Activated α2Macroglobulin Increases β-Amyloid (25–35)-Induced Toxicity in LAN5 Human Neuroblastoma Cells

Abstract

The presence of the α2macroglobulin receptor/low density lipoprotein receptor-related protein (α2Mr/LRP) and its ligands α2macroglobulin (α2M), apoliprotein E, and plasminogen activators was detected in senile plaques of Alzheimer's disease (AD). To explore a possible role of α2M in neurodegenerative processes occurring in AD, we analyzed the effect of α2M on Aβ 25–35-induced neurotoxicity. Treatment of LAN5 human neuroblastoma cells with 10 μM β-amyloid peptide fragment 25–35 (Aβ 25–35) for 72 h resulted in a 50% decrease in cell viability as determined by MTT incorporation and cell counts. The addition of α2M to the culture medium of these cells did not determine any effect, but when the activated form α2M* was used a dose-dependent decrease in cell viability was observed, the maximum effect being reached at 140 and 280 nM. Moreover, treatment of LAN5 cells with α2M* in combination with Aβ 25–35 increased the neurotoxicity of the amyloid peptide by 25%. This neurotoxic effect of α2M* seems to be related to its capability to bind and inactivate TGFβ in the culture medium, since it was mimicked by a TGFβ neutralizing antibody. A possible involvement of receptor-mediated endocytosis was ruled out, since α2M receptor is not present on LAN5, as revealed by RT-PCR and Western blotting experiments.The presence of α2M* in amyloid deposits of Alzheimer's disease has been recently reported and a possible impairment of LRP internalization processes has been hypothesized. Our data suggest that the local accumulation of α2M* in AD plaques may increase Aβ 25–35-induced neurotoxicity by neutralizing TGFβ-mediated neuroprotective mechanisms.