Macromolecular and small-molecule modulation of intracellular Aß42 aggregation and associated toxicity.

Aß (amyloid ß-peptide) has a central role in AD (Alzheimer's disease) where neuronal toxicity is linked to its extracellular and intracellular accumulation as oligomeric species. Searching for molecules that attenuate Aß aggregation could uncover novel therapies for AD, but most studies in mammalian cells have inferred aggregation indirectly by assessing levels of secreted Aß peptide. In the present study we establish a mammalian cell system for the direct visualization of Aß formation by expression of an Aß(42)-EGFP (enhanced green fluorescent protein) fusion protein in the human embryonic kidney cell line T-REx293, and use this to identify both macromolecules and small molecules that reduce aggregation and associated cell toxicity. Thus a molecular shield protein AavLEA1 [Aphelenchus avenae LEA (late embryogenesis abundant) protein 1], which limits aggregation of proteins with expanded poly(Q) repeats, is also effective against Aß(42)-EGFP when co-expressed in T-REx293 cells. A screen of polysaccharide and small organic molecules from medicinal plants and fungi reveals one candidate in each category, PS5 (polysaccharide 5) and ganoderic acid DM respectively, with activity against Aß. Both PS5 and ganoderic acid DM probably promote Aß aggregate clearance indirectly through the proteasome. The model is therefore of value to study the effects of intracellular Aß on cell physiology and to identify reagents that counteract those effects.