2004 Fiscal Year Final Research Report Summary
MOLECULAR MECHANISM OF CELL DEATH AND ITS PHYSIOLOGICAL ROLE
| Project/Area Number |
12219213
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Review Section |
Biological Sciences
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| Research Institution | Osaka University |
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Principal Investigator |
NAGATA Shigekazu Osaka University, Graduate School of Frontier Biosciences, Professor, 生命機能研究科, 教授 (70114428)
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| Co-Investigator(Kenkyū-buntansha) |
FUKUNAGA Rikiro Osaka University, Graduate School of Frontier Biosciences, Associate Professor, 生命機能研究科, 助教授 (40189965)
TANAKA Masato Osaka University, Graduate School of Medicine, Associate Professor, 医学系研究科, 助教授 (00294059)
FUKUYAMA Hidehiro Osaka University, Graduate School of Medicine, Assistant Professor, 医学系研究科, 助手 (70303956)
KAWANE Koki Osaka University, Graduate School of Frontier Biosciences, Assistant Professor, 生命機能研究科, 助手 (60362589)
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| Project Period (FY) |
2000 – 2004
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| Keywords | apoptosis / macrophages / DNA degradation / enucleation of erythroid cells / autoimmune disease / DNase II / Caspase-activated DNase / innate immunity |
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| Research Abstract |
In this project, we have examined the molecular mechanism of apoptotic DNA degradation, and its physiological role. That is, we characterized the enzymatic properties of CAD (caspase-activated DNase) that was previously identified in our laboratory as a DNase activated during apoptosis. We then demonstrated by establishing the CAD-deficient mice that CAD is solely responsible for the cell-autonomous DNA degradation in apoptotic cells. Analysis of the apoptotic cells in the CAD-deficient mice showed that the DNA of apoptotic cells could be degraded in vivo by DNase II present in the macrophages after the dead cells were engulfed by phagocytes. The DNase II-deficient mice were then established, and the analysis of the mice showed that the DNase digests not only DNA of apoptotic cells, but also the DNA expelled from erythroid precursor cells. The DNase II-null mice were embryonic lethal, which was due to the interferon-β that was produced in macrophages carrying a large amount of undigested DNA by the activation of innate immunity. Using the knowledge that the DNA of apoptotic cells can be cleaved by macrophages after the dead cells are engulfed, we established a reliable assay method for engulfment of apoptotic cells. Using this system, we identified a factor called Milk Fat Globule-EGF8 (MFG-E8). MFG-E8 recognized apoptotic cells by binding to phosphatidylserine exposed to the apoptotic cells. MFG-E8 also bound to macrophages via integrin, indicating that it serves as a bridge between apoptotic cells and phagocytes. MFG-E8 was found to be expressed in a set of macrophages including tingible-body macrophages in the germinal centers of the spleen, and in immature dendritic cells. The MFG-E8-deficient mice accumulated unengulfed apoptotic cells in the germinal centers of the spleen, and developed autoimmune diseases such as nephritis, indicating that if apoptotic cells are not swiftly cleared from our bodies, they will induce the autoimmunity.
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