Molecular Pathways Associated with Sperm Biofunction Are Not Affected by the Presence of Round Cell and Leukocyte Proteins in Human Sperm Proteome

Mapping the human sperm proteome - novel insights into reproductive research

INTRODUCTION

Spermatozoa are highly specialized cells with unique morphology. In addition, spermatozoa lose a considerable amount of cytoplasm during spermiogenesis, when they also compact their DNA, resulting in a transcriptionally quiescent cell. Throughout the male reproductive tract, sperm will acquire proteins that enable them to interact with the female reproductive tract. After ejaculation, proteins undergo post-translational modifications for sperm to capacitate, hyperactivate and fertilize the oocyte. Many proteins have been identified as predictors of male infertility, and also investigated in diseases that compromise reproductive potential.

AREAS COVERED

In this review we proposed to summarize the recent findings about the sperm proteome and how they affect sperm structure, function, and fertility. A literature search was performed using PubMed and Google Scholar databases within the past 5 years until August 2022.

EXPERT OPINION

Sperm function depends on protein abundance, conformation, and PTMs; understanding the sperm proteome may help to identify pathways essential to fertility, even making it possible to unravel the mechanisms involved in idiopathic infertility. In addition, proteomics evaluation offers knowledge regarding alterations that compromise the male reproductive potential.

Influence of Risk Factors for Male Infertility on Sperm Protein Composition

Male infertility is a common health problem that can be influenced by a host of lifestyle risk factors such as environment, nutrition, smoking, stress, and endocrine disruptors. These effects have been largely demonstrated on sperm parameters (e.g., motility, numeration, vitality, DNA integrity). In addition, several studies showed the deregulation of sperm proteins in relation to some of these factors. This review inventories the literature related to the identification of sperm proteins showing abundance variations in response to the four risk factors for male infertility that are the most investigated in this context: obesity, diabetes, tobacco smoking, and exposure to bisphenol-A (BPA). First, we provide an overview of the techniques used to identify deregulated proteins. Then, we summarise the main results obtained in the different studies and provide a compiled list of deregulated proteins in relation to each risk factor. Gene ontology analysis of these deregulated proteins shows that oxidative stress and immune and inflammatory responses are common mechanisms involved in sperm alterations encountered in relation to the risk factors.

Proteomics and metabolomics - Current and future perspectives in clinical andrology

Proteomics and metabolomics are emerging as promising tools to investigate the molecular mechanisms associated with male infertility. Proteins and metabolites play a pivotal role in regulating the molecular pathways associated with physiological functions of spermatozoa. Semen analysis, physical examination and laboratory work up cannot identify the etiology of infertility in 30%-40% of cases, which are classified as idiopathic. Therefore, the application of proteomics and metabolomics in the field of andrology will aid to overcome the limitations of the standard semen analysis. Understanding the molecular pathways associated with male infertility will help in planning ad hoc treatments, contributing to the clinical management of infertile patients. In this review, proteomics and metabolomics studies on spermatozoa and seminal plasma are discussed with a focus on molecular biomarkers associated with male infertility-related conditions.

Transcriptional response to a Mediterranean diet intervention exerts a modulatory effect on neuroinflammation signaling pathway

Background: The Traditional Mediterranean Diet (TMD) is known to have beneficial effects on several chronic diseases. However, data concerning the whole transcriptome modulation of the TMD are scarce.Objective: We aimed to explore the effects of the TMD on the whole transcriptome of individuals at high cardiovascular risk.Methods: Thirty-four participants at high cardiovascular risk were randomly assigned to a TMD enriched with extra-virgin olive oil (TMD + VOO), mixed nuts (TMD + Nuts), or a control diet based on low-fat diet recommendations. A microarray analysis in circulating peripheral blood mononuclear cells of the participants was conducted before and after 3 months of the intervention. The association of changes in gene expression was modeled into canonical pathways by conducting an untargeted functional analysis with the Ingenuity Pathway Analysis^® (IPA). Effects were considered significant when the absolute z-score values were ≥2.0 and the logarithm P (adjusted by the Benjamini-Hochberg procedure [BH]) values were ≥1.30.Results: According to IPA, interventions with TMD + Nuts, TMD + VOO, and control diet downregulated neuroinflammation, triggering receptor expressed on myeloid cells 1 , and cholecystokinin/gastrin-mediated signaling pathways, respectively. The gene expression among these pathways included cytokines, T-cell activation receptors, nuclear factor kappa β/inflammasome components, pro-inflammatory enzymes and cell cycle regulators.Conclusion: The current findings suggest that the TMD enriched with mixed nuts or VOO downregulate transcriptomic pathways, including those related to neuroinflammation, which could influence development of neurodegenerative diseases. Our data should be corroborated in other tissue cells, such as neurons and glial cells. The PREDIMED trial was registered at https://www.controlled-trials.com (ISRCTN35739639).

Proteomic Analyses of Human Sperm Cells: Understanding the Role of Proteins and Molecular Pathways Affecting Male Reproductive Health

Human sperm proteomics research has gained increasing attention lately, which provides complete information about the functional state of the spermatozoa. Changes in the sperm proteome are evident in several male infertility associated conditions. Global proteomic tools, such as liquid chromatography tandem mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight, are used to profile the sperm proteins to identify the molecular pathways that are defective in infertile men. This review discusses the use of proteomic techniques to analyze the spermatozoa proteome. It also highlights the general steps involved in global proteomic approaches including bioinformatic analysis of the sperm proteomic data. Also, we have presented the findings of major proteomic studies and possible biomarkers in the diagnosis and therapeutics of male infertility. Extensive research on sperm proteome will help in understanding the role of fertility associated sperm proteins. Validation of the sperm proteins as biomarkers in different male infertility conditions may aid the physician in better clinical management.

Round cells do not contaminate or mask human sperm proteome in proteomic studies using cryopreserved samples

Semen contains leucocytes and round cells, besides spermatozoa. The objective of this study was to identify whether the proteins from round cells and leucocytes affect the proteomic analysis of spermatozoa. Cryopreserved human sperm samples were divided into four groups: (1) samples with ≥1 × 10⁶ /ml leucocytes unprocessed; (2) samples with ≥1 × 10⁶ /ml leucocytes processed by 65% density centrifugation; (3) samples with round cells <1 × 10⁶ /ml unprocessed; and (4) samples with round cells <1 × 10⁶ /ml processed by 65% density centrifugation. Samples from each group (1, 2, 3 and 4) were pooled (n = 5) for quantitative proteomic analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Comparative analysis revealed nine differentially expressed proteins (DEPs) groups 1 and 2. Moreover, five DEPs were identified between groups 3 and 4. We observed that cylicin-1, Atlastin-1 and vesicle transport protein SFT2B are specific to spermatozoa, and none of them were associated with leucocytes. The number of DEPs in spermatozoa of processed and unprocessed cryopreserved semen samples was negligible. Our results indicate that the presence of round cells (<1 × 10⁶ /ml) in the seminal ejaculation does not interfere in the accurate detection of spermatozoa proteome by LC-MS/MS.