Insulin-degrading Enzyme Levels Research Articles

Effects of Chronic Glucocorticoid Administration on Insulin-Degrading Enzyme and Amyloid-Beta Peptide in the Aged Macaque

Insulin-degrading enzyme (IDE) has been identified as a candidate protease in the clearance of amyloid-delta (Abeta) peptides from the brain. IDE activity and binding to insulin are known to be inhibited by glucocorticoids in vitro. In Alzheimer disease (AD), both a decrease in IDE levels and an increase in peripheral glucocorticoid levels have been documented. Our study investigated the effects of glucocorticoid treatment on IDE expression in vivo in 12 nonhuman primates (Macaca nemestrina). Year-long, high-dose exposure to the glucocorticoid cortisol (hydrocortisone acetate) was associated with reduced IDE protein levels in the inferior frontal cortex and reduced IDE mRNA levels in the dentate gyrus of the hippocampus. We assessed Abeta40 and Abeta42 levels by ELISA in the brain and in plasma, total plaque burden by immunohistochemistry, and relative Abeta1-40 and Abeta1-42 levels in the brain by mass spectrometry. Glucocorticoid treatment increased Abeta42 relative to Abeta40 levels without a change in overall plaque burden within the brain, while Abeta42 levels were decreased in plasma. These findings support the notion that glucocorticoids regulate IDE and provide a mechanism whereby increased glucocorticoid levels may contribute to AD pathology.

Mechanisms involved in degradation of human insulin by cytosolic fractions of human, monkey, and rat liver.

The degradation of native and 125I-labeled human insulin (HI) was examined in the cytosolic fraction of human, monkey, and rat liver. The purpose of these studies was to provide a species comparison of the interaction of insulin-degrading enzyme (IDE) and protein disulfide isomerase (PDI) in the degradation of HI. Western-blot analysis with monoclonal antibodies indicated the presence of both IDE and PDI in the cytosolic fraction of human and monkey liver. In contrast, rat liver cytosol contained, detectable levels of IDE only. A species comparison of metabolic profiles was performed by fractionating peptide products with reversed-phase high-performance liquid chromatography. After a 60-min incubation, human liver cytosol degraded unlabeled HI into three major products. Two of these peptides coeluted with the products of the incubation of HI with purified rat liver PDI. The three peptides were isolated and determined by NH2-terminal sequence analysis to be intact A chain, B chain, and des(Phe1)-B chain. Human liver cytosol also formed 125I-A chain and 125I-B chain as major products when specifically labeled 125I-HI isomers were used as substrate. Significant proteolytic degradation was observed only when reactions with human liver cytosol were supplemented with Mn2+. In contrast, monkey and rat liver cytosol proteolytically degraded 125I-HI isomers to small peptide fragments. The rat and monkey metabolic profiles were similar to each other and to that observed with Mn(2+)-supplemented human liver cytosol. Proteolysis in monkey and rat was sensitive to inhibition by EDTA.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural regulatory mechanisms of insulin degradation by insulin degrading enzyme

Insulin-degrading enzyme (IDE) accounts for most of the insulin degrading activity in extracts of several tissues and plays an important role in the intracellular degradation of insulin. Using newly developed sandwich radioimmunoassay for rat IDE, this enzyme was detectable in all tissues we examined and liver had the highest level of IDE. The ratio of insulin degrading activity to IDE concentration was roughly the same in liver, brain and muscle, however, twice as high in kidney as compared with other tissues. On the contrary, its degrading activity in these tissue extracts, including kidney, was completely lost after immunoprecipitation of IDE. These results suggest that IDE degrades insulin in the initial step of cleavage and that there are some mechanisms to regulate insulin degrading activity by IDE in the tissues.

Developmental regulation of an insulin-degrading enzyme from Drosophila melanogaster.

The precise mechanism by which insulin is degraded in mammalian cells is not presently known. Several lines of evidence suggest that degradation is initiated by a specific nonlysosomal insulin-degrading enzyme (IDE). The potential importance of this insulin protease is illustrated by the fact that there is an IDE in Drosophila melanogaster Kc cells that shares both physical and kinetic properties with its mammalian counterpart. We now demonstrate that the IDE is present in other Drosophila cell lines and in the embryo, the larvae, the pupae, and adult tissues of the fruit fly. Further, the level of the IDE is developmentally regulated, being barely detectable in the embryo but elevated approximately 5-fold in the larvae and pupae and approximately 10-fold in the adult fly. The IDE levels in the cell lines are particularly high, at least 10-fold greater than in the adult fly. Analysis of Schneider L3 cells indicates that the addition of the Drosophila hormone ecdysone, which induces differentiation of the cells, causes a small but reproducible increase in the level of the IDE and the insulin-degrading activity. These results demonstrate that the IDE is evolutionarily conserved and that its expression is tightly regulated during differentiation of Drosophila. The particular pattern of developmental regulation suggests that the IDE plays a specific and critical role in the later stages of the life cycle of the fly.