Peptides of presenilin-1 bind the amyloid precursor protein ectodomain and offer a novel and specific therapeutic approach to reduce ß-amyloid in Alzheimer's disease.

ß-Amyloid (Aß) accumulation in the brain is widely accepted to be critical to the development of Alzheimer's disease (AD). Current efforts at reducing toxic Aß40 or 42 have largely focused on modulating γ-secretase activity to produce shorter, less toxic Aß, while attempting to spare other secretase functions. In this paper we provide data that offer the potential for a new approach for the treatment of AD. The method is based on our previous findings that the production of Aß from the interaction between the ß-amyloid precursor protein (APP) and Presenilin (PS), as part of the γ-secretase complex, in cell culture is largely inhibited if the entire water-soluble NH2-terminal domain of PS is first added to the culture. Here we demonstrate that two small, non-overlapping water-soluble peptides from the PS-1 NH2-terminal domain can substantially and specifically inhibit the production of total Aß as well as Aß40 and 42 in vitro and in vivo in the brains of APP transgenic mice. These results suggest that the inhibitory activity of the entire amino terminal domain of PS-1 on Aß production is largely focused in a few smaller sequences within that domain. Using biolayer interferometry and confocal microscopy we provide evidence that peptides effective in reducing Aß give a strong, specific and biologically relevant binding with the purified ectodomain of APP 695. Finally, we demonstrate that the reduction of Aß by the peptides does not affect the catalytic activities of ß- or γ-secretase, or the level of APP. P4 and P8 are the first reported protein site-specific small peptides to reduce Aß production in model systems of AD. These peptides and their derivatives offer new potential drug candidates for the treatment of AD.

An early specific cell-cell interaction occurs in the production of beta-amyloid in cell cultures.

We have earlier proposed that a cell-cell interaction, mediated by the specific binding of molecules of the beta-amyloid precursor protein (beta-APP) on one cell surface with molecules of presenilin (PS) on the other cell surface, is a required initial step in the ultimate production of beta-amyloid (Abeta) from beta-APP. Abeta is widely believed to be the neurotoxic agent in Alzheimer's disease. In this paper, we test this proposal by modifying cells to express surface beta-APP but no PS, and other cells to express surface PS but no beta-APP. Coculturing these two cell populations at appropriate cell densities produces substantial amounts of Abeta that appear both in cell extracts and culture media. Such Abeta production could occur only if the two cell types interacted with one another to provide the beta-APP and the PS required for the generation of Abeta. The addition to the coculture, from the start, of the soluble specific N-terminal domain of the appropriate PS significantly reduces the amount of Abeta produced. These and related experiments, therefore, suggest a very different mechanism for Abeta production than the one that is currently widely accepted.

Evidence that Perutz's double-beta-stranded subunit structure for beta-amyloids also applies to their channel-forming structures in membranes.

Although there is a growing body of evidence that different amyloidoses may have a similar molecular mechanism in common, the many details of this mechanism are not understood. In this study, we propose that there is a common molecular structure of the primary agents of these diseases, namely a small oligomer of Perutz's cylindrical double-beta-stranded subunit for polyglutamine and that this structure, which contains a central water-filled core, can spontaneously integrate into the bilayers of membranes to form aqueous pores. We suggest that this ability to produce permeable channels in appropriate neuronal membranes is a key element in the toxicity of the beta-amyloids. One strong criterion for the stability of the Perutz structure for an amyloid is that it contain approximately 40 or more amino acid residues. We show here that the neurotoxic Abeta amyloids 1-40 and 1-42, related to Alzheimer's disease, spontaneously enter the membranes of intact erythrocytes and cause their lysis but that Abeta 1-38 and Abeta 1-35, which are not neurotoxic, have no observable effects on erythrocytes, supporting our proposal. Other aspects of the proposed mechanism of cytotoxicity of the beta-amyloids are explored.

Some early history of membrane molecular biology.

This article is mostly about the beginnings of the molecular biology of membranes, covering the decade 1964-1974. It is difficult to read (or write) this article because of a sense of deja vu. Most of the material in it is considered commonplace today, having been established experimentally since then. But at the time this work was begun, practically nothing was known about the molecular structure and the mechanisms of the functions of membranes. This situation existed because no membrane proteins of the kind I called integral had as yet been isolated in a pure state, and therefore none had had their amino acid sequence determined. The first integral membrane protein to be so characterized was human erythrocyte glycophorin, in 1978. It was the use of the thermodynamic reasoning that had been developed for the study of water-soluble proteins, together with the information from several key experiments carried out in a number of laboratories during the early decade, that led us to the fluid mosaic model of membrane structure in 1972. Without direct evidence to confirm the model in 1971-1972, my colleagues and I nevertheless had the confidence in it to pursue some of the consequences of the model for a new understanding of many membrane functions, which I present here in some detail. Finally, I discuss two recent high-resolution X-ray crystallographic studies of integral proteins to ask how well the structural and functional proposals that we derived from the fluid mosaic model fit these remarkably detailed X-ray results.