IL-6 and PACAP Receptor Expression and Localization after Global Brain Ischemia in Mice

Pituitary Adenylate Cyclase-Activating Polypeptide: A Promising Neuroprotective Peptide in Stroke

The search for viable, effective treatments for acute stroke continues to be a global priority due to the high mortality and morbidity. Current therapeutic treatments have limited effects, making the search for new treatments imperative. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a well-established cytoprotective neuropeptide that participates in diverse neural physiological and pathological activities, such as neuronal proliferation, differentiation, and migration, as well as neuroprotection. It is considered a promising treatment in numerous neurological diseases. Thus, PACAP bears potential as a new therapeutic strategy for stroke treatment. Herein, we provide an overview pertaining to the current knowledge of PACAP, its receptors, and its potential neuroprotective role in the setting of stroke, as well as various mechanisms of neuroprotection involving ionic homeostasis, excitotoxicity, cell edema, oxidative stress, inflammation, and cell death, as well as the route of PACAP administration.

Age and Sex-Dependent ADNP Regulation of Muscle Gene Expression Is Correlated with Motor Behavior: Possible Feedback Mechanism with PACAP

The activity-dependent neuroprotective protein (ADNP), a double-edged sword, sex-dependently regulates multiple genes and was previously associated with the control of early muscle development and aging. Here we aimed to decipher the involvement of ADNP in versatile muscle gene expression patterns in correlation with motor function throughout life. Using quantitative RT-PCR we showed that Adnp^+/− heterozygous deficiency in mice resulted in aberrant gastrocnemius (GC) muscle, tongue and bladder gene expression, which was corrected by the Adnp snippet, drug candidate, NAP (CP201). A significant sexual dichotomy was discovered, coupled to muscle and age-specific gene regulation. As such, Adnp was shown to regulate myosin light chain (Myl) in the gastrocnemius (GC) muscle, the language acquisition gene forkhead box protein P2 (Foxp2) in the tongue and the pituitary-adenylate cyclase activating polypeptide (PACAP) receptor PAC1 mRNA (Adcyap1r1) in the bladder, with PACAP linked to bladder function. A tight age regulation was observed, coupled to an extensive correlation to muscle function (gait analysis), placing ADNP as a muscle-regulating gene/protein.

Neurovascular Unit as a Source of Ischemic Stroke Biomarkers-Limitations of Experimental Studies and Perspectives for Clinical Application

Cerebral stroke, which is one of the most frequent causes of mortality and leading cause of disability in developed countries, often leads to devastating and irreversible brain damage. Neurological and neuroradiological diagnosis of stroke, especially in its acute phase, is frequently uncertain or inconclusive. This results in difficulties in identification of patients with poor prognosis or being at high risk for complications. It also makes difficult identification of these stroke patients who could benefit from more aggressive therapies. In contrary to the cardiovascular disease, no single biomarker is available for the ischemic stroke, addressing the abovementioned issues. This justifies the need for identifying of effective diagnostic measures characterized by high specificity and sensitivity. One of the promising avenues in this area is studies on the panels of biomarkers characteristic for processes which occur in different types and phases of ischemic stroke and represent all morphological constituents of the brains' neurovascular unit (NVU). In this review, we present the current state of knowledge concerning already-used or potentially applicable biomarkers of the ischemic stroke. We also discuss the perspectives for identification of biomarkers representative for different types and phases of the ischemic stroke, as well as for different constituents of NVU, which concentration levels correlate with extent of brain damage and patients' neurological status. Finally, a critical analysis of perspectives on further improvement of the ischemic stroke diagnosis is presented.

Pituitary Adenylate Cyclase-Activating Polypeptide: 30 Years in Research Spotlight and 600 Million Years in Service

Emerging from the depths of evolution, pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (i.e., PAC1, VPAC1, VPAC2) are present in multicellular organisms from Tunicates to humans and govern a remarkable number of physiological processes. Consequently, the clinical relevance of PACAP systems spans a multifaceted palette that includes more than 40 disorders. We aimed to present the versatility of PACAP1-38 actions with a focus on three aspects: (1) when PACAP1-38 could be a cause of a malfunction, (2) when PACAP1-38 could be the cure for a malfunction, and (3) when PACAP1-38 could either improve or impair biology. PACAP1-38 is implicated in the pathophysiology of migraine and post-traumatic stress disorder whereas an outstanding protective potential has been established in ischemia and in Alzheimer’s disease. Lastly, PACAP receptors could mediate opposing effects both in cancers and in inflammation. In the light of the above, the duration and concentrations of PACAP agents must be carefully set at any application to avoid unwanted consequences. An enormous amount of data accumulated since its discovery (1989) and the first clinical trials are dated in 2017. Thus in the field of PACAP research: “this is not the end, not even the beginning of the end, but maybe the end of the beginning.”

Spatiotemporal Expression Changes of PACAP and Its Receptors in Retinal Ganglion Cells After Optic Nerve Crush

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been demonstrated to play a crucial part in protecting retinal ganglion cells (RGCs) from apoptosis in various retinal injury animal models. PACAP has two basic groups of receptors: PACAP receptor type 1 (PAC1R) and vasoactive intestinal polypeptide/PACAP receptors (VPAC1R and VPAC2R). However, few studies illustrated the spatial and temporal expression changes of endogenous PACAP and its receptors in a rodent optic nerve crush (ONC) model. In this study, a significant upregulation of PACAP and PAC1R in the retina after ONC was observed in both protein and RNA levels. The peak level of PACAP and PAC1R expression could be found on the fifth day following ONC. In addition, immunofluorescent labeling indicated that PACAP and PAC1R were localized mainly in RGCs. On the contrary, VPAC1R and VPAC2R were hardly detected in the retina. Collectively, the spatiotemporal expression of PACAP and its high-affinity receptor PAC1R were remarkably changed after ONC, and mainly expressed in the ganglion cell layer of the retina. This suggested that the upregulation of PACAP and PAC1R may play a vital role in RGC death after ONC.

Protective effects of PACAP in ischemia

Pituitary adenylate cyclase activating polypeptide (PACAP) is an ubiquitous peptide involved, among others, in neurodevelopment, neuromodulation, neuroprotection, neurogenic inflammation and nociception. Presence of PACAP and its specific receptor, PAC1, in the trigeminocervical complex, changes of PACAP levels in migraine patients and the migraine-inducing effect of PACAP injection strongly support the involvement of PACAP/PAC1 receptor in migraine pathogenesis. While antagonizing PAC1 receptor is a promising therapeutic target in migraine, the diverse array of PACAP's functions, including protection in ischemic events, requires that the cost-benefit of such an intervention is well investigated by taking all the beneficial effects of PACAP into account. In the present review we summarize the protective effects of PACAP in ischemia, especially in neuronal ischemic injuries, and discuss possible points to consider when developing strategies in migraine therapy interfering with the PACAP/PAC1 receptor system.

Beneficial potential of intravenously administered IL-6 in improving outcome after murine experimental stroke

Interleukin-6 (IL-6) is a pleiotropic cytokine with neuroprotective properties. Still, the therapeutic potential of IL-6 after experimental stroke has not yet been investigated in a clinically relevant way. Here, we investigated the therapeutic use of intravenously administered IL-6 and the soluble IL-6 receptor (sIL-6R) alone or in combination, early after permanent middle cerebral artery occlusion (pMCAo) in mice. IL-6 did not affect the infarct volume in C57BL/6 mice, at neither 24 nor 72h after pMCAo but reduced the infarct volume in IL-6 knockout mice at 24h after pMCAo. Assessment of post-stroke behavior showed an improved grip strength after a single IL-6 injection and also improved rotarod endurance after two injections, in C57BL/6 mice at 24h. An improved grip strength and a better preservation of sensory functions was also observed in IL-6 treated IL-6 knockout mice 24h after pMCAo. Co-administration of IL-6 and sIL-6R increased the infarct volume, the number of infiltrating polymorphonuclear leukocytes and impaired the rotarod endurance of C57BL/6 mice 24h after pMCAo. IL-6 administration to naïve C57BL/6 mice lead after 45min to increased plasma-levels of CXCL1 and IL-10, whereas IL-6 administration to C57BL/6 mice lead to a reduction in the ischemia-induced increase in IL-6 and CXCL1 at both mRNA and protein level in brain, and of IL-6 and CXCL1 in serum. We also investigated the expression of IL-6 and IL-6R after pMCAo and found that cortical neurons upregulated IL-6 mRNA and protein, and upregulated IL-6R after pMCAo. In conclusion, the results show a complex but potentially beneficial effect of intravenously administered IL-6 in experimental stroke.

PACAP suppresses dry eye signs by stimulating tear secretion

Dry eye syndrome is caused by a reduction in the volume or quality of tears. Here, we show that pituitary adenylate cyclase-activating polypeptide (PACAP)-null mice develop dry eye-like symptoms such as corneal keratinization and tear reduction. PACAP immunoreactivity is co-localized with a neuronal marker, and PACAP receptor (PAC1-R) immunoreactivity is observed in mouse infraorbital lacrimal gland acinar cells. PACAP eye drops stimulate tear secretion and increase cAMP and phosphorylated (p)-protein kinase A levels in the infraorbital lacrimal glands that could be inhibited by pre-treatment with a PAC1-R antagonist or an adenylate cyclase inhibitor. Moreover, these eye drops suppress corneal keratinization in PACAP-null mice. PACAP eye drops increase aquaporin 5 (AQP5) levels in the membrane and pAQP5 levels in the infraorbital lacrimal glands. AQP5 siRNA treatment of the infraorbital lacrimal gland attenuates PACAP-induced tear secretion. Based on these results, PACAP might be clinically useful to treat dry eye disorder.

Pituitary adenylate cyclase-activating polypeptide (PACAP) contributes to the proliferation of hematopoietic progenitor cells in murine bone marrow via PACAP-specific receptor

Pituitary adenylate cyclase-activating polypeptide (PACAP, encoded by adcyap1) plays an important role in ectodermal development. However, the involvement of PACAP in the development of other germ layers is still unclear. This study assessed the expression of a PACAP-specific receptor (PAC1) gene and protein in mouse bone marrow (BM). Cells strongly expressing PAC1⁺ were large in size, had oval nuclei, and merged with CD34⁺ cells, suggesting that the former were hematopoietic progenitor cells (HPCs). Compared with wild-type mice, adcyap1^−/− mice exhibited lower multiple potential progenitor cell populations and cell frequency in the S-phase of the cell cycle. Exogenous PACAP38 significantly increased the numbers of colony forming unit-granulocyte/macrophage progenitor cells (CFU-GM) with two peaks in semi-solid culture. PACAP also increased the expression of cyclinD1 and Ki67 mRNAs. These increases were completely and partially inhibited by the PACAP receptor antagonists, PACAP6-38 and VIP6-28, respectively. Little or no adcyap1 was expressed in BM and the number of CFU-GM colonies was similar in adcyap1^−/− and wild-type mice. However, PACAP mRNA and protein were expressed in paravertebral sympathetic ganglia, which innervate tibial BM, and in the sympathetic fibers of BM cavity. These results suggested that sympathetic nerve innervation may be responsible for PACAP-regulated hematopoiesis in BM, mainly via PAC1.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Is Involved in Adult Mouse Hippocampal Neurogenesis After Stroke

In the subgranular zone (SGZ) of the hippocampus, neurogenesis persists throughout life and is upregulated following ischemia. Accumulating evidence suggests that enhanced neurogenesis stimulated by ischemic injury contributes to recovery after stroke. However, the mechanisms underlying the upregulation of neurogenesis are unclear. We have demonstrated that a neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), exerts a wide range of effects on neural stem cells (NSCs) during neural development. Here, we examined the effects of endogenous and exogenous PACAP in adult NSCs of the SGZ. Immunostaining showed expression of the PACAP receptor PAC1R in nestin-positive NSCs of adult naive mice. PACAP injection into the lateral ventricle increased bromodeoxyuridine (BrdU)-positive proliferative cells in the SGZ. These data suggest that PACAP promoted the proliferation of NSCs. In global ischemia model mice, the number of BrdU-positive cells was increased in wild-type mice but not in PACAP heterozygous knockout mice. The BrdU-positive cells that increased in number after ischemia were immunopositive for SOX2, a marker of NSCs, and differentiated into NeuN-positive mature neurons at 4 weeks after ischemia. These findings suggest that PACAP contributes to the proliferation of NSCs and may be associated with recovery after brain injury.

Trans-resveratrol attenuates high fatty acid-induced P2X7 receptor expression and IL-6 release in PC12 cells: possible role of P38 MAPK pathway

Diabetic neuropathy (DNP) is the most common chronic complication of diabetes. Elevated free fatty acids (FFAs) have been recently recognized as major causes of inflammation and are relevant to the functional changes of nerve system in diabetes. Trans-resveratrol (RESV), a polyphenolic natural compound, has long been acknowledged to have anti-inflammation properties and may exert a neuroprotective effect on neuronal damage in diabetes, while the mechanisms underlying are largely unknown. Our previous study on differential PC12 cells cultured with high FFAs has shown chronic FFAs overload increased PC12 interleukin (IL)-6 release mediated by P2X7 receptor, a ligand-gated cation channel activated by extracellular adenosine triphosphate (ATP); a high FFA-induced activation of P38 mitogen-activated protein kinase (MAPK) pathway was pointed to be a potential underlying mechanism. Data from this study indicated that RESV, in a dose-dependent manner, reduced high FFA-induced IL-6 release by impeding the activation of P2X7 receptor, as shown by the results that both high FFA-elevated P2X7 receptor messenger RNA (mRNA) and protein expression as well as high FFA-evoked [Ca(2+)]i in response to 3'-O-(4-benzoyl) benzoyl-ATP (a selective P2X7 receptor agonist) were significantly attenuated. Meanwhile, high FFA-induced activation of P38 MAPK, an essential prerequisite for high FFA-activated P2X7 receptor and subsequent IL-6 release, was also dose-dependently abrogated by RESV. Furthermore, RESV may hamper the activation of P38a MAPK (one paramount P38 isoform) via forming hydrogen bonding with Thr175 residue, surrounding the two residues (Thy180 and Tyr182) essential for canonical activation of P38a MAPK. Taken together, RESV could inhibit high FFA-induced inflammatory IL-6 release mediated by P2X7 receptor through deactivation of P38 MAPK signaling pathway. All these results outline the potential mechanisms involved in the neuroprotective roles of RESV and highlight the clinical application of RESV in treatment of inflammation in relation to DNP.

Microglia-Induced Maladaptive Plasticity Can Be Modulated by Neuropeptides In Vivo

Microglia-induced maladaptive plasticity is being recognized as a major cause of deleterious self-sustaining pathological processes that occur in neurodegenerative and neuroinflammatory diseases. Microglia, the primary homeostatic guardian of the central nervous system, exert critical functions both during development, in neural circuit reshaping, and during adult life, in the brain physiological and pathological surveillance. This delicate critical role can be disrupted by neural, but also peripheral, noxious stimuli that can prime microglia to become overreactive to a second noxious stimulus or worsen underlying pathological processes. Among regulators of microglia, neuropeptides can play a major role. Their receptors are widely expressed in microglial cells and neuropeptide challenge can potently influence microglial activity in vitro. More relevantly, this regulator activity has been assessed also in vivo, in experimental models of brain diseases. Neuropeptide action in the central nervous system has been associated with beneficial effects in neurodegenerative and neuroinflammatory pathological experimental models. This review describes some of the mechanisms of the microglia maladaptive plasticity in vivo and how neuropeptide activity can represent a useful therapeutical target in a variety of human brain pathologies.

Neuroprotective effect of interleukin-6 in a rat model of cerebral ischemia

Interleukin (IL)-6 is known to be a key cytokine in immune regulation in addition to serving crucial functions in various autoimmune diseases; however, the neuroprotective potential of IL-6 has not been fully investigated. The aim of the present study was to investigate the neuroprotective effects of the inflammatory cytokine IL-6 in a rat model of cerebral ischemia. Rat cerebral ischemia was induced by intraluminal middle cerebral artery occlusion. Following treatment with 500 or 50 ng IL-6, the infarct volumes and symptoms of neurological deficit were ameliorated. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining suggested that the IL-6 treatment reduced neuronal apoptosis in vivo, which was consistent with a lower percentage of annexin V- and caspase-3-positive cortical neurons. In addition, IL-6 in vitro induced the phosphorylation of signal transducer and activator of transcription (STAT) 3 and the expression of induced myeloid leukemia cell differentiation protein Mcl-1, but not the expression of B-cell lymphoma 2, suggesting the activation of the Janus kinase/STAT pathway by IL-6. IL-6 also appeared to be involved in the regulation of cytokine secretion and blood-brain barrier (BBB) integrity in cerebral ischemia. IL-6 downregulated a number of inflammatory cytokines, including tumor necrosis factor-α and IL-1β, as well as myeloperoxidase activity, indicating the accumulation of granulocytes in the ischemic brain tissue. IL-6 was also observed to support the integrity of the BBB by reducing Evans blue leakage in vivo and suppressing the expression of matrix metalloproteinase-9 in ischemic brain tissue. In conclusion, the results of the present study indicate that the neuroprotective effects of IL-6 in cerebral ischemia are the result of a range of processes, including the modulation of cell apoptosis, cytokine secretion and the integrity of the BBB. IL-6 could therefore be used as a therapeutic agent in clinical practice.

Human mesenchymal stem/stromal cells suppress spinal inflammation in mice with contribution of pituitary adenylate cyclase-activating polypeptide (PACAP)

Background

Adult human mesenchymal stem/stromal cells (hMSCs) from bone marrow have been reported to exhibit beneficial effects on spinal cord injury (SCI). A neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP) is known to decrease neuronal cell death and inflammatory response after ischemia, SCI, and other neuronal disorders. Recently, we found that expression of the gene for mouse PACAP (Adcyap1) was greater in animals receiving hMSCs with neural injury such as ischemia. However, the association of PACAP with hMSCs to protect nerve cells against neural injuries is still unclear.

Methods

Wild-type and PACAP-gene-deficient (Adcyap1^+/−) mice were subjected to spinal cord transection, and hMSCs (5 × 10⁵ cells) were injected into the intervertebral spinal cord on day 1 post-operation (p.o.). Locomotor activity, injury volume, retention of hMSCs, mouse and human cytokine genes (which contribute to macrophage (MΦ) and microglial activation), and Adcyap1 were evaluated.

Results

hMSCs injected into wild-type mice improved locomotor activity and injury volume compared with vehicle-treated mice. In contrast, non-viable hMSCs injected into wild-type mice, and viable hMSCs injected into Adcyap1^+/− mice, did not. Wild-type mice injected with hMSCs exhibited increased Adcyap1 expression, and observed PACAP immunoreaction in neuron-like cells. Gene expression levels for IL-1, tumor necrosis factor α (TNFα), interleukin-10 (IL-10), and transforming growth factor β (TGFβ) decreased, while that for interleukin-4 (IL-4) increased, in hMSC-injected wild-type mice. In contrast, IL-1, TGFβ, and IL-4 gene expression levels were all abolished in hMSC-injected Adcyap1^+/− mice on day 7 post-operation. Moreover, the mice-implanted hMSCs increased an alternative activating macrophage/microglial marker, arginase activity. The human gene profile indicated that hMSCs upregulated the gene of IL-4 and growth factors which were reported to enhance Adcyap1 expression. Finally, we demonstrated that hMSCs express human ADCYAP1 and its receptor gene after the inflammation-related interferon-γ (IFNγ) in vitro.

Conclusions

These results suggest that hMSCs attenuate the deleterious effects of SCI by reducing associated inflammatory responses and enhancing IL-4 production. This effect could be mediated in part by cell-cell cross-talk involving the neuropeptide PACAP.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0252-5) contains supplementary material, which is available to authorized users.

IL-6 regulation of synaptic function in the CNS

A growing body of evidence supports a role for glial-produced neuroimmune factors, including the cytokine IL-6, in CNS physiology and pathology. CNS expression of IL-6 has been documented in the normal CNS at low levels and at elevated levels in several neurodegenerative or psychiatric disease states as well as in CNS infection and injury. The altered CNS function associated with these conditions raises the possibility that IL-6 has neuronal or synaptic actions. Studies in in vitro and in vivo models confirmed this possibility and showed that IL-6 can regulate a number of important neuronal and synaptic functions including synaptic transmission and synaptic plasticity, an important cellular mechanism of memory and learning. Behavioral studies in animal models provided further evidence of an important role for IL-6 as a regulator of CNS pathways that are critical to cognitive function. This review summarizes studies that have lead to our current state of knowledge. In spite of the progress that has been made, there is a need for a greater understanding of the physiological and pathophysiological actions of IL-6 in the CNS, the mechanisms underlying these actions, conditions that induce production of IL-6 in the CNS and therapeutic strategies that could ameliorate or promote IL-6 actions. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

VIP and PACAP: neuropeptide modulators of CNS inflammation, injury, and repair

Inflammatory processes play both regenerative and destructive roles in multiple sclerosis, stroke, CNS trauma, amyotrophic lateral sclerosis and aging-related neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's. Endogenous defence mechanisms against these pathologies include those that are directly neuroprotective, and those that modulate the expression of inflammatory mediators in microglia, astrocytes, and invading inflammatory cells. While a number of mechanisms and molecules have been identified that can directly promote neuronal survival, less is known about how the brain protects itself from harmful inflammation, and further, how it co-opts the healing function of the immune system to promote CNS repair. The two closely related neuroprotective peptides, vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating peptide (PACAP), which are up-regulated in neurons and immune cells after injury and/or inflammation, are known to protect neurons, but also exert powerful in vivo immunomodulatory actions, which are primarily anti-inflammatory. These peptide actions are mediated by high-affinity receptors expressed not only on neurons, but also astrocytes, microglia and peripheral inflammatory cells. Well-established immunomodulatory actions of these peptides are to inhibit macrophage and microglia production and release of inflammatory mediators such as TNF-α and IFN-γ, and polarization of T-cell responses away from Th1 and Th17, and towards a Th2 phenotype. More recent studies have revealed that these peptides can also promote the production of both natural and inducible subsets of regulatory T-cells. The neuroprotective and immunomodulatory actions of VIP and PACAP suggest that receptors for these peptides may be therapeutic targets for neurodegenerative and neuroinflammatory diseases and other forms of CNS injury.

PACAP38 suppresses cortical damage in mice with traumatic brain injury by enhancing antioxidant activity

The production of reactive oxygen species (ROS) and the resulting oxidative stress in mice in response to a controlled cortical impact (CCI) are typical exacerbating factors associated with traumatic brain injury (TBI). Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38) is a multifunctional peptide that has been shown to exhibit neuroprotective effects in response to a diverse range of injuries to neuronal cells. We recently reported that PACAP38 might regulate oxidative stress in mice. The aim of the present study was to determine whether PACAP38 exerts neuroprotective effects by regulating oxidative stress in mice with TBI. Reactive oxidative metabolites (ROMs) and biological antioxidant potential (BAP) were measured in male C57Bl/6 mice before and 3, 4, and 24 h after CCI. PACAP38 was administered intravenously immediately following CCI, and immunostaining for the oxidative stress indicator nitrotyrosine (NT), and for neuronal death as an indicator of the area affected by TBI, was measured 24 h later. Western blot experiments to determine antioxidant activity [as indicated by superoxide dismutase-2 (SOD-2) and glutathione peroxidase 1 (GPx-1)] in the neocortical region were also performed 3 h post-CCI. Results showed that plasma BAP and ROM levels were dramatically increased 3 h after CCI. PACAP38 suppressed the extent of TBI and NT-positive regions 24 h after CCI, and increased SOD-2 and GPx-1 levels in both hemispheres. Taken together, these results suggest that increasing antioxidant might be involving in the neuroprotective effect of PACAP38 in mice subjected to a CCI.

Investigation of the possible functions of PACAP in human trophoblast cells

Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide having a widespread distribution both in the nervous system and peripheral organs including the female reproductive system. Both the peptide and its receptors have been shown in the placenta but its role in placental growth, especially its human aspects, remains unknown. The aim of the present study was to investigate the effects of PACAP on invasion, proliferation, cell survival, and angiogenesis of trophoblast cells. Furthermore, cytokine production was investigated in human decidual and peripheral blood mononuclear cells. For in vitro studies, human invasive proliferative extravillous cytotrophoblast (HIPEC) cells and HTR-8/SVneo human trophoblast cells were used. Both cell types were used for testing the effects of PACAP on invasion and cell survival in order to investigate whether the effects of PACAP in trophoblasts depend on the examined cell type. Invasion was studied by standardized invasion assay. PACAP increased proliferation in HIPEC cells, but not in HTR-8 cells. Cell viability was examined using MTT test, WST-1 assay, and annexin V/propidium iodide flow cytometry assay. Survival of HTR-8/SVneo cells was studied under oxidative stress conditions induced by hydrogen peroxide. PACAP as pretreatment, but not as co-treatment, significantly increased the number of surviving HTR-8 cells. Viability of HIPEC cells was investigated using methotrexate (MTX) toxicity, but PACAP1-38 could not counteract its toxic effect. Angiogenic molecules were determined both in the supernatant and the cell lysate by angiogenesis array. In the supernatant, we found that PACAP decreased the secretion of various angiogenic markers, such as angiopoietin, angiogenin, activin, endoglin, ADAMTS-1, and VEGF. For the cytokine assay, human decidual and peripheral blood lymphocytes were separated and treated with PACAP1-38. Th1 and Th2 cytokines were analyzed with CBA assay and the results showed that there were no significant differences in control and PACAP-treated cells. In summary, PACAP seems to play various roles in human trophoblast cells, depending on the cell type and microenvironmental influences.

Pituitary adenylate cyclase activating polypeptide (PACAP) signalling exerts chondrogenesis promoting and protecting effects: implication of calcineurin as a downstream target

Pituitary adenylate cyclase activating polypeptide (PACAP) is an important neurotrophic factor influencing differentiation of neuronal elements and exerting protecting role during traumatic injuries or inflammatory processes of the central nervous system. Although increasing evidence is available on its presence and protecting function in various peripheral tissues, little is known about the role of PACAP in formation of skeletal components. To this end, we aimed to map elements of PACAP signalling in developing cartilage under physiological conditions and during oxidative stress. mRNAs of PACAP and its receptors (PAC1,VPAC1, VPAC2) were detectable during differentiation of chicken limb bud-derived chondrogenic cells in micromass cell cultures. Expression of PAC1 protein showed a peak on days of final commitment of chondrogenic cells. Administration of either the PAC1 receptor agonist PACAP 1-38, or PACAP 6-38 that is generally used as a PAC1 antagonist, augmented cartilage formation, stimulated cell proliferation and enhanced PAC1 and Sox9 protein expression. Both variants of PACAP elevated the protein expression and activity of the Ca-calmodulin dependent Ser/Thr protein phosphatase calcineurin. Application of PACAPs failed to rescue cartilage formation when the activity of calcineurin was pharmacologically inhibited with cyclosporine A. Moreover, exogenous PACAPs prevented diminishing of cartilage formation and decrease of calcineurin activity during oxidative stress. As an unexpected phenomenon, PACAP 6-38 elicited similar effects to those of PACAP 1-38, although to a different extent. On the basis of the above results, we propose calcineurin as a downstream target of PACAP signalling in differentiating chondrocytes either in normal or pathophysiological conditions. Our observations imply the therapeutical perspective that PACAP can be applied as a natural agent that may have protecting effect during joint inflammation and/or may promote cartilage regeneration during degenerative diseases of articular cartilage.

PACAP attenuates NMDA-induced retinal damage in association with modulation of the microglia/macrophage status into an acquired deactivation subtype

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been known as a neuroprotectant agent in several retinal injury models. However, a detailed mechanism of this effect is still not well understood. In this study, we examined the retinoprotective effects and associated underlying mechanisms of action of PACAP in the mouse N-methyl-D-aspartic acid (NMDA)-induced retinal injury model, focusing on the relationship between PACAP and retinal microglia/macrophage (MG/MΦ) status. Adult male C57BL/6 mice received an intravitreal injection of NMDA to induce retinal injury. Three days after NMDA injection, the number of MG/MΦ increased significantly in the retinas. The concomitant intravitreal injection of PACAP suppressed NMDA-induced cell loss in the ganglion cell layer (GCL) and significantly increased the number of MG/MΦ. These outcomes associated with PACAP were attenuated by cotreatment with PACAP6-38, while the beneficial effects of PACAP were not seen in interleukin-10 (IL-10) knockout mice. PACAP significantly elevated the messenger RNA levels of anti-inflammatory cytokines such as transforming growth factor beta 1 and IL-10 in the injured retina, with the immunoreactivities seen to overlap with markers of MG/MΦ. These results suggest that PACAP enhances the proliferation and/or infiltration of retinal MG/MΦ and modulates their status into an acquired deactivation subtype to favor conditions for neuroprotection.

PACAP protects against salsolinol-induced toxicity in dopaminergic SH-SY5Y cells: implication for Parkinson's disease

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous 38 amino acid containing neuropeptide with various cytoprotective functions including neuroprotection. Administration of PACAP has been shown to reduce damage induced by ischemia, trauma, or exogenous toxic substances. Moreover, mice deficient in PACAP are more vulnerable to damaging insults. In this study, we sought to determine whether PACAP may also be protective against salsolinol-induced toxicity in SH-SY5Y cells and, if so, elucidate its mechanism(s) of action. Salsolinol (SALS) is an endogenous dopamine metabolite with selective toxicity to nigral dopaminergic neurons, which are directly implicated in Parkinson's disease (PD). SH-SY5Y cells, derived from human neuroblastoma cells, express high levels of dopaminergic activity and are used extensively as a model to study these neurons. Exposure of SH-SY5Y cells to 400 μM SALS for 24 h resulted in approximately 50 % cell death that was mediated by apoptosis as determined by cell flow cytometry and increases in caspase-3 levels. Cellular toxicity was also associated with reductions in brain-derived neurotrophic factor and phosphorylated cyclic AMP response element-binding protein. Pretreatment with PACAP dose-dependently attenuated SALS-induced toxicity and the associated apoptosis and the chemical changes. PACAP receptor antagonist PACAP6-38, in turn, dose-dependently blocked the effects of PACAP. Neither PACAP nor PACAP antagonist had any effect of its own on cellular viability. These results suggest the protective effects of PACAP in a cellular model of PD. Hence, PACAP or its agonists could be of therapeutic benefit in PD.

Distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) in the human testis and in testicular germ cell tumors

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide expressed in the central nervous system and peripheral organs. Previous studies revealed the role and distribution of PACAP in the rodent testis, however, its presence in the human testis and in testicular germ cell tumors is not known. We used RT-PCR and immunohistological observations to investigate whether human testicular tissue and testicular germ cell tumors contain PACAP. The mRNAs for PACAP and its receptors were detected in total RNA extracted from human testes. PACAP immunoreactivity was observed in spermatogonia and spermatids from normal testes. In contrast, diffuse PACAP immunopositivity was observed in seminoma tumor cells, while only faint immunoreactivity was observed in embryonal carcinoma cells. Our data suggest that PACAP may play a role in human spermatogenesis and in testicular germ cell tumor development.

Inhibition of IL-6 signaling: A novel therapeutic approach to treating spinal cord injury pain

To characterize the contribution of interleukin-6 (IL-6) to spinal cord injury pain (SCIP), we employed a clinically relevant rat contusion model of SCIP. Using Western blots, we measured IL-6 levels in lumbar segments (L1-L5), at the lesion site (T10), and in the corresponding lumbar and thoracic dorsal root ganglia (DRG) in 2 groups of similarly injured rats: (a) SCI rats that developed hind-limb mechanical allodynia (SCIP), and (b) SCI rats that did not develop SCIP. Only in SCIP rats did we find significantly increased IL-6 levels. Immunocytochemistry showed elevated IL-6 predominantly in reactive astrocytes. Our data also showed that increased production of IL-6 in hyperreactive astrocytes in SCIP rats may explain still-poorly understood astrocytic contribution to SCIP. To test the hypothesis that IL-6 contributes to mechanical allodynia, we treated SCIP rats with neutralizing IL-6 receptor antibody (IL-6-R Ab), and found that one systemic injection abolished allodynia and associated weight loss; in contrast to gabapentin, the analgesic effect lasted for at least 2weeks after the injection, despite the shorter presence of the Ab in the circulation. We also showed that IL-6-R Ab partially reversed SCI-induced decreases in the protein levels of the glutamate transporter GLT-1 12hours and 8days after Ab injection, which may explain the lasting analgesic effect of the Ab in SCIP rats. A link between reactive astrocytes IL-6-GLT-1 has not been previously shown. Given that the humanized IL-6-R Ab tocilizumab is Food and Drug Administration-approved for rheumatoid arthritis, we are proposing tocilizumab as a novel and potentially effective treatment for SCIP.

High fatty acids modulate P2X(7) expression and IL-6 release via the p38 MAPK pathway in PC12 cells

Diabetic neuropathy (DNP) is the most common chronic complication of diabetes. Elevated free fatty acids (FFAs) have been recently recognized as a major cause of nervous system damage in diabetes. P2X receptors play a primary role in regulation of neuronal interleukin (IL)-6 release, which is of paramount relevance to the functional changes of nerve system. The present study aimed to investigate the effects of high FFAs on the P2X7 expression and IL-6 release in PC12 cells. High FFAs induced P2X7 expression and IL-6 release significantly in PC12 cells. Moreover, high FFAs enhanced ATP or BzATP-induced Ca(2+) signals in PC12 cells. Inhibition of P2X7 by transfection with P2X7-siRNA or co-culture with BBG (a specific P2X7 inhibitor) at high concentrations of FFAs decreased ATP or BzATP-promoted Ca(2+) signals and IL-6 release in PC12 cells. High FFAs induced the phosphorylation of p38 in PC12 cells. Blockade of p38 pathways by SB-203580 inhibited P2X7 up-expression, ATP or BzATP-evoked [Ca(2+)]i rises as well as IL-6 release in PC12 cells exposed to high FFAs. Therefore, high concentrations of FFAs increased the expression of P2X7 in PC12 cells via activation of p38 mitogen-activated protein kinase (MAPK) signaling pathway, which contributed to P2X7-mediated IL-6 release from PC12 cells.

Expression and distribution of pituitary adenylate cyclase-activating polypeptide receptor in reactive astrocytes induced by global brain ischemia in mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide acting as a neuroprotectant. We previously showed that PACAP receptor (PAC1R) immunoreactivity was elevated in reactive astrocytes after stab wound injury. However, the pattern of PAC1R expression in astrocytes after brain injury is still unknown. In this study, PAC1R expression was evaluated in mouse hippocampal astrocytes after bilateral common carotid artery occlusion. PAC1R mRNA levels in the hippocampus peaked on day 7, and glial fibrillary acidic protein (GFAP) mRNA levels increased from day 3 to day 7 after ischemia. We then observed co-localization of PAC1R and GFAP by double immunostaining. GFAP-immunopositive cells showed signs of hypertrophy 3 days after the ischemia, and by day 7 had fine processes, were hypertrophied, and are known as reactive astrocytes. A low number of PAC1R-immunopositive astrocytes were detectable in the hippocampal area until 3 days after ischemia. PAC1R-positive astrocytes were widely distributed in the hippocampus between day 7 and day 14 after ischemia, and they were converging around the damaged CA1 pyramidal cell layer by day 28. These results suggest that PAC1R might be expressed in the middle to late stage of reactive astrocytes and PACAP plays an important role in the reactive astrocytes after brain injury.

Transcriptomics and proteomics analyses of the PACAP38 influenced ischemic brain in permanent middle cerebral artery occlusion model mice

INTRODUCTION

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is considered to be a potential therapeutic agent for prevention of cerebral ischemia. Ischemia is a most common cause of death after heart attack and cancer causing major negative social and economic consequences. This study was designed to investigate the effect of PACAP38 injection intracerebroventrically in a mouse model of permanent middle cerebral artery occlusion (PMCAO) along with corresponding SHAM control that used 0.9% saline injection.

METHODS

Ischemic and non-ischemic brain tissues were sampled at 6 and 24 hours post-treatment. Following behavioral analyses to confirm whether the ischemia has occurred, we investigated the genome-wide changes in gene and protein expression using DNA microarray chip (4x44K, Agilent) and two-dimensional gel electrophoresis (2-DGE) coupled with matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), respectively. Western blotting and immunofluorescent staining were also used to further examine the identified protein factor.

RESULTS

Our results revealed numerous changes in the transcriptome of ischemic hemisphere (ipsilateral) treated with PACAP38 compared to the saline-injected SHAM control hemisphere (contralateral). Previously known (such as the interleukin family) and novel (Gabra6, Crtam) genes were identified under PACAP influence. In parallel, 2-DGE analysis revealed a highly expressed protein spot in the ischemic hemisphere that was identified as dihydropyrimidinase-related protein 2 (DPYL2). The DPYL2, also known as Crmp2, is a marker for the axonal growth and nerve development. Interestingly, PACAP treatment slightly increased its abundance (by 2-DGE and immunostaining) at 6 h but not at 24 h in the ischemic hemisphere, suggesting PACAP activates neuronal defense mechanism early on.

CONCLUSIONS

This study provides a detailed inventory of PACAP influenced gene expressions and protein targets in mice ischemic brain, and suggests new targets for thereaupetic interventions.

Distribution and protective function of pituitary adenylate cyclase-activating polypeptide in the retina

Pituitary adenylate cyclase-activating polypeptide (PACAP), which is found in 27- or 38-amino acid forms, belongs to the VIP/glucagon/secretin family. PACAP and its three receptor subtypes are expressed in neural tissues, with PACAP known to exert a protective effect against several types of neural damage. The retina is considered to be part of the central nervous system, and retinopathy is a common cause of profound and intractable loss of vision. This review will examine the expression and morphological distribution of PACAP and its receptors in the retina, and will summarize the current state of knowledge regarding the protective effect of PACAP against different kinds of retinal damage, such as that identified in association with diabetes, ultraviolet light, hypoxia, optic nerve transection, and toxins. This article will also address PACAP-mediated protective pathways involving retinal glial cells.