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theses

Autophagy captures intracellular components and delivers them to lysosomes for degradation and recycling. Conditional autophagy deficiency in adult mice causes liver damage, and shortens lifespan to three months due to neurodegeneration. As autophagy deficiency causes p53 induction and cell death in neurons, we sought to test if p53 mediates the toxic effects of autophagy deficiency. Here we conditionally deleted Trp53 (p53 hereafter) and/or the essential autophagy gene Atg7 throughout adult mice. Compared to Atg7Δ/Δ mice, life span of Atg7Δ/Δp53Δ/Δ mice was extended due to delayed neurodegeneration and resistance to death upon fasting. Atg7 also limited apoptosis induced by the p53 activator Nutlin-3, suggesting that autophagy inhibited p53 activation. To test if increased oxidative stress in Atg7Δ/Δ mice was responsible for p53 activation, Atg7 was deleted in the presence or absence of the master regulator of antioxidant defense Nuclear factor erythroid 2-related factor 2 (Nrf2). Nrf2-/-Atg7Δ/Δ mice died rapidly due to small intestine damage, which was not rescued by co-deletion of p53. Thus, autophagy limits p53 activation and p53-mediated neurodegeneration. In turn, NRF2 mitigates lethal intestine degeneration upon autophagy loss. These findings illustrate the tissue-specific roles for autophagy and functional dependencies on the p53 and NRF2 stress response mechanisms.

Atg7 and Atg5 are both essential autophagy genes (ATG) involved in autophagosome formation and deleting these genes leads to autophagy deficiency. As essential autophagy genes can function differently, we then sought to test whether whole-body conditional Atg5 deletion in adult mice (Atg5Δ/Δ mice) would have similar phenotype to that of Atg7 deletion. In contrast to Atg7Δ/Δ mice, Atg5Δ/Δ mice surprisingly lived for less than five days. Atg5Δ/Δ mice showed selective damage in the ileum part of intestine, with marked epithelial damage and loss of barrier function. In comparison to Atg7Δ/Δ mice, the ileum of Atg5Δ/Δ showed evidence of more rapid loss of autophagy, and loss of stem cells and malfunction of Paneth cells. Furthermore, Atg5Δ/Δ mice had decreased active β-catenin in the ileum, the key transcription factor for Wnt signaling that is essential for intestinal stem cell renewal. Atg5Δ/Δ mice lost PDGFRα+ mesenchymal cells (telocytes) in the ileum, which are required to provide Wnt signals to stem cells. Deletion of Atg5 more gradually overcame the loss of ileum telocytes and stem cells and resulted in death much later from neurodegeneration similar to deletion of Atg7 or Atg12. Atg5Δ/Δ telocytes displayed significantly decreased aspartate and nucleotides, which caused their loss. These findings reveal a novel function of autophagy in maintenance of telocytes, Wnt signaling, and thereby stem cells essential for intestinal homeostasis and the survival of adult mice. As impaired autophagy is associated with Inflammatory Bowel Diseases, this suggests that failure to maintain telocyte function is involved in development of this disease.

ETD_10450

Ph.D.

Includes bibliographical references

doi:10.7282/t3-2akb-q458

ETD doctoral

The author owns the copyright to this work.