Amyloid precursor protein‐processing products affect mononuclear phagocyte activation: pathways for sAPP‐ and Aβ‐mediated neurotoxicity

Abstract

Increasing evidence strongly supports the role of glial immunity in the pathogenesis of Alzheimer's disease (AD). To investigate such events we have developed cell systems mimicking the interactions between b-amyloid precursor protein (APP)-expressing neurons and brain mononuclear phagocytes (MP; macrophages and microglia). MP were co-cultured with neuronal cells expressing wild type APP or familial AD-linked APP mutants. The latter was derived from recombinant adenoviral constructs. Neuronal APP processing products induced MP activation, reactive oxygen species, and neurotoxic activities. These occurred without the addition of pro-inflammatory cytokines and were reversed by depletion of amyloid b-peptide (Ab) and secreted APP (sAPP). Neurotoxic activities were diminished by superoxide dismutase mimetics and NMDA receptor inhibitors. Microglial glutamate secretion was suppressed by the cystine-glutamate antiporter inhibitor and its levels paralleled the depletion of sAPP and Ab from conditioned media prepared from APP-expressing neurons. The excitotoxins from activated MP were potent enough to evoke recombinant NMDA receptor-mediated inward currents expressed in vitro in the Xenopus oocytes. These results demonstrate that neuronal APP-processing products can induce oxidative neurotoxicity through microglial activation.

β-Amyloid-Stimulated Microglia Induce Neuron Death via Synergistic Stimulation of Tumor Necrosis Factor α and NMDA Receptors

“…A number of previous reports have documented the ability of activated microglia to secrete this excitatory neurotransmitter (Barger and Basile, 2001;Ikezu et al, 2003;Nakamura et al, 2003). A␤ stimulation resulted in a significant increase of glutamate secretion into the conditioned media by microglia (Fig.…”

“…Previous efforts identified the proinflammatory cytokine TNF␣ as one factor necessary for microglial-conditioned mediadependent death. To begin identifying additional toxic components of the conditioned media, we first considered the possibility that activated microglia secrete glutamate or other NMDA receptor ligands (Giulian et al, 1995;Noda et al, 1999;Guillemin and Brew, 2002;Ikezu et al, 2003). For confirmation, we demonstrated that conditioned media from A␤-stimulated microglia were potently toxic to mouse cortical neuron cultures (Fig.…”

“…Although TNF␣ has been described as a neuronal anti-apoptotic agent (Barger et al, 1995;Gary et al, 1998;Glazner and Mattson, 2000), it is also capable of inducing neuronal death when presented to neurons as part of a glialderived inflammatory milieu (Gelbard et al, 1993;Chao and Hu, 1994;Venters et al, 1999;Combs et al, 2001). The excitatory neurotransmitter, glutamate, is another proinflammatory product secreted by microglia in response to A␤ fibril stimulation (Klegeris et al, 1997;Noda et al, 1999;Ikezu et al, 2003). It is known that NMDA receptor (NMDAR)-expressing neurons are vulnerable to AD-associated loss, supporting a hypothesis of excitotoxic NMDA receptor activity-mediated death (Greenamyre and Young, 1989;Francis et al, 1993).…”

Molecular Characterization of a Putative Antiretroviral Transcriptional Factor, OTK18

“…Recombinant adenoviruses expressing OTK18 and green fluorescent protein (GFP; R-OTK18 virus) were constructed by the AdEasy system (kindly provided by Dr. B. Vogelstein, Johns Hopkins University, Baltimore, MD) as described (28,29). Full-length OTK18 cDNA was subcloned into BglII-XhoI sites of the pAdTrack-CMV vector, which dually expresses GFP and target genes.…”

Rho-mediated regulation of tight junctions during monocyte migration across the blood-brain barrier in HIV-1 encephalitis (HIVE)

“…38 We used the control adenovirus (R-CON), which expresses GFP under the control of the CMV promoter but without DN-RhoK. 39 The viruses were amplified by repeated infection into human embryonic kidney (HEK) 293 cells, followed by purification using CsCl banding as described. 39 The purified virus was used at 3 ϫ 10 6 expressionforming units per milliliter for infecting 3 ϫ 10 4 cells in 4-well Lab-Tek Chamber Slide or Transwell inserts in the endothelial-cell culture media overnight, followed by washing twice with DMEM and incubation with fresh culture media.…”