Inhibition of TRPV1 by SHP-1 in nociceptive primary sensory neurons is critical in PD-L1 analgesia
Ben-Long Liu, … , Hui-Zhu Liu, Yu-Qiu Zhang
Ben-Long Liu, … , Hui-Zhu Liu, Yu-Qiu Zhang
Published September 22, 2020
Citation Information: JCI Insight. 2020;5(20):e137386. https://doi.org/10.1172/jci.insight.137386.
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Research Article Neuroscience

Inhibition of TRPV1 by SHP-1 in nociceptive primary sensory neurons is critical in PD-L1 analgesia

Abstract

Recently programmed death-ligand 1 (PD-L1) receptor PD-1 was found in dorsal root ganglion (DRG) neurons, and PD-L1 activates PD-1 to inhibit inflammatory and neuropathic pain by modulating neuronal excitability. However, the downstream signaling of PD-1 in sensory neurons remains unclear. Here, we show that PD-L1 activated Src homology 2 domain-containing tyrosine phosphatase-1 (SHP-1) to downregulate transient receptor potential vanilloid 1 (TRPV1) in DRG neurons and inhibit bone cancer pain in mice. Local injection of PD-L1 produced analgesia. PD-1 in DRG neurons colocalized with TRPV1 and SHP-1. PD-L1 induced the phosphorylation of SHP-1 in DRG TRPV1 neurons and inhibited TRPV1 currents. Loss of TRPV1 in mice abolished bone cancer–induced thermal hyperalgesia and PD-L1 analgesia. Conditioned deletion of SHP-1 in NaV1.8+ neurons aggravated bone cancer pain and diminished the inhibition of PD-L1 on TRPV1 currents and pain. Together, our findings suggest that PD-L1/PD-1 signaling suppresses bone cancer pain via inhibition of TRPV1 activity. Our results also suggest that SHP-1 in sensory neurons is an endogenous pain inhibitor and delays the development of bone cancer pain via suppressing TRPV1 function.

Authors

Ben-Long Liu, Qi-Lai Cao, Xin Zhao, Hui-Zhu Liu, Yu-Qiu Zhang

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Figure 3

Dynamic changes in TRPV1 in DRG neurons after tumor inoculation and effects of PD-L1 on TRPV1 function.

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Dynamic changes in TRPV1 in DRG neurons after tumor inoculation and effe...
(A) Western blot analysis reveals a significant increase in the level of TRPV1 in L3–L5 DRGs ipsilateral to the tumor-bearing bone after tumor inoculation. *P < 0.05, **P < 0.01 versus sham control; 1-way ANOVA followed by post hoc Student-Newman-Keuls test; n = 4 for all the groups (mice). (B) Capsaicin dose-response curves are left-shifted in small-diameter (<25 μm) DRG neurons from PTD 21 mice compared with those from sham ones. Insert represents 1.5 μM capsaicin–evoked TRPV1 current traces in individual DRG neurons of sham and PTD 21 mice. (C) Double immunofluorescence reveals colocalization of PD-1 with TRPV1 in L4 DRG neurons. Scale bar: 100 μm (upper), 25 μm (bottom). (D) Different doses of PD-L1 suppresses TRPV1 current density (pA/pF) in DRG neurons. Insert represents 1.5 μM capsaicin–evoked TRPV1 current traces in individual DRG neurons after different doses of PD-L1 treatment. *P < 0.05, **P < 0.01 versus vehicle control; 1-way ANOVA followed by post hoc Student-Newman-Keuls test; n = 23 vehicle, 20 PD-L1 0.1 ng/mL, 19 PD-L1 0.5 ng/mL, 15 PD-L1 1 ng/mL, 16 PD-L1 10 ng/mL, and 21 PD-L1 50 ng/mL (cells). (E) The inhibition ratio of PD-L1 (10 ng/mL) on TRPV1 currents by different concentrations of capsaicin. *P < 0.05 versus sham control; 2-way RM ANOVA followed by post hoc Student-Newman-Keuls test; n = 9 capsaicin 0.5 μM, 10 capsaicin 1 μM, 6 capsaicin 2 μM, and 16 capsaicin 4 μM from sham mice; n = 10 capsaicin 0.5 μM, 9 capsaicin 1 μM, 14 capsaicin 2 μM, and 10 capsaicin 4 μM from cancer mice (cells). (F) Traces (left) of calcium imaging from individual DRG neurons of bone cancer and sham mice challenged by capsaicin application. Scatter plot (right) showing that PD-L1 significantly attenuates capsaicin-induced increase in [Ca2+]i. **P < 0.01 versus vehicle control; 2-tailed Student’s t test; n = 23 vehicle and 31 PD-L1 (cells). (G) TRPV1–/– mice fail to develop thermal hyperalgesia in tumor-bearing limbs. *P < 0.05, **P < 0.01 versus WT mice; 2-way RM ANOVA followed by post hoc Student-Newman-Keuls test; n = 8 TRPV1–/– and 9 WT (mice). (H) TRPV1–/– mice develop lighter mechanical allodynia than the WT mice following the tumor inoculation. *P < 0.05, **P < 0.01 versus WT mice; 2-way RM ANOVA followed by post hoc Student-Newman-Keuls test; n = 8 TRPV1–/– and 9 WT (mice). (I and J) PD-L1 inhibits bone cancer–induced thermal hyperalgesia (I) and mechanical allodynia (J) in WT mice but not in TRPV1–/– mice on PTD 21. **P< 0.01; paired Student’s t test; n = 7 TRPV1–/– and 8 WT (mice). (K and L) Intraplantar injection of PD-L1 induces a significant increase in PWL (K) and an increasing tendency in PWT (L) in naive WT but not TRPV1–/– mice. **P < 0.01; 2-tailed paired Student’s t test; n = 7 TRPV1–/– and 8 WT (mice).