Critical role of H2O2 generated by NOX4 during cellular response under glucose deprivation

REDOX Imbalance and Oxidative Stress in the Intervertebral Disc: The Effect of Mechanical Stress and Cigarette Smoking on ER Stress and Mitochondrial Dysfunction

Low back pain is a widespread condition that significantly impacts quality of life, with intervertebral disc degeneration (IDD) being a major contributing factor. However, the underlying mechanisms of IDD remain poorly understood, necessitating further investigation. Environmental risk factors, such as mechanical stress and cigarette smoke, elevate reactive oxygen species levels from both endogenous and exogenous sources, leading to redox imbalance and oxidative stress. The endoplasmic reticulum (ER) and mitochondria, two key organelles responsible for protein folding and energy production, respectively, are particularly vulnerable to oxidative stress. Under oxidative stress conditions, ER stress and mitochondrial dysfunction occur, resulting in unfolded protein response activation, impaired biosynthetic processes, and disruptions in the tricarboxylic acid cycle and electron transport chain, ultimately compromising energy metabolism. Prolonged and excessive ER stress can further trigger apoptosis through ER-mitochondrial crosstalk. Given the unique microenvironment of the intervertebral disc (IVD)-characterized by hypoxia, glucose starvation, and region-specific cellular heterogeneity-the differential effects of environmental stressors on distinct IVD cell populations require further investigation. This review explores the potential mechanisms through which environmental risk factors alter IVD cell activities, contributing to IDD progression, and discusses future therapeutic strategies aimed at mitigating disc degeneration.

Influence of glucose and oxygen tension on the trophectoderm and the inner cell mass of in vitro produced bovine embryos

The first cell differentiation event that occurs in the embryo determines the inner cell mass (ICM) and the trophectoderm (TE). In the mouse, glucose (GLC) is essential for this process, while oxygen tension (O2) also interferes with TE formation. The roles of GLC and O2 in this event in bovine embryos are not completely elucidated. We hypothesized that the absence of glucose and a higher O2 tension negatively impact ICM and TE cell allocation in the bovine embryo. The objective of this study was to evaluate the effect of GLC within different O2 levels on the formation of the TE. In vitro-produced embryos were cultured in serum-free KSOM medium and randomly submitted to treatments on the day of IVC, according to a 2x2 factorial model, in which GLC (present [+GLC] or absent [-GLC]) and O2 (low [5%O2] or high [20%O2]) were the independent variables. Cleavage and blastocyst rates were obtained at D4 and D8, respectively. Embryos at D8 were subjected to autofluorescence analysis to quantitate NADH and FAD + or fixed for GATA3 and YAP1 immunostaining using a laser scanning confocal microscope. Total, TE, and ICM cell counts were obtained. Embryos were also harvested for gene expression quantification of GATA3, YAP1, SOX2, CDX2, TFAP2C and OCT4. Results indicate that there was an effect of O2 (p = 0.018) on cleavage rates, although no differences were observed in blastocyst rates. NADH was higher in -GLC compared to + GLC (p = 0.014) and no differences in FAD+ were observed. Total cell count data were not different between variables. There was an increase in the ICM cell count in the +GLC 5%O2 condition compared to the other three conditions. No effects of GLC, O2, or their interactions were observed on TE cell count or the TE/total cell ratio. CDX2 (p = 0.007) and TFAP2C (p = 0.038) were increased in -GLC 20%O2 compared to + GLC 20%O2. SOX2 was decreased in +GLC 20%O2 compared to + GLC 5%O2 (p = 0.027) or compared to -GLC 20%O2 (p = 0.005). GATA3, YAP1, and OCT4 genes did not present differences among conditions. In conclusion, both GLC and high oxygen tension did not impair TE formation and TE cell number, although a +GLC-low oxygen environment led to a higher number of ICM cells. Interestingly, the expression of TE-related gene CDX2 was increased in the absence of glucose within higher O2 tension. Our results implicate that according to the oxygen tension used in IVC, glucose can exert different effects on blastocyst cell allocation or gene expression.

The crosstalk among the physical tumor microenvironment and the effects of glucose deprivation on tumors in the past decade

The occurrence and progression of tumors are inseparable from glucose metabolism. With the development of tumors, the volume increases gradually and the nutritional supply of tumors cannot be fully guaranteed. The tumor microenvironment changes and glucose deficiency becomes the common stress environment of tumors. Here, we discuss the mutual influences between glucose deprivation and other features of the tumor microenvironment, such as hypoxia, immune escape, low pH, and oxidative stress. In the face of a series of stress responses brought by glucose deficiency, different types of tumors have different coping mechanisms. We summarize the tumor studies on glucose deficiency in the last decade and review the genes and pathways that determine the fate of tumors under harsh conditions. It turns out that most of these genes help tumor cells survive in glucose-deprivation conditions. The development of related inhibitors may bring new opportunities for the treatment of tumors.

PCK2 opposes mitochondrial respiration and maintains the redox balance in starved lung cancer cells

Cancer cells frequently lack nutrients like glucose, due to insufficient vascular networks. Mitochondrial phosphoenolpyruvate carboxykinase, PCK2, has recently been found to mediate partial gluconeogenesis and hence anabolic metabolism in glucose starved cancer cells. Here we show that PCK2 acts as a regulator of mitochondrial respiration and maintains the redox balance in nutrient-deprived human lung cancer cells. PCK2 silencing increased the abundance and interconversion of tricarboxylic acid (TCA) cycle intermediates, augmented mitochondrial respiration and enhanced glutathione oxidation under glucose and serum starvation, in a PCK2 re-expression reversible manner. Moreover, enhancing the TCA cycle by PCK2 inhibition severely reduced colony formation of lung cancer cells under starvation. As a conclusion, PCK2 contributes to maintaining a reduced glutathione pool in starved cancer cells besides mediating the biosynthesis of gluconeogenic/glycolytic intermediates. The study sheds light on adaptive responses in cancer cells to nutrient deprivation and shows that PCK2 confers protection against respiration-induced oxidative stress.

Glucose Depletion Enhances the Stem Cell Phenotype and Gemcitabine Resistance of Cholangiocarcinoma Organoids through AKT Phosphorylation and Reactive Oxygen Species

Cancer cells are strongly dependent on the glycolytic pathway for generation of energy even under aerobic condition through a phenomenon known as the Warburg effect. Rapid proliferation of cancer cells is often accompanied by high glucose consumption and abnormal angiogenesis, which may lead to glucose depletion. In the present study, we investigated how cholangiocarcinoma cells adapt to glucose depletion using a 3D organoid culture system. We cultured organoids derived from cholangiocarcinoma under glucose-free condition and investigated cell proliferation, expression of stem cell markers and resistance to gemcitabine. Cholangiocarcinoma organoids cultured under glucose-free condition showed reduced proliferation but were able to survive. We also observed an increase in the expression of stem cell markers including LGR5 and enhancement of stem cell phenotypic characteristics such as resistance to gemcitabine through AKT phosphorylation and reactive oxygen species. These findings indicate that cholangiocarcinoma cells are able to adapt to glucose depletion through enhancement of their stem cell phenotype in response to changes in microenvironmental conditions.

Caloric restriction induces H2O2 formation as a trigger of AMPK-eNOS-NO pathway in obese rats: Role for CAMKII

Caloric restriction (CR) improves endothelial function through the upregulation of adenosine monophosphate-activated protein kinase (AMPK) and endothelial nitric oxide synthase (eNOS). Moreover, hydrogen peroxide (H₂O₂) is upregulated in yeast subjected to CR. Our aim was to assess if mild short-term CR increases vascular H₂O₂ formation as a link with AMPK and eNOS activation. Twelve-week old Zucker obese (fa/fa) and control Zucker lean male rats were fed a standard chow either ad libitum (AL, n=10) or with a 20% CR (CR, n=10) for two weeks. CR significantly improved relaxation to ACh in fa/fa rats because of an enhanced endogenous production of H₂O₂ in aortic rings (H₂O₂ levels _fa/faAL=0.5 ± 0.05 nmol/mg vs. H₂O₂ levels _fa/faCR=0.76 ± 0.07 nmol/mg protein; p<0.05). Expression of mitochondrial superoxide dismutase (Mn-SOD) and total SOD activity were increased in aorta from fa/fa animals after CR. In cultured aortic endothelial cells, serum deprivation or 2-deoxy-d-glucose induced a significant increase in: i) superoxide anion and H₂O₂ levels, ii) p-AMPK/AMPK and p-eNOS/eNOS expression and iii) nitric oxide levels. This effect was reduced by catalase and strongly inhibited by Ca²⁺/calmodulin-dependent kinase II (CamkII) silencing. In conclusion, we propose that mild short-term CR might be a trigger of mechanisms aimed at protecting the vascular wall by the increase of H₂O₂, which then activates AMPK and nitric oxide release, thus improving endothelium-dependent relaxation. In addition, we demonstrate that CAMKII plays a key role in mediating CR-induced AMPK activation through H₂O₂ increase.

Resveratrol augments ER stress and the cytotoxic effects of glycolytic inhibition in neuroblastoma by downregulating Akt in a mechanism independent of SIRT1

Cancer cells typically display increased rates of aerobic glycolysis that are correlated with tumor aggressiveness and a poor prognosis. Targeting the glycolytic pathway has emerged as an attractive therapeutic route mainly because it should spare normal cells. Here, we evaluate the effects of combining the inhibition of glycolysis with application of the polyphenolic compound resveratrol (RSV) in neuroblastoma (NB) cancer cell lines. Inhibiting glycolysis with 2-deoxy-D-glucose (2-DG) significantly reduced NB cell viability and was associated with increased endoplasmic reticulum (ER) stress and Akt activity. Administration of 2-DG increased the expression of the ER molecular chaperones GRP78 and GRP94, the prodeath protein C/EBP homology protein (CHOP) and the phosphorylation of Akt at S473, T450 and T308. Combined treatment with both RSV and 2-DG reduced GRP78, GRP94 and Akt phosphorylation but increased CHOP and NB cell death when compared with the administration of 2-DG alone. The selective inhibition of Akt activity also decreased 2-DG-induced GRP78 and GRP94 expression and increased CHOP expression, suggesting that Akt can modulate ER stress. Protein phosphatase 1α (PP1α) was activated by RSV, as indicated by a reduction in PP1α phosphorylation at T320. Pretreatment of cells with tautomycin, a selective PP1α inhibitor, prevented the RSV-mediated decrease in Akt phosphorylation, suggesting that RSV enhances 2-DG-induced cell death by activating PP1 and downregulating Akt. The RSV-mediated inhibition of Akt in the presence of 2-DG was not prevented by the selective inhibition of SIRT1, a known target of RSV, indicating that the effects of RSV on this pathway are independent of SIRT1. We propose that RSV inhibits Akt activity by increasing PP1α activity, thereby potentiating 2-DG-induced ER stress and NB cell death.

Influence of partial and complete glutamine-and glucose deprivation of breast-and cervical tumorigenic cell lines

BACKGROUND

Due to their high proliferative requirements, tumorigenic cells possess altered metabolic systems whereby cells utilize higher quantities of glutamine and glucose. These altered metabolic requirements make it of interest to investigate the effects of physiological non-tumorigenic concentrations of glucose and glutamine on tumorigenic cells since deprivation of either results in a canonical amino acid response in mammalian cell.

METHODS

The influence of short-term exposure of tumorigenic cells to correlating decreasing glutamine- and glucose quantities were demonstrated in a highly glycolytic metastatic breast cell line and a cervical carcinoma cell line. Thereafter, cells were propagated in medium containing typical physiological concentrations of 1 mM glutamine and 6 mM glucose for 7 days. The effects on morphology were investigated by means of polarization-optical transmitted light differential interference contrast. Flow cytometry was used to demonstrate the effects of glutamine-and glucose starvation on cell cycle progression and apoptosis induction. Fluorometrics were also conducted to investigate the effects on intrinsic apoptosis induction (mitocapture), reactive oxygen species production (2,7-dichlorofluorescein diacetate) and acidic vesicle formation (acridine orange).

RESULTS

Morphological data suggests that glutamine-and glucose deprivation resulted in reduced cell density and rounded cells. Glutamine-and glucose starvation also resulted in an increase in the G2M phase and a sub-G1 peak. Complete starvation of glutamine and glucose resulted in the reduction of the mitochondrial membrane potential in both cell lines with MDA-MB-231 cells more prominently affected when compared to HeLa cells. Further, starved cells could not be rescued sufficiently by propagating since cells possessed an increase in reactive oxygen species, acidic compartments and vacuole formation.

CONCLUSION

Starvation from glutamine and glucose for short periods resulted in decreased cell density, rounded cells and apoptosis induction by means of reactive oxygen species generation and mitochondrial dysfunction. In addition, the metastatic cell line reacted more prominently to glutamine-and glucose starvation due to their highly glycolytic nature. Satisfactory cellular rescue was not possible as cells demonstrated oxidative stress and depolarized mitochondrial membrane potential. This study contributes to the knowledge regarding the in vitro effects and signal transduction of glucose and/or l-glutamine deprivation in tumorigenic cell lines.

Role of NADPH oxidase in the regulation of autophagy in cardiomyocytes

In the past several years, it has been demonstrated that the reactive oxygen species (ROS) may act as intracellular signalling molecules to activate or inhibit specific signalling pathways and regulate physiological cellular functions. It is now well-established that ROS regulate autophagy, an intracellular degradation process. However, the signalling mechanisms through which ROS modulate autophagy in a regulated manner have only been minimally clarified. NADPH oxidase (Nox) enzymes are membrane-bound enzymatic complexes responsible for the dedicated generation of ROS. Different isoforms of Nox exist with different functions. Recent studies demonstrated that Nox-derived ROS can promote autophagy, with Nox2 and Nox4 representing the isoforms of Nox implicated thus far. Nox2- and Nox4-dependent autophagy plays an important role in the elimination of pathogens by phagocytes and in the regulation of vascular- and cancer-cell survival. Interestingly, we recently found that Nox is also important for autophagy regulation in cardiomyocytes. We found that Nox4, but not Nox2, promotes the activation of autophagy and survival in cardiomyocytes in response to nutrient deprivation and ischaemia through activation of the PERK (protein kinase RNA-like endoplasmic reticulum kinase) signalling pathway. In the present paper, we discuss the importance of Nox family proteins and ROS in the regulation of autophagy, with a particular focus on the role of Nox4 in the regulation of autophagy in the heart.

Emerging strategies to overcome the resistance to current mTOR inhibitors in renal cell carcinoma

The mammalian target of rapamycin (mTOR) has emerged as an attractive cancer therapeutic target. Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. Unfortunately, a number of potential mechanisms that may lead to resistance to mTOR inhibitors have been proposed. In this paper, we discuss the mechanisms underlying resistance to mTOR inhibitors, which include the downstream effectors of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway, the activation of hypoxia-inducible factor (HIF), the PIM kinase family, PTEN expression, elevated superoxide levels, stimulation of autophagy, immune cell response and ERK/MAPK, Notch and Aurora signaling pathways. Moreover, we present an updated analysis of clinical trials available on PubMed Central and www.clinicaltrials.gov, which were pertinent to the resistance to rapalogs. The new frontier of inhibiting the mTOR pathway is to identify agents targeting the feedback loops and cross talks with other pathways involved in the acquired resistance to mTOR inhibitors. The true goal will be to identify biomarkers predictive of sensitivity or resistance to efficiently develop novel agents with the aim to avoid toxicities and to better choose the active drug for the right patient.

Forkhead box protein A1 inhibits the expression of uncoupling protein 2 in hydrogen peroxide-induced A549 cell line

Forkhead box protein A1 (FoxA1) is a transcription factor that is involved in embryonic development and cell differentiation. In this study, we show that hydrogen peroxide (H2O2) treatment upregulated expression of FoxA1 and UCP2 in the A549 cell line. Overexpression of FoxA1 by full-length complementary DNA reduced UCP2 expression, while silencing of FoxA1 expression by small interfering RNA significantly increased UCP2 levels. FoxA1 binds to a site from -919 to -913 bp relative to the UCP2 transcription start site. The overexpression of FoxA1 promoted the DNA binding activity and attenuated the transcription of UCP2 promoter as shown by electromobility shift, chromatin immunoprecipitation assays, and luciferase reporter assay. These data indicate an important role of FoxA1 in regulating expression of UCP2.