Differential expression and HIV-1 regulation of μ-opioid receptor splice variants across human central nervous system cell types

Osteopontin/secreted phosphoprotein-1 harnesses glial-, immune-, and neuronal cell ligand-receptor interactions to sense and regulate acute and chronic neuroinflammation

Osteopontin (OPN) also known by its official gene designation secreted phosphoprotein-1 (SPP1) is a fascinating, multifunctional protein expressed in a number of cell types that functions not only in intercellular communication, but also in the extracellular matrix (ECM). OPN/SPP1 possesses cytokine, chemokine, and signal transduction functions by virtue of modular structural motifs that provide interaction surfaces for integrins and CD44-variant receptors. In humans, there are three experimentally verified splice variants of OPN/SPP1 and CD44's ten exons are also alternatively spiced in a cell/tissue-specific manner, although very little is known about how this is regulated in the central nervous system (CNS). Post-translational modifications of phosphorylation, glycosylation, and localized cleavage by specific proteases in the cells and tissues where OPN/SPP1 functions, provides additional layers of specificity. However, the former make elucidating the exact molecular mechanisms of OPN/SPP1 function more complex. Flexibility in OPN/SPP1 structure and its engagement with integrins having the ability to transmit signals in inside-out and outside-in direction, is likely why OPN/SPP1 can serve as an early detector of inflammation and ongoing tissue damage in response to cancer, stroke, traumatic brain injury, pathogenic infection, and neurodegeneration, processes that impair tissue homeostasis. This review will focus on what is currently known about OPN/SPP1 function in the brain.

Modulation of OPRM1 Alternative Splicing by Morphine and HIV-1 Nef

Clinically used opioids, such as morphine, activate the mu opioid receptor (MOR) encoded by Opioid Receptor Mu 1 (OPRM1) gene. Examination of the opioid receptor genes showed that the human OPRM1 pre-mRNA undergoes extensive alternative splicing events and capable of expressing 21 isoforms. However, characterization of OPRM1 signaling is generalized, and only one isoform (MOR-1) has been extensively studied. Compounding this issue is the increasing significance of intravenous drug abuse in HIV neuropathogenesis. Here, we investigated the molecular impact of morphine and HIV-1 on regulation of OPRM1 pre-mRNA splicing in in vitro and in vivo models. Our results suggested that morphine treatment specifically induces the alternative splicing of MOR-1X isoform among the other isoforms analyzed in neuronal cells. Interestingly, alternative splicing and expression of MOR-1X isoform was also induced in postmortem brain tissues obtained from people with HIV (PWH). Additionally, treatment of control rats with morphine induced alternative splicing of MOR-1X in the brain regions involved in the reward pathways. More interestingly, HIV-1 transgenic (HIV-1Tg) rats, showed an additive induction of MOR-1X isoform with the exposure to morphine. To further assess the possible role of HIV secretory proteins in alternative splicing of OPRM1 gene, we analyzed the impact of HIV-1 Tat, gp120 and Nef proteins on alternative splicing of MOR-1X isoform. While the Tat and gp120 had no visible effects, treatment of neurons with Nef induced MOR-1X alternative splicing that was comparable to treatment with morphine. Altogether, our results suggest that HIV-1 may alter MOR isoform expression with Nef protein by amplifying the rate of MOR-1X alternative splicing induced by morphine.

Exploring Pharmacological Functions of Alternatively Spliced Variants of the Mu Opioid Receptor Gene, Oprm1, via Gene-Targeted Animal Models

The mu opioid receptor has a distinct place in the opioid receptor family, since it mediates the actions of most opioids used clinically (e.g., morphine and fentanyl), as well as drugs of abuse (e.g., heroin). The single-copy mu opioid receptor gene, OPRM1, goes through extensive alternative pre-mRNA splicing to generate numerous splice variants that are conserved from rodents to humans. These OPRM1 splice variants can be classified into three structurally distinct types: (1) full-length 7 transmembrane (TM) carboxyl (C)-terminal variants; (2) truncated 6TM variants; and (3) single TM variants. Distinct pharmacological functions of these splice variants have been demonstrated by both in vitro and in vivo studies, particularly by using several unique gene-targeted mouse models. These studies provide new insights into our understanding of the complex actions of mu opioids with regard to OPRM1 alternative splicing. This review provides an overview of the studies that used these gene-targeted mouse models for exploring the functional importance of Oprm1 splice variants.

Alternative Pre-mRNA Splicing of the Mu Opioid Receptor Gene, OPRM1: Insight into Complex Mu Opioid Actions

Most opioid analgesics used clinically, including morphine and fentanyl, as well as the recreational drug heroin, act primarily through the mu opioid receptor, a class A Rhodopsin-like G protein-coupled receptor (GPCR). The single-copy mu opioid receptor gene, OPRM1, undergoes extensive alternative splicing, creating multiple splice variants or isoforms via a variety of alternative splicing events. These OPRM1 splice variants can be categorized into three major types based on the receptor structure: (1) full-length 7 transmembrane (TM) C-terminal variants; (2) truncated 6TM variants; and (3) single TM variants. Increasing evidence suggests that these OPRM1 splice variants are pharmacologically important in mediating the distinct actions of various mu opioids. More importantly, the OPRM1 variants can be targeted for development of novel opioid analgesics that are potent against multiple types of pain, but devoid of many side-effects associated with traditional opiates. In this review, we provide an overview of OPRM1 alternative splicing and its functional relevance in opioid pharmacology.

Buprenorphine Increases HIV-1 Infection In Vitro but Does Not Reactivate HIV-1 from Latency

BACKGROUND

medication-assisted treatment (MAT) with buprenorphine is now widely prescribed to treat addiction to heroin and other illicit opioids. There is some evidence that illicit opioids enhance HIV-1 replication and accelerate AIDS pathogenesis, but the effect of buprenorphine is unknown.

METHODS

we obtained peripheral blood mononuclear cells (PBMCs) from healthy volunteers and cultured them in the presence of morphine, buprenorphine, or methadone. We infected the cells with a replication-competent CCR5-tropic HIV-1 reporter virus encoding a secreted nanoluciferase gene, and measured infection by luciferase activity in the supernatants over time. We also surveyed opioid receptor expression in PBMC, genital epithelial cells and other leukocytes by qPCR and western blotting. Reactivation from latency was assessed in J-Lat 11.1 and U1 cell lines.

RESULTS

we did not detect expression of classical opioid receptors in leukocytes, but did find nociception/orphanin FQ receptor (NOP) expression in blood and vaginal lymphocytes as well as genital epithelial cells. In PBMCs, we found that at physiological doses, morphine, and methadone had a variable or no effect on HIV infection, but buprenorphine treatment significantly increased HIV-1 infectivity (median: 8.797-fold increase with 20 nM buprenorphine, eight experiments, range: 3.570-691.9, p = 0.0078). Using latently infected cell lines, we did not detect reactivation of latent HIV following treatment with any of the opioid drugs.

CONCLUSIONS

our results suggest that buprenorphine, in contrast to morphine or methadone, increases the in vitro susceptibility of leukocytes to HIV-1 infection but has no effect on in vitro HIV reactivation. These findings contribute to our understanding how opioids, including those used for MAT, affect HIV infection and reactivation, and can help to inform the choice of MAT for people living with HIV or who are at risk of HIV infection.

Endogenous Opioid Peptides and Alternatively Spliced Mu Opioid Receptor Seven Transmembrane Carboxyl-Terminal Variants

There exist three main types of endogenous opioid peptides, enkephalins, dynorphins and β-endorphin, all of which are derived from their precursors. These endogenous opioid peptides act through opioid receptors, including mu opioid receptor (MOR), delta opioid receptor (DOR) and kappa opioid receptor (KOR), and play important roles not only in analgesia, but also many other biological processes such as reward, stress response, feeding and emotion. The MOR gene, OPRM1, undergoes extensive alternative pre-mRNA splicing, generating multiple splice variants or isoforms. One type of these splice variants, the full-length 7 transmembrane (TM) Carboxyl (C)-terminal variants, has the same receptor structures but contains different intracellular C-terminal tails. The pharmacological functions of several endogenous opioid peptides through the mouse, rat and human OPRM1 7TM C-terminal variants have been considerably investigated together with various mu opioid ligands. The current review focuses on the studies of these endogenous opioid peptides and summarizes the results from early pharmacological studies, including receptor binding affinity and G protein activation, and recent studies of β-arrestin2 recruitment and biased signaling, aiming to provide new insights into the mechanisms and functions of endogenous opioid peptides, which are mediated through the OPRM1 7TM C-terminal splice variants.

Escalating morphine dosing in HIV-1 Tat transgenic mice with sustained Tat exposure reveals an allostatic shift in neuroinflammatory regulation accompanied by increased neuroprotective non-endocannabinoid lipid signaling molecules and amino acids

BACKGROUND

Human immunodeficiency virus type-1 (HIV-1) and opiates cause long-term inflammatory insult to the central nervous system (CNS) and worsen disease progression and HIV-1-related neuropathology. The combination of these proinflammatory factors reflects a devastating problem as opioids have high abuse liability and continue to be prescribed for certain patients experiencing HIV-1-related pain.

METHODS

Here, we examined the impact of chronic (3-month) HIV-1 transactivator of transcription (Tat) exposure to short-term (8-day), escalating morphine in HIV-1 Tat transgenic mice that express the HIV-1 Tat protein in a GFAP promoter-regulated, doxycycline (DOX)-inducible manner. In addition to assessing morphine-induced tolerance in nociceptive responses organized at spinal (i.e., tail-flick) and supraspinal (i.e., hot-plate) levels, we evaluated neuroinflammation via positron emission tomography (PET) imaging using the [18F]-PBR111 ligand, immunohistochemistry, and cytokine analyses. Further, we examined endocannabinoid (eCB) levels, related non-eCB lipids, and amino acids via mass spectrometry.  RESULTS: Tat-expressing [Tat(+)] transgenic mice displayed antinociceptive tolerance in the tail withdrawal and hot-plate assays compared to control mice lacking Tat [Tat(-)]. This tolerance was accompanied by morphine-dependent increases in Iba-1 ± 3-nitrotryosine immunoreactive microglia, and alterations in pro- and anti-inflammatory cytokines, and chemokines in the spinal cord and striatum, while increases in neuroinflammation were absent by PET imaging of [18F]-PBR111 uptake. Tat and morphine exposure differentially affected eCB levels, non-eCB lipids, and specific amino acids in a region-dependent manner. In the striatum, non-eCB lipids were significantly increased by short-term, escalating morphine exposure, including peroxisome proliferator activator receptor alpha (PPAR-α) ligands N-oleoyl ethanolamide (OEA) and N-palmitoyl ethanolamide (PEA), as well as the amino acids phenylalanine and proline. In the spinal cord, Tat exposure increased amino acids leucine and valine, while morphine decreased levels of tyrosine and valine but did not affect eCBs or non-eCB lipids.

CONCLUSION

Overall results demonstrate that 3 months of Tat exposure increased morphine tolerance and potentially innate immune tolerance evidenced by reductions in specific cytokines (e.g., IL-1α, IL-12p40) and microglial reactivity. In contrast, short-term, escalating morphine exposure acted as a secondary stressor revealing an allostatic shift in CNS baseline inflammatory responsiveness from sustained Tat exposure.

Mu Opioids Induce Biased Signaling at the Full-Length Seven Transmembrane C-Terminal Splice Variants of the mu Opioid Receptor Gene, Oprm1

The biased signaling has been extensively studied in the original mu opioid receptor (MOR-1), particularly through G protein and β-arrestin2 signaling pathways. The concept that the G protein pathway is often linked to the therapeutic effect of the drug, while the β-arrestin pathway is associated to the side effects has been proposed to develop biased analgesic compounds with limited side-effects associated with traditional opiates. The mu opioid receptor gene, OPRM1, undergoes extensive alternative pre-mRNA splicing, generating multiple splice variants or isoforms that are conserved from rodent to human. One type of the Oprm1 splice variants are the full-length 7 transmembrane (7TM) C-terminal splice variants, which have identical receptor structures including entire binding pocket, but contain a different intracellular C-terminal tail resulted from 3' alternative splicing. Increasing evidence suggest that these full-length 7TM C-terminal variants play important roles in mu opioid pharmacology, raising questions regarding biased signaling at these multiple C-terminal variants. In the present study, we investigated the effect of different C-terminal variants on mu agonist-induced G protein coupling, β-arrestin2 recruitment, and ultimately, signaling bias. We found that mu agonists produced marked differences in G protein activation and β-arrestin2 recruitment among various C-terminal variants, leading to biased signaling at various level. Particularly, MOR-1O, an exon 7-associated variant, showed greater β-arrestin2 bias for most mu agonists than MOR-1, an exon 4-associated variant. Biased signaling of G protein-coupled receptors has been defined by evidences that different agonists can produce divergent signaling transduction pathways through a single receptor. Our findings that a single mu agonist can induce differential signaling through multiple 7TM splice variants provide a new perspective on biased signaling at least for Oprm1, which perhaps is important for our understanding of the complex mu opioid actions in vivo where all the 7TM splice variants co-exist.

Opioid and neuroHIV Comorbidity - Current and Future Perspectives

With the current national opioid crisis, it is critical to examine the mechanisms underlying pathophysiologic interactions between human immunodeficiency virus (HIV) and opioids in the central nervous system (CNS). Recent advances in experimental models, methodology, and our understanding of disease processes at the molecular and cellular levels reveal opioid-HIV interactions with increasing clarity. However, despite the substantial new insight, the unique impact of opioids on the severity, progression, and prognosis of neuroHIV and HIV-associated neurocognitive disorders (HAND) are not fully understood. In this review, we explore, in detail, what is currently known about mechanisms underlying opioid interactions with HIV, with emphasis on individual HIV-1-expressed gene products at the molecular, cellular and systems levels. Furthermore, we review preclinical and clinical studies with a focus on key considerations when addressing questions of whether opioid-HIV interactive pathogenesis results in unique structural or functional deficits not seen with either disease alone. These considerations include, understanding the combined consequences of HIV-1 genetic variants, host variants, and μ-opioid receptor (MOR) and HIV chemokine co-receptor interactions on the comorbidity. Lastly, we present topics that need to be considered in the future to better understand the unique contributions of opioids to the pathophysiology of neuroHIV.

Graphical Abstract

Morphine counteracts the antiviral effect of antiretroviral drugs and causes upregulation of p62/SQSTM1 and histone-modifying enzymes in HIV-infected astrocytes

Accelerated neurological disorders are increasingly prominent among the HIV-infected population and are likely driven by the toxicity from long-term use of antiretroviral drugs. We explored potential side effects of antiretroviral drugs in HIV-infected primary human astrocytes and whether opioid co-exposure exacerbates the response. HIV-infected human astrocytes were exposed to the reverse transcriptase inhibitor, emtricitabine, alone or in combination with two protease inhibitors ritonavir and atazanavir (ERA) with and without morphine co-exposure. The effect of the protease inhibitor, lopinavir, alone or in combination with the protease inhibitor, abacavir, and the integrase inhibitor, raltegravir (LAR), with and without morphine co-exposure was also explored. Exposure with emtricitabine alone or ERA in HIV-infected astrocytes caused a significant decrease in viral replication and attenuated HIV-induced inflammatory molecules, while co-exposure with morphine negated the inhibitory effects of ERA, leading to increased viral replication and inflammatory molecules. Exposure with emtricitabine alone or in combination with morphine caused a significant disruption of mitochondrial membrane integrity. Genetic analysis revealed a significant increase in the expression of p62/SQSTM1 which correlated with an increase in the histone-modifying enzyme, ESCO2, after exposure with ERA alone or in combination with morphine. Furthermore, several histone-modifying enzymes such as CIITA, PRMT8, and HDAC10 were also increased with LAR exposure alone or in combination with morphine. Accumulation of p62/SQSTM1 is indicative of dysfunctional lysosomal fusion. Together with the loss of mitochondrial integrity and epigenetic changes, these effects may lead to enhanced viral titer and inflammatory molecules contributing to the neuropathology associated with HIV.

Reduced intraepidermal nerve fibre density, glial activation, and sensory changes in HIV type-1 Tat-expressing female mice: involvement of Tat during early stages of HIV-associated painful sensory neuropathy

INTRODUCTION

HIV infection is associated with chronic pain states, including sensory neuropathy, which affects greater than 40% of patients.

OBJECTIVES AND METHODS

To determine the impact of HIV-Tat induction on nociceptive behaviour in female mice conditionally expressing HIV Tat1-86 protein through a doxycycline (DOX)-driven glial fibrillary acidic protein promoter, intraepidermal nerve fibre density and immune cell activation in the dorsal root ganglion (DRG) and spinal cord were assessed by immunohistochemistry. Mice were assessed for mechanical and thermal sensitivity for 9 weeks using von-Frey and Hargreaves tests.

RESULTS

Intraepidermal nerve fibre density was significantly reduced after 6 weeks of Tat induction, similar to sensory neuropathy seen in clinical HIV infection. Tat induction through DOX caused a significant reduction in paw withdrawal thresholds in a time-dependent manner starting the 4th week after Tat induction. No changes in paw withdrawal latencies were seen in Tat(-) control mice lacking the tat transgene. Although reductions in paw withdrawal thresholds increased throughout the study, no significant change in spontaneous motor activity was observed. Spinal cord (cervical and lumbar), DRG, and hind paw skin were collected at 8 days and 6 weeks after Tat induction. HIV-Tat mRNA expression was significantly increased in lumbar DRG and skin samples 8 days after DOX treatment. Tat induced a significant increase in the number of Iba-1 positive cells at 6 weeks, but not after 8 days, of exposure. No differences in glial fibrillary acidic protein immunoreactivity were observed.

CONCLUSION

These results suggest that Tat protein contributes to painful HIV-related sensory neuropathy during the initial stages of the pathogenesis.

Opioids Resistance in Chronic Pain Management

Chronic pain management represents a serious healthcare problem worldwide. Chronic pain affects approximately 20% of the adult European population and is more frequent in women and older people. Unfortunately, its management in the community remains generally unsatisfactory and rarely under the control of currently available analgesics. Opioids have been used as analgesics for a long history and are among the most used drugs; however, while there is no debate over their short term use for pain management, limited evidence supports their efficacy of long-term treatment for chronic non-cancer pain. Therapy with opioids is hampered by inter-individual variability and serious side effects and some opioids often result ineffective in the treatment of chronic pain and their use is controversial. Accordingly, for a better control of chronic pain a deeper knowledge of the molecular mechanisms underlying resistance to opiates is mandatory.

NFATc2 Modulates Microglial Activation in the AβPP/PS1 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) brains are characterized by fibrillar amyloid-β (Aβ) peptide containing plaques and associated reactive microglia. The proinflammatory phenotype of the microglia suggests that they may negatively affect disease course and contribute to behavioral decline. This hypothesis predicts that attenuating microglial activation may provide benefit against disease. Prior work from our laboratory and others has characterized a role for the transcription factor, nuclear factor of activated T cells (NFAT), in regulating microglial phenotype in response to different stimuli, including Aβ peptide. We observed that the NFATc2 isoform was the most highly expressed in murine microglia cultures, and inhibition or deletion of NFATc2 was sufficient to attenuate the ability of the microglia to secrete cytokines. In order to determine whether the NFATc2 isoform, in particular, was a valid immunomodulatory target in vivo, we crossed an NFATc2-/- line to a well-known AD mouse model, an AβPP/PS1 mouse line. As expected, the AβPP/PS1 x NFATc2-/- mice had attenuated cytokine levels compared to AβPP/PS1 mice as well as reduced microgliosis and astrogliosis with no effect on plaque load. Although some species differences in relative isoform expression may exist between murine and human microglia, it appears that microglial NFAT activity is a viable target for modulating the proinflammatory changes that occur during AD.

Opiate Drugs with Abuse Liability Hijack the Endogenous Opioid System to Disrupt Neuronal and Glial Maturation in the Central Nervous System

The endogenous opioid system, comprised of multiple opioid neuropeptide and receptor gene families, is highly expressed by developing neural cells and can significantly influence neuronal and glial maturation. In many central nervous system (CNS) regions, the expression of opioid peptides and receptors occurs only transiently during development, effectively disappearing with subsequent maturation only to reemerge under pathologic conditions, such as with inflammation or injury. Opiate drugs with abuse liability act to modify growth and development by mimicking the actions of endogenous opioids. Although typically mediated by μ-opioid receptors, opiate drugs can also act through δ- and κ-opioid receptors to modulate growth in a cell-type, region-specific, and developmentally regulated manner. Opioids act as biological response modifiers and their actions are highly contextual, plastic, modifiable, and influenced by other physiological processes or pathophysiological conditions, such as neuro-acquired immunodeficiency syndrome. To date, most studies have considered the acute effects of opiates on cellular maturation. For example, activating opioid receptors typically results in acute growth inhibition in both neurons and glia. However, with sustained opioid exposure, compensatory factors become operative, a concept that has been largely overlooked during CNS maturation. Accordingly, this article surveys prior studies on the effects of opiates on CNS maturation, and also suggests new directions for future research in this area. Identifying the cellular and molecular mechanisms underlying the adaptive responses to chronic opiate exposure (e.g., tolerance) during maturation is crucial toward understanding the consequences of perinatal opiate exposure on the CNS.

β-Adrenergic receptor gene expression in HIV-associated neurocognitive impairment and encephalitis: implications for MOR-1K subcellular localization

We previously reported that mRNA expression of the unique alternatively spliced OPRM1 isoform μ-opioid receptor-1K (MOR-1K), which exhibits excitatory cellular signaling, is elevated in HIV-infected individuals with combined neurocognitive impairment (NCI) and HIV encephalitis (HIVE). It has recently been shown that the β2-adrenergic receptor (β2-AR) chaperones MOR-1K, normally localized intracellularly, to the cell surface. Here, we found mRNA expression of the adrenoceptor beta 2 (ADRB2) gene is also elevated in NCI-HIVE individuals, as well as that β2-AR protein expression is elevated in HIV-1-infected primary human astrocytes treated with morphine, and discuss the implications for MOR-1K subcellular localization in this condition.

Oxidative Stress during HIV Infection: Mechanisms and Consequences

It is generally acknowledged that reactive oxygen species (ROS) play crucial roles in a variety of natural processes in cells. If increased to levels which cannot be neutralized by the defense mechanisms, they damage biological molecules, alter their functions, and also act as signaling molecules thus generating a spectrum of pathologies. In this review, we summarize current data on oxidative stress markers associated with human immunodeficiency virus type-1 (HIV-1) infection, analyze mechanisms by which this virus triggers massive ROS production, and describe the status of various defense mechanisms of the infected host cell. In addition, we have scrutinized scarce data on the effect of ROS on HIV-1 replication. Finally, we present current state of knowledge on the redox alterations as crucial factors of HIV-1 pathogenicity, such as neurotoxicity and dementia, exhaustion of CD4+/CD8+ T-cells, predisposition to lung infections, and certain side effects of the antiretroviral therapy, and compare them to the pathologies associated with the nitrosative stress.

Regulation and Functional Implications of Opioid Receptor Splicing in Opioid Pharmacology and HIV Pathogenesis

Despite the identification and characterization of four opioid receptor subtypes and the genes from which they are encoded, pharmacological data does not conform to the predications of a four opioid receptor model. Instead, current studies of opioid pharmacology suggest the existence of additional receptor subtypes; however, no additional opioid receptor subtype has been identified to date. It is now understood that this discrepancy is due to the generation of multiple isoforms of opioid receptor subtypes. While several mechanisms are utilized to generate these isoforms, the primary mechanism involves alternative splicing of the pre-mRNA transcript. Extensive alternative splicing patterns for opioid receptors have since been identified and discrepancies in opioid pharmacology are now partially attributed to variable expression of these isoforms. Recent studies have been successful in characterizing the localization of these isoforms as well as their specificity in ligand binding; however, the regulation of opioid receptor splicing specificity is poorly characterized. Furthermore, the functional significance of individual receptor isoforms and the extent to which opioid- and/or HIV-mediated changes in the opioid receptor isoform profile contributes to altered opioid pharmacology or the well-known physiological role of opioids in the exacerbation of HIV neurocognitive dysfunction is unknown. As such, the current review details constitutive splicing mechanisms as well as the specific architecture of opioid receptor genes, transcripts, and receptors in order to highlight the current understanding of opioid receptor isoforms, potential mechanisms of their regulation and signaling, and their functional significance in both opioid pharmacology and HIV-associated neuropathology.

Bivalent ligands targeting chemokine receptor dimerization: molecular design and functional studies

Increasing evidence has shown that chemokine receptors may form functional dimers with unique pharmacological profiles. A common practice to characterize such G protein-coupled receptor dimerization processes is to apply bivalent ligands as chemical probes which can interact with both receptors simultaneously. Currently, two chemokine receptor dimers have been studied by applying bivalent compounds: the CXCR4-CXCR4 homodimer and the CCR5-MOR heterodimer. These bivalent compounds have revealed how dimerization influences receptor function and may lead to novel therapeutics. Future design of bivalent ligands for chemokine receptor dimers may be aided with the recently available CXCR4 homodimer, and CCR5 monomer crystal structures by more accurately simulating chemokine receptors and their dimers.

The Immune Syntax Revisited: Opening New Windows on Language Evolution

Recent research has added new dimensions to our understanding of classical evolution, according to which evolutionary novelties result from gene mutations inherited from parents to offspring. Language is surely one such novelty. Together with specific changes in our genome and epigenome, we suggest that two other (related) mechanisms may have contributed to the brain rewiring underlying human cognitive evolution and, specifically, the changes in brain connectivity that prompted the emergence of our species-specific linguistic abilities: the horizontal transfer of genetic material by viral and non-viral vectors and the brain/immune system crosstalk (more generally, the dialogue between the microbiota, the immune system, and the brain).

Chronic HIV-1 Tat and HIV reduce Rbfox3/NeuN: evidence for sex-related effects

The NeuN antibody has been widely used to identify and quantify neurons in normal and disease situations based on binding to a nuclear epitope in most types of neurons. This epitope was recently identified as the RNA-binding, feminizing locus on X-3 (Rbfox3), a member of the larger, mammalian Fox1 family of RNA binding proteins. Fox1 proteins recognize a unique UGCAUG mRNA motif and regulate alternative splicing of precursor mRNA to control post-transcriptional events important in neuronal differentiation and central nervous system development. Recent clinical findings show that Rbfox3/NeuN gene dosage is altered in certain human neurodevelopmental disorders, and redistribution has been noted in HIV(+) tissue. We hypothesized that HIV-1 Tat might affect Rbfox3/NeuN expression, and examined this question in vivo using inducible transgenic mice, and in vitro using human mesencephalic-derived neurons. Rbfox3/NeuN expression and localization in HIV+ basal ganglia and hippocampus was also examined. Chronic Tat exposure reduced Rbfox3/NeuN protein levels and increased cytoplasmic localization, similar to the effect of HIV exposure. Cytoplasmic Rbfox3/NeuN signal has occasionally been reported, although the meaning or function of cytoplasmic versus nuclear localization remains speculative. Importantly, Rbfox3/NeuN reductions were more significant in male mice. Although Rbfox3/NeuN-expressing cells were significantly decreased by Tat exposure, stereology showed that Nissl(+) neuron numbers remained normal. Thus, loss of Rbfox3/NeuN may relate more to functional change than to neuron loss. The effects of Tat by itself are highly relevant to HIV(+) individuals maintained on antiretroviral therapy, since Tat is released from infected cells even when viral replication is inhibited.

Splice variation of the mu-opioid receptor and its effect on the action of opioids

An individual's response to opioids is influenced by a complex combination of genetic, molecular and phenotypic factors.Intra- and inter-individual variations in response to mu opioids have led to the suggestion that mu-opioid receptor subtypes exist.Scientists have now proven that mu-opioid receptor subtypes exist and that they occur through a mechanism promoting protein diversity, called alternative splicing.The ability of mu opioids to differentially activate splice variants may explain some of the clinical differences observed between mu opioids.This article examines how differential activation of splice variants by mu opioids occurs through alternative mu-opioid receptor binding, through differential receptor activation, and as a result of the distinct distribution of variants located regionally and at the cellular level.

Differing roles of autophagy in HIV-associated neurocognitive impairment and encephalitis with implications for morphine co-exposure

We investigated the role of autophagy in HIV-infected subjects with neurocognitive impairment (NCI) ± HIV encephalitis (HIVE), many of which had a history of polysubstance abuse/dependence, using post-mortem brain tissues to determine whether differences in autophagy related factors may be more associated with NCI or NCI-encephalitis. Using qRT-PCR, we detected significant differences in gene expression levels with SQSTM1, LAMP1 higher in HIV-infected subjects without NCI while ATG5, SQSTM1 were then lower in HIV infection/NCI and ATG7, SQSTM1 being higher in NCI-HIVE. Immunohistochemical labeling of these autophagy associated proteins (also including Beclin 1 and LC3B) in Iba1-positive microglial cells showed generally higher immunoreactivity in the NCI and NCI-HIVE groups with more focal vs. diffuse patterns of expression in the NCI-HIVE group. Furthermore, analysis of microarray data from these same subjects found significantly higher levels of LAMP1 in NCI-HIVE compared to uninfected subjects in the basal ganglia. Finally, we tested the effect of supernatant from HIV-1-infected microglia and HIV-1 Tat protein in combination with morphine on neurons in vitro and found opposing events with both significant inhibition of autophagic flux and reduced dendrite length for morphine and supernatant treatment while Tat and morphine exposure resulted in lower autophagic activity at an earlier time point and higher levels in the later. These results suggest autophagy genes and their corresponding proteins may be differentially regulated at the transcriptional, translational, and post-translational levels in the brain during various stages of the HIV disease and that infected individuals exposed to morphine can experience mixed signaling of autophagic activity which could lead to more severe NCI than those without opioid use.

Attenuation of microglial activation in a mouse model of Alzheimer's disease via NFAT inhibition

Background

Amyloid β (Aβ) peptide is hypothesized to stimulate microglia to acquire their characteristic proinflammatory phenotype in Alzheimer’s disease (AD) brains. The specific mechanisms by which Aβ leads to microglial activation remain an area of interest for identifying attractive molecular targets for intervention. Based upon the fact that microglia express the proinflammatory transcription factor, nuclear factor of activated T cells (NFAT), we hypothesized that NFAT activity is required for the Aβ-stimulated microgliosis that occurs during disease.

Methods

Primary murine microglia cultures were stimulated with Aβ in the absence or presence of NFAT inhibitors, FK506 and tat-VIVIT peptide, to quantify secretion of cytokines, neurotoxins, or Aβ phagocytosis. A transgenic mouse model of AD, APP/PS1, was treated subcutaneously via mini-osmotic pumps with FK506 or tat-VIVIT to quantify effects on cytokines, microgliosis, plaque load, and memory.

Results

Expression of various NFAT isoforms was verified in primary murine microglia through Western blot analysis. Microglial cultures were stimulated with Aβ fibrils in the absence or presence of the NFAT inhibitors, FK506 and tat-VIVIT, to demonstrate that NFAT activity regulated Aβ phagocytosis, neurotoxin secretion, and cytokine secretion. Delivery of FK506 and tat-VIVIT to transgenic APP/PS1 mice attenuated spleen but not brain cytokine levels. However, FK506 and tat-VIVIT significantly attenuated both microgliosis and Aβ plaque load in treated mice compared to controls. Surprisingly, this did not correlate with changes in memory performance via T-maze testing.

Conclusions

Our findings suggest that development of specific NFAT inhibitors may offer promise as an effective strategy for attenuating the microgliosis and Aβ plaque deposition that occur in AD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0255-2) contains supplementary material, which is available to authorized users.

Direct bidirectional μ-opioid control of midbrain dopamine neurons

The ventral tegmental area (VTA) is required for the rewarding and motivational actions of opioids and activation of dopamine neurons has been implicated in these effects. The canonical model posits that opioid activation of VTA dopamine neurons is indirect, through inhibition of GABAergic inputs. However, VTA dopamine neurons also express postsynaptic μ-opioid peptide (MOP) receptors. We report here that in Sprague Dawley rat, the MOP receptor-selective agonist DAMGO (0.5-3 μM) depolarized or increased the firing rate of 87 of 451 VTA neurons (including 22 of 110 dopamine neurons). This DAMGO excitation occurs in the presence of GABAA receptor blockade and its EC50 value is two orders of magnitude lower than for presynaptic inhibition of GABA release on to VTA neurons. Consistent with a postsynaptic channel opening, excitations were accompanied by a decrease in input resistance. Excitations were blocked by CdCl2 (100 μM, n = 5) and ω-agatoxin-IVA (100 nM, n = 3), nonselective and Cav2.1 Ca(2+) channel blockers, respectively. DAMGO also produced a postsynaptic inhibition in 233 of 451 VTA neurons, including 45 of 110 dopamine neurons. The mean reversal potential of the inhibitory current was -78 ± 7 mV and inhibitions were blocked by the K(+) channel blocker BaCl2 (100 μM, n = 7). Blockade of either excitation or inhibition unmasked the opposite effect, suggesting that MOP receptors activate concurrent postsynaptic excitatory and inhibitory processes in most VTA neurons. These results provide a novel direct mechanism for MOP receptor control of VTA dopamine neurons.

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.

Differential expression of the alternatively spliced OPRM1 isoform μ-opioid receptor-1K in HIV-infected individuals

OBJECTIVE

We previously examined the expression of specific C-terminal μ-opioid receptor (MOR) splice variants in human central nervous system cell types and HIV-infected brain tissue from individuals with neurocognitive impairment ± HIV encephalitis (HIVE). In the present study, we examined the N-terminal splice variant MOR-1K, which mediates excitatory cellular signaling.

METHODS AND RESULTS

We found segregation of expression ranging from undetectable to seemingly exclusive across nervous system cell types compared to the pool of C-terminal MOR splice variants using the real-time polymerase chain reaction (RT-PCR). Expression of MOR-1K mRNA was also increased in HIV-infected individuals with combined neurocognitive impairment and HIVE compared with the other groups. MOR-1K expression correlated with the level of patient neurocognitive impairment, whereas the pool of C-terminal MOR splice variants did not. HIVE was also associated with increased expression of the inflammatory mediators MCP-1, MCP-2, and RANTES, but not the host HIV coreceptors CXCR4 and CCR5 or the CD4 receptor using qRT-PCR. Network analysis of microarray data from these same patients revealed filamin A (FLNA) as a possible interaction partner with MOR-1K, and FLNA gene expression was also found to be upregulated in HIVE using qRT-PCR. Overexpression of FLNA in HEK293 cells redistributed MOR-1K from intracellular compartments to the cell surface.

CONCLUSION

These results suggest that HIVE, and neurocognitive impairment depending on its severity, are associated with enhanced MOR-1K signaling through both increased expression and trafficking to the cell surface, which may alter the contribution of MOR receptor isoforms and exacerbate the effects of MOR activation in neuroAIDS.

Interactions of HIV and drugs of abuse: the importance of glia, neural progenitors, and host genetic factors

Considerable insight has been gained into the comorbid, interactive effects of HIV and drug abuse in the brain using experimental models. This review, which considers opiates, methamphetamine, and cocaine, emphasizes the importance of host genetics and glial plasticity in driving the pathogenic neuron remodeling underlying neuro-acquired immunodeficiency syndrome and drug abuse comorbidity. Clinical findings are less concordant than experimental work, and the response of individuals to HIV and to drug abuse can vary tremendously. Host-genetic variability is important in determining viral tropism, neuropathogenesis, drug responses, and addictive behavior. However, genetic differences alone cannot account for individual variability in the brain "connectome." Environment and experience are critical determinants in the evolution of synaptic circuitry throughout life. Neurons and glia both exercise control over determinants of synaptic plasticity that are disrupted by HIV and drug abuse. Perivascular macrophages, microglia, and to a lesser extent astroglia can harbor the infection. Uninfected bystanders, especially astroglia, propagate and amplify inflammatory signals. Drug abuse by itself derails neuronal and glial function, and the outcome of chronic exposure is maladaptive plasticity. The negative consequences of coexposure to HIV and drug abuse are determined by numerous factors including genetics, sex, age, and multidrug exposure. Glia and some neurons are generated throughout life, and their progenitors appear to be targets of HIV and opiates/psychostimulants. The chronic nature of HIV and drug abuse appears to result in sustained alterations in the maturation and fate of neural progenitors, which may affect the balance of glial populations within multiple brain regions.

A novel bivalent HIV-1 entry inhibitor reveals fundamental differences in CCR5-μ-opioid receptor interactions between human astroglia and microglia

OBJECTIVE

We explored whether the opiate, morphine, affects the actions of maraviroc, as well as a recently synthesized bivalent derivative of maraviroc linked to an opioid antagonist, naltrexone, on HIV-1 entry in primary human glia.

METHODS

HIV-1 entry was monitored in glia transiently transfected with an LTR construct containing a luciferase reporter gene under control of a promoter for the HIV-1 transactivator protein Tat. The effect of maraviroc and the bivalent ligand with or without morphine on CCR5 surface expression and cytokine release was also explored.

RESULTS

Maraviroc inhibits HIV-1 entry into glial cells, whereas morphine negates the effects of maraviroc leading to a significant increase in viral entry. We also demonstrate that the maraviroc-containing bivalent ligand better inhibits R5-tropic viral entry in astrocytes than microglia compared to maraviroc when coadministered with morphine. Importantly, the inhibitory effects of the bivalent compound in astrocytes were not compromised by morphine. Exposure to maraviroc decreased the release of pro-inflammatory cytokines and restricted HIV-1-dependent increases in CCR5 expression in both astrocytes and microglia, whereas exposure to the bivalent had a similar effect in astrocytes but not in microglia. The CCR5-μ-opioid receptor (MOR) stoichiometric ratio varied among the two cell types with CCR5 expressed at much higher levels than MOR in microglia, which could explain the effectiveness of the bivalent ligand in astrocytes compared to microglia.

CONCLUSION

A novel bivalent compound reveals fundamental differences in CCR5-MOR interactions and HIV-1 infectivity among glia, and has unique therapeutic potential in opiate abuse-HIV interactive comorbidity.

Validation of housekeeping genes as internal controls for studying gene expression during Pacific oyster (Crassostrea gigas) development by quantitative real-time PCR

Hatchery-reared larvae of the Pacific oyster (Crassostrea gigas) often suffer from massive mortality induced by Ostreid herpesvirus 1 (OsHV-1) infection, indicating the importance of better understanding of oyster immune defense systems. The accuracy of measurements of gene expression levels based on quantitative real-time PCR assays relies on the use of housekeeping genes as internal controls; however, few studies have focused on the selection of such internal controls. In this study, we conducted a comprehensive investigation of internal control genes during oyster development in virus-infected and uninfected samples. Transcriptome data for 38 developmental stages were downloaded and the gene expression patterns were classified into 30 clusters. A total of 317 orthologs of classical housekeeping genes in the oyster genome were annotated. After combining the expression profiles and oyster housekeeping gene dataset, 14 candidate internal controls were selected for further investigation: Elongation factor-1α (EF-1α), 18S rRNA (18S), 28S rRNA (28S), Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), β-actin (ACT), Ribosomal protein L7 (RL7), Ribosomal protein L27 (RL27), Ribosomal protein L36 (RL36), Ribosomal protein S18 (RS18), Heterogeneous nuclear ribonucleoprotein A2/B1 (RO21), Eukaryotic translation elongation factor 2 (EF2), Ubiquitin-conjugating enzyme E2D2 (UBCD1), S-phase kinase-associated protein 1 (SKP1) and Heterogeneous nuclear ribonucleoprotein Q (HNRPQ). RNA was extracted from oyster larvae infected with OsHV-1 (group A; GA), and OsHV-1 free larvae (group B; GB). The expression levels of the 14 candidate internal controls were studied in GA and GB larvae by real-time PCR. Their expression stabilities were further analyzed using the GeNorm program. RL7 and RS18 were the most stable genes in both OsHV-1 infected (GA) and uninfected (GB) larvae. These results suggest that RL7 and RS18 could be used as internal controls for studying gene expression in normal growing oyster larvae and in OsHV-1 infected larvae. These high quality internal controls will be a valuable resource in future studies of oyster larval mortality.

Molecular clone and functional study of a novel hepatoma associated gene

HTA is a novel hepatoma associated gene screened by bioinformatic strategies in our previous study. In the present investigation, the full-length sequence of the HTA gene was cloned by 3'-rapid amplification of cDNA ends (RACE) and 5'-RACE, which was 1414 bp and the open reading frame (ORF) was constituted with 3 exons and 2 introns. There are two types of splicing of the mRNA of HTA. Northern blot analysis showed that the 1.4 kb HTA mRNA and 1.7 kb HTA mRNA transcripts were present in the hepatocellular carcinoma (HCC) cell lines HepG2 and QGY-7703 but not in the normal cell line L02 and the human umbilical vein endothelial cells (HUVECs). Overexpression of the HTA gene in the hepatic cell line QSG-7701 via stable transfection can promote its proliferation rate and colony forming ability and change the cell cycle distribution of the cell lines. These results showed that the HTA gene is a potential therapeutic target in HCC and the clarification of its gene structure and sequence information provide an essential tool for future research.

HIV-1 alters neural and glial progenitor cell dynamics in the central nervous system: coordinated response to opiates during maturation

HIV-associated neurocognitive disorders (HANDs) are common sequelae of human immunodeficiency virus (HIV) infection, even when viral titers are well controlled by antiretroviral therapy. Evidence in patients and animal models suggests that neurologic deficits are increased during chronic opiate exposure. We have hypothesized that central nervous system (CNS) progenitor cells in both adult and developing CNS are affected by HIV infection and that opiates exacerbate these effects. To examine this question, neural progenitors were exposed to HIV-1 Tat(1-86) in the developing brain of inducible transgenic mice and in vitro. We examined whether Tat affected the proliferation or balance of progenitor populations expressing nestin, Sox2, and Olig2. Disease relevance was further tested by exposing human-derived progenitors to supernatant from HIV-1 infected monocytes. Studies concentrated on striatum, a region preferentially targeted by HIV and opiates. Results were similar among experimental paradigms. Tat or HIV exposure reduced the proliferation of undifferentiated (Sox2(+)) progenitors and oligodendroglial (Olig2(+)) progenitors. Coexposure to morphine exacerbated the effects of Tat or HIV-1(SF162) supernatant, but partially reversed HIV-1(IIIB) supernatant effects. Populations of Sox2(+) and Olig2(+) cells were also reduced by Tat exposure, although progenitor survival was unaffected. In rare instances, p24 immunolabeling was detected in viable human progenitors by confocal imaging. The vulnerability of progenitors is likely to distort the dynamic balance among neuron/glial populations as the brain matures, perhaps contributing to reports that neurologic disease is especially prevalent in pediatric HIV patients. Pediatric disease is atypical in developed regions but remains a serious concern in resource-limited areas where infection occurs commonly at birth and through breast feeding.

Morphine efficacy is altered in conditional HIV-1 Tat transgenic mice

Opiate abuse reportedly can exaggerate complications of human immunodeficiency virus type-1 (HIV-1) infection in the central nervous system (CNS), while opiate drugs are often indicated in the treatment of HIV-1-related neuropathic pain. Despite this quandary, few studies have assessed the relationship between the duration or extent of HIV-1 infection and the intrinsic neurobehavioral responsiveness to opioids. To address this problem, doxycycline (DOX)-inducible HIV-Tat(1-86) transgenic mice were used as a model for HIV-1-associated neurocognitive disorders, which permitted the regulation of Tat exposure and duration. The effects of continuous Tat induction on the activity of morphine were examined at weekly intervals using standard behavioral assays for nociception and motor function. In the spinal cord, Tat mRNA levels did not increase until the second and third weeks following induction, which corresponded to a significant loss of morphine antinociception as assessed in the tail-flick test. Alternatively, in the striatum, sustained increases in Tat mRNA expression during the second week of induction coincided with significant decreases in rotarod performance and interactions with morphine. Importantly, the behavioral effects of morphine differed depending on the timing and location of Tat expression, with increases in Tat transcript levels in the spinal cord and striatum corresponding to significant alterations in morphine-dependent nociception and rotarod performance, respectively. Assuming Tat levels contribute to the clinical manifestations of HIV-1, the results suggest that regional differences in viral load and opioid phenotype might influence the nature and degree that opiate responsiveness is altered in HIV-1-infected individuals.