Nociceptin/Orphanin FQ (NOP) receptor is differentially expressed on glial cells

Abstract

Glial cells constitute the majority of the cellular components of the CNS. They are involved in a wide range of physiological and pathological conditions including immunomodulation, neuropathic pain, and opioid tolerance1. Opioid receptors are classified into classical (MOP, DOP and KOP) and non-classical (NOP). NOP receptor has been found to play a central role in pain processing and opioid tolerance2. In this study, we screened for the expression and function of the NOP receptor on glial cell lines. The pattern of NOP receptor expression at the level mRNA (qPCR)3 and protein ([leucyl-3H] N/OFQ saturation binding)4 was studied in a range of glial cell lines including 1321N1 human astrocytes, C6 rat astrocytes, MO3.13 human oligodendrocytes, HOG human oligodendrocytes, and EOC-20 mouse microglia. NOP receptor activity was assessed using a scratch wound healing/cell migration assay at a fixed time of 30 hours5. 1231N1, MO3.13, and HOG but not EOC-20 cells expressed NOP mRNA6. In addition, C6 cell lines were found to express NOP receptor mRNA. Furthermore, 1231N1, MO3.13 and HOG expressed NOP protein in a radioligand binding assay. Highest expression of mRNA was in MO3.13 and in radioligand binding was in HOG and 1321N16. In lines that expressed NOP receptor protein, we assessed the activity of N/OFQ, a structurally inactive derivative (desPhe1-N/OFQ) and the metabolically stable derivative PWT-N/OFQ. In both astrocytes (1321N1) and oligodendrocytes (MO3.13 and HOG) N/OFQ and PWT-N/OFQ but not desPhe1-N/OFQ (all at 1μM) reduced wound healing (migration), Table 1. NOP receptor is differentially expressed in a range of glial cell lines where it was functionally active. Interestingly there is no expression on microglia. Further studies in primary glial cell cultures are underway.Table 1The effect of NOP ligands on wound healing /cell migration of glial cells, data (% wound healing) from n=5, * = P≤0.05 after 30 hrs compared to control (ANOVA)Cell typeControlN/OFQPWT-N/OFQdesPhe1-N/OFQ1321N1 astrocytes55.6±2.042.5±5.8*35.8±1.8*50.0±1.8MO3.13 oligodendrocytes31.1±2.722.0±0.7*21.0±1.9*29.0±2.9HOG oligodendrocytes33.5±3.226.1±2.5*24.8±3.4*30.6±3.7 Open table in a new tab This work is sponsored by the Higher Committee for Education Development in Iraq HCED/Office of the Prime Minister/Iraq. Peptides were provided by Drs R Guerrini and G Calo/University of Ferrara /Italy. 1.Giaume et al. Cell Death Differ. 2007; 14: 1324–35.2.Lambert. Nat Rev Drug Discov. 2008; 7: 694–710.3.McDonald et al. Br J Anaesth. 2010; 104: 698–704.4.McDonald et al. Br J Pharmacol. 2003; 140: 61–70.5.Available from https://www2.le.ac.uk/colleges/medbiopsych/facilities-and-services/cbs/AIF/tips-and-tricks-1/wound-healing-assay.6.Available from https://www.bna.org.uk/static/uploads/resources/BNA2017_ABSTRACT_BOOK_SAGE_FINAL.pdf.