The selenoprotein TXNRD3 supports male fertility via the redox regulation of spermatogenesis

Thioredoxin/glutathione reductase (TGR, TXNRD3) is a selenoprotein composed of thioredoxin reductase and glutaredoxin domains; the function of this enzyme remains unknown. This NADPH-dependent thiol oxidoreductase evolved by gene duplication within the Txnrd family, is expressed in the testes and can reduce both thioredoxin and glutathione in vitro. To characterize the function of TXNRD3 in vivo, we generated a strain of mice with the deletion of Txnrd3 gene. We show that Txnrd3 knockout mice are viable and without discernable gross phenotypes, but TXNRD3 deficiency leads to fertility impairment in male mice. Txnrd3 knockout animals exhibit a lower fertilization rate in vitro, a sperm movement phenotype and an altered redox status of thiols. Proteomic analyses revealed a broad range of substrates reduced by TXNRD3 during sperm maturation, presumably as a part of quality control. The results show that TXNRD3 plays a critical role in male reproduction via the thiol redox control of spermatogenesis.