Cell surface proteoglycan-mediated uptake and accumulation of the Alzheimer's disease peptide A beta(1-42)

Proteoglycans (PGs) have been found in Alzheimer's disease amyloid-beta (A beta) plaques and their glycosaminoglycan chains reportedly influence A beta aggregation, neurotoxicity and intracellular accumulation in cell and animal models, but their exact pathophysiological role(s) remain unclear. We have studied the cellular uptake of fluorescently labelled A beta(1-42) and A beta(1-40) peptides in normal CHO cells (K1) and the mutant cell line (pgsA-745) which lacks all protein-attached heparan and chondroitin sulfate chains. After 24 h of incubation, CHO-K1 accumulates more A beta(1-42) and A beta(1-40) compared with CHO-pgsA-745, consistent with the suggested role of PGs in A beta uptake. However, after short incubation times (<= 3 h) there was no difference; moreover, the time evolution of A beta(1-42) accumulation in CHO-K1 followed an unusual sigmoidal-like trend, indicating a possible involvement of PG-mediated peptide aggregation in A beta endocytosis. Neither A beta(1-42) nor A beta(1-40) could stimulate uptake of a 10 kDa dextran (a general endocytosis marker) suggesting that A beta-induced upregulation of endocytosis does not occur. CHO-K1 cells contained a higher number of A beta(1-42)-positive vesicles, but the intensity difference per vesicle was only marginal suggesting that the superior accumulation of A beta(1-42) stems from a higher number of endocytic events. FRET imaging support that intracellular A beta(1-42) is aggregated in both cell types. We also report that CHO-pgsA-745 cells perform less endocytosis than CHO-K1 and, albeit this does not explain their difference in A beta internalisation, we discuss a general method for data compensation. Altogether, this study contributes new insights into the mechanisms of PG-mediated A beta uptake that may be relevant for our understanding of their role in AD pathology.