Letrozole Protects Against Cadmium-induced Inhibition of Spermatogenesis via LHCGR and Hsd3b6 to Activate Testosterone Synthesis in Mice

Abstract

The heavy metal cadmium is believed to be one of the environmental endocrine disruptors of spermatogenesis. Cadmium-induced inhibition of spermatogenesis is associated with hormone secretion disorder. Letrozole is an aromatase inhibitor that can raise peripheral androgen levels and stimulate spermatogenesis. However, the potential protective effects of letrozole against cadmium-induced reproductive toxicity remain to be elucidated. In this study, male mice were administered CdCl2 (4 mg/kg BW) orally by gavage alone or in combination with letrozole (0.25 mg/kg BW) for 30 days. Cd exposure caused a significant decrease in body weight, sperm count, motility, vitality and plasma testosterone levels. Histopathological changes revealed extensive vacuolization and decreased spermatozoa in the lumen. However, in the Cd+letrozole group, letrozole treatment compensated for deficits in sperm parameters (count, motility, and vitality) induced by Cd. Letrozole treatment significantly increased serum testosterone levels, which were reduced by Cd. Histopathological studies revealed a systematic array of all germ cells, a preserved basement membrane and relatively less vacuolization. For mechanistic exploration, RNA-seq was used to profile alterations in gene expression in response to letrozole. Compared with that in the Cd-treated group, RNA-Seq analysis showed that 214 genes were differentially expressed in the presence of letrozole. Gene ontology (GO) enrichment analysis and KEGG signaling pathway analysis showed that steroid biosynthetic processes were the processes most affected by letrozole treatment. Furthermore, we found that the expression of the testosterone synthesis-related genes LHCGR (luteinizing hormone/choriogonadotropin receptor) and Hsd3b6 (3 beta- and steroid delta-isomerase 6) was significantly downregulated in Cd‐induced testes, but in letrozole-treated testes, these genes maintained similar expression levels as the control group. However, the transcription levels of inflammatory cytokines, such as IL-1β and IL-6, and oxidative stress-related genes (Nrf2, Nqo1, and Ho-1) showed no changes. The present study suggests that the protective potential of letrozole against Cd-induced reproductive toxicity might be due to upregulation of LHCGR and Hsd3b6, which could beneficially increase testosterone synthesis to achieve optimum protection in sperm quality and spermatogenesis.