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Apolipoprotein D Transgenic Mice Develop Hepatic Steatosis through Activation of PPARγ and Fatty Acid Uptake.

Labrie M, Lalonde S, Najyb O, Thiery M, Daneault C, Des Rosiers C, Rassart E, Mounier C - PLoS ONE (2015)

Bottom Line: Elevated expression of AMPK in the liver of Tg leads to phosphorylation of acetyl CoA carboxylase, indicating a decreased activity of the enzyme.In addition, expression of carnitine palmitoyl transferase 1, the rate-limiting enzyme of beta-oxidation, is slightly upregulated.Finally, we show that overexpressing H-apoD in HepG2 cells in presence of arachidonic acid (AA), the main apoD ligand, increases the transcriptional activity of PPARγ.

View Article: PubMed Central - PubMed

Affiliation: Centre de recherche BioMed, Département des Sciences Biologiques, Université du Québec, Montréal, Québec, H3C 3P8, Canada.

ABSTRACT
Transgenic mice (Tg) overexpressing human apolipoprotein D (H-apoD) in the brain are resistant to neurodegeneration. Despite the use of a neuron-specific promoter to generate the Tg mice, they expressed significant levels of H-apoD in both plasma and liver and they slowly develop hepatic steatosis and insulin resistance. We show here that hepatic PPARγ expression in Tg mice is increased by 2-fold compared to wild type (WT) mice. Consequently, PPARγ target genes Plin2 and Cide A/C are overexpressed, leading to increased lipid droplets formation. Expression of the fatty acid transporter CD36, another PPARgamma target, is also increased in Tg mice associated with elevated fatty acid uptake as measured in primary hepatocytes. Elevated expression of AMPK in the liver of Tg leads to phosphorylation of acetyl CoA carboxylase, indicating a decreased activity of the enzyme. Fatty acid synthase expression is also induced but the hepatic lipogenesis measured in vivo is not significantly different between WT and Tg mice. In addition, expression of carnitine palmitoyl transferase 1, the rate-limiting enzyme of beta-oxidation, is slightly upregulated. Finally, we show that overexpressing H-apoD in HepG2 cells in presence of arachidonic acid (AA), the main apoD ligand, increases the transcriptional activity of PPARγ. Supporting the role of apoD in AA transport, we observed enrichment in hepatic AA and a decrease in plasmatic AA concentration. Taken together, our results demonstrate that the hepatic steatosis observed in apoD Tg mice is a consequence of increased PPARγ transcriptional activity by AA leading to increased fatty acid uptake by the liver.

No MeSH data available.


Related in: MedlinePlus

Lipid droplets formation in the liver of H-apoD Tg mice.A- Western blot analysis of Plin2 expression. The graph represents the level of Plin2 protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of Cide A (B), Cide B (C) and Cide C (D) mRNA expression. The graphs represent the level of mRNA expressions normalized by HPRT. Values are expressed relatively to the WT mice and are the means ± SD of 4 mice per group. E-Confocal analysis of lipid droplets in liver tissues of WT and H-apoD Tg mice. Lipid droplets are stained with bodipy (in green) and nucleus with propidium iodide (in red). Graphs represent the quantification of 18 images. *P<0.05, **P<0.01, P<0.001 vs WT mice.
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pone.0130230.g002: Lipid droplets formation in the liver of H-apoD Tg mice.A- Western blot analysis of Plin2 expression. The graph represents the level of Plin2 protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of Cide A (B), Cide B (C) and Cide C (D) mRNA expression. The graphs represent the level of mRNA expressions normalized by HPRT. Values are expressed relatively to the WT mice and are the means ± SD of 4 mice per group. E-Confocal analysis of lipid droplets in liver tissues of WT and H-apoD Tg mice. Lipid droplets are stained with bodipy (in green) and nucleus with propidium iodide (in red). Graphs represent the quantification of 18 images. *P<0.05, **P<0.01, P<0.001 vs WT mice.

Mentions: We then measured the expression level of key proteins known to be involved in LD formation. The expression of the PPARγ target gene Plin2 [51] was increased by 1.98-fold in Tg mice (Fig 2A). Similar observations were made regarding Cide A and Cide C (1.47 and 1.45-fold respectively), two other targets of PPARγ that are implicated in LD fusion [52] (Fig 2B and 2D). A well-documented independent gene of PPARγ regulation, Cide B remained unchanged (Fig 2C). Conversely, the expression of genes coding for several lipases (adipose triglyceride lipase (ATGL), hormone sensitive lipase (HSL) and monoglyceride lipase (MGL)) as well as for the ATGL coactivator comparative gene identification 58 (CGI-58) remained identical (data not shown). Consistently with an elevated expression of proteins involved in hepatic LD formation and fusion, we found that the size of the hepatic LD in H-apoD Tg mice was drastically increased (5.45-fold) compared to WT. However, we did not detect a significant modification in the number of LD between the Tg and WT mice suggesting that the observed phenomenon was a result of both LD fusion and formation of new LD (Fig 2E).


Apolipoprotein D Transgenic Mice Develop Hepatic Steatosis through Activation of PPARγ and Fatty Acid Uptake.

Labrie M, Lalonde S, Najyb O, Thiery M, Daneault C, Des Rosiers C, Rassart E, Mounier C - PLoS ONE (2015)

Lipid droplets formation in the liver of H-apoD Tg mice.A- Western blot analysis of Plin2 expression. The graph represents the level of Plin2 protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of Cide A (B), Cide B (C) and Cide C (D) mRNA expression. The graphs represent the level of mRNA expressions normalized by HPRT. Values are expressed relatively to the WT mice and are the means ± SD of 4 mice per group. E-Confocal analysis of lipid droplets in liver tissues of WT and H-apoD Tg mice. Lipid droplets are stained with bodipy (in green) and nucleus with propidium iodide (in red). Graphs represent the quantification of 18 images. *P<0.05, **P<0.01, P<0.001 vs WT mice.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4470830&req=5

pone.0130230.g002: Lipid droplets formation in the liver of H-apoD Tg mice.A- Western blot analysis of Plin2 expression. The graph represents the level of Plin2 protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of Cide A (B), Cide B (C) and Cide C (D) mRNA expression. The graphs represent the level of mRNA expressions normalized by HPRT. Values are expressed relatively to the WT mice and are the means ± SD of 4 mice per group. E-Confocal analysis of lipid droplets in liver tissues of WT and H-apoD Tg mice. Lipid droplets are stained with bodipy (in green) and nucleus with propidium iodide (in red). Graphs represent the quantification of 18 images. *P<0.05, **P<0.01, P<0.001 vs WT mice.
Mentions: We then measured the expression level of key proteins known to be involved in LD formation. The expression of the PPARγ target gene Plin2 [51] was increased by 1.98-fold in Tg mice (Fig 2A). Similar observations were made regarding Cide A and Cide C (1.47 and 1.45-fold respectively), two other targets of PPARγ that are implicated in LD fusion [52] (Fig 2B and 2D). A well-documented independent gene of PPARγ regulation, Cide B remained unchanged (Fig 2C). Conversely, the expression of genes coding for several lipases (adipose triglyceride lipase (ATGL), hormone sensitive lipase (HSL) and monoglyceride lipase (MGL)) as well as for the ATGL coactivator comparative gene identification 58 (CGI-58) remained identical (data not shown). Consistently with an elevated expression of proteins involved in hepatic LD formation and fusion, we found that the size of the hepatic LD in H-apoD Tg mice was drastically increased (5.45-fold) compared to WT. However, we did not detect a significant modification in the number of LD between the Tg and WT mice suggesting that the observed phenomenon was a result of both LD fusion and formation of new LD (Fig 2E).

Bottom Line: Elevated expression of AMPK in the liver of Tg leads to phosphorylation of acetyl CoA carboxylase, indicating a decreased activity of the enzyme.In addition, expression of carnitine palmitoyl transferase 1, the rate-limiting enzyme of beta-oxidation, is slightly upregulated.Finally, we show that overexpressing H-apoD in HepG2 cells in presence of arachidonic acid (AA), the main apoD ligand, increases the transcriptional activity of PPARγ.

View Article: PubMed Central - PubMed

Affiliation: Centre de recherche BioMed, Département des Sciences Biologiques, Université du Québec, Montréal, Québec, H3C 3P8, Canada.

ABSTRACT
Transgenic mice (Tg) overexpressing human apolipoprotein D (H-apoD) in the brain are resistant to neurodegeneration. Despite the use of a neuron-specific promoter to generate the Tg mice, they expressed significant levels of H-apoD in both plasma and liver and they slowly develop hepatic steatosis and insulin resistance. We show here that hepatic PPARγ expression in Tg mice is increased by 2-fold compared to wild type (WT) mice. Consequently, PPARγ target genes Plin2 and Cide A/C are overexpressed, leading to increased lipid droplets formation. Expression of the fatty acid transporter CD36, another PPARgamma target, is also increased in Tg mice associated with elevated fatty acid uptake as measured in primary hepatocytes. Elevated expression of AMPK in the liver of Tg leads to phosphorylation of acetyl CoA carboxylase, indicating a decreased activity of the enzyme. Fatty acid synthase expression is also induced but the hepatic lipogenesis measured in vivo is not significantly different between WT and Tg mice. In addition, expression of carnitine palmitoyl transferase 1, the rate-limiting enzyme of beta-oxidation, is slightly upregulated. Finally, we show that overexpressing H-apoD in HepG2 cells in presence of arachidonic acid (AA), the main apoD ligand, increases the transcriptional activity of PPARγ. Supporting the role of apoD in AA transport, we observed enrichment in hepatic AA and a decrease in plasmatic AA concentration. Taken together, our results demonstrate that the hepatic steatosis observed in apoD Tg mice is a consequence of increased PPARγ transcriptional activity by AA leading to increased fatty acid uptake by the liver.

No MeSH data available.


Related in: MedlinePlus