Bile Acid Alters Male Mouse Fertility in Metabolic Syndrome Context

Cholic acid inhibits ovarian steroid hormone synthesis and follicular development through farnesoid X receptor signaling in mice

This study investigated the effects of cholic acid (CA) on steroid hormone synthesis and follicular development in mouse ovaries and the regulatory mechanism of CA on the expression of steroidogenesis-related genes in granulosa cells. The mice were divided into control and CA groups, and serum and ovarian samples were collected after 1, 2, and 4 months of treatment, respectively. The results showed that CA treatment for 1, 2, and 4 months reduced ovarian weights, disrupted the estrous cycle, decreased the numbers of antral follicles and corpora lutea, and lowered the serum levels of progesterone and estradiol. Moreover, in the ovary, CA treatment upregulated the expression of farnesoid X receptor (FXR) and downregulated the expression of steroidogenesis-related genes, including StAR, CYP11A1, and HSD3B1. Mechanistically, FXR knockdown reversed the inhibitory effects of CA on steroidogenesis-related gene expression and cholesterol uptake in granulosa cells. In vitro follicle culture experiments further confirmed that CA suppressed follicle development, decreased the mRNA expression of steroidogenesis-related genes, and reduced progesterone and estradiol secretion. Collectively, our results demonstrated that CA inhibited follicular development and steroid hormone synthesis through FXR signaling.

Unveiling the hidden impact of long-term metal-rich volcanic pollution on male reproductive functions using isotope metallomics

Volcanic eruptions release particles in a range of sizes that can chronically affect the health of communities within tens of kilometers of the volcano. Many years after an eruption, resuspension of volcanic ash can exacerbate the health impact of primary eruptive events. So far, our global understanding of the health effects triggered by chronic exposure to volcanic particles at the whole-body scale is limited. Recently, it has been shown that mice chronically exposed to metal-rich volcanic ash deposits present metallome deregulations associated with pathophysiological changes. These deregulations preferentially impact the reproductive functions, questioning about the impact of ash on fertility. This work aims to further assess the mechanisms driving the ash-related fertility disorders and develop predictive biomarkers. For that, elemental concentrations and Cu-Zn-Fe isotope measurements coupled to metabolomic, proteomic and transcriptomic analyses were measured in blood, liver and two organs of the male reproductive system (testis, seminal vesicle). The samples were collected on wild-type and mice exposed over two months to volcanic ash. Mice exposed to ash are characterized by (i) significant metallomic deregulations, (ii) higher oxidative stress correlating with isotopic variations of redox-sensitive elements and (iii) testicular and hepatic alterations, marked by gains in organ mass, hepatic lipid accumulation and circulating bile acids overload, all of which might exacerbate testicular defects. Together, these results demonstrate that prolonged exposure to metal-rich ash is a threat for male reproduction and that investigating redox-sensitive isotopes might help identifying early signs of oxidative stress-related testicular injuries, with future implications for hepato-testicular disease prevention.

The preventive effect of heat-killed Lactobacillus plantarum on male reproductive toxicity induced by cholestasis in rats

This study investigated the preventive effect of heat-killed Lactobacillus plantarum (L. plantarum) on cholestasis-induced male reproductive toxicity in rats. Rats were divided into control normal, sham control, bile duct ligation (BDL) control, and BDL with heat-killed L. plantarum supplementation groups. The effects on sexual hormones, testicular and epididymal histology, sperm parameters, oxidative stress markers, and inflammatory gene expression were evaluated. Compared to the BDL control group, the BDL + heat-killed L. plantarum group showed higher levels of normal sperm, luteinizing hormone, testosterone, total antioxidant capacity, and catalase activity, indicating improved reproductive function. Conversely, markers of oxidative stress, such as total oxidative status, oxidative stress index, and carbonyl protein, were lower in the BDL + heat-killed L. plantarum group. The expression levels of inflammatory genes tumor necrosis factor-alpha and interleukin-6 were reduced, while interleukin-10 gene expression was increased in the BDL + heat-killed L. plantarum group. Histological evaluation confirmed the positive effects of heat-killed L. plantarum intervention on testicular parameters. In conclusion, heat-killed L. plantarum supplementation protects against cholestasis-induced male reproductive dysfunction in rats, as evidenced by improvements in hormonal balance, sperm quality, oxidative stress, and inflammation.

High fat diet causes distinct aberrations in the testicular proteome

Diet has important effects on normal physiology and the potential deleterious effects of high fat diets and obesity on male reproductive health are being increasingly described. We conducted a histological review of the effects of chronic high fat (HF) diet (using a mouse model fed a 45% fat diet for 21 weeks) with a discovery proteomic study to assess for changes in the abundance of proteins in the testis. Mice on a HF diet became obese and developed glucose intolerance. Using mass spectrometry, we identify 102 proteins affected in the testis of obese mice. These included structural proteins important for the blood testis barrier (filamin A, FLNA), proteins involved in oxidative stress responses (spermatogenesis associated 20, SPATA-20) and lipid homoeostasis (sterol regulatory element-binding protein 2, SREBP2 and apolipoprotein A1, APOA1). In addition, an important regulator protein paraspeckle component 1, PSPC-1, which interacts with the androgen receptor was significantly downregulated. Proteomic data was validated using both Western blotting and immunostaining which confirmed and localised protein expression in both mouse and human testis using biopsy specimens. This study focused mainly on the abnormalities that occurred at the protein level and as a result, we have identified several candidate proteins and conducted pathway analysis around the effects of HF diet on the testis providing novel insights not previously described. Some of the identified targets could be targeted therapeutically and future work is directed in this area.

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.

Crosstalk between BPA and FXRα Signaling Pathways Lead to Alterations of Undifferentiated Germ Cell Homeostasis and Male Fertility Disorders

Several studies have reported an association between the farnesoid X receptor alpha (FXRα) and estrogenic signaling pathways. Fxrα could thus be involved in the reprotoxic effects of endocrine disruptors such as bisphenol-A (BPA). To test this hypothesis, mice were exposed to BPA and/or stigmasterol (S), an FXRα antagonist. Following the exposure to both molecules, wild-type animals showed impaired fertility and lower sperm cell production associated with the alteration of the establishment and maintenance of the undifferentiated germ cell pool. The crosstalk between BPA and FXRα is further supported by the lower impact of BPA in mice genetically ablated for Fxrα and the fact that BPA counteracted the effects of FXRα agonists. These effects might result from the downregulation of Fxrα expression following BPA exposure. BPA and S act additively in human testis. Our data demonstrate that FXRα activity modulates the impact of BPA on male gonads and on undifferentiated germ cell population.

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BPA and S exposures synergistically induce male fertility disorders

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BPA regulates Fxr expression

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BPA and S act additively in human testis

Activated-farnesoid X receptor (FXR) expressed in human sperm alters its fertilising ability

The farnesoid X receptor alpha (FXR) is a bile acid sensor activated by binding to endogenous bile acids including chenodeoxycholic acid (CDCA). Although, FXR is expressed in male reproductive tissue, the relevance of the receptor on reproduction is scarcely known. Here, we demonstrated the FXR presence and its action on several human sperm features. Western blot and immunofluorescence assays evidenced the FXR expression in human spermatozoa and the localisation in the middle piece. CDCA increasing concentrations and GW4064, synthetic ligand of FXR, were used to study the FXR influence on sperm motility, survival, capacitation, acrosome reaction and on glucose as well as lipid metabolism. Interestingly, our data showed that increasing concentrations of CDCA negatively affected sperm parameters, while the receptor blockage by (Z)-Guggulsterone and by the anti-FXR Ab reversed the effects. Intriguingly, elevated CDCA levels increased triglyceride content, while lipase and G6PDH activities were reduced with respect to untreated samples, thus impeding the metabolic reprogramming typical of the capacitated sperm. In conclusion, in this study, we demonstrated for the first time a novel target for FXR and that the activated receptor alters the acquisition of sperm fertilising ability. We showed that sperm itself express the FXR and it is responsive to specific ligands of the receptor; therefore, bile acids influence this cell both in male and in female genital tracts. It might be hypothesized that bile acid levels could be involved in infertility with idiopathic origin as these compounds are not systematically measured in men undergoing medically assisted procreation.

Cholesterol: A Gatekeeper of Male Fertility?

Cholesterol is essential for mammalian cell functions and integrity. It is an important structural component maintaining the permeability and fluidity of the cell membrane. The balance between synthesis and catabolism of cholesterol should be tightly regulated to ensure normal cellular processes. Male reproductive function has been demonstrated to be dependent on cholesterol homeostasis. Here we review data highlighting the impacts of cholesterol homeostasis on male fertility and the molecular mechanisms implicated through the signaling pathways of some nuclear receptors.

The Bile Acid Nuclear Receptor FXRα Is a Critical Regulator of Mouse Germ Cell Fate

Spermatogenesis is the process by which spermatozoa are generated from spermatogonia. This cell population is heterogeneous, with self-renewing spermatogonial stem cells (SSCs) and progenitor spermatogonia that will continue on a path of differentiation. Only SSCs have the ability to regenerate and sustain spermatogenesis. This makes the testis a good model to investigate stem cell biology. The Farnesoid X Receptor alpha (FXRα) was recently shown to be expressed in the testis. However, its global impact on germ cell homeostasis has not yet been studied. Here, using a phenotyping approach in Fxrα^−/− mice, we describe unexpected roles of FXRα on germ cell physiology independent of its effects on somatic cells. FXRα helps establish and maintain an undifferentiated germ cell pool and in turn influences male fertility. FXRα regulates the expression of several pluripotency factors. Among these, in vitro approaches show that FXRα controls the expression of the pluripotency marker Lin28 in the germ cells.

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FXRα regulated germ cell apoptotis independently of androgen homeostasis

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FXRα controls germ cell differentiation

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FXRα regulates the establishment and maintenance of undifferentiated germ cells

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In germ cells, FXRα controls the expression of pluripotency markers such as Lin28

Bile acid homeostasis controls CAR signaling pathways in mouse testis through FXRalpha

Bile acids (BAs) are molecules with endocrine activities controlling several physiological functions such as immunity, glucose homeostasis, testicular physiology and male fertility. The role of the nuclear BA receptor FXRα in the control of BA homeostasis has been well characterized. The present study shows that testis synthetize BAs. We demonstrate that mice invalidated for the gene encoding FXRα have altered BA homeostasis in both liver and testis. In the absence of FXRα, BA exposure differently alters hepatic and testicular expression of genes involved in BA synthesis. Interestingly, Fxrα-/- males fed a diet supplemented with BAs show alterations of testicular physiology and sperm production. This phenotype was correlated with the altered testicular BA homeostasis and the production of intermediate metabolites of BAs which led to the modulation of CAR signaling pathways within the testis. The role of the CAR signaling pathways within testis was validated using specific CAR agonist (TCPOBOP) and inverse agonist (androstanol) that respectively inhibited or reproduced the phenotype observed in Fxrα-/- males fed BA-diet. These data open interesting perspectives to better define how BA homeostasis contributes to physiological or pathophysiological conditions via the modulation of CAR activity.

Bile acids and their receptors

Primary bile acids are synthetized from cholesterol within the liver and then transformed by the bacteria in the intestine to secondary bile acids. In addition to their involvement in digestion and fat solubilization, bile acids also act as signaling molecules. Several receptors are sensors of bile acids. Among these receptors, this review focuses on the nuclear receptor FXRα and the G-protein-coupled receptor TGR5. This review briefly presents the potential links between bile acids and cancers that are discussed in more details in the other articles of this special issue of Molecular Aspects of Medicine focused on "Bile acids, roles in integrative physiology and pathophysiology".