Role of pituitary adenylate cyclase-activating polypeptide in modulating hypothalamic-pituitary system

Pituitary adenylyl cyclase-activating polypeptide modulates the stress response: the involvement of different brain areas and microglia

Stress is necessary for survival. However, chronic unnecessary stress exposure leads to cardiovascular, gastrointestinal and neuropsychiatric disorders. Thus, understanding the mechanisms involved in the initiation and maintenance of the stress response is essential since it may reveal the underpinning pathophysiology of these disorders and may aid in the development of medication to treat stress-mediated diseases. Pituitary adenylyl cyclase activating polypeptide (PACAP) and its receptors (PAC1, VPAC1 and VPAC2) are expressed in the hypothalamus and other brain areas as well as in the adrenal gland. Previous research has shown that this peptide/receptor system serves as a modulator of the stress response. In addition to modulating the stress response, this system may also be connected to its emerging role as neuroprotective against hypoxia, ischemia, and neurodegeneration. This article aims to review the literature regarding the role of PACAP and its receptors in the stress response, the involvement of different brain regions and microglia in PACAP-mediated modulation of the stress response, and the long-term adaptation to stress recognizable clinically as survival with resilience while manifested in anxiety, depression and other neurobehavioral disorders.

Investigating the potential role of the pituitary adenylate cyclase-activating polypeptide (PACAP) in regulating the ubiquitin signaling pathway in poultry

The physiological processes in animal production are regulated through biologically active molecules like peptides, proteins, and hormones identified through the development of the fundamental sciences and their application. One of the main polypeptides that plays an essential role in regulating physiological responses is the pituitary adenylate cyclase-activating polypeptide (PACAP). PACAP belongs to the glucagon/growth hormone-releasing hormone (GHRH)/vasoactive intestinal proteins (VIP) family and regulates feed intake, stress, and immune response in birds. Most of these regulations occur after PACAP stimulates the cAMP signaling pathway, which can regulate the expression of genes like MuRF1, FOXO1, Atrogin 1, and other ligases that are essential members of the ubiquitin system. On the other hand, PACAP stimulates the secretion of CRH in response to stress, activating the ubiquitin signaling pathway that plays a vital role in protein degradation and regulates oxidative stress and immune responses. Many studies conducted on rodents, mammals, and other models confirm the regulatory effects of PACAP, cAMP, and the ubiquitin pathway; however, there are no studies testing whether PACAP-induced cAMP signaling in poultry regulates the ubiquitin pathway. Besides, it would be interesting to investigate if PACAP can regulate ubiquitin signaling during stress response via CRH altered by HPA axis stimulation. Therefore, this review highlights a summary of research studies that indicate the potential interaction of the PACAP and ubiquitin signaling pathways on different molecular and physiological parameters in poultry species through the cAMP and stress signaling pathways.

Prolactin and oxytocin: potential targets for migraine treatment

Migraine is a severe neurovascular disorder of which the pathophysiology is not yet fully understood. Besides the role of inflammatory mediators that interact with the trigeminovascular system, cyclic fluctuations in sex steroid hormones are involved in the sex dimorphism of migraine attacks. In addition, the pituitary-derived hormone prolactin and the hypothalamic neuropeptide oxytocin have been reported to play a modulating role in migraine and contribute to its sex-dependent differences. The current narrative review explores the relationship between these two hormones and the pathophysiology of migraine. We describe the physiological role of prolactin and oxytocin, its relationship to migraine and pain, and potential therapies targeting these hormones or their receptors.In summary, oxytocin and prolactin are involved in nociception in opposite ways. Both operate at peripheral and central levels, however, prolactin has a pronociceptive effect, while oxytocin appears to have an antinociceptive effect. Therefore, migraine treatment targeting prolactin should aim to block its effects using prolactin receptor antagonists or monoclonal antibodies specifically acting at migraine-pain related structures. This action should be local in order to avoid a decrease in prolactin levels throughout the body and associated adverse effects. In contrast, treatment targeting oxytocin should enhance its signalling and antinociceptive effects, for example using intranasal administration of oxytocin, or possibly other oxytocin receptor agonists. Interestingly, the prolactin receptor and oxytocin receptor are co-localized with estrogen receptors as well as calcitonin gene-related peptide and its receptor, providing a positive perspective on the possibilities for an adequate pharmacological treatment of these nociceptive pathways. Nevertheless, many questions remain to be answered. More particularly, there is insufficient data on the role of sex hormones in men and the correct dosing according to sex differences, hormonal changes and comorbidities. The above remains a major challenge for future development.

Female reproductive functions of the neuropeptide PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide originally isolated as a hypothalamic peptide. It has a widespread distribution in the body and has a diverse spectrum of actions. Among other processes, PACAP has been shown to be involved in reproduction. In this review we summarize findings related to the entire spectrum of female reproduction. PACAP is a regulatory factor in gonadal hormone production, influences follicular development and plays a role in fertilization and embryonic/placental development. Furthermore, PACAP is involved in hormonal changes during and after birth and affects maternal behavior. Although most data come from cell cultures and animal experiments, increasing number of evidence suggests that similar effects of PACAP can be found in humans. Among other instances, PACAP levels show changes in the serum during pregnancy and birth. PACAP is also present in the human follicular and amniotic fluids and in the milk. Levels of PACAP in follicular fluid correlate with the number of retrieved oocytes in hyperstimulated women. Human milk contains very high levels of PACAP compared to plasma levels, with colostrum showing the highest concentration, remaining steady thereafter for the first 7 months of lactation. All these data imply that PACAP has important functions in reproduction both under physiological and pathological conditions.

Stereology of gonadotropin-releasing hormone and kisspeptin neurons in PACAP gene-deficient female mice

The hypothalamic gonadotropin-releasing hormone (GnRH)-kisspeptin neuronal network regulates fertility in all mammals. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide isolated from the hypothalamus that is involved in the regulation of several releasing hormones and trop hormones. It is well-known that PACAP influences fertility at central and peripheral levels. However, the effects of PACAP on GnRH and kisspeptin neurons are not well understood. The present study investigated the integrity of the estrous cycle in PACAP-knockout (KO) mice. The number and immunoreactivity of GnRH (GnRH-ir) neurons in wild-type (WT) and PACAP KO female mice were determined using immunohistochemistry. In addition, the number of kisspeptin neurons was measured by counting kisspeptin mRNA-positive cells in the rostral periventricular region of the third ventricle (RP3V) and arcuate nucleus (ARC) using the RNAscope technique. Finally, the mRNA and protein expression of estrogen receptor alpha (ERα) was also examined. Our data showed that the number of complete cycles decreased, and the length of each cycle was longer in PACAP KO mice. Furthermore, the PACAP KO mice experienced longer periods of diestrus and spent significantly less time in estrus. There was no difference in GnRH-ir or number of GnRH neurons. In contrast, the number of kisspeptin neurons was decreased in the ARC, but not in the R3PV, in PACAP KO mice compared to WT littermates. Furthermore, ERα mRNA and protein expression was decreased in the ARC, whereas in the R3PV region, ERα mRNA levels were elevated. Our results demonstrate that embryonic deletion of PACAP significantly changes the structure and presumably the function of the GnRH-kisspeptin neuronal network, influencing fertility.

Estrogen mediates sex differences in preoptic neuropeptide and pituitary hormone production in medaka

The preoptic area (POA) is one of the most evolutionarily conserved regions of the vertebrate brain and contains subsets of neuropeptide-expressing neurons. Here we found in the teleost medaka that two neuropeptides belonging to the secretin family, pituitary adenylate cyclase-activating polypeptide (Pacap) and vasoactive intestinal peptide (Vip), exhibit opposite patterns of sexually dimorphic expression in the same population of POA neurons that project to the anterior pituitary: Pacap is male-biased, whereas Vip is female-biased. Estrogen secreted by the ovary in adulthood was found to attenuate Pacap expression and, conversely, stimulate Vip expression in the female POA, thereby establishing and maintaining their opposite sexual dimorphism. Pituitary organ culture experiments demonstrated that both Pacap and Vip can markedly alter the expression of various anterior pituitary hormones. Collectively, these findings show that males and females use alternative preoptic neuropeptides to regulate anterior pituitary hormones as a result of their different estrogen milieu.

Nesfatin-1 and Nesfatin-1-like peptide suppress basal and TRH-Induced expression of prolactin and prolactin regulatory element-binding protein mRNAs in rat GH3 somatolactotrophs

Prolactin (PRL), mainly synthesized and secreted by the lactotrophs and somatolactotrophs of the anterior pituitary, is a pleiotropic hormone that regulates lactation. In the last decade, nesfatin-1 (NESF) and NESF-like peptide (NLP), encoded in nucleobindin 1 and 2 (NUCB1 and NUCB2), respectively, were characterized as metabolic factors with a potential role in the control of pituitary hormones. We hypothesized that NUCBs and their encoded peptides (NESF and NLP) suppress PRL transcription in the pituitary. The main objective of this research was to determine whether exogenous NESF and NLP, and/or endogenous NUCB1 and NUCB2 regulate the expression of prl and preb mRNAs. Using immortalized rat somatolactotrophs (GH3 cells), dose-response studies were performed to test whether NESF and NLP affect prl and preb. Moreover, the ability of these peptides to modulate the effects of the PRL stimulator thyrotropin releasing hormone (TRH) was studied. Besides, the effects of siRNA-mediated knockdown of endogenous NUCBs on prl and preb mRNAs were determined. NESF and NLP reduced the transcription of prl and preb in GH3 cells. Both NESF and NLP also prevented the stimulatory effects of TRH prl and preb expression. The knockdown of endogenous NUCB1 attenuates both basal prl and TRH-induced expression of prl and preb, while the silencing of NUCBs did not affect the actions of exogenous NESF or NLP. Overall, this work reveals that NUCBs and encoded-peptides are novel regulators of PRL. Future research should test whether the effects observed here in GH3 cells are preserved both in vivo and at the post-transcriptional level.

Current State of Understanding of the Role of PACAP in the Hypothalamo-Hypophyseal Gonadotropin Functions of Mammals

PACAP was discovered 30 years ago in Dr. Akira Arimura's laboratory. In the past three decades since then, it has become evident that this peptide plays numerous crucial roles in mammalian organisms. The most important functions of PACAP are the following: 1. neurotransmitter, 2. neuromodulator, 3. hypophysiotropic hormone, 4. neuroprotector. This paper reviews the accumulated data regarding the distribution of PACAP and its receptors in the mammalian hypothalamus and pituitary gland, the role of PACAP in the gonadotropin hormone secretion of females and males. The review also summarizes the interaction between PACAP, GnRH, and sex steroids as well as hypothalamic peptides including kisspeptin. The possible role of PACAP in reproductive functions through the biological clock is also discussed. Finally, the significance of PACAP in the hypothalamo-hypophysial system is considered and the facts missing, that would help better understand the function of PACAP in this system, are also highlighted.

PACAP induces FSHβ gene expression via EPAC

Gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are heterodimers of a common α subunit and unique β subunits. Regulation of their levels, primarily by GnRH, is critical for reproductive function. Several other hormones modulate gonadotropin expression, either independently or by modifying the responsiveness to GnRH. Pituitary adenylate cyclase activating peptide (PACAP) is one such hormone. Four-hour treatment of female mouse primary pituitary cells by either GnRH or PACAP induced FSHβ expression, while 24-h treatment repressed FSHβ. Both PACAP and GnRH caused FSH secretion into the medium. In the gonadotropes, PACAP activates primarily Gαs and increases concentration of cAMP, while GnRH primarily functions via Gαq and increases calcium concentration. Herein, we compared PACAP and GnRH signaling pathways that lead to the induction of FSHβ expression. Interestingly, constitutively active Gαs represses LHβ and induces FSHβ expression, while Gαq induces both β-subunits. We determined that FSHβ induction by PACAP requires functional EPAC, a cAMP sensor protein that serves as a guanine exchange factors for small G proteins that then bridges cAMP signaling to MAPK pathway. We further demonstrate that in addition to the prototypical small G protein Ras, two members of the Rho subfamily, Rac and CDC42 are also necessary for PACAP induction of FSHβ, likely via activation of p38 MAPK that leads to induction of cFOS, a critical transcription factor that is necessary and sufficient for FSHβ induction. Therefore, PACAP-induced cAMP pathway leads to MAPK activation that stimulates cFOS induction, to induce the expression of FSHβ subunit and increase FSH concentration.