Free Cholesterol Loading of Macrophages Induces Apoptosis Involving the Fas Pathway

Macrophage death is an important feature of atherosclerosis, but the cellular mechanism for this process is largely unknown. There is increasing interest in cellular free cholesterol (FC) excess as an inducer of lesional macrophage death because macrophages accumulate large amounts of FC in vivo, and FC loading of macrophages in culture causes cell death. In this study, a cell culture model was used to explore the cellular mechanisms involved in the initial stages of FC-induced macrophage death. After 9 h of FC loading, some of the macrophages exhibited externalization of phosphatidylserine and DNA fragmentation, indicative of an apoptotic mechanism. Incubation of the cells with Z-DEVD-fluoromethylketone blocked these events, indicating dependence upon effector caspases. Macrophages from mice with mutations in either Fas or Fas ligand (FasL) demonstrated substantial resistance to FC-induced apoptosis, and FC-induced death in wild-type macrophages was blocked by an anti-FasL antibody. FC loading had no effect on the expression of cell-surface Fas but caused a small yet reproducible increase in cell-surface FasL. To determine the physiological significance of this finding, unloaded and FC-loaded Fas-deficient macrophages, which can only present FasL, were compared for their ability to induce apoptosis in secondarily added Fas-bearing macrophages. The FC-loaded macrophages were much more potent inducers of apoptosis than the unloaded macrophages, and this effect was almost completely blocked by an inhibitory anti-FasL antibody. In summary, during the early stages of FC loading of macrophages, a fraction of cells exhibited biochemical changes that are indicative of apoptosis. An important part of this event is FC-induced activation of FasL that leads to Fas-mediated apoptosis. In light of recent in vivo findings that show that apoptotic macrophages in atherosclerotic lesions express both Fas and FasL, we present a cellular model of Fas-mediated death in lesional foam cells. Macrophage death is an important feature of atherosclerosis, but the cellular mechanism for this process is largely unknown. There is increasing interest in cellular free cholesterol (FC) excess as an inducer of lesional macrophage death because macrophages accumulate large amounts of FC in vivo, and FC loading of macrophages in culture causes cell death. In this study, a cell culture model was used to explore the cellular mechanisms involved in the initial stages of FC-induced macrophage death. After 9 h of FC loading, some of the macrophages exhibited externalization of phosphatidylserine and DNA fragmentation, indicative of an apoptotic mechanism. Incubation of the cells with Z-DEVD-fluoromethylketone blocked these events, indicating dependence upon effector caspases. Macrophages from mice with mutations in either Fas or Fas ligand (FasL) demonstrated substantial resistance to FC-induced apoptosis, and FC-induced death in wild-type macrophages was blocked by an anti-FasL antibody. FC loading had no effect on the expression of cell-surface Fas but caused a small yet reproducible increase in cell-surface FasL. To determine the physiological significance of this finding, unloaded and FC-loaded Fas-deficient macrophages, which can only present FasL, were compared for their ability to induce apoptosis in secondarily added Fas-bearing macrophages. The FC-loaded macrophages were much more potent inducers of apoptosis than the unloaded macrophages, and this effect was almost completely blocked by an inhibitory anti-FasL antibody. In summary, during the early stages of FC loading of macrophages, a fraction of cells exhibited biochemical changes that are indicative of apoptosis. An important part of this event is FC-induced activation of FasL that leads to Fas-mediated apoptosis. In light of recent in vivo findings that show that apoptotic macrophages in atherosclerotic lesions express both Fas and FasL, we present a cellular model of Fas-mediated death in lesional foam cells. free cholesterol fluorescence-activated cell sorting Fas ligand fetal bovine serum generalized lymphoproliferative mutation low density lipoprotein lymphoproliferative mutation terminal deoxynucleotidyltransferase (TdT)-mediated dUTP nick end labeling benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone propidium iodide (3-decyldimethylsilyl-N-2-(4-methylphenyl)-1-phenylethylpropanamide Cholesterol-loaded macrophages are critical components of atherosclerotic lesions (1Ross R. Annu. Rev. Physiol. 1995; 57: 791-804Crossref PubMed Scopus (889) Google Scholar), and recent in vivo studies have demonstrated the importance of these cells in lesion progression (2Smith J.D. Trogan E. Ginsberg M. Grigaux C. Tian J. Miyata M. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 8264-8268Crossref PubMed Scopus (570) Google Scholar, 3Gu L. Okada Y. Clinton S.K. Gerard C. Sukhova G.K. Libby P. Rollins B.J. Mol. Cell. 1998; 2: 275-281Abstract Full Text Full Text PDF PubMed Scopus (1359) Google Scholar, 4Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 5Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar). In addition, lesional macrophages may also contribute to the complications of advanced atherosclerosis, such as plaque rupture and acute thrombosis (6Libby P. Clinton S.K. Curr. Opin. Lipidol. 1993; 4: 355-363Crossref Scopus (124) Google Scholar). Observational studies have noted that macrophage death is a prominent feature of atherosclerotic lesions (7Mitchinson M.J. Hardwick S.J. Bennett M.R. Curr. Opin. Lipidol. 1996; 7: 324-329Crossref PubMed Scopus (79) Google Scholar, 8Ball R.Y. Stowers E.C. Burton J.H. Cary N.R. Skepper J.N. Mitchinson M.J. Atherosclerosis. 1995; 114: 45-54Abstract Full Text PDF PubMed Scopus (197) Google Scholar, 9Berberian P.A. Myers W. Tytell M. Challa V. Bond M.G. Am. J. Pathol. 1990; 136: 71-80PubMed Google Scholar, 10Bauriedel G. Schmucking I. Hutter R. Schmidt T. Circulation. 1999; 96 (abstr.): I-190Google Scholar), and it is likely that dying macrophages influence lesion progression. On the one hand, macrophage death, particularly apoptotic death, may actually limit the cellularity of lesions. However, atherogenic and thrombogenic molecules as well as degradative enzymes released from dying macrophages may contribute to atherogenesis, plaque rupture, and acute thrombosis. In this light, plaque rupture and acute thrombosis are strongly associated with the presence of lipid cores in lesions (11Fuster V. Badimon L. Badimon J.J. Chesebro J.H. N. Engl. J. PubMed Scopus Google Scholar), that have to the of macrophages R.Y. Stowers E.C. Burton J.H. Cary N.R. Skepper J.N. Mitchinson M.J. Atherosclerosis. 1995; 114: 45-54Abstract Full Text PDF PubMed Scopus (197) Google Scholar, 9Berberian P.A. Myers W. Tytell M. Challa V. Bond M.G. Am. J. Pathol. 1990; 136: 71-80PubMed Google Scholar). G. Schmucking I. Hutter R. Schmidt T. Circulation. 1999; 96 (abstr.): I-190Google have that from with have the of cells compared with from with causes of macrophage death in atherosclerotic lesions G. M. J. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar), I. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), and to and such as and (7Mitchinson M.J. Hardwick S.J. Bennett M.R. Curr. Opin. Lipidol. 1996; 7: 324-329Crossref PubMed Scopus (79) Google Scholar, E. S. L. J. 1998; PubMed Scopus Google Scholar). and have particularly in death caused by excess cellular free cholesterol because macrophages in advanced lesions have to accumulate large amounts of FC Atherosclerosis. Full Text PDF PubMed Scopus Google Scholar, Bond M.G. M. J. Clin. Invest. PubMed Scopus Google Scholar, J.H. T. J. Full Text PDF PubMed Google Scholar, S. Invest. Google Scholar), and FC loading of macrophages is a potent inducer of cell death G. M. J. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). a recent in an model FC loading of macrophages in the of S. L. M. Circulation. 1999; (abstr.): Scholar). FC loading cells the of critical enzymes J. PubMed Scopus (79) Google Scholar, PubMed Scopus Google Scholar, I. 7: PubMed Scopus Google Scholar, G. 1998; PubMed Scopus Google Scholar). In J. PubMed Scopus (79) Google demonstrated that of critical and leads to cellular death and that these may an important in the of the in advanced to FC-induced macrophage death is the cellular and biochemical associated with apoptosis are is an important because death by apoptosis may have physiological and compared with death by macrophages in atherosclerotic lesions have to have cellular of both apoptosis and L. Skepper J.N. Cary Mitchinson M.J. J. Pathol. 1996; PubMed Scopus Google Scholar). In this we have used a of biochemical inhibitory and mutations to show that a of macrophages to excess FC apoptosis and that the Fas is involved in this recent in vivo that apoptotic macrophages in atherosclerotic lesions express both Fas and Fas ligand (FasL) W. W. J. Atherosclerosis. Full Text Full Text PDF PubMed Scopus Google Scholar, J. Circulation. 1998; (abstr.): Scholar), a cellular model of Fas-mediated death in lesional foam of FC-loaded macrophages fraction of macrophages to FC loading biochemical of apoptosis, externalization of phosphatidylserine and of of the Fas by FasL and inhibitory anti-FasL FC-induced apoptosis. FC loading expression of cell-surface FasL. FC loading of macrophages FasL is to induce apoptosis to macrophages Fas in a model to from these findings is that FC loading the and activation of cell-surface FasL Fas-mediated in this early during the process of FC The biochemical changes during this are with the studies of G. 1998; PubMed Scopus Google Scholar), which and in FC-loaded macrophages. more FC loading, the macrophages more of such as of and of the I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). to from these findings is early apoptosis in which or macrophages are FC loading this mechanism of of the Fas is one of the more findings to from this FC-loaded macrophages no increase in cell-surface Fas but show an increase in cell-surface FasL. FasL cellular FasL these likely that FasL was from to the cell as with the activation of P.A. S.J. J. Google Scholar). In this and M. J. 1996; PubMed Scopus Google have that cholesterol of cells the of a from to of the studies of FasL in apoptosis have noted a increase in cell-surface FasL J. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), we that the increase in cell-surface FasL in is to for the of apoptosis. is that a in cell-surface FasL by an increase in the of the may have to activation of this important is to the that of the Fas apoptosis in FC-loaded macrophages. studies to such as death R. M. Rev. 1999; PubMed Scopus Google Scholar, A. Curr. Opin. 1999; PubMed Scopus Google Scholar), the Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), or the T. N. E. J. J. Nature. PubMed Scopus Google studies have that macrophages express cell-surface Fas and can apoptosis to cells FasL such as cells P.A. C. S.J. J. PubMed Scopus Google Scholar). which can induce apoptosis in cell was to induce apoptosis in Fas-bearing macrophages P.A. C. S.J. J. PubMed Scopus Google Scholar). with this finding, we were to induce apoptosis or FasL in either macrophages or macrophages macrophages, cells T. M. T. S. J. PubMed Scopus Google and cells M. J. Clin. Invest. 1998; PubMed Scopus Google Scholar), FasL to the Fas In FasL was inhibitory in which is to the with cells as by T. M. T. S. J. PubMed Scopus Google Scholar). of FasL from the of cells P.A. S.J. J. Google Scholar, M.J. A. A. J. 1996; PubMed Scopus Google Scholar), it is that this process can apoptosis in macrophages in cell-surface FasL expression on macrophages either P.A. A. S.J. J. 1996; PubMed Scopus Google or low P.A. C. S.J. J. PubMed Scopus Google with the is likely that this low of cell-surface FasL expression macrophages from death important to from these studies is the of Fas-mediated apoptosis in FC-loaded macrophages. in the both FC-loaded macrophages and macrophage death are of atherosclerotic lesions. W. W. J. Atherosclerosis. Full Text Full Text PDF PubMed Scopus Google have that apoptotic macrophages in atherosclerotic but express In study, and J. Circulation. 1998; (abstr.): the presence of cells in of atherosclerotic that macrophages. these are with the that some of the macrophage death to in lesions is by FC loading and by the Fas these effect have on lesion In one apoptosis of FC-loaded macrophages a that the of these lesional foam cells 1998; PubMed Scopus Google Scholar). In this the cells by by macrophages and from lesions of cellular Am. J. Pathol. 103: Google Scholar, A. R. L. 4: PubMed Google Scholar). In apoptosis of FC-loaded macrophages may contribute to lesion particularly lipid by to the of apoptosis can to as and of cellular from dying cells J.J. Am. J. Physiol. 1999; Google Scholar, 1998; PubMed Scopus Google Scholar, C. I. G. 1998; PubMed Google Scholar, E. T. Cell. 1998; Google Scholar, J. R. M. A. T. Y. N. T. S. Nature. 1993; PubMed Scopus Google Scholar, N. R. M. M. Y. N. Am. J. Mol. PubMed Scopus Google Scholar). In addition, the of apoptotic may by the presence of and in atherosclerotic lesions or by the of the as demonstrated in cell culture studies M. C. A. S. P. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar, and J. in Scholar). the initial were the of foam cell apoptotic by macrophages, these with apoptotic foam cell the of lesional macrophages to this process the of FasL by FC loading of macrophages may have atherogenic than to apoptosis, as by the recent of G. S. R. R. PubMed Scopus Google that demonstrated that in had of cells. in vivo in which the macrophage Fas is to these summary, the that FC loading of macrophages leads to an apoptotic that is on of the Fas In vivo, lesional macrophages accumulate excess have to Fas and FasL, and apoptosis. the model the for studies the of macrophage death in and Fas-mediated apoptosis in in the of Cholesterol-loaded macrophages are critical components of atherosclerotic lesions (1Ross R. Annu. Rev. Physiol. 1995; 57: 791-804Crossref PubMed Scopus (889) Google Scholar), and recent in vivo studies have demonstrated the importance of these cells in lesion progression (2Smith J.D. Trogan E. Ginsberg M. Grigaux C. Tian J. Miyata M. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 8264-8268Crossref PubMed Scopus (570) Google Scholar, 3Gu L. Okada Y. Clinton S.K. Gerard C. Sukhova G.K. Libby P. Rollins B.J. Mol. Cell. 1998; 2: 275-281Abstract Full Text Full Text PDF PubMed Scopus (1359) Google Scholar, 4Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 5Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar). In addition, lesional macrophages may also contribute to the complications of advanced atherosclerosis, such as plaque rupture and acute thrombosis (6Libby P. Clinton S.K. Curr. Opin. Lipidol. 1993; 4: 355-363Crossref Scopus (124) Google Scholar). Observational studies have noted that macrophage death is a prominent feature of atherosclerotic lesions (7Mitchinson M.J. Hardwick S.J. Bennett M.R. Curr. Opin. Lipidol. 1996; 7: 324-329Crossref PubMed Scopus (79) Google Scholar, 8Ball R.Y. Stowers E.C. Burton J.H. Cary N.R. Skepper J.N. Mitchinson M.J. Atherosclerosis. 1995; 114: 45-54Abstract Full Text PDF PubMed Scopus (197) Google Scholar, 9Berberian P.A. Myers W. Tytell M. Challa V. Bond M.G. Am. J. Pathol. 1990; 136: 71-80PubMed Google Scholar, 10Bauriedel G. Schmucking I. Hutter R. Schmidt T. Circulation. 1999; 96 (abstr.): I-190Google Scholar), and it is likely that dying macrophages influence lesion progression. On the one hand, macrophage death, particularly apoptotic death, may actually limit the cellularity of lesions. However, atherogenic and thrombogenic molecules as well as degradative enzymes released from dying macrophages may contribute to atherogenesis, plaque rupture, and acute thrombosis. In this light, plaque rupture and acute thrombosis are strongly associated with the presence of lipid cores in lesions (11Fuster V. Badimon L. Badimon J.J. Chesebro J.H. N. Engl. J. PubMed Scopus Google Scholar), that have to the of macrophages R.Y. Stowers E.C. Burton J.H. Cary N.R. Skepper J.N. Mitchinson M.J. Atherosclerosis. 1995; 114: 45-54Abstract Full Text PDF PubMed Scopus (197) Google Scholar, 9Berberian P.A. Myers W. Tytell M. Challa V. Bond M.G. Am. J. Pathol. 1990; 136: 71-80PubMed Google Scholar). G. Schmucking I. Hutter R. Schmidt T. Circulation. 1999; 96 (abstr.): I-190Google have that from with have the of cells compared with from with causes of macrophage death in atherosclerotic lesions G. M. J. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar), I. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), and to and such as and (7Mitchinson M.J. Hardwick S.J. Bennett M.R. Curr. Opin. Lipidol. 1996; 7: 324-329Crossref PubMed Scopus (79) Google Scholar, E. S. L. J. 1998; PubMed Scopus Google Scholar). and have particularly in death caused by excess cellular free cholesterol because macrophages in advanced lesions have to accumulate large amounts of FC Atherosclerosis. Full Text PDF PubMed Scopus Google Scholar, Bond M.G. M. J. Clin. Invest. PubMed Scopus Google Scholar, J.H. T. J. Full Text PDF PubMed Google Scholar, S. Invest. Google Scholar), and FC loading of macrophages is a potent inducer of cell death G. M. J. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). a recent in an model FC loading of macrophages in the of S. L. M. Circulation. 1999; (abstr.): Scholar). FC loading cells the of critical enzymes J. PubMed Scopus (79) Google Scholar, PubMed Scopus Google Scholar, I. 7: PubMed Scopus Google Scholar, G. 1998; PubMed Scopus Google Scholar). In J. PubMed Scopus (79) Google demonstrated that of critical and leads to cellular death and that these may an important in the of the in advanced to FC-induced macrophage death is the cellular and biochemical associated with apoptosis are is an important because death by apoptosis may have physiological and compared with death by macrophages in atherosclerotic lesions have to have cellular of both apoptosis and L. Skepper J.N. Cary Mitchinson M.J. J. Pathol. 1996; PubMed Scopus Google Scholar). In this we have used a of biochemical inhibitory and mutations to show that a of macrophages to excess FC apoptosis and that the Fas is involved in this recent in vivo that apoptotic macrophages in atherosclerotic lesions express both Fas and Fas ligand (FasL) W. W. J. Atherosclerosis. Full Text Full Text PDF PubMed Scopus Google Scholar, J. Circulation. 1998; (abstr.): Scholar), a cellular model of Fas-mediated death in lesional foam cells. of FC-loaded macrophages fraction of macrophages to FC loading biochemical of apoptosis, externalization of phosphatidylserine and of of the Fas by FasL and inhibitory anti-FasL FC-induced apoptosis. FC loading expression of cell-surface FasL. FC loading of macrophages FasL is to induce apoptosis to macrophages Fas in a model to from these findings is that FC loading the and activation of cell-surface FasL Fas-mediated in this early during the process of FC The biochemical changes during this are with the studies of G. 1998; PubMed Scopus Google Scholar), which and in FC-loaded macrophages. more FC loading, the macrophages more of such as of and of the I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). to from these findings is early apoptosis in which or macrophages are FC loading this mechanism of of the Fas is one of the more findings to from this FC-loaded macrophages no increase in cell-surface Fas but show an increase in cell-surface FasL. FasL cellular FasL these likely that FasL was from to the cell as with the activation of P.A. S.J. J. Google Scholar). In this and M. J. 1996; PubMed Scopus Google have that cholesterol of cells the of a from to of the studies of FasL in apoptosis have noted a increase in cell-surface FasL J. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), we that the increase in cell-surface FasL in is to for the of apoptosis. is that a in cell-surface FasL by an increase in the of the may have to activation of this important is to the that of the Fas apoptosis in FC-loaded macrophages. studies to such as death R. M. Rev. 1999; PubMed Scopus Google Scholar, A. Curr. Opin. 1999; PubMed Scopus Google Scholar), the Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), or the T. N. E. J. J. Nature. PubMed Scopus Google studies have that macrophages express cell-surface Fas and can apoptosis to cells FasL such as cells P.A. C. S.J. J. PubMed Scopus Google Scholar). which can induce apoptosis in cell was to induce apoptosis in Fas-bearing macrophages P.A. C. S.J. J. PubMed Scopus Google Scholar). with this finding, we were to induce apoptosis or FasL in either macrophages or macrophages macrophages, cells T. M. T. S. J. PubMed Scopus Google and cells M. J. Clin. Invest. 1998; PubMed Scopus Google Scholar), FasL to the Fas In FasL was inhibitory in which is to the with cells as by T. M. T. S. J. PubMed Scopus Google Scholar). of FasL from the of cells P.A. S.J. J. Google Scholar, M.J. A. A. J. 1996; PubMed Scopus Google Scholar), it is that this process can apoptosis in macrophages in cell-surface FasL expression on macrophages either P.A. A. S.J. J. 1996; PubMed Scopus Google or low P.A. C. S.J. J. PubMed Scopus Google with the is likely that this low of cell-surface FasL expression macrophages from death important to from these studies is the of Fas-mediated apoptosis in FC-loaded macrophages. in the both FC-loaded macrophages and macrophage death are of atherosclerotic lesions. W. W. J. Atherosclerosis. Full Text Full Text PDF PubMed Scopus Google have that apoptotic macrophages in atherosclerotic but express In study, and J. Circulation. 1998; (abstr.): the presence of cells in of atherosclerotic that macrophages. these are with the that some of the macrophage death to in lesions is by FC loading and by the Fas these effect have on lesion In one apoptosis of FC-loaded macrophages a that the of these lesional foam cells 1998; PubMed Scopus Google Scholar). In this the cells by by macrophages and from lesions of cellular Am. J. Pathol. 103: Google Scholar, A. R. L. 4: PubMed Google Scholar). In apoptosis of FC-loaded macrophages may contribute to lesion particularly lipid by to the of apoptosis can to as and of cellular from dying cells J.J. Am. J. Physiol. 1999; Google Scholar, 1998; PubMed Scopus Google Scholar, C. I. G. 1998; PubMed Google Scholar, E. T. Cell. 1998; Google Scholar, J. R. M. A. T. Y. N. T. S. Nature. 1993; PubMed Scopus Google Scholar, N. R. M. M. Y. N. Am. J. Mol. PubMed Scopus Google Scholar). In addition, the of apoptotic may by the presence of and in atherosclerotic lesions or by the of the as demonstrated in cell culture studies M. C. A. S. P. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar, and J. in Scholar). the initial were the of foam cell apoptotic by macrophages, these with apoptotic foam cell the of lesional macrophages to this process the of FasL by FC loading of macrophages may have atherogenic than to apoptosis, as by the recent of G. S. R. R. PubMed Scopus Google that demonstrated that in had of cells. in vivo in which the macrophage Fas is to these summary, the that FC loading of macrophages leads to an apoptotic that is on of the Fas In vivo, lesional macrophages accumulate excess have to Fas and FasL, and apoptosis. the model the for studies the of macrophage death in and Fas-mediated apoptosis in in the of of FC-loaded macrophages fraction of macrophages to FC loading biochemical of apoptosis, externalization of phosphatidylserine and of of the Fas by FasL and inhibitory anti-FasL FC-induced apoptosis. FC loading expression of cell-surface FasL. FC loading of macrophages FasL is to induce apoptosis to macrophages Fas in a model to from these findings is that FC loading the and activation of cell-surface FasL Fas-mediated apoptosis. The in this early during the process of FC The biochemical changes during this are with the studies of G. 1998; PubMed Scopus Google Scholar), which and in FC-loaded macrophages. more FC loading, the macrophages more of such as of and of the I. S. N. Y. J. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). to from these findings is early apoptosis in which or macrophages are FC loading this The mechanism of of the Fas is one of the more findings to from this FC-loaded macrophages no increase in cell-surface Fas but show an increase in cell-surface FasL. FasL cellular FasL these likely that FasL was from to the cell as with the activation of P.A. S.J. J. Google Scholar). In this and M. J. 1996; PubMed Scopus Google have that cholesterol of cells the of a from to of the studies of FasL in apoptosis have noted a increase in cell-surface FasL J. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), we that the increase in cell-surface FasL in is to for the of apoptosis. is that a in cell-surface FasL by an increase in the of the may have to activation of this important is to the that of the Fas apoptosis in FC-loaded macrophages. studies to such as death R. M. Rev. 1999; PubMed Scopus Google Scholar, A. Curr. Opin. 1999; PubMed Scopus Google Scholar), the Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), or the T. N. E. J. J. Nature. PubMed Scopus Google Scholar). studies have that macrophages express cell-surface Fas and can apoptosis to cells FasL such as cells P.A. C. S.J. J. PubMed Scopus Google Scholar). which can induce apoptosis in cell was to induce apoptosis in Fas-bearing macrophages P.A. C. S.J. J. PubMed Scopus Google Scholar). with this finding, we were to induce apoptosis or FasL in either macrophages or macrophages macrophages, cells T. M. T. S. J. PubMed Scopus Google and cells M. J. Clin. Invest. 1998; PubMed Scopus Google Scholar), FasL to the Fas In FasL was inhibitory in which is to the with cells as by T. M. T. S. J. PubMed Scopus Google Scholar). of FasL from the of cells P.A. S.J. J. Google Scholar, M.J. A. A. J. 1996; PubMed Scopus Google Scholar), it is that this process can apoptosis in macrophages in cell-surface FasL expression on macrophages either P.A. A. S.J. J. 1996; PubMed Scopus Google or low P.A. C. S.J. J. PubMed Scopus Google with the is likely that this low of cell-surface FasL expression macrophages from death The important to from these studies is the of Fas-mediated apoptosis in FC-loaded macrophages. in the both FC-loaded macrophages and macrophage death are of atherosclerotic lesions. W. W. J. Atherosclerosis. Full Text Full Text PDF PubMed Scopus Google have that apoptotic macrophages in atherosclerotic but express In study, and J. Circulation. 1998; (abstr.): the presence of cells in of atherosclerotic that macrophages. these are with the that some of the macrophage death to in lesions is by FC loading and by the Fas these effect have on lesion In one apoptosis of FC-loaded macrophages a that the of these lesional foam cells 1998; PubMed Scopus Google Scholar). In this the cells by by macrophages and from lesions of cellular Am. J. Pathol. 103: Google Scholar, A. R. L. 4: PubMed Google Scholar). In apoptosis of FC-loaded macrophages may contribute to lesion particularly lipid by to the of apoptosis can to as and of cellular from dying cells J.J. Am. J. Physiol. 1999; Google Scholar, 1998; PubMed Scopus Google Scholar, C. I. G. 1998; PubMed Google Scholar, E. T. Cell. 1998; Google Scholar, J. R. M. A. T. Y. N. T. S. Nature. 1993; PubMed Scopus Google Scholar, N. R. M. M. Y. N. Am. J. Mol. PubMed Scopus Google Scholar). In addition, the of apoptotic may by the presence of and in atherosclerotic lesions or by the of the as demonstrated in cell culture studies M. C. A. S. P. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar, and J. in Scholar). the initial were the of foam cell apoptotic by macrophages, these with apoptotic foam cell the of lesional macrophages to this process the of FasL by FC loading of macrophages may have atherogenic than to apoptosis, as by the recent of G. S. R. R. PubMed Scopus Google that demonstrated that in had of cells. in vivo in which the macrophage Fas is to these In summary, the that FC loading of macrophages leads to an apoptotic that is on of the Fas In vivo, lesional macrophages accumulate excess have to Fas and FasL, and apoptosis. the model the for studies the of macrophage death in and Fas-mediated apoptosis in in the of for during the of this