Spatial and temporal pathophysiology of developmental dystonia

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PROJECT SUMMARY/ABSTRACT Neurological and neuropsychiatric diseases are a growing concern worldwide, as the consequences are often lethal, or at best they leave patients incapacitated. One such disease is dystonia, which overwhelms affected people with severe motor difficulties including painful muscle over-contractions, twisting of the body and tremor in the limbs. Despite recent efforts in identifying the brain circuits that contribute to dystonia, as well as the success of deep brain stimulation (DBS) as a therapy for adults, pediatric patients face unique long-term health concerns, with poor treatment options for many kids since the timing of disease onset is unclear. Such barriers arise as developing circuits are dynamic; and functional changes that promote brain maturation create hurdles for using deep brain stimulation. An overarching problem, however, is that we currently have little insight into how the brain regions and circuits that mediate dystonia emerge during embryonic and early postnatal life. As a first step towards better defining the developmental mechanisms that instigate dystonia, we have found that conditional loss of a single gene, engrailed1 (En1), which is required for brain morphogenesis, results in severe dystonia in mice. En1 and its homolog engrailed 2 (En2) are homeobox-containing genes that cooperate to control midbrain and hindbrain development. The basal ganglia, which are partly located in the midbrain, and the cerebellum, which is entirely located within the hindbrain, are the two main structures that are thought to drive dystonia pathophysiology. Intriguingly, manipulations of En1 alone leave the basal ganglia intact, but alter cerebellar circuit patterning. Based on the cerebellar focus of the En1 conditional phenotype, we argue that severe dystonia originates from genetically- defined defects that disrupt cerebellar circuit maturation. We generated three specific aims to test this hypothesis in vivo. In Aim1, we will use conditional genetic manipulations in combination with in vivo electrophysiology and quantitative behavioral paradigms to uncover the temporal dependence of En1 in setting the severity of developmental dystonia. In Aim2, we will perform cell-type specific deletions of En1 and then conduct in vivo electrophysiology in behaving pups to define the neural signatures of the En1-dependent cerebellar circuits that trigger early-onset dystonia. Although the cerebellum and basal ganglia are present in En1 mutants, it is unclear if their circuits are mis-wired to a point that is beyond repair. In Aim3, we will use the En1 lineage to target optogenetic DBS to the cerebellum and basal ganglia to test which region restores mobility in En1 mutants. Then, we will deliver optogenetic stimulation to the En1 lineage in control mice to test which of these regions can initiate dystonia in otherwise normal young and adult mice. Designing better treatment options for incurable motor diseases will improve healthcare considerations and enhance the quality of life for pediatric patients.