OBJECTIVE: To investigate the effect CD36 deficiency on muscle insulin signaling in mice fed a normal-fat diet and explore the possible mechanism. METHODS: Wild-type (WT) mice and systemic CD36 knockout (CD36^-/-) mice with normal feeding for 14 weeks (n=12) were subjected to insulin tolerance test (ITT) after intraperitoneal injection with insulin (1 U/kg). Real-time PCR was used to detect the mRNA expressions of insulin receptor (IR), insulin receptor substrate 1/2 (IRS1/2) and protein tyrosine phosphatase 1B (PTP1B), and Western blotting was performed to detect the protein expressions of AKT, IR, IRS1/2 and PTP1B in the muscle tissues of the mice. Tyrosine phosphorylation of IR and IRS1 and histone acetylation of PTP1B promoter in muscle tissues were detected using co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation (ChIP), respectively. RESULTS: CD36^-/- mice showed significantly lowered insulin sensitivity with obviously decreased area under the insulin tolerance curve in comparison with the WT mice (P < 0.05). CD36^-/- mice also had significantly higher serum insulin concentration and HOMA-IR than WT mice (P < 0.05). Western blotting showed that the p-AKT/AKT ratio in the muscle tissues was significantly decreased in CD36^-/- mice as compared with the WT mice (P < 0.01). No significant differences were found in mRNA and protein levels of IR, IRS1 and IRS2 in the muscle tissues between WT and CD36^-/- mice (P>0.05). In the muscle tissue of CD36^-/- mice, tyrosine phosphorylation levels of IR and IRS1 were significantly decreased (P < 0.05), and the mRNA and protein levels of PTP1B (P < 0.05) and histone acetylation level of PTP1B promoters (P < 0.01) were significantly increased as compared with those in the WT mice. Intraperitoneal injection of claramine, a PTP1B inhibitor, effectively improved the impairment of insulin sensitivity in CD36^-/- mice. CONCLUSION CD36 is essential for maintaining muscle insulin sensitivity under physiological conditions, and CD36 gene deletion in mice causes impaired insulin sensitivity by up-regulating muscle PTP1B expression, which results in detyrosine phosphorylation of IR and IRS1.
Animals ; Gene Deletion ; Histones/genetics* ; Insulin ; Insulin Receptor Substrate Proteins/metabolism* ; Insulin Resistance/genetics* ; Membrane Cofactor Protein/genetics* ; Mice ; Mice, Knockout ; Muscles/metabolism* ; Phosphoric Monoester Hydrolases/metabolism* ; Protein Tyrosine Phosphatase, Non-Receptor Type 1/metabolism* ; Proto-Oncogene Proteins c-akt/metabolism* ; RNA, Messenger/metabolism* ; Receptor, Insulin/metabolism* ; Tyrosine/genetics* ; Up-Regulation

This study aimed to investigate the effects and the underlying mechanism of CD36 gene on glucose and lipid metabolism disorder induced by high-fat diet in mice. Wild type (WT) mice and systemic CD36 knockout (CD36
Animals ; Diet, High-Fat/adverse effects* ; Fatty Liver/metabolism* ; Glucose/metabolism* ; Insulin/metabolism* ; Insulin Resistance ; Lipid Metabolism ; Liver ; Mice ; Triglycerides

This study aimed to investigate the effect of lipopolysaccharide (LPS) on lipophagy in hepatocytes and the underlying mechanism. Human hepatoma cell line HepG2 was cultured in vitro, treated with 0.1 mmol/L palmitic acid (PA), and then divided into control group (0 μg/mL LPS), LPS group (10 μg/mL LPS), LPS+DMSO group and LPS+RAPA (rapamycin, 10 μmol/L) group. Lipid accumulation in hepatocytes was observed by oil red O staining. The autophagic flux of the cells was assessed using confocal laser scanning microscope after being transfected with autophagy double-labeled adenovirus (mRFP-GFP-LC3). The level of intracellular lipophagy was visualized by the colocalization of lipid droplets (BODIPY 493/503 staining) and lysosomes (lysosome marker, lysosomal associated membrane protein 1, LAMP1). The expression levels of mammalian target of rapamycin (mTOR), phosphorylated mTOR (p-mTOR), ribosome protein subunit 6 kinase 1 (S6K1), p-S6K1, LC3II/I and P62 protein were examined by Western blot. The results showed that the number of red lipid droplets stained with oil red O was significantly increased in LPS group compared with that in control group (P < 0.001). Moreover, in LPS group, the number of autophagosomes was increased, while the number of autophagolysosomes and the colocalization rate of LAMP1 and BODIPY were significantly decreased (P < 0.05). Meanwhile, the ratios of p-mTOR/mTOR and p-S6K1/S6K1, the ratio of LC3II/LC3I and the protein expression of P62 were significantly increased (P < 0.05) in LPS group. Furthermore, compared with LPS+DMSO group, RAPA treatment obviously reduced the number of lipid droplets and autophagosomes, and raised the number of autophagolysosomes and the colocalization rate of LAMP1 and BODIPY (P < 0.05). In conclusion, the results demonstrate that LPS inhibits lipophagy in HepG2 cells via activating mTOR signaling pathway, thereby aggravating intracellular lipid accumulation.
Autophagy ; Hep G2 Cells ; Humans ; Lipopolysaccharides ; Palmitic Acid ; Signal Transduction ; TOR Serine-Threonine Kinases

Objective To investigate the effect of sirolimus on tumor necrosis factor alpha (TNF-o)-induced lipid accumulation in HepG2 cells.Methods Palmitate acid (PA)-loaded HepG2 cells were divided into three groups:Control group(0.2％ BSA + 0.16 mmol · mL-1 PA + 25 ng· mL-1 TNF-o),model group(0.2％ BSA +0.16 mmol · mL-1 PA +25 ng · mL-1TNF-α),experimental group(0.2％ BSA + 0.16 mmol · mL-1 PA +25 ng · mL-1 TNF-α + 10 ng · mL-1 sirolimus).After 24 h treatment,lipid accumulation in the HepG2 cells was visualized using oil red O staining.The phosphorylation of mammalian target of rapamycin (mTOR)and its downstream translation regulator including P70 ribosomal protein S6 kinase (P70S6K) in HepG2 cells were detected by Western blotting.The mRNA expression of sterol regulatory element binding protein 1 (SREBP1),acetyl CoA carboxylase(ACC),fatty acid synthetase(FAS) were detected by real-time PCR.Results TNF-o-induced lipid accumulation was significantly inhibited by sirolimus in HepG2 cells.The TNF-α-induced phosphorylation of mTOR and its downstream translation regulator P70S6K were also reduced by sirolimus:the relative levels of p-mTOR protein in control group,model group and experimental group were 1.00 ± 0.20,3.11 ± 0.60,2.38 ± 0.50,respectively;the relative levels of p-P70S6K protein in that three groups were 1.00 ±0.30,3.67 ±0.60,1.62 ±0.50,respectively.The differences between model group and control group or experimental group and model group were statistically significant (all P ＜ 0.05).Additionally,the mRNA expression of SREBP1,ACC and FAS were downregulated by sirolimus:the mRNA levels of FAS in control group,model group andexperimental group were 1.04 ± 0.32,2.85 ±0.90,1.68 ± 0.38,respectively;the mRNA levels of ACC in that three groups were 1.04 ± 0.30,3.23-±1.33,2.07 ± 0.52,respectively;the mRNA levels of SREBP1 in that three groups were 1.01 ± 0.16,3.85 ± 1.30,2.82 ±0.57,respectively.The differences between model group and control group or experimental group and model group were statistically significant (all P ＜ 0.05).Conclusion Sirolimus ameolirates TNF-α-induced lipid accumulation in HepG2 cells through inhibiting the mTOR signaling pathway.

Objective To investigate the effect of atorvastatin on oxidative stress and intracellular lipid accumulation in HepG2 cells under inflammatory state and explore the underlying mechanism.Methods HepG2 cells were treated with 100 ng · mL-1 TNF-α,100 ng · mL-1 TNF-α ± 10 μmol · L-1 atorvastatin in the presence of LDL for 24 h.Oil red O staining was used to examine the intracellular lipid contents.The mRNA and protein expressions of lipogenic genes (FAS,ACC and SREBP1) were detected by real-time polymerase chain reaction and Western blot.ROS levels were measured with the fluorescent probe of DCFH-DA.Contents of H2O2 and MDA were determined using the colorimetric method.Results Compared with normal group(the gray value of SREBP1 was 1.01 ± 0.001),the gray value of SREBP1 in model group was 1.61 ± 0.34.The mRNA levels in normal group of SREBP1,FAS,ACC respectively were 1.01 ± 0.16,1.03 ± 0.32,0.95 ± 0.29,the values in model group respectively were 3.61 ± 0.39,1.99 ± 0.36,2.37 ± 0.52,the differences were statistically significantly (P ＜ 0.05).Compared with model group,the mRNA levels of SREBP1,FAS,ACC and the gray value of SREBP1 in experimental group respectively were 2.95 ± 0.92,3.99 ± 1.16,2.85 ± 0.91,2.94 ± 0.65,the differences were statistically significantly(P ＜0.05).At the same time,compared with normal group,the levels of ROS(fluorescenceintensity),H2O2,MDA respectively were 1.00 ±0.20,and (2.30 ±0.31) (0.78 ±0.22) nmol · mg-1,the levels in model group respectively were 1.77 ± 0.25 and (4.32 ± 0.77),(1.86 ± 0.23) nmol · mg-1,the differences were statistically significantly (P ＜ 0.05).Compared with model group,the levels of ROS,H2 O2,MDA in HepG2 cells in experimental group respectively were 3.2 ±0.53 and (5.31 ±0.75),(3.43 ± 1.15) nmol · mg-1,the differences were statistically significantly(P ＜ 0.05).Conclusion Atorvastatin induced intracellular lipid accumulation in HepG2 cells under inflammatory stress,which may be associated with the increased oxidative stress.

Objective To investigated the effects of interleukin -1β( IL-1β) on the intracellular cholesterol contents of HepG 2 cells treated by compactin.Methods HepG2 cells were treated with different con-centrations of compactin (0, 1, 10, 50, 100 μmol· L-1 ) in the absence or presence of 20 ng· mL-1 IL-1βfor 24 hours.Commercial kits was used to evaluated the enzymatic activity of 3-hydroxy-3-methyl-glu-taryl (HMG) -CoA reductase ( HMG-CoA -R).Real -time PCR was used to determine the mRNA of low density lipoprotein ( LDL) rece-puter.Then HepG2 cells treated with 100 μmol · L-1 compactin in the absence or presence of 20 ng· mL-1 IL-1βwere chose to evaluated the content of intracellular cholesterol by commercial kits , real -time PCR was used to determine the mRNA of acyl coenzyme A -cholesterol acyl-transferase ( ACAT ).Results Compactin dose dependently reduced HMG-CoA -R enzymatic activity.IL -1βupregulated the enymatic activity of HMG-CoA reductase , LDL receptor , and the expression of acyl -coenzyme A -cholesterol acyltransferase mRNA , which was accompanied with increased intracellular cholesterol ester contents. Conclusion Inflammatory cytokine disrupted the suppressive effect of compactin on the HMG -CoA-R enzymatic ac-tivity in HepG2 cells and increased the expression of ACAT and LDL receptor and may contribute to hepatic cholesterol accumulation under inflammatory conditions.

Objective To investigate the effects of interleukin -1β( IL-1β) on the sensitivity of human vascular smooth muscle cells ( VSMC ) to compactin treatments.Methods VSMC were treated with different concentrations of compactin (0,1,10,20,50 μmol· L-1 ) in the absence or presence of IL -1β(20μg· L-1 ) for 24 h.Commercial kits was used to evaluated the enzymatic activity of HMGCoA reductase.Real-time PCR was used to determine the mRNA.50 μmol· L-1 com-pactin in the presence of IL -1β(20 μg· L-1 ) for 24 h was extracted, and western-blot was adopted to determine protein expression of target genes.Results Compactin inhibited enzymatic activity of HMGCoA in a dose -dependent manner and IL -1βweakened these suppressive effects.IL-1βupregulated enzymatic activity of HMGCoA reductase and was accompanied by increased HMGCoA reductase mRNA.Protein ex-pression mediated via activation of the sterol regulatory element binding protein cleavage -activating protein/sterol regulatory element binding protein -2 pathway.Conclusion Interleukin -1βcan decrease the sensitivity of vascular smooth muscle cells to compactin.

OBJECTIVETo investigate whether inflammatory stress exacerbates hepatic cholesterol accumulation and liver fibrosis using a C57BL/6J mouse model of chronic inflammation.

METHODSTwelve male C57BL/6J mice were given a high-fat diet (15.0% fat, 1.25% cholesterol, 0.5% cholic acid) and randomly assigned to the normal control group (n=6; subcutaneously injected with 0.5 mL of isotonic saline, every other day for 14 weeks) or the chronic inflammation model group (n=6; subcutaneously injected with of 0.5 mL of 10% casein, every other day for 14 weeks). At the end of week 14, the animals were sacrificed and blood was collected from the left ventricle for serological analysis of inflammatory markers and lipid profile, including serum amyloid A (SAA), interleukin-6 (IL-6), total cholesterol (TC) and free cholesterol (FC), low-density lipoprotein (LDL), and high-density lipoprotein (HDL)). Extracted liver tissues were divided for use in histological analysis (lipid accumulation and fibrosis evaluated by Oil Red O, Sirius red and Masson's trichrome staining) and quantitative fluorescence real-time PCR (to measure b-actin normalized expression of TNF-a MCP1, SREBP-2, LDLr, HMGCoA-r, ATF-6, GRP78, BMP-7, TGF-b, and collagens type I and type IV). Comparisons between groups were made by the two-samples t-test or Satterthwaite t-approximation test, collagen type I and type IV.

RESULTSCompared to the normal control group, the inflammation model group showed elevated serum IL-6 (12.55+/-4.75 vs. 32.41+/-7.42 pg/mL, P less than 0.01), reduced serum TC (14.82+/-1.56 vs. 10.62+/-0.48 mmol/L, P less than 0.01), up-regulated hepatic TNF-a mRNA expression (1.05+/-0.35 vs. 2.12+/-0.72, P less than 0.01), and elevated hepatic TC (12.10+/-2.57 vs. 23.21+/-8.75 mmol/L, P less than 0.05). In addition, the inflammation group showed abnormal lipid deposition, and increased and thickened reticular fibers. The livers of the inflammation group also showed up-regulated mRNA expression of SREBP-2 (normal control: 1.01+/-0.19 vs. 2.63+/-0.13, P less than 0.05), GRP78 (1.07+/-0.47 vs. 2.21+/-0.99, P less than 0.05), TGF-b (1.01+/-0.14 vs. 1.38+/-0.28, P less than 0.05), and collagen type I (1.02+/-0.27 vs. 1.71+/-0.51, P less than 0.05) and down-regulation of BMP-7 (1.01+/-0.15 vs. 0.55+/-0.25, P less than 0.01).

CONCLUSIONActivation of the inflammatory system exacerbates hepatic cholesterol accumulation and hepatic fibrosis in C57BL/6J mice.

Animals ; Cholesterol ; metabolism ; Disease Models, Animal ; Fatty Liver ; metabolism ; pathology ; Inflammation ; Liver ; metabolism ; pathology ; Liver Cirrhosis ; metabolism ; pathology ; Male ; Mice ; Mice, Inbred C57BL

BACKGROUNDPodocyte apoptosis is recently indicated as an early phenomenon of diabetic nephropathy. Pancreatic β-cells exposed to saturated free fatty acid palmitate undergo irreversible endoplasmic reticulum (ER) stress and consequent apoptosis, contributing to the onset of diabetes. We hypothesized that palmitate could induce podocyte apoptosis via ER stress, which initiates or aggravates proteinuria in diabetic nephropathy.

METHODSPodocyte apoptosis was detected by 4',6-diamidio-2-phenylindole (DAPI) stained apoptotic cell count and Annexin V-PI stain. The expressions of ER molecule chaperone glucose-regulated protein 78 (GRP78), indicators of ER-associated apoptosis C/EBP homologous protein (CHOP), and Bcl-2 were assayed by Western blotting and real-time PCR. GRP78 and synaptopodin were co-localized by immunofluorescence stain.

RESULTSPalmitate significantly increased the percentage of cultured apoptotic murine podocytes time-dependently when loading 0.75 mmol/L (10 hours, 13 hours, and 15 hours compared with 0 hour, P < 0.001) and dose-dependently when loading palmitate ranging from 0.25 to 1.00 mmol/L for 15 hours (compared to control, P < 0.001). Palmitate time-dependently and dose-dependently increased the protein expression of GRP78 and CHOP, and decreased that of Bcl-2. Palmitate loading ranging from 0.5 to 1.0 mmol/L for 12 hours significantly increased mRNA of GRP78 and CHOP, and decreased that of Bcl-2 compared to control (P < 0.001), with the maximum concentration being 0.75 mmol/L. Palmitate 0.5 mmol/L loading for 3 hours, 8 hours, and 12 hours significantly increased mRNA of GRP78 and CHOP, and decreased that of Bcl-2 compared to 0 hour (P < 0.001), with the maximum effect at 3 hours. Confocal microscopy demonstrated that GRP78 expression was significantly increased when exposed to 0.5 mmol/L of palmitate for 8 hours compared to control.

CONCLUSIONPalmitate could induce podocyte apoptosis via ER stress, suggesting podocyte apoptosis and consequent proteinuria caused by lipotoxic free fatty acid could be ameliorated by relief of ER stress.

Apoptosis ; drug effects ; Cells, Cultured ; Endoplasmic Reticulum Stress ; physiology ; Heat-Shock Proteins ; analysis ; physiology ; Humans ; Insulin Resistance ; Palmitic Acid ; pharmacology ; Podocytes ; drug effects ; pathology

OBJECTIVETo investigate the effect of RNA interference (RNAi)-mediated silencing of the SREBP2 on inflammatory cytokine-induced cholesterol accumulation in HepG2 cells.

METHODSShort-hairpin (sh)RNA targeting SREBP2 or negative control (NC) shRNA were transfected into HepG2 cells by a liposomal method. G418-selective culturing was used to obtain the SREBP2 shRNA HepG2 and NC shRNA HepG2 cell lines. The two cell lines were cultured in serum-free medium and left untreated (control) or treated with TNF-a (20 ng/ml), low-density lipoprotein (LDL) loading (100 mug/ml), or a combination LDL plus TNF-a treatment. Lipid accumulation was evaluated by oil red O (ORO) staining. Intracellular cholesterol level was measured by enzymatic assay. The mRNA and protein levels of SREBP2 and its downstream target genes, LDL receptor (LDLr), and HMGCoA reductase, were measured by real-time PCR and Western blotting, respectively.

RESULTSSREBP2 shRNA HepG2 and NC shRNA HepG2 stable cell lines were successfully established. ORO staining and cholesterol quantitative analysis showed that LDL loading significantly increased intracellular cholesterol and that expression of SREBP2 further exacerbated the inflammatory cytokine-induced lipid accumulation, as seen in NC shRNA HepG2 cells. LDL loading of NC shRNA HepG2 decreased the gene and protein expressions of SREBP2, LDLr, and HMGCoA reductase, but the suppressive effect was overridden by inflammatory cytokine. SREBP2 shRNA HepG2 cells showed lower levels of cholesterol accumulation under LDL loading and inflammatory stress conditions. Moreover, the mRNA and protein levels of SREBP2, LDLr, and HMGCoA reductase were much lower than in NC shRNA HepG2 cells under the same conditions.

CONCLUSIONInflammatory cytokine exacerbated cholesterol accumulation in HepG2 via disrupting SREBP2. RNAi-mediated inhibition of SREBP2 expression significantly ameliorated the cholesterol accumulation induced by inflammatory cytokine.

Cholesterol ; metabolism ; Hep G2 Cells ; Humans ; Inflammation ; RNA Interference ; RNA, Small Interfering ; Sterol Regulatory Element Binding Protein 2 ; genetics ; Tumor Necrosis Factor-alpha ; pharmacology