A tailored tetravalent peptide displays dual functions to inhibit amyloid ß production and aggregation.

Inhibition of amyloid-ß peptide (Aß) accumulation in the brain is a promising approach for treatment of Alzheimer's disease (AD). Aß is produced by ß-secretase and γ-secretase in endosomes via sequential proteolysis of amyloid precursor protein (APP). Aß and APP have a common feature to readily cluster to form multimers. Here, using multivalent peptide library screens, we identified a tetravalent peptide, LME-tet, which binds APP and Aß via multivalent interactions. In cells, LME-tet-bound APP in the plasma membrane is transported to endosomes, blocking Aß production through specific inhibition of ß-cleavage, but not γ-cleavage. LME-tet further suppresses Aß aggregation by blocking formation of the ß-sheet conformation. Inhibitory effects are not observed with a monomeric peptide, emphasizing the significance of multivalent interactions for mediating these activities. Critically, LME-tet efficiently reduces Aß levels in the brain of AD model mice, suggesting it may hold promise for treatment of AD.

A nontoxigenic form of Shiga toxin 2 suppresses the production of amyloid ß by altering the intracellular transport of amyloid precursor protein through its receptor-binding B-subunit.

Accumulation of amyloid-ß peptide (Aß) in neuronal cells and in the extracellular regions in the brain is a major cause of Alzheimer's disease (AD); therefore, inhibition of Aß accumulation offers a promising approach for therapeutic strategies against AD. Aß is produced by sequential proteolysis of amyloid precursor protein (APP) in late/recycling endosomes after endocytosis of APP located in the plasma membrane. Aß is then released from cells in a free form or in an exosome-bound form. Shiga toxin (Stx) is a major virulence factor of enterohemorrhagic Escherichia coli. Recently, we found that one of the Stx subtypes, Stx2a, has a unique intracellular transport route after endocytosis through its receptor-binding B-subunit. A part of Stx2a can be transported to late/recycling endosomes and then degraded in a lysosomal acidic compartment, although in general Stx is transported to the Golgi and then to the endoplasmic reticulum in a retrograde manner. In this study, we found that treatment of APP-expressing cells with a mutant Stx2a (mStx2a), lacking cytotoxic activity because of mutations in the catalytic A-subunit, stimulated the transport of APP to the acidic compartment, which led to degradation of APP and a reduction in the amount of Aß. mStx2a-treatment also inhibited the extracellular release of Aß. Therefore, mStx2a may provide a new strategy to inhibit the production of Aß by modulating the intracellular transport of APP.

Exosome-associated Shiga toxin 2 is released from cells and causes severe toxicity in mice.

Shiga toxin (Stx), a major virulence factor of enterohemorrhagic Escherichia coli (EHEC), is classified into two subgroups, Stx1 and Stx2. Clinical data clearly indicate that Stx2 is associated with more severe toxicity than Stx1, but the molecular mechanism underlying this difference is not fully understood. Here, we found that after being incorporated into target cells, Stx2, can be transported by recycling endosomes, as well as via the regular retrograde transport pathway. However, transport via recycling endosome did not occur with Stx1. We also found that Stx2 is actively released from cells in a receptor-recognizing B-subunit dependent manner. Part of the released Stx2 is associated with microvesicles, including exosome markers (referred to as exo-Stx2), whose origin is in the multivesicular bodies that formed from late/recycling endosomes. Finally, intravenous administration of exo-Stx2 to mice causes more lethality and tissue damage, especially severe renal dysfunction and tubular epithelial cell damage, compared to a free form of Stx2. Thus, the formation of exo-Stx2 might contribute to the severity of Stx2 in vivo, suggesting new therapeutic strategies against EHEC infections.