FOS, a Critical Downstream Mediator of PGR and EGF Signaling Necessary for Ovulatory Prostaglandins in the Human Ovary

CONTEXT

Fos null mice failed to ovulate and form a corpus luteum (CL) even when given exogenous gonadotropins, suggesting that ovarian Fos expression is critical for successful ovulation and CL formation. However, little is known about FOS in the human ovary.

OBJECTIVES

To determine the expression, regulation, and function of FOS in human periovulatory follicles.

DESIGN/PARTICIPANTS

Timed periovulatory follicles were obtained from normally cycling women. Granulosa/lutein cells were collected from in vitro fertilization patients.

MAIN OUTCOME MEASURES

The in vivo expression after human chorionic gonadotropin (hCG) administration and in vitro regulation of FOS, JUN, JUNB, and JUND was evaluated at the mRNA and protein level. Binding of progesterone receptor (PGR) and FOS to their target genes was assessed by chromatin immunoprecipitation analyses. Prostaglandin E2 (PGE2) and progesterone were measured.

RESULTS

The expression of FOS, JUNB, and JUND drastically increased in ovulatory follicles after hCG administration. In human granulosa/lutein cell cultures, hCG increased the expression of FOS and JUN proteins. Inhibitors of PGR and epidermal growth factor (EGF) receptors reduced hCG-induced increases in the expression and phosphorylation of FOS. PGR bound to the FOS gene. A selective FOS inhibitor blocked hCG-induced increases in PGE2 and the expression of prostaglandin (PG) synthases and transporters (PTGES, SLCO2A1, and ABCC1). FOS bound to the promoter regions of these genes.

CONCLUSIONS

The increase of FOS/activator protein 1 in human periovulatory follicles after hCG administration is mediated by collaborative actions of PGR and EGF signaling and critical for the upregulated expression of key ovulatory genes required for the rise in ovulatory PG in human granulosa cells.

Ovulatory Induction of SCG2 in Human, Nonhuman Primate, and Rodent Granulosa Cells Stimulates Ovarian Angiogenesis

The luteinizing hormone (LH) surge is essential for ovulation, but the intrafollicular factors induced by LH that mediate ovulatory processes (e.g., angiogenesis) are poorly understood, especially in women. The role of secretogranin II (SCG2) and its cleaved bioactive peptide, secretoneurin (SN), were investigated as potential mediators of ovulation by testing the hypothesis that SCG2/SN is induced in granulosa cells by human chorionic gonadotropin (hCG), via a downstream LH receptor signaling mechanism, and stimulates ovarian angiogenesis. Humans, nonhuman primates, and rodents were treated with hCG in vivo resulting in a significant increase in the messenger RNA and protein levels of SCG2 in granulosa cells collected early during the periovulatory period and just prior to ovulation (humans: 12 to 34 hours; monkeys: 12 to 36 hours; rodents: 4 to 12 hours post-hCG). This induction by hCG was recapitulated in an in vitro culture system utilizing granulosa-lutein cells from in vitro fertilization patients. Using this system, inhibition of downstream LH receptor signaling pathways revealed that the initial induction of SCG2 is regulated, in part, by epidermal growth factor receptor signaling. Further, human ovarian microvascular endothelial cells were treated with SN (1 to 100 ng/mL) and subjected to angiogenesis assays. SN significantly increased endothelial cell migration and new sprout formation, suggesting induction of ovarian angiogenesis. These results establish that SCG2 is increased in granulosa cells across species during the periovulatory period and that SN may mediate ovulatory angiogenesis in the human ovary. These findings provide insight into the regulation of human ovulation and fertility.

The expression of CXCR4 is induced by the luteinizing hormone surge and mediated by progesterone receptors in human preovulatory granulosa cells

The chemokine CXC motif ligand 12 (CXCL12) and its cognate receptor, CXCR4, have been implicated in the ovulatory process in various animal models. However, little is known about the expression and regulation of CXCL12 and CXCR4 and their functions during the ovulatory period in the human ovary. In this study, we characterized the expression patterns of CXCL12 and CXCR4 in preovulatory follicles collected before the luteinizing hormone (LH) surge and at defined hours after hCG administration in women with the regular menstrual cycle. The levels of mRNA and protein for CXCR4 were increased in granulosa cells of late ovulatory follicles, whereas CXCL12 expression was constant in follicles throughout the ovulatory period. Both CXCR4 and CXCL12 were localized to a subset of leukocytes around and inside the vasculature of human preovulatory follicles. Using a human granulosa cell culture model, the regulatory mechanisms and functions of CXCL12 and CXCR4 expression were investigated. Human chorionic gonadotropin (hCG) stimulated CXCR4 expression, whereas CXCL12 expression was not affected, mimicking in vivo expression patterns. Both RU486 (progesterone receptor antagonist) and CoCl2 (HIFs activator) blocked the hCG-induced increase in CXCR4 expression, whereas AG1478 (EGFR inhibitor) had no effect. The treatment with CXCL12 had no effect on granulosa cell viability but decreased hCG-stimulated CXCR4 expression.

Coordinated Regulation Among Progesterone, Prostaglandins, and EGF-Like Factors in Human Ovulatory Follicles

CONTEXT

In animal models, the luteinizing hormone surge increases progesterone (P4) and progesterone receptor (PGR), prostaglandins (PTGs), and epidermal growth factor (EGF)-like factors that play essential roles in ovulation. However, little is known about the expression, regulation, and function of these key ovulatory mediators in humans.

OBJECTIVE

To determine when and how these key ovulatory mediators are induced after the luteinizing hormone surge in human ovaries.

DESIGN AND PARTICIPANTS

Timed periovulatory follicles were obtained from cycling women. Granulosa/lutein cells were collected from in vitro fertilization patients.

MAIN OUTCOME MEASURES

The in vivo and in vitro expression of PGR, PTG synthases and transporters, and EGF-like factors were examined at the level of messenger RNA and protein. PGR binding to specific genes was assessed. P4 and PTGs in conditioned media were measured.

RESULTS

PGR, PTGS2, and AREG expressions dramatically increased in ovulatory follicles at 12 to 18 hours after human chorionic gonadotropin (hCG). In human granulosa/lutein cell cultures, hCG increased P4 and PTG production and the expression of PGR, specific PTG synthases and transporters, and EGF-like factors, mimicking in vivo expression patterns. Inhibitors for P4/PGR and EGF-signaling pathways reduced hCG-induced increases in PTG production and the expression of EGF-like factors. PGR bound to the PTGS2, PTGES, and SLCO2A1 genes.

CONCLUSIONS

This report demonstrated the time-dependent induction of PGR, AREG, and PTGS2 in human periovulatory follicles. In vitro studies indicated that collaborative actions of P4/PGR and EGF signaling are required for hCG-induced increases in PTG production and potentiation of EGF signaling in human periovulatory granulosa cells.

Induction of Tissue Factor Pathway Inhibitor 2 by hCG Regulates Periovulatory Gene Expression and Plasmin Activity

Increased proteolytic activity is a key event that aids in breakdown of the follicular wall to permit oocyte release. How the protease activity is regulated is still unknown. We hypothesize that tissue factor pathway inhibitor 2 (TFPI2), a Kunitz-type serine protease inhibitor, plays a role in regulating periovulatory proteolytic activity as in other tissues. TFPI2 is secreted into the extracellular matrix (ECM) where it is postulated to regulate physiological ECM remodeling. The expression profile of TFPI2 during the periovulatory period was assessed utilizing a well-characterized human menstrual cycle model and a gonadotropin-primed rat model. Administration of an ovulatory dose of human chorionic gonadotropin (hCG) increased TFPI2 expression dramatically in human and rat granulosa and theca cells. This increase in Tfpi2 expression in rat granulosa cells required hCG-mediated epidermal growth factor, protein kinase A, mitogen-activated protein kinase (MAPK) 1/2, p38 MAPK and protease activated receptor 1-dependent cell signaling. A small interferingRNA-mediated knockdown of TFPI2 in rat granulosa cells resulted in increased plasmin activity in the granulosa cell conditioned media. Knockdown of TFPI2 also reduced expression of multiple genes including interleukin 6 (Il6) and amphiregulin (Areg). Overexpression of TFPI2 using an adenoviral vector partially restored the expression of Il6 and Areg in TFPI2 siRNA treated rat granulosa cells. These data support the hypothesis that TFPI2 is important for moderating plasmin activity and regulating granulosa cell gene expression during the periovulatory period. We, therefore, propose that through these actions, TFPI2 aids in the tissue remodeling taking place during follicular rupture and corpus luteum formation.

Ovarian membrane-type matrix metalloproteinases: induction of MMP14 and MMP16 during the periovulatory period in the rat, macaque, and human

An intrafollicular increase in proteolytic activity drives ovulatory events. Surprisingly, the periovulatory expression profile of the membrane-type matrix metalloproteinases (MT-MMPs), unique proteases anchored to the cell surface, has not been extensively examined. Expression profiles of the MT-MMPs were investigated in ovarian tissue from well-characterized rat and macaque periovulatory models and naturally cycling women across the periovulatory period. Among the six known MT-MMPs, mRNA expression of Mmp14, Mmp16, and Mmp25 was increased after human chorionic gonadotropin (hCG) administration in rats. In human granulosa cells, mRNA expression of MMP14 and MMP16 increased following hCG treatment. In contrast, mRNA levels of MMP16 and MMP25 in human theca cells were unchanged before ovulation but declined by the postovulatory stage. In macaque granulosa cells, hCG increased mRNA for MMP16 but not MMP14. Immunoblotting showed that protein levels of MMP14 and MMP16 in rats increased, similar to their mRNA expression. In macaque granulosa cells, only the active form of the MMP14 protein increased after hCG, unlike its mRNA or the proprotein. By immunohistochemistry, both MMP14 and MMP16 localized to the different ovarian cell types in rats and humans. Treatment with hCG resulted in intense immunoreactivity of MMP14 and MMP16 proteins in the granulosa and theca cells. The present study shows that MMP14 and MMP16 are increased by hCG administration in the ovulating follicle, demonstrating that these MMPs are conserved among rats, macaques, and humans. These findings suggest that MT-MMPs could have an important role in promoting ovulation and remodeling of the ovulated follicle into the corpus luteum.

Ovarian expression, localization, and function of tissue inhibitor of metalloproteinase 3 (TIMP3) during the periovulatory period of the human menstrual cycle

Ovulation involves reorganization of the extracellular matrix of the follicle. This study examines the expression, localization, and potential function of the tissue inhibitor of metalloproteinase 3 (TIMP3) during ovulation in women. The dominant follicle of the menstrual cycle was collected at specified times throughout the ovulatory process: pre-, early, late, and postovulatory. For quantitative studies, the follicle was bisected; granulosa and theca cells were separated and collected. For immunohistochemistry (IHC), the intact follicle was embedded and TIMP3 was localized. Additionally, granulosa cells were collected from women undergoing in vitro fertilization and treated with increasing concentrations of recombinant TIMP3, and cell viability was assessed. Real-time PCR for TIMP3 mRNA revealed an increase in TIMP3 mRNA expression in granulosa cells from the early to the late ovulatory stage. Thecal TIMP3 mRNA expression was constitutive across the periovulatory period. TIMP3 protein was localized by IHC to the granulosa and theca cell layers in pre-, early, and late ovulatory follicles as well as to the vascular bed. The staining was most intense in the granulosa and theca cells in the late ovulatory group. Treatment of human granulosa-lutein cells with exogenous recombinant TIMP3 for 24 h decreased cell viability by 60%. Using human follicles collected throughout the periovulatory period of the menstrual cycle, we have demonstrated that TIMP3 mRNA expression increases and that TIMP3 protein is in the appropriate cellular layers to regulate proteolytic remodeling as the follicle progresses toward ovulation. In addition, we have shown that elevated levels of TIMP3 lead to decreased cell viability.

Ovarian expression and regulation of the stromelysins during the periovulatory period in the human and the rat

The matrix metalloproteinases (MMPs) are postulated to facilitate follicular rupture. In the present study, expression of the stromelysins (MMP3, MMP10, MMP11) was analyzed in the periovulatory human and rat ovary. Human granulosa and theca cells were collected from the dominant follicle at various times after human chorionic gonadotropin (hCG). Intact rat ovaries, granulosa cells, and residual tissue (tissue remaining after granulosa cell collection) were isolated from equine CG (eCG)-hCG-primed animals. Mmp10 mRNA was highly induced in human granulosa and theca cells and intact rat ovaries, granulosa cells, and residual tissue. Localization of MMP10 to granulosa and theca cells in both human and rat ovarian follicles was confirmed by immunohistochemistry. Mmp3 mRNA was unchanged in human cells and rat granulosa cells, but increased in intact rat ovaries and residual tissue. Mmp11 mRNA decreased following hCG treatment in human granulosa and theca cells as well as rat granulosa cells. Regulation of Mmp10 in cultured rat granulosa cells revealed that the EGF inhibitor AG1478 and the progesterone receptor antagonist RU486 suppressed the induction of Mmp10 mRNA, whereas the prostaglandin inhibitor NS398 had no effect. Studies on the Mmp10 promoter demonstrated that forskolin plus PMA stimulated promoter activity, which was dependent upon a proximal AP1 site. In conclusion, there are divergent patterns of stromelysin expression associated with ovulation, with a marked induction of Mmp10 mRNA and a decrease in Mmp11 mRNA, yet a species-dependent pattern on Mmp3 mRNA expression. The induction of Mmp10 expression suggests an important role for this MMP in the follicular changes associated with ovulation and subsequent luteinization.

Suppression of vasoactive intestinal polypeptide in the suprachiasmatic nucleus leads to aging-like alterations in cAMP rhythms and activation of gonadotropin-releasing hormone neurons

Input from the suprachiasmatic nucleus (SCN) to gonadotropin-releasing hormone (GnRH) neurons is critical to the occurrence of regular cyclic GnRH secretion. It is thought that an essential neuropeptide in the SCN that communicates this cyclic information to GnRH neurons is vasoactive intestinal polypeptide (VIP) and that it may act through cAMP. We tested the hypothesis that (1) aging involves a blunting of cAMP diurnal rhythmicity in the SCN; (2) administration of antisense oligonucleotides (anti-oligos) against VIP, which produces an aging-like pattern in VIP, would lead to an aging-like suppression of cAMP; and (3) this in turn would lead to inhibition of the steroid-induced activation of GnRH neurons. We measured cAMP concentrations in the SCN and rostral preoptic nucleus throughout the day in young and middle-aged rats that were ovariectomized (OVX) or OVX and treated with estradiol. Our results show that cAMP concentrations exhibit a diurnal rhythm in young rats, and that this rhythm is totally abolished by the time rats are middle age. Administration of antisense oligonucleotides against VIP or random oligos suppresses VIP concentrations and abolishes the cAMP rhythm, leading to significantly reduced activation of GnRH neurons. Together, these findings strongly suggest that the SCN conveys diurnal information to GnRH neurons by driving VIP-dependent cAMP rhythms. In addition, aging involves deterioration in this VIP-driven rhythmicity, which impacts the ability of steroids to induce GnRH neuronal activation.

Aging, estradiol and time of day differentially affect serotonin transporter binding in the central nervous system of female rats

Estrogen-related changes in serotonergic neuronal transmission, including changes in the number of serotonin transporter (SERT) binding sites, have been cited as a possible cause for changes in mood, memory and sleep that occur during the menopausal transition. However, both aging and estradiol regulate SERT binding sites in the brain. The goal of this experiment was to determine how aging and estrogen interact to regulate SERT levels in the forebrain of young and reproductively senescent female Sprague-Dawley rats using [3H]paroxetine. The density of specific [3H]paroxetine binding in various brain regions was compared in young (2-4 months) and reproductively senescent (10-12 months) female rats at three times of day. In most brain regions examined, estrogen and aging independently increased the number of [3H]paroxetine binding sites. The only region that displayed a reduction in [3H]paroxetine binding with age was the suprachiasmatic nucleus (SCN). Time of day influenced [3H]paroxetine binding in the SCN and the paraventricular thalamus (PVT), two regions known to be involved in the regulation of circadian rhythms. Aging and/or estrogen also altered the pattern of binding in these regions. Thus, based on the results of this study, we conclude that aging and estrogen both act to regulate SERT binding sites in the forebrain of female rats, and that this regulation is region specific.

Neuroendocrine modulation and repercussions of female reproductive aging

The menopause marks the end of a woman's reproductive life. During the postmenopausal period, plasma estrogen concentrations decrease dramatically and remain low for the rest of her life, unless she chooses to take hormone replacement therapy. During the past 20 years, we have learned that changes in the central nervous system are associated with and may influence the timing of the menopause in women. Recently, it has become clear that estrogens act on more than just the hypothalamus, pituitary, ovary, and other reproductive organs. In fact, they play roles in a wide variety of nonreproductive functions. With the increasing life span of humans from approximately 50 to 80 years and the relatively fixed age of the menopause, a larger number of women will spend over one third of their lives in the postmenopausal state. It is not surprising that interest has increased in factors that govern the timing of the menopause and the repercussions of the lack of estrogen on multiple aspects of women's health. We have used animal models to better understand the complex interactions between the ovary and the brain that lead to the menopause and the repercussions of the hypoestrogenic state. Our results show that when rats reach middle age, the patterns and synchrony of multiple neurochemical events that are critical to the preovulatory gonadotropin-releasing hormone (GnRH) surge undergo subtle changes. The precision of rhythmic pattern of neurotransmitter dynamics depends on the presence of estradiol. Responsiveness to this hormone decreases in middle-aged rats. The lack of precision in the coordination in the output of neural signals leads to a delay and attenuation of the luteinizing hormone surge, which lead to irregular estrous cyclicity and, ultimately, to the cessation of reproductive cycles. We also have examined the impact of the lack of estrogen on the vulnerability of the brain to injury. Our work establishes that the absence of estradiol increases the extent of cell death after stroke-like injury and that treatment with low physiological levels of estradiol are profoundly neuroprotective. We have begun to explore the cellular and molecular mechanisms that underlie this novel nonreproductive action of estrogens. In summary, our studies show that age-related changes in the ability of estradiol to coordinate the neuroendocrine events that lead to regular preovulatory GnRH surges contribute to the onset of irregular estrous cycles and eventually to acyclicity. Furthermore, we have shown that the lack of estradiol increases the vulnerability of the brain to injury and neurodegeneration.

Age differentially influences estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta) gene expression in specific regions of the rat brain

Estradiol's ability to influence neurochemical events that are critical to female reproductive cyclicity and behavior decreases with age. We tested the hypothesis that decreases in estrogen receptor-alpha (ERalpha) and/or ERbeta mRNA explain the brain's declining responsiveness to estradiol. We assessed ERalpha and ERbeta mRNA levels in intact and ovariectomized estradiol-treated rats. ERbeta mRNA was detected in several brain regions and decreased by middle-age in the cerebral cortex and supraoptic nucleus of estradiol-treated rats. ERbeta mRNA levels exhibited a diurnal rhythm in the suprachiasmatic nucleus of young and middle-aged rats and this rhythm was blunted in old rats. We examined ERalpha mRNA in the periventricular preoptic, medial preoptic, ventromedial and arcuate nuclei, and it was decreased only in the periventricular preoptic nucleus of the old rats. In summary, the expression of ERalpha and ERbeta mRNAs is differentially modulated in the aging brain and changes are region specific.

Estradiol is a protective factor in the adult and aging brain: understanding of mechanisms derived from in vivo and in vitro studies

We have shown that 17beta-estradiol exerts profound protective effects against stroke-like ischemic injury in female rats. These effects are evident using physiological levels of estradiol replacement in ovariectomized rats and require hormone treatment prior to the time of injury. The protective actions of estradiol appear to be most prominent in the cerebral cortex, where cell death is not apparent until at least 4 h after the initiation of ischemic injury and where cell death is thought to be apoptotic in nature. Middle-aged rats remain equally responsive to the protective actions of estradiol. The maintenance of responsiveness of the cerebral cortex to the neuroprotective actions of estradiol was unexpected since responsiveness of the hypothalamus to estradiol decreases dramatically by the time animals are middle-aged. We believe that the protective actions of estradiol require the estrogen receptor-alpha, since estradiol does not protect in estrogen receptor-alpha knockout mice. We have also implemented a method of culturing cerebral cortical explants to assess the protective effects of estradiol in vitro. This model exhibits remarkable parallelisms with our in vivo model of brain injury. We have found that 17beta-estradiol decreases the extent of cell death and that this protective effect requires hormone pretreatment. Finally, 17alpha-estradiol, which does not interact effectively with the estrogen receptor, does not protect; and addition of ICI 182,780, an estrogen receptor antagonist, blocks the protective actions of estradiol. We have begun to explore the molecular and cellular mechanisms of estradiol-mediated protection. In summary, our findings demonstrate that estradiol exerts powerful protective effects both in vivo and in vitro and suggest that these actions are mediated by estrogen receptors.

Fos-induction in gonadotropin-releasing hormone neurons receiving vasoactive intestinal polypeptide innervation is reduced in middle-aged female rats

A hallmark of reproductive aging in rats is a delay in the initiation and peak, and a decrease in the amplitude, of both proestrous and steroid-induced surges of LH and a decrease in the number of GnRH neurons that express Fos during the surge. The altered timing of the LH surge and the decline in Fos expression in GnRH neurons may be due to changes in the rhythmic expression of vasoactive intestinal polypeptide (VIP), a neuropeptide that carries time-of-day information from the circadian pacemaker, located in the suprachiasmatic nuclei (SCN), to GnRH neurons. The goals of our study were to determine if aging alters 1) the innervation of GnRH neurons by VIP and 2) the ability of VIP to activate GnRH neurons by examining the effects of aging on the number of GnRH neurons apposed by VIP fibers and the number of GnRH neurons that receive VIP input that express Fos. Immunocytochemistry for GnRH and VIP; or GnRH, VIP, and Fos was performed on tissue sections collected from young (2-4 mo), regularly cycling females and middle-aged (10-12 mo) females in constant estrus. The number of GnRH neurons, GnRH neurons apposed by VIP fibers, and GnRH neurons that express Fos and apposed by VIP fibers were counted in both age groups. Our results clearly demonstrate that aging does not alter the number of GnRH neurons that receive VIP innervation. However, the number of GnRH neurons that receive VIP innervation and coexpress Fos decreases significantly. We conclude that the age-related delay in the timing of the LH surge is not due to a change in VIP innervation of GnRH neurons, but instead may result from a decreased sensitivity of GnRH neurons to VIP input.

Neuroendocrine influences and repercussions of the menopause

In summary, the evidence that both the ovary and the brain are key pacemakers in the menopause is compelling. Our appreciation that estrogens are important neurotrophic and neuroprotective factors has grown rapidly. Future studies will allow us to better understand the ensemble of factors that interact to maintain regular reproductive cyclicity and how this precise dynamic balance changes with age. Furthermore, understanding how estrogen exerts trophic and protective actions should lead to its use as an important therapeutic agent in the maintenance of normal neural function during aging and after injury.

Sex differences in the daily rhythm of vasoactive intestinal polypeptide but not arginine vasopressin messenger ribonucleic acid in the suprachiasmatic nuclei

The timing of the preovulatory surge of LH in female rodents is tightly coupled to the environmental light/dark cycle. This coupling is mediated by the circadian pacemaker located in the suprachiasmatic nuclei (SCN). Studies indicate that vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP), which are synthesized in the SCN, transmit circadian information from the SCN to GnRH neurons, thereby regulating the timing of the LH surge. However, to date, the rhythmic expression of these two peptides in the SCN has only been examined in males. The pattern of VIP expression in males is difficult to reconcile with its role in the LH surge. The purpose of the present study was to assess the rhythm of VIP messenger RNA (mRNA) levels in the SCN of female rats under several endocrine conditions. We compared this rhythm to that in males and to AVP mRNA rhythms in all experimental groups. In all groups of females, VIP mRNA levels were rhythmic, with peak expression occurring during the light phase and a nadir occurring during the dark phase. The rhythm was approximately 12 h out of phase compared with that in males. The rhythmic expression of AVP mRNA in the SCN was virtually identical in all groups of animals. Based on these results, we conclude that 1) the rhythm of VIP seen in the SCN of females during the day may serve as a facilitory signal from the SCN to GnRH neurons; 2) the sex-specific pattern of VIP mRNA does not depend on estradiol; and 3) AVP gene expression within the SCN is not sexually differentiated or altered by estradiol.

Aging alters the rhythmic expression of vasoactive intestinal polypeptide mRNA but not arginine vasopressin mRNA in the suprachiasmatic nuclei of female rats

Our laboratory has shown that the ability of the suprachiasmatic nuclei (SCN) to regulate a number of rhythmic processes may be compromised by the time females reach middle age. Therefore, we examined the effects of aging on the rhythmic expression of two neuropeptides synthesized in the SCN, vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP), using in situ hybridization. Because both VIP and AVP are outputs of the SCN, we hypothesized that age-related changes in rhythmicity are associated with alterations in the patterns of expression of these peptides. We found that VIP mRNA levels exhibited a 24 hr rhythm in young females, but by the time animals were middle-aged, this rhythm was gone. The attenuation of rhythmicity was associated with a decline in the level of mRNA per cell and in the number of cells in the SCN producing detectable VIP mRNA. AVP mRNA also showed a robust 24 hr rhythm in young females. However, in contrast to VIP, the AVP rhythm was not altered in the aging animals. The amount of mRNA per cell and the number of cells expressing AVP mRNA also was not affected with age. Based on these results we conclude that (1) various components of the SCN are differentially affected by aging; and (2) age-related changes in various rhythms may be attributable to changes in the ability of the SCN to transmit timing information to target sites. This may explain why the deterioration of various rhythmic processes occurs at different rates and at different times during the aging process.

Aging of the female reproductive system: a window into brain aging

The menopause marks the permanent end of fertility in women. It was once thought that the exhaustion of ovarian follicles was the single, most important explanation for the transition to the menopause. Over the past decade, this perception has gradually changed with the realization that there are multiple pacemakers of reproductive senescence. We will present evidence that lends credence to the hypothesis that the central nervous system is a critical pacemaker of reproductive aging and that changes at this level contribute to the timing of the menopause. Studies demonstrate that an increasing de-synchronization of the temporal order of neuroendocrine signals may contribute to the accelerated rate of follicular loss that occurs during middle age. We suggest that the dampening and destabilization of the precisely orchestrated ultradian, circadian, and infradian neural signals lead to miscommunication between the brain and the pituitary-ovarian axis. This constellation of hypothalamic-pituitary-ovarian events leads to the inexorable decline of regular cyclicity and heralds menopausal transition.

In vivo antisense antagonism of vasoactive intestinal peptide in the suprachiasmatic nuclei causes aging-like changes in the estradiol-induced luteinizing hormone and prolactin surges

In mammals, the suprachiasmatic nuclei (SCN) regulate the timing of LH surges. Recent evidence suggests that vasoactive intestinal peptide (VIP), an abundantly expressed neuropeptide of the SCN, communicates time of day information from the SCN to GnRH neurons. VIP levels in the SCN decrease with age and may be responsible for alterations in LH surges that become apparent in middle-aged rats. We wished to determine whether suppression of VIP synthesis, through antisense oligonucleotides (oligos) directed at the SCN, results in 1) selective suppression of VIP levels in the SCN and 2) aging-like changes in the secretion of LH and PRL. To test the specificity of antisense oligo treatment, rats were ovariectomized and treated with estradiol. Antisense or control random oligos were infused into the peri-SCN region through stereotaxically placed bilateral cannulas. Beginning at lights off, rats were maintained in constant dim red illumination throughout the remainder of the experiment. They were killed at specific times, brains were microdissected, and VIP concentrations in the SCN, paraventricular nuclei, and cortex were assayed. As a control for the specificity of antisense VIP treatment, we monitored the levels of arginine vasopressin in the SCN. To test the effects of antisense treatment on the pattern of plasma LH and PRL secretion, blood samples were collected from atrial catheters from 1200-2000 h, and plasma samples were assayed for LH and PRL. The results indicate that the effects of antisense treatment were discrete, as they suppressed VIP concentrations in the SCN, but had no effect on VIP concentrations in the paraventricular nuclei or cortex or on arginine vasopressin concentrations in the SCN. Peak LH levels during the surge were delayed and attenuated in antisense-treated animals compared to random oligo-treated control rats in a manner strikingly similar to that observed previously in middle-aged rats. Likewise, PRL, which was unaffected in middle-aged rats, was also unaffected by targeted suppression of VIP. In summary, our findings clearly demonstrate that antisense VIP oligos suppress VIP levels in the SCN and do not affect peptide concentrations in other regions of the brain or other neuropeptides in the SCN. Further, we show that suppression of a single neuropeptide in the SCN can mimic the effects of age on the estradiol-induced surges of LH and PRL. These data support a central role for suprachiasmatic VIP in the regulation of the LH surge and suggest that age-related perturbations in the integrity of this axis may account for alterations in the pattern of LH secretion observed during middle age.

Acute effects of antisense antagonism of a single peptide neurotransmitter in the circadian clock

The circadian clock that resides in the suprachiasmatic nucleus (SCN) of the hypothalamus is the major neural pacemaker driving most 24-h rhythms in mammals. Several neurotransmitter peptides are synthesized within this nucleus and communicate rhythmically with other cells in the SCN as well as with cells in other regions of the brain. At the present time, little is known about their role in regulating outputs of the clock. We demonstrate that antisense oligodeoxynucleotides corresponding to the NH2-terminus and the translation start site of vasoactive intestinal peptide (VIP) mRNA infused into the suprachiasmatic region of rats temporarily abolishes the circadian rhythm of corticosterone secretion without influencing stress-related corticosterone secretion in the same animals. Levels of VIP peptide are suppressed 30% on the second day after antisense treatment. These results indicate that a single neuropeptide transmitter in the circadian clock may serve a distinct role in the control of specific circadian rhythms.

Effect of lactation on hypothalamic preproenkephalin gene expression

Enkephalin appears to modulate several aspects of reproductive function in female rats. The purpose of this study was to determine if lactation influences preproenkephalin gene expression in one or more hypothalamic nuclei known to be involved in maternal or reproductive behavior and prolactin secretion. Lactating rats were killed on day 3 (LAC 3) or day 10 (LAC 10) of lactation. Controls consisted of regular 4-day cycling rats that were killed on diestrous day 1, with 9 to 12 females per group. We used in situ hybridization histochemistry to assess preproenkephalin gene expression in individual cells in the medial preoptic nucleus, anterior, medial and posterior arcuate nucleus, magnocellular and parvocellular aspects of paraventricular nucleus, and ventromedial nucleus. Preproenkephalin mRNA in the anterior arcuate nucleus increased to reach significance (P < 0.05) at day 10 of lactation. Levels in the medial arcuate nucleus increased significantly (P < 0.001) by day 3 of lactation (LAC 3) and remained elevated on day 10 (LAC 10). No significant differences between lactating and control rats were detected in preproenkephalin mRNA levels in the posterior arcuate nucleus, medial preoptic nucleus or in the ventromedial nucleus. Substantial levels of preproenkephalin mRNA were found in the paraventricular nucleus, particularly in a limited region of the magnocellular portion. However, these levels did not change with lactation. These data provide evidence for differential regulation of the preproenkephalin gene during lactation. This change may contribute to lactational hyperprolactinemia and suppressed GnRH secretion, leading to reproductive acyclicity.

A period (per)-like protein exhibits daily rhythmicity in the suprachiasmatic nuclei of the rat

The period (per) gene of Drosophila melanogaster is considered an important biological clock gene, since it regulates multiple behavioral rhythms. Per mRNA and protein exhibit circadian rhythms in the fruitfly brain and these rhythms appear to influence each other through a feedback loop. More recently, using the same antibody as was used in the Drosophila studies, PER-like proteins were detected in the suprachiasmatic nuclei (SCN) of male rats. This region of the brain is considered to be a major neural circadian pacemaker in mammals. The purpose of this study was to confirm that PER-like proteins are detectable in the SCN of female rats and to determine whether PER-like proteins exhibit a circadian rhythm. Female rats were killed at several times of day under both light/dark and constant conditions. Using the same anti-PER antibody in Western blots with Enhanced Chemiluminescence (Western-ECL) detection, the levels of the PER-like proteins were quantified in the SCN and cerebral cortex. The antibody identified a doublet band of approximately 170-160 kDa and a single band at 115 kDa. Of the three PER-like proteins only the largest exhibited a daily rhythm in the SCN, which peaked in the middle of the dark and attained its nadir around lights off; levels during the light were intermediate with a tendency towards a second drop around lights on. This rhythm did not persist under constant dim red light.(ABSTRACT TRUNCATED AT 250 WORDS)