AAV-glycine receptor α3 alleviates CFA-induced inflammatory pain by downregulating ERK phosphorylation and proinflammatory cytokine expression in SD rats.

BACKGROUND

Glycine receptors (GlyRs) play key roles in the processing of inflammatory pain. The use of adeno-associated virus (AAV) vectors for gene therapy in human clinical trials has shown promise, as AAV generally causes a very mild immune response and long-term gene transfer, and there have been no reports of disease. Therefore, we used AAV for GlyRα1/3 gene transfer in F11 neuron cells and into Sprague-Dawley (SD) rats to investigate the effects and roles of AAV-GlyRα1/3 on cell cytotoxicity and inflammatory response.

METHODS

In vitro experiments were performed using plasmid adeno-associated virus (pAAV)-GlyRα1/3-transfected F11 neurons to investigate the effects of pAAV-GlyRα1/3 on cell cytotoxicity and the prostaglandin E2 (PGE2)-mediated inflammatory response. In vivo experiment, the association between GlyRα3 and inflammatory pain was analyzed in normal rats after AAV-GlyRα3 intrathecal injection and after complete Freund's adjuvant (CFA) intraplantar administration. Intrathecal AAV-GlyRα3 delivery into SD rats was evaluated in terms of its potential for alleviating CFA-induced inflammatory pain.

RESULTS

The activation of mitogen-activated protein kinase (MAPK) inflammatory signaling and neuronal injury marker activating transcription factor 3 (ATF-3) were evaluated by western blotting and immunofluorescence; the level of cytokine expression was measured by ELISA. The results showed that pAAV/pAAV-GlyRα1/3 transfection into F11 cells did not significantly reduce cell viability or induce extracellular signal-regulated kinase (ERK) phosphorylation or ATF-3 activation. PGE2-induced ERK phosphorylation in F11 cells was repressed by the expression of pAAV-GlyRα3 and administration of an EP2 inhibitor, GlyRαs antagonist (strychnine), and a protein kinase C inhibitor. Additionally, intrathecal AAV-GlyRα3 administration to SD rats significantly decreased CFA-induced inflammatory pain and suppressed CFA-induced ERK phosphorylation, did not induce obvious histopathological injury but increased ATF-3 activation in dorsal root ganglion (DRGs).

CONCLUSIONS

Antagonists of the prostaglandin EP2 receptor, PKC, and glycine receptor can inhibit PGE2-induced ERK phosphorylation. Intrathecal AAV-GlyRα3 administration to SD rats significantly decreased CFA-induced inflammatory pain and suppressed CFA-induced ERK phosphorylation, did not significantly induce gross histopathological injury but elicited ATF-3 activation. We suggest that PGE2-induced ERK phosphorylation can be modulated by GlyRα3, and AAV-GlyRα3 significantly downregulated CFA-induced cytokine activation.