NDRG4 prevents cerebral ischemia/reperfusion injury by inhibiting neuronal apoptosis

Cerebral ischemia is a major cause of mortality and long-term morbidity worldwide. NDRG4 has been shown to protect against cerebral ischemia, although the underlying mechanisms remain largely unclear. Here we found that NDRG4 expression was decreased in the brain tissues of ischemia/reperfusion (IR) rats, indicating increased apoptosis rates among cerebral cells. NDRG4 restoration via an adenovirus significantly attenuated cerebral infarct sizes and impairments in IR rats. Furthermore, adenovirus-mediated NDRG4 inhibited cell apoptosis in the brains of IR rats and regulated the expression of Bcl-2, Bax, caspase-3, and c-Fos. Moreover, we found that NDRG4 increased expression of BDNF, which is strongly related to cerebral ischemia and cellular apoptosis. Altogether, our findings demonstrate that NDRG4 protects cerebral IR injury by inhibiting cell apoptosis and regulates cerebral cell apoptosis by increasing BDNF expression. These results suggest that NDRG4 may be a therapeutic target for IR treatment.

The Sources of Reactive Oxygen Species and Its Possible Role in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra. The precise mechanism underlying pathogenesis of PD is not fully understood, but it has been widely accepted that excessive reactive oxygen species (ROS) are the key mediator of PD pathogenesis. The causative factors of PD such as gene mutation, neuroinflammation, and iron accumulation all could induce ROS generation, and the later would mediate the dopaminergic neuron death by causing oxidation protein, lipids, and other macromolecules in the cells. Obviously, it is of mechanistic and therapeutic significance to understand where ROS are derived and how ROS induce dopaminergic neuron damage. In the present review, we try to summarize and discuss the main source of ROS in PD and the key pathways through which ROS mediate DA neuron death.

4-Hydroxynonenal-induced GPR109A (HCA2 receptor) activation elicits bipolar responses, Gαi -mediated anti-inflammatory effects and Gβγ -mediated cell death

BACKGROUND AND PURPOSE

In this study, we examined the possibility that 4-hydroxynonenal (4-HNE) acting as a ligand for the HCA₂ receptor (GPR109A) elicits both anti-inflammatory and cell death responses.

EXPERIMENTAL APPROACH

Agonistic activity of 4-HNE was determined by observing the inhibition of cAMP generation in CHO-K1-GPR109A-G_i cell line, using surface plasmon resonance (SPR) binding and competition binding assays with [³ H]-niacin. 4-HNE-mediated signalling pathways and cellular responses were investigated in cells expressing GPR109A and those not expressing these receptors.

KEY RESULTS

Agonistic activity of 4-HNE was stronger than that of niacin or 3-OHBA at inhibiting forskolin-induced cAMP production and SPR binding affinity. In ARPE-19 and CCD-841 cells, activation of GPR109A by high concentrations of the agonists 4-HNE (≥10 μM), niacin (≥1000 μM) and 3-OHBA (≥1000 μM) induced apoptosis accompanied by elevated Ca²⁺ and superoxide levels. This 4-HNE-induced cell death was blocked by knockdown of GPR109A or NOX4 genes, or treatment with chemical inhibitors of G_βγ (gallein), intracellular Ca²⁺ (BAPTA-AM), NOX4 (VAS2870) and JNK (SP600125), but not by the cAMP analogue 8-CPT-cAMP. By contrast, low concentrations of 4-HNE, niacin and 3-OHBA down-regulated the expression of pro-inflammatory cytokines IL-6 and IL-8. These 4-HNE-induced inhibitory effects were blocked by a cAMP analogue but not by inhibitors of G_βγ -downstream signalling molecules.

CONCLUSIONS AND IMPLICATIONS

These results revealed that 4-HNE is a strong agonist for GPR109A that induces G_αi -dependent anti-inflammatory and G_βγ -dependent cell death responses. Moreover, the findings indicate that specific intracellular signalling molecules, but not GPR109A, can serve as therapeutic targets to block 4-HNE-induced cell death.

Mitochondrial dysfunction and oxidative stress in aging and cancer

Aging and cancer are the most important issues to research. The population in the world is growing older, and the incidence of cancer increases with age. There is no doubt about the linkage between aging and cancer. However, the molecular mechanisms underlying this association are still unknown. Several lines of evidence suggest that the oxidative stress as a cause and/or consequence of the mitochondrial dysfunction is one of the main drivers of these processes. Increasing ROS levels and products of the oxidative stress, which occur in aging and age-related disorders, were also found in cancer. This review focuses on the similarities between ageing-associated and cancer-associated oxidative stress and mitochondrial dysfunction as their common phenotype.

Pro-apoptotic effects of lipid oxidation products: HNE at the crossroads of NF-κB pathway and anti-apoptotic Bcl-2

The axis between lipid oxidation products and cell death is explicitly linked. 4-Hydroxynonenal (HNE), as well as other lipid oxidation products was also established to induce apoptosis in various experimental settings. Yet, the decision leading to apoptotic execution not only includes upregulation of pro-apoptotic signals but also involves a downregulation of anti-apoptotic signals. Within the frames of this paradigm, HNE acts significantly different from other lipid oxidation products in the regulation of two widely known anti-apoptotic elements, Nuclear Factor-κB (NF-κB) transcription factors and its target anti-apoptotic B-Cell Lymphoma-2 (Bcl-2) protein. Even so, a review inclusively linking these anti-apoptotic factors and their crosstalk upon HNE exposure is still at demand. In order to elucidate presence of such crosstalk, reports on the link between HNE and NF-κB pathway, on the link between HNE and anti-apoptotic Bcl-2 and on the crossroad of these links during HNE exposure were summarized and discussed. IKK, the upstream kinase of NF-κB, has been shown to regulate HNE mediated phosphorylation and inactivation of Bcl-2 by our group. Based on this observation and other studies reporting on HNE-NF-κB pathway interaction, IKK was proposed to mediate the crosstalk of NF-κB pathway and anti-apoptotic Bcl-2 protein, when HNE is present. These reports further suggested that HNE based inhibition of NF-κB pathway is highly likely. Besides, evidence on the HNE-anti-apoptotic Bcl-2 axis supported the deduction of HNE mediated NF-κB pathway inhibition and IKK mediated Bcl-2 inactivation. In conclusion, through combining all evidences, three possible scenarios intervening the HNE mediated crosstalk between NF-κB pathway and anti-apoptotic Bcl-2 protein, was extrapolated.

Neuroprotective effects of aldehyde dehydrogenase 2 activation in rotenone-induced cellular and animal models of parkinsonism

Many studies have shown that mitochondrial aldehyde dehydrogenase 2 (ALDH2) functions as a cellular protector against oxidative stress by detoxification of cytotoxic aldehydes. Within dopaminergic neurons, dopamine is metabolized by monoamine oxidase to yield 3,4-dihydroxyphenylacetaldehyde (DOPAL) then converts to a less toxic acid product by ALDH. The highly toxic and reactive DOPAL has been hypothesized to contribute to the selective neurodegeneration in Parkinson’s disease (PD). In this study, we investigated the neuroprotective mechanism and therapeutic effect of ALDH2 in rotenone models for parkinsonism. Overexpression of wild-type ALDH2 gene, but not the enzymatically deficient mutant ALDH2*2 (E504K), reduced rotenone-induced cell death. Application of a potent activator of ALDH2, Alda-1, was effective in protecting against rotenone-induced apoptotic cell death in both SH-SY5Y cells and primary cultured substantia nigra (SN) dopaminergic neurons. In addition, intraperitoneal administration of Alda-1 significantly reduced rotenone- or MPTP-induced death of SN tyrosine hydroxylase (TH)-positive dopaminergic neurons. The attenuation of rotenone-induced apoptosis by Alda-1 resulted from decreasing ROS accumulation, reversal of mitochondrial membrane potential depolarization, and inhibition of activation of proteins related to mitochondrial apoptotic pathway. The present study demonstrates that ALDH2 plays a crucial role in maintaining normal mitochondrial function to protect against neurotoxicity and that Alda-1 is effective in ameliorating mitochondrial dysfunction and inhibiting mitochondria-mediated apoptotic pathway. These results indicate that ALDH2 activation could be a neuroprotective therapy for PD.

Role of aldehyde dehydrogenase 2 in 1-methy-4-phenylpyridinium ion-induced aldehyde stress and cytotoxicity in PC12 cells

Aldehyde stress contributes to molecular mechanisms of cell death and the pathogenesis of Parkinson's disease (PD). The neurotoxin 1-Methy-4-Phenylpyridinium Ion (MPP(+)) is commonly used to model PD. Aldehyde dehydrogenase 2 (ALDH2) is an important enzyme detoxifying aldehydes. The aim of this study is to evaluate whether MPP(+)-induced neurotoxicity is involved in aldehyde stress by modulation of ALDH2. Our results demonstrated that treatment of PC12 cells with MPP(+) leads to aldehyde stress by increasing in loads of malondialdehyde and 4-hydroxynonenal, which indicated that MPP(+)-induced aldehyde stress contributes to its cytotoxicity in PC12 cells. We also showed that MPP(+) up-regulates the expression and activity of ALDH2 in PC12 cells and that inhibition of ALDH2 by its specific inhibitor daidzin prevents MPP(+)-induced decrease in cell viability and increases in apoptosis, oxidative stress and aldehyde stress in PC12 cells. These findings suggest that aldehyde stress contributes to MPP(+)-induced toxicity in PC12 cells by upregulation of ALDH2. This study provides a novel insight into the role of ALDH2 in the neurotoxicity of MPP(+).

4-Hydroxy-trans-2-nonenal (4-HNE) induces neuronal SH-SY5Y cell death via hampering ATP binding at kinase domain of Akt1

Inhibition mechanism(s) of protein kinase B/Akt1 and its consequences on related cell signaling were investigated in human neuroblastoma SH-SY5Y cells exposed to 4-hydroxy-trans-2-nonenal (4-HNE), one of the most reactive aldehyde by-products of lipid peroxidation. In silico data indicate that 4-HNE interacts with kinase domain of Akt1 with the total docking score of 6.0577 and also forms H-bond to Glu234 residue similar to highly potent Akt1 inhibitor imidazopiperidine analog 8b, in which the protonated imidazole nitrogen involves in two hydrogen bonds between Glu234 and Asp292. The strong hydrogen bonding with Glu234 and hydrophobic interactions with several residues, namely Leu156, Gly157, Val164, Ala177, Tyr229, Ala230, Met281 and Thr291, at the vicinity which is normally occupied by the ribose of ATP, appear to be the main causes of Akt1 inhibition and lead to the significant conformational change on this region of protein. Results of mutational docking prove that Glu234 plays a major role in 4-HNE-mediated Akt1 inhibition. In silico data on Akt inhibition were further validated by observing the down-regulated levels of phosphorylated (Thr308/Ser493) Akt1 as well as the altered levels of the downstream targets of pAkt, namely downregulated levels of pGSK3β (Ser9), β-catenin, Bcl2 and upregulated levels of pro-apoptotic markers, namely Bad, Bax, P(53) and caspase-9/3. The cellular fate of such pAkt inhibition was evidenced by increased reactive oxygen species, degraded nuclei, transferase dUTP nick end labeling positive cells and upregulated levels of pJNK1/2. We identified that 4-HNE-mediated Akt1 inhibition was due to the competitive inhibition of ATP by 4-HNE at the kinase domain of ATP binding sites.

4-Hydroxynonenal induces an increase in expression of Receptor for Activating C Kinase 1 (RACK1) in Chinese hamster V79-4 lung cells

4-Hydroxy-trans-2-nonenal (HNE) is a cytotoxic α,β-unsaturated aldehyde implicated in the pathology of several diseases that have an oxidative stress mechanism, including atherosclerosis, diabetes, alcohol-induced liver disease, and neurodegenerative disorders. As the most toxic aldehydic product of lipid peroxidation, HNE is known to exert a range of biological effects in a concentration-dependent manner. In this study, the effect of HNE on the levels of proteins in V79-4 Chinese hamster lung cells was investigated using two-dimensional electrophoresis and mass spectrometry. The results revealed that the expression of 23 proteins was increased by at least 2-fold and the expression of 19 proteins was decreased by at least 2-fold after exposure to 10 μM HNE for 24 h. Decreased proteins included the metabolic enzyme phosphoglycerate kinase 1 (PGK1), levels of which were decreased by 47%. Levels of the apoptotic indicator Lamin C were decreased by 33%. In contrast, levels of the scaffolding protein Receptor for Activating C Kinase 1 (RACK1) were increased by 2-fold after treatment with 10 μM HNE for 24h, and this was confirmed using quantitative PCR of reverse-transcribed mRNA and Western blots. The role of RACK1 in mediating the induction of apoptosis in response to 10 μM HNE was confirmed using RACK1-specific siRNA. The results from this study provide new information on the mechanism of adaptive stress response to HNE and also identify potential new biomarkers of exposure to HNE.

Cell death and diseases related to oxidative stress: 4-hydroxynonenal (HNE) in the balance

During the last three decades, 4-hydroxy-2-nonenal (HNE), a major α,β-unsaturated aldehyde product of n-6 fatty acid oxidation, has been shown to be involved in a great number of pathologies such as metabolic diseases, neurodegenerative diseases and cancers. These multiple pathologies can be explained by the fact that HNE is a potent modulator of numerous cell processes such as oxidative stress signaling, cell proliferation, transformation or cell death. The main objective of this review is to focus on the different aspects of HNE-induced cell death, with a particular emphasis on apoptosis. HNE is a special apoptotic inducer because of its abilities to form protein adducts and to propagate oxidative stress. It can stimulate intrinsic and extrinsic apoptotic pathways and interact with typical actors such as tumor protein 53, JNK, Fas or mitochondrial regulators. At the same time, due to its oxidant status, it can also induce some cellular defense mechanisms against oxidative stress, thus being involved in its own detoxification. These processes in turn limit the apoptotic potential of HNE. These dualities can imbalance cell fate, either toward cell death or toward survival, depending on the cell type, the metabolic state and the ability to detoxify.

Rotenone-induced oxidative stress and apoptosis in human liver HepG2 cells

Rotenone, a commonly used pesticide, is well documented to induce selective degeneration in dopaminergic neurons and motor dysfunction. Such rotenone-induced neurodegenration has been primarily suggested through mitochondria-mediated apoptosis and reactive oxygen species (ROS) generation. But the status of rotenone induced changes in liver, the major metabolic site is poorly investigated. Thus, the present investigation was aimed to study the oxidative stress-induced cytotoxicity and apoptotic cell death in human liver cells-HepG2 receiving experimental exposure of rotenone (12.5-250 μM) for 24 h. Rotenone depicted a dose-dependent cytotoxic response in HepG2 cells. These cytotoxic responses were in concurrence with the markers associated with oxidative stress such as an increase in ROS generation and lipid peroxidation as well as a decrease in the glutathione, catalase, and superoxide dismutase levels. The decrease in mitochondrial membrane potential also confirms the impaired mitochondrial activity. The events of cytotoxicity and oxidative stress were found to be associated with up-regulation in the expressions (mRNA and protein) of pro-apoptotic markers viz., p53, Bax, and caspase-3, and down-regulation of anti-apoptotic marker Bcl-2. The data obtain in this study indicate that rotenone-induced cytotoxicity in HepG2 cells via ROS-induced oxidative stress and mitochondria-mediated apoptosis involving p53, Bax/Bcl-2, and caspase-3.