Hormone-sensitive Lipase Ser660 Research Articles

Effects of liraglutide on lipolysis and the AC3/PKA/HSL pathway.

BackgroundLiraglutide reduces blood glucose, body weight and blood lipid levels. Hormone-sensitive lipase (HSL) is a key enzyme in lipolysis. Evidence from our and other studies have demonstrated that adenylate cyclase 3 (AC3) is associated with obesity and can be upregulated by liraglutide in obese mice. In the present study, we investigated whether hepatic HSL activity is regulated by liraglutide and characterized the effect of liraglutide in the AC3/protein kinase A (PKA)/HSL signalling pathway.MethodsObese mice or their lean littermates were treated with liraglutide or saline for 8 weeks. Serum was collected for the measurement of insulin and lipids. We investigated hepatic AC3, HSL and phosphorylated HSL Ser-660 (p-HSL(S660)) protein expression levels andAC3 and HSL mRNA expression levels and cyclic adenosine monophosphate (cAMP), PKA activity in liver tissue.ResultsLiraglutide treatment decreased triglycerides (TGs) and free fatty acids (FFAs), increased glycerol, and upregulated hepatic AC3 and p-HSL(s660) levels and cAMP and PKA activities.ConclusionThe results suggest that liraglutide can upregulates AC3/PKA/HSL pathway and may promotes lipolysis.

AMPK activation by A-769662 and 991 does not affect catecholamine-induced lipolysis in human adipocytes.

Activation of AMP-activated protein kinase (AMPK) is considered an attractive strategy for the treatment of type 2 diabetes. Favorable metabolic effects of AMPK activation are mainly observed in skeletal muscle and liver tissue, whereas the effects in human adipose tissue are only poorly understood. Previous studies, which largely employed the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), suggest an antilipolytic role of AMPK in adipocytes. The aim of this work was to reinvestigate the role of AMPK in the regulation of lipolysis, using the novel allosteric small-molecule AMPK activators A-769662 and 991, with a focus on human adipocytes. For this purpose, human primary subcutaneous adipocytes were treated with A-769662, 991, or AICAR, as a control, before being stimulated with isoproterenol. AMPK activity status, glycerol release, and the phosphorylation of hormone-sensitive lipase (HSL), a key regulator of lipolysis, were then monitored. Our results show that both A-769662 and 991 activated AMPK to a level that was similar to, or greater than, that induced by AICAR. In contrast to AICAR, which as expected was antilipolytic, neither A-769662 nor 991 affected lipolysis in human adipocytes, although 991 treatment led to altered HSL phosphorylation. Furthermore, we suggest that HSL Ser660 is an important regulator of lipolytic activity in human adipocytes. These data suggest that the antilipolytic effect observed with AICAR in previous studies is, at least to some extent, AMPK independent.

Insulin Resistance and In Vivo Lipolytic Rate Are Positively Associated with Body Iron Stores in Obese Women

High body iron stores are positively related to insulin resistance in humans, but the underlying mechanisms remain unresolved. Iron stimulates lipolysis in murine adipocytes in vitro, but the influence of iron stores on lipolytic rate in vivo is unknown. Our aim was to determine if body iron stores are associated with lipolytic rate and whole-body insulin sensitivity in obese, pre-menopausal women. We studied 20 subjects with clinically-normal (20-200 ng/mL) plasma [ferritin], an index of body iron stores. Fatty acid rate of appearance into systemic circulation (FA Ra) was assessed by 13C-palmitate isotope dilution, insulin resistance was assessed by hyperinsulinemic-euglycemic clamp, and abdominal subcutaneous adipose tissue protein expression was assessed via immunoblot. [Ferritin] was significantly (p < 0.01), positively correlated with FA Ra (r2 = 0.42), adipose hormone sensitive lipaseser660 phosphorylation (p-HSLser660, a marker of lipolytic activation in adipose tissue; r2 = 0.41), and whole-body insulin resistance (r2 = 0.33). Importantly, [ferritin] remained a significant, independent predictor for these parameters in multiple regression models including body mass index, plasma [adiponectin], and plasma [CRP] as covariates. We stratified subjects into tertiles based on [ferritin] to compare high-normal and low-normal [ferritin] groups (138 ± 30 vs. 40 ± 15 ng/mL). Compared with the low-normal [ferritin] group, the high-normal [ferritin] group had significantly (p < 0.02) higher FA Ra (15.6 ± 5.5 vs. 8.8 ± 2.4 µmol/kg fat mass/min), adipose p-HSLser660 (1.3 ± 0.4 vs. 0.6 ± 0.2 AU) and whole-body insulin resistance (glucose infusion rate 9.2 ± 2.3 vs. 14.3 ± 3.5 mg/kg fat free mass/min). There were no between-group differences in anthropometric characteristics, plasma [adiponectin], or plasma [CRP]. Our findings suggest that iron-mediated activation of adipose lipolysis may be a mechanism linking body iron stores and insulin resistance in obese humans. Disclosure B.J. Ryan: None. D.W. Van Pelt: None. L.M. Guth: None. A. Ludzki: None. R.A. Gioscia-Ryan: None. C. Ahn: None. J.F. Horowitz: None.

B56α/Protein Phosphatase 2A Inhibits Adipose Lipolysis in High-Fat Diet-Induced Obese Mice

Lipolysis and lipogenesis are two opposite processes that control lipid storage in adipocytes. Impaired adipose lipolysis has been observed in both obese human subjects and animal models. This study investigated the mechanisms underlying impaired adipose lipolysis in a high-fat diet-induced obese (DIO) mouse model. DIO models were created using male C57BL/6 mice. Our results show that beta3 adrenergic receptor-specific agonist BRL37344 induced adipose lipolysis was significantly blunted in DIO mice. The levels of Ser660 phosphorylation of hormone-sensitive lipase (HSL) were significantly decreased in the epididymal fat of DIO mice. However, protein levels of HSL, adipose triglyceride lipase and its coactivator comparative gene identification-58 were similar between DIO and control mice. It is known that upon lipolytic hormone stimulation, protein kinase A phosphorylates HSL Ser660 and activates HSL, whereas protein phosphatase 2A (PP2A) dephosphorylates and inactivates HSL. Interestingly, our study shows that high-fat feeding did not alter epididymal fat cAMP and protein kinase A protein levels but significantly increased the expression of the alpha-isoform of PP2A regulatory subunit B' (B56alpha). To study the role of B56alpha in obesity-associated lipolytic defect, B56alpha was overexpressed or knocked down by adenovirus-mediated gene transduction in cultured 3T3-L1CARDelta1 adipocytes. Overexpression of B56alpha significantly decreased HSL Ser660 phosphorylation. In contrast, knocking down B56alpha increased hormone-stimulated HSL activation and lipolysis in mature 3T3-L1CARDelta1 adipocytes. These results strongly suggest that elevated B56alpha/PP2A inhibits HSL and lipolysis in white adipose tissue of DIO mice.

Adrenergic regulation of HSL serine phosphorylation and activity in human skeletal muscle during the onset of exercise

Skeletal muscle hormone-sensitive lipase (HSL) activity is increased by contractions and increases in blood epinephrine (EPI) concentrations and cyclic AMP activation of the adrenergic pathway during prolonged exercise. To determine the importance of hormonal stimulation of HSL activity during the onset of moderate- and high-intensity exercise, nine men [age 24.3 +/- 1.2 yr, 80.8 +/- 5.0 kg, peak oxygen consumption (VO2 peak) 43.9 +/- 3.6 ml x kg(-1) x min(-1)] cycled for 1 min at approximately 65% VO2 peak, rested for 60 min, and cycled at approximately 90% VO2 peak for 1 min. Skeletal muscle biopsies were taken pre- and postexercise, and arterial blood was sampled throughout exercise. Arterial EPI increased (P < 0.05) postexercise at 65% (0.45 +/- 0.10 to 0.78 +/- 0.27 nM) and 90% VO2 peak (0.57 +/- 0.34 to 1.09 +/- 0.50 nM). HSL activity increased (P < 0.05) following 1 min of exercise at 65% VO2 peak [1.05 +/- 0.39 to 1.78 +/- 0.54 mmol x min(-1) x kg dry muscle (dm)(-1)] and 90% VO2 peak (1.07 +/- 0.24 to 1.91 +/- 0.62 mmol x min(-1) x kg dm(-1)). Cyclic AMP content also increased (P < 0.05) at both exercise intensities (65%: 1.52 +/- 0.67 to 2.75 +/- 1.12, 90%: 1.85 +/- 0.65 to 2.64 +/- 0.93 micromol/kg dm). HSL Ser660 phosphorylation (approximately 55% increase) and ERK1/2 phosphorylation ( approximately 33% increase) were augmented following exercise at both intensities, whereas HSL Ser563 and Ser565 phosphorylation were not different from rest. The results indicate that increases in arterial EPI concentration during the onset of moderate- and high-intensity exercise increase cyclic AMP content, which results in the phosphorylation of HSL Ser660. This adrenergic stimulation contributes to the increase in HSL activity that occurs in human skeletal muscle in the first minute of exercise at 65% and 90% VO2 peak.