Identification of a Crosstalk among TGR5, GLIS2, and TP53 Signaling Pathways in the Control of Undifferentiated Germ Cell Homeostasis and Chemoresistance

Abstract

Spermatogonial stem cells regenerate and maintain spermatogenesis throughout life, making testis a good model for studying stem cell biology. The effects of chemotherapy on fertility have been well‐documented previously. This study investigates how busulfan, an alkylating agent that is often used for chemotherapeutic purposes, affects male fertility. Specifically, the role of the TGR5 pathway is investigated on spermatogonia homeostasis using in vivo, in vitro, and pharmacological methods. In vivo studies are performed using wild‐type and Tgr5‐deficient mouse models. The results clearly show that Tgr5 deficiency can facilitate restoration of the spermatogonia homeostasis and allow faster resurgence of germ cell lineage after exposure to busulfan. TGR5 modulates the expression of key genes of undifferentiated spermatogonia such as Gfra1 and Fgfr2. At the molecular level, the present data highlight molecular mechanisms underlying the interactions among the TGR5, GLIS2, and TP53 pathways in spermatogonia associated with germ cell apoptosis following busulfan exposure. This study makes a significant contribution to the literature because it shows that TGR5 plays key role on undifferentiated germ cell homeostasis and that modulating the TGR5 signaling pathway could be used as a potential therapeutic tool for fertility disorders.

Identification of the Role of TGR5 in the Regulation of Leydig Cell Homeostasis

“…The present data suggest that in the mouse Leydig cells, TGR5 activation leads to a decrease in CREB phosphorylation. This is quite unexpected as in other cell types, TGR5 activation was mainly associated with an increase in CREB phosphorylation [ 10 , 22 ]. Further studies are needed to better decipher the molecular mechanisms explaining why in Leydig cells TGR5 acts in an opposite way on PKA-CREB pathway.…”

“…To define the role of TGR5 in mouse Leydig cells, we explored its impact on endocrine function by measuring the production of testosterone using the mLTC1 cell line. As TGR5 modulates the protein kinase (PKA) pathway [ 10 , 14 , 15 ], which is a fast second cellular messenger, we decided to analyze the effect of TGR5 activation in short-time experiments. Treatment of mLTC1 cells with the TGR5 agonist INT-777 for 3 h resulted in a significant decrease in intracellular testosterone levels compared to vehicle-treated cells, while this effect was not observed after 6 h ( Figure 2 A).…”

“…TGR5 is known to act through the downstream PKA pathway [ 10 , 15 , 18 ]. To ensure the involvement of the PKA signaling pathway in response to INT-777, experiments using H89, a selective and potent PKA inhibitor, were performed.…”

“…The role of the bile acid receptor TGR5 in the testis has been previously demonstrated in germ cell lineage [ 8 , 9 , 10 ]. However, its roles on the testicular endocrine cells have not been studied so far.…”

“…In addition to FXRα, bile acids are ligands for the G-protein-coupled membrane bile acid receptor 1 (GPBAR1; TGR5). While the role of TGR5 in the testis has been explored in relation to the regulation of germ cell homeostasis [ 8 , 9 , 10 ], no study has thus far analyzed its potential impact on endocrine Leydig cells. The present study, using in vitro approaches, deciphers novel roles for TGR5 to control Leydig cell homeostasis.…”