Identification and functional characterization of a putative IDE, C28F5.4 (ceIDE-1), in Caenorhabditis elegans: Implications for Alzheimer's disease

Insulin-degrading enzyme (IDE) is a zinc metalloprotease, known to degrade insulin peptide and amyloid-beta (Aβ); the key protein involved in Alzheimer's disease (AD). Considering the important role played by IDE in disease progression of AD and type 2 diabetes mellitus (T2DM), we endeavored to identify the Caenorhabditis elegans (C. elegans) IDE orthologous genes and test them for their role in AD related outcomes. We employed bioinformatics, reverse genetics and molecular biology approaches towards identification and functional characterization of putative IDE candidates in C. elegans. Using in-silico analysis we have identified seven C. elegans genes that possess HXXEH motif, an identifying marker of IDE. We further carried out functional analysis of the identified genes in Aβ expressing C. elegans strain CL4176 [myo-3/Aβ1-42 long 3′-UTR] via studying effect on Aβ induced toxicity, cholinergic neuroanatomy, content of acetylcholine/acetylcholine-esterase, extent of reactive oxygen species and expression of FOXO transcription factor DAF-16. Our findings reveal that amongst the identified putative IDE orthologs, a functionally uncharacterized gene C28F5.4 had a profound effect on the tested endpoints. Knocking down C28F5.4 modulated the AD associated conditions by decreasing Aβ induced toxicity, severely compromising cholinergic neuroanatomy, reducing expression of acetylcholine-transporter, decreasing acetylcholine content, elevating ROS, with no effect on DAF-16 stress-response protein. These studies provide crucial insight into the structural/functional orthology of IDEs across human and nematode species and further our understanding of the involvement of these proteins and insulin pathway in AD. Further studies could aid in identifying novel drug-targets and in understanding the common modulating factors between AD and T2DM.