Osteoarthritis (OA) pain remains a major clinical problem. It is urgent to identify novel therapeutic approaches for OA pain states. Bromodomain and extraterminal (BET) protein inhibitors have robust anti-inflammatory effects in several pain models. However, the underlying mechanisms of these inhibitors in OA pain are yet to be determined. We, therefore, investigate the efficacy of BET inhibition on pain-related behaviors in a rat model of monosodium iodoacetate (MIA)-induced osteoarthritis pain and their underlying mechanisms.OA was established by intra-articular injection of MIA in rat knees. Pain behaviors were assessed in rats by hindlimb weight-bearing asymmetry, mechanical allodynia, and thermal hyperalgesia. Possible mechanisms underlying BET inhibition were explored in the MIA-induced OA pain model in the spinal cord and dorsal root ganglia (DRG).Inhibiting bromodomain-containing protein 4 (Brd4) with either JQ1 or MS417 or AAV2/9-shRNA-Brd4-EGFP-mediated knockdown of Brd4 genes significantly attenuated MIA-induced pain behaviors. Brd4 inhibition suppressed nuclear factor-kappa B (NF-κB) and NF-κB-mediated inflammatory cytokines both in the spinal cord and DRG in MIA-induced OA pain rats. Brd4 inhibition also attenuated the oxidative stress and promoted nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent antioxidant genes both in the spinal cord and DRG in MIA-induced OA pain rats.In conclusion, Brd4 inhibition alleviates MIA-induced OA pain via suppression of neuroinflammation and activation of Nrf2-mediated antioxidant signaling. Though the model used in this work doesn't perfectly represent how OA develops in humans, Brd4 inhibition may provide novel insights into the treatment of OA pain.This article is protected by copyright. All rights reserved.