Pituitary adenylate cyclase-activating polypeptide regulates rat Leydig cell function in vitro

Seasonal changes in the expression of PACAP, VPAC1, VPAC2, PAC1 and testicular activity in the testis of the muskrat (<em>Ondatra zibethicus</em>)

Pituitary adenylate cyclase-activating polypeptide (PACAP) plays an important role in the steroidogenesis and spermatogenesis in the testis through its receptors PAC1, VPAC1, and VPAC2. In this study, we investigated the seasonal expressions of PACAP, PAC1, VPAC1, VPAC2, luteinizing hormone receptor (LHR), follicle stimulating hormone receptor (FSHR), steroidogenic acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), and CYP17A1 in the testis of the male muskrat during the breeding season and the non-breeding season. Histologically, we found the presence of Leydig cells, Sertoli cells and all kinds of germ cells in the testis during the breeding season but only Leydig cells, Sertoli cells, spermatogonia and primary spermatocyte during the non-breeding season. The immunohistochemical localizations of PACAP and VPAC1 were identified in the Leydig cells, spermatogonia and spermatozoa during the breeding season while only in Leydig cells and spermatogonia during the non-breeding season, and PAC1 and VPAC2 were localized in the Leydig cells in both seasons, in which LHR, StAR, 3β-HSD and CYP17A1 were also expressed. Meanwhile, protein and mRNA expression levels of PACAP, PAC1, VPAC1, VPAC2, LHR, FSHR, StAR, 3β-HSD and CYP17A1 in the testis during the breeding season were significantly higher than those during the non-breeding season. These results suggested that PACAP may involve in the regulation of, steroidogenesis and spermatogenesis via an endocrine, autocrine or paracrine manner in the testis of the muskrat.

Pituitary adenylate cyclase-activating peptide (PACAP) and its receptors in Mus musculus testis

To enlighten the involvement of PACAP/receptors system in the control of mammal testis, we investigated the expression of PACAP and the localization of PACAP and its receptors PAC1, VPAC1, and VPAC2 in the testis of Mus musculus. By molecular and immunohistochemical investigations, we highlighted that PACAP and its receptors are widely represented in germ cells of Mus testis, particularly in spermatocytes I, spermatids, and spermatozoa, strongly suggesting their involvement in spermatogenesis process. Moreover, for the first time in the adult mouse testis we highlighted that PACAP is present within Leydig cells, as PACAP receptors, confirming its involvement in the control of steroidogenesis in mouse.

Pituitary adenylate cyclase-activating polypeptide in the testis of the quail Coturnix coturnix: Expression, localization, and phylogenetic analysis

To evaluate the involvement of pituitary adenylate cyclase-activating polypeptide (PACAP)/receptors system in the control of testis activity, we have investigated the expression and localization of PACAP and the distribution of its receptors in the testis of mature samples of quail Coturnix coturnix, and we have performed a phylogenetic analysis of PACAP in birds. Using histological, molecular, and bioinformatics tools, we demonstrated that (a) PACAP messenger RNA shows a high sequence identity with that reported in other birds studied so far and in other vertebrates. Furthermore, we showed that purifying selection acts on PACAP; (b) the PACAP peptide is present only in Leydig cells, whereas its receptors are localized within both Leydig and germ cells; (c) the synthesis of PACAP does not take place in seminiferous tubules. The role of PACAP in the control of spermatogenesis and steroidogenesis in birds is discussed. Finally, we talk about the phylogenetic and evolutionary relationships between PACAP in birds and in other vertebrates.

Role of PACAP on testosterone and 17β-estradiol production in the testis of wall lizard Podarcis sicula

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide that in mammalian testis is involved in the control of testosterone and 17β-estradiol synthesis. A similar involvement was recently postulated in the testis of a nonmammalian vertebrate, the wall lizard Podarcis sicula. Indeed, we reported the presence of PACAP and its receptors throughout the reproductive cycle within both germ and somatic cells. Now, we investigated the effects of PACAP on steroidogenesis in significant periods of Podarcis reproductive cycle: winter stasis, reproductive period and summer stasis. Using different in vitro treatments, in the absence or presence of receptor antagonists, we demonstrated that in P. sicula testis PACAP is involved in the control of testosterone and 17β-estradiol production. In particular we demonstrated that treatment with PACAP induced a testosterone increase only in stasis periods (winter and summer stasis); differently they induced a 17β-estradiol production in all periods analyzed (summer stasis, winter stasis and reproductive period).

A genome-wide association study in catfish reveals the presence of functional hubs of related genes within QTLs for columnaris disease resistance

Background

Columnaris causes severe mortalities among many different wild and cultured freshwater fish species, but understanding of host resistance is lacking. Catfish, the primary aquaculture species in the United States, serves as a great model for the analysis of host resistance against columnaris disease. Channel catfish in general is highly resistant to the disease while blue catfish is highly susceptible. F2 generation of hybrids can be produced where phenotypes and genotypes are segregating, providing a useful system for QTL analysis. To identify genes associated with columnaris resistance, we performed a genome-wide association study (GWAS) using the catfish 250 K SNP array with 340 backcross progenies derived from crossing female channel catfish (Ictalurus punctatus) with male F1 hybrid catfish (female channel catfish I. punctatus × male blue catfish I. furcatus).

Results

A genomic region on linkage group 7 was found to be significantly associated with columnaris resistance. Within this region, five have known functions in immunity, including pik3r3b, cyld-like, adcyap1r1, adcyap1r1-like, and mast2. In addition, 3 additional suggestively associated QTL regions were identified on linkage groups 7, 12, and 14. The resistant genotypes on the QTLs of linkage groups 7 and 12 were found to be homozygous with both alleles being derived from channel catfish. The paralogs of the candidate genes in the suggestively associated QTL of linkage group 12 were found on the QTLs of linkage group 7. Many candidate genes on the four associated regions are involved in PI3K pathway that is known to be required by many bacteria for efficient entry into the host.

Conclusion

The GWAS revealed four QTLs associated with columnaris resistance in catfish. Strikingly, the candidate genes may be arranged as functional hubs; the candidate genes within the associated QTLs on linkage groups 7 and 12 are not only co-localized, but also functionally related, with many of them being involved in the PI3K signal transduction pathway, suggesting its importance for columnaris resistance.

Role of pituitary adenylate cyclase-activating polypeptide in modulating hypothalamus-pituitary neuroendocrine functions in mouse cell models

Pituitary adenylate cyclase-activating polypeptide (PACAP) was originally identified as a hypothalamic activator of cyclic adenosine monophosphate production in pituitary cells. PACAP and its receptor are expressed not only in the central nervous system, but also in peripheral organs, and function to stimulate pituitary hormone synthesis and secretion as both a hypothalamic-pituitary-releasing factor and an autocrine-paracrine factor within the pituitary. PACAP stimulates the expression of the gonadotrophin α, luteinising hormone (LH) β and follicle-stimulating hormone (FSH) β subunits, as well as the gonadotrophin-releasing hormone (GnRH) receptor and its own PACAP type I receptor (PAC1R) in gonadotrophin-secreting pituitary cells. In turn, GnRH, which is known to be a crucial component of gonadotrophin secretion, stimulates the expression of PACAP and PAC1R in gonadotrophs. In addition, PAC1R and PACAP modulate the functions of GnRH-producing neurones in the hypothalamus. This review summarises the current understanding of the possible roles of PACAP and PAC1R in modulating hypothalamus and pituitary neuroendocrine cells in the mouse models.

PACAP and PAC₁ receptor in the reproductive cycle of male lizard Podarcis sicula

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide involved in multiple functions, including vertebrate reproduction. Recently, we reported the presence of PACAP in the testis of Italian wall lizard Podarcis sicula during reproductive period (May-June). Herein we investigated the PACAP mRNA expression and the localization of PACAP/PACAP receptor system, in the other periods of the Podarcis reproductive cycle, namely in summer stasis, early autumnal resumption, mid-autumnal resumption, winter stasis, and spring resumption. Using biomolecular and immunohistochemical investigations, we demonstrated that PACAP mRNA was widely expressed in all germ and somatic cells; in summer stasis (July-August) and early autumnal resumption (September) in particular, the mRNA was always found in Sertoli cells while was transiently expressed in germ and in Leydig cells. Differently from the mRNA, the protein was always present in germ and somatic cells independently from the reproductive cycle phase. As PACAP, the PAC1 receptor was always present in the testis, except for the summer stasis (July-August) and the early autumnal resumption (September), when PACAP was lacking in germ and somatic cells (Leydig and Sertoli cells). The present results strongly suggest that PACAP/PAC1 receptor system is widely represented during the reproductive cycle of male lizard. The possible involvement of PACAP/PACAP receptor system in the control of spermatogenesis is discussed.

Androgen receptor drives transcription of rat PACAP in gonadotrope cells

Gonadotropin expression is precisely regulated within the hypothalamic-pituitary-gonadal axis through the complex interaction of neuropeptides, gonadal steroids. and both gonadal- and pituitary-derived peptides. In the anterior pituitary gland, the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) modulates gonadotropin biosynthesis and secretion, acting both alone and in conjunction with GnRH. Steroid hormone feedback also influences gonadotropin expression via both direct and indirect mechanisms. Evidence from nonpituitary tissues suggests that PACAP may be a target for gonadal steroid regulation. In the present study, we show that androgen markedly stimulates rat (r) PACAP promoter-reporter activity in the LβT2 mature mouse gonadotrope cell line. 5'-Serial deletion analysis of reporter constructs identifies 2 regions of androgen responsiveness located at (-915 to -818) and (-308 to -242) of the rPACAP promoter. Androgen receptor (AR) binds directly to DNA cis-elements in each of these regions in vitro. Site-directed mutagenesis of 3 conserved hormone response element half-sites straddling the (-308 to -242) region dramatically blunts androgen-dependent PACAP promoter activity and prevents AR binding at the mutated promoter element. Chromatin immunoprecipitation demonstrates that endogenous AR binds the homologous region on mouse chromatin in LβT2 cells in both the presence and absence of androgen. These data demonstrate that androgen stimulates PACAP gene expression in the pituitary gonadotrope via direct binding of AR to a specific cluster of evolutionarily conserved hormone response elements in the proximal rPACAP gene promoter. Thus, androgen regulation of pituitary PACAP expression may provide an additional layer of control over gonadotropin expression within the hypothalamic-pituitary-gonadal axis.

Pituitary adenylate cyclase-activating polypeptide and its receptor PAC1 in the testis of Triturus carnifex and Podarcis sicula

The pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the glucagon-related family that occurs in two amidated forms with 38 (PACAP38) and 27 (PACAP27) amino acids. First discovered in the brain, it was then localized in several peripheral tissues of mammals, including the testis. However, current knowledge of the expression and function of PACAP and its receptor PAC(1) in the reproductive system of non-mammalian vertebrates, and particularly in the testis, is still limited. The aim of this work was to study the presence of PACAP and its receptor PAC(1) in the testis of two non-mammalian vertebrates during the breeding season: the crested newt Triturus carnifex and the wall lizard Podarcis sicula. The expression and distribution of this neuropeptide and its receptor PAC(1) were investigated by using in situ hybridization and immunohistochemistry techniques. Our results demonstrated that PACAP and its receptor PAC(1) were highly represented in the testis of these two species. In particular, we showed that they are present within some germ cells and that PACAP, unlike in mammals, is expressed also in the somatic cells (Sertoli and Leydig cells) of the testis of these two non-mammalian vertebrates, suggesting that this neuropeptide is involved in the hormonal control of spermatogenesis and steroidogenesis.

Characterization of the testis-specific promoter region in the human pituitary adenylate cyclase-activating polypeptide (PACAP) gene

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide localized in the testis at concentration comparable to that found in the brain, suggesting involvement in spermatogenesis. In this study, we identified the human PACAP testis-specific exon (TSE) 10.9 kb upstream from the translational start site and found that the testis-specific transcript of the human PACAP gene was found to be spliced from the TSE into a region of intron 2 without a frameshift. The resulting PACAP precursor has no signal peptide, suggesting that PACAP functions physiologically in an intracrine manner in the testis. The 5'-flanking region of the TSE contains an 80-bp fragment with potent promoter activity in testicular F9 cell. Electrophoresis mobility shift assays showed that proteins from the F9 nuclear extract interacted specifically with the 80-bp fragment. DNA affinity chromatography allowed isolation of the specific proteins bound to the 80-bp fragment, two of which were identified as Poly (ADP-ribose) polymerase-1 (PARP-1) and TIA-1-related protein (TIAR) by mass spectrometry. By using their siRNAs, the depletion of their proteins in F9 cells affected the potent promoter activity of the 80-bp fragment, suggesting that they might be involved in the testis-specific gene expression of PACAP.

Leydig cells: From stem cells to aging

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Four distinct stages of adult Leydig cell development have been identified and characterized: stem Leydig cells, progenitor Leydig cells, immature Leydig cells and adult Leydig cells. The stem Leydig cells are undifferentiated cells that are capable of indefinite self-renewal, differentiation, and replenishment of the Leydig cell niche. Progenitor Leydig cells are derived from the stem Leydig cells. These spindle-shaped cells are luteinizing hormone (LH) receptor positive, have high mitotic activity, and produce little testosterone but rather testosterone metabolites. The progenitor Leydig cells give rise to immature Leydig cells which are round, contain large amounts of smooth endoplasmic reticulum, and produce some testosterone but also very high levels of testosterone metabolites. A single division of these cells produces adult Leydig cells, which are terminally differentiated cells that produce high levels of testosterone. As men age, serum testosterone levels decline, and this is associated with alterations in body composition, energy level, muscle strength, physical, sexual and cognitive functions, and mood. In the Brown Norway rat, used extensively as a model for male reproductive aging, age-related reductions in serum testosterone result from significant decline in the ability of aged Leydig cells to produce testosterone in response to LH stimulation. This review describes Leydig cell development and aging. Additionally, the molecular mechanisms by which testosterone synthesis declines with aging are discussed.

Suppressive action of pituitary adenylate cyclase activating polypeptide (PACAP) on proliferation of immature mouse Leydig cell line TM3 cells

We aimed in the current study to understand the participation of PACAP in stage-specific Leydig and Sertoli cell functions. For this purpose, clonal cell lines TM3 (Leydig) and TM4 (Sertoli) cells, derived from the testis of immature BALB/c mice, were used. PACAP-specific receptors were detected in TM3 cells, but not in TM4 cells, which were characterized as PAC1 (type I) receptors. Stimulation of cAMP accumulation and testosterone secretion were observed in TM3 cells during 1-2 h treatment with PACAP38 (10(-10)-10(-7) M) or PACAP27 (10(-11)-10(-7) M). After around 10 h treatment with 10(-11)-10(-7) M PACAP38 or PACAP27, proliferation of TM3 cells was suppressed in time- and dose-dependent manners, which was confirmed by real-time cell electronic sensing (RT-CES) system and phase-contrast microscopy. At 6 h after the addition of PACAP38, the percent cell population in G(2)/M phases increased significantly, while that in S phase showed significant decrease with little change in G(0)/G(1) phases. The results revealed that PACAP exerts, in addition to early stimulatory effect on cAMP formation-steroidogenesis, sustained suppressive effect on cell proliferation in TM3 cells by controlling progression of the cell cycle. The suppressive action of PACAP on proliferation in TM3 cells supports the stage-specific participation of the peptide in differentiation of immature mouse Leydig cells.

Deficits in social behavior and reversal learning are more prevalent in male offspring of VIP deficient female mice

Blockage of vasoactive intestinal peptide (VIP) receptors during early embryogenesis in the mouse has been shown to result in developmental delays in neonates, and social behavior deficits selectively in adult male offspring. Offspring of VIP deficient mothers (VIP +/-) also exhibited developmental delays, and reductions in maternal affiliation and play behavior. In the current study, comparisons among the offspring of VIP deficient mothers (VIP +/-) mated to VIP +/- males with the offspring of wild type (WT) mothers mated to VIP +/- males allowed assessment of the contributions of both maternal and offspring VIP genotype to general health measures, social behavior, fear conditioning, and spatial learning and memory in the water maze. These comparisons revealed few differences in general health among offspring of WT and VIP deficient mothers, and all offspring exhibited normal responses in fear conditioning and in the acquisition phase of spatial discrimination in the water maze. WT mothers produced offspring that were normal in all tests; the reduced VIP in their VIP +/- offspring apparently did not contribute to any defects in the measures under study. However, regardless of their own VIP genotype, all male offspring of VIP deficient mothers exhibited severe deficits in social approach behavior and reversal learning. The deficits in these behaviors in the female offspring of VIP deficient mothers were less severe than in their male littermates, and the extent of their impairment was related to their own VIP genotype. This study has shown that intrauterine conditions had a greater influence on behavioral outcome than did genetic inheritance. In addition, the greater prevalence of deficits in social behavior and the resistance to change seen in reversal learning in the male offspring of VIP deficient mothers indicate a potential usefulness of the VIP knockout mouse in furthering the understanding of neurodevelopmental disorders such as autism.

CCAAT/enhancer binding protein beta, but not steroidogenic factor-1, modulates the phthalate-induced dysregulation of rat fetal testicular steroidogenesis

Prolonged in utero exposure of fetal male rats to dibutyl phthalate (DBP) can result in a feminized phenotype characterized by malformed epididymides, hypospadias, cryptorchidism, and retained thoracic nipples, among others. These symptoms likely result, in part, from decreased expression of steroidogenic enzymes and, therefore, reduced testosterone biosynthesis. However, the molecular mechanisms involved in these changes in gene expression profiles are unknown. To understand these mechanisms in rats, in vivo DNase footprinting was adapted to provide a semiquantitative map of changes in DNA-protein interactions in the promoter region of steroidogenic genes, including steroidogenic acute regulatory, scavenger receptor B-1, cytochrome P450 side chain cleavage, and cytochrome P450 17A1, that are down-regulated after an in utero DBP exposure. Regions with altered DNase protection were coordinated with a specific DNA binding protein event by EMSA, and binding activity confirmed with chromatin immunoprecipitation. Results demonstrated altered DNase protection at regions mapping to CCAAT/enhancer binding protein beta (c/ebp beta) and steroidogenic factor-1 (SF-1). Chromatin immunoprecipitation confirmed declines in DNA-protein interactions of c/ebp beta in DBP treated animals, whereas SF-1 was reduced in both diethyl phthalate (nontoxic) and DBP (toxic) treatments. These results suggest that inhibition of c/ebp beta, and not SF-1, is critical in DBP induced inhibition of steroidogenic genes. In addition, these observations suggest a pathway redundancy in the regulation of steroidogenesis in fetal testis. In conclusion, this study presents a snapshot of changes in the structure of transcriptional machinery and proposes a mechanism of action resulting from DBP exposure.

Vasoactive intestinal peptide antagonist treatment during mouse embryogenesis impairs social behavior and cognitive function of adult male offspring

Vasoactive intestinal peptide (VIP) is a regulator of rodent embryogenesis during the period of neural tube closure. VIP enhanced growth in whole cultured mouse embryos; treatment with a VIP antagonist during embryogenesis inhibited growth and development. VIP antagonist treatment during embryogenesis also had permanent effects on adult brain chemistry and impaired social recognition behavior in adult male mice. The neurological deficits of autism appear to be initiated during neural tube closure and social behavior deficits are among the key characteristics of this disorder that is more common in males and is frequently accompanied by mental retardation. The current study examined the blockage of VIP during embryogenesis as a model for the behavioral deficits of autism. Treatment of pregnant mice with a VIP antagonist during embryonic days 8 through 10 had no apparent effect on the general health or sensory or motor capabilities of adult offspring. However, male offspring exhibited reduced sociability in the social approach task and deficits in cognitive function, as assessed through cued and contextual fear conditioning. Female offspring did not show these deficiencies. These results suggest that this paradigm has usefulness as a mouse model for aspects of autism as it selectively impairs male offspring who exhibit the reduced social behavior and cognitive dysfunction seen in autism. Furthermore, the study indicates that the foundations of some aspects of social behavior are laid down early in mouse embryogenesis, are regulated in a sex specific manner and that interference with embryonic regulators such as VIP can have permanent effects on adult social behavior.

Delayed testicular aging in pituitary adenylate cyclase-activating peptide (PACAP) null mice

Age-related decline in male sex hormones is a direct consequence of testicular aging. These changes in the hormonal complement cause physiological disturbances affecting the quality of life for millions of aging men. To assess the influence on testicular aging of pituitary adenylate cyclase-activating peptide (PACAP), a polypeptide that regulates testicular steroidogenesis in vitro, we compared the testicular structure and function between C57BL/6 wild-type and PACAP-/- male mice, at 4 and 15 months of age. We show that, in 4-month-old PACAP-/- mice, steroidogenesis (evaluated by levels of testosterone, steroidogenic acute regulatory protein, 3beta-hydroxysteroid dehydrogenase, and P450c17) was impaired. However, the testicular structure of these animals was not affected. At 15 months of age, wild-type testis displayed typical signs of aging (patchy seminiferous tubules, germ cell depletion, and vacuolization), whereas testicular structure was remarkably well conserved in PACAP-/- animals. The depletion of germ cells found in wild-type animals was associated with a higher content of peroxynitrites, a marker of reactive oxygen species, and a higher number of apoptotic cells compared with PACAP-/- mice. Our results show that testicular aging is delayed in PACAP-/- animals. Because the expression levels of steroidogenic factors are low and constant over time in knockout animals, a proposed mechanism for the protection against testicular degeneration is that production of reactive oxygen species, a byproduct of steroidogenesis that induces apoptosis, is down-regulated in PACAP-/- animals.

Decrease of Pituitary Adenylate Cyclase Activating Polypeptide and Its Type I Receptor mRNAs in Rat Testes by Ethanol Exposure

The present study was designed to evaluate the effect of ethanol on pituitary adenylate cyclase activating polypeptide (PACAP) and its typ I (PAC1) receptor 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, the present study showed the reduction of PACAP mRNA levels in rat testes by ethanol administration. Also, ethanol decreased the expression level of PAC1 receptor in testes. In particular, in situ hybridization clearly showed the decrease of PAC1 receptor mRNA expression in Leydig cells, which produce testosterone. Furthermore, the serum level of testosterone was significantly decreased in the ethanol-treated group. In conclusion, our findings suggest that the decrease of PACAP and PAC1 receptor expression in rat testes by ethanol exposure may partly contribute to the suppression of male reproductive activity.

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.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Growth hormone-releasing hormone and pituitary adenylate cyclase-activating polypeptide in the reproductive system

Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) are both members of the glucagon superfamily that, with gonadotropins, act at central and peripheral levels as paracrine and autocrine coregulators of reproductive function. GHRH and PACAP are ancient peptides. Their original forms (both 27 amino acids long) were encoded by a single ancestral gene, several duplications of which led to the genes that encode the neuropeptides of the glucagon superfamily. In the male and female reproductive tracts, GHRH and PACAP interact with a subset of G protein-coupled receptors that are structurally similar to the PACAP receptor and variants of the vasoactive intestinal peptide receptor, and share several biological actions. These are related mainly to the modulation of cAMP-dependent and other signal transduction pathways in several cells of the pituitary-gonadal axis. The recent discovery that antagonists of GHRH and PACAP suppress the growth of human cancer cell lines that are derived from reproductive tissues indicates the potential importance of these peptides as local regulators of cell division, cell cycle arrest, differentiation and cell death.

Cyclooxygenase 2 pathway mediates IL-1beta regulation of IL-1alpha, -1beta, and IL-6 mRNA levels in Leydig cell progenitors

Prostanoids are arachidonic acid (AA) metabolites derived from the cyclooxygenase (COX1 and COX2 isozymes) pathway and are involved in signal transduction pathways activated by distinct ILs. Although COX1 is the constitutive isoform of COX, IL-1beta is a potent inducer of COX2 expression in distinct cell types. This study was designed to determine whether cyclooxygenases could mediate endogenous cytokine regulation in rat progenitor Leydig cells. COX and IL (IL-1alpha, IL-1beta, and IL-6) mRNAs were measured by PCR and real-time PCR analyses, respectively. COX function was assessed using COX activity inhibitors: indomethacin (INDO; COX1 and COX2 inhibitor) and NS-398 (COX2 selective inhibitor). Our data indicate that endogenous progenitor COX1 mRNA levels are low and are not regulated by IL-1beta. In contrast, COX2 mRNA is induced by IL-1beta at 6, 9, and 24 h. IL-1beta induction of IL mRNAs was in part significantly impaired in the presence of INDO or NS-398. Among the prostanoids tested, prostaglandin E(2) (PGE(2)), PGF(2alpha), and carbaprostacyclin reversed the INDO inhibition of IL production. PGs alone have no (IL-1alpha and IL-1beta) or a modest (IL-6) effect on IL mRNA levels. PGE(2), PGF(2alpha), and PGI(2) measurements show that IL-1beta treatment significantly increases progenitor Leydig cell production of these PGs. Taken together, our data demonstrate that this COX2 cascade is a regulator of cytokines in Leydig progenitors.

Pituitary adenylate cyclase-activating polypeptide induces testicular testosterone synthesis through PGE(2) mediation in crested newt, Triturus carnifex

The aim of the present work was to study the possible role of adenylate cyclase-activating polypeptide (PACAP) 38 in the testicular intracellular mechanism regulating steroidogenesis of crested newt, Triturus carnifex. Gonads were incubated in vitro with PACAP 38 and prostaglandin (PG) E(2) alone or with inhibitors of cyclooxygenase (COX), adenylate cyclase (AC), and phospholipase C (PLC) for 30 min and 60 min. PGE(2), PGF(2 alpha), testosterone, and estradiol-17 beta were measured in the culture medium; aromatase (AR) activity and cAMP were assessed in the tissue. PACAP 38 increased PGE(2) (30 min and 60 min), estradiol-17 beta (60 min), cAMP (60 min), and AR (60 min) but decreased testosterone (60 min). PGE(2) increased estradiol-17 beta, cAMP, and AR and decreased testosterone at 30 and 60 min.PLC inhibitor counteracted the effects of PACAP 38, while AC inhibitor counteracted these effects except for PGE(2) increase. AC inhibitor counteracted the effects of PGE(2), while PLC did not. COX inhibitor decreased PGF(2 alpha) (30 min and 60 min), PGE(2) (30 min and 60 min), estradiol-17 beta (60 min), cAMP (60 min), and AR (60 min), but increased testosterone (60 min). These in vitro results suggest that, in newt testis, PACAP 38 acts on PLC, inducing the increase of PGE(2) which, in turn, acting on AC, increases AR activity with the consequent estradiol-17 beta increase and testosterone decrease.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Interplay of pituitary adenylate cyclase-activating polypeptide with a silencer element to regulate the upstream promoter of the human gonadotropin-releasing hormone receptor gene

Multiple transcription start sites were identified in the human gonadotropin releasing hormone receptor (hGnRHR) gene. Recently, an upstream promoter residing at -1727/-1674, in vicinity of a CAP site at -1673, was characterized. In this report, we elucidated the underlying mechanisms for the regulation of this promoter. Functionally, this promoter was constitutively suppressed by a silencer element (-1673/-1351) situated immediately downstream to it. On the other hand, pituitary adenylate cyclase-activating polypeptide (PACAP), via the cAMP pathway, was found to be the extracellular cue to control the upstream promoter. Following PACAP-27, PACAP-38 (30 nM) and forskolin (25 microM) treatment, there were significant increases in the reporter gene activities. By deletion analysis, the region residing at -1727 to -1577, containing the distal promoter and 97 bp of the silencer was subsequently found to be responsible for PACAP/cAMP induction. To localize the PACAP-dependent cis-acting element(s) within the silencer, block replacement scanning mutation was performed and a hGnRHR gene PACAP-responsive element (GPRE) was identified at -1676/-1648. The actions of PACAPs and forskolin on the GPRE were further evidenced by gel mobility shift assays. There was an increase in protein binding onto this element only after peptide treatment. As GnRH receptor number on gonadotrope cell surface is a key factor in regulating gonadotropin release, the present study provides an insight into the interplay between PACAP and GnRH receptors on pituitary gonadotropes to control human reproductive functions.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Pituitary adenylate cyclase-activating peptide stimulates acute progesterone production in rat granulosa/Lutein cells via two receptor subtypes

Pituitary adenylate cyclase-activating peptide (PACAP) is transiently expressed in ovarian granulosa/lutein cells from eCG/hCG-treated rats, and in vitro immunoneutralization of endogenously released PACAP inhibits acute progesterone secretion and subsequent luteinization in such cells. This suggests that PACAP mediates locally some of the effects of the LH surge, but the putative PACAP receptor(s) involved in such an auto or paracrine activity is presently unknown. Reverse-transcription polymerase chain reaction with specific primers to the three cloned PACAP-binding receptors called PAC(1), VPAC(1), and VPAC(2) demonstrated both PAC(1) and VPAC(2) mRNA in extracts from preovulatory follicular cells. Radioligand-binding assays revealed the presence of high-affinity binding sites with characteristics of these two receptors on the intact cells, and autoradiography demonstrated that the binding was restricted to a minor proportion of the follicular cells as well as the oocytes. Pituitary adenylate cyclase-activating peptide and vasoactive intestinal peptide (VIP) dose-dependently stimulated cAMP accumulation and acute progesterone accumulation. Forskolin and db-cAMP also stimulated acute progesterone accumulation, and the protein kinase A inhibitor H89 dose-dependently inhibited peptide induced acute progesterone accumulation, suggesting involvement of cAMP and the protein kinase A pathway in the process. In conclusion, two of the three PACAP binding receptors are present on preovulatory follicular cells and are involved in the effects of PACAP on acute progesterone production. The data provide further evidence to establish PACAP as an auto- or paracrine regulator of LH-induced acute progesterone production in rat preovulatory follicles.

Pituitary adenylate cyclase-activating polypeptide induces hyperthermia in the rat

The effects of centrally administered pituitary adenylate cyclase-activating polypeptide (PACAP-38) on body temperature were investigated in rats. Intracerebroventricular (i.c.v.) administration of PACAP-38 in doses of 500 and 1000 ng induced a dose-related elevation in colon temperature 2, 3, 4, 5 and 6 h after injection. The i.c.v. pretreatment of the animals with different dilutions of PACAP-38 antiserum prevented the development of hyperthermia in PACAP-38-treated animals, whereas PACAP-38 antiserum alone did not modify the colon temperature. An intramuscular injection of noraminophenazone (a cyclooxygenase inhibitor) abolished the PACAP-38-induced hyperthermia. Our data indicate that PACAP may induce hyperthermia via the central nervous system, and this hyperthermic effect may be mediated via a cyclooxygenase-involved pathway.

Galanin stimulates steroidogenesis in rat Leydig cells

The present study was designed to evaluate whether galanin could play a role in the regulation of testicular steroidogenesis. To this purpose, using purified rat Leydig cells, we examined the effects of galanin on basal and hCG- or LHRH-induced testosterone production and the interference of a specific galanin receptor antagonist, galantide, on galanin activity. Moreover, since it has been shown that galanin-induced stimulation of LHRH secretion appears to involve the release of prostaglandin E2 (PGE2) as intracellular mediator, we evaluated also the effect of galanin on Leydig cells PGE2 output and the interference of indomethacin, a cycloxygenase blocker, on its activity. Furthermore, the effect of nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, was also examined. Data obtained indicate that galanin amplified testosterone response to hCG or LHRH whilst galantide prevented its potentiating activity. Moreover, galanin stimulated PGE2 output though this fatty acid is not involved in galanin activity on Leydig cells as indomethacin failed to affect its amplification of testosterone production. The possible involvement of leukotrienes should also be excluded as NDGA did not modify galanin action. In summary, the present study indicates that galanin potentiates acute gonadotropin or LHRH steroidogenic action on Leydig cells and that this activity is specific and receptor-mediated as it is prevented by a specific receptor antagonist.

Vasoactive intestinal peptide is an important endocrine regulatory factor of fetal rat testicular steroidogenesis

This study elaborates our recent preliminary finding that vasoactive intestinal peptide (VIP) has a specific stimulatory effect on fetal rat Leydig cells. We examined the dose-response relationship for the effect of VIP on cAMP and testosterone production by dispersed fetal Leydig cells isolated from rat testes on embryonic day (E) 18.5. Further, we used RT-PCR to examine the expression of the VIP gene in fetal brain and testes and that of the VIP receptor genes in fetal testes and used RIA to measure VIP in testes and plasma during the fetal period. VIP stimulated fetal testicular cAMP production at a dose of 10(-9) mol/liter, whereas a dose as low as 10(-12) mol/liter stimulated testosterone production. This suggests that VIP at low doses may stimulate testosterone production using second messenger pathways other than cAMP. RT-PCR analysis could not reveal either VIP messenger RNA (mRNA) in fetal tissues or VIP1 receptor mRNA in the fetal or newborn testes, whereas VIP2 receptor mRNA was detected in fetal testes as early as E15.5. Northern hybridization analysis showed that the level of expression of VIP2 receptor mRNA is very low in fetal and neonatal testes and increases with age. The testicular VIP content was unmeasurable by our RIA method (i.e. <1 fmol/testis), whereas the circulating level of VIP was 82.9 +/- 1.1 pmol/liter on E17.5 and decreased with advancing fetal age. In conclusion, our results suggest that VIP from an extratesticular source, possibly from the maternal compartment, may regulate fetal testicular steroidogenesis through type 2 receptors as early as E15.5. These findings may be of physiological significance, because the onset of fetal testicular steroidogenesis occurs at an age (E15.5-19.5) before the onset of pituitary LH secretion.