Opioid dependence plays a major role in abuse of these drugs and is a concern in the clinic. It is important to understand mechanisms underlying dependence if we are to improve the treatment of pain and to treat and/or prevent opioid abuse. Acutely, mu- opioids activate Gai/o proteins to inhibit adenylyl cyclase, but following chronic treatment dependence can be demonstrated at the cellular level by the compensatory increase in adenylyl cyclase activation, referred to as sensitization. The objective of this project is to better understand the mechanisms of the development of dependence at the cellular level, particularly how the compensatory changes in adenylyl cyclase are modulated by co-localization with other signaling proteins in plasma membrane microdomains referred to as lipid rafts. Mu-opioid receptors are found in lipid rafts and the adenylyl cyclase isoforms which are sensitized tend to be localized in lipid rafts, while some signaling proteins which have a role in sensitization are able to relocalize into or out of lipid rafts. To determine the role of lipid rafts in the development and expression of mu-opioid mediated adenylyl cyclase sensitization, we will: 1) Examine the distribution of mu-opioid signaling components in lipid rafts and non-raft fractions and develop assays to measure their function. 2) Prepare lipid-raft enriched and non-raft plasma membrane fractions from cells treated with mu-opioid agonist to compare sensitization of adenylyl cyclase and determine if changes in sensitization are related to relocalization of signaling proteins into or out of lipid rafts. 3) Determine if lipid rafts play a necessary role in adenylyl cyclase sensitization across different receptors and in different cell types. Changes occur in signaling proteins, such as adenylyl cyclase, in membranes of neuronal cells following long term exposure to opioid drugs, such as morphine or heroin. These compensatory changes result in withdrawal on removal of the opioid. To better treat and prevent opioid dependence, the goal is to understand the mechanisms causing these changes, particularly in relation to the location of modulatory signaling proteins in or out of cell membrane microdomains referred to as lipid rafts. ? ?
| Levitt, Erica S; Clark, Mary J; Jenkins, Paul M et al. (2009) Differential effect of membrane cholesterol removal on mu- and delta-opioid receptors: a parallel comparison of acute and chronic signaling to adenylyl cyclase. J Biol Chem 284:22108-22 |
