Department of Physiology, School of Medicine, Erciyes University, Kayseri, Turkey.
Pharmacol Rep. 2021 Jun;73(3):828-840. doi: 10.1007/s43440-021-00254-y. Epub 2021 Apr 2.
The present study examined whether inhibition of guanylate cyclase (GC) is associated with the plasticity-related microtubule-stabilizing protein tau phosphorylation in the dentate gyrus (DG) of hippocampal formation.
To address this issue, methylene blue (MB 50 μM) or saline was infused into the DG starting from the induction of long-term potentiation (LTP) or depression (LTD) for 1 h. Then, protein phosphatase 1 alpha (PP1α), glycogen synthase kinase 3 beta (GSK3β), and tau total and phosphorylated protein levels were measured in these hippocampi using western blotting. LTP and LTD were induced by application of high- and low-frequency stimulation protocols (HFS and LFS), respectively. 5-min averages of the excitatory postsynaptic potential (EPSP) slopes and population spike amplitudes at the end of recording were averaged to measure the magnitude of LTP or LTD.
Low-frequency stimulation protocols was unable to phosphorylate thr and threpitopes of tau, but possessed kinase activity similar to the HFS in phosphorylation of ser and ser epitopes. MB infusion during LTD induction attenuated LTD, prevented EPSP/spike dissociation and increased tau phosphorylation at ser and ser epitopes, without changing tau phosphorylation at thr and thr epitopes. Neither LTP nor LTP-related tau phosphorylation state was changed by MB infusion.
Although MB can benefit to stabilize the balance between LTP and LTD, and to fix the increased spike wave discharges, it might trigger deregulation of tau phosphorylation, leading to the development of Alzheimer's disease by a mechanism that goes awry during induction of LTD. Thereby detailed studies to reveal more precise evidence for the use of MB in this disease are needed.
本研究探讨了抑制鸟苷酸环化酶（GC）是否与海马结构齿状回（DG）中与可塑性相关的微管稳定蛋白 tau 磷酸化有关。
为了解决这个问题，在诱导长时程增强（LTP）或长时程抑制（LTD）后 1 小时，将亚甲蓝（MB，50 μM）或生理盐水注入 DG。然后，使用 Western blot 法测量这些海马中的蛋白磷酸酶 1α（PP1α）、糖原合成酶激酶 3β（GSK3β）和 tau 总蛋白和磷酸化蛋白水平。通过应用高频刺激（HFS）和低频刺激（LFS）方案分别诱导 LTP 和 LTD。在记录结束时，将兴奋性突触后电位（EPSP）斜率和群体锋电位幅度的 5 分钟平均值平均，以测量 LTP 或 LTD 的幅度。
低频刺激方案不能使 tau 的 thr 和 threpitopes 磷酸化，但具有与 HFS 相似的激酶活性，可磷酸化 ser 和 ser 表位。在 LTD 诱导期间注入 MB 可减弱 LTD，防止 EPSP/锋电位分离，并增加 ser 和 ser 表位的 tau 磷酸化，而不改变 thr 和 thr 表位的 tau 磷酸化。MB 注入既不改变 LTP 也不改变 LTP 相关的 tau 磷酸化状态。
尽管 MB 可以有助于稳定 LTP 和 LTD 之间的平衡，并固定增加的锋电位波放电，但它可能会触发 tau 磷酸化的失调，通过 LTD 诱导过程中出现故障的机制导致阿尔茨海默病的发生。因此，需要进行详细的研究，以揭示在这种疾病中使用 MB 的更精确证据。
