Subtle changes in striatal muscarinic M1 and M4 receptor expression in the DYT1 knock-in mouse model of dystonia.

Franziska Richter,Laura Klein,Angelika Richter,Christin Helmschrodt,Yuqing Li

doi:10.1371/journal.pone.0226080

Abstract

In early-onset generalized torsion dystonia, caused by a GAG deletion in TOR1A (DYT1), enhanced striatal cholinergic activity has been suggested to be critically involved. Previous studies have shown increased acetylcholine levels in the striatum of DYT1 knock-in (KI) mice. Ex vivo data indicated that muscarinic receptor antagonists normalize the activity of striatal cholinergic interneurons. Currently receptor subtype specific antagonists are developed for therapy, however, it is yet unknown whether the levels of targeted receptors are unaltered. In the present study, we firstly examined the expression of M1 and M4 receptors in DYT1 KI mice in comparison to wildtype mice. While no changes in mRNA were found in the motor cortex, the expression of M1 was higher in the striatum of DYT1 KI. However, M1 protein did not differ in striatum and cortex between the animal groups as shown by immunohistochemistry and western blot. M4 receptor protein, unaltered in the cortex, was slightly lower in lateral subparts of the striatum, but unchanged in somata of cholinergic interneurons and substance P immunoreactive projection neurons. Functional alterations of the cholinergic system and of aberrant striatal plasticity, demonstrated by previous studies, seem not to be related to overt changes in M1 and M4 expression. This critically informs the ongoing development of respective antagonists for therapy of dystonia.

Highlights

Various types of generalized dystonia, characterized by sustained or intermittent involuntary movements, are regarded as a network disorder that involves corticostriatal dysfunctions and abnormal basal ganglia outflow [1, 2]
In order to extend the knowledge on striatal cholinergic dysfunctions in DYT1 dystonia, we examined the expression of cortical and striatal muscarinic 1 (M1) and M4 receptors in DYT1 (ΔGAG) knock-in mice (DYT1 KI) mice in the present study
In view of therapeutic benefit of M1-preferring receptor antagonists in some patients with isolated, generalized dystonia [19], strong evidence for striatal cholinergic dysregulation in DYT1 models such as DYT1 knock-in mice [3, 6], and the hypothesis that M4 receptors could be an interesting target for the treatment of dystonia [15, 20], we determined the expression of M1 and M4 receptors in the striatum and motor cortex in the DYT1 KI model in the present study

Summary

Introduction

Various types of generalized dystonia, characterized by sustained or intermittent involuntary movements, are regarded as a network disorder that involves corticostriatal dysfunctions and abnormal basal ganglia outflow [1, 2]. Symptoms like other viable DYT1 models [4], extracellular acetylcholine was found to be increased in the striatum and blocking of acetylcholine receptors normalized D2 receptor mediated effects on striatal ChI [5]. In addition to these interesting findings, our data on in vivo optogenetic stimulations of striatal ChI supported an endophenotype of dysregulated cholinergic activity, depolarizing of these interneurons was not sufficient to induce overt dystonia in DYT1 KI mice [6]

Methods

Results

Conclusion