Morphine-induced trafficking of a mu-opioid receptor interacting protein in rat locus coeruleus neurons

Abstract

Opiate addiction is a devastating health problem, with approximately 2 million people currently addicted to heroin or non-medical prescription opiates in the United States alone. In neurons, adaptations in cell signaling cascades develop following opioid actions at the mu opioid receptor (MOR). A novel putative target for intervention involves interacting proteins that may regulate trafficking of MOR. Morphine has been shown to induce a re-distribution of a MOR-interacting protein Wntless (WLS, a transport molecule necessary for secretion of neurotrophic Wnt proteins), from cytoplasmic to membrane compartments in rat striatal neurons. Given its opiate-sensitivity and its well-characterized molecular and cellular adaptations to morphine exposure, we investigated the anatomical distribution of WLS and MOR in the rat locus coeruleus (LC)-norepinephrine (NE) system. Dual immunofluorescence microscopy was used to test the hypothesis that WLS is localized to noradrenergic neurons of the LC and that WLS and MOR co-exist in common LC somatodendritic processes, providing an anatomical substrate for their putative interactions. We also hypothesized that morphine would influence WLS distribution in the LC. Rats received saline, morphine or the opiate agonist [D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO), and tissue sections through the LC were processed for immunogold-silver detection of WLS and MOR. Statistical analysis showed a significant re-distribution of WLS to the plasma membrane following morphine treatment in addition to an increase in the proximity of gold-silver labels for MOR and WLS. Following DAMGO treatment, MOR and WLS were predominantly localized within the cytoplasmic compartment when compared to morphine and control. In a separate cohort of rats, brains were obtained from saline-treated or heroin self-administering male rats for pulldown co-immunoprecipitation studies. Results showed an increased association of WLS and MOR following heroin exposure. As the LC-NE system is important for cognition as well as decisions underlying substance abuse, adaptations in WLS trafficking and expression may play a role in modulating MOR function in the LC and contribute to the negative sequelae of opiate exposure on executive function.

Dopamine D3R antagonist VK4-116 attenuates oxycodone self-administration and reinstatement without compromising its antinociceptive effects

“…Growing evidence suggests that the noradrenergic locus coeruleus (LC) is a major brain site involved in the onset of opioid withdrawal [41,42]. Neurons in the LC possess a high density of μ opioid receptors (MORs) [43]. When opioids bind to MORs in the LC, they suppress neuronal activity by inhibiting adenylyl cyclase-resulting in physical symptoms such as drowsiness, slow respiration, and low blood pressure [42].…”

Alternative splicing of the Wnt trafficking protein, Wntless and its effects on protein-protein interactions

“…Similarly, we have previously shown that Wls interacts with the MOR, DOR, and cannabinoid receptors type 1 and 2 albeit through different regions of the proteins (C-tail of Wls with IL2 of opioid receptors) [34, 36]. Opioid drug-induced internalization of MOR also drives the internalization of Wls in cells and in rat striatal dendrites [32, 54]. Morphine, an opioid agonist that delays MOR internalization, increases cell surface localization of Wls and decreases Wls recycling, resulting in an overall decrease in Wnt secretion [32–34, 54].…”

“…Opioid drug-induced internalization of MOR also drives the internalization of Wls in cells and in rat striatal dendrites [32, 54]. Morphine, an opioid agonist that delays MOR internalization, increases cell surface localization of Wls and decreases Wls recycling, resulting in an overall decrease in Wnt secretion [32–34, 54]. Future studies will assess whether GPM6a alters the constitutive recycling of Wls and whether GPM6a is important for co-internalization of Wls and MOR in cells treated with opioids that promote robust internalization.…”

Pentazocine Protects SN4741 Cells Against MPP+-Induced Cell Damage via Up-Regulation of the Canonical Wnt/β-Catenin Signaling Pathway

“…Furthermore, morphine has been showed to induce the secretion of Wnt signaling proteins (Jaremko et al, 2014). Besides, the opioids have many beneficial roles against the damage in central nervous system (Cui et al, 2011).…”