Orexin A Affects INS-1 Rat Insulinoma Cell Proliferation via Orexin Receptor 1 and the AKT Signaling Pathway

Orexins in apoptosis: a dual regulatory role

The orexins, also referred to as hypocretins, are neuropeptides that originate from the lateral hypothalamus (LH) region of the brain. They are composed of two small peptides, orexin-A, and orexin-B, which are broadly distributed throughout the central and peripheral nervous systems. Orexins are recognized to regulate diverse functions, involving energy homeostasis, the sleep-wake cycle, stress responses, and reward-seeking behaviors. Additionally, it is suggested that orexin-A deficiency is linked to sleepiness and narcolepsy. The orexins bind to their respective receptors, the orexin receptor type 1 (OX1R) and type 2 (OX2R), and activate different signaling pathways, which results in the mediation of various physiological functions. Orexin receptors are widely expressed in different parts of the body, including the skin, muscles, lungs, and bone marrow. The expression levels of orexins and their receptors play a crucial role in apoptosis, which makes them a potential target for clinical treatment of various disorders. This article delves into the significance of orexins and orexin receptors in the process of apoptosis, highlighting their expression levels and their potential contributions to different diseases. The article offers an overview of the existing understanding of the orexin/receptor system and how it influences the regulation of apoptosis.

A molecular network map of orexin-orexin receptor signaling system

Orexins are excitatory neuropeptides, which are predominantly associated with feeding behavior, sleep-wake cycle and energy homeostasis. The orexinergic system comprises of HCRTR1 and HCRTR2, G-protein-coupled receptors of rhodopsin family and the endogenous ligands processed from HCRT pro-hormone, Orexin A and Orexin B. These neuropeptides are biosynthesized by the orexin neurons present in the lateral hypothalamus area, with dense projections to other brain regions. The orexin-receptor signaling is implicated in various metabolic as well as neurological disorders, making it a promising target for pharmacological interventions. However, there is limited information available on the collective representation of the signal transduction pathways pertaining to the orexin-orexin receptor signaling system. Here, we depict a compendium of the Orexin A/B stimulated reactions in the form of a basic signaling pathway map. This map catalogs the reactions into five categories: molecular association, activation/inhibition, catalysis, transport, and gene regulation. A total of 318 downstream molecules were annotated adhering to the guidelines of NetPath curation. This pathway map can be utilized for further assessment of signaling events associated with orexin-mediated physiological functions and is freely available on WikiPathways, an open-source pathway database ( https://www.wikipathways.org/index.php/Pathway:WP5094 ).

Exploring the active components and potential mechanisms of Rosa roxburghii Tratt in treating type 2 diabetes mellitus based on UPLC-Q-exactive Orbitrap/MS and network pharmacology

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a global disease with growing prevalence that is difficult to cure. Rosa roxburghii Tratt is an edible and medicinal plant, and modern pharmacological studies have shown that it has potential anti-diabetic activity. This is the first study to explore the active components and potential mechanisms of Rosa roxburghii Tratt fruit for treating T2DM based on UPLC-Q-Exactive Orbitrap/MS and network pharmacology.

METHODS

The active components of Rosa roxburghii Tratt fruit were obtained from UPLC-Q-Exactive Orbitrap/MS analysis and retrieval in the SciFinder, PubMed, Web of Science, and CNKI databases. The potential targets of the active components were obtained from the SwissTargetPrediction and PharmMapper databases. The disease targets for T2DM were obtained from GeneCards, OMIM, TTD, DisGENent, and GEO databases. The intersection of the two datasets was used to obtain the potential targets of Rosa roxburghii Tratt fruit against T2DM. The target protein interaction network was constructed using the String database and Cytoscape software. The R software ClusterProfiler package was used for target enrichment analysis and the Cytoscape CytoNCA plug-in was used to screen core targets. Molecular docking and result visualization were performed using PyMOL and Autodock Vina software.

RESULTS

We obtained 20 bioactive ingredients, including alphitolic acid, quercetin, and ellagic acid, as well as 13 core targets, such as AKT1, TNF, SRC, and VEGFA. All bioactive ingredients in Rosa roxburghii Tratt fruit were active against T2DM-related therapeutic targets. Rosa roxburghii Tratt fruit may play a therapeutic role in T2DM by regulating the PI3K/AKT, RAS, AGE-RAGE, and other signaling pathways.

CONCLUSIONS

This study explored the active components and potential mechanisms of Rosa roxburghii Tratt fruit in the treatment of T2DM, laying the foundation for a further experimental study based on pharmacodynamic substances and their mechanisms of action.

Orexin/hypocretin system dysfunction in patients with Takotsubo syndrome: A novel pathophysiological explanation

Takotsubo syndrome (TTS) is an acute heart failure syndrome. Emotional or physical stressors are believed to precipitate TTS, while the pathophysiological mechanism is not yet completely understood. During the coronavirus disease (COVID-19) pandemic, an increased incidence of TTS has been reported in some countries; however, the precise pathophysiological mechanism for developing TTS with acute COVID-19 infection is unknown. Nevertheless, observing the symptoms of COVID-19 might lead to new perspectives in understanding TTS pathophysiology, as some of the symptoms of the COVID-19 infection could be assessed in the context of an orexin/hypocretin-system dysfunction. Orexin/hypocretin is a cardiorespiratory neuromodulator that acts on two orexin receptors widely distributed in the brain and peripheral tissues. In COVID-19 patients, autoantibodies against one of these orexin receptors have been reported. Orexin-system dysfunction affects a variety of systems in an organism. Here, we review the influence of orexin-system dysfunction on the cardiovascular system to propose its connection with TTS. We propose that orexin-system dysfunction is a potential novel explanation for the pathophysiology of TTS due to direct or indirect dynamics of orexin signaling, which could influence cardiac contractility. This is in line with the conceptualization of TTS as a cardiovascular syndrome rather than merely a cardiac abnormality or cardiomyopathy. To the best of our knowledge, this is the first publication to present a plausible connection between TTS and orexin-system dysfunction. We hope that this novel hypothesis will inspire comprehensive studies regarding orexin's role in TTS pathophysiology. Furthermore, confirmation of this plausible pathophysiological mechanism could contribute to the development of orexin-based therapeutics in the treatment and prevention of TTS.

New Aspects of Corpus Luteum Regulation in Physiological and Pathological Conditions: Involvement of Adipokines and Neuropeptides

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones-adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

Hypocretin/orexin modulates body weight and the metabolism of glucose and insulin

The hypocretin/orexin (Hcrt/orexin) unit affects the functions of the nervous, cardiovascular, gastrointestinal, and reproductive systems. Hcrt/orexin ligands and receptors have been localized to different parts of the central and peripheral nervous systems, cerebrospinal fluid and blood, exocrine (pancreas, salivary, lacrimal) as well as endocrine (pancreatic islets, pituitary, adrenal) glands. Several factors including stress, glucagon-like peptide-1 agonists, glutamate, nicotine, glucose, and hypoglycaemia stimulate the expression of Hcrt/orexin system, but it is inhibited by ageing, bone morphogenetic protein, hypoxia/hypercapnia, melanocortin receptor accessory protein 2, and glucagon. Literature reports show that Hcrt/orexin can significantly increase insulin secretion from normal and diabetic rat pancreata. Hcrt/orexin decreases blood glucose concentration and reduces insulin resistance partly via increased tissue expression of glucose transporter type 4. It reduces obesity by increasing browning of fat cells and energy expenditure. Taken together, Hcrt/orexin modulates obesity and the metabolism of glucose and insulin. The Hcrt/orexin system may thus be a target in the development of new therapies for the treatment of diabetes mellitus.

Hypoxylonol F Isolated from Annulohypoxylon annulatum Improves Insulin Secretion by Regulating Pancreatic β-cell Metabolism

Insulin plays a key role in glucose homeostasis and is hence used to treat hyperglycemia, the main characteristic of diabetes mellitus. Annulohypoxylon annulatum is an inedible ball-shaped wood-rotting fungus, and hypoxylon F is one of the major compounds of A. annulatum. The aim of this study is to evaluate the effects of hypoxylonol F isolated from A. annulatum on insulin secretion in INS-1 pancreatic β-cells and demonstrate the molecular mechanisms involved. Glucose-stimulated insulin secretion (GSIS) values were evaluated using a rat insulin ELISA kit. Moreover, the expression of proteins related to pancreatic β-cell metabolism and insulin secretion was evaluated using Western blotting. Hypoxylonol F isolated from A. annulatum was found to significantly enhance glucose-stimulated insulin secretion without inducing cytotoxicity. Additionally, hypoxylonol F enhanced insulin receptor substrate-2 (IRS-2) levels and activated the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. Interestingly, it also modulated the expression of peroxisome proliferator-activated receptor γ (PPARγ) and pancreatic and duodenal homeobox 1 (PDX-1). Our findings showed that A. annulatum and its bioactive compounds are capable of improving insulin secretion by pancreatic β-cells. This suggests that A. annulatum can be used as a therapeutic agent to treat diabetes.

Orexins Facilitates Osteogenic Differentiation of MC3T3-E1 Cells

Dysfunction of osteoblastic bone formation and matrix mineralization plays a key role in the pathological development of osteoporosis. The orexin peptide orexin-A, a highly excitatory neuropeptide hormone, possesses various biological functions by activating its specific G protein-coupled receptors, orexin-1 receptor (OX1R) and orexin-2 receptor (OX2R). Here, we report that OX1R but not OX2R was expressed in MC3T3-E1 cells. Importantly, we found that orexin-A accelerated osteoblast differentiation and matrix mineralization in MC3T3-E1 cells, as manifested by elevation of physiological markers of osteoblastic differentiation [alkaline phosphatase (ALP) and osteogenic genes] and Alizarin Red staining, respectively. Importantly, our findings indicated that orexin-A significantly increased the expression of runt-related transcription factor 2 (Runx-2), which is the central transcriptional factor. Orexin-A treatment phosphorylated the kinase p38 mitogen-activated protein kinase (MAPK) in a dose- and time-dependent manner. Also, orexin-induced increase in gene expression (Runx-2, ALP, osteocalcin, and osterix) and matrix mineralization were prevented by the p38 MAPK specific inhibitor SB203580. Additionally, we also revealed that protein kinase D (PKD) is involved in the effects of Orexin-A on p38 MAPK activation and Runx-2 expression. Finally, we found that Orexin-A-induced osteoblastic formation and matrix mineralization and the activation of the PKD/p38 MAPK pathway are mediated by OX1R. Based on these findings, we concluded that activation of OX1R by orexin-A might possess a therapeutic strategy for bone disease. © 2018 IUBMB Life, 70(7):633-641, 2018.

Orexin-A protects SH-SY5Y cells against H2O2-induced oxidative damage via the PI3K/MEK1/2/ERK1/2 signaling pathway

Orexin-A elicits multiple potent effects on a variety of tumor cells via different signaling pathways. However, it is unknown whether it has a neuroprotective effect on SH-SY5Y human neuroblastoma cells. This study investigated the neuroprotective effect of Orexin-A against hydrogen peroxide (H₂O₂)-induced oxidative damage in SH-SY5Y cells and the underlying mechanism. H₂O₂ treatment decreased the viability of SH-SY5Y cells, induced apoptosis, and decreased superoxide dismutase activity. Orexin-A attenuated these effects, indicating that it protects SH-SY5Y cells against H₂O₂-induced oxidative damage. Pre-treatment with Orexin-A also attenuated H₂O₂-induced increases in phosphorylation of MEK_1/2 and ERK_1/2. Moreover, these effects of Orexin-A were reduced in the presence of the PI3K inhibitor LY294002. Finally, pre-treatment with LY294002 abrogated attenuation of the H₂O₂-induced decrease in cell viability and increase in caspase-3/7 activity by Orexin-A. These results show that the PI3K/MEK_1/2/ERK_1/2 signaling pathway is involved in the neuroprotective effects of Orexin-A against H₂O₂-induced oxidative damage in SH-SY5Y cells. Our findings provide insight into the neuroprotective effects of Orexin-A and the underlying mechanism, which will be useful for the treatment of nervous system diseases.

The Orexin/Receptor System: Molecular Mechanism and Therapeutic Potential for Neurological Diseases

Orexins, also known as hypocretins, are two neuropeptides secreted from orexin-containing neurons, mainly in the lateral hypothalamus (LH). Orexins orchestrate their effects by binding and activating two G-protein–coupled receptors (GPCRs), orexin receptor type 1 (OX1R) and type 2 (OX2R). Orexin/receptor pathways play vital regulatory roles in many physiological processes, especially feeding behavior, sleep–wake rhythm, reward and addiction and energy balance. Furthermore several reports showed that orexin/receptor pathways are involved in pathological processes of neurological diseases such as narcolepsy, depression, ischemic stroke, drug addiction and Alzheimer’s disease (AD). This review article summarizes the expression patterns, physiological functions and potential molecular mechanisms of the orexin/receptor system in neurological diseases, providing an overall framework for considering these pathways from the standpoints of basic research and clinical treatment of neurological diseases.

Orexin-A Protects Human Neuroblastoma SH-SY5Y Cells Against 6-Hydroxydopamine-Induced Neurotoxicity: Involvement of PKC and PI3K Signaling Pathways

Parkinson's disease (PD) is a common neurodegenerative disorder that is characterized by progressive and selective death of dopaminergic neurons. Multifunctional neuropeptide orexin-A is involved in many biological events of the body. It has been shown that orexin-A has protective effects in neurodegenerative disease such as PD. However, its cellular mechanisms have not yet been fully clarified. Here, we investigated the intracellular signaling pathway of orexin-A neuroprotection in 6-hydroxydopamine (6-OHDA)-induced SH-SY5H cells damage as an in vitro model of PD. The cells were incubated with 150 μM 6-OHDA, and the viability was examined by 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2-tetrazolium bromide (MTT) assay. Mitochondrial membrane potential and intracellular calcium were measured by fluorescent probes. Western blotting was also used to determine cyclooxygenase type 2 (COX-2), nuclear factor erythroid 2 related factor 2 (Nrf2), and HSP70 protein levels. The data showed that 6-OHDA has decreasing effects on cell viability, Nrf2, and HSP70 protein expression and increases the level of mitochondrial membrane potential, intracellular calcium, and COX-2 protein. Orexin-A (500 pM) significantly attenuated the 6-OHDA-induced cell damage. Furthermore, Orexin-A significantly prevented the mentioned effects of 6-OHDA on SH-SY5Y cells. Orexin 1 receptor antagonist (SB3344867), PKC, and PI3-kinase (PI3K) inhibitors (chelerythrin and LY294002, respectively) could suppress the orexin-A neuroprotective effect. In contrast, blockage of PKA by a selective inhibitor (KT5720) had no effects on the orexin protection. The results suggest that orexin-A protective effects against 6-OHDA-induced neurotoxicity are performed via its receptors, PKC and PI3K signaling pathways.

Original Research: Orexins A and B stimulate proliferation and differentiation of porcine preadipocytes

Orexin A (OXA) and B (OXB) are neuropeptides which regulate appetite, energy expenditure, and arousal via G-protein coupled receptors termed as OXR1 and OXR2. The aim of this study was to characterize the effects of OXA and OXB on proliferation and differentiation of porcine preadipocytes. Porcine preadipocytes express both OXRs. OXA and OXB enhance porcine preadipocyte proliferation by 54.8% or 63.2 %, respectively. OXA and OXB potentiate differentiation of porcine preadipocytes, as judged by the increased lipid accumulation and expression of proadipogenic genes. Cellular lipid content after exposure of preadipocytes for six days to 100 nM OXA or OXB increased by 82.2% or 59.2%, respectively. OXA and OXB suppressed glycerol release by 23.9% or 24.9% in preadipocytes differentiated for six days. OXA (100 nM) increased peroxisome proliferator-activated receptor gamma (PPARγ) expression in cells differentiated for 24 h by 100.5%. PPARγ expression was also stimulated in preadipocytes differentiated in the presence of 10 nM (58.3%) or 100 nM OXA (50.6%) for three days. OXB potentiated PPARγ mRNA expression at 1 nM (59%), 10 nM (53.2%), and 100 nM (73.9%) in cells differentiated for three days. OXA increased CCAAT/enhancer binding protein alpha expression in preadipocytes differentiated for six days by 65%. OXB stimulated CCAAT/enhancer binding protein beta expression in preadipocytes differentiated for three days at 10 nM (149.5%) as well as 100 nM (207.2%). Lipoprotein lipase mRNA expression increased in cells treated with 10 nM OXA by 152.6% and 100 nM OXA by 162%. Lipoprotein lipase expression increased by 134% at 100 nM OXB. Furthermore, OXA (100 nM) and OXB (100 nM) increased leptin mRNA expression in preadipocytes differentiated for three days by 49.9% or 71.3%, respectively. These data indicate that orexin receptors may be relevant in the context of white adipose tissue formation.

Expression and potential role of the peptide orexin-A in prostate cancer

The peptides orexin-A and orexin-B and their G protein-coupled OX1 and OX2 receptors are involved in multiple physiological processes in the central nervous system and peripheral organs. Altered expression or signaling dysregulation of orexins and their receptors have been associated with a wide range of human diseases including narcolepsy, obesity, drug addiction, and cancer. Although orexin-A, its precursor molecule prepro-orexin and OX1 receptor have been detected in the human normal and hyperplastic prostate tissues, their expression and function in the prostate cancer (PCa) remains to be addressed. Here, we demonstrate for the first time the immunohistochemical localization of orexin-A in human PCa specimens, and the expression of prepro-orexin and OX1 receptor at both protein and mRNA levels in these tissues. Orexin-A administration to the human androgen-dependent prostate carcinoma cells LNCaP up-regulates OX1 receptor expression resulting in a decrease of cell survival. Noteworthy, nanomolar concentrations of the peptide counteract the testosterone-induced nuclear translocation of the androgen receptor in the cells: the orexin-A action is prevented by the addition of the OX1 receptor antagonist SB-408124 to the test system. These findings indicate that orexin-A/OX1 receptor interaction interferes with the activity of the androgen receptor which regulates PCa onset and progression, thus suggesting that orexin-A and its receptor might represent novel therapeutic targets to challenge this aggressive cancer.

Effect of Orexin-A on Cortisol Secretion in H295R Cells via p70S6K/4EBP1 Signaling Pathway

Orexin-A is a neuropeptide that orchestrates diverse central and peripheral processes. It is now clear that orexin system plays a central role in the regulation of endocrine, paracrine, and neurocrine. It is involved in the regulation of growth hormone, adrenocorticotropic hormone, thyroid, mineralocorticoid, and cortisol secretion. These hormones may also serve as a kind of signal linking energy balance regulation, reproduction, stress response, and cardiovascular regulation. Many studies have demonstrated the ability of orexin-A to regulate adrenocortical cells through the MAPK (mitogen-activated protein kinases) pathway. The aim of our study is to investigate the effect of orexin-A on cortisol secretion via the protein 70 ribosomal protein S6 kinase-1 (p70S6K) and eukaryotic translation initiation factor 4E binding proteins (4EBP1) signaling pathway in adrenocortical cells. We reported the first evidence that orexin-A stimulated p70S6K and 4EBP1 in human H295R adrenocortical cells in a concentration and time-dependent manner. 10(-6) M orexin-A treatment for 1 hour was the most potent. Our results also indicated that p70S6K and 4EBP1 kinases participated in controlling cortisol secretion via OX1 receptor in H295R cells, which implied important role of p70S6K and 4EBP1 kinases in regulating adrenal function induced by orexin-A.

The orexin type 1 receptor is overexpressed in advanced prostate cancer with a neuroendocrine differentiation, and mediates apoptosis

AIM

In the present study, we have examined the presence of orexins and their receptors in prostate cancer (CaP) and investigated their effects on the apoptosis of prostate cancer cells.

METHODS

We have localised the orexin type 1 and 2 receptors (OX1R and OX2R) and orexin A (OxA) in CaP sections of various grades and we have quantified tumour cells containing OX1R. Expression of OX1R was evaluated in the androgeno-dependent (AD) LNCaP and the androgeno-independent (AI) DU145 prostate cancer cells submitted or not to a neuroendocrine differentiation. The effects of orexins on the apoptosis and viability of DU145 cells were also investigated.

RESULTS

OX1R is strongly expressed in carcinomatous foci exhibiting a neuroendocrine differentiation, and the number of OX1R-stained cancer cells increases with the grade of the CaP. In contrast, OX2R is only detected in scattered malignant cells in high grade CaP. OX1R is expressed in the AI DU145 cells but is undetectable in the LNCaP cells. Acquisition of a neuroendocrine phenotype by the DU145 cells is associated with an overexpression of OX1R. Orexins induce the apoptosis of DU145 cells submitted to a neuroendocrine differentiation.

CONCLUSION

The present data indicate that OX1R-driven apoptosis is overexpressed in AI CaP exhibiting a neuroendocrine differentiation opening a gate for novel therapies for these aggressive cancers which are incurable until now.