Pre-cholesterol precursors in gametogenesis

The spectrum of in vitro maturation in clinical practice: the current insight

In vitro oocyte maturation (IVM) has been used worldwide. Despite the long-term implementation, the uptake of this procedure to complement current in vitro fertilization (IVF) remains low. The main reason is likely due to the non-synchronization of protocol and definition criteria, leading to difficulty in collective proper outcome data worldwide and, thus, lack of understanding of the exact IVM procedure. The review aims to consolidate the current clinical practice of IVM by dissecting relevant publications to be tailored for a current spectrum of clinical practice. Nevertheless, the background theories of oocyte maturation were also explored to provide a comprehensive understanding of the basis of IVM theories. Additional discussion of other potential uses of IVM in the future, such as in ovarian tissue cryopreservation known as OTO-IVM for fertility preservation and among women with diminished ovarian reserve, was also explored. Otherwise, future collaboration among all IVM centers is paramount for better collection of clinical data to provide valid recommendations for IVM in clinical practice, especially in molecular integrity and possible DNA alteration if present for IVM offspring outcome safety purposes.

Role of cholesterol metabolism in the anticancer pharmacology of selective estrogen receptor modulators

Selective estrogen receptor modulators (SERMs) are a class of compounds that bind to estrogen receptors (ERs) and possess estrogen agonist or antagonist actions in different tissues. As such, they are widely used drugs. For instance, tamoxifen, the most prescribed SERM, is used to treat ERα-positive breast cancer. Aside from their therapeutic targets, SERMs have the capacity to broadly affect cellular cholesterol metabolism and handling, mainly through ER-independent mechanisms. Cholesterol metabolism reprogramming is crucial to meet the needs of cancer cells, and different key processes involved in cholesterol homeostasis have been associated with cancer progression. Therefore, the effects of SERMs on cholesterol homeostasis may be relevant to carcinogenesis, either by contributing to the anticancer efficacy of these compounds or, conversely, by promoting resistance to treatment. Understanding these aspects of SERMs actions could help to design more efficacious therapies. Herein we review the effects of SERMs on cellular cholesterol metabolism and handling and discuss their potential in anticancer pharmacology.

Brood size is reduced by half in birds feeding on flutriafol-treated seeds below the recommended application rate

Despite the efforts of the European Commission to implement measures that offset the detrimental effects of agricultural intensification, farmland bird populations continue to decline. Pesticide use has been pointed out as a major cause of decline, with growing concern about those agro-chemicals that act as endocrine disruptors. We report here on the effects of flutriafol, a ubiquitous systemic fungicide used for cereal seed treatment, on the physiology and reproduction of a declining gamebird. Captive red-legged partridges (Alectoris rufa; n = 11-13 pairs per treatment) were fed wheat treated with 0%, 20% or 100% of the flutriafol application rate during 25 days in late winter. We studied treatment effects on the reproductive performance, carotenoid-based coloration and cellular immune responsiveness of adult partridges, and their relationship with changes in oxidative stress biomarkers and plasma biochemistry. We also studied the effect of parental exposure on egg antioxidant content and on the survival, growth and cellular immune response of offspring. Exposed partridges experienced physiological effects (reduced levels of cholesterol and triglycerides), phenotypical effects (a reduction in the carotenoid-based pigmentation of their eye rings), and most importantly, severe adverse effects on reproduction: a reduced clutch size and fertile egg ratio, and an overall offspring production reduced by more than 50%. No effects on body condition or cellular immune response of either exposed adult or their surviving offspring were observed. These results, together with previous data on field exposure in wild partridges, demonstrate that seed treatment with flutriafol represents a risk for granivorous birds; they also highlight a need to improve the current regulation system used for foreseeing and preventing negative impacts of Plant Protection Products on wildlife.

Disrupting Hepatocyte Cyp51 from Cholesterol Synthesis Leads to Progressive Liver Injury in the Developing Mouse and Decreases RORC Signalling

Development of mice with hepatocyte knockout of lanosterol 14α-demethylase (H^Cyp51−/−) from cholesterol synthesis is characterized by the progressive onset of liver injury with ductular reaction and fibrosis. These changes begin during puberty and are generally more aggravated in the knockout females. However, a subgroup of (pre)pubertal knockout mice (runts) exhibits a pronounced male prevalent liver dysfunction characterized by downregulated amino acid metabolism and elevated Casp12. RORC transcriptional activity is diminished in livers of all runt mice, in correlation with the depletion of potential RORC ligands subsequent to CYP51 disruption. Further evidence for this comes from the global analysis that identified a crucial overlap between hepatic Cyp51^−/− and Rorc^−/− expression profiles. Additionally, the reduction in RORA and RORC transcriptional activity was greater in adult H^Cyp51−/− females than males, which correlates well with their downregulated amino and fatty acid metabolism. Overall, we identify a global and sex-dependent transcriptional de-regulation due to the block in cholesterol synthesis during development of the Cyp51 knockout mice and provide in vivo evidence that sterol intermediates downstream of lanosterol may regulate the hepatic RORC activity.

Cytochrome P450 metabolism of the post-lanosterol intermediates explains enigmas of cholesterol synthesis

Cholesterol synthesis is among the oldest metabolic pathways, consisting of the Bloch and Kandutch-Russell branches. Following lanosterol, sterols of both branches are proposed to be dedicated to cholesterol. We challenge this dogma by mathematical modeling and with experimental evidence. It was not possible to explain the sterol profile of testis in cAMP responsive element modulator tau (Crem τ) knockout mice with mathematical models based on textbook pathways of cholesterol synthesis. Our model differs in the inclusion of virtual sterol metabolizing enzymes branching from the pathway. We tested the hypothesis that enzymes from the cytochrome P450 (CYP) superfamily can participate in the catalysis of non-classical reactions. We show that CYP enzymes can metabolize multiple sterols in vitro, establishing novel branching points of cholesterol synthesis. In conclusion, sterols of cholesterol synthesis can be oxidized further to metabolites not dedicated to production of cholesterol. Additionally, CYP7A1, CYP11A1, CYP27A1, and CYP46A1 are parts of a broader cholesterol synthesis network.

Genetic alterations affecting cholesterol metabolism and human fertility

Single nucleotide polymorphisms (SNPs) represent genetic variations among individuals in a population. In medicine, these small variations in the DNA sequence may significantly impact an individual's response to certain drugs or influence the risk of developing certain diseases. In the field of reproductive medicine, a significant amount of research has been devoted to identifying polymorphisms which may impact steroidogenesis and fertility. This review discusses current understanding of the effects of genetic variations in cholesterol metabolic pathways on human fertility that bridge novel linkages between cholesterol metabolism and reproductive health. For example, the role of the low-density lipoprotein receptor (LDLR) in cellular metabolism and human reproduction has been well studied, whereas there is now an emerging body of research on the role of the high-density lipoprotein (HDL) receptor scavenger receptor class B type I (SR-BI) in human lipid metabolism and female reproduction. Identifying and understanding how polymorphisms in the SCARB1 gene or other genes related to lipid metabolism impact human physiology is essential and will play a major role in the development of personalized medicine for improved diagnosis and treatment of infertility.

HSL-knockout mouse testis exhibits class B scavenger receptor upregulation and disrupted lipid raft microdomains

There is a tight relationship between fertility and changes in cholesterol metabolism during spermatogenesis. In the testis, class B scavenger receptors (SR-B) SR-BI, SR-BII, and LIMP II mediate the selective uptake of cholesterol esters from HDL, which are hydrolyzed to unesterified cholesterol by hormone-sensitive lipase (HSL). HSL is critical because HSL knockout (KO) male mice are sterile. The aim of the present work was to determine the effects of the lack of HSL in testis on the expression of SR-B, lipid raft composition, and related cell signaling pathways. HSL-KO mouse testis presented altered spermatogenesis associated with decreased sperm counts, sperm motility, and infertility. In wild-type (WT) testis, HSL is expressed in elongated spermatids; SR-BI, in Leydig cells and spermatids; SR-BII, in spermatocytes and spermatids but not in Leydig cells; and LIMP II, in Sertoli and Leydig cells. HSL knockout male mice have increased expression of class B scavenger receptors, disrupted caveolin-1 localization in lipid raft plasma membrane microdomains, and activated phospho-ERK, phospho-AKT, and phospho-SRC in the testis, suggesting that class B scavenger receptors are involved in cholesterol ester uptake for steroidogenesis and spermatogenesis in the testis.

Cytochrome P450s in the synthesis of cholesterol and bile acids--from mouse models to human diseases

The present review describes the transgenic mouse models that have been designed to evaluate the functions of the cytochrome P450s involved in cholesterol and bile acid synthesis, as well as their link with disease. The knockout of cholesterogenic Cyp51 is embrionally lethal, with symptoms of Antley-Bixler syndrome occurring in mice, whereas the evidence for this association is conflicting in humans. Disruption of Cyp7a1 from classic bile acid synthesis in mice leads to either increased postnatal death or a milder phenotype with elevated serum cholesterol. The latter is similar to the case in humans, where CYP7A1 mutations associate with high plasma low-density lipoprotein and hepatic cholesterol content, as well as deficient bile acid excretion. Disruption of Cyp8b1 from an alternative bile acid pathway results in the absence of cholic acid and a reduced absorption of dietary lipids; however, the human CYP8B1 polymorphism fails to explain differences in bile acid composition. Unexpectedly, apparently normal Cyp27a1(-/-) mice still synthesize bile acids that originate from the compensatory pathway. In humans, CYP27A1 mutations cause cerebrotendinous xanthomatosis, suggesting that only mice can compensate for the loss of alternative bile acid synthesis. In line with this, Cyp7b1 knockouts are also apparently normal, whereas human CYP7B1 mutations lead to a congenital bile acid synthesis defect in children or spastic paraplegia in adults. Mouse knockouts of the brain-specific Cyp46a1 have reduced brain cholesterol excretion, whereas, in humans, CYP46A1 polymorphisms associate with cognitive impairment. At present, cytochrome P450 family 39 is poorly characterized. Despite important physiological differences between humans and mice, mouse models prove to be an invaluable tool for understanding the multifactorial facets of cholesterol and bile acid-related disorders.

Gonadotropin-regulated expressions of lanosterol 14alpha-demethylase, sterol Delta14-reductase and C-4 sterol methyl oxidase contribute to the accumulation of meiosis-activating sterol in rabbit gonads

Meiosis-activating sterol (MAS), the intermediate of cholesterol biosynthesis, is an important lipophilic molecule mediating gonadotropins' action in inducing oocyte meiotic resumptions in various mammalian species. With respect to MAS's physiological relevance during oocyte maturation in the rabbit, early study has demonstrated that luteinizing hormone (LH), but not follicle stimulating hormone (FSH) can induce FF-MAS accumulation facilitating oocyte maturation in rabbits. However, the potential underlying mechanism for the MAS accumulation in the rabbit gonad remained unclear. We hypothesized that differential expression of MAS synthetic and metabolic enzymes would contribute to the timely MAS accumulation in the rabbit gonad. To address this issue, in the present investigation, we first cloned the cDNAs encoding there pre- and post-MAS enzymes, lanosterol 14alpha-demethylase (CYP51), sterol Delta14-reductase (14-SR) and C-4 sterol methyl oxidase (C4MO), respectively, using rapid amplification of cDNA ends (RACE) cloning, and then performed northern hybridization experiments to explore their expression profiles in the rabbit ovary, testis, and various other tissues. We observed that CYP51 expression was significantly upregulated only by LH/hCG in the antral follicle exhibiting its peak levels in preovulatory follicles; whereas both FSH and LH significantly downregulated 14-SR expression with the progression of antral follicular development. These findings provided here novel evidence that an inverse upregulation of CYP51 and downregulation of 14-SR expression under FSH/LH stimulation functions as the machinery for FF-MAS accumulation in preovulatory follicles prior to ovulation in the rabbit.

Structural basis of human CYP51 inhibition by antifungal azoles

The obligatory step in sterol biosynthesis in eukaryotes is demethylation of sterol precursors at the C14-position, which is catalyzed by CYP51 (sterol 14-alpha demethylase) in three sequential reactions. In mammals, the final product of the pathway is cholesterol, while important intermediates, meiosis-activating sterols, are produced by CYP51. Three crystal structures of human CYP51, ligand-free and complexed with antifungal drugs ketoconazole and econazole, were determined, allowing analysis of the molecular basis for functional conservation within the CYP51 family. Azole binding occurs mostly through hydrophobic interactions with conservative residues of the active site. The substantial conformational changes in the B' helix and F-G loop regions are induced upon ligand binding, consistent with the membrane nature of the protein and its substrate. The access channel is typical for mammalian sterol-metabolizing P450 enzymes, but is different from that observed in Mycobacterium tuberculosis CYP51. Comparison of the azole-bound structures provides insight into the relative binding affinities of human and bacterial P450 enzymes to ketoconazole and fluconazole, which can be useful for the rational design of antifungal compounds and specific modulators of human CYP51.

Temporal profiling of rat transcriptomes in retinol-replenished vitamin A-deficient testis

At least in mammals, retinoic acid is a pivotal factor in maintaining the functionality of the testis, in particular, for the progression of germ cells from mitosis to meiosis. Removal of dietary vitamin A or a targeted deletion of retinoic acid receptor alpha gene (Rara), the receptor for retinoic acid, in mice, led to testicular degeneration by a dramatic loss of germ cells and a loss of control of the spermatogenic cycle. The germ cells that remained in the vitamin A deficient (VAD) rat testis were spermatogonia and a few preleptotene spermatocytes. Spermatogenesis can be reinitiated by injection of VAD rats with retinol, the metabolic precursor of retinoic acid, but to date, the functions of retinoic acid in the testis remain elusive. We have applied DNA microarray technology to investigate the time-dependent transcriptome changes that occur 4 to 24 h after retinol replenishment in the VAD rat testis. The retinol-regulated gene expression occurred both in germ cells and Sertoli cells. Bioinformatic analyses revealed time-dependent clusters of genes and canonical pathways that may have critical functions for proper progression through spermatogenesis. In particular, gene clusters that emerged dealt with: (1) cholesterol and oxysterol homeostasis, * (2) the regulation of steroidogenesis, (3) glycerophospholipid metabolism, (4) the regulation of acute inflammation, (5) the regulation of the cell cycle including ubiquitin-mediated degradation of cell cycle proteins and control of centrosome and genome integrity, and (6) the control of membrane scaffolding proteins that can integrate multiple small GTPase signals within a cell. These results provide insights into the potential role of retinoic acid in the testis.

Combined gas chromatographic/mass spectrometric analysis of cholesterol precursors and plant sterols in cultured cells

We developed a powerful gas chromatographic/mass spectrometric method allowing quantitative analysis of 11 structurally similar cholesterol precursors and plant sterols (squalene, desmosterol, 7-dehydrocholesterol, lathosterol, zymosterol, dihydro-lanosterol, lanosterol, FF-MAS, T-MAS, campesterol, sitosterol) from cultured human hepatocytes in a single chromatographic run. Deuterium labelled cholesterol, sitosterol and lathosterol were used as internal standards. Care was taken to select ions for the detection that gave the most appropriate discrimination in the assay. Replicate analyses gave a coefficient of variation less than 6%. Recovery experiments were satisfactory for 7-dehydrocholesterol, campesterol, desmosterol, lathosterol, zymosterol and cholesterol with less than 7% difference between expected and found levels. For other sterols, the difference between expected and found levels varied between 10 and 16%. It is concluded that this method is suitable for studies on the effect of different inhibitors and stimulators of cholesterol synthesis in cultured cells. Additionally, the method is relevant also for clinical applications since abnormally increased late cholesterol intermediates in patients are representations of the inherited disorders linked to different enzyme defects in the post-squalene cholesterol biosynthesis.

Mammalian cytochromes P450—Importance of tissue specificity

Mammals express multiple cytochromes P450 simultaneously in a variety of tissues, including the liver, kidney, lung, adrenal, gonads, brain, and most others. For cytochromes P450 that are expressed in many tissues or cell types, the tissue/cell type-specific expression might be associated with their special physiological roles. Several cytochrome P450 enzymes are found not only in different cell types and tissues, but also in different subcellular compartments. Generally, all mammalian cytochrome P450 enzymes are membrane bound. The two major groups are represented by microsomal cytochromes P450 that reside in the endoplasmic reticulum, and mitochondrial cytochromes P450, that reside in the inner mitochondrial membrane. However, the outer nuclear membrane, different Golgi compartments, peroxisomes and the plasma membrane are also sites where cytochromes P450 were observed. For example, CYP51 is an ER enzyme in majority of tissues but in male germ cells it trafficks through the Golgi to acrosome, where it is stabilized for several weeks. Surprisingly, in brains of heme synthesis deficient mice, a soluble form of CYP1A1 was detected whose activity has been restored by the addition of heme. In the majority of cases each cytochrome P450 enzyme resides in a single subcellular compartment in a certain cell, however, examples of simultaneous localization in different subcellular compartments have also been described, such as endoplasmic reticulum, Golgi and plasma membrane for CYP2E1. This review will focus on the physiological importance of mammalian cytochrome P450 expression and localization in different tissues or cell types and subcellular compartments.

Cholesterol precursors stabilize ordinary and ceramide-rich ordered lipid domains (lipid rafts) to different degrees. Implications for the Bloch hypothesis and sterol biosynthesis disorders

Genetic disorders of cholesterol biosynthesis result in accumulation of cholesterol precursors and cause severe disease. We examined whether cholesterol precursors alter the stability and properties of ordered lipid domains (rafts). Tempo quenching of a raft-binding fluorophore was used to measure raft stability in vesicles containing sterol, dioleoylphosphatidylcholine, and one of the following ordered domain-forming lipids/lipid mixtures: dipalmitoylphosphatidylcholine (DPPC), sphingomyelin (SM), a SM/cerebroside mixture or a SM/ceramide (cer) mixture. Relative to cholesterol, early cholesterol precursors containing an 8-9 double bond (lanosterol, dihydrolanosterol, zymosterol, and zymostenol) only weakly stabilized raft formation by SM or DPPC. Desmosterol, a late precursor containing the same 5-6 double bond as cholesterol, but with an additional 24-25 double bond, also stabilized domain formation weakly. In contrast, two late precursors containing 7-8 double bonds (lathosterol and 7-dehydrocholesterol) were better raft stabilizers than cholesterol. For vesicles containing SM/cerebroside and SM/cer mixtures the effect of precursor upon raft stability was small, although the relative effects of different precursors were the same. Using both detergent resistance and a novel assay involving fluorescence quenching induced by certain sterols we found cholesterol precursors were displaced from cer-rich rafts, and could displace cer from rafts. Precursor displacement by cer was inversely correlated to precursor raft-stabilizing abilities, whereas precursor displacement of cer was greatest for the most highly raft-stabilizing precursors. These observations support the hypothesis that sterols and cer compete for raft-association (Megha, and London, E. (2004) J. Biol. Chem. 279, 9997-10004). The results of this study have important implications for how precursors might alter raft structure and function in cells, and for the Bloch hypothesis, which postulates that sterol properties are gradually optimized for function along the biosynthetic pathway.

cDNA Cloning, Genomic Structure and Expression Analysis of the Bovine Lanosterol 14.ALPHA.-Demethylase (CYP51) in Gonads

Meiosis activating sterol (MAS), the intermediate of cholesterol biosynthesis, is an important substance to stimulate oocytes maturation in FSH-induced signal transduction pathway. Lanosterol 14alpha-demethylase (CYP51) converts lanosterol to MAS. Although MAS is firstly isolated from bovine testis, the information about bovine CYP51 gene and its expression is little. In present studies, the cDNA cloning, genomic structure, chromosomal mapping, and expression patterns of bovine CYP51 were demonstrated. The cDNA coding bovine CYP51 contains a 1509 bp open reading frame and a 1119 bp 3' untranslated region. And the bovine CYP51 gene includes 10 exons and spans about 17 kb. Screening the cattle RH5000 panel bovine CYP51 is mapped to chromosome 4 (0cR). The sequenced promoter region is TATA-less and contains several highly conserved regulatory elements, such as GC-box, cAMP-responsive elements (CRE), sterol regulatory element (SRE) which is important fragment for its transcription. No evidence of processed pseudogenes is found using long PCR and Southern blot. Northern blot analysis reveals that an approximately 2.7 kb mRNA is expressed in all the examined bovine tissues, while a 1.8 kb mRNA is found only in the mature bovine testis where the MAS is accumulated. Immunochemistry analysis shows that leydig cells express the highest level of the CYP51 protein in testis. Among different stages follicles it is localized primarily to the oocytes with the level varying slightly. Granulosa cells of primordial, primary and secondary follicles show background staining. While granulosa cells facing the antrum and cumulus granulosa cells of antral follicles show considerably heavier staining. The highest level is expressed in corpus lutea. These data indicate a stage- and cell type-specific expression of CYP51 protein in bovine oogenesis.