Expression of the steroidogenic acute regulatory protein and luteinizing hormone receptor and their regulation by tumor necrosis factor alpha in rat corpora lutea

Rat Ovarian Function Is Impaired during Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease affecting the CNS and occurring far more prevalently in women than in men. In both MS and its animal models, sex hormones play important immunomodulatory roles. We have previously shown that experimental autoimmune encephalomyelitis (EAE) affects the hypothalamic-pituitary-gonadal axis in rats of both sexes and induces an arrest in the estrous cycle in females. To investigate the gonadal status in female rats with EAE, we explored ovarian morphometric parameters, circulating and intraovarian sex steroid levels, and the expression of steroidogenic machinery components in the ovarian tissue. A prolonged state of diestrus was recorded during the peak of EAE, with maintenance of the corpora lutea, elevated intraovarian progesterone levels, and increased gene and protein expression of StAR, similar to the state of pseudopregnancy. The decrease in CYP17A1 protein expression was followed by a decrease in ovarian testosterone and estradiol levels. On the contrary, serum testosterone levels were slightly increased. With unchanged serum estradiol levels, these results point at extra-gonadal sites of sex steroid biosynthesis and catabolism as important regulators of their circulating levels. Our study suggests alterations in the function of the female reproductive system during central autoimmunity and highlights the bidirectional relationships between hormonal status and EAE.

ALK4-SMAD3/4 mediates the effects of activin A on the upregulation of PAI-1 in human granulosa lutein cells

In the mammalian ovary, the proteolysis of the extracellular matrix is dynamically regulated by plasminogen activator and plasminogen activator inhibitor (PAI), and it is a critical event that influences various physiological and pathological processes. Activin A is a member of the transforming growth factor-β superfamily and is expressed at a high level in human luteal cells that play an essential role in the regulation of the luteal function. At present, it is not known whether activin A can regulate the expression and production of PAI in human granulosa lutein (hGL) cells. The present study aimed to examine the effects of activin A on the expression and production of intraovarian PAI-1 and the underlying molecular mechanisms. Using primary and immortalized hGL cells as the cell model, we demonstrated that activin A upregulated the expression of PAI-1 and increased the production of PAI-1 in an autocrine/paracrine manner. Additionally, using a dual inhibition approach (molecular inhibitors and siRNA-mediated knockdown), we showed that this biological function is mediated by the ALK4-mediated SMAD3-SMAD4-dependent signaling pathway. Our findings suggest that activin A may be involved in the regulation of luteal function via the induction of PAI-1 expression and an increase in PAI-1 production.

Luteolysis and the Auto-, Paracrine Role of Cytokines From Tumor Necrosis Factor α and Transforming Growth Factor β Superfamilies

Successful pregnancy establishment demands optimal luteal function in mammals. Nonetheless, regression of the corpus luteum (CL) is absolutely necessary for normal female cyclicity. This dichotomy relies on intricate molecular signals and rapidly activated biological responses, such as angiogenesis, extracellular matrix (ECM) remodeling, or programmed cell death. The CL establishment and growth after ovulation depend not only on the luteinizing hormone-mediated endocrine signal but also on a number of auto-, paracrine interactions promoted by cytokines and growth factors like fibroblast growth factor 2, vascular endothelial growth factor A, and tumor necrosis factor α (TNF), which coordinate vascularigenesis and ECM reorganization as well as steroidogenesis. With the organ fully developed, the release of the uterine prostaglandin F2α activates luteolysis, an intricate process supported by intraluteal interactions that ensure the loss of steroidogenic function (functional luteolysis) and the involution of the organ (structural luteolysis). This chapter provides an overview of the local action of cytokines during luteal function, with particular emphasis on the role of TNF and transforming growth factor β superfamilies during luteolysis.

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

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

The role for runt related transcription factor 2 (RUNX2) as a transcriptional repressor in luteinizing granulosa cells

Transcription factors induced by the LH surge play a vital role in reprogramming the gene expression in periovulatory follicles. The present study investigated the role of RUNX2 transcription factor in regulating the expression of Runx1, Ptgs2, and Tnfaip6 using cultured granulosa cells isolated from PMSG-primed immature rats. hCG or forskolin+PMA induced the transient increase in Runx1, Ptgs2, and Tnfaip6 expression, while the expression of Runx2 continued to increase until 48 h. The knockdown of the agonist-stimulated Runx2 expression increased Runx1, Ptgs2, and Tnfaip6 expression and PGE(2) levels in luteinizing granulosa cells. Conversely, the over-expression of RUNX2 inhibited the expression of these genes and PGE(2) levels. The mutation of RUNX binding motifs in the Runx1 promoter enhanced transcriptional activity of the Runx1 promoter. The knockdown and overexpression of Runx2 increased and decreased Runx1 promoter activity, respectively. ChIP assays revealed the binding of RUNX2 in the Runx1 and Ptgs2 promoters. Together, these novel findings provide support for the role of RUNX2 in down-regulation of Runx1, Ptgs2, and Tnfaip6 during the late ovulatory period to support proper ovulation and/or luteinization.

Tumor necrosis factor-α inhibits the stimulatory effect of luteinizing hormone and prostaglandin E(2) on progesterone secretion by the bovine corpus luteum

Tumor necrosis factor-α (TNF-α) is involved in the tissue remodeling that occurs in the corpus luteum (CL) during its development and regression. This cytokine is also implicated in the regulation of reproduction by its actions on ovarian steroidogenic cells. The aim of this study was to examine the influence of TNF-α on (1) progesterone (P(4)) output by the bovine CL and on (2) the responsiveness of the CL to LH or prostaglandin E(2) (PGE(2)) in vitro. In experiment 1, CL (days 8 to 10 of the estrous cycle) were perfused by using an in vitro microdialysis system with TNF-α (0.1, 0.5, or 1 μg/mL) alone or with TNF-α (1 μg/mL) followed by LH (1000 ng/mL) or PGE(2) (2 × 10(-5) M). Basal P(4) release (P < 0.05) was increased by TNF-α (0.5 or 1 μg/mL). Moreover, TNF-α (1 μg/mL) inhibited the stimulatory effect of LH or PGE(2) on P(4) output (P < 0.05). In experiment 2, 4 h after intrauterine infusion of TNF-α (0.01 μg/mL or 1 μg/mL), CL (days 8 to 10 of the estrous cycle) were collected by colpotomy, cultured, and stimulated with LH (10 ng/mL) or PGE(2) (10(-6) M). Intrauterine infusion of TNF-α at a concentration of 1 μg/mL increased basal P(4) output by CL (P < 0.05). Moreover, the intrauterine infusion of TNF-α at a concentration of 0.01 μg/mL inhibited the stimulatory effect of LH or PGE(2) on P(4) output (P < 0.05). These results indicate that TNF-α (1) does not have an effect on the autonomous, pulsatile release of P(4); (2) increases P(4) secretion by bovine CL with increasing doses, and (3) reduces in a dose-dependent manner the responsiveness of CL to luteotropic factors both directly (after infusion to CL) and indirectly (after intrauterine infusion).

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

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

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.

Functional corpora lutea are formed in matrix metalloproteinase inhibitor-treated plasminogen-deficient mice

Corpus luteum (CL) formation involves dramatic tissue remodeling and angiogenesis. To determine the functional roles of the plasminogen activator and matrix metalloproteinase (MMP) systems in these processes, we have studied CL formation and function in plasminogen (plg)-deficient mice, with or without treatment with the broad-spectrum synthetic MMP inhibitor galardin. Both the adult pseudopregnant CL model and the gonadotropin-primed immature mouse model were used. We found that CL formed normally not only in plasminogen-deficient mice and in galardin-treated wild-type mice, but also in galardin-treated plg-deficient mice, suggesting that neither of the plasminogen activator and MMP systems is essential for CL formation. Nevertheless, in plg-deficient mice, serum progesterone levels were reduced by approximately 50%, and the progesterone levels were not reduced further by galardin treatment. When CL from plg-deficient mice were stained for several molecular markers for CL development and regression, they appeared healthy and vascularized, and were indistinguishable from CL from wild-type mice. This implies that the reduced progesterone levels were not caused by impaired CL formation. Taken together, our data suggest that neither plasmin nor MMPs, alone or in combination, are required for CL formation. Therefore, the tissue remodeling and angiogenesis processes during CL formation may be mediated by redundant protease systems. However, the reduced serum progesterone levels in plg-deficient mice suggest that plasmin, but not MMPs, plays a role in maintenance of luteal function. This role may be performed through proteolytic activation of growth factors and other paracrine factors.

Temporal and spatial expression of MMP-2,-9,-14 and their inhibitors TIMP-1,-2,-3 in the corpus luteum of the cycling rhesus monkey

The corpus luteum (CL) is a transient endocrine organ that secretes progesterone to support early pregnancy. If implantation is unsuccessful, luteolysis is initiated. Extensive tissue remodeling occurs during CL formation and luteolysis. In this study, we have studied the possible involvement of MMP-2, -9, -14, and their inhibitors, TIMP-1, -2, -3 in the CL of cycling rhesus monkey at various stages by in situ hybridization, immunohistochemistry and microscopic assessment. The results showed that the MMP-2 mRNA and protein were mainly expressed in the endothelial cells at the early and middle stages of the CL development, while their expressions were observed in the luteal cells at the late stage during luteal regression. MMP-9 protein was detected in the CL at the early and middle stages, and obviously increased at the late stage. The expressions of MMP-14 and TIMP-1 mRNA were high at the early and late stages, and low at the middle stage. TIMP-2 mRNA was high throughout all the stages, the highest level could be observed at the late stage. The TIMP-3 production was detected throughout all the stages, but obviously declined during CL regression. MMP-9, -14 and TIMP-1, -2, -3 were mainly localized in the cytoplasm of the steroidogenic cells. The results suggest that the MMP/TIMP system is involved in regulation of CL development in the primate, and the coordinated expression of MMP-2, -14 and TIMP-1, -3 may have a potential role in the CL formation and the functional maintaining, while the interaction of MMP-2, -9, -14 and TIMP-1, -2, -3 might also play a role in CL regression at the late stage of CL development in the primate.

Involvement of molecules related to angiogenesis, proteolysis and apoptosis in implantation in rhesus monkey and mouse

We have established the well-defined cycling, pseudo-pregnant and pregnant rhesus monkey models, and used these to analyze expression of the common molecules specifically related to angiogenesis, apoptosis or proteolysis, such as vascular endothelial growth factor (VEGF) and its receptors KDR, flt-1, flt-4 and flk-1, basic fibroblast growth factor (bFGF) and its receptors Flg, transforming growth factor-alpha and beta1 (TGF-a/beta1), and TGF-beta1 receptor type I (TbetaR-I) and type II (TbetaR-II), as well as steroidogenic acute regulatory protein (StAR), tissue type plasminogen activator/urokinase plasminogen activator/plasminogen activator inhibitor type 1 (tPA/uPA/PAI-1) and matrix matalloproteinase type 1, -3/tissue inhibitor matalloproteinase type 1, -2, -3 (MMP-1, -3/TIMP-1, -2, -3), Fas/FasL, BcL-2/Bax, in the corpus luteum (CL), in the functional layer of the endometrium and in the materno-fetal boundary of the implantation site. We have demonstrated that: expression of these molecules in the monkey CL, endometrium and materno-fetal boundary of the implantation site is correlated well with CL functional and vascular development and with the processes involved in the establishment of the implantation window as well as with the early stages of placentation. A coordinated increase in tPA and its inhibitor PAI-1 expression in the monkey and rat CL may be instrumental in initiating luteal regression in both species, and correlated well with the timing of the closure of the implantation window, whereas high uPA activity in the CL is important for the early formation of the CL and for maintaining its function which is closely correlated to the period of establishment of the implantation window. Apoptosis, proteolysis and angiogenesis occur in the CL and in the endometrium during the time of establishment of the implantation window, as well as in the materno-fetal boundary of the implantation site at the early stages of placentation. It seems that these processes occur in these tissues in a coordinated and time- and cell-dependent manner, and are reliant on each other. Based on these observations, we have designed experiments to test the actions of some related available compounds on mouse implantation, used alone or in combination. The preliminary data showed that the compounds which could effectively affect apoptosis, angiogenesis or proteolysis in the implantation site were capable of effectively inhibiting implantation by acting on the endometrium and/or on the CL. Furthermore, the combined use of these compounds produced an obvious additive effect on inhibiting implantation. This finding suggested this may be a good approach for developing an anti-implantation agent.

TNF-alpha is a critical effector and a target for therapy in antiphospholipid antibody-induced pregnancy loss

The antiphospholipid syndrome (APS) is characterized by recurrent fetal loss, intrauterine growth restriction, and vascular thrombosis in the presence of antiphospholipid (aPL) Abs. Our studies in a murine model of APS induced by passive transfer of human aPL Abs have shown that activation of complement and recruitment of neutrophils into decidua are required for fetal loss, and emphasize the importance of inflammation in aPL Ab-induced pregnancy loss. In this study, we examine the role of TNF-alpha in pregnancy complications associated with aPL Abs in a murine model of APS. We show that aPL Abs are specifically targeted to decidual tissue and cause a rapid increase in decidual and systemic TNF-alpha levels. We identify the release of TNF-alpha as a critical intermediate that acts downstream of C5 activation, based on the fetal protective effects of TNF-alpha deficiency and TNF blockade and on the absence of increased TNF-alpha levels in C5-deficient mice treated with aPL Abs. Our results suggest that TNF-alpha links pathogenic aPL Abs to fetal damage and identify TNF blockade as a potential therapy for the pregnancy complications of APS.

Possible actions of tumor necrosis factor-alpha in ovarian function

Tumor necrosis factor-alpha (TNFalpha) is a multifunctional cytokine that was first described as a tumoricidal factor produced by activated macrophages. Extensive research over the last two decades has suggested that TNFalpha has physiologically diverse actions in ovarian function in a variety of species. TNFalpha and its specific receptors are present in the ovaries of many species. Furthermore, TNFalpha plays multiple and probably important roles in corpus luteum (CL) function as well as ovarian cell function throughout the estrous cycle. This review focuses on recent studies documenting TNFalpha in ovarian follicles and CL in several mammals. In addition, possible roles of TNFalpha in ovarian function throughout the estrous cycle and in the gestation period are discussed.

Ovarian insufficiency and early pregnancy loss induced by activation of the innate immune system

We describe a murine model of early pregnancy failure induced by systemic activation of the CD40 immune costimulatory pathway. Although fetal loss involved an NK cell intermediate, it was not due to lymphocyte-mediated destruction of the fetus and placenta. Rather, pregnancy failure resulted from impaired progesterone synthesis by the corpus luteum of the ovary, an endocrine defect in turn associated with ovarian resistance to the gonadotropic effects of prolactin. Pregnancy failure also required the proinflammatory cytokine TNF-alpha and correlated with the luteal induction of the prolactin receptor signaling inhibitors suppressor of cytokine signaling 1 (Socs1) and Socs3. Such links between immune activation and reproductive endocrine dysfunction may be relevant to pregnancy loss and other clinical disorders of reproduction.

Prostaglandin F2α amplifies tumor necrosis factor-α promoter activity by the FPB prostanoid receptor

This study examines the regulation of tumor necrosis factor-alpha (TNF-alpha) promoter activity by prostaglandin F2alpha ( PGF2alpha ) in HEK cells stably expressing either the FPA or FPB prostanoid receptors. Cells were transiently transfected with a luciferase reporter plasmid under the control of a TNF-alpha promoter and luciferase activity was measured. In the absence of PGF2alpha basal TNF-alpha reporter gene activity is elevated in FPB cells as compared with FPA cells. This elevated basal activity is blocked by pretreatment with a Rho inhibitor, but not by pretreatment with an inhibitor of protein kinase C (PKC). TNF-alpha reporter activity in FPB cells is stimulated by PGF2alpha and this is decreased by pretreatment with a chelator of intracellular calcium or by a gap junction inhibitor. In FPB cells pretreatment with a Rho inhibitor combined with either a calcium chelator or a gap junction inhibitor decreases both basal and PGF2alpha stimulated TNF-alpha reporter activity. Interestingly post-treatment of FPB cells with an inhibitor of PKC decreased PGF2alpha stimulated TNF-alpha reporter gene activity even though pretreatment did not. It, therefore, appears that PGF2alpha stimulated TNF-alpha reporter activity in FPB cells is amplified by a Rho-dependent mechanism involving calcium, gap junctions, and PKC. These findings may help in understanding the function of the FPB isoform in the corpus luteum.

Expressions of VEGF and its receptors in rat corpus luteum during interferon alpha administration in early and pseudopregnancy

It is accepted that angiogenesis plays an important role in the development of the corpus luteum (CL) and is probably necessary for normal lutein cell function. A number of drugs currently being tested in clinical trials as possible angiogenesis inhibitors were not originally developed with the intention of suppressing tumor angiogenesis. Interferon alpha (IFN-alpha) is one of the notable examples of such 'accidental angiogenesis inhibitors' and daily administration of IFN-alpha is known to suppress tumor growth, tumor vascularization, and down-regulation of various growth factors. We investigated the effects of IFN-alpha treatment on the expression of vascular endothelial growth factor (VEGF), and its receptors KDR and Flt-1, and CD34 in CL during the first week of pseudopregnancy and pregnancy in hormonally induced rat ovaries by immunohistochemistry and Western blot techniques. Basal body temperatures of the drug-treated rats, as an indicator of treatment effect, were determined daily and were increased significantly when compared to controls (38.03 +/- 0.18 vs. 36.6 +/- 0.1 degrees C), respectively. The effect of IFN-alpha treatment was minimal when the entire week was evaluated, however, the expression of VEGF decreased at 3rd, 5th, and 7th days of both pregnancy and pseudopregnancy, when compared to the 1st day, whereas there was not a such alteration in the untreated rats regarding these days. The daily subcutaneous administrations of 672.500 U IFN-alpha2b had minimal effects on the expressions of VEGF, and its two receptors KDR and Flt-1 in either pregnant or pseudopregnant corpora lutea utilizing HSCORE.

Multiple roles of TNF super family members in corpus luteum function

The main function of the corpus luteum (CL) is the production of progesterone. Adequate luteal progesterone is crucial for determining the physiological duration of the estrous cycle and for achieving a successful pregnancy. The CL is regulated not only by hypophyseal gonadotropin, but also by a number of cytokines that are locally produced. Tumor necrosis factor-alpha (TNF) and its specific receptors (TNFR) are present in the CL of many species. TNF plays multiple and likely important roles in CL function throughout the estrous cycle. TNF appears to have luteotropic and luteolytic roles in the CLs. In contrast, Fas ligand (Fas L), another member of TNF super family (TNF-SF), is primarily recognized for its apoptotic actions. Presumably, Fas L binds its cognate receptor (Fas) to induce structural luteolysis. This review is designed to focus on recent studies documenting the expression of TNF and Fas L, their receptors, and intracellular signaling mechanisms in the CL.

Expression and regulation of plasminogen activators, plasminogen activator inhibitor type-1, and steroidogenic acute regulatory protein in the rhesus monkey corpus luteum

The corpus luteum (CL) is a transient endocrine organ that secretes progesterone to support early pregnancy. Using primate materials obtained from rhesus monkeys, we have in this study investigated the expression and regulation of the plasminogen activators (PAs) and PA inhibitor type 1 (PAI-1) during CL development and regression. Adult (5-7 yr old) female rhesus monkeys were treated with pregnant mare serum gonadotropin/human chorionic gonadotropin to induce ovulation and follicular luteinization. At various luteal developmental stages, CL or whole ovaries were obtained for preparing luteal cells, Northern blot, in situ hybridization, and immunohistochemistry. We demonstrated that luteal cells from the rhesus monkey were able to produce both tissue type PA (tPA) and urokinase type PA, as well as the physiological PAI-1. During luteal development in the monkey, urokinase type PA was the major PA species taking part in the active angiogenesis and tissue remodeling processes in the forming CL. However, the mRNA as well as the enzymatic activity levels of tPA increased dramatically in monkey CL with the advent of luteolysis. This change of tPA levels was in a temporal coordination with the regulation of PAI-1 expression, resulting in an increased tPA activity at the initiation of luteolysis. Therefore, we suggest that tPA might be a luteolytic factor to the monkey CL. A PAI-1 modulated tPA activity might be important for the initiation of luteolysis in the monkey. In addition, we have also demonstrated that the expression of steroidogenic acute regulatory protein in the monkey CL was in accordance with the changes of progesterone production, suggesting that steroidogenic acute regulatory protein expression may be considered as a reliable marker for CL function in primates.

Influence of cytokines and growth factors on distinct steroidogenic enzymes in vitro: a short tabular data collection

Cytokines (IL-1, IL-6, IL-8, IL-11, TNF, IFN-gamma, and TGF-beta) and growth factors (EGF, bFGF, aFGF, and KGF) play an important role in modulation of hormone secretion by directly influencing specific enzyme steps of steroidogenesis in various endocrine cell types. For this tabular data collection, the following enzyme steps were considered: steroidogenic acute regulatory protein (StAR), side chain cleavage enzyme (P450scc), 3 beta-hydroxysteroid dehydrogenase, 17-alpha-hydroxylase/17,20-lyase (P450c17), 17-beta-hydroxysteroid-dehydrogenase, aromatase complex, 5-alpha-reductase, P450c21, DHEAS sulfatase, and DHEA sulfotransferase. This collection summarizes the current information on how the mentioned cytokines and growth factors influence particular enzyme steps.

Induction of apoptosis in granulosa cells by TNF alpha and its attenuation by glucocorticoids involve modulation of Bcl-2

Tumor necrosis factor alpha (TNF alpha) plays a role in mammalian ovarian follicular development, steroidogenesis, ovulation, luteolysis, and atresia, but the exact mechanism of TNF alpha action is not completely understood. Induction of apoptosis and suppression of steroidogenesis by TNF alpha in primary preovulatory rat and human granulosa cells, as well as, in human granulosa cells immortalized by mutated p53, were characterized in the present work. Dexamethasone (Dex) and hydrocortisone efficiently suppressed TNF alpha-induced apoptosis in granulosa cells. TNF alpha dramatically reduced intracellular levels of Bcl-2, while Dex abrogated this reduction. TNF alpha reduced considerably intracellular levels of StAR protein, a key regulating factor in steroidogenesis. This reduction can be explained only in part by elimination of cells through apoptosis, since loss of steroidogenic capacity was much higher and faster than the rate and extent of loss of cell viability induced by TNF alpha, suggesting independent mechanisms for TNF alpha-induction of apoptosis and TNF alpha-suppression of steroidogenesis.

Effect of iron deficiency on placental cytokine expression and fetal growth in the pregnant rat

Iron deficiency anemia is the most common nutritional disorder in the world. Anemia is especially serious during pregnancy, with deleterious consequences for both the mother and her developing fetus. We have developed a model to investigate the mechanisms whereby fetal growth and development are affected by maternal anemia. Weanling rats were fed a control or iron-deficient diet before and throughout pregnancy and were killed at Day 21. Dams on the deficient diet had lower hematocrits, serum iron concentrations, and liver iron levels. Similar results were recorded in the fetus, except that the degree of deficiency was markedly less, indicating compensation by the placenta. No effect was observed on maternal weight or the number and viability of fetuses. The fetuses from iron-deficient dams, however, were smaller than controls, with higher placental:fetal ratios and relatively smaller livers. Iron deficiency increased levels of tumor necrosis factor alpha (TNFalpha) only in the trophoblast giant cells of the placenta. In contrast, levels of type 1 TNFalpha receptor increased significantly in giant cells, labyrinth, cytotrophoblast, and fetal vessels. Leptin levels increased significantly in labyrinth and marginally (P = 0.054) in trophoblast giant cells. No change was observed in leptin receptor levels in any region of the placentas from iron-deficient dams. The data show that iron deficiency not only has direct effects on iron levels and metabolism but also on other regulators of growth and development, such as placental cytokines, and that these changes may, in part at least, explain the deleterious consequences of maternal iron deficiency during pregnancy.

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.

Influence of the drinking water disinfection by-product dibromoacetic acid on rat estrous cyclicity and ovarian follicular steroid release in vitro

The drinking water disinfection by-product, dibromoacetic acid (DBA) has been reported to affect gonadal functions in the male rat. However, there is little information regarding the influence of DBA on female reproductive activity. Consequently, the present study investigated the effects of DBA on estrous cyclicity and the impact in vitro of DBA on ovarian follicular steroid secretion. Regularly cycling animals were dosed with DBA (0 to 270 mg/kg/day) for 14 days and estrous cyclicity was monitored during treatment and for an additional 2-week posttreatment interval. A dose-related alteration in cyclicity was observed at 90 and 270 mg/kg/day, which persisted through the posttreatment monitoring in the high dose group. An in vitro exposure of preovulatory follicles to DBA was then used to assess the influence of DBA on steroid release. To select a concentration for use, a single oral exposure to 270 mg/kg was administered, and the mean blood levels were determined over a 5-h interval. For this in vitro work, pairs of preovulatory follicles from PMSG-primed immature rats were exposed to 0 or 50 microg/mL DBA over a 24-h period and evaluated for estradiol and progesterone release under baseline and hCG-stimulated conditions. The influence of tumor necrosis factor (TNFalpha) exposures under these conditions was also determined. In the nonstimulated condition, DBA was found to increase the release of estradiol, but had no detectable effect in response to hCG. Progesterone, however, showed marked suppression under hCG stimulation following exposure to DBA, while nonstimulated secretion was unaffected. TNFalpha by itself also suppressed stimulated progesterone release, but had no additional effect in combination with DBA. The data suggest that one factor in the disruption in estrous cyclicity could be an alteration in steroid production, which was characterized by separate effects on both estradiol and progesterone secretion.