A novel post-transcriptional mechanism of regulation of luteinizing hormone receptor expression by an RNA binding protein from the ovary

miR-122 Regulates LHR Expression in Rat Granulosa Cells by Targeting Insig1 mRNA

Luteinizing hormone/chorionic gonadotropin receptor (LHR) expression in the ovary is regulated by a messenger RNA (mRNA) binding protein, which specifically binds to the coding region of LHR mRNA. We have shown that miR-122, a short noncoding RNA, mediates LHR mRNA levels by modulating the expression of LHR mRNA-binding protein (LRBP) through the regulation of sterol regulatory element binding protein (SREBP) activation. The present results show that miR-122 regulates LRBP levels by increasing the processing of SREBP through the degradation of Insig1, the anchoring protein of SREBP. We present evidence showing that mRNA and protein levels of Insig1 undergo a time-dependent increase following the treatment of rat granulosa cells with follicle-stimulating hormone (FSH), which leads to a decrease in LRBP levels. Furthermore, overexpression of miR-122 using an adenoviral vector (AdmiR-122) abolished FSH-induced increases in Insig1 mRNA and protein. We further confirmed the role of Insig1 by showing that inhibition of Insig1 using a specific small interfering RNA prior to FSH treatment resulted in the abrogation of LHR upregulation. Silencing of Insig1 also reversed FSH-mediated decreases in SREBP and LRBP activation. These results show that decreased levels of miR-122 increase Insig1 and suppress SREBP processing in response to FSH stimulation of rat granulosa cells.

Profile of follitropin alpha/lutropin alpha combination for the stimulation of follicular development in women with severe luteinizing hormone and follicle-stimulating hormone deficiency

A severe gonadotropin deficiency together with chronic estradiol deficiency leading to amenorrhea characterizes patients suffering from hypogonadotropic hypogonadism. Administration of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to these patients has been shown to be essential in achieving successful stimulation of follicular development, ovulation, and rescue of fertility. In recent years, the availability of both recombinant FSH (rFSH) and recombinant LH (rLH) has provided a new therapeutic option for the stimulation of follicular growth in hypopituitary–hypogonadotropic women (World Health Organization Group I). In this article, we review the data reported in the literature to highlight the role and the efficacy of using recombinant gonadotropins, rFSH and rLH, in the treatment of women with severe LH/FSH deficiency. Although the studies on this issue are limited and the experiences available in the literature are few due to the small number of such patients, it is clearly evident that the recombinant gonadotropins rFSH and rLH are efficient in treating patients affected by hypogonadotropic hypogonadism. The results observed in the studies reported in this review suggest that recombinant gonadotropins are able to induce proper follicular growth, oocyte maturation, and eventually pregnancy in this group of women. Moreover, the clinical use of recombinant gonadotropins in this type of patients has given more insight into some endocrinological aspects of ovarian function that have not yet been fully understood.

Eukaryotic initiation factor 5A plays an essential role in luteinizing hormone receptor regulation

Down-regulation of LH receptor (LHR) in the ovary by its ligand is mediated by a specific RNA-binding protein, designated LH receptor mRNA-binding protein (LRBP), through translational suppression and mRNA degradation. Using yeast 2-hybrid screens, we previously identified eukaryotic initiation factor 5A (eIF5A) as one of the proteins that interacts with LRBP during LHR mRNA down-regulation. The present study examined the role of eIF5A and its hypusination in the context of LHR mRNA down-regulation. The association of eIF5A with LRBP or LHR mRNA was determined using immunoprecipitation and RNA immunoprecipitation assays. The results showed that the association of eIF5A with the LHR mRNA-LRBP complex increased significantly during down-regulation. Furthermore, gel fractionation and the hypusination activity assay both showed increased hypusination of eIF5A during LHR mRNA down-regulation. Abolishment of hypusination by pretreatment with the chemical inhibitor GC7 prevented the association of eIF5A with LHR mRNA and LRBP. Inhibition of hypusination also reduced the extent of ligand-induced down-regulation of LHR mRNA as well as the expression of functional LHRs assessed by real-time PCR and (125)I-human chorionic gonadotropin (hCG) binding assays, respectively. The loss of human chorionic gonadotropin-mediated downstream signaling during LHR down-regulation was also restored by inhibition of hypusination of eIF5A. Thus, the present study, for the first time, reveals the crucial role of eIF5A and its hypusination in the regulation of LHR expression in the ovary.

A review of luteinising hormone and human chorionic gonadotropin when used in assisted reproductive technology

Gonadotropins extracted from the urine of post-menopausal women have traditionally been used to stimulate folliculogenesis in the treatment of infertility and in assisted reproductive technology (ART). Products, such as human menopausal gonadotropin (hMG), consist not only of a mixture of the hormones, follicle-stimulating hormone (FSH), luteinising hormone (LH) and human chorionic gonadotropin (hCG), but also other biologically active contaminants, such as growth factors, binding proteins and prion proteins. The actual amount of molecular LH in hMG preparations varies considerably due to the purification process, thus hCG, mimicking LH action, is added to standardise the product. However, unlike LH, hCG plays a different role during the natural human menstrual cycle. It is secreted by the embryo and placenta, and its main role is to support implantation and pregnancy. More recently, recombinant gonadotropins (r-hFSH and r-hLH) have become available for ART therapies. Recombinant LH contains only LH molecules. In the field of reproduction there has been controversy in recent years over whether r-hLH or hCG should be used for ART. This review examines the existing evidence for molecular and functional differences between LH and hCG and assesses the clinical implications of hCG-supplemented urinary therapy compared with recombinant therapies used for ART.

The effect of luteal phase progesterone supplementation on natural frozen-thawed embryo transfer cycles

Objective

To evaluate the effect of progesterone supplementation during the luteal phase on pregnancy outcome in natural frozen-thawed embyo transfer (FTET) cycles.

Methods

In this retrospective cohort study, 228 consecutive patients who underwent FTET cycles between January 2009 and September 2012 were included. One hundred forty-five patients received luteal progesterone support (P group) but 83 patients did not receive any progesterone supplementation during luteal phase (control group).

Results

There were no differences in patients' characteristics between the two groups. The two groups were similar with respect to the characteristics of previous fresh in vitro fertilization cycle in which embryos were cryopreserved including the numbers of oocytes retrieved, mature oocytes, fertilized oocytes, grade 1 or 2 embryos and frozen embryos. Also, significant differences were not observed between the P and control groups in clinical pregnancy rate, embryo implantation rate and multiple pregnancy rate. However, miscarriage rate was significantly lower in the P group and live birth rate was significantly higher in the P group than in the control group (P<0.05, P<0.05).

Conclusion

Our results suggest that luteal phase progesterone supplementation decreases miscarriage rate and improves live birth rate in natural FTET cycles.

Gene expression profiles of cumulus cells obtained from women treated with recombinant human luteinizing hormone + recombinant human follicle-stimulating hormone or highly purified human menopausal gonadotropin versus recombinant human follicle-stimulating hormone alone

OBJECTIVE

To evaluate cumulus cell (CC) expression profile modulation after different stimulation protocols.

DESIGN

CCs transcriptome variations were evaluated by microarray in patients undergoing different treatments for ovarian stimulation, namely, r-hLH + r-hFSH and hp-hMG, compared with a control group treated with r-hFSH.

SETTING

Healthy patients undergoing assisted reproduction protocols.

PATIENT(S)

Sixteen healthy women with regular cycles and tubal disease or unexplained infertility.

INTERVENTION(S)

Four patients received hp-hMG, four received r-hFSH + r-hLH, and eight received r-hFSH daily. Aspiration of the oocytes was performed 36 hours after hCG administration. Only samples derived from cumulus-oocyte complexes containing mature oocytes showing polar body were processed.

MAIN OUTCOME MEASURE(S)

Comparison of genes differentially expressed in both treatment groups with the use of a hierarchic clustering analysis.

RESULT(S)

Data clustering analysis allowed detection of four clusters containing genes differentially expressed in both treatment groups compared with control. Functional analysis of the affected transcripts revealed genes involved in oocyte development and maturation.

CONCLUSION(S)

r-hLH and hCG, though acting on the same receptor, produce a differential activation of intracellular pathways. It can be hypothesized that this effect depends on their different structures and specific binding affinity for the receptor.

Association of luteinizing hormone receptor (LHR) mRNA with its binding protein leads to decapping and degradation of the mRNA in the p bodies

Luteinizing hormone receptor undergoes downregulation during preovulatory Luteinizing hormone surge through a post-transcriptional mechanism involving an RNA binding protein designated as LRBP. The present study examined the mechanism by which LRBP induces the degradation of Luteinizing hormone receptor mRNA, specifically the role of decapping of Luteinizing hormone receptor mRNA and the translocation of LRBP-bound Luteinizing hormone receptor mRNA to degradative machinery. Immunoprecipitation of the complex with the 5'cap structure antibody followed by real time PCR analysis showed progressive loss of capped Luteinizing hormone receptor mRNA during downregulation suggesting that Luteinizing hormone receptor mRNA undergoes decapping prior to degradation. RNA immunoprecipitation analysis confirmed dissociation of eukaryotic initiation factor 4E from the cap structure, a step required for decapping. Furthermore, RNA immunoprecipitation analysis using antibody against the p body marker protein, DCP1A showed that Luteinizing hormone receptor mRNA was associated with the p bodies, the cytoplasmic foci that contain RNA degradative enzymes and decapping complex. Immunohistochemical studies using antibodies against LRBP and DCP1A followed by confocal analysis showed colocalization of LRBP with DCP1A during downregulation. This was further confirmed by co-immunoprecipitation of LRBP with DCP1A. The association of LRBP and Luteinizing hormone receptor mRNA in the p bodies during downregulation was further confirmed by examining the association of a second p body component, rck/p54, using immunoprecipitation and RNA immunoprecipitation respectively. These data suggest that the association of LRBP with Luteinizing hormone receptor mRNA results in the translocation of the messenger ribonucleoprotein complex to the p bodies leading to decapping and degradation.

Efficacy of different gonadotropin combinations to support ovulation induction in WHO type I anovulation infertility: clinical evidences of human recombinant FSH/human recombinant LH in a 2:1 ratio and highly purified human menopausal gonadotropin stimulation protocols

BACKGROUND

The World Helath Organization (WHO) Group I anovulation, or hypogonadotropic hypogonadism (HH), is characterized by reduced hypothalamic/pituitary activity which results in abnormally low serum FSH and LH levels and negligible estrogen activity.

AIM

To compare the efficacy of human recombinant FSH (r-hFSH) plus human recombinant LH (r-hLH) in a 2:1 ratio with highly purified human menopausal gonadotropin (hMG-HP) urinary extract, containing LH-like activity, in women with HH.

SUBJECTS AND METHODS

This two-arm randomized open-label study included 35 HH women (aged 25-36 yr) attending our Center. Eighteen patients received 150 IU hMG-HP (150 IU FSH + 150 IU LH-like activity) and seventeen received 150IU r-hFSH/75IU rhLH daily for a maximum of 16 days. Ovulation was induced by a single administration of hCG on the day after the last hMG-HP or r-hFSH/r-hLH.

RESULTS

The primary efficacy endpoint was ovulation induction as measured by follicle ≥17 mm, pre-ovulatory estradiol (E 2 ) ≥400 pmol/l and mid-luteal phase progesterone (P 4 ) ≥25 nmol/l. Secondary efficacy endpoints included E 2 levels/follicle at mid-cycle, number of follicles at mid-cycle and pregnancy rate (PR). Following a total of 70 cycles, 70% of r-hFSH/r-hLH treated patients met the primary endpoint vs 88% in hMG-HP group (p=0.11). However, PR in r-hFSH/r-hLH group was 55.6% compared to 23.3% in hMG-HP group (p=0.01).

CONCLUSIONS

The primary endpoint achievement did not correlate with PR. This study has shown the superiority of LH compared to hCG in supporting FSH-induced follicular development in HH women.

Revisiting the role of hCG: new regulation of the angiogenic factor EG-VEGF and its receptors

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF) is an angiogenic factor reported to be specific for endocrine tissues, including the placenta. Its biological activity is mediated via two G protein-coupled receptors, prokineticin receptor 1 (PROKR1) and prokineticin receptor 2 (PROKR2). We have recently shown that (i) EG-VEGF expression peaks between the 8th and 11th weeks of gestation, (ii) its mRNA and protein levels are up-regulated by hypoxia, (iii) EG-VEGF is a negative regulator of trophoblast invasion and (iv) its circulating levels are increased in preeclampsia (PE), the most threatening pathology of pregnancy. Here, we investigated the regulation of the expression of EG-VEGF and its receptors by hCG, a key pregnancy hormone that is also deregulated in PE. During the first trimester of pregnancy, hCG and EG-VEGF exhibit the same pattern of expression, suggesting that EG-VEGF is potentially regulated by hCG. Both placental explants (PEX) and primary cultures of trophoblasts from the first trimester of pregnancy were used to investigate this hypothesis. Our results show that (i) LHCGR, the hCG receptor, is expressed both in cyto- and syncytiotrophoblasts, (ii) hCG increases EG-VEGF, PROKR1 and PROKR2 mRNA and protein expression in a dose- and time-dependent manner, (iii) hCG increases the release of EG-VEGF from PEX conditioned media, (iv) hCG effects are transcriptional and post-transcriptional and (v) the hCG effects are mediated by cAMP via cAMP response elements present in the EG-VEGF promoter region. Altogether, these results demonstrate a new role for hCG in the regulation of EG-VEGF and its receptors, an emerging regulatory system in placental development.

Current opinion on use of luteinizing hormone supplementation in assisted reproduction therapy: an Asian perspective

LH and FSH have complementary functions in ensuring optimal oocyte maturation and ovulation. In women undergoing assisted reproduction technology protocols with gonadotrophin-releasing hormone analogues, LH and FSH concentrations are reduced. While FSH use in assisted reproduction technology is well established, there is no published consensus on the need for exogenous LH in Asian patients. Having reviewed the concept of the LH therapeutic window and differences between recombinant human LH (r-HLH) and human menopausal gonadotrophin, a consensus was reached on which patient subgroups may benefit from LH supplementation. Adjuvant r-HLH gives clinicians precise control over the dose of LH bioactivity administered to target the therapeutic window. The use of r-HLH is recommended in women with poor response in a previous cycle or suboptimal follicular progression in a current cycle by day 6-8 of stimulation. r-HLH should also be considered in women at risk of suboptimal response, specifically age > 35 years. Other risk markers that suggest the need for LH supplementation, which include baseline/day-6 serum LH and anti-Müllerian hormone concentrations, antral follicle count and LH polymorphisms require further research and verification. For measurement of LH response adequacy, the monitoring of follicular progression, oestradiol concentrations and endometrial thickness is recommended.

The differential transcriptome and ontology profiles of floating and cumulus granulosa cells in stimulated human antral follicles

Communication between various ovarian cell types is a prerequisite for folliculogenesis and ovulation. In antral follicles granulosa cells divide into two distinct populations of mural and cumulus granulosa cells (CGC), enveloping the antrum and surrounding the oocyte, respectively. Both cell types, with the mural compartment in excess, contribute to the floating granulosa cell (FGC) population in the follicular fluid. The aim of this study was to compare the transcriptomes of FGC and CGC in stimulated antral follicles obtained from 19 women undergoing IVF-ICSI procedure. FGC were obtained from follicular fluid during the follicle puncture procedure and CGC were acquired after oocyte denudation for micromanipulation. Gene expression analysis was conducted using the genome-wide Affymetrix transcriptome array. The expression profile of the two granulosa cell populations varied significantly. Out of 28 869 analysed transcripts 4480 were differentially expressed (q-value < 10(-4)) and 489 showed > or =2-fold difference in the expression level with 222 genes up-regulated in FGC and 267 in CGC. The transcriptome of FGC showed higher expression of genes involved in immune response, hematological system function and organismal injury, although CGC had genes involved in protein degradation and nervous system function up-regulated. Cell-to-cell signalling and interaction pathways were noted in both cell populations. Furthermore, numerous novel transcripts that have not been previously described in follicular physiology were identified. In conclusion, our results provide a solid basis for future studies in follicular biology that will help to identify molecular markers for oocyte and embryo viability in IVF.

Evidence for the association of luteinizing hormone receptor mRNA-binding protein with the translating ribosomes during receptor downregulation

Luteinizing hormone receptor (LHR) mRNA is post-transcriptionally regulated during ligand-induced downregulation. This process involves interaction of LHR mRNA with a specific mRNA-binding protein (LRBP), identified as mevalonate kinase (MVK), resulting in inhibition of translation followed by targeting the ribonucleoprotein complex to accelerated degradation. The present study investigated the endogenous association of LRBP with the translational machinery and its interaction with LHR mRNA during LH/hCG-induced downregulation. Ovaries were collected from rats that were injected with the ligand, hCG, to induce downregulation of LHR mRNA expression. Western blot analysis showed significantly higher levels of LRBP in polysomes from downregulated ovaries compared to controls. Western blot analysis of ribosome-rich fractions from FPLC-assisted gel filtration of post-mitochondrial supernatants confirmed the presence of LRBP in translating ribosomes isolated from the downregulated state but not from controls. The association of LRBP with LHR mRNA in the downregulated polysomes was demonstrated by immunoprecipitation with LRBP antibody followed by qPCR analysis of the associated RNA. Increased association of LHR mRNA with LRBP during downregulation was also demonstrated by subjecting the polysome-associated RNAs to oligo(dT) cellulose chromatography followed by immunoprecipitation and qPCR analysis. Additionally, analysis of in vitro translation of LHR mRNA showed increased inhibition of translation by polysomes from downregulated ovaries compared to control. This study provides strong in vivo and in vitro evidence to show that during ligand-induced downregulation, LRBP translocates to ribosomes and associates with LHR mRNA to form an untranslatable ribonucleoprotein complex and inhibits LHR mRNA translation, paving the way to its degradation.

Role of Dicer in female fertility

Dicer is an RNAse III endonuclease that is essential for the biogenesis of microRNAs and small interfering RNAs. These small RNAs post-transcriptionally regulate mRNA gene expression through several mechanisms to affect key cellular events including proliferation, differentiation and apoptosis. Recently, the role of Dicer function in female reproductive tissues has begun to be elucidated through the use of knockout mouse models. Loss of Dicer within ovarian granulosa cells, luteal tissue, oocyte, oviduct and, potentially, the uterus renders females infertile. This review discusses these early studies and other data describing the current understanding of microRNAs and small interfering RNAs in female reproduction.

Expression of gonadotropin and gonadotropin receptor genes during early sexual maturation in male Atlantic salmon parr

Atlantic salmon males may mature already as small parr in freshwater. Sexual maturation in teleosts as in vertebrates is characterized by the activation of the brain-pituitary-gonad axis. The endocrine regulation of early puberty is still not well understood. In the present study, one-summer-old male Atlantic salmon parr were sampled regularly from December several months prior to the beginning of spermatogenesis until spawning in October. Pituitary expression levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) beta subunit genes were analyzed in parallel with testis expression of FSH receptor (FSHR) and LH receptor (LHR) genes by RT-PCR and plasma 11-ketostestosterone (11-KT) was measured. Expression levels of FSHbeta, low during winter and spring started to increase prior to the onset of gonadal growth at the end of May while LHbeta mRNA levels were hardly detectable. Both gonadotropin receptor genes were expressed in immature testis with FSHR transcripts being more abundant (8-fold). FSHR transcript levels increased in parallel to FSHbeta levels from early spermatogenesis onwards, while LHR mRNA started to increase prior to any large changes in LHbeta expression. Both transcript levels of LHbeta and LHR were highest during spermiation. Plasma 11-KT increased at the beginning of spermatogenesis reaching highest levels at spermiogenesis suggesting a possible role of FSH in inducing 11-KT production during early spermatogenesis while LH stimulates via its specific receptor 11-KT production at spermiogenesis. The commitment into sexual maturation appears to be dependant on both the presence of FSHR in immature testis and the increase of FSH expression.

The gonadotropin receptors FSH-R and LH-R of Atlantic halibut (Hippoglossus hippoglossus), 1: isolation of multiple transcripts encoding full-length and truncated variants of FSH-R

As a first step towards understanding the regulatory mechanisms underlying the asynchronous oogenesis in repetitive spawning fish, full-length cDNAs encoding the receptors for follicle stimulating hormone (FSH-R) and luteinizing hormone (LH-R) were isolated from the gonads of the flatfish Atlantic halibut (Hippoglossus hippoglossus). The predicted halibut FSH-R and LH-R of 664 and 698 amino acids, respectively, both contain the characteristic features of a large extracellular (EC) domain, a hepta-helical transmembrane (TM) domain, and a short cytoplasmic C-terminal tail. Halibut FSH-R and LH-R share only 42% overall sequence identity mostly due to low homology in the ligand-binding EC domain. Both receptors show high sequence identity to their orthologs of Nile tilapia, but seem to be more remotely related to the receptors in catfish, zebrafish and salmonids. In contrast to the intron-less TM domain of almost all vertebrate gonadotropin receptors, three introns were identified in this domain of halibut FSH-R, thus resembling the gene structure of Drosophila glycoprotein hormone receptor type I. The FSH-R pre-mRNA was shown to be processed in alternative ways by isolating two different transcripts encoding the complete receptor and four alternative spliced transcripts encoding different truncated receptor variants. Based on the DNA sequence variation and chromosomal organization of the gonadotropin receptors in several teleosts, we propose that the encoding genes have been duplicated in the fish lineage.

The gonadotropin receptors FSH-R and LH-R of Atlantic halibut (Hippoglossus hippoglossus)--2. Differential follicle expression and asynchronous oogenesis

The biological activity and spatio-temporal expression patterns of the gonadotropin receptors FSH-R and LH-R were examined in the repetitive spawner Atlantic halibut to elucidate the gonadotropic regulation of the asynchronous follicle development. The cloned receptors were expressed in mammalian COS-7 cells, and stimulation with sea bass FSH and LH increased the cAMP production. The halibut FSH-R and LH-R genes were shown to be highly expressed in the gonads of sexually mature fish, but the transcripts were also found in extra-gonadal tissues such as pituitary and brain. Different expression patterns of FSH-R and LH-R in the developing follicles were documented by semi-quantitative RT-PCR. Abundant FSH-R mRNA was found in the small follicles during primary growth and vitellogenesis, and the signals were localized to the granulosa cells by in situ hybridization. In contrast, follicular LH-R mRNA was hardly detectable during the early stages. Conversely, in follicles during final maturation FSH-R mRNA levels tended to decrease, while the expression of LH-R was highly upregulated. Whereas the pituitary FSH and LH are asynchronously expressed in annual spawners, both gonadotropins were expressed in the female halibut pituitary throughout the reproductive cycle, except in the prespawning females. Hence, the sequential gonadotropic activation of ovarian follicle growth and maturation in repetitive spawners is probably regulated by modulating the temporal expression of FSH-R and LH-R in the follicle membrane.

Pulsatile luteinizing hormone amplitude and progesterone metabolite excretion are reduced in obese women

CONTEXT

Female obesity is linked to abnormal menstrual cycles, infertility, reproductive wastage, and deficient LH, FSH, and progesterone secretion.

OBJECTIVE AND DESIGN

To elucidate the reproductive defects associated with obesity, we sampled 18 eumenorrheic (nonpolycystic ovary syndrome) women with a mean +/- sem body mass index of 48.6 +/- 1.4 kg/m2 with daily, first morning voided urine collections, seven of whom also had early follicular phase 12-h, every 10-min blood sampling to assess LH pulses. Daily hormones were compared with 11 eumenorrheic, normal-weight controls. A separate control group of 12 eumenorrheic, normal-weight women was used for the LH pulse studies.

MAIN OUTCOME MEASURES

Assays for LH (serum and urine) and FSH, and estradiol and progesterone metabolites (estrone conjugate and pregnanediol glucuronide; urine) were performed. Daily hormones were meaned and normalized to a 28-d cycle length. LH pulsations were determined using two objective methods. Group means were compared using t tests.

RESULTS

Reduced whole-cycle mean, normalized pregnanediol glucuronide was observed in obese (38.2 +/- 2.1 microg/mg creatine) compared with normal-weight women (181.3 +/- 35.1 microg/mg creatine; P = 0.002), without significant differences in LH, FSH, or estrone conjugate. Early follicular phase LH pulse frequency did not differ from normal-weight women, but both amplitude and mean LH were dramatically reduced in obese women (0.8 +/- 0.1 and 2.0 +/- 0.3 IU/liter) compared with controls (1.6 +/- 0.2 and 3.4 +/- 0.2 IU/liter; P < 0.01).

CONCLUSIONS

A novel defect in the amplitude but not the frequency of LH pulsations appears to underlie the reproductive phenotype of obesity. The deficit in pregnanediol glucuronide appears to exceed the deficit in LH. The patterns of hypothalamic-pituitary-ovarian axis function unique to the obese state differ from other abnormal reproductive states.

Luteinizing hormone receptor mediates neuronal pregnenolone production via up-regulation of steroidogenic acute regulatory protein expression

The functional consequences of luteinizing hormone/human chorionic gonadotropin signaling via neuronal luteinizing hormone/human chorionic gonadotropin receptors expressed throughout the brain remain unclear. A primary function of luteinizing hormone (LH) in the gonads is the stimulation of sex steroid production. As LH can cross the blood-brain barrier, present in cerebrospinal fluid and is expressed by neuronal cells, we tested whether LH might also modulate steroid synthesis in the brain. Treatment of differentiated rat primary hippocampal neurons and human M17 neuroblastoma cells with LH (100 mIU/mL) resulted in a twofold increase in pregnenolone secretion in both cell types, suggesting an increase in P450scc-mediated cleavage of cholesterol to pregnenolone and its secretion from neurons. To explore how LH might regulate the synthesis of pregnenolone, the precursor for steroid synthesis, we treated rat primary hippocampal neurons with LH (0, 10 and 100 mIU/mL) and measured changes in the expression of LH receptor and steroidogenic acute regulatory protein (StAR). LH induced a rapid (within 30 min) increase in the expression of StAR, but induced a dose-dependent decrease in LH receptor expression. Consistent with these results, the suppression of serum LH in young rats treated with leuprolide acetate for 4 months down-regulated StAR expression, but increased LH receptor expression in the brain. Taken together, these results indicate that LH induces neuronal pregnenolone production by modulating the expression of the LH receptor, increasing mitochondrial cholesterol transport and increasing P450scc-mediated cleavage of cholesterol for pregnenolone synthesis and secretion.