Decline in the immune system is a feature of human aging. Reduction in naive T cell repertoire to combat novel pathogens stems from decreased function of the thymus where T cells develop. Stage-specific signal transduction and gene expression, resulting from reciprocal cell-cell interactions and locally produced cytokines and hormones, is critical for T cell development. Cues from stromal cells regulate an exquisite balance of proliferation, quiescence, cell-death and cell-fate decisions in developing thymocytes. In turn, thymocytes regulate the maturation of thymic epithelial cells. Rearrangement and expression of the T cell receptor (TCR) beta-chain marks commitment to the T cell lineage, which is followed by expression of the pre-TCR. Signals through the pre-TCR facilitate transition through the first checkpoint, known as beta-selection that selects for immature thymocytes expressing a functional TCR beta chain. We are interested in the molecular mechanisms involved in beta-selection. Recently, we have demonstrated that beta-catenin is a transcriptional target of pre-TCR signals and in turn regulates the expression of several proteins that are crucial for proper navigation of the beta-selection checkpoint. Thymocytes that successfully negotiate the beta-selection checkpoint rearrange and express the TCR alpha chain and the alpha-beta-TCR. The alpha-beta-TCR expressing thymocytes face a second checkpoint known as positive and negative selection where self-restricted but not self-reactive thymocytes are selected for further maturation. The molecular mechanisms that operate at this checkpoint are also of interest to our laboratory. We have shown that beta-catenin regulates positive selection of thymocytes. Positive selection and IL-7R signaling are both facilitated in mice expressing transgenic beta-catenin resulting in increased generation of CD8 T cells. Mature thymocytes migrate to the peripheral lymphoid organs such as the spleen and the lymph nodes where upon encountering antigen provide T cell mediated immune protection. Beta-catenin regulates mature T cell function by regulating cytokine production as well as proliferation in response to antigenic stimulation. Finally, transgenic mice expressing beta-catenin exhibit accelerated age-dependent thymic involution and aging. The mechanistic basis for beta-catenin-mediated thymic involution remains a major focus of our laboratory. The long-term goal of our research is to delineate molecular interactions that significantly regulate T cell development in the thymus with the aim of further defining these processes and establish protocols to boost thymic function in the elderly and immunocompromised subjects.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Intramural Research (Z01)
Project #
1Z01AG000768-05
Application #
7732322
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
5
Fiscal Year
2008
Total Cost
$298,408
Indirect Cost
Name
National Institute on Aging
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Yu, Qing; Xu, Mai; Sen, Jyoti Misra (2007) Beta-catenin expression enhances IL-7 receptor signaling in thymocytes during positive selection. J Immunol 179:126-31
Yu, Qing; Sen, Jyoti Misra (2007) Beta-catenin regulates positive selection of thymocytes but not lineage commitment. J Immunol 178:5028-34
Mulroy, Thomas; Xu, Youyuan; Sen, Jyoti Misra (2003) beta-Catenin expression enhances generation of mature thymocytes. Int Immunol 15:1485-94