Monoaminergic neuronal development is not affected in PACAP-gene-deficient mice

Altered Notch Signaling in Developing Molar Teeth of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP)-Deficient Mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with neuroprotective and neurotrophic effects. This suggests its influence on the development of teeth, which are, similarly to the nervous system, ectoderm and neural crest derivatives. Our earlier studies have shown morphological differences between wild-type (WT) and PACAP-deficient mice, with upregulated sonic hedgehog (SHH) signaling in the lack of PACAP. Notch signaling is a key element of proper tooth development by regulating apoptosis and cell proliferation. In this study, our main goal was to evaluate the possible effects of PACAP on Notch signaling pathway. Immunohistochemical staining was performed of Notch receptors (Notch1, 2, 3, 4), their ligands [delta-like protein (DLL)1, 3, 4, Jagged1, 2], and intracellular target molecules [CSL (CBF1 humans/Su (H) Drosophila/LAG1 Caenorhabditis elegans transcription factor); TACE (TNF-α converting enzyme), NUMB] in molar teeth of 5-day-old WT, and homozygous and heterozygous PACAP-deficient mice. We measured immunopositivity in the enamel-producing ameloblasts and dentin-producing odontoblasts. Notch2 receptor and DLL1 expression were elevated in ameloblasts of PACAP-deficient mice compared to those in WT ones. The expression of CSL showed similar results both in the ameloblasts and odontoblasts. Jagged1 ligand expression was elevated in the odontoblasts of homozygous PACAP-deficient mice compared to WT mice. Other Notch pathway elements did not show significant differences between the genotype groups. The lack of PACAP leads to upregulation of Notch pathway elements in the odontoblast and ameloblast cells. The underlying molecular mechanisms are yet to be elucidated; however, we propose SHH-dependent and independent processes. We hypothesize that this compensatory upregulation of Notch signaling by the lack of PACAP could represent a salvage pathway in PACAP-deficient animals.

Aging-Induced Modulation of Pituitary Adenylate Cyclase-Activating Peptide- and Vasoactive Intestinal Peptide-Induced Vasomotor Responses in the Arteries of Mice

Pituitary adenylate cyclase-activating peptide (PACAP; 1-38 and 1-27) and vasoactive intestinal peptide (VIP) are related neuropeptides of the secretin/glucagon family. Overlapping signaling through G-protein-coupled receptors mediates their vasomotor activity. We previously showed that PACAP deficiency (PACAP-KO) shifts the mechanisms of vascular response and maintains arterial relaxation through the VIP backup mechanism and (mainly) its VPAC1R, but their age-dependent modulation is still unknown. We hypothesized that backup mechanisms exist, which maintain the vasomotor activity of these peptides also in older age. Thus, we investigated the effects of exogenous VIP and PACAP peptides in isolated carotid arteries of 2- and 15-month-old wild-type (WT) and PACAP-KO mice. All peptides induced relaxation in the arteries of young WT mice, whereas in young PACAP-KO mice PACAP1-27 and VIP, but not PACAP1-38, induced relaxation. Unlike VIP, PACAP-induced vasomotor responses were reduced in aging WT mice. However, in the arteries of aging PACAP-KO mice, PACAP1-27- and VIP-induced responses were reduced, but PACAP1-38 showed a greater vasomotor response compared to that of young PACAP-KO animals. There were no significant differences between the vasomotor responses of aging WT and PACAP-KO mice. Our data suggest that, in the absence of PACAP both in young and old ages, the vascular response is mediated through backup mechanisms, most likely VIP, maintaining proper vascular relaxation in aging-induced PACAP insufficiency.

Early Neurobehavioral Development of Mice Lacking Endogenous PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide. In addition to its diverse physiological roles, PACAP has important functions in the embryonic development of various tissues, and it is also considered as a trophic factor during development and in the case of neuronal injuries. Data suggest that the development of the nervous system is severely affected by the lack of endogenous PACAP. Short-term neurofunctional outcome correlates with long-term functional deficits; however, the early neurobehavioral development of PACAP-deficient mice has not yet been evaluated. Therefore, the aim of the present study was to describe the postnatal development of physical signs and neurological reflexes in mice partially or completely lacking PACAP. We examined developmental hallmarks during the first 3 weeks of the postnatal period, during which period most neurological reflexes and motor coordination show most intensive development, and we describe the neurobehavioral development using a complex battery of tests. In the present study, we found that PACAP-deficient mice had slower weight gain throughout the observation period. Interestingly, mice partially lacking PACAP weighed significantly less than homozygous mice. There was no difference between male and female mice during the first 3 weeks. Some other signs were also more severely affected in the heterozygous mice than in the homozygous mice, such as air righting, grasp, and gait initiation reflexes. Interestingly, incisor teeth erupted earlier in mice lacking PACAP. Motor coordination, shown by the number of foot-faults on an elevated grid, was also less developed in PACAP-deficient mice. In summary, our results show that mice lacking endogenous PACAP have slower weight gain during the first weeks of development and slower neurobehavioral development regarding a few developmental hallmarks.

Comparative protein composition of the brains of PACAP-deficient mice using mass spectrometry-based proteomic analysis

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a widespread neuropeptide acting as a neurotransmitter, neuromodulator, or neurotrophic factor. The diverse biological actions provide the background for the variety of deficits observed in mice lacking endogenous PACAP. PACAP-deficient mice display several abnormalities, such as sudden infant death syndrome (SIDS)-like phenotype, decreased cell protection, and increased risk of Parkinson's disease. However, the molecular and proteomic background is still unclear. Therefore, our aim was to investigate the differences in peptide and protein composition in the brains of PACAP-deficient and wild-type mice using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometric (MS)-based proteomic analysis. Brains from PACAP-deficient mice were removed, and different brain areas (cortex, hippocampus, diencephalon, mesencephalon, brainstem, and cerebellum) were separated. Brain pieces were weighed, homogenized, and further processed for electrophoretic analysis. Our results revealed several differences in diencephalon and mesencephalon. The protein bands of interest were cut from the gel, samples were digested with trypsin, and the tryptic peptides were measured by matrix-assisted laser desorption ionization time of flight (MALDI TOF) MS. Results were analyzed by MASCOT Search Engine. Among the altered proteins, several are involved in metabolic processes, energy homeostasis, and structural integrity. ATP-synthase and tubulin beta-2A were expressed more strongly in PACAP-knockout mice. In contrast, the expression of more peptides/proteins markedly decreased in knockout mice, like pyruvate kinase, fructose biphosphate aldolase-A, glutathione S-transferase, peptidyl propyl cis-trans isomerase-A, gamma enolase, and aspartate amino transferase. The altered expression of these enzymes might partially account for the decreased antioxidant and detoxifying capacity of PACAP-deficient mice accompanying the increased vulnerability of these animals. Our results provide novel insight into the altered biochemical processes in mice lacking endogenous PACAP.

PACAP and PAC1 receptor in brain development and behavior

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) act through three class B G-protein coupled receptors, PAC1, VPAC1 and VPAC2, initiating multiple signaling pathways. In addition to natural peptides ligands, a number of synthetic peptides and a small molecular antagonist have been generated. Genetically modified animals have been produced for the neuropeptides and receptors. Neuroanatomical, electrophysiological, behavioral and pharmacological characterization of the mutants and transgenic mice uncovered diverse roles of PACAP-PAC1-VAPC2 signaling in peripheral tissues and in the central nervous system. Human genetic studies suggest that the PACAP-PAC1-VPAC2 signaling can be associated with psychiatric illness via mechanisms of not only loss-of-function, but also gain-of-function. For example, a duplication of chromosome 7q36.3 (encoding the VPAC2 receptor) was shown to be associated with schizophrenia, and high levels of PACAP-PAC1 signaling are associated with posttraumatic stress disorder. Whereas knockout animals are appropriate to address loss-of-function of human genetics, transgenic mice overexpressing human transgenes in native environment using artificial chromosomes are particularly valuable and essential to address the consequences of gain-of-function. This review focuses on role of PACAP and PAC1 receptor in brain development, behavior of animals and potential implication in human neurodevelopmental disorders. It also encourages keeping an open mind that alterations of VIP/PACAP signaling may associate with psychiatric illness without overt neuroanatomic changes, and that tuning of VIP/PACAP signaling may represent a novel avenue for the treatment of the psychiatric illness.

Role of endogenous pituitary adenylate cyclase activating polypeptide (PACAP) in myelination of the rodent brain: lessons from PACAP-deficient mice

Pituitary adenylate-cyclase activator polypeptide (PACAP), as a consequence of its effect on the elevation of intracellular cAMP level, strongly influences brain development including myelination. While proliferation of oligodendroglial progenitors is stimulated by PACAP applied in vitro, their differentiation is inhibited. However, the in vivo role of PACAP on myelination has never been examined. In the present study the role of endogenous PACAP in myelination was examined in PACAP-deficient mice, in several areas of the brain with a special attention to the cerebral cortex. In young postnatal and adult mice myelination was studied with immunohistochemistry detecting a protein present in the myelin sheath, the myelin basic protein, with Luxol Fast Blue staining and with electron microscopy. Results obtained in PACAP-deficient mice were compared to age-matched wild type controls. We found that the sequence of myelination in the PACAP-deficient animals was similar to that observed in controls. According to this, in both PACAP-deficient and wild type mice, the somatosensory cortex was myelinated before motor areas that preceded the myelination of associational cortical areas. Archicortical associational areas such as the cingulate cortex were myelinated before neocortical areas. Myelination in the corpus callosum followed the known rostro-caudal direction in both PACAP-deficient and wild type animals, and the ventrolateral part of the corpus callosum was myelinated earlier than the dorsomedial part in both groups. In contrast to the similarity in its sequence, striking difference was found in the onset of myelination that started earlier in PACAP-deficient mice than in wild type controls in all of the examined brain regions, including cerebral archi- and neocortex. The first myelinated axons in each of the examined brain regions were observed earlier in the PACAP-deficient mice than in controls. When age-matched animals of the two groups were compared, density of myelinated fibers in the PACAP-deficient mice was higher than in controls in all of the examined areas. We propose that endogenous PACAP exerts an inhibitory role on myelination in vivo. Since myelin sheath of the central nervous system contains several factors blocking neurite outgrowth, inhibition of myelination by PACAP gives time for axonal development and synapse formation, and therefore, strengthens neuronal plasticity.

Pituitary adenylyl cyclase-activating peptide counteracts hedgehog-dependent motor neuron production in mouse embryonic stem cell cultures

Pituitary adenylyl cyclase-activating peptide (PACAP; ADCYAP1) is a neuropeptide that regulates a wide array of functions within the brain and periphery. We and others have previously demonstrated that PACAP and its high-affinity receptor PAC1 are expressed in the embryonic mouse neural tube, suggesting that PACAP plays a role in early brain development. Moreover, we previously showed that PACAP antagonizes the mitotic action of Sonic hedgehog (Shh) in postnatal cerebellar granule precursors. In the present study, we demonstrate that PACAP completely blocked Shh-dependent motor neuron generation from embryonic stem cell cultures and reduced mRNA levels of the Shh target gene Gli-1 and several ventral spinal cord patterning genes. In vivo examination of motor neuron and other patterning markers in embryonic day 12.5 spinal cords of wild-type and PACAP-deficient mice by immunofluorescence, on the other hand, revealed no obvious alterations in expressions of Islet1/2, MNR2, Lim1/2, Nkx2.2, or Shh, although the Pax6-positive area was slightly expanded in PACAP-deficient spinal cord. Caspase-3 staining revealed low, and similar, numbers of cells undergoing apoptosis in embryonic wild-type vs. PACAP-deficient spinal cords, whereas a slight but significant increase in number of mitotic cells was observed in PACAP-deficient mice. Thus, although PACAP has a strong capacity to counteract Shh signaling and motor neuron production in vitro, corresponding patterning defects associated with PACAP loss may be obscured by compensatory mechanisms.

The role of PACAP in central cardiorespiratory regulation

Pituitary adenylate cyclase activating polypeptide (PACAP) plays a role in almost every biological process from reproduction to hippocampal function. One area where a role for PACAP is not clearly delineated is central cardiorespiratory regulation. PACAP and its receptors (PAC1, VPAC1 and VPAC2) are present in cardiovascular areas of the ventral medulla and spinal cord and in the periphery. Central administration of PACAP generally increases arterial pressure. Knowledge about the role of PACAP in central cardiovascular regulation is growing, but even less is known about PACAP in central respiratory regulation. No specific data is currently available regarding the presence of PACAP or receptors in key respiratory centers, although it is known that neonatal PACAP knock-out mice die suddenly in a manner similar to sudden infant death syndrome (SIDS). Future studies in mature preparations investigating the role of PACAP in the physiology and integration of central cardiorespiratory reflexes are clearly essential for a full understanding of this important neuropeptide in breathing.

The role of endogenous PACAP in motor stimulation and conditioned place preference induced by morphine in mice

RATIONALE

The neuropeptide pituitary adenylyl cyclase-activating peptide (PACAP) and its receptors (PAC1 and VPAC2) are expressed in the ventral tegmental area and nucleus accumbens, raising the possibility that PACAP could be a potential modulator of the mesolimbic dopaminergic system.

OBJECTIVE

The present study was designed to determine if PACAP plays a role in acute motor stimulatory and rewarding actions of morphine.

METHODS

The effect of intracerebroventricular PACAP administration (0, 0.03, 0.3, 1.0, or 3.0 microg/3 microL) was studied on basal motor activity as well as on morphine (5 mg/kg)-stimulated motor activity. Motor stimulation and conditioned place preference (CPP) induced by morphine (5 or 10 mg/kg) were also determined in mice lacking PACAP and their wild-type controls.

RESULTS

Intracerebroventricular PACAP dose-dependently suppressed basal motor activity and PACAP-deficient mice exhibited higher basal motor activity than control mice, providing evidence that the action of endogenous PACAP on basal motor activity is inhibitory. Paradoxically, low doses of PACAP which did not alter basal motor activity were found to enhance the motor stimulatory action of morphine. Furthermore, morphine-induced motor stimulation was blunted in PACAP-deficient mice. Additionally, morphine-induced CPP following a single, but not repeated, alternate-day saline/morphine (10 mg/kg) conditioning was blunted in PACAP-deficient mice compared to their wild-type littermates/controls.

CONCLUSION

The present results suggest that endogenous PACAP, at low doses, positively modulates the acute motor stimulatory and rewarding actions of morphine.

Role of PACAP in the physiology and pathology of the sympathoadrenal system

Sympathetic neurons and chromaffin cells derive from common sympathoadrenal precursors which arise from the neural crest. Cells from this lineage migrate to their final destination and differentiate by acquiring a catecholaminergic phenotype in response to different environmental factors. It has been shown that the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) and its PAC1 receptor are expressed at early stages of sympathetic development, and participate to the control of neuroblast proliferation and differentiation. PACAP also acts as a neurotransmitter to stimulate catecholamine and neuropeptide biosynthesis and release from sympathetic neurons and chromaffin cells, during development and in adulthood. In addition, PACAP and its receptors have been described in neuroblastoma and pheochromocytoma, and the neuropeptide regulates the differentiation and activity of sympathoadrenal-derived tumoral cell lines, suggestive of an important role in the pathophysiology of the sympathoadrenal lineage. Transcriptome studies uncovered genes and pathways of known and unknown roles that underlie the effects of PACAP in the sympathoadrenal system.

The neuropeptide pituitary adenylate cyclase-activating polypeptide exerts anti-apoptotic and differentiating effects during neurogenesis: focus on cerebellar granule neurones and embryonic stem cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) was originally isolated from ovine hypothalamus on the basis of its hypophysiotrophic activity. It has subsequently been shown that PACAP and its receptors are widely distributed in the central nervous system of adult mammals, indicating that PACAP may act as a neurotransmitter and/or neuromodulator. It has also been found that PACAP and its receptors are expressed in germinative neuroepithelia, suggesting that PACAP could be involved in neurogenesis. There is now compelling evidence that PACAP exerts neurotrophic activities in the developing cerebellum and in embryonic stem (ES) cells. In particular, the presence of PACAP receptors has been demonstrated in the granule layer of the immature cerebellar cortex, and PACAP has been shown to promote survival, inhibit migration and activate neurite outgrowth of granule cell precursors. In cerebellar neuroblasts, PACAP is a potent inhibitor of the mitochondrial apoptotic pathway through activation of the MAPkinase extracellular regulated kinase. ES cells and embryoid bodies (EB) also express PACAP receptors and PACAP facilitates neuronal orientation and induces the appearance of an electrophysiological activity. Taken together, the anti-apoptotic and pro-differentiating effects of PACAP characterised in cerebellar neuroblasts as well as ES and EB cells indicate that PACAP acts not only as a neurohormone and a neurotransmitter, but also as a growth factor.