C16 ceramide is crucial for triacylglycerol-induced apoptosis in macrophages

• DOI: 10.1038/cddis.2012.17
• Publication Date: 2012-03-15T11:07:23Z
• Authors: E Aflaki; P Doddapattar; B Radović; S Povoden; D Kolb; N Vujić; M Wegscheider; H Koefeler; T Hornemann; W F Graier; R Malli; F Madeo; D Kratky
• Keywords: Male; 0301 basic medicine; 2804 Cellular and Molecular Neuroscience; 610 Medicine & health; Apoptosis; Lipoproteins, VLDL; Ceramides; Endoplasmic Reticulum; Fumonisins; 1307 Cell Biology; Mice; 03 medical and health sciences; 540 Chemistry; Animals; Humans; 1306 Cancer Research; Enzyme Inhibitors; Endoplasmic Reticulum Chaperone BiP; Heat-Shock Proteins; 10038 Institute of Clinical Chemistry; Mice, Knockout; 2403 Immunology; Macrophages; Lipase; Activating Transcription Factor 4; Activating Transcription Factor 6; Mitochondria; CCAAT-Enhancer-Binding Proteins; Original Article; Calcium

Triacylglycerol (TG) accumulation caused by adipose triglyceride lipase (ATGL) deficiency or very low-density lipoprotein (VLDL) loading of wild-type (Wt) macrophages results in mitochondrial-mediated apoptosis. This phenotype is correlated to depletion of Ca(2+) from the endoplasmic reticulum (ER), an event known to induce the unfolded protein response (UPR). Here, we show that ER stress in TG-rich macrophages activates the UPR, resulting in increased abundance of the chaperone GRP78/BiP, the induction of pancreatic ER kinase-like ER kinase, phosphorylation and activation of eukaryotic translation initiation factor 2A, the translocation of activating transcription factor (ATF)4 and ATF6 to the nucleus and the induction of the cell death executor CCAAT/enhancer-binding protein homologous protein. C16:0 ceramide concentrations were increased in Atgl-/- and VLDL-loaded Wt macrophages. Overexpression of ceramide synthases was sufficient to induce mitochondrial apoptosis in Wt macrophages. In accordance, inhibition of ceramide synthases in Atgl-/- macrophages by fumonisin B1 (FB1) resulted in specific inhibition of C16:0 ceramide, whereas intracellular TG concentrations remained high. Although the UPR was still activated in Atgl-/- macrophages, FB1 treatment rescued Atgl-/- macrophages from mitochondrial dysfunction and programmed cell death. We conclude that C16:0 ceramide elicits apoptosis in Atgl-/- macrophages by activation of the mitochondrial apoptosis pathway.