Curcumin Inhibits The Inflammatory Response Via CPG Demethylation Of The Promoter And Restoration Of Nep In The Cellular Model Of Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common dementia. Excessive and dysregulated inflammation induced by amyloid β-peptide (Aβ) contributes to the initiation and progression of AD. Neprilysin (NEP, EP24.11), a zinc-dependent metallopeptidase, has been characterized as capable of degradation of Aβ in AD. Increasing evidence also indicates an important function of its inhibition in AKT activation. However, NEP decreases in AD brains. It is demonstrated that hypermethylation of CpG islands within NEP gene is an important mechanism to inactive NEP expression. With anti-inflammatory and anti-oxidative properties, Curcumin (CUR) is a concerned natural compound. Accumulating evidence indicates that CUR also possesses inhibitory effects on DNA methyltransferases (DNMTs) with low concentration. To date, little is known about the role of CUR in the CpG methylation of potential genes in AD and whether this hypomethylating activity of CUR is associated with its role of anti-inflammation. In the present research, we used wild-type mouse neuroblastoma N2a cells (N2a/wt) and N2a cells stably expressing Swedish mutant human amyloid precursor protein (APP) (N2a/APPswe) as cell models. Bisulfite-sequencing PCR (BSP) assay was used to detecte the methylation status of NEP gene promoter regions. The mRNA level of NEP was tested by Q-PCR, the protein level of NEP was determined by Western blot and the distribution of NEP was tested by Immunocytochemistry Staining. After blocking NEP by Thiorphan, Western blot and Immunocytochemistry Staining were used to detecte the activation of AKT/NF-κB signaling and its downstream gene expression. Results:①5μM of CUR induces restoration of NEP.②5μM of CUR reverses hypermethylated CpG Sites of NEP Gene. ③NEP inhibitor Thiorphan preventes CUR-induced inactivation of AKT and NF-κB.④5μM of CUR leads to a decrease in COX-2 and iNOS levels in a time-dependent manner. This study reveals that CUR inhibits the AKT/NF-κB Signaling via inducing CpG demethylation of the promoter and restoration of NEP in the AD cellular model. Our findings illuminate the involvement of DNA methylation in the anti-inflammatory effects of CUR in AD and provide a new basis for potential NEP-based epigenetic modifying therapeutic intervention in AD.