Astrocyte proliferation is regulated by the OGF-OGFr axis in vitro and in experimental autoimmune encephalomyelitis

Enkephalins and Pain Modulation: Mechanisms of Action and Therapeutic Perspectives

Enkephalins, a subclass of endogenous opioid peptides, play a pivotal role in pain modulation. Enkephalins primarily exert their effects through opioid receptors located widely throughout both the central and peripheral nervous systems. This review will explore the mechanisms by which enkephalins produce analgesia, emotional regulation, neuroprotection, and other physiological effects. Furthermore, this review will analyze the involvement of enkephalins in the modulation of different pathologies characterized by severe pain. Understanding the complex role of enkephalins in pain processing provides valuable insight into potential therapeutic strategies for managing pain disorders.

Opioid growth factor receptor: Anatomical distribution and receptor colocalization in neurons of the adult mouse brain

The opioid growth factor (OGF) is an endogenous peptide that binds to the nuclear-associated receptor (OGFr), and plays a significant role in the proliferation of developing, renewing, and healing tissues. The receptor is widely expressed in a variety of organs, however its distribution in the brain remains unknown. In this study, we investigated the distribution of OGFr in different brain regions of male heterozygous (-/+ Lepr ^db/J), non -diabetic mice and determined the localization of the receptor in three major brain cell types, astrocytes, microglia, and neurons. Immunofluorescence imaging revealed that the highest number of OGFr was in hippocampal CA3 subregion followed by primary motor cortex, hippocampal CA2, thalamus, caudate and hypothalamus in a descending order. Double immunostaining revealed receptor colocalization with neurons and little or no colocalization in microglia and astrocytes. The highest percentage of OGFr positive neurons was identified in the CA3. Hippocampal CA3 neurons play an important role in memory processing, learning and behavior, and motor cortex neurons are important for muscle movement. However, the significance of the OGFr receptor in these brain regions and its relevance in diseased conditions are not known. Our findings provide a basis for understanding the cellular target and interaction of the OGF- OGFr pathway in neurodegenerative diseases such as Alzheimer's, Parkinson's, and stroke where hippocampus and cortex have an important role. This foundational data may also be useful in drug discovery to modulate OGFr by opioid receptor antagonist in various CNS diseases.

Multiple Sclerosis and the Endogenous Opioid System

Multiple sclerosis (MS) is an autoimmune disease characterized by chronic inflammation, neuronal degeneration and demyelinating lesions within the central nervous system. The mechanisms that underlie the pathogenesis and progression of MS are not fully known and current therapies have limited efficacy. Preclinical investigations using the murine experimental autoimmune encephalomyelitis (EAE) model of MS, as well as clinical observations in patients with MS, provide converging lines of evidence implicating the endogenous opioid system in the pathogenesis of this disease. In recent years, it has become increasingly clear that endogenous opioid peptides, binding μ- (MOR), κ- (KOR) and δ-opioid receptors (DOR), function as immunomodulatory molecules within both the immune and nervous systems. The endogenous opioid system is also well known to play a role in the development of chronic pain and negative affect, both of which are common comorbidities in MS. As such, dysregulation of the opioid system may be a mechanism that contributes to the pathogenesis of MS and associated symptoms. Here, we review the evidence for a connection between the endogenous opioid system and MS. We further explore the mechanisms by which opioidergic signaling might contribute to the pathophysiology and symptomatology of MS.

Research progress of opioid growth factor in immune-related diseases and cancer diseases

Methionine enkephalin (MENK) has an important role in both neuroendocrine and immune systems. MENK was known as an opioid growth factor (OGF) for its growth regulatory characteristics. OGF interacts with the OGF receptor (OGFr) to inhibit DNA synthesis by upregulating p16 and/or p21, which delays the cell cycle transition from G0/G1 to S phase, and inhibits cell proliferation. In addition, OGF combines with OGFr in immune cells to exert its immunomodulatory activity and regulate immune function. OGF has been studied as an immunomodulator in a variety of autoimmune diseases, including multiple sclerosis, inflammatory bowel disease, diabetes and viral infections, and has been proven to relieve symptoms of certain diseases in animal and in vitro experiments. Also, OGF and OGFr have various anti-tumor molecular mechanisms. OGF can be used as the primary therapy alone or combined with other drugs to treat tumors. This article summarizes the research progress of OGF in immune-related diseases and cancer diseases.

Mettl14-mediated m6A modification modulates neuron apoptosis during the repair of spinal cord injury by regulating the transformation from pri-mir-375 to miR-375

BACKGROUND

Spinal cord injury (SCI) is a disabling disorder, resulting in neurological impairments. This study investigated the mechanism of methyltransferase-like 14 (Mettl14) on apoptosis of spinal cord neurons during SCI repair by mediating pri-microRNA (miR) dependent N6-methyladenosine (m6A) methylation.

METHODS

The m6A content in total RNA and Mettl14 levels in spinal cord tissues of SCI rats were detected. Mettl14 expression was intervened in SCI rats to examine motor function, neuron apoptosis, and recovery of neurites. The cell model of SCI was established and intervened with Mettl14. miR-375, related to SCI and positively related to Mettl14, was screened out. The expression of miR-375 and pri-miR-375 after Mettl14 intervention was detected. The expression of pri-miR-375 combined with DiGeorge critical region 8 (DGCR8) and that modified by m6A was detected. Furthermore, the possible downstream gene and pathway of miR-375 were analysed. SCI cell model with Mettl14 intervention was combined with Ras-related dexamethasone-induced 1 (RASD1)/miR-375 intervention to observe the apoptosis.

RESULTS

Mettl14 level and m6A content in spinal cord tissue were significantly increased. After Mettl14 knockdown, the injured motor function was restored and neuron apoptosis was reduced. In vitro, Mettl14 silencing reduced the apoptosis of SCI cells; miR-375 was reduced and pri-miR-375 was increased; miR-375 targeted RASD1. Silencing Mettl14 inactivated the mTOR pathway. The apoptosis in cells treated with silencing Mettl14 + RASD1/miR-375 was inhibited.

CONCLUSIONS

Mettl14-mediated m6A modification inhibited RASD1 and induced the apoptosis of spinal cord neurons in SCI by promoting the transformation of pri-miR-375 to mature miR-375.

Endomorphin-2 Analog Inhibits the Growth of DLD-1 and RKO Human Colon Cancer Cells by Inducing Cell Apoptosis

Background

In developed countries, colon cancer is a leading cause of cancer-associated mortality. Dietary changes have resulted in an increased incidence of colon cancer in Asia. This study aimed to investigate the effects of the structural analog of endomorphin-2 (H-Tyr-Pro-Phe-Phe-NH₂) on human colon cancer cells in vitro.

Material/Methods

Human DLD-1 and RKO colon cancer cells and CCD-18Co normal human colonic fibroblasts were treated with increasing doses of the structural analog of endomorphin-2. Cells underwent the MTT assay, fluorescence confocal flow cytometry, and Hoechst 33258 staining to investigate cell proliferation, the cell cycle, and apoptosis. Western blot was used to measure the expression levels of poly(ADP-ribose) polymerase-1 (PARP-1), cytochrome c, caspase-3, and caspase-9. The 2′,7′-dichlorofluorescein diacetate (DCFH-DA) fluorescence method measured reactive oxygen species (ROS).

Results

Cell proliferation of DLD-1 and RKO cells was inhibited by the endomorphin-2 analog in a dose-dependent manner, and a 100 μM dose reduced DLD-1 and RKO cell proliferation by 28% and 23%, respectively, at 72 h. Endomorphin-2 analog induced cell apoptosis and the generation of ROS, activated caspase-3 and caspase-9, and increased the levels of p53 and cytochrome c release, and down-regulated of Akt activation in DLD-1 and RKO cells in a dose-dependent manner. Treatment of the DLD-1 and RKO cells with the endomorphin-2 analog increased the expression of Bax and reduced the expression of Bcl-2.

Conclusions

Endomorphin-2 analog inhibited colon cancer cell proliferation, activated apoptosis, and down-regulated Akt phosphorylation of human DLD-1 and RKO colon cancer cells in vitro in a dose-dependent manner.

The Interplay between Retinal Pathways of Cholesterol Output and Its Effects on Mouse Retina

In mammalian retina, cholesterol excess is mainly metabolized to oxysterols by cytochromes P450 27A1 (CYP27A1) and 46A1 (CYP46A1) or removed on lipoprotein particles containing apolipoprotein E (APOE). In contrast, esterification by sterol-O-acyltransferase 1 (SOAT) plays only a minor role in this process. Accordingly, retinal cholesterol levels are unchanged in Soat1^-/- mice but are increased in Cyp27a1^-/-Cyp46a1^-/- and Apoe^-/- mice. Herein, we characterized Cyp27a1^-/-Cyp46a1^-/-Soat1^-/- and Cyp27a1^-/-Cyp46a1^-/-Apoe^-/- mice. In the former, retinal cholesterol levels, anatomical gross structure, and vasculature were normal, yet the electroretinographic responses were impaired. Conversely, in Cyp27a1^-/-Cyp46a1^-/-Apoe^-/- mice, retinal cholesterol levels were increased while anatomical structure and vasculature were unaffected with only male mice showing a decrease in electroretinographic responses. Sterol profiling, qRT-PCR, proteomics, and transmission electron microscopy mapped potential compensatory mechanisms in the Cyp27a1^-/-Cyp46a1^-/-Soat1^-/- and Cyp27a1^-/-Cyp46a1^-/-Apoe^-/- retina. These included decreased cholesterol biosynthesis along with enhanced formation of intra- and extracellular vesicles, possibly a reserve mechanism for lowering retinal cholesterol. In addition, there was altered abundance of proteins in Cyp27a1^-/-Cyp46a1^-/-Soat1^-/- mice that can affect photoreceptor function, survival, and retinal energy homeostasis (glucose and fatty acid metabolism). Therefore, the levels of retinal cholesterol do not seem to predict retinal abnormalities, and it is rather the network of compensatory mechanisms that appears to determine retinal phenotype.

Intermittent blockade of OGFr and treatment of autoimmune disorders

IMPACT STATEMENT

This mini-review presents information on the intermittent blockade of the opioid growth factor (OGF)-OGF receptor (OGFr) axis by low-dose naltrexone (LDN), and the role of enkephalin (i.e. OGF) in autoimmune disorders, specifically multiple sclerosis, Crohn's, and fibromyalgia. Clinical reports on subjects taking LDN have documented reduced fatigue, few side-effects, and improved overall health. Preclinical studies on mice with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, revealed that immunization for EAE reduces serum OGF. Intermittent OGFr blockade with LDN restores serum enkephalin levels that correlate with reduced behavioral and pathological signs of EAE; LDN also increases enkephalin levels in naïve mice. The interplay between LDN, and the onset and treatment of autoimmune diseases, chronic pain, and other addictive behaviors requires further investigation, but highlights a central role for enkephalins and intermittent blockade of the OGF-OGFr pathway in pathogenesis and treatment of these disorders.

Modulation of mitochondrial DNA copy number in a model of glioblastoma induces changes to DNA methylation and gene expression of the nuclear genome in tumours

Background

There are multiple copies of mitochondrial DNA (mtDNA) present in each cell type, and they are strictly regulated in a cell-specific manner by a group of nuclear-encoded mtDNA-specific replication factors. This strict regulation of mtDNA copy number is mediated by cell-specific DNA methylation of these replication factors. Glioblastoma multiforme, HSR-GBM1, cells are hyper-methylated and maintain low mtDNA copy number to support their tumorigenic status. We have previously shown that when HSR-GBM1 cells with 50% of their original mtDNA content were inoculated into mice, tumours grew more aggressively than non-depleted cells. However, when the cells possessed only 3% and 0.2% of their original mtDNA content, tumour formation was less frequent and the initiation of tumorigenesis was significantly delayed. Importantly, the process of tumorigenesis was dependent on mtDNA copy number being restored to pre-depletion levels.

Results

By performing whole genome MeDIP-Seq and RNA-Seq on tumours generated from cells possessing 100%, 50%, 0.3% and 0.2% of their original mtDNA content, we determined that restoration of mtDNA copy number caused significant changes to both the nuclear methylome and its transcriptome for each tumour type. The affected genes were specifically associated with gene networks and pathways involving behaviour, nervous system development, cell differentiation and regulation of transcription and cellular processes. The mtDNA-specific replication factors were also modulated.

Conclusions

Our results highlight the bidirectional control of the nuclear and mitochondrial genomes through modulation of DNA methylation to control mtDNA copy number, which, in turn, modulates nuclear gene expression during tumorigenesis.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0223-z) contains supplementary material, which is available to authorized users.

Long-term treatment with low dose naltrexone maintains stable health in patients with multiple sclerosis

Introduction

A retrospective study was conducted on patients at Penn State Hershey Medical Center diagnosed with relapsing–remitting multiple sclerosis between 2006 and 2015.

Methodology

Laboratory and clinical data collected over this 10-year period were reviewed. Two cohorts of patients were established based on their relapsing–remitting multiple sclerosis therapy at the time of their first visit to Penn State. One group of patients (n = 23) was initially prescribed low dose naltrexone at the time first seen at Hershey. This group was offered low dose naltrexone because of symptoms of fatigue or refusal to take an available disease-modifying therapy. The second group of patients (n = 31) was treated with the glatiramer acetate (Copaxone) and offered low dose naltrexone as an adjunct therapy to their disease-modifying therapy.

Results

Patient data from visits after 1–50 months post-diagnosis were evaluated in a retrospective manner. Data obtained from patient charts included clinical laboratory values from standard blood tests, timed 25-foot walking trials, and changes in magnetic resonance imaging reports. Statistical analyses between the groups and for each patient over time indicated no significant differences in clinical laboratory values, timed walking, or changes in magnetic resonance imaging.

Conclusion

These data suggest that the apparently non-toxic, inexpensive, biotherapeutic is safe and if taken alone did not result in an exacerbation of disease symptoms.

Improved clinical behavior of established relapsing-remitting experimental autoimmune encephalomyelitis following treatment with endogenous opioids: implications for the treatment of multiple sclerosis

Relapse-remitting multiple sclerosis is a chronic disease of the CNS that affects 350,000 individuals in the U.S., reducing the quality of life and often resulting in paralysis. Most current therapies do not target the underlying pathophysiology of multiple sclerosis (MS). This study examined the therapeutic efficacy of an endogenous peptide (opioid growth factor, OGF) known to inhibit cell replication in a receptor-mediated manner, utilizing a mouse model of relapse-remitting experimental autoimmune encephalomyelitis (RR-EAE). RR-EAE was induced by immunization of SJL/J mice with proteolipid protein. Two days following establishment of clinical disease, treatment with OGF (10mg/kg) or saline was initiated and mice were observed on a daily basis. OGF treated mice had markedly reduced clinical signs of disease over the course of 40 days. OGF treatment increased the incidence and lengthened the time of remissions relative to saline-treated mice with RR-EAE. OGF therapy also reduced relapses, and facilitated extended periods of mild disease. Neuropathological examination of lumbar spinal cord after 40 days of treatment revealed decreased numbers of Iba-1 and CD3+ reactive cells, suggesting that OGF inhibited proliferation of microglia/macrophages and T lymphocytes, as well as decreasing the number of proliferating activated astrocytes (Ki-67 and GFAP dual labeled sections). Peptide treatment for 40 days diminished levels of demyelination in comparison to saline-treated mice with RR-EAE. These data are the first to demonstrate that exposure to OGF initiated at the time of established disease can reverse the course of RR-EAE and reduce neuropathological deficits.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Drug abuse and the neurovascular unit

Drug abuse continues to create a major international epidemic affecting society. A great majority of past drug abuse research has focused mostly on the mechanisms of addiction and the specific effects of substance use disorders on brain circuits and pathways that modulate reward, motivation, craving, and decision making. Few studies have focused on the neurobiology of acute and chronic substance abuse as it relates to the neurovascular unit (brain endothelial cell, neuron, astrocyte, microglia, and pericyte). Increasing research indicates that all cellular components of the neurovascular unit play a pivotal role in both the process of addiction and how drug abuse affects the brain response to diseases. This review will focus on the specific effects of opioids, amphetamines, alcohol, and nicotine on the neurovascular unit and its role in addiction and adaption to brain diseases. Elucidation of the role of the neurovascular unit on the neurobiology associated with drug addiction will help to facilitate the development of better therapeutic approaches for drug-dependent individuals.

Featured Article: Selective blockade of the OGF–OGFr pathway by naltrexone accelerates fibroblast proliferation and wound healing

Naltrexone (NTX) is an opioid receptor antagonist that acts at classical and non-classical opioid receptors including the opioid growth factor receptor (OGFr). Animal models of type 1 and type 2 diabetes, as well as normal rodents, have shown that topical NTX enhances the healing rates of corneal epithelium and full-thickness cutaneous wounds. The mechanism of this general opioid antagonist on growth, and in particular the specific receptor pathway involved, is not understood. Tissue culture studies using NIH 3T3 fibroblasts and primary rat auricular fibroblasts were established to evaluate growth following opioid receptor antagonist treatment. Treatment of cells with CTOP, naltrindole, or nalmefene, selective antagonists for mu, delta, and kappa opioid receptors, respectively, did not accelerate cell replication. Addition of the classical opioid receptor peptides DAMGO, DPDPE, or EKC did not alter cell growth, suggesting that the classical opioid receptors were not involved in cutaneous wound healing. However, NTX (10−6 M) increased the growth of NIH 3T3 fibroblasts in culture over a 96-h period, and the specific ligand OGF decreased cell growth, supporting that the OGF-OGFr axis is tonically active and constitutively expressed in fibroblasts, the primary cell type in granulation tissue of the skin. Transfection of NIH 3T3 cells with OGFr siRNA reduced receptor protein; subsequent treatment with NTX did not accelerate cell proliferation. These data indicate that blockade of the OGFr pathway enhances proliferation of fibroblasts in vitro, and in a primary culture of auricular fibroblasts, suggesting that the effect of NTX on growth is mediated through the OGF-OGFr axis. Finally, antagonists for classical opioid receptors as well as NTX were topically applied to cutaneous wounds in type 1 diabetic rats; only NTX accelerated wound closure. These studies indicate that the mechanistic pathway underlying the effects of NTX to enhance cutaneous wound closure in diabetic and nondiabetic subjects is specific blockade of the OGF–OGFr regulatory axis.

Molecular hydrogen suppresses reactive astrogliosis related to oxidative injury during spinal cord injury in rats

AIMS

Spinal cord injury (SCI) can induce excessive astrocyte activation. Hydrogen has been deemed as a novel antioxidant. We investigated whether molecular hydrogen could act as an antiastrogliosis agent during SCI and oxidative injury in experimental rats and cultured astrocytes.

METHODS

Hydrogen-rich saline (HS, 8 mL/kg, i.p.) was injected every 12 h after SCI in rats. The expression of STAT3, p-STAT3, and glial fibrillary acidic protein (GFAP); the release of IL-1β, IL-6, and TNF-α; and astrogliosis, along with the BBB score, were evaluated. Culturing astrocytes with hydrogen-rich medium, the intracellular reactive oxygen species (ROS), astrogliosis, and the release of proinflammatory cytokines were assessed after H2O2-induced injury.

RESULTS

In the HS group, the expression of STAT3, p-STAT3, and GFAP and the proinflammatory cytokines were decreased in local spinal cord on postoperation day (POD) 3; on PODs 7 and 14, reactive astrogliosis was suppressed, and the locomotor function was also improved. Furthermore, hydrogen-rich medium attenuated the intracellular production of ROS (especially HO•), astrogliosis, and the secretion of proinflammatory cytokines in astrocytes 12 h after H2O2-induced injury.

CONCLUSIONS

Molecular hydrogen could suppress reactive astrogliosis after contusive SCI and reduce the release of proinflammatory cytokines produced by active astrocytes related to oxidative injury. Thus, molecular hydrogen is potential to be a neuroprotective agent.