Suppression of testosterone production by nanoparticulate TiO 2 is associated with ERK1/2-PKA-PKC signaling pathways in rat primary cultured leydig cells

Abstract

Background: Nanoparticulate titanium dioxide (nano-TiO 2 ) enters the body through various routes and causes organ damage. Exposure to nano-TiO 2 is reported to cause testicular injury in mice or rats and decrease testosterone synthesis, sperm number, and motility. Importantly, nano-TiO 2 suppresses testosterone production by Leydig cells (LCs) and impairs the reproductive capacity of animals. Methods: In an attempt to establish the molecular mechanisms underlying the inhibitory effect of nano-TiO 2 on testosterone synthesis, primary cultured rat LCs were exposed to varying concentrations of nano-TiO 2 (0, 10, 20, and 40 µg/mL) for 24 hours, and alterations in cell viability, cell injury, testosterone production, testosterone-related factors (StAR, 3βHSD, P450scc, SR-BI, and DAX1), and signaling molecules (ERK1/2, PKA, and PKC) were investigated. Results: The data show that nano-TiO 2 crosses the membrane into the cytoplasm or nucleus, triggering cellular vacuolization and nuclear condensation. LC viability decreased in a time-dependent manner at the same nano-TiO 2 concentration, nano-TiO 2 treatment (10, 20, and 40 µg/mL) decreased MMP (36.13%, 45.26%, and 79.63%), testosterone levels (11.40% and 44.93%), StAR (14.7%, 44.11%, and 72.05%), 3βHSD (26.56%, 50%, and 79.69%), pERK1/2 (27.83%, 63.61%, and 78.89%), PKA (47.26%, 70.54%, and 85.61%), PKC (30%, 50%, and 71%), SR-BI (16.41%, 41.79%, and 67.16%), and P450scc (39.41%, 55.26%, and 86.84%), and upregulated DAX1 (1.31-, 1.63-, and 3.18-fold) in primary cultured rat LCs. Conclusion: Our collective findings indicated that nano-TiO 2 -mediated suppression of testosterone in LCs was associated with regulation of ERK1/2–PKA–PKC signaling pathways.