Blockade of Piezo2 Pathway Attenuates Inflammatory and Neuropathic Pain in the Orofacial Area

Abstract

Although previous studies suggest that Piezo2 regulates chronic pain in the orofacial area, few studies have reported the direct evidence of Piezo2's involvement in inflammatory and neuropathic pain in the orofacial region. In this study, we used male Sprague Dawley rats to investigate the role of the Piezo2 pathway in the development of inflammatory and neuropathic pain. The present study used interleukin (IL)-1β-induced pronociception as an inflammatory pain model. Subcutaneous injection of IL-1β produced significant mechanical allodynia and thermal hyperalgesia. Subcutaneous injection of a Piezo2 inhibitor significantly blocked mechanical allodynia and thermal hyperalgesia induced by subcutaneously injected IL-1β. Furthermore, the present study also used a neuropathic pain model caused by the misplacement of a dental implant, leading to notable mechanical allodynia as a consequence of inferior alveolar nerve injury. Western blot analysis revealed increased levels of Piezo2 in the trigeminal ganglion and the trigeminal subnucleus caudalis after inferior alveolar nerve injury. Furthermore, subcutaneous and intracisternal injections of a Piezo2 inhibitor blocked neuropathic mechanical allodynia. These results suggest that the Piezo2 pathway plays a critical role in the development of inflammatory and neuropathic pain in the orofacial area. Therefore, blocking the Piezo2 pathway could be the foundation for developing new therapeutic strategies to treat orofacial pain conditions.

Keywords: Piezo2; acute pain; antinociception; interleukin-1β; neuropathic pain.

Figure 1

Interleukin (IL)-1β–induced mechanical allodynia and thermal hyperalgesia. (a) Subcutaneous injection of IL-1β (1 ng) significantly reduced the air-puff threshold compared to the vehicle group, resulting in mechanical allodynia for over 24 h. (b) Subcutaneous injection of IL-1β (1 ng) significantly reduced head withdrawal latency, leading to thermal hyperalgesia for up to 6 h. Vehicle administration does not affect either air-puff thresholds or head withdrawal latency. n = 7 animals per group. ^∗p < 0.05. Vehicle- vs. IL-1β-treated group.

Figure 2

The effects of subcutaneously injected D-GsMTx4, a Piezo2 inhibitor, on IL-1β–induced pronociception. (a) Subcutaneous administration of D-GsMTx4 resulted in the inhibition of mechanical allodynia induced by the subcutaneous injection of IL-1β (1 ng). The antiallodynic effects were observed 4 h after the injection and persisted for up to 8 h. (b) Subcutaneous injection of D-GsMTx4 suppressed IL-1β–induced thermal hyperalgesia for up to 8 h. Vehicle administration does not affect the air-puff threshold or head withdrawal latency. n = 7 animals per group. ^∗p < 0.05. Vehicle- vs. D-GsMTx4-treated group. The arrow indicates the injection of D-GsMTx4.

Figure 3

Changes in air-puff thresholds and Piezo2 expression following inferior alveolar nerve injury. (a) The misplacement of a dental implant resulted in significant mechanical allodynia in the experimental animals due to damage to the inferior alveolar nerve. Mechanical allodynia began to appear significantly from Day 1 after the nerve injury, lasted until 28 days postinjury, gradually recovered over time, and returned to the same level as before the nerve injury by Day 50. In the sham group, air-puff thresholds were not significantly altered compared to naïve rats. n = 7 animals per group. (b) and (c) Western blotting analysis showed upregulation of Piezo2 expression on POD 5 in the ipsilateral trigeminal ganglion (b) and trigeminal subnucleus caudalis (c). GAPDH was used as a loading control. n = 6 animals per group. ^∗p < 0.05, comparing the sham group with the inferior alveolar nerve-injured group.

Figure 4

Effects of subcutaneous treatment with D-GsMTx4 on mechanical allodynia in rats with an inferior alveolar nerve injury. Subcutaneous administration of D-GsMTx4 (5 or 10 μg), a Piezo2 inhibitor, produced antiallodynic effects 4 h after injection, which continued for up to 10 h. The vehicle administration did not affect the air-puff threshold. n = 7 animals per group. ^∗p < 0.05. Vehicle- vs. D-GsMTx4-treated group.

Figure 5

Effects of intracisternal treatment with D-GsMTx4 on mechanical allodynia in rats with an inferior alveolar nerve injury. Intracisternal administration of D-GsMTx4 (5 or 10 μg), a Piezo2 inhibitor, produced antiallodynic effects 4 h after injection, which continued for up to 10 h. The vehicle administration did not affect the air-puff threshold. n = 7 animals per group. ^∗p < 0.05. Vehicle- vs. D-GsMTx4-treated group.