Abstract
The thymic epithelium plays critical roles in the positive and negative selection of T cells. Recently, it was proposed that autophagy in thymic epithelial cells is essential for the induction of T cell tolerance to self antigens and thus for the prevention of autoimmune diseases. Here we have tested this hypothesis using mouse models in which autophagy was blocked specifically in epithelial cells expressing keratin 14 (K14), including the precursor of thymic epithelial cells. While the thymic epithelial cells of mice carrying the floxed Atg7 gene (ATG7 f/f) showed a high level of autophagy, as determined by LC3 Western blot analysis and fluorescence detection of the recombinant green fluorescent protein (GFP)-LC3 reporter protein on autophagosomes, autophagy in the thymic epithelium was efficiently suppressed by deletion of the Atg7 gene using the Cre-loxP system (ATG7 f/f K14-Cre). Suppression of autophagy led to the massive accumulation of p62/sequestosome 1 (SQSTM1) in thymic epithelial cells. However, the structure of the thymic epithelium as well as the organization and the size of the thymus were not altered in mutant mice. The ratio of CD4 to CD8-positive T cells, as well as the frequency of activated (CD69+) CD4 T cells in lymphoid organs, did not differ between mice with autophagy-competent and autophagy-deficient thymic epithelium. Inflammatory infiltrating cells, potentially indicative of autoimmune reactions, were present in the liver, lung, and colon of a similar fraction of ATG7 f/f and ATG7 f/f K14-Cre mice. In contrast to previously reported mice, that had received an autophagy-deficient thymus transplant, ATG7 f/f K14-Cre mice did not suffer from autoimmunity-induced weight loss. In summary, the results of this study suggest that autophagy in the thymic epithelium is dispensable for negative selection of autoreactive T cells.
Highlights
Autophagy is an evolutionarily conserved process in which the cell degrades its own components
Cre-mediated deletion of ATG7 (GFP-light chain 3 (LC3) ATG7 f/f keratin 14 (K14)-Cre) abolished the formation of green fluorescent protein (GFP)-LC3 puncta and led to a diffuse cytoplasmic accumulation of fluorescence in the epithelia of both thymic compartments (Fig. 1A, B). This suggested that GFP-LC3 is subjected to degradation by ATG7-dependent autophagy in the cortical and medullary epithelium of K14-Cre-negative mice and that K14Cre-mediated deletion of ATG7 f/f efficiently abrogated this autophagic flux in all Thymic epithelial cells (TECs)
In this study we have tested the hypothesis that the molecular machinery of macroautophagy in the thymic epithelium is required to achieve negative selection of T cells
Summary
Autophagy is an evolutionarily conserved process in which the cell degrades its own components. Atg and Atg are among the best characterized autophagy-related genes as their protein products play essential roles in a key step of autophagy, i.e. the conversion of the cytosolic form of microtubule-associated protein light chain 3 (LC3), LC3-I, into the lipidated form, LC3-II. The latter binds to the isolation membrane of the forming autophagosome and interacts with p62/SQSTM1, an adaptor protein that targets cytoplasmic proteins for selective degradation [2,6]. The phenotypes of mice carrying deletions of Atg and Atg were essentially identical [11]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
