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

Bourdenx M, Dovero S, Engeln M, Bido S, Bastide MF, Dutheil N, Vollenweider I, Baud L, Piron C, Grouthier V, Boraud T, Porras G, Li Q, Baekelandt V, Scheller D, Michel A, Fernagut PO, Georges F, Courtine G, Bezard E, Dehay B - Acta Neuropathol Commun (2015)

Bottom Line: However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression.Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-syn pathology per se.

View Article: PubMed Central - PubMed

Affiliation: University de Bordeaux, Institut des Maladies Neurodégénératives, UMR 5293, 33000, Bordeaux, France.

ABSTRACT

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. α-synuclein (α-syn) is a major constituent of Lewy bodies, and the first disease-causing protein characterized in PD. Several α-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 α-syn toxicity remains however unexplored. In this study, we developed and exploited a recombinant adeno-associated viral (AAV) vector of serotype 9 overexpressing mutated α-syn to elucidate the influence of ageing on the dynamics of PD-related neurodegeneration associated with α-syn pathology in different mammalian species.

Results: Identical AAV pseudotype 2/9 vectors carrying the DNA for human mutant p.A53T α-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 α-syn pathology and second to investigate the relationship between the kinetics of α-syn-induced nigrostriatal degeneration and the progressive onset of motor dysfunctions, strikingly reminiscent of the impairments observed in PD patients. In mice, AAV2/9-hα-syn injection into the substantia nigra was associated with accumulation of α-syn and phosphorylated hα-syn, regardless of mouse strain. However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression. Of note, p-α-syn levels correlated with nigrostriatal degeneration in mice. In monkeys, hα-syn-induced degeneration of the nigrostriatal pathway was not affected by the age of the animals. Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.

Conclusions: In conclusion, AAV2/9-mediated hα-syn induces robust nigrostriatal neurodegeneration in mice, rats and monkeys, allowing translational comparisons among species. Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-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.

No MeSH data available.


Related in: MedlinePlus

rAAV2/9 vector-mediated overexpression of hα-syn in rat SNpc induces progressive dopaminergic neurodegeneration related to hα-syn expression dynamics. (a-e) Representative photomicrographs of dopaminergic markers and human α-syn immunostaining at striatal (a-c) and SNpc (d,e) levels at several time points after injection. (a,d): tyrosine hydroxylase (TH); (b): dopamine transporter (DAT); (c,e): human α-syn. (f) Quantification of the different markers over time. Briefly, stereological quantification of the number of TH-positive cells in the SNpc of rat are reported on the left axis, all staining intensity have been normalized between min (0 %) and max (100 %) and reported on the right axis to allow comparison of the evolution. Dot-lines represent actual values while plain curves are regression curves. Colors are the same as in the upper part of the panel: light blue: striatal TH, purple: striatal DAT, yellow: striatal α-syn, blue: SNpc TH, red: SNpc α-syn. Scales applies to all pictures: 1 mm
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Fig1: rAAV2/9 vector-mediated overexpression of hα-syn in rat SNpc induces progressive dopaminergic neurodegeneration related to hα-syn expression dynamics. (a-e) Representative photomicrographs of dopaminergic markers and human α-syn immunostaining at striatal (a-c) and SNpc (d,e) levels at several time points after injection. (a,d): tyrosine hydroxylase (TH); (b): dopamine transporter (DAT); (c,e): human α-syn. (f) Quantification of the different markers over time. Briefly, stereological quantification of the number of TH-positive cells in the SNpc of rat are reported on the left axis, all staining intensity have been normalized between min (0 %) and max (100 %) and reported on the right axis to allow comparison of the evolution. Dot-lines represent actual values while plain curves are regression curves. Colors are the same as in the upper part of the panel: light blue: striatal TH, purple: striatal DAT, yellow: striatal α-syn, blue: SNpc TH, red: SNpc α-syn. Scales applies to all pictures: 1 mm

Mentions: To determine the course of dopamine neuron degeneration, adult Sprague–Dawley rats received intranigral stereotactic injection of AAV2/9 carrying human p.A53T α-syn (AAV-hα-syn). We then assessed several markers of the nigrostriatal pathway: tyrosine hydroxylase (TH) and dopamine transporter (DAT) immunoreactivities in the striatum as well as the number of TH-positive cells in the SNpc which all correlated with the protein expression of hα-syn in both striatum and SNpc at five time points (72 h, 1, 4, 8 and 16 weeks) (Fig. 1). Intranigral injection of AAV-hα-syn resulted in a markedly significant reduction of dopaminergic fibers, evidenced by a reduction of TH (Fig. 1a and f, Additional file 5: Figure S1a) and DAT (Fig. 1b and f, Additional file 5: Figure S1b) immunostaining, beginning at 1 week and reaching a plateau at 4 weeks, associated with progressive dopamine neuron death ranging from 50 % at 1 week to approximately 80 % at 16 weeks after surgery (Fig. 1d and f, Additional file 5: Figure S1c). A two-phase exponential decay equation models the time-course of SNpc dopaminergic neuron loss (y =2230 + 3707.2728e-2.171x + 3417.877e-0.1069x, r2 = 0.66, Fig. 1f). These results indicate that nigral expression of hα-syn induces progressive dopamine neuron degeneration in rat, in agreement with previous findings [10, 19, 20].Fig. 1


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

Bourdenx M, Dovero S, Engeln M, Bido S, Bastide MF, Dutheil N, Vollenweider I, Baud L, Piron C, Grouthier V, Boraud T, Porras G, Li Q, Baekelandt V, Scheller D, Michel A, Fernagut PO, Georges F, Courtine G, Bezard E, Dehay B - Acta Neuropathol Commun (2015)

rAAV2/9 vector-mediated overexpression of hα-syn in rat SNpc induces progressive dopaminergic neurodegeneration related to hα-syn expression dynamics. (a-e) Representative photomicrographs of dopaminergic markers and human α-syn immunostaining at striatal (a-c) and SNpc (d,e) levels at several time points after injection. (a,d): tyrosine hydroxylase (TH); (b): dopamine transporter (DAT); (c,e): human α-syn. (f) Quantification of the different markers over time. Briefly, stereological quantification of the number of TH-positive cells in the SNpc of rat are reported on the left axis, all staining intensity have been normalized between min (0 %) and max (100 %) and reported on the right axis to allow comparison of the evolution. Dot-lines represent actual values while plain curves are regression curves. Colors are the same as in the upper part of the panel: light blue: striatal TH, purple: striatal DAT, yellow: striatal α-syn, blue: SNpc TH, red: SNpc α-syn. Scales applies to all pictures: 1 mm
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4513748&req=5

Fig1: rAAV2/9 vector-mediated overexpression of hα-syn in rat SNpc induces progressive dopaminergic neurodegeneration related to hα-syn expression dynamics. (a-e) Representative photomicrographs of dopaminergic markers and human α-syn immunostaining at striatal (a-c) and SNpc (d,e) levels at several time points after injection. (a,d): tyrosine hydroxylase (TH); (b): dopamine transporter (DAT); (c,e): human α-syn. (f) Quantification of the different markers over time. Briefly, stereological quantification of the number of TH-positive cells in the SNpc of rat are reported on the left axis, all staining intensity have been normalized between min (0 %) and max (100 %) and reported on the right axis to allow comparison of the evolution. Dot-lines represent actual values while plain curves are regression curves. Colors are the same as in the upper part of the panel: light blue: striatal TH, purple: striatal DAT, yellow: striatal α-syn, blue: SNpc TH, red: SNpc α-syn. Scales applies to all pictures: 1 mm
Mentions: To determine the course of dopamine neuron degeneration, adult Sprague–Dawley rats received intranigral stereotactic injection of AAV2/9 carrying human p.A53T α-syn (AAV-hα-syn). We then assessed several markers of the nigrostriatal pathway: tyrosine hydroxylase (TH) and dopamine transporter (DAT) immunoreactivities in the striatum as well as the number of TH-positive cells in the SNpc which all correlated with the protein expression of hα-syn in both striatum and SNpc at five time points (72 h, 1, 4, 8 and 16 weeks) (Fig. 1). Intranigral injection of AAV-hα-syn resulted in a markedly significant reduction of dopaminergic fibers, evidenced by a reduction of TH (Fig. 1a and f, Additional file 5: Figure S1a) and DAT (Fig. 1b and f, Additional file 5: Figure S1b) immunostaining, beginning at 1 week and reaching a plateau at 4 weeks, associated with progressive dopamine neuron death ranging from 50 % at 1 week to approximately 80 % at 16 weeks after surgery (Fig. 1d and f, Additional file 5: Figure S1c). A two-phase exponential decay equation models the time-course of SNpc dopaminergic neuron loss (y =2230 + 3707.2728e-2.171x + 3417.877e-0.1069x, r2 = 0.66, Fig. 1f). These results indicate that nigral expression of hα-syn induces progressive dopamine neuron degeneration in rat, in agreement with previous findings [10, 19, 20].Fig. 1

Bottom Line: However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression.Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-syn pathology per se.

View Article: PubMed Central - PubMed

Affiliation: University de Bordeaux, Institut des Maladies Neurodégénératives, UMR 5293, 33000, Bordeaux, France.

ABSTRACT

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. α-synuclein (α-syn) is a major constituent of Lewy bodies, and the first disease-causing protein characterized in PD. Several α-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 α-syn toxicity remains however unexplored. In this study, we developed and exploited a recombinant adeno-associated viral (AAV) vector of serotype 9 overexpressing mutated α-syn to elucidate the influence of ageing on the dynamics of PD-related neurodegeneration associated with α-syn pathology in different mammalian species.

Results: Identical AAV pseudotype 2/9 vectors carrying the DNA for human mutant p.A53T α-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 α-syn pathology and second to investigate the relationship between the kinetics of α-syn-induced nigrostriatal degeneration and the progressive onset of motor dysfunctions, strikingly reminiscent of the impairments observed in PD patients. In mice, AAV2/9-hα-syn injection into the substantia nigra was associated with accumulation of α-syn and phosphorylated hα-syn, regardless of mouse strain. However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression. Of note, p-α-syn levels correlated with nigrostriatal degeneration in mice. In monkeys, hα-syn-induced degeneration of the nigrostriatal pathway was not affected by the age of the animals. Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.

Conclusions: In conclusion, AAV2/9-mediated hα-syn induces robust nigrostriatal neurodegeneration in mice, rats and monkeys, allowing translational comparisons among species. Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-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.

No MeSH data available.


Related in: MedlinePlus