β-Catenin mediates the anti-adipogenic effect of baicalin

doi:10.1016/j.bbrc.2010.07.015

Biochemical and Biophysical Research Communications

Volume 398, Issue 4, 6 August 2010, Pages 741-746

https://doi.org/10.1016/j.bbrc.2010.07.015 Get rights and content

Abstract

β-Catenin reportedly inhibits adipogenesis through the down-regulations of peroxisome proliferator-activated receptor (PPAR)γ and CCAAT/enhancer binding protein (C/EBP)α. We report that baicalin, a natural flavonoid compound, inhibits adipogenesis by modulating β-Catenin. During 3T3-L1 cell adipogenesis, β-Catenin was down-regulated, but baicalin treatment maintained β-Catenin expression. Anti-adipogenic effects of baicalin were significantly attenuated by β-Catenin siRNA transfection. β-Catenin siRNA rescued the reduced expressions of PPARγ, C/EBPα, fatty acid binding protein 4 and lipoprotein lipase by baicalin. Furthermore, baicalin modulated members of the WNT/β-Catenin pathway by maintaining the expressions of low-density lipoprotein receptor-related protein 6, disheveled (DVL)2 and DVL3. These findings suggest that β-Catenin mediates the anti-adipogenic effects of baicalin.

Research highlights

► Baicalin maintains the levels of β-Catenin during adipogenesis. ► β-Catenin mediates the anti-adipogenic effect of baicalin. ► Baicalin maintains the WNT/β-Catenin pathway during adipogenesis.

Introduction

Adipogenesis is the differentiation process of preadipocytes into adipocytes which play pivotal roles in fat metabolism and closely related to the etiology of obesity and related metabolic disorders [1], [2], [3]. A mouse preadipocyte cell line, 3T3-L1 has been commonly used as an in vitro model system to investigate the molecular mechanisms of adipogenesis [4]. In the presence of 3-isobutyl-1-methylxanthine, dexamethasone and insulin, 3T3-L1 preadipocytes differentiate into adipocytes and express adipocyte-specific genes [5]. Among them, peroxisome proliferator-activated receptor (PPAR)γ and CCAAT/enhancer binding protein (C/EBP)α are key transcription factors of adipogenesis [6], [7]. These two transcription factors together activate the expression of adipocyte maker genes such as lipoprotein lipase (LPL), fatty acid binding protein (FABP)4 and fatty acid synthase, which are involved in fat metabolism [8]. The physiological regulation of adipogenesis is influenced by the balance of positive and negative adipogenic regulators that act upstream of PPARγ and C/EBPα[9].

The WNT/β-Catenin pathway is a negative regulator of adipogenesis, inhibiting both expression and activity of PPARγ and C/EBPα[10], [11]. WNT binding to frizzled (FZ) receptor and low-density lipoprotein receptor-related protein (LRP) co-receptor disrupts the AXIN-glycogen synthesis kinase (GSK)-adenomatous polyposis coli (APC) complex by recruiting disheveled (DVL) and degrading AXIN [12]. Disruption of AXIN–APC–GSK complex enhances the nuclear translocation of β-Catenin. In the nucleus, β-Catenin binds to T-cell factor/lymphoid-enhancing factor (TCF/LEF) and induces transcription of genes such as cyclin D (CCND)1, PPARδ and c-MYC [13], [14]. β-Catenin directly binds and inhibits PPARγ activity [15] and also indirectly suppresses the expression and activity of PPARγ and C/EBPα by inducing CCND1, PPARδ and c-MYC [13], [14], [16].

In our previous study, baicalin, a natural flavonoid compound found in Scutellaria baicalensis, inhibited fat accumulation by down-regulating PPARγ and C/EBPα in 3T3-L1 cells [17]. This study was conducted to elucidate the detailed mechanisms for the modulations of PPARγ and C/EBPα by baicalin, and it was found that β-Catenin is a mediator.

Section snippets

Chemicals and reagents

Cell culture reagents were obtained from Life Technologies (Grand Island, NY, USA). Anti-C/EBPα, anti-DVL2 and anti-AXIN antibodies were purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Anti-PPARγ, anti-FABP4 antibodies and secondary antibody were purchased from Cell Signaling (Beverly, MA, USA). Anti-β-Catenin antibody was purchased from BD Transduction Laboratories (Lexington, KY, USA). Baicalin and other chemicals were purchased from Sigma–Aldrich (St. Louis, MO, USA).

Cell culture

3T3-L1

Baicalin maintains the levels of β-Catenin during adipogenesis

In our previous report, baicalin inhibited fat accumulation by modulating genes in the adipogenesis pathway. Among these genes, PPARγ and C/EBPα seem to be the major mediators of baicalin that inhibit adipogenesis. Though baicalin significantly reduced PPARγ and C/EBPα expression, C/EBPβ and C/EBPδ were not down-regulated by it [17]. Therefore, we analyzed β-Catenin, which is known to suppress PPARγ and C/EBPα but not C/EBPβ and C/EBPδ[10], [21]. During 3T3-L1 cell adipogenesis, the FABP4,

Discussion

Adipogenesis is regulated by interactions between various positive and negative regulators that affect the expression and activity of the major transcription factors, PPARγ and C/EBPα[7], [9]. β-Catenin is a major component of the cadherin cell adhesion complex and involved in various processes such as development, regeneration, and tumorigenesis [22], [23], [24]. Recently, β-Catenin has been identified as a negative regulator of adipogenesis [15], [25], and suppressor of PPARγ and C/EBPα

Conflict of interest statement

The authors declare that there are no conflicts of interest.

Acknowledgments

This research was supported by a grant of the Oriental Medicine R&D Project (B080020) from Ministry of Health, Welfare and Family Affairs, and also by the Biogreen 21 project (20100301-061-065-001) of the Rural Development Administration, Republic of Korea.

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β-Catenin mediates the anti-adipogenic effect of baicalin

Abstract

Research highlights

Introduction

Section snippets

Chemicals and reagents

Cell culture

Baicalin maintains the levels of β-Catenin during adipogenesis

Discussion

Conflict of interest statement

Acknowledgments

Cell

Cell

Cell Metab.

Trends Endocrinol. Metab.

J. Biol. Chem.

Curr. Opin. Cell Biol.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

Methods

Biochem. Biophys. Res. Commun.

Genomics

J. Biol. Chem.

Biochem. Biophys. Res. Commun.