[The effects of PDK1-Akt signaling pathway intervention on cardiomyocyte HCN4 ion channels].

Objective: To explore the effects of 3-phosphate dependent protein kinase 1-protein kinase B (PDK1-Akt) signaling pathway on the transcription, expression and function of cardiac hyperpolarized activated cyclic nucleotide gated 4 (HCN4) ion channels. Methods: Atrial myocytes were obtained from healthy male wild-type C57 mice and heart-specific PDK1 knockout mice (PDK1-KO) by enzymolysis. Then the atrial myocytes were divided into blank control group and PDK1-KO group. In further studies, the isolated atrial myocytes were cultured and further divided into drug control group (treated with dimethyl sulfoxide (DMSO)) and PDK1 knockdown group (treated with 1 μg/ml PDK1 short hairpin RNA (shRNA) interference plasmid), SC79 group (treated with 8 μmol/ml SC79), GSK2334470 group (treated with 10 nmol/L GSK2334470) and PDK1 knockdown+SC79 group (8 μmol/ml SC79 and 1 μg/ml PDK1 shRNA interference plasmid). Real time quantitative PCR (qRT-PCR) was used to detect the mRNA expression levels of PDK1 and HCN4, Western blot was used to detect the protein expression levels of PDK1, Akt and HCN4, the whole cell patch clamp was used to detecte the current density of HCN, and immunofluorescence was used to detecte the expression of HCN4 protein on atrial cells. Results: (1) the expression levels of HCN4 mRNA (1.46±0.03 vs. 0.99±0.01, P<0.001) and protein (1.14±0.02 vs. 1.00±0.06, P=0.017) in PDK1-KO group were higher than those in blank control group. The HCN current density in PDK1-KO group was higher than that in blank control group((-17.47±2.00) pA/pF vs. (-12.15±2.25) pA/pF, P=0.038). (2) The functions of PDK1 shRNA and specific Akt agonist SC79 were verified by comparing the PDK1 knockdown group and SC79 group with the drug control group. The results showed that the expression levels of PDK1 mRNA and protein in PDK1 knockdown group were lower than those in drug control group, and the expression level of phosphorylated Akt (Thr 308) protein in SC79 group was higher than that in drug control group. (3) The expression levels of HCN4 mRNA (3.61±0.46 vs. 1.00±0.08, P<0.001) and protein (2.33±0.11 vs. 1.00±0.05, P<0.001) in GSK2334470 group were higher than those in drug control group. (4) To reduce the effect of drug-miss target, the cultured atrial myocytes were transfected with shRNA plasmid of PDK1 and intervened with SC79. The results showed that the expression of HCN4 mRNA in PDK1 knockdown group was higher than that in the drug control group (1.76±0.11 vs. 1.00±0.06, P<0.001), and PDK1 knockdown+SC79 group (1.76±0.11 vs. 1.33±0.07, P=0.003). In PDK1 knockdown+SC79 group, the mRNA expression level was also higher than that in the drug control group (1.33±0.07 vs. 1.00±0.06, P<0.001). The expression level of HCN4 protein in PDK1 knockdown group was higher than that in drug control group (1.15±0.04 vs. 1.00±0.05, P=0.003). As for the The expression level of HCN4 protein, there was no significantly statistical difference between the PDK1 knockdown+SC79 group and the drug control group (P>0.05), but PDK1 knockdown+SC79 group was lower than PDK1 knockdown group (0.95±0.01 vs. 1.15±0.04, P<0.001). In patch clamp experiments, the results showed that the HCN current density was (-13.27±1.28) pA/pF in the drug control group, (-18.76±2.03) pA/pF in the PDK1 knockdown group, (-13.50±2.58) pA/pF in the PDK1 knockdown+SC79 group; the HCN current density of PDK1 knockdown group was higher than that of drug control group (P<0.001), but there was no significant difference between PDK1 knockdown+SC79 group and drug control group (P>0.05). (5) The results of immunofluorescence showed that the brightness of green fluorescence of PDK1 knockdown group was higher than that of drug control group, indicating that the expression of HCN4 localized on cell membrane was increased. However, the green fluorescence of PDK1 knockdown+SC79 group was lighter than that of PDK1 knockdown group, suggesting that the expression of HCN4 in PDK1-knockdown cell membrane decreased after further activating Akt. Conclusion: PDK1-Akt signaling pathway is involved in the regulation of HCN4 ion channel transcription, expression and function.目的： 探讨3-磷酸肌醇依赖性蛋白激酶1-蛋白激酶B（PDK1-Akt）信号通路干预对心肌细胞超极化激活环核苷酸门控离子通道4（HCN4）转录、表达及功能的影响。 方法： 使用酶解法从健康雄性野生型C57小鼠和心脏特异性敲除PDK1小鼠获得心房肌细胞，分别为空白对照组和PDK1-KO组；另外，对急性分离自C57小鼠的心房肌细胞进行培养，将其分为药物对照组［予二甲基亚砜（DMSO）干预）］、PDK1敲低组［予1 μg/ml PDK1的短发夹状RNA（shRNA）干扰质粒干预］、SC79组［予Akt激动剂SC79（8 μmol/ml）干预］、GSK2334470组［予PDK1抑制剂GSK2334479（10 nmol/ml）干预］和PDK1敲低+SC79组（予8 μmol/ml SC79和1 μg/ml PDK1的shRNA干扰质粒干预）。为进一步减少药物脱靶的可能，故运用PDK1的shRNA质粒转染培养的心肌细胞，并在此基础上加用SC79干预。采用实时荧光定量PCR（qRT-PCR）检测相应组心房肌细胞PDK1及HCN4的mRNA表达水平，Western blot检测PDK1、Akt及HCN4蛋白表达水平，全细胞膜片钳检测HCN的电流密度，免疫荧光技术检测HCN4蛋白表达情况。 结果： （1）PDK1-KO组的HCN4的mRNA（1.46±0.03比0.99±0.01，P<0.001）及蛋白（1.14±0.02比1.00±0.06，P=0.017）表达水平高于空白对照组。全细胞膜片钳结果显示，PDK1-KO组的HCN电流密度大于空白对照组［（-17.47±2.00）pA/pF比（-12.15±2.25）pA/pF，P=0.038］。（2）通过比较PDK1敲低组、SC79组和药物对照组细胞，对PDK1 shRNA及Akt特异性激动剂SC79进行功能验证，结果显示PDK1敲低组细胞的PDK1 mRNA及蛋白表达水平低于药物对照组，SC79组细胞的磷酸化-Akt（Thr 308）蛋白表达水平高于药物对照组。（3）GSK2334470组细胞的HCN4 mRNA（3.61±0.46比1.00±0.08，P<0.001）及蛋白（2.33±0.11比1.00±0.05，P<0.001）表达水平高于药物对照组。（4）PDK1敲低组细胞的HCN4 mRNA表达水平高于药物对照组（1.76±0.11比1.00±0.06，P<0.001）及PDK1敲低+SC79组（1.76±0.11比1.33±0.07，P=0.003），PDK1敲低+SC79组的HCN4 mRNA表达水平亦高于药物对照组（1.33±0.07比1.00±0.06，P<0.001）。PDK1敲低组细胞的HCN4蛋白表达水平高于药物对照组（1.15±0.04比1.00±0.05，P=0.003），PDK1敲低+SC79组的HCN4蛋白表达水平与药物对照组比较差异无统计学意义（P>0.05），但低于PDK1敲低组（0.95±0.01比1.15±0.04，P<0.001）。全细胞膜片钳实验结果示，药物对照组细胞的HCN电流密度为（-13.27±1.28）pA/pF，PDK1敲低组细胞为（-18.76±2.03）pA/pF，PDK1敲低+SC79组细胞为（-13.50±2.58）pA/pF；PDK1敲低组细胞的HCN电流密度大于药物对照组（P<0.001），而PDK1敲低+SC79组与药物对照组比较差异无统计学差异（P>0.05）。（5）免疫荧光检测结果显示PDK1敲低组的绿色荧光较药物对照组增强，提示定位于细胞膜的HCN4表达量增加。而PDK1敲低+SC79组的绿色荧光较PDK1敲低组减弱，提示当敲低PDK1后再进一步激动Akt，定位于细胞膜HCN4表达量下降。 结论： PDK1-Akt信号通路参与心肌细胞HCN4离子通道转录、表达水平及功能的调控。.