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Activation of peroxisome proliferator-activated receptor gamma by rosiglitazone increases sirt6 expression and ameliorates hepatic steatosis in rats.

Yang SJ, Choi JM, Chae SW, Kim WJ, Park SE, Rhee EJ, Lee WY, Oh KW, Park SW, Kim SW, Park CY - PLoS ONE (2011)

Bottom Line: AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1.In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway.

View Article: PubMed Central - PubMed

Affiliation: Diabetes Research Institute, Sungkyunkwan University School of Medicine, Kangbuk Samsung Hospital, Seoul, Korea.

ABSTRACT

Background: Sirt6 has been implicated in the regulation of hepatic lipid metabolism and the development of hepatic steatosis. The aim of this study was to address the potential role of Sirt6 in the protective effects of rosiglitazone (RGZ) on hepatic steatosis.

Methods: To investigate the effect of RGZ on hepatic steatosis, rats were treated with RGZ (4 mg·kg⁻¹·day⁻¹) by stomach gavage for 6 weeks. The involvement of Sirt6 in the RGZ's regulation was evaluated by Sirt6 knockdown in AML12 mouse hepatocytes.

Results: RGZ treatment ameliorated hepatic lipid accumulation and increased expression of Sirt6, peroxisome proliferator-activated receptor gamma coactivtor-1-α (Ppargc1a/PGC1-α) and Forkhead box O1 (Foxo1) in rat livers. AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1. Interestingly, in free fatty acid-treated cells, Sirt6 knockdown increased hepatocyte lipid accumulation measured as increased triglyceride contents (p = 0.035), suggesting that Sirt6 may be beneficial in reducing hepatic fat accumulation. In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.

Conclusion: Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway. We propose Sirt6 as a possible therapeutic target for hepatic steatosis.

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Related in: MedlinePlus

The effect of Sirt6 knockdown on phosphorylation of LKB1 and AMP-activated protein kinase (AMPK) in hepatocytes.(A) Representative western blots for phosphorylated LKB1 at Ser428 (pLKB1), LKB1, phosphorylated AMPKα at Thr172 (pAMPKα), pAMPKα, and β-actin. (B) Densitometric analysis of pLKB1 and pAMPKα. Levels of phosphorylated LKB1 at Ser428 and AMPKα at Thr172 were normalized to values for LKB1 and AMPKα, respectively. FFA, free fatty acids; RGZ, rosiglitazone. Data are means±SEM (n = 6 per group). *p<0.05 vs control (CON; white bar), †p<0.05 vs FFA alone.
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pone-0017057-g007: The effect of Sirt6 knockdown on phosphorylation of LKB1 and AMP-activated protein kinase (AMPK) in hepatocytes.(A) Representative western blots for phosphorylated LKB1 at Ser428 (pLKB1), LKB1, phosphorylated AMPKα at Thr172 (pAMPKα), pAMPKα, and β-actin. (B) Densitometric analysis of pLKB1 and pAMPKα. Levels of phosphorylated LKB1 at Ser428 and AMPKα at Thr172 were normalized to values for LKB1 and AMPKα, respectively. FFA, free fatty acids; RGZ, rosiglitazone. Data are means±SEM (n = 6 per group). *p<0.05 vs control (CON; white bar), †p<0.05 vs FFA alone.

Mentions: Lastly, we investigated whether the phosphorylation levels of LKB1 and AMPK is altered by Sirt6 knockdown with RGZ treatment in AML12 mouse hepatocytes. RGZ increased phosphorylation levels of LKB1 (Ser428) and AMPK (Thr172) in the presence of FFA, and the knockdown of Sirt6 suppressed the effects of RGZ on the phosphorylation of LKB1 and AMPK (Figure 7), suggesting that Sirt6 regulates the phosphorylation of LKB1 and AMPK.


Activation of peroxisome proliferator-activated receptor gamma by rosiglitazone increases sirt6 expression and ameliorates hepatic steatosis in rats.

Yang SJ, Choi JM, Chae SW, Kim WJ, Park SE, Rhee EJ, Lee WY, Oh KW, Park SW, Kim SW, Park CY - PLoS ONE (2011)

The effect of Sirt6 knockdown on phosphorylation of LKB1 and AMP-activated protein kinase (AMPK) in hepatocytes.(A) Representative western blots for phosphorylated LKB1 at Ser428 (pLKB1), LKB1, phosphorylated AMPKα at Thr172 (pAMPKα), pAMPKα, and β-actin. (B) Densitometric analysis of pLKB1 and pAMPKα. Levels of phosphorylated LKB1 at Ser428 and AMPKα at Thr172 were normalized to values for LKB1 and AMPKα, respectively. FFA, free fatty acids; RGZ, rosiglitazone. Data are means±SEM (n = 6 per group). *p<0.05 vs control (CON; white bar), †p<0.05 vs FFA alone.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3044155&req=5

pone-0017057-g007: The effect of Sirt6 knockdown on phosphorylation of LKB1 and AMP-activated protein kinase (AMPK) in hepatocytes.(A) Representative western blots for phosphorylated LKB1 at Ser428 (pLKB1), LKB1, phosphorylated AMPKα at Thr172 (pAMPKα), pAMPKα, and β-actin. (B) Densitometric analysis of pLKB1 and pAMPKα. Levels of phosphorylated LKB1 at Ser428 and AMPKα at Thr172 were normalized to values for LKB1 and AMPKα, respectively. FFA, free fatty acids; RGZ, rosiglitazone. Data are means±SEM (n = 6 per group). *p<0.05 vs control (CON; white bar), †p<0.05 vs FFA alone.
Mentions: Lastly, we investigated whether the phosphorylation levels of LKB1 and AMPK is altered by Sirt6 knockdown with RGZ treatment in AML12 mouse hepatocytes. RGZ increased phosphorylation levels of LKB1 (Ser428) and AMPK (Thr172) in the presence of FFA, and the knockdown of Sirt6 suppressed the effects of RGZ on the phosphorylation of LKB1 and AMPK (Figure 7), suggesting that Sirt6 regulates the phosphorylation of LKB1 and AMPK.

Bottom Line: AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1.In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway.

View Article: PubMed Central - PubMed

Affiliation: Diabetes Research Institute, Sungkyunkwan University School of Medicine, Kangbuk Samsung Hospital, Seoul, Korea.

ABSTRACT

Background: Sirt6 has been implicated in the regulation of hepatic lipid metabolism and the development of hepatic steatosis. The aim of this study was to address the potential role of Sirt6 in the protective effects of rosiglitazone (RGZ) on hepatic steatosis.

Methods: To investigate the effect of RGZ on hepatic steatosis, rats were treated with RGZ (4 mg·kg⁻¹·day⁻¹) by stomach gavage for 6 weeks. The involvement of Sirt6 in the RGZ's regulation was evaluated by Sirt6 knockdown in AML12 mouse hepatocytes.

Results: RGZ treatment ameliorated hepatic lipid accumulation and increased expression of Sirt6, peroxisome proliferator-activated receptor gamma coactivtor-1-α (Ppargc1a/PGC1-α) and Forkhead box O1 (Foxo1) in rat livers. AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1. Interestingly, in free fatty acid-treated cells, Sirt6 knockdown increased hepatocyte lipid accumulation measured as increased triglyceride contents (p = 0.035), suggesting that Sirt6 may be beneficial in reducing hepatic fat accumulation. In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.

Conclusion: Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway. We propose Sirt6 as a possible therapeutic target for hepatic steatosis.

Show MeSH
Related in: MedlinePlus