Investigation of the Signal Pathways of Green Tea Epigallocatechin Gallate to Regulate Microrna-143 and Microrna-Let-7a Gene Expressions in Fat Cells(2/3)

Obesity is a common disease in the world’s population, including Taiwan, and it associates with risks of cancer, diabetes, hypertension, and cardiovascular disease. Obesity is characterized by increased number of fat cells and lipid droplet due to mitogenesis and differentiation. In turn, the two processes can be regulated by nutritional factors and microRNA (miR) molecules.《In particular, our recent preliminary data indicated that green tea epigallocatechin gallate (EGCG) upregulated 24 miR expressions and downregulated 26 miR expressions in 3T3-L1 white preadipocytes. Among them, miR-143 and miR-let-7a expressions in 3T3-L1 white preadipocytes were increased after EGCG treatment. Decreases in expressions of their respective target genes, such as DLK1 and HMGA2, induced by EGCG were also observed. When miR-143 mimics was transfected into 3T3-L1 cells in the absence of EGCG, the level of miR-143 mRNA expression was increased, the level of DLK1 gene expression was reduced, and the number of cells was decreased. Whereas, an inhibitor for miR-143 knockdown in 3T3-L1 preadipocytes antagonized EGCG-induced increase in miR-143 expression and prevented EGCG-induced decrease in cell number. EGCG also altered miR-143 and let-7a expressions in brown and brite fat cells. Interestingly, actions of EGCG on expressions of these genes were similar to those altered by a glutathione (GSH) precursor. The effects of EGCG on miR-143/DLK1 expressions were reversed by an AMPK inhibitor. However, the action mechanisms of GSH and AMPK on EGCG-mediated miR expression require further demonstrations. Whether the miR-let-7a/HMGA2-regulated pathway mediate the inhibitory effect of EGCG on the growth and differentiation of white fat cells still requires thorough demonstrations. EGCG was found by our lab to regulate fat cell functions through the ERK, AMPK, GSH, and EGCG receptor pathways; thus, the hypothesis arises that any of these signaling molecules may mediate EGCG’s actions on miR-143 and miR-let-7a genes in fat cells and thereby coordinating fat cell growth and differentiation.》【To understand the miR signaling pathway of green tea EGCG involved in its impacts on obesity and fat cell functions, the overall objective of this 3-year study is to investigate the signal pathways involved in EGCG modulations of miR-143 and miR-let-7a gene expressions in fat cells and thereby coordinating fat cell growth and differentiation. Aims I and II will study how the miR-143 and miR-let-7a signaling pathways mediate the inhibitory effects of EGCG on fat cell growth and differentiation, respectively. Aims III and IV will study if the respective MAPK and AMPK signaling pathways are involved in EGCG modulations of miR-143 and miR-let-7a gene expressions in fat cells in relation to growth and differentiation processes. Aims V and VI will study the respective GSH and EGCG receptor signaling pathways involved in EGCG modulations of miR-143 and miR-let-7a expressions in fat cells in relation to growth and differentiation processes. Aims VII will study the in vivo effects of EGCG on miR-143 and miR-let-7a levels in adipose tissues of normal and high-fat diet-induced obesity mice, respectively.】