Endosomal signaling of delta opioid receptors is an endogenous mechanism and therapeutic target for relief from inflammatory pain

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 26; pp. 15281 - 15292
• Main Authors: Jimenez-Vargas, Nestor N., Gong, Jing, Wisdom, Matthew J., Jensen, Dane D., Latorre, Rocco, Hegron, Alan, Teng, Shavonne, DiCello, Jesse J., Rajasekhar, Pradeep, Veldhuis, Nicholas A., Carbone, Simona E., Yu, Yang, Lopez-Lopez, Cintya, Jaramillo-Polanco, Josue, Canals, Meritxell, Reed, David E., Lomax, Alan E., Schmidt, Brian L., Leong, Kam W., Vanner, Stephen J., Halls, Michelle L., Bunnett, Nigel W., Poole, Daniel P.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 30.06.2020
• Subjects: Activation; Agonists; Animals; Biological Sciences; Biopsy; Colitis; Colon; Colon - innervation; Cytosol; Endocytosis; Endosomes; Enkephalin, Leucine-2-Alanine - administration & dosage; Enkephalin, Leucine-2-Alanine - pharmacology; Excitability; Extracellular signal-regulated kinase; G protein-coupled receptors; HEK293 Cells; Humans; Inflammation; Inflammation - complications; Kinases; Membranes; Metabolic pathways; Mice; Mucosa; Nanoparticles; Nanoparticles - administration & dosage; Narcotics; Neurons; Nociceptors; Nociceptors - metabolism; Opioid receptors (type delta); Pain; Pain - drug therapy; Pain - metabolism; Pain perception; Protein kinase C; Proteins; Receptors; Receptors, Opioid, delta - agonists; Receptors, Opioid, delta - metabolism; Signal processing; Signal Transduction - drug effects; Signal Transduction - physiology; Signaling; Silica; Silicon dioxide; Therapeutic applications; nanomedicine; pain; G protein-coupled receptors; signaling; inflammation
• DOI: 10.1073/pnas.2000500117
• ISSN: 0027-8424

Whether G protein-coupled receptors signal from endosomes to control important pathophysiological processes and are therapeutic targets is uncertain. We report that opioids from the inflamed colon activate δ-opioid receptors (DOPr) in endosomes of nociceptors. Biopsy samples of inflamed colonic mucosa from patients and mice with colitis released opioids that activated DOPr on nociceptors to cause a sustained decrease in excitability. DOPr agonists inhibited mechanically sensitive colonic nociceptors. DOPr endocytosis and endosomal signaling by protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) pathways mediated the sustained inhibitory actions of endogenous opioids and DOPr agonists. DOPr agonists stimulated the recruitment of Gαi/o and β-arrestin1/2 to endosomes. Analysis of compartmentalized signaling revealed a requirement of DOPr endocytosis for activation of PKC at the plasma membrane and in the cytosol and ERK in the nucleus. We explored a nanoparticle delivery strategy to evaluate whether endosomal DOPr might be a therapeutic target for pain. The DOPr agonist DADLE was coupled to a liposome shell for targeting DOPr-positive nociceptors and incorporated into a mesoporous silica core for release in the acidic and reducing endosomal environment. Nanoparticles activated DOPr at the plasma membrane, were preferentially endocytosed by DOPr-expressing cells, and were delivered to DOPr-positive early endosomes. Nanoparticles caused a long-lasting activation of DOPr in endosomes, which provided sustained inhibition of nociceptor excitability and relief from inflammatory pain. Conversely, nanoparticles containing a DOPr antagonist abolished the sustained inhibitory effects of DADLE. Thus, DOPr in endosomes is an endogenous mechanism and a therapeutic target for relief from chronic inflammatory pain.