Hypoxia, a lack of oxygen in the body's tissues, is thought to be a cause of male infertility. This is the conclusion of the work of Australian researcher Tessa Lord published in the journal Nature Reviews Urology.
Several situations can cause hypoxia throughout the body, such as high altitude or sleep apnea (see box below). In addition, at the testicular level, varicocele, i.e. the appearance of varicose veins (abnormal dilation of the veins) in the scrotum (the envelope supporting the testicles), or a phenomenon of testicular torsion (twisting of the cord containing the veins and arteries supplying the testicle) can also be the cause of reduced oxygen supply.
After studying the level of oxygen needed for the development of the different cells present in the testicles, Tessa Lord wanted to know what the effects of a state of hypoxia would be on the " germ cells (reproductive cells, editor's note) in differentiation (which undergo a transformation to become spermatozoa, editor's note)". And therefore the impact on male fertility.
What is sleep apnea?
THE sleep apnea syndrome (SAOS) is a sleep disorder characterized by involuntary pauses in breathing. According to the Center for Snoring and Sleep Disorders (CRTS), sleep apnea affects between 5 and 7% of the French adult population and up to 15% of people aged over 70.
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Hypoxia causes changes in reproductive cells
For her work, Tessa Lord used mice and rats whose sperm development process is similar to that of men. The researcher therefore observed that when the testicles lack oxygen, the germ cells undergo changes, particularly in the expression of their genes. This change leads to an alteration in the differentiation of reproductive cells, when they become spermatozoa, but also to abnormal remodeling during the last stage of this differentiation as well as apoptosis (i.e. self-destruction of the cell).
At the level of the epididymis, the place of storage and conservation of mature spermatozoa located next to the testicle, hypoxic exposure can cause a modification in the number of epithelial cells, present on the surface of the body and organs, but also in their genetic imprint (i.e. their genetic profile). These changes cause an increase in the pH contained in the luminal fluid, present in the epididymis. This fluid in turn directly influences the maturation of spermatozoa and their ability to fertilize the oocyte.
Beyond the direct impact on the father's sperm, hypoxia could also cause changes that are passed down from one generation to the next. An embryo from a father who suffered from a lack of oxygen could therefore potentially have compromised development. Furthermore, according to Tessa Lord, it is also possible that these offspring could also be affected by "reduced fertility despite never having been exposed to hypoxia itself". However, "We don't know if a similar thing could happen in humans, it's something we would like to look at in the future", says the scientist. Further studies on the subject are therefore necessary to know if such effects exist in humans.
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A cause of reversible infertility
However, this abnormality in fertility could be reversible. Indeed, it would be enough to return to normal conditions of oxygen supply. However, it would be necessary to wait at least one or two cycles of spermatogenesis (process of sperm development lasting approximately 74 days in humans), for new spermatozoa to form normally, without hypoxia.
Thus, by descending to lower altitudes, or by treating sleep apnea, testicular torsion or even a varicocele, it would be possible to return to normal oxygen levels in the testicles, allowing uncompromised sperm production, leading to an increase in fertility.
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