Sex as a response to oxidative stress: stress genes co-opted for sex

Despite a great deal of interest, the evolutionary origins and roles of sex remain unclear. Recently, we showed that in the multicellular green alga, Volvox carteri, sex is a response to increased levels of reactive oxygen species (ROS), which could be indicative of the ancestral role of sex as an adaptive response to stress-induced ROS. To provide additional support for the suggestion that sex evolved as a response to oxidative stress, this study addresses the hypothesis that genes involved in sexual induction are evolutionarily related to genes associated with various stress responses. In particular, this study investigates the evolutionary history of genes specific to the sexual induction process in V. carteri--including those encoding the sexual inducer (SI) and several SI-induced extracellular matrix (ECM) proteins. Surprisingly, (i) a highly diversified multigene family with similarity to the V. carteri SI and SI-induced pherophorin family is present in its unicellular relative, Chlamydomonas reinhardtii (which lacks both a SI and an ECM) and (ii) at least half of the 12 identified gene members are induced (as inferred from reported expressed sequence tags) under various stress conditions. These findings suggest an evolutionary connection between sex and stress at the gene level, via duplication and/or co-option.     

AROS-29 is involved in adaptive response to oxidative stress

Transient adaptation to mild oxidative stress was induced in human osteosarcoma cells chronically grown in sub-toxic concentrations of diethylmaleate (DEM), a glutathione (GSH) depleting agent. The adapted cells, compared to untreated cells, contain increased concentrations of GSH (4-6 fold) which, upon DEM withdrawal from the culture medium, return to normal values and are more resistant to subsequent oxidizing stress induced either by toxic concentrations of the same agent or by (H₂O₂) treatment. To investigate the molecular mechanisms involved in the adaptive response to oxidative stress, we analyzed the gene expression profiles of DEM-adapted cells by differential display. The expression of adaptive response to oxidative stress (AROS)-29 gene, coding for a transmembrane protein of unknown function, as well as of some known genes involved in energy metabolism, protein folding and membrane traffic is up-regulated in adapted cells. The increased resistance to both DNA damage and apoptosis, in cells stably overexpressing AROS-29, demonstrated its functional role in the protection against oxidative stress.     

Aging, sex differences, and oxidative stress in human respiratory and limb muscles

Oxidative stress is involved in the sarcopenia of aging muscles. On the grounds that ventilatory muscles are permanently active, and their activity may even increase with aging, we hypothesized that the levels of oxidative stress would probably be increased in the external intercostals of elderly healthy individuals. We conducted a case-control study in which reactive carbonyl groups, malondialdehyde-protein adducts, 3-nitrotyrosine immunoreactivity, Mn-superoxide dismutase (Mn-SOD), and catalase were detected using immunoblotting in external intercostals and quadriceps (open muscle biopsies) obtained from 12 healthy elderly and 12 young individuals of both sexes. In elderly subjects, reactive carbonyls, malondialdehyde-protein adducts, 3-nitrotyrosine, Mn-SOD, and catalase were significantly greater in the external intercostals than in the young controls. A post hoc analysis, in which men and women from both groups were analyzed separately, revealed that the external intercostals of elderly women, but not those of elderly men, showed significantly increased levels of reactive carbonyls, malondialdehyde-protein adducts, 3-nitrotyrosine, and Mn-SOD compared to those of control females. This study suggests that differences in muscle activity might explain the differential pattern of oxidative stress observed in human respiratory and limb muscles with aging as well as the likely existence of a sex-related regulation of this phenomenon in these muscles.     

Oxidative stress contributes to sex differences in angiotensin II-mediated hypertension in spontaneously hypertensive rats

NADPH oxidase has been implicated in ANG II-induced oxidative stress and hypertension in males; however, the contribution of oxidative stress to ANG II hypertension in females is unknown. In the present study, we tested the hypothesis that greater antioxidant capacity in female spontaneously hypertensive rats (SHR) blunts ANG II-induced oxidative stress and hypertension relative to males. Whole body and renal cortical oxidative stress levels were assessed in female and male SHR left untreated or following 2 wk of chronic ANG II infusion. Chronic ANG II infusion increased NADPH oxidase enzymatic activity in the renal cortex of both sexes; however, this increase only reached significance in female SHR. In contrast, male SHR demonstrated a greater increase in all measurements of reactive oxygen species production in response to chronic ANG II infusion. ANG II infusion increased plasma superoxide dismutase activity only in female SHR (76 ± 9 vs. 190 ± 7 Units·ml(-1)·mg(-1), P < 0.05); however, cortical antioxidant capacity was unchanged by ANG II in either sex. To assess the functional implication of alterations in NADPH enzymatic activity and oxidative stress levels following ANG II infusion, additional experiments assessed the ability of the in vivo antioxidant apocynin to modulate ANG II hypertension. Apocynin significantly blunted ANG II hypertension in male SHR (174 ± 2 vs. 151 ± 1 mmHg, P < 0.05), with no effect in females (160 ± 11 vs. 163 ± 10 mmHg). These data suggest that ANG II hypertension in male SHR is more dependent on increases in oxidative stress than in female SHR.     

Structural and functional differences among human surfactant proteins SP-A1, SP-A2 and co-expressed SP-A1/SP-A2: role of supratrimeric oligomerization

SP-A (surfactant protein A) is a membrane-associated SP that helps to maintain the lung in a sterile and non-inflamed state. Unlike SP-As from other mammalian species, human SP-A consists of two functional gene products: SP-A1 and SP-A2. In all the functions examined, recombinant human SP-A1 invariably exhibits lower biological activity than SP-A2. The objective of the present study was to investigate why SP-A2 possesses greater biological activity than SP-A1 and what advantage accrues to having two polypeptide chains instead of one. We analysed structural and functional characteristics of recombinant baculovirus-derived SP-A1, SP-A2 and co-expressed SP-A1/SP-A2 using a wide array of experimental approaches such as analytical ultracentrifugation, DSC (differential scanning calorimetry) and fluorescence. We found that the extent of supratrimeric assembly is much lower in SP-A1 than SP-A2. However, the resistance to proteolysis is greater for SP-A1 than for SP-A2. Co-expressed SP-A1/SP-A2 had greater thermal stability than SP-A1 and SP-A2 and exhibited properties of each protein. On the one hand, SP-A1/SP-A2, like SP-A2, had a higher degree of oligomerization than SP-A1, and consequently had lower K(d) for binding to bacterial Re-LPS (rough lipopolysaccharide), higher self-association in the presence of calcium and greater capability to aggregate Re-LPS and phospholipids than SP-A1. On the other hand, SP-A1/SP-A2, like SP-A1, was more resistant to trypsin degradation than SP-A2. Finally, the importance of the supratrimeric assembly for SP-A immunomodulatory function is discussed.     

ERK1/2 and p38-MAPK signalling pathways, through MSK1, are involved in NF-kappaB transactivation during oxidative stress in skeletal myoblasts

Skeletal muscle is highly adapted to respond to oxidative imbalances, since it is continuously subjected to an increased production of reactive oxygen species (ROS) during exercise. Oxidative stress, however, has been associated with skeletal muscle atrophy and damage in many diseases. In this study, we examined whether MAPK and NF-κB pathways participate in the response of skeletal myoblasts to oxidative stress, and whether there is a cross talk between these pathways. H₂O₂ induced a strong activation of ERKs, JNKs and p38-MAPK in a time- and dose-dependent profile. ERK and JNK activation by H₂O₂, but not that of p38-MAPK, was mediated by Src kinase and, at least in part, by EGFR. H₂O₂ also stimulated a mild translocation of NF-κB to the nucleus, as well as a moderate phosphorylation of its endogenous cytoplasmic inhibitor IκB (at Ser32/36), without any significant decrease in IκB total levels. Moreover, oxidative stress induced a strong phosphorylation of NF-κB p65 subunit at Ser536 and Ser276. Inhibition of MAPK pathways by selective inhibitors did not appear to affect H₂O₂-induced nuclear translocation of NF-κB or the phosphorylation of IκB. In contrast, phosphorylation of p65 at Ser276 was found to be mediated by MSK1, a substrate of both ERKs and p38-MAPK. In conclusion, it seems that, during oxidative stress, NF-κB translocation to the nucleus is most likely not related with the MAPK activation, while p65 phosphorylations are in part mediated by MAPKs pathways, probably modifying signal specificity.     

Gender related differences in paraoxonase 1 response to high-fat diet-induced oxidative stress

Objective: To evaluate the influence of the pro‐oxidant and proinflammatory state related to dietary obesity on serum paraoxonase 1 (PON1) activity in male and female rats. Methods and Procedures: Adult Wistar rats of both genders were fed on a high‐fat diet to induce weight gain or standard diet for 14 weeks. Body weight was assessed weekly and food intake fortnightly throughout the dietary treatment. Biometrical parameters and serum lipid profile, glucose, insulin, and adipokine levels were measured. To assess the effect of dietary obesity on oxidative stress, levels of liver and serum thiobarbituric acid reactive substances, liver protein carbonyl groups, liver antioxidant enzymes activities, and serum PON1 activities were measured. Results: High‐fat diet feeding induced a significant body weight gain in both male and female rats, as well as a reduction of liver antioxidant protection. High‐fat diet increased serum lipid peroxides in male rats and reduced serum PON1 activities and serum apolipoprotein A‐I (apoA‐I) levels in females, although did not alter serum PON1 or apolipoprotein J (apoJ) levels. Discussion: Our results reveal a gender dimorphism in the high‐fat diet‐induced reduction of serum PON1 activity, which is likely to be related to the greater obese and proinflammatory state achieved in female rats. We suggest that the enhanced oxidative stress caused by dietary increased body weight, on leading to high‐density lipoprotein (HDL), apoA‐I or PON1 oxidation could entail the destabilization of the PON1 association to HDL or a direct inactivation of PON1 enzymatic activity, thus accounting for the decreased serum PON1 activities observed in female rats.     

Signaling pathways involved in virulence and stress response of plant-pathogenic Fusarium species

Fungal pathogens face similar stress conditions to those affecting plants and saprotrophic fungi. Therefore, mechanisms underlying fungal response to the stress factors may be well-conserved across various taxa. Saccharomyces cerevisiae was the most researched for signal transduction pathways but many of the pathways' components were later reported for filamentous fungi as well. The most widely studied pathways are those involving the G proteins, adenylate cyclase (cAMP) and mitogen-activated protein kinases (MAPKs). Apart from these, the target-of-rapamycin (TOR), calcium/calcineurin and cell wall integrity (CWI) pathways are of significant interest when stress response is considered. All these pathways were included in this review. It seems that the TOR-received signals are transferred to the CWI pathway, secondary metabolism and virulence. Specific and non-specific cellular responses of Fusarium species, triggered by signals received from the environment, were discussed, with particular focus on stress response and pathogenicity towards the plant host.     

Identification of the Clostridium perfringens genes involved in the adaptive response to oxidative stress

Clostridium perfringens is a ubiquitous gram-positive pathogen that is present in the air, soil, animals, and humans. Although C. perfringens is strictly anaerobic, vegetative and stationary cells can survive in a growth-arrested stage in the presence of oxygen and/or low concentrations of superoxide and hydroxyl radicals. Indeed, it possesses an adaptive response to oxidative stress, which can be activated in both aerobic and anaerobic conditions. To identify the genes involved in this oxidative stress response, C. perfringens strain 13 mutants were generated by Tn916 insertional mutagenesis and screened for resistance or sensitivity to various oxidative stresses. Three of the 12 sensitive mutants examined harbored an independently inserted single copy of the transposon in the same operon as two genes orthologous to the ydaD and ycdF genes of Bacillus subtilis, which encode a putative NADPH dehydrogenase. Complementation experiments and knockout experiments demonstrated that these genes are both required for efficient resistance to oxidative stress in C. perfringens and are probably responsible for the production of NADPH, which is required for maintenance of the intracellular redox balance in growth-arrested cells. Other Tn916 disrupted genes were also shown to play important roles in the oxidative stress response. This is the first time that some of these genes (e.g., a gene encoding an ATP-dependent RNA helicase, the beta-glucuronidase gene, and the gene encoding the atypical iron sulfur prismane protein) have been shown to be involved in the oxidative response.     

Inflammation, gene mutation and photoimmunosuppression in response to UVR-induced oxidative damage contributes to photocarcinogenesis

Ultraviolet (UV) radiation causes inflammation, gene mutation and immunosuppression in the skin. These biological changes are responsible for photocarcinogenesis. UV radiation in sunlight is divided into two wavebands, UVB and UVA, both of which contribute to these biological changes, and therefore probably to skin cancer in humans and animal models. Oxidative damage caused by UV contributes to inflammation, gene mutation and immunosuppression. This article reviews evidence for the hypothesis that UV oxidative damage to these processes contributes to photocarcinogenesis. UVA makes a larger impact on oxidative stress in the skin than UVB by inducing reactive oxygen and nitrogen species which damage DNA, protein and lipids and which also lead to NAD+ depletion, and therefore energy loss from the cell. Lipid peroxidation induces prostaglandin production that in association with UV-induced nitric oxide production causes inflammation. Inflammation drives benign human solar keratosis (SK) to undergo malignant conversion into squamous cell carcinoma (SCC) probably because the inflammatory cells produce reactive oxygen species, thus increasing oxidative damage to DNA and the immune system. Reactive oxygen or nitrogen appears to cause the increase in mutational burden as SK progress into SCC in humans. UVA is particularly important in causing immunosuppression in both humans and mice, and UV lipid peroxidation induced prostaglandin production and UV activation of nitric oxide synthase is important mediators of this event. Other immunosuppressive events are likely to be initiated by UV oxidative stress. Antioxidants have also been shown to reduce photocarcinogenesis. While most of this evidence comes from studies in mice, there is supporting evidence in humans that UV-induced oxidative damage contributes to inflammation, gene mutation and immunosuppression. Available evidence implicates oxidative damage as an important contributor to sunlight-induced carcinogenesis in humans.     

Cu/Zn-superoxide dismutase and glutathione are involved in response to oxidative stress induced by protein denaturing effect of alachlor in Saccharomyces cerevisiae

Alachlor is a widely used pre-emergent chloroacetanilide herbicide which has been shown to have many harmful ecological and environmental effects. However, the mechanism of alachlor-induced oxidative stress is poorly understood. We found that, in Saccharomyces cerevisiae, the intracellular levels of reactive oxygen species (ROS) including superoxide anions were increased only after long-term exposure to alachlor, suggesting that alachlor is not a pro-oxidant. It is likely that alachlor-induced oxidative stress may result from protein denaturation because alachlor rapidly induced an increased protein aggregation, leading to upregulation of SSA4 and HSP82 genes encoding heat shock proteins (Hsp) of Hsp70 and Hsp90 family, respectively. Although only SOD1 encoding Cu/Zn-superoxide dismutase (SOD), but not SOD2 encoding Mn-SOD, is essential for alachlor tolerance, both SODs play a crucial role in reducing alachlor-induced ROS. We found that, after alachlor exposure, glutathione production was inhibited while its utilization was increased, suggesting the role of glutathione in protecting cells against alachlor, which becomes more important when lacking Cu/Zn-SOD. Based on our results, it seems that alachlor primarily causes damages to cellular macromolecules such as proteins, leading to an induction of endogenous oxidative stress, of which intracellular antioxidant defense systems are required for elimination.     

Adaptive response to oxidative stress: Bacteria, fungi, plants and animals

Reactive oxygen species (ROS) are continuously produced and eliminated by living organisms normally maintaining ROS at certain steady-state levels. Under some circumstances, the balance between ROS generation and elimination is disturbed leading to enhanced ROS level called "oxidative stress". The primary goal of this review is to characterize two principal mechanisms of protection against oxidative stress - regulation of membrane permeability and antioxidant potential. The ancillary goals of this work are to describe up to date knowledge on the regulation of the previously mentioned mechanisms and to identify areas of prospective research and emerging directions in investigation of adaptation to oxidative stress. The ubiquity for challenges leading to oxidative stress development calls for identification of common mechanisms. They are cysteine residues and [Fe,S]-clusters of specific regulatory proteins. The latter mechanism is realized via SoxR bacterial protein, whereas the former mechanism is involved in operation of bacterial OxyR regulon, yeast H(2)O(2)-stimulon, plant NPR1/TGA and Rap2.4a systems, and animal Keap1/Nrf2, NF-κB and AP-1, and others. Although hundreds of studies have been carried out in the field with different taxa, the comparative analysis of adaptive response is quite incomplete and therefore, this work aims to cover a plethora of phylogenetic groups to delineate common mechanisms. In addition, this article raises some questions to be elucidated and points out future directions of this research. The comparative approach is used to shed light on fundamental principles and mechanisms of regulation of antioxidant systems. The idea is to provide starting points from which we can develop novel tools and hypothesis to facilitate meaningful investigations in the physiology and biochemistry of organismic response to oxidative stress.     

Distinct osmo-sensing protein kinase pathways are involved in signalling moderate and severe hyper-osmotic stress

Plant growth is severely affected by hyper-osmotic salt conditions. Although a number of salt-induced genes have been isolated, the sensing and signal transduction of salt stress is little understood. We provide evidence that alfalfa cells have two osmo-sensing protein kinase pathways that are able to distinguish between moderate and extreme hyper-osmotic conditions. A 46 kDa protein kinase was found to be activated by elevated salt concentrations (above 125 mM NaCl). In contrast, at high salt concentrations (above 750 mM NaCl), a 38 kDa protein kinase, but not the 46 kDa kinase, became activated. By biochemical and immunological analysis, the 46 kDa kinase was identified as SIMK, a member of the family of MAPKs (mitogen-activated protein kinases). SIMK is not only activated by NaCl, but also by KCl and sorbitol, indicating that the SIMK pathway is involved in mediating general hyper-osmotic conditions. Salt stress induces rapid but transient activation of SIMK, showing maximal activity between 8 and 16 min before slow inactivation. When inactive, most mammalian and yeast MAPKs are cytoplasmic but undergo nuclear transloca- tion upon activation. By contrast, SIMK was found to be a constitutively nuclear protein and the activity of the kinase was not correlated with changes in its intra-cellular compartmentation, suggesting an intra-nuclear mechanism for the regulation of SIMK activity.