A review of physiological functions of orexin: From instinctive responses to subjective cognition.

Orexin, also known as hypocretin, is an excitatory neuropeptide secreted by the hypothalamus. Orexin is divided into orexin-A (OXA) and orexin-B (OXB), which are derived from a common precursor secreted by hypothalamic neurons. Orexin acts on orexin receptor-1 (OX1R) and orexin receptor-2 (OX2R). Orexin neurons, as well as receptors, are widely distributed in various regions of the brain as well as in the peripheral system and have a wider range of functions. This paper reviews the latest research results of orexin in the aspects of food intake, sleep, addiction, depression and anxiety. Because orexin has certain physiological functions in many systems, we further explored the possibility of orexin as a new target for the treatment of bulimia, anorexia nervosa, insomnia, lethargy, anxiety and depression. It is precisely because orexin has physiological functions in multiple systems that orexin, as a new target for the treatment of the above diseases, has potential contradictions. For example, it promotes the function of 1 system and may inhibit the function of another system. How to study a new drug, which can not only treat the diseases of this system, but also do not affect other system functions, is what we need to focus on.

α-Synuclein Induced the Occurrence of RBD via Interaction with OX1R and Modulated Its Degradation.

Rapid eye movement (REM) sleep behavior disorder (RBD) is a powerful early sign of Parkinson's disease (PD), but the pathogenetic mechanism involved in RBD remains largely unexplored. α-Synuclein has been verified to form Lewy bodies in the orexin neurons, whose activity and function rely on the orexin 1 receptor (OX1R). Dysfunction of the OX1R may induce the occurrence of RBD. Here, we determined the role of the interaction between α-Synuclein and OX1R in the pathogenesis of RBD, in vitro and in vivo. We found that injection of α-Synuclein into the lateral hypothalamus area (LHA) damaged orexin neurons and induced the RBD-like sleep pattern, to further damage dopaminergic neurons and result in locomotor dysfunction in mice. α-Synuclein interacted with OX1R, promoting the degradation of OX1R through proteasomal and lysosomal pathways. In addition, overexpression of α-Synuclein downregulated OX1R-mediated signaling, subsequently leading to orexin neuron damage. We conclude that α-Synuclein induced the occurrence of RBD via interaction with OX1R and modulated its degradation. These findings provide evidence for a novel mechanism by which the association of α-Synuclein with OX1R was attributed to α-Synuclein-induced orexin neuron damage, which may be a new molecular target for an effective therapeutic strategy for RBD pathology.

Upregulated mGluR5 induces ER stress and DNA damage by regulating the NMDA receptor subunit NR2B.

Dysfunction caused by mGluR5 expression or activation is an important mechanism in the development of Parkinson's disease (PD). Early clinical studies on mGluR5 negative allosteric modulators have shown some limitations. It is therefore necessary to find a more specific approach to block mGluR5-mediated neurotoxicity. Here, we determined the role of N-methyl-D-aspartate (NMDA) receptor subunit NR2B in mGluR5-mediated ER stress and DNA damage. In vitro study, rotenone-induced ER stress and DNA damage were accompanied by an increase in mGluR5 expression and overexpressed or activated mGluR5 with agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) induced ER stress and DNA damage, while blocking mGluR5 with antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP) alleviated the effect. Furthermore, the damage caused by CHPG was blocked by NMDA receptor antagonist MK-801. Additionally, rotenone or CHPG increased the p-Src and p-NR2B, which was inhibited by MPEP. Blocking p-Src or NR2B with PP2 or CP101,606 alleviated CHPG-induced ER stress and DNA damage. Overactivation of mGluR5 accompanied with the increase of p-Src and p-NR2B in the ER stress and DNA damage was found in rotenone-induced PD rat model. These findings suggest a new mechanism wherein mGluR5 induces ER stress and DNA damage through the NMDA receptor and propose NR2B as the molecular target for therapeutic strategy for PD.

Defective STING expression potentiates IL-13 signaling in epithelial cells in eosinophilic chronic rhinosinusitis with nasal polyps.

BACKGROUND: Stimulator of interferon genes (STING) activation favors effective innate immune responses against viral infections. Its role in chronic rhinosinusitis with nasal polyps (CRSwNP) remains unknown. OBJECTIVE: Our aim was to explore the expression, regulation, and function of STING in CRSwNP. METHODS: STING expression in sinonasal mucosal samples was analyzed by means of quantitative RT-PCR, immunohistochemistry, flow cytometry, and Western blotting. Regulation and function of STING expression were explored by using cultured primary human nasal epithelial cells (HNECs) and cells of the line BEAS-2B in vitro. RESULTS: STING expression was reduced in eosinophilic nasal polyps compared with that in noneosinophilic nasal polyps and control tissues. STING was predominantly expressed by epithelial cells in nasal tissue and was downregulated by IL-4 and IL-13 in a signal transducer and activator of transcription 6 (STAT6)-dependent manner. HNECs derived from eosinophilic polyps displayed compromised STING-dependent type I interferon production but heightened IL-13-induced STAT6 activation and CCL26 production as compared with HNECs from noneosinophilic polyps and control tissues, which were rescued by exogenous STING overexpression. Knocking down or overexpressing STING decreased or enhanced expression of suppressor of cytokine signaling 1 (SOCS1) in BEAS-2B cells, respectively, independent of the canonic STING pathway elements TBK1 and IRF3. Knocking down SOCS1 abolished the inhibitory effect of STING on IL-13 signaling in BEAS-2B cells. STING expression was positively correlated with SOCS1 expression but negatively correlated with CCL26 expression in nasal epithelial cells from patients with CRSwNP. CONCLUSIONS: Reduced STING expression caused by the type 2 milieu not only impairs STING-dependent type I interferon production but also amplifies IL-13 signaling by decreasing SOCS1 expression in nasal epithelial cells in eosinophilic CRSwNP.

Deficiency in interleukin-10 production by M2 macrophages in eosinophilic chronic rhinosinusitis with nasal polyps.

BACKGROUND: M2 macrophages are characterized by high interleukin-10 (IL-10) expression and are critical for resolving inflammation. Although increased accumulation of M2 macrophages has been demonstrated in chronic rhinosinusitis with nasal polyps (CRSwNP), particularly the eosinophilic type, their functional relevance in CRSwNP remains poorly understood. METHODS: M1 and M2 macrophages and IL-10 expression in sinonasal tissues were detected by double-immunofluorescence staining. THP-1 cells, a human monocytic leukemia cell line, were stimulated with various cytokines to study macrophage polarization and IL-10 expression. Polyp size, computed tomography (CT) scans, and symptom severity were scored. RESULTS: Compared with numbers in control tissues, the numbers of total CD68+ macrophages, interferon regulatory factor 5-positive and CD68+ M1 macrophages, and CD163+ CD68+ and CD206+ CD68+ M2 macrophages were increased in both eosinophilic and non-eosinophilic polyps. However, compared with non-eosinophilic polyps, eosinophilic polyps contained fewer M1 macrophages and more M2 macrophages. Consistent with this, the M1/M2 macrophage ratio was increased in non-eosinophilic polyps, whereas it decreased in eosinophilic polyps. Strikingly, the numbers of IL-10+ CD68+ macrophages and the percentage of IL-10+ CD68+ macrophages relative to the total number of macrophages were decreased in eosinophilic polyps, despite the upregulation of M2 macrophages in this type of polyp. The number of IL-10+ CD68+ M2 macrophages correlated negatively with total symptoms scores, polyp sizes, total CT scores, and the total number of inflammatory cells in patients with eosinophilic CRSwNP. Poly I:C downregulated IL-10 expression in M2 macrophages differentiated from THP-1 cells in vitro. CONCLUSION: Impaired IL-10 production by M2 macrophages may contribute to sustained inflammation in eosinophilic CRSwNP.vv.

IgD-activated mast cells induce IgE synthesis in B cells in nasal polyps.

BACKGROUND: Although upregulated expression of local IgD has been reported in patients with chronic rhinosinusitis (CRS), its function is unclear. OBJECTIVE: We sought to explore the expression and function of soluble IgD in patients with CRS, particularly CRS with nasal polyps. METHODS: IgD levels in sinonasal mucosa were analyzed by using RT-PCR and ELISA. Numbers and phenotypes of IgD+ cells were studied by means of immunohistochemistry, immunofluorescence, and flow cytometry. HMC-1 cells, a human mast cell line, and mast cells purified from eosinophilic polyps were cultured alone or with naive B cells purified from peripheral blood. The antigen specificity of nasal IgD was investigated by using ELISA. RESULTS: The mRNA expression of immunoglobulin heavy constant delta gene, numbers of IgD+ cells, and protein levels of secretory IgD in sinonasal mucosa were increased in patients with CRS with or without nasal polyps compared with control subjects. Numbers of IgD+ plasmablasts were increased in both eosinophilic and noneosinophilic polyps, whereas numbers of IgD+ mast cells were only increased in eosinophilic polyps. Cross-linking IgD induced serum preincubated HMC-1 cells and polyp mast cells to produce B-cell activating factor, IL-21, IL-4, and IL-13 and to promote IgM, IgG, IgA, and IgE production from B cells. In eosinophilic polyps expression of those B cell-stimulating factors in mast cells and close contact between mast cells and B cells were found. Moreover, positive correlations of total IgD levels with total IgE levels and eosinophilia and upregulation of specific IgD against house dust mites were discovered in eosinophilic polyps. CONCLUSION: IgD-activated mast cells can facilitate IgE production and eosinophilic inflammation in patients with CRS with nasal polyps.