PNU282987 inhibits amyloid-β aggregation by upregulating astrocytic endogenous αB-crystallin and HSP-70 via regulation of the α7AChR, PI3K/Akt/HSF-1 signaling axis

Alzheimer's disease (AD) is a chronic and irreversible neurodegenerative disorder. Abnormal aggregation of the neurotoxic amyloid-beta (A beta) peptide is an early event in AD. The activation of astrocytic alpha 7 nicotinic acetylcholine receptor (alpha 7 nAChR) can inhibit A beta aggregation; thus, the molecular mechanism between alpha 7 nAChR activation and A beta aggregation warrants further investigation. In the present study, A beta oligomer levels were assessed in astrocytic cell lysates after treatment with PNU282987 (a potent agonist of alpha 7 nAChRs) or co-treatment with LY294002, a p-Akt inhibitor. The levels of heat shock factor-1 (HSF-1), heat shock protein 70 (HSP-70), and alpha B-crystallin (Cryab) in astrocytes treated with PNU282987 at various time-points or co-treated with methyllycaconitine (MLA), a selective alpha 7 nAChR antagonist, as well as co-incubated with LY294002 were determined by western blotting. HSP-70 and Cryab levels were determined after HSF-1 knockdown (KD) in astrocytes. PNU282987 markedly inhibited A beta aggregation and upregulated HSF-1, Cryab, and HSP-70 in primary astrocytes, while the PNU282987-mediated neuroprotective effect was reversed by pre-treatment with MLA or LY294002. Moreover, the HSF-1 KD in astrocytes effectively decreased Cryab, but not HSP-70 expression. HSF-1 is necessary for the upregulation of Cryab expression, but not for that of HSP-70. HSF-1 and HSP-70 have a neuroprotective effect. Furthermore, the neuroprotective effect of PNU282987 against A beta aggregation was mediated by the canonical PI3K/Akt signaling pathway activation.