Glucose, insulin, and leptin signaling pathways modulate nitric oxide synthesis in glucose-inhibited neurons in the ventromedial hypothalamus.
Glucose-sensing neurons in the ventromedial hypothalamus (VMH) are involved in the regulation of glucose homeostasis. Glucose-sensing neurons alter their action potential frequency in response to physiological changes in extracellular glucose, insulin, and leptin. Glucose-excited neurons decrease, whereas glucose-inhibited (GI) neurons increase, their action potential frequency when extracellular glucose is reduced. Central nitric oxide (NO) synthesis is regulated by changes in local fuel availability, as well as insulin and leptin. NO is involved in the regulation of food intake and is altered in obesity and diabetes. Thus this study tests the hypothesis that NO synthesis is a site of convergence for glucose, leptin, and insulin signaling in VMH glucose-sensing neurons. With the use of the NO-sensitive dye 4-amino-5-methylamino-2',7'-difluorofluorescein in conjunction with the membrane potential-sensitive dye fluorometric imaging plate reader, we found that glucose and leptin suppress, whereas insulin stimulates neuronal nitric oxide synthase (nNOS)-dependent NO production in cultured VMH GI neurons. The effects of glucose and leptin were mediated by suppression of AMP-activated protein kinase (AMPK). The AMPK activator 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) increased both NO production and neuronal activity in GI neurons. In contrast, the effects of insulin on NO production were blocked by the phosphoinositide 3-kinase inhibitors wortmannin and LY-294002. Furthermore, decreased glucose, insulin, and AICAR increase the phosphorylation of VMH nNOS, whereas leptin decreases it. Finally, VMH neurons express soluble guanylyl cyclase, a downstream mediator of NO signaling. Thus NO may mediate, in part, glucose, leptin, and insulin signaling in VMH glucose-sensing neurons.
Canabal
Debra D
DD
Department of Pharmacology amd Physiology, New Jersey Medical School, 185 S. Orange Ave., PO Box 1709, Newark, NJ 07101-1709, USA.
Song
Zhentao
Z
Potian
Joseph G
JG
Beuve
Annie
A
McArdle
Joseph J
JJ
Routh
Vanessa H
VH
D000091162:AMP-Activated Protein Kinase Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005947:Glucose / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D020738:Leptin / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D009569:Nitric Oxide / Q000032:analysis / Q000096:biosynthesis*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012265:Ribonucleotides / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D013997:Time Factors; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D000077191:Wortmannin
C503301:4-amino-5-methylamino-2',7'-difluorofluorescein diacetate; D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D005456:Fluorescent Dyes; D007328:Insulin; D020738:Leptin; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012265:Ribonucleotides; D009569:Nitric Oxide; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D000620:Aminoimidazole Carboxamide; D052248:Nitric Oxide Synthase Type I; D011494:Protein Kinases; D000091162:AMP-Activated Protein Kinase Kinases; C031143:AICA ribonucleotide; D005947:Glucose; D000077191:Wortmannin