Inactivation of neuronal forebrain A receptors protects dopaminergic neurons in a mouse model of Parkinson's disease - PubMed (original) (raw)

Inactivation of neuronal forebrain A receptors protects dopaminergic neurons in a mouse model of Parkinson's disease

Anna R Carta et al. J Neurochem. 2009 Dec.

Abstract

Adenosine A(2A) receptors antagonists produce neuroprotective effects in animal models of Parkinson's disease (PD). As neuroinflammation is involved in PD pathogenesis, both neuronal and glial A(2A) receptors might participate to neuroprotection. We employed complementary pharmacologic and genetic approaches to A(2A) receptor inactivation, in a multiple MPTP mouse model of PD, to investigate the cellular basis of neuroprotection by A(2A) antagonism. MPTP.HCl (20 mg/kg daily for 4 days) was administered in mice treated with the A(2A) antagonist SCH58261, or in conditional knockout mice lacking A(2A) receptors on forebrain neurons (fbnA(2A)KO mice). MPTP-induced partial loss of dopamine neurons in substantia nigra pars compacta (SNc) and striatum (Str), associated with increased astroglial and microglial immunoreactivity in these areas. Astroglia was similarly activated 1, 3, and 7 days after MPTP administration, whereas maximal microglial reactivity was detected on day 1, returning to baseline 7 days after MPTP administration. SCH58261 attenuated dopamine cell loss and gliosis in SNc and Str. Selective depletion of A(2A) receptors in fbnA(2A)KO mice completely prevented MPTP-induced dopamine neuron degeneration and gliosis in SNc, and partially counteracted gliosis in Str. Results provide evidence of a primary role played by neuronal A(2A) receptors in neuroprotective effects of A(2A) antagonists in a multiple MPTP injections model of PD. With the symptomatic antiparkinsonian potential of several A(2A) receptor antagonists being pursued in clinical trials, this study adds to the rationale for broader clinical benefit and use of these drugs early in the treatment of PD.

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Figures

Fig 1

Fig 1. Adenosine A2A receptor antagonist SCH58261 prevents dopaminergic cell loss in the SNc

(A) shows representative sections immunostained for TH from SNc of mice sacrificed 3 days after MPTP treatment. Left insert shows TH-positive cells at higher magnification, right insert shows cresyl violet-stained sections; scale bar: 50 μm. Mice were treated with MPTP-HCl (20 mg/kg once a day for 4 days), plus SCH58261 (0.5 mg/kg) or vehicle (twice a day during MPTP treatment and once daily thereafter until sacrifice), and sacrificed 1, 3, 7 days after MPTP treatment. (B) shows analysis of TH immunostaining at 1, 3, 7 days after MPTP, reported as a percentage of TH-positive cells as compared to vehicle-treated mice. * indicates p<0.001 versus vehicle; # indicates p<0.001 versus MPTP group, by Tukey’s post hoc test. Scale bar: 50 μm.

Fig 2

Fig 2. Adenosine A2A receptor antagonist SCH58261 attenuates degeneration of dopaminergic terminals in the Str

(A) representative sections immunostained for TH, from the Str of mice sacrificed 3 days after MPTP treatment. (B) Results from pharmacological blockade with SCH58261 or genetic A2AR depletion are presented. In the left column, − and + indicate the administration of vehicle or SCH58261to MPTP-treated mice. In the right column + and − indicate fbnA2AWT and fbnA2AKO mice, respectively.

Fig 3

Fig 3. Adenosine A2A receptor antagonist SCH58261 counteracts astroglia activation in the SNc and Str

(A) shows representative sections immunostained for GFAP, from SNc (upper images) and Str (lower images) of mice sacrificed 3 days after MPTP treatment. Mice were treated as described in Fig 1. (B) shows analysis of GFAP immunostaining 1, 3, 7 days after MPTP, reported as percentage of GFAP-positive cells as compared to vehicle-treated mice in the SNc (left graph) and in the Str (right graph). * indicates p<0.001 versus corresponding vehicle and MPTP+SCH58261 groups; # indicates p<0.001 versus corresponding MPTP group, by Tukey’s post hoc test. Scale bar: 50 μm.

Fig 4

Fig 4. Adenosine A2A receptor antagonist SCH58261 counteracts microglia activation

(A) Representative images from the SNc immunostained for CD11b as a marker of microglia activation. Mice were treated as described in Fig 1 and sacrificed 1, 3, 7 days after MPTP treatment. (B) CD11b analysis in SNc and Str was performed in grey-scale digitized images. The area occupied by grey values above a threshold was calculated and expressed as square pixels and as percentage of vehicle-treated mice. Tukey’s post hoc test: * p<0.001 versus vehicle and MPTP+SCH58261 group; # p<0.001 versus MPTP group; ^, ^^ p<0.05, p<0.001 versus the indicated time point. Scale bar: 50 μm.

Fig 5

Fig 5. fbnA2A KO mice are protected against MPTP-induced loss of dopaminergic cells in the SNc

(A) shows representative sections from SNc immunostained for TH. Inserts show higher magnification of TH-labelled (left) and cresyl violet-labelled (right) cells. Mice were treated with MPTP (20 mg/kg once a day for 4 days)or vehicle. (B) shows analysis of TH immunostaining in fbnA2AKO mice, reported as a percentage of TH-positive cells as compared to vehicle-treated mice. Tukey’s post hoc test: * p<0.05 versus vehicle group; # p<0.05 versus WT MPTP group. Scale bar: 50 μm.

Fig 6

Fig 6. Astroglia activation is attenuated in SNc and Str of fbnA2AKO mice

(A) representative images from the SNc immunostained for GFAP, as a marker of astroglial cells. (B) Graphs show the analysis of GFAP immunostaining in SNc and Str, in fbnWT and fbnA2AKO mice treated with vehicle or MPTP. Tukey’s post hoc test: * p<0.001 versus vehicle group; # p<0.001 versus WT MPTP group. Scale bar: 50 μm.

Fig 7

Fig 7. Microglia activation is prevented in SNc and Str of fbnA2AKO mice

(A) representative images from the SNc immunostained for CD11b, as a marker of microglia activation. (B) Graphs show the analysis of CD11b immunostaining in SNc and Str, in fbnWT and fbnA2AKO mice treated with vehicle or MPTP. Tukey’s post hoc test: * p<0.001 versus vehicle group; # p<0.001 versus WT MPTP group. Scale bar: 50 μm.

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