β-Amyloid-induced IL-1 β release from an activated human monocyte cell line is calcium- and G-protein-dependent

Abstract

The proinflammatory cytokine, interleukin-1 (IL-1) is elevated in the Alzheimer's disease (AD) brain [1–3]. Studies from our laboratory have demonstrated that β-amyloid (A β) 1–42, fibrillar A β 1–40 and A β 25–35 induce the release of IL-1 β from activated THP-1 cells, a human monocyte cell line [4, 9]. A β also is chemotactic for primary rodent microglia and peritoneal macrophages [5]. We hypothesize that A β is a chemokine and induces these responses by interaction with chemotactic receptors. If this is true, then these A β-induced responses should be calcium-dependent and require activation of pertussis toxin-sensitive G-proteins. To test this hypothesis, THP-1 cells were grown in culture with lipopolysaccharide (LPS) and incubated with A β 1–42 (5 μM) in the presence and absence of a calcium chelator, an inhibitor of intracellular calcium mobilization, a calcium channel blocker, or pertussis toxin, a bacterial endotoxin which uncouples G proteins from receptors by catalyzing the ADP ribosylation of cysteine near the carboxy-terminus of the α subunit [6]. The media was collected and IL-1 β present in the media was measured using an ELISA. Treatment of LPS-activated THP-1 cells with A β 1–42 significantly elevated IL-1 β released into the media as previously shown. Addition of ethylene glycol-bis ( β-aminothyl ether) N, N, N′, N′-tetraacetic acid (EGTA) (0.5 mM), a calcium chelator, to the media blocked A β-induced IL-1 β release, but had no effect on LPS-activated THP-1 cell release of IL-1 β. The presence of 3,4,5-trimethoxybenzoic acid 8-(diethyl amino)-octyl ester (TMB-8), an inhibitor of intracellular calcium mobilization, as well as nickel chloride, a non-specific calcium channel blocker, in the media also inhibited A β-induced IL-1 release from LPS-activated THP-1 cells. IL-1 β release from activated THP-1 monocytes incubated with TMB-8 and nickel chloride without A β remained at baseline values. Pretreatment of THP-1 monocytes with pertussis toxin for 4 h, followed by LPS activation and incubation with A β, antagonized the release of IL-1 β from these cells, but did not alter IL-1 β release from activated THP-1 monocytes. These data suggest that A β-induced IL-1 β release from these cells is calcium-dependent and requires the activation of specific G-proteins. These findings are consistent with known second messengers that are activated following stimulation of chemotactic receptors.