Effect Of Adipocyte Coculture On Expression Of HDL Related Proteins In HepG2 Cell

ObjectiveAdipose tissue is not only a passive organ for energy storage,but also an active endocrine and paracrine organ that releases a large number of cytokines and bioactive mediators.It is prevailingly observed that in obesity individuals,especially visceral obesity,the plasma HDL-C levels is significantly reduced.The mechanism of lowered HDL-C in obesity has to be clarified.We hypothesized that the adipose tissue can influence the HDL metabolism in the liver directly or indirectly.To mimic the in vivo conditions,we employed a 3-D Transwell coculture system for the 3T3-L1 adipocyte and HePG2 cells.This system was used to examine the effect of adipocyte coculture on mRNA or protein expression of apoAI, SAA,and ApoM in HepG2 cells,which are closely associated with the HDL-C levels and functions.METHODSInsulin,Dexamethasone(DXM) and 3-isobutyl-1-methyl-xanthine (IBMX) were added to 3T3-L1 cells to induce its differentiation into mature adipocytes.Transwell system was used to conduct coculture of 3T3-L1 adipocyte and HepG2 cells with unstimulated 3T3-L1 cells and blank as controls.Forty-eight hours after coculture,HepG2 cells were collected and RNA and protein was isolated.Protein expression of apoAI and ApoM,and mRNA levels of SAA were assessed by Western blot and RT-PCR respectively.RESULTS1.The Transwell coculture system of 3T3-L1 adipocyte and HepG2 cells were successfully established.2.Western Blot results showed that adipocyte coculture could inhibit protein expression of apoAI and ApoM in HepG2 cells. 3.RT-PCR analysis showed that adipocyte coculture upregulated the mRNA levels of SAA in HepG2 cell.CONCLUSIONAdipocyte coculture can suppress the expression of apoAI and ApoM and can increase expression of SAA in HepG2 cells,suggesting that the abnormal HDL levels and function was due in part to the direct paracrine effect of adipocyte.