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Znf202 affects high density lipoprotein cholesterol levels and promotes hepatosteatosis in hyperlipidemic mice.

Vrins CL, Out R, van Santbrink P, van der Zee A, Mahmoudi T, Groenendijk M, Havekes LM, van Berkel TJ, Willems van Dijk K, Biessen EA - PLoS ONE (2013)

Bottom Line: The repressive activity of Znf202 was firmly confirmed in an apoE reporter assay and Znf202 responsive elements within the ApoE promoter were identified.Interestingly, key genes in bile flux (abcg5/8 and bsep) and in bile acid synthesis (cyp7a1) were also downregulated.Znf202 overexpression in vivo reveals an important role of this transcriptional regulator in liver lipid homeostasis, while firmly establishing the proposed key role in the control of HDL levels.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Biochemistry, Academic Medical Center, Amsterdam, The Netherlands. c_vrins@hotmail.com

ABSTRACT

Background: The zinc finger protein Znf202 is a transcriptional suppressor of lipid related genes and has been linked to hypoalphalipoproteinemia. A functional role of Znf202 in lipid metabolism in vivo still remains to be established.

Methodology and principal findings: We generated mouse Znf202 expression vectors, the functionality of which was established in several in vitro systems. Next, effects of adenoviral znf202 overexpression in vivo were determined in normo- as well as hyperlipidemic mouse models. Znf202 overexpression in mouse hepatoma cells mhAT3F2 resulted in downregulation of members of the Apoe/c1/c2 and Apoa1/c3/a4 gene cluster. The repressive activity of Znf202 was firmly confirmed in an apoE reporter assay and Znf202 responsive elements within the ApoE promoter were identified. Adenoviral Znf202 transfer to Ldlr-/- mice resulted in downregulation of apoe, apoc1, apoa1, and apoc3 within 24 h after gene transfer. Interestingly, key genes in bile flux (abcg5/8 and bsep) and in bile acid synthesis (cyp7a1) were also downregulated. At 5 days post-infection, the expression of the aforementioned genes was normalized, but mice had developed severe hepatosteatosis accompanied by hypercholesterolemia and hypoalphalipoproteinemia. A much milder phenotype was observed in wildtype mice after 5 days of hepatic Znf202 overexpression. Interestingly and similar to Ldl-/- mice, HDL-cholesterol levels in wildtype mice were lowered after hepatic Znf202 overexpression.

Conclusion/significance: Znf202 overexpression in vivo reveals an important role of this transcriptional regulator in liver lipid homeostasis, while firmly establishing the proposed key role in the control of HDL levels.

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Related in: MedlinePlus

Proposed mechanism for Znf202.Elevated hepatic levels of Znf202 downregulate bile flux genes. Together with an increase in cholesterol synthesis and attenuated bile acid synthesis, this could result in the observed lipid accumulation in the liver and increased VLDL secretion (A). Under normolipidemic conditions, feedback mechanisms are able to reverse most of the initial effects of Znf202 overexpression (B). These initial effects cannot be sufficiently restored in mice under the hyperlipidemic conditions caused by the low density lipoprotein receptor deficiency. As a result, the mice become more hyperlipidemic and the lipid accumulation in the liver is followed by hepatic steatosis (C).
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pone-0057492-g006: Proposed mechanism for Znf202.Elevated hepatic levels of Znf202 downregulate bile flux genes. Together with an increase in cholesterol synthesis and attenuated bile acid synthesis, this could result in the observed lipid accumulation in the liver and increased VLDL secretion (A). Under normolipidemic conditions, feedback mechanisms are able to reverse most of the initial effects of Znf202 overexpression (B). These initial effects cannot be sufficiently restored in mice under the hyperlipidemic conditions caused by the low density lipoprotein receptor deficiency. As a result, the mice become more hyperlipidemic and the lipid accumulation in the liver is followed by hepatic steatosis (C).

Mentions: Whereas lipid homeostasis in hyperlipidemic LDLr−/− mice was strongly affected by Znf202 overexpression, normolipidemic mice only showed mild effects. The moderate effect on total serum lipid levels in WT mice could be attributed in part to clearance via the LDLR. Moreover, additional secondary effects due to a progressively increased VLDL-TG lipolysis and panlobular lipid accumulation are not opportune in WT mice. In contrast to Ldlr−/−, the livers of WT mice show no accumulation of lipids upon Znf202 overexpression at day 5. Interestingly, while in Ldlr−/− the gene expression of cyp7a1, a key enzyme in bile acid synthesis [42], was apparently normalized after an initial strong Znf202 induced downregulation, it was strongly upregulated in normolipidemic mice. The latter response may underly the mild phenotype seen in WT mice which leads us to propose that the in vivo impact of Znf202 expression depends on the hyperlipidemic status (Fig. 6). Znf202 overexpression directly modulates bile flux gene expression resulting in hepatic lipid accumulation and a subsequent increase in VLDL secretion. Whereas initial effects on many of the established znf202 responsive hepatic genes appear to be compensated by a yet unknown mechanism, Znf202 overexpression did result in reduced HDL-cholesterol levels both in normo- and in hyperlipidemic mice. Whether or not Znf202 is the responsible gene within the identified chromosomal region that has been linked to hypoalphalipoproteinemia in the study with Utah pedigrees [11] and has a direct or indirect association with the increased risk of coronary heart disease requires further investigation.


Znf202 affects high density lipoprotein cholesterol levels and promotes hepatosteatosis in hyperlipidemic mice.

Vrins CL, Out R, van Santbrink P, van der Zee A, Mahmoudi T, Groenendijk M, Havekes LM, van Berkel TJ, Willems van Dijk K, Biessen EA - PLoS ONE (2013)

Proposed mechanism for Znf202.Elevated hepatic levels of Znf202 downregulate bile flux genes. Together with an increase in cholesterol synthesis and attenuated bile acid synthesis, this could result in the observed lipid accumulation in the liver and increased VLDL secretion (A). Under normolipidemic conditions, feedback mechanisms are able to reverse most of the initial effects of Znf202 overexpression (B). These initial effects cannot be sufficiently restored in mice under the hyperlipidemic conditions caused by the low density lipoprotein receptor deficiency. As a result, the mice become more hyperlipidemic and the lipid accumulation in the liver is followed by hepatic steatosis (C).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585336&req=5

pone-0057492-g006: Proposed mechanism for Znf202.Elevated hepatic levels of Znf202 downregulate bile flux genes. Together with an increase in cholesterol synthesis and attenuated bile acid synthesis, this could result in the observed lipid accumulation in the liver and increased VLDL secretion (A). Under normolipidemic conditions, feedback mechanisms are able to reverse most of the initial effects of Znf202 overexpression (B). These initial effects cannot be sufficiently restored in mice under the hyperlipidemic conditions caused by the low density lipoprotein receptor deficiency. As a result, the mice become more hyperlipidemic and the lipid accumulation in the liver is followed by hepatic steatosis (C).
Mentions: Whereas lipid homeostasis in hyperlipidemic LDLr−/− mice was strongly affected by Znf202 overexpression, normolipidemic mice only showed mild effects. The moderate effect on total serum lipid levels in WT mice could be attributed in part to clearance via the LDLR. Moreover, additional secondary effects due to a progressively increased VLDL-TG lipolysis and panlobular lipid accumulation are not opportune in WT mice. In contrast to Ldlr−/−, the livers of WT mice show no accumulation of lipids upon Znf202 overexpression at day 5. Interestingly, while in Ldlr−/− the gene expression of cyp7a1, a key enzyme in bile acid synthesis [42], was apparently normalized after an initial strong Znf202 induced downregulation, it was strongly upregulated in normolipidemic mice. The latter response may underly the mild phenotype seen in WT mice which leads us to propose that the in vivo impact of Znf202 expression depends on the hyperlipidemic status (Fig. 6). Znf202 overexpression directly modulates bile flux gene expression resulting in hepatic lipid accumulation and a subsequent increase in VLDL secretion. Whereas initial effects on many of the established znf202 responsive hepatic genes appear to be compensated by a yet unknown mechanism, Znf202 overexpression did result in reduced HDL-cholesterol levels both in normo- and in hyperlipidemic mice. Whether or not Znf202 is the responsible gene within the identified chromosomal region that has been linked to hypoalphalipoproteinemia in the study with Utah pedigrees [11] and has a direct or indirect association with the increased risk of coronary heart disease requires further investigation.

Bottom Line: The repressive activity of Znf202 was firmly confirmed in an apoE reporter assay and Znf202 responsive elements within the ApoE promoter were identified.Interestingly, key genes in bile flux (abcg5/8 and bsep) and in bile acid synthesis (cyp7a1) were also downregulated.Znf202 overexpression in vivo reveals an important role of this transcriptional regulator in liver lipid homeostasis, while firmly establishing the proposed key role in the control of HDL levels.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Biochemistry, Academic Medical Center, Amsterdam, The Netherlands. c_vrins@hotmail.com

ABSTRACT

Background: The zinc finger protein Znf202 is a transcriptional suppressor of lipid related genes and has been linked to hypoalphalipoproteinemia. A functional role of Znf202 in lipid metabolism in vivo still remains to be established.

Methodology and principal findings: We generated mouse Znf202 expression vectors, the functionality of which was established in several in vitro systems. Next, effects of adenoviral znf202 overexpression in vivo were determined in normo- as well as hyperlipidemic mouse models. Znf202 overexpression in mouse hepatoma cells mhAT3F2 resulted in downregulation of members of the Apoe/c1/c2 and Apoa1/c3/a4 gene cluster. The repressive activity of Znf202 was firmly confirmed in an apoE reporter assay and Znf202 responsive elements within the ApoE promoter were identified. Adenoviral Znf202 transfer to Ldlr-/- mice resulted in downregulation of apoe, apoc1, apoa1, and apoc3 within 24 h after gene transfer. Interestingly, key genes in bile flux (abcg5/8 and bsep) and in bile acid synthesis (cyp7a1) were also downregulated. At 5 days post-infection, the expression of the aforementioned genes was normalized, but mice had developed severe hepatosteatosis accompanied by hypercholesterolemia and hypoalphalipoproteinemia. A much milder phenotype was observed in wildtype mice after 5 days of hepatic Znf202 overexpression. Interestingly and similar to Ldl-/- mice, HDL-cholesterol levels in wildtype mice were lowered after hepatic Znf202 overexpression.

Conclusion/significance: Znf202 overexpression in vivo reveals an important role of this transcriptional regulator in liver lipid homeostasis, while firmly establishing the proposed key role in the control of HDL levels.

Show MeSH
Related in: MedlinePlus