Perlecan binds to the beta-amyloid proteins (A beta) of Alzheimer's disease, accelerates A beta fibril formation, and maintains A beta fibril stability.
Perlecan is a specific heparan sulfate proteoglycan that accumulates in the fibrillar beta-amyloid (A beta) deposits of Alzheimer's disease. Perlecan purified from the Engelbreth-Holm-Swarm tumor was used to define perlecan's interactions with A beta and its effects on A beta fibril formation. Using a solid-phase binding immunoassay, freshly solubilized full-length A beta peptides bound immobilized perlecan at two sites, representing both high-affinity [K(D) = approximately 5.8 x 10(-11) M for A beta (1-40); K(D) = approximately 6.5 x 10(-12) M for A beta (1-42)] and lower-affinity [K(D) = 3.5 x 10(-8) M for A beta (1-40); K(D) = 4.3 x 10(-8) M for A beta (1-42)] interactions. An increase in the binding capacity of A beta (1-40) to perlecan correlated with an increase in A beta amyloid fibril formation during a 1-week incubation period. The high-capacity binding of A beta (1-40) to perlecan was similarly observed using perlecan heparan sulfate glycosaminoglycans and was completely abolished by heparin, but not by chondroitin-4-sulfate. Using a thioflavin T fluorometry assay, perlecan accelerated the rate of A beta (1-40) amyloid fibril formation, causing a significant increase in A beta fibril assembly over a 2-week incubation period at 1 h (2.8-fold increase), 1 day (3.6-fold increase), and 3 days (2.8-fold increase) in comparison with A beta (1-40) alone. Perlecan also initially accelerated the formation of A beta (1-42) fibrils within 1 h and maintained significantly higher levels of A beta (1-42) thioflavin T fluorescence throughout a 2-week experimental period in comparison with A beta (1-42) alone, suggesting perlecan's ability to maintain amyloid fibril stability. Perlecan's effects on A beta (1-40) fibril formation and maintenance of A beta (1-42) fibril stability occurred in a dose-dependent manner and was also mediated primarily by perlecan's glycosaminoglycan chains. Perlecan was the most effective enhancer and accelerator of A beta fibril formation when compared directly with other amyloid plaque components, including apolipoprotein E, alpha1-antichymotrypsin, P component, C1q, and C3. This study, therefore, demonstrates that perlecan not only binds to the predominant isoforms of A beta, but also accelerates A beta fibril formation and stabilizes amyloid fibrils once formed, confirming pivotal roles for perlecan in the pathogenesis of A beta amyloidosis in Alzheimer's disease.
Castillo
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GM
Neuropathology Laboratories, University of Washington, Seattle 98195-6480, U.S.A.
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Cummings
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Wight
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Snow
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D000544:Alzheimer Disease / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D001667:Binding, Competitive; D006025:Glycosaminoglycans / Q000502:physiology; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology* / Q000502:physiology; D010446:Peptide Fragments / Q000378:metabolism; D011509:Proteoglycans / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D013997:Time Factors
D016229:Amyloid beta-Peptides; D006025:Glycosaminoglycans; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D010446:Peptide Fragments; D011509:Proteoglycans; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42); C071927:perlecan