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A mitogen-activated protein kinase pathway is required for mu-opioid receptor desensitization
R D Polakiewicz1, S M Schieferl, L F Dorner
1Cell Signaling Laboratory, New England Biolabs, Beverly, Massachusetts 01915, USA. polakiew@neb.com
Abstract:
The mu-opioid receptor mediates not only the beneficial painkilling effects of opiates like morphine but also the detrimental effects of chronic exposure such as tolerance and dependence. Different studies have linked tolerance to opioid receptor desensitization. Agonist activation of the mu-opioid receptor stimulates a mitogen-activated protein kinase (MAPK) activity, but the functional significance of this pathway remains unclear. We have focused on the MAPK signaling cascade to study mu-opioid receptor desensitization. We report that inhibition of the MAPK pathway blocks desensitization of mu-opioid receptor signaling as well as the loss of receptor density due to internalization. Our results suggest that a feedback signal emanating from the MAPK cascade is required for mu-opioid receptor desensitization.
Insights
The mu-opioid receptor (MOR) pathway is crucial for opiate effects. Inhibiting the mitogen-activated protein kinase (MAPK) pathway blocks MOR desensitization and receptor loss, suggesting MAPK signaling is key to tolerance.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- The mu-opioid receptor (MOR) mediates opiate effects, including pain relief and adverse outcomes like tolerance and dependence.
- Opioid tolerance is often linked to receptor desensitization, a process where receptor signaling diminishes with prolonged exposure.
- Mitogen-activated protein kinase (MAPK) pathways are activated by MOR agonists, but their role in desensitization is not fully understood.
Purpose of the Study:
- To investigate the role of the MAPK signaling cascade in mu-opioid receptor desensitization.
- To determine if inhibiting MAPK activity affects MOR signaling and receptor density.
Main Methods:
- Focusing on the MAPK signaling cascade in cellular models.
- Utilizing pharmacological inhibitors to block MAPK pathway activity.
- Measuring MOR signaling and receptor internalization following agonist stimulation.
Main Results:
- Inhibition of the MAPK pathway effectively blocked the desensitization of mu-opioid receptor signaling.
- Blocking MAPK activity also prevented the loss of receptor density caused by internalization.
- These findings indicate a critical role for MAPK in MOR desensitization.
Conclusions:
- The MAPK signaling cascade is essential for mu-opioid receptor desensitization.
- A feedback signal originating from the MAPK pathway is required for MOR desensitization and the development of tolerance.
- Targeting the MAPK pathway may offer strategies to mitigate opioid tolerance.