Neuronal adenosine A2A receptor overexpression is neuroprotective towards 3-nitropropionic acid-induced striatal toxicity: a rat model of Huntington's disease

Abstract

The A_2A adenosine receptor (A_2AR) is widely distributed on different cellular types in the brain, where it exerts a broad spectrum of pathophysiological functions, and for which a role in different neurodegenerative diseases has been hypothesized or demonstrated. To investigate the role of neuronal A_2ARs in neurodegeneration, we evaluated in vitro and in vivo the effect of the neurotoxin 3-nitropropionic acid (3-NP) in a transgenic rat strain overexpressing A_2ARs under the control of the neural-specific enolase promoter (NSEA_2A rats). We recorded extracellular field potentials (FP) in corticostriatal slice and found that the synaptotoxic effect of 3-NP was significantly reduced in NSEA_2A rats compared with wild-type animals (WT). In addition, after exposing corticostriatal slices to 3-NP 10 mM for 2 h, we found that striatal cell viability was significantly higher in NSEA_2A rats compared to control rats. These in vitro results were confirmed by in vivo experiments: daily treatment of female rats with 3-NP 10 mg/kg for 8 days induced a selective bilateral lesion in the striatum, which was significantly reduced in NSEA_2A compared to WT rats. These results demonstrate that the overexpression of the A_2AR selectively at the neuronal level reduced 3-NP-induced neurodegeneration, and suggest an important function of the neuronal A_2AR in the modulation of neurodegeneration.

Keywords: 3-Nitropropionic acid; Adenosine A2A receptors; Huntington’s disease; Striatum; Synaptic transmission.

Fig. 1

Electrophysiological experiments showing the effect of 3-NP on synaptic transmission in corticostriatal slices. a The concentration of 5 mM 3-NP, applied for 20 min, induced a reduction of synaptic transmission in both WT (n = 9) and NSEA_2A (n = 8) rats, that partially recovered 20 min after the washout, with no difference between the two genotypes (b); c slice perfusion with 3-NP 10 mM induced a stronger effect in both WT (n = 8) and NSEA_2A (n = 8) and the recovery 20 min after 3-NP washout was significantly higher in NSEA_2A than in WT (d); the application of ZM 241385 to corticostriatal slices from NSEA_2A rats (1 μM, 10 min before and along with 3-NP, n = 4) worsened 3-NP-induced synaptic depression and, as a result, the effect of 3-NP was comparable to that in WT slices (e). Each point represents the mean of three responses; insets in a show FPs before, during, and after 3-NP application in WT and NSEA_2A rats. Horizontal bars indicate the period of drug application. *p ≤ 0.05 vs. WT, Student’s t test

Fig. 2

Different effect of 3-NP on striatal cell viability in corticostriatal slices from WT and NSEA_2A rats. Corticostriatal slices were incubated for 2 h with 3-NP (10 mM) and then cell viability of the striatal area was evaluated by MTT assay. Bar graphs show the mean ± S.E.M. of cell viability in WT (n = 12) and NSEA_2A (n = 9) slices with respect to control values. *p ≤ 0.05 vs. CTR, Student’s t test

Fig. 3

Histological evaluation of 3-NP lesions in WT and NSEA_2A rats. a Serial brain sections obtained from WT and NSEA_2A rats showing striatal lesions (uncolored areas) induced by i.p. injection of 3-NP. b Bar graphs represent the mean of the lesioned areas (mm²) in WT (n = 6) and NSEA_2A (n = 5) rats calculated by Image J software. *p ≤ 0.05 vs. WT, Mann–Whitney U test