The “quality” of sperm could be altered by microbes

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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 is explained solely by economic and behavioral factors, or whether biological factors may also be involved. The causes are complex: declining sperm quality is part of a larger trend of deteriorating 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. . Initially considered parasites contained in the 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 noted that other cells, this time not human, would have a role alongside them in human fertility. The number of published studies on the microbiota according to the tissues: the associate. with sperm is underrepresented (data extracted through the Pubmed bibliographic search until 2021) – Pubmed (via The Conversation)​The microbiota in us In all multicellular organisms live countless microorganisms (bacteria, yeasts, fungi and viruses) . 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 , the skin, etc. Weighing 2 to 3 kilograms 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. Therefore, they would be associated, for some, with good health and greater longevity. Launched in 2008, the Human Microbiome Project aims to characterize the diversity of these sets of microorganisms and explore 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 the 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. Therefore, the scientific community has begun to explore the microbiota of other tissues, less studied in the first instance, 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 not leave no doubt that the spermatozoa are not alone in the ejaculate… The spermatozoa are not alone in the semen. And the quality of the latter depends in part on the microorganisms present – Vasin-ks / Wikimedia CC BY-SA 4.0 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 spermatozoa oxygen (or reactive oxygen species, an excess of which can damage cellular structures) and would 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, dietary supplementation with Lactobacillum and Bifidobacterium 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 markers of inflammation. However, these observations have not been made in large enough populations to draw clear conclusions… The bacterium Lactobacillus acidophilus (here under scanning microscopy) may be beneficial in the male genital tract. On the other hand, it has a negative effect on the vagina, probably due to a very high concentration – Mogana Das Murtey & Patchamuthu Ramasamy / Wikimedia CC BY-SA 3.0​Spermatozoa facing the vaginal microbiota Once they have penetrated the female genital tract, the spermatozoa the existence of the local microbiota must also be faced… Few studies have been done on the effects of this other microbiota on spermatozoa, but several results nevertheless indicate that vaginal bacteria can have effects harmful to 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 discriminating lower quality spermatozoa, since the latter would be more sensitive to the bacteria housed by the female genital apparatus. Future paths Knowing the seminal microbiota and its modifications would allow a better understanding of the impact of this medium 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. The exploration of the biological mechanisms of this sperm-microbe company is just beginning… However, it already offers new diagnostic or therapeutic avenues for infertile couples. This analysis has been written by Jean-François Bodart, professor of cell biology and Developmental Biology at the University of Lille The original article was published on The Conversation website. Access to this content has been blocked in order to respect your choice of consent. 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