Neuronal nitric oxide synthase protects the pancreatic beta cell from glucolipotoxicity-induced endoplasmic reticulum stress and apoptosis.
OBJECTIVE
Cytokines stimulate nitric oxide production in pancreatic beta cells, leading to endoplasmic reticulum (ER) stress and apoptosis. Treatment of beta cells with glucose and NEFA induces nitric oxide synthase (NOS) as well as ER stress. However, the role of NO in glucolipotoxicity-induced ER stress in beta cells is not clear.


METHODS
We studied the effect of high glucose and palmitate levels on NOS isoform production in rat and Psammomys obesus islets and in insulinoma-1E beta cells. The effects of neuronal NOS (nNOS) inhibition by small interfering RNA or by N (omega)-nitro-L-arginine methyl ester (L-NAME) on beta cell function, ER stress and apoptosis under conditions of glucolipotoxicity were investigated.


RESULTS
Overnight incubation of rat and P. obesus islets at 22.2 mmol/l glucose with 0.5 mmol/l palmitate induced the production of nNOS but not inducible NOS (iNOS), in contrast with the robust stimulation of iNOS by cytokines. NOS inhibition by L-NAME did not prevent the decrease in glucose-stimulated insulin secretion and proinsulin biosynthesis or the depletion of islet insulin content observed under conditions of glucolipotoxicity. Moreover, treatment of beta cells with palmitate and L-NAME together resulted in marked activation of the IRE1alpha and PERK pathways of the unfolded protein response. This was associated with increased JNK phosphorylation and apoptosis in islets and beta cells. Moreover, partial nNos knockdown increased JNK phosphorylation and CHOP production, leading to apoptosis.


CONCLUSIONS
In beta cells subjected to glucolipotoxic conditions, chronic inhibition of NOS exacerbates ER stress and activates JNK. Therefore, induction of nNOS is an adaptive response to glucolipotoxicity that protects beta cells from stress and apoptosis.
Bachar
E
E
Endocrinology and Metabolism Service, Department of Medicine, Hadassah Hebrew University Medical Center, P.O. Box 12000, Jerusalem 91120, Israel.
Ariav
Y
Y
Cerasi
E
E
Kaiser
N
N
Leibowitz
G
G
D000704:Analysis of Variance; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D019308:Palmitic Acid / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011863:Radioimmunoassay; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects
D004791:Enzyme Inhibitors; D007328:Insulin; D019308:Palmitic Acid; D052248:Nitric Oxide Synthase Type I; D048670:MAP Kinase Kinase 4; D005947:Glucose; D019331:NG-Nitroarginine Methyl Ester