The aggregation of amyloid-β (Aβ) peptides plays a crucial role in the onset and progression of Alzheimer's disease. Monomeric form of Aβ, indeed, could exert a physiological role. Considering the anti-oligomerization property of all-trans retinoic acid (ATRA), the involvement of monomeric Aβ1–42 in ATRA-induced neuronal differentiation has been investigated. Four-day ATRA treatment increases β-secretase 1 (BACE1) level, Aβ1–42 production, and receptor for advanced glycation end-products (RAGE) expression. RAGE is a well-recognized receptor for Aβ, and the block of both RAGE and Aβ1–42 with specific antibodies strongly impairs neurite formation in ATRA-treated cells. The involvement of Aβ1–42 and RAGE in ATRA-induced morphologic changes has been confirmed treating undifferentiated cells with different molecular assemblies of peptide: 1 μM monomeric, but not oligomeric, Aβ1–42 increases RAGE expression and favors neurite elongation. The block of RAGE completely prevents this effect. Furthermore, our data underline the involvement of the RAGE-dependent adhesion molecule amphoterin-induced gene and open reading frame-1 as downstream effector of both ATRA and Aβ1–42. In conclusion, our findings identify a novel physiological role for monomeric Aβ1–42 and RAGE in neuronal differentiation.
