Understanding the actions and transgenerational effects of bisphenols on the reproductive functions in female mice

Abstract

Abstract of the thesis entitled with

Understanding the actions and transgenerational effects of Bisphenols on the reproductive functions in female mice

Submitted by JIANG Luhan For the degree of Doctor of Philosophy at the University of Hong Kong November 2020

Bisphenols are one of the most ubiquitously used synthetic chemicals in plastics industry. It can be found in food cans, paper and medical instruments. Due to the weak estrogenic activities, the use of Bisphenol A (BPA) has raised public concerns. Some BPA analogues such as Bisphenol F (BPF) has been used as a safer substitute. Yet, the effect of BPF on human reproductive health remains largely unknown. The objectives of this study were to use in vitro and in vivo models to (1) study the effect of BPA, BPF and their combination on preimplantation embryo development and implantation, (2) investigate the transgenerational effect of bisphenols on female mouse fertility, and delineate the effect of bisphenols on mouse follicle development.

It was found that 2-cell stage embryos treated with BPF and BPA+F at 1M treatment have reduced developmental potential to the blastocyst stage. Moreover, bisphenols at 10 μM strongly suppressed the development of morula to blastocyst stage. BPA+F at 10 μM also elicited more server toxic effect to mouse embryo. Using in vitro embryo-endometrial cell co-culture assay, 10 μM BPA and BPA+F treated blastocysts have reduced attachment rate on Ishikawa cells. However, the implantation rate on day 7.5 of in utero transferred bisphenol-treated blastocysts was not significantly different from the control.

To study the effect of chronic low-dose bisphenols on female fertility, adult female mice (F0) were treated with 500g/Kg bisphenols for 1 month before and during the gestation period. The fertility performance of F0 and their subsequent generations (F1-F3) was monitored. Although bisphenol treatments did not alter the fertility of F0 female, the cumulative litter size was increased in F1 females. Interestingly, 500g/Kg BPA, BPF and BPA+F treated females had reduced cumulative litter size in F2, but not F3 female mice. Although the estrus cycle regularity, serum estradiol and progesterone levels were not altered, the pre-weaning mortality rate increased in F1 to F3 generations.

To understand why BPA increased the cumulative litter size in F1 generation, follicle stages and numbers of F1 female mouse were studied. BPA and BPF treatment increased the number of activated (primary and secondary) follicle in the ovaries. However, higher apoptosis signal was found in the granulosa cells of BPA, and BPA+F treated ovaries. Moreover, lower proliferation marker Ki67 expression was found in the granulosa cells of in BPA and BPA+F, but not BPF treated mouse ovaries.

In conclusion, BPA and BPF manifest a detrimental effect on in vitro preimplantation mouse embryo development, but not in vivo implantation after blastocyst transfer. Chronic low-dose BPA, BPF and BPA+F altered fertility of the female mice in F1 and F2 generations as well as pre-weaning mortality rate in F1 to F3 generations. Moreover, prenatal low-dose bisphenols exposure would increase follicle activation and apoptosis in the granulosa cells of growing follicles. Yet, whether these changes increase cumulative litter size in F1 female mice remained to be confirmed. (Word count: 477)