Drug-Induced HSP90 Inhibition Alleviates Pain in Monoarthritic Rats and Alters the Expression of New Putative Pain Players at the DRG
Purinergic receptors (P2XRs) have been widely associated with pain states mostly due to their involvement in neuron–glia communication. Interestingly, we have previously shown that satellite glial cells (SGC), surrounding dorsal root ganglia (DRG) neurons, become activated and proliferate during monoarthritis (MA) in the rat. Here, we demonstrate that P2X7R expression increases in ipsilateral DRG after 1 week of disease, while P2X3R immunoreactivity decreases. We have also reported a significant induction of the activating transcriptional factor 3 (ATF3) in MA. In this study, we show that ATF3 knocked down in DRG cell cultures does not affect the expression of P2X7R, P2X3R, or glial fibrillary acidic protein (GFAP). We suggest that P2X7R negatively regulates P2X3R, which, however, is unlikely mediated by ATF3. Interestingly, we found that ATF3 knockdown in vitro induced significant decreases in the heat shock protein 90 (HSP90) expression. Thus, we evaluated in vivo the involvement of HSP90 in MA and demonstrated that the HSP90 messenger RNA levels increase in ipsilateral DRG of inflamed animals. We also show that HSP90 is mostly found in a cleaved form in this condition. Moreover, administration of a HSP90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), attenuated MA-induced mechanical allodynia in the first hours. The drug also reversed the HSP90 upregulation and cleavage. 17-DMAG seemed to attenuate glial activation and neuronal sensitization (as inferred by downregulation of GFAP and P2X3R in ipsilateral DRG) which might correlate with the observed pain alleviation. Our data indicate a role of HSP90 in MA pathophysiology, but further investigation is necessary to clarify the underlying mechanisms.
KeywordsJoint inflammatory pain DRG neurons ATF3 P2X receptors SGC activation HSP90 inhibition
The study was supported by the Chair on Pain Medicine of the Faculty of Medicine, University of Porto and by the Grünenthal Foundation—Portugal. The first author DSMN received a doctoral grant (SFRH/BD/79497/2011) by Fundação para a Ciência e a Tecnologia (FCT), Portugal. CSP was also supported by a post-doctoral grant (SFRH/BPD/87537/2012) from FCT. The authors would also like to thank José Pedro Castro (from Deutsches Institut für Ernährungsforschung Potsdam-Rehbrücke; Germany) and Francisco Nóvoa Faria (from Dept. Fisiologia e Cirurgia Cardiotorácica, CIM-FMUP) for their help and expertise concerning HSP90 fluorescent detection using LI-COR system.
Compliance with Ethical Standards
The experiments were authorized by the animal welfare body (ORBEA) of the Faculty of Medicine of the University of Porto. Procedures were carried out according to the European Communities Council Directive of September 22, 2010 (2010/63/EC), the ethical guidelines for investigation of experimental pain in animals  and the “Principles of laboratory animal care” (NIH publication no. 86-23, revised 1985).
Conflict of Interest
The authors declare that they have no conflict of interest.
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