(312) - Heat shock protein 90 promotes opioid anti-nociception in the brain and represses opioid anti-nociception in the spinal cord through the differential regulation of ERK MAPK signaling

Abstract

Opioid drugs are efficacious in treating moderate to severe acute and chronic pain, but are limited by serious side effects. Recent efforts to create biased opioids without these side effects by selectively engaging downstream signal transduction (e.g. βarrestin2) has been limited by our lack of knowledge of the mu opioid receptor (MOR) signaling complex. In our earlier work, we identified Heat shock protein 90 (Hsp90) as a novel MOR signaling regulator. We found that intracerebroventricular (icv) 17-AAG, a well-established Hsp90 inhibitor, strongly blocked or abolished morphine anti-nociception in paw incision and HIV neuropathy pain in mice. In our current work, we've extended from these findings to examine the role of Hsp90 in the spinal cord. In contrast to our findings in the brain, we found that intrathecal (it) .5 nmol 17-AAG for 24 hours in CD-1 mice caused strongly increased morphine anti-nociception in tail flick and paw incision pain (80.7–88.6% increase). This was confirmed using the alternate Hsp90 inhibitor KU-32 as well as Rotarod testing, ruling out off-target effects. We examined ERK MAPK signaling in the brain and spinal cord in response to opioids after 17-AAG inhibition, and found that ERK MAPK activation was lost in the brain, but potentiated in the spinal cord. By using icv and it administration of 5 µg U0126, a selective ERK inhibitor, we demonstrated that the effects of Hsp90 inhibition in the brain and spinal cord could be completely explained by ERK signaling changes. By using selective inhibitors, we further found that the molecular isoform Hsp90α and the co-chaperones p23 and Cdc37 (but not Aha1) were responsible for the signaling and anti-nociception changes observed in the brain. Overall, these results demonstrate different regional effects of Hsp90 and ERK signaling that have a strong impact on opioid anti-nociception, which could be used to improve opioid drug discovery.