Dystonia is characterized by involuntary muscle contractions that cause debilitating twisting movements and postures. Striatal dysfunction has been implicated in many forms of dystonia, including idiopathic dystonias, inherited dystonias and iatrogenic dystonias. The vast majority of neurons in the striatum are GABAergic spiny projection neurons (SPNs). SPNs express either D1 dopamine receptors (D1Rs) or D2 dopamine receptors (D2Rs). D1Rs are expressed on direct pathway SPNs (dSPNs) that project to the GPi to promote movement. D2Rs are expressed on indirect pathway SPNs (iSPNs) that project to the external pallidum (GPe) to inhibit movement. Convergent results from genetic, imaging and physiological studies in patients suggest that abnormalities of both dSPNs and iSPNs contribute to the expression of dystonia. Despite the overwhelming evidence implicating striatal dysfunction in dystonia, the precise nature of the striatal defects that give rise to dystonia are not known. Research focused on understanding striatal dysfunction in dystonia has been stymied by the lack of animal models with dystonic movements that are specifically associated with striatal dysfunction. To overcome this obstacle, we recently generated a knockin mouse model of DOPA-responsive dystonia (DRD). The DRD mouse strain carries the human DRD-causing Q381K mutation in tyrosine hydroxylase (ThDRD; DRD mice). Like the human disorder, DRD mice exhibit dystonic movements that that improve in response to L-DOPA administration. Notably, striatal DA neurotransmission, including abnormal D1R and D2R signaling, plays a central role in the expression of dystonia. Thus, this novel mouse model provides an unparalleled opportunity to understand the molecular mechanisms underlying dSPN and iSPN dysfunction in dystonia.
The Specific Aim i s to identify cell-type specific changes in the translatome of dSPNs and iSPNs in DRD mice. In light of how little is known about striatal dysfunction in dystonia, a hypothesis-generating approach that provides a comprehensive account of dSPN and iSPN cell-type specific molecular adaptations is needed to fully decipher the pathogenesis of dystonia. However, a major challenge to understanding cell-type specific molecular changes in dystonia is the complexity of striatal anatomy. Because dSPNs and iSPNs are intermingled throughout the striatum, traditional whole tissue RNA-seq is not useful for delineating cell-type specific abnormalities. Therefore, we will isolate translating ribosomes (Translating Ribosome Affinity Purification (TRAP)) from genetically identified dSPNs and iSPNs in normal and DRD mice to identify abnormally regulated processes and pathways associated with dystonia. This approach will provide unprecedented insight into the cell-type specific molecular abnormalities in dystonia.
Although dystonia is the third most common movement disorder after tremor and Parkinson?s disease, treatments for dystonia are inadequate because the underlying neuronal dysfunction is not well understood. Several lines of evidence implicate basal ganglia pathophysiology in dystonia. Understanding cell-type specific molecular adaptations of neurons within the basal ganglia will provide the foundation critically needed to discover specific neuronal defects that cause dystonia and to discover highly specific targets for the treatment of dystonia.
