Myeloperoxidase promotes nitration and aggregation of a-synuclein in the A53T-a-syn mouse model of Parkinson’s Disease and exacerbates motor disabilities
Myeloperoxidase promotes nitration and aggregation of a-synuclein in the A53T-a-syn mouse model of Parkinson's Disease and exacerbates motor disabilities Wanda F. Reynolds, Marzia Scortegagna, Ze'ev A. Ronai, Richard A. Maki Sanford Burnham Prebys Medical Discovery Institute La Jolla, CA
Protein-aggregation induced pathogenesis is a hallmark of a number of neurodegenerative diseases including Parkinson's disease (PD). There is some evidence that oxidative stress promotes misfolding of a-synuclein giving rise to neurotoxic aggregates. Myeloperoxidase is an oxidizing enzyme normally expressed in myeloid precursor cells but the human MPO gene can be induced in stressed conditions in some non-myeloid cells including neurons or astrocytes in PD and Alzheimer's disease (AD). We previously reported hMPO expression in astrocytes in human AD as well as in an APP overexpressing model of AD (APP23) when crossed to our hMPO transgenic mice that express a single BAC copy of the native -463G-hMPO gene with introns and extensive flanking regions (Maki et al, (2009) J Biol Chem. 284:3158-69). Compared to the APP23 mice, the hMPO-APP23 mice exhibited greater memory impairment in Morris water maze correlating with greater phospholipid peroxidation. In the current study, we investigate the effects of hMPO expression in a PD model, Thy-1-A53T-a-synuclein (B6.Cg-Tg THY1-SNCA A53T)M53Sud/J ), that overexpresses the A53T-a-syn mutant linked to familial PD. Behavior assays were used to assess the effect of MPO expression on motor abilities in the A53T-a-syn model. As early as two months of age, the hMPO-A53T-a-syn model exhibited greater impairment of motor skills such as reduced ability to maintain balance on a rotating rod, reduced ability to walk across a balance beam, and reduced ability to support their weight on an inverted cage top. These findings indicate earlier onset of motor impairment in the hMPO-A53T-a-syn model. Survival curves further showed the hMPO-A53T-asyn mice reached end stage paralysis earlier than A53T-a-syn mice. Immunohistology and in situ hybridization revealed MPO protein and mRNA expression in subsets of neurons in cortex, hippocampus, midbrain, thalamus, and spinal base of hMPO-A53T-a-syn. MPO was also detected in neurons in human PD substantia nigra. Notably, some neurons contained MPO-positive granules surrounding large aggregates of nitrated a-synuclein. Biochemical analysis showed increased nitration of a-synuclein in the hMPO-A53T-a-syn model. Synaptosomal extracts from MPO-A53T-a-syn brain showed increased levels of nitrated a-synuclein dimers by western analysis (ab509), along with increased levels of insoluble nitrated a-synuclein aggregates detected by cellulose acetate filter trap. Our more recent studies investigate the ability of Siah E3 ubiquitin ligases to target misfolded a-synuclein or other synaptic proteins for proteolytic degradation in the A53T-a-syn model. Findings suggest Siah is less able to protect against neuropathology in the hMPO-A53T-a-syn. In summary, these findings provide evidence that the human MPO gene is expressed in neurons in human PD substantia nigra and in the hMPO-A53T-a-syn model. The hMPO transgene leads to exacerbation of motor impairment correlating with increased nitrated and aggregated a-synuclein.
Funding provided by NIH grant R01NS074303 to W.R.
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