Mercury Reduces the Enzymatic Activity of Neprilysin in Differentiated SH-SY5Y Cells

Abstract

Levels of amyloid beta (Aβ) in the central nervous system are regulated by the balance between its synthesis and degradation. Neprilysin (NEP) is associated with Alzheimer's disease (AD) by its ability to degrade Aβ. Some studies have involved the exposure to mercury (Hg) in AD pathogenesis; therefore, our aim was to investigate the effects on the anabolism and catabolism of Aβ in differentiated SH-SY5Y cells incubated with 1-20 μM of Hg. Exposure to 20 µM of Hg induced an increase in Aβ-42 secretion, but did not increase the expression of the amyloid precursor protein (APP). Hg incubation (10 and 20 µM) increased NEP protein levels; however, it did not change NEP mRNA levels nor the levels of the amyloid intracellular domain peptide, a protein fragment with transcriptional activity. Interestingly, Hg reduced NEP activity at 10 and 20 µM, and circular dichroism analysis using human recombinant NEP showed conformational changes after incubation with molar equivalents of Hg. This suggests that the Hg-induced inhibition of NEP activity may be mediated by a conformational change resulting in reduced Aβ-42 degradation. Finally, the comparative effects of lead (Pb, 50 μM) were evaluated. We found a significant increase in Aβ-42 levels and a dramatic increase in APP protein levels; however, no alteration in NEP levels was observed nor in the enzymatic activity of this metalloprotease, despite the fact that Pb slightly modified the rhNEP conformation. Overall, our data suggest that Hg and Pb increase Aβ levels by different mechanisms.

Environmental pollutants as risk factors for neurodegenerative disorders: Alzheimer and Parkinson diseases

“…Another study performed in differentiated SH-SY5Y cells showed an increase in Aβ secretion and APP expression, as well as reduced expression and protein levels of NEP (an Aβ IDE), suggesting that Pb can target both the synthesis and degradation of Aβ (Huang et al, 2011 ). However, in a recent work conducted in our laboratory, Pb did not show changes in NEP expression in differentiated SH-SY5Y cells exposed to 50 µM Pb, but an increase in APP levels (Chin-Chan et al, 2015 ). Another mechanism by which Pb increases Aβ levels is by reducing the brain Aβ clearance.…”

“…Rat pheochromocytoma (PC12) cells exposed to both inorganic and organic (MeHg) Hg (10–1000 nM) also showed a dose-dependent overproduction of Aβ-40 probably by an increase in APP levels as well as to a reduction in Aβ degradation by NEP (Song and Choi, 2013 ). However, an increase in Aβ-42 levels was observed in differentiated SH-SY5Y cells exposed to Hg (10 and 20 µM) but not in the APP expression, and rather a reduced activity of the Aβ-degrading enzyme, NEP was observed (Chin-Chan et al, 2015 ). Negative effects of Hg on Aβ aggregation have also been published, for example, Atwood et al ( 1998 ) studied the role of the pH and the ability of various metals to aggregate Aβ; Zn, Cu and Fe showed the highest potential on Aβ aggregation, and Hg did not show an important effect (Atwood et al, 1998 ).…”

Fungicide Residues Exposure and β-amyloid Aggregation in a Mouse Model of Alzheimer’s Disease

“…This suggests a potential role of heavy metals in Alzheimer's disease, but it is not yet clear whether they interfere in the development or the progression of the disease. However, experimental studies have showed that incubation of SH-SY5Y cells with lead (5 to 100 lM) can induce an increase of APP expression and Ab peptides secretion, associated with a decreased NEP expression (Chin-Chan et al 2015;Huang et al 2011). Furthermore, an acute injection of lead [27 mg=kg via the intraperitoneal (ip) route] in a mouse model of Alzheimer's disease (APP V717F) has resulted in a lower expression of LRP1 in the choroid plexus than injection of vehicle (Gu et al 2011).…”

“…Furthermore, an acute injection of lead [27 mg=kg via the intraperitoneal (ip) route] in a mouse model of Alzheimer's disease (APP V717F) has resulted in a lower expression of LRP1 in the choroid plexus than injection of vehicle (Gu et al 2011). Mercury was shown to be involved in the disruption of Ab peptide clearance pathways both in vivo [in rats: 2 mg=kg per day for 4 weeks by gavage (Kim et al 2014)] and in vitro [in SH-SY5Y cells: 10 and 20 lM (Chin-Chan et al 2015)]. Moreover, rats orally treated with aluminum (20 g=d, twice a week) through diet, from 6 months of age until the end of their life and who developed cognitive deficits, presented an epidemiological standpoint, it is difficult to assess the impact of a long-term exposure to pesticide residues on neurodegenerative diseases such as Alzheimer's disease.…”

Heavy Metal-Induced Inhibition of Enzymatic Activity in Hen Egg White Lysozyme

“…Toxic heavy metals including copper (Cu), zinc (Zn), iron (Fe), aluminum (Al), cadmium (Cd), lead (Pb), and mercury (Hg) have been associated to degenerative diseases such as Alzheimer's disease [42,43], and some of these metals have the ability to aggregate amyloid beta peptide in vitro [44]. Chin-Chan et al (2015) [45] reported a reduction of enzymatic activity of neprilysin, a metalloprotease involved in Alzheimer's disease. A decrease of antioxidants and catalase (CAT) enzyme in thalassemic patients leads to an increased hydrogen peroxide, resulting in lipid peroxidation in β-thalassemic patients [46].…”