The human sperm proteome—Toward a panel for male fertility testing

Abstract

BackgroundAlthough male factor accounts for 40%–50% of unintended childlessness, we are far from fully understanding the detailed causes. Usually, affected men cannot even be provided with a molecular diagnosis.ObjectivesWe aimed at a higher resolution of the human sperm proteome for better understanding of the molecular causes of male infertility. We were particularly interested in why reduced sperm count decreases fertility despite many normal‐looking spermatozoa and which proteins might be involved.Material and methodsApplying mass spectrometry analysis, we qualitatively and quantitatively examined the proteomic profiles of spermatozoa from 76 men differing in fertility. Infertile men had abnormal semen parameters and were involuntarily childless. Fertile subjects exhibited normozoospermia and had fathered children without medical assistance.ResultsWe discovered proteins from about 7000 coding genes in the human sperm proteome. These were mainly known for involvements in cellular motility, response to stimuli, adhesion, and reproduction. Numbers of sperm proteins showing at least threefold deviating abundances increased from oligozoospermia (N = 153) and oligoasthenozoospermia (N = 154) to oligoasthenoteratozoospermia (N = 368). Deregulated sperm proteins primarily engaged in flagellar assembly and sperm motility, fertilization, and male gametogenesis. Most of these participated in a larger network of male infertility genes and proteins.DiscussionWe expose 31 sperm proteins displaying deviant abundances under infertility, which already were known before to have fertility relevance, including ACTL9, CCIN, CFAP47, CFAP65, CFAP251 (WDR66), DNAH1, and SPEM1. We propose 18 additional sperm proteins with at least eightfold differential abundance for further testing of their diagnostic potential, such as C2orf16, CYLC1, SPATA31E1, SPATA31D1, SPATA48, EFHB (CFAP21), and FAM161A.ConclusionOur results shed light on the molecular background of the dysfunctionality of the fewer spermatozoa produced in oligozoospermia and syndromes including it. The male infertility network presented may prove useful in further elucidating the molecular mechanism of male infertility.

Ether lipids and a peroxisomal riddle in sperm

“…As stated before, it is currently accepted that sperm are devoid of peroxisomes, but reports on the proteome of these cells from different species have consistently identified peroxisomal proteins (Chauvin et al, 2012;Amaral et al, 2013;Castillo et al, 2018;Martín-Cano et al, 2020;Greither et al, 2023). Based on available data on peroxisomal residents at the time, Amaral and others highlighted the presence of fifteen proteins with exclusive peroxisomal localization in the human sperm tail proteome.…”

“…As such, the source of ether lipids in sperm may be linked to early stages of the spermatogenesis or to acquisition during epididymal transit, particularly since the incorporation of exogenous phospholipids is possible through extracellular vesicles such as epididymosomes ( Sullivan and Saez, 2013 ). Intriguingly, reports on sperm proteomes from different species have consistently identified peroxisomal resident proteins, including the enzymes involved in the production of ether lipids ( Chauvin et al, 2012 ; Amaral et al, 2013 ; 2014 ; Castillo et al, 2018 ; Martín-Cano et al, 2020 ; Greither et al, 2023 ). Therefore, sperm seem to preserve selected peroxisomal pathways relevant for lipid metabolism.…”

“…In somatic cells, ether lipid biosynthesis is initiated in peroxisomes (A) and is finalized in the endoplasmic reticulum (B) where enzymes may be able to use both acyl and alkyl precursors (question mark). Boxed enzymes and pathways labelled in gold are found in sperm according to Chauvin et al, 2012 ; Amaral et al, 2013 , 2014 ; Castillo et al, 2018 ; Martín-Cano et al, 2020 and Greither et al, 2023 . Note peroxisome and ER compartments are believed to be missing in sperm.…”

“…Consistent with MS/MS results using sperm tails, both Pex11 and Acaa1 proteins localized to sperm midpiece and in the case of Acaa1, the full protein was detected by Western blot, indicating it is potentially functional. In order to better define the extent of the peroxisomal presence in the sperm proteome we conducted a meticulous analysis of published proteomic data from human and mouse sperm ( Chauvin et al, 2012 ; Amaral et al, 2013 ; 2014 ; Castillo et al, 2018 ; Greither et al, 2023 ) and compared it to the known mammalian peroxisomal resident list of proteins ( Yifrach et al, 2018 ). Out of 195 peroxisomal residents, 138 proteins (∼71%) were detected at least once in sperm from humans or mice, representing a much larger incidence than previously anticipated ( Supplementary Table S1 ).…”

Biomarker-based human and animal sperm phenotyping: the good, the bad and the ugly

“…Since then, numerous studies identified sub-proteomes associated with normal sperm function and fertility, and even with specific ART-related traits such as cryosurvival/freezability. The most extensive human sperm proteomic study, comparing proteome profiles among male subjects with varied fertility, showed the number of proteins with at least threefold deviating abundance increased from oligozoospermia ( N = 153) and oligoasthenozoospermia ( N = 154) to oligoasthenoteratozoospermia ( N = 368) when compared to normozoospermic males [ 10 ]. In a different study, proteomic profiling of spermatozoa in infertile men with severe oligoasthenoteratozoospermia identified 938 differentially expressed proteins significantly enriched in metabolic pathways and multiple pathways of neurodegeneration [ 11 ].…”