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Saturated Fatty Acids Induce Ceramide-associated Macrophage Cell Death
Published on: October 31, 2017
Acid Sphingomyelinase Mediates Oxidized-LDL Induced Apoptosis in Macrophage via Endoplasmic Reticulum Stress
Min Zhao1, Wei Pan, Rui-Zheng Shi
1Departments of Nuclear Medicine, Xiangya Hospital, Central South University.
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.
Insights
Oxidized low-density lipoprotein (ox-LDL) triggers macrophage apoptosis through the acid sphingomyelinase (ASM)/ceramide pathway, which involves endoplasmic reticulum (ER) stress. Inhibiting ASM or ceramide reduces this ox-LDL-induced cell death.
Area of Science:
- Cardiovascular Biology
- Cellular Stress Responses
- Lipid Metabolism
Background:
- Macrophage apoptosis is a critical process in advanced atherosclerosis.
- Oxidized low-density lipoprotein (ox-LDL) significantly contributes to macrophage apoptosis.
- The acid sphingomyelinase (ASM) and ceramide pathway are implicated in apoptosis induction.
Purpose of the Study:
- To investigate the role of ASM in ox-LDL-induced macrophage apoptosis.
- To elucidate the involvement of the ASM/ceramide signaling pathway in endoplasmic reticulum (ER) stress during ox-LDL-induced apoptosis.
Main Methods:
- Macrophages (human THP-1 and mouse peritoneal) were treated with ox-LDL in vitro.
- ASM activity and ceramide levels were measured using ultra-performance liquid chromatography.
- Protein and mRNA expression were analyzed via Western blot and quantitative real-time PCR.
- Apoptosis was assessed using Hoechst staining and flow cytometry.
Main Results:
- Ox-LDL induced macrophage apoptosis via ER stress, upregulating ASM activity and ceramide levels.
- Inhibition of ASM (siRNA, desipramine) or ceramide degradation (recombinant acid ceramidase) attenuated ER stress and apoptosis.
- Recombinant ASM increased ceramide and ER stress, while its inhibition, along with ceramide degradation or ER stress inhibition (4-phenylbutyric acid), blocked CHOP upregulation and apoptosis.
Conclusions:
- The ASM/ceramide signaling pathway plays a significant role in ox-LDL-induced macrophage apoptosis.
- This pathway mediates apoptosis through the induction of endoplasmic reticulum (ER) stress.
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