Neuroscience
The cellular basis of protease activated receptor type 2 (PAR2) evoked mechanical and affective pain
Abstract
Protease-activated receptor 2 (PAR2) has long been implicated in inflammatory and visceral pain, but the cellular basis of PAR2-evoked pain has not been delineated. While PAR2-evoked pain has been attributed to sensory neuron expression, RNA-sequencing experiments show ambiguous F2rl1 mRNA detection. Moreover, many pharmacological tools for PAR2 are nonspecific, acting also on the Mas-related GPCR family (Mrg) that are highly enriched in sensory neurons. We sought to bring clarity to the cellular basis of PAR2 pain. We developed a PAR2 conditional mutant mouse and specifically deleted PAR2 in all sensory neurons using the PirtCre mouse line. Our behavioral findings show that PAR2 agonist-evoked mechanical hyperalgesia and facial grimacing, but not thermal hyperalgesia, is dependent on PAR2 expression in sensory neurons that project to the hind paw in male and female mice. F2rl1 mRNA is expressed in a discrete population (~4%) of mostly small-diameter sensory neurons that co-express the Nppb and IL31ra genes. This cell population has been implicated in itch, but our work shows that PAR2 activation in these cells causes clear pain-related behaviors from the skin. Our findings show that a discreet population of DRG sensory neurons mediate PAR2-evoked pain.
Authors
Shayne N. Hassler, Moeno Kume, Juliet Mwirigi, Ayesha Ahmad, Stephanie Shiers, Andi Wangzhou, Pradipta Ray, Sergei N. Belugin, Dhananjay K. Naik, Michael D. Burton, Josef Vagner, Scott Boitano, Armen N. Akopian, Gregory Dussor, Theodore J. Price
Abstract
Discovery strategies commonly focus on the identification of chemical libraries or natural products, but the modulation of endogenous ligands offers a much better therapeutic strategy due to their low adverse potential. Recently, we have seen that hexadecanamide (Hex) is present in hippocampal nuclei of normal mice as an endogenous ligand of peroxisome proliferator-activated receptor alpha (PPARα). This study underlines the importance of Hex in inducing the expression of brain-derived neurotrophic factor (BDNF) from hippocampal neurons via PPARα. The level of Hex was less in the hippocampus of 5xFAD mice as compared to non-Tg mice. Oral administration of Hex increased the level of this molecule in the hippocampus to stimulate BDNF and its downstream plasticity-associated molecules, promote synaptic functions in the hippocampus and improve memory and learning in 5xFAD mice. However, oral Hex remained unable to stimulate hippocampal plasticity and improve cognitive behaviors in 5xFADPparα-null (5x with global PPARα-/-) and 5xFADPparα-ΔHippo (5x with hippocampus-specific PPARα-/-) mice, indicating an essential role of hippocampal PPARα in Hex-mediated improvement in hippocampal functions. This is the first demonstration of protection of hippocampal functions by oral administration of a hippocampus-based drug, suggesting that hexadecanamide may be explored for therapeutic intervention in AD.
Authors
Dhruv R. Patel, Avik Roy, Sumita Raha, Madhuchhanda Kundu, Frank Gonzalez, Kalipada Pahan
Abstract
Although human endogenous retroviruses (HERVs) represent a substantial proportion of the human genome and some HERVs, such as HERV-K(HML-2), are reported to be involved in neurological disorders, little is known about their biological function. We report that RNA from an HERV-K(HML-2) envelope gene region binds to and activates human Toll-like receptor (TLR) 8, as well as murine Tlr7, expressed in neurons and microglia, thereby causing neurodegeneration. HERV-K(HML-2) RNA introduced into the cerebrospinal fluid (CSF) of either C57BL/6 wild-type mice or APPPS1 mice, a mouse model for Alzheimer’s disease (AD), resulted in neurodegeneration and microglia accumulation. Tlr7-deficient mice were protected against neurodegenerative effects but were resensitized toward HERV-K(HML-2) RNA when neurons ectopically expressed murine Tlr7 or human TLR8. Transcriptome data sets of human AD brain samples revealed a distinct correlation of upregulated HERV-K(HML-2) and TLR8 RNA expression. HERV-K(HML-2) RNA was detectable more frequently in CSF from individuals with AD compared with controls. Our data establish HERV-K(HML-2) RNA as an endogenous ligand for species-specific TLRs 7/8 and imply a functional contribution of human endogenous retroviral transcripts to neurodegenerative processes, such as AD.
Authors
Paul Dembny, Andrew G. Newman, Manvendra Singh, Michael Hinz, Michal Szczepek, Christina Krüger, Robert Adalbert, Omar Dzaye, Thorsten Trimbuch, Thomas Wallach, Gunnar Kleinau, Katja Derkow, Bernhard C. Richard, Carola Schipke, Claus Scheidereit, Harald Stachelscheid, Douglas Golenbock, Oliver Peters, Michael Coleman, Frank L. Heppner, Patrick Scheerer, Victor Tarabykin, Klemens Ruprecht, Zsuzsanna Izsvák, Jens Mayer, Seija Lehnardt
Abstract
Glucokinase (GK) is highly expressed in the hypothalamic paraventricular nucleus (PVN); however its role is currently unknown. We found that glucokinase in the PVN acts as part of a glucose sensing mechanism within the PVN that regulates glucose homeostasis by controlling glucagon like peptide 1 (GLP-1) release. GLP-1 is released from enteroendocrine L-cells in response to oral glucose. Here we identify a brain mechanism critical to the release of GLP-1 in response to oral glucose. We show that increasing expression of GK or injection of glucose into the PVN increases GLP-1 release in response to oral glucose. On the contrary decreasing expression of GK or injection of non-metabolisable glucose into the PVN prevents GLP-1 release. Our results demonstrate that glucosensitive GK neurones in the PVN, are critical to the response to oral glucose and subsequent release of GLP-1.
Authors
Yue Ma, Risheka Ratnasabapathy, Ivan De Backer, Chioma Izzi-Engbeaya, Marie-Sophie Nguyen-Tu, Joyceline Cuenco, Ben Jones, Christopher D. John, Brian Y. H. Lam, Guy A. Rutter, Giles Yeo, Waljit Dhillo, James Gardiner
Abstract
Semaglutide, a glucagon-like peptide 1 (GLP-1) analog, induces weight loss, lowers glucose levels, and reduces cardiovascular risk in patients with diabetes. Mechanistic preclinical studies suggest weight loss is mediated through GLP-1 receptors (GLP-1Rs) in the brain. The findings presented here show that semaglutide modulated food preference, reduced food intake, and caused weight loss without decreasing energy expenditure. Semaglutide directly accessed the brainstem, septal nucleus, and hypothalamus but did not cross the blood-brain barrier; it interacted with the brain through the circumventricular organs and several select sites adjacent to the ventricles. Semaglutide induced central c-Fos activation in 10 brain areas, including hindbrain areas directly targeted by semaglutide, and secondary areas without direct GLP-1R interaction, such as the lateral parabrachial nucleus. Automated analysis of semaglutide access, c-Fos activity, GLP-1R distribution, and brain connectivity revealed that activation may involve meal termination controlled by neurons in the lateral parabrachial nucleus. Transcriptomic analysis of microdissected brain areas from semaglutide-treated rats showed upregulation of prolactin-releasing hormone and tyrosine hydroxylase in the area postrema. We suggest semaglutide lowers body weight by direct interaction with diverse GLP-1R populations and by directly and indirectly affecting the activity of neural pathways involved in food intake, reward, and energy expenditure.
Authors
Sanaz Gabery, Casper G. Salinas, Sarah J. Paulsen, Jonas Ahnfelt-Rønne, Tomas Alanentalo, Arian F. Baquero, Stephen T. Buckley, Erzsébet Farkas, Csaba Fekete, Klaus S. Frederiksen, Hans Christian C. Helms, Jacob F. Jeppesen, Linu M. John, Charles Pyke, Jane Nøhr, Tess T. Lu, Joseph Polex-Wolf, Vincent Prevot, Kirsten Raun, Lotte Simonsen, Gao Sun, Anett Szilvásy-Szabó, Hanni Willenbrock, Anna Secher, Lotte Bjerre Knudsen
Abstract
BACKGROUND. Seizure-induced inhibition of respiration plays a critical role in sudden unexpected death in epilepsy (SUDEP). However, the mechanisms underlying seizure-induced central apnea in pediatric epilepsy are unknown. METHODS. We studied eight pediatric patients with intractable epilepsy undergoing intracranial electroencephalography (iEEG). We recorded respiration during seizures and during electrical stimulation mapping of 174 forebrain sites. A machine learning algorithm was used to delineate brain regions that inhibit respiration. RESULTS. In two patients, apnea coincided with seizure spread to the amygdala. Supporting a role for the amygdala in breathing inhibition in children, electrically stimulating the amygdala produced apnea in all eight subjects (3- to 17-years-old). These effects did not depend on epilepsy type and were relatively specific to the amygdala as no other site affected breathing. Remarkably, patients were unaware that they had stopped breathing, and none reported dyspnea or arousal, findings critical for SUDEP. Finally, a machine learning algorithm based on 45 stimulation sites and 210 stimulation trials identified a focal subregion in the human amygdala that consistently produced apnea. This site, which we refer to as the Amygdala Inhibition of Respiration (AIR) site includes the medial subregion of the basal nuclei, cortical and medial nuclei, amygdala transition areas, and intercalated neurons. CONCLUSIONS. A focal site in the amygdala inhibits respiration and induces apnea (AIR site) when electrically stimulated and during seizures in children with epilepsy. This site may prove valuable for determining those at greatest risk for SUDEP and as a therapeutic target. TRIAL REGISTRATION. This study was not affiliated with any formal clinical trial. FUNDING. NIH, CNS, Roy J. Carver Charitable Trust.
Authors
Ariane E. Rhone, Christopher K. Kovach, Gail I.S. Harmata, Alyssa W. Sullivan, Daniel Tranel, Michael A. Ciliberto, Matthew A. Howard, George B. Richerson, Mitchell Steinschneider, John A. Wemmie, Brian J. Dlouhy
Abstract
Detailed spatial information of low-molecular-weight compounds distribution, especially in the brain, is crucial towards understanding their mechanism of actions. Imaging techniques that can directly visualize drugs in the brain at a high resolution will complement existing tools for drug distribution analysis. Here, we performed surface-enhanced Raman scattering (SERS) imaging using a bioorthogonal alkyne tag to visualize drugs directly in situ at a high resolution. Focusing on the selective serotonin reuptake inhibitor S-citalopram (S-Cit), which possesses a nitrile group, we substituted an alkynyl group into its structure and synthesized alkynylated S-Cit (Alk-S-Cit). The brain transitivity and the serotonin reuptake inhibition of Alk-S-Cit were not significantly different as compared to S-Cit. Alk-S-Cit was visualized in the coronal mouse brain section using SERS imaging with silver nanoparticles. Further, SERS imaging combined with fluorescence microscopy allowed Alk-S-Cit to be visualized in the adjacent neuronal membranes, and in the brain vessel and parenchyma. Thus, our multimodal imaging technique is an effective method for detecting low-molecular-weight compounds in their original tissue environment and can potentially offer additional information regarding the precise spatial distribution of such drugs.
Authors
Masato Tanuma, Atsushi Kasai, Kazuki Bando, Naoyuki Kotoku, Kazuo Harada, Masafumi Minoshima, Kosuke Higashino, Atsushi Kimishima, Masayoshi Arai, Yukio Ago, Kaoru Seiriki, Kazuya Kikuchi, Satoshi Kawata, Katsumasa Fujita, Hitoshi Hashimoto
Abstract
Accumulation of amyloid β protein (Aβ) due to increased generation and/or impaired degradation plays an important role in Alzheimer’s disease (AD) pathogenesis. In this report, we describe the identification of rare coding mutations in the endothelin-converting enzyme 2 (ECE2) gene in 1 late-onset AD family, and additional case-control cohort analysis indicates ECE2 variants associated with the risk of developing AD. The 2 mutations (R186C and F751S) located in the peptidase domain in the ECE2 protein were found to severely impair the enzymatic activity of ECE2 in Aβ degradation. We further evaluated the effect of the R186C mutation in mutant APP–knockin mice. Overexpression of wild-type ECE2 in the hippocampus reduced amyloid load and plaque formation, and improved learning and memory deficits in the AD model mice. However, the effect was abolished by the R186C mutation in ECE2. Taken together, the results demonstrated that ECE2 peptidase mutations contribute to AD pathogenesis by impairing Aβ degradation, and overexpression of ECE2 alleviates AD phenotypes. This study indicates that ECE2 is a risk gene for AD development and pharmacological activation of ECE2 could be a promising strategy for AD treatment.
Authors
Xinxin Liao, Fang Cai, Zhanfang Sun, Yun Zhang, Juelu Wang, Bin Jiao, Jifeng Guo, Jinchen Li, Xixi Liu, Lina Guo, Yafang Zhou, Junling Wang, Xinxiang Yan, Hong Jiang, Kun Xia, Jiada Li, Beisha Tang, Lu Shen, Weihong Song
Abstract
IL-4 is a pleiotropic antiinflammatory cytokine, which can be neuroprotective after nervous system injury. The beneficial actions of IL-4 are thought to result from the blunting of action of inflammatory mediators, such as proinflammatory cytokines. Here, we demonstrate that IL-4 induces M2 macrophages to continuously produce opioid peptides and ameliorate pain. IL-4 application at injured nerves in mice shifted F4/80+ macrophages from the proinflammatory M1 to the antiinflammatory M2 phenotype, which synthesized opioid peptides (Met-enkephalin, β-endorphin, and dynorphin A 1-17). These effects were accompanied by a long-lasting attenuation of neuropathy-induced mechanical hypersensitivity, beyond the IL-4 treatment. This IL-4-induced analgesia was decreased by opioid peptide antibodies and opioid receptor (δ, μ, κ) antagonists applied at injured nerves, which confirms the involvement of the local opioid system. The participation of M2 macrophages was supported by analgesia in recipient mice injected at injured nerves with F4/80+ macrophages from IL-4–treated donors. Together, IL-4–induced M2 macrophages at injured nerves produced opioid peptides, which activated peripheral opioid receptors to diminish pain. Fostering the opioid-mediated actions of intrinsic M2 macrophages may be a strategy to tackle pathological pain.
Authors
Melih Ö. Celik, Dominika Labuz, Jacqueline Keye, Rainer Glauben, Halina Machelska
Abstract
Long-term memory depends on the control of activity-dependent neuronal gene expression, which is regulated by epigenetic modifications. The epigenetic modification of histones is orchestrated by the opposing activities of two classes of regulatory complexes: permissive co-activators and silencing co-repressors. Much work has focused on co-activator complexes, but little is known about the co-repressor complexes that suppress the expression of plasticity-related genes. Here, we define a critical role for the co-repressor SIN3A in memory and synaptic plasticity, showing that postnatal neuronal deletion of Sin3a enhances hippocampal long-term potentiation and long-term contextual fear memory. SIN3A regulates the expression of genes encoding proteins in the post-synaptic density. Loss of SIN3A increases expression of the synaptic scaffold Homer1, alters the mGluR1α- and mGluR5-dependence of long-term potentiation, and increases activation of extracellular signal regulated kinase (ERK) in the hippocampus after learning. Our studies define a critical role for co-repressors in modulating neural plasticity and memory consolidation and reveal that Homer1/mGluR signaling pathways may be central molecular mechanisms for memory enhancement.
Authors
Morgan S. Bridi, Hannah Schoch, Cédrick Florian, Shane G. Poplawski, Anamika Banerjee, Joshua D. Hawk, Giulia S. Banks, Camille Lejards, Chang-Gyu Hahn, Karl Peter Giese, Robbert Havekes, Nelson Spruston, Ted Abel
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