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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

Analysis of genes involved in β-oxidation in the liver of H-apoD Tg mice.A- Western blot analysis of PPARα protein expression. The graph represents the level of PPARα protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of PGC-1α (B) and CPT1 (C) expression in liver of WT and H-apoD Tg mice. PGC1α and CPT1 gene expression was normalized by HPRT. For each graph, the H-apoD Tg values were normalized by the WT values and are the means ± SD of 4 mice per group. *P<0.05 and **P<0.01 vs WT mice.
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pone.0130230.g005: Analysis of genes involved in β-oxidation in the liver of H-apoD Tg mice.A- Western blot analysis of PPARα protein expression. The graph represents the level of PPARα protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of PGC-1α (B) and CPT1 (C) expression in liver of WT and H-apoD Tg mice. PGC1α and CPT1 gene expression was normalized by HPRT. For each graph, the H-apoD Tg values were normalized by the WT values and are the means ± SD of 4 mice per group. *P<0.05 and **P<0.01 vs WT mice.

Mentions: We previously demonstrated that PPARα mRNA was increased in H-apoD Tg mice liver suggesting an elevated hepatic lipid β-oxidation [15]. A similar increase was observed at the protein level (2.73 fold) (Fig 5A). Since PPARα is known to regulate the expression of genes involved in the β-oxidation pathway, we examined the expression of two key proteins involved in this process. The mRNA of PGC-1α, a co-activator of PPARα remained unchanged (Fig 5B). However, the mRNA expression of the carnitine palmitoyltransferase I (CPT-1), the rate limiting enzyme of the mitochondrial lipid transfer was slightly increased (1.26-fold) in the liver of H-apoD Tg mice compared to WT (Fig 5C). This might be associated to a slight upregulation of lipid β-oxidation in the liver of H-apoD Tg mice.


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)

Analysis of genes involved in β-oxidation in the liver of H-apoD Tg mice.A- Western blot analysis of PPARα protein expression. The graph represents the level of PPARα protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of PGC-1α (B) and CPT1 (C) expression in liver of WT and H-apoD Tg mice. PGC1α and CPT1 gene expression was normalized by HPRT. For each graph, the H-apoD Tg values were normalized by the WT values and are the means ± SD of 4 mice per group. *P<0.05 and **P<0.01 vs WT mice.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130230.g005: Analysis of genes involved in β-oxidation in the liver of H-apoD Tg mice.A- Western blot analysis of PPARα protein expression. The graph represents the level of PPARα protein expression standardized by amidoblack staining. A representative gel is presented. Semi-quantitative RT-PCR analysis of PGC-1α (B) and CPT1 (C) expression in liver of WT and H-apoD Tg mice. PGC1α and CPT1 gene expression was normalized by HPRT. For each graph, the H-apoD Tg values were normalized by the WT values and are the means ± SD of 4 mice per group. *P<0.05 and **P<0.01 vs WT mice.
Mentions: We previously demonstrated that PPARα mRNA was increased in H-apoD Tg mice liver suggesting an elevated hepatic lipid β-oxidation [15]. A similar increase was observed at the protein level (2.73 fold) (Fig 5A). Since PPARα is known to regulate the expression of genes involved in the β-oxidation pathway, we examined the expression of two key proteins involved in this process. The mRNA of PGC-1α, a co-activator of PPARα remained unchanged (Fig 5B). However, the mRNA expression of the carnitine palmitoyltransferase I (CPT-1), the rate limiting enzyme of the mitochondrial lipid transfer was slightly increased (1.26-fold) in the liver of H-apoD Tg mice compared to WT (Fig 5C). This might be associated to a slight upregulation of lipid β-oxidation in the liver of H-apoD Tg mice.

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