Loss of Phospholipid Asymmetry and Surface Exposure of Phosphatidylserine Is Required for Phagocytosis of Apoptotic Cells by Macrophages and Fibroblasts*
- From the Program in Cell Biology, Department of Pediatrics, National Jewish Medical and Research Center, Denver, Colorado 80206 and the §Department of Biochemistry and Molecular Biology/Medical Sciences, Indiana University, Bloomington, Indiana 47405
Abstract
Removal of apoptotic cells during tissue remodeling or resolution of inflammation is critical to the restoration of normal tissue structure and function. During apoptosis, early surface changes occur, which trigger recognition and removal by macrophages and other phagocytes. Loss of phospholipid asymmetry results in exposure of phosphatidylserine (PS), one of the surface markers recognized by macrophages. However, a number of receptors have been reported to mediate macrophage recognition of apoptotic cells, not all of which bind to phosphatidylserine. We therefore examined the role of membrane phospholipid symmetrization and PS externalization in uptake of apoptotic cells by mouse macrophages and human HT-1080 fibrosarcoma cells by exposing them to cells that had undergone apoptosis without loss of phospholipid asymmetry. Neither mouse macrophages nor HT-1080 cells recognized or engulfed apoptotic targets that failed to express PS, in comparison to PS-expressing apoptotic cells. If, however, their outer leaflets were repleted with thel-, but not the d-, stereoisomer ofsn-1,2-PS by liposome transfer, engulfment by both phagocytes was restored. These observations directly demonstrate that loss of phospholipid asymmetry and PS expression is required for phagocyte engulfment of apoptotic cells and imply a critical, if not obligatory, role for PS recognition in the uptake process.
Footnotes
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↵* This work was supported by National Institutes of Health Grants GM 48211, GM 47230, HL 60980, and HL 30343.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: National Jewish Medical and Research Center, D509, 1400 Jackson St., Denver, CO 80206. Tel.: 303-398-1281; Fax: 303-398-1381; E-mail: fadokv@njc.org.
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Published, JBC Papers in Press, September 13, 2000, DOI 10.1074/jbc.M003649200
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↵1 C. A. Ogden, D. L. Bratton, V. A. Fadok, and P. M. Henson, unpublished data.
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↵3 V. A. Fadok, unpublished data.
- Abbreviations:
- PS
-
phosphatidylserine
- DFMO
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difluoromethylornithine
- POP-l-S
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1-palmitoyl-2-oleoyl-sn-3-glycerophospho-l-serine
- POP-d-S
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1-palmitoyl-2-oleoyl-sn-3-glycerophospho-d-serine
- PBS
-
phosphate-buffered saline
- FITC
-
fluorescein isothiocyanate
- mAb
-
monoclonal antibody
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- Received April 28, 2000.
- Revision received September 10, 2000.
- The American Society for Biochemistry and Molecular Biology, Inc.
