Upregulation of uncoupling protein Ucp2 through acute cold exposure increases post-thaw sperm quality in zebrafish

Impaired fertility in 4930590J08Rik mutant male mice is associated with defective sperm energy metabolism

Testis-specifically expressed genes are important for male reproduction according to their unique expression patterns. However, the functions of most of these genes in reproduction are unclear. Here, we showed that mouse 4930590J08Rik was a testis-specifically expressed gene. 4930590J08Rik knockout mice exhibited a delay in the first wave of spermatogenesis and a reduction of cauda epididymal sperm. Furthermore, knockout spermatozoa exhibited defective acrosome reactions and decreased progressive motility, which led to impaired in vivo fertilization. Transcriptome analysis of testes revealed that most of the differentially expressed genes in knockout testes were associated with metabolic processes. 4930590J08Rik knockout sperm exhibited oxidative phosphorylation deficiency and were highly dependent on increased anaerobic glycolysis to compensate for ATP demands. Taken together, the 4930590J08Rik-disrupted mouse partially mimics the phenotypes of human asthenospermia and oligozoospermia, which provides a new model for further understanding the pathogenesis of idiopathic male infertility.

Sublethal Xanthine Oxidase Stress Prefreezing of Bull Sperm Improves the Post-Thaw Functionality and Fertility Potential Parameters

Oxidative stress during cryopreservation causes mechanical, biochemical, and structural damage to the sperm, leading to lower viability and fertility potential. In recent years, a novel method based on the use of mild stress for preconditioning of sperm before cryopreservation has been applied to improve the quality of thawed sperm, although its molecular mechanism remains unknown. In this study, we investigated the protective effects of sublethal oxidative stress by xanthine oxidase (XO) on thawed bull sperm performance through modulations of mitochondrial uncoupling protein 2 (UCP2) expression. Semen samples were collected from six bulls, then mixed and divided into four aliquots: frozen control (XO-0) and frozen groups treated with different concentrations of XO, 0.01 μM (XO-0.01), 0.1 μM (XO-0.1), and 1 μM (XO-1). Thawed sperm were evaluated for motion parameters, viability, acrosome integrity, mitochondria activity, membrane integrity, and UCP2 expression. A significant increase of total motility and viability rate was observed in XO-0.1 compared with other frozen groups (p < 0.05). The highest percentage of progressive motility was in XO-0.01 and XO-0.1 compared with other groups (p < 0.05). Moreover, a significantly higher level of sperm mitochondrial membrane potential and membrane integrity was observed in XO-0.1 (p < 0.05). We also found the lowest percentage of sperm mitochondria activity in XO-1 (p < 0.05). In addition, the highest expression of UCP2 was observed in XO-1 (p < 0.05). Our findings suggest that stress preconditioning of bull sperm before cryopreservation can improve thawed sperm functions, which might be mediated through an increase of UCP2 expression.

Effects of early low temperature exposure on the growth, glycolipid metabolism and growth hormone (gh) gene methylation in the late stage of Chinese perch (Siniperca chuatsi)

Temperature is an important factor affecting the early development, growth and physiology of fish, as well as on aspects of feeding and metabolism. Here, we investigated the impact of low temperature on the growth, glycolipid metabolism and growth hormone (gh) gene methylation in the late stage of Chinese perch (Siniperca chuatsi). Chinese perch larvae were exposed to temperatures with 21 °C (low temperature group (LT)) and 25 °C (control group) for 7 days, and then the LT group was slowly heated to 25 °C and raised at this temperature for two months. Results indicated that the LT group exhibited significantly lower growth rate and weight gain rate than the control group (p < 0.05), but no obvious food intake (FI) were detected yet between LT group and control group. The larvae exposed at 21 °C relative to the 25 °C group had significant decreased transcript levels of GH-IGF axis genes (gh, igf1 and igf2) in Chinese perch juvenile (p < 0.05). Further analysis of the DNA methylation levels of gh showed that the LT group had higher at the CpG sites of -3029 and - 3032 than the control group in larvae (p < 0.05), whereas the DNA methylation levels at CpG sites of -2982 and - 3039 of gh were significantly lower compared with the control group in juveniles (p < 0.05). In addition, the plasma glucose was significantly increased in the LT group (p < 0.05), suggesting the metabolism of blood glucose slowed at low temperature. In larvae, the expressions of glycolipid metabolism genes (ins-ra and ins-rb) in LT group were significantly up-regulated compared to control group in larvae (p < 0.05), while down-regulated in juveniles (p < 0.05). The expression level of ucp2 mRNA was continuously up-regulated under low temperature stress. All these data demonstrate that early exposure to low temperature affected the growth and glycolipid metabolism of Chinese perch.

Preconditioning of bull semen with sub-lethal oxidative stress before cryopreservation: Possible mechanism of mitochondrial uncoupling protein 2

Preconditioning of sperm using sub-lethal oxidative stress before cryopreservation is an innovative approach that can improve sperm cryo-survival. Mitochondrial uncoupling proteins (UCPs) are critical in reducing ROS level during stress conditions. The aim of the current study was to investigate whether mild sub-lethal stress induced by low concentrations of nitric oxide and hydrogen peroxide has a protective effect on quality parameters of post-thaw bull semen through modulations of mitochondrial uncoupling protein 2 (UCP2) expression. Semen samples were collected from 6 mature Holstein bulls, then mixed and divided into 8 aliquots: fresh, frozen control and frozen groups treated with NO: 0.1 (NO-0.1), 1(NO-1), 10 μM (NO-10), and H₂O₂: 0.1(H₂O₂-0.1), 1(H₂O₂-1) and 10μM (H₂O₂-10). A significantly higher percentage of total motility, progressive motility and viability was observed in NO-1 and H₂O₂-10 compared to the other frozen groups (P < 0.05). Sperm exposed to 1 μM NO and 10μM H₂O₂ showed significantly increased percentages of mitochondria activity and membrane integrity (P < 0.05). Moreover, the lowest percentage of apoptotic percentage was observed in the NO-1 and H₂O₂-10 in comparison to the other frozen groups. In addition, the expression level of UCP2 was higher in the NO-1 and H₂O₂-10 compared to the other groups (P < 0.05). It can be concluded that stress preconditioning of bull sperm before cryopreservation can increase UCP2 expression of sperm, that can play a protective role against cryoinjury after thawing.

Oxidative Stress and DNA Damage of Zebrafish Sperm at Different Stages of the Cryopreservation Process

Although gamete cryopreservation has facilitated advancement of reproduction research by allowing the storage of cells over prolonged periods of time, during freezing-thawing cycles, cells inevitably suffer from cryoinjuries. Here, we evaluate oxidative stress and DNA damage of zebrafish sperm at different stages of the cryopreservation process. It was generally observed that the freezing and thawing of the samples led to an increase in the generation of reactive oxygen species and the activity of the catalase enzyme and a reduction in the generation of sulfhydryl groups and superoxide dismutase activity. The alkaline comet assay demonstrated that DNA damage increased after equilibration time, with an even greater increase after freezing and thawing. The comet assay modified with the enzyme formamidopyrimidine glycosylase, and Endonuclease III demonstrated greater DNA damage than the standard comet assay, demonstrating a high degree of oxidation of purines and pyrimidines at all stages of cryopreservation. Our results show that the freeze and thaw processes cause greater oxidative stress and DNA damage than cryoprotectant toxicity during exposure at the equilibrium stage.

Skim milk powder used as a non-permeable cryoprotectant reduces oxidative and DNA damage in cryopreserved zebrafish sperm

Cryoprotectants play a vital role in the cryopreservation process, protecting biological samples from freezing damage. Here, we evaluate the effects of the combination and interaction of different extenders with permeable and non-permeable cryoprotectants, on the cryopreservation of Danio rerio sperm, analyzing the effects of cryopreservation through a broad approach to variables. Two extenders were used, Hank's balanced salt solution (HBSS) and Ginsburg's solution. Eight cryoprotective solutions (CS) were used: CS1 (HBSS + Me₂SO 8%), CS2 (HBSS + Methanol 8%), CS3 (HBSS + Me₂SO 8% + Skim milk powder 15%), CS4 (HBSS + Methanol 8% + Skim milk powder 15%), CS5 (Ginsburg + Me₂SO 8%), CS6 (Ginsburg + Methanol 8%), CS7 (Ginsburg + Me₂SO 8% + Skim milk powder 15%) and CS8 (Ginsburg + Methanol 8% + Skim milk powder 15%). The samples were cryopreserved in cryovials for 20 min on dry ice, stored in liquid nitrogen, thawed at 38 °C for 10 s, and analyzed. In addition to increasing viability, we show that powdered milk also allows for better preservation of the membrane and normal cell morphology, and protects the sperm cells from DNA damage and oxidative stress caused by cryopreservation.

Morphological abnormalities in zebrafish cryopreserved sperm

The aim of the present study was to evaluate the effect of cryopreservation on the morphology of zebrafish sperm (Danio rerio). Sperm from 30 males were collected and divided in two treatments: fresh and cryopreserved semen. The following were measured sperm morphology, motility and membrane integrity. Cryopreservation reduced motility, the number of normal cells and the membrane integrity, as well as increased the percentage of sperm abnormalities. The most frequent types of morphological changes found in cryopreserved semen were macrocephaly, loose head, degenerated head, proximal gout, curled tail and short tail. This study opens the way for further investigations on morphological changes and for a new classification of these changes in fish semen due to cryopreservation.

Cryoprotectants synergy improve zebrafish sperm cryopreservation and offspring skeletogenesis

The synergy obtained by the combination of cryoprotectants is a successful strategy that can be beneficial on the optimization of zebrafish sperm cryopreservation. Recently, a protocol was established for this species using an electric ultrafreezer (-150 °C) performing cooling rate (-66 °C/min) and storage within one step. The ultimate objective of sperm cryopreservation is to generate healthy offspring. Therefore, the objective of this study was to select the most adequate cryoprotectant combination, for the previously established protocol, that generate high quality offspring with normal skeletogenesis. Among the permeating cryoprotectant concentrations studied 12.5% and 15% of N,N-dimethylformamide (DMF) yielded high post-thaw sperm quality and hatching rates. For these two concentrations, the presence of bovine serum albumin (10 mg/mL), egg yolk (10%), glycine (30 mM) and bicine (50 mM) was evaluated for post-thaw sperm motility, viability, in vitro fertilization success and offspring skeletal development (30 days post fertilization). Higher concentration of permeating cryoprotectant (15%) decreased the incidence of deformed arches and severe skeletal malformations, which suggests higher capacity to protect the cell against cold stress and DNA damage. Extender containing 15% DMF with Ctrl, Bicine and egg yolk were the non-permeating cryoprotectants with higher post-thaw quality. The use of these compounds results in a reduction in vertebral fusions, compressions and severity of skeletal malformations in the offspring. Therefore, these extender compositions are beneficial for the quality of zebrafish offspring sired by cryopreserved sperm with -66 °C/min freezing rate. To the best of our knowledge, this is the first report on skeletal development of the offspring sired by cryopreserved sperm performed with different freezing media compositions in zebrafish.

Electric ultrafreezer (- 150 °C) as an alternative for zebrafish sperm cryopreservation and storage

Zebrafish sperm cryopreservation is a fundamental methodology to manage and back-up valuable genetic resources like transgenic and mutant strains. Cryopreservation usually requires liquid nitrogen for storage, which is expensive and hazardous. Our objective was to evaluate if electric ultrafreezers (- 150 °C) are a viable alternative for zebrafish sperm storage. Zebrafish sperm was cryopreserved in the same conditions (- 20 °C/min), stored either in liquid nitrogen or in an ultrafreezer, and thawed after 1 week, 1 month, and 3 months. Sperm motility, membrane integrity, and fertilization ability were assessed. There were no significant differences in motility and hatching rate throughout storage time. Additionally, we aimed at understanding if cryopreservation directly in an ultrafreezer (- 66 °C/min) could improve post-thaw sperm quality. Freezing at - 20 °C/min was performed as before, and compared to samples cryopreserved with a fast cooling rate by placing directly in an ultrafreezer (- 66 °C/min). Sperm quality was assessed according to motility, viability, DNA fragmentation, and apoptosis (annexin V). The - 66 °C/min cooling rate showed significantly higher membrane and DNA integrity, and lower number of cells in late apoptosis in comparison to the other treatments. This study showed that zebrafish sperm cryopreservation and storage in an ultrafreezer system is possible and a fast cooling rate directly in ultrafreezer improves post-thaw sperm quality.

Mitochondrial Uncoupling Protein 2 in human cumulus cells is associated with regulating autophagy and apoptosis, maintaining gap junction integrity and progesterone synthesis

To explore the roles of mitochondrial Uncoupling Protein 2 (UCP2) in cumulus cells (CCs), human CCs were cultured in vitro, and the UCP2 was inhibited by treatment with Genipin, a special UCP inhibitor, or by RNA interference targeting UCP2. No significant differences in adenosine triphosphate levels and the ratio of ADP/ATP were observed after UCP2 inhibition. UCP2 inhibition caused a significant increase in cellular oxidative damage, which was reflected in alterations to several key parameters, including reactive oxygen species (ROS) and lipid peroxidation levels and the ratio of reduced GSH to GSSG. UCP2 blocking resulted in an obvious increase in active Caspase-3, accompanied by the decline of proactive Caspase-3 and a significant increase in the LC3-II/LC3-I ratio, suggesting that UCP2 inhibition triggered cellular apoptosis and autophagy. The mRNA and protein expression of connexin 43 (Cx43), a gap junction channel protein, were significantly reduced after treatment with Genipin or siRNA. The progesterone level in the culture medium was also significantly decreased after UCP2 inhibition. Our data indicated that UCP2 plays highly important roles in mediating ROS production and regulating apoptosis and autophagy, as well as maintaining gap junction integrity and progesterone synthesis, which suggests that UCP2 is involved in the regulation of follicle development and early embryo implantation and implies that it might serve as a potential biomarker for oocyte quality and competency.