Cadmium induces ferroptosis in mouse spermatocytes by activating the ROS–TCA pathway

It is currently unclear whether cadmium-induced ferroptosis in testis is related to the mitochondrial TCA cycle. Therefore, we performed in vitro experiments on GC-2spd spermatocytes to elucidate the mechanisms of Cd-induced ferroptosis. We analyzed mitochondrial morphology in real-time using 3D Cell Explorer and determined the levels of markers related to oxidative stress, ferroptosis, and mitochondrial TCA cycle. Cd exposure for 36 h significantly decreased cell viability and the expression of proliferating cell nuclear antigen ( p  < 0.05). The Cd-exposed group exhibited significantly increased malondialdehyde contents, significantly decreased GPX4 expression, and increased Nrf2 and HO-1 expressions. GC-2spd cells in the control group (no Cd exposure) appeared healthy with long filamentous mitochondria, whereas the Cd-exposed group exhibited cell death and increased mitochondria fragmentation. Western blotting revealed significantly upregulated expressions of FTH1, FTL, SLC40A1 in the Cd-exposed group, as well as increased contents of mitochondrial ROS, succinate, and α-ketoglutarate. The mRNA expression and activity of pyruvate carboxylase were markedly enhanced in the Cd-exposed group. Association analysis between RNA sequencing and metabolomic analyses showed that the signaling pathway of Cd-induced cell damage predominantly involved ferroptosis, whereas the metabolic pathway predominantly involved the mitochondrial TCA cycle and energy metabolism. Thus, Cd exposure in GC-2spd cells directly damages mitochondria, resulting in excessive ROS production, activating the Nrf2/pyruvate carboxylase signaling pathway, further caused paradoxical activation of the mitochondrial TCA cycle, which finally enhances ROS production and triggers ferroptosis. Our study provides a new training of thought for in-depth study on Cd-induced ferroptosis in spermatocyte.