal thymus are also known. In particular, the Manley and Blackburn labs and others have shown that the transcription factor Foxnl is required for fetal thymic epithelial cell (TEC) differentiation and proliferation, and is widely expressed in postnatal TECs; however, its role in the postnatal thymus generally, �33m can R-) con 0 twig C-0 vin m-� M,� t0/0 a'c (n3-� coo �_o vii �>_ w.:. c-0 -0o BCD Q.. (L6 DLL .0) pt- 7a- ... 3-� -a' Modified Project Summary/Abstract Section Project 2 Thymic epithelial cells (TECs) comprise a diverse group of cells that form a complex microenvironmental network required for T cell development and repertoire selection. Several years ago, we defined four major TEC subsets in the postnatal thymus based on differential expression of distinct keratin (K) species together 000 subset development, homeostasis and involution, with particular emphasis on medullary epithelium. Development of a functional medullary epithelial compartment is vital for establishing central tolerance. Medullary TECs (mTECs) are unique in their expression of a highly diverse array of tissue restricted antigens (TRAs) that are required to negatively select self-reactive thymocytes. Widespread autoimmune disease occurs in patients or mice with genetic defects in TRA expression. In addition, our lab and others have shown that autoimmunity develops in mice with genetic defects that prevent mTEC development during ontogeny. It is well established that the incidence of autoimmunity increases with age. Therefore, an attractive hypothesis is that progressive loss of a previously established mTEC compartment during thymus involution compromises negative selection and central tolerance, thereby increasing the risk of developing autoimmune disease with advancing age. Despite a growing appreciation for the essential role of mTECs in negative selection, the precise mechanisms that regulate their development and homeostasis, as well as their lineage relationships and functional potential remain to be determined. Our preliminary data suggest a precursor-progeny relationship between the major mTEC subsets defined as K5K14UEA-1 and K5K14UEA-14. This hypothesis E (-0 -�Q with the ability to bind the lectin, UEA-1. This proposal focuses on pathways and mechanisms involved in TEC 3-0 ..v -aoo� con .-. con -vo -oo 07m 7_< will be tested in Aim 1. A strategy to prevent or reverse loss of the mTEC population with age requires identification of the molecular pathways that regulate mTEC differentiation and proliferation. Our preliminary data show that expression of a K5 promoter driven constitutively active Stat3 transgene induces mTEC development in RAG-2 mice that are normally devoid of organized medullary regions due to an early block in thymocyte differentiation. Specific Aim 3 will determine whether Stat3 activation in mTEC precursors is required to generate or sustain the mTEC compartment. (<p 3.0 0G,� (n: -�Dv-n mama) (n' C.. m Q�) o)- >-a nom�.r ma) 0-�m ago ma) SQL E (C0 N-0 -ow 5'c cam' Modified Project Summary/Abstract Section E Project 3 Entirety of Project 3 has been deleted. Modified Project Summary/Abstract Section Core B 0 ,a, Entirety of Core B has been deleted. C,' m