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

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

International audienceLiver X receptor (LXR) a and LXRb 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 (−/−) pointed out their physiological activies 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 −/−, −/− and −/− mice

Implication de l'homéostasie lipidique dans la maturation post-testiculaire des spermatozoïdes : apports des modèles murins KO LXR

L’épididyme est un organe accolé au testicule, formé d’un long tubule dont l’épithélium est constitué de 6 types cellulaires différents aux fonctions partiellement connues. Le tubule épididymaire est entouré de muscles lisses participant, par leurs contractions, à l’avancée des spermatozoïdes. Au centre du canal se retrouve le fluide épididymaire dont la composition est régulée par les absorptions et sécrétions de l’épithélium épididymaire. Les gamètes arrivant du testicule sont inaptes à assurer la fécondation. La maturation post-testiculaire des spermatozoïdes, durant leur descente dans le tubule épididymaire, va leur permettre d’acquérir la mobilité et la capacité à reconnaître et féconder un ovule (qualités regroupées sous le terme de “pouvoir fécondant”). Cette maturation se fait grâce aux interactions permanentes des spermatozoïdes avec le fluide. Les LXRs sont des régulateurs majeurs de l’homéostasie du cholestérol, un élément fondamental dans la physiologie de la reproduction puisqu’il est le précurseur des hormones stéroïdes (androgènes) et un régulateur du pouvoir fécondant des spermatozoïdes. Les souris mâles invalidées pour les 2 isoformes de ces récepteurs (lxrα;β-/-) ont une fertilité perturbée en association avec des altérations testiculaires et épididymaires. Ces mâles présentent une infertilité dès 6 mois conduisant à une stérilité complète à 9 mois. Le but de ce travail est de comprendre la relation entre la régulation de l’homéostasie du cholestérol et le phénotype épididymaire de ces souris. A l’âge de 4 mois, alors que les souris mâles lxrα;β-/- sont fertiles, le phénotype est caractérisé par une accumulation de lipides dans certains types cellulaires de l’épithélium et dans les muscles lisses entourant le tubule. Chez les mâles lxrα;β-/- âgés de 9 mois, lorsque le phénotype d’infertilité complète est installé, on observe une destructuration de la partie proximale de l’épididyme comprenant une diminution de la hauteur de l’épithélium, une perte des muscles lisses péritubulaires et la présence de spermatozoïdes non mobiles et malformés dans la lumière du tubule. Mes travaux ont permis de mettre en évidence différents phénomènes : 1/ Une nouvelle fonction d’un type cellulaire particulier, les cellules “apicales”, dans la régulation de l’homéostasie du cholestérol épididymaire. En effet, ces cellules accumulent du cholestérol en association avec la perte de “ABCA1” (ATP Binding Cassette A1), codée par un gène cible de LXR, impliquée dans l’export de l’excédent de cholestérol cellulaire. Suite à cela, ces cellules apicales entrent en apoptose et contribuent à la perte de fonction de l’épithélium. 2/ Une altération des cellules musculaires lisses péritubulaires associée au vieillissement des souris lxrα;β-/-. Ces cellules accumulent elles aussi du cholestérol et se transforment en cellules invasives, les cellules “spumeuses” migrant à travers l’épithélium. Ce phénomène est très proche des phases de développement de la pathologie artérielle liée au cholestérol et au vieillissement, l’athérosclérose. La perte des muscles lisses va limiter la progression des spermatozoïdes et accompagner la perte de fonction des cellules épithéliales qui ne seront plus aptes à effectuer des échanges avec le fluide, empêchant ainsi l’acquisition du pouvoir fécondant des spermatozoïdes. (...)The epididymis is a long tubule which epithelium is made of 6 different cellular types with partially unknown functions. The epididymal tubule is surrounded by smooth muscles participating, by their contractions, to the sperm progression. At the center of the tubule is present the epididymal fluid which composition is regulated by the absorptions and secretions of the epithelium. The spermatozoa coming from the testis are unable to fertilize an oocyte. Post-testicular maturation of spermatozoa, during their transit through the epididymis, allows them to become motile, to recognize and to fertilize an oocyte. This maturation is due to the constant interaction of the spermatozoon with the epididymal fluid. LXR are the major sensors of cholesterol homeostasis, a fundamental element in reproductive physiology because it is the steroid hormones precursor and a regulator of the sperm fertilizing capacities. LXR deficient mice (lxrα;β-/-) have fertility disorder associated with testicular and epididymal alterations. These males present an infertility since 6 months of age leading to a complete infertility at 9 months of age. The purpose of this work is to understand the relation between cholesterol homeostasis regulation and epididymal sperm maturation. At 4 months of age, the lxrα;β-/- males are fertile but present an epididymal phenotype characterized by neutral lipid accumulations in some epithelial cell types and in the smooth muscle cells surrounding the tubule. At 9 months of age, the totally infertile lxrα;β-/- male, present a complete destructuration of the proximal epididymis associated with a complete shrinking of the epithelium height, the loss of the peritubular smooth muscle cells and the presence of immotile and abnormal spermatozoa in the cauda epididymis. My works put in light : 1/ A novel function of a particular cell type, the “apical cells”, in the regulation of the epididymal cholesterol homeostasis. These cells accumulate cholesteryl esters in association with the loss of the ATP Binding Cassette A1 “ABCA1”, a transporter implicated in the cholesterol efflux. Following this, apical cells become apoptotic participating to the epithelial function loss. 2/ An alteration of peritubular smooth muscle cells associated with the mice aging. These cells also accumulate cholesteryl esters and transdifferentiate into invasive foam cells migrating through the epithelium. This phenomenon is very similar to what is observed in the arterial pathology related to cholesterol and aging, the atherosclerosis. The loss of smooth muscle cells limit the progression of the spermatozoa in the lumen and lead to the loss of function of the epithelial cells which become unable to make any exchange with the fluid, hence disturbing spermatozoa maturation. 3/ A deleterious effect of a cholesterol enriched diet on the fertility in 3-month-old lxrα;β-/- male, which are normally fertile and without epididymal phenotype. When submitted to the diet during 4 weeks, these mice become completely infertile, showing the epididymal phenotype of the 9-month-old lxrα;β-/- male mice. The infertility of these mice is characterized by defects in spermatozoa motility, viability and functional parameters. Our results show, on the one hand, the importance of LXR in the post testicular maturation of spermatozoa and in the maintenance of the integrity and functionality of the epididymis. On the other hand, the data that we collected put in evidence the impact of the alimentation and in particular cholesterol enriched diet on the post-testicular maturation

Implication de l'homéostasie lipidique dans la maturation post-testiculaire des spermatozoïdes (apports des modèles murins KO LXR)

L épididyme est un organe accolé au testicule, formé d un long tubule dont l épithélium est constitué de 6 types cellulaires différents aux fonctions partiellement connues. Le tubule épididymaire est entouré de muscles lisses participant, par leurs contractions, à l avancée des spermatozoïdes. Au centre du canal se retrouve le fluide épididymaire dont la composition est régulée par les absorptions et sécrétions de l épithélium épididymaire. Les gamètes arrivant du testicule sont inaptes à assurer la fécondation. La maturation post-testiculaire des spermatozoïdes, durant leur descente dans le tubule épididymaire, va leur permettre d acquérir la mobilité et la capacité à reconnaître et féconder un ovule (qualités regroupées sous le terme de pouvoir fécondant ). Cette maturation se fait grâce aux interactions permanentes des spermatozoïdes avec le fluide. Les LXRs sont des régulateurs majeurs de l homéostasie du cholestérol, un élément fondamental dans la physiologie de la reproduction puisqu il est le précurseur des hormones stéroïdes (androgènes) et un régulateur du pouvoir fécondant des spermatozoïdes. Les souris mâles invalidées pour les 2 isoformes de ces récepteurs (lxra;b-/-) ont une fertilité perturbée en association avec des altérations testiculaires et épididymaires. Ces mâles présentent une infertilité dès 6 mois conduisant à une stérilité complète à 9 mois. Le but de ce travail est de comprendre la relation entre la régulation de l homéostasie du cholestérol et le phénotype épididymaire de ces souris. A l âge de 4 mois, alors que les souris mâles lxra;b-/- sont fertiles, le phénotype est caractérisé par une accumulation de lipides dans certains types cellulaires de l épithélium et dans les muscles lisses entourant le tubule. Chez les mâles lxra;b-/- âgés de 9 mois, lorsque le phénotype d infertilité complète est installé, on observe une destructuration de la partie proximale de l épididyme comprenant une diminution de la hauteur de l épithélium, une perte des muscles lisses péritubulaires et la présence de spermatozoïdes non mobiles et malformés dans la lumière du tubule. Mes travaux ont permis de mettre en évidence différents phénomènes : 1/ Une nouvelle fonction d un type cellulaire particulier, les cellules apicales , dans la régulation de l homéostasie du cholestérol épididymaire. En effet, ces cellules accumulent du cholestérol en association avec la perte de ABCA1 (ATP Binding Cassette A1), codée par un gène cible de LXR, impliquée dans l export de l excédent de cholestérol cellulaire. Suite à cela, ces cellules apicales entrent en apoptose et contribuent à la perte de fonction de l épithélium. 2/ Une altération des cellules musculaires lisses péritubulaires associée au vieillissement des souris lxra;b-/-. Ces cellules accumulent elles aussi du cholestérol et se transforment en cellules invasives, les cellules spumeuses migrant à travers l épithélium. Ce phénomène est très proche des phases de développement de la pathologie artérielle liée au cholestérol et au vieillissement, l athérosclérose. La perte des muscles lisses va limiter la progression des spermatozoïdes et accompagner la perte de fonction des cellules épithéliales qui ne seront plus aptes à effectuer des échanges avec le fluide, empêchant ainsi l acquisition du pouvoir fécondant des spermatozoïdes. (...)The epididymis is a long tubule which epithelium is made of 6 different cellular types with partially unknown functions. The epididymal tubule is surrounded by smooth muscles participating, by their contractions, to the sperm progression. At the center of the tubule is present the epididymal fluid which composition is regulated by the absorptions and secretions of the epithelium. The spermatozoa coming from the testis are unable to fertilize an oocyte. Post-testicular maturation of spermatozoa, during their transit through the epididymis, allows them to become motile, to recognize and to fertilize an oocyte. This maturation is due to the constant interaction of the spermatozoon with the epididymal fluid. LXR are the major sensors of cholesterol homeostasis, a fundamental element in reproductive physiology because it is the steroid hormones precursor and a regulator of the sperm fertilizing capacities. LXR deficient mice (lxra;b-/-) have fertility disorder associated with testicular and epididymal alterations. These males present an infertility since 6 months of age leading to a complete infertility at 9 months of age. The purpose of this work is to understand the relation between cholesterol homeostasis regulation and epididymal sperm maturation. At 4 months of age, the lxra;b-/- males are fertile but present an epididymal phenotype characterized by neutral lipid accumulations in some epithelial cell types and in the smooth muscle cells surrounding the tubule. At 9 months of age, the totally infertile lxra;b-/- male, present a complete destructuration of the proximal epididymis associated with a complete shrinking of the epithelium height, the loss of the peritubular smooth muscle cells and the presence of immotile and abnormal spermatozoa in the cauda epididymis. My works put in light : 1/ A novel function of a particular cell type, the apical cells , in the regulation of the epididymal cholesterol homeostasis. These cells accumulate cholesteryl esters in association with the loss of the ATP Binding Cassette A1 ABCA1 , a transporter implicated in the cholesterol efflux. Following this, apical cells become apoptotic participating to the epithelial function loss. 2/ An alteration of peritubular smooth muscle cells associated with the mice aging. These cells also accumulate cholesteryl esters and transdifferentiate into invasive foam cells migrating through the epithelium. This phenomenon is very similar to what is observed in the arterial pathology related to cholesterol and aging, the atherosclerosis. The loss of smooth muscle cells limit the progression of the spermatozoa in the lumen and lead to the loss of function of the epithelial cells which become unable to make any exchange with the fluid, hence disturbing spermatozoa maturation. 3/ A deleterious effect of a cholesterol enriched diet on the fertility in 3-month-old lxra;b-/- male, which are normally fertile and without epididymal phenotype. When submitted to the diet during 4 weeks, these mice become completely infertile, showing the epididymal phenotype of the 9-month-old lxra;b-/- male mice. The infertility of these mice is characterized by defects in spermatozoa motility, viability and functional parameters. Our results show, on the one hand, the importance of LXR in the post testicular maturation of spermatozoa and in the maintenance of the integrity and functionality of the epididymis. On the other hand, the data that we collected put in evidence the impact of the alimentation and in particular cholesterol enriched diet on the post-testicular maturation.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Epididymis cholesterol homeostasis and sperm fertilizing ability

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Liver X Receptors (LXRs) Alpha and Beta Play Distinct Roles in the Mouse Epididymis1

International audienceAfter its production in the testis, a spermatozoon has to undergo posttesticular maturation steps to become fully motile and fertile. The first step is epididymal maturation, during which immature spermatozoa are transformed into biochemically mature cells ready to proceed to the next step, capacitation, a physiological process occurring in the female genital tract. The biochemical transformations include modification of sperm lipid composition during epididymal transit, with significant changes in fatty acids, phospholipids, and sterols between the caput and the cauda epididymal spermatozoa. Although quantitative aspects of these changes are well documented for several mammalian species, molecular mechanisms governing these steps are poorly understood. Transgenic male mice invalidated for the two liver X receptors (LXRalpha and LXRbeta, nuclear oxysterol receptors regulating cholesterol and lipid metabolism) become sterile when aging, showing an epididymal phenotype. We used single-knockout-model mice to characterize the role of each LXR isoform during sperm maturation in the epididymis. We show here that although a certain redundancy exists in the functions of the two LXR isoforms, some physiological processes are more under the influence of only one of them. In both cases, aging males showed slight subfertility, associated with dyslipidemia, emphasizing the importance of lipid metabolism in relation with male fertility

LXR and ABCA1 control cholesterol homeostasis in the proximal mouse epididymis in a cell-specific manner

Mammalian spermatozoa undergo important plasma membrane maturation steps during epididymal transit. Among these, changes in lipids and cholesterol are of particular interest as they are necessary for fertilization. However, molecular mechanisms regulating these transformations inside the epididymis are still poorly understood. Liver X receptors (LXRs), the nuclear receptors for oxysterols, are of major importance in intracellular cholesterol homeostasis, and LXR−/−-deficient male mice have already been shown to have reduced fertility at an age of 5 months and complete sterility for 9-month-old animals. This sterility phenotype is associated with testes and caput epididymides epithelial defects. The research presented here was aimed at investigating how LXRs act in the male caput epididymidis by analyzing key actors in cholesterol homeostasis. We show that accumulation of cholesteryl esters in LXR−/− male mice is associated with a specific loss of ABCA1 and an increase in apoptosis of apical cells of the proximal caput epididymidis. ATP-binding cassette G1 (ABCG1) and scavenger receptor B1 (SR-B1), two other cholesterol transporters, show little if any modifications. Our study also revealed that SR-B1 appears to have a peculiar expression pattern along the epididymal duct. These results should help in understanding the functional roles of LXR in cholesterol trafficking processes in caput epididymidis