Small extracellular vesicles from follicular fluid as transport carriers of LHR: possible mediators of follicle growth and dominance acquisition in bovine reproduction.

Luteinizing hormone (LH) plays a crucial role in follicle development, ovulation induction, and the regulation of key reproductive events. However, the efficacy of LH within the follicular microenvironment largely depends on the capacity of follicular cells to express its receptor. This study aims to investigate whether granulosa cells (GCs) can acquire LHR through extracellular vesicles (sEVs) present in follicular fluid (FF) from follicles of varying sizes. In the first experiment, GCs and sEVs were collected from the FF of small (3-5 mm), medium (5.1-7 mm), and large (7.1-9 mm) ovarian follicles from Bos taurus indicus cows. In the second experiment, GCs and sEVs were collected from the FF of small (3-6 mm) and large (8-14 mm) follicles from Bos taurus taurus cows. Initially, we assessed the ability of sEVs to carry LHR mRNA by comparing its expression profiles in sEVs derived from different size follicles. Our findings revealed that as follicular development progresses, LHR levels in FF sEVs decrease, while in corresponding GCs, from which the sEVs primarily originate, show increased LHR expression. To further investigate whether GCs represent an additional source of FF sEVs carrying LHR mRNA, GC cultures were established and sEVs secreted into the culture medium (ME-sEVs) were analyzed for LHR mRNA levels. A similar pattern was observed in ME-sEVs derived from GCs of small versus large follicles, with decreased LHR mRNA levels in sEVs secreted by GCs from large follicles compared to small follicles. This suggests that LHR is likely packaged into sEVs in small follicles stage, and shuttled into follicular cells during follicular growth, preparing them for the ovulatory stimulus. Our study uncovers a possible mechanism of LHR acquisition by GCs, which involves EVs and can possibly be involved in follicle quality and ability to respond to LH stimulus.