Opiate agonist-induced re-distribution of Wntless, a mu-opioid receptor interacting protein, in rat striatal neurons

Hair Growth Promotion by δ-Opioid Receptor Activation

Literature has revealed that the delta opioid receptor (DOR) exhibited diverse pharmacological effects on neuron and skin. In the present study, we have investigated whether the activation of DOR has hair-growth promotion effects. Compared with other opioid receptor, DOR was highly expressed in epidermal component of hair follicle in human and rodents. The expression of DOR was high in the anagen phase, but it was low in the catagen and telogen phases during mouse hair cycle. Topical application of UFP-512, a specific DOR agonist, significantly accelerated the induction of the anagen in C₃H mice. Topical application of UFP-512 also increased the hair length in hair organ cultures and promoted the proliferation and the migration of outer root sheath (ORS) cells. Similarly, pharmacological inhibition of DOR by naltrindole significantly inhibited the anagen transition process and decreased hair length in hair organ cultures. Thus, we further examined whether Wnt/β-catenin pathway was related to the effects of DOR on hair growth. We found that Wnt/β-catenin pathway was activated by UFP-512 and siRNA for β-catenin attenuated the UFP-512 induced proliferation and migration of ORS cells. Collectively, result established that DOR was involved in hair cycle regulation, and that DOR agonists such as UFP-512 should be developed for novel hair-loss treatment.

Wnt signaling contributes to withdrawal symptoms from opioid receptor activation induced by morphine exposure or chronic inflammation

Preventing and treating opioid dependence and withdrawal is a major clinical challenge, and the underlying mechanisms of opioid dependence and withdrawal remain elusive. We hypothesized that prolonged morphine exposure or chronic inflammation-induced μ-opioid receptor activity serves as a severe stress that elicits neuronal alterations and recapitulates events during development. Here, we report that Wnt signaling, which is important in developmental processes of the nervous system, plays a critical role in withdrawal symptoms from opioid receptor activation in mice. Repeated exposures of morphine or peripheral inflammation produced by intraplantar injection of complete Freund's adjuvant significantly increase the expression of Wnt5b in the primary sensory neurons in dorsal root ganglion (DRG). Accumulated Wnt5b in DRG neurons quickly transmits to the spinal cord dorsal horn (DH) after naloxone treatment. In the DH, Wnt5b, acts through the atypical Wnt-Ryk receptor and alternative Wnt-YAP/TAZ signaling pathways, contributing to the naloxone-precipitated opioid withdrawal-like behavioral symptoms and hyperalgesia. Inhibition of Wnt synthesis and blockage of Wnt signaling pathways greatly suppress the behavioral and neurochemical alterations after naloxone-precipitated withdrawal. These findings reveal a critical mechanism underlying naloxone-precipitated opioid withdrawal, suggesting that targeting Wnt5b synthesis in DRG neurons and Wnt signaling in DH may be an effective approach for prevention and treatment of opioid withdrawal syndromes, as well as the transition from acute to chronic pain.

Alternative splicing of the Wnt trafficking protein, Wntless and its effects on protein-protein interactions

Background

Wntless (Wls) is a protein that regulates secretion of Wnt signaling molecules from Wnt-producing cells. Wnt signaling is known to be critical for several developmental and homeostatic processes. However, Wnt-independent functions of Wls are now being elucidated. Primates express an alternative splice variant of Wls (here termed WlsX). WlsX contains an alternatively spliced COOH-terminus, and does not appear to be able to sustain significant levels of WNT secretion because of its inability to undergo retrograde trafficking to the endoplasmic reticulum. The functional significance for this alternatively spliced form of Wls has not yet been elucidated. We previously identified a cohort of Wls interacting proteins using a combination of yeast 2-hybrid and candidate gene approaches.

Results

In the present study, we analyzed the interaction of WlsX with previously identified Wls interactors, and additionally screened for novel protein interactors of WlsX utilizing a membrane yeast two hybrid screen. Three novel Wls interactors, Glycoprotein M6A (GPM6A), Alkylglycerol Monooxygenase (AGMO), and ORAI1 were identified. Each of these novel WlsX interactors, as well as all other Wls interacting proteins identified previously, with the exception of the mu-opioid receptor, were found to interact with both Wls and WlsX splice forms. We show that WlsX can form homodimers, but that WlsX may not interact with Wls.

Conclusions

WlsX has the ability to form homodimers and to interact with most known Wls interacting proteins. Taken together, our results suggest that Wls and WlsX may have overlapping, but distinct functions, including sensitivity to opioid drugs. While studies have focused on the ability of Wls interacting proteins to affect Wnt secretion, future efforts will explore the reciprocal regulation of these proteins by Wls, possibly via Wnt-independent mechanisms.

Loss of Sfrp2 contributes to the neurological disorders related with morphine withdrawal via Wnt/β-catenin signaling

Morphine administration is a medical problem characterized by compulsive opioid use that causes terrible negative consequences. The exact mechanisms of morphine-induced dependence and morphine withdrawal symptoms remain unclear. Recent studies have revealed that the upregulation of Wnt/β-catenin signaling plays important roles in morphine exposure and morphine withdrawal. Secreted frizzled-related protein 2 (Sfrp2) can prevent the activation of Wnt/β-catenin signaling by competing with the Frizzled receptor for Wnt ligands. We conducted this study aimed to evaluate the effect of iatrogenic trauma induced by stereotactic surgery and the protective effect of stereotaxic Sfrp2 injection on morphine withdrawal symptoms in Male Sprague Dawley (SD) rats. Many techniques including western blot analysis and immunoprecipitation were used. Anxiety-related behaviors, morphine withdrawal syndrome, and dendritic spines were also examined in male SD rats after morphine treatment and stereotaxic injection of Sfrp2. Western blot results suggested that Wnt signaling was activated in the nucleus accumbens of SD rats suffering from morphine withdrawal and that Sfrp2 attenuated the overexpression of Wnt signaling. Similarly, the withdrawal-like symptoms of morphine dependent rats were abrogated by intracerebral Sfrp2 injection. The iatrogenic trauma induced by stereotactic surgery showed no influence on the Wnt signaling and withdrawal-like symptoms. Moreover, the results of Golgi-cox staining and DiI staining indicated that the damage on proximal spine density caused by morphine treatment was restored by intracerebral Sfrp2 injection. Together, the data presented here indicated that Sfrp2 abrogated the neurological disorders and loss of proximal spine related with morphine withdrawal via Wnt/β-catenin signaling.

Suppression of RGSz1 function optimizes the actions of opioid analgesics by mechanisms that involve the Wnt/β-catenin pathway

Regulator of G protein signaling z1 (RGSz1), a member of the RGS family of proteins, is present in several networks expressing mu opioid receptors (MOPRs). By using genetic mouse models for global or brain region-targeted manipulations of RGSz1 expression, we demonstrated that the suppression of RGSz1 function increases the analgesic efficacy of MOPR agonists in male and female mice and delays the development of morphine tolerance while decreasing the sensitivity to rewarding and locomotor activating effects. Using biochemical assays and next-generation RNA sequencing, we identified a key role of RGSz1 in the periaqueductal gray (PAG) in morphine tolerance. Chronic morphine administration promotes RGSz1 activity in the PAG, which in turn modulates transcription mediated by the Wnt/β-catenin signaling pathway to promote analgesic tolerance to morphine. Conversely, the suppression of RGSz1 function stabilizes Axin2-Gαz complexes near the membrane and promotes β-catenin activation, thereby delaying the development of analgesic tolerance. These data show that the regulation of RGS complexes, particularly those involving RGSz1-Gαz, represents a promising target for optimizing the analgesic actions of opioids without increasing the risk of dependence or addiction.

Identifying novel members of the Wntless interactome through genetic and candidate gene approaches

Wnt signaling is an important pathway that regulates several aspects of embryogenesis, stem cell maintenance, and neural connectivity. We have recently determined that opioids decrease Wnt secretion, presumably by inhibiting the recycling of the Wnt trafficking protein Wntless (Wls). This effect appears to be mediated by protein-protein interaction between Wls and the mu-opioid receptor (MOR), the primary cellular target of opioid drugs. The goal of this study was to identify novel protein interactors of Wls that are expressed in the brain and may also play a role in reward or addiction. Using genetic and candidate gene approaches, we show that among a variety of protein, Wls interacts with the dopamine transporter (target of cocaine), cannabinoid receptors (target of THC), Adenosine A2A receptor (target of caffeine), and SGIP1 (endocytic regulator of cannabinoid receptors). Our study shows that aside from opioid receptors, Wntless interacts with additional proteins involved in reward and/or addiction. Future studies will determine whether Wntless and WNT signaling play a more universal role in these processes.

Localization of the delta opioid receptor and corticotropin-releasing factor in the amygdalar complex: role in anxiety

It is well established that central nervous system norepinephrine (NE) and corticotropin-releasing factor (CRF) systems are important mediators of behavioral responses to stressors. More recent studies have defined a role for delta opioid receptors (DOPR) in maintaining emotional valence including anxiety. The amygdala plays an important role in processing emotional stimuli, and has been implicated in the development of anxiety disorders. Activation of DOPR or inhibition of CRF in the amygdala reduces baseline and stress-induced anxiety-like responses. It is not known whether CRF- and DOPR-containing amygdalar neurons interact or whether they are regulated by NE afferents. Therefore, this study sought to better define interactions between the CRF, DOPR and NE systems in the basolateral (BLA) and central nucleus of the amygdala (CeA) of the male rat using anatomical and functional approaches. Irrespective of the amygdalar subregion, dual immunofluorescence microscopy showed that DOPR was present in CRF-containing neurons. Immunoelectron microscopy confirmed that DOPR was localized to both dendritic processes and axon terminals in the BLA and CeA. Semi-quantitative dual immunoelectron microscopy analysis of gold-silver labeling for DOPR and immunoperoxidase labeling for CRF revealed that 55 % of the CRF neurons analyzed contained DOPR in the BLA while 67 % of the CRF neurons analyzed contained DOPR in the CeA. Furthermore, approximately 41 % of DOPR-labeled axon terminals targeted BLA neurons that expressed CRF while 29 % of DOPR-labeled axon terminals targeted CeA neurons that expressed CRF. Triple label immunofluorescence microscopy revealed that DOPR and CRF were co-localized in common cellular profiles that were in close proximity to NE-containing fibers in both subregions. These anatomical results indicate significant interactions between DOPR and CRF in this critical limbic region and reveal that NE is poised to regulate these peptidergic systems in the amygdala. Functional studies were performed to determine if activation of DOPR could inhibit the anxiety produced by elevation of NE in the amygdala using the pharmacological stressor yohimbine. Administration of the DOPR agonist, SNC80, significantly attenuated elevated anxiogenic behaviors produced by yohimbine as measured in the rat on the elevated zero maze. Taken together, results from this study demonstrate the convergence of three important systems, NE, CRF, and DOPR, in the amygdala and provide insight into their functional role in modulating stress and anxiety responses.

Low expression of D2R and Wntless correlates with high motivation for heroin

Drug overdose now exceeds car accidents as the leading cause of accidental death in the United States. Of those drug overdoses, a large percentage of the deaths are due to heroin and/or pharmaceutical overdose, specifically misuse of prescription opioid analgesics. It is imperative, then, that we understand the mechanisms that lead to opioid abuse and addiction. The rewarding actions of opioids are mediated largely by the mu-opioid receptor (MOR), and signaling by this receptor is modulated by various interacting proteins. The neurotransmitter dopamine also contributes to opioid reward, and opioid addiction has been linked to reduced expression of dopamine D2 receptors (D2R) in the brain. That said, it is not known if alterations in the expression of these proteins relate to drug exposure and/or to the "addiction-like" behavior exhibited for the drug. Here, we held total drug self-administration constant across acquisition and showed that reduced expression of the D2R and the MOR interacting protein, Wntless, in the medial prefrontal cortex was associated with greater addiction-like behavior for heroin in general and with a greater willingness to work for the drug in particular. In contrast, reduced expression of the D2R in the nucleus accumbens and hippocampus was correlated with greater seeking during signaled nonavailability of the drug. Taken together, these data link reduced expression of both the D2R and Wntless to the explicit motivation for the drug rather than to differences in total drug intake per se.

Ultrastructural evidence for synaptic contacts between cortical noradrenergic afferents and endocannabinoid-synthesizing post-synaptic neurons

Endocannabinoids (eCBs) are involved in a myriad of physiological processes that are mediated through the activation of cannabinoid receptors, which are ubiquitously distributed within the nervous system. One neurochemical target at which cannabinoids interact to have global effects on behavior is brain noradrenergic circuitry. We, and others, have previously shown that CB type 1 receptors (CB1r) are positioned to pre-synaptically modulate norepinephrine (NE) release in the rat frontal cortex (FC). Diacylglycerol lipase (DGL) is a key enzyme in the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). While DGL-α is expressed in the FC in the rat brain, it is not known whether noradrenergic afferents target neurons expressing synthesizing enzymes for the endocannabinoid, 2-AG. In the present study, we employed high-resolution neuroanatomical approaches to better define cellular sites for interactions between noradrenergic afferents and FC neurons expressing DGL-α. Immunofluorescence microscopy showed close appositions between processes containing the norepinephrine transporter (NET) or dopamine-β-hydroxylase (DβH) and cortical neurons expressing DGL-α-immunoreactivity. Ultrastructural analysis using immunogold-silver labeling for DGL-α and immunoperoxidase labeling for NET or DβH confirmed that NET-labeled axon terminals were directly apposed to FC somata and dendritic processes that exhibited DGL-α-immunoreactivity. Finally, tissue sections were processed for immunohistochemical detection of DGL-α, CB1r and DβH. Triple label immunofluorescence revealed that CB1r and DβH were co-localized in common cellular profiles and these were in close association with DGL-α. Taken together, these data provide anatomical evidence for direct synaptic associations between noradrenergic afferents and cortical neurons exhibiting endocannabinoid synthesizing machinery.

Whole-genome expression profile in zebrafish embryos after chronic exposure to morphine: identification of new genes associated with neuronal function and mu opioid receptor expression

BACKGROUND

A great number of studies have investigated changes induced by morphine exposure in gene expression using several experimental models. In this study, we examined gene expression changes during chronic exposure to morphine during maturation and differentiation of zebrafish CNS.

RESULTS

Microarray analysis showed 254 genes whose expression was identified as different by at least 1.3 fold change following chronic morphine exposure as compared to controls. Of these, several novel genes (grb2, copb2, otpb, magi1b, grik-l, bnip4 and sox19b) have been detected for the first time in an experimental animal model treated with morphine. We have also identified a subset of genes (dao.1, wls, bnip4 and camk1γb) differentially expressed by chronic morphine exposure whose expression is related to mu opioid receptor gene expression. Altered expression of copb2, bnip4, sox19b, otpb, dao.1, grik-l and wls is indicative of modified neuronal development, CNS patterning processes, differentiation and dopaminergic neurotransmission, serotonergic signaling pathway, and glutamatergic neurotransmission. The deregulation of camk1γb signaling genes suggests an activation of axonogenesis and dendritogenesis.

CONCLUSIONS

Our study identified different functional classes of genes and individual candidates involved in the mechanisms underlying susceptibility to morphine actions related to CNS development. These results open new lines to study the treatment of pain and the molecular mechanisms involved in addiction. We also found a set of zebrafish-specific morphine-induced genes, which may be putative targets in human models for addiction and pain processes.

Using high resolution imaging to determine trafficking of corticotropin-releasing factor receptors in noradrenergic neurons of the rat locus coeruleus

Trafficking of G protein-coupled receptors (GPCRs) is a critical determinant of cellular sensitivity of neurons. To understand how endogenous or exogenous ligands impact cell surface expression of GPCRs, it is essential to employ approaches that achieve superior anatomical resolution at the synaptic level. In situations in which light and fluorescence microscopy techniques may provide only limited resolution, electron microscopy provides enhanced subcellular precision. Dual labeling immunohistochemistry employing visually distinct immunoperoxidase and immunogold markers has been an effective approach for elucidating complex receptor profiles at the synapse and to definitively establish the localization of individual receptors and neuromodulators to common cellular profiles. The immuno-electron microscopy approach offers the potential for determining membrane versus intracellular protein localization, as well as the association with various identifiable cellular organelles. Corticotropin-releasing factor (CRF) is an important regulator of endocrine, autonomic, immunological, behavioral and cognitive limbs of the stress response. Dysfunction of this neuropeptide system has been associated with several psychiatric disorders. This review summarizes findings from neuroanatomical studies, with superior spatial resolution, that indicate that the distribution of CRF receptors is a highly dynamic process that, in addition to being sexually dimorphic, involves complex regulation of receptor trafficking within extrasynaptic sites that have significant consequences for adaptations to stress, particularly within the locus coeruleus (LC), the major brain norepinephrine-containing nucleus.

Morphine-induced trafficking of a mu-opioid receptor interacting protein in rat locus coeruleus neurons

Opiate addiction is a devastating health problem, with approximately 2million people currently addicted to heroin or non-medical prescription opiates in the United States alone. In neurons, adaptations in cell signaling cascades develop following opioid actions at the mu opioid receptor (MOR). A novel putative target for intervention involves interacting proteins that may regulate trafficking of MOR. Morphine has been shown to induce a re-distribution of a MOR-interacting protein Wntless (WLS, a transport molecule necessary for secretion of neurotrophic Wnt proteins), from cytoplasmic to membrane compartments in rat striatal neurons. Given its opiate-sensitivity and its well-characterized molecular and cellular adaptations to morphine exposure, we investigated the anatomical distribution of WLS and MOR in the rat locus coeruleus (LC)-norepinephrine (NE) system. Dual immunofluorescence microscopy was used to test the hypothesis that WLS is localized to noradrenergic neurons of the LC and that WLS and MOR co-exist in common LC somatodendritic processes, providing an anatomical substrate for their putative interactions. We also hypothesized that morphine would influence WLS distribution in the LC. Rats received saline, morphine or the opiate agonist [d-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO), and tissue sections through the LC were processed for immunogold-silver detection of WLS and MOR. Statistical analysis showed a significant re-distribution of WLS to the plasma membrane following morphine treatment in addition to an increase in the proximity of gold-silver labels for MOR and WLS. Following DAMGO treatment, MOR and WLS were predominantly localized within the cytoplasmic compartment when compared to morphine and control. In a separate cohort of rats, brains were obtained from saline-treated or heroin self-administering male rats for pulldown co-immunoprecipitation studies. Results showed an increased association of WLS and MOR following heroin exposure. As the LC-NE system is important for cognition as well as decisions underlying substance abuse, adaptations in WLS trafficking and expression may play a role in modulating MOR function in the LC and contribute to the negative sequelae of opiate exposure on executive function.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Direct targeting of peptidergic amygdalar neurons by noradrenergic afferents: linking stress-integrative circuitry

Amygdalar norepinephrine (NE) plays a key role in regulating neural responses to emotionally arousing stimuli and is involved in memory consolidation of emotionally charged events. Corticotropin-releasing factor (CRF) and dynorphin (DYN), two neuropeptides that mediate the physiological and behavioral responses to stress, are abundant in the central nucleus of the amygdala (CeA), and directly innervate brainstem noradrenergic locus coeruleus (LC) neurons. Whether the CRF- and DYN-containing amygdalar neurons receive direct noradrenergic innervation has not yet been elucidated. The present study sought to define cellular substrates underlying noradrenergic modulation of CRF- and DYN-containing neurons in the CeA using immunohistochemistry and electron microscopy. Ultrastructural analysis revealed that NE-labeled axon terminals form synapses with CRF- and DYN-containing neurons in the CeA. Semi-quantitative analysis showed that approximately 31 % of NET-labeled axon terminals targeted CeA neurons that co-expressed DYN and CRF. As a major source of CRF innervation to the LC, it is also not known whether CRF-containing CeA neurons are directly targeted by noradrenergic afferents. To test this, retrograde tract tracing using FluoroGold from the LC was combined with immunocytochemical detection of CRF and NET in the CeA. Our results revealed a population of LC-projecting CRF-containing CeA neurons that are directly innervated by NE afferents. Analysis showed that approximately 34 % of NET-labeled axon terminals targeted LC-projecting CeA neurons that contain CRF. Taken together, these results indicate significant interactions between NE, CRF and DYN in this critical limbic region and reveal direct synaptic interactions of NE with amygdalar CRF that influence the LC-NE arousal system.

MOR is not enough: identification of novel mu-opioid receptor interacting proteins using traditional and modified membrane yeast two-hybrid screens

The mu-opioid receptor (MOR) is the G-protein coupled receptor primarily responsible for mediating the analgesic and rewarding properties of opioid agonist drugs such as morphine, fentanyl, and heroin. We have utilized a combination of traditional and modified membrane yeast two-hybrid screening methods to identify a cohort of novel MOR interacting proteins (MORIPs). The interaction between the MOR and a subset of MORIPs was validated in pulldown, co-immunoprecipitation, and co-localization studies using HEK293 cells stably expressing the MOR as well as rodent brain. Additionally, a subset of MORIPs was found capable of interaction with the delta and kappa opioid receptors, suggesting that they may represent general opioid receptor interacting proteins (ORIPS). Expression of several MORIPs was altered in specific mouse brain regions after chronic treatment with morphine, suggesting that these proteins may play a role in response to opioid agonist drugs. Based on the known function of these newly identified MORIPs, the interactions forming the MOR signalplex are hypothesized to be important for MOR signaling and intracellular trafficking. Understanding the molecular complexity of MOR/MORIP interactions provides a conceptual framework for defining the cellular mechanisms of MOR signaling in brain and may be critical for determining the physiological basis of opioid tolerance and addiction.

In vivo regulation of the μ opioid receptor: role of the endogenous opioid agents

It is well known that genotypic differences can account for the subject-specific responses to opiate administration. In this regard, the basal activity of the endogenous system (either at the receptor or ligand level) can modulate the effects of exogenous agonists as morphine and vice versa. The μ opioid receptor from zebrafish, dre-oprm1, binds endogenous peptides and morphine with similar affinities. Morphine administration during development altered the expression of the endogenous opioid propeptides proenkephalins and proopiomelanocortin. Treatment with opioid peptides (Met-enkephalin [Met-ENK], Met-enkephalin-Gly-Tyr [MEGY] and β-endorphin [β-END]) modulated dre-oprm1 expression during development. Knocking down the dre-oprm1 gene significantly modified the mRNA expression of the penk and pomc genes, thus indicating that oprm1 is involved in shaping penk and pomc expression. In addition, the absence of a functional oprm1 clearly disrupted the embryonic development, since proliferation was disorganized in the central nervous system of oprm1-morphant embryos: mitotic cells were found widespread through the optic tectum and were not restricted to the proliferative areas of the mid- and hindbrain. Transferase-mediated dUTP nick-end labeling (TUNEL) staining revealed that the number of apoptotic cells in the central nervous system (CNS) of morphants was clearly increased at 24-h postfertilization. These findings clarify the role of the endogenous opioid system in CNS development. Our results will also help unravel the complex feedback loops that modulate opioid activity and that may be involved in establishing a coordinated expression of both receptors and endogenous ligands. Further knowledge of the complex interactions between the opioid system and analgesic drugs will provide insights that may be relevant for analgesic therapy.