Low-dose irradiation of mouse embryos increases Smad-p21 pathway activity and preserves pluripotency

DNA-damage orchestrates self-renewal and differentiation via reciprocal p53 family and Hippo/Wnt/TGF-β pathway activation in embryonic stem cells

The mechanism by which DNA-damage affects self-renewal and pluripotency remains unclear. DNA damage and repair mechanisms have been largely elucidated in mutated cancer cells or simple eukaryotes, making valid interpretations on early development difficult. Here we show the impact of ionizing irradiation on the maintenance and early differentiation of mouse embryonic stem cells (ESCs). Our findings demonstrate that irradiation induces the upregulation of the p53 family genes, including p53, p63, and p73, resulting in elevated expression of the E3 ubiquitin ligases Itch and Trim32. Consequently, this impairs ESC maintenance by reducing the protein levels of key pluripotency transcription factors in both mouse ESCs and early embryos. Notably, our study reveals that irradiation-induced DNA damage leads to the recruitment of the BAF complex, causing it to dissociate from its binding sites on the target genes associated with the Yap, Wnt, and TGF-β pathways, thereby increasing signaling and promoting differentiation of ESCs into all three lineages. Importantly, pathway inhibition demonstrates that DNA damage accelerated ESC differentiation relies on Wnt and TGF-β, and is selectively dependent on p53 or p63/ p73 for mesoderm and endoderm respectively. Finally, our study reveals that p53 family proteins form complexes with effector proteins of key signaling pathways which actively contribute to ESC differentiation. In summary, this study uncovered a mechanism by which multiple differentiation signaling pathways converge on the p53 family genes to promote ESC differentiation and are impacted by exposure to ionizing radiation.

Cyclophosphamide activates ferroptosis-induced dysfunction of Leydig cells via SMAD2 pathway†

Cyclophosphamide (CP) is a widely used chemotherapeutic drug and immunosuppressant in the clinic, and the hypoandrogenism caused by CP is receiving more attention. Some studies found that ferroptosis is a new mechanism of cell death closely related to chemotherapeutic drugs and plays a key role in regulating reproductive injuries. The purpose of this study is to explore ferroptosis' role in testicular Leydig cell dysfunction and molecular mechanisms relating to it. In this study, the level of ferroptosis in the mouse model of testicular Leydig cell dysfunction induced by CP was significantly increased and further affected testosterone synthesis. The ferroptosis inhibitors ferrostatin-1 (Fer-1) and iron chelator deferoxamine (DFO) can improve injury induced by CP. The results of immunohistochemistry showed that Fer-1 and DFO could improve the structural disorder of seminiferous tubules and the decrease of the number of Leydig cells in testicular tissue induced by CP. Immunofluorescence and western blot confirmed that Fer-1 and DFO could improve the expression of key enzymes in testosterone synthesis. The activation of SMAD family member 2 (Smad2)/cyclin-dependent kinase inhibitor 1A (Cdkn1a) pathway can improve the ferroptosis of Leydig cells induced by CP and protect the function of Leydig cells. By inhibiting the Smad2/Cdkn1a signal pathway, CP can regulate ferroptosis, resulting in testicular Leydig cell dysfunction. In this study, CP-induced hypoandrogenism is explained theoretically and a potential therapeutic strategy is provided.

Evaluation of the TMRW vapor phase cryostorage platform using reproductive specimens and in vitro extended human embryo culture

OBJECTIVE

To assess the impact of shipment and storage of sperm, oocytes, and blastocysts in vapor phase nitrogen compared with static storage in liquid phase nitrogen.

DESIGN

Prospective cohort-matched study.

SETTING

Multiple in vitro fertilization laboratories in an in vitro fertilization network.

PATIENT(S)

Fifty-eight human embryos, 32 human oocytes, 15 units of bovine semen.

INTERVENTION(S)

Vapor vs. liquid nitrogen.

MAIN OUTCOME MEASURE(S)

The postwarming survival of oocytes, sperm, and blastocysts, and the developmental potential of blastocysts during in vitro extended culture.

RESULT(S)

Custom-designed labware, for use with the TMRW platform, enables continuous temperature monitoring during shipment and/or storage in the vapor phase robotic storage system. The highest temperature recorded for specimens shipped to a domestic laboratory was -180.2 °C with a mean ± SD of -190.4 ± 0.5 °C during shipment and -181.1 ± 0.6 °C during storage. Likewise, specimens shipped internationally had a high of -180.2 °C with a mean ± SD of -193.5 ± 0.6 °C during shipment and -181.2 ± 0.7 °C during storage. Results from the extended culture assays have revealed no deleterious effect of shipment and storage in nitrogen vapor. The viability of mammalian gametes and embryos was equivalent between the vapor phase and liquid phase storage.

CONCLUSION(S)

The evaluated system did not have any deleterious effects on the postwarming survival of sperm, oocytes, and blastocysts. The postwarming developmental potential of human blastocysts during in vitro extended culture was unaffected by storage and handling in the vapor phase nitrogen TMRW platform when compared with static liquid phase nitrogen storage. Our results suggest that the vapor phase cryostorage platform is a safe system to handle and store reproductive specimens for human assisted reproductive technology.

Effect of X-ray exposure during hysterosalpingography on capabilities of female germ cells

PURPOSE

To elucidate the effect of X-ray exposure during hysterosalpingography (HSG) on subsequent laboratory outcomes in in vitro fertilization (IVF).

METHODS

A total of 1458 oocytes, consisting of 990 oocytes retrieved from 70 women (89 cycles) who underwent HSG prior to IVF and 468 oocytes from 45 women (57 cycles) who underwent IVF without HSG, were evaluated for their retrieval number, maturity, fertilization, and development post fertilization. X-ray exposure during HSG was recorded as reference air kerma (RAK) (mGy). Subjects were stratified according to the amount of RAK (Nil: IVF without HSG, L-RAK: RAK < 16.23, mH-RAK: RAK ≥ 16.23). The number of oocytes retrieved, oocyte maturation, fertilization, and embryo development was compared among 3 groups. Further, multivariate analyses were performed to investigate the effect of X-ray exposure on laboratory outcomes in IVF.

RESULTS

There was a statistically significant difference in the fertilization rate among 3 groups (Nil: 71.6%, L-RAK: 80.5%, mH-RAK: 78.3%). The good-quality blastocyst rate in mH-RAK (46.2%) was significantly higher than L-RAK (35.3%) and Nil (32.4%). Multivariate analyses revealed that X-ray exposure was associated with higher fertilization, higher blastocyst development, and higher good-quality blastocyst development rates with adjustment for patient age, BMI, ovarian stimulation types, and fertilization methods. Association between X-ray exposure and the number of oocytes retrieved, and oocyte maturation was not confirmed.

CONCLUSIONS

The present study suggests that X-ray exposure of the female reproductive organs during HSG could enhance the potential of oocytes rather than adversely.

Simulation of Air Travel-Related Irradiation Exposure of Cryopreserved Mouse Germplasm Samples

Cryopreservation of genetically modified mouse lines prevents the loss of specific mutants that are of enormous scientific value for both basic and applied research. Cryopreservation of spermatozoa or preimplantation embryos enables discontinuation of breeding as well as archiving of specific lines for future studies. Regarding active inter-laboratory exchange of mutants, cryopreserved material is more advantageous to transport than live animals. However, transportation stress should not be trivialized. Security scanning of transport boxes at airports and customs, in particular, as well as additional cosmic radiation, pose a threat to undefined dosages of irradiation exposure. To simulate this, cryopreserved samples of mouse spermatozoa and preimplantation embryos were exposed to an X-ray dosage of 1 mGy in an X-ray machine. For subsequent investigation of the cell integrity of irradiated spermatozoa and embryos, spermatozoa forward motility as well as embryo developmental capacity and apoptosis values were examined and compared with nonirradiated control samples. The percentage of forward-moving spermatozoa per sample appears to be significantly reduced after irradiation exposure. The in vitro developmental capacity of preimplantation embryos as well as their relative share of apoptotic cells do not seem to be influenced by irradiation exposure. This leads to the assumption that, at least in preimplantation embryos, X-ray dosages of 1 mGy do not induce sudden severe cellular harm. Nevertheless, stochastic effects of ionizing irradiation, such as mutations, do not have a dosage threshold and always represent the potential danger of alterations to cells and cellular components, especially the DNA. This could lead to undefined mutations inducing genetic drift, in the worst case to the loss of a mutant line. We therefore strongly recommend minimizing "transportation stress," in particular by irradiation exposure, to keep its potential consequences in mind, and to standardize shipping procedures.

Comparison of Anti-Oxidative Effect of Human Adipose- and Amniotic Membrane-Derived Mesenchymal Stem Cell Conditioned Medium on Mouse Preimplantation Embryo Development

Oxidative stress is a major cause of damage to the quantity and quality of embryos produced in vitro. Antioxidants are usually supplemented to protect embryos from the suboptimal in vitro culture (IVC) environment. Amniotic membrane-derived mesenchymal stem cells (AMSC) have emerged as a promising regenerative therapy, and their paracrine factors with anti-oxidative effects are present in AMSC conditioned medium (CM). We examined the anti-oxidative potential of human AMSC-CM treatment during IVC on mouse preimplantation embryo development and antioxidant gene expression in the forkhead box O (FoxO) pathway. AMSC-CM (10%) was optimal for overall preimplantation embryo developmental processes and upregulated the expression of FoxOs and their downstream antioxidants in blastocysts (BL). Subsequently, compared to adipose-derived mesenchymal stem cell (ASC)-CM, AMSC-CM enhanced antioxidant gene expression and intracellular GSH levels in the BL. Total antioxidant capacity and SOD activity were greater in AMSC-CM than in ASC-CM. Furthermore, SOD and catalase were more active in culture medium supplemented with AMSC-CM than in ASC-CM. Lastly, the anti-apoptotic effect of AMSC-CM was observed with the regulation of apoptosis-related genes and mitochondrial membrane potential in BL. In conclusion, the present study established AMSC-CM treatment at an optimal concentration as a novel antioxidant intervention for assisted reproduction.

Radiation Response of Murine Embryonic Stem Cells

To understand the mechanisms of disturbed differentiation and development by radiation, murine CGR8 embryonic stem cells (mESCs) were exposed to ionizing radiation and differentiated by forming embryoid bodies (EBs). The colony forming ability test was applied for survival and the MTT test for viability determination after X-irradiation. Cell cycle progression was determined by flow cytometry of propidium iodide-stained cells, and DNA double strand break (DSB) induction and repair by γH2AX immunofluorescence. The radiosensitivity of mESCs was slightly higher compared to the murine osteoblast cell line OCT-1. The viability 72 h after X-irradiation decreased dose-dependently and was higher in the presence of leukemia inhibitory factor (LIF). Cells exposed to 2 or 7 Gy underwent a transient G2 arrest. X-irradiation induced γH2AX foci and they disappeared within 72 h. After 72 h of X-ray exposure, RNA was isolated and analyzed using genome-wide microarrays. The gene expression analysis revealed amongst others a regulation of developmental genes (Ada, Baz1a, Calcoco2, Htra1, Nefh, S100a6 and Rassf6), downregulation of genes involved in glycolysis and pyruvate metabolism whereas upregulation of genes related to the p53 signaling pathway. X-irradiated mESCs formed EBs and differentiated toward cardiomyocytes but their beating frequencies were lower compared to EBs from unirradiated cells. These results suggest that X-irradiation of mESCs deregulate genes related to the developmental process. The most significant biological processes found to be altered by X-irradiation in mESCs were the development of cardiovascular, nervous, circulatory and renal system. These results may explain the X-irradiation induced-embryonic lethality and malformations observed in animal studies.

Involvement of CDKN1A (p21) in cellular senescence in response to heat and irradiation stress during preimplantation development

This study examined the role of cyclin-dependent kinase inhibitor 1a (CDK1A, p21) in response to exogenous stressors during mouse preimplantation embryo development. CDKN1A knockdown (KD) one-cell zygotes were exposed to 39 °C heat stress (HS) for 4 days or irradiated by 1 (1-Gy) or 3 (3-Gy) Gy X-rays, and their developmental competence and gene expression were compared with control embryos. CDKN1A KD and HS did not influence early cleavage or subsequent embryonic development; however, HS delayed cavitation and induced elevated Cdkn1a expression in control embryos. Exposure to 1- or 3-Gy had no effect on development to the morula stage; however, a significant number of morulae failed to develop to the blastocyst stage. Interestingly, under the 1-Gy condition, the blastocyst rate of CDKN1A KD embryos (77.7%) was significantly higher than that of the controls (44.4%). In summary, exposure to cellular stressors resulted in the upregulation of Cdkn1a in embryos exposed to HS or X-ray irradiation, particularly in response to heat stress or low-dose X-ray irradiation, and depleting Cdkn1a mRNA alleviated cell cycle arrest. These findings suggest that CDKN1A plays a vital role in cellular senescence during preimplantation embryo development.