CD8 T cell-mediated killing of orexinergic neurons induces a narcolepsy-like phenotype in mice

Abstract

Narcolepsy with cataplexy is a rare and severe sleep disorder caused by the destruction of orexinergic neurons in the lateral hypothalamus. The genetic and environmental factors associated with narcolepsy, together with serologic data, collectively point to an autoimmune origin. The current animal models of narcolepsy, based on either disruption of the orexinergic neurotransmission or neurons, do not allow study of the potential autoimmune etiology. Here, we sought to generate a mouse model that allows deciphering of the immune mechanisms leading to orexin + neuron loss and narcolepsy development. We generated mice expressing the hemagglutinin (HA) as a "neo-self-antigen" specifically in hypothalamic orexin + neurons (called Orex-HA), which were transferred with effector neo-self-antigen-specific T cells to assess whether an autoimmune process could be at play in narcolepsy. Given the tight association of narcolepsy with the human leukocyte antigen (HLA) HLA-DQB1*06:02 allele, we first tested the pathogenic contribution of CD4 Th1 cells. Although these T cells readily infiltrated the hypothalamus and triggered local inflammation, they did not elicit the loss of orexin + neurons or clinical manifestations of narcolepsy. In contrast, the transfer of cytotoxic CD8 T cells (CTLs) led to both T-cell infiltration and specific destruction of orexin + neurons. This phenotype was further aggravated upon repeated injections of CTLs. In situ, CTLs interacted directly with MHC class I-expressing orexin + neurons, resulting in cytolytic granule polarization toward neurons. Finally, drastic neuronal loss caused manifestations mimicking human narcolepsy, such as cataplexy and sleep attacks. This work demonstrates the potential role of CTLs as final effectors of the immunopathological process in narcolepsy.arcolepsy with cataplexy, referred to as type 1 narcolepsy (T1N), is a rare and chronic neurological disease characterized by excessive daytime sleepiness, sudden loss of muscle tone triggered by emotions (cataplexy), sleep paralysis, hypnagogic hallucinations, and fragmented nocturnal sleep (1). T1N is caused by a defective neurotransmission by the orexin/hypocretin neuropeptide and is associated with a selective and almost complete loss (85-100%) of orexinergic neurons in the hypothalamus (2, 3). The mechanisms leading to this neuronal loss are not yet elucidated, although current evidence points to an autoimmune process. Indeed, T1N is tightly associated with the human leukocyte antigen (HLA) HLA-DQB1*06:02 allele, carried by 98.4% of patients vs. 17.7% of the general European population (4). An independent association with HLA class I alleles was recently revealed in two independent studies (5, 6). Additionally, an association with polymorphisms in the T-cell receptor (TCR) α chain locus was found and replicated (7,8). Moreover, autoantibodies recognizing different antigenic targets expressed in the central nervous system (CNS) have been identified in the serum and cerebrospinal fluid (CSF) of narcoleptic patients (9-11)....

Retrograde interferon‐gamma signaling induces major histocompatibility class I expression in human‐induced pluripotent stem cell‐derived neurons

“…Somatic upregulation of MHC I on neurons may also mark these cells for elimination by anti‐neuronal T cells, leading to loss of neurons in otherwise normal appearing gray matter. Indeed several studies have shown that targeting neoantigens to CNS neuronal subsets results in rapid clearance by antigen‐specific CD8 + T cells 15, 69, 70, 71. Finally, anterograde transport of MHC class I molecules into the distal axon makes these molecules available near the site of inflammation, where they may increase vulnerability to attack by autoreactive anti‐axonal CD8 + T cells 10.…”

“…Indeed several studies have shown that targeting neoantigens to CNS neuronal subsets results in rapid clearance by antigen-specific CD8 + T cells. 15,[69][70][71] Finally, anterograde transport of MHC class I molecules into the distal axon makes these molecules available near the site of inflammation, where they may increase vulnerability to attack by autoreactive anti-axonal CD8 + T cells. 10 As discussed below, these findings have significance for the study of neurological conditions in which axonal injury processes may contribute to clinical progression.…”

Autoimmunity to hypocretin and molecular mimicry to flu antigens in Type 1 narcolepsy

“…Extending on prior work 1-6 a large recent GWAS analysis in over 4,500 patients across multiple ethnic groups confirmed primordial importance of the Human Leukocyte Antigen (HLA) DQ0602 heterodimer in disease predisposition, with important secondary associations in T cell receptor loci and and other loci suggesting importance of DQ0602 presentation of antigens to CD4 + by Antigen Presenting Cells (APC) and likely subsequent CD8 + destruction of hypocretin cells 29 . Hypocretin cell killing through CD4 + and CD8 + mediation has also been shown to cause narcolepsy in an animal model 30 .…”

Pathology of inflammatory diseases of the nervous system: Human disease versus animal models

“…Since it is very difficult to induce a CD8 + T‐cell mediated autoimmune response directly by active sensitization, such models are either induced by coupling a brain antigen with a virus vaccine (Ji et al, ) or by using a transgenic approach. In the latter, a foreign protein is expressed in transgenic animals in different cells of the central nervous system, such as astrocytes (Cabarrocas et al, ), oligodendrocytes (Na et al, ; Saxena et al, ), or neurons (Bernard‐Valnet et al, ). Disease is then transferred by the systemic injection of specific CD8 + T‐cell lines into the transgenic recipient animals.…”