Hydrogen peroxide-induced translocation of glycolipid-anchored (c)AMP-hydrolases to lipid droplets mediates inhibition of lipolysis in rat adipocytes.
BACKGROUND
The insulin-independent inhibition of lipolysis by palmitate, the anti-diabetic sulphonylurea glimepiride and H2O2 in rat adipocytes involves stimulation of the glycosylphosphatidylinositol (GPI)-specific phospholipase-C (GPI-PLC) and subsequent translocation of the GPI-anchored membrane ectoproteins (GPI-proteins), Gce1 and cluster of differentiation antigen (CD73), from specialized plasma membrane microdomains (DIGs) to cytosolic lipid droplets (LDs). This results in cAMP degradation at the LD surface and failure to activate hormone-sensitive lipase. Reactive oxygen species (ROS) may trigger this sequence of events in response to palmitate and glimepiride.


METHODS
The effects of various inhibitors of ROS production on the release of H2O2, GPI anchor cleavage and translocation of the photoaffinity-labelled or metabolically labelled Gce1 and CD73 from DIGs to LD and inhibition of lipolysis by different fatty acids and sulphonylureas were studied with primary rat adipocytes.


RESULTS
Glimepiride and palmitate induced the production of H2O2 via the plasma membrane NADPH oxidase and mitochondrial complexes I and III, respectively. Inhibition of ROS production was accompanied by the loss of (i) GPI-PLC activation, (ii) Gce1 and CD73 translocation and (iii) lipolysis inhibition in response to palmitate and glimepiride. Non-metabolizable fatty acids and the sulphonylurea drug tolbutamide were inactive. NADPH oxidase and GPI-PLC activities colocalized at DIGs were stimulated by glimepiride but not tolbutamide.


CONCLUSIONS
The data suggest that ROS mediate GPI-PLC activation at DIGs and subsequent GPI-protein translocation from DIGs to LD in adipocytes which leads to inhibition of lipolysis by palmitate and glimepiride. This insulin-independent anti-lipolytic mechanism may be engaged by future anti-diabetic drugs.
Müller
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Sanofi-Aventis Pharma Deutschland GmbH, TD Metabolism, Frankfurt am Main, Germany. Guenter.Mueller@sanofi-aventis.com
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Jung
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D015720:5'-Nucleotidase / Q000378:metabolism; D017667:Adipocytes; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D005227:Fatty Acids / Q000494:pharmacology; D054800:Glycosylphosphatidylinositol Diacylglycerol-Lyase / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008066:Lipolysis / Q000187:drug effects; D021962:Membrane Microdomains / Q000378:metabolism; D019255:NADPH Oxidases / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017382:Reactive Oxygen Species / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013453:Sulfonylurea Compounds / Q000494:pharmacology
D005227:Fatty Acids; D017261:Glycosylphosphatidylinositols; D017382:Reactive Oxygen Species; D013453:Sulfonylurea Compounds; D006861:Hydrogen Peroxide; D000242:Cyclic AMP; D019255:NADPH Oxidases; D015720:5'-Nucleotidase; D054800:Glycosylphosphatidylinositol Diacylglycerol-Lyase