(-)-Epigallocatechin gallate suppresses adipocyte differentiation through the MEK/ERK and PI3K/Akt pathways

EGCG [(-)-epigallocatechin gallate], tea catechin, is one of the compounds that has been reported to act against obesity and diabetes. To determine the effect of EGCG on adipocyte differentiation, we treated 3T3-L1 preadipocytes with different catechins. Oil Red 0 staining showed significantly reduced intracellular lipid accumulation, especially with EGCG. Cell cycle analysis showed that EGCG inhibited cell proliferation by disturbing the cell cycle during the clonal expansion of 3T3-L1. RT-PCR (real-time PCR) demonstrated that EGCG noticeably reduced mRNA expression of PPAR gamma (peroxisome proliferator-activated receptor gamma), C/EBP alpha (CCAAT/enhancer-binding protein alpha) and FoxO1 (forkhead box class 01). EGCG also caused a significant decrease in the transcription of FoxO1 - the forkhead transcription factor class 01 involved in adipocyte differentiation - via the PI3K (phosphoinositide 3-kinase)/Akt and MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase] pathways. These results suggest that EGCG suppresses the clonal expansion of adipocytes by inactivating FoxO1 via insulin signalling and stress-dependent MAPK pathways.