Introduction Mukhri Hamdan, Keith T. Jones, Ying Cheong and Simon I. R. Lane. “The Sensitivity of the DNA Damage Checkpoint Prevents Oocyte maturation in Endometriosis”. Scientific Reports. Published on 14 November, 2016.
The article chosen is “The Sensitivity of the DNA Damage Checkpoint Prevents Oocyte maturation in Endometriosis”, written by Hamdan, Jones, Cheong, & Lane, (2016). The article discusses on the possibility of reactive oxygen species (ROS) associated with endometriosis to be the cause of DNA damage in oocytes and thus result in reduced fertility in women with endometriosis.
It has been suggested that endometriosis is associated with reduced success in conception either spontaneous or medically assisted conception (Giudice & Kao, 2004). The reduced fertility rate in women with endometriosis is exerted through the oocyte and no other factor as suggested by several other studies (Barnhart, Dunsmoor-Su, & Coutifaris, 2002). These studies look at pregnancy rate in women with and without endometriosis where the implantation and pregnancy rate in these women were not significantly different (Matorras et al., 2010; Singh et al., 2014). Further suggestions on alterations in oocyte as the contributing factor for reduced fertility in women with endometriosis are observed in women with endometriosis who received oocyte from donors with or without endometriosis (Simón et al., 1994). Oocyte donated from donor with endometriosis shown significant reduction in implantation rate as compared to control.
Endometriosis is a disease associated with elevates reactive oxygen species (ROS). ROS are chemically reactive chemical species found in both plant and animal/human containing oxygen including peroxides, and hydroxyl radical. These reactive molecules are formed by a number of different mechanisms and can be detected by various techniques. They are the by-products during the mitochondrial electron transport of aerobic respiration or by-products of oxyreductase enzymes and metal catalysed reaction. ROS is strong oxidants that can damage other molecules including cell structure in which they part of it. In other hand, production of ROS also essential for macrophages and neutrophils to kill some types of bacteria. But in this case, elevated ROS is known to cause bad effects including DNA damage. The authors of the present article suggested that ROS associated with endometriosis may cause damage in the oocytes, leading to oocyte maturation impairment and reduced fertility.
Development of mature oocytes prior to ovulation takes place in antral follicles which require an elaborate process involving Spindle Assembly Checkpoint (SAC). This checkpoint is important in controlling the completion of oocyte maturation by preventing the cell from progressing to anaphase in the cell cycle until the spindles are fully formed and the chromosomes are fully attached. In oocyte, however, the SAC is unique as it has an additional ability to prevent oocyte maturation in response to DNA damage. The authors aimed to investigate the effects of elevated levels of ROS and DNA damage in oocyte maturation using follicular fluid from patients with endometriosis.
Article summary As indicated in the article, patients suffering from endometriosis have reduced pregnancy rate due to oocyte impairments. The oocyte maturation process is controlled by SAC which controls the oocyte progression in the cell cycle when the spindles have been fully formed and the chromosomes are fully attached. In addition, SAC also responds to DNA damage caused by elevated ROS thus preventing oocyte maturation.
To test the hypothesis, the authors harvested immature oocytes from young C57/BL6 mice and cultured the oocytes in follicular fluid taken from patients undergoing in vitro fertilization (IVF) that confirmed having mild or severe endometriosis and no endometriosis. Treated oocytes were assessed for the formation of polar body at 14 – 16 hours to determine the maturation of mouse oocyte. When compared between oocyte cultured in FF of severe endometriosis (endo-FF), mild and no endometriosis, the polar body extrusion (PBE) was found to be significantly reduced in the endo-FF and 50% of mild FF.
Then the authors conduct another test to examine FF for its ability to raise ROS levels in oocytes. The mouse oocytes were pre-incubated with fluorescein-based ROS reporter then were exposed to control-FF, no-FF, endo-FF or hydrogen peroxide (H2O2), which will generate increased level of ROS. Interestingly, endo-FF caused significantly higher ROS production when compared to control-FF and no-FF. The extent of DNA damage in the oocyte was tested by examining the histone H2AX phosphorylation (γH2AX), where significant increase of γH2AX was observed in endo-FF treated oocytes.
To further determine if DNA damage and ROS associated with Endo-FF would activate the DNA damage response DDR-SAC pathway, the authors inhibited ATM, a kinase important to activate the pathway. A significant increase of PBE was observed in oocytes treated with endo-FF when co incubated with ATM kinase inhibitor (ATMi) suggesting ATM is required to arrest the oocyte following exposure to endo-FF. In addition, oocyte maturation also increased in endo-FF and reversine, an Mps1 kinase inhibitor treatment. Furthermore, antisense knockdown of Mad2, a member of SAC pathway led to PBE rate.
To test if ROS was responsible for delay oocyte maturation in endo-FF, antioxidants of resveratrol and melatonin were utilised. The oocytes matured in endo-FF treated with the antioxidants had increased PBE rates when compared to untreated suggesting that the restore of PBE was likely due to reduced ROS.
All of the experiments performed suggest for involvement of ROS associated endometriosis can arrest mouse oocyte maturation via DDR-SAC pathway.
Critical evaluation This article provides additional insights for reduced pregnancy rate in women diagnose with endometriosis. The authors of this article are really expert in field of medical, obstetrics and gynecology of human development and health. This article may benefit the scientific field as to better understand the relation between reduced fertility rate in women with endometriosis and oocyte maturation. Moreover, the article is the first to suggest and test the relation between ROS associated endometriosis and DNA damage in oocyte. This could encourage other researchers to further investigate the relation. Furthermore, this article is useful for medical field to find the treatment available to overcome the pregnancy problem in women with endometriosis.
Then, the methods used to investigate the correlation between ROS associated endometriosis and oocyte maturation were suitable and well explained. In addition, figure showing the process to test the hypothesis was very helpful for the reader to get a full picture of the whole study. Furthermore, additional explanations of the terms used in the experiments as stated at the end of the article allow the readers to better understand this article.
Nevertheless, the article should include a brief explanation on ROS in the introduction to help the readers to better understand the importance of studying the correlation of ROS associated endometriosis and oocyte maturation. It also would help the readers to understand the importance of using the antioxidants of resveratrol and melatonin, in the study. Without the basic understanding of ROS and antioxidants, it is difficult for the better understanding.
Additionally, it would be helpful as well to include detailed explanation of the DDR-SAC pathway in the introduction for readers to understand the pathway. Without a clear picture of the pathway, it is difficult to understand the experiment involving the inhibition of kinases and the knockdown of antisense.
The suggested title for this article is ROS in endometriosis affect oocyte maturation. It is because the overview of this article involves and explains much about the relation of oocyte maturation affected by elevated ROS taken from endo-FF. In conclusion, Hamdan, Jones, Cheong, & Lane, (2016) have presented a research that could have a huge influence on the medical field on the factors involving reduced rate of fertility in women with endometriosis as well as the importance of ROS associated endometriosis in oocyte maturation. The experiments performed support the claims by the authors.
References Barnhart, K., Dunsmoor-Su, R., & Coutifaris, C. (2002). Effect of endometriosis on in vitro fertilization. Fertility and Sterility. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12057720 Giudice, L. C., & Kao, L. C. (2004). Endometriosis. The Lancet. Retrived from https://doi.org/10.1016/S0140-6736(04)17403-5 Hamdan, M., Jones, K. T., Cheong, Y., & Lane, S. I. R. (2016). The sensitivity of the DNA damage checkpoint prevents oocyte maturation in endometriosis, 6, 36994. Retrieved from http://dx.doi.org/10.1038/srep36994 Matorras, R., Corcóstegui, B., Esteban, J., Ramón, O., Prieto, B., Expsito, A., & Pijoan, J. I. (2010). Fertility in women with minimal endometriosis compared with normal women was assessed by means of a donor insemination program in unstimulated cycles. American Journal of Obstetrics and Gynecology. Retrived from https://doi.org/10.1016/j.ajog.2010.05.019 Simón, C., Gutiérrez, A., Vidal, A., de los Santos, M. J., Tarín, J. J., Remohí, J., & Pellicer, A. (1994). Outcome of patients with endometriosis in assisted reproduction: results from in-vitro fertilization and oocyte donation. Human Reproduction (Oxford, England). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8046030 Singh, N., Tiwari, A., Vanamail, P., Lata, K., Malhotra, N., & Naha, M. (2014). Effect of endometriosis on implantation rates when compared to tubal factor in fresh non donor in vitro fertilization cycles. Journal of Human Reproductive Sciences. Retrived from https://doi.org/10.4103/0974-1208.138874 University of Southampton. (2016, November 15). New hope given to women struggling to conceive. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2016/11/161115120140.htm