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Individuals with narcolepsy suffer from abnormal sleep patterns due to loss of neurons that uniquely supply hypocretin (HCRT). Previous studies found associations of narcolepsy with the human leukocyte antigen (HLA)-DQ6 allele and T-cell receptor α (TRA) J24 gene segment and also suggested that in vitro-stimulated T cells can target HCRT. Here, we present evidence of in vivo expansion of DQ6-HCRT tetramer + /TRAJ24 + /CD4 + T cells in DQ6 + individuals with and without narcolepsy. We identify related TRAJ24 + TCRαβ clonotypes encoded by identical α/β gene regions from two patients and two controls. TRAJ24-G allele + clonotypes only expand in the two patients, whereas a TRAJ24-C allele + clonotype expands in a control. A representative tetramer + /G-allele + TCR shows signaling reactivity to the epitope HCRT 87-97 . Clonally expanded G-allele + T cells exhibit an unconventional effector phenotype. Our analysis of in vivo expansion of HCRT-reactive TRAJ24 + cells opens an avenue for further investigation of the autoimmune contribution to narcolepsy development.

The sleep disorder narcolepsy with cataplexy is characterized by a highly specific loss of hypocretin (orexin) neurons, leading to the hypothesis that the condition is caused by an immune or autoimmune mechanism. All genetic variants associated with narcolepsy are immune-related. Among these are single nucleotide polymorphisms in the P2RY11-EIF3G locus. It is unknown how these genetic variants affect narcolepsy pathogenesis and whether the effect is directly related to P2Y11 signalling or EIF3G function. Exome sequencing in 18 families with at least two affected narcolepsy with cataplexy subjects revealed non-synonymous mutations in the second exon of P2RY11 in two families, and P2RY11 re-sequencing in 250 non-familial cases and 135 healthy control subjects revealed further six different non-synonymous mutations in the second exon of P2RY11 in seven patients. No mutations were found in healthy controls. Six of the eight narcolepsy-associated P2Y11 mutations resulted in significant functional deficits in P2Y11 signalling through both Ca2+ and cAMP signalling pathways. In conclusion, our data show that decreased P2Y11 signalling plays an important role in the development of narcolepsy with cataplexy., (© The Author (2017). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Objectives: To investigate whether cerebrospinal fluid (CSF) biomarkers of neurodegeneration are altered in narcolepsy in order to evaluate whether the hypocretin deficiency and abnormal sleep-wake pattern in narcolepsy leads to neurodegeneration., Methods: Twenty-one patients with central hypersomnia (10 type 1 narcolepsy, 5 type 2 narcolepsy, and 6 idiopathic hypersomnia cases), aged 33 years on average and with a disease duration of 2-29 years, and 12 healthy controls underwent CSF analyses of the levels of β-amyloid, total tau protein (T-tau), phosphorylated tau protein (P-tau181), α-synuclein, neurofilament light chain (NF-L), and chitinase 3-like protein-1 (CHI3L1)., Results: Levels of β-amyloid were lower in patients with type 1 narcolepsy (375.4 ± 143.5 pg/mL) and type 2 narcolepsy (455.9 ± 65.0 pg/mL) compared to controls (697.9 ± 167.3 pg/mL, p < .05). Furthermore, in patients with type 1 narcolepsy, levels of T-tau (79.0 ± 27.5 pg/mL) and P-tau181 (19.1 ± 4.3 pg/mL) were lower than in controls (162.2 ± 49.9 pg/mL and 33.8 ± 9.2 pg/mL, p < .05). Levels of α-synuclein, NF-L, and CHI3L1 in CSF from narcolepsy patients were similar to those of healthy individuals., Conclusion: Six CSF biomarkers of neurodegeneration were decreased or normal in narcolepsy indicating that taupathy, synucleinopathy, and immunopathy are not prevalent in narcolepsy patients with a disease duration of 2-29 years. Lower CSF levels of β-amyloid, T-tau protein, and P-tau181 in narcolepsy may indicate that hypocretin deficiency and an abnormal sleep-wake pattern alter the turnover of these proteins in the central nervous system., (© Sleep Research Society 2016. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail journals.permissions@oup.com.)

Focus on the purinergic receptor P2Y 11 has increased following the finding of an association between the sleep disorder narcolepsy and a genetic variant in P2RY11 causing decreased gene expression. Narcolepsy is believed to arise from an autoimmune destruction of the hypothalamic neurons that produce the neuropeptide hypocretin/orexin. It is unknown how a decrease in expression of P2Y 11 might contribute to an autoimmune reaction towards the hypocretin neurons and the development of narcolepsy. To advance narcolepsy research it is therefore extremely important to determine the neuroanatomical localization of P2Y 11 in the brain with particular emphasis on the hypocretin neurons. In this article we used western blot, staining of blood smears, and flow cytometry to select two antibodies for immunohistochemical staining of macaque monkey brain. Staining was seen in neuron-like structures in cortical and hypothalamic regions. Rats do not have a gene orthologue to the P2Y 11 receptor and therefore rat brain was used as negative control tissue. The chromogenic signal observed in macaque monkey brain in neurons was not considered reliable, because the antibodies stained rat brain in a similar distribution pattern. Hence, the neuroanatomical localization of the P2Y 11 receptor remains undetermined due to the lack of specific P2Y 11 antibodies for brain immunohistochemistry., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The hypocretin/orexin system regulates, among other things, sleep and energy homeostasis. The system is likely regulated by both homeostatic and circadian mechanisms. Little is known about local differences in the regulation of hypocretin activity. The aim of this study was to establish an optimized peptide quantification method for hypocretin-1 extracted from different mouse brain areas and use this method for investigating circadian fluctuations of hypocretin-1 levels in these areas. The results show that hypocretin-1 peptide can be extracted from small pieces of intact tissue, with sufficient yield for measurements in a standard radioimmunoassay. Utilizing the optimized method, it was found that prepro-hypocretin mRNA and peptide show circadian fluctuations in the mouse brain. This study further demonstrates that the hypocretin-1 peptide level in the frontal brain peaks during dark as does prepro-hypocretin mRNA in the hypothalamus. However, in midbrain and brainstem tissue caudal to the hypothalamus, there was less circadian fluctuation and a tendency for higher levels during the light phase. These data suggest that regulation of the hypocretin system differs between brain areas., (Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.)