Alteration of striatal dopaminergic neurotransmission in a mouse model of DYT11 myoclonus-dystonia

Abstract

Background: DYT11 myoclonus-dystonia (M-D) syndrome is a neurological movement disorder characterized by myoclonic jerks and dystonic postures or movement that can be alleviated by alcohol. It is caused by mutations in SGCE encoding ε-sarcoglycan (ε-SG); the mouse homolog of this gene is Sgce. Paternally-inherited Sgce heterozygous knockout (Sgce KO) mice exhibit myoclonus, motor impairment and anxiety- and depression-like behaviors, modeling several clinical symptoms observed in DYT11 M-D patients. The behavioral deficits are accompanied by abnormally high levels of dopamine and its metabolites in the striatum of Sgce KO mice. Neuroimaging studies of DYT11 M-D patients show reduced dopamine D2 receptor (D2R) availability, although the possibility of increased endogenous dopamine, and consequently, competitive D2R occupancy cannot be ruled out.

Methodology/principal findings: The protein levels of striatal D2R, dopamine transporter (DAT), and dopamine D1 receptor (D1R) in Sgce KO mice were analyzed by Western blot. The striatal dopamine release after amphetamine injection in Sgce KO mice were analyzed by microdialysis in vivo. The striatal D2R was significantly decreased in Sgce KO mice without altering DAT and D1R. Sgce KO mice also exhibited a significant increase of dopamine release after amphetamine injection in comparison to wild-type (WT) littermates.

Conclusion/significance: The results suggest ε-SG may have a role in the regulation of D2R expression. The loss of ε-SG results in decreased striatal D2R, and subsequently leads to increased discharge of dopamine which could contribute to the behavioral impairment observed in DYT11 dystonia patients and in Sgce KO mice. The results suggest that reduction of striatal D2R and enhanced striatal dopamine release may contribute to the pathophysiology of DYT11 M-D patients.

Figure 1. Extracellular dopamine levels in the mouse striatum after amphetamine administration.

(A) Amphetamine (5 mg/kg, s.c.) was administrated to conscious mice. Extracellular levels of dopamine in the striatum were measured by in vivo microdialysis. The basal extracellular dopamine levels were 4.013±0.267 pg/20 µl (mean ± SEM of 6 Sgce KO mice) and 4.297±0.412 pg/20 µl (mean ± SEM of 8 WT littermates). The data are the mean ± SEM of 6 or 8 mice (*p<0.05). (B) A representative coronal section of the striatum of probe implanted mouse. The black arrow indicates the location of the probe. Scale bar represents 500 µm.

Figure 2. Western blot analysis of striatal D1R, D2R and DAT.

Western blot analysis by using the striatal protein extracts from paternally inherited Sgce KO mice and their WT littermates. The representative bands D2R (Fig. 2A), D1R (Fig. 2C), DAT (Fig. 2B), and GAPDH are shown in the left side, and the quantified results are shown in the right side. The vertical bars represent means ± SEM of 3 or 4 mice (**p<0.01).