Selenium-binding protein 1 (SELENBP1) is a marker of mature adipocytes

Holger Steinbrenner,Mustafa Micoogullari,Ngoc Anh Hoang,Ina Bergheim,Lars-Oliver Klotz,Helmut Sies

doi:10.1016/j.redox.2018.11.004

Abstract

Selenium-binding protein 1 (SELENBP1) has recently been reported to catalyse the oxidation of methanethiol, an organosulfur compound produced by gut microbiota. Two of the reaction products of methanethiol oxidation, hydrogen peroxide and hydrogen sulphide, serve as signalling molecules for cell differentiation. Indeed, colonocyte differentiation has been found to be associated with SELENBP1 induction. Here, we show that SELENBP1 is induced when 3T3-L1 preadipocytes undergo terminal differentiation and maturation to adipocytes. SELENBP1 induction succeeded the up-regulation of known marker proteins of white adipocytes and the intracellular accumulation of lipids. Immunofluorescence microscopy revealed predominant cytoplasmic localisation of SELENBP1 in 3T3-L1 adipocytes, as demonstrated by co-staining with the key lipogenic enzyme, acetyl-CoA-carboxylase (ACC), located in cytosol. In differentiating 3T3-L1 cells, the mTOR inhibitor rapamycin and the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-α) likewise suppressed SELENBP1 induction, adipocyte differentiation and lipid accumulation. However, lipid accumulation per se is not linked to SELENBP1 induction, as hepatic SELENBP1 was down-regulated in high fructose-fed mice despite increased lipogenesis in the liver and development of non-alcoholic fatty liver disease (NAFLD). In conclusion, SELENBP1 is a marker of cell differentiation/maturation rather than being linked to lipogenesis/lipid accumulation.

Highlights

The essential trace element selenium (Se) exerts most of its biological actions through selenocysteine-containing selenoproteins, many of which are enzymes involved in redox regulation and antioxidant protection [1,2,3]
SELENBP1 was strongly induced in 3T3-L1 cells undergoing adipocyte differentiation: SELENBP1 mRNA levels began to rise during terminal differentiation and were highest in mature adipocytes (> 70-fold induction compared to preadipocytes) at day 14 (Fig. 1A)
Induction of perilipin 1 and peroxisomal proliferator-activated receptor gamma (PPAR-γ) are shown in additional representative immunoblots. (C) Intracellular lipid accumulation, as measured by Oil Red O staining (n = 3; means ± S.E.M.; *p < 0.05, **p < 0.01, ***p < 0.001 vs. day 0 (-Se); # p < 0.05, ## p < 0.01, ### p < 0.001 vs. day 0 (+Se)).). (D) Gene expression of glutathione peroxidase 1 (GPx1), as analysed by real-time RT-PCR with normalisation against hypoxanthine-guanine phosphoribosyl transferase (HPRT) (n = 4; means ± S.E.M.; *p < 0.05, **p < 0.01, ***p < 0.001 vs. day 0 (-Se); #p < 0.05 vs. day 0 (+Se)). (E) Localisation of SELENBP1 in mature adipocytes, as depicted in an immunoblot representative of 3 independent experiments

Summary

Introduction

The essential trace element selenium (Se) exerts most of its biological actions through selenocysteine-containing selenoproteins, many of which are enzymes involved in redox regulation and antioxidant protection [1,2,3]. SELENBP1 is a marker of terminally differentiated epithelial cells in the colon [9], and it may act as tumour suppressor [14]. In the multi-step process of adipogenesis, mesenchymal precursor cells first become committed preadipocytes (adipocyte determination), before undergoing mitotic clonal expansion, terminal differentiation and maturation (adipocyte differentiation) [18]. Both H2O2 and H2S augment adipocyte differentiation and lipid accumulation [19,20,21]. Intracellular H2O2 levels increase during mitotic clonal expansion of preadipocytes, which is counter-balanced through antioxidant enzymes [16,19,20,22]. H2S levels increase during adipocyte differentiation, through up-regulation of H2S-generating enzymes [21]

Methods

Results

Conclusion