Macrophage-mediated degradation of β-amyloid via an apolipoprotein e isoform-dependent mechanism

Lingzhi Zhao, Suizhen Lin, Kelly R. Bales, Valentina Gelfanova, Deanna Koger, Cynthia DeLong, John Hale, Feng Liu, Jesse M. Hunter, Steven M. Paul

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


Recent studies suggest that bone marrow-derived macrophages can effectively reduce β-amyloid (Aβ) deposition in brain. To further elucidate the mechanisms by which macrophages degrade Aβ, we cultured murine macrophages on top of Aβ 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 Aβ in a time-dependent manner and markedly eliminate thioflavine-S positive amyloid deposits. Because macrophages express and secrete apolipoprotein £ (apoE), we compared the efficiency of Aβ degradation by macrophages prepared from apoE-deficient mice or mice expressing human apoE2, apoE3, or apoE4. Macrophages expressing apoE2 were more efficient at degrading Aβ than apoE3-expressing, apoE4-expressing, or apoE-deficient macrophages. Moreover, macrophage-induced degradation of Aβ 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 Aβ-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 Aβ degradation by macrophages. These apoE isoform-dependent effects of macrophages on Aβ degradation suggest a novel "peripheral" mechanism for Aβ clearance from brain that may also, in part, explain the isoformdependent effects of apoE in determining the genetic risk for Alzheimer's disease.

Original languageEnglish
Pages (from-to)3603-3612
Number of pages10
JournalJournal of Neuroscience
Issue number11
StatePublished - Mar 18 2009


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