Walker John, Jijon Humberto B, Diaz Hugo, Salehi Payam, Churchill Thomas, Madsen Karen L
Division of Gastroenterology, University of Alberta, 6146 Dentistry Pharmacy Building, Edmonton, Alberta, Canada T6G 2C2.
Biochem J. 2005 Jan 15;385(Pt 2):485-91. doi: 10.1042/BJ20040694.
AMPK (AMP-activated protein kinase) is a key sensor of energy status within the cell. Activated by an increase in the AMP/ATP ratio, AMPK acts to limit cellular energy depletion by down-regulating selective ATP-dependent processes. The purpose of the present study was to determine the role of AMPK in regulating intestinal glucose transport. [3H]3-O-methyl glucose fluxes were measured in murine jejunum in the presence and absence of the AMPK activators AICAR (5-aminoimidazole-4-carboxamide riboside) and metformin and the p38 inhibitor, SB203580. To differentiate between a sodium-coupled (SGLT1) and diffusive (GLUT2) route of entry, fluxes were measured in the presence of the SGLT1 and GLUT2 inhibitors phloridzin and phloretin. Glucose transporter mRNA levels were measured by reverse transcriptase-PCR, and localization by Western blotting. Surface-expressed GLUT2 was assessed by luminal biotinylation. Activation of p38 mitogen-activated protein kinase was analysed by Western blotting. We found that treatment of jejunal tissue with AICAR resulted in enhanced net glucose uptake and was associated with phosphorylation of p38 mitogen-activated protein kinase. Inhibition of p38 abrogated the stimulation of AICAR-stimulated glucose uptake. Phloretin abolished the AICAR-mediated increase in glucose flux, whereas phloridzin had no effect, suggesting the involvement of GLUT2. In addition, AICAR decreased total protein levels of SGLT1, concurrently increasing levels of GLUT2 in the brush-border membrane. The anti-diabetic drug metformin, a known activator of AMPK, also induced the localization of GLUT2 to the luminal surface. We conclude that the activation of AMPK results in an up-regulation of non-energy requiring glucose uptake by GLUT2 and a concurrent down-regulation of sodium-dependent glucose transport.
AMPK（AMP激活的蛋白激酶）是细胞内能量状态的关键传感器。由AMP/ATP比值升高激活后，AMPK通过下调选择性ATP依赖过程来限制细胞能量消耗。本研究的目的是确定AMPK在调节肠道葡萄糖转运中的作用。在存在和不存在AMPK激活剂AICAR（5-氨基咪唑-4-甲酰胺核苷）和二甲双胍以及p38抑制剂SB203580的情况下，测量小鼠空肠中的[3H]3-O-甲基葡萄糖通量。为了区分钠偶联（SGLT1）和扩散（GLUT2）的进入途径，在存在SGLT1和GLUT2抑制剂根皮苷和根皮素的情况下测量通量。通过逆转录酶PCR测量葡萄糖转运蛋白mRNA水平，并通过蛋白质印迹进行定位。通过腔内生物素化评估表面表达的GLUT2。通过蛋白质印迹分析p38丝裂原活化蛋白激酶的激活情况。我们发现用AICAR处理空肠组织会导致净葡萄糖摄取增加，并与p38丝裂原活化蛋白激酶的磷酸化有关。抑制p38可消除AICAR刺激的葡萄糖摄取。根皮素消除了AICAR介导的葡萄糖通量增加，而根皮苷没有影响，表明GLUT2参与其中。此外，AICAR降低了SGLT1的总蛋白水平，同时增加了刷状缘膜中GLUT2的水平。抗糖尿病药物二甲双胍是一种已知的AMPK激活剂，也诱导GLUT2定位于腔内表面。我们得出结论，AMPK的激活导致GLUT2介导的非能量依赖性葡萄糖摄取上调，同时钠依赖性葡萄糖转运下调。
