Insulin improves spermatogenesis in a mouse model of aging

Aging can have adverse effects on the chance of fertility in men. In fact, men over 40 years old usually suffer from low sperm quality, sperm motility, and low level of serum testosterone that leads to infertility. In addition, the structure of DNA is more vulnerable in aged testes due to the high level of reactive oxygen species (ROS) and nitric oxide. However, it has been showed that insulin is able to decrease oxidative stress and apoptosis. Moreover, some studies showed that insulin can enhance both spermatogenesis and fertility. In this regard, we investigate the impacts of insulin on spermatogenesis, the number of sperm, and the level of gonadal hormones in aged testes of mice. Thirty-six adult male NMRI mice were used. They were kept under standard conditions. The animals were divided into two groups control and insulin. The insulin group received 100 µL insulin with a 72-hour interval by intraperitoneal (IP) injection for 33 weeks and the control group received water. At the 8, 12, and 33 weeks of treatment, the testes of mice were removed for histological, cellular (ROS and glutathione [GSH]) and molecular (Bcal2, caspase-3, and Bax) analysis. For measurement of the level of hormones (testosterone, LH, and FSH), the blood samples were collected from the heart. According to our findings, insulin could significantly increase the volume of the testes and the total number of spermatogonial stem cells, primary spermatocytes, round spermatids as well as leydig cells. In addition, activity of GPX was considerably high in the insulin group. Furthermore, in the insulin group, the level of ROS was reduced. In conclusion, insulin may be effective in enhancing the function of the testes in aged male mice.