Department of Cardiology, Shengjing Hospital of China Medical University, Shenyang, China.
Department of Otolaryngology, Affiliated Zhongshan Hospital of Dalian University, Dalian, China.
J Cardiovasc Pharmacol. 2018 Nov;72(5):205-213. doi: 10.1097/FJC.0000000000000615.
We previously found that metformin regulates the ion current conducted by the small conductance calcium-activated potassium channels (SK channels) in the atria of rats with type 2 diabetes mellitus (T2DM) as well as the mRNA and protein expression of the SK2 and SK3 subtypes of SK channels. In this study, we hypothesized that the nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4)/p38 mitogen-activated protein kinase (p38MAPK) signaling pathway was involved in the metformin-mediated regulation of SK2 and SK3 expression in the atria of rats with T2DM. We randomly divided Wistar rats into the control group, the untreated T2DM group, the metformin-treated group, the group receiving subcutaneous injections of the nicotinamide adenine dinucleotide phosphate oxidase (NOX) inhibitor diphenyleneiodonium (DPI), and the group receiving tail vein injections of the p38MAPK agonist anisomycin. Real-time polymerase chain reaction, Western blot, and immunohistochemistry were applied to examine the expression levels of SK2, SK3, NOX4, and phospho-p38MAPK (p-p38MAPK) mRNAs and proteins in the atrial tissue of relevant groups. We observed that the expression levels of NOX4 mRNA and protein and p-p38MAPK protein were significantly elevated in the atria of rats with T2DM compared with the control group. In addition, SK2 protein expression was reduced, whereas SK3 protein expression was increased. The 8-week treatment with metformin markedly reduced the expression levels of NOX4 mRNA and protein and p-p38MAPK protein, upregulated the SK2 expression, and downregulated the SK3 expression. Tail vein injection with anisomycin significantly increased the p-p38MAPK expression while further inhibiting the expression of SK2 and enhancing the expression of SK3. Subcutaneous injection with DPI considerably inhibited the expression of NOX4, further enhanced the expression of SK2 and suppressed the expression of SK3. In addition, subcutaneous injection with DPI significantly suppressed the phosphorylation of p38MAPK. In conclusion, the NOX4/p38MAPK signaling pathway mediates the downregulation of SK2 and the upregulation of SK3 in the atria of rats with T2DM. Long-term metformin treatment upregulates SK2 protein expression and downregulates SK3 protein expression by inhibiting the NOX4/p38MAPK signaling pathway.
我们之前发现二甲双胍可调节 2 型糖尿病大鼠心房中小电导钙激活钾通道（SK 通道）的离子电流，并调节 SK2 和 SK3 亚型 SK 通道的 mRNA 和蛋白表达。在这项研究中，我们假设烟酰胺腺嘌呤二核苷酸磷酸氧化酶 4（NOX4）/p38 丝裂原激活的蛋白激酶（p38MAPK）信号通路参与了二甲双胍调节 2 型糖尿病大鼠心房中 SK2 和 SK3 表达的过程。我们将 Wistar 大鼠随机分为对照组、未经治疗的 2 型糖尿病组、二甲双胍治疗组、烟酰胺腺嘌呤二核苷酸磷酸氧化酶（NOX）抑制剂二苯基碘（DPI）皮下注射组和 p38MAPK 激动剂anisomycin 尾静脉注射组。实时聚合酶链反应、Western blot 和免疫组织化学检测相关各组心房组织中 SK2、SK3、NOX4 和磷酸化 p38MAPK（p-p38MAPK）mRNA 和蛋白的表达水平。我们观察到，与对照组相比，2 型糖尿病大鼠心房中 NOX4mRNA 和蛋白以及 p-p38MAPK 蛋白的表达水平显著升高。此外，SK2 蛋白表达减少，而 SK3 蛋白表达增加。8 周的二甲双胍治疗明显降低了 NOX4mRNA 和蛋白以及 p-p38MAPK 蛋白的表达水平，上调了 SK2 的表达，下调了 SK3 的表达。尾静脉注射 anisomycin 显著增加了 p-p38MAPK 的表达，同时进一步抑制了 SK2 的表达，增强了 SK3 的表达。DPI 皮下注射显著抑制了 NOX4 的表达，进一步增强了 SK2 的表达，抑制了 SK3 的表达。此外，DPI 皮下注射显著抑制了 p38MAPK 的磷酸化。总之，NOX4/p38MAPK 信号通路介导了 2 型糖尿病大鼠心房中 SK2 的下调和 SK3 的上调。长期二甲双胍治疗通过抑制 NOX4/p38MAPK 信号通路而上调 SK2 蛋白表达，下调 SK3 蛋白表达。
