Neurokinin 1 Receptors Regulate Morphine-Induced Endocytosis and Desensitization of μ-Opioid Receptors in CNS Neurons

Abstract

-Opioid receptors (MORs) are G-protein-coupled receptors (GPCRs) that mediate the physiological effects of endogenous opioid neuropeptides and opiate drugs such as morphine. MORs are coexpressed with neurokinin 1 receptors (NK1Rs) in several regions of the CNS that control opioid dependence and reward. NK1R activation affects opioid reward specifically, however, and the cellular basis for this specificity is unknown. We found that ligand-induced activation of NK1Rs produces a cell-autonomous and nonreciprocal inhibition of MOR endocytosis induced by diverse opioids. Studies using epitope-tagged receptors expressed in cultured striatal neurons and a neuroblastoma cell model indicated that this heterologous regulation is mediated by NK1R-dependent sequestration of arrestins on endosome membranes. First, endocytic inhibition mediated by wild-type NK1Rs was overcome in cells overexpressing ␤-arrestin2, a major arrestin isoform expressed in striatum. Second, NK1R activation promoted sequestration of ␤-arrestin2 on endosomes, whereas MOR activation did not. Third, heterologous inhibition of MOR endocytosis was prevented by mutational disruption of ␤-arrestin2 sequestration by NK1Rs. NK1R-mediated regulation of MOR trafficking was associated with reduced opioid-induced desensitization of adenylyl cyclase signaling in striatal neurons. Furthermore, heterologous regulation of MOR trafficking was observed in both amygdala and locus ceruleus neurons that naturally coexpress these receptors. These results identify a cell-autonomous mechanism that may underlie the highly specific effects of NK1R on opioid signaling and suggest, more generally, that receptor-specific trafficking of arrestins may represent a fundamental mechanism for coordinating distinct GPCR-mediated signals at the level of individual CNS neurons.

Expression of tachykinin receptors (tacr1a and tacr1b) in zebrafish: influence of cocaine and opioid receptors

“…As DOR and MOR interact (in the cell membrane) and DOR modulates the function of MOR (Gomes et al 2004), TACRs (via MOR or indirectly via DOR) would modulate the activity of the opioid receptors. In this study, the knockdown of ZfDOR2 and ZfMOR regulated the expression of tacr1a and tacr1b respectively, indicating that tachykinin and the opioid systems are closely interrelated in zebrafish, as has been described in mammals (Minami et al 1995, Pfeiffer et al 2003, Guan et al 2005, Yu et al 2009). As the set of MOs of opioid receptors was effective, as previously demonstrated by Sanchez-Simon et al (2010), and replicated in our study, we are convinced that the changes on the expression of the TACRs are a consequence of the downregulation of the opioid receptors.…”

“…expression (of Tacr1a and Tacr1b) in whole-mount zebrafish embryos in one stage of embryonic development (48 hpf) while the other studies were done in adult rats and mice. Also, several studies have described that TACR1/MOR functionally interact and mediate the regulation of MOR-TACR1 trafficking, where the activation of TACR1 by SP can induce or inhibit the endocytosis of MOR (Pfeiffer et al 2003, Yu et al 2009). Our results show that downregulation of ZfMOR increases the expression of tacr1b, suggesting that MOR could be positively regulating TACR1.…”

“…Moreover, in vitro experiments reported that MOR and NK 1 R form heterodimers in HEK-293 (NK 1 -MOR) where the activation of either type, by SP and DAMGO respectively, induces endocytosis (Pfeiffer et al 2003). Besides, it has also been described that NK 1 R activation by SP inhibits the endocytosis of MOR (Yu et al 2009), indicating that SP and its receptor are involved in the modulation of MOR. Several studies have also shown that tachykinin and opioid systems are related in the addiction process, as NK 1 R and MOR are localized in different reward-related regions (Nakaya et al 1994, Pickel et al 2000, Garzó n & Pickel 2001, Gadd et al 2003, Laurent et al 2012.…”

Opioid Regulation of Mu Receptor Internalisation: Relevance to the Development of Tolerance and Dependence

“…These authors demonstrated, firstly in HEK293 cells, that the chimeric mu-delta receptor construct previously described predominantly in recycling endocytic vesicles [53]. Another recent report has described the regulation of mu receptor endocytosis and desensitisation by NK1 neurokinin receptors [54].…”

“…In addition, this heterologous pairing also resulted in a functionally significant attenuation of morphine-induced desensitisation of mu receptor signalling via adenylyl cyclases. Studies involving over-expression of β-arrestin 2-GFP and a neurokinin 1 receptor mutant unable to interact with β-arrestin2 indicated that the negative modulation of mu receptor endocytosis by 21 the neurokinin 1 receptor might be achieved by sequestering arrestins in endosomes and hence limited their availability to interact with the mu receptor [54].…”