Curcumin is known to have neuroprotective properties in cerebral ischemia reperfusion (I/R) injury. However, the underlying molecular mechanisms remain largely unknown. Recently, emerging evidences suggested that increased mitochondrial biogenesis enabled preventing I/R injury. Here, we sought to determinate whether curcumin alleviates I/R damage through regulation of mitochondrial biogenesis. Sprague-Dawley rats were subjected to a 2-h period of right middle cerebral artery occlusion followed by 24 h of reperfusion. Prior to onset of occlusion, rats had been pretreated with either low (50 mg/kg, intraperitoneal injection) or high (100 mg/kg, intraperitoneal injection) dose of curcumin for 5 days. Consequently, we found that curcumin pretreatment enabled improving neurological deficit, diminishing infarct volume and increasing the number of NeuN-labeled neurons in the I/R rats. Accordingly, the index of mitochondrial biogenesis including nuclear respiratory factor-1, mitochondrial transcription factor A and mitochondrial number significantly down-regulated in I/R rats were reversed by curcumin pretreatment in a dose-dependent manner, and the mitochondrial uncoupling protein 2 presented the similar change. Taken together, our findings provided novel evidence that curcumin may exert neuroprotective effects by increasing mitochondrial biogenesis.

Epigenetic modifications, particularly histone acetylation, have been implicated in Alzheimer's disease (AD). While previous studies have suggested that histone hypoacetylation may regulate the expression of genes associated with memory and learning in AD, little is known about histone regulation of AD-related genes such as Presenilin 1(PS1) and beta-site amyloid precursor protein cleaving enzyme 1(BACE1). By utilizing neuroblastoma N2a cells transfected with Swedish mutated human amyloid precursor protein (APP) (N2a/APPswe) and wild-type APP (N2a/APPwt) as cellular models of AD, we examined the alterations of histone acetylation at the promoter regions of PS1 and BACE1 in these cells. Our results revealed that histone H3 acetylation in PS1 and BACE1 promoters is markedly increased in N2a/APPswe cells when compared to N2a/APPwt cells and control cells (vector-transfected), respectively, causing the elevated expression of PS1 and BACE1. In addition, expression of histone acetyltransferase (HAT) adenoviral E1A-associated 300-kDa protein (p300) is dramatically enhanced in N2a/APPswe cells compared to N2a/APPwt and control cells. We have further demonstrated the direct binding of p300 protein to the PS1 and BACE1 promoters in N2a/APPswe cells. The expression levels of H3 acetylation of the PS1 and BACE1 promoters and p300 protein, however, were found to be not significantly different in N2a/APPwt cells when compared to controls in our studies. Furthermore, curcumin, a natural selective inhibitor of p300 in HATs, significantly suppressed the expression of PS1 and BACE1 through inhibition of H3 acetylation in their promoter regions in N2a/APPswe cells. These findings indicated that histone acetyltransferase p300 plays a critical role in controlling the expression of AD-related genes through regulating the acetylation of their promoter regions, suggesting that p300 may represent a novel potential therapeutic target for AD.

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.

Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important transcription factor in the defense against oxidative stress. Cumulative evidence has shown that oxidative stress plays a key role in the pathogenesis of Alzheimer’s disease (AD). Previous animal and clinical studies had observed decreased expression of Nrf2 in AD. However, the underlying regulation mechanisms of Nrf2 in AD remain unclear. Here, we used the DNA methyltransferases (Dnmts) inhibitor 5-aza-2′-deoxycytidine (5-Aza) to test whether Nrf2 expression was regulated by methylation in N2a cells characterizing by expressing human Swedish mutant amyloid precursor protein (N2a/APPswe). We found 5-Aza treatment increased Nrf2 at both messenger RNA and protein levels via downregulating the expression of Dnmts and DNA demethylation. In addition, 5-Aza-mediated upregulation of Nrf2 expression was concomitant with increased nuclear translocation of Nrf2 and higher expression of Nrf2 downstream target gene NAD(P)H:quinone oxidoreductas (NQO1). Our study showed that DNA demethylation promoted the Nrf2 cell signaling pathway, which may enhance the antioxidant system against AD development.

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