Soluble Neuregulin-1 from Microglia Enhances Amyloid Beta-induced Neuronal Death

Neuregulin-1 (NRG-1) is a ligand of the epidermal growth factor receptor (erbB), and its interaction involves activation of the glutamatergic N-methyl-Daspartate receptor, which increases the expression of the β2 subunit of the γ- aminobutyric acid receptor and subunits of the nicotinic acetylcholine receptor. In the dentate gyrus of 14-month-old Tg2576 mice, NRG-1 was strongly expressed compared with age-matched controls. The supernatant of oligomeric amyloid β peptide (Aβ42)-treated glial cells enhanced the Aβ42-induced cytotoxic effects, but the expression of Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand in microglial cells was not changed upon cytotoxic treatment. This suggests that the oligomeric form of Aβ42 toxicity is not related to apoptosis, which is mediated by cell-to-cell interaction. During the 24-h incubation, the secretion of the soluble form of NRG-1 was increased, but interleukin 6 secretion was not changed. Further, soluble NRG-1 increased Aβ42-induced toxicity. In conclusion, soluble NRG-1 significantly enhanced oligomeric Aβ42-induced toxicity through the activation of endoplasmic reticulum stress by the increase of a phospho-translation initiation factor 2 alpha (p-eIF2α).