Differential proteomics of sperm: insights, challenges and future prospects

Towards a Multi-Omics of Male Infertility

Infertility is a common problem affecting one in six couples and in 30% of infertile couples, the male factor is a major cause. A large number of genes are involved in spermatogenesis and a significant proportion of male infertility phenotypes are of genetic origin. Studies on infertility have so far primarily focused on chromosomal abnormalities and sequence variants in protein-coding genes and have identified a large number of disease-associated genes. However, it has been shown that a multitude of factors across various omics levels also contribute to infertility phenotypes. The complexity of male infertility has led to the understanding that an integrated, multi-omics analysis may be optimal for unravelling this disease. While there is a vast array of different factors across omics levels associated with infertility, the present review focuses on known factors from the genomics, epigenomics, transcriptomics, proteomics, metabolomics, glycomics, lipidomics, miRNomics, and integrated omics levels. These include: repeat expansions in AR, POLG, ATXN1, DMPK, and SHBG, multiple SNPs, copy number variants in the AZF region, disregulated miRNAs, altered H3K9 methylation, differential MTHFR, MEG3, PEG1, and LIT1 methylation, altered protamine ratios and protein hypo/hyperphosphorylation. This integrative review presents a step towards a multi-omics approach to understanding the complex etiology of male infertility. Currently only a few genetic factors, namely chromosomal abnormalities and Y chromosome microdeletions, are routinely tested in infertile men undergoing intracytoplasmic sperm injection. A multi-omics approach to understanding infertility phenotypes may yield a more holistic view of the disease and contribute to the development of improved screening methods and treatment options. Therefore, beside discovering as of yet unknown genetic causes of infertility, integrating multiple fields of study could yield valuable contributions to the understanding of disease development. Future multi-omics studies will enable to synthesise fragmented information and facilitate biomarker discovery and treatments in male infertility.

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.

Variability in the protein profiles in spermatozoa of two sturgeon species

Conventional sperm analysis (i.e., motility and fertility) has been used to evaluate sperm quality. Understanding the quality of sperm on the molecular level in the sturgeons, Acipenser baerii and A. schrenckii, is essential for the improvement of the conservation of genetic resources and farming performance. In this study, we used the iTRAQ proteomics approach to perform proteomic profiling of spermatozoa associated with sperm quality in sturgeons (Data are available via ProteomeXchange with identifier PXD006108). The results showed 291 and 359 differentially expressed proteins in A. baerii and A. schrenckii, respectively, of which 72 were common to both species and all were upregulated in high quality compared with low quality samples. The differentially expressed proteins were mainly categorized into the generation of precursor metabolites and energy and oxidation, and they were localized to the mitochondria. Three distinguishing pathways, Arginine and proline metabolism, Pyruvate metabolism and the Citrate cycle (TCA cycle) were found to play an important role in energy metabolism, and some substrates could be used in the sperm medium for storage and cryopreservation. The quantity levels of two proteins, CKMT1 and LDHB, were verified by western blot analysis. Moreover, other potential biomarkers involved in oxidation reduction, ubiquitin-proteasome-dependent proteolysis, chaperones and binding activity were also discussed. Our study is the first to use the iTRAQ-based proteomics approach to analyse the sturgeon spermatozoa proteome, and the results that we obtained are valuable for the prediction of sperm quality and reproduction management in these threatened species.

Differential proteomics of human seminal plasma: A potential target for searching male infertility marker proteins

The clinical fertility tests, available in the market, fail to define the exact cause of male infertility in almost half of the cases and point toward a crucial need of developing better ways of infertility investigations. The protein biomarkers may help us toward better understanding of unknown cases of male infertility that, in turn, can guide us to find better therapeutic solutions. Many clinical attempts have been made to identify biomarkers of male infertility in sperm proteome but only few studies have targeted seminal plasma. Human seminal plasma is a rich source of proteins that are essentially required for development of sperm and successful fertilization. This viewpoint article highlights the importance of human seminal plasma proteome in reproductive physiology and suggests that differential proteomics integrated with functional analysis may help us in searching potential biomarkers of male infertility.