Date of Award

Spring 2022

Document Type

Open Access Dissertation

Department

Environmental Health Sciences

First Advisor

Geoffrey I. Scott

Abstract

Harmful algal blooms (HABs) have become a global emerging environmental concern; however, its impact on women’s reproductive health is poorly understood. Microcystin-LR (MC-LR) is the most common and hazardous type of HAB toxin. Using both a chronic oral exposure mouse model and an acute exposure mouse model, I found that human-relevant exposure to MC-LR could compromise follicle ovulation via affecting follicle maturation. Both in vivo mouse exposure model and encapsulated in vitro follicle growth (eIVFG) model revealed that exposure to MC-LR did not affect follicle development, but significantly reduced the expression of some follicle maturation-related genes, such as Lhcgr and Pappa. Mechanistic studies demonstrated that MC-LR could inhibit the protein phosphatase 1 (PP1) and further block the activation of PI3K/AKT/FOXO1 signaling pathway. In addition, OATP inhibitor Ritonavir could inhibit the accumulation of MC-LR in the follicles and rescue the MC-LR-disrupted follicle ovulation. Taken together, these results demonstrate that human-relevant exposure to MCLR compromises ovulation via disrupting follicle maturation by inhibiting PP1/PI3K/AKT/FOXO1 signaling pathway in the granulosa cells. More than 279 MC congeners have been identified and a broad spectrum of environmental chemicals and pharmaceutical compounds cause female ovarian toxicity (ovotoxicity). The eIVFG is a robust in vitro model for ovotoxicity testing. However, the follicle preparation process is complex and highly dependent on technical skills. Here, I aimed to use vitrification method to cryopreserve murine immature follicles for a high-content eIVFG, chemical exposure, and ovotoxicity screening. Results indicated that a closed vitrification system combined with optimized vitrification protocols preserved mouse follicle viability and functionality and vitrified follicles exhibited comparable follicle and oocyte reproductive outcomes to freshly harvested follicles during eIVFG, including follicle survival and development, ovarian steroidogenesis, and oocyte maturation and ovulation. Moreover, vitrified follicles consistently responded to ovotoxic chemical, doxorubicin (DOX). I further used vitrified follicles to test the ovotoxicity of 4 MC congeners, including MC-LA, LF, LR, and LY, and found that different congeners of MCs exhibited differential ovotoxicities. In summary, my research study demonstrates a novel toxic mechanism of HAB toxin MC-LR in compromising follicle ovulation and introduces a follicle vitrification strategy to build a long-term-storage and ready-to-use ovarian follicle bank for high-throughput ovotoxicity screening, which identifies endocrine disrupting effects of MCs.

Rights

© 2022, Yingzheng Wang

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