75 Impact of microplastics on porcine endometrial barrier integrity, functional receptivity, and maternal-embryo interaction

Plastic pollution is a steadily increasing global phenomenon that causes climate and environmental changes, resulting in a negative impact on human and animal health. In parallel, non-biodegradable plastic waste is improperly managed, and it accumulates in oceans, air, and soil. In addition, its slow degradation induces plastic fragmentation and the generation of small breakdown products, known as microplastics (MPs) that, owing to their small size, can easily enter the animal body through ingestion, inhalation, and dermal contact, negatively affecting several systems. It is estimated that mammals are exposed to 210 MP kg⁻¹ bw per day (Zuri et al. 2023 Environ. Int. 179, 108150; https://doi.org/10.1016/j.envint.2023.108150). Among the organs affected, those belonging to the female reproductive system require particular attention, because of their role in fertility, pregnancy, and newborn health. We investigated the possible effects of MP exposure on the endometrial barrier and implantation processes. To this purpose, we first generated an advanced three-dimensional porcine endometrial in vitro model capable of mimicking the complex multicellular architecture and functions of the in vivo epithelial barrier. We exposed this model to different MP concentrations (0, 0.25, 0.50, 0.75, 1.5, 3, 5, 10, 12.5, 25, and 50 mg mL⁻¹) for 24 and 48 h. MP effects on endometrial barrier integrity and the functional receptivity were analyzed by measuring trans-epithelial electrical resistance (TEER) and investigating the apoptosis- and fibrotic-related pathways. Endometrial ability to allow an embryo to successfully attach was also evaluated by co-culturing the exposed endometrial cells with trophoblast spheroids for 24 h. Statistical analysis was performed using two-way ANOVA. Differences of P ≤ 0.05 were considered significant. Our results demonstrate that exposure to MPs for 24 h did not affect porcine endometrial barrier integrity, its functional receptivity, or maternal-embryo interaction, regardless of the concentrations used. In contrast, when exposure was prolonged to 48 h, TEER values were significantly reduced at MP concentrations higher than 10 mg mL⁻¹ (from 131.2 ± 4.34 Ω∙cm² to 83 ± 3.19 Ω∙cm² vs. CTR 158 ± 4.23 Ω∙cm²). This was accompanied by an upregulation of P53 (pro-apoptotic), WNT-β, α-SMA, COL3A1, and COL4A (pro-fibrotic) gene transcription. Consistent with the activation of a fibrotic-related pathway, MMP1, MMP2, and MMP3 gene expression was significantly downregulated. The functional relevance of the gene response was supported by a statistically significant increment of collagen deposition (from 36 ± 1.58% to 48 ± 3.95% vs. CTR 28 ± 1.69% volume density) in the endometrial barrier, detected by measuring picrosirius red staining. In addition, co-culture with trophoblast spheroids showed a significantly lower attachment rate (from 61 ± 1.64% to 38 ± 3.2% vs. CTR 84 ± 2.11%), indicating a reduced endometrial attachment competence. Altogether, the data obtained indicate that MPs exert deleterious effects on female reproductive functions and, in particular, have a negative impact on endometrial receptivity.

This study was supported by the Carraresi Foundation, HORIZON-WIDERA-2021 project no. 101079349 (OH-Boost), PRIN 2022 Funded by the European Union-Next Generation EU, PSR2022, PSR2023.