High density lipoprotein (HDL) promotes glucose uptake in adipocytes and glycogen synthesis in muscle cells - PubMed (original) (raw)
High density lipoprotein (HDL) promotes glucose uptake in adipocytes and glycogen synthesis in muscle cells
Qichun Zhang et al. PLoS One. 2011.
Abstract
Background: High density lipoprotein (HDL) was reported to decrease plasma glucose and promote insulin secretion in type 2 diabetes patients. This investigation was designed to determine the effects and mechanisms of HDL on glucose uptake in adipocytes and glycogen synthesis in muscle cells.
Methods and results: Actions of HDL on glucose uptake and GLUT4 translocation were assessed with 1-[(3)H]-2-deoxyglucose and plasma membrane lawn, respectively, in 3T3-L1 adipocytes. Glycogen analysis was performed with amyloglucosidase and glucose oxidase-peroxidase methods in normal and palmitate-treated L6 cells. Small interfering RNA was used to observe role of scavenger receptor type I (SR-BI) in glucose uptake of HDL. Corresponding signaling molecules were detected by immunoblotting. HDL stimulated glucose uptake in a time- and concentration-dependent manner in 3T3-L1 adipocytes. GLUT4 translocation was significantly increased by HDL. Glycogen deposition got enhanced in L6 muscle cells paralleling with elevated glycogen synthase kinase3 (GSK3) phosphorylation. Meanwhile, increased phosphorylations of Akt-Ser473 and AMP activated protein kinase (AMPK) α were detected in 3T3-L1 adipocytes. Glucose uptake and Akt-Ser473 activation but not AMPK-α were diminished in SR-BI knock-down 3T3-L1 cells.
Conclusions: HDL stimulates glucose uptake in 3T3-L1 adipocytes through enhancing GLUT4 translocation by mechanisms involving PI3K/Akt via SR-BI and AMPK signaling pathways, and increases glycogen deposition in L6 muscle cells through promoting GSK3 phosphorylation.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures
Figure 1. HDL stimulates glucose uptake in 3T3-L1 adipocytes.
3T3-L1 adipocytes were incubated with vehicle or stimulators for 30 min before being incubated for another 30 min with 1-[3H]-2- deoxyglucose. (A) 3T3-L1 adipocytes were incubated with vehicle (BSA), HDL (50 µg protein/ml), insulin (100 nmol/L) or indicated combination. (B) 3T3-L1 adipocytes were incubated with vehicle and HDL of indicated concentrations. (C) 3T3-L1 adipocytes were incubated with vehicle, HDL (50 µg protein/ml) at indicated time points. (D) 3T3-L1 adipocytes were incubated with vehicle, HDL (50 µg protein/ml), apoAI (50 µg/ml) and indicated combination with LY294002 (2 µmol/L), L-NAME (2 mmol/L) and PD98059 (1 µmol/L). Data are expressed as means±SEM of three independent experiments, n = 6. * p<0.05, ** p<0.01, vs vehicle; ## p<0.01, vs HDL.
Figure 2. HDL increases glycogen synthesis in L6 cells and muscle tissue in vivo.
(A) L6 cells starved overnight were incubated with vehicle, HDL (50 µg protein/ml), insulin (100 nmol/L) or indicated combination for 2 h, n = 6. (B and C) GSK3α (B) and GSK3β (C) phosphorylation in lysates from incubated L6 cells at basal condition and after incubation with stimulators as (A), n = 3. (D) L6 cells were treated with palmitate (0.4 mmol/L) for 12 h followed by incubation with HDL of indicated concentrations for 2 h, n = 6. (E) GSK3β phosphorylation in lysates from incubated L6 cells under conditions as (D), n = 3. Data are expressed as means±SEM of three independent experiments performed in vitro. * p<0.05, ** p<0.01, vs vehicle; § p<0.05, vs palmitate.
Figure 3. HDL enhances GLUT4 exocytosis and inhibits GLUT4 endocytosis in 3T3-L1 adipocytes.
(A) 3T3-L1 adipocytes were treated in the absence and presence of 50 µg protein/ml HDL for indicated time points. GLUT4 was immunofluorescently labeled with GLUT4 antibody and followed by FITC-conjugated goat anti-rabbit IgG incubation in plasma membrane sheets. (B) 3T3-L1 adipocytes were chilled to 4°C, and labeled with FITC-cholera toxin B. Then adipocytes were incubated in the absence or presence of HDL for 2.5 h to allow cholera toxin B internalization. (C and D) Akt (C) and AMPKα (D) phosphorylation in lysates from 3T3-L1 adipocytes incubated with vehicle and indicated stimulators analyzed with corresponding antibodies. Data are expressed as mean±SEM of three independent experiments. n = 3. * p<0.05, ** p<0.01, vs vehicle.
Figure 4. HDL prompts glucose uptake via SR-BI.
(A) The relative expression of SR-BI to GAPDH in 3T3-L1 adipocytes with treatment of vehicle, control siRNA and SR-BI siRNA. (B) Glucose uptake in 3T3-L1 adipocytes with and without SR-BI RNA interfering were incubated in the absence or presence of HDL (50 µg protein/ml), n = 6. (C and D) Akt (C) and AMPKα (D) phosphorylation in 3T3-L1 adipocytes with and without SR-BI RNA interfering were incubated in the absence or presence of HDL (50 µg protein/ml), n = 3. Data are expressed as mean±SEM of three independent experiments. ** p<0.01, vs vehicle; §§ p<0.01, vs control RNA interfering.
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