Nicotine induced autophagy of Leydig cells rather than apoptosis is the major reason of the decrease of serum testosterone.

A new report has shown that nicotine exposure can decrease serum testosterone by apoptosis in Leydig cells; however, in our previous studies, we have almost never observed apoptosis there. The purpose of this study is to ensure whether apoptosis or autophagy in Leydig cells occurred. Our results confirmed again that the concentration of testosterone in the sera of nicotine-treated mice statistically decreased (P < 0.05). Furthermore, the data of single cell transcriptome indicated that the expression of autophagy-related genes was increased after nicotine exposure. Likewise, chemical and immune-histological staining demonstrated that autophagy of the Leydig cells increased after nicotine treatment rather than apoptosis. Apoptosis mainly exists in spermatids. Further, the expression of autophagy-related genes, such as Beclin1 and LC3, were up-regulated after nicotine exposure (P < 0.05). Additionally, the data of transmission electron microscopy showed more autophagosomes in the Leydig cells of the nicotine-exposed groups than the cells of the control groups. Moreover, immunofluorescent staining of LC3 in the TM3 Leydig cell line indicated that rapamycin and nicotine exposure up-regulates the autophagy phenotype/process and down-regulates their testosterone synthesis. In addition, the methylation level of the promoter region of TCL1 is increased in the nicotine-treated group compared to the control group, consequently decreasing the expression of TCL1. In conclusion, the autophagy in Leydig cells induced by nicotine, which is set by the hyper-methylation of the TCL1 promoter region via the TCL1-mTOR-autophagy signaling pathway.