Macrophage-mediated degradation of beta-amyloid via an apolipoprotein E isoform-dependent mechanism.
Recent studies suggest that bone marrow-derived macrophages can effectively reduce beta-amyloid (Abeta) deposition in brain. To further elucidate the mechanisms by which macrophages degrade Abeta, we cultured murine macrophages on top of Abeta plaque-bearing brain sections from transgenic mice expressing PDAPP [human amyloid precursor protein (APP) with the APP(717V>F) mutation driven by the platelet-derived growth factor promoter]. Using this ex vivo assay, we found that macrophages from wild-type mice very efficiently degrade both soluble and insoluble Abeta in a time-dependent manner and markedly eliminate thioflavine-S positive amyloid deposits. Because macrophages express and secrete apolipoprotein E (apoE), we compared the efficiency of Abeta degradation by macrophages prepared from apoE-deficient mice or mice expressing human apoE2, apoE3, or apoE4. Macrophages expressing apoE2 were more efficient at degrading Abeta than apoE3-expressing, apoE4-expressing, or apoE-deficient macrophages. Moreover, macrophage-induced degradation of Abeta was effectively blocked by an anti-apoE antibody and receptor-associated protein, an antagonist of the low-density lipoprotein (LDL) receptor family, suggesting involvement of LDL receptors. Measurement of matrix metalloproteinase-9 (MMP-9) activity in the media from human apoE-expressing macrophages cocultured with Abeta-containing brain sections revealed greater levels of MMP-9 activity in apoE2-expressing than in either apoE3- or apoE4-expressing macrophages. Differences in MMP-9 activity appear to contribute to the isoform-specific differences in Abeta degradation by macrophages. These apoE isoform-dependent effects of macrophages on Abeta degradation suggest a novel "peripheral" mechanism for Abeta clearance from brain that may also, in part, explain the isoform-dependent effects of apoE in determining the genetic risk for Alzheimer's disease.
Zhao
Lingzhi
L
Neuroscience Discovery Research and Integrative Biology, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA.
Lin
Suizhen
S
Bales
Kelly R
KR
Gelfanova
Valentina
V
Koger
Deanna
D
Delong
Cynthia
C
Hale
John
J
Liu
Feng
F
Hunter
Jesse M
JM
Paul
Steven M
SM
D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000682:Amyloid / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000235:genetics / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques / Q000379:methods; D006801:Humans; D008264:Macrophages / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology
D000682:Amyloid; D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D001057:Apolipoproteins E; D020033:Protein Isoforms