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

Understanding the regulation of the testicular endocrine function leading to testosterone production is a major objective as the alteration of endocrine function is associated with the development of many diseases such as infertility. In the last decades, it has been demonstrated that several endogenous molecules regulate the steroidogenic pathway. Among them, bile acids have recently emerged as local regulators of testicular physiology and particularly endocrine function. Bile acids act through the nuclear receptor FXRα (Farnesoid-X-receptor alpha; NR1H4) and the G-protein-coupled bile acid receptor (GPBAR-1; TGR5). While FXRα has been demonstrated to regulate testosterone synthesis within Leydig cells, no data are available regarding TGR5. Here, we investigated the potential role of TGR5 within Leydig cells using cell culture approaches combined with pharmacological exposure to the TGR5 agonist INT-777. The data show that activation of TGR5 results in a decrease in testosterone levels. TGR5 acts through the PKA pathway to regulate steroidogenesis. In addition, our data show that TGR5 activation leads to an increase in cholesterol ester levels. This suggests that altered lipid homeostasis may be a mechanism explaining the TGR5-induced decrease in testosterone levels. In conclusion, the present work highlights the impact of the TGR5 signaling pathway on testosterone production and reinforces the links between bile acid signaling pathways and the testicular endocrine function. The testicular bile acid pathways need to be further explored to increase our knowledge of pathologies associated with impaired testicular endocrine function, such as fertility disorders.

Farnesoid X receptor alpha (FXRα) is a critical actor of the development and pathologies of the male reproductive system.

The farnesoid-X-receptorα (FXRα; NR1H4) is one of the main bile acid (BA) receptors. During the last decades, through the use of pharmalogical approaches and transgenic mouse models, it has been demonstrated that the nuclear receptor FXRα controls numerous physiological functions such as glucose or energy metabolisms. It is also involved in the etiology or the development of several pathologies. Here, we will review the unexpected roles of FXRα on the male reproductive tract. FXRα has been demonstrated to play functions in the regulation of testicular and prostate homeostasis. Even though additional studies are needed to confirm these findings in humans, the reviewed reports open new field of research to better define the effects of bile acid-FXRα signaling pathways on fertility disorders and cancers.

Nuclear Receptor Metabolism of Bile Acids and Xenobiotics: A Coordinated Detoxification System with Impact on Health and Diseases.

Structural and functional studies have provided numerous insights over the past years on how members of the nuclear hormone receptor superfamily tightly regulate the expression of drug-metabolizing enzymes and transporters. Besides the role of the farnesoid X receptor (FXR) in the transcriptional control of bile acid transport and metabolism, this review provides an overview on how this metabolic sensor prevents the accumulation of toxic byproducts derived from endogenous metabolites, as well as of exogenous chemicals, in coordination with the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). Decrypting this network should provide cues to better understand how these metabolic nuclear receptors participate in physiologic and pathologic processes with potential validation as therapeutic targets in human disabilities and cancers.

Metallome deregulation and health-related impacts due to long-term exposure to recent volcanic ash deposits: New chemical and isotopic insights.

Volcanic ash exposure can lead to significant health risks. Damage to the respiratory and pulmonary systems are the most evident toxic side effects although the causes of these symptoms remain unclear. Conversely, the effects on other organs remain largely under-explored, limiting our understanding of the long-term volcanic ash-related risk at the whole-body scale. The metallome i.e. metal concentrations and isotopic compositions within the body, is suspected to be affected by volcanic ash exposure, having thus the potential for capturing some specificities of ash toxicity. However, the means by and extent to which the metallome is affected at the entire body scale and how the consequent chemical and isotopic deregulations correlate with pathophysiological dysfunctions are currently poorly understood. Here, we adopt a transdisciplinary approach combining high precision chemical analyses (major and trace element concentrations) and CuZn isotope measurements in seven organs and two biological fluids of isogenic mice (C57BL/6) exposed to eruption products from La Soufrière de Guadeloupe (Eastern Carribean), in tandem with biological parameters including physiological and morphological data. Based on principal component analysis, we show that after one month of exposure to volcanic ash deposits, the mice metallome; originally organ-specific and isotopically-typified, is highly disrupted as shown for example by heavy metal accumulation in testis (e.g., Fe, Zn) and Cu, Zn isotopic divergence in liver, intestine and blood. These metallomic variations are correlated with early testicular defects and might reflect the warning signs of premature (entero)hepatic impairments that may seriously affect fertility and favor the emergence of liver diseases after prolonged exposure. Monitoring the temporal evolution of the Cu and Zn isotope compositions seems to be a promising technique to identify the main biological processes and vital functions that are vulnerable to environmental volcanogenic pollutants although this will require further validation on human subjects.

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

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.

Analysis of the Reversible Impact of the Chemodrug Busulfan on Mouse Testes.

Spermatogenesis is a process within the testis that leads to the production of spermatozoa. It is based on a population of spermatogonial stem cells, which have the capacity to self-renew and to differentiate throughout life to ensure the functions of reproduction are maintained. Male fertility disorders are responsible for half of the cases of infertility in couples worldwide. It is well known that cancer treatments are associated with reversible or irreversible fertility disorders. Busulfan (Bu) is an alkylating agent that significantly inhibits spermatogenesis. The present study relied on a combination of in vivo and in vitro approaches as well as RNAseq analysis to characterize the effects of Bu, in which mouse testes were used as a model. An in silico analysis revealed that many of the Bu-modulated genes are potentially regulated by the SIN3 Transcription Regulator Family Member A (SIN3A) and E2F Transcription Factor (E2F) families of transcription factors. The results demonstrate that the deregulated genes function in processes related to the cell cycle, DNA repair, and cell death mechanisms, including the Tumor Protein 53 (TP53) pathway. This reinforces the role of the TP53 signaling pathway as a major player in Bu effects. In addition, Bu altered the patterns of mRNA accumulation for various genes in undifferentiated spermatogonia. This work provides significant insight into the kinetics and impacts of busulfan, which could pave the way for developing strategies to minimize the impact of chemodrugs and, thus, could lead to germ cell lineage regeneration following anticancer treatments.

FXRα modulates leydig cell endocrine function in mouse.

The hypothalamic-pituitary axis exert a major control over endocrine and exocrine testicular functions. The hypothalamic-pituitary axis corresponds to a cascade with the Gonadotropin Releasing Hormone secreted by the hypothalamus, which stimulates the synthesis and the release of Luteinizing Hormone (LH) and Follicle Stimulating Hormone by the gonadotropic cells of the anterior pituitary. The LH signaling pathway controls the steroidogenic activity of the Leydig cells via the activation of the luteinizing hormone/choriogonadotropin receptor. In order to avoid a runaway system, sex steroids exert a negative feedback within hypothalamus and pituitary. Testicular steroidogenesis is locally controlled within Leydig cells. The present work reviews some local regulations of steroidogenesis within the Leydig cells focusing mainly on the roles of the Farnesoid-X-Receptor-alpha and its interactions with several orphan members of the nuclear receptor superfamily. Further studies are required to reinforce our knowledge of the regulation of testicular endocrine function, which is necessary to ensure a better understanding of fertility disorders and then proposed an adequate treatment of the diseases.

Fxralpha gene is a target gene of hCG signaling pathway and represses hCG induced steroidogenesis.

The bile acid receptor Farnesoid-X-Receptor alpha (FXRα), a member of the nuclear receptor superfamily, is well known for its roles in the enterohepatic tract. In addition, FXRα regulates testicular physiology through the control of both endocrine and exocrine functions. The endocrine function of the Leydig cells is mainly controlled by the hypothalamo-pituitary axis viaLH/chorionic gonadotropin (CG). If FXRα was demonstrated to control the expression of the Lhcgr gene, encoding the LH receptor; the impact of the LH/CG signaling on the Fxrα expression has not been defined so far. Here, we demonstrate that hCG increases the Fxrα gene expression through the protein kinase-A signaling pathway. Fxrα is then involved in a negative feedback of steroid synthesis. These data improve our knowledge of the local control of the testicular steroidogenesis with the identification of the link between the hypothalamo-pituitary axis and the FXRα signaling pathway.