Prostaglandin F(2alpha) induces a rapid decline in progesterone production and steroidogenic acute regulatory protein expression in isolated rat corpus luteum without altering messenger ribonucleic acid expression

Moringa oleifera leaf ethanolic extract benefits cashmere goat semen quality via improving rumen microbiota and metabolome

Background

Artificial insemination (AI) is an effective reproductive technique to improve the performance of cashmere goats and prevent the spread of diseases, and the quality of the semen determines the success of AI. The potential of Moringa oleifera leaf powder (MOLP) and Moringa oleifera leaf ethanolic extract (MOLE) to improve semen quality has been reported, but the underlying mechanisms remain unclear. For the purpose, 18 mature male cashmere goats were randomly assigned into three groups: the control (CON), MOLP, and MOLE groups. The CON group received distilled water orally; the MOLP group was orally treated with 200 mg/kg body weight (BW) MOLP; and the MOLE group was orally treated with 40 mg/kg BW MOLE.

Results

Results showed that MOLE contained long-chain fatty acids and flavonoids. Treatment with MOLP and MOLE increased the activities of the serum catalase, superoxide dismutase, and glutathione peroxidase (P < 0.05), enhanced the total antioxidant capacity (P < 0.05), and reduced the serum malondialdehyde level (P < 0.05). At the same time, MOLE increased the contents of serum gonadotropin releasing hormone and testosterone (P < 0.05). Moreover, MOLE significantly increased sperm concentration, motility, and viability (P < 0.05). Meanwhile, MOLE raised the Chao1 index (P < 0.05) and altered the composition of the rumen microbiota; it also raised the relative abundance of Treponema (P < 0.05) and Fibrobacter (P < 0.05) and reduced the relative abundance of Prevotella (P < 0.1). Correlation analysis revealed the genus Prevotella was significantly negatively correlated with sperm concentration, as well as sperm motility and viability. Furthermore, MOLE significantly increased the rumen levels of the steroid hormones testosterone and dehydroepiandrosterone (P < 0.05), as well as the polyunsaturated fatty acids (PUFAs) alpha-Linolenic acid, gamma-Linolenic acid, docosapentaenoic acid, and 9-S-Hydroperoxylinoleicacid (P < 0.05).

Conclusions

Oral MOLE supplementation can improve semen quality by increasing the antioxidant capacity and altering the rumen microbiota and metabolites of cashmere goats. Moreover, the MOLP supplementation could enhance the antioxidant capacity of cashmere goats.

Effects of omega-3 polyunsaturated fatty acids on cellular development in human ovarian granulosa tumor cells (KGN)

Emerging research has shown that polyunsaturated fatty acids (PUFAs) benefit human health and exert anti-cancer effects. However, there is little understanding of the specific mechanisms by which PUFAs regulate the cells of the ovarian granulosa tumor. In the current study, we investigate the effects and the possible mechanisms of PUFAs on human ovarian tumor cells development. KGN cells were treated with omega-3. Small interfering (siRNA) and specific activator were used to knock down and overexpress gene expression in KGN cells. The protein content levels were analyzed by Western blot. Cell viability, proliferation and apoptosis assay were performed to examine the cellular development. And the level of glucose uptake in KGN cells were assessed by 2-DG measurement. The results showed that omega-3 treatment reduced cell viability, proliferation and increased cell apoptosis. Further studies showed that omega-3 also reduced GLUT1/4 protein content and cellular glucose uptake. Subsequent knockdown and overexpression of OCT4 using Oct4 siRNA and O4I2 (OCT4 activator) showed that OCT4 was involved in the regulations of omega-3 on GLUT1/4 expression and cell development. Our data demonstrate that omega-3 inhibits cellular development by down-regulating GLUT1/4 expression and glucose uptake in KGN cells, which are mediated through OCT4.

Roles of different n-3/n-6 PUFA ratios in ovarian cell development and steroidogenesis in PCOS rats

Polycystic ovary syndrome (PCOS) is a complex and common endocrine disorder characterized by hyperandrogenism, which is accompanied by follicle growth arrest at the small antral stage, minimal granulosa cell proliferation, and chronic anovulation. Polyunsaturated fatty acids (PUFAs) are necessary for the body's metabolism, growth and development. Although PUFAs play an important role in the regulation of female reproduction, their role in ovarian development in PCOS is still unclear. The present study was conducted to investigate the effects of different ratios of n-3/n-6 PUFAs (omega-3/omega-6) on ovary development in PCOS rats. Serum levels of reproductive hormones and enzymes related to steroidogenesis were assessed. The results indicated that PUFAs (n-3/n-6: 1/15) significantly increased ovarian weight and improved the ovarian structure although they had no significant effect on body weight in PCOS rats. Meanwhile, apoptosis was attenuated accompanied by increased cell proliferation by PUFAs (n-3/n-6: 1/15). Moreover, serum levels of hormones (FSH and E₂) were also significantly increased by PUFAs (n-3/n-6: 1/15) accompanied by decreased T levels. To investigate whether PUFAs regulate the expression of enzymes related to hormone synthesis, western blotting was used to determine the protein levels of CYP51, CYP19, StAR and 3β-HSD. The results showed that PUFAs significantly increased the protein levels of all of these enzymes. These results indicate that PUFAs enhance the reproductive performance of PCOS by increasing the expression of steroidogenesis enzymes, which are related to hormone secretion and ovarian functions. These findings provide evidence that a balanced n-3/n-6 PUFA ratio is beneficial for PCOS reproduction.

Bisphenol A stimulates steroidogenic acute regulatory protein expression via an unknown mechanism in adrenal cortical cells

Bisphenol A (BPA) is one of the most widespread endocrine disrupting chemicals in the environment. Exposure to BPA is known to be associated with disruption of steroidogenesis in reproductive tissues, but little is known about its effects on the adrenal gland. We previously showed that prenatal BPA exposure resulted in elevated plasma corticosterone levels concomitant with increased adrenal levels of steroidogenic acute regulatory protein (StAR), the rate-limiting step in steroidogenesis, in adult female mouse offspring. However, the molecular mechanisms underlying the BPA-induced StAR protein expression in the adrenal gland remain unknown. Therefore, the current study was designed to address this important question using the human cortical cell line, H295A cells, as an in vitro model system. We found that: (1) BPA increased StAR protein levels in a dose-dependent manner; (2) both estrogen receptor alpha (ERα)- and ERβ-specific agonists mimicked while the ER antagonist ICI abrogated the stimulatory effects of BPA on StAR protein levels; and (3) BPA did not alter StAR messenger RNA, 37kDa preprotein or protein half-life. Taken together, these findings demonstrate that BPA increases StAR protein levels through an unknown mechanism independent of StAR gene transcription, translation, and protein half-life. Furthermore, such effects are likely mediated by ERα and/or ERβ.

Effects of omega-3 polyunsaturated fatty acids on steroidogenesis and cellular development in PCOS rats

Polycystic ovary syndrome (PCOS) is a common endocrine disorder, which is characterized by hyperandrogenism.

Effects of dietary omega-3 PUFAs on growth and development: Somatic, neurobiological and reproductive functions in a murine model

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are relevant to fetal and infant growth and development. Objective: to assess whether long-term exposure to dietary ω-3 PUFA imbalance alters pre- and/or postnatal pups' development and reproductive function later in life. Mice dams were fed with ω-3 PUFA Control (soybean oil, 7%), Deficient (sunflower oil, 7%) or Excess (blend oil; 4.2% cod-liver+2.8% soybean) diet before conception and throughout gestation-lactation and later on, their pups received the same diet from weaning to adulthood. Offspring somatic, neurobiological and reproductive parameters were evaluated. Excess pups were lighter during the preweaning period and shorter in length from postnatal day (PND) 7 to 49, compared to Control pups (P<.05). On PND14, the percentage of pups with eye opening in Excess group was lower than those from Control and Deficient groups (P<.05). In Excess female offspring, puberty onset (vaginal opening and first estrus) occurred significantly later and the percentage of parthenogenetic oocytes on PND63 was higher than Control and Deficient ones (P<.05). Deficient pups were shorter in length (males: on PND14, 21, 35 and 49; females: on PND14, 21 and 42) compared with Control pups (P<.05). Deficient offspring exhibited higher percentage of bending spermatozoa compared to Control and Excess offspring (P<.05). These results show that either an excessively high or insufficient ω-3 PUFA consumption prior to conception until adulthood seems inadvisable because of the potential risks of short-term adverse effects on growth and development of the progeny or long-lasting effects on their reproductive maturation and function.

Expression patterns of claudin-5 and its related signals during luteal regression in pseudopregnant rats: The enhanced effect of additional PGF treatment

To study the expression patterns of claudin-5 and its related signals during luteal regression in rats, a sequential PMSG/hCG treatment paradigm was used to obtain a single, well-defined generation of corpus luteum (CL). A total of 35 rats were treated with one PGF or two PGF at an interval of 24 h from day 7 of pseudopregnancy to induce CL regression. Serum and ovaries were collected at 0, 2, 4, 8 or 24 h after one PGF injection (1 PGF), 2 or 24 h after two PGF injections (2 PGF). The serum progesterone level was detected by RIA; the ovarian expression of claudin-5, the phosphorylations of STAT3 (p-STAT3), Akt (p-Akt), ERK1/2 (p-ERK) and p38 MAPK (p-p38) were detected by western blot, real-time PCR and IHC. Results showed that serum progesterone (P₄) decreased after PGF treatment. Claudin-5 mRNA decreased at 4 h and 8 h after 1 PGF and 2 h after 2 PGF, and claudin-5 protein decreased at 4 h after 1 PGF. p-STAT3 increased at 4 h after 1 PGF and 2 h after 2 PGF. p-ERK increased at 2 h after 2 PGF. The level of p-Akt decreased at 4 h after 1 PGF. PGF treatment did not alter the phosphorylation of p38 MAPK at any time points in this study. IHC results revealed that claudin-5 was expressed in the nuclei and cytoplasm of steroidogenic cells and in the vessels, while PGF induced-p-STAT3 was expressed uniformly in the cytoplasm of luteal steroidogenic cells. In conclusion, PGF treatment decreased the expression of claudin-5 and the additional PGF treatment enhanced the decrease in claudin-5 mRNA expression and the increases in ERK1/2 and STAT3 phosphorylation in the corpus luteum of pseudopregnant rats, which will contribute new information to the further study of molecular mechanism of luteal regression.

Progesterone Receptor Signaling in Uterine Myometrial Physiology and Preterm Birth

Myometrium holds the structural integrity for the uterus and generates force for parturition with its primary component, the smooth muscle cells. The progesterone receptor mediates progesterone-dependent signaling and connects to a network of pathways for regulation of contractility and inflammatory responses in myometrium. Dysfunctional progesterone signaling has been linked to pregnancy complications including preterm birth. In the present review, we summarize recent findings on modifiers and effectors of the progesterone receptor signaling. Discussions include novel conceptual discoveries and new development in legacy pathways such as the signal transducers NF-κB, ZEB, microRNA, and the unfolded protein response pathways. We also discuss the impact of progesterone receptor isoform composition and ligand accessibility in modification of the progesterone receptor genomic actions.

A comparative analysis of the response of the hepatic transcriptome to dietary docosahexaenoic acid in Atlantic salmon (Salmo salar) post-smolts

Background

The present study aimed to explore the impact of dietary docosahexaenoic acid (DHA) on aspects of the metabolism of Atlantic salmon (Salmo salar). The effects of diets containing increasing levels of DHA (1 g kg⁻¹, 3 g kg⁻¹, 6 g kg⁻¹, 10 g kg⁻¹ and 13 g kg⁻¹) on the liver transcriptome of post-smolt salmon was examined to elucidate patterns of gene expression and responses of specific metabolic pathways. Total RNA was isolated from the liver of individual fish and analyzed using a custom gene expression 44K feature Atlantic salmon oligo-microarray.

Results

The expression of up to 911 unique annotated genes was significantly affected by dietary DHA inclusion relative to a low DHA reference diet. Analysis of a total of 797 unique genes were found with a significant linear correlation between expression level and dietary DHA. Gene-Set Enrichment Analysis (GSEA) identified a range of pathways that were significantly affected by dietary DHA content.

Conclusions

Pathways that showed a significant response to dietary DHA level included those for long-chain polyunsaturated fatty acid biosynthesis, fatty acid elongation, steroid biosynthesis, glycan biosynthesis, protein export and protein processing in the endoplasmic reticulum. These findings suggest that in addition to clear roles in influencing lipid metabolic pathways, DHA might also have key functional roles in other pathways distinct from lipid metabolism.

Steroid receptor coactivators 1 and 2 mediate fetal-to-maternal signaling that initiates parturition

The precise mechanisms that lead to parturition are incompletely defined. Surfactant protein-A (SP-A), which is secreted by fetal lungs into amniotic fluid (AF) near term, likely provides a signal for parturition; however, SP-A-deficient mice have only a relatively modest delay (~12 hours) in parturition, suggesting additional factors. Here, we evaluated the contribution of steroid receptor coactivators 1 and 2 (SRC-1 and SRC-2), which upregulate SP-A transcription, to the parturition process. As mice lacking both SRC-1 and SRC-2 die at birth due to respiratory distress, we crossed double-heterozygous males and females. Parturition was severely delayed (~38 hours) in heterozygous dams harboring SRC-1/-2-deficient embryos. These mothers exhibited decreased myometrial NF-κB activation, PGF2α, and expression of contraction-associated genes; impaired luteolysis; and elevated circulating progesterone. These manifestations also occurred in WT females bearing SRC-1/-2 double-deficient embryos, indicating that a fetal-specific defect delayed labor. SP-A, as well as the enzyme lysophosphatidylcholine acyltransferase-1 (LPCAT1), required for synthesis of surfactant dipalmitoylphosphatidylcholine, and the proinflammatory glycerophospholipid platelet-activating factor (PAF) were markedly reduced in SRC-1/-2-deficient fetal lungs near term. Injection of PAF or SP-A into AF at 17.5 days post coitum enhanced uterine NF-κB activation and contractile gene expression, promoted luteolysis, and rescued delayed parturition in SRC-1/-2-deficient embryo-bearing dams. These findings reveal that fetal lungs produce signals to initiate labor when mature and that SRC-1/-2-dependent production of SP-A and PAF is crucial for this process.

Modulation of adrenocorticotrophin hormone (ACTH)-induced expression of stress-related genes by PUFA in inter-renal cells from European sea bass (Dicentrarchus labrax)

Dietary fatty acids have been shown to exert a clear effect on the stress response, modulating the release of cortisol. The role of fatty acids on the expression of steroidogenic genes has been described in mammals, but little is known in fish. The effect of different fatty acids on the release of cortisol and expression of stress-related genes of European sea bass (Dicentrarchus labrax) head kidney, induced by a pulse of adenocorticotrophin hormone (ACTH), was studied. Tissue was maintained in superfusion with 60 min of incubation with EPA, DHA, arachidonic acid (ARA), linoleic acid or α-linolenic acid (ALA) during 490 min. Cortisol was measured by RIA. The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real-time RT-PCR. There was an effect of the type of fatty acid on the ACTH-induced release of cortisol, values from ALA treatment being elevated within all of the experimental period. The expression of some steroidogenic genes, such as the steroidogenic acute regulatory protein (StAR) and c-fos, were affected by fatty acids, ALA increasing the expression of StAR after 1 h of ACTH stimulation whereas DHA, ARA and ALA increased the expression of c-fos after 20 min. ARA increased expression of the 11β-hydroxylase gene. Expression of heat shock protein 70 (HSP70) was increased in all the experimental treatments except for ARA. Results corroborate previous studies of the effect of different fatty acids on the release of cortisol in marine fish and demonstrate that those effects are mediated by alteration of the expression of steroidogenic genes.

Effects of dietary omega-3/omega-6 fatty acid ratios on reproduction in the young breeder rooster

Background

Polyunsaturated fatty acids (PUFAs) are necessary for the body's metabolism, growth and development. Although PUFAs play an important role in the regulation of reproduction, their role in testis development in the rooster is unknown. The present study was conducted to investigate the effects of omega-3/omega-6 (n-3/n-6, PUFAs) ratios on reproductive performance in young breeder roosters. Plasma levels of reproductive hormones, testis development, and reproductive hormone receptor and StAR mRNA expression were also assessed.

Results

Although PUFAs (n-3/n-6: 1/4.15) had no significant effect on the testis index (P > 0.05), the spermatogonial development and germ cell layers were increased. Moreover, serum levels of hormones (GnRH, FSH, LH and T) on day 35 were also significantly increased by PUFAs (n-3/n-6: 1/4.15). To investigate whether PUFAs regulate the expression of hormone receptors and StAR, real time-PCR was used to measure GnRHR, FSHR, LHR and StAR mRNA levels. PUFAs significantly increased the mRNA levels of all of these genes.

Conclusions

These results indicate that PUFAs enhance the reproductive performance of young roosters by increasing hormone secretion and function, the latter by up-regulating receptor expression. These findings provide a sound basis for a balanced n-3/n-6 PUFA ratio being beneficial to young rooster reproduction.

Dietary n-3 polyunsaturated fatty acid supplementation alters the expression of genes involved in the control of fertility in the bovine uterine endometrium

The potential for dietary supplementation with n-3 polyunsaturated fatty acids (n-3 PUFA) to improve reproductive efficiency in cattle has received much interest. The mechanisms by which n-3 PUFA may affect physiological and biochemical processes in key reproductive tissues are likely to be mediated by significant alterations in gene expression. The objective of this study was to examine the effects of dietary n-3 PUFA supplementation on global uterine endometrial gene expression in cattle. Beef heifers were supplemented with a rumen protected source of either a saturated fatty acid (CON; palmitic acid) or high n-3 PUFA (n-3 PUFA; 275 g) diet per animal per day for 45 days and global gene expression was determined in uterine endometrial tissue using an Affymetrix oligonucleotide bovine array. A total of 1,807 (946 up- and 861 downregulated) genes were differentially expressed following n-3 PUFA supplementation. Dietary n-3 PUFA altered numerous cellular processes potentially important in the control of reproduction in cattle. These included prostaglandin biosynthesis, steroidogenesis and transcriptional regulation, while effects on genes involved in maternal immune response and tissue remodeling were also observed. This study provides new insights into the effects of n-3 PUFA supplementation on the regulation of gene expression in the bovine uterus.

Exogenous arachidonate restores the dimethoate-induced inhibition of steroidogenesis in rat interstitial cells

The present work studies the potential restorative effect of polyunsaturated fatty acids (PUFA, 5 μM/24 h) on the dimethoate (DMT)-induced inhibition of testosterone biosynthesis in Leydig cells isolated from rat testes. Various fatty acids (FA) from the n-6 (18:2, 20:3, 20:4, 22:4 and 22:5) and n-3 (18.3, 20:5, 22:5, 22:6) series were assayed in Leydig cells, alone (as delipidated BSA complexes) and in combination with DMT (1 ppm). The n-6 FA stimulated lipid peroxidation (LPO) and inhibited the activities of steroidogenic enzymes (3β- and 17β-hydroxysteroid dehydrogenases). The n-3 FA exerted an anti-oxidant effect, decreasing the production of thiobarbituric-acid reactive substances (TBARS) and inhibiting phospholipase A(2) activity. The biosynthesis of testosterone in DMT-treated cultures was completely normalized by ARA (20:4n-6) and partially restored by the addition of 20:3n-6, increasing ARA content inside the mitochondria. The other FA assayed failed to restore androgenesis. COX-2 protein and prostaglandin F2α and E2 production were stimulated by 20:3n-6, ARA, 18:3n-3 and 20:5 n-3. COX-2 protein decreased upon addition of 22:5n-3 and 22:6n-3. StAR protein was increased by ARA and partially increased by 20:3n-6, likely due to its metabolic conversion into ARA. Both FA increased the mitochondrial cholesterol pool available for testosterone biosynthesis. The rate of androgenesis is likely the result of various regulatory factors acting concomitantly on the physiology of Leydig cells.

Sphingosine-1-phosphate rapidly increases cortisol biosynthesis and the expression of genes involved in cholesterol uptake and transport in H295R adrenocortical cells

In the acute phase of adrenocortical steroidogenesis, adrenocorticotrophin (ACTH) activates a cAMP/PKA-signaling pathway that promotes the transport of free cholesterol to the inner mitochondrial membrane. We have previously shown that ACTH rapidly stimulates the metabolism of sphingolipids and the secretion of sphingosine-1-phosphate (S1P) in H295R cells. In this study, we examined the effect of S1P on genes involved in the acute phase of steroidogenesis. We show that S1P increases the expression of steroidogenic acute regulatory protein (StAR), 18-kDa translocator protein (TSPO), low-density lipoprotein receptor (LDLR), and scavenger receptor class B type I (SR-BI). S1P-induced StAR mRNA expression requires Gα(i) signaling, phospholipase C (PLC), Ca(2+)/calmodulin-dependent kinase II (CamKII), and ERK1/2 activation. S1P also increases intracellular Ca(2+), the phosphorylation of hormone sensitive lipase (HSL) at Ser(563), and cortisol secretion. Collectively, these findings identify multiple roles for S1P in the regulation of glucocorticoid biosynthesis.

Effect of decreasing intraluteal progesterone on sensitivity of the early porcine corpus luteum to the luteolytic actions of prostaglandin F2alpha

Prostaglandin F2alpha (PGF) causes luteolysis of the pig corpus luteum (CL) only after Day 12 of the estrous cycle. Recent evidence indicates that progesterone (P4) may protect the CL from cell death. The present study tested the hypothesis that acute inhibition of P4 by treatment with epostane (EPO; 3betaHSD inhibitor) in CL lacking luteolytic capacity (Day 9 CL) will allow PGF to induce responses associated with luteolysis. Multiple PGF-induced responses were evaluated, including genes involved in production of PGF and estradiol-17beta, apoptosis (caspase 3), and transcription (FOSB). These responses are associated with PGF-induced luteolysis and do not normally occur in CL lacking luteolytic capacity. Animals on Day 7 after estrus were divided into four groups: 1) control (C), 2) PGF, 3) EPO, and 4) PGF plus EPO (PGF+EPO). Treatment with EPO (10 mg/kg) or vehicle was given every 12 h for 36 h. Treatment with PGF (25 mg) or vehicle was given at 38 h, and CL were collected from all animals at 48 h. Some CL from each animal were frozen in liquid nitrogen for mRNA and protein analysis. Remaining CL were incubated in media for 2 h for determination of P4 and PGF production. EPO dramatically decreased production of P4 by luteal tissue (ng/mg tissue) by 90% and 95% in EPO and PGF+EPO groups, respectively, compared to C (P < 0.01). Low production of PGF by luteal tissue was found in C, PGF, and EPO groups; however, treatment with PGF+EPO dramatically increased (782%) luteal PGF production. Similar to intraluteal PGF production, increased mRNA for cyclooxygenase 2 (PTGS2) and phospholipase A2 (group IB; PLA2G1B) was found in the PGF+EPO, but not in the EPO or PGF, group. Aromatase (CYP19A1) mRNA was not induced by PGF or EPO; however, PGF+EPO caused a more than 40-fold increase in CYP19A1 mRNA (P < 0.01). CASP3 mRNA was increased (P < 0.01) by EPO (3.4-fold) and by PGF (2.7-fold) but was most dramatically increased by PGF+EPO (5.3-fold), whereas caspase activity was only increased by PGF (1.5-fold) or PGF+EPO (2.2-fold). Thus, these data support the hypothesis that elimination of the protective effect of intraluteal P4 does not directly cause luteolysis of the early CL but allows PGF to induce luteolytic responses in CL lacking luteolytic capacity.

Involvement of lipids in dimethoate-induced inhibition of testosterone biosynthesis in rat interstitial cells

The mechanism involved in the inhibition of testosterone (Te) biosynthesis after a sub-chronic exposure to low doses of dimethoate (D) was studied in rat interstitial cells (IC). Expression of COX-2 in IC isolated from D-treated rats increased by 44% over C data, while transcription of StAR decreased by approx. 50% and the expression of this protein was diminished by approximately 40%. PGE(2) and PGF(2alpha) were increased by 61 and 78%, respectively. Te concentration decreased by 49% in IC homogenates. Concomitantly, plasma concentration of LH and FSH both increased. Araquidonate (ARA) and C(22) fatty acyl chains in phospholipids from IC mitochondrial fraction decreased by approx. 30% after D treatment. Protein carbonyls, lipoperoxides and nitrite content increased while alpha-tocopherol and the antioxidant capacity of the soluble cellular fraction decreased significantly. Stimulation with h-CG 10 nM overnight failed to overcome the inhibition caused by D on both Te biosynthesis and 3beta- and 17beta-hydroxysteroid dehydrogenases. Decreased Te biosynthesis may be attributed to (1) inhibition of StAR protein activity due to the stimulation of COX-2 and the overproduction of PGF(2alpha), (2) decreased stimulatory effect of ARA on StAR with a subsequent reduction in the availability of CHO for the androgenic pathway, and/or (3) indirect inhibition of steroidogenic enzymes by a lower transcriptional rate caused by elevated PGF(2alpha). Rofecoxib administration prevents the deleterious effect(s) exerted by D.

The expression of tumor necrosis factor-alpha, its receptors and steroidogenic acute regulatory protein during corpus luteum regression

BACKGROUND

Corpus luteum (CL) regression is known to occur as two parts; functional regression when steroidogenesis declines and structural regression when apoptosis is induced. Previous studies suggest this process occurs by the production of luteolytic factors, such as tumour necrosis factor-alpha (TNF-alpha).

METHODS

We examined TNF-alpha, TNF-alpha receptors (TNFR1 and 2) and steroidogenic acute regulatory (StAR) protein expression during CL regression in albino Wistar rats. CL from Days 16 and 22 of pregnancy and Day 3 post-partum were examined, in addition CL from Day 16 of pregnancy were cultured in vitro to induce apoptosis. mRNA was quantitated by kinetic RT-PCR and protein expression examined by immunohistochemistry and Western blot analyses.

RESULTS

TNF-alpha mRNA increased on Day 3 post-partum. TNFR were immunolocalized to luteal cells, and an increase in TNFR2 mRNA observed on Day 3 post-partum whilst no change was detected in TNFR1 mRNA relative to Day 16. StAR protein decreased on Day 3 post-partum and following trophic withdrawal but no change was observed following exogenous TNF-alpha treatment. StAR mRNA decreased on Day 3 post-partum; however, it increased following trophic withdrawal and TNF-alpha treatment in vitro.

CONCLUSION

These results demonstrate the existence of TNFR1 and TNFR2 in rat CL and suggest the involvement of TNF-alpha in rat CL regression following parturition. Furthermore, decreased StAR expression over the same time points was consistent with the functional regression of the CL.

Prostaglandin F2alpha suppresses rat steroidogenic acute regulatory protein expression via induction of Yin Yang 1 protein and recruitment of histone deacetylase 1 protein

Prostaglandin F2alpha (PGF2alpha) plays a pivotal role in ovarian luteolysis by inhibiting the expression of steroidogenic acute regulatory (StAR) protein, leading to a decrease in intracellular cholesterol transport and luteal steroid production. Previously we have demonstrated that the transcription factor Yin Yang 1 (YY1) bound to three regions in the StAR promoter in vitro and repressed promoter activity. This study further defined the YY1-mediated PGF2alpha effect on the inhibition of StAR protein expression through YY1 interaction with a single region in the StAR promoter in vivo. PGF2alpha consistently suppressed StAR mRNA and protein expression in cultured luteal cells in a dose-dependent manner. PGF2alpha also enhanced YY1 protein expression and binding to its cis-element in a time-dependent pattern that preceded the decline in StAR protein levels. The StAR promoter region bound by YY1 was also associated with histone deacetylase 1 (HDAC1). PGF2alpha treatment promoted HDAC1 binding to and suppressed the histone H3 acetylation in this region. On the contrary, YY1 knockdown decreased HDAC1 binding, increased histone H3 acetylation, enhanced StAR protein expression, and negated PGF2alpha effect on StAR protein expression. Luciferase assays showed that YY1 overexpression inhibited StAR promoter activity and the addition of a HDAC inhibitor, trichostatin A, abrogated the effect of YY1. Trichostatin A-treated luteal cells displayed increased StAR protein expression. These data indicate that PGF2alpha enhances a direct YY1/StAR promoter interaction and the recruitment of HDAC1 to the promoter, thereby preventing transcriptional activation of the StAR gene.

Polyunsaturated fatty acids in male and female reproduction

In Westernized societies, average consumption of n-6 polyunsaturated fatty acids (PUFAs) far exceeds nutritional requirements. The ratio of n-6 to n-3 PUFAs is generally >10:1 whereas on a primitive human diet it was closer to 1:1. Diets fed to intensively farmed livestock have followed a similar trend. Both n-6 and n-3 PUFAs can influence reproductive processes through a variety of mechanisms. They provide the precursors for prostaglandin synthesis and can modulate the expression patterns of many key enzymes involved in both prostaglandin and steroid metabolism. They are essential components of all cell membranes. The proportions of different PUFAs in tissues of the reproductive tract reflect dietary consumption. PUFA supplements (particularly n-3 PUFAs in fish oil) are promoted for general health reasons. Fish oils may also benefit fertility in cattle and reduce the risk of preterm labor in women, but in both cases current evidence to support this is inconclusive. Gamma-linolenic acid containing oils can alter the types of prostaglandins produced by cells in vitro, but published data to support claims relating to effects on reproductive health are lacking. Spermatozoa require a high PUFA content to provide the plasma membrane with the fluidity essential at fertilization. However, this makes spermatozoa particularly vulnerable to attack by reactive oxygen species, and lifestyle factors promoting oxidative stress have clear associations with reduced fertility. Adequately powered trials that control for the ratios of different PUFAs consumed are required to determine the extent to which this aspect of our diets does influence our fertility.

Reproductive phenotypes in mice with targeted disruption of the 20alpha-hydroxysteroid dehydrogenase gene

In the corpus luteum of rats and mice, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) catalyzes the conversion of progesterone to a biologically inactive metabolite, 20alpha-dihydroprogesterone (20alpha-OHP). The reduction of progesterone by 20alpha-HSD is believed to be important for functional luteolysis in these rodent species. In addition to the corpus luteum, expression of 20alpha-HSD has been demonstrated in tissues such as the placenta, endometrial epithelia, and fetal skin, although the roles it plays in the latter tissues remain to be determined. To determine the contribution of 20alpha-HSD to functional luteolysis and to the rodent reproductive system more generally, we generated a strain of mice with targeted disruption of the 20alpha-HSD gene. In the 20alpha-HSD-/- mice we obtained, which lacked the genomic region essential for catalytic reaction, neither 20alpha-HSD activity in the corpus luteum nor an increase in the serum concentrations of 20alpha-OHP during pseudopregnancy or pregnancy was detected. The durations of the estrous cycle, pseudopregnancy, and pregnancy were significantly prolonged in the 20alpha-HSD-/- mice, although the serum progesterone levels decreased to levels low enough for delivery of pups at term of pregnancy. In addition, the number of pups, especially live pups, was markedly decreased in the 20alpha-HSD-/- mice. These findings suggest that the role of 20alpha-HSD in functional luteolysis is relatively minor but that it is involved in the survival of newborn mice.

Cyclooxygenase-2 and prostaglandin F2 alpha in Syrian hamster Leydig cells: Inhibitory role on luteinizing hormone/human chorionic gonadotropin-stimulated testosterone production

We have previously found that cyclooxygenase-2 (COX-2), a key enzyme in the biosynthesis of prostaglandins (PGs), is present in the testicular interstitial cells of infertile men, whereas it is absent in human testes with no evident morphological changes or abnormalities. To find an animal model for further investigating COX-2 and its role in testicular steroidogenesis, we screened testes from adult species ranging from mice to monkeys. By using immunohistochemical assays, we found COX-2 expression only in Leydig cells of the reproductively active (peripubertal, pubertal, and adult) seasonal breeder Syrian hamster. COX-2 expression in hamster Leydig cells was confirmed by RT-PCR. In contrast, COX-1 expression was not detected in hamster testes. Because COX-2 expression implies PG synthesis, we investigated the effect of various PGs on testosterone production and found that PGF2 alpha stood out because it significantly reduced human chorionic gonadotropin-stimulated testosterone release from isolated hamster Leydig cells in a dose-dependent manner. This mechanism involves a decreased expression of testicular steroidogenic acute regulatory protein and 17beta-hydroxysteroid dehydrogenase. Testicular concentration and content of PGF2 alpha in reproductively active hamsters as well as production of PGF2 alpha from isolated hamster Leydig cells were also determined. Moreover, PGF2 alpha receptors were localized in Leydig cells of hamsters and testicular biopsies from patients with Sertoli cell only and germ arrest syndromes. Thus, in this study, we described a COX-2-initiated pathway that via PGF2 alpha production, PGF2 alpha receptors, steroidogenic acute regulatory protein, and 17beta-hydroxysteroid dehydrogenase represents a physiological local inhibitory system of human chorionic gonadotropin-stimulated testosterone production in the Syrian hamster testes.

Nucleic acids and protein content in relation to growth and regression of buffalo (Bubalus bubalis) corpora lutea

Information on nucleic acids and protein content of buffalo corpus luteum (CL) in relation to growth, development and regression is not available. An experiment was thus conducted to investigate the variation and relationship between nucleic acids and protein content in CL during different developmental stages and to determine the qualitative differences in protein constituents in any of these stages. Buffalo corpora lutea of different developmental stages viz., developing (day 5-10, n = 16), developed (day 11-17, n = 12) and regressed (day 18-21, n = 10) stages were collected from non-pregnant and -pathological genitalia (n = 38). The DNA, RNA and protein content in tissue extracts were determined and the proteins in pooled samples were analyzed by polyacrylamide gel electrophoresis. Developing stage CL had more total and per gram tissue level of DNA and RNA with significant positive relationship with total and per gram RNA and protein contents. Although there was no significant difference in total weight, a significant decrease in total DNA as well as per gram level of DNA and RNA was observed in developed stage compared to developing stage CL. The total protein content in developed stage CL was compared to developing and regressed stage CL. Non-denaturing PAGE analysis of CL proteins of different stages showed five protein bands of 210, 190, 82, 68 and 66 kDa and one that migrated with the dye front in all the stages however, not shown any differences in banding pattern. Denaturing PAGE showed 15 bands viz., 205, 66, 53, 42, 35, 27, 24, 22, 20, 18, 17, 14, 9, 7.5 and 6.5 kDa. Out of these 66 and 53 kDa bands appeared with maximum intensity in all the three stages of CL. Comparison of bands between the three stages revealed five 57, 31, 27, 19 and 16 kDa stage-specific bands in regressed stage CL. The present study indicated that the DNA, RNA and protein content of buffalo CL varied with the stages of development and regressed stage CL contained some unique protein bands which were not observed either in developed or developing stage CL.

Regulation of Progesterone Levels during Pregnancy and Parturition by Signal Transducer and Activator of Transcription 5 and 20α-Hydroxysteroid Dehydrogenase

The two highly related signal transducers and activators of transcription (Stats), Stat5a and Stat5b, are major mediators of prolactin signaling in both the mammary gland and in the ovary. Deficiencies in Stat5b, or in both Stat5a and Stat5b, result in loss of pregnancy during midgestation and are correlated with an increase in ovarian 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) and a decrease in serum progesterone, which normally declines only immediately before parturition. To determine the relative contribution of 20alpha-HSD to progesterone metabolism and Stat5 function during pregnancy and parturition, we created a 20alpha-HSD-deficient strain of mice by gene disruption. Mice deficient for 20alpha-HSD sustain high progesterone levels and display a delay in parturition of several days demonstrating that 20alpha-HSD regulates parturition downstream of the prostaglandin F2alpha receptor in an essential and nonredundant manner. Moreover, 20alpha-HSD deficiency partially corrected the abortion of pregnancies associated with Stat5b deficiency, supporting the concept that prolactin activation of Stat5b is important in suppressing 20alpha-HSD gene expression and thereby allowing the maintenance of progesterone levels that are required to sustain pregnancy.

Acquisition of luteolytic capacity involves differential regulation by prostaglandin F2alpha of genes involved in progesterone biosynthesis in the porcine corpus luteum

Luteolytic capacity is defined as the ability of corpora lutea (CL) to undergo luteolysis after prostaglandin (PG) F2alpha treatment. The mechanisms causing acquisition of luteolytic capacity are not yet identified but CL without luteolytic capacity have PGF2alpha receptors and respond to PGF2alpha with some changes in gene expression. Inhibition of progesterone biosynthesis is a key feature of luteolysis and therefore we postulated that genes involved in progesterone biosynthesis would be regulated by PGF2alpha differently in CL with or without luteolytic capacity. Gilts on day 9 after estrus (lack luteolytic capacity) or day 17 of pseudopregnancy (with luteolytic capacity) were treated with saline or a PGF2alpha analog (cloprostenol) and CL were collected 0.5 (Experiment I) or 10 h (Experiment II) later. In Experiment III, large luteal cells from CL on day 9 or 17 were cultured for 1, 12 and 24h with or without PGF2alpha. PGF2alpha decreased LDL receptor mRNA (27%), steroidogenic acute regulatory protein (StAR) mRNA (41%), StAR protein (75%), LH receptor mRNA (55%), and LH receptor protein (45%) at 10 h after treatment in day 17 but not day 9 CL. PGF2alpha increased DAX-1 mRNA at 0.5 h (43%) and 10 h (46%) after PGF2alpha in day 17 but not day 9 CL but decreased 3betaHSD mRNA ( approximately 20% at 10 h) in both days 9 and 17 CL. In vitro, PGF2alpha decreased StAR mRNA at 12 h only in day 17 luteal cells; however, continuous treatment with PGF2alpha for 24 h decreased StAR mRNA in both days 9 and 17 luteal cells. Thus, luteolytic capacity involves a critical change in responsiveness of DAX-1, StAR, and LH receptor to PGF2alpha that results in inhibition of luteal progesterone biosynthesis.

Changes in bovine luteal progesterone metabolism in response to exogenous prostaglandin F(2alpha)

An experiment was conducted to determine the effect of prostaglandin F2alpha (PGF2alpha) on luteal synthesis of progesterone (P4) and related progestins. Sixteen beef heifers were assigned in equal numbers to four groups in a 2x2 factorial arrangement of treatments. The experiment consisted of two levels of PGF2alpha analog (0 and 500 microg) and two levels of time (4 and 24 h after injection) of corpus luteum collection. All heifers were injected intravenously with saline (2 ml) or PGF2alpha (cloprostenol) on day 8 of the estrous cycle (estrus=day 0). Jugular blood was collected at 0, 1, 2, 3, 4 and 20, 21, 22, 23, and 24 h after injection. Resulting sera were analyzed for P4 by use of radioimmunoassay. Luteal tissue was analyzed by gas chromatography/mass spectrometry for P4, 20beta-hydroxyprogesterone, pregnenolone, and allopregnanolone (3beta-hydroxy-5alpha-pregnan-20-one). Treatment with PGF2alpha reduced serum concentrations of P4 as early as 1 h after injection (P<0.005) and steroid levels remained low over 24 h. Similarly, administration of PGF2alpha caused a decline in luteal P4 (P<0.005), 20beta-hydroxyprogesterone (P<0.10), and pregnenolone (P<0.05). In contrast, treatment with PGF(2alpha) caused an increase in luteal allopregnanolone over time (time x treatment interaction; P<0.05). These data are interpreted to suggest that PGF2alpha promotes conversion of P4 to the metabolite allopregnanolone.

Pronounced induction of testicular PGF2$alpha; and suppression of testosterone by cadmium?prevention by zinc

In order to investigate the effects of cadmium (Cd) on testicular prostaglandin F(2 alpha) (PGF(2 alpha)) production, adult male Sprague-Dawley rats were exposed to CdCl(2) by subcutaneous injections. Dose-response as well as temporal-response experiments were performed, and PGF(2 alpha) levels were determined by radioimmunoassay (RIA). The highest cadmium dose (10 micromol/kg) caused a dramatic elevation of testicular PGF(2 alpha), which was established to occur 48 h after exposure. At this point of time, cadmium-treated animals displayed PGF(2 alpha) levels 16.7 times higher than saline-injected controls. No significant differences were found with the lower doses used (1 and 5 micromol/kg). In addition, the influence of pre-treatment with zinc (Zn) was assessed. The very strong stimulatory effect on PGF(2 alpha) synthesis (22.3-fold) detected after exposure to 20 micromol/kg cadmium, was completely absent in the group given zinc (1 mmol/kg) prior to cadmium exposure. Plasma testosterone concentrations were determined in the three experiments, and all groups with strongly elevated PGF(2 alpha) levels showed drastically lowered concentrations of testosterone. Zinc pre-treatment abolished not only the cadmium-induced rise in PGF(2 alpha) but also the testosterone reduction. Additionally, cadmium was found to inhibit the expression of steroidogenic acute regulatory protein (StAR), which is responsible for the rate-limiting step in steroidogenesis. The present findings establish that cadmium can cause a strong induction of testicular PGF(2 alpha) production, which might help to explain the well-known antisteroidogenic effect of this heavy metal. Such an inhibitory effect could be due to reduced levels of StAR.

StAR and steroidogenic enzyme transcriptional regulation in the rat brain: effects of acute alcohol administration

In this study, we showed the presence of steroidogenic acute regulatory protein (StAR) mRNA in the rat brain using Northern blot analysis and revealed its localization using in situ hybridization histochemistry. Although the expression level is less than peripheral steroidogenic organs, the brain has two kinds of StAR transcripts with the same size as peripheral endocrine organs. As expected, StAR mRNA levels were maintained in the brain after gonadectomy and adrenalectomy, which indicates its independent expression. Acute alcohol administration affected the mRNA expression of a variety of steroidogenic enzymes, as well as StAR, in several brain regions, and these changes varied from one region to another. It is suggested that StAR may take part in brain steroidogenesis along with steroidogenic enzymes and that various neurosteroids are synthesized differentially to meet local demands.

Apoptosis during spontaneous and prostaglandin F(2alpha)-induced luteal regression in the buffalo cow (Bubalus bubalis): involvement of mitogen-activated protein kinases

The present study was conducted to evaluate whether the corpus luteum (CL) of the water buffalo (Bubalus bubalis) cow undergoes luteal regression by the process of apoptosis and to examine the involvement of mitogen-activated protein (MAP) kinases during prostaglandin (PG) F(2alpha)-induced luteolysis. Sections of CL from late in the estrous cycle, i.e., during spontaneous luteolysis, stained for 4',6'-diamidino-2-phenylindole revealed increased numbers of condensed nuclei, indicating cell death by apoptosis, which was confirmed further by the occurrence of pronounced oligonucleosome formation. For morphological and biochemical characterization during PGF(2alpha)-induced apoptosis, CL were collected at 0, 4, 12, and 18 h after injection of 750 micro g of Tiaprost, a synthetic analogue of PGF(2alpha), to midestrous buffalo cows. Serum progesterone concentrations fell within 4 h and decreased (P < 0.05) maximally by 18 h. Concomitant decreases (P < 0.05) in the levels of steroidogenic acute regulatory mRNA and protein were observed in CL during 12-18 h, with the more profound effect on mRNA levels. Quantitative analysis of the genomic DNA showed a >5-fold increase (P < 0.05) in the low molecular weight DNA fragments by 18 h postinjection. Immunoblot analysis of CL tissue lysates showed increased (P < 0.05) levels of phospho-Jun N-terminal kinase (JNK) 1 (4- to 14-fold during 4-18 h) and phospho-p38 (2- to 4-fold at 18 h). Immunohistochemical evaluation of CL sections revealed an increased nuclear localization of phospho-JNK after treatment. These findings demonstrate that the CL of the buffalo cow undergoes cell death by the process of apoptosis both during spontaneous and PGF(2alpha)-induced luteolysis and that MAP kinases are involved during PGF(2alpha)-mediated apoptosis in the CL.

Involvement of endothelin-1 and its receptors in PGF2alpha-induced luteolysis in the rat

The possible mediatory role of endothelin-1 (ET-1) in prostaglandin F(2alpha) (PGF(2alpha))-induced luteolysis in the rat was examined. The effect of PGF(2alpha) was tested on day 9 of pregnancy either in vivo, by injecting cloprostenol, an analog of PGF(2alpha) or in vitro, in isolated intact corpora lutea incubated with PGF(2alpha). Luteolysis was confirmed by progesterone determination in the peripheral blood serum or in the culture medium, respectively. Administration of cloprostenol (.0025 mg/rat) induced within 1 hr, a significant fall (from 56.8 to 27.6 ng/ml, P < 0.0001) in serum progesterone concentrations that was associated with an increased expression of the mRNA to ET-1 and its protein product in rat luteal tissue. Elevated level of ET-1 were also determined at the spontaneous regression of the CL, upon parturition. Expression of the ET receptors, ETA and ETB was not affected by cloprostenol. On the other hand, this PGF(2alpha) analog induced expression of luteal VEGF mRNA. In vitro experiments demonstrate that the LH (100 ng/ml)-induced increase in luteal progesterone secretion was reduced by PGF(2alpha) (1 microg/ml). The inhibitory effect of PGF(2alpha) was reversed by BQ123 (10(- 7) M), that is a selective ETA receptor antagonist. We conclude that the PGF(2alpha)-induced elevation in luteal expression of ET-1 combined with the reversal of its luteolytic effect by an ETA receptor antagonist suggest that ET-1 may take part in the PGF(2alpha)-induced luteolysis in the rat.

Regulation of progesterone and prostaglandin F2alpha production in the CL

After the luteinizing hormone (LH) surge, the cells that remain from the ovulated follicle undergo a process of differentiation termed luteinization. Two key features of the cells after luteinization are the capacity for tremendous production of progesterone [10(16) molecules of progesterone per (min/(g of CL))] and the capacity to undergo regression or death of the cells at the appropriate time. There are two steroidogenic cell types, the small and large luteal cells that are regulated by different mechanisms. In small luteal cells, production of progesterone is stimulated by LH through the protein kinase A (PKA) pathway. The large luteal cells of ruminants produce large quantities of progesterone that is independent of LH stimulation. Although luteotrophins clearly regulate luteal function, much of luteal progesterone production in some species appears to be constitutive, consistent with the autonomous aspects of the large luteal cell. The key regulated step in luteal progesterone production appears to be regulation of transport of cholesterol to the inner mitochondrial membrane apparently mediated by the steroidogenic acute regulatory protein (StAR). In addition, our recent research indicates that PKA is tonically active in large luteal cells and this may be responsible for the high, relatively autonomous nature of luteal progesterone production. Regression of the corpus luteum (CL) in many species is initiated by prostaglandin (PG) F2alpha secreted from the uterus. Luteal cells also have the capacity for production of PGF2alpha. Luteal PGF2alpha production can be regulated by a variety of substances including inhibition by progesterone and stimulation by cytokines. We have also characterized a positive feedback pathway in ruminant and porcine CL in which small amounts of uterine PGF(2alpha) stimulate intraluteal production of PGF2alpha due to induction of the cycloxygenase-2 (Cox-2) enzyme in large luteal cells. This positive feedback pathway is only present in CL that has acquired the capacity for luteal regression ( approximately day 7 in cow, approximately day 13 in pig). Regulation by protein kinase C (PKC) of transcriptional factors interacting with an E-box in the 5' flanking region of the Cox-2 gene is the critical regulatory element involved in this positive feedback pathway. Thus, luteinization in some species appears to change specific gene transcription such that progesterone production becomes relatively independent of acute luteotrophic regulation and intraluteal PGF2alpha synthesis is induced by the second messenger pathways that are activated by PGF2alpha.

Dependence on prolactin of the luteolytic effect of prostaglandin F2alpha in rat luteal cell cultures

Luteal regression is a multistep, prolonged process, and long-term luteal cultures are required for studying it in vitro. Cell suspensions from ovaries of superovulated rats were enriched with steroidogenic cells, seeded on laminin or fibronectin, and maintained in defined medium for up to 10 days. Progesterone secretion was much lower than that of 20alpha-dihydroprogesterone, a product of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD). Prolactin added throughout the incubation period gradually increased the percent progesterone out of total progestins to fourfold, while reducing 20alpha-HSD mRNA by 73%. Luteinizing hormone accelerated the establishment of higher percent progesterone by prolactin but by itself had no effect. Prolactin did not increase total progestin production or cytochrome P450 side-chain cleavage (P450(scc)) mRNA. Cell viability was unaffected by prolactin and/or LH. Prostaglandin F2alpha (PGF2alpha) was added 7-8 days after seeding. In prolactin-treated cells, PGF2alpha reduced steroidogenesis after 4-45 h, and at 45 h total progestins and P450(scc) mRNA were reduced by 45%. At 8-45 h PGF2alpha reduced the percent progesterone out of total progestins, and at 45 h 20alpha-HSD mRNA was doubled. In contrast, in prolactin-deprived cultures, PGF2alpha had little effect on total progestins or 20alpha-HSD mRNA but doubled P450(scc) mRNA. Phospholipase C activity was stimulated by PGF2alpha regardless of prolactin. Thus, when prolactin-treated, our cultures are a good model for mature corpora lutea challenged with PGF2alpha; the finding that without prolactin PGF2alpha has an alternative set of actions could help in identifying the signaling pathways of PGF2alpha responsible for its luteolytic effects.

Luteal expression of cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, 3beta-hydroxysteroid dehydrogenase, and 20alpha-hydroxysteroid dehydrogenase genes in late pregnant rats: effect of luteinizing hormone and RU486

A decrease in serum progesterone at the end of pregnancy is essential for the induction of parturition in rats. We have previously demonstrated that LH participates in this process through: 1) inhibiting 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity and 2) stimulating progesterone catabolism by inducing 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activity. The objective of this investigation was to determine the effect of LH and progesterone on the luteal expression of the steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (P450(scc)), 3beta-HSD, and 20alpha-HSD genes. Gene expression was analyzed by Northern blot analysis 24 and 48 h after administration of LH or vehicle on Day 19 of pregnancy. StAR and 3beta-HSD mRNA levels were lower in LH-treated rats than in rats administered with vehicle at both time points studied. P450(scc) mRNA levels were unaffected by LH. The 20alpha-HSD mRNA levels were not different between LH and control rats 24 h after treatment; however, greater expression of 20alpha-HSD, with respect to controls, was observed in LH-treated rats 48 h after treatment. Luteal progesterone content dropped in LH-treated rats at both time points studied, whereas serum progesterone decreased after 48 h only. In a second set of experiments, the anti-progesterone RU486 was injected intrabursally on Day 20 of pregnancy. RU486 had no effect on 3beta-HSD or P450(scc) expression but increased 20alpha-HSD mRNA levels after 8 h treatment. In conclusion, the luteolytic effect of LH is mediated by a drop in StAR and 3beta-HSD expression without effect on P450(scc) expression. We also provide the first in vivo evidence indicating that a decrease in luteal progesterone content may be an essential step toward the induction of 20alpha-HSD expression at the end of pregnancy in rats.

StAR protein and the regulation of steroid hormone biosynthesis

Steroid hormone biosynthesis is acutely regulated by pituitary trophic hormones and other steroidogenic stimuli. This regulation requires the synthesis of a protein whose function is to translocate cholesterol from the outer to the inner mitochondrial membrane in steroidogenic cells, the rate-limiting step in steroid hormone formation. The steroidogenic acute regulatory (StAR) protein is an indispensable component in this process and is the best candidate to fill the role of the putative regulator. StAR is expressed in steroidogenic tissues in response to agents that stimulate steroid production, and mutations in the StAR gene result in the disease congenital lipoid adrenal hyperplasia, in which steroid hormone biosynthesis is severely compromised. The StAR null mouse has a phenotype that is essentially identical to the human disease. The positive and negative expression of StAR is sensitive to agents that increase and inhibit steroid biosynthesis respectively. The mechanism by which StAR mediates cholesterol transfer in the mitochondria has not been fully characterized. However, the tertiary structure of the START domain of a StAR homolog has been solved, and identification of a cholesterol-binding hydrophobic tunnel within this domain raises the possibility that StAR acts as a cholesterol-shuttling protein.

Actions of prostaglandin F2alpha and prolactin on intercellular adhesion molecule-1 expression and monocyte/macrophage accumulation in the rat corpus luteum

Expression of intercellular adhesion molecule-1 (ICAM-1) and the accumulation of monocytes/macrophages are inflammatory events that occur during PRL (PRL)-induced regression of the rat corpus luteum. Here we have compared the ability of prostaglandin F2alpha (PGF) and PRL to induce, in rat corpora lutea, inflammatory events thought to perpetuate luteal regression. Immature rats were ovulated with eCG-hCG and then hypophysectomized (Day 0), which resulted in a single cohort of persistent, functional corpora lutea. On Days 9-11, the rats received twice daily injections of saline, PGF (Lutalyse, 250 microg/injection), or PRL (312 microg/injection) to induce luteal regression. Surprisingly, luteal weight and plasma progestin concentrations (progesterone and 20alpha-dihydroprogesterone) did not differ between PGF-treated rats and controls; whereas both luteal weight and plasma progestins declined significantly in PRL-treated rats. Furthermore, corpora lutea of PGF-treated rats and controls contained relatively minimal ICAM-1 staining and few monocytes/macrophages. In contrast, but as expected, corpora lutea of PRL-treated rats stained intensely for ICAM-1 and contained numerous monocytes/macrophages. In an additional experiment, there was no indication that luteal prostaglandin F2alpha receptor mRNA diminished as a result of hypophysectomy. These findings suggest that prolactin, not PGF, induces the inflammatory events that accompany regression of the rat corpus luteum.

Prostaglandin F2alpha-induced expression of 20alpha-hydroxysteroid dehydrogenase involves the transcription factor NUR77

Prostaglandin F(2)alpha (PGF(2)alpha) binding to its receptor on the rat corpus luteum triggers various signal transduction pathways that lead to the activation of a steroidogenic enzyme, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), which in turn catabolizes progesterone. The molecular mechanism underlying PGF(2)alpha-induced 20alpha-HSD enzyme activity has not yet been explored. In this report we show, using mice lacking PGF(2)alpha receptor and pregnant rats, that PGF(2)alpha is responsible for the rapid and massive expression of the 20alpha-HSD gene at the end of pregnancy leading to a decrease in progesterone secretion. We also present evidence that PGF(2)alpha enhances 20alpha-HSD promoter activity. We have determined a region upstream of the -1590 position in the 20alpha-HSD promoter that confers regulation by PGF(2)alpha in ovarian primary cells. This region encompasses a unique transcription factor-binding site with a sequence of a NUR77 response element. Deletion of this motif or overexpression of a NUR77 dominant negative protein caused a complete loss of 20alpha-HSD promoter activation by PGF(2)alpha. NUR77 also transactivated the 20alpha-HSD promoter in transient transfection experiments in corpus luteum-derived cells (GG-CL). This induction required the NUR77-transactivating domain. We also show that PGF(2)alpha induces a very rapid expression of NUR77 that binds to a distal response element located at -1599/-1606 but does not interact with another proximal putative NUR77 response element located downstream in the promoter. A rapid increase in NUR77 mRNA was observed in mice corpora lutea just before parturition at a time when 20alpha-HSD becomes expressed. This increase in the expression of both genes was not seen in PGF(2)alpha receptor knockout mice. By using cyclosporin A and PGF(2)alpha treatment, we established that inhibition of NUR77 DNA binding in vivo prevents PGF(2)alpha induction of the 20alpha-HSD gene in the corpus luteum. Taken together, our results demonstrate, for the first time, that PGF(2)alpha induces in the corpus luteum the expression of the nuclear orphan receptor and transcription factor, NUR77, which in turn leads to the transcriptional stimulation of 20alpha-HSD, triggering the decrease in serum progesterone essential for parturition.

Effects of lindane on steroidogenesis and steroidogenic acute regulatory protein expression

Lindane, the gamma isomer of hexachlorocyclohexane (HCH), is one of the oldest synthetic pesticides still in use worldwide. Numerous reports have shown that this pesticide adversely affects reproductive function in animals. Although the pathogenesis of reproductive dysfunction is not yet fully understood, recent reports indicate that lindane can directly inhibit adrenal and gonadal steroidogenesis. Because Leydig cells play a pivotal role in male reproductive function through the production of testosterone, the mouse MA-10 Leydig tumor cell line was used to assess the potential effects of gamma-HCH and its isomers, alpha-HCH and delta-HCH, on steroid production, steroidogenic enzyme expression and activity, and steroidogenic acute regulatory (StAR) protein expression. StAR mediates the rate-limiting and acutely regulated step in hormone-stimulated steroidogenesis, the intramitochondrial transfer of cholesterol to the P450(scc) enzyme. Our studies demonstrate that alpha-, delta-, and gamma-HCH inhibited dibutyryl ([Bu](2)) cAMP-stimulated progesterone production in MA-10 cells in a dosage-dependent manner without affecting general protein synthesis; and protein kinase A or steroidogenic enzyme expression, activity, or both. In contrast, each of these isomers dramatically reduced (Bu)(2)cAMP-stimulated StAR protein levels. Therefore, our results are consistent with the hypothesis that alpha-, delta-, and gamma-HCH inhibited steroidogenesis by reducing StAR protein expression, an action that may contribute to the pathogenesis of lindane-induced reproductive dysfunction.

The role of arachidonic acid in steroidogenesis and steroidogenic acute regulatory (StAR) gene and protein expression

This study was conducted to examine the mechanism for arachidonic acid (AA) regulation of steroidogenic acute regulatory (StAR) protein expression and the relationship between AA and cAMP in hormone-induced steroidogenesis. Dibutyryl cyclic AMP (Bt(2)cAMP)-stimulated MA-10 Leydig cells were treated with AA and/or the phospholipase A(2) inhibitor, dexamethasone. Dexamethasone significantly reduced Bt(2)cAMP-stimulated progesterone production, StAR promoter activity, StAR mRNA, and StAR protein. The inhibitory effects of dexamethasone were reversed by the addition of 150 microm AA to MA-10 cells. In addition, MA-10 cells were treated with the lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), the 5-lipoxygenase inhibitor, AA861, the epoxygenase inhibitor, miconazole, and the cyclooxygenase inhibitor, indomethacin. Both NDGA and AA861 inhibited progesterone production and StAR protein expression. AA861-inhibited progesterone synthesis and StAR protein were partially reversed by addition of the 5- lipoxygenase metabolite, 5(S)-hydroperoxy-(6E,8Z,11Z, 14Z)-eicosatetraenoic acid. Inhibition of epoxygenase activity inhibited progesterone production significantly, but StAR protein was only slightly reduced. Indomethacin enhanced StAR protein expression and significantly increased progesterone production. Inhibition of AA release or lipoxygenase activities did not affect protein kinase A activity, whereas inhibition of protein kinase A activity using H89 reduced Bt(2)cAMP-induced StAR protein. AA alone did not induce StAR protein expression nor steroid production. These results demonstrate the essential role of AA in steroid biosynthesis and StAR gene transcription and suggest the possible involvement of the lipoxygenase pathway in steroidogenesis. This study further indicates that AA and cAMP transduce signals from trophic hormone receptors to the nucleus through two separate pathways and act to co-regulate steroid production and StAR gene expression and indicates that both pathways are required for trophic hormone-stimulated steroidogenesis.