ABSTRACT
AIM: Macrophage apoptosis is a vital event in advanced atherosclerosis, and oxidized low-density lipoprotein (ox-LDL) is a major contributor to this process. Acid sphingomyelinase (ASM) and ceramide are also involved in the induction of apoptosis, particularly in macrophages. Our current study focuses on ASM and investigates its role in ox-LDL-induced macrophage apoptosis. METHODS: Human THP-1 and mouse peritoneal macrophages were cultured in vitro and treated with ox-LDL. ASM activity and ceramide levels were quantified using ultra performance liquid chromatography. Protein and mRNA levels were analyzed using Western blot analysis and quantitative real-time PCR, respectively. Cell apoptosis was determined using Hoechst staining and flow cytometry. RESULTS: Ox-LDL-induced macrophage apoptosis was triggered by profound endoplasmic reticulum (ER) stress, leading to an upregulation of ASM activity and ceramide levels at an early stage. ASM was inhibited by siRNA or desipramine (DES), and/or ceramide was degraded by recombinant acid ceramidase (AC). These events attenuated the effect of ox-LDL on ER stress. In contrast, recombinant ASM upregulated ceramide and ER stress. ASM siRNA, DES, recombinant AC, and ER stress inhibitor 4-phenylbutyric acid were blocked by elevated levels of C/EBP homologous protein (CHOP); ox-LDL induced elevated levels of CHOP. These events attenuated macrophage apoptosis. CONCLUSION: These results indicate that ASM/ceramide signaling pathway is involved in ox-LDL-induced macrophage apoptosis via ER stress pathway.
Subject(s)
Apoptosis/drug effects , Endoplasmic Reticulum Stress/drug effects , Lipoproteins, LDL/pharmacology , Macrophages, Peritoneal/pathology , Monocytes/pathology , Sphingomyelin Phosphodiesterase/metabolism , Animals , Blotting, Western , Cells, Cultured , Flow Cytometry , Fluorescent Antibody Technique , Humans , Macrophages, Peritoneal/drug effects , Mice , Monocytes/drug effects , Real-Time Polymerase Chain ReactionABSTRACT
OBJECTIVE@#To determine the effect of different concentrations of glucose on the differentiation of 3T3-L(1) and the expression of insig-1 and insig-2 mRNA, and to explore the effect of insulin-induced gene in the differentiation and formation of adipocytes and lipogenesis.@*METHODS@#The 3T3-L(1) cells were induced to differentiate in high glucose concentration (25 mol/L G.S), low glucose concentration (5.5 mol/L G.S), and mannitol (19.5 mol/L Mannitol +5.5 mol/L G.S), respectively. The differentiation of 3T3-L(1) cells was examined by oil red "O" straining, and the expression of insig-1,insig-2 mRNA and AP2 mRNA was examined by RT-PCR and in situ hybridization.@*RESULTS@#With the differentiation of 3T3-L(1) cells, the expression of insig-1 and insig-2 mRNA was gradually up-regulated. The expression of insig-1 and insig-2 mRNA significantly increased while AP(2) mRNA decreased in the low glucose concentration inducing group and mannitol inducing group. In the high glucose concentration inducing group, the cell differentiation was poor (P<0.05). There was no difference between the low glucose concentration and the mannitol group in the differentiation of 3T3-L(1) cells, and in the expression of insig-1 and insig-2 and AP(2) mRNA.@*CONCLUSION@#Different concentrations of glucose may influence the cell differentiation and the low glucose concentration promotes insig-1 and insig-2 gene expression, which may lead to the inhibition of the differentiation and lipogenesis of preadipocytes.
