Descifrando el impacto del balance h2o2 y el estrés oxidativo generado por la dieta en la espermatogénesis/deciphering the impact of h2o2 balance and diet-induced oxidative stress on spermatogenesis

Resumen

Throughout the last decades, a decline in fertility has been reported, mainly as a consequence of a reduction in sperm quality. If this trend continues, the decrease in fertility could be much exacerbated in the next few years. For that reason, the search for solutions to approach the different fecundability issues is now becoming a prime concern. In 25% cases of male infertility, etiology is unknown and recently, the involvement of oxidative stress in male infertility has been proposed as a feasible cause of idiopathic male infertility. For that reason, maintaining redox homeostasis is crucial for the correct function of the male reproductive system. In order to counteract an excessive amount of reactive oxygen species (ROS), cells harbor efficient endogenous antioxidant defenses. Because of its location in the mitochondrial matrix, superoxide dismutase 2 (SOD2) constitutes a first line of defense against ROS. Moreover, SOD2, by controlling ROS levels, has been found to mediate redox-regulated stem cell fate. Moreover, some lifestyle and environmental factors have been found to increase ROS production, affecting negatively male fertility. Particularly, diet has been proposed to play an independent role in male reproduction. Nowadays, diets are characterized by a high content of sugars and saturated fatty acids due to an increase in the consumption of processed foods, which has been associated with an increase in oxidative stress as well as with a decrease in sperm quality. Diabetes, a diet-related disease, has also been suggested to mediate male infertility since it concurs with increased ROS production that causes oxidative damage to sperm cells. Additionally, some diet compounds called advanced glycation endproducts (AGEs), which have been reported to trigger oxidative stress and inflammation, have been associated with diet-related diseases such as diabetes and might be a cause of male infertility in people suffering from these pathological conditions. These evidences prompted us to study the role of H2O2 balance after altering SOD2 levels and the potential role of oxidants of the diet on male infertility. In this thesis project, we describe that Sod2 genetic load influenced reproductive physiology. Thus, when the male parent displayed low SOD2 levels, it took a longer time for pregnancy and delivery, and also delivered less pups per litter. Interestingly, when altering SOD2 levels in the females, they showed no differences when compared to WT females. We also found that, under SOD2 imbalance, the number of spermatogonia remained constant but, the number of spermatocytes was much lower in Sod2+/- mice and the number of elongated spermatids was highly increased in Sod2+/++ mice. We also report here that the levels of SOD2 were not constant but, on the contrary, increased along sperm cell differentiation. Concomitantly, H2O2 concentration decreased during spermatogenesis and we found the lowest levels in elongated spermatids. We also found that neither the number of Leydig cells nor the production of testosterone was affected by SOD2 imbalance. However, androgen receptor levels were decreased in Sod2+/++ testes. Interestingly, we found that spermatogenesis was impaired in a 33% of our diabetic mice, which showed only Sertoli cells and spermatogonia in their seminiferous tubules but lacked differentiated sperm cells. Nevertheless, this condition was reverted under treatment with insulin. We also found that, spermatogenic cells produced the receptor for AGEs (RAGE) which levels were increased along spermatogenesis. Finally, we assayed some of the AGEs and their precursors, dicarbonyls, most commonly present in foods, in cell culture. We found that dicarbonyls, but not AGEs, had a cytotoxic effect on cells, triggering ROS production, increasing antioxidant defenses and, in particular, methylglyoxal produced cell death by apoptosis.