Curcumin, a polyphenol found in the rhizomes of Curcuma longa , improves obesity-associated inflammation and diabetes in obese mice. Curcumin also suppresses adipocyte differentiation, although the underlying mechanism remains unclear. Here, we used 3T3-L1 cells to investigate the details of the mechanism underlying the anti-adipogenic effects of curcumin. Curcumin inhibited mitogen-activated protein kinase (MAPK) (ERK, JNK, and p38) phosphorylation that was associated with differentiation of 3T3-L1 cells into adipocytes. During differentiation, curcumin also restored nuclear translocation of the integral Wnt signaling component β-catenin in a dose-dependent manner. In parallel, curcumin reduced differentiation-stimulated expression of CK1α, GSK-3β, and Axin, components of the destruction complex targeting β-catenin. Accordingly, quantitative PCR analysis revealed that curcumin inhibited the mRNA expression of AP2 (mature adipocyte marker) and increased the mRNA expression of Wnt10b, Fz2 (Wnt direct receptor), and LRP5 (Wnt coreceptor). Curcumin also increased mRNA levels of c-Myc and cyclin D1, well-known Wnt targets. These results suggest that the Wnt signaling pathway participates in curcumin-induced suppression of adipogenesis in 3T3-L1 cells.

Sirtuin 1 (SIRT1) plays a critical role in the maintenance of metabolic homeostasis and promotes fat mobilization in white adipose tissue. However, regulation of SIRT1 during adipogenesis, particularly through microRNAs, remains unclear. We observed that miR‐146b expression was markedly increased during adipogenesis in 3T3‐L1 cells. Differentiation of 3T3‐L1 was induced by overexpression of miR‐146b. Conversely, inhibition of miR‐146b decreased adipocyte differentiation. Bioinformatics‐based studies suggested that SIRT1 is a target of miR‐146b. Further analysis confirmed that SIRT1 was negatively regulated by miR‐146b. We also observed that miR‐146b bound directly to the 3′‐untranslated region of SIRT1 and inhibited adipogenesis through SIRT1 downregulation. The miR‐146b/SIRT1 axis mediates adipogenesis through increased acetylation of forkhead box O1 (FOXO1). Expression of miR‐146b was increased and SIRT1 mRNA subsequently decreased in the adipose tissues of diet‐induced and genetically obese mice. Furthermore, in vivo knockdown of miR‐146b by a locked nucleic acid miR‐146b antagomir significantly reduced body weight and fat volume in accordance with upregulation of SIRT1 and subsequent acetylation of FOXO1. Therefore, the miR‐146b/SIRT1 pathway could be a potential target for obesity prevention and treatment.

Curcumin is a well‐known component of traditional turmeric (Curcuma longa), which has been reported to prevent obesity and diabetes. However, the effect of curcumin on hepatic lipid metabolism remains unclear. The aim of this study was to examine the effects of curcumin on hepatic steatosis in high‐fat/cholesterol diet (HFD)‐induced obese mice. Male C57BL/6J mice were fed a normal diet (ND), HFD or HFD with 0.15% curcumin (HFD+C) for 11 weeks. We found that curcumin significantly lowered the body‐weight and adipose tissue weight of mice in the HFD+C group compared with the findings for the HFD group (p < 0.05). The levels of total cholesterol, fasting glucose and insulin in serum were decreased, and HFD‐induced impairment of insulin sensitivity was improved by curcumin supplementation (p < 0.05). Curcumin protected against the development of hepatic steatosis by reducing hepatic fat accumulation. Moreover, curcumin activated AMP‐activated protein kinase (AMPK) and elevated the gene expression of peroxisome proliferator‐activated receptor alpha. By contrast, curcumin suppressed the HFD‐mediated increases in sterol regulatory element‐binding protein‐1, acetyl‐CoA carboxylase 1, fatty acid synthase and cluster of differentiation 36 expression. Taken together, these findings indicate that curcumin attenuates HFD‐induced hepatic steatosis by regulating hepatic lipid metabolism via AMPK activation, suggesting its use as a therapeutic for hepatic steatosis.