Role of MnSOD and p66shc in mitochondrial response to p53

Implications of p53 in mitochondrial dysfunction and Parkinson's disease

Purpose: To study the underlying molecular mechanisms of p53 in the mitochondrial dysfunction and the pathogenesis of Parkinson's disease (PD), and provide a potential therapeutic target for PD treatment.

Methods: We review the contributions of p53 to mitochondrial changes leading to apoptosis and the subsequent degeneration of dopaminergic neurons in PD.

Results: P53 is a multifunctional protein implicated in the regulation of diverse cellular processes via transcription-dependent and transcription-independent mechanisms. Mitochondria are vital subcellular organelles for that maintain cellular function, and mitochondrial defect and impairment are primary causes of dopaminergic neuron degeneration in PD. Increasing evidence has revealed that mitochondrial dysfunction-associated dopaminergic neuron degeneration is tightly regulated by p53 in PD pathogenesis. Neurodegenerative stress triggers p53 activation, which induces mitochondrial changes, including transmembrane permeability, reactive oxygen species production, Ca2+ overload, electron transport chain defects and other dynamic alterations, and these changes contribute to neurodegeneration and are linked closely with PD occurrence and development. P53 inhibition has been shown to attenuate mitochondrial dysfunction and protect dopaminergic neurons from degeneration under conditions of neurodegenerative stress.

Conclusions: p53 appears to be a potential target for neuroprotective therapy of PD.

Manganese matere bonds in biological systems: PDB inspection and DFT calculations

A Protein Data Bank (PDB) survey has revealed noncovalent contacts involving Mn centres and protein residues. Their geometrical features are in line with the interaction between low electron density sites located along the Mn-O/N coordination bonds (σ-holes) and the lone pairs belonging to TYR, SER or HIS residues, known as a matere bond (MaB). Calculations at the PBE0-D3/def2-TZVP level of theory were used to investigate the strength and shed light on the physical nature of the interaction. We expect the results presented herein will be useful for those scientists working in the fields of bioinorganic chemistry, particulary in protein-metal docking, by providing new insights into transition metal⋯Lewis base interactions as well as a retrospective point of view to further understand the structural and functional implications of this key transition metal ion.

Association of p53 with Neurodegeneration in Parkinson's Disease

p53 is a vital transcriptional protein implicated in regulating diverse cellular processes, including cell cycle arrest, DNA repair, mitochondrial metabolism, redox homeostasis, autophagy, senescence, and apoptosis. Recent studies have revealed that p53 levels and activity are substantially increased in affected neurons in cellular and animal models of Parkinson's disease (PD) as well as in the brains of PD patients. p53 activation in response to neurodegenerative stress is closely associated with the degeneration of dopaminergic neurons accompanied by mitochondrial dysfunction, reactive oxygen species (ROS) production, abnormal protein aggregation, and impairment of autophagy, and these pathogenic events have been implicated in the pathogenesis of PD. Pathogenic p53 integrates diverse cellular stresses and activate these downstream events to induce the degeneration of dopaminergic neurons; thus, it plays a crucial role in the pathogenesis of PD and appears to be a potential target for the treatment of the disease. We reviewed the current knowledge concerning p53-dependent neurodegeneration to better understand the underlying mechanisms and provide possible strategies for PD treatment by targeting p53.

Crosstalk Between ROS and Autophagy in Tumorigenesis: Understanding the Multifaceted Paradox

Cancer formation is a highly regulated and complex process, largely dependent on its microenvironment. This complexity highlights the need for developing novel target-based therapies depending on cancer phenotype and genotype. Autophagy, a catabolic process, removes damaged and defective cellular materials through lysosomes. It is activated in response to stress conditions such as nutrient deprivation, hypoxia, and oxidative stress. Oxidative stress is induced by excess reactive oxygen species (ROS) that are multifaceted molecules that drive several pathophysiological conditions, including cancer. Moreover, autophagy also plays a dual role, initially inhibiting tumor formation but promoting tumor progression during advanced stages. Mounting evidence has suggested an intricate crosstalk between autophagy and ROS where they can either suppress cancer formation or promote disease etiology. This review highlights the regulatory roles of autophagy and ROS from tumor induction to metastasis. We also discuss the therapeutic strategies that have been devised so far to combat cancer. Based on the review, we finally present some gap areas that could be targeted and may provide a basis for cancer suppression.

Oxidative Stress, Mitochondrial Function and Adaptation to Exercise: New Perspectives in Nutrition

Cells have the ability to adapt to stressful environments as a part of their evolution. Physical exercise induces an increase of a demand for energy that must be met by mitochondria as the main (ATP) provider. However, this process leads to the increase of free radicals and the so-called reactive oxygen species (ROS), which are necessary for the maintenance of cell signaling and homeostasis. In addition, mitochondrial biogenesis is influenced by exercise in continuous crosstalk between the mitochondria and the nuclear genome. Excessive workloads may induce severe mitochondrial stress, resulting in oxidative damage. In this regard, the objective of this work was to provide a general overview of the molecular mechanisms involved in mitochondrial adaptation during exercise and to understand if some nutrients such as antioxidants may be implicated in blunt adaptation and/or an impact on the performance of exercise by different means.

Functional Role of p53 in the Regulation of Chemical-Induced Oxidative Stress

The nuclear transcription factor p53, discovered in 1979, has a broad range of biological functions, primarily the regulation of apoptosis, the cell cycle, and DNA repair. In addition to these canonical functions, a growing body of evidence suggests that p53 plays an important role in regulating intracellular redox homeostasis through transcriptional and nontranscriptional mechanisms. Oxidative stress induction and p53 activation are common responses to chemical exposure and are suggested to play critical roles in chemical-induced toxicity. The activation of p53 can exert either prooxidant or antioxidant activity, depending on the context. In this review, we discuss the functional role of p53 in regulating chemical-induced oxidative stress, summarize the potential signaling pathways involved in p53's regulation of chemically mediated oxidative stress, and propose issues that should be addressed in future studies to improve understanding of the relationship between p53 and chemical-induced oxidative stress.

Cell quality control mechanisms maintain stemness and differentiation potential of P19 embryonic carcinoma cells

Given the relatively long life of stem cells (SCs), efficient mechanisms of quality control to balance cell survival and resistance to external and internal stress are required. Our objective was to test the relevance of cell quality control mechanisms for SCs maintenance, differentiation and resistance to cell death. We compared cell quality control in P19 stem cells (P19SCs) before and after differentiation (P19dCs). Differentiation of P19SCs resulted in alterations in parameters involved in cell survival and protein homeostasis, including the redox system, cardiolipin and lipid profiles, unfolded protein response, ubiquitin-proteasome and lysosomal systems, and signaling pathways controlling cell growth. In addition, P19SCs pluripotency was correlated with stronger antioxidant protection, modulation of apoptosis, and activation of macroautophagy, which all contributed to preserve SCs quality by increasing the threshold for cell death activation. Furthermore, our findings identify critical roles for the PI3K-AKT-MTOR pathway, as well as autophagic flux and apoptosis regulation in the maintenance of P19SCs pluripotency and differentiation potential.Abbreviations: 3-MA: 3-methyladenine; AKT/protein kinase B: thymoma viral proto-oncogene; AKT1: thymoma viral proto-oncogene 1; ATG: AuTophaGy-related; ATF6: activating transcription factor 6; BAX: BCL2-associated X protein; BBC3/PUMA: BCL2 binding component 3; BCL2: B cell leukemia/lymphoma 2; BNIP3L: BCL2/adenovirus E1B interacting protein 3-like; CASP3: caspase 3; CASP8: caspase 8; CASP9: caspase 9; CL: cardiolipin; CTSB: cathepsin B; CTSD: cathepsin D; DDIT3/CHOP: DNA-damage inducible transcript 3; DNM1L/DRP1: dynamin 1-like; DRAM1: DNA-damage regulated autophagy modulator 1; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; EIF2S1/eIF2α: eukaryotic translation initiation factor 2, subunit alpha; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; ESCs: embryonic stem cells; KRT8/TROMA-1: cytokeratin 8; LAMP2A: lysosomal-associated membrane protein 2A; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NANOG: Nanog homeobox; NAO: 10-N-nonyl acridine orange; NFE2L2/NRF2: nuclear factor, erythroid derived 2, like 2; OPA1: OPA1, mitochondrial dynamin like GTPase; P19dCs: P19 differentiated cells; P19SCs: P19 stem cells; POU5F1/OCT4: POU domain, class 5, transcription factor 1; PtdIns3K: phosphatidylinositol 3-kinase; RA: retinoic acid; ROS: reactive oxygen species; RPS6KB1/p70S6K: ribosomal protein S6 kinase, polypeptide 1; SCs: stem cells; SOD: superoxide dismutase; SHC1-1/p66SHC: src homology 2 domain-containing transforming protein C1, 66 kDa isoform; SOX2: SRY (sex determining region Y)-box 2; SQSTM1/p62: sequestosome 1; SPTAN1/αII-spectrin: spectrin alpha, non-erythrocytic 1; TOMM20: translocase of outer mitochondrial membrane 20; TRP53/p53: transformation related protein 53; TUBB3/betaIII-tubulin: tubulin, beta 3 class III; UPR: unfolded protein response; UPS: ubiquitin-proteasome system.

SIRT3 Inactivation Promotes Acute Kidney Injury Through Elevated Acetylation of SOD2 and p53

BACKGROUND

The deactivation of SIRT3, a novel deacetylase located in mitochondria, can aggravate multiple organ dysfunction. However, the role of SIRT3 and its downstream targets in ischemia/reperfusion (I/R)-induced acute kidney injury (AKI) remain unknown.

MATERIALS AND METHODS

I/R was reproduced in a rat model using a clamp placed on the left and right renal pedicles for 40 min. The rats were intraperitoneally injected with either the vehicle or a selective SIRT3 inhibitor (3-TYP) and scarified at different time points (4, 8, and 24 h after I/R). A portion of the renal tissue was extracted for histological analysis, and another portion was collected for the isolation of renal tubular epithelial cells for Western blotting, SOD2 and SIRT3 activity, cell apoptosis, and the determination of oxidative stress.

RESULTS

The I/R-induced AKI model was successfully reproduced and SIRT3 activity was considerably reduced than control (sham operated) group, accompanied by increased acetylation of SOD2 and p53, as well as their elevated physical interaction in extracted mitochondrial protein (all P values < 0.05). Moreover, SIRT3 suppression by 3-TYP treatment (comparing with the vehicle treatment group) aggravated AKI, as evidenced by increased indicators of oxidative stress (increased mitochondrial red fluorescence MitoSOX and decreased reduced glutathione/oxidized glutathione ratio, all P values < 0.01).

CONCLUSIONS

The elevation of SOD2 and p53 protein acetylation in the mitochondria of renal tubular epithelial cells is an important signaling event in the pathogenesis of I/R-induced AKI. Thus, deacetylase SIRT3 may be an upstream regulator of both SOD2 and p53, and the SIRT3 deactivation may aggravate AKI.

Dietary supplementation with ketoacids protects against CKD-induced oxidative damage and mitochondrial dysfunction in skeletal muscle of 5/6 nephrectomised rats

Background

A low-protein diet supplemented with ketoacids (LPD + KA) maintains the nutritional status of patients with chronic kidney disease (CKD). Oxidative damage and mitochondrial dysfunction associated with the upregulation of p66SHC and FoxO3a have been shown to contribute to muscle atrophy. This study aimed to determine whether LPD + KA improves muscle atrophy and attenuates the oxidative stress and mitochondrial damage observed in CKD rats.

Methods

5/6 nephrectomy rats were randomly divided into three groups and fed with either 22% protein (normal-protein diet; NPD), 6% protein (low-protein diets; LPD) or 5% protein plus 1% ketoacids (LPD + KA) for 24 weeks. Sham-operated rats with NPD intake were used as the control.

Results

KA supplementation improved muscle atrophy and function in CKD + LPD rats. It also reduced the upregulation of genes related to the ubiquitin-proteasome system and 26S proteasome activity, as well as protein and mitochondrial oxidative damage in the muscles of CKD + LPD rats. Moreover, KA supplementation prevented the drastic decrease in activities of mitochondrial electron transport chain complexes, mitochondrial respiration, and content in the muscles of CKD + LPD rats. Furthermore, KA supplementation reversed the elevation in p66Shc and FoxO3a expression in the muscles of CKD + LPD rats.

Conclusions

Our results showed that KA supplementation to be beneficial to muscle atrophy in CKD + LPD, which might be associated with improvement of oxidative damage and mitochondrial dysfunction through suppression of p66Shc and FoxO3a.

Fish-oil-derived eicosapentaenoic acid decreases survivin expression and induces wt-p53 accumulation with caspase-3 activation in acute lymphoblastic leukemia cells

BACKGROUND

Defects in modulating wild-type (wt) p53 and survivin are associated with a resistant disease in acute lymphoblastic leukemia (ALL). Yet, no wt-p53 and survivin modulating drugs have been approved for clinical application in ALL. Here, we investigated if in vitro eicosapentaenoic acid (EPA) concentrations equal to human plasma levels are able to target wt-p53 and survivin.

METHODS

Wt-p53 Molt-4 cells (ALL cell line) were treated with 50, 100, 150, and 200 µM of EPA after which cell number, viability, proliferation rate, survivin expression, wt-p53 accumulation, caspase-3 activation, and apoptosis were evaluated.

RESULTS

After 48- and 72-h treatments with EPA at concentrations ranging from 50 to 200 µM, cell proliferation rates were measured to be 71.5-32.6% and 68.2-13.7% and metabolic activities were measured to be 77-44% and 71-26%, respectively. Treatment with 50-200 µM of EPA for 48 h resulted in 14.1-74.6% and 69.5-45.5% decreases in survivin mRNA and protein levels, respectively. EPA induced 1.3-6 and 1.9-20-fold increases in caspase-3 activation and wt-p53 accumulation, respectively. Increase in wt-p53/survivin and caspase-3/survivin ratios from 1 in untreated cells to 20.3 and 5.8 was measured for 150 µM of EPA. Low necrotic rates ranging from 0.3% to 2.8% and an increase in the number of total apoptotic cells (early + late) ranging from 9.8% to 81% were also observed with increasing EPA concentrations.

CONCLUSION

EPA induces strongly wt-p53 with a remarkable decrease in survivin expression, representing an attractive compound to modulate wt-p53 and survivin in ALL cells.

Increased p16 and p53 protein expression predicts poor prognosis in mucosal melanoma

Primary mucosal melanoma (MM) is a rare, and aggressive, neoplasm with a poor prognosis. To date, few prognostic markers of MM have been well-defined. The aim of this study is to clarify the prognostic value of p53 and p16 proteins in predicting the clinical outcome of Chinese patients with MM.

A total of 59 MM samples were contained from biopsy specimens, and, expressions of p53 and p16 proteins were assessed by immunohistochemistry. Cox regression analysis was performed to investigate the association of these proteins with the overall survival of MM patients. Increased p16 expression was significantly associated with reduced survival at three years (P=0.039). Increased p53 expression correlates with reduced one-year (P=0.025), and, two-year survival (P=0.037).

Increased p53 and p16 protein expression may be helpful prognostic indicators for the management of these patients.

Reduction-oxidation pathways involved in cancer development: a systematic review of literature reviews

Oxidative stress results from an imbalance of the reactive oxygen species/reactive nitrogen species (ROS/RNS) production and the oxidants defense system. Extensive research during the last decades has revealed that oxidative stress can mediate cancer initiation and development by leading not only to molecular damage but also to a disruption of reduction-oxidation (redox) signaling. In order to provide a global overview of the redox signaling pathways, which play a role in cancer formation, we conducted a systematic literature search in PubMed and ISI Web of Science and identified 185 relevant reviews published in the last 10 years. The 20 most frequently described pathways were selected to be presented in this systematic review and could be categorized into 3 groups: Intracellular ROS/RNS generating organelles and enzymes, signal transduction cascades kinases/phosphatases and transcription factors. Intracellular ROS/RNS generation organelles are mitochondria, endoplasmic reticulum and peroxisomes. Enzymes, including NOX, COX, LOX and NOS, are the most prominent enzymes generating ROS/RNS. ROS/RNS act as redox messengers of transmembrane receptors and trigger the activation or inhibition of signal transduction kinases/phosphatases, such as the family members of protein tyrosine kinases and protein tyrosine phosphatases. Furthermore, these reactions activate downstream signaling pathways including protein kinase of the MAPK cascade, PI3K and PKC. The kinases and phosphatases regulate the phosphorylation status of transcription factors including APE1/Ref-1, HIF-1α, AP-1, Nrf2, NF-κB, p53, FOXO, STAT, and β-catenin. Finally, we briefly discuss cancer prevention and treatment opportunities, which address redox pathways and further research needs.

Oncogenic MCT-1 activation promotes YY1-EGFR-MnSOD signaling and tumor progression

Tumor cells often produce high levels of reactive oxygen species (ROS) and display an increased ROS scavenging system. However, the molecular mechanism that balances antioxidative and oxidative stress in cancer cells is unclear. Here, we determined that oncogenic multiple copies in T-cell malignancy 1 (MCT-1) activity promotes the generation of intracellular ROS and mitochondrial superoxide. Overexpression of MCT-1 suppresses p53 accumulation but elevates the manganese-dependent superoxide dismutase (MnSOD) level via the YY1-EGFR signaling cascade, which protects cells against oxidative damage. Conversely, restricting ROS generation and/or targeting YY1 in lung cancer cells effectively inhibits the EGFR-MnSOD signaling pathway and cell invasiveness induced by MCT-1. Significantly, MCT-1 overexpression in lung cancer cells promotes tumor progression, necrosis and angiogenesis, and increases the number of tumor-promoting M2 macrophages and cancer-associated fibroblasts in the microenvironment. Clinical evidence further confirms that high expression of MCT-1 is associated with an increase in YY1, EGFR and MnSOD expression, accompanied by tumor recurrence, poor overall survival and EGFR mutation status in patients with lung cancers. Together, these data indicate that the MCT-1 oncogenic pathway is implicated in oxidative metabolism and lung carcinogenesis.

Influence of oxygen partial pressure on the characteristics of human hepatocarcinoma cells

Most of the in vitro studies using liver cell lines have been performed under atmospheric oxygen partial pressure (21% O₂). However, the oxygen concentrations in the liver and cancer cells are far from this value. In the present study, we have evaluated the influence of oxygen on 1) the tumor cell lines features (growth, steady-state ROS levels, GSH content, activities of antioxidant enzymes, p66 Shc and SOD expressions, metalloproteinases secretion, migration, invasion, and adhesion) of human hepatocellular carcinoma cell lines, and b) the response of the cells to an oxidant stimulus (aqueous leaf extract of the V. baccifera plant species). For this purpose, three hepatocarcinoma cell lines with different p53 status, HepG2 (wild-type), Huh7 (mutated), and Hep3B (deleted), were cultured (6–30 days) under atmospheric (21%) and more physiological (8%) pO₂. Results showed that after long-term culturing at 8% versus 21% O₂, the cellular proliferation rate and the steady-state levels of mitochondrial O₂^- were unaffected. However, the intracellular basal ROS levels were higher independently of the characteristics of the cell line. Moreover, the lower pO₂ was associated with lower glutathione content, the induction of p66 Shc and Mn-SOD proteins, and increased SOD activity only in HepG2. This cell line also showed a higher migration rate, secretion of active metalloproteinases, and a faster invasion. HepG2 cells were more resistant to the oxidative stress induced by V. baccifera. Results suggest that the long-term culturing of human hepatoma cells at a low, more physiological pO₂ induces antioxidant adaptations that could be mediated by p53, and may alter the cellular response to a subsequent oxidant challenge. Data support the necessity of validating outcomes from studies performed with hepatoma cell cultures under ambient O₂.

•

The influence of pO₂ on human hepatocellular carcinoma cell features is analyzed.

•

Low oxygen tension (8% O₂) induces antioxidant adaptations in HepG2.

•

Low O₂ increases the migration and invasion rates of HepG2.

•

Antioxidant adaptations could be p53-dependent.

•

Validating results from in vitro studies using cells cultured at 21% O₂ are required.

The pro-oxidant gene p66shc increases nicotine exposure-induced lipotoxic oxidative stress in renal proximal tubule cells

Nicotine (NIC) exposure augments free fatty acid (FFA) deposition and oxidative stress, with a concomitant increase in the expression of the pro-oxidant p66shc. In addition, a decrease in the antioxidant manganese superoxide dismutase (MnSOD) has been observed in the kidneys of mice fed a high‑fat diet. The present study aimed to determine whether the pro‑oxidant p66shc mediates NIC‑dependent increases in renal oxidative stress by augmenting the production of reactive oxygen species (ROS) and suppressing the FFA‑induced antioxidant response in cultured NRK52E renal proximal tubule cells. Briefly, NRK52E renal proximal tubule cells were treated with 200 µM NIC, 100 µM oleic acid (OA), or a combination of NIC and OA. The expression levels of p66shc and MnSOD were modulated according to genetic methods. ROS production and cell injury, in the form of lactate dehydrogenase release, were subsequently detected. Promoter activity of p66shc and MnSOD, as well as forkhead box (FOXO)‑dependent transcription, was investigated using reporter luciferase assays. The results demonstrated that NIC exacerbated OA‑mediated intracellular ROS production and cell injury through the transcriptional activation of p66shc. NIC also suppressed OA‑mediated induction of the antioxidant MnSOD promoter activity through p66shc‑dependent inactivation of FOXO activity. Overexpression of p66shc and knockdown of MnSOD had the same effect as treatment with NIC on OA‑mediated lipotoxicity. These data may be used to generate a therapeutic means to ameliorate renal lipotoxicity in obese smokers.

Nicotine Enhances High-Fat Diet-Induced Oxidative Stress in the Kidney

INTRODUCTION

Life expectancy of an obese smoker is 13 years less than a normal weight smoker, which could be linked to the increased renal risk imposed by smoking. Both smoking-through nicotine (NIC)-and obesity-by free fatty acid overload-provoke oxidative stress in the kidney, which ultimately results in development of chronic kidney injury. Their combined renal risk, however, is virtually unknown. We tested the hypothesis that chronic NIC exposure worsens renal oxidative stress in mice on high-fat diet (HFD) by altering the balance between expression of pro-oxidant and antioxidant genes.

METHODS

Nine-week-old male C57Bl/6J mice consumed normal diet (ND) or HFD and received either NIC (200 μg/ml) or vehicle (2% saccharine) in their drinking water. Body weight, plasma clinical parameters, renal lipid deposition, markers of renal oxidative stress and injury, as well as renal expression of the pro-oxidant p66shc and the antioxidant MnSOD were determined after 12 weeks.

RESULTS

NIC significantly augmented levels of circulating free fatty acid, as well as lipid deposition, oxidative stress and sublethal injury in the kidneys of mice on HFD. In addition, NIC exposure suppressed HFD-mediated induction of MnSOD while increased expression of p66shc in the kidney.

CONCLUSIONS

Tobacco smoking or the increasingly popular E-cigarettes-via NIC exposure-could worsen obesity-associated lipotoxicity in the kidney. Hence, our findings could help to develop strategies that mitigate adverse effects of NIC on the obese kidney.

IMPLICATIONS

Life expectancy of an obese smoker is 13 years less than a normal weight smoker, which could be linked to the increased renal risk imposed by smoking. NIC-the main component of tobacco smoke, E-cigarettes and replacement therapies-links smoking to renal injury via oxidative stress, which could superimpose renal oxidative stress caused by obesity. Our results substantiate this scenario using a mouse model of diet induced obesity and NIC exposure and imply the augmented long-term renal risk in obese smokers. Also, our study may help to develop strategies that mitigate adverse effects of NIC on the obese kidney.

Cyclometallated iridium complexes inducing paraptotic cell death like natural products: synthesis, structure and mechanistic aspects

Mononuclear cyclometallated iridium complexes of polypyridyl-phenazine based ligands have been synthesized and characterized which display excellent anticancer activity through paraptosis.

Basal brain oxidative and nitrative stress levels are finely regulated by the interplay between superoxide dismutase 2 and p53

Superoxide dismutases (SODs) are the primary reactive oxygen species (ROS)-scavenging enzymes of the cell and catalyze the dismutation of superoxide radicals O2- to H2O2 and molecular oxygen (O2). Among the three forms of SOD identified, manganese-containing SOD (MnSOD, SOD2) is a homotetramer located wholly in the mitochondrial matrix. Because of the SOD2 strategic location, it represents the first mechanism of defense against the augmentation of ROS/reactive nitrogen species levels in the mitochondria for preventing further damage. This study seeks to understand the effects that the partial lack (SOD2(-/+) ) or the overexpression (TgSOD2) of MnSOD produces on oxidative/nitrative stress basal levels in different brain isolated cellular fractions (i.e., mitochondrial, nuclear, cytosolic) as well as in the whole-brain homogenate. Furthermore, because of the known interaction between SOD2 and p53 protein, this study seeks to clarify the impact that the double mutation has on oxidative/nitrative stress levels in the brain of mice carrying the double mutation (p53(-/-) × SOD2(-/+) and p53(-/-) × TgSOD2). We show that each mutation affects mitochondrial, nuclear, and cytosolic oxidative/nitrative stress basal levels differently, but, overall, no change or reduction of oxidative/nitrative stress levels was found in the whole-brain homogenate. The analysis of well-known antioxidant systems such as thioredoxin-1 and Nrf2/HO-1/BVR-A suggests their potential role in the maintenance of the cellular redox homeostasis in the presence of changes of SOD2 and/or p53 protein levels.

The Interplay Between Respiratory Supercomplexes and ROS in Aging

SIGNIFICANCE

The molecular mechanism of aging is still vigorously debated, although a general consensus exists that mitochondria are significantly involved in this process. However, the previously postulated role of mitochondrial-derived reactive oxygen species (ROS) as the damaging agents inducing functional loss in aging has fallen out of favor in the recent past. In this review, we critically examine the role of ROS in aging in the light of recent advances on the relationship between mitochondrial structure and function.

RECENT ADVANCES

The functional mitochondrial respiratory chain is now recognized as a reflection of the dynamic association of respiratory complexes in the form of supercomplexes (SCs). Besides providing kinetic advantage (channeling), SCs control ROS generation by the respiratory chain, thus providing a means to regulate ROS levels in the cell. Depending on their concentration, these ROS are either physiological signals essential for the life of the cell or toxic species that damage cell structure and functions.

CRITICAL ISSUES

We propose that under physiological conditions the dynamic nature of SCs reversibly controls the generation of ROS as signals involved in mitochondrial-nuclear communication. During aging, there is a progressive loss of control of ROS generation so that their production is irreversibly enhanced, inducing a vicious circle in which signaling is altered and structural damage takes place.

FUTURE DIRECTIONS

A better understanding on the forces affecting SC association would allow the manipulation of ROS generation, directing these species to their physiological signaling role.

Acute exercise induced mitochondrial H₂O₂ production in mouse skeletal muscle: association with p(66Shc) and FOXO3a signaling and antioxidant enzymes

Exercise induced skeletal muscle phenotype change involves a complex interplay between signaling pathways and downstream regulators. This study aims to investigate the effect of acute exercise on mitochondrial H2O2 production and its association with p(66Shc), FOXO3a, and antioxidant enzymes. Male ICR/CD-1 mice were subjected to an acute exercise. Muscle tissues (gastrocnemius and quadriceps femoris) were taken after exercise to measure mitochondrial H2O2 content, expression of p(66Shc) and FOXO3a, and the activity of antioxidant enzymes. The results showed that acute exercise significantly increased mitochondrial H2O2 content and expressions of p(66Shc) and FOXO3a in a time-dependent manner, with a linear correlation between the increase in H2O2 content and p(66Shc) or FOXO3a expression. The activity of mitochondrial catalase was slightly reduced in the 90 min exercise group, but it was significantly higher in groups with 120 and 150 min exercise compared to that of 90 min exercise group. The activity of SOD was not significantly affected. The results indicate that acute exercise increases mitochondrial H2O2 production in the skeletal muscle, which is associated with the upregulation of p(66Shc) and FOXO3a. The association of p(66Shc) and FOXO3a signaling with exercise induced H2O2 generation may play a role in regulating cellular oxidative stress during acute exercise.

The interplay between p66Shc, reactive oxygen species and cancer cell metabolism

The adaptor protein p66Shc links membrane receptors to intracellular signalling pathways and has the potential to respond to energy status changes and regulate mitogenic signalling. Initially reported to mediate growth signals in normal and cancer cells, p66Shc has also been recognized as a pro-apoptotic protein involved in the cellular response to oxidative stress. Moreover, it is a key element in processes such as cancer cell proliferation, tumor progression, metastasis and metabolic reprogramming. Recent findings on the role of p66Shc in the above-mentioned processes have been obtained through the use of various tumor cell types, including prostate, breast, ovarian, lung, colon, skin and thyroid cancer cells. Interestingly, the impact of p66Shc on the proliferation rate was mainly observed in prostate tumors, while its impact on metastasis was mainly found in breast cancers. In this review, we summarize the current knowledge about the possible roles of p66Shc in different cancers.

Drp1 stabilizes p53 on the mitochondria to trigger necrosis under oxidative stress conditions in vitro and in vivo

Oxidative-stress-induced necrosis is considered to be one of the main pathological mediators in various neurological disorders, such as brain ischaemia. However, little is known about the mechanism by which cells modulate necrosis in response to oxidative stress. In the present study, we showed that Drp1 (dynamin-related protein 1), a primary mitochondrial fission protein, stabilizes the well-known stress gene p53 and is required for p53 translocation to the mitochondria under conditions of oxidative stress. We found that Drp1 binding to p53 induced mitochondria-related necrosis. In contrast, inhibition of Drp1 hyperactivation by Drp1 siRNA reduced necrotic cell death in cell cultures exposed to oxidative stress. Most significantly, we demonstrated that inhibition of Drp1 by the Drp1 peptide inhibitor P110, which was developed recently by our group, abolished p53 association with the mitochondria and reduced brain infarction in rats subjected to brain ischaemia/reperfusion injury. Taken together, these findings reveal a novel mechanism of Drp1 hyperactivation in the induction of mitochondrial damage and subsequent cell death. We propose that a Drp1 inhibitor such as P110 is a possible therapeutic agent for diseases in which hyperactivated Drp1 contributes to the pathology.

Mitochondrial function and mitochondrial DNA maintenance with advancing age

We review the impact of mitochondrial DNA (mtDNA) maintenance and mitochondrial function on the aging process. Mitochondrial function and mtDNA integrity are closely related. In order to create a protective barrier against reactive oxygen and nitrogen species (RONS) attacks and ensure mtDNA integrity, multiple cellular mtDNA copies are packaged together with various proteins in nucleoids. Regulation of antioxidant and RONS balance, DNA base excision repair, and selective degradation of damaged mtDNA copies preserves normal mtDNA quantities. Oxidative damage to mtDNA molecules does not substantially contribute to increased mtDNA mutation frequency; rather, mtDNA replication errors of DNA PolG are the main source of mtDNA mutations. Mitochondrial turnover is the major contributor to maintenance of mtDNA and functionally active mitochondria. Mitochondrial turnover involves mitochondrial biogenesis, mitochondrial dynamics, and selective autophagic removal of dysfunctional mitochondria (i.e., mitophagy). All of these processes exhibit decreased activity during aging and fall under greater nuclear genome control, possibly coincident with the emergence of nuclear genome instability. We suggest that the age-dependent accumulation of mutated mtDNA copies and dysfunctional mitochondria is associated primarily with decreased cellular autophagic and mitophagic activity.

The cytoplasmic side of p53's oncosuppressive activities

The tumor suppressor p53 is a transcription factor that in response to a plethora of stress stimuli activates a complex and context-dependent cellular response ultimately protecting genome integrity. In the last two decades, the discovery of cytoplasmic p53 localization has driven an intense research on its extra-nuclear functions. The ability to induce apoptosis acting directly at mitochondria and the related mechanisms of p53 localization and translocation in the cytoplasm and mitochondria have been dissected. However, recent works indicate the involvement of cytoplasmic p53 also in biological processes such as autophagy, metabolism, oxidative stress and drug response. This review will focus on the mechanisms of cytoplasmic p53 activation and the pathophysiological role of p53's transcription-independent functions, highlighting possible therapeutic implications.

Inhibition of glutathione synthesis distinctly alters mitochondrial and cytosolic redox poise

The glutathione couple GSH/GSSG is the most abundant cellular redox buffer and is not at equilibrium among intracellular compartments. Perturbation of glutathione poise has been associated with tumorigenesis; however, due to analytical limitations, the underlying mechanisms behind this relationship are poorly understood. In this regard, we have implemented a ratiometric, genetically encoded redox-sensitive green fluorescent protein fused to human glutaredoxin (Grx1-roGFP2) to monitor real-time glutathione redox potentials in the cytosol and mitochondrial matrix of tumorigenic and non-tumorigenic cells. First, we demonstrated that recovery time in both compartments depended upon the length of exposure to oxidative challenge with diamide, a thiol-oxidizing agent. We then monitored changes in glutathione poise in cytosolic and mitochondrial matrices following inhibition of glutathione (GSH) synthesis with L-buthionine sulphoximine (BSO). The mitochondrial matrix showed higher oxidation in the BSO-treated cells indicating distinct compartmental alterations in redox poise. Finally, the contributory role of the p53 protein in supporting cytosolic redox poise was demonstrated. Inactivation of the p53 pathway by expression of a dominant-negative p53 protein sensitized the cytosol to oxidation in BSO-treated tumor cells. As a result, both compartments of PF161-T+p53(DD) cells were equally oxidized ≈20 mV by inhibition of GSH synthesis. Conversely, mitochondrial oxidation was independent of p53 status in GSH-deficient tumor cells. Taken together, these findings indicate different redox requirements for the glutathione thiol/disulfide redox couple within the cytosol and mitochondria of resting cells and reveal distinct regulation of their redox poise in response to inhibition of glutathione biosynthesis.

The p66(Shc) adaptor protein controls oxidative stress response in early bovine embryos

The in vitro production of mammalian embryos suffers from high frequencies of developmental failure due to excessive levels of permanent embryo arrest and apoptosis caused by oxidative stress. The p66Shc stress adaptor protein controls oxidative stress response of somatic cells by regulating intracellular ROS levels through multiple pathways, including mitochondrial ROS generation and the repression of antioxidant gene expression. We have previously demonstrated a strong relationship with elevated p66Shc levels, reduced antioxidant levels and greater intracellular ROS generation with the high incidence of permanent cell cycle arrest of 2-4 cell embryos cultured under high oxygen tensions or after oxidant treatment. The main objective of this study was to establish a functional role for p66Shc in regulating the oxidative stress response during early embryo development. Using RNA interference in bovine zygotes we show that p66Shc knockdown embryos exhibited increased MnSOD levels, reduced intracellular ROS and DNA damage that resulted in a greater propensity for development to the blastocyst stage. P66Shc knockdown embryos were stress resistant exhibiting significantly reduced intracellular ROS levels, DNA damage, permanent 2-4 cell embryo arrest and diminished apoptosis frequencies after oxidant treatment. The results of this study demonstrate that p66Shc controls the oxidative stress response in early mammalian embryos. Small molecule inhibition of p66Shc may be a viable clinical therapy to increase the developmental potential of in vitro produced mammalian embryos.

p53 and mitochondrial function in neurons

The p53 tumor suppressor plays a central role in dictating cell survival and death as a cellular sensor for a myriad of stresses including DNA damage, oxidative and nutritional stress, ischemia and disruption of nucleolar function. Activation of p53-dependent apoptosis leads to mitochondrial apoptotic changes via the intrinsic and extrinsic pathways triggering cell death execution most notably by release of cytochrome c and activation of the caspase cascade. Although it was previously believed that p53 induces apoptotic mitochondrial changes exclusively through transcription-dependent mechanisms, recent studies suggest that p53 also regulates apoptosis via a transcription-independent action at the mitochondria. Recent evidence further suggests that p53 can regulate necrotic cell death and autophagic activity including mitophagy. An increasing number of cytosolic and mitochondrial proteins involved in mitochondrial metabolism and respiration are regulated by p53, which influences mitochondrial ROS production as well. Cellular redox homeostasis is also directly regulated by p53 through modified expression of pro- and anti-oxidant proteins. Proper regulation of mitochondrial size and shape through fission and fusion assures optimal mitochondrial bioenergetic function while enabling adequate mitochondrial transport to accommodate local energy demands unique to neuronal architecture. Abnormal regulation of mitochondrial dynamics has been increasingly implicated in neurodegeneration, where elevated levels of p53 may have a direct contribution as the expression of some fission/fusion proteins are directly regulated by p53. Thus, p53 may have a much wider influence on mitochondrial integrity and function than one would expect from its well-established ability to transcriptionally induce mitochondrial apoptosis. However, much of the evidence demonstrating that p53 can influence mitochondria through nuclear, cytosolic or intra-mitochondrial sites of action has yet to be confirmed in neurons. Nonetheless, as mitochondria are essential for supporting normal neuronal functions and in initiating/propagating cell death signaling, it appears certain that the mitochondria-related functions of p53 will have broader implications than previously thought in acute and progressive neurological conditions, providing new therapeutic targets for treatment.

Inhibition of mitochondrial fragmentation diminishes Huntington's disease-associated neurodegeneration

Huntington's disease (HD) is the result of expression of a mutated Huntingtin protein (mtHtt), and is associated with a variety of cellular dysfunctions including excessive mitochondrial fission. Here, we tested whether inhibition of excessive mitochondrial fission prevents mtHtt-induced pathology. We developed a selective inhibitor (P110-TAT) of the mitochondrial fission protein dynamin-related protein 1 (DRP1). We found that P110-TAT inhibited mtHtt-induced excessive mitochondrial fragmentation, improved mitochondrial function, and increased cell viability in HD cell culture models. P110-TAT treatment of fibroblasts from patients with HD and patients with HD with iPS cell-derived neurons reduced mitochondrial fragmentation and corrected mitochondrial dysfunction. P110-TAT treatment also reduced the extent of neurite shortening and cell death in iPS cell-derived neurons in patients with HD. Moreover, treatment of HD transgenic mice with P110-TAT reduced mitochondrial dysfunction, motor deficits, neuropathology, and mortality. We found that p53, a stress gene involved in HD pathogenesis, binds to DRP1 and mediates DRP1-induced mitochondrial and neuronal damage. Furthermore, P110-TAT treatment suppressed mtHtt-induced association of p53 with mitochondria in multiple HD models. These data indicate that inhibition of DRP1-dependent excessive mitochondrial fission with a P110-TAT-like inhibitor may prevent or slow the progression of HD.

The role of mitochondria in age-related hearing loss

Age-related hearing loss (ARHL), the hearing loss associated with aging, is a vital problem in present society. The severity of hearing loss is possibly associated with the degeneration of cochlear cells. Mitochondria play a key role in the energy supply, cellular redox homeostasis, signaling, and regulation of programmed cell death. In this review, we focus on the central role of mitochondria in ARHL. The mitochondrial redox imbalance and mitochondrial DNA mutation might collaboratively involve in the process of cochlear senescence in response to the aging stress. Subsequent responses, including alteration of mitochondrial biogenesis, mitophagy, apoptosis and paraptosis, participate in the aging process from different respects.

NRF2 and p53: Januses in cancer?

The transcription factor nuclear factor (erythroid-derived 2)-like 2, also known as NFE2L2 or NRF2, is a master regulator of the anti-oxidative stress response and positively controls the expression of a battery of anti-oxidative stress response proteins and enzymes implicated in detoxification and glutathione generation. Although its detoxifying activity is important in cancer prevention, it has recently been shown that cancer cells also exploit its protective functions to thrive and resist chemotherapy. NRF2 was also shown to the pentose phosphate pathway and glutaminolysis, which promotes purine synthesis for supporting rapid proliferation and glutathione for providing anti-oxidative stress protection. Evidence obtained from cancer patients and cell lines suggest that NRF2 is highly active in a variety of human cancers and is associated with aggressiveness. p53 is a tumor suppressor that also promotes an anti-oxidative stress metabolic program and glutaminolysis. Here we will discuss the similarities between NRF2 and p53 and review evidence that p53 might be exploited by cancer cells to gain protection against oxidative stress, as is the case for NRF2. We discuss findings of co-regulation between these transcription factors and propose possible therapeutic strategies that can be used for treatment of cancers that harbor WT p53 and express high levels of NRF2.

Expression of CYP1A1, CYP1B1 and MnSOD in a panel of human cancer cell lines

The expression of P450 enzymes and antioxidative enzymes in tumour tissue can have a major impact on the responsiveness of tumours to cancer chemotherapeutic drugs, therefore such information may be very precious when experiments are designed. The compressive information, concerning the expression of drug metabolism enzymes or antioxidative enzymes is still lacking, therefore in this study the expression of CYP1A1, CYP1B1 and mitochondrial superoxide dismutase MnSOD (both mRNA and protein) in a panel of eight commonly used cancer cell lines, representing four tumour tissues was assayed. In the study two ovarian cancer cell lines A2780 and SKOV-3, two colorectal cancer LOVO and DLD-1, two breast cancer derived MCF-7 and MDA-MB-231 and two cervical cancer cell lines HeLa and C33A were employed. The relatively high expression of all assayed enzymes was shown in MDA-MB-231 breast cancer cells, lack of cancer cell specific CYP1B1 protein was discovered in LOVO colorectal cells. In order to test possible correlation between expression of CYP1A1, CYP1B1 and MnSOD and modulators of their activity, cytotoxicity of resveratrol and its promising hydroxylated analogue 3,3′,4,4′,5,5′-trans-hexahydroxystilbene against cell lines used in experiment was assayed. The relatively high correlation was found between IC₅₀ values calculated for 3,3′,4,4′,5,5′-trans-hexahydroxystilbene and expression of MnSOD (r = 0.6562).

Reactive oxygen species regulation of autophagy in cancer: implications for cancer treatment

Reactive oxygen species (ROS) are important in regulating normal cellular processes, but deregulated ROS contribute to the development of various human diseases including cancers. Autophagy is one of the first lines of defense against oxidative stress damage. The autophagy pathway can be induced and upregulated in response to intracellular ROS or extracellular oxidative stress. This leads to selective lysosomal self-digestion of intracellular components to maintain cellular homeostasis. Hence, autophagy is the survival pathway, conferring stress adaptation and promoting viability under oxidative stress. However, increasing evidence has demonstrated that autophagy can also lead to cell death under oxidative stress conditions. In addition, altered autophagic signaling pathways that lead to decreased autophagy are frequently found in many human cancers. This review discusses the advances in understanding of the mechanisms of ROS-induced autophagy and how this process relates to tumorigenesis and cancer therapy.

Pifithrin-μ increases mitochondrial COX biogenesis and MnSOD activity in skeletal muscle of middle-aged mice

We investigated the biogenesis and mitochondrial antioxidant capacity of cytochrome c oxidase (COX) within the skeletal muscle under the treatments of p53 inhibitors (pifithrin, PFTα and PFTμ). Significantly, PFTμ increased mtDNA content and COX biogenesis. These changes coincided with increases in the activity and expression of manganese superoxide dismutase (MnSOD), the key antioxidant enzyme in mitochondria. Conversely, PFTα caused muscle loss, increased oxidative damage and decreased MnSOD activity in intermyofibrillar (IMF) mitochondria. Mechanically, PFTμ inhibited p53 translocation to mitochondria and thus increased its transcriptional activity for expression of synthesis of cytochrome c oxidase 2 (SCO2), an important assembly protein for COX. This study provides in vivo evidence that PFTμ, superior to PFTα, preserves muscle mass and increases mitochondrial antioxidant activity.

The critical role of catalase in prooxidant and antioxidant function of p53

The tumor suppressor p53 is an important regulator of intracellular reactive oxygen species (ROS) levels, although downstream mediators of p53 remain to be elucidated. Here, we show that p53 and its downstream targets, p53-inducible ribonucleotide reductase (p53R2) and p53-inducible gene 3 (PIG3), physically and functionally interact with catalase for efficient regulation of intracellular ROS, depending on stress intensity. Under physiological conditions, the antioxidant functions of p53 are mediated by p53R2, which maintains increased catalase activity and thereby protects against endogenous ROS. After genotoxic stress, high levels of p53 and PIG3 cooperate to inhibit catalase activity, leading to a shift in the oxidant/antioxidant balance toward an oxidative status, which could augment apoptotic cell death. These results highlight the essential role of catalase in p53-mediated ROS regulation and suggest that the p53/p53R2-catalase and p53/PIG3-catalase pathways are critically involved in intracellular ROS regulation under physiological conditions and during the response to DNA damage, respectively.

Disrupted ATP synthase activity and mitochondrial hyperpolarisation-dependent oxidative stress is associated with p66Shc phosphorylation in fibroblasts of NARP patients

p66Shc is an adaptor protein involved in cell proliferation and differentiation that undergoes phosphorylation at Ser36 in response to oxidative stimuli, consequently inducing a burst of reactive oxygen species (ROS), mitochondrial disruption and apoptosis. Its role during several pathologies suggests that p66Shc mitochondrial signalling can perpetuate a primary mitochondrial defect, thus contributing to the pathophysiology of that condition. Here, we show that in the fibroblasts of neuropathy, ataxia and retinitis pigmentosa (NARP) patients, the p66Shc phosphorylation pathway is significantly induced in response to intracellular oxidative stress related to disrupted ATP synthase activity and mitochondrial membrane hyperpolarisation. We postulate that the increased phosphorylation of p66Shc at Ser36 is partially responsible for further increasing ROS production, resulting in oxidative damage of proteins. Oxidative stress and p66Shc phosphorylation at Ser36 may be mitigated by antioxidant administration or the use of a p66Shc phosphorylation inhibitor. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Oxidative stress in apoptosis and cancer: an update

The oxygen paradox tells us that oxygen is both necessary for aerobic life and toxic to all life forms. Reactive oxygen species (ROS) touch every biological and medical discipline, especially those involving proliferative status, supporting the idea that active oxygen may be increased in tumor cells. In fact, metabolism of oxygen and the resulting toxic byproducts can cause cancer and death. Efforts to counteract the damage caused by ROS are gaining acceptance as a basis for novel therapeutic approaches, and the field of prevention of cancer is experiencing an upsurge of interest in medically useful antioxidants. Apoptosis is an important means of regulating cell numbers in the developing cell system, but it is so important that it must be controlled. Normal cell death in homeostasis of multicellular organisms is mediated through tightly regulated apoptotic pathways that involve oxidative stress regulation. Defective signaling through these pathways can contribute to both unbalance in apoptosis and development of cancer. Finally, in this review, we discuss new knowledge about recent tools that provide powerful antioxidant strategies, and designing methods to deliver to target cells, in the prevention and treatment of cancer.

Targeting metabolism and autophagy in the context of haematologic malignancies

Autophagy is a cellular process that maintains the homeostasis of the normal cell. It not only allows for cell survival in times of metabolic stress with nutrient recycling but also is able to lead to cell death when required. During malignant transformation the cell is able to proliferate and survive. This is due to altered cell metabolism and the presence of altered genetic changes that maintain the cell survival. Metabolism was considered an innocent bystander that was a consequence of the increased nutrient requirement for the survival and proliferation of haematological malignancies. The interdependency of metabolism and cellular mechanisms such as autophagy are becoming more evident and important. This interdependence contributes to increased cancer progression and drug resistance. In this paper we aim to discuss autophagy, how it pertains to metabolism in the context of hematologic malignancies, and the implications for therapy.

Metabolic regulation by p53

We are increasingly aware that cellular metabolism plays a vital role in diseases such as cancer, and that p53 is an important regulator of metabolic pathways. By transcriptional activation and other means, p53 is able to contribute to the regulation of glycolysis, oxidative phosphorylation, glutaminolysis, insulin sensitivity, nucleotide biosynthesis, mitochondrial integrity, fatty acid oxidation, antioxidant response, autophagy and mTOR signalling. The ability to positively and negatively regulate many of these pathways, combined with feedback signalling from these pathways to p53, demonstrates the reciprocal and flexible nature of the regulation, facilitating a diverse range of responses to metabolic stress. Intriguingly, metabolic stress triggers primarily an adaptive (rather than pro-apoptotic) p53 response, and p53 is emerging as an important regulator of metabolic homeostasis. A better understanding of how p53 coordinates metabolic adaptation will facilitate the identification of novel therapeutic targets and will also illuminate the wider role of p53 in human biology.