Institute of Pharmacology and Toxicology, University of Zurich, Zürich, Switzerland.
Drug Discovery Network Zurich, University of Zurich and ETH Zurich, Zürich, Switzerland.
Pain. 2021 Sep 1;162(9):2436-2445. doi: 10.1097/j.pain.0000000000002236.
Glycinergic neurons and glycine receptors (GlyRs) exert a critical control over spinal nociception. Prostaglandin E2 (PGE2), a key inflammatory mediator produced in the spinal cord in response to peripheral inflammation, inhibits a certain subtype of GlyRs (α3GlyR) that is defined by the inclusion of α3 subunits and distinctly expressed in the lamina II of the spinal dorsal horn, ie, at the site where most nociceptive nerve fibers terminate. Previous work has shown that the hyperalgesic effect of spinal PGE2 is lost in mice lacking α3GlyRs and suggested that this phenotype results from the prevention of PGE2-evoked protein kinase A (PKA)-dependent phosphorylation and inhibition of α3GlyRs. However, direct proof for a contribution of this phosphorylation event to inflammatory hyperalgesia was still lacking. To address this knowledge gap, a phospho-deficient mouse line was generated that carries a serine to alanine point mutation at a strong consensus site for PKA-dependent phosphorylation in the long intracellular loop of the GlyR α3 subunit. These mice showed unaltered spinal expression of GlyR α3 subunits. In behavioral experiments, they showed no alterations in baseline nociception, but were protected from the hyperalgesic effects of intrathecally injected PGE2 and exhibited markedly reduced inflammatory hyperalgesia. These behavioral phenotypes closely recapitulate those found previously in GlyR α3-deficient mice. Our results thus firmly establish the crucial role of PKA-dependent phosphorylation of α3GlyRs in inflammatory hyperalgesia.
甘氨酸能神经元和甘氨酸受体（GlyRs）对脊髓伤害性感受具有关键的控制作用。前列腺素 E2（PGE2）是一种在脊髓中产生的关键炎症介质，对周围炎症做出反应，它抑制了特定亚型的 GlyRs（α3GlyR），该亚型由α3 亚基组成，并在脊髓背角的 II 层中明显表达，即在大多数伤害性神经纤维终止的部位。以前的工作表明，缺乏α3GlyRs 的小鼠的脊髓 PGE2 的痛觉过敏效应丧失，并表明这种表型是由于 PGE2 诱导的蛋白激酶 A（PKA）依赖性磷酸化和α3GlyRs 抑制的预防所致。然而，仍然缺乏这种磷酸化事件对炎症性痛觉过敏的直接证据。为了解决这一知识空白，生成了一种磷酸缺陷型小鼠系，该小鼠在 GlyR α3 亚基的长细胞内环中有一个 PKA 依赖性磷酸化的强共识位点，该位点发生丝氨酸到丙氨酸的点突变。这些小鼠的脊髓 GlyR α3 亚基表达没有改变。在行为实验中，它们在基础痛觉感受方面没有改变，但对鞘内注射 PGE2 的痛觉过敏效应有保护作用，并且炎症性痛觉过敏明显减轻。这些行为表型与之前在 GlyR α3 缺陷型小鼠中发现的表型非常相似。我们的结果因此牢固地确立了 PKA 依赖性α3GlyRs 磷酸化在炎症性痛觉过敏中的关键作用。
