Purified recombinant insulin-degrading enzyme degrades amyloid β-protein but does not promote its oligomerization

Abstract

Amyloid beta-protein (Abeta) has been implicated as an early and essential factor in the pathogenesis of Alzheimer's disease. Although its cellular production has been studied extensively, little is known about Abeta clearance. Recently, insulin-degrading enzyme (IDE), a 110-kDa metalloendopeptidase, was found to degrade both endogenously secreted and synthetic Abeta peptides. Surprisingly, IDE-mediated proteolysis of [(125)I]Abeta(1-40) in microglial cell-culture media was accompanied by the formation of (125)I-labelled peptides with higher apparent molecular masses, raising the possibility that the degradation products act as 'seeds' for Abeta oligomerization. To directly address the role of IDE in Abeta degradation and oligomerization, we investigated the action of purified recombinant wild-type and catalytically inactive IDEs. Our data demonstrate that (i) IDE alone is sufficient to cleave purified Abeta that is either unlabelled, iodinated or (35)S-labelled; (ii) the initial cleavage sites are His(14)-Gln(15), Phe(19)-Phe(20) and Phe(20)-Ala(21); and (iii) incubation of IDE with [(125)I]Abeta, but not with [(35)S]-Abeta, leads to the formation of slower migrating species on gels. Since iodination labels N-terminal fragments of Abeta, and (35)S labels C-terminal products, we analysed unlabelled synthetic fragments of Abeta and determined that only the N-terminal fragments migrate with anomalously high molecular mass. These results indicate that IDE alone is sufficient to degrade Abeta at specific sites, and that its degradation products do not promote oligomerization of the intact Abeta peptide.

17β-Estradiol regulates insulin-degrading enzyme expression via an ERβ/PI3-K pathway in hippocampus: Relevance to Alzheimer's prevention

“…The present investigation in both in vitro and in vivo models revealed that 17β-E2 rapidly increased brain IDE protein levels after a 12 to 48-h treatment. A number of recent studies indicate that IDE cleaves APP-derived peptides including Aβ and APP intracellular domain at multiple sites and that the velocity of the reaction is extremely high (Chesneau, et al, 2000; Edbauer, et al, 2002; Mukherjee, et al, 2000). For instance, in an in vitro experiment, purified recombinant wild-type human IDE degraded about 75% of Aβ following just a 1-h co-incubation (Chesneau, et al, 2000).…”

“…A number of recent studies indicate that IDE cleaves APP-derived peptides including Aβ and APP intracellular domain at multiple sites and that the velocity of the reaction is extremely high (Chesneau, et al, 2000; Edbauer, et al, 2002; Mukherjee, et al, 2000). For instance, in an in vitro experiment, purified recombinant wild-type human IDE degraded about 75% of Aβ following just a 1-h co-incubation (Chesneau, et al, 2000). These findings suggest again the significance of the role played by estrogen on brain IDE, and such a role could serve as a key contributory mechanism underlying estrogen-mediated prevention of AD.…”

Type 1 diabetes exaggerates features of Alzheimer's disease in APP transgenic mice

“…In addition to increased processing of APP by GSK3, the accumulation of soluble and insoluble Aβ in the diabetic-APP transgenic mice brain may result from reduced degradation. The Insulin-Degrading Enzyme (IDE) degrades insulin but also a number of other small proteins, including Aβ (Chesneau, et al, 2000). IDE protein levels and activity are reduced in AD brains (Perez, et al, 2000).…”

Are amyloid‐degrading enzymes viable therapeutic targets in Alzheimer’s disease?

“…1998) and a wide range of evidence now supports its role in this regard from studies in vitro through cell‐based and animal models (e.g. Chesneau et al. 2000; Farris et al.…”