Amyloid-β peptide levels in brain are inversely correlated with insulysin activity levels in vivo

Abstract

Factors that elevate amyloid-␤ (A␤) peptide levels are associated with an increased risk for Alzheimer's disease. Insulysin has been identified as one of several proteases potentially involved in A␤ degradation based on its hydrolysis of A␤ peptides in vitro. In this study, in vivo levels of brain A␤40 and A␤42 peptides were found to be increased significantly (1.6-and 1.4-fold, respectively) in an insulysin-deficient gene-trap mouse model. A 6-fold increase in the level of the ␥-secretase-generated C-terminal fragment of the A␤ precursor protein in the insulysin-deficient mouse also was found. In mice heterozygous for the insulysin gene trap, in which insulysin activity levels were decreased Ϸ50%, brain A␤ peptides were increased to levels intermediate between those in wild-type mice and homozygous insulysin gene-trap mice that had no detectable insulysin activity. These findings indicate that there is an inverse correlation between in vivo insulysin activity levels and brain A␤ peptide levels and suggest that modulation of insulysin activity may alter the risk for Alzheimer's disease.A myloid-␤ (A␤) peptide-containing senile plaques are a prominent feature of the pathology of Alzheimer's disease (AD) and occur consistently in AD of all etiology, from earlyonset, familial-linked AD to late-onset AD of indeterminate origin (1). A␤ is formed from the amyloid precursor protein (APP) by sequential enzymatic processing. A ␤-secretase cleavage first yields the 99-aa C-terminal fragment (CTF) of APP, CTF␤, which then is cleaved by ␥-secretase to release A␤ peptides, predominately A␤40 and A␤42, and the CTF␥ peptides of 49-51 residues (2).The proteolysis of APP to yield A␤ peptides is a normal physiologic process observed in multiple cell types, although the endogenous function of APP processing and its products is still not well defined (3). To date, all of the genetic mutations linked to AD result in increased A␤ accumulation, albeit by distinct mechanisms.Although considerable effort has been directed toward generating specific inhibitors of the ␤-and ␥-secretases as a means of preventing A␤ formation (4), the mechanism of A␤ clearance also is of considerable interest because the steady-state concentrations of A␤ peptides are dependent on both their rates of synthesis and their rates of clearance. Recent studies suggest that an important route of A␤ clearance is through hydrolytic cleavage by proteases and peptidases (recently reviewed in refs. 36-38). The peptidase insulysin (EC 3.4.24.56) is one of the enzymes that has been suggested as a candidate A␤-degrading enzyme primarily based on its ability to degrade A␤ peptides in vitro (5-7).Insulysin is a zinc metalloprotease, originally identified as an insulin-degrading enzyme (8), that migrates with reported molecular masses of 110-115 kDa on SDS͞polyacrylamide gels and has no demonstrated posttranslational modifications. The observed molecular mass of insulysin is consistent with the use of the second of its two potential translation initiation sites, although N-te...

Anion Activation Site of Insulin-degrading Enzyme

“…The concentration of ATP needed to achieve 50% activation (K a ) appears to be ϳ2-fold lower for the mutants than the wild type enzyme (K a ϭ 1.6 mM for IDE and 0. 6 Both mutants bound TNP-ATP with a greater fluorescent enhancement than IDE (Fig. 5, top spectrum in each panel).…”

“…Insulin-degrading enzyme (IDE) 6 is a zinc metallopeptidase from the M16 family that has been extensively studied because of its role in regulating cellular insulin (1)(2)(3). More recently, IDE has received considerable attention for its role in degrading amyloid ␤ (A␤) peptides (4 -7), and a genetic link between IDE and late onset Alzheimer disease has been reported (8).…”

Genetic variation in a haplotype block spanningIDE influences Alzheimer disease

“…On this basis, diminished IDE activity might lead to reduced extracellular clearance of Ab, thereby promoting AD development. Animal model studies have proven the viability of this putative mode of action, in that IDE deficiency has been observed to promote significant net increases in Ab deposition in the mouse brain [Farris et al, 2003;Miller et al, 2003].…”

Gene-Centric Analysis of Serum Cotinine Levels in African and European American Populations

“…However, whether and how this interferes with behavioral aspects of nicotine, namely insulin's regulation of dopamine and/or other neurotransmitters (Garcia et al, 2005;Owens et al, 2005;Williams et al, 2007), relevant to cellular and behavioral aspects of psychostimulant addiction (Sugano et al, 2006;Williams et al, 2007), or with insulin's effect on ERK signaling, essential for learning and memory formation, still needs to be determined. IDE is highly expressed in the brain (Farris et al, 2005) where the mechanism of IDE to degrade amyloid-b protein (Farris et al, 2003;Farris et al, 2004;Qiu et al, 1998;Qiu and Folstein, 2006;Vekrellis et al, 2000;Baskin et al, 1994;Miller et al, 2003) has been extensively evaluated.…”