Activated alpha(2)macroglobulin increases beta-amyloid (25-35)-induced toxicity in LAN5 human neuroblastoma cells

The presence of the alpha(2)macroglobulin receptor/low density lipoprotein receptor-related protein (alpha(2)Mr/LPR) and its ligands alpha(2)macroglob ulin (alpha(2)M), apoliprotein E, and plasminogen activators was detected i n senile plaques of Alzheimer's disease (AD). To explore a possible role of alpha(2)M in neurodegenerative processes occurring in AD, we analyzed the effect of alpha(2)M On A beta 25-35-induced neurotoxicity. Treatment of LAN E human neuroblastoma cells with 10 mu M beta-amyloid peptide fragment 25-3 5 (A beta 25-35) for 72 h resulted in a 50% decrease in cell viability as d etermined by MTT incorporation and cell counts. The addition of alpha(2)M t o the culture medium of these cells did not determine any effect, but when the activated form alpha(2)M* was used a dose dependent decrease in cell vi ability was observed, the maximum effect being reached at 140 and 280 nM. M oreover, treatment of LAN5 cells with alpha(2)M* in combination with A beta 25-35 increased the neurotoxicity of the amyloid peptide by 25%. This neur otoxic effect of alpha(2)M* seems to be related to its capability to bind a nd inactivate TGF beta in the culture medium, since it was mimicked by a TG F beta neutralizing antibody. A possible involvement of receptor-mediated e ndocytosis was ruled out, since alpha(2)M receptor is not present on LAN5, as revealed by RT-PCR and Western blotting experiments. The presence of alpha(2)M* in amyloid deposits of Alzheimer's disease has b een recently reported and a possible impairment of LRP internalization proc esses has been hypothesized. Our data suggest that the local accumulation o f alpha(2)M* in AD plaques may increase AP 25-35-induced neurotoxicity by n eutralizing TGF beta-mediated neuroprotective mechanisms. (C) 1999 Academic Press.