DL-alpha-tocopherol acetate mitigates maternal hyperthermia-induced pre-implantation embryonic death accompanied by a reduction of physiological oxidative stress in mice

Heat stress: a major threat to ruminant reproduction and mitigating strategies

Stress is an external event or condition that puts pressure on a biological system. Heat stress is defined as the combination of internal and external factors acting on an animal to cause an increase in body temperature and elicit a physiological response. Heat stress is a set of conditions caused by overexposure to or overexertion at excess ambient temperature and leads to the inability of animals to dissipate enough heat to sustain homeostasis. Heat exhaustion, heat stroke, and cramps are among the symptoms. For the majority of mammalian species, including ruminants, heat stress has a negative impact on physiological, reproductive, and nutritional requirements. Reproductive functions, including the male and female reproductive systems, are negatively affected by heat stress. It decreases libido and spermatogenic activity in males and negatively affects follicle development, oogenesis, oocyte maturation, fertilization, implantation, and embryo-fetal development in females. These effects lead to a decrease in the rate of reproduction and financial losses for the livestock industry. Understanding the impact of heat stress on reproductive tissues will aid in the development of strategies for preventing heat stress and improving reproductive functions. Modification of the microenvironment, nutritional control, genetic development of heat-tolerant breeds, hormonal treatment, estrous synchronization, timed artificial insemination, and embryo transfer are among the strategies used to reduce the detrimental effects of heat stress on reproduction. These strategies may also increase the likelihood of establishing pregnancy in farm animals.

Redox Status and Hematological Variables in Melatonin-Treated Ewes during Early Pregnancy under Heat Stress

The preovulatory follicles and preimplantation stage embryos are found to be rather sensitive to heat stress due to their low potential for scavenging reactive oxygen species (ROS). The aim of the present study was to assess the impact of melatonin administration on redox status and hematological variables during the preovulatory period and early stages of embryogenesis in heat-stressed ewes in vivo. Forty Karagouniko-breed ewes were divided in two groups, the melatonin (M, n = 20) group and control (C, n = 20) one. All animals were subjected to heat stress throughout the study, which lasted forty days (D0 to D40). In M group, melatonin implants were administered on D0. Then, oestrous synchronization was applied (D19-D33). On D34, six rams were introduced into the ewe flock for mating. Ultrasonographic examination was conducted on D73 for pregnancy diagnosis. The temperature humidity index (THI), the rectal temperature (RT), and the number of breaths per minute (BR) were evaluated twice daily. Redox biomarkers, namely total antioxidant capacity (TAC), reduced glutathione (GSH), and thiobarbituric acid reactive substances (TBARS), were assayed in blood samples collected on D0, D33, and D40. In addition, packed cell volume (PCV), white blood cells (WBCs), leukocyte differential count, and cortisol assessment were conducted in blood samples on D33 and D40. The results indicated improved fertility rate and mean number of lambs born per ewe due to improved redox status (p < 0.05) in ewes that received melatonin implants 34 days approximately before the onset of oestrus. The PCV decreased in both groups between the two time-points (p < 0.05). However, the NEU/LYMPH ratio decreased (p < 0.05) only in group M. The low cortisol levels and the decreased NEU/LYMPH ratio in both groups support the hypothesis that ewes of the indigenous Karagouniko breed may exhibit adaptation to environmental thermal stress. The administration of melatonin as an antioxidant regime may improve the reproductive competence of heat stressed ewes and may also enhance their ability to adapt at high ambient temperatures.

NQO2 inhibition relieves reactive oxygen species effects on mouse oocyte meiotic maturation and embryo development

NRH: quinone oxidoreductase 2 (NQO2) is a cytosolic and ubiquitously expressed flavoprotein that catalyzes the two-electron reduction of quinone to hydroquinones. Herein, we assessed the protein expression, subcellular localization, and possible functions of NQO2 in mouse oocyte meiotic maturation and embryo development. Western blot analysis detected high and stable protein expression of NQO2 in mouse oocytes during meiotic progression. Immunofluorescence illustrated NQO2 distribution on nuclear membrane, chromosomes, and meiotic spindles. Microtubule poisons treatment (nocodazole and taxol) showed that filamentous assembly of NQO2 and its co-localization with microtubules require microtubule integrity and normal dynamics. Increased levels of NQO2, reactive oxygen species (ROS), malondialdehyde (MDA), and autophagy protein Beclin1 expression were detected in oocytes cultured with ROS stimulator vitamin K3 (VK3), combined with decreased antioxidant glutathione (GSH). These oocytes were arrested at metaphase I with abnormal spindle structure and chromosome configuration. However, this impact was counteracted by melatonin or NQO2 inhibitor S29434, and the spindle configuration and first polar body extrusion were restored. Similarly, morpholino oligo-induced NQO2 knockdown suppressed ROS, MDA, and Beclin1, instead increased GSH in oocytes under VK3. Supplementary S29434 or melatonin limited changes in NQO2, ROS, MDA, Beclin1, and GSH during in vitro aging of ovulated oocytes, thereby maintaining spindle structure, as well as ordered chromosome separation and embryo development potential after parthenogenetic activation with SrCl2. Taken together, NQO2 is involved in ROS generation and subsequent cytotoxicity in oocytes, and its inhibition can restore oocyte maturation and embryo development, suggesting NQO2 as a pharmacological target for infertility cure.

Melatonin protects porcine oocyte in vitro maturation from heat stress

Melatonin is a pleiotropic molecule which plays an important role in animal reproductive activities. Because of the increased global warming, the impact of heat stress (HS) on stockbreeding has become an inevitable issue to be solved. To investigate the potential effects of melatonin on the in vitro maturation of porcine oocyte under the HS, a HS model for porcine oocyte maturation has been used in this study and the different concentrations of melatonin (10(-6) -10(-9)  m) were also tested for their protective effects on oocytes. The polar body rate, the index of the nuclear maturation of the oocytes, and the cleavage rate as well as the blastocyst rate were measured to evaluate the developmental competence of the oocytes after parthenogenetic activation (PA). The results showed that HS [in vitro maturation (IVM) 20-24 hr, 42°C] significantly reduced the polar body rate of oocytes and the blastocyte rate of porcine PA embryos, while melatonin (10(-7)  m) application not only improved polar body rate and blastocyte rate, but also preserved the normal levels of steroid hormone which is disrupted by HS. The presence of melatonin (10(-7)  m) during the oocyte maturation under the HS reduced reactive oxygen species (ROS) formation, enhanced glutathione (GSH) production, inhibited cell apoptosis, and increased the gene expressions of SIRT1, AKT2, and Polg2. Importantly, the endogenously occurring melatonin of cumulus-oocyte complexes was significantly induced by HS. The results indicated that melatonin application effectively protected the oocytes from HS. These observations warranted the further studies in vivo regarding to improve the reproductive activities of animals under the global warming environment.

Changes in the transcriptome of morula-stage bovine embryos caused by heat shock: relationship to developmental acquisition of thermotolerance

BACKGROUND

While initially sensitive to heat shock, the bovine embryo gains thermal resistance as it progresses through development so that physiological heat shock has little effect on development to the blastocyst stage by Day 5 after insemination. Here, experiments using 3' tag digital gene expression (3'DGE) and real-time PCR were conducted to determine changes in the transcriptome of morula-stage bovine embryos in response to heat shock (40 degrees C for 8 h) that could be associated with thermotolerance.

RESULTS

Using 3'DGE, expression of 173 genes were modified by heat shock, with 94 genes upregulated by heat shock and 79 genes downregulated by heat shock. A total of 38 differentially-regulated genes were associated with the ubiquitin protein, UBC. Heat shock increased expression of one heat shock protein gene, HSPB11, and one heat shock protein binding protein, HSPBP1, tended to increase expression of HSPA1A and HSPB1, but did not affect expression of 64 other genes encoding heat shock proteins, heat shock transcription factors or proteins interacting with heat shock proteins. Moreover, heat shock increased expression of five genes associated with oxidative stress (AKR7A2, CBR1, GGH, GSTA4, and MAP2K5), decreased expression of HIF3A, but did not affect expression of 42 other genes related to free radical metabolism. Heat shock also had little effect on genes involved in embryonic development. Effects of heat shock for 2, 4 and 8 h on selected heat shock protein and antioxidant genes were also evaluated by real-time PCR. Heat shock increased steady-state amounts of mRNA for HSPA1A (P<0.05) and tended to increase expression of HSP90AA1 (P<0.07) but had no effect on expression of SOD1 or CAT.

CONCLUSIONS

Changes in the transcriptome of the heat-shocked bovine morula indicate that the embryo is largely resistant to effects of heat shock. As a result, transcription of genes involved in thermal protection is muted and there is little disruption of gene networks involved in embryonic development. It is likely that the increased resistance of morula-stage embryos to heat shock as compared to embryos at earlier stages of development is due in part to developmental acquisition of mechanisms to prevent accumulation of denatured proteins and free radical damage.

Repressive effects of a capacitive-resistive electric transfer (CRet) hyperthermic apparatus combined with provitamin C on intracellular lipid-droplets formation in adipocytes

PURPOSE

The aim of this study was to evaluate inhibitory effects of L-ascorbic acid-2-O-phosphate-Na(2) (APS), a pro-vitamin C, combined with hyperthermia on adipogenic differentiation of mouse stromal cells, OP9.

MATERIALS AND METHODS

OP9 preadipocytes were differentiated with serum replacement, administered with APS, and simultaneously treated with hyperthermia using a capacitive-resistive electric transfer (CRet) apparatus, which was conducted repeatedly twice a day. After 2 days, intracellular lipid droplets were stained with Oil Red O, then observed by microscopy and assessed spectrophotometrically.

RESULTS

After stimulation by serum replacement for 2 days, lipid droplets were accumulated surrounding nucleus of OP9 cells. When APS of 0.15-0.6 mM was administered without hyperthermia, the amount of lipid droplets was markedly suppressed to 50.5%∼-11.3% versus the undifferentiated control, and diminished huge aggregates of lipid droplets. In OP9 cells treated by hyperthermia at 42°C for 0.5 min, 1 min or 3 min in the absence of APS, adipogenesis was suppressed abruptly in a time-dependent manner to 95.4%, 18.7% or -5.5%, respectively. Whereas, the percentage of adipogenesis was 96.8% in OP9 cells treated by mild hyperthermia alone at 41°C for 1 min. The simultaneous application of APS and hyperthermia at 41°C for 1 min markedly suppressed the accumulation of lipid droplets to 25.7%∼-66.2%. By scanning electron microscopy (SEM) observation, the surface of OP9 cells treated with APS and hyperthermia appeared to have the morphological property of undifferentiated OP9 cells.

CONCLUSION

Combined treatment of APS and mild hyperthermia suppresses adipogenesis in OP9 cells, particularly in lipid droplets accumulation during spontaneous differentiation of OP9 preadipocytes.

Effects of elevated ambient temperature on reproductive outcomes and offspring growth depend on exposure time

Reproductive performance has been shown to be greatly affected by changes in environmental factors, such as temperature. However, it is also crucial to identify the particular stage of pregnancy that is most adversely affected by elevated ambient temperature. The aims of this study were to determine the effect on reproductive outcomes of exposure to elevated ambient temperature during different stages of pregnancy and to determine the effect of prenatal heat stress on offspring growth. Sixty pregnant rats were used in this study. The rats were divided equally into four groups as group 1 (control), group 2 (exposed to elevated temperature following implantation), group 3 (exposed to elevated temperature during pre- and periimplantation), and group 4 (exposed to elevated temperature during pre- and periimplantation and following implantation). Groups 3 and 4 had prolonged gestation periods, reduced litter sizes, and male-biased sex ratios. Moreover, the growth patterns of group 3 and 4 pups were adversely affected by prenatal exposure to elevated temperature. The differences between group 1 and group 3 and between group 1 and group 4 were highly significant. However, no significant differences were observed between groups 1 and 2 in the gestation length, sex ratios, and growth patterns. Thus, it can be concluded that exposure to elevated ambient temperature during pre- and periimplantation has stronger adverse effects on reproductive outcomes and offspring growth than postimplantation exposure.

Heat stress on reproductive function and fertility in mammals

In most mammalian species including cattle, heat stress has deleterious effects on nutritional, physiological and reproductive functions. Exposure of animals to a hot environment causes an increase in body temperature in mammals, including domestic animals. High ambient temperature also causes a decrease in the length and intensity of estrus by disturbing ovarian function as well as decreasing pregnancy rate after artificial insemination. Therefore, it is important to understand the effects of heat stress on reproductive function in order to improve the production of domestic animals. Heat stress decreases appetite, weight gain, and milk yield in dairy cattle. It also adversely affects the reproductive performance of both sexes. In males, it reduces spermatogenic activity, while in females it adversely impacts oogenesis, oocyte maturation, fertilization development and implantation rate. Detection and evaluation of the deteriorating effects of heat stress on reproductive organs and cells can help to design measures to prevent them and improve reproductive functions. In this review, we discuss the impacts of heat stress on reproductive functions.

Maximal heat dissipation capacity and hyperthermia risk: neglected key factors in the ecology of endotherms

1. The role of energy in ecological processes has hitherto been considered primarily from the standpoint that energy supply is limited. That is, traditional resource-based ecological and evolutionary theories and the recent 'metabolic theory of ecology' (MTE) all assume that energetic constraints operate on the supply side of the energy balance equation. 2. For endothermic animals, we provide evidence suggesting that an upper boundary on total energy expenditure is imposed by the maximal capacity to dissipate body heat and therefore avoid the detrimental consequences of hyperthermia--the heat dissipation limit (HDL) theory. We contend that the HDL is a major constraint operating on the expenditure side of the energy balance equation, and that processes that generate heat compete and trade-off within a total boundary defined by heat dissipation capacity, rather than competing for limited energy supply. 3. The HDL theory predicts that daily energy expenditure should scale in relation to body mass (M(b)) with an exponent of about 0.63. This contrasts the prediction of the MTE of an exponent of 0.75. 4. We compiled empirical data on field metabolic rate (FMR) measured by the doubly-labelled water method, and found that they scale to M(b) with exponents of 0.647 in mammals and 0.658 in birds, not significantly different from the HDL prediction (P > 0.05) but lower than predicted by the MTE (P < 0.001). The same statistical result was obtained using phylogenetically independent contrasts analysis. Quantitative predictions of the model matched the empirical data for both mammals and birds. There was no indication of curvature in the relationship between Log(e) FMR and Log(e)M(b). 5. Together, these data provide strong support for the HDL theory and allow us to reject the MTE, at least when applied to endothermic animals. 6. The HDL theory provides a novel conceptual framework that demands a reframing of our views of the interplay between energy and the environment in endothermic animals, and provides many new interpretations of ecological and evolutionary phenomena.

Effects of heat stress on mammalian reproduction

Heat stress can have large effects on most aspects of reproductive function in mammals. These include disruptions in spermatogenesis and oocyte development, oocyte maturation, early embryonic development, foetal and placental growth and lactation. These deleterious effects of heat stress are the result of either the hyperthermia associated with heat stress or the physiological adjustments made by the heat-stressed animal to regulate body temperature. Many effects of elevated temperature on gametes and the early embryo involve increased production of reactive oxygen species. Genetic adaptation to heat stress is possible both with respect to regulation of body temperature and cellular resistance to elevated temperature.