Departments of Molecular Genetics.
Biochemistry and.
Am J Physiol Endocrinol Metab. 2014 Jul 15;307(2):E225-36. doi: 10.1152/ajpendo.00655.2013. Epub 2014 Jun 3.
Activation of AMP-activated protein kinase (AMPK) in cardiomyocytes induces translocation of glucose transporter GLUT4 and long-chain fatty acid (LCFA) transporter CD36 from endosomal stores to the sarcolemma to enhance glucose and LCFA uptake, respectively. Ca(2+)/calmodulin-activated kinase kinase-β (CaMKKβ) has been positioned directly upstream of AMPK. However, it is unknown whether acute increases in [Ca(2+)]i stimulate translocation of GLUT4 and CD36 and uptake of glucose and LCFA or whether Ca(2+) signaling converges with AMPK signaling to exert these actions. Therefore, we studied the interplay between Ca(2+) and AMPK signaling in regulation of cardiomyocyte substrate uptake. Exposure of primary cardiomyocytes to inhibitors or activators of Ca(2+) signaling affected neither AMPK-Thr(172) phosphorylation nor basal and AMPK-mediated glucose and LCFA uptake. Despite their lack of an effect on substrate uptake, Ca(2+) signaling activators induced GLUT4 and CD36 translocation. In contrast, AMPK activators stimulated GLUT4/CD36 translocation as well as glucose/LCFA uptake. When cardiomyocytes were cotreated with Ca(2+) signaling and AMPK activators, Ca(2+) signaling activators further enhanced AMPK-induced glucose/LCFA uptake. In conclusion, Ca(2+) signaling shows no involvement in AMPK-induced GLUT4/CD36 translocation and substrate uptake but elicits transporter translocation via a separate pathway requiring CaMKKβ/CaMKs. Ca(2+)-induced transporter translocation by itself appears to be ineffective to increase substrate uptake but requires additional AMPK activation to effectuate transporter translocation into increased substrate uptake. Ca(2+)-induced transporter translocation might be crucial under excessive cardiac stress conditions that require supraphysiological energy demands. Alternatively, Ca(2+) signaling might prepare the heart for substrate uptake during physiological contraction by inducing transporter translocation.
在心肌细胞中，激活 AMP 激活的蛋白激酶 (AMPK) 会诱导葡萄糖转运体 GLUT4 和长链脂肪酸 (LCFA) 转运体 CD36 从内体库转位到肌小节，分别增强葡萄糖和 LCFA 的摄取。钙/钙调蛋白激活的蛋白激酶激酶-β (CaMKKβ) 被直接置于 AMPK 的上游。然而，尚不清楚细胞内钙离子浓度 ([Ca2+]i) 的急性增加是否会刺激 GLUT4 和 CD36 的转位以及葡萄糖和 LCFA 的摄取，或者钙信号是否与 AMPK 信号汇聚以发挥这些作用。因此，我们研究了钙信号和 AMPK 信号在调节心肌细胞底物摄取中的相互作用。钙信号的抑制剂或激活剂暴露于原代心肌细胞中，既不影响 AMPK-Thr(172)磷酸化，也不影响基础和 AMPK 介导的葡萄糖和 LCFA 的摄取。尽管它们对底物摄取没有影响，但钙信号激活剂诱导 GLUT4 和 CD36 的转位。相比之下，AMPK 激活剂刺激 GLUT4/CD36 转位以及葡萄糖/LCFA 的摄取。当心肌细胞同时用钙信号和 AMPK 激活剂处理时，钙信号激活剂进一步增强了 AMPK 诱导的葡萄糖/LCFA 摄取。总之，钙信号不参与 AMPK 诱导的 GLUT4/CD36 转位和底物摄取，但通过需要 CaMKKβ/CaMKs 的独立途径引发转运体转位。钙诱导的转运体转位本身似乎不足以增加底物摄取，但需要额外的 AMPK 激活来实现转运体转位以增加底物摄取。钙诱导的转运体转位在需要超生理能量需求的过度心脏应激条件下可能至关重要。或者，钙信号可能通过诱导转运体转位为生理收缩期间的底物摄取做准备。
