Limits...
Cholesterol-induced macrophage apoptosis requires ER stress pathways and engagement of the type A scavenger receptor.

Devries-Seimon T, Li Y, Yao PM, Stone E, Wang Y, Davis RJ, Flavell R, Tabas I - J. Cell Biol. (2005)

Bottom Line: Additionally, two other signaling pathways must cooperate with p38-CHOP to effect apoptosis.One involves the type A scavenger receptor (SRA).Thus, FC-induced apoptosis requires cholesterol trafficking to the ER, which triggers p38-CHOP and JNK2, and engagement of the SRA.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Columbia University, New York, NY 10032, USA.

ABSTRACT
Macrophage death in advanced atherosclerosis promotes necrosis and plaque destabilization. A likely cause of macrophage death is accumulation of free cholesterol (FC) in the ER, leading to activation of the unfolded protein response (UPR) and C/EBP homologous protein (CHOP)-induced apoptosis. Here we show that p38 MAPK signaling is necessary for CHOP induction and apoptosis. Additionally, two other signaling pathways must cooperate with p38-CHOP to effect apoptosis. One involves the type A scavenger receptor (SRA). As evidence, FC loading by non-SRA mechanisms activates p38 and CHOP, but not apoptosis unless the SRA is engaged. The other pathway involves c-Jun NH2-terminal kinase (JNK)2, which is activated by cholesterol trafficking to the ER, but is independent of CHOP. Thus, FC-induced apoptosis requires cholesterol trafficking to the ER, which triggers p38-CHOP and JNK2, and engagement of the SRA. These findings have important implications for understanding how the UPR, MAPKs, and the SRA might conspire to cause macrophage death, lesional necrosis, and plaque destabilization in advanced atherosclerotic lesions.

Show MeSH

Related in: MedlinePlus

SRA engagement triggers apoptosis in macrophages that have been FC loaded before exposure to SRA ligand. (A) Macrophages were incubated with CD-cholesterol (CD-Chol)/58035 for 32 h. Some of the cells received no fucoidan (Fuc), some received fucoidan (25 μg/ml) at the beginning of the incubation period, and some received fucoidan after 24 h of incubation. (B) Macrophages were incubated with 10 μg/ml β-VLDL plus 58035 for 24 h. Some of the cells received no fucoidan and some received fucoidan after 16 h of incubation. For both sets of experiments, the cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images are shown. Quantitative apoptosis data for each condition are shown as described in the legend for Fig. 4. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2171235&req=5

fig8: SRA engagement triggers apoptosis in macrophages that have been FC loaded before exposure to SRA ligand. (A) Macrophages were incubated with CD-cholesterol (CD-Chol)/58035 for 32 h. Some of the cells received no fucoidan (Fuc), some received fucoidan (25 μg/ml) at the beginning of the incubation period, and some received fucoidan after 24 h of incubation. (B) Macrophages were incubated with 10 μg/ml β-VLDL plus 58035 for 24 h. Some of the cells received no fucoidan and some received fucoidan after 16 h of incubation. For both sets of experiments, the cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images are shown. Quantitative apoptosis data for each condition are shown as described in the legend for Fig. 4. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm.

Mentions: In the experiments described thus far, the SRA ligand was added to the macrophages at the same time as the source of cholesterol. To determine whether addition of the SRA ligand after cholesterol loading could trigger apoptosis, macrophages were loaded with CD-cholesterol (plus 58035) for 24 h, and then treated with fucoidan for an additional 8 h. As shown in Fig. 8 A, cells that were treated with CD-cholesterol for 24 h and left untreated for an additional 8 h had very little induction of apoptosis. However, when the cholesterol-loaded cells were treated subsequently with fucoidan for 8 h, there was a marked increase in apoptosis. As expected, cells that were treated with CD-cholesterol plus fucoidan for the entire 32-h period had an even greater induction of apoptosis. Similar results were obtained using β-VLDL instead of CD-cholesterol (Fig. 8 B). Apoptosis also was seen when the macrophages were incubated with fucoidan, and then with β-VLDL plus 58035 (unpublished data). Thus, engagement of the SRA before, or subsequent to, cholesterol loading is able to induce apoptosis in FC-loaded, UPR-activated macrophages.


Cholesterol-induced macrophage apoptosis requires ER stress pathways and engagement of the type A scavenger receptor.

Devries-Seimon T, Li Y, Yao PM, Stone E, Wang Y, Davis RJ, Flavell R, Tabas I - J. Cell Biol. (2005)

SRA engagement triggers apoptosis in macrophages that have been FC loaded before exposure to SRA ligand. (A) Macrophages were incubated with CD-cholesterol (CD-Chol)/58035 for 32 h. Some of the cells received no fucoidan (Fuc), some received fucoidan (25 μg/ml) at the beginning of the incubation period, and some received fucoidan after 24 h of incubation. (B) Macrophages were incubated with 10 μg/ml β-VLDL plus 58035 for 24 h. Some of the cells received no fucoidan and some received fucoidan after 16 h of incubation. For both sets of experiments, the cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images are shown. Quantitative apoptosis data for each condition are shown as described in the legend for Fig. 4. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171235&req=5

fig8: SRA engagement triggers apoptosis in macrophages that have been FC loaded before exposure to SRA ligand. (A) Macrophages were incubated with CD-cholesterol (CD-Chol)/58035 for 32 h. Some of the cells received no fucoidan (Fuc), some received fucoidan (25 μg/ml) at the beginning of the incubation period, and some received fucoidan after 24 h of incubation. (B) Macrophages were incubated with 10 μg/ml β-VLDL plus 58035 for 24 h. Some of the cells received no fucoidan and some received fucoidan after 16 h of incubation. For both sets of experiments, the cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images are shown. Quantitative apoptosis data for each condition are shown as described in the legend for Fig. 4. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm.
Mentions: In the experiments described thus far, the SRA ligand was added to the macrophages at the same time as the source of cholesterol. To determine whether addition of the SRA ligand after cholesterol loading could trigger apoptosis, macrophages were loaded with CD-cholesterol (plus 58035) for 24 h, and then treated with fucoidan for an additional 8 h. As shown in Fig. 8 A, cells that were treated with CD-cholesterol for 24 h and left untreated for an additional 8 h had very little induction of apoptosis. However, when the cholesterol-loaded cells were treated subsequently with fucoidan for 8 h, there was a marked increase in apoptosis. As expected, cells that were treated with CD-cholesterol plus fucoidan for the entire 32-h period had an even greater induction of apoptosis. Similar results were obtained using β-VLDL instead of CD-cholesterol (Fig. 8 B). Apoptosis also was seen when the macrophages were incubated with fucoidan, and then with β-VLDL plus 58035 (unpublished data). Thus, engagement of the SRA before, or subsequent to, cholesterol loading is able to induce apoptosis in FC-loaded, UPR-activated macrophages.

Bottom Line: Additionally, two other signaling pathways must cooperate with p38-CHOP to effect apoptosis.One involves the type A scavenger receptor (SRA).Thus, FC-induced apoptosis requires cholesterol trafficking to the ER, which triggers p38-CHOP and JNK2, and engagement of the SRA.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Columbia University, New York, NY 10032, USA.

ABSTRACT
Macrophage death in advanced atherosclerosis promotes necrosis and plaque destabilization. A likely cause of macrophage death is accumulation of free cholesterol (FC) in the ER, leading to activation of the unfolded protein response (UPR) and C/EBP homologous protein (CHOP)-induced apoptosis. Here we show that p38 MAPK signaling is necessary for CHOP induction and apoptosis. Additionally, two other signaling pathways must cooperate with p38-CHOP to effect apoptosis. One involves the type A scavenger receptor (SRA). As evidence, FC loading by non-SRA mechanisms activates p38 and CHOP, but not apoptosis unless the SRA is engaged. The other pathway involves c-Jun NH2-terminal kinase (JNK)2, which is activated by cholesterol trafficking to the ER, but is independent of CHOP. Thus, FC-induced apoptosis requires cholesterol trafficking to the ER, which triggers p38-CHOP and JNK2, and engagement of the SRA. These findings have important implications for understanding how the UPR, MAPKs, and the SRA might conspire to cause macrophage death, lesional necrosis, and plaque destabilization in advanced atherosclerotic lesions.

Show MeSH
Related in: MedlinePlus