Localization of the steroidogenic acute regulatory protein in human tissues

Six Decades of Research on Human Fetal Gonadal Steroids

Human fetal gonads acquire endocrine steroidogenic capabilities early during their differentiation. Genetic studies show that this endocrine function plays a central role in the sexually dimorphic development of the external genitalia during fetal development. When this endocrine function is dysregulated, congenital malformations and pathologies are the result. In this review, we explain how the current knowledge of steroidogenesis in human fetal gonads has benefited from both the technological advances in steroid measurements and the assembly of detailed knowledge of steroidogenesis machinery and its expression in human fetal gonads. We summarise how the conversion of radiolabelled steroid precursors, antibody-based assays, mass spectrometry, ultrastructural studies, and the in situ labelling of proteins and mRNA have all provided complementary information. In this review, our discussion goes beyond the debate on recommendations concerning the best choice between the different available technologies, and their degrees of reproducibility and sensitivity. The available technologies and techniques can be used for different purposes and, as long as all quality controls are rigorously employed, the question is how to maximise the generation of robust, reproducible data on steroid hormones and their crucial roles in human fetal development and subsequent functions.

Synergistic inhibition of csal1 and csal3 in granulosa cell proliferation and steroidogenesis of hen ovarian prehierarchical development†

SALL1 and SALL3 are transcription factors that play an essential role in regulating developmental processes and organogenesis in many species. However, the functional role of SALL1 and SALL3 in chicken prehierarchical follicle development is unknown. This study aimed to explore the potential role and mechanism of csal1 and csal3 in granulosa cell proliferation, differentiation, and follicle selection within the prehierarchical follicles of hen ovary. Our data demonstrated that the csal1 and csal3 transcriptions were highly expressed in granulosa cells of prehierarchical follicles, and their proteins were mainly localized in the cytoplasm of granulosa cells and oocytes as well as in the ovarian stroma and epithelium. It initially revealed that both csal1 and csal3 may be involved in chicken prehierarchical follicle development via a translocation mechanism. Furthermore, our results showed an abundance of CCND1, Bcat, StAR, CYP11A1, and FSHR mRNA in granulosa cells, and the proliferation levels of granulosa cells from the prehierarchical follicles were significantly increased by siRNA-mediated knockdown of csal1 or/and csal3. Conversely, the overexpression of csal1 or/and csal3 in the granulosa cells led to a remarkably decreased of them. Moreover, csal1 and csal3 together exert a much stronger effect on the regulation than any of csal1 or csal3. These results indicated that csal1 and csal3 play synergistic inhibitory roles on granulosa cell proliferation, differentiation, and steroidogenesis during prehierarchical follicle development in vitro. The current data provide a basis of molecular mechanisms of csal1 and csal3 in controlling the prehierarchical follicle development and growth of hen ovary in vivo.

Effects of RAC1 on Proliferation of Hen Ovarian Prehierarchical Follicle Granulosa Cells

Simple Summary

The growth and development of ovary follicles is an intricate, highly organized process involving many local intra-ovarian factors. Ras-related C3 botulinum toxin substrate1 (RAC1) is speculated to be associated with prehierarchical follicle development of hen ovaries. The current study initially revealed RAC1 mRNA to be expressed in varied-size follicles and stroma and its expression levels in the prehierarchical follicles of 1.0–3.9 mm, 6.0–6.9 mm and 7.0–8.0 mm in diameter were remarkably higher than the other groups. Moreover, RAC1 protein was mainly expressed in the oocytes and granulosa cells (GC), as well as in stromal tissues of the follicles. To understand the exact roles of the RAC1 gene in regulation of follicular GC proliferation and differentiation, siRNA interference and overexpression of the RAC1 gene were conducted. Our experiments demonstrated that the RAC1 gene can significantly promote the expression of mRNA and proteins of FSHR, CCND2, CYP11A1, PCNA and StAR genes in GC and directly elevate the proliferation of GC in vitro. These results indicated RAC1 played a crucial role in regulation of GC proliferation and differentiation and steroidogenesis during the development of prehierarchical follicles. This study provided a base for elucidating the molecular mechanisms underlying the biological effect of RAC1 on the hen ovary follicle growth and development.

Abstract

RAC1 belongs to the small G protein Rho subfamily and is implicated in regulating gene expression, cell proliferation and differentiation in mammals and humans; nevertheless, the function of RAC1 in growth and development of hen ovarian follicles is still unclear. This study sought to understand the biological effects of RAC1 on granulosa cell (GC) proliferation and differentiation of hen ovarian prehierarchical follicles. Firstly, our results showed expression levels of RAC1 mRNA in the follicles with diameters of 7.0–8.0 mm, 6.0–6.9 mm and 1.0–3.9 mm were greater than other follicles (p < 0.05). The RAC1 protein was mainly expressed in oocyte and its around GCs and stromal tissues of the prehierarchical follicles by immunohistochemistry. Further investigation revealed the RAC1 gene remarkably enhanced the mRNA and protein expression levels of FSHR (a marker of follicle selection), CCND2 (a marker of cell-cycle progression and GC differentiation), PCNA (a marker of GC proliferation), StAR and CYP11A1 (markers of GC differentiation and steroidogenesis) (p < 0.05). Furthermore, our data demonstrated siRNA interference of RAC1 significantly reduced GC proliferation (p < 0.05), while RAC1 gene overexpression enhanced GC proliferation in vitro (p < 0.05). Collectively, this study provided new evidence that the biological effects of RAC1 on GC proliferation, differentiation and steroidogenesis of chicken ovary follicles.

Abnormal histology in testis from prepubertal boys with monorchidism

BACKGROUND

Little is known about the histology of contralateral descended testes in boys with unilaterally absent testis. We investigated whether absence of one testis is associated with abnormal tissue architecture of the solitary contralaterally descended testis.

DESIGN SETTING AND PATIENTS

For this retrospective study, we examined the results of biopsies of the contralateral descended testis in 43 boys with monorchidism. Data from 26 control testes from boys of matching ages were selected from results published in 1977 and 2009. During surgery, any nubbins were removed. In each case, the scrotal testis was biopsied, and the testis fixed by subdartos pouch or suture.

RESULTS

Of the 43 affected boys, 23 had normal testicular histology in the contralateral descended testis, whereas 20 (46%) had abnormal histology. Eight of the abnormal biopsies matched the criteria for high infertility risk. Samples from three boys in this latter group revealed a Sertoli-cell-only phenotype. Immunohistochemical assays were positive for steroidogenic acute regulatory (STAR) protein in Leydig cells and spermatogonia. STAR expression was stronger in the monorchid group with normal testicular histology.

CONCLUSIONS

Almost half of the patients with unilateral absent testis were at risk for subfertility or infertility. Our results emphasize the need for testicular biopsy of the solitary testis in boys with monorchidism to appropriately assess infertility risk.

An immunohistochemical study on testicular steroidogenesis in the Sunda porcupine (Hystrix javanica)

In the testes of the Sunda porcupine (Hystrix javanica), the expression of the steroidogenic acute regulatory protein (StAR) and steroidogenic enzymes, such as cytochrome P450 side chain cleavage (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase (P450c17) and cytochrome P450 aromatase (P450arom), was immunohistochemically examined to clarify the location of steroidogenesis. In this study, complete spermatogenesis (spermiogenesis) was observed in the testes of the examined Sunda porcupine, and spermatozoa of the Sunda porcupine had a spatulate sperm head unlike that of rats and mice which has an apical hook. On immunostaining of StAR, P450scc, 3β-HSD, P450c17 and P450arom, immunoreactivity for all proteins was only detected in the Leydig cells and not observed within the seminiferous tubules, suggesting that the Leydig cells can synthesize both androgen and estrogen from cholesterol in the Sunda porcupine testes.

Current knowledge on the acute regulation of steroidogenesis

How rapid induction of steroid hormone biosynthesis occurs in response to trophic hormone stimulation of steroidogenic cells has been a subject of intensive investigation for approximately six decades. A key observation made very early was that acute regulation of steroid biosynthesis required swift and timely synthesis of a new protein whose role appeared to be involved in the delivery of the substrate for all steroid hormones, cholesterol, from the outer to the inner mitochondrial membrane where the process of steroidogenesis begins. It was quickly learned that this transfer of cholesterol to the inner mitochondrial membrane was the regulated and rate-limiting step in steroidogenesis. Following this observation, the quest for this putative regulator protein(s) began in earnest in the late 1950s. This review provides a history of this quest, the candidate proteins that arose over the years and facts surrounding their rise or decline. Only two have persisted-translocator protein (TSPO) and the steroidogenic acute regulatory protein (StAR). We present a detailed summary of the work that has been published for each of these two proteins, the specific data that has appeared in support of their role in cholesterol transport and steroidogenesis, and the ensuing observations that have arisen in recent years that have refuted the role of TSPO in this process. We believe that the only viable candidate that has been shown to be indispensable is the StAR protein. Lastly, we provide our view on what may be the most important questions concerning the acute regulation of steroidogenesis that need to be asked in future.

MicroRNA-424/503 cluster members regulate bovine granulosa cell proliferation and cell cycle progression by targeting SMAD7 gene through activin signalling pathway

BACKGROUND

The granulosa cells are indispensable for follicular development and its function is orchestrated by several genes, which in turn posttranscriptionally regulated by microRNAs (miRNA). In our previous study, the miRRNA-424/503 cluster was found to be highly abundant in bovine granulosa cells (bGCs) of preovulatory dominant follicle compared to subordinate counterpart at day 19 of the bovine estrous cycle. Other study also indicated the involvement of miR-424/503 cluster in tumour cell resistance to apoptosis suggesting this miRNA cluster may involve in cell survival. However, the role of miR-424/503 cluster in granulosa cell function remains elusive Therefore, this study aimed to investigate the role of miRNA-424/503 cluster in bGCs function using microRNA gain- and loss-of-function approaches.

RESULTS

The role of miR-424/503 cluster members in granulosa cell function was investigated by overexpressing or inhibiting its activity in vitro cultured granulosa cells using miR-424/503 mimic or inhibitor, respectively. Luciferase reporter assay showed that SMAD7 and ACVR2A are the direct targets of the miRNA-424/503 cluster members. In line with this, overexpression of miRNA-424/503 cluster members using its mimic and inhibition of its activity by its inhibitor reduced and increased, respectively the expression of SMAD7 and ACVR2A. Furthermore, flow cytometric analysis indicated that overexpression of miRNA-424/503 cluster members enhanced bGCs proliferation by promoting G1- to S- phase cell cycle transition. Modulation of miRNA-424/503 cluster members tended to increase phosphorylation of SMAD2/3 in the Activin signalling pathway. Moreover, sequence specific knockdown of SMAD7, the target gene of miRNA-424/503 cluster members, using small interfering RNA also revealed similar phenotypic and molecular alterations observed when miRNA-424/503 cluster members were overexpressed. Similarly, to get more insight about the role of miRNA-424/503 cluster members in activin signalling pathway, granulosa cells were treated with activin A. Activin A treatment increased cell proliferation and downregulation of both miRNA-424/503 members and its target gene, indicated the presence of negative feedback loop between activin A and the expression of miRNA-424/503.

CONCLUSION

This study suggests that the miRNA-424/503 cluster members are involved in regulating bovine granulosa cell proliferation and cell cycle progression. Further, miRNA-424/503 cluster members target the SMAD7 and ACVR2A genes which are involved in the activin signalling pathway.

De novo sequencing and comparative analysis of testicular transcriptome from different reproductive phases in freshwater spotted snakehead Channa punctatus

The spotted snakehead Channa punctatus is a seasonally breeding teleost widely distributed in the Indian subcontinent and economically important due to high nutritional value. The declining population of C. punctatus prompted us to focus on genetic regulation of its reproduction. The present study carried out de novo testicular transcriptome sequencing during the four reproductive phases and correlated differential expression of transcripts with various testicular events in C. punctatus. The Illumina paired-end sequencing of testicular transcriptome from resting, preparatory, spawning and postspawning phases generated 41.94, 47.51, 61.81 and 44.45 million reads, and 105526, 105169, 122964 and 106544 transcripts, respectively. Transcripts annotated using Rattus norvegicus reference protein sequences and classified under various subcategories of biological process, molecular function and cellular component showed that the majority of the subcategories had highest number of transcripts during spawning phase. In addition, analysis of transcripts exhibiting differential expression during the four phases revealed an appreciable increase in upregulated transcripts of biological processes such as cell proliferation and differentiation, cytoskeleton organization, response to vitamin A, transcription and translation, regulation of angiogenesis and response to hypoxia during spermatogenically active phases. The study also identified significant differential expression of transcripts relevant to spermatogenesis (mgat3, nqo1, hes2, rgs4, cxcl2, alcam, agmat), steroidogenesis (star, tkt, gipc3), cell proliferation (eef1a2, btg3, pif1, myo16, grik3, trim39, plbd1), cytoskeletal organization (espn, wipf3, cd276), sperm development (klhl10, mast1, hspa1a, slc6a1, ros1, foxj1, hipk1), and sperm transport and motility (hint1, muc13). Analysis of functional annotation and differential expression of testicular transcripts depending on reproductive phases of C. punctatus helped in developing a comprehensive understanding on genetic regulation of spermatogenic and steroidogenic events in seasonally breeding teleosts. Our findings provide the basis for future investigation on the precise role of testicular genes in regulation of seasonal reproduction in male teleosts.

A brief history of the search for the protein(s) involved in the acute regulation of steroidogenesis

The synthesis of steroid hormones occurs in specific cells and tissues in the body in response to trophic hormones and other signals. In order to synthesize steroids de novo, cholesterol, the precursor of all steroid hormones, must be mobilized from cellular stores to the inner mitochondrial membrane (IMM) to be converted into the first steroid formed, pregnenolone. This delivery of cholesterol to the IMM is the rate-limiting step in this process, and has long been known to require the rapid synthesis of a new protein(s) in response to stimulation. Although several possibilities for this protein have arisen over the past few decades, most of the recent attention to fill this role has centered on the candidacies of the proteins the Translocator Protein (TSPO) and the Steroidogenic Acute Regulatory Protein (StAR). In this review, the process of regulating steroidogenesis is briefly described, the characteristics of the candidate proteins and the data supporting their candidacies summarized, and some recent findings that propose a serious challenge for the role of TSPO in this process are discussed.

The Steroidogenic Acute Regulatory Protein (StAR) Is Regulated by the H19/let-7 Axis

The steroidogenic acute regulatory protein (StAR) governs the rate-limiting step in steroidogenesis, and its expression varies depending on the needs of the specific tissue. Tight control of steroid production is essential for multiple processes involved in reproduction, including follicular development, ovulation, and endometrial synchronization. Recently, there has been a growing interest in the role of noncoding RNAs in the regulation of reproduction. Here we demonstrate that StAR is a novel target of the microRNA let-7, which itself is regulated by the long noncoding RNA (lncRNA) H19. Using human and murine cell lines, we show that overexpression of H19 stimulates StAR expression by antagonizing let-7, which inhibits StAR at the post-transcriptional level. Our results uncover a novel mechanism underlying the regulation of StAR expression and represent the first example of lncRNA-mediated control of the rate-limiting step of steroidogenesis. This work thus adds to the body of literature describing the multiple roles in oncogenesis, cellular growth, glucose metabolism, and now regulation of steroidogenesis, of this complex lncRNA.

Endocrine Gland-Derived Vascular Endothelial Growth Factor/Prokineticin-1 in Cancer Development and Tumor Angiogenesis

A lot of data suggests endocrine gland-derived vascular endothelial growth factor (EG-VEGF) to be restricted to endocrine glands and to some endocrine-dependent organs. Many evidences show that EG-VEGF stimulates angiogenesis and cell proliferation, although it is not a member of the VEGF family. At the time, a lot of data regarding the role of this growth factor in normal development are available. However, controversial results have been published in the case of pathological conditions and particularly in malignant tumors. Thus, our present paper has been focused on the role of EG-VEGF in normal tissues and various malignant tumors and their angiogenic processes.

Characterization and Developmental Expression Profile of the Steroidogenic Acute Regulatory Protein (StAR) in the Gonad-Mesonephros Complex of Lithobates sylvaticus

The steroidogenic acute regulatory (StAR) protein is responsible for the movement of cholesterol across mitochondrial membranes and is therefore a key factor in regulating the timing and rate of steroidogenesis. In this study, we characterized the coding region of the star gene in the ranid Lithobates sylvaticus and studied star mRNA levels in steroidogenic tissues during development and under natural conditions. Our results support previous research showing that the StAR sequence is well conserved. We determined that star is expressed in both the interrenal and gonadal tissues of adults and in the tadpole gonad-mesonephros complex (GMC). The mRNA levels of star in the GMC were found to increase during tadpole development, reaching a maximum between Gosner stages (Gs) 32 and 38. We observed a significant drop in star mRNA levels at the end of prometamorphosis (Gs40-41), just before the start of the metamorphic climax. Significant differences in star levels between females and males, with males presenting higher levels than females, were detected at Gs36-38. To our knowledge, this is the first study that reports transitory star sex differences in tadpoles' developing GMC. Our results suggest an involvement of StAR in anuran late male GMC formation and development that requires further investigation.

New Insights in the Functional Zonation of the Canine Adrenal Cortex

BACKGROUND

Current understanding of adrenal steroidogenesis is that the production of aldosterone or cortisol depends on the expression of aldosterone synthase (CYP11B2) and 11β-hydroxylase cytochrome P450 (CYP11B1), respectively. However, this has never been studied in dogs, and in some species, a single CYP11B catalyzes both cortisol and aldosterone formation. Analysis of the canine genome provides data of a single CYP11B gene which is called CYP11B2, and a large sequence gap exists near the so-called CYP11B2 gene.

OBJECTIVES

To investigate the zonal expression of steroidogenic enzymes in the canine adrenal cortex and to determine whether dogs have 1 or multiple CYP11B genes.

ANIMALS

Normal adrenal glands from 10 healthy dogs.

METHODS

Zona fasciculata (zF) and zona glomerulosa (zG) tissue was isolated by laser microdissection. The mRNA expression of steroidogenic enzymes and their major regulators was studied with RT-qPCR. Southern blot was performed to determine whether the sequence gap contains a CYP11B gene copy. Immunohistochemistry (IHC) was performed for 17α-hydroxylase/17,20-lyase (CYP17).

RESULTS

Equal expression (P = .62) of the so-called CYP11B2 gene was found in the zG and zF. Southern blot revealed a single gene. CYP17 expression (P = .05) was significantly higher in the zF compared with the zG, which was confirmed with IHC.

CONCLUSIONS AND CLINICAL IMPORTANCE

We conclude that there is only 1 CYP11B gene in canine adrenals. The zone-specific production of aldosterone and cortisol is probably due to zone-specific CYP17 expression, which makes it an attractive target for selective inhibition of cortisol synthesis without affecting mineralocorticoid production in the zG.

Mixed germ cell-sex cord-stromal tumor with a concurrent interstitial cell tumor in a ferret

A 5-year-old male ferret presented with an enlarged canalicular testis in the left inguinal region. Microscopically, the enlarged testis consisted of a diffuse intimately admixed proliferation of c-kit-positive germ cell-like and Wilms tumor-1 protein-positive Sertoli cell-like components, but no Call-Exner body was detected. In addition, the compact proliferation of steroidogenic acute regulatory protein-intense positive interstitial cells was identified in a separate peripheral area of the mass. Based on histopathological and immunohistochemical findings, the tumor was diagnosed as a mixed germ cell-sex cord-stromal tumor with a concurrent interstitial cell tumor.

Developmental expression of translocator protein/peripheral benzodiazepine receptor in reproductive tissues

Translocator protein (TSPO) present in the outer mitochondrial membrane has been suggested to be critical for cholesterol import, a rate-limiting step for steroid hormone biosynthesis. Despite the importance of steroidogenesis in regulating reproductive functions, the developmental profile of TSPO expression in the gonads and accessory sex organs has not been completely characterized. As a first step towards understanding the function of TSPO, we studied its expression in male and female murine reproductive organs. We examined testes and ovaries at embryonic days 14.5 and 18.5, and postnatal days 0, 7, 14, 21 and 56 of development. In the adult testis, TSPO was expressed in both Leydig cells and Sertoli cells. In the developing testes TSPO expression was seen in immature Sertoli cells, fetal Leydig cells and gonocytes. In the ovary, TSPO was expressed in the ovarian surface epithelium, interstitial cells granulosa cells and luteal cells. Corpora lutea of ovaries from pregnant mice showed strong expression of TSPO. In the developing ovary, TSPO expression was seen in the squamous pregranulosa cells associated with germ line cysts, together with progressively increasing expression in interstitial cells and the ovarian surface epithelium. In adult mice, the epithelia of other reproductive tissues like the epididymis, prostate, seminal vesicle, oviduct and uterus also showed distinct patterns of TSPO expression. In summary, TSPO expression in both male and female reproductive tissues was not only restricted to steroidogenic cells. Expression in Sertoli cells, ovarian surface epithelium, efferent ductal epithelium, prostatic epithelium, seminal vesiclular epithelium, uterine epithelium and oviductal epithelium suggest either previously unknown sites for de novo steroidogenesis or functions for TSPO distinct from its well-studied role in steroid hormone production.

The emerging role of the molecular marker p27 in the differential diagnosis of adrenocortical tumors

Malignant adrenocortical tumors (ACTs) are rare and highly aggressive; conversely, benign tumors are common and frequently found incidentally (the so-called incidentalomas). Currently, the use of molecular markers in the diagnosis of ACTs is still controversial. The aim of this study was to analyze the molecular profile of different ACTs with the purpose of identifying markers useful for differentiating between these tumors. The ACTs that were studied (n=31) included nonfunctioning adenomas (ACAn)/incidentalomas (n=13), functioning adenomas with Cushing's syndrome (ACAc) (n=7), and carcinomas (n=11); normal adrenal glands (n=12) were used as controls. For each sample, the percentage area stained for the markers StAR, IGF2, IGF1R, p53, MDM2, p21, p27, cyclin D1, Ki-67, β-catenin, and E-cadherin was quantified using a morphometric computerized tool. IGF2, p27, cyclin D1, and Ki-67 were the markers for which the percentage of stained area was significantly higher in carcinoma samples than in adenoma samples. Ki-67 and p27 were the markers that exhibited the highest discriminative power for differential diagnosis between carcinomas and all type of adenomas, while IGF2 and StAR were only found to be useful for differentiating between carcinomas and ACAn and between carcinomas and ACAc respectively. The usefulness of Ki-67 has been recognized before in the differential diagnosis of malignant tumors. The additional use of p27 as an elective marker to distinguish benign ACTs from malignant ACTs should be considered.

Altered rhythm of adrenal clock genes, StAR and serum corticosterone in VIP receptor 2-deficient mice

The circadian time-keeping system consists of clocks in the suprachiasmatic nucleus (SCN) and in peripheral organs including an adrenal clock linked to the rhythmic corticosteroid production by regulating steroidogenic acute regulatory protein (StAR). Clock cells contain an autonomous molecular oscillator based on a group of clock genes and their protein products. Mice lacking the VPAC2 receptor display disrupted circadian rhythm of physiology and behaviour, and therefore, we using real-time RT-PCR quantified (1) the mRNAs for the clock genes Per1 and Bmal1 in the adrenal gland and SCN, (2) the adrenal Star mRNA and (3) the serum corticosterone concentration both during a light/dark (L/D) cycle and at constant darkness in wild type (WT) and VPAC2 receptor-deficient mice (VPAC2-KO). We also examined if PER1 and StAR were co-localised in the adrenal steroidogenic cells. Per1 and Bmal1 mRNA showed a 24-h rhythmic expression in the adrenal of WT mice under L/D and dark conditions. During a L/D cycle, the adrenal clock gene rhythm in VPAC2-KO mice was phase-advanced by approximately 6 h compared to WT mice and became arrhythmic in constant darkness. A significant 24-h rhythmic variation in the adrenal Star mRNA expression and circulating corticosterone concentration was similarly phase-advanced during the L/D cycle. The loss of adrenal clock gene rhythm in the VPAC2 receptor knockout mice after transfer into constant darkness was accompanied by disappearance of rhythmicity in Star mRNA expression and serum corticosterone concentration. Double immunohistochemistry showed that the PER1 protein and StAR were co-localised in the same steroidogenic cells. Circulating corticosterone plays a role in the circadian timing system and the misaligned corticosterone rhythm in the VPAC2 receptor knockout mice could be involved in their abnormal rhythms of physiology.

Translocator protein (Tspo) gene promoter-driven green fluorescent protein synthesis in transgenic mice: an in vivo model to study Tspo transcription

Translocator protein (TSPO), previously known as the peripheral-type benzodiazepine receptor, is a ubiquitous drug- and cholesterol-binding protein primarily found in the outer mitochondrial membrane as part of a mitochondrial cholesterol transport complex. TSPO is present at higher levels in steroid-synthesizing and rapidly proliferating tissues and its biological role has been mainly linked to mitochondrial function, steroidogenesis and cell proliferation/apoptosis. Aberrant TSPO levels have been linked to multiple diseases, including cancer, endocrine disorders, brain injury, neurodegeneration, ischemia-reperfusion injury and inflammatory diseases. Investigation of the functions of this protein in vitro and in vivo have been mainly carried out using high-affinity drug ligands, such as isoquinoline carboxamides and benzodiazepines and more recently, gene silencing methods. To establish a model to study the regulation of Tspo transcription in vivo, we generated a transgenic mouse model expressing green fluorescent protein (GFP) from Aequorea coerulescens under control of the Tspo promoter region (Tspo-AcGFP). The expression profiles of Tspo-AcGFP, endogenous TSPO and Tspo mRNA were found to be well-correlated. Tspo-AcGFP synthesis in the transgenic mice was seen in almost every tissue examined and as with TSPO in wild-type mice, Tspo-AcGFP was highly expressed in steroidogenic cells of the endocrine and reproductive systems, epithelial cells of the digestive system, skeletal muscle and other organs. In summary, this transgenic Tspo-AcGFP mouse model recapitulates endogenous Tspo expression patterns and could be a useful, tractable tool for monitoring the transcriptional regulation and function of Tspo in live animal experiments.

How to make a gonad: cellular mechanisms governing formation of the testes and ovaries

Sex determination of the gonad is an extraordinary process by which a single organ anlage is directed to form one of two different structures, a testis or an ovary. Morphogenesis of these two organs utilizes many common cellular events; differences in the timing and execution of these events must combine to generate sexually dimorphic structures. In this chapter, we review recent research on the cellular processes of gonad morphogenesis, focusing on data from mouse models. We highlight the shared cellular mechanisms in testis and ovary morphogenesis and examine the differences that enable formation of the two organs responsible for the perpetuation of all sexually reproducing species.

In vitro culture of precision-cut testicular tissue as a novel tool for the study of responses to LH

In vitro culture systems are valuable tools for investigating reproductive mechanisms in the testis. Here, we report the use of the precision-cut in vitro system using equine testicular slices. Testes were collected from immature light breed stallions (n=3) and cut into slices (mean slice weight= 13.85 ± 0.20 mg; mean slice thickness=515.00 ± 2.33 μm) using the precision-cut tissue-slicing method. Four tissue slices were placed on a grid floating on medium in individual vials. After a 1-h preincubation, they were exposed to medium containing ovine luteinizing hormone (oLH) at concentrations of 0, 5, 50, and 500 ng/ml for 6 h at 32 °C. Viability of the tissue was maintained based on histological integrity and lack of appreciable lactate dehydrogenase in the medium. The production and release of testosterone (T) and estradiol-17β (E2) into the medium was measured following in vitro culture. The addition of oLH increased T and E2 at least 400% and 120%, respectively, over the 0-ng oLH control cultures. Testicular gene expression was assessed with in situ hybridization methodology for steroidogenic acute regulatory protein (StAR protein), phosphodiesterase 3B (PDE3B), and outer dense fiber of sperm tails 2 (ODF2) mRNAs. In situ hybridization revealed an oLH concentration-dependent increase in the concentration of StAR protein mRNA in Leydig cells. No differences were observed for the expression of PDE3B or ODF2 genes in seminiferous tubules among treatment groups as expected. These results demonstrate the value of in vitro culture of the precision-cut tissue slices for studies of the regulation of steroidogenesis and gene expression in the stallion testes.

Minireview: roles of the forkhead transcription factor FOXL2 in granulosa cell biology and pathology

The forkhead transcription factor (FOXL2) is an essential transcription factor in the ovary. It is important in ovarian development and a key factor in female sex determination. In addition, FOXL2 plays a significant role in the postnatal ovary and follicle maintenance. The diverse transcriptional activities of FOXL2 are likely attributable to posttranslational modifications and binding to other key proteins involved in granulosa cell function. Mutations of FOXL2 lead to disorders of ovarian function ranging from premature follicle depletion and ovarian failure to unregulated granulosa cell proliferation leading to tumor formation. Thus, FOXL2 is a key regulator of granulosa cell function and a master transcription factor in these cells.

Effects of varicocele on testosterone, apoptosis and expression of StAR mRNA in rat Leydig cells

The aim of this study was to explore the effects of varicocele on the morphology and function of Leydig cells in the rat testis. Forty male Sprague-Dawley rats were divided into two groups: the experimental group underwent surgery to create a left varicocele (VC), and the control group underwent a sham operation. Serum testosterone and intratesticular testosterone levels were measured using a radioimmunoassay after 4 and 8 weeks of operation. Leydig cells were studied for apoptosis and expression of steroidogenetic acute regulatory (StAR) protein mRNA levels. Serum testosterone levels declined after 4 and 8 weeks of operation but were not significant (P>0.05). However, the intratesticular testosterone levels after 8 weeks were significantly decreased compared with the control group (P<0.01). The mean apoptosis index of Leydig cells in the experimental group was significantly higher than that in the control group after 4 or 8 weeks (P<0.01). StAR mRNA levels in the Leydig cells of the experimental group were significantly lower compared to those of the control group (P<0.01). Our data show that varicocele did impair Leydig cell function by increasing apoptosis and suppressing the expression of the StAR protein.

LATS1 phosphorylates forkhead L2 and regulates its transcriptional activity

Forkhead L2 (FOXL2) is expressed in the ovary and acts as a transcriptional repressor of the steroidogenic acute regulatory (StAR) gene, a marker of granulosa cell differentiation. Human FOXL2 mutations that produce truncated proteins lacking the COOH terminus result in blepharophimosis/ptosis/epicanthus inversus (BPES) syndrome type I, which is associated with premature ovarian failure (POF). In this study, we investigated whether FOXL2's activity as a transcriptional repressor is regulated by phosphorylation. We found that FOXL2 is phosphorylated at a serine residue and, using yeast two-hybrid screening, identified LATS1 as a potential FOXL2-interacting protein. LATS1 is a serine/threonine kinase whose deletion in mice results in an ovarian phenotype similar to POF. Using coimmunoprecipitation and kinase assays, we confirmed that LATS1 binds to FOXL2 and demonstrated that LATS1 phosphorylates FOXL2 at a serine residue. Moreover, we found that FOXL2 and LATS1 are coexpressed in developing mouse gonads and in granulosa cells of small and medium follicles in the mouse ovary. Last, we demonstrated that coexpression with LATS1 enhances FOXL2's activity as a repressor of the StAR promoter, and this results from the kinase activity of LATS1. These results provide novel evidence that FOXL2 is phosphorylated by LATS1 and that this phosphorylation enhances the transcriptional repression of the StAR gene, a marker of granulosa cell differentiation. These data support our hypothesis that phosphorylation of FOXL2 may be a control mechanism regulating the rate of granulosa cell differentiation and hence, follicle maturation, and its dysregulation may contribute to accelerated follicular development and POF in BPES type I.

Cellular cholesterol delivery, intracellular processing and utilization for biosynthesis of steroid hormones

Steroid hormones regulate diverse physiological functions such as reproduction, blood salt balance, maintenance of secondary sexual characteristics, response to stress, neuronal function and various metabolic processes. They are synthesized from cholesterol mainly in the adrenal gland and gonads in response to tissue-specific tropic hormones. These steroidogenic tissues are unique in that they require cholesterol not only for membrane biogenesis, maintenance of membrane fluidity and cell signaling, but also as the starting material for the biosynthesis of steroid hormones. It is not surprising, then, that cells of steroidogenic tissues have evolved with multiple pathways to assure the constant supply of cholesterol needed to maintain optimum steroid synthesis. The cholesterol utilized for steroidogenesis is derived from a combination of sources: 1) de novo synthesis in the endoplasmic reticulum (ER); 2) the mobilization of cholesteryl esters (CEs) stored in lipid droplets through cholesteryl ester hydrolase; 3) plasma lipoprotein-derived CEs obtained by either LDL receptor-mediated endocytic and/or SR-BI-mediated selective uptake; and 4) in some cultured cell systems from plasma membrane-associated free cholesterol. Here, we focus on recent insights into the molecules and cellular processes that mediate the uptake of plasma lipoprotein-derived cholesterol, events connected with the intracellular cholesterol processing and the role of crucial proteins that mediate cholesterol transport to mitochondria for its utilization for steroid hormone production. In particular, we discuss the structure and function of SR-BI, the importance of the selective cholesterol transport pathway in providing cholesterol substrate for steroid biosynthesis and the role of two key proteins, StAR and PBR/TSO in facilitating cholesterol delivery to inner mitochondrial membrane sites, where P450scc (CYP11A) is localized and where the conversion of cholesterol to pregnenolone (the common steroid precursor) takes place.

Tyrosine hydroxylase, chromogranin A, and steroidogenic acute regulator as markers for successful separation of human adrenal medulla

Progress in high throughput "-omic" techniques now allows the simultaneous measurement of expression levels of thousands of genes and promises the improved understanding of the molecular biology of diseases such as cancer. Detection of the dysfunction of molecular pathways in diseases requires healthy control tissue. This is difficult to obtain from pheochromocytomas (PHEOs), rare chromaffin tumors derived from adrenal medulla. The two options for obtaining adrenal tissue are: (1) whole organ removal post-mortem or during radical nephrectomy; (2) removal during PHEO surgery. Access to high quality normal adrenal tissue is limited. Removal of whole adrenals during nephrectomy is rare, because of improved surgical techniques. For adrenals removed post-mortem, the lag time to proper organ perfusion causes uncontrolled tissue degradation. Adjacent normal adrenal tissue can almost never be obtained from resected PHEOs, because they often replace the entire medulla or are well-encapsulated. If a margin of normal adrenal is attached to a resected PHEO, it seldom contains any medulla. The clean separation of medulla and cortex is further complicated, because their border is convoluted, and because adult adrenal consists of approximately 90% cortex. Thus, the quality of separation has to be evaluated with specific medullary and cortical markers. We describe the successful dissection of highly pure, medullary tissue from adrenals snap-frozen upon resection during radical nephrectomy or after brain death. Separation quality has been verified by quantitative reverse transcription with polymerase chain reaction for the medullary enzymes, tyrosine hydroxylase, and chromogranin A, and for the cortical enzyme, steroidogenic acute regulator.

Human forkhead L2 represses key genes in granulosa cell differentiation including aromatase, P450scc, and cyclin D2

FOXL2 is expressed in granulosa cells (GC) of small and medium ovarian follicles, functions as a repressor of the human steroidogenic acute regulatory gene, a marker of a GC differentiation, and its mutation is associated with premature ovarian failure (POF) in women with blepharophimosis-ptosis-epicanthus inversus syndrome (BPES), type I. We now report that FOXL2 also represses the transcription of aromatase, P450scc, and cyclin D2, three other key genes involved in GC proliferation, differentiation, and steroidogenesis, and that a FOXL2 mutation found in patients with BPES type I, also fails to repress aromatase transcription, further supporting a role for FOXL2 in follicle maturation.

Sumoylation of forkhead L2 by Ubc9 is required for its activity as a transcriptional repressor of the Steroidogenic Acute Regulatory gene

Forkhead L2 (FOXL2) is a member of the forkhead/hepatocyte nuclear factor 3 (FKH/HNF3) gene family of transcription factors and acts as a transcriptional repressor of the Steroidogenic Acute Regulatory (StAR) gene, a marker of granulosa cell differentiation. FOXL2 may play a role in ovarian follicle maturation and prevent premature follicle depletion leading to premature ovarian failure. In this study, we found that FOXL2 interacts with Ubc9, an E2-conjugating enzyme that mediates sumoylation, a key mechanism in transcriptional regulation. FOXL2 and Ubc9 are co-expressed in granulosa cells of small and medium ovarian follicles. FOXL2 is sumoylated by Ubc9, and this Ubc9-mediated sumoylation is essential to the transcriptional activity of FOXL2 on the StAR promoter. As FOXL2 is endogenous to granulosa cells, we generated a stable cell line expressing FOXL2 and found that activity of the StAR promoter in this cell line is greatly decreased in the presence of Ubc9. The sumoylation site was identified at lysine 25 of FOXL2. Mutation of lysine 25 to arginine leads to loss of transcriptional repressor activity of FOXL2. Taken together, we propose that Ubc9-mediated sumoylation at lysine 25 of FOXL2 is required for transcriptional repression of the StAR gene and may be responsible for controlling the development of ovarian follicles.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

Regulation of the steroidogenic acute regulatory protein gene expression: present and future perspectives

Steroid hormones are synthesized in the adrenal gland, gonads, placenta and brain and are critical for normal reproductive function and bodily homeostasis. The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroid biosynthesis, i.e. the delivery of cholesterol from the outer to the inner mitochondrial membrane. The expression of the StAR protein is predominantly regulated by cAMP-dependent mechanisms in the adrenal and gonads. Whereas StAR plays an indispensable role in the regulation of steroid biosynthesis, a complete understanding of the regulation of its expression and function in steroidogenesis is not available. It has become clear that the regulation of StAR gene expression is a complex process that involves the interaction of a diversity of hormones and multiple signaling pathways that coordinate the cooperation and interaction of transcriptional machinery, as well as a number of post-transcriptional mechanisms that govern mRNA and protein expression. However, information is lacking on how the StAR gene is regulated in vivo such that it is expressed at appropriate times during development and is confined to the steroidogenic cells. Thus, it is not surprising that the precise mechanism involved in the regulation of StAR gene has not yet been established, which is the key to understanding the regulation of steroidogenesis in the context of both male and female development and function.

The orphan nuclear receptor NUR77 regulates hormone-induced StAR transcription in Leydig cells through cooperation with Ca2+/calmodulin-dependent protein kinase I

Cholesterol transport in the mitochondrial membrane, an essential step of steroid biosynthesis, is mediated by a protein complex containing the steroidogenic acute regulatory (StAR) protein. The importance of this transporter is underscored by mutations in the human StAR gene that cause lipoid congenital adrenal hyperplasia, male pseudohermaphroditism, and adrenal insufficiency. StAR transcription in steroidogenic cells is hormonally regulated and involves several transcription factors. The nuclear receptor NUR77 is present in steroidogenic cells, and its expression is induced by hormones known to activate StAR expression. We have now established that StAR transcription in cAMP-stimulated Leydig cells requires de novo protein synthesis and involves NUR77. We found that cAMP-induced NUR77 expression precedes that of StAR both at the mRNA and protein levels in Leydig cells. In these cells, small interfering RNA-mediated NUR77 knockdown reduces cAMP-induced StAR expression. Chromatin immunoprecipitation assays revealed a cAMP-dependent increase in NUR77 recruitment to the proximal StAR promoter, whereas transient transfections in MA-10 Leydig cells confirmed that NUR77 can activate the StAR promoter and that this requires an element located at -95 bp. cAMP-induced StAR and NUR77 expression in Leydig cells was found to require a Ca2+/calmodulin-dependent protein kinase (CaMK)-dependent signaling pathway. Consistent with this, we show that within the testis, CaMKI is specifically expressed in Leydig cells. Finally, we report that CaMKI transcriptionally cooperates with NUR77, but not steroidogenic factor 1, to further enhance StAR promoter activity in Leydig cells. All together, our results implicate NUR77 as a mediator of cAMP action on StAR transcription in steroidogenic Leydig cells and identify a role for CaMKI in this process.

An essential component in steroid synthesis, the steroidogenic acute regulatory protein, is expressed in discrete regions of the brain

Recent data implicate locally produced steroids, termed neurosteroids, as regulators of neuronal function. Adrenal and gonadal steroidogenesis is controlled by changes in the steroidogenic acute regulatory protein (StAR); however, little is known about the regulation of neurosteroid production. We now demonstrate unequivocally that StAR mRNA and protein are expressed within glia and neurons in discrete regions of the mouse brain, and that glial StAR expression is inducible. Consistent with a role in de novo neurosteroidogenesis, StAR colocalizes with the cholesterol side-chain cleavage enzyme P450(scc) in both mouse and human brains. These data support a role for StAR in the production of neurosteroids and identify potential sites of active de novo steroid synthesis in the brain.