PTPRD expression regulates sleep consolidation in Drosophila

Abstract

Restless legs syndrome/Willis-Ekbom Disease (RLS/WED) is a common sleep disorder, yet its underlying pathophysiology is poorly understood. Genome-wide association studies (GWAS) point to allelic variants in multiple genes that confer susceptibility to RLS/WED. They offer potential insights into molecular pathways that govern expressivity of symptoms and signs. We used Drosophila melanogaster to explore sleep related physiology of two genes harboring at-risk alleles for RLS which also have highly conserved fly homologs, BTBD9 and PTPRD. Here, we complement our recent report of RLS phenotypes in BTBD9 mutants by exploring whether similar phenotypes exist in PTPRD mutants and probe whether sleep phenotypes are mimicked by dual mutants (i.e., suggesting a common molecular pathway) or are more severely disrupted (i.e., consistent with parallel pathways). Sleep phenotypes resulting from mutations in the fly homolog of PTPRD (dLar) were assayed with the Drosophila Activity Monitor. Flies transgenic for either mutated or wild-type dLar protein allowed for cell-specific manipulation of expression levels. The impact of combined dLar and BTBD9 mutations on sleep architecture was also assessed. Disruption of dLar/PTPRD expression in flies yielded viable, hyperlocomotive animals. dLar mutants exhibit sleep fragmentation and increased wake after sleep onset similar to that observed in BTBD9 mutant flies, the latter of which bears close resemblance to human RLS. The magnitude of fragmentation, as measured by sleep bout number and average sleep bout length, was not further increased by introduction of BTBD9 mutations into the dLar mutant background. Neuron specific expression of dLar constructs, using the GAL4-UAS system, yielded disrupted sleep consolidation similar to whole animal dLar mutants. These results further validate GWAS as a hypothesis independent means to delineate the molecular pathophysiology underlying RLS/WED. While the role of PTPRD in neuronal development and plasticity has been studied previously in flies, this is the first exploration of its function in the context of sleep and, more specifically, RLS/WED. Our results suggest neuronal PTPRD expression regulates sleep architecture and most likely operates in a molecular pathway that also includes BTBD9. Ongoing efforts to delineate the mechanistic basis of sleep regulation by PTPRD and BTBD9 are underway. Supported by RLS Foundation, Sleep Research Society, and Emory Neuroscience Initiative grants to S.S.