The sperm, a nest of microbes still little known


For several years, observations about the evolution of sperm quality have been of concern as they seem to go hand in hand with a decline in the fertility rate. A decline that has become a global concern… One of the most crucial questions is whether this decline can be explained solely by economic and behavioral factors, or whether biological factors may also be involved. The causes are complex. Sperm is part of a wider trend. of deterioration in male reproductive health, which is beginning to turn into a general fertility crisis. If it is already established that environmental factors negatively influence sperm quality, to fully understand the situation, understanding the biology of sperm remains a crucial issue: with the impact of the cellular environment, unknowns are still reserved. .. At first considered as parasites. contained in semen, half worms half eels, spermatozoa were isolated and later recognized as cellular actors of male reproduction in the 17th century. But they are not the only ones… For several years, scientific circles have noticed that other cells, this time not human, play a role alongside them in human fertility. READ ALSO The microbiota, a hidden world The microbiota in us Countless microorganisms (bacteria, yeasts, fungi and viruses) live in all multicellular organisms. They constitute real ecosystems called microbiota, and whose physiological functions have been the subject of study for twenty years, these microorganisms live in colonies within many tissues: digestive and respiratory systems (especially studied and known to the general public), but also the nose, skin, etc. Weighing 2 to 3 kg in an adult, these microbial communities are intriguing. And they are all the more interesting because they give each person unique characteristics and are likely to vary throughout an individual’s life. They would therefore be associated, for some, with good health and greater longevity. READ ALSO A diversified microbiota, guarantee of good health Launched in 2008, the Human Microbiome Project aims to characterize the diversity of these sets of microbiota. organisms and explore them. the link between the presence or variation of these communities and the development of diseases. Between 2009 and 2021, nearly 40,000 articles were written about the gut microbiota, which constitutes the largest mass of microbiota in an adult individual. The discovery of the physiological importance of this microbiota has altered our relationship with health and has opened up new therapeutic perspectives. The scientific community has therefore begun to explore the microbiota of other tissues, less studied in the first place READ ALSO The intestinal microbiota, our second brain. The sperm microbiota, this unknown sperm, and the testicular environment are not sterile, in both senses of the word: they naturally contain many microorganisms. Less rich but more diverse than the vaginal microbiota, it is enriched or altered during the life of an individual. These two microbiota are of particular interest in human fertility studies. The comparative analysis of more than fifty studies has revealed, in fact, the complexity and modifications of the sperm microbiota, the culture, the microbiota are analyzed now using molecular biology techniques to access bacterial genomes. High-throughput genome sequencing techniques and advances in bioinformatics contribute to the characterization and analysis of these ecosystems of microorganisms and their relationships with the health status of their respective hosts. These two methods of analysis have been able to highlight the existence of different types of bacteria. in the semen of fertile and non-fertile subjects Culture methods frequently observe the presence of staphylococci, enterococci, escherichia and ureaplasma. Sequencing methods report an abundance of Lactobacilli, Prevotella, Pseudomonas as well as other opportunistic anaerobic pathogens (microorganisms that live in an environment without oxygen) These results certainly illustrate the limits of these detection methods, but leave no room for doubt that spermatozoa are not the only ones in ejaculates… What origin and what impact for the sperm microbiota? Two origins are accepted. One involves the upper genital tract (including the prostate), the other tissues outside the urogenital system (the digestive tract, the oral cavity, the blood or the vagina), the sharing of microbiota between the two can occur through sexual intercourse. studies report a correlation between the presence of particular microbes and sperm quality. For example, they would be able to adhere to spermatozoa and, therefore, modify their functions, such as mobility, until they are immobilized. The reported effects are very variable… The presence of lactobacilli would therefore be favorable to sperm functions, while the presence of proteobacteria, Anaerococcus and Bacteroides ureolyticus would be more associated with lower quality sperm. How can these different impacts on sperm functions be explained?, first possibility, the microorganisms could have a positive effect on the functions of the testicle itself… But, second hypothesis, they could act as antioxidants: they would reduce the concentration of reactive derivatives of sperm oxygen (or reactive oxygen species, an excess of which can damage cellular structures) and thus reduce DNA fragmentation and alteration The contribution of live microorganisms, in the form of probiotics, shows beneficial effects on sperm motility in rabbits. In humans, Lactobacillus and Bifidobacterium dietary supplementation increases motility and decreases DNA fragmentation in individuals with asthenozoospermia (reduced or absent sperm motility, in more than 50% of them one hour after ejaculation) . More recent studies of probiotic administration have also shown improvements. in sperm concentration and motility, as well as decreased cell death or inflammation markers. However, these observations have not been made in large enough populations to draw clear conclusions… Sperm and the vaginal microbiota Once they have entered the female genital tract, sperm must also contend with the existence of the local microbiota… Few studies have been done. performed on the effects of this other microbiota on spermatozoa, however, several results indicate that vaginal bacteria may have deleterious effects on sperm survival. Thus, if lactobacilli prefer to have a protective effect on the male genital system, their massive presence in the vagina alters the quality of the spermatozoa and sperm adhesion and agglutination phenomena are observed, which can trigger other cellular mechanisms such as the decrease in cell motility or destruction of spermatozoa by apoptosis. This programmed cell death could be caused either by the interaction between the bacterial molecules and the surface of the acrosome of the sperm (at the level of its head), or by the alteration of its membrane It has been suggested that the vaginal microbiota can act by distinguishing between spermatozoa of lower quality, since the latter would be more sensitive to the bacteria housed in the female genital tract. Ways of the future Knowing the seminal microbiota and its modifications would allow a better understanding of the impact of this environment on sperm quality: Can these bacteria have a real beneficial effect on sperm quality? According to its nature, can this microbiota promote or impair male fertility? The sperm microbiota tends to be increasingly recognized as a potential cause of infertility, but there are few studies that have focused on these aspects, which therefore remain controversial. cautious and that the hypothesis offered by these studies be decided: if the presence of microbiota is sometimes correlated with pathological states, the cause-effect relationship has not been clearly established. Therefore, the exploration of the biological mechanisms of this sperm-microbe partnership is just beginning… It already offers, despite everything, new diagnostic or therapeutic avenues for infertile couples. * Jean-François Bodart, University Professor, Cell Biology and Developmental Biology, University of Lille
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