Abstract
Abstract Study question Do EVs from human follicular fluid (FF-EVs), cervicovaginal fluid (CVF-EVs), and endometrial stromal cells spent medium (ESCs-EVs) induce sperm capacitation and enhance sperm motility? Summary answer In humans, EVs from different female reproductive tracts actively contribute to sperm maturation by inducing capacitation and enhancing sperm progressive motility. What is known already In the human body, EVs represent crucial players in cell-to-cell communication. EVs presence has been detected also in the female and male reproductive systems, specifically in seminal, follicular, oviductal, endometrial and vaginal fluid, as well as in embryo secretions. Moreover, EVs have been shown to be of pivotal importance in the fertilization process, as they support the maturation of spermatozoa and oocytes, as well as embryos in their development and endometrial implantation. The majority of these studies, though, have been conducted in animal models, underscoring the necessity to replicate analogous investigations also in humans. Study design, size, duration Follicular fluid (FF, n = 8), cervicovaginal fluid (CVF, n = 20) and endometrial tissue (n = 8) samples were collected from women undergoing assisted reproductive technology (ART) cycles at San Raffaele Hospital Fertility Centre (Milan). CVF were collected 2 and 7 days after the LH peak (CVF LH + 2 and CVF LH + 7, respectively). ESCs-EVs were isolated from both decidualized (dESCs-EVs) and not decidualized (eESCs-EVs) endometrial cells. Semen samples (n = 15) were collected from normozoospermic men. Participants/materials, setting, methods EVs were isolated using differential centrifugations and characterized using Transmission Electron Microscopy (TEM), Nanoparticle Tracking Analysis (NTA), and western blotting (WB). EVs capture by spermatozoa was assessed using flow cytometry. EVs impact on sperm progressive motility was evaluated following WHO guidelines. EVs potential to induce sperm capacitation was examined through sperm acrosome reaction (AR) induction using a Ca2+ ionophore, followed by Coomassie blue staining. All experiments were performed using EVs at 50 and 100 μg/mL. Main results and the role of chance Isolated EVs displayed comparable size, with mean diameters ranging from 147,9±11,6 nm to 168,1±6,2 nm (mean ± SEM) and average concentrations from 9,53E+10 ± 8,11E+09 to 2,70E+11 ± 3,49E+10 particles/ml (mean ± SEM). TEM analysis confirmed their round-shaped morphology and structural integrity, while WB confirmed their positivity for EVs markers (Alix, TSG101, CD63, CD9). Spermatozoa efficiency in capturing these fluorescently-labeled EVs, measured as the percentage of fluorescence-positive spermatozoa, reached up to 3,6±1,1% for FF-EVs, 12,1±3,7% for CVF-EVs and 9,4±1,9% for ESCs-EVs (mean ± SEM). Sperm cells co-incubated with any EVs group maintained unaffected vitality. Following a 4-hour incubation with EVs, a rise in the proportion of progressively motile spermatozoa was observed, with percentages of progressively motile spermatozoa ranging from a minimum of 45,4±3,8% for CVF-EVs LH + 7 to a maximum of 52,7±2,7% for dESCs-EVs (mean ± SEM). This increase resulted to be statistically significant (p < 0.05 and p < 0.01, respectively) compared to the untreated (UT) condition, which exhibited 26,2±0,7% of progressively motile sperm cells. Spermatozoa that completed the AR, indicating capacitation, after 4-hour incubation with EVs resulted to be up to 25,8±3,2% for FF-EVs, 35,0±6,6% for CVF-EVs and 26,9±3,0% for ESCs-EVs, compared to an average of 13% in the UT control. Limitations, reasons for caution This study constitutes a pilot investigation characterized by a limited sample size, necessitating larger cohorts to validate results. Wider implications of the findings Studied EVs may exert beneficial effects on capacitation and progressive motility also on asthenozoospermic (AS) men’s spermatozoa. Therefore, they could be used in ART cycles to prime spermatozoa from AS men and increase the percentage of sperm cells displaying progressive motility, potentially favouring fertilization via classical IVF instead of ICSI. Trial registration number not applicable
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