Mei-Hua Li

Role of Nrf2-mediated heme oxygenase-1 upregulation in adaptive survival response to nitrosative stress

Nitrosative stress caused by reactive nitrogen species such as nitric oxide and peroxynitrite overproduced during inflammation leads to cell death and has been implicated in the pathogenesis of many human ailments. However, relatively mild nitrosative stress may fortify cellular defense capacities, rendering cells tolerant or adaptive to ongoing and subsequent cytotoxic challenges, a phenomenon known as ‘preconditioning’ or ‘hormesis’. One of the key components of cellular stress response is heme oxygenase-1 (HO-1), the rate limiting enzyme in the process of degrading potentially toxic free heme into biliverdin, free iron and carbon monoxide. HO-1 is upregulated by a wide array of stimuli and has antioxidant, anti-inflammatory and other cytoprotective functions. This review is intended to provide readers with a welldocumented account of the research done in the area of cellular adaptive survival response against nitrosative stress with special focus on the role of HO-1 upregulation, especially through activation of the transcription factor, Nrf2.

15-Deoxy-Δ12,14-prostaglandin J2 rescues PC12 cells from H2O2-induced apoptosis through Nrf2-mediated upregulation of heme oxygenase-1: Potential roles of Akt and ERK1/2

Oxidative stress induced by reactive oxygen intermediates has been implicated in a variety of human diseases including rheumatoid arthritis and neurodegenerative disorders. 15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), a terminal dehydration product of prostaglandin D(2), is an endogenous ligand of peroxisome proliferator-activated receptor-gamma and exhibits a number of biological activities including the proapoptotic activity. Recent studies have revealed that this cyclopentenone prostaglandin, at non-toxic concentrations, can also exert antiapoptotic or cytoprotective effects. In this study, the underlying mechanisms involved in the protective effects of 15d-PGJ(2) on the H2O2-induced cytotoxicty were explored using cultured rat pheochromocytoma (PC12) cells. PC12 cells treated with H2O2 underwent apoptosis, which was attenuated by pretreatment with non-toxic concentrations of 15d-PGJ(2). Treatment of the PC12 cells with 15d-PGJ(2) resulted in increased nuclear translocation, DNA-binding and transcriptional activity of NF-E2-related factor 2 (Nrf2), leading to upregulation of heme oxygenase-1 (HO-1) expression, which provided an adaptive survival response against the H2O2-derived oxidative cytotoxicity. Transfection of PC12 cells with dominant-negative Nrf2 gene abolished the 15d-PGJ(2)-derived induction of HO-1 expression. Moreover, the 15d-PGJ(2)-mediated increases in Nrf2-ARE binding and ARE luciferase activity were suppressed by the dominant-negative mutation as well as the pharmacological inhibition of Akt/protein kinase B or extracellular signal-regulated kinase 1/2 (ERK1/2). Taken together, these findings suggest that 15d-PGJ(2) augments cellular antioxidant defense capacity through activation of Akt and ERK signal pathways that leads to Nrf2 activation, and subsequently HO-1 induction, thereby protecting the PC12 cells from H2O2-induced oxidative cell death.

Carbon Monoxide Produced by Heme Oxygenase-1 in Response to Nitrosative Stress Induces Expression of Glutamate-Cysteine Ligase in PC12 Cells via Activation of Phosphatidylinositol 3-Kinase and Nrf2 Signaling

Induction of heme oxygenase-1 (HO-1) expression has been associated with adaptive cytoprotection against a wide array of toxic insults, but the underlying molecular mechanisms remain largely unresolved. In this study, we investigated the potential role of carbon monoxide (CO), one of the by-products of the HO-1 reaction, in the adaptive survival response to peroxynitrite-induced PC12 cell death. Upon treatment of rat pheochromocytoma (PC12) cells with the peroxynitrite generator 3-morpholinosydnonimine hydrochloride (SIN-1), the cellular GSH level decreased initially, but was gradually restored to the basal level. This was accompanied by increased expression of the catalytic subunit of glutamate-cysteine ligase (GCLC), the rate-limiting enzyme in GSH biosynthesis. The SIN-1-induced GCLC up-regulation was preceded by induction of HO-1 and subsequent CO production. Inhibition of HO activity by zinc protoporphyrin IX or knockdown of HO-1 gene expression by small interfering RNA abrogated the up-regulation of GCLC expression and the subsequent GSH restoration induced by SIN-1. In contrast, additional exposure to the CO-releasing molecule (CO-RM) restored the GSH level previously reduced by inhibition of CO production using zinc protoporphyrin IX. Furthermore, CO-RM treatment up-regulated GCLC expression through activation of Nrf2. The CO-RM-induced activation of Nrf2 was under the control of the phosphatidylinositol 3-kinase/Akt signaling pathway. In conclusion, CO produced by HO-1 rescues PC12 cells from nitrosative stress through induction of GCLC, which is mediated by activation of phosphatidylinositol 3-kinase/Akt and subsequently Nrf2 signaling.

Protective Effects of Oligomers of Grape Seed Polyphenols Against β-Amyloid-Induced Oxidative Cell Death

Abstract: β‐Amyloid (Aβ) is considered to be responsible for the formation of senile plaques that accumulate in the brains of patients with Alzheimers disease (AD). There is compelling evidence supporting the notion that Aβ‐induced cytotoxicity is mediated through the generation of reactive oxygen species (ROS). Recently, considerable attention has been focused on a wide array of non‐vitamin antioxidants present in edible plants that are able to scavenge ROS, thereby protecting against oxidative damage. In this study, we have investigated the possible protective effects of formulated polyphenol oligomers (Oligonol) derived from grape seed extracts on Aβ‐induced oxidative cell death. Rat pheochromocytoma (PC12) cells treated with Aβ exhibited increased accumulation of intracellular ROS and underwent apoptosis, as determined by positive in situ terminal end labeling, decreased mitochondrial membrane potential, and the cleavage of poly(ADP‐ribose)polymerase. Oligonal attenuated Aβ‐induced cytotoxicity, apoptotic features, intracellular ROS accumulation, and lipid peroxidation and increased the cellular glutathione pool. Moreover, Aβ transiently induced the activation of nuclear factor κB in PC12 cells, which was suppressed by pretreatment with Oligonol.

Nrf2-Mediated heme oxygenase-1 upregulation as adaptive survival response to glucose deprivation-induced apoptosis in HepG2 cells.

Induction of heme oxygenase-1 (HO-1) represents an important cellular adaptive survival response to oxidative stress and other toxic insults. In the present study, HepG2 cells grown in glucose-free media underwent apoptotic cell death, but they exhibited elevated expression of HO-1 before apoptosis manifested. Treatment of HepG2 cells with SnCl₂, a HO-1 inducer, rescued these cells from glucose deprivation-induced apoptosis, while inhibition of the HO activity with zinc protoporphyrin IX exacerbated apoptosis under the same condition. HepG2 cells transfected with a dominant negative Nrf2 were more vulnerable to glucose deprivation-induced apoptosis compared to cells transfected with empty vector alone. To confirm the involvement of Nrf2 in the induction of HO-1 caused by glucose deprivation, we used embryonic fibroblasts prepared from nrf2⁻(/)⁻, nrf2(+/)⁻, and nrf2(+/+) embryos. Compared to the wild-type and the nrf2(+/)⁻ embryonic fibroblasts, nrf2⁻(/)⁻ cells were less prone to induce HO-1 expression upon glucose deprivation. Exposure of HepG2 cells to glucose-deprived media resulted in an elevated accumulation of reactive oxygen species (ROS). Pretreatment with N-acetylcysteine prevented the glucose deprivation-induced ROS accumulation and also the HO-1 expression. In conclusion, the Nrf2-mediated HO-1 upregulation upon glucose deprivation is mediated by ROS in HepG2 cells, and responsible for the adaptive survival response.