Previous studies have demonstrated the immunolocalization of
perlecan, a specific
heparan sulfate proteoglycan, to the
beta-amyloid protein (A beta)-containing
amyloid deposits within the walls of blood vessels (i.e.,
congophilic angiopathy) in
Alzheimer's disease (AD) brain. In the present investigation, the differential binding of previously characterized endothelial cell (EC)- and smooth muscle cell (SMC)-derived PGs to A beta was examined to determine whether the accumulation of A beta in cerebrovascular
amyloid deposits may be due to its interactions with
perlecan. Pretreatment of AA amyloidotic splenic and liver tissue sections with synthetic A beta (1-28) produced strong immunoreactivity with A beta
antibodies at tissue sites enriched in
perlecan which was partially removed by pretreatment with
heparitinase, but not by
chondroitin ABC lyase. [35S]-
Sulfate labeled
proteoglycans (PGs) derived from cultured ECs and SMCs bound to affinity columns containing A beta (1-28) or (1-40), with virtually no binding to A beta (40-1) (reverse
peptide),
beta-amyloid precursor
protein (410-429), or
bovine serum albumin. Characterization of EC and SMC PGs bound to A beta (1-28) revealed strong binding by
perlecan, weak binding by
decorin and
biglycan, two
dermatan sulfate proteoglycans, and lack of binding by
versican/PG-M, a large
chondroitin sulfate proteoglycan. Binding of 125I-labeled
perlecan to A beta (1-28) was strongly inhibited by isolated
perlecan and to a lesser extent by
heparin, but not by chondroitin-6-sulfate or unsulfated
dextran sulfate.
Heparitinase treatment decreased, but did not eliminate the binding of 125I-labeled
perlecan to A beta (1-28). Scatchard analysis of the interaction of A beta (1-28)- and EC-derived
perlecan in solid-phase assays indicated high-affinity (Kd = 8.3 x 10(-11) M) and lower-affinity (Kd = 4.2 x 10(-8) M) binding sites, with approximately 1 mol of
perlecan binding 1.8 mol of A beta. A significant decrease in binding of EC-derived
perlecan to A beta (1-28) was observed when a sequence within the putative
heparin-binding motif of A beta (His13His14Gln15Lys16) was replaced by the uncharged
peptide sequence, Gly13Gly14Gln15Gly16, indicating a
perlecan binding site on A beta near the postulated
alpha-secretase site (at Lys-16). Overall, the results indicate that specific vascular cell-derived PGs differentially interact with A beta, and that the interactions of highest affinity occur between A beta and binding sites on both the core
protein and
glycosaminoglycan chains of
perlecan.(ABSTRACT TRUNCATED AT 400 WORDS)