title: Regional deficiencies in chaperone-mediated autophagy underlie α-synuclein aggregation and neurodegeneration.
abstract: In neurodegenerative diseases, it remains unclear why certain brain regions are selectively vulnerable to protein aggregation. In transgenic mice expressing human A53T α-synuclein, the brainstem and spinal cord develop the most prominent α-synuclein inclusions which correlate with age-dependent motor dysfunction. Herein we present the novel finding that this selective aggregation is in part dependent on the inability of chaperone-mediated autophagy (CMA) to effectively degrade α-synuclein in these brain regions. Lysosomal assays revealed that CMA activity was significantly decreased in aggregation-prone regions compared to the remainder of the brain. Previously, CMA activity has been shown to be proportional to levels of the CMA receptor Lamp-2a. Using antibodies, brain tissue from Lamp-2a null mice, enzymatic deglycosylation, and mass spectrometry, we identified Lamp2a as a novel 72kDa glycoprotein in the mouse brain. Examination of Lamp-2a levels revealed differences in expression across brain regions. The brainstem and the spinal cord had a more than three-fold greater levels of Lamp-2a as compared to regions less vulnerable to aggregation and exhibited a selective upregulation of Lamp-2a during development of α-synuclein inclusions. Despite this dynamic response of Lamp-2a, the levels of substrates bound to the brain lysosomes as well as the rates of substrate uptake and degradation were not proportional to the levels of Lamp-2a. These regional differences in CMA activity and Lamp-2a expression were found in both non-transgenic mice as well as A53T α-syn mice. Therefore, these are inherent variations and not a transgene-specific effect. However, differences in CMA activity may render select brain regions vulnerable to homeostatic dysfunction in the presence of stressors such as overexpression of human A53T α-syn. Collectively, the data provide a potential mechanism to explain the dichotomy of vulnerability or resistance that underlies brain regions during aggregate formation in neurodegenerative disease.
authors.affiliation: Departments of Pediatrics and Pharmacology, The Children's Hospital of Philadelphia Research Institute and The Perelman School of Medicine at the University of Pennsylvania Philadelphia, Pennsylvania 19104-4318, USA.
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Malkus
authors.forename: Harry
authors.initials: H
authors.lastname: Ischiropoulos
mesh_terms: D000818:Animals; D001343:Autophagy / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D001921:Brain / Q000473:pathology; D001923:Brain Chemistry / Q000235:genetics; D001933:Brain Stem / Q000473:pathology; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D006801:Humans; D002479:Inclusion Bodies / Q000235:genetics / Q000473:pathology; D052119:Lysosomal-Associated Membrane Protein 2 / Q000235:genetics / Q000378:metabolism; D008247:Lysosomes / Q000235:genetics / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009069:Movement Disorders / Q000235:genetics / Q000473:pathology; D019636:Neurodegenerative Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016133:Polymerase Chain Reaction; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D013116:Spinal Cord / Q000473:pathology; D051844:alpha-Synuclein / Q000235:genetics / Q000502:physiology*
chemical_list: D052119:Lysosomal-Associated Membrane Protein 2; D018832:Molecular Chaperones; D051844:alpha-Synuclein; D012313:RNA; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases