Differential androgen and estrogen substrates specificity in the mouse and primates type 12 17beta-hydroxysteroid dehydrogenase

Characterization of eight types of 17β-hydroxysteroid dehydrogenases from the Japanese sardine Sardinops melanostictus: The probable role of type 12a in ovarian estradiol synthesis

17β-hydroxysteroid dehydrogenases (Hsd17bs) play a critical role in sex steroid biosynthesis. Although multiple types of Hsd17b have been found in fish, there is limited research on their expression and function. Recently, we succeeded in identifying eight types of Hsd17b (types 3, 4, 7, 8, 10, 12a, 12b, and 14) by RNA sequencing in the Japanese sardine Sardinops melanostictus, a commercially important clupeoid fish; however, a homologous sequence of Hsd17b1, which catalyzes the key reaction of estradiol-17β (E2) synthesis, was absent. Here, we aimed to identify the Hsd17b type that plays a major role in E2 synthesis during ovarian development in Japanese sardine. The cDNAs encoding those eight types of Hsd17b were cloned and sequenced. The expressions of hsd17b3, hsd17b12a, and hsd17b12b were higher in ovary than in testis. In particular, hsd17b12a was predominantly expressed in the ovary. Expression of hsd17b3, hsd17b4, hsd17b12a, and hsd17b12b in the ovary increased during ovarian development. The enzymatic activities of Hsd17b3, Hsd17b12a, and Hsd17b12b were evaluated by expressing their recombinants in human embryonic kidney 293T cells. Hsd17b12a and Hsd17b12b catalyzed the conversion of androstenedione (AD) to testosterone (T) and estrone (E1) to E2. The results of in vitro bioassays using sardine ovaries indicated that E2 is synthesized from pregnenolone via AD and T, but not E1. These results suggest that Hsd17b12a plays a major role in E2 synthesis in sardine ovary by catalyzing the conversion of AD to T.

The mitochondrial protease PARL is required for spermatogenesis

Mitochondrial function plays an important role in the maintenance of male fertility. However, the mechanisms underlying mitochondrial defect-related infertility remain mostly unclear. Here we show that a deficiency of PARL (Parl-/-), a mitochondrial protease, causes complete arrest of spermatogenesis during meiosis I. PARL deficiency led to severe downregulation of proteins of respiratory chain complex IV in testes that did not occur in other tested organs, causing a deficit in complex IV activity and ATP production. Furthermore, Parl-/- testes showed an almost complete loss of HSD17B3, a protein of the sER responsible for the last step in testosterone synthesis. While testosterone production appeared to be restored by overexpression of HSD17B12, loss of the canonical testosterone synthesis led to an upregulation of luteinizing hormone (LH) and of LH-regulated responses. These results suggest an important impact of the downstream regulation of mitochondrial defects that manifest in a cell-type-specific manner and extend beyond mitochondria.

Loss of NR5A1 in mouse Sertoli cells after sex determination changes cellular identity and induces cell death by anoikis

To investigate the role of the nuclear receptor NR5A1 in the testis after sex determination, we analyzed mice lacking NR5A1 in Sertoli cells (SCs) from embryonic day (E) 13.5 onwards. Ablation of Nr5a1 impaired the expression of genes characteristic of SC identity (e.g. Sox9 and Amh), caused SC death from E14.5 onwards through a Trp53-independent mechanism related to anoikis, and induced disorganization of the testis cords. Together, these effects caused germ cells to enter meiosis and die. Single-cell RNA-sequencing experiments revealed that NR5A1-deficient SCs changed their molecular identity: some acquired a 'pre-granulosa-like' cell identity, whereas other reverted to a 'supporting progenitor-like' cell identity, most of them being 'intersex' because they expressed both testicular and ovarian genes. Fetal Leydig cells (LCs) did not display significant changes, indicating that SCs are not required beyond E14.5 for their emergence or maintenance. In contrast, adult LCs were absent from postnatal testes. In addition, adult mutant males displayed persistence of Müllerian duct derivatives, decreased anogenital distance and reduced penis length, which could be explained by the loss of AMH and testosterone synthesis due to SC failure.

Structural basis of lipid-droplet localization of 17-beta-hydroxysteroid dehydrogenase 13

Hydroxysteroid 17-beta-dehydrogenase 13 (HSD17B13) is a hepatic lipid droplet-associated enzyme that is upregulated in patients with non-alcoholic fatty liver disease. Recently, there have been several reports that predicted loss of function variants in HSD17B13 protect against the progression of steatosis to non-alcoholic steatohepatitis with fibrosis and hepatocellular carcinoma. Here we report crystal structures of full length HSD17B13 in complex with its NAD+ cofactor, and with lipid/detergent molecules and small molecule inhibitors from two distinct series in the ligand binding pocket. These structures provide insights into a mechanism for lipid droplet-associated proteins anchoring to membranes as well as a basis for HSD17B13 variants disrupting function. Two series of inhibitors interact with the active site residues and the bound cofactor similarly, yet they occupy different paths leading to the active site. These structures provide ideas for structure-based design of inhibitors that may be used in the treatment of liver disease.

Time- and glucose-dependent differentiation of 3T3-L1 adipocytes mimics dysfunctional adiposity

The 3T3-L1 murine adipocyte cell line remains one of the most widely used models to study the mechanisms of obesity and related pathologies. Most studies investigate such mechanisms using mature adipocytes that have been chemically induced to differentiate for 7 days in media containing 25 mM glucose. However, the dysfunctional characteristics commonly observed in obesity including adipocyte hypertrophy, increased expression of inflammatory markers, enhanced production of reactive oxygen species (ROS), increased steroidogenic enzyme expression/activity and production of steroid hormones, are not necessarily mimicked in these cells. The aim of this study was to provide an inexpensive model which represents the well-known characteristics of obesity by manipulating the time of adipocyte differentiation and increasing the concentration of glucose in the cell media. Our results showed a glucose- and time-dependent increase in adipocyte hypertrophy, ROS production and gene expression of the pro-inflammatory cytokine interleukin-6 (IL-6), as well as a time-dependent increase in lipolysis and in the gene expression of the chemokine monocyte chemoattractant protein 1 (MCP1). We also showed that gene expression of the steroidogenic enzymes 11-beta-hydroxysteroid dehydrogenase type 1 (11βHSD1), 17βHSD type 7 and 12, as well as CYP19A1 (aromatase), were significantly higher in the hypertrophic model relative to the control adipocytes differentiated using the conventional method. The increase in 11βHSD1 and 17βHSD12 expression was consistent with the enhanced conversion of cortisone and androstenedione to cortisol and testosterone, respectively. As these characteristics reflect those commonly observed in obesity, hypertrophic 3T3-L1 adipocytes are an appropriate in vitro model to study mechanisms of adipocyte dysfunction in an era where the rise in obesity incidence is a global health concern, and where access to adipose tissue from obese patients are limited.

New Insights into Testosterone Biosynthesis: Novel Observations from HSD17B3 Deficient Mice

Androgens such as testosterone and dihydrotestosterone (DHT) are essential for male sexual development, masculinisation, and fertility. Testosterone is produced via the canonical androgen production pathway and is essential for normal masculinisation and testis function. Disruption to androgen production can result in disorders of sexual development (DSD). In the canonical pathway, 17β-hydroxysteroid dehydrogenase type 3 (HSD17B3) is viewed as a critical enzyme in the production of testosterone, performing the final conversion required. HSD17B3 deficiency in humans is associated with DSD due to low testosterone concentration during development. Individuals with HSD17B3 mutations have poorly masculinised external genitalia that can appear as ambiguous or female, whilst having internal Wolffian structures and testes. Recent studies in mice deficient in HSD17B3 have made the surprising finding that testosterone production is maintained, male mice are masculinised and remain fertile, suggesting differences between mice and human testosterone production exist. We discuss the phenotypic differences observed and the possible other pathways and enzymes that could be contributing to testosterone production and male development. The identification of alternative testosterone synthesising enzymes could inform the development of novel therapies to endogenously regulate testosterone production in individuals with testosterone deficiency.

Blood and adipose tissue steroid metabolomics and mRNA expression of steroidogenic enzymes in periparturient dairy cows differing in body condition

In high-yielding dairy cows, the rapidly increasing milk production after parturition can result in a negative nutrient balance, since feed intake is insufficient to cover the needs for lactation. Mobilizing body reserves, mainly adipose tissue (AT), might affect steroid metabolism. We hypothesized, that cows differing in the extent of periparturient lipomobilization, will have divergent steroid profiles measured in serum and subcutaneous (sc)AT by a targeted metabolomics approach and steroidogenic enzyme profiles in scAT and liver. Fifteen weeks antepartum, 38 multiparous Holstein cows were allocated to a high (HBCS) or normal body condition (NBCS) group fed differently until week 7 antepartum to either increase (HBCS BCS: 3.8 ± 0.1 and BFT: 2.0 ± 0.1 cm; mean ± SEM) or maintain BCS (NBCS BCS: 3.0 ± 0.1 and BFT: 0.9 ± 0.1 cm). Blood samples, liver, and scAT biopsies were collected at week -7, 1, 3, and 12 relative to parturition. Greater serum concentrations of progesterone, androsterone, and aldosterone in HBCS compared to NBCS cows after parturition, might be attributed to the increased mobilization of AT. Greater glucocorticoid concentrations in scAT after parturition in NBCS cows might either influence local lipogenesis by differentiation of preadipocytes into mature adipocytes and/or inflammatory response.

Transcriptomic analysis of MA-10 tumor Leydig cells treated with adipose derived hormones adiponectin and resistin

Obesity contributes to a decrease in testosterone production in men. Indeed, adipose tissue produces several hormones, including adiponectin and resistin, and these may influence the activity of signaling pathways responsible for regulating the expression of genes related to steroidogenesis. In this study, we wanted to identify which genes are directly regulated by these hormones using the MA-10 tumor Leydig cell model. To do this, we treated these cells with adiponectin or resistin, followed by RNA extraction and RNA-Seq transcriptome analysis. Interestingly, genes upregulated by the globular form of adiponectin (gACRP30) were associated to steroid hormones biosynthesis, whereas resistin had no effect on the transcriptome of MA-10 Leydig cells. Moreover, the expression of the Star gene, encoding the steroidogenic acute regulatory protein, was increased in response to treatments with 0.5 mM 8Br-cAMP. Such stimulation was further increased by adiponectin, resulting in increased progesterone production. However, resistin had no effect on steroid production from MA-10 tumor Leydig cells under the treatment conditions investigated. Thus, our data suggest that a direct regulation of steroidogenic genes' expressions in Leydig cells by adipose derived hormones involves cooperation between the cAMP/PKA pathway and adiponectin, but not resistin, to activate Star expression and improve progesterone synthesis.

Japanese eel retinol dehydrogenases 11/12-like are 17-ketosteroid reductases involved in sex steroid synthesis

The synthesis of 11-ketotestosterone (11KT) and estradiol-17β (E2), which play important roles in the regulation of gametogenesis in teleost fishes, is catalyzed by several steroidogenic enzymes. In particular, 17β-hydroxysteroid dehydrogenases (Hsd17bs) with 17-ketosteroid reducing activity (17KSR activity) are essential enzymes in the formation of these sex steroid hormones in the gonads and other tissues. Retinol dehydrogenase 11 (RDH11) has been suggested to be a novel tentative HSD17B (HSD17B15) in humans for a decade, however no definitive proof has been provided yet. In this study, three cDNAs related to human RDH11 were isolated from Japanese eel testis and characterized. Sequence similarity and phylogenetic analyses revealed their close relationship to human rdh11 and rdh12 gene products and they were designated as rdh11/12-like 1, rdh11/12-like 2, and rdh11/12-like 3. Three recombinant Rdh11/12-like proteins expressed in HEK293T cells catalyzed the transformation of estrone into E2 and androstenedione into testosterone. Only Rdh11/12-like 1 catalyzed the conversion of 11-ketoandrostenedione into 11KT. Tissue-distribution analysis by quantitative real-time polymerase chain reaction revealed, in immature male Japanese eel, that rdh11/12-like 1 and rdh11/12-like 2 are predominantly expressed in testis and brain, while rdh11/12-like 3 is expressed ubiquitously. Moreover, we analyzed the effects of gonadotropins and 11KT on the expression of the three rdh11/12-like mRNAs in the immature testis. In vitro incubation of immature testes with various doses of recombinant Japanese eel follicle stimulating hormone, luteinizing hormone, and 11KT indicated that the expression of rdh11/12-like 1 mRNA, rdh11/12-like 2, and rdh11/12-like 3 did not change. These findings suggest that the three Rdh11/12-like proteins metabolize sex steroids. Rdh11/12-like 1 may be one of the enzymes with 17KSR activity involved in the production of 11KT in the testis.

Potential GnRH and steroidogenesis pathways in the scallop Patinopecten yessoensis

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on GnRH and steroidogenesis pathways is still limited. In this study, we first identified two gonadotropin receptor like genes (LGR and LGR5L) and four steroidogenesis-related genes (CYP17A, HSD17B12, HSD3B1 and HSD3B2) in the scallop Patinopecten yessoensis. By examining the expression of 11 genes in the ganglia and/or gonad as well as the concentration of progesterone, testosterone and estradiol in the gonad, we postulate that a potential GnRH signaling pathway (GnRH-GnRHR-GPB5-LGR/LGR5L) in the cerebral and pedal ganglia (CPG) and steroidogenesis pathway (CYP17A, HSD17B12 and HSD3B1) in the gonad are involved in regulating sex steroid hormones. E₂/T index that indicates aromatase activity is higher in the ovary than testis and is positively correlated with the expression of FOXL2 in the gonad, implying the presence of aromatase in the scallop. In addition, we confirmed that expression of most of the downstream genes in the two pathways was significantly elevated after injection of mature py-GnRH peptide. This study would contribute to a new understanding of the molecular basis underlying reproduction regulation by GnRH in mollusks.

Ablation of the canonical testosterone production pathway via knockout of the steroidogenic enzyme HSD17B3, reveals a novel mechanism of testicular testosterone production

Male development, fertility, and lifelong health are all androgen-dependent. Approximately 95% of circulating testosterone is synthesized by the testis and the final step in this canonical pathway is controlled by the activity of the hydroxysteroid-dehydrogenase-17-beta-3 (HSD17B3). To determine the role of HSD17B3 in testosterone production and androgenization during male development and function we have characterized a mouse model lacking HSD17B3. The data reveal that developmental masculinization and fertility are normal in mutant males. Ablation of HSD17B3 inhibits hyperstimulation of testosterone production by hCG, although basal testosterone levels are maintained despite the absence of HSD17B3. Reintroduction of HSD17B3 via gene-delivery to Sertoli cells in adulthood partially rescues the adult phenotype, showing that, as in development, different cell-types in the testis are able to work together to produce testosterone. Together, these data show that HS17B3 acts as a rate-limiting-step for the maximum level of testosterone production by the testis but does not control basal testosterone production. Measurement of other enzymes able to convert androstenedione to testosterone identifies HSD17B12 as a candidate enzyme capable of driving basal testosterone production in the testis. Together, these findings expand our understanding of testosterone production in males.

Characteristics and sex dimorphism of 17β-hydroxysteroid dehydrogenase family genes in the olive flounder Paralichthys olivaceus

Sex steroid hormones play important roles in fish sex differentiation, gonadal development and secondary sexual characteristics. Olive flounder Paralichthys olivaceus is a valuable commercial marine fish species and has marked sexual dimorphism. However, the mechanisms of action of sex hormones in flounder sex are still unclear. In this study, a total of ten Hsd17b family genes, including Hsd17b3, -4, -7, -8, -9, -10, -12a, -12b, -14 and -15, were identified in the flounder, which encoded critical enzymes acting on sex steroid synthesis and metabolism. Hsd17b genes were distributed on eight chromosomes. Hsd17b12a and -12b were located on chromosomes 19 and 7, respectively. It was speculated that these two genes were just highly similar rather than different transcripts derived from the same gene. According to the results of domain and motif analyses, they all belonged to the SDR superfamily and contained conserved Hsd17b motifs TGxxxGxG, PGxxxT, NNAG and YxxxK. Analysis of amino acid sequences predicted that Hsd17b1, -4, -7, -12a and -14 were hydrophilic proteins. The stability of Hsd17b1, -3 and -12b proteins was predicted to be low. The various Hsd17b family genes differed in tissue expression pattern, and Hsd17b10, -12a and -12b were highly expressed in the flounder ovary. Moreover, throughout gonadal development, Hsd17b3 was highly expressed in the testis, and Hsd17b1, -12a and -12b were highly expressed in the ovary, suggesting that they might play an important role in testosterone synthesis in the testis or estrogen synthesis in the ovary. Activities of Hsd17b3 at stages I-V were all significantly higher in the testis than in the ovary (P < 0.05, P < 0.01). Transfection analysis in HEK293T cells showed that Hsd17b1 and -3 were located in both the cytoplasm and nucleus. Additionally, after challenging fish with tamoxifen, Hsd17b3 expression level in the testis decreased significantly (P < 0.01), and in the ovary no significant change was observed. Moreover, the expression of Hsd17b1 in the ovary was significantly upregulated after injection with flutamide (P < 0.05). These findings introduce the characteristics of the flounder Hsd17b in subfamily, which contribute to our understanding of the regulation of sex steroid hormone synthesis in fish gonadal development.

17β-Hydroxysteroid dehydrogenase type 12a responsible for testicular 11-ketotestosterone synthesis in the Japanese eel, Anguilla japonica

The production of 11-ketotestosterone (11KT), an important steroid hormone in piscine spermatogenesis, is regulated by the pituitary gonadotropins [Gths: follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh)] and it is synthesized by catalytic reactions involving several steroidogenic enzymes. Among these enzymes, the role of 17β-hydroxysteroid dehydrogenases (Hsd17bs) that exhibited 17-ketosteroid reducing activity (17KSR activity) responsible for 11KT synthesis is still poorly understood. In the present study, for the deeper understanding of testicular 11KT biosynthesis, we first investigated the steroidogenic pathway to produce 11KT in Japanese eel testis. In vitro incubation of the testis with androstenedione (A4) and the subsequent analysis of the metabolites by thin-layer chromatography indicated that 11KT was synthesized from A4 via 11β-hydroxyandrostenedione (11OHA4) and 11-ketoandrostenedione (11KA4), which indicated that the steroidogenic enzyme exhibiting the 17KSR activity responsible for converting 11KA4 to 11KT is crucial for 11KT production. Subsequently, cDNAs encoding three candidate enzymes, Hsd17b type3 (Hsd17b3), Hsd17b type12a (Hsd17b12a), and 20β-hydroxysteroid dehydrogenase type2 (Hsd20b2), potentially with the 17KSR activity were isolated and characterized in the Japanese eel. The isolated hsd17b3, hsd17b12a, and hsd20b2 cDNAs putatively encoded 308, 314, and 327 amino acid residues with high homology to those of other vertebrate counterparts, respectively. The Hsd17b3, Hsd17b12a, and Hsd20b2 expressed either in HEK293T or in Hepa-E1 converted 11KA4 to 11KT. Tissue-distribution analysis by quantitative real time PCR revealed that hsd17b12a and hsd20b2 mRNAs were detected in the testis, while hsd17b3 mRNA was not detectable. Furthermore, we examined the effects of Gths on the 17KSR activity and the expression of the candidate genes in the immature testis. The 17KSR activity was upregulated by administration of Gths. Furthermore, only expression of hsd17b12a among three candidates was upregulated by Gths as well as the 17KSR activity. These findings strongly suggested that Hsd17b12a is one of the enzymes with 17KSR activity responsible for 11KT synthesis in the testis of Japanese eel.

Gaps in Understanding Mechanism and Lack of Treatments: Potential Use of a Nonhuman Primate Model of Oxaliplatin-Induced Neuropathic Pain

The antineoplastic agent oxaliplatin induces an acute hypersensitivity evoked by cold that has been suggested to be due to sensitized central and peripheral neurons. Rodent-based preclinical studies have suggested numerous treatments for the alleviation of oxaliplatin-induced neuropathic pain, but few have demonstrated robust clinical efficacy. One issue is that current understanding of the pathophysiology of oxaliplatin-induced neuropathic pain is primarily based on rodent models, which might not entirely recapitulate the clinical pathophysiology. In addition, there is currently no objective physiological marker for pain that could be utilized to objectively indicate treatment efficacy. Nonhuman primates are phylogenetically and neuroanatomically similar to humans; thus, disease mechanism in nonhuman primates could reflect that of clinical oxaliplatin-induced neuropathy. Cold-activated pain-related brain areas in oxaliplatin-treated macaques were attenuated with duloxetine, the only drug that has demonstrated clinical efficacy for chemotherapy-induced neuropathic pain. By contrast, drugs that have not demonstrated clinical efficacy in oxaliplatin-induced neuropathic pain did not reduce brain activation. Thus, a nonhuman primate model could greatly enhance understanding of clinical pathophysiology beyond what has been obtained with rodent models and, furthermore, brain activation could serve as an objective marker of pain and therapeutic efficacy.

Intracrine androgen biosynthesis, metabolism and action revisited

Androgens play an important role in metabolic homeostasis and reproductive health in both men and women. Androgen signalling is dependent on androgen receptor activation, mostly by testosterone and 5α-dihydrotestosterone. However, the intracellular or intracrine activation of C₁₉ androgen precursors to active androgens in peripheral target tissues of androgen action is of equal importance. Intracrine androgen synthesis is often not reflected by circulating androgens but rather by androgen metabolites and conjugates. In this review we provide an overview of human C₁₉ steroid biosynthesis including the production of 11-oxygenated androgens, their transport in circulation and uptake into peripheral tissues. We conceptualise the mechanisms of intracrinology and review the intracrine pathways of activation and inactivation in selected human tissues. The contribution of liver and kidney as organs driving androgen inactivation and renal excretion are also highlighted. Finally, the importance of quantifying androgen metabolites and conjugates to assess intracrine androgen production is discussed.

Transcript levels of genes implicated in steroidogenesis in the testes and fat tissue in relation to androstenone accumulation in fat of pubertal pigs

The present study was performed to measure messenger RNA levels of steroidogenic enzymes in testes and fat tissue and determine whether they are related to fat androstenone level. Real-time polymerase chain reaction experiments were performed on 26 testes and 12 adipose tissue samples from pubertal boars using 21 genes. The absence of significant correlations between fat androstenone and the transcriptional activity of the SRD5A2 and SRD5A3 genes but the high correlation coefficient with that of the SRD5A1 gene (r = 0.62, P < 0.05) suggests that the enzyme coded by SRD5A1 is mainly responsible for the last step of androstenone synthesis. The testicular transcriptional activities of CYP17, CYP11A1, CYP19A, AKR1C-pig6, SRD5A1, LHCGR, and AR were significantly correlated. Only transcriptional levels of CYP17, CYP11A1, CYP19A, SRD5A1, and AKR1C-pig6 were correlated with the fat concentration of androstenone (0.57 < r < 0.70, P < 0.05) confirming that the amount of androstenone stored in fat is related to the production in testes of androstenone and more generally to all sex steroids. Altogether, our data are in favor of a preponderant role of AKR1C-pig6 instead of HSD17B3 for testicular synthesis of steroids. Concerning fat tissue, our data do not support a significant de novo biosynthesis of steroids in porcine adipose tissues. The presence of transcripts coding for steroid enzymes, especially those of AKR1C-pig6, suggests that steroids can be transformed. None of transcript abundance was related to androstenone accumulation (P > 0.1). Therefore, steroids synthesized elsewhere can be transformed in fat tissue but synthesis of androstenone is unlikely.

Reductive 17beta-hydroxysteroid dehydrogenases which synthesize estradiol and inactivate dihydrotestosterone constitute major and concerted players in ER+ breast cancer cells

The reductive 17β-hydroxysteroid dehydrogenases which catalyze the last step in estrogen activation for estrogen dependent breast cancer cells were studied. Their biological function and the effects of their knockdown for cancer cell proliferation were demonstrated. The multidisciplinary study involves enzyme catalysis, sex-hormone and cell cycle regulation, as well as cell proliferation in breast cancer cells. Reductive 17β-HSD1, -7 and -12 were studied in the main breast cancer epithelial cells MCF-7 and T47D. Modification of estradiol and 5α-dihydrotestosterone concentrations was monitored by ELISA assay while corresponding cell viability measured by MTT assay. Cell cycle was determined by flow cytometry. Dual activity of estradiol activation and 5α-dihydrotestosterone reduction by 17β-HSD1 and -7 was critical for breast cancer cell (T47D and MCF-7) viability. Cell viability was decreased by 35.8% ± 1.6% in T47D cells after simultaneously knocking down 17β-HSD1 and -7. MCF-7 cell viability was decreased by 29.3% ± 4.2% using a combination of siRNAs and inhibitors. By knocking down 17β-HSD7, we have provided the first demonstration of the significant role of this enzyme in the stimulation of breast cancer cell viability as a result of its high activity on androgen reduction with positive feedback on estradiol production. A further decrease in cell viability was not observed with additional knockdown of 17β-HSD12 after 17β-HSD1 and 7. Breast cancer cell cycle progression was impeded to enter the S phase from G0-G1 after knocking down 17β-HSD1 and -7. In summary, this is the first demonstration that the dual activity in estrone activation and 5α-dihydrotestosterone reduction are the functional basis of reductive 17β-HSDs in breast cancer cells. 17β-HSD1 and -7 are principal reductive 17β-HSDs and major players in the viability of estrogen-dependent breast cancer cells. Combined targeting of these enzymes may be potential for molecular therapy of such cancer.

Target deletion of the bifunctional type 12 17β-hydroxysteroid dehydrogenase in mice results in reduction of androgen and estrogen levels in heterozygotes and embryonic lethality in homozygotes

17β-Hydroxysteroid dehydrogenases (17β-HSDs) are enzymes issued from convergent evolution of activity from various ancestral genes having different functions. Type 12 17β-HSD (17β-HSD12) was described as a bifunctional enzyme, involved in the biosynthesis of estradiol (E2) and the elongation of very long chain fatty acid (VLCFA). It catalyzes selectively the transformation of estrone (E1) into estradiol (E2) in human and primates, whereas in the mouse and Caenorhabditis elegans the enzyme catalyzes the 17β-reduction of both androgens and estrogens. It is also able to catalyze the reduction of 3-keto-acylCoA into 3-hydroxy-acylCoA in the elongation cycle of VLCFA biosynthesis. To further understand the physiological role of 17β-HSD12, we performed targeted disruption of the Hsd17b12 gene by substituting exons 8 and 9 that contain the active site with a neomycin cassette. The data indicate that heterozygous (HSD17B12+/-) mice are viable with reduced levels of sex steroids, whereas homozygous (HSD17B12-/-) mice show embryonic lethality. The present data are in agreement with the bifunctional activities of 17β-HSD12 suggesting that the VLCFA elongation activity, having its origin in the yeast, is most probably responsible for embryonic lethality in HSD17B12-/-, whereas the more recently acquired 17β-HSD12 activity is responsible for reduced sex steroid levels in HSD17B12+/-.

Expression of the estrogen receptors and steroidogenic enzymes involved in estradiol formation in the monkey vagina

OBJECTIVE

Estrogens are well recognized to have beneficial effects on vulvovaginal atrophy because of menopause. The distribution of estrogen receptors and enzymes responsible for estradiol (E2) formation within the vagina may provide insight into how dehydroepiandrosterone, a precursor of both estrogens and androgens, improves vulvovaginal atrophy.

STUDY DESIGN

The purpose of the study was to determine where the steroidogenic enzymes responsible for E2 formation as well as estrogen receptors are localized in vaginal specimens collected from cynomolgus monkeys (Macaca fascicularis), the closest model to the human. HSD3B1, HSD17B1, HSD17B5, HSD17B12, aromatase (CYP19A1), estrogen receptor (ER)-α, and ER-β were measured or localized by quantitative real-time polymerase chain reaction, immunohistochemistry, and immunofluorescence. Estrogens were quantified by liquid chromatography/tandem mass spectrometry.

RESULTS

All steroidogenic enzymes and estrogen receptors are localized mainly in the superficial layer of the stratified squamous epithelium, blood vessel walls, and muscle fibers of the vagina. Immunolabeling of HSD17B5 and HSD17B12 shows that these enzymes are uniformly distributed from the basal membrane to the superficial keratinized cells, whereas HSD3B1 and aromatase are particularly localized in the outer (external) portion of the epithelial layer. ER-α and ER-β are also distributed within the vaginal epithelium, with expression especially elevated at the basal membrane level.

CONCLUSION

The enzymes responsible for E2 formation as well as ERs are expressed mainly in the superficial layer of the stratified epithelium as well as the muscle layer of the vagina. The present data provide morphologic and biochemical support for the role of local dehydroepiandrosterone transformation into estrogens in regulating epithelial cell maturation, pH, fluid secretion, smooth muscle activity, and blood flow regulation in the primate vagina.

Cloning, characterization and functional expression of Taenia solium 17 beta-hydroxysteroid dehydrogenase

The 17β-hydroxysteroid dehydrogenases (17β-HSD) are key enzymes involved in the formation (reduction) and inactivation (oxidation) of sex steroids. Several types have been found in vertebrates including fish, as well as in invertebrates like Caenorhabditis elegans, Ciona intestinalis and Haliotis diversicolor supertexta. To date limited information is available about this enzyme in parasites. We showed previously that Taenia solium cysticerci are able to synthesize sex steroid hormones in vitro when precursors are provided in the culture medium. Here, we identified a T. solium 17β-HSD through in silico blast searches in the T. solium genome database. This coding sequence was amplified by RT-PCR and cloned into the pcDNA 3.1(+) expression vector. The full length cDNA contains 957bp, corresponding to an open reading frame coding for 319 aa. The highest identity (84%) at the protein level was found with the Echinococcus multilocularis 17β-HSD although significant similarities were also found with other invertebrate and vertebrate 17β-HSD sequences. The T. solium Tsol-17βHSD belongs to the short-chain dehydrogenase/reductase (SDR) protein superfamily. HEK293T cells transiently transfected with Tsol17β-HSD induced expression of Tsol17β-HSD that transformed 3H-androstenedione into testosterone. In contrast, 3H-estrone was not significantly transformed into estradiol. In conclusion, T. solium cysticerci express a 17β-HSD that catalyzes the androgen reduction. The enzyme belongs to the short chain dehydrogenases/reductase family and shares motifs and activity with the type 3 enzyme of some other species.

Assessment of steroidogenesis and steroidogenic enzyme functions

There is some confusion in the literature about steroidogenesis in endocrine glands and steroidogenesis in peripheral intracrine tissues. The objective of the present review is to bring some clarifications and better understanding about steroidogenesis in these two types of tissues. Concerns about substrate specificity, kinetic constants and place of enzymes in the pathway have been discussed. The role of 17α-hydroxylase/17-20 lyase (CYP17A1) in the production of dehydroepiandrosterone and back-door pathways of dihydrotestosterone biosynthesis is also analyzed. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Cloning and expression analysis of the 17β hydroxysteroid dehydrogenase type 12 (HSD17B12) in the neogastropod Nucella lapillus

HSD17B12 is a member of the hydroxysteroid dehydrogenase superfamily, a multifunctional group of enzymes involved in the metabolism of steroids, retinoids, bile and fatty acids. Whether the main role of HSD17B12 in mammals is in steroid or fatty acid metabolism is a subject of intense debate. In mollusks it has been shown that an HSD17B12 orthologue can convert estrone into estradiol in vitro, although its primary in vivo function remains unknown. To gain insight into its role in gastropods, we provide here the first cloning of Hsd17b12 in Nucella lapillus and its detailed tissue distribution through quantitative PCR. Furthermore, given that the endocrine disruptor tributyltin (TBT) has been reported to unbalance steroid and lipid levels in gastropods, we tested its impact in on NlHsd17b12 transcript expression. Our results show that NlHsd17b12 is ubiquitously expressed in all tissues analyzed, with higher levels in organs with high metabolic rates, such as kidney and digestive gland, a pattern consistent with an involvement in lipid metabolism. Exposure to TBT chloride at 100 ng Sn/L caused a decrease in NlHsd17b12 mRNA levels in digestive gland, after one and two months, while no effect was observed in gonads. Overall, these results suggest that in mollusks, as in mammals, this enzyme is likely to be involved in lipid metabolism, and emphasize the need to perform more detailed studies on its in vivo function, in order to understand its physiological role and the biological impact of its disruption by pollutants such as TBT.

The mouse as a model to investigate sex steroid metabolism in the normal and pathological prostate

Metabolism of sex steroids within the prostate is an important factor affecting its growth and pathology. Mouse models with genetic gain- and especially loss-of-function have characterised different steroid metabolic pathways and their contribution to prostate pathology. With reference to the human prostate, this review aims to summarize the steroidogenic pathways in the mouse prostate as the basis for using the mouse as a model for intraprostatic steroid signalling. In this review we summarize the current information for three main components of the steroid signalling pathway in the mouse prostate: circulating steroids, steroid receptors and steroidogenic enzymes with regard to signalling via androgen, estrogen, progesterone and glucocorticoid pathways. This review reveals many opportunities for characterisation steroid metabolism in various mouse models. The knowledge of steroid metabolism within prostate tissue and in a lobe (rodent)/region (human) specific manner, will give valuable information for future, novel hypotheses of intraprostatic control of steroid actions. This review summarizes knowledge of steroid metabolism in the mouse prostate and its relevance to the human.

Cloning, characterization, and expression analysis of a putative 17 beta-hydroxysteroid dehydrogenase 11 in the abalone, Haliotis diversicolor supertexta

The 17-beta-hydroxysteroid dehydrogenases (17β-HSDs) are key enzymes for sex steroid biosynthesis. To date, relatively little is known about the presence and function of 17β-HSDs in marine gastropods. In the present study, a cDNA sequence encoding putative 17β-HSD type 11 (17β-HSD-11) was identified in marine abalone (Haliotis diversicolor supertexta). The full-length cDNA contains 1058bp, including an open reading frame (ORF) of 900bp that encodes a protein of 299 amino acids. Comparative structural analysis revealed that abalone 17β-HSD-11 shares relatively high homology with other 17b-HSD-11 hormologues, and a lesser degree of amino acid identity with other forms of 17b-HSD, especially in the functional domains, including the cofactor binding domain (TGxxxGxG) and catalytic site (YxxSK). Phylogenetic analysis showed that abalone 17β-HSD-11 belongs to the short-chain dehydrogenase/reductase (SDR) family. Functional analysis following transient transfection of the ORF into human embryonic kidney-293 (HEK-293) cells indicated that abalone 17β-HSD-11 has the ability to convert 5α-androstane-3α,17β-diol (3α-diol) to androsterone (A) and testosterone (T) to androstenedione (4A). Expression analysis in vivo demonstrated that abalone 17β-HSD-11 is differentially expressed during three stages (non-reproductive, reproductive, and post-reproductive). Taken together, these results indicate that ab-17β-HSD-11 is an SDR family member with a potential role in steroid regulation during the reproductive stage.

The diversity of sex steroid action: novel functions of hydroxysteroid (17β) dehydrogenases as revealed by genetically modified mouse models

Disturbed action of sex steroid hormones, i.e. androgens and estrogens, is involved in the pathogenesis of various severe diseases in humans. Interestingly, recent studies have provided data further supporting the hypothesis that the circulating hormone concentrations do not explain all physiological and pathological processes observed in hormone-dependent tissues, while the intratissue sex steroid concentrations are determined by the expression of steroid metabolising enzymes in the neighbouring cells (paracrine action) and/or by target cells themselves (intracrine action). This local sex steroid production is also a valuable treatment option for developing novel therapies against hormonal diseases. Hydroxysteroid (17β) dehydrogenases (HSD17Bs) compose a family of 14 enzymes that catalyse the conversion between the low-active 17-keto steroids and the highly active 17β-hydroxy steroids. The enzymes frequently expressed in sex steroid target tissues are, thus, potential drug targets in order to lower the local sex steroid concentrations. The present review summarises the recent data obtained for the role of HSD17B1, HSD17B2, HSD17B7 and HSD17B12 enzymes in various metabolic pathways and their physiological and pathophysiological roles as revealed by the recently generated genetically modified mouse models. Our data, together with that provided by others, show that, in addition to having a role in sex steroid metabolism, several of these HSD17B enzymes possess key roles in other metabolic processes: for example, HD17B7 is essential for cholesterol biosynthesis and HSD17B12 is involved in elongation of fatty acids. Additional studies in vitro and in vivo are to be carried out in order to fully define the metabolic role of the HSD17B enzymes and to evaluate their value as drug targets.

Assessment of steroidogenic pathways that do not require testosterone as intermediate

Traditional literature and textbooks generally describe that estradiol (E2) and dihydrotestosterone (DHT) are synthesized from the aromatization and 5α-reduction of testosterone (T), respectively, following a pathway in which T is an essential intermediate (Tpath). This pathway implies that the steps of aromatization and 5α-reduction follow the reaction of the androgenic 17β-hydroxysteroid dehydrogenase (17β-HSD) that catalyzes the conversion of 4-androstenedione (4-dione) into T, and that estrogenic 17β-HSDs are not required. Contrary to this belief, the cloning of many estrogen-specific 17β-HSDs and the observation of higher affinity of aromatase and 5α-reductase for 4-dione than T are strongly in favor of biosynthetic pathways in which the steps catalyzed by aromatase and 5α-reductase precede that catalyzed by 17β-HSDs. Such pathways do not require T as an intermediate, as demonstrated by experiments using [14C]-labeled DHEA and 4-dione as substrates and incubation with SZ95 sebaceous gland, DU-145 prostate cancer and JEG-3 choriocarcinoma cell lines cultured in the presence of inhibitors of 5α-reductase and aromatase. A review of early literature about patients with testicular 17β-HSD deficiency and of steroid metabolism appears to confirm the physiological functionality of the E2 and DHT biosynthetic pathway not requiring T as intermediate (noTpath).

Relationships between the transcriptome and physiological indicators of reproduction in female rainbow trout over an annual cycle

Normal transcriptomic patterns along the brain-pituitary-gonad-liver (BPGL) axis should be better characterized if endocrine-disrupting compound-induced changes in gene expression are to be understood. Female rainbow trout were studied over a complete year-long reproductive cycle. Tissue samples from pituitary, ovary, and liver were collected for microarray analysis using the 16K Genomic Research on Atlantic Salmon Project (GRASP) microarray and for quantitative polymerase chain reaction measures of estrogen receptor (ER) isoform messenger RNA (mRNA) levels. Plasma was collected to determine levels of circulating estradiol-17β (E2), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). As an a priori hypothesis, changes in gene expression were correlated to either circulating levels of E2, FSH, and LH, or ER mRNAs quantified by quantitative polymerase chain reaction. In the liver, most transcriptomic patterns correlated to levels of either E2, LH, or ERs. Fewer ovarian transcripts could be correlated to levels of E2, ERα, or FSH. No significant associations were obvious in the pituitary. As a post hoc hypothesis, changes in transcript abundance were compared with microarray features with known roles in gonadal maturation. Many altered transcripts in the ovary correlated to transcript levels of estradiol 17-beta-dehydrogenase 8 or 17 B HSD12, or to glycoprotein alpha chain 1 or 2. In the pituitary, genes involved with the growth axis (e.g., growth hormone, insulin-related growth factor binding protein) correlated with the most transcripts. These results suggest that transcriptional networks along the BPGL axis may be regulated by factors other than circulating steroid hormones.

The intracrine sex steroid biosynthesis pathways

There is an increasing number of differences reported between the steroidogenesis pathways described in the traditional literature related to gonadal steroidogenesis and the more recent observations achieved using new technologies, especially molecular cloning, pangenomic expression studies, precise quantification of mRNA expression using real-time PCR, use of steroidogenic enzymes stably transfected in cells, detailed enzymatic activity analysis in cultured cell lines and mass spectrometry analysis of steroids. The objective of this chapter is to present steroidogenesis in the light of new findings that demonstrate pathways of biosynthesis of estradiol (E(2)) and dihydrotestosterone (DHT) from adrenal dehydroepiandrosterone (DHEA) in peripheral intracrine tissues which do not involve testosterone as intermediate as classically found in the testis and ovary. Steroidogenic enzymes different from those of the ovary and testis act in a tissue-specific manner to catalyze the transformation of DHEA into active sex steroids. These new pathways are especially important in post-menopausal women where all estrogens and practically all androgens are made at their site of action in peripheral tissues from DHEA, the precursor of adrenal origin. In men, on the other hand, from 40 to 50% of androgens are made in peripheral tissues from adrenal DHEA, thus indicating the major importance of the intracrine pathways in both men and women. We also examine the molecular evolution of steroidogenic enzymes which explains the major differences in steroid metabolism observed between laboratory animals and humans.

Hydroxysteroid (17{beta}) dehydrogenase 12 is essential for mouse organogenesis and embryonic survival

Hydroxysteroid (17beta) dehydrogenases (HSD17Bs) have a significant role in steroid metabolism by catalyzing the conversion between 17-keto and 17beta-hydroxysteroids. However, several studies in vitro have shown that some of these enzymes may also be involved in other metabolic pathways. Among these enzymes, HSD17B12 has been shown to be involved in both the biosynthesis of estradiol and the elongation of the essential very long fatty acids in vitro and in vivo. To investigate the function of mammalian HSD17B12 in vivo, we generated mice with a null mutation of the Hsd17b12 gene (HSD17B12KO mice) by using a gene-trap vector, resulting in the expression of the lacZ gene of the trapped allele. The beta-galactosidase staining of the heterozygous HSD17B12KO mice revealed that Hsd17b12 is expressed widely in the embryonic day (E) 7.5-E9.5 embryos, with the highest expression in the neural tissue. The HSD17B12KO mice die at E9.5 at latest and present severe developmental defects. Analysis of the knockout embryos revealed that the embryos initiate gastrulation, but organogenesis is severely disrupted. As a result, the E8.5-E9.5 embryos were void of all normal morphological structures. In addition, the inner cell mass of knockout blastocysts showed decreased proliferation capacity in vitro, and the amount of arachidonic acid was significantly decreased in heterozygous HSD17B12 ES cells. This, together with the expression pattern, suggests that in mouse, the HSD17B12 is involved in the synthesis of arachidonic acid and is essential for normal neuronal development during embryogenesis.

Proteomic analysis of V-ATPase-rich cells harvested from the kidney and epididymis by fluorescence-activated cell sorting

Proton-transporting cells are located in several tissues where they acidify the extracellular environment. These cells express the vacuolar H(+)-ATPase (V-ATPase) B1 subunit (ATP6V1B1) in their plasma membrane. We provide here a comprehensive catalog of the proteins that are expressed in these cells, after their isolation by enzymatic digestion and fluorescence-activated cell sorting (FACS) from transgenic B1-enhanced green fluorescent protein (EGFP) mice. In these mice, type A and B intercalated cells and connecting segment cells of the kidney, and narrow and clear cells of the epididymis, which all express ATP6V1B1, also express EGFP, while all other cell types are negative. The proteome of renal and epididymal EGFP-positive (EGFP(+)) cells was identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and compared with their respective EGFP-negative (EGFP(-)) cell populations. A total of 2,297 and 1,564 proteins were detected in EGFP(+) cells from the kidney and epididymis, respectively. Out of these proteins, 202 and 178 were enriched by a factor greater than 1.5 in EGFP(+) cells compared with EGFP(-) cells, in the kidney and epididymis respectively, and included subunits of the V-ATPase (B1, a4, and A). In addition, several proteins involved in intracellular trafficking, signaling, and cytoskeletal dynamics were identified. A novel common protein that was enriched in renal and epididymal EGFP(+) cells is the progesterone receptor, which might be a potential candidate for the regulation of V-ATPase-dependent proton transport. These proteomic databases provide a framework for comprehensive future analysis of the common and distinct functions of V-ATPase-B1-expressing cells in the kidney and epididymis.

Brain pathways mediating the pro-aggressive effect of the steroid sulfatase (Sts) gene

STS is the single enzyme that converts all steroid sulfates into their free steroid forms. Initiation of attack behavior against conspecific male mice appeared to be linked to Sts. Here we have confirmed the role of Sts through an association study with attack behavior. Previous studies indicated a positive correlation between the initiation of attack behavior and liver STS concentration levels in male mice, but this finding was not compatible with established knowledge of STS mechanisms. High STS concentrations induce low concentrations of sulfated steroids. Sulfated and un-sulfated steroids are GABA(A) receptor agonists and NMDA receptor positive allosteric modulators. This synaptic pattern of functioning can generate attack behavior and we have confirmed here that an injection of the sulfated steroid dehydroepiandrosterone sulfate (DHEA-S) increases attack behavior. To solve the paradox, we measured the transcription activity of the genes underlying the pathways involved in the hydrolysis of sulfated steroids and leading to the formation of un-conjugated steroids in the mouse brain. We observed that the genes monitoring the steroid biosynthesis pathways exhibited a transcription pattern resulting in an increased sulfotransferase activity in the attacking males that could counterbalance the de-sulfating activity of Sts in the attacking mice.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Differential estrogenic 17beta-hydroxysteroid dehydrogenase activity and type 12 17beta-hydroxysteroid dehydrogenase expression levels in preadipocytes and differentiated adipocytes

Estradiol (E2) is produced locally in adipose tissue and could play an important role in fat distribution and accumulation, especially in women. It is well recognized that aromatase is expressed in adipose tissue; however the identity of its estrogenic 17beta-hydroxysteroid dehydrogenase (17beta-HSD) partner is not identified. To gain a better knowledge about the enzyme responsible for the conversion of estrone into estradiol, we determined the activity and expression levels of known estrogenic 17beta-HSDs, namely types 1, 7 and 12 17beta-HSD in preadipocytes before and after differentiation into mature adipocytes using an adipogenic media. Estrogenic 17beta-HSD activity was assessed using [(14)C]-labelled estrone, while mRNA expression levels of types 1, 7 and 12 17beta-HSD were quantified using real-time PCR and protein expression levels of type 12 17beta-HSD was determined using immunoblot analysis. The data indicate that there is a low conversion of E1 into E2 in preadipocytes; however this activity is increased approximately 5-fold (p<0.0001) in differentiated adipocytes. The increased estrogenic 17beta-HSD activity is consistent with the increase in protein expression levels of 17beta-HSD12.

Integrated view on 17beta-hydroxysteroid dehydrogenases

17beta-Hydroxysteroid dehydrogenases (17beta-HSDs) are important enzymes in steroid metabolism. Long known members of the protein family seemed to be well characterised concerning their role in the regulation of the biological potency of steroid hormones, but today more and more evidence points to pivotal contributions of these enzymes in a variety of other metabolic pathways. Therefore, studies on 17beta-HSDs develop towards metabolomic survey. Latest research results give new insights into the complex metabolic interconnectivity of the 17beta-HSDs. In this paper metabolic activities of 17beta-HSDs will be compared, their interplay with endogenous substrates summarised, and interlacing pathways depicted. Strategies on deciphering the physiological role of 17beta-HSDs and the genetic predisposition for associated diseases will be presented.

Recent advances in 17beta-hydroxysteroid dehydrogenases

The metabolism of steroids at position 17 is catalysed by a growing number of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs). Several human diseases like breast or prostate cancer, endometriosis,metabolic syndrome and mental diseases were associated with dysfunctions of 17beta-HSDs, which consequently became drug targets. This review will focus on identities of 17beta-HSDs and recent advances in analyses of their physiological roles in steroid and lipid metabolism. It will also address the potential of metabolomics in drug development.

Androgen biosynthetic pathways in the human prostate

It is well recognized that there are two androgens, namely testosterone (T) and dihydrotestosterone (DHT); T plays an important role in the testis and muscle, and DHT is crucial for the development, function and pathology of the prostate. It is generally thought that DHT is produced from the 5alpha-reduction of circulating T before being inactivated by 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) that converts DHT into 5alpha-androstane-3alpha,17beta-diol (3alpha-diol). However, the presence of various steroidogenic enzymes in the prostate as well as the availability at high levels of various steroid precursors such as dehydroepiandrosterone sulphate (DHEAS), dehydroepiandrosterone (DHEA) and 4-androstenedione (4-dione) strongly suggest the existence of additional pathways involved in the biosynthesis and metabolism of DHT. Because steroidogenesis could be different in different species, data from the literature obtained from various human, dog, rat and mouse prostate tissues, as well as primary cells and prostatic cancer cell lines, provide a somewhat confusing picture. In the present chapter, we review the data in order to provide a clearer picture of the pathways involved in DHT biosynthesis and metabolism in the human prostate.