Salvianolic acid A protects RPE cells against oxidative stress through activation of Nrf2/HO-1 signaling

Reactive oxygen species (ROS) impair the physiological functions of retinal pigment epithelial (RPE) cells, which is known as one major cause of age-related macular degeneration. Salvianolic acid A (Sal A) is the main effective aqueous extract of Salvia miltiorrhiza. The aim of this study was to test the potential role of Sal A against oxidative stress in cultured RPE cells and to investigate the underlying mechanistic signaling pathways. We observed that Sal A significantly inhibited hydrogen peroxide (H₂O₂)-induced primary and transformed RPE cell death and apoptosis. H₂O₂-stimulated mitogen-activated protein kinase activation, ROS production, and subsequent proapoptotic AMP-activated protein kinase activation were largely inhibited by Sal A. Further, Sal A stimulation resulted in a fast and dramatic activation of Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling, followed by phosphorylation, accumulation, and nuclear translocation of the NF-E2-related factor 2 (Nrf2), along with increased expression of the antioxidant-response element-dependent gene heme oxygenase-1 (HO-1). Both Nrf2 and HO-1 were required for Sal A-mediated cytoprotective effect, as Nrf2/HO-1 inhibition abolished Sal A-induced beneficial effects against H₂O₂. Meanwhile, the PI3K/Akt/mTORC1 chemical inhibitors not only suppressed Sal A-induced Nrf2/HO-1 activation, but also eliminated its cytoprotective effect in RPE cells. These observations suggest that Sal A activates the Nrf2/HO-1 axis in RPE cells and protects against oxidative stress via activation of Akt/mTORC1 signaling.     

Nrf2/HO-1/HMGB1信号通路在白血病细胞K562/A02化疗耐药中的机制研究

目的:通过观察高迁移率族蛋白1(HMGB1)、转录因子NF-E2相关因子2(Nrf2)及血红素加氧酶1(HO-1)基因沉默对白血病化疗耐药细胞(K562/A02细胞株)的影响,探讨该信号通路在白血病化疗耐药中的作用及其可能机制。方法:将HMGB1基因、Nrf2基因及HO-1基因的特异性干扰RNA分别转染阿霉素耐药细胞株K562/A02,荧光实时定量(RT-PCR)方法检测HMGB1、Nrf2及HO-1的mRNA表达水平,Western blot方法检测HMGB1、Nrf2及HO-1的蛋白表达水平,免疫荧光方法检测Nrf2的蛋白表达,并使用CCK-8方法检测转染前后K562/A02细胞株的细胞活性。结果:HMGB1基因、Nrf2基因或HO-1基因沉默的K562/A02细胞活性皆显著低于对照组及空白组(P0.05),化疗敏感性恢复。结论:HMGB1高表达导致了白血病细胞株K562/A02对阿霉素的化疗耐药,Nrf2/HO-1信号通路参与了HMGB1诱导的K562/A02细胞的化疗耐药,其表达上调可恢复K562/A02细胞对阿霉素的敏感性。     

Eriodictyol inhibits high glucose-induced oxidative stress and inflammation in retinal ganglial cells

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes mellitus and is considered as a leading cause of blindness. Oxidative stress and inflammation are significant drivers for the development of DR. Eriodictyol, a flavonoid compound, was proved to possess anti-inflammatory, antioxidative, and antidiabetic activities. However, the role of eriodictyol in DR has not been unveiled. In the current study, we explored the protective effects of eriodictyol on high glucose (HG)-induced rat retinal ganglial cells (RGCs). The results suggested that eriodictyol improved cell viability of HG-induced rat RGC-5 cells in a dose-dependent manner. Eriodictyol reduced the reactive oxygen species production and increased the activities of superoxide dismutase, glutathione peroxidase and catalase in rat RGC-5 cells in response to HG stimulation. The production of proinflammatory cytokines including tumor necrosis factor alpha and interleukin-8 was diminished after eriodictyol treatment. Eriodictyol also suppressed cell apoptosis induced HG in rat RGC-5 cells. Furthermore, eriodictyol enhanced the nuclear translocation of nuclear factor erythroid-2 (E2)-related factor 2 (Nrf2) and elevated the expression of antioxidant enzyme heme-oxygenase-1 (HO-1). These findings suggested that eriodictyol protects the RGC-5 cells from HG-induced oxidative stress, inflammation, and cell apoptosis through regulating the activation of Nrf2/HO-1 pathway.     

The role of Nrf2/HO-1 signal pathway in regulating aluminum-induced apoptosis of PC12 cells

BackgroundAluminum has definite neurotoxicity and can lead to apoptosis of nerve cells, but the specific mechanism remains to be further explored. The aim of this study was to investigate the role of Nrf2/HO-1 signaling pathway in neural cell apoptosis induced by aluminum exposure.MethodsIn this study, PC12 cells were used as the research object, aluminum maltol [Al(mal)₃] was used as the exposure agent, and tert-butyl hydroquinone (TBHQ), an agonist of Nrf2, was used as the intervention agent to construct an in vitro cell model. Cell viability was detected by CCK-8 method, cell morphology was observed by light microscope, cell apoptosis was measured by flow cytometry, and expression of Bax and Bcl-2 proteins and Nrf2/HO-1 signaling pathway proteins were investigated by western blotting.ResultsWith the increase of Al(mal)₃ concentration, PC12 cell viability decreased, the early apoptosis rate and total apoptosis rate increased, the ratio of Bcl-2 and Bax protein expression decreased, and Nrf2/HO-1 pathway protein expression decreased. The use of TBHQ could activate the Nrf2/HO-1 pathway and reverse the apoptosis of PC12 cells induced by aluminum exposure.ConclusionNrf2/HO-1 signaling pathway plays a neuroprotective role in the apoptosis of PC12 cells caused by Al(mal)₃, which provides a possible target for the intervention of aluminum induced neurotoxicity.     

Thymoquinone protects human retinal pigment epithelial cells against hydrogen peroxide induced oxidative stress and apoptosis

Oxidative stress in retinal pigment epithelium (RPE) cells may contribute to the progression of age-related macular degeneration. Thymoquinone (TQ), an active component derived from Nigella sativa, possesses antioxidative effect. However, the role of TQ in RPE cells under oxidative stress condition remains unclear. The present study aimed to examine the protective effect of TQ against hydrogen peroxide (H₂O₂)-induced oxidative stress in human RPE cells. Our results showed that TQ improved the cell viability and apoptosis in H₂O₂-induced ARPE cells. We also found that the levels of reactive oxygen species and malondialdehyde induced by H₂O₂ were reduced after the pretreatment of TQ. In addition, the inhibitory effect of H₂O₂ on the glutathione (GSH) level and superoxide dismutase activity was markedly attenuated by TQ pretreatment. Moreover, TQ enhanced the activation of Nrf2/heme oxygenase 1 (HO-1) signaling pathway in H₂O₂-induced ARPE cells. Knockdown of Nrf2 abolished the protective effect of TQ on H₂O₂-induced oxidative damage. These results suggested that TQ protected ARPE cells from H₂O₂-induced oxidative stress and apoptosis via the Nrf2/HO-1 signaling pathway.     

Novel protective mechanism of reducing renal cell damage in diabetes: Activation AMPK by AICAR increased NRF2/OGG1 proteins and reduced oxidative DNA damage

Exposure of renal cells to high glucose (HG) during diabetes has been recently proposed to be involved in renal injury. In the present study, we investigated a potential mechanism by which AICAR treatment regulates the DNA repair enzyme, 8-oxoG-DNA glycosylase (OGG1) in renal proximal tubular mouse cells exposed to HG and in kidney of db/db mice. Cells treated with HG for 2 days show inhibition in OGG1 promoter activity as well as OGG1 and Nrf2 protein expression. In addition, activation of AMPK by AICAR resulted in an increase raptor phosphorylation at Ser⁷⁹² and leads to increase the promoter activity of OGG1 through upregulation of Nrf2. Downregulation of AMPK by DN-AMPK and raptor and Nrf2 by siRNA resulted in significant decease in promoter activity and protein expression of OGG1. On the other hand, downregulation of Akt by DN-Akt and rictor by siRNA resulted in significant increase in promoter activity and protein expression of Nrf2 and OGG1. Moreover, gel shift analysis shows reduction of Nrf2 binding to OGG1 promoter in cells treated with HG while cells treated with AICAR reversed the effect of HG. Furthermore, db/db mice treated with AICAR show significant increased in AMPK and raptor phosphroylation as well as OGG1 and Nrf2 protein expression that associated with significant decrease in oxidative DNA damage (8-oxodG) compared to non-treated mice. In summary, our data provide a novel protective mechanism by which AICAR prevents renal cell damage in diabetes and the consequence complications of hyperglycemia with a specific focus on nephropathy.     

Activation of the UPR Protects against Cigarette Smoke-induced RPE Apoptosis through Up-Regulation of Nrf2

Recent studies have revealed a role of endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) in the regulation of RPE cell activity and survival. Herein, we examined the mechanisms by which the UPR modulates apoptotic signaling in human RPE cells challenged with cigarette smoking extract (CSE). Our results show that CSE exposure induced a dose- and time-dependent increase in ER stress markers, enhanced reactive oxygen species (ROS), mitochondrial fragmentation, and apoptosis of RPE cells. These changes were prevented by the anti-oxidant NAC or chemical chaperone TMAO, suggesting a close interaction between oxidative and ER stress in CSE-induced apoptosis. To decipher the role of the UPR, overexpression or down-regulation of XBP1 and CHOP genes was manipulated by adenovirus or siRNA. Overexpressing XBP1 protected against CSE-induced apoptosis by reducing CHOP, p-p38, and caspase-3 activation. In contrast, XBP1 knockdown sensitized the cells to CSE-induced apoptosis, which is likely through a CHOP-independent pathway. Surprisingly, knockdown of CHOP reduced p-eIF2α and Nrf2 resulting in a marked increase in caspase-3 activation and apoptosis. Furthermore, Nrf2 inhibition increased ER stress and exacerbated cell apoptosis, while Nrf2 overexpression reduced CHOP and protected RPE cells. Our data suggest that although CHOP may function as a pro-apoptotic gene during ER stress, it is also required for Nrf2 up-regulation and RPE cell survival. In addition, enhancing Nrf2 and XBP1 activity may help reduce oxidative and ER stress and protect RPE cells from cigarette smoke-induced damage.     

Activation of KGFR-Akt-mTOR-Nrf2 signaling protects human retinal pigment epithelium cells from Ultra-violet

Ultra-violet (UV) radiation causes oxidative injuries to human retinal pigment epithelium (RPE) cells. We tested the potential effect of keratinocyte growth factor (KGF) against the process. KGF receptor (KGFR) is expressed in ARPE-19?cells and primary human RPE cells. Pre-treatment with KGF inhibited UV-induced reactive oxygen species (ROS) production and RPE cell death. KGF activated nuclear-factor-E2-related factor 2 (Nrf2) signaling in RPE cells, causing Nrf2 Ser-40 phosphorylation, stabilization and nuclear translocation as well as expression of Nrf2-dependent genes (HO1, NOQ1 and GCLC). Nrf2 knockdown (by targeted shRNAs) or S40T mutation almost reversed KGF-induced RPE cell protection against UV. Further studies demonstrated that KGF activated KGFR-Akt-mTORC1 signaling to mediate downstream Nrf2 activation. KGFR shRNA or Akt-mTORC1 inhibition not only blocked KGF-induced Nrf2 Ser-40 phosphorylation and activation, but also nullified KGF-mediated RPE cell protection against UV. We conclude that KGF-KGFR activates Akt-mTORC1 downstream Nrf2 signaling to protect RPE cells from UV radiation.     

Ethyl pyruvate-mediated Nrf2 activation and hemeoxygenase 1 induction in astrocytes confer protective effects via autocrine and paracrine mechanisms

Ethyl pyruvate (EP), a simple ester of pyruvic acid, has been shown to act as an anti-inflammatory molecule under various pathological conditions, such as, during cerebral ischemia and sepsis in animal models. Here, the authors investigated the novel molecular mechanism underlying the anti-oxidative effect of EP in primary astrocyte cultures, particularly with respect to nuclear factor E2-related factor 2 (Nrf2) activation and hemeoxygenase 1 (HO-1) induction. EP was found to induce Nrf2 translocation and the inductions of various genes downstream of Nrf2 and these resulted in the amelioration of the oxidative damage of H(2)O(2). Furthermore, EP dose-dependently suppressed H(2)O(2)-induced astrocyte cell death (12h preincubation with 5mM EP increased cell survival after 1h exposure to 100 μM H(2)O(2) from 32.6±0.7% to 63±1.8%). HO-1 was markedly induced (4.9-fold) in EP-treated primary astrocyte cultures and Nrf2 was found to translocate from the cytosol to the nucleus and bind to the antioxidant response element (ARE) located on HO-1 promoter after EP treatment. siRNA-mediated HO-1 or Nrf2 knockdown and zinc protoporphyrin (ZnPP)-mediated inhibition of HO-1 activity showed that Nrf2 activation and HO-1 induction were responsible for the observed cytoprotective effect of EP, which was found to involve the ERK and Akt signaling pathways. Furthermore, EP-conditioned astrocyte culture media was found to have neuroprotective effects on primary neuronal cultures exposed to oxidative or excitotoxic stress, and this seemed to be mediated by glial cell line-derived neurotrophic factor (GDNF) and glutathione (GSH), which accumulated in EP-treated astrocyte culture media. Interestingly, we also found that in addition to HO-1, EP-induced Nrf2 activation increased the expressions of various anti-oxidant genes, including GST, NQO1, and GCLM. The study shows that EP-mediated Nrf2 activation and HO-1 induction in astrocytes act via autocrine and paracrine mechanisms to confer protective effects.     

LL202 ameliorates colitis against oxidative stress of macrophage by activation of the Nrf2/HO-1 pathway

LL202, a newly synthesized flavonoid derivative, has been confirmed to inhibit the mitogen-activated protein kinase pathway and activation protein-1 activation in monocytes; however, the anti-inflammatory mechanism has not been clearly studied. Uncontrolled overproduction of reactive oxygen species (ROS) has involved in oxidative damage of inflammatory bowel disease. In this study, we investigated that LL202 reduced lipopolysaccharide (LPS)-induced ROS production and malondialdehyde levels and increased superoxide dismutase, glutathione, and total antioxidant capacity in RAW264.7 cells. Mechanically, LL202 could upregulate heme oxygenase-1 (HO-1) via promoting nuclear translocation of nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) to regulate LPS-induced oxidative stress in macrophages. In vivo, we validated the role of LL202 in dextran sulfate sodium- and TNBS-induced colitis models, respectively. The results showed that LL202 decreased the proinflammatory cytokine expression and regulated colonic oxidative stress by activating the Nrf2/HO-1 pathway. In conclusion, our study showed that LL202 exerts an anti-inflammatory effect by enhancing the antioxidant capacity of the Nrf2/HO-1 pathway to macrophages.     

Heme oxygenase 1 regulates apoptosis induced by heat stress in bovine ovarian granulosa cells via the ERK1/2 pathway

Heat stress can inhibit follicular development in dairy cows, and thus can affect their reproductive performance. Follicular granulosa cells can synthesize estrogen, that affects the development and differentiation of follicles by apoptosis. Heme oxygenase 1 (HO-1/heat shock protein 32) plays an antiapoptotic and cytoprotective role in various cells during stress-induced apoptosis, but little is known about its definitive function in bovine (ovarian) granulosa cells (bGCs). In our study, the roles and mechanism of HO-1 on the heat stress-induced apoptosis of bGCs were studied. Our results show that the expression of HO-1 was significantly increased under heat stress. Moreover, HO-1 silencing increased apoptosis, whereas its overexpression dampened apoptosis by regulating the expression of Bax/Bcl-2 and the levels of cleaved caspase-3. In addition, HO-1 can also play a cytoprotective role by affecting estrogen levels and decomposing heme to produce biologically active metabolite carbon monoxide (CO). Meanwhile, CO significantly increased the level of HO-1, decreased Bax/Bcl-2 levels, and inhibited the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. The apoptosis of ovarian GCs can affect the secretion of estrogen and lead to disorder of the ovarian microenvironment, thus affecting the normal function of the ovary. Our results indicate that HO-1 acts as a cytoprotective enzyme and plays a protective role in heat-induced apoptosis of bGCs. In conclusion, HO-1 and its metabolite CO inhibit the apoptosis of bGCs induced by heat stress through the ERK1/2 pathway. The results of this study provide a valuable clue for improving the fertility of heat stressed cows in summer.