Effects of 4-Hydroxy-Nonenal and Amyloid-β on Expression and Activity of Endothelin Converting Enzyme and Insulin Degrading Enzyme in SH-SY5Y Cells

Abstract

The cerebral accumulation of amyloid-β (Aβ) is a consistent feature of and likely contributor to the development of Alzheimer's disease (AD). In addition to dysregulated production, increasing experimental evidence suggests reduced catabolism plays an important role in Aβ accumulation. Although endothelin converting enzyme (ECE) and insulin degrading enzyme (IDE) degrade and thus contribute to regulating the steady-state levels of Aβ, how these enzymes are regulated remain poorly understood. In this study, we investigated the effects of 4-hydroxy-nonenal (HNE) and Aβ on the expression and activity of ECE-1 and IDE in human neuroblastoma SH-SY5Y cells. Treatment with HNE or Aβ upregulated ECE-1 mRNA and protein, while IDE was unchanged. Although both ECE-1 and IDE were oxidized within 24 h of HNE or Aβ treatment, ECE-1 catalytic activity was elevated while IDE specific activity was unchanged. The results demonstrated for the first time that both ECE-1 and IDE are substrates of HNE modification induced by Aβ. In addition, the results suggest complex mechanisms underlying the regulation of their enzymatic activity.

A neglected modulator of insulin-degrading enzyme activity and conformation: The pH

“…MS results confirm that such different binding features affect IDE capability to degrade insulin, as the enzyme is inactive toward the hormone at acidic pH. Moreover, the insulin fragments detected by MS at basic pH involve the C-terminal residues of the insulin A chain [A (14-21) and A (15)(16)(17)(18)(19)(20)(21)] and the fragments B (17-24) and B (17)(18)(19)(20)(21)(22)(23)(24)(25). The same set of insulin fragments are known to be produced in solutions containing IDE at high concentrations, where the equilibrium in the oligomerization state of the enzyme is mainly shifted toward the dimeric and/or tetrameric forms.…”

“…Interestingly, apart from the changes on the overall activity, it is possible to note that the insulin fragments detected at alkaline pH are different from the ones detected at physiological pH. Particularly, the insulin fragments involving the C-terminal residues of the insulin B (17)(18)(19)(20)(21)(22)(23)(24)(25) are mainly produced at alkaline pH [15]. The same set of insulin fragments are known to be produced in solutions containing IDE at high concentrations [15] and therefore it is easy to speculate that the pH, as well as the enzyme concentration, has an effect on IDE oligomerization state, acidic pH shifting the equilibrium toward the monomeric form.…”

“…Indeed, considerable evidence suggests that IDE inhibitors may hold therapeutic value, particularly for type 2 diabetes and other disorders involving impaired insulin signaling [12], while IDE activators could be used as possible drugs aiming at lowering Aβ levels in AD [13]. Moreover, the effect that other experimental factors such as oligomerization state [14][15][16], presence of metal ions [17][18][19][20] and oxidative stress [21][22][23] can have on IDE activity has also been widely investigated.…”

Mechanisms of Amyloid-β Peptide Clearance: Potential Therapeutic Targets for Alzheimer's Disease

“…The ACE activity was increased in AD (Savaskan et al ., 2001; Miners et al ., 2008c, 2010b). The levels of ECE-1 (Wang et al ., 2009a), ECE-2 (Palmer et al ., 2009), MMP-2 (Yan et al ., 2006), MMP-3, MMP-9 (Bruno et al ., 2009) and ACE-2 were reported to increase in AD, but other studies showed no alterations in those of MMP-2, MMP-3, and MMP-9 (Baig et al ., 2008). Similarly, ADE activity was also found to be increased in the cortex of aged Tg2576 mice (Deb et al ., 1999; Tucker et al ., 2000; Leal et al ., 2006; Palmer et al ., 2009).…”

“…This hypothesis is supported by other in vitro and in vivo results; the induction of NEP in AD Tg mouse brain after injection of Aβ 1-42 (Mohajeri et al ., 2002) in a dose-dependent manner. Similarly, the activity of ADE including GCPII is increased in cells treated with aggregated Aβ (Deb et al ., 1999; Lee et al ., 2003; Jung et al ., 2003; Leal et al ., 2006; Mueller-Steiner et al ., 2006; Wang et al ., 2009a, 2009b; Palmer et al ., 2009; Miners et al ., 2010b). Taken together, these findings argue strongly against a notion that deficit of ADE is associated with AD.…”