Endocrinol Metab.  2021 Dec;36(6):1243-1253. 10.3803/EnM.2021.1100.

The Effects of PPAR Agonists on Atherosclerosis and Nonalcoholic Fatty Liver Disease in ApoE^−/−FXR^−/− Mice

• Lee Y
• Kim BR
• Kang GH
• Lee GJ
• Park YJ
• Kim H
• Jang HC
• Choi SH

• KMID: 2523493
• DOI: http://doi.org/10.3803/EnM.2021.1100

Abstract

Background
Farnesoid X receptor (FXR), a bile acid–activated nuclear receptor, is a potent regulator of glucose and lipid metabolism as well as of bile acid metabolism. Previous studies have demonstrated that FXR deficiency is associated with metabolic derangements, including atherosclerosis and nonalcoholic fatty liver disease (NAFLD), but its mechanism remains unclear. In this study, we investigated the role of FXR in atherosclerosis and NAFLD and the effect of peroxisome proliferator-activated receptor (PPAR) agonists in mouse models with FXR deficiency.
Methods
En face lipid accumulation analysis, liver histology, serum levels of glucose and lipids, and mRNA expression of genes related to lipid metabolism were compared between apolipoprotein E (ApoE)^−/− and ApoE^−/−FXR^−/− mice. The effects of PPARα and PPARγ agonists were also compared in both groups of mice.
Results
Compared with ApoE^−/− mice, ApoE^−/−FXR^−/− mice showed more severe atherosclerosis, hepatic steatosis, and higher levels of serum cholesterol, low-density lipoprotein cholesterol, and triglycerides, accompanied by increased mRNA expression of FAS, ApoC2, TNFα, IL-6 (liver), ATGL, TGH, HSL, and MGL (adipocytes), and decreased mRNA expressions of CPT2 (liver) and Tfam (skeletal muscle). Treatment with a PPARα agonist, but not with a PPARγ agonist, partly reversed atherosclerosis and hepatic steatosis, and decreased plasma triglyceride levels in the ApoE^−/−FXR^−/− mice, in association with increased mRNA expression of CD36 and FATP and decreased expression of ApoC2 and ApoC3 (liver).
Conclusion
Loss of FXR is associated with aggravation of atherosclerosis and hepatic steatosis in ApoE-deficient mice, which could be reversed by a PPARα agonist through induction of fatty acid uptake, β-oxidation, and triglyceride hydrolysis.

Keyword

FXR; Peroxisome proliferator-activated receptors; Apolipoproteins E; Atherosclerosis; Non-alcoholic fatty liver disease

Figure

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  Fig. 1. Atherosclerotic lesions of the aorta stained with Oil Red O in mice fed a Western diet (WD) with or without pioglitazone/fenofibrate treatment. (A) Representative photographs of aorta prepared using the en face method (a, apolipoprotein E [ApoE]−/− WD; b, ApoE−/− farnesoid X receptor [FXR]−/− WD; c, ApoE−/−FXR−/− WD+pioglitazone; d, ApoE−/−FXR−/− WD+fenofibrate). (B) Comparison of percentage of atherosclerotic lesions in the aorta in ApoE−/− (n=7) and ApoE−/−FXR−/− (n=9) mice fed a WD. The horizontal bars represent the mean percentage of atherosclerotic lesions. (C) Comparison of percentage of atherosclerotic lesions in the aorta in ApoE−/−FXR−/− mice fed a WD with or without pioglitazone (n=8) or fenofibrate (n=9) treatment. The horizontal bars represent the mean percentage of atherosclerotic lesions. Error bars show standard deviations. aA significant difference between ApoE−/− and ApoE−/−FXR−/− mice; bA significant difference between ApoE−/−FXR−/− mice with no treatment and ApoE−/−FXR−/− mice treated with fenofibrate.

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  Fig. 2. Comparison of liver histology and nonalcoholic fatty liver disease (NAFLD) activity scores (NAS) in apolipoprotein E (ApoE)−/− and ApoE−/− farnesoid X receptor (FXR)−/− mice fed a Western diet (WD) with or without pioglitazone or fenofibrate treatment. (A) Microscopic findings of the liver (H&E stain, ×200) (a, ApoE−/− [n=7]; b, ApoE−/−FXR−/− [n=9]; c, ApoE−/−FXR−/−+pioglitazone [n=8]; d, ApoE−/−FXR−/−+fenofibrate [n=9]). (B) Comparison of NAS between ApoE−/− (n=7) and ApoE−/−FXR−/− (n=9) mice. (C) Comparison of NAS among treatment groups in ApoE−/−FXR−/− mice (n=8 for control, n=8 for pioglitazone treatment, and n=9 for fenofibrate treatment). Error bars show standard deviations. aA significant difference between ApoE−/− and ApoE−/−FXR−/− mice.

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  Fig. 3. Comparison of gene expression related to lipid metabolism analyzed by quantitative polymerase chain reaction in liver, related to fatty acid synthesis (A), fatty acid uptake and catabolism (B), triglyceride hydrolysis (C), cholesterol metabolism (D), inflammation and hepatic fibrosis in the liver (E), lipolysis in adipose tissue (F), and mitochondrial activation in skeletal muscle (G) between apolipoprotein E (ApoE)−/− and ApoE−/− farnesoid X receptor (FXR)−/− mice. Error bars show standard deviations. WD, Western diet; SREBP1c, sterol regulatory element-binding protein 1c; FAS, fatty acid synthase; ACC1, acetyl-CoA carboxylase 1; SCD, stearoyl CoA desaturase; ACLY, ATP citrate lyase; FAT, fatty acid translocase; FATP1, fatty acid transport protein 1; CPT, carnitine palmitoyltranferase; ACS, acyl-CoA synthase; ACO, acyl-CoA oxidase; ACAA1A, acetyl-coenzyme A acyltransferease 1A; ApoC, apolipoprotein C; ANGPTL3, angiopoietin-like 3; PPAR, peroxisome proliferator-activated receptor; ApoA, apolipoprotein A; PLTP, phospholipid transfer protein; ABCG1, ATP-binding cassette sub-family G member 1; ABCA1, ATP-binding cassette transporter sub-family A member 1; SRB1, scavenger receptor class B type 1; CLA1, CD36 and LIMPII analogous-1; LXR, liver X receptor; MTP, microsomal triglyceride transfer protein; ApoB100, apolipoprotein B100; LDLR, low density lipoprotein receptor; TNFα, tumor necrosis factor-α; IL-6, interleukin-6; TGFβ, transforming growth factor β1; Col1α1, α1-collagen; TIMP, tissue inhibitor of metalloproteinase; αSMA, α smooth muscle actin; ATGL, adipocyte triglyceride lipase; TGH, triglycerol hydrolase; HSL, hormone sensitive lipase; MGL, monoglyceride lipase; Nrf-1, nuclear respiratory factor 1; PGC1, peroxisome proliferator-activated receptor gamma coactivator 1. aP<0.05.

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  Fig. 4. Comparison of gene expression related to lipid metabolism analyzed by quantitative polymerase chain reaction in the liver, related to fatty acid synthesis (A), fatty acid uptake and catabolism (B), triglyceride hydrolysis (C), cholesterol metabolism (D), inflammation and hepatic fibrosis in the liver (E), lipolysis in adipose tissue (F), and mitochondrial activation in skeletal muscle (G) among apolipoprotein E (ApoE)−/− farnesoid X receptor (FXR)−/− mice with or without fenofibrate or pioglitazone treatment. Error bars show standard deviations. WD, Western diet; SREBP1c, sterol regulatory element-binding protein 1c; FAS, fatty acid synthase; ACC1, acetyl-CoA carboxylase 1; SCD, stearoyl CoA desaturase; ACLY, ATP citrate lyase; FAT, fatty acid translocase; FATP1, fatty acid transport protein 1; CPT, carnitine palmitoyltranferase; ACS, acyl-CoA synthase; ACO, acyl-CoA oxidase; ACAA1A, acetyl-coenzyme A acyltransferease 1A; ApoC, apolipoprotein C; ANGPTL3, angiopoietin-like 3; PPAR, peroxisome proliferator-activated receptor; ApoA, apolipoprotein A; PLTP, phospholipid transfer protein; ABCG1, ATP-binding cassette sub-family G member 1; ABCA1, ATP-binding cassette transporter sub-family A member 1; SRB1, scavenger receptor class B type 1; CLA1, CD36 and LIMPII analogous-1; LXR, liver X receptor; MTP, microsomal triglyceride transfer protein; ApoB100, apolipoprotein B100; LDLR, low density lipoprotein receptor; SOD, superoxide dismutase; TNFα, tumor necrosis factor-α; IL-6, interleukin-6; TGFβ, transforming growth factor β1; Col1α1, α1-collagen; TIMP, tissue inhibitor of metalloproteinase; αSMA, α smooth muscle actin; ATGL, adipocyte triglyceride lipase; TGH, triglycerol hydrolase; HSL, hormone sensitive lipase; MGL, monoglyceride lipase; Nrf-1, nuclear respiratory factor 1; PGC1, peroxisome proliferator-activated receptor gamma coactivator 1. aP<0.05.

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