EXTRACELLULAR VESICLES IN OVARIAN ANTRAL FOLLICLES: CHARACTERIZATION AND FUNCTIONS

Abstract

Formation of the follicular fluid antrum within the ovarian follicle provides a unique environment for the developing oocyte. Follicular fluid contains factors including nucleic acids, proteins, lipids, hormones, and metabolic factors secreted by both ovarian somatic cells and the oocyte that are critical for follicle development. In addition, lipid bi-layer extracellular vesicles (EVs) comprised of exosomes and microvesicles are highly abundant in follicular fluid. Whether these EVs play a role in ovarian cell signaling, provide a mechanism for transport of metabolic products or are nonfunctional within the ovarian follicle is unknown. In this dissertation, I will test the hypothesis that ovarian follicular fluid EVs are unique and determine whether they can elicit functional effects on the cumulus-oocyte-complex and the mural granulosa cells. To accomplish these goals, follicular fluid from three different sizes of bovine antral follicles, [i.e. small (3-5 mm), medium (6-9 mm), and large (9 mm)] were collected and EVs were isolated and characterized by electron microscopy, nanoparticle tracking analysis (NTA), protein marker analysis, and small RNAseq. Electron microscopy and NTA indicated the presence of a uniform (50-200 nm) population of EVs that had different microRNA within them based on follicle size. An EV marker, CD81, showed decreased abundance in EVs as follicle size increased. Fluorescent labeling of the follicular fluid EVs followed by culture indicated that both cumulus and mural granulosa cells took up the fluorescent-labeled EVs. To test for functional activity, cumulus-oocyte-complexes and granulosa cells were exposed to EVs isolated from different size follicles. Extracellular vesicle treatment caused expansion of cumulus cells and increased expression of prostaglandin-endoperoxide synthase 2 (Ptgs2), pentraxin-related protein 3 (Ptx3), and tumor necrosis factor, alpha-induced protein 6 (Tnfaip6) genes, genes associated with normal cumulus expansion. Additionally, EVs from small follicles induced granulosa cell proliferation, and we determined that the Src and JNK pathways were involved in the cell proliferation induced by EVs. Moreover, we determined that the differential ability of EVs to affect granulosa cell proliferation was primarily a result of preferential uptake by EVs from small follicles versus those of medium and large follicles. In summary, these studies provide insight into the unique characteristics of EVs isolated from three different stages of antral follicles. This work also provides the first functional evidence that EVs from ovarian follicular fluid are able to elicit functional physiologic changes in both cumulus and granulosa cells and provides clues to the cell signaling pathways that are modulated in cells following exposure to these small lipid enclosed vesicles. Lastly, this study provides an approach to further purify EVs, and indicates the ovarian follicle as an excellent model for studying general extracellular vesicle biology.