P1-379: Heparan sulphate proteoglycans affect the biological activity of Aβ

Abstract

Amyloid beta (Aβ) deposits in Alzheimer's disease brains, i.e. senile plaques and vascular amyloid, also contain heparan sulphate proteoglycans (HSPGs). HSPGs consist of a protein core with sulphated glycosaminoglycans (GAGs) attached. The expression of HSPG in plaques suggests that these proteins play a role in the deposition of Aβ. It has been suggested that HSPGs may affect Aβ aggregation and clearance. However, the spatiotemporal association between HSPGs and Aβ has not yet been studied. Similarly, it is not known how HSPG/GAG expression relates to Aβ expression and biological activity. 1) to study in vitro (in human brain pericytes) the expression of HSPGs in response to Aβ; 2) to study in vitro (in human brain pericytes and smooth muscle cells) the role of GAGs in Aβ–mediated cellular toxicity; 3) to investigate the spatiotemporal association of HSPGs with Aβ. Protein expression of HSPGs was determined using Western blot analysis. RNA expression was measured using a quantitative RT–PCR (Taqman). The effect of GAGs on Aβ–mediated cellular toxicity was investigated using viability assays. In vitro, protein expression of the HSPGs agrin and glypican–1 and the degree of glycosylation of these HSPGs in pericytes was upregulated after treatment with Aβ. To confirm these findings at the mRNA level, quantitative PCR was performed. Finally, we demonstrated that several GAGs dose–dependently inhibited Aβ–mediated cellular degeneration in pericytes and smooth muscle cells. Moreover, we observed that the degree of inhibition was dependent on the degree of sulphation of the GAGs. In conclusion, GAGs may modulate the biological activity of Aβ and this capacity is related to the degree of negatively charged sulphate groups present in these GAGs. Furthermore, HSPG expression (both at the protein level and degree of glycosylation) is increased in response to Aβ. This suggests that HSPG expression in senile plaques and vascular amyloid follows the expression of Aβ. Currently, a study to confirm this association between Aβ and HSPGs, by investigating the expression of HSPGs in relation to Aβ expression in transgenic mice (APPSwe/PS–1 and SwDI Tg mice) during different stages of lesion development, is in progress.