AMP-activated protein kinase and nitric oxide regulate the glucose sensitivity of ventromedial hypothalamic glucose-inhibited neurons.
The mechanisms by which glucose regulates the activity of glucose-inhibited (GI) neurons in the ventromedial hypothalamus (VMH) are largely unknown. We have previously shown that AMP-activated protein kinase (AMPK) increases nitric oxide (NO) production in VMH GI neurons. We hypothesized that AMPK-mediated NO signaling is required for depolarization of VMH GI neurons in response to decreased glucose. In support of our hypothesis, inhibition of neuronal nitric oxide synthase (nNOS) or the NO receptor soluble guanylyl cyclase (sGC) blocked depolarization of GI neurons to decreased glucose from 2.5 to 0.7 mM or to AMPK activation. Conversely, activation of sGC or the cell-permeable analog of cGMP, 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), enhanced the response of GI neurons to decreased glucose, suggesting that stimulation of NO-sGC-cGMP signaling by AMPK is required for glucose sensing in GI neurons. Interestingly, the AMPK inhibitor compound C completely blocked the effect of sGC activation or 8-Br-cGMP, and 8-Br-cGMP increased VMH AMPKalpha2 phosphorylation. These data suggest that NO, in turn, amplifies AMPK activation in GI neurons. Finally, inhibition of the cystic fibrosis transmembrane regulator (CFTR) Cl(-) conductance blocked depolarization of GI neurons to decreased glucose or AMPK activation, whereas decreased glucose, AMPK activation, and 8-Br-cGMP increased VMH CFTR phosphorylation. We conclude that decreased glucose triggers the following sequence of events leading to depolarization in VMH GI neurons: AMPK activation, nNOS phosphorylation, NO production, and stimulation of sGC-cGMP signaling, which amplifies AMPK activation and leads to closure of the CFTR.
Murphy
Beth Ann
BA
Dept. of Pharmacology and Physiology, New Jersey Medical School, PO Box 1709, Newark, NJ 07101-1709, USA.
Fakira
Kurt A
KA
Song
Zhentao
Z
Beuve
Annie
A
Routh
Vanessa H
VH
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002712:Chlorides / Q000378:metabolism; D006152:Cyclic GMP; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D015248:Gemfibrozil; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006162:Guanylate Cyclase; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction; D000071756:Soluble Guanylyl Cyclase; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology* / Q000378:metabolism
D002712:Chlorides; D018160:Receptors, Cytoplasmic and Nuclear; D012265:Ribonucleotides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D009569:Nitric Oxide; D000620:Aminoimidazole Carboxamide; D052248:Nitric Oxide Synthase Type I; D055372:AMP-Activated Protein Kinases; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; C031143:AICA ribonucleotide; D006152:Cyclic GMP; D005947:Glucose; D015248:Gemfibrozil