Expression of spinal PD-L1 in bone cancer pain model mice and its effect on pain behaviors

Abstract

Objective To evaluate the role of programmed cell death ligand-1(PD-L1) in a mouse model of bone cancer pain. Methods Ninety-six male C3H/HeN mice (20-25 g, 4-6 weeks old), which inoculated with osteolytic NCTC 2472 cells, were used to build the model of bone cancer pain. Part one: sixty-four male C3H/HeJ mice were randomly divided into sham group (group Sham, n=32) and tumor group (group Tumor, n=32). Part two: Twenty-four male C3H/HeJ mice which were inoculated with osteolytic NCTC 2472 cells were randomly divided into group T (tumor, n=8), group PD-L1 (intrathecal injection with PLX3397, 1μg /5μl, n=8) and group NS (intrathecal injection with normal saline, n=8). Also, there were eight male C3H/HeJ mice in group S which were intra-femur inoculated with α-MEM. The pain behaviors of Sham group and Tumor group were observed and the expression of PD-L1 was detected before inoculation and on 4 , 7 , 10 , 14 and 21 days after inoculation, including paw withdrawal mechanical threshold (PWMT) and the number of spontaneous flinches (NSF). On 14 d after inoculation, the mice of group PD-L1 and group NS were intrathecal injected with drugs respectively. Pain behaviors were observed before injection and 2, 4, 6, 24h after injection. Results Compared with group Sham, PWMT was significantly decreased and NSF was increased on 7~21 d after inoculation in group Tumor (P<0.05). Compared with baseline and group S (baseline (0.38±0.06), group Sham (0.35±0.08), (0.38±0.08), (0.36±0.07)), the expression of PD-L1 was up-regulated on 10-21 d after inoculation in group Tumor ((0.77±0.06), (1.21±0.04), (1.18±0.06)) (P<0.05). Compared with group NS, PWMT was significantly increased (group NS (0.25±0.12), (0.25±0.12), (0.31±0.12), group PD-L1 (1.43±0.49), (1.35±0.44), (0.95±0.26)), and NSF was decreased on 2-6 h after injection in group PD-L1 (group NS(11.74±1.31), (13.78±0.0.91), (13.63±1.06), group PD-L1(4.90±0.82), (4.15±0.71), (7.65±0.56)) (P<0.05). Conclusion Expression of PD-L1 in spinal cord was up-regulated in the mouse model of bone cancer pain. Intrathecal injection of recombinant PD-L1 has an analgesic effect on mice with bone cancer. Key words: Bone cancer pain; Spinal cord; Programmed cell death ligand-1; Mice