Distribution of nociceptin/orphanin FQ receptor transcript in human central nervous system and immune cells

Abstract

We have examined the distribution of the opioid receptor-like-1 (ORL-1) transcript in the human CNS as well as human immune cells by RT-PCR and RNAse protection. The hORL-1 mRNA was distributed throughout the brain and particularly abundant in cortical areas, striatum, thalamus and hypothalamus. In the immune system, gene transcription was observed in normal circulating lymphocytes and monocytes as well as in T, B and monocytic cell lines. A splice variant, lacking 15 nucleotides at the junction between exon 1 and exon 2, showed a distribution similar to the already known ORL-1 transcript. Altogether these results show comparable expression levels of the hORL-1 gene in both nervous and immune systems, suggesting that the ORL-1-encoded receptor may participate to neuronal and non-neuronal physiological functions in humans.

Introduction

An opioid receptor-like (ORL-1) has recently been cloned on the basis of high homology to opioid receptors (Bunzow et al., 1994; Fukuda et al., 1994; Mollereau et al., 1994; Wang et al., 1994; Lachowicz et al., 1995; Pan et al., 1996). Since no binding with opioid ligands could be observed, this receptor was classified as an orphan receptor. Recently, a heptadecapeptide was purified from the mouse brain and proposed as the putative endogenous ligand for the receptor. This peptide, named nociceptin (Meunier et al., 1995) or orphanin FQ (Reinscheid et al., 1995), shows nanomolar affinity for the ORL-1 receptor and promotes a number of intracellular responses, including inhibition of adenylate cyclase (Meunier et al., 1995; Reinscheid et al., 1995), inhibition of calcium channels (Connor et al., 1996; Knoflach et al., 1996) and activation of inward rectifying K⁺ channels (Zhang and Yu, 1995; Matthes et al., 1996; Vaughan and Macdonald, 1996). The physiological role of this novel neurotransmitter system remains to be established. Distribution of nociceptin/orphanin FQ peptide and ORL-1 receptor has been extensively investigated in rodent brain (Bunzow et al., 1994; Fukuda et al., 1994; Mollereau et al., 1994; Lachowicz et al., 1995; Anton et al., 1996; Mollereau et al., 1996; Nothacker et al., 1996), where both peptide and receptor were shown to be abundantly expressed, suggesting that they may play a major functional role in the nervous system. Behavioural studies have shown that nociceptin/orphanin FQ affects locomotion (Reinscheid et al., 1995; Devine et al., 1996; Florin et al., 1996) and a role in nociception different from that of opioids has been proposed (Meunier et al., 1995; Reinscheid et al., 1995; Grisel et al., 1996; Mogil et al., 1996a). Involvement of nociceptin/orphanin FQ in peripheral functions has been recently documented (Calò et al., 1996; Gumusel et al., 1997; Kapusta et al., 1997) and some investigations have reported a role for nociceptin/orphanin FQ receptor in the immune system. Antisense oligonucleotides of the mouse ORL-1 have been shown to suppress in vitro polyclonal immunoglobulin production (Halford et al., 1995) and an upregulation of hORL-1 (human ORL-1) receptor mRNA has been observed when human peripheral blood lymphocytes (PBL) are stimulated in vitro (Wick et al., 1995). We have focused our efforts on human tissues and have extensively examined the distribution of hORL-1 transcript in the human central nervous system (CNS) as well as in immune cells. We report here that hORL-1 receptor is expressed in both systems at similar levels, indicating that it may act as an important mediator of both nervous and immune responses in humans.