Silica nanoparticles inhibit the development of mouse preantral follicle in vitro 3D culture via a decrease in cell...

Silica nanoparticles (SNPs) are promising nanomaterial with desirable chemical and physical properties for their applications in agriculture, biomedicine and others. There are serious concerns regarding the biosafety of SNPs. SNPs can induce follicular atresia, leading to ovarian toxicity. However, studying only oocytes or ovarian granulosa cells seems insufficient to fully reveal the impact of SNPs on the development of follicles. An in vitro 3D culture system of the follicles was established to investigate mouse ovarian toxicity of SNPs. Follicular development was evaluated through observation of follicular morphology, measurement of follicular diameter, number of mature follicles and oocyte maturation. The secretion of 17-β estradiol (E₂) was measured by ELISA. Microfilament distribution was examined by phalloidin-iFluor, and mitochondria distribution was detected by Mitotracker Red. The results showed that SNPs disrupted ovarian granulosa cell arrangement, inhibited their growth, and hindered follicular antrum formation and oocyte maturation. SNPs significantly increased cell apoptosis in ovarian granulosa cells and elevated Caspase-3 mRNA level. Additionally, SNPs significantly reduced E₂ secretion and STAR, CYP11A1, and CYP19A1 mRNA levels. Furthermore, SNPs caused mitochondria to distribute unevenly, forming clusters or even diffusely within the oocytes. SNPs also shortened the length and reduced the number of microvilli in the follicles. Meanwhile, both CX37 protein and mRNA level were significantly decreased in the oocytes. In summary, SNPs induced follicular atresia, at least partly, via inhibition of oocyte maturation and damage of the gap functions between the oocytes and ovarian granulosa cells. This study confirmed the toxicity of SNPs on follicles using in vitro 3D culture of preantral follicles, providing a new perspective for the study of SNP-induced ovarian toxicity.