Curcumin Inhibits the AKT/NF-κB Signaling via CpG Demethylation of the Promoter and Restoration of NEP in the N2a Cell Line

Abstract

Abstract. Curcumin (CUR), a non-toxic polyphenol from Curcuma longa, has been investigated as a potential therapy with anti-inflammatory and anti-oxidative effects for Alzheimer's disease (AD), which depicts features of chronic inflammatory environment resulting in cellular death. However, it remains largely unknown whether the anti-inflammatory effect of CUR in AD is associated with its property of CpG demethylation, which is another function of CUR with the most research interest during recent years. Neprilysin (NEP, EP24.11), a zinc-dependent metallopeptidase expressed relatively low in the brain, is emerging as a potent inhibitor of AKT/Protein Kinase B. In addition, hypermethylated promoter of NEP has been reported to be associated with decreases in NEP expression. In the present study, using bisulfite-sequencing PCR (BSP) assay, we showed that the CpG sites in NEP gene were hypermethylated both in wild-type mouse neuroblastoma N2a cells (N2a/wt) and N2a cells stably expressing human Swedish mutant amyloid precursor protein (APP) (N2a/APPswe) associated with familial early onset AD. CUR treatment induced restoration of NEP gene via CpG demethylation. This CUR-mediated upregulation of NEP expression was also concomitant with the inhibition of AKT, subsequent suppression of nuclear transcription factor-κB (NF-κB) and its downstream pro-inflammatory targets including COX-2, iNOS in N2a/APPswe cells. This study represents the first evidence on a link between CpG demethylation effect on NEP and anti-inflammation ability of CUR that may provide a novel mechanistic insight into the anti-inflammatory actions of CUR as well as new basis for using CUR as a therapeutic intervention for AD.

Protective Effects of Indian Spice Curcumin Against Amyloid-β in Alzheimer’s Disease

“…Deng and colleagues (2014) [85] using bisulfite-sequencing PCR (BSP) assay, they demonstrated that the CpG sites in NEP gene were hypermethylated both in wild-type mouse neuroblastoma N2a cells (N2a/wt) and N2a cells stably expressing human Swedish mutant amyloid precursor protein (N2a/APPswe) associated with familial early onset AD. CUR treatment induced restoration of NEP gene via CpG demethylation.…”

“…This CUR-mediated upregulation of NEP expression was also concomitant with the inhibition of AKT, subsequent suppression of nuclear transcription factor-κβ (NF-κβ) and its downstream pro-inflammatory targets including COX-2, iNOS in N2a/APPswe cells. This study represents the first evidence on a link between CpG demethylation effect on NEP and anti-inflammation ability of CUR that may provide a novel mechanistic insight into the anti-inflammatory actions of CUR as well as new basis for using CUR as a therapeutic intervention for AD [85]. …”

“Curcumin, the King of Spices”: Epigenetic Regulatory Mechanisms in the Prevention of Cancer, Neurological, and Inflammatory Diseases

“…One study showed that curcumin treatment induced the reactivation of the NEP gene via CpG demethylation. In curcumin-treated N2a/APPswe cells, the upregulation of NEP expression was also concomitant with AKT inhibition and the subsequent suppression of NF-κB and its downstream proinflammatory targets, including COX-2 and iNOS [38], Furthermore, the Fanconi anemia (FA) complementation group F (FANCF) gene plays an important role in the FA pathway and is frequently inactivated due to promoter hypermethylation in specific types of cancer [39]. Curcumin treatment produces a 5-fold increase in FANCF gene expression due to the demethylation of 12 of the 15 CpGs present in the promoter region [40].…”

Amyloid-clearing proteins and their epigenetic regulation as a therapeutic target in Alzheimer’s disease

“…(Melzig and Janka, 2003; Ayoub and Melzig, 2006; Kiss et al, 2006; Deng et al, 2014; Fujiwara et al, 2014). Green tea catechins were shown to be preventive in AD animal models via up-regulation of NEP (Lim et al, 2013).…”