Hippocampal PKR/NLRP1 Inflammasome Pathway Is Required for the Depression-Like Behaviors in Rats with Neuropathic Pain.

The chronic neuropathic pain-associated psychiatric disorders have seriously disturbed the quality of patients' life, such as depression and anxiety. Neuroinflammation in the hippocampus plays an important role in the neuropathic pain-associated depressive and anxiety disorders, but the underlying mechanism has not been thoroughly elucidated to date. The Nod-like receptor protein (NLRP)-1 inflammasome, which controls the production of pro-inflammatory cytokines, was broadly involved in the neuroinflammation-related diseases. In the present study, we show that the NLRP1 inflammasome is significantly activated in the hippocampus of rats subjected to the chronic constriction injury (CCI)-induced neuropathic pain. Inhibiting the product of NLRP1 inflammasome not only attenuated the depression-like behaviors but also suppressed the production of mature IL-1ß in the hippocampus of CCI rats. The double-stranded RNA-dependent protein kinase (PKR, also known as EIF2AK2) has been recently shown to be a pivotal regulator for the activation of inflammasome. In the rats subjected to CCI neuropathic pain, the PKR was simultaneously activated in hippocampus. Functional inhibition of PKR suppressed the NLRP1 inflammasome activation and effectively attenuated the CCI-induced depression-like behaviors. These results indicate that the hippocampal PKR/NLRP1 inflammasome pathway play an important role in the development of the depressive behaviors after chronic neuropathic pain. Thus, interrupting this pathway might provide a novel therapeutic strategy for neuropathic pain-associated depressive disorders.