Regulation of chaperone-mediated autophagy
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Autophagy, the turnover of intracellular components in lysosomes, is critical for maintaining cellular homeostasis. We have focused on chaperone-mediated autophagy (CMA), a selective type of autophagy. CMA activity is altered in several human disorders and is decreased with age due to decreased lysosomal levels of the CMA receptor.;The goal of this thesis was to elucidate the mechanisms that regulate CMA including the interaction of CMA with other autophagic pathways, and how changes in these regulatory mechanisms contribute to functional decline of CMA with age.;We have identified the presence of lipid microdomains at the lysosomal membrane and their novel role in CMA regulation. Distribution of CMA receptor in/out of these microdomains determines CMA activity. This is the first description of membrane organization in the lysosomal compartment, underscoring a previously unknown role for lipids in the CMA regulation.;We have also found that CMA regulation depends on its relation with other autophagic pathways, in particular with macroautophagy. Thus, blockage of macroautophagy leads to constitutive upregulation of CMA. The lysosomal chaperone required for translocation of substrate proteins through CMA is a critical component mediating this newly identified autophagic cross-talk.;We have found that macroautophagy regulates lipid metabolism by degrading intracellular lipid droplets. Conversely, excessive cellular lipids, as in cells subjected to chronic lipogenic stimulus have an inhibitory effect on autophagy. Interestingly, this chronic treatment mimics the metabolic syndrome of aging, suggesting that changes in lipid metabolism with age could be behind the functional failure of the autophagic pathways. In this respect, we have found a critical role of changes in the lipid composition of the lysosomal membrane with age on CMA activity. Thus, there are striking changes in the organization of the CMA receptor in the lysosomal membrane with age due to changes in the lysosomal lipid microdomains which decrease the stability of this protein with age.;In summary, our work has revealed a novel interplay between lipids and autophagy and among the different autophagic pathways. A better understanding of the mechanisms regulating these interactions could set the basis for future attempts to selectively activate one pathway for therapeutic purposes.