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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.

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The MKK3/p38 MAPK pathway is necessary for FC-induced macrophage apoptosis. WT, Mkk3−/− (A), and p38α-deficient (C) macrophages were left untreated or were FC loaded (ac-LDL plus 58035) for 16–18 h. The cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images and quantitative apoptosis data from four fields of cells for each condition are shown. The data are expressed as the percent of total cells that stained with Annexin V and propidium iodide. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm. (B) Esterification of [14C] oleate in WT or Mkk3−/− macrophages incubated 5 h with medium containing [14C] oleate with or without 100 μg/ml ac-LDL. Shown is the mean ± SEM (n = 3) of cholesteryl [14C] oleate cpm per μg of total protein.
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fig4: The MKK3/p38 MAPK pathway is necessary for FC-induced macrophage apoptosis. WT, Mkk3−/− (A), and p38α-deficient (C) macrophages were left untreated or were FC loaded (ac-LDL plus 58035) for 16–18 h. The cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images and quantitative apoptosis data from four fields of cells for each condition are shown. The data are expressed as the percent of total cells that stained with Annexin V and propidium iodide. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm. (B) Esterification of [14C] oleate in WT or Mkk3−/− macrophages incubated 5 h with medium containing [14C] oleate with or without 100 μg/ml ac-LDL. Shown is the mean ± SEM (n = 3) of cholesteryl [14C] oleate cpm per μg of total protein.

Mentions: CHOP is required for apoptosis in macrophages that are loaded with FC by ac-LDL plus an ACAT inhibitor; MKK3 is required for the induction of CHOP under these conditions. Therefore, we hypothesized that the MKK3/p38 pathway is required for FC-induced apoptosis. As shown in Fig. 4 A, incubation of WT macrophages with ac-LDL plus 58035 caused a substantial increase in apoptosis, but apoptosis was diminished markedly in FC-loaded Mkk3−/− macrophages. These results cannot be explained by a decrease in ac-LDL uptake or trafficking of ac-LDL–derived cholesterol to the ER in Mkk3−/− macrophages, because ac-LDL–induced cholesterol esterification was very similar between the WT and Mkk3−/− macrophages (Fig. 4 B). Similar results were shown using p38α-deficient (Fig. 4 C) and Mk2−/− macrophages (Fig. S2; available at http://www.jcb.org/cgi/content/full/jcb.200502078/DC1). Therefore, activation of the MKK3/p38 pathway by FC loading of macrophages is required for CHOP induction and subsequent apoptosis.


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)

The MKK3/p38 MAPK pathway is necessary for FC-induced macrophage apoptosis. WT, Mkk3−/− (A), and p38α-deficient (C) macrophages were left untreated or were FC loaded (ac-LDL plus 58035) for 16–18 h. The cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images and quantitative apoptosis data from four fields of cells for each condition are shown. The data are expressed as the percent of total cells that stained with Annexin V and propidium iodide. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm. (B) Esterification of [14C] oleate in WT or Mkk3−/− macrophages incubated 5 h with medium containing [14C] oleate with or without 100 μg/ml ac-LDL. Shown is the mean ± SEM (n = 3) of cholesteryl [14C] oleate cpm per μg of total protein.
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Related In: Results  -  Collection

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fig4: The MKK3/p38 MAPK pathway is necessary for FC-induced macrophage apoptosis. WT, Mkk3−/− (A), and p38α-deficient (C) macrophages were left untreated or were FC loaded (ac-LDL plus 58035) for 16–18 h. The cells were stained with Alexa 488 Annexin V (green) and propidium iodide (red). Representative fluorescent images and quantitative apoptosis data from four fields of cells for each condition are shown. The data are expressed as the percent of total cells that stained with Annexin V and propidium iodide. Data are expressed as mean ± SEM (n = 4). Bar, 25 μm. (B) Esterification of [14C] oleate in WT or Mkk3−/− macrophages incubated 5 h with medium containing [14C] oleate with or without 100 μg/ml ac-LDL. Shown is the mean ± SEM (n = 3) of cholesteryl [14C] oleate cpm per μg of total protein.
Mentions: CHOP is required for apoptosis in macrophages that are loaded with FC by ac-LDL plus an ACAT inhibitor; MKK3 is required for the induction of CHOP under these conditions. Therefore, we hypothesized that the MKK3/p38 pathway is required for FC-induced apoptosis. As shown in Fig. 4 A, incubation of WT macrophages with ac-LDL plus 58035 caused a substantial increase in apoptosis, but apoptosis was diminished markedly in FC-loaded Mkk3−/− macrophages. These results cannot be explained by a decrease in ac-LDL uptake or trafficking of ac-LDL–derived cholesterol to the ER in Mkk3−/− macrophages, because ac-LDL–induced cholesterol esterification was very similar between the WT and Mkk3−/− macrophages (Fig. 4 B). Similar results were shown using p38α-deficient (Fig. 4 C) and Mk2−/− macrophages (Fig. S2; available at http://www.jcb.org/cgi/content/full/jcb.200502078/DC1). Therefore, activation of the MKK3/p38 pathway by FC loading of macrophages is required for CHOP induction and subsequent apoptosis.

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