title: Engagement of the GABA to KCC2 signaling pathway contributes to the analgesic effects of A3AR agonists in neuropathic pain.
abstract: More than 1.5 billion people worldwide suffer from chronic pain, yet current treatment strategies often lack efficacy or have deleterious side effects in patients. Adenosine is an inhibitory neuromodulator that was previously thought to mediate antinociception through the A1 and A2A receptor subtypes. We have since demonstrated that A3AR agonists have potent analgesic actions in preclinical rodent models of neuropathic pain and that A3AR analgesia is independent of adenosine A1 or A2A unwanted effects. Herein, we explored the contribution of the GABA inhibitory system to A3AR-mediated analgesia using well-characterized mouse and rat models of chronic constriction injury (CCI)-induced neuropathic pain. The deregulation of GABA signaling in pathophysiological pain states is well established: GABA signaling can be hampered by a reduction in extracellular GABA synthesis by GAD65 and enhanced extracellular GABA reuptake via the GABA transporter, GAT-1. In neuropathic pain, GABAAR-mediated signaling can be further disrupted by the loss of the KCC2 chloride anion gradient. Here, we demonstrate that A3AR agonists (IB-MECA and MRS5698) reverse neuropathic pain via a spinal mechanism of action that modulates GABA activity. Spinal administration of the GABAA antagonist, bicuculline, disrupted A3AR-mediated analgesia. Furthermore, A3AR-mediated analgesia was associated with reductions in CCI-related GAD65 and GAT-1 serine dephosphorylation as well as an enhancement of KCC2 serine phosphorylation and activity. Our results suggest that A3AR-mediated reversal of neuropathic pain increases modulation of GABA inhibitory neurotransmission both directly and indirectly through protection of KCC2 function, underscoring the unique utility of A3AR agonists in chronic pain.
authors: Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104.
authors: Amanda
authors: A
authors: Ford
authors: Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada.
authors: Annie
authors: 0000-0001-8065-3359
authors: A
authors: Castonguay
authors: Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada.
authors: Martin
authors: 0000-0002-2790-7046
authors: M
authors: Cottet
authors: Department of Surgery, Center for Anatomical Science and Education, St. Louis University School of Medicine, St. Louis, Missouri 63104.
authors: Joshua W
authors: JW
authors: Little
authors: Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104.
authors: Zhoumou
authors: Z
authors: Chen
authors: Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5050, and.
authors: Ashley M
authors: 0000-0001-7353-5047
authors: AM
authors: Symons-Liguori
authors: Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104.
authors: Timothy
authors: T
authors: Doyle
authors: Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104.
authors: Terrance M
authors: TM
authors: Egan
authors: Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5050, and.
authors: Todd W
authors: TW
authors: Vanderah
authors: Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada.
authors: Yves
authors: Y
authors: De Koninck
authors: Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810.
authors: Dilip K
authors: DK
authors: Tosh
authors: Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810.
authors: Kenneth A
authors: 0000-0001-8104-1493
authors: KA
authors: Jacobson
authors: Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104, salvemd@slu.edu.
authors: Daniela
authors: D
authors: Salvemini
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D058909:Adenosine A3 Receptor Agonists / Q000627:therapeutic use*; D000700:Analgesics / Q000627:therapeutic use*; D000818:Animals; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D006930:Hyperalgesia / Q000188:drug therapy / Q000209:etiology; D008297:Male; D051379:Mice; D017288:Pain Threshold / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism; D012585:Sciatica / Q000150:complications / Q000188:drug therapy*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013126:Spinal Nerve Roots / Q000378:metabolism / Q000473:pathology; D027981:Symporters / Q000378:metabolism*; D013844:Thiazoles / Q000494:pharmacology / Q000627:therapeutic use; D013864:Thioglycolates / Q000494:pharmacology / Q000627:therapeutic use; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D000096922:K Cl- Cotransporters
chemical_list: D000241:Adenosine; D058909:Adenosine A3 Receptor Agonists; D000700:Analgesics; D011725:Pyridines; D011963:Receptors, GABA-A; D027981:Symporters; D013844:Thiazoles; D013864:Thioglycolates; D005680:gamma-Aminobutyric Acid; D000096922:K Cl- Cotransporters; C419146:2,3-diethyl-4,5-dipropyl-6-phenylpyridine-3-thiocarboxylate-5-carboxylate; C572191:N-(4-methylthiazol-2-yl)-2-(6-phenylpyridazin-3-ylthio)acetamide; C084956:N(6)-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine
keywords: GABA; KCC2; adenosine; adenosine receptors; neuropathic pain