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The Journal of Neuroscience, February 25, 2009, 29(8):2534-2544; doi:10.1523/JNEUROSCI.5865-08.2009

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Cellular/Molecular
Morphine Increases Brain Levels of Ferritin Heavy Chain Leading to Inhibition of CXCR4-Mediated Survival Signaling in Neurons

Rajarshi Sengupta,^1 * Silvia Burbassi,^1 * Saori Shimizu,¹ Silvia Cappello,² Richard B. Vallee,² Joshua B. Rubin,³ and Olimpia Meucci¹

¹Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, ²Department of Pathology, Columbia University Medical Center, New York, New York 10032, and ³Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110

Correspondence should be addressed to Dr. Olimpia Meucci, Department of Pharmacology and Physiology, Drexel University College of Medicine, 245 North 15th Street, Philadelphia, PA 19102. Email: omeucci{at}drexelmed.edu

This study focuses on the effect of µ-opioid receptor agonists on CXCR4 signaling in neurons and the mechanisms involved in regulation of neuronal CXCR4 by opiates. The data show that CXCR4 is negatively modulated by long-term morphine treatments both in vitro and in vivo; CXCR4 inhibition is caused by direct stimulation of µ-opioid receptors in neurons, leading to alterations of ligand-induced CXCR4 phosphorylation and upregulation of protein ferritin heavy chain (FHC), a negative intracellular regulator of CXCR4. Reduced coupling of CXCR4 to G-proteins was found in the brain of morphine-treated rats, primarily cortex and hippocampus. CXCR4-induced G_i/Gβ activities were suppressed after 24 h treatment of cortical neurons with morphine or the selective µ-opioid agonist DAMGO (D-Ala2-N-Me-Phe⁴-glycol⁵-enkephalin), as shown by analysis of downstream targets of CXCR4 (i.e., cAMP, Akt, and ERK1/2). These agonists also prevented CXCL12-induced phosphorylation of CXCR4, indicating a deficit of CXCR4 activation in these conditions. Indeed, morphine (or DAMGO) inhibited prosurvival signaling in neurons. These effects are not attributable to a reduction in CXCR4 expression or surface levels but rather to upregulation of FHC by opioids. The crucial role of FHC in inhibition of neuronal CXCR4 was confirmed by in vitro and in vivo RNA interference studies. Overall, these findings suggest that opiates interfere with normal CXCR4 function in the brain. By this mechanism, opiates could reduce the neuroprotective functions of CXCR4 and exacerbate neuropathology in opiate abusers who are affected by neuroinflammatory/infectious disorders, including neuroAIDS.

Key words: ferritin; opioids; chemokine; neurons; HIV; GPCRs

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Received Dec. 10, 2008; revised Jan. 15, 2009; accepted Jan. 22, 2009.

Correspondence should be addressed to Dr. Olimpia Meucci, Department of Pharmacology and Physiology, Drexel University College of Medicine, 245 North 15th Street, Philadelphia, PA 19102. Email: omeucci{at}drexelmed.edu

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