Oxidative stress and cellular differentiation

Impact of Oxidative Stress on Molecular Mechanisms of Cervical Ripening in Pregnant Women

Uterine cervix is one of the essential factors in labor and maintaining the proper course of pregnancy. During the last days of gestation, the cervix undergoes extensive changes manifested by transformation from a tight and rigid to one that is soft and able to dilate. These changes can be summarized as “cervical ripening”. Changes in the cervical tissue can be referred to as remodeling of the extracellular matrix. The entire process is the result of a close relationship between biochemical and molecular pathways, which is strictly controlled by inflammatory and endocrine factors. When the production of reactive oxygen species exceeds the antioxidant capacity, oxidative stress occurs. A physiologic increase of reactive oxygen species (ROS) and reactive nitrogen species (RNS) is observed through pregnancy. ROS play important roles as second messengers in many intracellular signaling cascades contributing to the course of gestation. This review considers their involvement in the cervical ripening process, emphasizing the molecular and biochemical pathways and the clinical implications.

Gene Expression During Early Folliculogenesis in Goats Using Microarray Analysis

Understanding of gene expression and metabolic, biological and physiological pathways in ovarian follicular development can have a significant impact on the dynamics of follicular atresia or survival. In fact, some oocyte loss occurs during the transition from secondary to early tertiary follicles. This study aimed to understand, by microarray analysis, the temporal changes in transcriptional profiles of secondary and early antral (tertiary) follicles in caprine ovaries. Ovarian follicles were microdissected and pooled to extract total RNA. The RNA was cross hybridized with the bovine array. Among 23,987 bovine genes, a total of 14,323 genes were hybridized with goat mRNAs while 9,664 genes were not. Of all the hybridized genes, 2,466 were stage-specific, up- and down-regulated in the transition from secondary to early tertiary follicles. Gene expression profiles showed that three major metabolic pathways (lipid metabolism, cell death, and hematological system) were significantly differentiated between the two follicle stages. In conclusion, this study has identified important genes and pathways which may potentially be involved in the transition from secondary to early tertiary follicles in goats.

In utero oxidative stress epigenetically programs antioxidant defense capacity and adulthood diseases

SIGNIFICANCE

Maternal health and diet during gestation are critical for predicting fetal outcomes, both immediately at birth and in adulthood. While epigenetic modifications have previously been tightly linked to carcinogenesis, recent advances in the field have suggested that numerous adulthood diseases, including those characteristic of metabolic syndrome, could be programmed in utero in response to maternal exposures, and these "programmable" diseases are associated with epigenetic modifications of vital genes.

RECENT ADVANCES

While little is currently known about the epigenetic regulation of the antioxidant (AOX) defense system, several studies in animals show that AOX defense capacity may be programmed in utero, making it likely that the critical genes involved in this pathway are epigenetically regulated, either by DNA methylation or by the modification of histone tails.

CRITICAL ISSUES

This article presents the most current knowledge of the in utero regulation of the AOX defense capacity, and will specifically focus on the potential epigenetic regulation of this system in response to various in utero exposures or stimuli. The ability to appropriately respond to oxidative stress is critical for the health and survival of any organism, and the potential programming of this capacity may provide a link between the in utero environment and the tendency of certain individuals to be more susceptible toward disease stimuli in their postnatal environments.

FUTURE DIRECTIONS

We sincerely hope that future studies which result in a deeper understanding of the in utero programming of the epigenome will lead to novel and effective therapies for the treatment of epigenetically linked diseases.

The redox stress hypothesis of aging

The main objective of this review is to examine the role of endogenous reactive oxygen/nitrogen species (ROS) in the aging process. Until relatively recently, ROS were considered to be potentially toxic by-products of aerobic metabolism, which, if not eliminated, may inflict structural damage on various macromolecules. Accrual of such damage over time was postulated to be responsible for the physiological deterioration in the postreproductive phase of life and eventually the death of the organism. This "structural damage-based oxidative stress" hypothesis has received support from the age-associated increases in the rate of ROS production and the steady-state amounts of oxidized macromolecules; however, there are increasing indications that structural damage alone is insufficient to satisfactorily explain the age-associated functional losses. The level of oxidative damage accrued during aging often does not match the magnitude of functional losses. Although experimental augmentation of antioxidant defenses tends to enhance resistance to induced oxidative stress, such manipulations are generally ineffective in the extension of life span of long-lived strains of animals. More recently, in a major conceptual shift, ROS have been found to be physiologically vital for signal transduction, gene regulation, and redox regulation, among others, implying that their complete elimination would be harmful. An alternative notion, advocated here, termed the "redox stress hypothesis," proposes that aging-associated functional losses are primarily caused by a progressive pro-oxidizing shift in the redox state of the cells, which leads to the overoxidation of redox-sensitive protein thiols and the consequent disruption of the redox-regulated signaling mechanisms.

Human umbilical cord blood-derived mesenchymal stem cells undergo cellular senescence in response to oxidative stress

Since human mesenchymal stem cells (MSCs) are therapeutically attractive for tissue regeneration and repair, we examined the physiological responses of human umbilical cord blood-derived MSCs (hUCB-MSCs) to genotoxic stress. We found that that sublethal doses of reactive oxygen species (ROS) and ionizing radiation cause DNA damage and reduce DNA synthesis and cell proliferation in hUCB-MSCs, resulting in cellular senescence. In contrast, these physiological changes were limited in human fibroblast and cancer cells. Our data show that reduced activities of antioxidant enzymes, which may occur due to low gene expression levels, cause hUCB-MSCs to undergo cellular senescence in response to oxidative stress and ionizing radiation. Resistance of hUCB-MSCs to oxidative stresses was restored by increasing the intracellular antioxidant activity in hUCB-MSCs via exogenous addition of antioxidants. Therefore, the proliferation and fate of hUCB-MSCs can be controlled by exposure to oxidative stresses.

Expression of antioxidant defense and poly(ADP-ribose) polymerase-1 in rat developing Sertoli cells

Sertoli cells play an essential role in the development of a functional testis. ROS (reactive oxygen species) are normally produced by the developing testicular cells and may be dangerous to spermatogenesis. The aim of this study was to investigate the developmental expression of genes involved in antioxidant defense as well as in the DNA damage response in rat Sertoli cells. As revealed by quantitative RT-PCR analysis, the expression pattern of the antioxidant enzymes GST (glutathione-S-transferase), CAT (catalase) and SOD (superoxide dismutase) showed a progressive decrease from birth to puberty. The expression level of the oncosuppressor p53 revealed a net reduction as well. We next focused on PARP-1 [poly(ADP-ribose) polymerase-1], a 'guardian of the genome' that combats stress conditions. At both the mRNA and protein level, PARP-1 expression was low at the early stage of development and increased later on. Maximal PARP-1 expression was preceded by a rise in the transcript level for MTs (metallothioneins), which provide zinc to zinc-dependent enzymes and proteins, including PARP-1. Our results showed an increased expression of PARP-1 during Sertoli cell development, together with a decrease in the expression of antioxidant enzymes. In conclusion, a role of PARP-1 in protecting the testicular differentiation is suggested.

Correlation between circulating biomarkers of oxidative stress of maternal and umbilical cord blood at birth

The objective of the work was to study the relationship between the oxidative state of the mother and the newborn at the moment of birth. We measured oxidative stress markers (carbonyl groups, lipid peroxides and total antioxidant capacity (TAC)) and found a good correlation between the oxidative state of the normal mother and the neonate, since a high mother oxidative stress corresponds to an even higher oxidative stress of the newborn in umbilical cord blood. We also found that smoking mothers and their newborns had a higher concentration of the carbonyl group, lipid peroxides and less TAC. Newborns from these mothers weighed significantly less than others at birth. These data suggest a need for interest in monitoring the oxidative state of mothers during the pregnancy period, especially taking into account that the oxidative level could be involved in later risks of metabolic diseases for both mother and newborn.

Acute mild hypothermia caused by a low dose of X-irradiation induces a protective effect against mid-lethal doses of X-rays, and a low level concentration of ozone may act as a radiomimetic

Acute changes in core body temperature following exposure to a low dose of X-rays were assessed in unanaesthetized and unrestrained mice. Radiotelemetry techniques were used to monitor core body temperature continuously. Following exposure to a 20 cGy dose of X-rays, the mice displayed a rapid and significant reduction in core body temperature relative to the sham-treated (non-irradiated) control animals. The present studies, and those by others, showed that pre-exposure to X-rays at doses as low as 20 cGy may result in a reduced mortality rate following subsequent exposure to X-rays at mid-lethal dose levels. This indicates an increased tolerance to radiation. An additional experiment was conducted to examine whether the reduction in the mortality rate following exposure to mid-lethal doses of radiation could be found when mice were subjected to a stressor, ozone inhalation, which induced a suppression in body temperature. The results showed that following inhalation of ozone at a concentration of 0.5 ppm, 93% of the treated animals survived a mid-lethal dose of radiation, whereas 50% of the sham-control animals died within 30 days. These results suggest that low-dose-induced tolerance to radiation may be dependent on a brief exposure to ozone, and a reduction in core temperature may be necessary to obtain tolerance effects in response to a mid-lethal dose of radiation.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Disappearance of stress-induced hyperthermia following a low dose of X-irradiation: involvement of the vomeronasal system in the modulation of the radiation-induced effects

When the rectal temperatures of group-housed mice are measured sequentially, the temperature of the last mouse to be measured is higher than that of the first mouse. The hyperthermia effect observed in the last animal to be measured forms the basis of an experimental paradigm for studying the neurobiology of anticipatory anxiety. Stress-induced hyperthermia (SIH) was calculated as the difference (delta T) between the basal temperature (the averages of the first three mice) and the final temperature (the averages of the last three mice) when the temperatures of the 15 mice were measured sequentially, with a 2 min interval between each temperature measurement. The hyperthermia observed in the last animals measured was abolished by prior treatment with X-irradiation at the relatively low dose of 5-15 cGy. Prevention of the SIH response could be found when the irradiation was confined to the head region only, suggesting the importance of the brain in the radiation-induced effect. Relatively higher doses of 25 or 35 cGy failed to reduce the hyperthermia stress effect. Furthermore, the effect of X-irradiation was not observed following olfactory bulbectomy or resection of the vomeronasal tract. These results indicate that the disappearance of SIH response may only be found following irradiation at low dose levels. Furthermore, the results implicate the olfactory system in the radiation-induced anti-stress effect.

Analgesia induced by repeated exposure to low dose x-rays in mice, and involvement of the accessory olfactory system in modulation of the radiation effects

The effects of low-dose x-rays on mouse nociceptive behavior were examined using a formalin injected test that rated the amount of time the animals spent licking the injected hind paw. Male ICR White Swiss mice showed a marked suppression of licking behavior after repeated low-dose x-irradiation (5 cGy/day, 6 consecutive days). The most profound effect was observed on the day 30 after irradiation. The decline of licking behavior, however, was not observed at all following olfactory bulbectomy or vomeronasal tract cut. The analgesic effects could be observed in writhing animals administered acetic acid intraperitoneally. Moreover, analgesia was totally blocked by the administration of N-nitro-L-arginine, a nitric oxide synthase inhibitor, to accessory olfactory bulbs prior to the exposure. The present results indicate that the olfactory system plays an important role in modulation of radiation-induced analgesia, and a possible involvement of nitric oxide in the formation of recognition memory subjected to repeated x-rays. Relatively higher doses (5 cGy x 9 days, 5 cGy x 12 days), however, did not induce such effects, namely, the decline of nociceptive response was limited to the animals irradiated with the smaller dose.

Head-portion exposure to low-level X-rays reduces isolation-induced aggression of mouse, and involvement of the olfactory carnosine in modulation of the radiation effects

Social isolation has been widely described to induce a compulsive aggressive behavior. The aggressiveness due to isolation in mice has often been used as a means for the better understanding of disturbed behavior in human beings. In the course of a study of the behavioral effects, we have noticed that fighting injuries, usually observed among male ICR mice, tend to decrease in mice irradiated with low-dose X-rays. We, therefore, quantitatively examined the effects of low-dose X-irradiation on aggressive behavior using a resident-intruder paradigm in which a resident mouse attacks an intruder that entered its territory. Male ICR white Swiss mice became gradually calm, and showed remarkably quiet behavior 7-10 days after whole-head 5 or 15 cGy X-irradiation. Only exposure of the anterior part of the head (olfactory system including orbits) also induced the remarkable suppression of the aggressive behavior. The olfactory system has direct access to the limbic system, a central part of the brain concerned with emotion. The calm behavior induced by low-dose X-irradiation might be related to the changes in the olfactory function. We also obtained data on brain biochemistry giving further support for the above low-dose effects on mouse behavior. The carnosine content and its synthetase activity in the olfactory bulbs decreased significantly after only the anterior part of the head had been exposed. Higher doses (25-35 cGy), however, did not induce such effects. The results suggest that the depression of aggressive behavior is limited to animals irradiated with the smaller doses.

The free radical hypothesis of aging: an appraisal of the current status

The objective of this review article is to assess the current status of the predictions of the free radical hypothesis of aging, highlighting some of the controversies surrounding the previous assumptions. Topics for discussion include: metabolic rate and aging, oxidative stress and molecular damage during aging, antioxidants and aging, antioxidant defenses and life spans of different species, and pro-oxidant generation and aging. On the basis of currently available evidence, it is concluded that the free radical hypothesis has neither been proven nor disproven. Some of the earlier assumptions such as that antioxidant intake increases life span, or antioxidant defenses decline with age, or antioxidant defenses are positively correlated with life spans of different species, or that longer life spans are associated with lower autoxidizability, are not clearly supportable. Similarly, the assumption that oxygen free radicals govern the rate of aging via the infliction of molecular damage lacks compelling support. Enough information to lift the free radical hypothesis above the level of speculation has not yet been amassed. Clearly, further studies, some of which specifically focus on disproving this hypothesis, are needed to confirm its veracity.

DNA strand breaks and DNA repair response in lymphocytes after chronic in vivo exposure to very low doses of ionizing radiation in mice

In contrast to the well-documented negative effects of high-dose oxidant exposure, accumulating evidence supports a positive, perhaps essential physiologic role for very low-level oxidant stress. For example, low-level oxidant exposure, within or below the physiologic range, has been reported to stimulate membrane signal transduction, proliferation, antioxidant defense and DNA repair. In the present study, we have examined whether whole-body exposure to low-dose radiation (LDR) results in an alteration in constitutive (steady state) levels of DNA-strand breaks and whether an adaptive increase in DNA-repair response is induced. C57B1/6J mice were exposed to 0.04 Gy (4 cGy) of gamma-radiation as a model of low level oxidant stress. End points measured after chronic in vivo LDR included: (1) constitutive expression of DNA-strand breaks in quiescent spleen cells; (2) sensitivity to DNA damage after high-dose radiation exposure in vitro; (3) repair of constitutive and radiation-induced DNA strand breaks after mitogen stimulation: (4) activity of the DNA-repair associated enzyme, poly(ADP-ribose)transferase (ADPRT) and its substrate, NAD. The results indicated that the constitutive expression of DNA-strand breaks is significantly decreased after chronic LDR; however, DNA-repair capacity after high-dose radiation exposure is not increased above that observed in sham-irradiated mice. Associated with the reduction in constitutive DNA-strand break accumulation was a decrease in resting levels of the DNA-repair-associated enzyme poly(ADP-ribose) transferase (ADPRT). These results are consistent with the interpretation that cumulative DNA damage and associated DNA-repair activity in unstimulated cells are both reduced after chronic LDR exposure.

Oxidative stress in mitochondria: its relationship to cellular Ca2+ homeostasis, cell death, proliferation, and differentiation

A variety of chemically different prooxidants causes Ca2+ release from mitochondria. This prooxidant-induced Ca2+ release occurs from intact mitochondria via a route which is physiologically relevant and may be regulated by protein monoADP-ribosylation. When the released Ca2+ is excessively 'cycled' by mitochondria (continuously taken up and released) the inner membrane is damaged. This leads to a decreased ability of mitochondria to retain Ca2+, uncoupling of mitochondria, and an impairment of ATP synthesis, which in turn deprives the cell of the energy necessary for the proper functioning of the Ca2+ ATPases of the endoplasmic (sarcoplasmic) reticulum, the nucleus and the plasma membrane. The ensuing rise of the cytosolic Ca2+ level cannot be counterbalanced by the damaged mitochondria which, under normoxic conditions, act as a safety device against an increase of the cytosolic Ca2+ concentration. The impaired ability of mitochondria to retain Ca2+ may lead to cell death. However, there is also evidence emerging that release of Ca2+ from mitochondria may be physiologically important for cell proliferation and differentiation.

Oxidative stress as a causal factor in differentiation and aging: a unifying hypothesis

In this article, the authors have pointed out flaws in the current version of the free radical hypothesis of aging and have advanced a new hypothesis that reconciles and encapsulates existing information. The main premise of this hypothesis is that aging is a continuation of development and is thus influenced by genetically programmed phenomena. Completion of various genetic programs and the duration of life are linked to a metabolic potential which is itself a genetically determined sum of energy expenditure. Nevertheless, the rate at which metabolic potential is reached is linked to the rate of metabolism and the level of oxidative stress both of which are influenced by epigenetic stimuli. The current version of the free radical hypothesis postulates that partially reduced oxygen species are produced in aerobic cells in an uncontrolled fashion and do not play any useful physiological function. The principle tenet of the free radical hypothesis is that molecular damage is the underlying cause of aging and that O2- radicals and derivatives induce most of the damage sustained by cells during aging. The authors regard this hypothesis as flawed because it fails to explain either low randomly occurring damage can lead to age-associated changes that are species-specific, or the sequential nature of the changes that occur in aging organisms. In contrast to the free radical hypothesis, our hypothesis can explain the specific and sequential nature of aging-related changes because they are postulated to be neither dependent upon uncontrolled damage nor the cellular capacity to prevent it. Instead, the authors suggest that the damage accumulated during aging is a secondary effect rather than a direct cause of senescence. The authors have shown that cells exert control not only on their level of antioxidant defense but also on their rate of oxidant production. The authors postulate that aging is the terminal stage of development, and as such is influenced genetically. The authors also postulate that a definite sum of energy is required to complete the genetic programs associated with aging. Thus, the rate of aging is linked to the level of oxidative stress; the rate of energy utilization is postulated to determine the level of oxidative stress. Oxidative stress is one of the factors which appears to govern changes in gene expression during differentiation and we suggest that it causes alterations in gene expression during aging. In the authors revised hypothesis, free radicals promote aging by affecting specific genetic programs and the incidental damage they inflict in cells is only a by-product of this process.(ABSTRACT TRUNCATED AT 400 WORDS)