P2X7 Receptor-Induced Bone Cancer Pain by Regulating Microglial Activity via NLRP3/IL-1beta Signaling

Bone cancer pain (BCP) is the most severe and intractable type of cancer pain. Emerging evidence has demonstrated that activated microglia in the spinal cord could release a series of neurotoxic substances to stimulate neurons and form neuronal sensitization. The P2X7 receptor (P2X7R) is a nonselective ATP-gated ion channel predominantly present in microglia in the spinal cord as the key modulator of microglial activity. However, the specific effect and underlying molecular mechanism of P2X7R in BCP have not yet been elucidated. Objectives: This study aimed at investigating whether P2X7R-induced BCP by regulating microglial activity through NLRP3/IL-1beta signaling involvement in BCP. Study design: Controlled animal study.

These findings suggest that targeting the microglial P2X7R activated NLRP3/IL-1beta signaling pathway could serve as a potential strategy for BCP treatment.

A BCP animal model was established by injecting Walker-256 breast cancer cells into the tibia of female rats. Fifty percent paw withdrawal thresholds (50% PWTs), number of spontaneous flinches (NSF), and limb use scores were used to evaluate behavior in rats. P2X7R inhibitor brilliant blue G (BBG) was used to assess the role of P2X7R in BCP-induced NLRP3 inflammasome activation. Western blot, RT-PCR, and immunofluorescence were used for quantitative comparison. In vitro, BV2 cells were treated with lipopolysaccharide (LPS) and BzATP, in the presence or absence of P2X7 siRNA, with nigericin (an agonist of the NLRP3 inflammasome) to further study the mechanism of P2X7R regulate NLRP3/IL-1beta signaling.

The inhibition of spinal P2X7R with BBG could effectively inhibit BCP due to suppressing the expression of NF-kappaB p-p65, NLRP3 inflammasome formation, and downstream pain factors IL-1beta. Furthermore, P2X7 siRNA could reduce microglial activity, the nuclear translocation of NF-kappaB, and the synthesis of NLRP3 and IL-1beta in BV2 cells. In addition, nigericin partially reversed the ameliorating effect of P2X7 siRNA on BV2 cells induced by LPS and BzATP. Limitations: BBG could relieve BCP but not improve the destruction of bone, which may be related to the specificity of inoculated cells. Further mechanisms should be investigated.