The role of Siglec-1 in chemokines secretion and phagocytosis of oxidized low-density lipoprotein on macrophages / 中华检验医学杂志

ABSTRACT

Objective By in vitro culture of mouse macrophage cell line RAW264. 7 and primary mouse bone marrow macrophages, the expression of Siglec-1 when stimulated by ox-LDL was observed. Meanwhile, Siglec-1 was up-regulated by M-CSF and down-regulated by small interference RNA targeting Siglec-1 ( si-RNA-Siglec-1) , and the expression of chemokines and lipid uptake ability by macrophages were observed, to explore the role of Siglec-1 on macrophages in atherosclerosis. Methods LDL was oxidized by copper. According to preliminary experiment results, ox-LDL 100 μg/ml was selected as a stimulus. There were 6 experimental groupsnormal control group,ox-LDL 100 μg/ml group, ox-LDL 100 μg/ml + si-RNA 2509 2 ng/ml group,ox-LDL 100 μg/ml + si-RNA 3618 2 ng/ml group,ox-LDL 100 μg/ml + M-CSF 5 ng/ml group and ox-LDL 100 μg/ml + M-CSF 10 ng/ml group. si-RNA-Siglec-1 was transfected into macrophage to inhibit the expression of Siglec-1, whereas M-CSF 10 ng/ml or 5 ng/ml were added into the culture medium to enhance the expression of Siglec-1. Quantitative real-time polymerase chain reaction ( qRT-PCR) was used to determine the interfere efficiency of si-RNA-Siglec-1 or M-CSF. After stimulation with ox-LDL for 48 h, cell culture supernatants were collected to determine MIP-1 alpha, MCP-1 and IL-8 concentration by ELISA (n =3 for each group) to evaluate the activation of macrophages. Internalization of lipid particles by macrophages was analyzed by oil red 0 staining. Results Observed by fluorescence microscope, si-RNA-Siglec-1 could be effectively transfected into macrophages with a transfection efficiency about 90% ;PCR results showed that si-RNA 2509 and si-RNA 3618 in a concentration of 40 pmol/L had an inhibition rate of 0. 54 ±0. 11 or 0. 52 ±0. 16 vs 1. 00 ±0. 24 (control group) , t =5. 227 and 4. 992, respectively, all P < 0.01, while M-CSF 10 ng/ml could increase Siglec-1 mRNA expression approximately 4-fold (4. 16 ± 1. 25 vs 1.00 ±0. 24, t =7. 448, P<0. 01). The secretion of MCP-1, MIP-1 alpha, and MIP-2 in si-RNA3618-Siglec-1 group [(359. 28±47. 80) pg/ml, (33. 76 ± 14. 28) ng/ml and (7.87±1.55) ng/ml for MCP-1,MIP-1 alpha, and MIP-2, respectively] was significantly reduced in compare with ox-LDL 100 μg/ml group [ (577. 89 ± 35. 95 ) pg/ml, (69. 17 ± 11. 82) ng/ml and (12.28 ± 1.19) ng/ml for MCP-1, MIP-1 alpha, and MIP-2, respectively], with P value of 0.01, 0.05 and 0.01. In contrary, ox-LDL 100 μg/ml plus M-CSF 10 ng/ml group could significantly promote macrophage chemokine secretion [ (672. 89 ± 43.80) pg/ml, (101.31 ±24.17) ng/ml and (14.81 ±0.54) ng/ml for MCP-1, MIP-1 alpha, and MIP-2, respectively], with P < 0.05 compared with ox-LDL 100 μg/ml group. Meanwhile, lipid intemalization and foam cell formation was inhibited in si-RNA3618-Siglec-l group while ox-LDL 100 μg/ml plus M-CSF 10 ng/ml group could enhance the phagocytosis of ox-LDL by macrophage. Conclusions Siglec-1 may served as a potential phagocytic receptor for ox-LDL involving in macrophage uptake of lipid and turn into foam cells. Furthermore, it can active macrophages and enhance the secretion of MIP-1 alpha, MCP-1 and IL-8, attracting more macrophages and lymphocytes to the site of inflammatory plaque. Targeted inhibition of Siglec-1 reduces macrophage uptake of lipid and secretion of chemokines. Siglec-1 may possibly serve as a potential target of treatment or delay the development of atherosclerosis.