Hyperglycemia impairs glucose and insulin regulation of nitric oxide production in glucose-inhibited neurons in the ventromedial hypothalamus.
Physiological changes in extracellular glucose, insulin, and leptin regulate glucose-excited (GE) and glucose-inhibited (GI) neurons in the ventromedial hypothalamus (VMH). Nitric oxide (NO) signaling, which is involved in the regulation of food intake and insulin signaling, is altered in obesity and diabetes. We previously showed that glucose and leptin inhibit NO production via the AMP-activated protein kinase (AMPK) pathway, while insulin stimulates NO production via the phosphatidylinositol-3-OH kinase (PI3K) pathway in VMH GI neurons. Hyperglycemia-induced inhibition of AMPK reduces PI3K signaling by activating the mammalian target of rapamycin (mTOR). We hypothesize that hyperglycemia impairs glucose and insulin-regulated NO production in VMH GI neurons. This hypothesis was tested in VMH neurons cultured in hyperglycemic conditions or from streptozotocin-induced type 1 diabetic rats using NO- and membrane potential-sensitive dyes. Neither decreased extracellular glucose from 2.5 to 0.5 mM, nor 5 nM insulin increased NO production in VMH neurons in either experimental condition. Glucose- and insulin-regulated NO production was restored in the presence of the AMPK activator, 5-aminoimidazole-4-carboxamide-1-b-4-ribofuranoside or the mTOR inhibitor rapamycin. Finally, decreased glucose and insulin did not alter membrane potential in VMH neurons cultured in hyperglycemic conditions or from streptozotocin-induced rats. These data suggest that hyperglycemia impairs glucose and insulin regulation of NO production through AMPK inhibition. Furthermore, glucose and insulin signaling pathways interact via the mTOR pathway.
Canabal
Debra D
DD
Department of Pharmacology & Physiology, New Jersey Medical School, 185 S. Orange Ave., PO Box 1709, Newark, NJ 07101-1709, USA.
Potian
Joseph G
JG
Duran
Ricardo G
RG
McArdle
Joseph J
JJ
Routh
Vanessa H
VH
D055372:AMP-Activated Protein Kinases; D000208:Acute Disease; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism; D005260:Female; D005452:Fluoresceins; D006943:Hyperglycemia / Q000378:metabolism*; D007328:Insulin / Q000097:blood*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009097:Multienzyme Complexes / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D058570:TOR Serine-Threonine Kinases; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology / Q000378:metabolism*
C503301:4-amino-5-methylamino-2',7'-difluorofluorescein diacetate; D001786:Blood Glucose; D005452:Fluoresceins; D007328:Insulin; D009097:Multienzyme Complexes; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases