title: DKK1 mediated inhibition of Wnt signaling in postnatal mice leads to loss of TEC progenitors and thymic degeneration.
abstract: BACKGROUND
  Thymic epithelial cell (TEC) microenvironments are essential for the recruitment of T cell precursors from the bone marrow, as well as the subsequent expansion and selection of thymocytes resulting in a mature self-tolerant T cell repertoire. The molecular mechanisms, which control both the initial development and subsequent maintenance of these critical microenvironments, are poorly defined. Wnt signaling has been shown to be important to the development of several epithelial tissues and organs. Regulation of Wnt signaling has also been shown to impact both early thymocyte and thymic epithelial development. However, early blocks in thymic organogenesis or death of the mice have prevented analysis of a role of canonical Wnt signaling in the maintenance of TECs in the postnatal thymus.
  
  
  RESULTS
  Here we demonstrate that tetracycline-regulated expression of the canonical Wnt inhibitor DKK1 in TECs localized in both the cortex and medulla of adult mice, results in rapid thymic degeneration characterized by a loss of DeltaNP63(+) Foxn1(+) and Aire(+) TECs, loss of K5K8DP TECs thought to represent or contain an immature TEC progenitor, decreased TEC proliferation and the development of cystic structures, similar to an aged thymus. Removal of DKK1 from DKK1-involuted mice results in full recovery, suggesting that canonical Wnt signaling is required for the differentiation or proliferation of TEC populations needed for maintenance of properly organized adult thymic epithelial microenvironments.
  
  
  CONCLUSIONS
  Taken together, the results of this study demonstrate that canonical Wnt signaling within TECs is required for the maintenance of epithelial microenvironments in the postnatal thymus, possibly through effects on TEC progenitor/stem cell populations. Downstream targets of Wnt signaling, which are responsible for maintenance of these TEC progenitors may provide useful targets for therapies aimed at counteracting age associated thymic involution or the premature thymic degeneration associated with cancer therapy and bone marrow transplants.
authors.affiliation: Department of Biology, The City College of New York, New York, New York, United States of America.
authors.forename: Masako
authors.initials: M
authors.lastname: Osada
authors.forename: Logan
authors.initials: L
authors.lastname: Jardine
authors.forename: Ruth
authors.initials: R
authors.lastname: Misir
authors.forename: Thomas
authors.initials: T
authors.lastname: Andl
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Millar
authors.forename: Mark
authors.initials: M
authors.lastname: Pezzano
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002452:Cell Count; D049109:Cell Proliferation / Q000187:drug effects; D004318:Doxycycline / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D007633:Keratins / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013234:Stem Cells / Q000187:drug effects / Q000378:metabolism; D013752:Tetracycline / Q000494:pharmacology; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C501127:Dkk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D015534:Trans-Activators; D051153:Wnt Proteins; C490508:Wnt7a protein, mouse; D007633:Keratins; D013752:Tetracycline; D004318:Doxycycline