Human hepatic lipase overexpression in mice induces hepatic steatosis and obesity through promoting hepatic lipogenesis and white adipose tissue lipolysis and fatty acid uptake

Figures

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  Fig 1. Overexpression of hHL in liver promotes diet-induced obesity and hepatomegaly. (A) Average monthly weight in WT and hHL transgenic mice. (B) Food intake per day and per mouse was monitored over 48 hours in the last week of the 16-week feeding regimen. (C) Representative adipose fat and liver from both WT and hHL transgenic mice. (D) Serum and tissue HL activities were measured using a radiolabeled glycerol tri[9,10-(n)-3H]oleate emulsion. For A, B, and D, values are mean ± SEM of 6 WT and 8 hHL transgenic mice and * indicates p <0.05 vs WT mice.

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  Fig 2. Human HL overexpression promotes hepatic steatosis. (A) Liver weights after the 16-week feeding experiment in hHL transgenic and WT mice. (B) Hepatic lipid levels of triglycerides (TG), esterified cholesterol (EC), free cholesterol (FC), and phospholipids (PL) were determined after lipid extraction with isopropyl alcohol-hexane. Values are mean ± SEM of 6 WT and 8 hHL transgenic mice and * indicates p <0.05 vs WT mice. Representative liver tissue sections from WT (C) and hHL transgenic mice (D) stained with H&E. Representative liver tissue sections from WT (E) and hHL transgenic mice (F) stained with Oil Red O. Livers from hHL transgenic mice showed severe macrovesicular steatosis with positive staining for neutral lipids.

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  Fig 3. Transgenic mice overexpressing hHL showed increased fatty acid β-oxidation. (A) Liver fatty acid oxidation was determined as nmols of palmitoyl-CoA produced in both WT and hHL transgenic mice. B) Transcriptional expression of hepatic Cd36 and the PPARα target genes Cpt1a and Acox1. Values are mean ± SEM of 6 individual animals per group and * indicates p <0.05 vs WT mice.

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  Fig 4. Expression of hHL promotes hepatic de novo lipogenesis without affecting triglyceride secretion. (A) De novo synthesis of fatty acids in livers of hHL transgenic and WT mice. The incorporation of 3H2O into fatty acids was determined after i.p. injection of 10 mCi/kg of 3H2O into each mouse. Values are mean ± SEM of 7 WT mice and 9 hHL transgenic mice. (B) Transcriptional expression of hepatic Nr1h3 and the SREBP-1c target genes Fasn and Acaca (N = 6 mice/group). (C) In vivo triglyceride secretion rate in mice injected intravenously with Triton WR-1339. Mice were bled immediately prior to Triton WR-1339 injection and 60 and 120 min afterwards. Triglycerides were measured and their change with respect to the baseline result is shown (N = 3 mice/group). (D) Hepatic expression of Apob, Mttp, or Dgat1 (N = 6 mice/group). * indicates p <0.05 vs WT mice.

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  Fig 5. HL transgenic mice exhibit more adiposity and upregulated adipose LPL-mediated FFA influx. (A) Fat pad mass weights after the 16-week feeding experiment in hHL transgenic and WT mice. Each value represents the mean ± SEM of data from 6 WT mice and 8 hHL transgenic mice. (B) Quantitation of adipocyte size (N = 3 mice/group). Representative photomicrographs of H&E stained sections from eWAT of WT (C) and hHL transgenic mice (D). (E) Transcriptional expression of eWAT Lpl and tissue activity (N = 5 mice/group). (F) [3H]-triglyceride labeled triglyceride-rich lipoproteins were injected intravenously into WT and hHL transgenic mice under postprandial conditions and radiolabeled FFA and triglycerides were measured in WAT fat pads. Radiolabeled triglycerides + FFA in the collected fat depots did not differ between genotypes (0.92 ± 0.05 vs 0.80 ± 0.16% of the injected dose in WT and hHL transgenic mice, respectively). [3H]FFA/triglyceride ratios are shown (N = 3 mice/group). * indicates p <0.05 vs WT mice.