Label-free proteomics of spermatozoa identifies candidate protein markers of idiopathic recurrent pregnancy loss

Recurrent pregnancy loss (RPL) affects a large number of couples worldwide, increasing their mental and financial burdens. While female factors that contribute to RPL have been studied extensively, the role of male factors is largely unknown, and approximately 40 % RPL cases remain unexplained despite thorough clinical examinations. These cases are clinically termed as idiopathic RPL (iRPL). Several studies have recently found that spermatozoa play an important role, beyond fertilization, in iRPL, specifically in early embryonic development. Consequently, scientists explored spermatozoa to understand iRPL and revealed that both oxidative stress and DNA fragmentation contribute to RPL. In this study, we analyzed sperm samples from male partners of iRPL patients and fertile men who recently fathered a child by LC-MS/MS to identify proteomic markers of iRPL. A total of 1,988 proteins were quantified by a label-free method, and stringent statistical analysis was performed for the selection of candidate biomarkers of iRPL. Out of 1,647 proteins quantified, only 7 proteins qualified the selection criteria, which are lactotransferrin, ATP synthase subunit beta mitochondrial, fatty acid synthase, anterior gradient protein 2 homolog, hemoglobin subunit beta, short-chain specific acyl-CoA dehydrogenase mitochondrial, cytoplasmic dynein 1 heavy chain, and 14-3-3 protein sigma. We then performed gene annotations, pathways, and network analyses to gain more biological insights, identifying an association between oxidative stress and iRPL.