title: Inhibition of autophagy with 3-methyladenine results in impaired turnover of lysosomes and accumulation of lipofuscin-like material.
abstract: Autophagy (which includes macro-, micro-, and chaperone-mediated autophagy) is an important biological mechanism for degradation of damaged/obsolete macromolecules and organelles. Ageing non-dividing cells, however, progressively accumulate oxidised proteins, defective organelles and intralysosomal lipofuscin inclusions, suggesting inherent insufficiency of autophagy. To learn more about the role of macroautophagy in the turnover of organelles and lipofuscin formation, we inhibited autophagic sequestration with 3-methyladenine (3 MA) in growth-arrested human fibroblasts, a classical model of cellular ageing. Such treatment resulted in a dramatic accumulation of altered lysosomes, displaying lipofuscin-like autofluorescence, as well as in a moderate increase of mitochondria with lowered membrane potential. The size of the late endosomal compartment appeared not to be significantly altered following 3 MA exposure. The accumulation of lipofuscin-like material was enhanced when 3 MA administration was combined with hyperoxia. The findings suggest that macroautophagy is essential for normal turnover of lysosomes. This notion is supported by reports in the literature of lysosomal membrane proteins inside lysosomes and/or late endosomes, as well as lysosomes with active hydrolases within autophagosomes following vinblastine-induced block of fusion between lysosomes and autophagosomes. The data also suggest that specific components of lysosomes, such as membranes and proteins, may be direct sources of lipofuscin.
authors.affiliation: Division of Pathology II, Department of Neuroscience and Locomotion, Faculty of Health Sciences, Linköping University, Sweden. yurst@inr.liu.se
authors.forename: Yuri
authors.initials: Y
authors.lastname: Stroikin
authors.forename: Helge
authors.initials: H
authors.lastname: Dalen
authors.forename: Sara
authors.initials: S
authors.lastname: Lööf
authors.forename: Alexei
authors.initials: A
authors.lastname: Terman
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects; D002403:Cathepsins / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism; D008062:Lipofuscin / Q000378:metabolism*; D008247:Lysosomes / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D008928:Mitochondria / Q000187:drug effects / Q000648:ultrastructure; D011347:Procollagen / Q000187:drug effects; D013997:Time Factors
chemical_list: D008062:Lipofuscin; D011347:Procollagen; C025946:3-methyladenine; D002403:Cathepsins; D000225:Adenine