Objective:Apoptosis inhibitor 6(Api6)

also known as AIM(Apoptosis Inhibitor expressed by Macrophage)or SPα(Soluble Protein alpha)

is a newly defined member of the group B scavenger receptor cysteine-rich(SRCR)superfamily.Previous studies have suggested its important roles in immune system regulation

but the involvement of Api6 in lipid metabolism is seldomly studied.Methods:The aim of this study was to define the expression pattern of Api6 in lipid loading and inflammatory macrophages.The human monocyte/macrophage lineage THP-1 cells and murine Raw264.7 macrophages were incubated in the presence of 100 μg/ml oxidized low-density lipoprotein(oxLDL)alone

LDL plus 200 ng/ml lipopolysaccharide(LPS)and LPS alone.Results:Foam cell formation after treatment was evidenced by oil red O staining.Real-time PCR results showed that after LPS or oxLDL treatment

the mRNA levels of Scavenger receptor SRA were increased 6-fold

2.5-fold and 6-fold

44-fold in Raw264.7 cells and THP-1 cellls respectively

but the expression of Api6 in Raw264.7 did not change.The mRNA levels of Api6 increased 2.7-fold after LPS and oxLDL treatment in THP-1 cells.Conclusion:The expression levels of Api6 in these macrophages were highly related to the presence of nuclear receptor liver X receptor(LXR)isoform LXRα.This study revealed that due to the lack of LXRα isoform

the basic expression level of Api6 was low in Raw264.7 macrophages

that makes it an ideal cell line for further study related to pathophysiological function of Api6 in lipid metabolism.