IDE Degrades Nociceptin/Orphanin FQ through an Insulin Regulated Mechanism

Abstract

Insulin-degrading enzyme (IDE) was applied to catalyze hydrolysis of Nociceptin/Orphanin 1-16 (OFQ/N) to show the involvement of the enzyme in degradation of neuropeptides engaged in pain transmission. Moreover, IDE degradative action towards insulin (Ins) was inhibited by the OFQ/N fragments, suggesting a possible regulatory mechanism in the central nervous system. It has been found that OFQ/N and Ins affect each other degradation by IDE, although in a different manner. Indeed, while the digestion of OFQ/N is significantly affected by the presence of Ins, the kinetic profile of the Ins hydrolysis is not affected by the presence of OFQ/N. However, the main hydrolytic fragments of OFQ/N produced by IDE exert inhibitory activity towards the IDE-mediated Ins degradation. Here, we present the results indicating that, besides Ins, IDE cleaves neuropeptides and their released fragments act as inhibitors of IDE activity toward Ins. Having in mind that IDE is present in the brain, which also contains Ins receptors, it cannot be excluded that this enzyme indirectly participates in neural communication of pain signals and that neuropeptides involved in pain transmission may contribute to the regulation of IDE activity. Finally, preliminary results on the metabolism of OFQ/N, carried out in the rat spinal cord homogenate in the presence of various inhibitors specific for different classes of proteases, show that OFQ/N proteolysis in rat spinal cord could be due, besides IDE, also to a cysteine protease not yet identified.

Expression of IDE and PITRM1 genes in ERN1 knockdown U87 glioma cells: effect of hypoxia and glucose deprivation

“…It was also shown that insulin-degrading enzyme is applied to catalyze hydrolysis of Nociceptin/ Orphanin 1-16 (OFQ/N) indicating the involvement of the enzyme in the degradation of neuropeptides engaged in pain transmission (Zingale et al 2019). Moreover, IDE degradative action towards insulin was inhibited by the OFQ/N fragments, suggesting a possible regulatory mechanism in the central nervous system.…”

“…IDE cleaves neuropeptides and their released fragments act as inhibitors of IDE activity toward insulin. It is possible that IDE enzyme indirectly participates in neural communication of pain signals and that neuropeptides involved in pain transmission may contribute to the regulation of IDE activity (Zingale et al 2019).…”

The insulin-degrading enzyme as a link between insulin and neuropeptides metabolism

“…Finally, we have also demonstrated that NPAF, but not NPFF, plays an activatory role on the degradation of insulin by IDE in a site-specific manner, favouring the action of the enzyme mainly at the B13-14 insulin cleavage site. Once again, this result demonstrates the pivotal role of IDE in the interplay between NPs and insulin metabolism, giving a molecular insight into the link between type 2 or type 1 diabetes and pain transmission and pain threshold 13,29 .…”

“…Once the degradation of the two peptides by IDE was assessed, the next question that needed a more thorough explanation was how this enzymatic activity affects/is affected by insulin degradation. The latter has been already well characterised in our previous reports 13,14,20 and here we investigated only how the presence of insulin in the incubation mixture affects NPFF and NPAF degradation, and how NPFF and NPAF and their fragments affect insulin degradation by IDE. In order to elucidate the first point, that is how insulin affects NPFF and NPAF degradation, we co-incubated insulin, IDE and NPFF or NPAF together and studied the time courses of the cryptic peptides which are formed.…”

“…We have recently demonstrated that insulin-degrading enzyme (IDE) is able to degrade specific amino acid sequences present in the NP pro-NPFFA, generating some cryptic peptides 1 . It is possible that NPs involved in pain transmission may be partly responsible for the regulation of IDE or IDE indirectly participates in neural communication of pain signals 13 . Intracellular interactions of insulin with IDE may be involved in insulin control of cellular protein degradation and fat oxidation [14][15][16][17] .…”