Background/Aims: In fat cells of obese humans, basal lipolysis is increased but catecholamine-stimulated lipolysis is blunted. This is linked to decreased expression of hormone-sensitive lipase (HSL). Upon stimulation by cAMP, HSL is phosphorylated at several serine residues (P-Ser552, P-Ser649 and P-Ser650) leading to enzymatic activation. In contrast, P-Ser554 prevents phosphorylation at Ser552 and is thus considered an inactivating site. We hypothesized that differences in HSL phosphorylation could be linked to disturbed adipocyte lipolysis in obesity. Methods: Phosphorylation at Ser552, Ser554, Ser650 as well as total HSL and adipose triglyceride lipase (ATGL) protein expression were assessed by Western blot in subcutaneous adipose tissue samples of 32 obese women. Basal and stimulated lipolysis in isolated fat cells were correlated to phosphorylation levels. Results: While there was no correlation between basal lipolysis and P-Ser650 or P-Ser554, there was a negative correlation with P-Ser552 (r = 0.39; p < 0.05). In contrast, only P-Ser554 was strongly and negatively correlated with noradrenaline- (r = –0.50; p < 0.01) and dibutyryl cAMP-stimulated (r = –0.45; p < 0.05) lipolysis. There were no significant correlations between any measure of lipolysis and total levels of HSL and ATGL. Conclusion: In contrast to total HSL and ATGL levels, phosphorylation at Ser554 and Ser552, but not at Ser650, may differentially predict adipocyte lipolysis in vitro. Posttranslational modifications of HSL may therefore constitute an important regulator of adipocyte lipolysis, at least in adipose tissue of obese women. Whether this is also relevant in lean individuals remains to be demonstrated.

Keywords:
Adipocyte, Lipolysis, Obesity
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© 2011 S. Karger AG, Basel
2011
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