Expression of pituitary adenylate cyclase activating polypeptide (PACAP) and PACAP type I A receptor mRNAs in granulosa cells of preovulatory follicles of the rat ovary

Differential regulation of kit ligand A (kitlga) expression in the zebrafish ovarian follicle cells--evidence for the existence of a cyclic adenosine 3', 5' monophosphate-mediated binary regulatory system during folliculogenesis

Kit ligand (Kitl) is an important paracrine factor involved in the activation of primordial follicles from the quiescent pool and in the maintenance of meiotic arrest before germinal vesicle breakdown (GVBD). It has been reported that follicle-stimulating hormone (FSH) stimulates but luteinizing hormone (LH) suppresses the expression of Kitl in the granulosa cells in mammals. Considering that both gonadotropins signal in the follicle cells mainly by activating cyclic adenosine 3', 5'-monophosphate (cAMP) pathway, we are intrigued by how cAMP differentially regulates Kitl expression. In the present study, we demonstrated that both human chorionic gonadotropin (hCG) and pituitary adenylate cyclase activating polypeptide (PACAP) inhibited insulin-like growth factor I (IGF-I)-induced Akt phosphorylation and kitlga expression in the zebrafish follicle cells. Further experiments showed that cAMP was involved in regulating the expression of kitlga. However, two cAMP-activated effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), had converse effects. PKA promoted whereas Epac inhibited the expression of kitlga, as demonstrated by the respective activators. Interestingly, cAMP also appeared to exert differential effects on kitlga expression at different stages of follicle development during folliculogenesis, significantly stimulating kitlga expression at the early growth stage but suppressing it at the full-grown stage before final oocyte maturation, implying a potential mechanism for differential effects of the same pathway at different stages. The inhibitory effect of forskolin (activator of adenylate cyclase) and H89 (inhibitor of PKA) on IGF-I-induced expression of kitlga suggested cross-talk between the cAMP and IGF-I-activated PI3K-Akt pathways. This study, together with our previous findings on IGF-I regulation of kitlga expression, provides important clues to the underlying mechanism that regulates Kit ligand expression during folliculogenesis in the ovary.

Inhibitory effect of pituitary adenylate cyclase activating polypeptide on the initial stages of rat follicle development

Pituitary adenylate cyclase activating polypeptide (PACAP) is transiently expressed in preovulatory follicles of different species and positively affects parameters correlated with the ovulatory process. It has also been shown to be expressed in the interstitial tissue and in interstitial glandular cells in the proximity of primordial and preantral follicles. The aim of the present study was to investigate whether PACAP influences the recruitment of primordial follicles and the growth and differentiation of preantral follicles. Rat ovaries from 2-day-old animals were cultured for 5 days in the presence of PACAP. This treatment significantly inhibited the primordial to primary follicle transition. PACAP inhibited granulosa cell proliferation without affecting cell viability. PACAP also inhibited the growth of isolated preantral follicles cultured under basal conditions or in the presence of follicle-stimulating hormone (FSH). These results suggest that PACAP is significantly involved in the cyclic recruitment of primordial follicles and in the FSH-dependent growth of preantral follicles.

Expression and in vitro regulation of pituitary adenylate cyclase-activating polypeptide (pacap38) and its type I receptor (pac1-r) in the gonads of tilapia (Oreochromis mossambicus)

Pituitary adenylate cyclase-activating polypeptide (PACAP), a pleiotropic neuropeptide, has diverse functions in mammals. However, studies of the expression and function of PACAP and its receptor in fish, particularly in the reproductive system, are still limited. In this report, semi-quantitative RT-PCR and immunohistochemical staining were performed to identify expression domains of commercially important tilapia (Oreochromis mossambicus). PACAP (tpacap(38)) and its type I receptor (tpac(1)-r). Transcripts were detected in the brain, gallbladder, gill, heart, intestine, kidney, muscles, pancreas, spleen, stomach, testes, and ovaries, but not in the liver. Expression of tpacap(38) and tpac(1)-r mRNA in brain tissue was significantly higher in both sexes compared with other tissues. Addition of exogenous ovine PACAP(38) (0.25-5 nM), cAMP analog (dibutyryl-cAMP, 0.25-1.5 mM) or forskolin (adenylate cyclase activator, 1-10 microM) significantly upregulated tpacap(38) in the gonads via a dose- and time-dependent fashion. This effect reached a maximal level at 2 h after induction, and then decreased with prolonged culture for up to 4 or 8 h. Additionally, the expression levels of tpac(1)-r were not significantly affected by ovine PACAP(38) or dibutyryl-cAMP in either sex. Forskolin had a slightly inductive effect and its function could be suppressed with the addition of protein kinase A (PKA) inhibitor, H89 (10 microM), indicating involvement of the cAMP-PKA signaling pathway in the regulation of tpacap(38). Expression of tpacap(38) and tpac(1)-r in the gonads of tilapia suggests that PACAP may mediate gonadotropin action via paracrine/autocrine mechanisms in this bony fish.

Gonadotropin stimulation of ovarian fractalkine expression and fractalkine augmentation of progesterone biosynthesis by luteinizing granulosa cells

Recent studies indicated that ovarian functions are regulated by diverse paracrine factors induced by the preovulatory increases in circulating LH. Based on DNA microarray analyses and real-time RT-PCR, we found a major increase in the transcript levels of a chemokine fractalkine after human chorionic gonadotropin (hCG) treatment during the preovulatory period in gonadotropin-primed immature mice and rats. Although CX3CR1, the seven-transmembrane receptor for fractalkine, was also found in murine ovaries, its transcripts displayed minimal changes. Using tandem RT-PCR and immunohistochemistry, fractalkine transcripts and proteins were localized in cumulus, mural granulosa, and theca cells as well as the oocytes, whereas CX3CR1 was found in the same cells except the oocyte. Real-time RT-PCR further indicated the hCG induction of fractalkine transcripts in different ovarian compartments, with the highest increases found in granulosa cells. In cultured granulosa cells, treatment with fractalkine augmented hCG stimulation of progesterone but not estradiol and cAMP biosynthesis with concomitant increases in transcript levels for key steroidogenic enzymes (steroidogenic acute regulatory protein, CYP11A, and 3beta-hydroxysteroid dehydrogenase). In cultured preovulatory follicles, treatment with fractalkine also augmented progesterone production stimulated by hCG. Furthermore, treatment with fractalkine augmented the phosphorylation of P38 MAPK in cultured granulosa cells. The present data demonstrated that increases in preovulatory LH/hCG induce the expression of fractalkine to augment the luteinization of preovulatory granulosa cells and suggest the fractalkine/CX3CR1 signaling system plays a potential paracrine/autocrine role in preovulatory follicles.

Gonadotropin-dependent regulation of bovine pituitary adenylate cyclase-activating polypeptide in ovarian follicles prior to ovulation

To study the regulation of bovine pituitary adenylate cyclase-activating polypeptide (PACAP) in preovulatory follicles prior to ovulation, PACAP cDNA was isolated by RT-PCR. Its open reading frame (ORF) is composed of 531 bp, and encodes for a 176-amino acid protein that bears 76-90% identity with other PACAP homologs. Using bovine preovulatory follicles obtained between 0 and 24 h after human chorionic gonadotropin (hCG) and semiquantitative RT-PCR/Southern blot, we demonstrate that levels of PACAP mRNA were low at 0 h, markedly increased at 6 and 12 h (P<0.05), and declined 18 and 24 h after hCG. Levels of PACAP mRNA were high in the bovine pituitary, testis, intestine and uterus, but moderate to low in other tissues. Analyses performed on isolated preparations of granulosa and theca cells showed a significant increase of PACAP transcripts in both cell types after hCG, whereas primary granulosa cell cultures revealed high levels of PACAP as well as its receptors PAC-1 and VPAC-2 mRNA after forskolin treatment. Overexpression of the catalytic subunit of protein kinase A (PKA) in granulosa cells stimulated, but treatment with H89 or PKA inhibitor protein inhibited PACAP mRNA expression, whereas PACAP overexpression stimulated an increase in abundance of transcripts for PGHS-2, PGES, EP2 receptor, progesterone receptor, and ADAMTS-1, but not for P450-side chain cleavage and P450 aromatase. Thus, this study demonstrates the gonadotropin-dependent regulation of PACAP mRNA in bovine preovulatory follicles, the importance of PKA activation in the expression of PACAP in granulosa cells, and stimulating effect of PACAP on gene expression during the ovulatory process.

Expression localisation and functional activity of pituitary adenylate cyclase-activating polypeptide, vasoactive intestinal polypeptide and their receptors in mouse ovary

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) positively affect several parameters correlated with the ovulatory process. PACAP is transiently expressed in rat preovulatory follicles, while VIP is present in nerve fibres at all stages of development. These two peptides act by interacting with three types of receptors: PACAP type I receptor (PAC1-R), which binds with higher affinity to PACAP, and two VIP receptors (VPAC1-R and VPAC2-R), which bind to PACAP and VIP with equal affinity. The aim of the present study was to characterise the PACAP/VIP/receptor system in the mouse ovary. Results obtained by RT-PCR, immunohistochemistry and in situ hybridisation showed that PACAP was transiently expressed in granulosa cells of preovulatory follicles after human chorionic gonadotrophin (hCG) stimulation, while VIP mRNA was never observed. All the receptors were present in 22-day-old untreated mice. In preovulatory follicles, PAC1-R was expressed both in granulosa cells and in residual ovarian tissue but was stimulated by hCG mainly in granulosa cells; VPAC2-R was present in both the cell compartments and was only mildly stimulated; VPAC1-R was present mainly in the residual ovarian tissue and was downregulated by hCG. PACAP and VIP were equipotent in inhibiting apoptosis in granulosa cells, confirming the presence of functional PACAP/VIP receptors. The contemporary induction by hCG of PACAP and PAC1-R in granulosa cells of preovulatory follicles suggests that, also in mouse ovary, PACAP may play a significant role around the time of ovulation. Moreover, the presence of PACAP/VIP receptors in the untreated ovary suggests a possible role for PACAP and VIP during follicle development.

Endogenous Ligands of PACAP/VIP Receptors in the Autocrine–Paracrine Regulation of the Adrenal Gland

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the main endogenous ligands of a class of G protein-coupled receptors (Rs). Three subtypes of PACAP/VIP Rs have been identified and named PAC(1)-Rs, VPAC(1)-Rs, and VPAC(2)-Rs. The PAC(1)-R almost exclusively binds PACAP, while the other two subtypes bind with about equal efficiency VIP and PACAP. VIP, PACAP, and their receptors are widely distributed in the body tissues, including the adrenal gland. VIP and PACAP are synthesized in adrenomedullary chromaffin cells, and are released in the adrenal cortex and medulla by VIPergic and PACAPergic nerve fibers. PAC(1)-Rs are almost exclusively present in the adrenal medulla, while VPAC(1)-Rs and VPAC(2)-Rs are expressed in both the adrenal cortex and medulla. Evidence indicates that VIP and PACAP, acting via VPAC(1)-Rs and VPAC(2)-Rs coupled to adenylate cyclase (AC)- and phospholipase C (PLC)-dependent cascades, stimulate aldosterone secretion from zona glomerulosa (ZG) cells. There is also proof that they can also enhance aldosterone secretion indirectly, by eliciting the release from medullary chromaffin cells of catecholamines and adrenocorticotropic hormone (ACTH), which in turn may act on the cortical cells in a paracrine manner. The involvement of VIP and PACAP in the regulation of glucocorticoid secretion from inner adrenocortical cells is doubtful and surely of minor relevance. VIP and PACAP stimulate the synthesis and release of adrenomedullary catecholamines, and all three subtypes of PACAP/VIP Rs mediate this effect, PAC(1)-Rs being coupled to AC, VPAC(1)-Rs to both AC and PLC, and VPAC(2)-Rs only to PLC. A privotal role in the catecholamine secretagogue action of VIP and PACAP is played by Ca(2+). VIP and PACAP may also modulate the growth of the adrenal cortex and medulla. The concentrations attained by VIP and PACAP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their adrenal content is consistent with a local autocrine-paracrine mechanism of action.

Ethanol Decreases the Expression of Pituitary Adenylate Cyclase Activating Polypeptide in Rat Testes

The present study was designed to evaluate the effect of ethanol on pituitary adenylate cyclase activating polypeptide (PACAP) expression in adult rat testes. Ethanol (3 g/kg i.p., 15% v/v in saline) was administrated to adult male rats for 10 days. Using northern blot analysis, we elucidated the decrease of PACAP mRNA in rat testes by ethanol administration. The level of PACAP mRNA was decreased by 46.5% in testes of the ethanol-treated animals, compared to that of saline-treated animals. In particular, ethanol exposure decreased the expression of PACAP mRNA and protein in developing germ cells, which are sperm cell progenitors. Thus, our findings suggest that the decrease of PACAP in developing germ cells by ethanol administration may contribute to the suppression of male reproductive activity.

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.

Expression patterns of pituitary adenylate cyclase activating polypeptide and its type I receptor mRNAs in the rat placenta

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated from ovine hypothalamus and is known to act as a tropic factor in various cells. Recent report revealed the expression of PACAP and the PACAP type I (PAC(1)) receptor in human and rat placentas at term. Placenta is a critical organ that synthesizes several growth and angiogenic factors for its own growth as well as fetal development. However, there is little information regarding the expression pattern and cellular localization of PACAP and PAC(1) during pregnancy. The aim of this study was to define the expression and distribution of PACAP and PAC(1) receptor mRNAs in the rat placenta during pregnancy. PACAP and PAC(1) receptor mRNAs were expressed in decidual cells, chorionic vessels, and stromal cells of the chorionic villi. Interestingly, the expression of these genes varied with the day of gestation. For example, PACAP and PAC(1) receptor mRNAs expressed in decidual cells on day 13.5 and 15.5, their expression was strong in chorionic vessels and stromal cells of the chorionic villi within the labyrinth zone on day 17.5, 19.5, and 21.5. In fact, as gestation advanced, the expression of PACAP and PAC(1) receptor mRNAs in the decidua cells disappeared, as their high expression became evident in the chorionic vessels and stromal cells of the chorionic villi. Our finding that PACAP and the PAC(1) receptor are co-localized and their genes seemingly co-regulated within specific placental areas, strongly suggest that this peptide may play an important role, as an autoregulator or pararegulator via its PAC(1) receptor, in physiological functioning of the placenta for gestational maintenance.

Changes of steroidogenic acute regulatory protein mRNA expression in postnatal rat development

The present study investigated the expression pattern of steroidogenic acute regulatory protein (StAR) mRNA in several brain regions and peripheral endocrine organs using Northern blot, RT-PCR and in situ hybridization. StAR mRNA in the adrenal gland was detected at birth and decreased for 2 weeks postnatally. In gonads, it was also detected at birth though at a lower level than adrenal, and was maintained until week 3. Thereafter StAR mRNA expression in both endocrine organs was increased. Though the amount of StAR mRNA in the brain was much less than that of peripheral endocrine organs, it was expressed from birth and, in general, appeared to gradually increase during postnatal development. A gradual increase was found in the hypothalamus, while a sigmoidal expression was shown in the olfactory bulb. The increased expression of StAR mRNA in the postnatal period suggests that it might have a role in the regulation of neurosteroidogenesis needed in neuronal cell growth and differentiation in postnatal rat brain development.

Temporal and spatial patterns of ovarian gene transcription following an ovulatory dose of gonadotropin in the rat

In recent years, there have been a number of efforts to identify genes that are expressed in mature ovarian follicles in response to an ovulatory dose of LH or its homologue hCG. This review keys on 20 ovulation-specific genes that we have identified by the molecular procedure known as differential display. The objective is to use this sampling of genes to illustrate the diversity in the temporal and spatial patterns of expression of genes in the ovary following the stimulus of this gonadal target tissue by a single glycoprotein hormone. The specific genes that are surveyed include 5-aminolevulinate synthase; early growth response protein-1; gamma-glutamylcysteine synthetase; cyclooxygenase-2; epiregulin; pituitary adenylate cyclase-activating polypeptide; tumor necrosis factor-stimulated gene-6; regulator of G-protein signaling protein-2; adrenodoxin; steroidogenic acute regulatory protein; 3alpha-hydroxysteroid dehydrogenase; CD63, a disintegrin and metalloproteinase with thrombospondin motifs; tissue inhibitor of metalloproteinase-1; carbonyl reductase, a G-protein-coupled receptor; pancreatitis-associated protein-III; glutathione S-transferase; and metallothionein-1. The ovulatory expression of these different genes is predominantly within the granulosa layer of mature follicles. However, there were also instances of expression in the thecal and stromal tissue of the ovary, as well as in vascular endothelial cells and in luteal tissue. The overwhelming impression is that the molecular events of ovulation are far more complex, and therefore more highly ordered, than originally imagined.

Progesterone receptor activation mediates LH-induced type-I pituitary adenylate cyclase activating polypeptide receptor (PAC(1)) gene expression in rat granulosa cells

We have previously reported that the pituitary adenylate cyclase activating polypeptide (PACAP) gene is regulated in ovarian granulosa cells by the autocrine and/or paracrine interaction between progesterone and its nuclear receptor progesterone receptor (PR). To initiate studies on the functional significance of the progesterone-induced PACAP production in luteinizing granulosa cells, we sought to determine the expression and hormonal regulation of PACAP receptors in the rat ovary. The relative mRNA levels of three known PACAP receptor subtypes (PAC(1), VPAC(1), and VPAC(2)) were determined in ovaries of immature rats treated with gonadotropins, by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. Results show that all PAC(1), VPAC(1), and VPAC(2) transcripts are expressed at a detectable level in immature rat ovaries. Importantly, the ovarian level of PAC(1), but not VPAC(1) or VPAC(2), mRNA notably changes during gonadotropin challenges. Ovarian PAC(1) mRNA expression decreases during the pregnant mare's serum gonadotropin (PMSG)-induced follicular phase but substantially increases during the human chorionic gonadotropin (hCG)-induced periovulatory period. Because the hCG-induced increase in ovarian PAC(1) mRNA expression is attributable to the hormone-induced PAC(1) mRNA expression in granulosa cells of the preovulatory follicles, we next examined whether hCG regulates PAC(1) mRNA expression by directly acting on granulosa cells. When granulosa cells isolated from PMSG (40 h)-primed immature rats were challenged with hCG (or forskolin), PAC(1), but not VPAC(1) or VPAC(2), mRNA expression significantly increased within 6 h. Because the LH-induced PAC(1) mRNA expression (6 h) proceeds PR activation (3 h) in granulosa cells as the LH-induced PACAP mRNA expression (6 h) does, we further determined the cause-effect relationship among LH, PR activation and PAC(1) receptor gene expression, by examining the effect of PR antagonist, ZK98299, on the ability of LH to increase PAC(1) mRNA levels in luteinizing granulosa cells. Results show that ZK98299 inhibited the stimulatory effect of hCG (or forskolin) on PAC(1) mRNA expression, at the level of all known splice variants of PAC(1) mRNA in granulosa cells. In summary, our results demonstrating that PR activation is critical for the LH-induced PAC(1) gene expression in luteinizing granulosa cells suggest that PR activation regulates the finely tuned expression of the PACAP/PACAP receptor genes in luteinizing granulosa cells and thus dictates the timing of the autocrine and/or paracrine function of PACAP in preovulatory follicles.