Macrophage colony stimulatory factor and interferon‐γ trigger distinct mechanisms for augmentation of β‐amyloid‐induced microglia‐mediated neurotoxicity

Abstract

Dysregulated stimulation of microglia, the resident macrophages in the brain, can lead to excessive induction of inflammatory agents and subsequently damage to neurons. Fibrillar b-amyloid peptide (fAb), a major component of senile plaques in Alzheimer's disease (AD) brain, is known to induce microglial-mediated neurotoxicity under certain conditions. Microglial 'priming' by macrophage colony stimulatory factor (MCSF) or interferon-gamma (IFNc) appears to be required for this fAb-induced microglia mediated neurotoxicity in vitro. We report here that while both MCSF and IFNc induce microglial-mediated fAb neurotoxicity, their mechanisms of toxicity differ. The enhancement of neurotoxicity by IFNc or MCSF is not due to enhanced Ab ingestion by microglia or to the direct effect of proinflammatory cytokine production. The neurotoxicity resulting from IFNc/fAb treatment was blocked by pretreatment with nitric oxide synthase inhibitor L-N-5-(1-iminoethyl) ornithine hydrochloride (L-NIO), consistent with a role for nitric oxide in the IFNc-mediated toxicity mechanism. In contrast, no induction of nitric oxide production was detected for microglia treated with MCSF/fAb. Furthermore, inhibiting the generation of reactive oxygen species (ROS) using the specific NADPH oxidase inhibitor apocynin reversed fAb/MCSF-induced neurotoxicity while L-NIO had little effect. As MCSF is endogenously expressed within the brain, and both its level and that of the MCSF receptor are dramatically increased in the AD brain, the neurotoxicity resulting from ROS release by fAb/MCSF coactivated microglia may be a more appropriate model for assessing fAb-induced microglialmediated neuropathology in AD.

Comparative study of microglia activation induced by amyloid‐beta and prion peptides: Role in neurodegeneration

“…Moreover, it was observed that IL-6 secretion was induced only by PrP 106-126 at an early phase (3-6 hr), but Ab 1-40 was more efficient than PrP 106-126 for longer incubation periods, inducing a higher production of this cytokine. In accordance with our results, it was shown that PrP 106-126 induces IL-6 and IL-1b release in cultured mouse microglia (Peyrin et al, 1999;Veerhuis et al, 2002), and fibrillar Ab is unable to induce IL-1 (b and a) release (Li et al, 2004).…”

The neuroprotective effects of apocynin

“…Abeta has been reported to increase the generation of ROS by NADPH-oxidase in neurons, microglia, monocytes, neutrophils and astrocytes (58)(59)(60)(61), and apocynin is neuroprotective in cell culture models of AD (62,63). There is convincing evidence suggesting a role for glial cell NADPH oxidase in Abeta-induced neurotoxicity (19,(64)(65)(66)(67).…”

ERK1/2 Activation Mediates Aβ Oligomer-induced Neurotoxicity via Caspase-3 Activation and Tau Cleavage in Rat Organotypic Hippocampal Slice Cultures

“…Lactate Dehydrogenase Activity-LDH enzymatic activity in the culture medium was used to evaluate the extent of cellular damage produced in cultured slices subjected to the different treatments as described previously (34). Briefly, culture medium was collected after incubation of slices, as indicated in the figures, and from the vehicle-treated control cultures.…”

“…PAGE and Western Blotting-Immunoblotting was carried out as recently described in detail (31,34). Briefly, slices were homogenized in ice-cold extraction buffer (10 mM triethanolamine, pH 7.4, 1 mM CaCl 2 , 1 mM MgCl 2 , 0.15 M NaCl, 0.3% Nonidet P-40) supplemented with the protease inhibitors pepstatin (2 g/ml), leupeptin (10 g/ml), aprotinin (10 g/ml), phenylmethylsulfonyl fluoride (1 mM), and the phosphatase inhibitor sodium orthovanadate (1 mM).…”