MiR-25 suppresses 3T3-L1 adipogenesis by directly targeting KLF4 and C/EBPα.

In the past decade, miRNA emerges as a vital player in orchestrating gene regulation and maintaining cellular homeostasis. It is well documented that miRNA influences a variety of biological events, including embryogenesis, cell fate decision, and cellular differentiation. Adipogenesis is an organized process of cellular differentiation by which pre-adipocytes differentiate towards mature adipocytes. It has been shown that adipogenesis is tightly modulated by a number of transcription factors such as PPARγ, KLF4, and C/EBPα. However, the molecular mechanisms underlying the missing link between miRNA and adipogenesis-related transcription factors remain elusive. In this study, we unveiled that miR-25, a member of miR-106b-25 cluster, was remarkably downregulated during 3T3-L1 adipogenesis. Restored expression of miR-25 significantly impaired 3T3-L1 adipogenesis and downregulated the expression of serial adipogenesis-related genes. Further experiments presented that ectopic expression of miR-25 did not affect cell proliferation and cell cycle progression. Finally, KLF4 and C/EBPα, two key regulators of adipocyte differentiation, were experimentally identified as bona fide targets for miR-25. These data indicate that miR-25 is a novel negative regulator of adipocyte differentiation and it suppressed 3T3-L1 adipogenesis by targeting KLF4 and C/EBPα, which provides novel insights into the molecular mechanism of miRNA-mediated cellular differentiation.

Characterization of miR-210 in 3T3-L1 adipogenesis.

Although accumulating evidences indicate that miRNA emerge as a vital player in cell growth, development, and differentiation, how they contribute to the process of adipocyte differentiation remains elusive. In the present study, we revealed that the expression level of miR-210 was dramatically upregulated during 3T3-L1 adipogenesis. Ectopic introduction of miR-210 into 3T3-L1 cells promoted terminal differentiation as well as the expression of adipogenic markers. MTT assay showed that miR-210 significantly inhibited cell proliferation whereas the BrdU incorporation assay and flow cytometry analysis showed that miR-210 did not impair G1/S phase transition. Further experiments demonstrated that enhanced expression of miR-210 in 3T3-L1 cells provoked adipocyte differentiation via activation of PI3K/Akt pathway by targeting SHIP1, a negative regulator of PI3K/Akt pathway. Moreover, blockade of endogenous miR-210 during adipogenesis significantly repressed adipocyte differentiation. In summary, we have identified miR-210 as an important positive regulator in adipocyte differentiation through the activation of PI3K/Akt pathway.

Choosing hamsters but not rats as a model for studying plasma cholesterol-lowering activity of functional foods.

Rats and hamsters are commonly used rodents to test the efficacy of cholesterol-lowering functional foods. In general, a diet containing 1% cholesterol for rats whereas a diet containing 0.1% cholesterol for hamsters is used to induce the hypercholesterolemia. The present study was carried out to compare hamsters with rats as a hypercholesterolemia model. Golden Syrian hamsters and Sprague Dawley rats were randomly divided into four groups and fed one of the four diets containing 0-0.9% cholesterol. Results demonstrated that serum total cholesterol (TC) in hamsters was raised 73-81% higher than that in rats fed the same cholesterol diets. Unlike rats in which HDL-C accounted very little for serum TC, the lipoprotein profile in hamsters was closer to that in humans. We investigated interaction of higher cholesterol diets with 3-hydroxy-3-methylglutary-CoA (HMG-CoA) reductase, low-density lipoprotein receptor (LDL-R) and cholesterol-7alpha-hydroxylase (CYP7A1), sterol regulatory element binding protein-2 (SREBP-2), and liver X receptor (LXR-alpha). Results showed hamsters and rats metabolized cholesterol differently. In view that hamsters synthesize and excrete cholesterol and bile acids in a manner similar to that in humans, it is concluded that hamsters but not rats shall be chosen as a model to study efficacy of cholesterol-lowering functional foods.