Tài liệu Báo cáo khoa học: Modulation of a-synuclein aggregation by dopamine in the presence of MPTP

Modulation of a-synuclein aggregation by dopamine in the

presence of MPTP and its metabolite

Prashant N. Jethva, Jay R. Kardani and Ipsita Roy

Department of Biotechnology, National Institute of Pharmaceutical Education and Research (NIPER), S.A.S. Nagar, India

Introduction

The inability of the cell to degrade various stable mis￾folded proteins leads to the formation of aggregates

and inclusion bodies in the cell. Parkinson’s disease,

Alzheimer’s disease, Huntington’s disease, prion dis￾ease, etc. are disorders in which aggregation of normal

and ⁄ or mutant protein occurs and leads to neurode￾generation. Whether the aggregate itself is cytotoxic or

if it is a defence mechanism of the cell, remains a mat￾ter of debate [1,2]. Although the proteins involved in

such diseases do not have any similarity in their pri￾mary sequence and ⁄ or structure, the aggregates formed

do exhibit similarity in their topology. They exhibit

crossed b-sheet structure and common properties

regarding their binding with different staining dyes,

e.g. Congo red and Thioflavin T (ThT).

Parkinson’s disease is a progressive neurological dis￾order and is the second most prevalent neurodegenera￾tive disease after Alzheimer’s disease, affecting 1%

of people beyond 65 years of age. The etiological

factors that are involved in the development of Parkin￾son’s disease include genetic factors, susceptibility to

various drugs and environmental factors [3–5]. The

pathological changes that occur in the brain include

selective loss of dopaminergic neurons in substantia

nigra pars compacta and appearance of Lewy bodies

consisting of aggregated protein, mainly a-synuclein, in

Keywords

amyloid; fibrillation; Parkinson’s disease;

synuclein; thioflavin T

Correspondence

I. Roy, Department of Biotechnology,

National Institute of Pharmaceutical

Education and Research (NIPER), Sector 67,

S.A.S. Nagar, Punjab 160 062, India

Fax: +91 172 221 4692

Tel: +91 172 229 2061

E-mail: [email protected]

(Received 28 September 2010, revised 24

February 2011, accepted 7 March 2011)

doi:10.1111/j.1742-4658.2011.08093.x

The neurotransmitter dopamine has been shown to inhibit fibrillation of

a-synuclein by promoting the formation of nonamyloidogenic oligomers.

Fibrillation of a-synuclein is accelerated in the presence of pesticides and

the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The

aim of this study was to determine whether dopamine continues to have an

adverse effect on the fibrillation of a-synuclein in the presence of MPTP

and its metabolite 1-methyl-4-phenylpyridinum ion (MPP+). We also

attempted to answer the ambiguous question of whether conversion of

MPTP to MPP+ is required for the fibrillation of a-synuclein. For this,

a-synuclein was incubated in the presence of MPTP and MPP+ along with

dopamine. The fibrillation of a-synuclein was monitored by Thioflavin T

fluorescence and immunoblotting. The morphology of the aggregates

formed was observed using scanning electron microscopy. The concentra￾tions of the neurotoxin and its metabolite were estimated by reverse phase

HPLC. We found definitive evidence that the conversion of MPTP to

MPP+ is not required for aggregation of a-synuclein. MPP+ was found to

accelerate the rate of a-synuclein aggregation even in the absence of com￾ponents of mitochondrial complex I. In contrast to the effect of dopamine

on the aggregation of a-synuclein alone, in the presence of MPTP or

MPP+, the aggregates formed are Thioflavin T-positive and amyloidogenic.

Thus, the effect of dopamine on the nature of aggregates formed in case of

a-synuclein alone and in the presence of MPTP⁄MPP+ is different.

Abbreviations

MPP, 1-methyl-4-phenylpyridinum; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; ThT, thioflavin T.

1688 FEBS Journal 278 (2011) 1688–1698 ª 2011 The Authors Journal compilation ª 2011 FEBS