Oxidative damage and the Nrf2-ARE pathway in neurodegenerative diseases

Oxidative damage contributes to pathogenesis in many neurodegenerative diseases. As the indicator and regulator of oxidative stress, the Nrf2-ARE pathway has been shown dynamic changes and examined for its neuroprotective role in many cases. In this review, we summarize the progress of the Nrf2-ARE pathway in combating toxicity induced from typical misfolded protein aggregates in neurodegenerative diseases, and specifically the effects on the clearance of protein aggregates. This article is part of a Special Issue entitled: Misfolded Proteins, Mitochondrial Dysfunction, and Neurodegenerative Diseases.     

Biogenic nanoselenium particles activate Nrf2-ARE pathway by phosphorylating p38, ERK1/2, and AKT on IPEC-J2 cells

As the intestinal epithelium is vulnerable to oxidative stress because of frequent enterocyte renewal and continuous exposure to exogenous agents, it is meaningful to figure out how the epithelial cells exert antioxidant function. We previously synthesized a novel biogenic nanoselenium (BNS) particles and proved that BNS could effectively improve intestinal antioxidative function through activating Nrf2-ARE pathway. The objective of the present study was to investigate the mechanism by which BNS activate Nrf2-ARE pathway on the physiological function of intestinal epithelial cells. In the present study, we demonstrated that treatment of IPEC-J2 cells with BNS particles not only elevated the levels of downstream proteins of nuclear factor (erythroid-derived-2)-like 2 (Nrf2) such as heme oxygenase-1 and NQO-1 in a time-dependent manner which started to weaken at 12 hr after treatment but also significantly activated Nrf2, mitogen-activated protein kinase (MAPK), and protein kinase B (AKT) pathway in a time-dependent manner within 24 hr. BNS particles significantly increased the content of phosphorylated-Nrf2, without evident influence on the level of Kelch-like ECH-associated protein 1 (Keap1). Moreover, BNS also induced the activation of p38, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase, and AKT while phosphorylating Nrf2. Using specific protein kinase inhibitors, we found that the Nrf2-phosphorylating and antioxidative effects of BNS particles were abolished when p38, ERK1/2, and AKT were significantly inhibited. Overall, our data demonstrated that BNS particles activated Nrf2-ARE pathway through p38, ERK1/2, and AKT mediated-phosphorylation of Nrf2 to improve the antioxidant function of intestinal epithelial cells     

The effect of resveratrol and its methylthio-derivatives on the Nrf2-ARE pathway in mouse epidermis and HaCaT keratinocytes

Resveratrol is the most extensively studied stilbene derivative. We previously showed that methylthiostilbenes were more effective inhibitors of CYP1A1 and 1B1 activity than resveratrol. In this study, we investigated whether resveratrol and its methylthio-substituted derivatives, i.e. 3-M-4′-MTS (S2), 3,5-DM-4′-MTS (S5) and 3,4,5-TM-4′-MTS (S7) could activate Nrf2 signaling in the mouse epidermis and in human keratinocytes. Western blot analysis showed translocation of Nrf2 from the cytosol to the nucleus in both models. All of the tested stilbenes increased GST activity, but resveratrol was the most effective inducer. Moreover, only resveratrol increased the protein level of GSTP in the mouse epidermis. GSTM was enhanced in HaCaT cells after the treatment with derivatives S2 and S5. The same effect was observed for GSTP in the case of compound S2. Resveratrol and its derivatives reduced the NQO2 protein level in HaCaT cells. Thus, it is possible that increased expression of GSTP or GSTM and GST activity was linked with NQO2 inhibition in these cells. The results of this study indicate that resveratrol and its methylthioderivatives activate Nrf2 not only in the mouse epidermis, but also in human keratinocytes. Upregulating GST isozymes might be particularly important for deactivating chemical carcinogens, such as PAH.     

Nrf2-ARE信号通路在神经退行性疾病中的作用研究进展

神经退行性疾病(Neurodegenerative disease)是一类以神经元退行性病变为基础的慢性、进行性、不可逆的神经系统疾病的总称,主要包括阿尔茨海默病(Alzheimer's disease,AD)、帕金森病(Parkinson's disease,PD)、亨廷顿舞蹈病(Huntington disease,HD)、肌萎缩侧索硬化症(amyotrophic lateral sclerosis,ALS)、脊髓肌萎缩症(spinal muscular atrophy,SMA)、不同类型脊髓小脑共济失调(spinal cerebella ataxias,SCA)等。其病因和发病机制十分复杂,其中,氧化应激学说近年来受到了人们的广泛关注和普遍认可。而研究表明,Nrf2-ARE信号通路是体内抗氧化应答机制中最重要的通路之一,其能对氧化应激导致的神经细胞损伤产生保护作用,即阻止神经细胞的病变和凋亡,进而延缓神经退行性疾病的发生发展,因而有望成为神经退行性疾病的有效治疗靶标。本文就Nrf2-ARE信号通路结构特点及Nrf2-ARE信号通路在神经退行性疾病中的作用研究进展作一综述。     

Methylseleninic acid activates Keap1/Nrf2 pathway via up-regulating miR-200a in human oesophageal squamous cell carcinoma cells

Oesophageal squamous cell carcinoma (ESCC) occurs at a very high rates in certain regions of China. There are increasing evidences demonstrating that selenium could act as a potential anti-oesophageal cancer agent, but the precise mechanisms involved are still not completely understood. Methylseleninic acid (MSA), as a potent second-generation selenium compound, is a promising chemopreventive agent. Previous studies demonstrated that the kelch-like ECH-associated protein 1 (Keap1)/nuclear factor E2-related factor 2 (Nrf2) system plays a critical role in cancer prevention, but little is known about its association with MSA in ESCC cells. In the present study, we observed that MSA treatment significantly down-regulated Keap1, induced nuclear accumulation of Nrf2 and enhance the antioxidant response element (ARE) promoter activity in ESCC cells. MSA could also significantly induce miR-200a expression and inhibit Keap1 directly. Antagomir-200a could attenuate MSA treatment-induced Keap1 down-regulation in ESCC cells. Moreover, MSA-induced miR-200a expression was dependent on the mediation of Krüpple-like factor 4 (KLF4). These results reaffirm the potential role of MSA as a chemopreventive agent via the regulation of KLF4/miR-200a/Keap1/Nrf2 axis in ESCC cells.     

Igalan induces detoxifying enzymes mediated by the Nrf2 pathway in HepG2 cells

Igalan is one of the sesquiterpene lactones found in Inula helenium L., which is used as the traditional medicine to treat inflammatory diseases. However, the pharmacological effects of igalan have not been characterized. In this study, we isolated igalan from I. helenium L. and evaluated the effects of igalan on signaling pathways and expression of target genes in HepG2 cells. Igalan activated the nuclear factor erythroid 2‐related factor 2 (Nrf2) pathway by increasing the inactive form of GSK3β, the phosphorylated form of AKT, and the nuclear accumulation of Nrf2. Thus, target genes of Nrf2 such as HO‐1 and NQO1 increased in HepG2 cells. Moreover, igalan inhibited the tumor necrosis factor‐α (TNF‐α)‐induced nuclear factor‐κB activation and suppressed the expression of its target genes, including TNF‐α, interleukin (IL)‐6, and IL‐8 in HepG2 cells. Our results indicate the potential of igalan as an activator of cellular defense mechanisms and a detoxifying agent.     

Testosterone modulates K(+)ATP channels in Sertoli cell membrane via the PLC-PIP2 pathway.

Testosterone at physiological intratesticular concentrations induces a dose-dependent depolarisation and an increase in input resistance together with an increment of 45Ca2+ uptake in the Sertoli cells from seminiferous tubules of immature rat. Previous studies have implicated K(+)ATP channels in these testosterone actions. This study demonstrates that testosterone and sulphonylureas (glibenclamide and tolbutamide) depolarise the membrane potential, augment resistance and 45Ca2+ uptake in the Sertoli cells of seminiferous tubules from 10-15 day-old rats. These actions were nullified by the presence of the K(+)ATP channel opener diazoxide. The depolarisation was also observed with the impermeant bovine serum albumin-bound testosterone. Testosterone actions were blocked by both pertussis toxin and the phospholipase C (PLC) inhibitor U73122 implying the involvement of PLC - phosphatidylinositol 4-5 bisphosphate (PIP2) hydrolysis via G protein in testosterone actions. Polycations, including spermine and LaCl3, depolarised the membrane potential and increased the resistance. Hyperpolarisation caused by EGTA was reversed by LaCl3 and by the presence of testosterone. This last effect was nullified by the presence of U73122. All of the above results indicate that the action of testosterone on the Sertoli cell membrane is exercised on the K(+)ATP channels through PLC-PIP2 hydrolysis that closes the channel, depolarises the membrane, and stimulates 45Ca2+ uptake.     

Cholesterol modulates PAF-stimulated Ca2(+)-mobilization in monocytic U937 cells

We investigated the effect of cellular cholesterol content on platelet activating factor (PAF)-stimulated Ca2+ mobilization in the human monocytic cell line U937. When cholesterol auxotroph U937 cells were depleted of cellular cholesterol by a 48-h incubation in delipidated medium, a 40% reduction in the PAF (100 nM)-stimulated increase in cytosolic Ca2+ concentration was seen. Ca2+ mobilization following stimulation with LTD4 (10 nM) or ATP (10 microM) was not affected. Addition of LDL (100 micrograms/ml, 24 h) to the delipidated medium completely recovered cellular cholesterol content and PAF-induced Ca2+ mobilization. These two LDL effects had very similar time- and dose-dependences. Partial recoveries of PAF-induced Ca2+ mobilization, seen after addition of pure cholesterol dissolved in ethanol (30 micrograms/ml, 24 h) or acetyl-LDL (100 micrograms/ml, 24 h), were associated with partial recoveries of cellular cholesterol content. Our results indicate that cellular cholesterol influences PAF-stimulated events in monocytic cells.     

Enhancement of dopaminergic activity and region-specific activation of Nrf2-ARE pathway by intranasal supplements of testosterone propionate in aged male rats

The potential influence of intranasal testosterone propionate (InTP) supplements on mesodopaminergic system in aged male rats was investigated by analyzing the exploratory and motor behaviors as well as dopamine neurobiochemical indices. Meanwhile, oxidative stress parameters and pathway of nuclear factor erythroid 2-related factor 2 (Nrf2)-binding antioxidant response elements (Nrf2-ARE) were examined to check whether the Nrf2-ARE pathway was involved in the InTP-induced alteration of mesodopaminergic system in aged male rats. The exploratory and motor behavioral deficits, as well as the reduced expression of dopamine, tyrosine hydroxylase, and dopamine transporter, which indicated the declined activity of mesodopaminergic system, were ameliorated in rats administered with 12-week InTP. The results indicated that chronic InTP supplements could effectively influence the brain function activity in a way opposite to the effect of aging on the mesodopaminergic system of rats. The increased levels of Nrf2, heme oxygenase-1, and NAD(P)H:quinone oxidoreductase-1 in the substantia nigra and ventral tegmental area, but not in the hippocampus of InTP-administered aged male rats, indicated that the ameliorative effect of InTP supplements on mesodopaminergic system might be related to the region-specific activation of the Nrf2-ARE pathway.