Immunology of Human Narcolepsy

Stanford University, Stanford CA

Investigators

Linked publications & trials

Abstract

Narcolepsy is a life long disorder characterized by excessive daytime sleepiness, cataplexy and symptoms of abnormal Rapid Eye Movement (REM) sleep. It is a common disorder that affects 1 in 2,000 individuals in North America and Western Europe. Recent discoveries have provided firm evidence that narcolepsy/hypocretin deficiency is an autoimmune disorder affecting the brain, and more particularly hypocretin-expressing neurons, with resulting hypocretin loss causing sleep disturbances. In addition to the established role of HLA DQB1*0602, two additional immune-related susceptibility genes have now been identified: the T Cell Receptor Alpha locus, and an understudied purinergic receptor, P2RY11. Recent studies of patients close to disease onset have also demonstrated other autoimmune hallmarks: an increased presence of antistreptolysin-0 (ASO) antibody, implicating a role for streptococcal infections as a trigger for the autoimmune process, as well as the detection autoantibodies directed against the protein of TRIB2 in sera. In this project, we will examine how these molecular players are involved in the autoimmune pathogenesis of narcolepsy. T-cell receptor (TCR) loci are unique in that repertoire diversity is generated through somatic cell recombination of V, D, and J segments. The genetic association of the TCRA locus with narcolepsy strongly suggests the presence of one or more VJ recombinants that predispose to the disease. To study this possibility, we will first perform deep sequencing of the expressed TCR alpha/ beta chain repertoire to identify potential disease-associated TCR variants. Second, we will perform functional studies to determine how the newly identified purinergic receptor P2RY11, and narcolepsy-associated polymorphisms in the P2RY11 locus modulate immune function in controls and subjects with narcolepsy. We hypothesize that narcolepsy is the result of specific environmental exposures in genetically susceptible individuals and that specific bacterial infections could serve as a trigger for the disease. We will therefore characterize the autoantibody and post-infectious profile in narcolepsy sera close to disease onset. To do so, we will search for specific S. pyogenes DNA sequences, and perform bacterial 16S rRNA-based community-wide surveys in pharyngeal swab samples from narcolepsy (close to onset) versus controls. We will also screen sera of recent onset samples to search for autoantibodies directed against proteins likely to be enriched in hypocretin expressing neurons based on BAC-TRAP technology mRNA profiling results. As very few autoimmune disorders are known to directly target neurons, and immune-brain interactions are only starting to be studied, a better understanding of the pathophysiology of narcolepsy is likely to Illuminate the cause of other neuropsychiatric disorders with a neuroimmune component as well.