Spatial mRNA expression patterns of orexin receptors in the dorsal hippocampus

Orexins are wake-promoting neuropeptides that originate from hypothalamic neurons projecting to widespread brain areas throughout the central nervous system. They modulate various physiological functions via their orexin 1 (OXR1) and 2 (OXR2) receptors, including sleep-wake rhythm but also cognitive functions such as memory formation. Here, we provide a detailed analysis of OXR1 and OXR2 mRNA expression profiles in the dorsal hippocampus as a key region for memory formation, using RNAscope multiplex in situ hybridization. Interconnected subareas relevant for cognition and memory such as the medial prefrontal cortex and the nucleus reuniens of the thalamus were assessed as well. Both receptor types display distinct profiles, with the highest percentage of OXR1 mRNA-positive cells in the hilus of the dentate gyrus. Here, the content of OXR1 mRNA per cell was slightly modulated at selected time points over a 12 h light/ 12 dark light phase. Using RNAScope and quantitative polymerase chain reaction approaches, we began to address a cell-type specific expression of OXR1 in hilar GABAergic interneurons. The distinct expression profiles of both receptor subtypes within hippocampal subareas and circuits provide an interesting basis for future interventional studies on orexin receptor function in spatial and contextual memory.

Hypocretin-1/Hypocretin Receptor 1 Regulates Neuroplasticity and Cognitive Function through Hippocampal Lactate Homeostasis in Depressed Model

Cognitive dysfunction is not only a common symptom of major depressive disorder, but also a more common residual symptom after antidepressant treatment and a risk factor for chronic and recurrent disease. The disruption of hypocretin regulation is known to be associated with depression, however, their exact correlation is remains to be elucidated. Hypocretin-1 levels are increased in the plasma and hypothalamus from chronic unpredictable mild stress (CUMS) model mice. Excessive hypocretin-1 conducted with hypocretin receptor 1 (HCRTR1) reduced lactate production and brain-derived neurotrophic factor (BDNF) expression by hypoxia-inducible factor-1α (HIF-1α), thus impairing adult hippocampal neuroplasticity, and cognitive impairment in CUMS model. Subsequently, it is found that HCRTR1 antagonists can reverse these changes. The direct effect of hypocretin-1 on hippocampal lactate production and cognitive behavior is further confirmed by intraventricular injection of hypocretin-1 and microPET-CT in rats. In addition, these mechanisms are further validated in astrocytes and neurons in vitro. Moreover, these phenotypes and changes in molecules of lactate transport pathway can be duplicated by specifically knockdown of HCRTR1 in hippocampal astrocytes. In summary, the results provide molecular and functional insights for involvement of hypocretin-1-HCRTR1 in altered cognitive function in depression.

High-resolution HLA sequencing and hypocretin receptor 2 autoantibodies in narcolepsy type 1 and type 2

Narcolepsy is a sleep disorder caused by an apparent degeneration of orexin/hypocretin neurons in the lateral hypothalamic area and a subsequent decrease in orexin/hypocretin levels in the cerebrospinal fluid. Narcolepsy is classified into type 1 (NT1) and type 2 (NT2). While genetic associations in the human leukocyte antigen (HLA) region and candidate autoantibodies have been investigated in NT1 to imply an autoimmune origin, less is known about the pathogenesis in NT2. Twenty-six NT1 and 15 NT2 patients were included, together with control groups of 24 idiopathic hypersomnia (IH) patients and 778 general population participants. High-resolution sequencing was used to determine the alleles, the extended haplotypes, and the genotypes of HLA-DRB3, -DRB4, -DRB5, -DRB1, -DQA1, -DQB1, -DPA1, and -DPB1. Radiobinding assay was used to determine autoantibodies against hypocretin receptor 2 (anti-HCRTR2 autoantibodies). NT1 was associated with HLA-DRB5*01:01:01, -DRB1*15:01:01, -DQA1*01:02:01, -DQB1*06:02:01, -DRB5*01:01:01, -DRB1*15:01:01, -DQA1*01:02:01, -DQB1*06:02:01 (odds ratio [OR]: 9.15; p = 8.31 × 10-4) and HLA-DRB5*01:01:01, -DRB1*15:01:01, -DQA1*01:02:01, -DQB1*06:02:01, -DRB4*01:03:01, -DRB1*04:01:01, -DQA1*03:02//03:03:01, -DQB1*03:01:01 (OR: 23.61; p = 1.58 × 10-4) genotypes. Lower orexin/hypocretin levels were reported in the NT2 subgroup (n = 5) that was associated with the extended HLA-DQB1*06:02:01 haplotype (p = .001). Anti-HCRTR2 autoantibody levels were not different between study groups (p = .8524). We confirmed the previous association of NT1 with HLA-DQB1*06:02:01 extended genotypes. A subgroup of NT2 patients with intermediate orexin/hypocretin levels and association with HLA-DQB1*06:02:01 was identified, indicating a possible overlap between the two distinct narcolepsy subtypes, NT1 and NT2. Low anti-HCRTR2 autoantibody levels suggest that these receptors might not function as autoimmune targets in either NT1 or NT2.

Knockdown of type 2 orexin receptor in adult mouse testis potentiates testosterone production and germ cell proliferation

Orexins (OXs) are neuropeptides which regulate various physiological processes. OXs exist in two different forms, mainly orexin A (OXA) and orexin B (OXB) and their effects are mediated via OX1R and OX2R. Presence of OXB and OX2R in mouse testis is also reported. However, the role of OXB/OX2R in the male gonad remains unexplored. Herein we investigated the role of OXB/OX2R system in testicular physiology under in vivo and ex vivo conditions. Adult mice were given a single dose of bilateral intratesticular injection of siRNA targeting OX2R and were sacrificed 96 h post-injection. OX2R-knockdown potentiated serum and intratesticular testosterone levels with up-regulation in the expressions of major steroidogenic proteins. Germ cell proliferation also increased in siRNA-treated mice. Results of the ex vivo experiment also supported the findings of the in vivo study. In conclusion, OX2R may regulate testosterone production and thereby control the fine-tuning between steroidogenesis and germ cell dynamics.

Deep Immune and RNA Profiling Revealed Distinct Circulating CD163+ Monocytes in Diabetes-Related Complications

CD163, a scavenger receptor with anti-inflammatory function expressed exclusively on monocytes/macrophages, is dysregulated in cases of diabetes complications. This study aimed to characterize circulating CD163+ monocytes in the presence (D+Comps) or absence (D-Comps) of diabetes-related complications. RNA-sequencing and mass cytometry were conducted on CD163+ monocytes in adults with long-duration diabetes and D+Comps or D-Comps. Out of 10,868 differentially expressed genes identified between D+Comps and D-Comps, 885 were up-regulated and 190 were down-regulated with a ≥ 1.5-fold change. In D+Comps, 'regulation of centrosome cycle' genes were enriched 6.7-fold compared to the reference genome. MIR27A, MIR3648-1, and MIR23A, the most up-regulated and CD200R1, the most down-regulated gene, were detected in D+Comps from the list of 75 'genes of interest'. CD163+ monocytes in D+Comps had a low proportion of recruitment markers CCR5, CD11b, CD11c, CD31, and immune regulation markers CD39 and CD86. A gene-protein network identified down-regulated TLR4 and CD11b as 'hub-nodes'. In conclusion, this study reports novel insights into CD163+ monocyte dysregulation in diabetes-related complications. Enriched centrosome cycle genes and up-regulated miRNAs linked to apoptosis, coupled with down-regulated monocyte activation, recruitment, and immune regulation, suggest functionally distinct CD163+ monocytes in cases of diabetes complications. Further investigation is needed to confirm their role in diabetes-related tissue damage.

The regulation of NFKB1 on CD200R1 expression and their potential roles in Parkinson's disease

BACKGROUND

Overactivated microglia are a key contributor to Parkinson's disease (PD) by inducing neuroinflammation. CD200R1, a membrane glycoprotein mainly found on microglia, is crucial for maintaining quiescence with its dysregulation linked to microglia's abnormal activation. We and other groups have reported a decline in CD200R1 levels in several neurological disorders including PD. However, the mechanism regulating CD200R1 expression and the specific reasons for its reduction in PD remain largely unexplored. Given the pivotal role of transcription factors in gene expression, this study aimed to elucidate the transcriptional regulation of CD200R1 and its implications in PD.

METHODS

The CD200R1 promoter core region was identified via luciferase assays. Potential transcription factors were predicted using the UCSC ChIP-seq database and JASPAR. NFKB1 binding to the CD200R1 core promoter was substantiated through electrophoretic mobility shift and chromatin immunoprecipitation assays. Knocking-down or overexpressing NFKB1 validated its regulatory effect on CD200R1. Correlation between decreased CD200R1 and deficient NFKB1 was studied using Genotype-Tissue Expression database. The clinical samples of the peripheral blood mononuclear cells were acquired from 44 PD patients (mean age 64.13 ± 9.78, 43.2% male, median Hoehn-Yahr stage 1.77) and 45 controls (mean age 64.70 ± 9.41, 52.1% male). NFKB1 knockout mice were utilized to study the impact of NFKB1 on CD200R1 expression and to assess their roles in PD pathophysiology.

RESULTS

The study identified the CD200R1 core promoter region, located 482 to 146 bp upstream of its translation initiation site, was directly regulated by NFKB1. Significant correlation between NFKB1 and CD200R1 expression was observed in human PMBCs. Both NFKB1 and CD200R1 were significantly decreased in PD patient samples. Furthermore, NFKB1-/- mice exhibited exacerbated microglia activation and dopaminergic neuron loss after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment.

CONCLUSION

Our study identified that NFKB1 served as a direct regulator of CD200R1. Reduced NFKB1 played a critical role in CD200R1 dysregulation and subsequent microglia overactivation in PD. These findings provide evidence that targeting the NFKB1-CD200R1 axis would be a novel therapeutic strategy for PD.

A male-specific mechanism of meningeal nociceptor sensitization promoting migraine headache

BACKGROUND

We wished to explore possible sexual dimorphism in mechanisms sensitizing or activating meningeal nociceptors that can promote the headache phase of migraine.

METHODS

Male and female C57BL6J mice received either supradural orexin B and an inflammatory mediator cocktail (IM) with migraine-like pain behaviors and photophobia recorded. Expression of orexin 2 receptor (OX2R) in trigeminal ganglion (TG) and phosphorylated extracellular signal-regulated kinases (ERK) levels in trigeminal nucleus caudalis (TNC) were evaluated. Orexin B-induced excitability of TG cells was assessed with patch-clamp electrophysiology. Intranasal delivery of CRISPR/Cas9 plasmids was used to edit the expression of OX2R in the TG.

RESULTS

Supradural orexin B induced migraine-like pain behaviors, photophobia and increased TNC ERK phosphorylation exclusively in males. Blockade of orexin signaling with supradural suvorexant, a dual orexin receptor antagonist, prevented, but did not reverse, migraine-like pain in males induced by supradural IM cocktail. OX2R expression was higher in male TG and orexin B increased TG neuron excitability in males. Intranasal OX2R CRISPR/Cas9 reduced TG receptor expression and orexin B-induced TNC ERK phosphorylation and prevented migraine-like pain induced by supradural orexin B in males.

CONCLUSIONS

Our studies reveal a male-specific mechanism of TG nociceptor sensitization and migraine-like pain behavior mediated by orexin B/OX2R signaling. Sexually dimorphic mechanisms of trigeminal nociceptor sensitization and activation offer opportunities to improve patient outcomes by considering patient sex and may influence clinical trial design and interpretation.

A high-fat diet induced depression-like phenotype via hypocretin-HCRTR1 mediated inflammation activation

Background: A high-fat diet (HFD) is generally associated with an increased risk of mental disorders that constitute a sizeable worldwide health. A HFD results in the gut microbiota-brain axis being altered and linked to mental disorders. Hypocretin-1, which can promote appetite, has been previously confirmed to be associated with depression. However, no exact relationship has been found for hypocretin between depression and HFDs. Methods: Adult male SD rats were randomly assigned to either a HFD or a normal diet for eight weeks, followed by behavioral tests and plasma biochemical analyses. Then, we investigated the protein and mRNA levels of inflammation-related factors in the hippocampus. We also observed morphological changes in brain microglia and lipid accumulation. Additionally, metagenomic and metabolomic analyses of gut microbiomes were performed. 3T3-L1 cells were utilized in vitro to investigate the impact of hypocretin receptor 1 antagonists (SB334867) on lipid accumulation. To consider the connection between the brain and adipose tissue, we used a conditioned medium (CM) treated with 3T3-L1 cells to observe the activation and phagocytosis of BV2 cells. Following a 12-week period of feeding a HFD to C57BL/6 mice, a three-week intervention period was initiated during which the administration of SB334867 was observed. This was followed by a series of assessments, including monitoring of body weight changes and emotional problems, as well as attention to plasma biochemical levels and microglial cell phenotypes in the brain. Results: The HFD rats displayed anxiety and depressive-like behaviors. HFD rats exhibited increased plasma HDL, LDL, and TC levels. A HFD also causes an increase in hypocretin-1 and hypocretin-2 in the hypothalamus. Metagenomics and metabolomics revealed that the HFD caused an increase in the relative abundance of associated inflammatory bacteria and decreased the abundance of anti-inflammatory and bile acid metabolites. Compared with the CTR group, hippocampal microglia in the HFD group were significantly activated and accompanied by lipid deposition. At the same time, protein and mRNA expression levels of inflammation-related factors were increased. We found that SB334867 could significantly reduce lipid accumulation in 3T3-L1 cells after differentiation. The expression of inflammatory factors decreased in the SB334867 group. The administration of SB334867 was found to reverse the adverse effects of the HFD on body weight, depressive-like behaviour and anxiety-like mood. Furthermore, this treatment was associated with improvements in plasma biochemical levels and a reduction in the number of microglia in the brain. Conclusions: In summary, our results demonstrated that a HFD induced anxiety and depressive-like behaviors, which may be linked to the increased hypocretin-1 level and lipid accumulation. Supplementation with SB334867 improved the above. These observations highlight the possibility of hypocretin-1 inducing the risk of HFD-associated emotional dysfunctions.

The differential effects of blocking retinal orexin receptors on the expression of retinal c-fos and hypothalamic Vip, PACAP, Bmal1, and c-fos in Male Wistar Rats

Orexin A and B (OXA and OXB) and their receptors are expressed in the majority of retinal neurons in humans, rats, and mice. Orexins modulate signal transmission between the different layers of the retina. The suprachiasmatic nucleus (SCN) and the retina are central and peripheral components of the body's biological clocks; respectively. The SCN receives photic information from the retina through the retinohypothalamic tract (RHT) to synchronize bodily functions with environmental changes. In present study, we aimed to investigate the impact of inhibiting retinal orexin receptors on the expression of retinal Bmal1 and c-fos, as well as hypothalamic c-fos, Bmal1, Vip, and PACAP at four different time-points (Zeitgeber time; ZT 3, 6, 11, and ZT-0). The intravitreal injection (IVI) of OX1R antagonist (SB-334867) and OX2R antagonist (JNJ-10397049) significantly up-regulated c-fos expression in the retina. Additionally, compared to the control group, the combined injection of SB-334867 and JNJ-10397049 showed a greater increase in retinal expression of this gene. Moreover, the expression of hypothalamic Vip and PACAP was significantly up-regulated in both the SB-334867 and JNJ-10397049 groups. In contrast, the expression of Bmal1 was down-regulated. Furthermore, the expression of hypothalamic c-fos was down-regulated in all groups treated with SB-334867 and JNJ-10397049. Additionally, the study demonstrated that blocking these receptors in the retina resulted in alterations in circadian rhythm parameters such as mesor, amplitude, and acrophase. Finally, it affected the phase of gene expression rhythms in both the retina and hypothalamus, as identified through cosinor analysis and the zero-amplitude test. This study represents the initial exploration of how retinal orexin receptors influence expression of rhythmic genes in the retina and hypothalamus. These findings could provide new insights into how the retina regulates the circadian rhythm in both regions and illuminate the role of the orexinergic system expression within the retina.

Increased Expression of Orexin-A in Patients Affected by Polycystic Kidney Disease

Orexin-A is a neuropeptide product of the lateral hypothalamus that acts on two receptors, OX1R and OX2R. The orexinergic system is involved in feeding, sleep, and pressure regulation. Recently, orexin-A levels have been found to be negatively correlated with renal function. Here, we analyzed orexin-A levels as well as the incidence of SNPs in the hypocretin neuropeptide precursor (HCRT) and its receptors, HCRTR1 and HCRTR2, in 64 patients affected by autosomal dominant polycystic kidney disease (ADPKD) bearing truncating mutations in the PKD1 or PKD2 genes. Twenty-four healthy volunteers constituted the control group. Serum orexin-A was assessed by ELISA, while the SNPs were investigated through Sanger sequencing. Correlations with the main clinical features of PKD patients were assessed. PKD patients showed impaired renal function (mean eGFR 67.8 ± 34.53) and a statistically higher systolic blood pressure compared with the control group (p < 0.001). Additionally, orexin-A levels in PKD patients were statistically higher than those in healthy controls (477.07 ± 69.42 pg/mL vs. 321.49 ± 78.01 pg/mL; p < 0.001). Furthermore, orexin-A inversely correlated with blood pressure (p = 0.0085), while a direct correlation with eGFR in PKD patients was found. None of the analyzed SNPs showed any association with orexin-A levels in PKD. In conclusion, our data highlights the emerging role of orexin-A in renal physiology and its potential relevance to PKD. Further research is essential to elucidate the intricate mechanisms underlying orexin-A signaling in renal function and its therapeutic implications for PKD and associated cardiovascular complications.

CD200R promotes high glucose-induced oxidative stress and damage in human retinal pigment epithelial cells by activating the mTOR signaling pathway

Diabetic retinopathy (DR) is established as the primary cause of visual impairment and preventable blindness, posing significant social and economic burdens on healthcare systems worldwide. Oxidative stress has been identified as a major contributor to DR, yet the precise role of the transmembrane glycoprotein CD200R in this context remains elusive. We studied human retinal pigment epithelia ARPE-19 cells to investigate the role of CD200R in high-glucose (HG) induced oxidative stress. Under HG conditions, we found a significant increase in CD200R expression in a time-dependent pattern. Conversely, knockdown of CD200R effectively alleviated oxidative stress and restored cell viability in HG-treated ARPE-19 cells, a phenomenon corroborated by the addition of a reactive oxygen species (ROS) scavenger. Exploration of the AKT/mTOR signaling pathway confirmed its mediating role regarding CD200R knockdown suppression of the expression of key proteins induced by HG conditions. Additionally, we found that the inhibition of mTOR signaling with Rapamycin effectively countered HG-induced oxidative stress in ARPE-19 cells, suggesting a promising therapeutic target against oxidative stress in the context of DR. This study establishes the crucial role of CD200R in HG-induced oxidative stress and identifies potential therapeutic avenues for the treatment of DR.

The protective effects of orexin-A in alleviating cell senescence against interleukin-1β (IL-1β) in chondrocytes

Osteoarthritis (OA) is one of the most important causes of global disability, and dysfunction of chondrocytes is an important risk factor. The treatment of OA is still a challenge. Orexin-A is a hypothalamic peptide, and its effects in OA are unknown. In this study, we found that exposure to interleukin-1β (IL-1β) reduced the expression of orexin-2R, the receptor of orexin-A in TC-28a2 chondrocytes. Importantly, the senescence-associated β-galactosidase (SA-β-gal) staining assay demonstrated that orexin-A treatment ameliorates IL-1β-induced cellular senescence. Importantly, the presence of IL-1β significantly reduced the telomerase activity of TC-28a2 chondrocytes, which was rescued by orexin-A. We also found that orexin-A prevented IL-1β-induced increase in the levels of Acetyl-p53 and the expression of p21. It is shown that orexin-A mitigates IL-1β-induced reduction of sirtuin 3 (SIRT3). Silencing of SIRT3 abolished the protective effects of orexin-A against IL-1β-induced cellular senescence. These results imply that orexin-A might serve as a promising therapeutic agent for OA.

Effect of electroacupuncture at "Neiguan" (PC6) on pain and brain orexin 1 receptor in mice with inflammatory pain

OBJECTIVES

To observe the effect of electroacupuncture (EA) at "Neiguan" (PC6) on pain response in mice injected with complete Freund's adjuvant (CFA) in the hind paw, so as to investigate the mechanism of orexin 1 receptor (OX1R) -endogenous cannabinoid 1 receptor (CB1R) pathway in acupuncture analgesia.

METHODS

A total of 48 male C57BL/6 mice were used in the present study. In the first part of this study, 18 mice were randomized into control, model and EA groups, with 6 mice in each group. In the second part of this study, 30 mice were randomized into control, model, EA, EA+Naloxone, EA+OX1R antagonist (SB33486) groups, with 6 mice in each group. Inflammatory pain model was established by subcutaneous injection of 20 μL CFA solution in the left hind paw. EA (2 Hz, 2 mA ) was applied to bilateral PC6 for 20 min, once a day for 5 consecutive days. The mice in the EA+Naloxone and EA+SB33486 groups were intraperitoneally injected with naloxone (10 mg/kg) or SB33486 (15 mg/kg) 15 min before EA intervention on day 5, respectively. Tail-flick method and Von Frey method were used to detect the thermal pain threshold and mechanical pain threshold of mice. Quantitative real-time PCR was used to detect the expression level of β-endorphin mRNA in periaqueductal gray (PAG) of mice. The expression of OX1R positive cells in the lateral hypothalamic area (LH) and CB1R positive cells in the ventrolateral periaqueductal gray (vlPAG) were detected by immunofluorescence.

RESULTS

Compared with the control group, the thermal pain threshold and mechanical pain threshold of the model group were decreased (P<0.001), the expression level of β-endorphin mRNA in PAG was decreased (P<0.001), and the numbers of OX1R positive cells in LH and CB1R positive cells in vlPAG were decreased (P<0.05, P<0.001). Compared with the model group, the thermal pain threshold and mechanical pain threshold of the EA group were significantly increased (P<0.001), and the numbers of OX1R positive cells in LH and CB1R positive cells in vlPAG were increased (P<0.01, P<0.001). Compared with the EA group, the mechanical pain threshold in the EA+SB33486 group was significantly decreased (P<0.01), but there was no significant difference in the mechanical pain threshold between the EA+Naloxone group and EA group, and the numbers of OX1R positive neurons in LH and CB1R positive neurons in vlPAG were decreased in the EA+SB33486 group (P<0.001).

CONCLUSIONS

EA at PC6 can achieve analgesic effect on CFA mice by activating the OX1R-CB1R pathway in the brain, and this effect is opioid-independent.

CD200R activation on naïve T cells by B cells induces suppressive activity of T cells via IL-24

CD200 is an anti-inflammatory protein that facilitates signal transduction through its receptor, CD200R, in cells, resulting in immune response suppression. This includes reducing M1-like macrophages, enhancing M2-like macrophages, inhibiting NK cell cytotoxicity, and downregulating CTL responses. Activation of CD200R has been found to modulate dendritic cells, leading to the induction or enhancement of Treg cells expressing Foxp3. However, the precise mechanisms behind this process are still unclear. Our previous study demonstrated that B cells in Peyer's patches can induce Treg cells, so-called Treg-of-B (P) cells, through STAT6 phosphorylation. This study aimed to investigate the role of CD200 in Treg-of-B (P) cell generation. To clarify the mechanisms, we used wild-type, STAT6 deficient, and IL-24 deficient T cells to generate Treg-of-B (P) cells, and antagonist antibodies (anti-CD200 and anti-IL-20RB), an agonist anti-CD200R antibody, CD39 inhibitors (ARL67156 and POM-1), a STAT6 inhibitor (AS1517499), and soluble IL-20RB were also applied. Our findings revealed that Peyer's patch B cells expressed CD200 to activate the CD200R on T cells and initiate the process of Treg-of-B (P) cells generation. CD200 and CD200R interaction triggers the phosphorylation of STAT6, which regulated the expression of CD200R, CD39, and IL-24 in T cells. CD39 regulated the expression of IL-24, which sustained the expression of CD223 and IL-10 and maintained the cell viability. In summary, the generation of Treg-of-B (P) cells by Peyer's patch B cells was through the CD200R-STAT6-CD39-IL-24 axis pathway.

Trigeminal nerve electrical stimulation attenuates early traumatic brain injury through the TLR4/NF-κB/NLRP3 signaling pathway mediated by orexin-A/OX1R system

BACKGROUND

Traumatic brain injury (TBI) is a significant contributor to global mortality and disability, and emerging evidence indicates that trigeminal nerve electrical stimulation (TNS) is a promising therapeutic intervention for neurological impairment following TBI. However, the precise mechanisms underlying the neuroprotective effects of TNS in TBI are poorly understood. Thus, the objective of this study was to investigate the potential involvement of the orexin-A (OX-A)/orexin receptor 1 (OX1R) mediated TLR4/NF-κB/NLRP3 signaling pathway in the neuroprotective effects of TNS in rats with TBI.

METHODS

Sprague-Dawley rats were randomly assigned to four groups: sham, TBI, TBI+TNS+SB334867, and TBI+TNS. TBI was induced using a modified Feeney's method, and subsequent behavioral assessments were conducted to evaluate neurological function. The trigeminal nerve trunk was isolated, and TNS was administered following the establishment of the TBI model. The levels of neuroinflammation, brain tissue damage, and proteins associated with the OX1R/TLR4/NF-κB/NLRP3 signaling pathway were assessed using hematoxylin-eosin staining, Nissl staining, western blot analysis, quantitative real-time polymerase chain reaction, and immunofluorescence techniques.

RESULTS

The findings of our study indicate that TNS effectively mitigated tissue damage, reduced brain edema, and alleviated neurological deficits in rats with TBI. Furthermore, TNS demonstrated the ability to attenuate neuroinflammation levels and inhibit the expression of proteins associated with the TLR4/NF-κB/NLRP3 signaling pathway. However, it is important to note that the aforementioned effects of TNS were reversible upon intracerebroventricular injection of an OX1R antagonist.

CONCLUSION

TNS may prevent brain damage and relieve neurological deficits after a TBI by inhibiting inflammation, possibly via the TLR4/NF-κB/NLRP3 signaling pathway mediated by OX-A/OX1R.

Molecular incompatibility between pig CD200 and human CD200 receptor in in vitro xenogeneic immune responses

Overexpression of human CD200 (hCD200) in porcine endothelial cells (PECs) has been reported to suppress xenogeneic immune responses of human macrophages against porcine endothelial cells. The current study aimed to address whether the above-mentioned beneficial effect of hCD200 is mediated by overcoming the molecular incompatibility between porcine CD200 (pCD200) and hCD200 receptor or simply by increasing the expression levels of CD200 without any molecular incompatibility across the two species. We overexpressed hCD200 or pCD200 using lentiviral vectors with V5 marker in porcine endothelial cells and compared their suppressive activity against U937-derived human macrophage-like cells (hMCs) and primary macrophages. In xenogeneic coculture of porcine endothelial cells and human macrophage-like cells or macrophages, hCD200-porcine endothelial cells suppressed phagocytosis and cytotoxicity of human macrophages to a greater extent than pCD200-porcine endothelial cells. Secretion of tumor necrosis factor-α, interleukin-1β, and monocyte chemoattractant protein-1 from human macrophages and expression of M1 phenotypes (inducible nitric oxide synthase, dectin-1, and CD86) were also suppressed by hCD200 to a greater extent than pCD200. Furthermore, in signal transduction downstream of CD200 receptor, hCD200 induced Dok2 phosphorylation and suppressed IκB phosphorylation to a greater extent than pCD200. The above data supported the possibility of a significant molecular incompatibility between pCD200 and human CD200 receptor, suggesting that the beneficial effects of hCD200 overexpression in porcine endothelial cells could be mediated by overcoming the molecular incompatibility across the species barrier rather than by simple overexpression effects of CD200.

Characterization of a putative orexin receptor in Ciona intestinalis sheds light on the evolution of the orexin/hypocretin system in chordates

Tunicates are evolutionary model organisms bridging the gap between vertebrates and invertebrates. A genomic sequence in Ciona intestinalis (CiOX) shows high similarity to vertebrate orexin receptors and protostome allatotropin receptors (ATR). Here, molecular phylogeny suggested that CiOX is divergent from ATRs and human orexin receptors (hOX1/2). However, CiOX appears closer to hOX1/2 than to ATR both in terms of sequence percent identity and in its modelled binding cavity, as suggested by molecular modelling. CiOX was heterologously expressed in a recombinant HEK293 cell system. Human orexins weakly but concentration-dependently activated its Gq signalling (Ca2+ elevation), and the responses were inhibited by the non-selective orexin receptor antagonists TCS 1102 and almorexant, but only weakly by the OX1-selective antagonist SB-334867. Furthermore, the 5-/6-carboxytetramethylrhodamine (TAMRA)-labelled human orexin-A was able to bind to CiOX. Database mining was used to predict a potential endogenous C. intestinalis orexin peptide (Ci-orexin-A). Ci-orexin-A was able to displace TAMRA-orexin-A, but not to induce any calcium response at the CiOX. Consequently, we suggested that the orexin signalling system is conserved in Ciona intestinalis, although the relevant peptide-receptor interaction was not fully elucidated.

Interaction modes of human orexin 2 receptor with selective and nonselective antagonists studied by NMR spectroscopy

Orexin neuropeptides have many physiological roles in the sleep-wake cycle, feeding behavior, reward demands, and stress responses by activating cognitive receptors, the orexin receptors (OX1R and OX2R), distributed in the brain. There are only subtle differences between OX1R and OX2R in the orthosteric site, which has hindered the rational development of subtype-selective antagonists. In this study, we utilized solution-state NMR to capture the structural plasticity of OX2R labeled with 13CH3-ε-methionine in complex with antagonists. Mutations in the orthosteric site allosterically affected the intracellular tip of TM6. Ligand exchange experiments with the subtype-selective EMPA and the nonselective suvorexant identified three methionine residues that were substantially perturbed. The NMR spectra suggested that the suvorexant-bound state exhibited more structural plasticity than the EMPA-bound state, which has not been foreseen from the close similarity of their crystal structures, providing insights into dynamic features to be considered in understanding the ligand recognition mode.

Whole Brain Mapping of Orexin Receptor mRNA Expression Visualized by Branched In Situ Hybridization Chain Reaction

Orexins, which are produced within neurons of the lateral hypothalamic area, play a pivotal role in the regulation of various behaviors, including sleep/wakefulness, reward behavior, and energy metabolism, via orexin receptor type 1 (OX1R) and type 2 (OX2R). Despite the advanced understanding of orexinergic regulation of behavior at the circuit level, the precise distribution of orexin receptors in the brain remains unknown. Here, we develop a new branched in situ hybridization chain reaction (bHCR) technique to visualize multiple target mRNAs in a semiquantitative manner, combined with immunohistochemistry, which provided comprehensive distribution of orexin receptor mRNA and neuron subtypes expressing orexin receptors in mouse brains. Only a limited number of cells expressing both Ox1r and Ox2r were observed in specific brain regions, such as the dorsal raphe nucleus and ventromedial hypothalamic nucleus. In many brain regions, Ox1r-expressing cells and Ox2r-expressing cells belong to different cell types, such as glutamatergic and GABAergic neurons. Moreover, our findings demonstrated considerable heterogeneity in Ox1r- or Ox2r-expressing populations of serotonergic, dopaminergic, noradrenergic, cholinergic, and histaminergic neurons. The majority of orexin neurons did not express orexin receptors. This study provides valuable insights into the mechanism underlying the physiological and behavioral regulation mediated by the orexin system, as well as the development of therapeutic agents targeting orexin receptors.

GxE interaction effects of HCRTR2 single nucleotide polymorphism and adverse childhood experiences on methamphetamine use disorder

Background: Methamphetamine use disorder (MUD) is a worldwide health concern. The hypothalamic orexin system regulates stress response and addictive behaviors. The genetic variation in the hypocretin receptor 2 (HCRTR2), rs2653349, is associated with substance use disorder.Objectives: We explored the gene-environment (GxE) interaction of rs2653349 and adverse childhood experiences (ACEs) associated with MUD susceptibility.Methods: Four hundred and one individuals (336 males, 65 females) with MUD and 348 healthy controls (288 males, 60 females) completed a self-report questionnaire evaluating ACEs, encompassing childhood abuse and household dysfunction categories, and were genotyped for SNP rs2653349. Methamphetamine use variables were collected using the Diagnostic Interview for Genetic Studies. We used regression analyses to assess the GxE effect on MUD risk.Results: The MUD group had a comparable genotypic distribution for rs2653349 to the control group, albeit with a higher prevalence and number of types of ACEs, correlating with an increased MUD risk (p < .05). No significant genetic impact of rs2653349 on MUD risk was found. However, we observed a GxE interaction effect between the minor allele of rs2653349 and the number of childhood abuse or household dysfunction types, correlating with a reduced MUD risk (OR = -0.71, p = .04, Benjamini-Hochberg adjusted p = .08 and OR = -0.59, p = .045, Benjamini-Hochberg adjusted p = .09, respectively).Conclusion: HCRTR2 SNP rs2653349 has no significant impact on MUD risk, but ACEs may increase this risk. GxE results suggest that rs2653349 could offer protection against developing MUD in individuals experiencing multiple types of ACEs.

CD200R1 immune checkpoint blockade by the first-in-human anti-CD200R1 antibody 23ME-00610: molecular mechanism and engineering of a surrogate antibody

Human CD200R1 (hCD200R1), an immune inhibitory receptor expressed predominantly on T cells and myeloid cells, was identified as a promising immuno-oncology target by the 23andMe database. Blockade of CD200R1-dependent signaling enhances T cell-mediated antitumor activity in vitro and in vivo. 23ME-00610 is a potential first-in-class, humanized IgG1 investigational antibody that binds hCD200R1 with high affinity. We have previously shown that 23ME-00610 inhibits the hCD200R1 immune checkpoint function. Herein, we dissect the molecular mechanism of 23ME-00610 blockade of hCD200R1 by solving the crystal structure of 23ME-00610 Fab in complex with hCD200R1 and performing mutational studies, which show 23ME-00610 blocks the interaction between hCD200 and hCD200R1 through steric hindrance. However, 23ME-00610 does not bind CD200R1 of preclinical species such as cynomolgus monkey MfCD200R1. To enable preclinical toxicology studies of CD200R1 blockade in a pharmacologically relevant non-clinical species, we engineered a surrogate antibody with high affinity toward MfCD200R1. We used phage display libraries of 23ME-00610 variants with individual CDR residues randomized to all 20 amino acids, from which we identified mutations that switched on MfCD200R1 binding. Structural analysis suggests how the surrogate, named 23ME-00611, acquires the ortholog binding ability at the equivalent epitope of 23ME-00610. This engineering approach does not require a priori knowledge of structural and functional mapping of antibody-antigen interaction and thus is generally applicable for therapeutic antibody development when desired ortholog binding is lacking. These findings provide foundational insights as 23ME-00610 advances in clinical studies to gain understanding of the hCD200R1 immune checkpoint as a target in immuno-oncology.

Combined genotype of HCRTR2 and CLOCK variants in a large family of cluster headache with familial periodicity phenotype

PURPOSE

Cluster headache (CH) is a debilitating condition with severe and recurrent headaches characterized by circannual and circadian rhythms. A genetic contingent was suggested, and several loci were described in large cohorts. However, no variant associated with CH for multiplex families has been described. The purpose of our study was to examine candidate genes and new genetic variants in a multigenerational family of cluster headaches in which two members have original chronobiological characteristics that we have called the phenomenon of "family periodicity".

METHODS AND RESULTS

We performed a whole genome sequencing in four patients in a large multigenerational family of cluster headache to identify additional loci associated with CH. This allowed us to replicate the genomic association of HCRTR2 and CLOCK as candidate genes. In two family members with the same phenotypic circadian pattern (familial periodicity) the association of polymorphism NM_001526.4:c.922G > A was shown in the HCRTR2 gene, and NM_004898.4:c.213T > C in the CLOCK gene.

INTERPRETATION

This whole genome sequencing reproduced two genetic risk loci for CH already involved in its pathogenicity. This is the first time that the combination of HCRTR2 and CLOCK gene variants is identified in a multigenerational family of CH with striking periodicity characteristics. Our study supports the hypothesis that the combination of HCRTR2 and CLOCK gene variants can contribute to the risk of cluster headache and offer the prospect of a new area of research on the molecular circadian clock.

Anterior cingulate cortex orexin signaling mediates early-life stress-induced social impairment in females

Early-life stress has long-term impacts on the structure and function of the anterior cingulate cortex (ACC), and raises the risk of adult neuropsychiatric disorders including social dysfunction. The underlying neural mechanisms, however, are still uncertain. Here, we show that, in female mice, maternal separation (MS) during the first three postnatal weeks results in social impairment accompanied with hypoactivity in pyramidal neurons (PNs) of the ACC. Activation of ACC PNs ameliorates MS-induced social impairment. Neuropeptide Hcrt, which encodes hypocretin (orexin), is the top down-regulated gene in the ACC of MS females. Activating ACC orexin terminals enhances the activity of ACC PNs and rescues the diminished sociability observed in MS females via an orexin receptor 2 (OxR2)-dependent mechanism. Our results suggest orexin signaling in the ACC is critical in mediating early-life stress-induced social impairment in females.

Attenuation of Hypocretin/Orexin Signaling Is Associated With Increased Mortality After Myocardial Infarction

Background The hypocretin/orexin system has been shown to play a role in heart failure. Whether it also influences myocardial infarction (MI) outcomes is unknown. We evaluated the effect of the rs7767652 minor allele T associated with decreased transcription of the hypocretin/orexin receptor-2 and circulating orexin A concentrations on mortality risk after MI. Methods and Results Data from a single-center, prospectively designed registry of consecutive patients hospitalized for MI at a large tertiary cardiology center were analyzed. Patients without previous history of MI or heart failure were included. A random population sample was used to compare allele frequencies in the general population. Out of 1009 patients (aged 64±12 years, 74.6% men) after MI, 6.1% were homozygotes (TT) and 39.4% heterozygotes (CT) for minor allele. Allele frequencies in the MI group did not differ from 1953 subjects from general population (χ2 P=0.62). At index hospitalization, MI size was the same, but ventricular fibrillation and the need for cardiopulmonary resuscitation were more prevalent in the TT allele variant. Among patients with ejection fraction ≤40% at discharge, the TT variant was associated with a lower increase in left ventricular ejection fraction during follow-up (P=0.03). During the 27-month follow-up, there was a statistically significant association of the TT variant with increased mortality risk (hazard ratio [HR], 2.83; P=0.001). Higher circulating orexin A was associated with a lower mortality risk (HR, 0.41; P<0.05). Conclusions Attenuation of hypocretin/orexin signaling is associated with increased mortality risk after MI. This effect may be partially explained by the increased arrhythmic risk and the effect on the left ventricular systolic function recovery.

OX2R-selective orexin agonism is sufficient to ameliorate cataplexy and sleep/wake fragmentation without inducing drug-seeking behavior in mouse model of narcolepsy

Acquired loss of hypothalamic orexin (hypocretin)-producing neurons causes the chronic sleep disorder narcolepsy-cataplexy. Orexin replacement therapy using orexin receptor agonists is expected as a mechanistic treatment for narcolepsy. Orexins act on two receptor subtypes, OX1R and OX2R, the latter being more strongly implicated in sleep/wake regulation. However, it has been unclear whether the activation of only OX2R, or both OX1R and OX2R, is required to replace the endogenous orexin functions in the brain. In the present study, we examined whether the selective activation of OX2R is sufficient to rescue the phenotype of cataplexy and sleep/wake fragmentation in orexin knockout mice. Intracerebroventricular [Ala¹¹, _D-Leu¹⁵]-orexin-B, a peptidic OX2R-selective agonist, selectively activated OX2R-expressing histaminergic neurons in vivo, whereas intracerebroventricular orexin-A, an OX1R/OX2R non-selective agonist, additionally activated OX1R-positive noradrenergic neurons in vivo. Administration of [Ala¹¹, _D-Leu¹⁵]-orexin-B extended wake time, reduced state transition frequency between wake and NREM sleep, and reduced the number of cataplexy-like episodes, to the same degree as compared with orexin-A. Furthermore, intracerebroventricular orexin-A but not [Ala¹¹, _D-Leu¹⁵]-orexin-B induced drug-seeking behaviors in a dose-dependent manner in wild-type mice, suggesting that OX2R-selective agonism has a lower propensity for reinforcing/drug-seeking effects. Collectively, these findings provide a proof-of-concept for safer mechanistic treatment of narcolepsy-cataplexy through OX2R-selective agonism.