P4‐115: Expression and Functional Profiling of Neprilysin, Insulin Degrading Enzyme and Endothelin Converting Enzyme in Prospectively Studied Elderly and Alzheimer's Brains

The brain steady state level of Aβ is determined by the balance between its production and removal, the latter through egress across blood and CSF barriers as well as Aβ degradation. The major Aβ degrading enzymes are neprilysin (NEP), insulin degrading enzyme (IDE) and endothelin converting enzyme (ECE-1). Although evidence suggests that NEP is down-regulated in AD, the role of IDE and ECE in the Aβ accumulation in aging and dementia remains less certain. In this study, we examined mRNA and protein expression, as well as biological activity of NEP, IDE and ECE-1 in human frontal cortex by real-time RT-PCR for mRNA, immunoblotting for protein and highly sensitive and specific fluorescence assays for activity. The relationships between Aβ degrading enzymes and pathologic measures and clinical features were also assessed. The results showed that NEP mRNA, protein level and activity were decreased in AD compared with normal controls with no cognitive impairment (NCI). In contrast IDE activity was unchanged, but there was higher expression of IDE mRNA, indicating a possible compensatory reaction due to deficits in activity. ECE-1 expression in AD brain showed no significant difference compared to age-matched controls. Correlation analyses suggested that NEP expression was correlated with Aβ accumulation and clinical diagnosis, being lower in AD than in NCI. In contrast, neither IDE nor ECE-1 correlated with Aβ or clinical diagnosis. These findings provide additional support for NEP as the major protease involved in Aβ degradation and suggest its possible therapeutic targeting in AD.