Human Neural Precursor Cells Express Functional κ-Opioid Receptors

Endogenous Opioids and Their Role in Stem Cell Biology and Tissue Rescue

Opioids are considered the oldest drugs known by humans and have been used for sedation and pain relief for several centuries. Nowadays, endogenous opioid peptides are divided into four families: enkephalins, dynorphins, endorphins, and nociceptin/orphanin FQ. They exert their action through the opioid receptors (ORs), transmembrane proteins belonging to the super-family of G-protein-coupled receptors, and are expressed throughout the body; the receptors are the δ opioid receptor (DOR), μ opioid receptor (MOR), κ opioid receptor (KOR), and nociceptin/orphanin FQ receptor (NOP). Endogenous opioids are mainly studied in the central nervous system (CNS), but their role has been investigated in other organs, both in physiological and in pathological conditions. Here, we revise their role in stem cell (SC) biology, since these cells are a subject of great scientific interest due to their peculiar features and their involvement in cell-based therapies in regenerative medicine. In particular, we focus on endogenous opioids’ ability to modulate SC proliferation, stress response (to oxidative stress, starvation, or damage following ischemia–reperfusion), and differentiation towards different lineages, such as neurogenesis, vasculogenesis, and cardiogenesis.

Kappa opioid receptor controls neural stem cell differentiation via a miR-7a/Pax6 dependent pathway

Although the roles of opioid receptors in neurogenesis have been implicated in previous studies, the mechanism by which κ-opioid receptor (OPRK1) regulates adult neurogenesis remains elusive. We now demonstrate that two agonists of OPRK1, U50,488H and dynorphin A, inhibit adult neurogenesis by hindering neuronal differentiation of mouse hippocampal neural stem cells (NSCs), both in vitro and in vivo. This effect was blocked by nor-binaltorphimine (nor-BNI), a specific antagonist of OPRK1. By examining neurogenesis-related genes, we found that OPRK1 agonists were able to downregulate the expression of Pax6, Neurog2, and NeuroD1 in mouse hippocampal NSCs, in a way that Pax6 regulates the transcription of Neurog2 and Neurod1 by directly interacting with their promoters. Moreover, this effect of OPRK1 was accomplished by inducing expression of miR-7a, a miRNA that specifically targeted Pax6 by direct interaction with its 3'-UTR sequence, and thereby decreased the levels of Pax6, Neurog2, and NeuroD1, thus resulted in hindrance of neuronal differentiation of NSCs. Thus, by modulating Pax6/Neurog2/NeuroD1 activities via upregulation of miR-7a expression, OPRK1 agonists hinder the neuronal differentiation of NSCs and hence inhibit adult neurogenesis in mouse hippocampus.

Neurodevelopmental signatures of narcotic and neuropsychiatric risk factors in 3D human-derived forebrain organoids

It is widely accepted that narcotic use during pregnancy and specific environmental factors (e.g., maternal immune activation and chronic stress) may increase risk of neuropsychiatric illness in offspring. However, little progress has been made in defining human-specific in utero neurodevelopmental pathology due to ethical and technical challenges associated with accessing human prenatal brain tissue. Here we utilized human induced pluripotent stem cells (hiPSCs) to generate reproducible organoids that recapitulate dorsal forebrain development including early corticogenesis. We systemically exposed organoid samples to chemically defined "enviromimetic" compounds to examine the developmental effects of various narcotic and neuropsychiatric-related risk factors within tissue of human origin. In tandem experiments conducted in parallel, we modeled exposure to opiates (μ-opioid agonist endomorphin), cannabinoids (WIN 55,212-2), alcohol (ethanol), smoking (nicotine), chronic stress (human cortisol), and maternal immune activation (human Interleukin-17a; IL17a). Human-derived dorsal forebrain organoids were consequently analyzed via an array of unbiased and high-throughput analytical approaches, including state-of-the-art TMT-16plex liquid chromatography/mass-spectrometry (LC/MS) proteomics, hybrid MS metabolomics, and flow cytometry panels to determine cell-cycle dynamics and rates of cell death. This pipeline subsequently revealed both common and unique proteome, reactome, and metabolome alterations as a consequence of enviromimetic modeling of narcotic use and neuropsychiatric-related risk factors in tissue of human origin. However, of our 6 treatment groups, human-derived organoids treated with the cannabinoid agonist WIN 55,212-2 exhibited the least convergence of all groups. Single-cell analysis revealed that WIN 55,212-2 increased DNA fragmentation, an indicator of apoptosis, in human-derived dorsal forebrain organoids. We subsequently confirmed induction of DNA damage and apoptosis by WIN 55,212-2 within 3D human-derived dorsal forebrain organoids. Lastly, in a BrdU pulse-chase neocortical neurogenesis paradigm, we identified that WIN 55,212-2 was the only enviromimetic treatment to disrupt newborn neuron numbers within human-derived dorsal forebrain organoids. Cumulatively this study serves as both a resource and foundation from which human 3D biologics can be used to resolve the non-genomic effects of neuropsychiatric risk factors under controlled laboratory conditions. While synthetic cannabinoids can differ from naturally occurring compounds in their effects, our data nonetheless suggests that exposure to WIN 55,212-2 elicits neurotoxicity within human-derived developing forebrain tissue. These human-derived data therefore support the long-standing belief that maternal use of cannabinoids may require caution so to avoid any potential neurodevelopmental effects upon developing offspring in utero.

Induced pluripotent stem cells as a platform to understand patient-specific responses to opioids and anaesthetics

Recent advances in human induced pluripotent stem cell (iPSC) technology may provide unprecedented opportunities to study patient-specific responses to anaesthetics and opioids. In this review, we will (1) examine the advantages and limitations of iPSC technology, (2) summarize studies using iPSCs that have contributed to our current understanding of anaesthetics and opioid action on the cardiovascular system and central nervous system (CNS), and (3) describe how iPSC technology can be used to further develop personalized analgesic and sedative pharmacotherapies with reduced or minimal detrimental cardiovascular effects.

Clinical and basic research investigations into the long-term effects of prenatal opioid exposure on brain development

Coincident with the opioid epidemic in the United States has been a dramatic increase in the number of children born with neonatal abstinence syndrome (NAS), a form of withdrawal resulting from opioid exposure during pregnancy. Many research efforts on NAS have focused on short-term care, including acute symptom treatment and weaning of the infants off their drug dependency prior to authorizing their release. However, investigations into the long-term effects of prenatal opioid exposure (POE) on brain development, from the cellular to the behavioral level, have not been as frequent. Given the importance of the perinatal period for human brain development, opioid-induced disturbances in the formation and function of nascent synaptic networks and glia have the potential to impact brain connectivity and cognition long after the drug supply is cutoff shortly after birth. In this review, we will summarize the current state of NAS research, bringing together findings from human studies and preclinical animal models to highlight what is known about how POE can induce significant, prolonged deficits in brain structure and function. With rates of NAS continuing to rise, particularly in regions that already face substantial socioeconomic challenges, we speculate as to the most promising avenues for future research to alleviate this growing multigenerational threat.

Non-nociceptive roles of opioids in the CNS: opioids' effects on neurogenesis, learning, memory and affect

Mortality due to opioid use has grown to the point where, for the first time in history, opioid-related deaths exceed those caused by car accidents in many states in the United States. Changes in the prescribing of opioids for pain and the illicit use of fentanyl (and derivatives) have contributed to the current epidemic. Less known is the impact of opioids on hippocampal neurogenesis, the functional manipulation of which may improve the deleterious effects of opioid use. We provide new insights into how the dysregulation of neurogenesis by opioids can modify learning and affect, mood and emotions, processes that have been well accepted to motivate addictive behaviours.

Expression of kappa opioid receptors in developing rat brain - Implications for perinatal buprenorphine exposure

Buprenorphine, a mu opioid receptor partial agonist and kappa opioid receptor (KOR) antagonist, is an emerging therapeutic agent for maternal opioid dependence in pregnancy and neonatal abstinence syndrome. However, the endogenous opioid system plays a critical role in modulating neurodevelopment and perinatal buprenorphine exposure may detrimentally influence this. To identify aspects of neurodevelopment vulnerable to perinatal buprenorphine exposure, we defined KOR protein expression and its cellular associations in normal rat brain from embryonic day 16 to postnatal day 23 with double-labelling immunohistochemistry. KOR was expressed on neural stem and progenitor cells (NSPCs), choroid plexus epithelium, subpopulations of cortical neurones and oligodendrocytes, and NSPCs and subpopulations of neurones in postnatal hippocampus. These distinct patterns of KOR expression suggest several pathways vulnerable to perinatal buprenorphine exposure, including proliferation, neurogenesis and neurotransmission. We thus suggest the cautious use of buprenorphine in both mothers and infants until its impact on neurodevelopment is better defined.

Involvement of extracellular signal-regulated kinase (ERK1/2)-p53-p21 axis in mediating neural stem/progenitor cell cycle arrest in co-morbid HIV-drug abuse exposure

Neurological complications in opioid abusing Human Immunodeficiency Virus-1 (HIV-1) patients suggest enhanced neurodegeneration as compared to non-drug abusing HIV-1 infected population. Neural precursor cells (NPCs), the multipotent cells of the mammalian brain, are susceptible to HIV-1 infection and as opiates also perturb their growth kinetics, detailed mechanistic studies for their co-morbid exposure are highly warranted. Using a well characterized in vitro model of human fetal brain-derived neural precursor cells, we investigated alterations in NPC properties at both acute and chronic durations. Chronic morphine and Tat treatment attenuated proliferation in NPCs, with cells stalled at G1-phase of the cell cycle. Furthermore HIV-Tat and morphine exposure increased activation of extracellular signal-regulated kinase-1/2 (ERK1/2), enhanced levels of p53 and p21, and decreased cyclin D1 and Akt levels in NPCs. Regulated by ERK1/2 and p53, p21 was found to be indispensible for Tat and morphine mediated cell cycle arrest. Our study elaborates on the cellular and molecular machinery in NPCs and provides significant mechanistic details into HIV-drug abuse co-morbidity that may have far reaching clinical consequences both in pediatric as well as adult neuroAIDS.

G-protein-coupled receptors in adult neurogenesis

The importance of adult neurogenesis has only recently been accepted, resulting in a completely new field of investigation within stem cell biology. The regulation and functional significance of adult neurogenesis is currently an area of highly active research. G-protein-coupled receptors (GPCRs) have emerged as potential modulators of adult neurogenesis. GPCRs represent a class of proteins with significant clinical importance, because approximately 30% of all modern therapeutic treatments target these receptors. GPCRs bind to a large class of neurotransmitters and neuromodulators such as norepinephrine, dopamine, and serotonin. Besides their typical role in cellular communication, GPCRs are expressed on adult neural stem cells and their progenitors that relay specific signals to regulate the neurogenic process. This review summarizes the field of adult neurogenesis and its methods and specifies the roles of various GPCRs and their signal transduction pathways that are involved in the regulation of adult neural stem cells and their progenitors. Current evidence supporting adult neurogenesis as a model for self-repair in neuropathologic conditions, adult neural stem cell therapeutic strategies, and potential avenues for GPCR-based therapeutics are also discussed.

Immunomodulatory properties of kappa opioids and synthetic cannabinoids in HIV-1 neuropathogenesis

Anti-retroviral therapy (ART) has had a tremendous impact on the clinical outcomes of HIV-1 infected individuals. While ART has produced many tangible benefits, chronic, long-term consequences of HIV infection have grown in importance. HIV-1-associated neurocognitive disorder (HAND) represents a collection of neurological syndromes that have a wide range of functional cognitive impairments. HAND remains a serious threat to AIDS patients, and there currently remains no specific therapy for the neurological manifestations of HIV-1. Based upon work in other models of neuroinflammation, kappa opioid receptors (KOR) and synthetic cannabinoids have emerged as having neuroprotective properties and the ability to dampen pro-inflammatory responses of glial cells; properties that may have a positive influence in HIV-1 neuropathogenesis. The ability of KOR ligands to inhibit HIV-1 production in human microglial cells and CD4 T lymphocytes, demonstrate neuroprotection, and dampen chemokine production in astrocytes provides encouraging data to suggest that KOR ligands may emerge as potential therapeutic agents in HIV neuropathogenesis. Based upon findings that synthetic cannabinoids inhibit HIV-1 expression in human microglia and suppress production of inflammatory mediators such as nitric oxide (NO) in human astrocytes, as well as a substantial literature demonstrating neuroprotective properties of cannabinoids in other systems, synthetic cannabinoids have also emerged as potential therapeutic agents in HIV neuropathogenesis. This review focuses on these two classes of compounds and describes the immunomodulatory and neuroprotective properties attributed to each in the context of HIV neuropathogenesis.

The κ opioid system regulates endothelial cell differentiation and pathfinding in vascular development

The opioid system (opioid peptides and receptors) regulates a variety of neurophysiologic functions, including pain control. Here we show novel roles of the κ opioid system in vascular development. Previously, we revealed that cAMP/protein kinase A (PKA) signaling enhanced differentiation of vascular progenitors expressing VEGF receptor-2 (fetal liver kinase 1; Flk1) into endothelial cells (ECs) through dual up-regulation of Flk1 and Neuropilin1 (NRP1), which form a selective and sensitive VEGF(164) receptor. Kappa opioid receptor (KOR), an inhibitory G protein-coupled receptor, was highly expressed in embryonic stem cell-derived Flk1(+) vascular progenitors. The addition of KOR agonists to Flk1(+) vascular progenitors inhibited EC differentiation and 3-dimensional vascular formation. Activation of KOR decreased expression of Flk1 and NRP1 in vascular progenitors. The inhibitory effects of KOR were reversed by 8-bromoadenosine-3',5'-cAMP or a PKA agonist, N(6)-benzoyl-cAMP, indicating that KOR inhibits cAMP/PKA signaling. Furthermore, KOR-null or dynorphin (an endogenous KOR agonist)-null mice showed a significant increase in overall vascular formation and ectopic vascular invasion into somites at embryonic day -10.5. ECs in these null mice showed significant increase in Flk1 and NRP1, along with reciprocal decrease in plexinD1, which regulates vascular pathfinding. The opioid system is, thus, a new regulator of vascular development that simultaneously modifies 2 distinct vascular properties, EC differentiation and vascular pathfinding.

Mu and kappa opioids modulate mouse embryonic stem cell-derived neural progenitor differentiation via MAP kinases

As embryonic stem cell-derived neural progenitors (NPs) have the potential to be used in cell replacement therapy, an understanding of the signaling mechanisms that regulate their terminal differentiation is imperative. In previous studies, we discovered the presence of functional mu opioid receptors (MOR) and kappa opioid receptors (KOR) in mouse embryonic stem cells and NPs. Here, MOR and KOR immunoreactivity was detected in NP-derived oligodendrocytes during three stages of their maturation in vitro. Moreover, we examined the modulation of retinoic acid-induced NP differentiation to astrocytes and neurons by mu, [D-ala(2), mephe(4), gly-ol(5)] enkephalin, or kappa, U69, 593, opioids. Both opioid agonists inhibited NP-derived neurogenesis and astrogenesis via their corresponding receptors as determined by immunocytochemistry. By administering selective inhibitors, we found that opioid inhibition of NP-derived astrogenesis was driven via extracellular-signal regulated kinase (ERK), while the p38 mitogen-activated protein kinase pathway was implicated in opioid attenuation of neurogenesis. In addition, mu and kappa opioids stimulated oligodendrogenesis from NP-derived NG2(+) oligodendrocyte progenitors via both ERK and p38 signaling pathways. Accordingly, both opioids induced ERK phosphorylation in NG2(+) cells. These results indicate that small molecules, such as MOR and KOR agonists may play a modulatory role in NP terminal differentiation.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 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.

Acute in utero morphine exposure slows G2/M phase transition in radial glial and basal progenitor cells in the dorsal telencephalon of the E15.5 embryonic mouse

The antiproliferative effects of opiate exposure on neurogenesis in vitro have been well documented, but the effects of opiates on brain development in vivo are less well understood. We have recently shown that mu opioid receptors are expressed on radial glia of the lateral ventricle, the neuronal and glial progenitor cells of the developing cortex. In the present study we show that in vivo morphine treatment of the E15.5 mouse increases the length of the G(2)/M phase of the radial glial cell cycle in the dorsal telencephalon, as well as slows interkinetic nuclear migration of radial glial nuclei from the basal ventricular zone to the apical surface. A prolonged G(2)/M phase was also observed in basal progenitor cells. Although morphine exposure altered the duration of the cell cycle for progenitor cells in the embryonic telencephalon, it did not affect whether the progenitors remained proliferative and re-entered the S phase, or whether they exited the cell cycle and became quiescent. In addition, morphine treatment did not change the proportion of basal to apical mitoses. These findings indicate that opioid signalling plays a role in cell cycle progression of both radial glia and basal progenitor cells in vivo in the developing cerebral cortex.