Predictions from a mathematical approach to model ionic signaling for rapid responses of Sertoli cells exhibit similarities to pharmacological approaches

Sertoli cells are essential for the male reproduction system as they provide morphological support and nutrients for germ cells to guarantee ongoing spermatogenesis. The aim of this work was to predict the electrical properties at the plasma membrane that trigger Sertoli cell rapid responses by involving ionic channels. The rapid responses of Sertoli cells in culture were monitored using patch clamp electrical measurement and compared to data obtained using pharmacological tools (from intact seminiferous tubules). A mathematical model was used to define the roles of potassium channels and the ATP-dependent Na+/K+pump in these responses. Mathematical data verification was also performed to determine the resting and hormonal stimulated membrane potentials of Sertoli cells in the intact seminiferous tubules and of Sertoli cells in culture (patch clamp measurements). The prediction of these data based on mathematical modeling demonstrated, for the first time, the involvement of potassium channels and the activation of Na+/K+pump in the hyperpolarization of Sertoli cells and their consequent rapid responses. Moreover, the mathematical analysis showing the involvement of ionic balance in the rapid responses of these cells to hormones, such as follicle-stimulating hormone, is consistent with previous reports obtained using pharmacological techniques in Sertoli cells. Thus, the validation of such data is reliable and represents a first step in the proposition for a mathematical model to predict rapid responses of Sertoli cells to hormonal stimuli.

Estradiol and 1α,25(OH)2 vitamin D3 share plasma membrane downstream signal transduction through calcium influx and genomic activation in immature rat testis

The aim of this study was to investigate the rapid response pathway and gene and protein expression profiles of the rat testis in response to estradiol (E₂) and 1α,25(OH)₂ vitamin D₃ (1,25-D₃), to understand how they mediate their effects on the first spermatogenic wave. To do this, we compared the effects of 1,25-D₃ and E₂ on ⁴⁵calcium(Ca²⁺) uptake and the involvement of estrogen receptors (ESR) in their rapid responses. Additionally, we studied the downstream signal transduction effects of 1,25-D₃ and E₂ on cyclin A1/B1 and cellular cycle protein expression. As previously observed for 1,25-D₃, E₂ also increased ⁴⁵Ca²⁺ uptake in immature rat testes via voltage-dependent Ca²⁺ channels, Ca²⁺-dependent chloride channels and via the activation of protein kinase C, protein kinase A and mitogen-activated protein kinase kinase (MEK). Elevated aromatase expression by testes was observed in the presence of 1,25-D₃ and both hormones decreased ESR mRNA expression. Furthermore, 1,25-D₃ and E₂ diminished cyclin A1 mRNA expression, but E₂ did not affect cyclin B1 mRNA levels. Consistent with these findings, the immunocontent of cyclin A1 and B1 in the testes was also increased by 1,25-D₃ and E₂. 1,25-D₃ increased expressions of the p16 and p53 proteins, supporting the anti-proliferative and pro-apoptotic properties of 1,25-D_3, while E₂ also augmented p16. Data indicate that both hormones trigger rapid responses at the plasma membrane that may control the expression of gene and proteins related to cell cycle regulation, and thereby modulate spermatogenesis.

1,25(OH)2 vitamin D3 signalling on immature rat Sertoli cells: gamma-glutamyl transpeptidase and glucose metabolism

1α,25-Dihydroxyvitamin D₃ (1,25-D₃) is critical for the maintenance of normal male reproduction since reduced fertility is observed in vitamin D-deficient rats. Gamma-glutamyl transpeptidase (GGT) is a membrane-bound enzyme that is localized on Sertoli cells and catalyses the transfer of the gamma-glutamyl residues to an amino acid or peptide acceptor. Sertoli cells are also responsible for providing nutrients, as lactate, to the development of germ cells. The aim of this study was to investigate the effect and the mechanism of action of 1,25-D₃ on GGT on Sertoli cell functions from 30-day-old immature rat testis. Results demonstrated that 1,25-D₃ stimulates GGT activity at Sertoli cells plasma membrane through a PKA-dependent mechanism of action, which was not dependent of active de novo protein synthesis. The hormone increases glucose uptake, as well as lactate production and release by Sertoli cells without altering the reactive oxygen species (ROS) generation. In addition, 1,25-D₃ did not change reduced glutathione (GSH) amount or oxygen consumption, and diminished Sertoli cell death. These findings demonstrate that 1,25-D₃ stimulatory effect on GGT activity, glucose uptake, LDH activity and lactate production seem to be an important contribution of Sertoli cells for germ cells nutrition and for a full and active ongoing spermatogenesis.