G Protein and cAMP-Dependent Protein Kinase Mediate Amyloid -Peptide Inhibition of Neuronal Glucose Uptake 1 Teerasak Prapong, Etsuro Uemura, and Walter H. Hsu Department of Biomedical Sciences, 2008 Veterinary Medicine Building, Iowa State University, Ames, Iowa 50011 Received July 12, 1999; accepted July 19, 2000 The mechanism by which amyloid -peptide (A) inhibits glucose uptake in cultured cells is not known. Here we demonstrated a signaling pathway in which A25-35, a neurotoxic portion of the A peptide corre- sponding to amino acids 25–35, inhibits neuronal glu- cose uptake by hippocampal neurons. The GP antago- nist-2, which blocks Gs, prevented the inhibitory ef- fect of A on the glucose uptake. Exposure of cells to A resulted in a transitory increase in intracellular levels of cAMP. To assess the role of cAMP in neuronal glucose uptake, cultured neurons were exposed to dibutyryl cAMP (Bt 2 cAMP) or an adenylyl cyclase ac- tivator, forskolin. Both Bt 2 cAMP and forskolin inhib- ited neuronal glucose uptake, and cAMP-dependent protein kinase (PKA) inhibitor KT5720 blocked the A-mediated inhibition of glucose uptake. Cholera toxin, which stimulates adenylyl cyclase by activating Gs protein, also inhibited neuronal glucose uptake, and A potentiated this inhibitory effect of cholera toxin on glucose uptake. Thus, our findings suggest that A inhibits glucose uptake by activating the Gs- coupled receptors and involves the cAMP–PKA system. © 2001 Academic Press Key Words: Alzheimer’s disease; -amyloid; glucose uptake; hippocampal neuron; G protein; cAMP. INTRODUCTION Alzheimer’s disease (AD) is characterized by deposi- tion of amyloid -peptide (A), a 39- to 43-amino-acid protein (40). It has been shown that A impairs glucose uptake in cultured hippocampal neurons (20) and as- trocytes (26); however, it is not known whether A affects glucose uptake in the brain of AD patients. There is some evidence suggesting that glucose metab- olism is changed in the brains of AD patients (4, 12, 29, 31). It was calculated that reduction of cerebral glucose utilization ranges from 19% in mild cases to 40% and more in severe cases of AD (11, 17). Immunohistochem- ical studies revealed a decrease in glucose transporters (GLUT1, GLUT3) in several brain regions, including the hippocampus, the area commonly affected in AD patients (9, 36). Reduced glucose uptake by individuals genetically at risk for developing AD also supports the notion that glucose deprivation precedes neuronal de- generation (16, 27, 30). In healthy, nonstarved mammalian brain, glucose is the only substrate for the formation of energy in the form of ATP (5). Glucose deprivation results in in- creased use of endogenous substrates, depletion of ATP, membrane depolarization, extracellular accumu- lation of excitatory amino acids, loss of neuronal ho- meostasis, and ultimately neuronal cell death (21). Neurons interfered with glucose uptake or exposed to A result in impaired mitochondrial activity and sup- pressed production of ATP (21). Based on the rates of oxidized glucose and oxygen, it was estimated that the rate of cerebral ATP formation decreases by 7% in early-onset AD and 20% in late-onset AD (10). Such metabolic impairment increases neuronal vulnerabil- ity to glutamate toxicity and oxidative insults (21). There are numerous published reports linking A to neurotoxicity in vivo and in vitro. However, how A inhibits glucose uptake is not known. It was shown that A induces conjugation of 4-hydroxynonenal (HNE), the product of lipid peroxidation, with neuronal transporter GLUT3, resulting in impaired glucose transport (20). Subsequent studies in synaptosomes from the rat cerebral cortex showed that A and HNE impair glucose transport and severely compromise mi- tochondrial function (15). These studies suggest that A-mediated oxidative stress inhibits neuronal glucose uptake. In the present study, we found that A inhibi- tion on neuronal glucose uptake involves Gs–adenylyl cyclase coupling and activation of cAMP-dependent protein kinase (PKA), suggesting the presence of alter- native mechanism by which A inhibits glucose uptake in cultured hippocampal neurons. 1 This study was supported by a special research initiation grant from the Iowa State University Graduate College and the Thai government. Experimental Neurology 167, 59 – 64 (2001) doi:10.1006/exnr.2000.7519, available online at http://www.idealibrary.com on 59 0014-4886/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved.