Role of RAC3 coactivator in the adipocyte differentiation

Green Tea Epigallocatechin-3-gallate Ameliorates Lipid Accumulation and Obesity-Associated Metabolic Syndrome via Regulating Autophagy and Lipolysis in Preadipocytes and Adipose Tissue

Previous studies have shown that epigallocatechin-3-gallate (EGCG), the most abundant catechin in green tea, demonstrates promising antiobesity effects. While autophagy mediates obesity via preadipocyte differentiation and lipogenesis, EGCG's potential autophagy-dependent antiobesity mechanism remains unclear. We used 3T3-L1 cells and high-fat-diet (HFD)-fed mice to examine how EGCG inhibits adipogenesis and lipogenesis via autophagy. EGCG (50 or 100 mg/kg) significantly attenuated HFD-induced weight gain, fat accumulation, hyperlipidemia, and glucose intolerance in mice. It also enhanced autophagy and lipolysis in white adipose tissue (WAT). EGCG profoundly inhibited terminal preadipocyte differentiation and lipid droplet formation in 3T3-L1 cells accompanied by reduced PPARγ, C/EBPα, and FASN expressions. Mechanistically, EGCG inhibited autophagy during the early stage of preadipocyte differentiation, as evidenced by increased autophagosome accumulation and impaired autophagic flux. The antiadipogenic effect of EGCG was further aggravated by the autophagy inhibitor chloroquine. Meanwhile, EGCG increased p38 and AMPK/ACC phosphorylation while inhibiting JNK phosphorylation in 3T3-L1 cells at an early stage of adipogenesis. Interestingly, EGCG reduced the expression of lipolytic enzymes HSL and ATGL, and it decreased glycerol contents in differentiated 3T3-L1 cells. These findings provide novel insights into the mechanism of using green tea EGCG in functional foods to combat obesity by targeting autophagy and lipolysis.

Regulatory mechanisms of the early phase of white adipocyte differentiation: an overview

The adipose organ comprises two main fat depots termed white and brown adipose tissues. Adipogenesis is a process leading to newly differentiated adipocytes starting from precursor cells, which requires the contribution of many cellular activities at the genome, transcriptome, proteome, and metabolome levels. The adipogenic program is accomplished through two sequential phases; the first includes events favoring the commitment of adipose tissue stem cells/precursors to preadipocytes, while the second involves mechanisms that allow the achievement of full adipocyte differentiation. While there is a very large literature about the mechanisms involved in terminal adipogenesis, little is known about the first stage of this process. Growing interest in this field is due to the recent identification of adipose tissue precursors, which include a heterogenous cell population within different types of adipose tissue as well as within the same fat depot. In addition, the alteration of the heterogeneity of adipose tissue stem cells and of the mechanisms involved in their commitment have been linked to adipose tissue development defects and hence to the onset/progression of metabolic diseases, such as obesity. For this reason, the characterization of early adipogenic events is crucial to understand the etiology and the evolution of adipogenesis-related pathologies, and to explore the adipose tissue precursors’ potential as future tools for precision medicine.

The synthesis of branched-chain fatty acids is limited by enzymatic decarboxylation of ethyl- and methylmalonyl-CoA

Most fatty acids (FAs) are straight chains and are synthesized by fatty acid synthase (FASN) using acetyl-CoA and malonyl-CoA units. Yet, FASN is known to be promiscuous as it may use methylmalonyl-CoA instead of malonyl-CoA and thereby introduce methyl-branches. We have recently found that the cytosolic enzyme ECHDC1 degrades ethylmalonyl-CoA and methylmalonyl-CoA, which presumably result from promiscuous reactions catalyzed by acetyl-CoA carboxylase on butyryl- and propionyl-CoA. Here, we tested the hypothesis that ECHDC1 is a metabolite repair enzyme that serves to prevent the formation of methyl- or ethyl-branched FAs by FASN. Using the purified enzyme, we found that FASN can incorporate not only methylmalonyl-CoA but also ethylmalonyl-CoA, producing methyl- or ethyl-branched FAs. Using a combination of gas-chromatography and liquid chromatography coupled to mass spectrometry, we observed that inactivation of ECHDC1 in adipocytes led to an increase in several methyl-branched FAs (present in different lipid classes), while its overexpression reduced them below wild-type levels. In contrast, the formation of ethyl-branched FAs was observed almost exclusively in ECHDC1 knockout cells, indicating that ECHDC1 and the low activity of FASN toward ethylmalonyl-CoA efficiently prevent their formation. We conclude that ECHDC1 performs a typical metabolite repair function by destroying methyl- and ethylmalonyl-CoA. This reduces the formation of methyl-branched FAs and prevents the formation of ethyl-branched FAs by FASN. The identification of ECHDC1 as a key modulator of the abundance of methyl-branched FAs opens the way to investigate their function.