Peroxisome proliferator-activated receptor alpha (PPARalpha) protects against oleate-induced INS-1E beta cell dysfunction by preserving carbohydrate metabolism.
OBJECTIVE
Pancreatic beta cells chronically exposed to fatty acids may lose specific functions and even undergo apoptosis. Generally, lipotoxicity is triggered by saturated fatty acids, whereas unsaturated fatty acids induce lipodysfunction, the latter being characterised by elevated basal insulin release and impaired glucose responses. The peroxisome proliferator-activated receptor alpha (PPARalpha) has been proposed to play a protective role in this process, although the cellular mechanisms involved are unclear.


METHODS
We modulated PPARalpha production in INS-1E beta cells and investigated key metabolic pathways and genes responsible for metabolism-secretion coupling during a culture period of 3 days in the presence of 0.4 mmol/l oleate.


RESULTS
In INS-1E cells, the secretory dysfunction primarily induced by oleate was aggravated by silencing of PPARalpha. Conversely, PPARalpha upregulation preserved glucose-stimulated insulin secretion, essentially by increasing the response at a stimulatory concentration of glucose (15 mmol/l), a protection we also observed in human islets. The protective effect was associated with restored glucose oxidation rate and upregulation of the anaplerotic enzyme pyruvate carboxylase. PPARalpha overproduction increased both beta-oxidation and fatty acid storage in the form of neutral triacylglycerol, revealing overall induction of lipid metabolism. These observations were substantiated by expression levels of associated genes.


CONCLUSIONS
PPARalpha protected INS-1E beta cells from oleate-induced dysfunction, promoting both preservation of glucose metabolic pathways and fatty acid turnover.
Frigerio
F
F
Department of Cell Physiology and Metabolism, University of Geneva Medical Center, 1 rue Michel-Servet, 1211 Geneva 4, Switzerland.
Brun
T
T
Bartley
C
C
Usardi
A
A
Bosco
D
D
Ravnskjaer
K
K
Mandrup
S
S
Maechler
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D018955:CD36 Antigens / Q000235:genetics; D002241:Carbohydrates / Q000502:physiology*; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics; D018929:Cell Culture Techniques; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology; D005786:Gene Expression Regulation; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D019301:Oleic Acid / Q000633:toxicity*; D047493:PPAR alpha / Q000494:pharmacology / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014404:Tubulin / Q000235:genetics
D018955:CD36 Antigens; D002241:Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D047493:PPAR alpha; D014404:Tubulin; D019301:Oleic Acid; D000255:Adenosine Triphosphate; D002334:Carnitine O-Palmitoyltransferase; D005947:Glucose