Macromolecular and small-molecule modulation of intracellular Aβ42 aggregation and associated toxicity

A beta (amyloid beta-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 A beta aggregation could uncover novel therapies for AD, but most studies in mammalian cells have inferred aggregation indirectly by assessing levels of secreted A beta peptide. In the present study we establish a mammalian cell system for the direct visualization of At formation by expression of an A beta(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 [Aphelencluis avenue LEA (late embryogenesis abundant) protein 1] which limits aggregation of proteins with expanded poly(Q) repeats, is also effective against A beta(42)-EGFP when co-expressed in T-REx293 cells. A screen of polysatcharide 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 A beta. Both PS5 and ganoderic acid DM probably promote A beta aggregate clearance indirectly through the proteasome. The model is therefore of value to study the effects of intracellular At on cell physiology and to identify reagents that counteract those effects.