Huang Cathy C Y, Shi Liheng, Lin Chia-Hung, Kim Andy Jeesu, Ko Michael L, Ko Gladys Y-P
Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
Texas A&M Institute of Neuroscience, Texas A&M University, College Station, Texas, USA.
J Neurochem. 2015 Nov;135(4):727-41. doi: 10.1111/jnc.13349. Epub 2015 Sep 22.
AMP-activated protein kinase (AMPK) is a cellular energy sensor, which is activated when the intracellular ATP production decreases. The activities of AMPK display circadian rhythms in various organs and tissues, indicating that AMPK is involved in the circadian regulation of cellular metabolism. In vertebrate retina, the circadian clocks regulate many aspects of retinal function and physiology, including light/dark adaption, but whether and how AMPK was involved in the retinal circadian rhythm was not known. We hypothesized that the activation of AMPK (measured as phosphorylated AMPK) in the retina was under circadian control, and AMPK might interact with other intracellular signaling molecules to regulate photoreceptor physiology. We combined ATP assays, western blots, immunostaining, patch-clamp recordings, and pharmacological treatments to decipher the role of AMPK in the circadian regulation of photoreceptor physiology. We found that the overall retinal ATP content displayed a diurnal rhythm that peaked at early night, which was nearly anti-phase to the diurnal and circadian rhythms of AMPK phosphorylation. AMPK was also involved in the circadian phase-dependent regulation of photoreceptor L-type voltage-gated calcium channels (L-VGCCs), the ion channel essential for sustained neurotransmitter release. The activation of AMPK dampened the L-VGCC currents at night with a corresponding decrease in protein expression of the L-VGCCα1 pore-forming subunit, while inhibition of AMPK increased the L-VGCC current during the day. AMPK appeared to be upstream of extracellular-signal-regulated kinase and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) but downstream of adenylyl cyclase in regulating the circadian rhythm of L-VGCCs. Hence, as a cellular energy sensor, AMPK integrates into the cell signaling network to regulate the circadian rhythm of photoreceptor physiology. We found that in chicken embryonic retina, the activation of AMP-activated protein kinase (AMPK) is under circadian control and anti-phase to the retinal ATP rhythm. While ATP content is higher at night, phosphorylated AMPK (pAMPK) is higher during the day. AMPK appears to be upstream of extracellular signal-regulated kinase (ERK), protein kinase B (AKT), and mammalian target of rapamycin complex 1 (mTORC1) but downstream of adenylyl cyclase in regulating the circadian rhythm of L-VGCCs. Therefore, as a cellular energy sensor, AMPK integrates into the cell signaling network to regulate the circadian rhythm of photoreceptor physiology.
AMP激活的蛋白激酶（AMPK）是一种细胞能量传感器，当细胞内ATP生成减少时被激活。AMPK的活性在各种器官和组织中呈现昼夜节律，这表明AMPK参与细胞代谢的昼夜调节。在脊椎动物视网膜中，生物钟调节视网膜功能和生理的许多方面，包括光/暗适应，但AMPK是否以及如何参与视网膜昼夜节律尚不清楚。我们推测视网膜中AMPK的激活（以磷酸化的AMPK衡量）受昼夜节律控制，并且AMPK可能与其他细胞内信号分子相互作用以调节光感受器生理。我们结合ATP测定、蛋白质免疫印迹、免疫染色、膜片钳记录和药理学处理来解读AMPK在光感受器生理昼夜调节中的作用。我们发现视网膜整体ATP含量呈现昼夜节律，在深夜达到峰值，这与AMPK磷酸化的昼夜和生物钟节律几乎呈反相。AMPK还参与光感受器L型电压门控钙通道（L-VGCCs）的生物钟相依赖性调节，L-VGCCs是持续神经递质释放所必需的离子通道。AMPK的激活在夜间减弱L-VGCC电流，同时L-VGCCα1孔形成亚基的蛋白表达相应降低，而抑制AMPK则在白天增加L-VGCC电流。在调节L-VGCCs的昼夜节律方面，AMPK似乎位于细胞外信号调节激酶和哺乳动物雷帕霉素靶蛋白复合物1（mTORC1）的上游，但在腺苷酸环化酶的下游。因此，作为一种细胞能量传感器，AMPK整合到细胞信号网络中以调节光感受器生理的昼夜节律。我们发现在鸡胚视网膜中，AMP激活的蛋白激酶（AMPK）的激活受昼夜节律控制，并且与视网膜ATP节律呈反相。虽然夜间ATP含量较高，但磷酸化的AMPK（pAMPK）在白天较高。在调节L-VGCCs的昼夜节律方面，AMPK似乎位于细胞外信号调节激酶（ERK）、蛋白激酶B（AKT）和哺乳动物雷帕霉素靶蛋白复合物1（mTORC1）的上游，但在腺苷酸环化酶下游。因此，作为一种细胞能量传感器，AMPK整合到细胞信号网络中以调节光感受器生理的昼夜节律。
