The liver X receptor-{beta} is essential for maintaining cholesterol homeostasis in the testis

Targeting dysregulated phago-/auto-lysosomes in Sertoli cells to ameliorate late-onset hypogonadism

Age-related changes in testicular function can impact health and well-being. The mechanisms underlying age-related testicular dysfunction, such as late-onset hypogonadism (LOH), remain incompletely understood. Using single-cell RNA sequencing on human testes with LOH, we delineated Sertoli cells (SCs) as pivotal metabolic coordinators within the testicular microenvironment. In particular, lysosomal acidity probing revealed compromised degradative capacity in aged SCs, hindering autophagy and phagocytic flux. Consequently, SCs accumulated metabolites, including cholesterol, and have increased inflammatory gene expression; thus, we termed these cells as phago-/auto-lysosomal deregulated SCs. Exposure to a high-fat diet-induced phago-/auto-lysosomal dysregulated-like SCs, recapitulating LOH features in mice. Notably, efferent ductular injection and systemic TRPML1 agonist administration restored lysosomal function, normalizing testosterone deficiency and associated abnormalities in high-fat diet-induced LOH mice. Our findings underscore the central role of SCs in testis aging, presenting a promising therapeutic avenue for LOH.

DHCR24-mediated sterol homeostasis during spermatogenesis is required for sperm mitochondrial sheath formation and impacts male fertility over time

Desmosterol and cholesterol are essential lipid components of the sperm plasma membrane. Cholesterol efflux is required for capacitation, a process through which sperm acquire fertilizing ability. In this study, using a transgenic mouse model overexpressing 24-dehydrocholesterol reductase (DHCR24), an enzyme in the sterol biosynthesis pathway responsible for the conversion of desmosterol to cholesterol, we show that disruption of sterol homeostasis during spermatogenesis led to defective sperm morphology characterized by incomplete mitochondrial packing in the midpiece, reduced sperm count and motility, and a decline in male fertility with increasing paternal age, without changes in body fat composition. Sperm depleted of desmosterol exhibit inefficiency in the acrosome reaction, metabolic dysfunction, and an inability to fertilize the egg. These findings provide molecular insights into sterol homeostasis for sperm capacitation and its impact on male fertility.

Mevalonate pathway and male reproductive aging

Male fertility declines with age. The mevalonate pathway, through which cholesterol and nonsteroidal isoprenoids are synthesized, plays key role in metabolic processes and is an essential pathway for cholesterol production and protein prenylation. Male reproductive aging is accompanied by dramatic changes in the metabolic microenvironment of the testis. Since the mevalonate pathway has an important role in spermatogenesis, we attempted to explore the association between male reproductive aging and the mevalonate pathway to explain the mechanism of male reproductive aging. Alterations in the mevalonate pathway may affect male reproductive aging by decreasing cholesterol synthesis and altering testis protein prenylation. Decreased cholesterol levels affect cholesterol modification, testosterone production, and remodeling of germ cell membranes. Aging-related metabolic disorders also affect the metabolic coupling between somatic cells and spermatogenic cells, leading to male fertility decline. Therefore, we hypothesized that alterations in the mevalonate pathway represent one of the metabolic causes of reproductive aging.

Hormone-sensitive lipase deficiency affects the expression of SR-BI, LDLr, and ABCA1 receptors/transporters involved in cellular cholesterol uptake and efflux and disturbs fertility in mouse testis

Hormone-sensitive lipase (HSL) hydrolyse acylglycerols, cholesteryl and retinyl esters. HSL is a key lipase in mice testis, as HSL deficiency results in male sterility. The present work study the effects of the deficiency and lack of HSL on the localization and expression of SR-BI, LDLr, and ABCA1 receptors/transporters involved in uptake and efflux of cholesterol in mice testis, to determine the impact of HSL gene dosage on testis morphology, lipid homeostasis and fertility. The results of this work show that the lack of HSL in mice alters testis morphology and spermatogenesis, decreasing sperm counts, sperm motility and increasing the amount of Leydig cells and lipid droplets. They also show that there are differences in the localization of HSL, SR-BI, LDLr and ABCA1 in HSL+/+, HSL+/- and HSL-/- mice. The deficiency or lack of HSL has effects on protein and mRNA expression of genes involved in lipid metabolisms in mouse testis. HSL-/- testis have augmented expression of SR-BI, LDLr, ABCA1 and LXRβ, a critical sterol sensor that regulate multiple genes involved in lipid metabolism; whereas LDLr expression decreased in HSL+/- mice. Plin2, Abca1 and Ldlr mRNA levels increased; and LXRα (Nr1h3) and LXRβ (Nr1h2) decreased in testis from HSL-/- compared with HSL+/+; with no differences in Scarb1. Together these data suggest that HSL deficiency or lack in mice testis induces lipid homeostasis alterations that affect the cellular localization and expression of key receptors/transporter involved in cellular cholesterol uptake and efflux (SR-BI, LDRr, ABCA1); alters normal cellular function and impact fertility.

Liver X receptor regulates bile volume and the expression of aquaporins and cystic fibrosis transmembrane conductance regulator in the gallbladder

The gallbladder is considered an important organ in maintaining digestive and metabolic homeostasis. Given that therapeutic options for gallbladder diseases are often limited to cholecystectomy, understanding gallbladder pathophysiology is essential in developing novel therapeutic strategies. Since liver X receptor β (LXRβ), an oxysterol-activated transcription factor, is strongly expressed in gallbladder cholangiocytes, the aim was to investigate LXRβ physiological function in the gallbladder. Thus, we studied the gallbladders of WT and LXRβ-/- male mice using immunohistochemistry, electron microscopy, qRT-PCR, bile duct cannulation, bile and blood biochemistry, and duodenal pH measurements. LXRβ-/- mice presented a large gallbladder bile volume with high duodenal mRNA levels of the vasoactive intestinal polypeptide (VIP), a strong mediator of gallbladder relaxation. LXRβ-/- gallbladders showed low mRNA and protein expression of Aquaporin-1, Aquaporin-8, and cystic fibrosis transmembrane conductance regulator (CFTR). A cystic fibrosis-resembling phenotype was evident in the liver showing high serum cholestatic markers and the presence of reactive cholangiocytes. For LXRβ being a transcription factor, we identified eight putative binding sites of LXR on the promoter and enhancer of the Cftr gene, suggesting Cftr as a novel LXRβ regulated gene. In conclusion, LXRβ was recognized as a regulator of gallbladder bile volume through multiple mechanisms involving CFTR and aquaporins.NEW & NOTEWORTHY This report reveals a novel and specific role of the nuclear receptor liver X receptor β (LXRβ) in controlling biliary tree pathophysiology. LXRβ-/- mice have high gallbladder bile volume and are affected by a cholangiopathy that resembles cystic fibrosis. We found LXRβ to regulate the expression of both aquaporins water channels and the cystic fibrosis transmembrane conductance regulator. This opens a new field in biliary tree pathophysiology, enlightening a possible transcription factor controlling CFTR expression.

Diabetes Type 1 Negatively Influences Leydig Cell Function in Rats, Which is Partially Reversible By Insulin Treatment

Type 1 diabetes mellitus (T1DM) is associated with impaired spermatogenesis and lower testosterone levels and epididymal weight. However, the underlying processes in the testis are unknown and remain to be elucidated. Therefore, the present study focused on the effects of T1DM on testicular function in a spontaneously diabetic rat model. BB/OKL rats after diabetes manifestation were divided into 3 groups: those without insulin treatment and insulin treatment for a duration of 2 and of 6 weeks. Anthropometrical data, circulating levels of gonadotrophins, testosterone, and inhibin B were measured. Intratesticular testosterone, oxidative stress, inflammation, and apoptosis were analyzed. Key enzymes of steroidogenesis were evaluated in the testis. Untreated diabetic rats had significantly lower serum follicle-stimulating hormone and luteinizing hormone levels. Serum and intratesticular testosterone levels significantly decreased in untreated diabetic rats compared to healthy controls. Key markers of Leydig cell function were significantly downregulated at the RNA level: insulin-like factor 3 (Insl3) by 53% (P = .006), Star by 51% (P = .004), Cyp11A1 by 80% (P = .003), 3Beta-Hsd2 by 61% (P = .005), and Pbr by 52% (P = .002). In the insulin-treated group, only Cyp11A1 and 3Beta-Hsd2 transcripts were significantly lower. Interestingly, the long-term insulin-treated group showed significant upregulation of most steroidogenic enzymes without affecting testosterone levels. Tumor necrosis factor α and apoptosis were significantly increased in the long-term insulin-treated rats. In conclusion T1DM, with a severe lack of insulin, has an adverse action on Leydig cell function. This is partially reversible with well-compensated blood glucose control. Long-term T1DM adversely affects Leydig cell function because of the process of inflammation and apoptosis.

Liver X receptors and skeleton: Current state-of-knowledge

The liver X receptors (LXR) is a nuclear receptor that acts as a prominent regulator of lipid homeostasis and inflammatory response. Its therapeutic effectiveness against various diseases like Alzheimer's disease and atherosclerosis has been investigated in detail. Emerging pieces of evidence now reveal that LXR is also a crucial modulator of bone remodeling. However, the molecular mechanisms underlying the pharmacological actions of LXR on the skeleton and its role in osteoporosis are poorly understood. Therefore, in the current review, we highlight LXR and its actions through different molecular pathways modulating skeletal homeostasis. The studies described in this review propound that LXR in association with estrogen, PTH, PPARγ, RXR hedgehog, and canonical Wnt signaling regulates osteoclastogenesis and bone resorption. It regulates RANKL-induced expression of c-Fos, NFATc1, and NF-κB involved in osteoclast differentiation. Additionally, several studies suggest suppression of RANKL-induced osteoclast differentiation by synthetic LXR ligands. Given the significance of modulation of LXR in various physiological and pathological settings, our findings indicate that therapeutic targeting of LXR might potentially prevent or treat osteoporosis and improve bone quality.

Liver X Receptors and Male (In)fertility

Liver X receptors (LXRs) are ligand-dependent transcription factors acting as ‘cholesterol sensors’ to regulate lipid homeostasis in cells. The two isoforms, LXRα (NR1H3) and LXRβ (NR1H2), are differentially expressed, with the former expressed predominantly in metabolically active tissues and the latter more ubiquitously. Both are activated by oxidised cholesterol metabolites, endogenously produced oxysterols. LXRs have important roles in lipid metabolism and inflammation, plus a number of newly emerging roles. They are implicated in regulating lipid balance in normal male reproductive function and may provide a link between male infertility and lipid disorders and/or obesity. Studies from Lxr knockout mouse models provide compelling evidence to support this. More recently published data suggest distinct and overlapping roles of the LXR isoforms in the testis and recent evidence of a role for LXRs in human male fertility. This review summarises the current literature and explores the likely link between LXR, lipid metabolism and male fertility as part of a special issue on Liver X receptors in International Journal of Molecular Sciences.

Functional importance of palmitoyl protein thioesterase 1 (PPT1) expression by Sertoli cells in mediating cholesterol metabolism and maintenance of sperm quality

Sertoli cells are a type of nurse cell in the seminiferous epithelium that are crucial for sustaining spermatogenesis by extending nutritional and energy support to the developing germ cells. Dysfunction of Sertoli cells could cause disordered spermatogenesis and reduced fertility in males. In this study, we focused on the expression and function of palmitoyl protein thioesterase 1 (PPT1), a lysosomal depalmitoylating enzyme, in Sertoli cells. Here, we show that PPT1 expression in Sertoli cells is responsive to cholesterol treatment and that specific knockout of Ppt1 in Sertoli cells causes male subfertility associated with poor sperm quality and a high ratio of sperm deformity. Specifically, Ppt1 deficiency leads to poor cell variably accompanied with abnormal lysosome accumulation and increased cholesterol levels in Sertoli cells. Further, Ppt1 deficiency results in poor adhesion of developing germ cells to Sertoli cells in the seminiferous epithelium, which is likely to be responsible for the reduced male fertility as a consequence of declines in sperm count and motility as well as a high incidence of sperm head deformity. In summary, PPT1 affects sperm quality and male fertility through regulating lysosomal function and cholesterol metabolism in Sertoli cells.

Molecular characterization and homology modeling of liver X receptor in Asian seabass, Lates calcarifer: predicted functions in reproduction and lipid metabolism

Liver X receptor (LXR) is a ligand-activated transcription factor that plays vital roles in maintaining cholesterol and lipid homeostasis. Much work has been done on mammalian LXRs, but the role of LXR in fish remains unclear. In the present study, LXR gene was identified from adult Asian seabass, Lates calcarifer, and its predicted protein structure was docked with several cholesterol derivatives at the binding site. The LXR cDNA consisted of 1495 bp encoding a putative LXR protein of 494 amino acids. The Asian seabass LXR retained many important structural features found in LXRs of other fishes and mammals, such as putative signal peptide, activation function-1 (AF-1) domain, DNA-binding domain (DBD), ligand-binding domain (LBD), activation function-2 (AF-2) domain, and eight conserved cysteine residues. The deduced amino acid sequence of LXR shared significant identity with those of other species ranging from 65.7 to 95.8%. The homology modeling and in silico molecular docking demonstrated that Asian seabass LXR could interact with cholesterol derivatives at amino acid residues Phe274 and Ile312. Real-time PCR further revealed that LXR transcripts are ubiquitously expressed in all tissues examined, with the highest levels detected in the gonad followed by the liver. Given the well-known importance of cholesterol-mediated signaling in these tissues, Asian seabass LXR may reasonably be involved in reproduction and lipid metabolism.

Morbid obesity-related changes in the expression of lipid receptors, transporters, and HSL in human sperm

OBJECTIVE

To study the location and expression of receptors (SR-BI/CLA-1, SR-BII, and LDLr) and transporter (ABCA1) involved in uptake and efflux of cholesterol in human spermatozoa and assess whether obesity alters its location/expression and whether this could be related to infertility.

DESIGN

Observational study.

SETTING

None PATIENT(S): Ten controls and 20 obese patients.

INTERVENTION(S)

Anthropometric parameters. Serum and semen samples were collected.

MAIN OUTCOME MEASURE(S)

Spermatozoon concentration, immunolocalization, and protein expression in semen.

RESULTS

Spermatozoon concentration and motility was decreased in morbidly obese patients. SR-BI/CLA-1, SR-BII, LDLr, and ABCA1 are located in the spermatozoon cell membrane and the localization does not change between obese patients and controls. Control spermatozoa showed high SR-BI expression, and less expression for the rest of the receptors analyzed, indicating that SR-BI/CLA-1 is relevant in human spermatozoon cholesterol uptake/efflux. On the contrary, spermatozoa of obese patients showed less SR-BI/CLA-1 expression than controls, and more intense positive staining for SR-BII, LDLr, and ABCA1. Finally, human sperm expresses the 130- and 82-kDa hormone-sensitive lipase (HSL) isoforms. The 130-kDa isoform is expressed in the control sperm, and the expression disappears in the obese patients.

CONCLUSION(S)

The presence of lipid receptors/transporters and HSL in human spermatozoa suggests their role in the process of maturation/capacitation. The changes in the expression of lipid receptors/transporters and the lack of the 130-kDa HSL isoform in obese patients prevent the hydrolysis of cholesterol esters internalized by these receptors, and favor their accumulation in the cytoplasm of the spermatozoa that could contribute to lipotoxicity and infertility.

Effect of Early Calf-Hood Nutrition on the Transcriptional Regulation of the Hypothalamic-Pituitary-Testicular axis in Holstein-Friesian Bull Calves

The aim of this study was to investigate the effect of early calf-hood nutrition on the transcriptomic profile of the arcuate nucleus of the hypothalamus, anterior pituitary and testes in Holstein-Friesian bulls. Holstein-Friesian bull calves with a mean (±S.D.) age and bodyweight of 19 (±8.2) days and 47.5 (±5.3) kg, respectively, were offered a high (n = 10) or low (n = 10) plane of nutrition in order to achieve an overall growth rate of 1.2 and 0.5 kg/day. At 126 (±3) days of age, calves were euthanized, hypothalamus (arcuate region), anterior pituitary and testicular parenchyma samples were harvested and RNAseq analysis was performed. There were 0, 49 and 1,346 genes differentially expressed in the arcuate nucleus, anterior pituitary and testicular tissue of bull calves on the low relative to the high plane of nutrition, respectively (P < 0.05; False Discovery Rate <0.05). Cell cycle processes in the anterior pituitary were down regulated in the low relative to the high plane of nutrition; there was no differential expression of genes related to reproductive processes. Gene expression involved in cholesterol and androgen biosynthesis in the testes were down regulated in animals on the low plane of nutrition. This study provides insight into the effect of early life plane of nutrition on the regulation of the HPT axis.

Adipose Tissue is a Potential Source of Hyperandrogenism in Obese Female Rats

OBJECTIVE

Obesity in females is often associated with metabolic complications and hyperandrogenism, but the sources of androgens are not completely understood. Therefore, this study investigated whether adipose tissue could be a source of androgens promoting hyperandrogenism development in obese female rats.

METHODS

Gene expression of steroidogenic enzymes and testosterone levels were determined in periovarian and inguinal adipose tissue and in the supernatant of cultured preadipocytes and adipocytes. The conversion of pregnenolone to androgens was analyzed by thin-layer chromatography.

RESULTS

Substantial amounts of testosterone in adipose tissue (25-153 ng/g tissue) and in the supernatant of adipocytes (0.33-0.69 ng/ten thousand cells]) were found. StAR and steroidogenic enzymes encoded by genes including Cyp11A1, Cyp17A1, Cyp19, Hsd3b2, Hsd17b3, and Srd5a2 were expressed in adipose tissue and cultured cells. Thin layer chromatography data revealed that preadipocytes and adipocytes were able to convert pregnenolone to testosterone. Higher levels for all steroidogenic enzymes were found in both depots of obese animals compared with lean animals, with significantly higher levels in inguinal tissue.

CONCLUSIONS

The whole steroidogenic machinery and capacity for testosterone biosynthesis were found in fat depots of female rats. These findings support the hypothesis that adipose tissue may contribute substantially to the hyperandrogenism in female obesity.

Characterization of cholesterol metabolism in Sertoli cells and spermatogenesis (Review)

The Sertoli cell, which is the supporting cell of spermatogenesis, has an important role in the endocrine and paracrine control of spermatogenesis. Functionally, it provides the cells of the seminiferous epithelium with nutrition, conveys mature spermatids to the lumen of seminiferous tubules, secretes androgen‑binding protein and interacts with endocrine Leydig cells. In addition, the levels of cholesterol, as well as its intermediates, vary greatly between nongonadal tissues and the male reproductive system. Throughout spermatogenesis, a dynamic and constant alteration in the membrane lipid composition of Sertoli cells occurs. In several mammalian species, testis meiosis‑activating sterol and desmosterol, as well as other cholesterol precursors, accumulate in the testes and spermatozoa. In addition, certain cholesterogenic genes exhibit stage‑specific expression patterns during spermatogenesis, including the cytochrome P450 enzyme lanosterol 14α‑demethylase. Inconsistency in the patterns of gene expression during spermatogenesis indicates a cell‑type specific and complex temporary modulation of lipids and cholesterol, which also implicates the dynamic interactions between Sertoli cells and germ cells. Furthermore, in the female reproductive tract and during epididymal transit, which is a prerequisite for valid fertilization, the modulation of cholesterol occurring in spermatozoal membranes further indicates the functional importance of sterol compounds in spermatogenesis. However, the exact role of cholesterol metabolism in Sertoli cells in sperm production is unknown. The present review article describes the progress made in the research regarding the characteristics of the Sertoli cell, particularly the regulation of its cholesterol metabolism during spermatogenesis.

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.

Effects of velvet antler polypeptide on sexual behavior and testosterone synthesis in aging male mice

Twenty-four-month-old male C57BL/6 mice with low serum testosterone levels were used as a late-onset hypogonadism (LOH) animal model for examining the effects of velvet antler polypeptide (VAP) on sexual function and testosterone synthesis. These mice received VAP for 5 consecutive weeks by daily gavage at doses of 100, 200, or 300 mg kg⁻¹ body weight per day (n = 10 mice per dose). Control animals (n = 10) received the same weight-based volume of vehicle. Sexual behavior and testosterone levels in serum and interstitial tissue of testis were measured after the last administration of VAP. Furthermore, to investigate the mechanisms of how VAP affects sexual behavior and testosterone synthesis in vivo, the expression of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD) in Leydig cells was also measured by immunofluorescence staining and quantitative real-time PCR. As a result, VAP produced a significant improvement in the sexual function of these aging male mice. Serum testosterone level and intratesticular testosterone (ITT) concentration also increased in the VAP-treated groups. The expression of StAR, P450scc, and 3β-HSD was also found to be enhanced in the VAP-treated groups compared with the control group. Our results suggested that VAP was effective in improving sexual function in aging male mice. The effect of velvet antler on sexual function was due to the increased expression of several rate-limiting enzymes of testosterone synthesis (StAR, P450scc, and 3β-HSD) and the following promotion of testosterone synthesis in vivo.

Liver X receptor β increases aquaporin 2 protein level via a posttranscriptional mechanism in renal collecting ducts

Liver X receptors (LXRs) including LXRα and LXRβ are nuclear receptor transcription factors and play an important role in lipid and glucose metabolism. It has been previously reported that mice lacking LXRβ but not LXRα develop a severe urine concentrating defect, likely via a central mechanism. Here we provide evidence that LXRβ regulates water homeostasis through increasing aquaporin 2 (AQP2) protein levels in renal collecting ducts. LXRβ^-/- mice exhibited a reduced response to desmopressin (dDAVP) stimulation, suggesting that the diabetes insipidus phenotype is of both central and nephrogenic origin. AQP2 protein abundance in the renal inner medulla was significantly reduced in LXRβ^-/- mice but with little change in AQP2 mRNA levels. In vitro studies showed that AQP2 protein levels were elevated upon LXR agonist treatment in both primary cultured mouse inner medullary duct cells (mIMCD) and the mIMCD3 cell line with stably expressed AQP2. In addition, LXR agonists including TO901317 and GW3965 failed to induce AQP2 gene transcription but diminished its protein ubiquitination in primary cultured mIMCD cells, thereby inhibiting its degradation. Moreover, LXR activation-induced AQP2 protein expression was abolished by the protease inhibitor MG132 and the ubiquitination-deficient AQP2 (K270R). Taken together, the present study demonstrates that activation of LXRβ increases AQP2 protein levels in the renal collecting ducts via a posttranscriptional mechanism. As such, LXRβ represents a key regulator of body water homeostasis.

Prepubertal onset of obesity negatively impacts on testicular steroidogenesis in rats

Obesity is a global health problem and impacts negatively on levels of testosterone and quality of sperm production. At present little is known about mechanisms that attenuate testicular function in obese males. Our study characterized testicular steroidogenesis and explored levels of relevant paracrine and hormonal factors in rats with short- and long-term obesity. We have found that obesity state increased serum levels of estradiol and leptin in both groups of obese rats and inhibited the expression of StAR and Cyp11a1 associated with low levels of intratesticular testosterone in rats with long-term obesity. Further, long-term obesity reduced the number of Leydig cells, increased the testicular levels of the proinflammatory adipocytokine TNFα and the number of testicular macrophages. All together, our data indicate that long-term obesity may cause chronic inflammation in the testis and negatively impacts on Leydig cell steroidogenesis.

Leptin Within the Subphysiological to Physiological Range Dose Dependently Improves Male Reproductive Function in an Obesity Mouse Model

Obesity has recently been linked with reduced fertility, and the mechanisms underpinning this effect are currently unknown. The adipokine leptin is dysregulated in obesity and affects reproductive tracts; therefore, we investigated the dose-dependent effects of leptin on Leydig cell function and spermatogenesis. Eight-week-old leptin-deficient obese (ob/ob) male mice were treated with subphysiological (0.1- or 0.5-mg/kg body weight [BW]/d) or physiological (3.0-mg/kg BW/d) doses of leptin or saline for 12 weeks (chronic treatment) or 72 hours (acute treatment). We then evaluated male reproductive function markers. Mean testis weight increased significantly in the 0.1- and 3.0-mg/kg BW/d groups compared with saline controls (both P < .05). Intratesticular testosterone levels relative to testis weight significantly increased in the 0.5-mg/kg BW/d group compared with saline controls (P < .05). FSH levels increased in a dose-dependent manner with leptin treatment, whereas LH levels did not change. Leptin treatment significantly up-regulated both mRNA and protein expression of the steroidogenic enzyme cytochrome P450 17A1. Spermatogenesis improved in leptin-treated animals. Significantly more seminiferous tubules were observed in stages I-VIII (P < .01), and there were fewer abnormal seminiferous tubule structures (P < .01). Acute treatment with physiological leptin doses partially improved male reproductive markers without changing BW. Administration of subphysiological to physiological doses of leptin improves Leydig cell function and spermatogenesis.

LXR regulate cholesterol homeostasis in the proximal mouse epididymis

Oxysterol nuclear receptors liver x receptors (LXRalpha and LXRbeta) regulate lipid homeostasis when cells have to face high amounts of cholesterol and/or fatty acids. Male mice invalidated for both lxr (LXR-/-) are infertile by 5 months of age, and become sterile by the age of 9 months. The epididymis was previously shown to be affected by the gene invalidation, a phenotype specifically located in the two proximal segments of this organ. We demonstrate here that cholesteryl esters are accumulated in a specific cell type of the epididymal epithelium, the apical cells, in these two first segments, in LXR-/- male mice. These accumulations are correlated to a decrease in the amount of a specific membrane cholesterol transporter, ATP-binding cassette A1 (ABCA1) in the caput epididymidis of LXR-/- mice. This decrease is due to a transcriptional down-regulation, and we further demonstrate that ABCA1, in the two first segments of the caput epididymidis, is located in the apical cells, and that its accumulation is lost in these cells for LXR-/- male mice as soon as 4 months of age. These data bring new elements in the cholesterol trafficking pathways in the epididymis, and will help a better understanding of the molecular mechanisms occurring in this organ in relation to the sperm cells maturation process.

Role of the steroidogenic acute regulatory protein in health and disease

Steroid hormones are an important class of regulatory molecules that are synthesized in steroidogenic cells of the adrenal, ovary, testis, placenta, brain, and skin, and influence a spectrum of developmental and physiological processes. The steroidogenic acute regulatory protein (STAR) predominantly mediates the rate-limiting step in steroid biosynthesis, i.e., the transport of the substrate of all steroid hormones, cholesterol, from the outer to the inner mitochondrial membrane. At the inner membrane, cytochrome P450 cholesterol side chain cleavage enzyme cleaves the cholesterol side chain to form the first steroid, pregnenolone, which is converted by a series of enzymes to various steroid hormones in specific tissues. Both basic and clinical evidence have demonstrated the crucial involvement of the STAR protein in the regulation of steroid biosynthesis. Multiple levels of regulation impinge on STAR action. Recent findings demonstrate that hormone-sensitive lipase, through its action on the hydrolysis of cholesteryl esters, plays an important role in regulating STAR expression and steroidogenesis which involve the liver X receptor pathway. Activation of the latter influences macrophage cholesterol efflux that is a key process in the prevention of atherosclerotic cardiovascular disease. Appropriate regulation of steroid hormones is vital for proper functioning of many important biological activities, which are also paramount for geriatric populations to live longer and healthier. This review summarizes the current level of understanding on tissue-specific and hormone-induced regulation of STAR expression and steroidogenesis, and provides insights into a number of cholesterol and/or steroid coupled physiological and pathophysiological consequences.

Identification of the Functions of Liver X Receptor-β in Sertoli Cells Using a Targeted Expression-Rescue Model

Liver X receptors (LXRs) are key regulators of lipid homeostasis and are involved in multiple testicular functions. The Lxrα(-/-);Lxrβ(-/-) mice have illuminated the roles of both isoforms in maintenance of the epithelium in the seminiferous tubules, spermatogenesis, and T production. The requirement for LXRβ in Sertoli cells have been emphasized by early abnormal cholesteryl ester accumulation in the Lxrβ(-/-) and Lxrα(-/-);Lxrβ(-/-) mice. Other phenotypes, such as germ cell loss and hypogonadism, occur later in life in the Lxrα(-/-);Lxrβ(-/-) mice. Thus, LXRβ expression in Sertoli cells seems to be essential for normal testicular physiology. To decipher the roles of LXRβ within the Sertoli cells, we generated Lxrα(-/-);Lxrβ(-/-):AMH-Lxrβ transgenic mice, which reexpress Lxrβ in Sertoli cells in the context of Lxrα(-/-);Lxrβ(-/-) mice. In addition to lipid homeostasis, LXRβ is necessary for maintaining the blood-testis barrier and the integrity of the germ cell epithelium. LXRβ is also implicated in the paracrine action of Sertoli cells on Leydig cells to modulate T synthesis. The Lxrα(-/-);Lxrβ(-/-) and Lxrα(-/-);Lxrβ(-/-):AMH-Lxrβ mice exhibit lipid accumulation in germ cells after the Abcg8 down-regulation, suggesting an intricate LXRβ-dependent cooperation between the Sertoli cells and germ cells to ensure spermiogenesis. Further analysis revealed also peritubular smooth muscle defects (abnormal lipid accumulation and disorganized smooth muscle actin) and spermatozoa stagnation in the seminiferous tubules. Together the present work elucidates specific roles of LXRβ in Sertoli cell physiology in vivo beyond lipid homeostasis.

Research resource: the dynamic transcriptional profile of sertoli cells during the progression of spermatogenesis

Sertoli cells (SCs), the only somatic cells within seminiferous tubules, associate intimately with developing germ cells. They not only provide physical and nutritional support but also secrete factors essential to the complex developmental processes of germ cell proliferation and differentiation. The SC transcriptome must therefore adapt rapidly during the different stages of spermatogenesis. We report comprehensive genome-wide expression profiles of pure populations of SCs isolated at 5 distinct stages of the first wave of mouse spermatogenesis, using RNA sequencing technology. We were able to reconstruct about 13 901 high-confidence, nonredundant coding and noncoding transcripts, characterized by complex alternative splicing patterns with more than 45% comprising novel isoforms of known genes. Interestingly, roughly one-fifth (2939) of these genes exhibited a dynamic expression profile reflecting the evolving role of SCs during the progression of spermatogenesis, with stage-specific expression of genes involved in biological processes such as cell cycle regulation, metabolism and energy production, retinoic acid synthesis, and blood-testis barrier biogenesis. Finally, regulatory network analysis identified the transcription factors endothelial PAS domain-containing protein 1 (EPAS1/Hif2α), aryl hydrocarbon receptor nuclear translocator (ARNT/Hif1β), and signal transducer and activator of transcription 1 (STAT1) as potential master regulators driving the SC transcriptional program. Our results highlight the plastic transcriptional landscape of SCs during the progression of spermatogenesis and provide valuable resources to better understand SC function and spermatogenesis and its related disorders, such as male infertility.

Cholesterol-enriched diet disrupts the blood-testis barrier in rabbits

About 15% of heterosexual couples in the USA suffer from infertility issues; male infertility accounts for ∼50% of all infertility cases and roughly 50% of male infertility is idiopathic. Increased levels of plasma cholesterol affect spermatogenesis and male fertility negatively, but by unclear mechanisms. Clearly, spermatogenesis occurs in immune-privileged seminiferous tubules that are protected by the blood-testis barrier (BTB), and BTB disruption results in sperm damage and male infertility. Accordingly, using rabbits fed a 2% cholesterol-enriched diet for 2, 4, and 6 wk to raise levels of plasma cholesterol, we tested the hypothesis that elevated levels of plasma cholesterol disrupt the BTB functionally and biochemically. The cholesterol-enriched diet increased lipid deposition dramatically and time-dependently in the seminiferous tubules and disrupted the BTB as evidenced by increased IgG staining within the seminiferous tubules. Total protein levels of the tight-junction proteins ZO-1 and occludin were increased in the seminiferous tubules of rabbits fed the cholesterol-enriched diet, and the distribution patterns of tight-junction proteins were markedly affected, including an increased accumulation of tight-junction proteins in endosomes. Disruption of the integrity of the BTB due to increased plasma levels of cholesterol might play a role in male infertility.

28-Homobrassinolide: a novel oxysterol transactivating LXR gene expression

Cholesterol is the template for steroid hormone biosynthesis. Cholesterol homeostasis is regulated by Cyt-P450 oxygenated cholesterols acting as ligands on LXR-α and LXR-β transcription factors that are now emerging as drug targets. Heterodimerization of LXRs with retinoic acid receptor is considered a prerequisite for target gene activation. Dietary plant oxysterol 28-homobrassinolide (28-HB) is a proven antihyperglycemic and a pro-steroidogenic agent in the rat. Whether 28-HB has a role in LXR gene expression was therefore investigated using oral gavage (15 days) of 28-HB (333 µg/kg b w) to normal and diabetic rat. PCR amplified LXR-α and β mRNA transcripts from treated rat liver and testis exhibited quantitative differences in their expression. Conformational differences in 28-HB docking to LXR-α and β binding domains were also noted through in silico studies, LXR-β adopting lesser specificity. We report that 28-HB transactivates LXR genes in the rat tissues.

Bortezomib treatment causes long-term testicular dysfunction in young male mice

Background

With increased long-term survivors of childhood cancer patients, therapy-associated infertility has become one of the most common late side-effects and significantly affects their life-quality. Therefore, evaluation of anti-cancer agents on male reproduction and infertility prevention are urgently demanding. The proteasome inhibitor bortezomib has been launched in clinical trials for childhood cancers, however, its potential side effects on reproduction have so far been neither investigated experimentally nor reported in treated children. Thus the present study is designed to explore the impact of bortezomib on male reproductive function and to gain insights into how bortezomib exerts its adverse effects on man gonad, thereby providing pediatric oncologists relevant information.

Methods

35 day-old male mice were treated with one 11-day cycle of bortezomib and then sacrificed 2 days, 45 days, or 6 months later. A mating study was performed in the group followed for 6 months, and their pups were analyzed on postnatal day 50. Serum follicle-stimulating hormone (FSH) and testicular testosterone levels were measured. Testicular morphology was evaluated by light- and electron microscopy, and the underlying mechanisms and pathways of testis damage were investigated.

Results

Testicular damage was visible already 2 days after stopping bortezomib and increased in severity by day 45. Then 80% of seminiferous tubules exhibited hypospermatogenesis with arrest at the levels of spermatogonia, spermatocytes and round spermatids. Germ cells were specifically targeted by bortezomib as evidenced by increased apoptosis mediated through activation of p53 and caspases. Even six months after the bortezomib treatment, testis weight, sperm concentration and seminiferous tubule length remained at a decreased level, indicating that spermatogenesis and tubular outgrowth could not fully recover. Combined with persistently increased serum levels of FSH in these mice, our results demonstrate that bortezomib can have long-term effects on testicular function, although fertility of bortezomib-exposed males remained and their offspring looked healthy.

Conclusion

Bortezomib treatment causes long-term gonadal dysfunction in male mice. Careful monitoring of gonadal function in male childhood cancer patients treated with bortezomib is thus strongly recommended.

Levels of liver X receptors in testicular biopsies of patients with azoospermia

OBJECTIVE

To determine whether the transcription factors liver X receptors (LXRs) and their downstream genes, which are involved in the regulation of several testicular functions in mouse models, are differentially expressed in testes of men with nonobstructive azoospermia (NOA) or obstructive azoospermia (OA).

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

Patients with various types of NOA (n=22) and with OA (n=5).

INTERVENTION(S)

Human testicular biopsies.

MAIN OUTCOME MEASURE(S)

Transcript levels were measured in testicular biopsies with the use of quantitative polymerase chain reaction. Correlations of LXR mRNA levels with the number of germ cells, the expression of proliferation and apoptosis markers, and the amount of intratesticular lipids and testosterone were evaluated. The localization of LXRα was analyzed by immunofluorescence.

RESULT(S)

LXR mRNA levels were decreased by 49%-98% in NOA specimens and positively correlated with germ cell number. Accumulations of IDOL and SREBP1c (LXR targets involved in lipid homeostasis) were 1.8-2.1 times lower in NOA samples and mRNA levels of the SREBP1c target gene ELOVL6 were increased 1.9-2.4-fold. Interestingly, the amount of triglycerides and free fatty acids were higher in NOA testes (3.4-12.2-fold). LXRα was present in Leydig cells. Accumulations of LXR downstream genes encoding the steroidogenic proteins StAR and 3βHSD2 were higher in NOA testes (5.9-12.8-fold).

CONCLUSION(S)

Knowledge of changes in the transcript levels of LXRs and some of their downstream genes during altered spermatogenesis may help us to better understand the physiopathology of testicular failure in azoospermic patients.

Nutritional signals and reproduction

There is extensive evidence that nutrition influences reproductive function in various mammalian species (agricultural animals, rodents and human). However, the mechanisms underlying the relationship between nutrition, energy metabolism and reproductive function are poorly understood. This review considers nutrient sensors as a molecular link between food molecules and consequences for female and male fertility. It focuses on the roles and the molecular mechanisms of some of the relevant hormones, such as insulin and adipokines, and of energy substrates (glucose, fatty acids and amino acids), in the gonadotropic axis (central nervous system and gonads). A greater understanding of the interactions between nutrition and fertility is required for both better management of the physiological processes and the development of new molecules to prevent or cure metabolic diseases and their consequences for fertility.

Cholesterol and male fertility: what about orphans and adopted?

The link between cholesterol homeostasis and male fertility has been clearly suggested in patients who suffer from hyperlipidemia and metabolic syndrome. This has been confirmed by the generation of several transgenic mouse models or in animals fed with high cholesterol diet. Next to the alteration of the endocrine signaling pathways through steroid receptors (androgen and estrogen receptors); "orphan" and "adopted" nuclear receptors, such as the Liver X Receptors (LXRs), the Proliferating Peroxisomal Activated Receptors (PPARs) or the Liver Receptor Homolog-1 (LRH-1), have been involved in this cross-talk. These transcription factors show distinct expression patterns in the male genital tract, explaining the large panel of phenotypes observed in transgenic male mice and highlighting the importance of lipid homesostasis and the complexity of the molecular pathways involved. Increasing our knowledge of the roles of these nuclear receptors in male germ cell differentiation could help in proposing new approaches to either treat infertile men or define new strategies for contraception.

Mechanisms of action of hormone-sensitive lipase in mouse Leydig cells: its role in the regulation of the steroidogenic acute regulatory protein

Hormone-sensitive lipase (HSL) catalyzes the hydrolysis of cholesteryl esters in steroidogenic tissues and, thus, facilitates cholesterol availability for steroidogenesis. The steroidogenic acute regulatory protein (StAR) controls the rate-limiting step in steroid biosynthesis. However, the modes of action of HSL in the regulation of StAR expression remain obscure. We demonstrate in MA-10 mouse Leydig cells that activation of the protein kinase A (PKA) pathway, by a cAMP analog Bt2cAMP, enhanced expression of HSL and its phosphorylation (P) at Ser-660 and Ser-563, but not at Ser-565, concomitant with increased HSL activity. Phosphorylation and activation of HSL coincided with increases in StAR, P-StAR (Ser-194), and progesterone levels. Inhibition of HSL activity by CAY10499 effectively suppressed Bt2cAMP-induced StAR expression and progesterone synthesis. Targeted silencing of endogenous HSL, with siRNAs, resulted in increased cholesteryl ester levels and decreased cholesterol content in MA-10 cells. Depletion of HSL affected lipoprotein-derived cellular cholesterol influx, diminished the supply of cholesterol to the mitochondria, and resulted in the repression of StAR and P-StAR levels. Cells overexpressing HSL increased the efficacy of liver X receptor (LXR) ligands on StAR expression and steroid synthesis, suggesting HSL-mediated steroidogenesis entails enhanced oxysterol production. Conversely, cells deficient in LXRs exhibited decreased HSL responsiveness. Furthermore, an increase in HSL was correlated with the LXR target genes, steroid receptor element-binding protein 1c and ATP binding cassette transporter A1, demonstrating HSL-dependent regulation of steroidogenesis predominantly involves LXR signaling. LXRs interact/cooperate with RXRs and result in the activation of StAR gene transcription. These findings provide novel insight and demonstrate the molecular events by which HSL acts to drive cAMP/PKA-mediated regulation of StAR expression and steroidogenesis in mouse Leydig cells.

Sterols in spermatogenesis and sperm maturation

Mammalian spermatogenesis is a complex developmental program in which a diploid progenitor germ cell transforms into highly specialized spermatozoa. One intriguing aspect of sperm production is the dynamic change in membrane lipid composition that occurs throughout spermatogenesis. Cholesterol content, as well as its intermediates, differs vastly between the male reproductive system and nongonadal tissues. Accumulation of cholesterol precursors such as testis meiosis-activating sterol and desmosterol is observed in testes and spermatozoa from several mammalian species. Moreover, cholesterogenic genes, especially meiosis-activating sterol-producing enzyme cytochrome P450 lanosterol 14α-demethylase, display stage-specific expression patterns during spermatogenesis. Discrepancies in gene expression patterns suggest a complex temporal and cell-type specific regulation of sterol compounds during spermatogenesis, which also involves dynamic interactions between germ and Sertoli cells. The functional importance of sterol compounds in sperm production is further supported by the modulation of sterol composition in spermatozoal membranes during epididymal transit and in the female reproductive tract, which is a prerequisite for successful fertilization. However, the exact role of sterols in male reproduction is unknown. This review discusses sterol dynamics in sperm maturation and describes recent methodological advances that will help to illuminate the complexity of sperm formation and function.

Cholesterogenic genes expression in brain and liver of ganglioside-deficient mice

The aim of this study was to determine the effect of changed ganglioside profile on transcription of selected genes involved in cholesterol homeostasis. For that purpose, the expression of 11 genes related to cholesterol synthesis, regulation, and cholesterol transport was investigated in selected brain regions (frontal cortex, hippocampus, brain stem, cerebellum) and liver of St8sia1 knockout (KO) mice characterized by deficient synthesis of b- and c-series gangliosides and accumulation of a-series gangliosides. The expression of majority of the analyzed genes, as determined using quantitative real time PCR, was slightly higher in St8sia1 KO compared to wild-type (wt) controls. More prominent changes were observed in Hmgr, Cyp51, and Cyp46 expression in brain (hippocampus and brain stem) and Srebp1a, Insig2a, and Ldlr in liver. In addition, the expression of master transcriptional regulators, Srebp1a, Srebp1c, and Insig2a, as well as transporters Ldlr and Vldlr differed between liver and brain, and within brain regions in wt animals. Cyp46 expression was expectedly brain-specific, with brain region difference in both wt and St8sia1 KO. The established change in transcriptome of cholesterogenic genes is associated to specific alteration of ganglioside composition which indicates relationship between gangliosides and regulation of cholesterol metabolism.

Inactivation of AMPKα1 induces asthenozoospermia and alters spermatozoa morphology

AMP-activated protein kinase (AMPK), a key regulator of cellular energy homeostasis, is present in metabolic tissues (muscle and liver) and has been identified as a modulator of the female reproductive functions. However, its function in the testis has not yet been clearly defined. We have investigated the potential role of AMPK in male reproduction by using transgenic mice lacking the activity of AMPK catalytic subunit α1 gene [α1AMPK knockout (KO)]. In the testis, the α1AMPK subunit is expressed in germ cells and also in somatic cells (Sertoli and Leydig cells). α1AMPK KO male mice show a decrease in fertility, despite no clear alteration in the testis morphology or sperm production. However, in α1AMPK(-/-) mice, we demonstrate that spermatozoa have structural abnormalities and are less motile than in control mice. These spermatozoa alterations are associated with a 50% decrease in mitochondrial activity, a 60% decrease in basal oxygen consumption, and morphological defects. The α1AMPK KO male mice had high androgen levels associated with a 5- and 3-fold increase in intratesticular cholesterol and testosterone concentrations, respectively. High concentrations of proteins involved in steroid production (3β-hydroxysteroid dehydrogenase, cytochrome steroid 17 alpha-hydroxylase/17,20 lysate, and steroidogenic acute regulatory protein) were also detected in α1AMPK(-/-) testes. In the pituitary, the LH and FSH concentrations tended to be lower in α1AMPK(-/-) male mice, probably due to the negative feedback of the high testosterone levels. These results suggest that total α1AMPK deficiency in male mice affects androgen production and quality of spermatozoa, leading to a decrease in fertility.

Anxiety in liver X receptor β knockout female mice with loss of glutamic acid decarboxylase in ventromedial prefrontal cortex

Anxiety disorders are the most prevalent mental disorders in adolescents in the United States. Female adolescents are more likely than males to be affected with anxiety disorders, but less likely to have behavioral and substance abuse disorders. The prefrontal cortex (PFC), amygdala, and dorsal raphe are known to be involved in anxiety disorders. Inhibitory input from the PFC to the amygdala controls fear and anxiety typically originating in the amygdala, and disruption of the inhibitory input from the PFC leads to anxiety, fear, and personality changes. Recent studies have implicated liver X receptor β (LXRβ) in key neurodevelopmental processes and neurodegenerative diseases. In the present study, we used elevated plus-maze, startle and prepulse inhibition, open field, and novel object recognition tests to evaluate behavior in female LXRβ KO (LXRβ(-/-)) mice. We found that the female LXRβ(-/-) mice were anxious with impaired behavioral responses but normal locomotion and memory. Immunohistochemistry analysis revealed decreased expression of the enzyme responsible for GABA synthesis, glutamic acid decarboxylase (65+67), in the ventromedial PFC. Expression of tryptophan hydroxylase 2 in the dorsal raphe was normal. We conclude that the anxiogenic phenotype in female LXRβ(-/-) mice is caused by reduced GABAergic input from the ventromedial PFC to the amygdala.

Dietary cholesterol-induced post-testicular infertility

This work shows that an overload of dietary cholesterol causes complete infertility in dyslipidemic male mice (the Liver X Receptor-deficient mouse model). Infertility resulted from post-testicular defects affecting the fertilizing potential of spermatozoa. Spermatozoa of cholesterol-fed lxr−/− animals were found to be dramatically less viable and motile, and highly susceptible to undergo a premature acrosome reaction. We also provide evidence, that this lipid-induced infertility is associated with the accelerated appearance of a highly regionalized epididymal phenotype in segments 1 and 2 of the caput epididymidis that was otherwise only observed in aged LXR-deficient males. The epididymal epithelial phenotype is characterized by peritubular accumulation of cholesteryl ester lipid droplets in smooth muscle cells lining the epididymal duct, leading to their transdifferentiation into foam cells that eventually migrate through the duct wall, a situation that resembles the inflammatory atherosclerotic process. These findings establish the high level of susceptibility of epididymal sperm maturation to dietary cholesterol overload and could partly explain reproductive failures encountered by young dyslipidemic men as well as ageing males wishing to reproduce.

Sterol regulation of metabolism, homeostasis, and development

Sterol metabolites are critical signaling molecules that regulate metabolism, development, and homeostasis. Oxysterols, bile acids (BAs), and steroids work primarily through cognate sterol-responsive nuclear hormone receptors to control these processes through feed-forward and feedback mechanisms. These signaling pathways are conserved from simple invertebrates to mammals. Indeed, results from various model organisms have yielded fundamental insights into cholesterol and BA homeostasis, lipid and glucose metabolism, protective mechanisms, tissue differentiation, development, reproduction, and even aging. Here, we review how sterols act through evolutionarily ancient mechanisms to control these processes.

Liver X Receptor: an oxysterol sensor and a major player in the control of lipogenesis

De novo fatty acid biosynthesis is also called lipogenesis. It is a metabolic pathway that provides the cells with fatty acids required for major cellular processes such as energy storage, membrane structures and lipid signaling. In this article we will review the role of the Liver X Receptors (LXRs), nuclear receptors that sense oxysterols, in the transcriptional regulation of genes involved in lipogenesis.

Liver X receptors, lipids and their reproductive secrets in the male

Liver X receptor (LXR) α and LXRβ belong to the nuclear receptor superfamily. For many years, they have been called orphan receptors, as no natural ligand was identified. In the last decade, the LXR natural ligands have been shown to be oxysterols, molecules derived from cholesterol. While these nuclear receptors have been abundantly studied for their roles in the regulation of lipid metabolism, it appears that they also present crucial activities in reproductive organs such as testis and epididymis, as well as prostate. Phenotypic analyses of mice lacking LXRs (lxr-/-) pointed out their physiological activities in the various cells and organs regulating reproductive functions. This review summarizes the impact of LXR-deficiency in male reproduction, highlighting the novel information coming from the phenotypic analyses of lxrα-/-, lxrβ-/- and lxrα;β-/- mice. This article is part of a Special Issue entitled: Translating nuclear receptor from health to disease.

Epididymis cholesterol homeostasis and sperm fertilizing ability

Cholesterol, being the starting point of steroid hormone synthesis, is a long known modulator of both female and male reproductive physiology especially at the level of the gonads and the impact cholesterol has on gametogenesis. Less is known about the effects cholesterol homeostasis may have on postgonadic reproductive functions. Lately, several data have been reported showing how imbalanced cholesterol levels may particularly affect the post-testicular events of sperm maturation that lead to fully fertile male gametes. This review will focus on that aspect and essentially centers on how cholesterol is important for the physiology of the mammalian epididymis and spermatozoa.

Liver X receptor (LXR) and the reproductive system--a potential novel target for therapeutic intervention

Liver X receptor (LXR) alpha and beta are ligand-activated transcription factors that regulate the expression of genes involved in the removal of cholesterol from cells by high-density lipoproteins, the transport of cholesterol to the liver and the biliary excretion of cholesterol. LXRs are activated by oxygenated cholesterol derivatives such as 24(S),25-epoxycholesterol or 24(S)-, 25- and 27-hydroxycholesterol. In this review, we will discuss the role of LXR in the reproductive system and perspectives on the application of LXR agonists in the treatment of reproductive pathologies. Interestingly, progressive age-related impairment of fertility is observed in both female and male LXR knockout mice. Reduced fertility in female LXR knockout mice is associated with resistance to follicular fluid meiosis-activating sterol (FF-MAS), the intermediate of cholesterol synthesis generated in the ovaries that is responsible for stimulating oocyte meiosis partially in a LXR-dependent manner. Female mice lacking both LXR isoforms exhibit symptoms of ovarian hyperstimulation syndrome when treated with pharmacological doses of gonadotropins. LXR agonists have mainly been considered as potential anti-atherosclerotic medications. However, experimental studies suggest that natural or synthetic LXR agonists may also effectively treat some reproductive pathologies, such as infertility, impaired uterine contractility, hormone-dependent cancers and insulin resistance in patients with polycystic ovarian syndrome. However, the specific adverse effects of LXR agonists on the reproductive system must also be considered. Adverse effects of LXR agonists include impaired trophoblast invasion, excessive transplacental cholesterol transport from the mother to the fetus leading to fetal hypercholesterolemia, and augmented estrogen deficiency after menopause.