Perfluorooctane Sulphonate Impacts Mouse Oocyte Maturation In Vitro Through Oxidative Stress And Apoptosis Induced By Mitochondrial Dysfunction

In recent years,with the increasingly serious environmental problems,Pharmaceutical and Personal Care Products(PPCPs),as an emerging pollutant has received increasing attention.There are various types of PPCPs,including antibiotics,fungicides,plasticizers,surfactants,etc.Since this kind of substance is continuously introduced into the environment even when it is removed,it is also called a"pseudo-persistent" pollutant.Exposure to PPCPs can cause DNA damage,which in turn lead to toxicity related to development,reproduction,gastrointestinal and other systems.Among them,the effect of PPCPs on the function of the reproductive system has aroused researchers’ extensive attention.Studies have shown that exposure to a certain dose of PPCPs causes mitochondrial dysfunction and oxidative stress to inhibit the maturation of oocytes in vitro.A long-term accumulation of PPCPs in vivo can also cause adverse reproductive outcomes,such as abnormal ovulation,premature ovarian failure(POF)and even infertility.As a member of PPCPs,perfluorooctane sulphonate(PFOS)is an important perfluorinated surfactant,which is widely used in agricultural activities,textile industry,food packaging,cosmetics and other fields.Humans are mainly exposed to PFOS via close contact with personal care items,as well as respiratory tract inhalation or water and food intake.Since its long half-life and slow metabolism in the human body,PFOS is easy to accumulate in various organs after invading the body,causing neurotoxicity,developmental toxicity,reproductive toxicity,endocrine interference,etc.The impact of PFOS on female reproductive health cannot be ignored.Epidemiological studies have shown that organic pollutants such as PFOS have been detected in female follicular fluid,which can directly influence the function of granulosa cells in the ovary.In addition,PFOS exposure in follicular fluid is associated with an increased risk of infertility factors and a decreased fertilization rate.In animal experiments,the reproductive toxicity of PFOS was further confirmed.Mammalian oocyte maturation is a complex process which is of great significance for fertilization and embryonic development,including nuclear and cytoplasmicmaturation.Many different intercellular and intracellular signaling molecular processes are involved in this process.Such as the regulation of mitochondrial dynamics,the interaction between chromosomes and the oocyte cortex,and the reorganization of the endoplasmic reticulum(ER)all affect the maturation process of oocytes.With the rupture of germinal vesicle during the first meiosis of oocytes,chromosomes are directly exposed in the cytoplasm of oocytes,causing the oocyte highly sensitive to external chemicals at this time.Studies have reported that exposure to PPCPs can disrupt cytoskeletal dynamics,induce oocyte apoptosis related to DNA damage,and promote excessive production of ROS,which triggers mitochondrial-mediated apoptosis.The decline of oocyte quality will eventually be detrimental to the formation and development of embryos.However,the mechanism of PFOS toxicity on mouse oocytes maturation is still uncovered.However,as the most basic part of female reproduction,whether PFOS can interfere with the meiosis of oocytes and the related mechanisms have not been reported.In this paper,mouse oocytes were cultured in vitro to investigate the toxicological effects of PFOS on oocytes and try to find out the mechanism.Given the content of PFOS in women’s body varies with individual exposure,the results in vitro are not equal to the results in vivo.Our experiment only revealed what concentration of PFOS would cause toxicity to oocytes and the possible mechanism in vitro.We first analyzed the PBE rate of PFOS-treated oocytes,and explored the effect of PFOS exposure on oocyte maturation in vitro.The results showed that when the concentration of PFOS reached 600μM,the PBE rate was significantly reduced,indicating that high concentrations of PFOS interfered with the maturation process of oocytes.In addition,the results of immunofluorescence showed that PFOS destroyed the dynamics of actin filaments,which was reflected in the decreased expression of microfilaments in oocytes during MI.At the same time,oocytes exposed to PFOS also showed varying degrees of spindle defects and chromosomal misalignment.Once the chromosomes are arranged on the spindle-shaped equatorial plate,the SAC is silenced,the anaphase promotion complex(APC)is activated,then the chromosomes separate,and the oocyte enters the anaphase.The continuous activation of SAC in MI cells canlead to chromosomal segregation errors and lead to aneuploidy,which is usually accompanied by K-M junction defects.Our results also confirmed that PFOS interfered with the stability of K-M attachment,further leading to a significant increase in the number of aneuploid oocytes.We further confirmed that PFOS can affect mouse oocytes in terms of apoptosis and epigenetic modification.The results showed that the proportion of annexin-V positive cells increased,ROS level and endoplasmic reticulum stress level increased,mitochondrial distribution was abnormal and depolarized,and the methylation degree of h3k4me3 and h3k9me3 corresponding sites decreased.In summary,our study comfirmed that PFOS exposure could deteriorate the quality of mouse oocytes and arrested the process of meiosis,specifically by affecting the dynamic changes of the cytoskeleton,damaging mitochondrial function,inducing oxidative stress,accelerating early cell apoptosis and changing the histone modification.Our findings supplement the possible mechanism of PFOS’s reproductive toxicity to oocytes,and provide a possible hypothesis for the accumulation of PFOS in women.