Activation of Autophagy by Low-Dose Silica Nanoparticles Enhances Testosterone Secretion in Leydig Cells

Silica nanoparticles (SNPs) can cause abnormal spermatogenesis in male reproductive toxicity. However, the toxicity and toxicological mechanisms of SNPs in testosterone synthesis and secretion in Leydig cells are not well known. Therefore, this study aimed to determine the effect and molecular mechanism of low doses of SNPs in testosterone production in Leydig cells. For this, mouse primary Leydig cells (PLCs) were exposed to 100 nm Stöber nonporous spherical SNPs. We observed significant accumulation of SNPs in the cytoplasm of PLCs via transmission electron microscopy (TEM). CCK-8 and flow cytometry assays confirmed that low doses (50 and 100 μg/mL) of SNPs had no significant effect on cell viability and apoptosis, whereas high doses (more than 200 μg/mL) decreased cell viability and increased cell apoptosis in PLCs. Monodansylcadaverine (MDC) staining showed that SNPs caused the significant accumulation of autophagosomes in the cytoplasm of PLCs. SNPs activated autophagy by upregulating microtubule-associated protein light chain 3 (LC3-II) and BCL-2-interacting protein (BECLIN-1) levels, in addition to downregulating sequestosome 1 (SQSTM1/P62) level at low doses. In addition, low doses of SNPs enhanced testosterone secretion and increased steroidogenic acute regulatory protein (StAR) expression. SNPs combined with rapamycin (RAP), an autophagy activator, enhanced testosterone production and increased StAR expression, whereas SNPs combined with 3-methyladenine (3-MA) and chloroquine (CQ), autophagy inhibitors, had an opposite effect. Furthermore, BECLIN-1 depletion inhibited testosterone production and StAR expression. Altogether, our results demonstrate that low doses of SNPs enhanced testosterone secretion via the activation of autophagy in PLCs.