Activation of spinal PGC-1α regulates microglial polarization through a feedback loop between ROS-mediated mitochondrial dysfunction and the NLRP3 inflammasome in neuropathic pain

Background: An imbalance in microglial polarization plays an important role in the pathogenesis of neuropathic pain. PPARγ coactivator-1α (PGC-1α), a master coregulator of gene expression in mitochondrial biogenesis, is related to microglial polarization. However, the underlying mechanism involved is poorly understood.The aim of the present study was to explore the role of PGC-1α in regulating microglial polarization through a feedback loop between Reactive Oxygen Species (ROS)-mediated mitochondrial dysfunction and the NOD-like Receptor family pyrin domain containing 3 (NLRP3) inflammasome in a rat model of chronic constriction injury (CCI).

Methods: we quantified pain behavior after CCI; analysed the localization of PGC-1α and the changes in the expression of CD68 (an M1 microglial marker)/IBA1 and ARG1 (an M2 microglial marker)/IBA1 in the dorsal horn (DH) via immunofluorescence. Western blotting and immunofluorescence were used to examine the expression of target proteins. Quantitative Real-Time PCR (qPCR) was used to investigate the mitochondrial DNA copy number (mtDNA). ROS production was measured via dihydroethidium (DHE). SOD activity and the MDA content were measured via SOD and MDA assay kits, respectively. In addition, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6 and IL-10 levels were measured via enzyme-linked immunosorbent assay (ELISA).

Results: The results revealed ROS-mediated mitochondrial dysfunction and NLRP3 inflammasome activation, microglia phenotype from the M2 to the M1 phenotype in the CCI rats.Interesting, ROS-mediated mitochondrial dysfunction is one of the critical mediators of NLRP3 inflammasome activation.NLRP3 inflammasome in turn cause ROS production and mitochondrial dysfunction, suggesting for the first time a feedback loop between ROS-mediated mitochondrial dysfunction and NLRP3 inflammasome in the neuropathic pain.The activation of PGC-1α shifts the microglial phenotype via the modulation of a feedback loop between ROS-mediated mitochondrial dysfunction and the NLRP3 inflammasome.

Conclusions: These findings indicate that activation of PGC-1α could be a potential therapeutic approach to ameliorate neuropathic pain.

Microglia polarization; NLRP3 inflammasome; Neuroinflammation; PGC-1α; ROS.