Faculty Bibliography

Amyloid beta (A beta) is a fibrillar component in Alzheimers' disease amyloid deposits and a soluble peptide (sA beta) normally present in body fluids. We have recently reported that the blood-brain barrier (BBB) has a capability to control cerebrovascular sequestration and transport of circulating sA beta. In this study, we examined whether two circulating amyloid-associated proteins shown to bind sA beta, apolipoproteins J (apo J) and E (apo E), can cross the BBB alone and/or complexed to a synthetic peptide homologous to a major form of sA beta, sA beta 1-40. Brain perfusion experiments in guinea pigs showed significant uptake of both apo J and sA beta 1-40-apo J complexes. In contrast, blood-brain transport of sA beta 1-40-apo E was negligible, while apo E had a limited access across the BBB, indicating that the apo E found within the brain is produced locally. It is concluded that sA beta 1-40 binding to apo J and apo E results in significant (> 100-fold) difference in brain uptake of their respective complexes. We hypothesize that in normal brain apo J facilitates sA beta transport

Late-onset and sporadic Alzheimer's disease are associated with the apolipoprotein E (apoE) type 4 allele expressing the protein isoform apoE4. Apolipoprotein E binds avidly to beta amyloid (A beta) peptide, a major component of senile plaque of Alzheimer's disease, in an isoform-specific manner. The apoE4 isoform binds to A beta peptide more rapidly than apoE3. We observed that soluble SDS-stable complexes of apoE3 or apoE4, formed by coincubation with A beta peptide, precipitated after several days of incubation at 37 degrees C with apoE4 complexes precipitating more rapidly than apoE3 complexes. A beta(1-28) and A beta(1-40) peptides were incubated in the presence or absence of apoE3, apoE4, or bovine serum albumin for 4 d at 37 degrees C (pH 7.3). Negative stain electron microscopy revealed that the A beta peptide alone self-assembled into twisted ribbons containing two or three strands but occasionally into multistranded sheets. The apoE/A beta coincubates yielded monofibrils 7 nm in diameter. ApoE4/A beta coincubates yielded a denser matrix of monofibrils than apoE3/A beta coincubates. Unlike purely monofibrillar apoE4/A beta coincubates, apoE3/A beta coincubates also contained double- and triple-stranded structures. Both apoE isoforms were shown by immunogold labeling to be uniformly distributed along the A beta peptide monofibrils. Monofibrils appeared earlier in apoE4/A beta than in apoE3/A beta in time-course experiments. Thus apoE3 and apoE4 each interact with beta amyloid peptide to form novel monofibrillar structures, apoE4 more avidly, a finding consistent with the biochemical and genetic association between apoE4 and Alzheimer's disease

Numerous studies have established a linkage between the apolipoprotein (apo) E4 allele and late-onset Alzheimer's disease. It remains unclear if apo E plays a direct role in the pathogenesis of Alzheimer's disease and what, if any, are its significant interactions with amyloid beta (A beta) and tau. Apo E has been found immunohistochemically in all types of amyloid deposits and apo E fragments have been isolated from amyloid. Furthermore, apo E has been shown to bind soluble A beta. It has been proposed that apo E acts to promote and/or modulate A beta fibril formation. It is well established that peptides homologous to A beta will form amyloid-like fibrils in solution. With the use of electron microscopy and a thioflavin T assay for fibril formation we found that apo E and apo E4 in particular enhance this spontaneous fibrillogenesis of A beta peptides under the in vitro conditions used. These in vitro data suggest that the apo E4 isoform is a risk factor for Alzheimer's disease that acts to accelerate a process that can occur in its absence

The amyloid fibrils of Alzheimer's neuritic plaques and cerebral blood vessels are mainly composed of aggregated forms of a 39 to 44 amino acids peptide, named amyloid beta (A beta). A similar although soluble form of A beta (sA beta) has been identified in plasma, cerebrospinal fluid and cell culture supernatants, indicating that it is produced under physiologic conditions. We report here that sA beta in normal human plasma is associated with lipoprotein particles, in particular to the HDL3 and VHDL fractions where it is complexed to ApoJ and, to a lesser extent, to ApoAI. This was assessed by immunoprecipitation experiments of purified plasma lipoproteins and lipoprotein-depleted plasma and confirmed by means of amino acid sequence analysis. Moreover, biotinylated synthetic peptide A beta 1-40 was traced in normal human plasma in in vitro experiments. As in the case of sA beta, biotinylated A beta 1-40 was specifically recovered in the HDL3 and VHDL fractions. This data together with the previous demonstration that A beta 1-40 is taken up into the brain via a specific mechanism and possibly as an A beta 1-40-ApoJ complex indicate a role for HDL3- and VHDL-containing ApoJ in the transport of the peptide in circulation and suggest their involvement in the delivery of sA beta across the blood-brain barrier

The 39-43 amino acid (similar to 4 kD) amyloid beta-protein (A beta) deposited as amyloid Alzheimer's disease is an infernal peptide beginning 99 residues from the COOH end of a much larger amyloid beta-protein precursor (beta APP). In cultured cells, normal processing of the beta APP produces similar to 8.7, similar to 9.6, similar to 10.9, and similar to 11.4 kD COOH-terminal derivatives that appear to contain all or part of the A beta domain. In this study, we metabolically labeled transfected human neuroblastoma (M17) cells with [H-3]phenylalanine plus [S-35]methionine and then radiosequenced the immunoprecipitated COOH-terminal beta APP derivatives faking advantage of the fact that the A beta has phenylalanines at positions 4, 19, and 20, and a single methionine at position 35. Our analysis of the derivatives produced by transfected M17 cells expressing beta APP(695) confirms that the similar to 8.7 kD COOH-terminal derivative begins at A beta(17) and indicates that the similar to 9.6 and similar to 10.9 kD derivatives begin at A beta(10) and A beta(4) respectively. Significantly we find that the 11.4 kD derivative begins at A beta(1). Thus normal beta APP processing produces a potentially amyloidogenic COOH-terminal derivative that has the AP domain intact at its amino terminus. We have previously shown that cells expressing beta APP(Delta NL) a mutant linked to familial Alzheimer's disease, produce an increased amount of the 11.4 kD COOH-terminal derivative and secrete more A beta. Radiosequencing of these derivatives showed that the Delta NL mutant is cleaved at the same location as wild type beta APP producing an 11.4 kD COOH-terminal derivative and A beta that both begin at A beta(1). Thus the Delta NL mutation appears to accelerate a cleavage that releases an 11.4 kD COOH-terminal derivative identical to that normally produced from wild type beta APP, and it appears that this 11.4 kD derivative is further processed to release excess A beta