iPLA2、TRPM8 和 TRPA1 在化学诱导冷过敏反应中的作用。

BACKGROUND: The cooling agents menthol and icilin act as agonists at TRPM8 and TRPA1. In vitro, activation of TRPM8 by icilin and cold, but not menthol, is dependent on the activity of a sub-type of phospholipase A2, iPLA2. Lysophospholipids (e.g. LPC) produced by PLA2 activity can also activate TRPM8. The role of TRPA1 as a primary cold sensor in vitro is controversial, although there is evidence that TRPA1 plays a role in behavioural responses to noxious cold stimuli. In this study, we have investigated the roles of TRPM8 and TRPA1 and the influence of iPLA2 on noxious cold sensitivities in naïve animals and after local administration of menthol, icilin and LPC. The roles of the channels in cold sensitivity were investigated in mice lacking either TRPM8 (Trpm8-/-) or TRPA1 (Trpa1-/-). RESULTS: Intraplantar administration of icilin evoked a dose-dependent increase in sensitivity to a 10 degrees C stimulus that was inhibited by iPLA2 inhibition with BEL. In contrast the cold hypersensitivities elicited by intraplantar menthol and LPC were not inhibited by BEL treatment. BEL had no effect on basal cold sensitivity and mechanical hypersensitivities induced by the TRPV1 agonist, capsaicin, and the P2X3 agonist alpha,beta-methylene ATP. Both Trpm8-/- and Trpa1-/- mice showed longer latencies for paw withdrawal from a 10 degrees C stimulus than wild-type littermates. Cold hypersensitivities induced by either icilin or LPC were absent in Trpm8-/- mice but were retained in Trpa1-/- mice. In contrast, cold hypersensitivity evoked by menthol was present in Trpm8-/- mice but was lost in Trpa1-/- mice. CONCLUSIONS: The findings that iPLA2 inhibition blocked the development of cold hypersensitivity after administration of icilin but failed to affect menthol-induced hypersensitivity agree well with our earlier in vitro data showing a differential effect of iPLA2 inhibition on the agonist activities of these agents. The ability of LPC to induce cold hypersensitivity supports a role for iPLA2 in modulating TRPM8 activity in vivo. Studies on genetically modified mice demonstrated that the effects of icilin and LPC were mediated by TRPM8 and not TRPA1. In contrast, menthol-induced cold hypersensitivity was dependent on expression of TRPA1 and not TRPM8.

背景：薄荷醇和异丁香酚作为 TRPM8 和 TRPA1 的激动剂。在体外，异丁香酚和冷刺激激活 TRPM8 依赖于一种亚型的 PLA2，即 iPLA2。PLA2 活性产生的溶血磷脂（例如 LPC）也可以激活 TRPM8。TRPA1 作为体外主要冷感受器的作用存在争议，尽管有证据表明 TRPA1 在对有害冷刺激的行为反应中起作用。在这项研究中，我们研究了 TRPM8 和 TRPA1 的作用以及 iPLA2 对新生动物和局部给予薄荷醇、异丁香酚和 LPC 后有害冷敏感性的影响。在缺乏 TRPM8（Trpm8-/-）或 TRPA1（Trpa1-/-）的小鼠中，研究了这些通道在冷敏感性中的作用。

结果：皮内注射异丁香酚可引起对 10°C 刺激的敏感性呈剂量依赖性增加，该增加可被 iPLA2 抑制剂 BEL 抑制。相比之下，皮内给予薄荷醇和 LPC 引起的冷敏性不受 BEL 处理的抑制。BEL 对基础冷敏感性和 TRPV1 激动剂辣椒素以及 P2X3 激动剂α，β-亚甲基 ATP 诱导的机械性超敏反应均无影响。Trpm8-/-和 Trpa1-/-小鼠从 10°C 刺激中撤回爪子的潜伏期均长于野生型同窝小鼠。异丁香酚或 LPC 诱导的冷敏性在 Trpm8-/-小鼠中缺失，但在 Trpa1-/-小鼠中保留。相反，薄荷醇诱导的冷敏性在 Trpm8-/-小鼠中存在，但在 Trpa1-/-小鼠中消失。

结论：iPLA2 抑制阻断了异丁香酚给药后冷敏性的发展，但未能影响薄荷醇诱导的超敏性，这与我们之前的体外数据非常吻合，表明 iPLA2 抑制对这些药物的激动剂活性有不同的影响。LPC 诱导冷敏性的能力支持 iPLA2 在体内调节 TRPM8 活性的作用。对基因修饰小鼠的研究表明，异丁香酚和 LPC 的作用是由 TRPM8 介导的，而不是 TRPA1。相比之下，薄荷醇诱导的冷敏性依赖于 TRPA1 的表达，而不是 TRPM8。