Lack of additive role of ageing in nigrostriatal neurodegeneration triggered by alpha-synuclein overexpression

Introduction: Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons as well as the presence of proteinaceous inclusions named Lewy bodies. alpha synuclein (alpha-syn) is a major constituent of Lewy bodies, and the first disease-causing protein characterized in PD. Several alpha-syn-based animal models of PD have been developed to investigate the pathophysiology of PD, but none of them recapitulate the full picture of the disease. Ageing is the most compelling and major risk factor for developing PD but its impact on alpha-syn toxicity remains however unexplored. In this study, we developed and exploited a recombinant adeno-associated viral (AAV) vector of serotype 9 overexpressing mutated alpha-syn to elucidate the influence of ageing on the dynamics of PD-related neurodegeneration associated with alpha-syn pathology in different mammalian species. Results: Identical AAV pseudotype 2/9 vectors carrying the DNA for human mutant p.A53T alpha-syn were injected into the substantia nigra to induce neurodegeneration and synucleinopathy in mice, rats and monkeys. Rats were used first to validate the ability of this serotype to replicate alpha-syn pathology and second to investigate the relationship between the kinetics of alpha-syn-induced nigrostriatal degeneration and the progressive onset of motor dysfunctions, strikingly reminiscent of the impairments observed in PD patients. In mice, AAV2/9-h alpha-syn injection into the substantia nigra was associated with accumulation of alpha-syn and phosphorylated h alpha-syn, regardless of mouse strain. However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to h alpha-syn overexpression. Of note, p-alpha-syn levels correlated with nigrostriatal degeneration in mice. In monkeys, h alpha-syn-induced degeneration of the nigrostriatal pathway was not affected by the age of the animals. Unlike mice, m onkeys did not exhibit correlations between levels of phosphorylated alpha-syn and neurodegeneration. Conclusions: In conclusion, AAV2/9-mediated h alpha-syn induces robust nigrostriatal neurodegeneration in mice, rats and monkeys, allowing translational comparisons among species. Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor alpha-syn pathology per se. Our unprecedented multi-species investigation thus favours the multiple-hit hypothesis for PD wherein ageing would merely be an aggravating, additive, factor superimposed upon an independent disease process.

Conditional expression of Parkinson's disease-related R1441C LRRK2 in midbrain dopaminergic neurons of mice causes nuclear abnormalities without neurodegeneration

Shi-Yan Caroline Foo, Liliane Glauser, Meghna Kannan, Graham Knott, Darren Moore, Elpida Tsika

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause late-onset, autosomal dominant Parkinson's disease (PD). The clinical and neurochemical features of LRRK2-linked PD are similar to idiopathic disease although neuropathology is somewhat heterogeneous. Dominant mutations in LRRK2 precipitate neurodegeneration through a toxic gain-of-function mechanism which can be modeled in transgenic mice overexpressing human LRRK2 variants. A number of LRRK2 transgenic mouse models have been developed that display abnormalities in dopaminergic neurotransmission and alterations in tau metabolism yet without consistently inducing dopaminergic neurodegeneration. To directly explore the impact of mutant LRRK2 on the nigrostriatal dopaminergic pathway, we developed conditional transgenic mice that selectively express human R1441C LRRK2 in dopaminergic neurons from the endogenous murine ROSA26 promoter. The expression of R1441C LRRK2 does not induce the degeneration of substantia nigra dopaminergic neurons or striatal dopamine deficits in mice up to 2 years of age, and fails to precipitate abnormal protein inclusions containing alpha-synuclein, tau, ubiquitin or autophagy markers (LC3 and p62). Furthermore, mice expressing R1441C LRRK2 exhibit normal motor activity and olfactory function with increasing age. Intriguingly, the expression of R1441C LRRK2 induces age-dependent abnormalities of the nuclear envelope in nigral dopaminergic neurons including reduced nuclear circularity and increased invaginations of the nuclear envelope. In addition, R1441C LRRK2 mice display increased neurite complexity of cultured midbrain dopaminergic neurons. Collectively, these novel R1441C LRRK2 conditional transgenic mice reveal altered dopaminergic neuronal morphology with advancing age, and provide a useful tool for exploring the pathogenic mechanisms underlying the R1441C LRRK2 mutation in PD. (C) 2014 Elsevier Inc All rights reserved.

Elsevier2014

Exploring the pathological interaction between LRRK2 and alpha-synuclein

Alessandra Musso

Parkinson’s disease (PD) is the most common age-related neurodegenerative movement disorder that affects 1-2% of the general population over the age of 65 and rising to 4-5% over 80 years of age. It is estimated that 6.3 million people worldwide have Parkinson’s disease and 1.2 million in the European Union (EU) alone. As the disease progresses, patients frequently develop a mask-like facial expression, festinating gait and cognitive impairment and the final clinical symptoms are muscle rigidity, bradykinesia, resting tremor and postural instability in addition to non-motor problems that result in a marked reduction in quality of life. The motor symptoms of PD arise from the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) leading to a deficiency of the neurotransmitter dopamine (DA) in the striatum. While dopamine replacement therapy is initially effective in treating the motor symptoms of PD, there is no known cure or neuroprotective therapy for this debilitating disease. Although the pathology underlying the disease is well defined, it is still unclear why DAergic neurons degenerate and die. PD is generally considered as a sporadic disease of unknown etiology, however in the last two decades it has become clear that heritability plays an important role in the pathogenesis of PD. Of the different genes associated with familial disease, mutations in two genes encoding for α-synuclein and leucine-rich repeat kinase 2 (LRRK2) proteins cause autosomal dominant PD. One of the neuropathological hallmarks of idiopathic and some familial forms of PD are Lewy bodies, which are intracytoplasmic inclusions that are enriched with fibrillar α- synuclein protein. Notably, LRRK2 mutation carriers with PD predominantly develop Lewy body pathology suggesting that LRRK2 may lie upstream of α-synuclein aggregation. These observations and other in vivo studies have suggested a common pathogenic pathway with LRRK2 potentially regulating the aggregation and neuronal toxicity of α-synuclein. However, the relationship between LRRK2 and α-synuclein in the mammalian brain is presently unclear and requires further evaluation, especially within midbrain dopaminergic neurons that degenerate in PD. The aim of this thesis work was to delineate a potential pathogenic interplay between these two PD-related gene products in mediating neurodegeneration in vivo. Understanding how and where the functional pathways of LRRK2 and α-synuclein converge will provide important insight into the common mechanisms underlying neurodegeneration in PD.[...]

EPFL2014

PGC-1 alpha activity in nigral dopamine neurons determines vulnerability to alpha-synuclein

Wojciech Janusz Bobela, Graham Knott, Bernard Schneider, Lu Zheng

Introduction: Mitochondrial dysfunction and oxidative stress are critical factors in the pathogenesis of age-dependent neurodegenerative diseases. PGC-1 alpha, a master regulator of mitochondrial biogenesis and cellular antioxidant defense, has emerged as a possible therapeutic target for Parkinson's disease, with important roles in the function and survival of dopaminergic neurons in the substantia nigra. The objective of this study is to determine if the loss of PGC-1 alpha activity contributes to alpha-synuclein-induced degeneration. Results: We explore the vulnerability of PGC-1 alpha null mice to the accumulation of human alpha-synuclein in nigral neurons, and assess the neuroprotective effect of AAV-mediated PGC-1 alpha expression in this experimental model. Using neuronal cultures derived from these mice, mitochondrial respiration and production of reactive oxygen species are assessed in conditions of human alpha-synuclein overexpression. We find ultrastructural evidence for abnormal mitochondria and fragmented endoplasmic reticulum in the nigral dopaminergic neurons of PGC-1 alpha null mice. Furthermore, PGC-1 alpha null nigral neurons are more prone to degenerate following overexpression of human alpha-synuclein, an effect more apparent in male mice. PGC-1 alpha overexpression restores mitochondrial morphology, oxidative stress detoxification and basal respiration, which is consistent with the observed neuroprotection against alpha-synuclein toxicity in male PGC-1 alpha null mice. Conclusions: Altogether, our results highlight an important role for PGC-1 alpha in controlling the mitochondrial function of nigral neurons accumulating alpha-synuclein, which may be critical for gender-dependent vulnerability to Parkinson's disease.

Biomed Central Ltd2015