Modelling Parkinson's disease with α-synuclein transgenic mice

• Main Author: Scudamore, Owen
• Other Authors: Wang, Xin
• Published: University of Manchester 2013
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.764268

Parkinson's disease is a chronic, progressive, neurodegenerative movement disorder characterised by bradykinesia, tremor at rest, rigidity and postural instability. The pathological hallmark of the malady is a loss of dopaminergic nigrostriatal neurons, coupled with the inclusion of Lewy bodies and Lewy neurites within the axons and processes of remaining neurons. The exact cause of the disorder remains elusive; however, rare inherited forms of the disease have highlighted specific genes involved in pathogenic pathways that could be germane to sporadic cases. alpha-Synuclein is one such gene, wherein mutations and multiplications provoke abnormal folding and aggregation of the protein to induce pathology. The relevance of alpha-synuclein to sporadic Parkinson's disease is strongly supported by the fact that it is the primary component of Lewy bodies. This has prompted the development of numerous transgenic animals based on alpha-synuclein overexpression; however, none of the models to date represents a perfect replicate of the human Parkinsonian pathology. Indeed, the use of different promoters and transgenes in mice has led to various phenotypes coupled with non-specific, non-existent or late-onset neurodegeneration. Since the majority of alpha-synuclein found within aggregates in PD brain is phosphorylated, it has been postulated that this post-translational modification could be the aggravating factor that initiates aggregation; however, phosphorylation could also be a late event, which occurs after alpha-synuclein is sequestered into inclusions, but where it remains accessible by relevant kinases. In the literature, there is contrasting evidence suggesting that phosphorylated alpha-synuclein is either inductive or preventative of aggregation. Therefore I produced two inducible transgenic mice that would overexpress mutant human alpha-synuclein in Purkinje cells to investigate the in vivo affect of alpha-synuclein phosphorylation on aggregation. The two constructs both contained the PD-linked A53T mutation, in addition to either an S87A or an S129A mutation; the substitution of serine with alanine in these constructs blocks phosphorylation occurring at that position. The mice were then aged and characterised on both a behavioural and a histopathological level. Although at present (age: 16 months) neither of the two lines exhibits any obvious alpha-synuclein pathology, they both present with a seizure phenotype and exhibit significantly reduced horizontal and vertical movement than wild-type controls in the Actimot open field. A different theory for the pathogenesis of PD indicates a role for malfunctioning mitochondria and oxidative stress. In a third mutant line, I wanted to assess the impact of increased oxidative stress on alpha-synuclein aggregation in vivo. Therefore I crossed a previously characterised mouse model of PD with a line haplodeficient for SOD2. This gene codes for a mitochondrial enzyme that scavenges free radicals, thus normally protecting the mitochondria from oxidative stress. The pathology of the haplodeficient SOD2 alpha-synuclein mice was compared with that of wt SOD2 alpha-synuclein mice at an age of 16 months using a combination of Western-blot, PK-PET-blot and immunohistochemical techniques. A significant difference was detected between the two lines suggesting that SOD2 deficiency accelerated alpha-synuclein pathology.