Macroautophagy in sporadic and the genetic form of Parkinson's disease with the A53T α-synuclein mutation

Yue Huang,Germaine Chua,Fariba Chegini,Karen Murphy,Glenda M Halliday,Weiping Gai

doi:10.1186/2047-9158-1-2

Yue Huang, Germaine Chua + Show 4 more

Open Access

https://doi.org/10.1186/2047-9158-1-2

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Abstract

BackgroundThe A53T mutation in the α-synuclein gene causes autosomal-dominant Lewy body Parkinson's disease (PD). Cultured cell models have linked this mutation to increased cell macroautophagy, although evidence of enhanced macroautophagy in patients with this mutation has not been assessed.ObjectiveTo determine whether macroautophagy is increased by the A53T α-synuclein gene mutation in PD patients and cell models.MethodsFormalin-fixed paraffin-embedded 10 μm-thick tissue sections from the substantia nigra and anterior cingulate cortex of two PD patients with the A53T α-synuclein gene mutation were compared with four sporadic PD cases and four controls obtained from the Sydney Brain Bank. Lewy bodies were isolated from frontal cortex of a case with late stage PD (recruited from South Australian Brain Bank). Immunohistochemistry was performed for α-synuclein and the macroautophagy markers autophagy-specific gene (ATG) 5, ATG6/Beclin1 and ATG8/LC3. SH-SY5Y cells were transfected with wild type or A53T mutant α-synuclein plasmids and observable changes in macroautophagy marker protein levels assessed using Western blotting.Resultsα-Synuclein immunoreactive neurites and dots were more numerous in patients with A53T mutations compared with late stage sporadic PD patients, and perinuclear cytoplasmic α-synuclein aggregates were observed in the α-synuclein A53T gene transfected SH-SY5Y cells compared to wild type transfections. All PD patients (with or without A53T mutations) had increased immunohistochemical evidence for macroautophagy compared with controls, and the levels of the ATG5 complex were equally increased in wild type and A53T α-synuclein gene transfected cells compared to controls.ConclusionDespite increased α-synuclein accumulation with A53T mutations, macroautophagy is not increased above that observed in sporadic patients with PD or in cells transfected with wild type α-synuclein, suggesting that mutated α-synuclein protein is not removed by macroautophagy.

Highlights

Genetic forms of Parkinson’s disease (PD), the most common neurodegenerative movement disorder affecting the elderly, provide important information on major cellular abnormalities occurring in sporadic PD and are used in relevant models to understand disease pathogenesis
Despite increased a-synuclein accumulation with A53T mutations, macroautophagy is not increased above that observed in sporadic patients with PD or in cells transfected with wild type a-synuclein, suggesting that mutated a-synuclein protein is not removed by macroautophagy
Differences in the amount and type of a-synuclein aggregates in A53T versus sporadic PD Both A53T and sporadic PD had moderate to severe loss of substantia nigra neurons, as previously described [19]

Summary

Introduction

Genetic forms of Parkinson’s disease (PD), the most common neurodegenerative movement disorder affecting the elderly, provide important information on major cellular abnormalities occurring in sporadic PD and are used in relevant models to understand disease pathogenesis. Missense mutations in (A53T [1], A30P [2], E46K [3]) or multiplications of [4] the a-synuclein gene [5,6] occur only rarely in PD patients, abnormalities in the cellular processing of a-synuclein are considered core to PD pathogenesis due to its abnormal deposition and fibrilisation within the characteristic pathological inclusions of PD [7,8]. The formation of cytoplasmic a-synuclein pathologies in PD has been attributed to the dysfunction of protein degradation pathways through the proteasome [9] and/ or lysosomal autophagy [10,11]. Macroautophagy sequesters damaged organelles and unused long-lived proteins in a specialised autophagic vacuole or autophagosome, which fuses with a lysosome. Cultured cell models have linked this mutation to increased cell macroautophagy, evidence of enhanced macroautophagy in patients with this mutation has not been assessed

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