Expression of human E46K-mutated α-synuclein in BAC-transgenic rats replicates early-stage Parkinson's disease features and enhances vulnerability to mitochondrial impairment

Abstract

Parkinson’s disease (PD), the second most common neurodegenerative disorder, is etiologically heterogeneous, with most cases thought to arise from a combination of environmental factors and genetic predisposition; about 10% of cases are caused by single gene mutations. While neurotoxin models replicate many of the key behavioral and neurological features, they often have limited relevance to human exposures. Genetic models replicate known disease-causing mutations, but are mostly unsuccessful in reproducing major features of PD. In this study, we created a BAC (bacterial artificial chromosome) transgenic rat model of PD expressing the E46K mutation of α-synuclein, which is pathogenic in humans. The mutant protein was expressed at levels ~2–3-fold above endogenous α-synuclein levels. At 12 months of age, there was no overt damage to the nigrostriatal dopamine system; however, (i) alterations in striatal neurotransmitter metabolism, (ii) accumulation and aggregation of α-synuclein in nigral dopamine neurons, and (iii) evidence of oxidative stress suggest this model replicates several preclinical features of PD. Further, when these animals were exposed to rotenone, a mitochondrial toxin linked to PD, they showed heightened sensitivity, indicating that α-synuclein expression modulates the vulnerability to mitochondrial impairment. We conclude that these animals are well-suited to examination of gene-environment interactions that are relevant to PD.

Chronic exposure to rotenone, a dopaminergic toxin, results in peripheral neuropathy associated with dopaminergic damage

“…A minipump-mediated continuous intravenous infusion of rotenone for 7-35 days resulted in selective pathologic and biochemical changes in the nigro-striatal dopaminergic system [1]. In a recent study, animals expressing a pathogenic mutant of the alpha-synuclein protein, a protein accumulated in Lewy bodies of PD patients, showed a greatly increased sensitivity to rotenone exposure that was accompanied by significantly impaired mitochondrial function and progressive nigro-striatal damage [4]. Additionally, chronic rotenone intoxication, that causes enhanced oxidative and nitrosative stress and induces mitochondrial dysfunction and ultrastructural damage, also resulted in apoptotic cell death in the striatum via a cytochrome c/caspase-3 signaling cascade [11].…”

Subacute manganese exposure in rats is a neurochemical model of early manganese toxicity

“…After immersion in Histoclear for 10 min, slides were blotted dry and coverslipped with DPX mountant. Immunofluorescence quantification was performed similar to previously described (Cannon et al, 2013; Tapias et al, 2014). Briefly, immunofluorescence was detected with the Odyssey infrared imaging system (Li-Cor; Lincoln, NE) at 21μm resolution.…”

From the Cover: Alterations in Optineurin Expression and Localization in Pre-clinical Parkinson’s Disease Models

“…The emergence of qualitative behavioral deficits such as bradykinesia, postural insatiability, and rigidity have been shown to coincide with development of a lesion to the nigrostriatal dopamine system characteristic of late stage PD ). This specific model has been extensively characterized in terms of the temporal development of quantitative behavioral deficits and the emergence of a lesion to the nigrostriatal DA system (Cannon et al, , 2013Tapias et al, 2010Tapias et al, , 2014Zharikov et al, 2015). Of note, sampling time can easily be adjusted to obtain a "pre-clinical" model, where endpoints are assessed prior to the emergence of a behavioral phenotype and overt lesion to the nigrostriatal DA system Sanders et al, 2014aSanders et al, , 2014b.…”

“…Rotenone was administered at 3 mg/kg/ day by intraperitoneal injection as previously described . This model has been extensively characterized in terms of the temporal development of behavioral, neurochemical, and neuropathological alterations in the nigrostriatal dopamine system that are relevant to PD Cannon et al, 2009Cannon et al, , 2013Tapias et al, 2010Tapias et al, , 2014Zharikov et al, 2015). Of note, the dose and/or time of exposure can be adjusted to produce a pre-clinical model, where early stage pathogenesis can be studied, prior to overt cell death Sanders et al, 2014a, b).…”