Effects Of Arachidonic Acid On Cell Lipid-accumulation And Cell Cycle In Macrophages

Arachidonic acid(AA or ARA) is one of the most widely-distributed polyunsaturated fatty acids in the body which mainly exists in the form of phospholipids in cell membranes, playing an important role in maintaining the structure and function of cell membrane. AAis freed from the membrane phospholipids during the hydrolysis catalyzed by phospholipases, and then participates in a series of metabolic process. AA and its metabolites constitute the main inflammation network and participate in a variety of inflammatory reactions of body, including some chronic inflammatory diseases such as atherosclerosis and rheumatoid disease. Atherosclerosis(AS) is a kind of chronic inflammation disease occurring in the cardiovascular system. The accumulation of lipid-rich macrophages in the damaged arterial intimal and subsequentharmful immune responses are the main causes of atherosclerosis.As an important immune cell in vivo, macrophage involve in the formation, stability and rupture of the plaque in all processes of AS. Of note, the formation of foam cells caused by metabolic disorder of lipid have been considered as the first step of advancing AS.ROS has a close relationship with the lipid accumulated in cells,and the level of ROS can be increased by lipid. Excessive ROS could damage the mitochondria and reduce the production of ATP, which can combine with ABCA1 to promote cellular cholesterol outflow and accelerate the lipid metabolism in cells. The intracellular ROS can induce cell cycle arrest or apoptosis through activating the JNK signal pathway. In addition, Fox O proteins were reported to regulate cell cycle and apoptosis, DNA damage repair and oxidative stress. Several strands of evidence show that JNK signal pathway affects the cell cycle through regulating Fox O proteins.A lot of researches have been done on the roles of AA and its metabolites in AS, but the effects and mechanisms of AA on macrophages in AS have not been well understood. This study focus on the effects of AA on the lipid-accumulation and cell proliferation or apoptosis in raw264.7 cells. Our results :(i) After treating with AA in a concentration gradient(0、40、60、80μM), the viability of PBMCs(peripheral blood mononuclear cells) and raw264.7 were inhibited significantly in a dose-dependent manner, and the cell viability for the 48 h group is higher than the 24 hgroup. The levels of TGand ROSincreased while the level of ATP decreased with the treatment of AA. Increasing lipid drops and foaming were also observed.(ii) After treating with AA,the proportion of cells in the S phase increased while almost no cells stayed in the G2/M phase in 80μM group. The expression of cyclin D and CDK4 decreased whilethe expression of p53 and p27 increased. Theresult did not observe obviouschanges in the expression of caspase 3.(iii) The expression of JNK and Fox O increased after treating raw264.7 with AA. When inhibiting the function of JNK, the effects of AA on cyclin D, CDK4, p53, p27 and Fox O were blocked. Our results indicated that:(i) AA impeded the lipid metabolism of raw264.7 cells;(ii) AAinduced cell cycle arrest but not apoptosis mainly through the JNK signal pathway.