Sex differences in PD-L1-induced analgesia in paclitaxel-induced peripheral neuropathy mice depend on TRPV1-based inhibition of CGRP.

ABSTRACT

AIMS: Paclitaxel (PTX) is extensively utilized in the management of diverse solid tumors, frequently resulting in paclitaxel-induced peripheral neuropathy (PIPN). The present study aimed to investigate sex differences in the behavioral manifestations and underlying pathogenesis of PIPN and search for clinically efficacious interventions. METHODS: Male and female C57BL/6 mice (5-6 weeks and 12 months, weighing 18-30 g) were intraperitoneally (i.p.) administered paclitaxel diluted in saline (NaCl 0.9%) at a dose of 2 mg/kg every other day for a total of 4 injections. Von Frey and hot plate tests were performed before and after administration to confirm the successful establishment of the PIPN model and also to evaluate the pain of PIPN and the analgesic effect of PD-L1. On day 14 after PTX administration, PD-L1 protein (10 ng/pc) was injected into the PIPN via the intrathecal (i.t.) route. To knock down TRPV1 in the spinal cord, adeno-associated virus 9 (AAV9)-Trpv1-RNAi (5 µL, 1 × 1013 vg/mL) was slowly injected via the i.t. route. Four weeks after AAV9 delivery, the downregulation of TRPV1 expression was verified by immunofluorescence staining and Western blotting. The levels of PD-L1, TRPV1 and CGRP were measured via Western blotting, RT-PCR, and immunofluorescence staining. The levels of TNF-α and IL-1ß were measured via RT-PCR. RESULTS: TRPV1 and CGRP protein and mRNA levels were higher in the spinal cords of control female mice than in those of control male mice. PTX-induced nociceptive behaviors in female PIPN mice were greater than those in male PIPN mice, as indicated by increased expression of TRPV1 and CGRP. The analgesic effects of PD-L1 on mechanical hyperalgesia and thermal sensitivity were significantly greater in female mice than in male mice, with calculated relative therapeutic levels increasing by approximately 2.717-fold and 2.303-fold, respectively. PD-L1 and CGRP were partly co-localized with TRPV1 in the dorsal horn of the mouse spinal cord. The analgesic effect of PD-L1 in PIPN mice was observed to be mediated through the downregulation of TRPV1 and CGRP expression following AAV9-mediated spinal cord specific decreased TRPV1 expression. CONCLUSIONS: PTX-induced nociceptive behaviors and the analgesic effect of PD-L1 in PIPN mice were sexually dimorphic, highlighting the significance of incorporating sex as a crucial biological factor in forthcoming mechanistic studies of PIPN and providing insights for potential sex-specific therapeutic approaches.