Wnt Secretion Proteins Modulate RANKL-Induced Expression of Aire in Thymic Epithelial Cells
Thymic epithelial cells (TEC) are essential for a proper adaptive immune response by regulating thymocyte development and establishing central tolerance. In the thymus, TECs differentially express Wnt proteins, which activate canonical and non-canonical Wnt signaling pathways. Wnt signaling is thought to regulate cell survival, proliferation, and development although the direct molecular mechanisms in TECs have yet to be elucidated. The inducible inhibition of canonical Wnt signaling with Dkk1 leads to a rapid loss of TEC progenitors as well as a decline in mature Aire-expressing mTECs. Therefore, we explore the role of Wnt ligands potentially responsible for stimulating and/or regulating Wnt signaling in TECs by analyzing the genetic expression of various TEC populations in TCF/Lef:H2B/GFP Wnt reporter mice. Here we show that previously uncharacterized populations of postnatal mTECs undergoing canonical Wnt signaling differentially express Wnt proteins and we further identify Wnt-5a and Wnt-5b as possible candidates for regulating Wnt signaling in mTECs. It is well known that developing thymocytes indirectly affect TEC development—in order to study the effects of Wnt stimulation on TECs, we generate fetal thymic organ cultures (FTOC) in which we eliminate the developing thymocytes and instead use exogenous RANKL to drive TEC specific maturation, while simultaneously culture the TECs with different Wnt proteins. Our results show that the Wnt antagonist, Sfrp-1, and the Wnt ligand, Wnt-5b, interfere with RANKL-induced maturation as demonstrated by a reduced frequency of Aire+ fetal TECs. Furthermore, we show two proteins that are hallmarks of thymic development, FoxN1 and Dll4, regulate Wnt-5b genetic expression in vitro. However, further work is needed to determine if Wnt-5b is affecting TEC development through canonical or non-canonical Wnt signaling and whether the modulation is due to an altering of cell-fate, increased apoptosis, or by the preservation of cells in an undifferentiated state.
Wnt, Thymus, Aire, Wnt-5b, Thymic Epithelial Cells, mTEC, Allergy and Immunology, Cell Biology, Developmental Biology, Hemic and Immune Systems, Medical Immunology, Medical Molecular Biology, Molecular Biology
City University of New York - City College
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