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

CGCom: a framework for inferring Cell-cell Communication based on Graph Neural Network

Cell-cell communication is crucial in maintaining cellular homeostasis, cell survival and various regulatory relationships among interacting cells. Thanks to recent advances of spatial transcriptomics technologies, we can now explore if and how cells' proximal information available from spatial transcriptomics datasets can be used to infer cell-cell communication. Here we present a cell-cell communication inference framework, called CGCom, which uses a graph neural network (GNN) to learn communication patterns among interacting cells by combining single-cell spatial transcriptomic datasets with publicly available ligand-receptor information and the molecular regulatory information down-stream of the ligand-receptor signaling. To evaluate the performance of CGCom, we applied it to mouse embryo seqFISH datasets. Our results demonstrate that CGCom can not only accurately infer cell communication between individual cell pairs but also generalize its learning to predict communication between different cell types. We compared the performance of CGCom with two existing methods, CellChat and CellPhoneDB, and our comparative study revealed both common and unique communication patterns from the three approaches. Commonly found communication patterns include three sets of ligand-receptor communication relationships, one between surface ectoderm cells and spinal cord cells, one between gut tube cells and endothelium, and one between neural crest and endothelium, all of which have already been reported in the literature thus offering credibility of all three methods. However, we hypothesize that CGCom is superior in reducing false positives thanks to its use of cell proximal information and its learning between specific cell pairs rather than between cell types. CGCom is a GNN-based solution that can take advantage of spatially resolved single-cell transcriptomic data in predicting cell-cell communication with a higher accuracy.

Long-term Effects of the pituitary-adenylate cyclase-activating Polypeptide (PACAP38) in the Adult Mouse Retina: Microglial Activation and Induction of Neural Proliferation

The degenerative retinal disorders characterized by progressive cell death and exacerbating inflammation lead ultimately to blindness. The ubiquitous neuropeptide, PACAP38 is a promising therapeutic agent as its proliferative potential and suppressive effect on microglia might enable cell replacement and attenuate inflammation, respectively. Our previous finding that PACAP38 caused a marked increase of the amacrine cells in the adult (1-year-old) mouse retina, served as a rationale of the current study. We aimed to determine the proliferating elements and the inflammatory status of the PACAP38-treated retina. Three months old mice were intravitreally injected with 100 pmol PACAP38 at 3 months intervals (3X). Retinas of 1-year-old animals were dissected and effects on cell proliferation, and expression of inflammatory regulators were analyzed. Interestingly, both mitogenic and anti-mitogenic actions were detected after PACAP38-treatment. Further analysis of the mitogenic effect revealed that proliferating cells include microglia, endothelial cells, and neurons of the ganglion cell layer but not amacrine cells. Furthermore, PACAP38 stimulated retinal microglia to polarize dominantly into M2-phenotype but also might cause subsequent angiogenesis. According to our results, PACAP38 might dampen pro-inflammatory responses and help tissue repair by reprogramming microglia into an M2 phenotype, nonetheless, with angiogenesis as a warning side effect.

Diagnostic and Prognostic Value of PACAP in Multiple Myeloma

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide with well-known anti-inflammatory, antioxidant, antitumor, and immunomodulatory effects. PACAP regulates the production of various proinflammatory factors and may influence the complex cytokine network of the bone marrow microenvironment altered by plasma cells, affecting the progression of multiple myeloma (MM) and the development of end-organ damage. The aim of our study was to investigate the changes in PACAP-38 levels in patients with MM to explore its value as a potential biomarker in this disease. We compared the plasma PACAP-38 levels of MM patients with healthy individuals by ELISA method and examined its relationship with various MM-related clinical and laboratory parameters. Lower PACAP-38 levels were measured in MM patients compared with the healthy controls, however, this difference vanished if the patient achieved any response better than partial response. In addition, lower peptide levels were found in elderly patients. Significantly higher PACAP-38 levels were seen in patients with lower stage, lower plasma cell infiltration in bone marrow, lower markers of tumor burden in serum, lower total urinary and Bence-Jones protein levels, and in patients after lenalidomide therapy. Higher PACAP-38 levels in newly diagnosed MM patients predicted longer survival and a higher probability of complete response to treatment. Our findings confirm the hypothesis that PACAP plays an important role in the pathomechanism of MM. Furthermore, our results suggest that PACAP might be used as a valuable, non-invasive, complementary biomarker in diagnosis, and may be utilized for prognosis prediction and response monitoring.

Targeting VIP and PACAP Receptor Signaling: New Insights into Designing Drugs for the PACAP Subfamily of Receptors

Pituitary Adenylate Cyclase-Activating Peptide (PACAP) and Vasoactive Intestinal Peptide (VIP) are neuropeptides involved in a diverse array of physiological and pathological processes through activating the PACAP subfamily of class B1 G protein-coupled receptors (GPCRs): VIP receptor 1 (VPAC1R), VIP receptor 2 (VPAC2R), and PACAP type I receptor (PAC1R). VIP and PACAP share nearly 70% amino acid sequence identity, while their receptors PAC1R, VPAC1R, and VPAC2R share 60% homology in the transmembrane regions of the receptor. PACAP binds with high affinity to all three receptors, while VIP binds with high affinity to VPAC1R and VPAC2R, and has a thousand-fold lower affinity for PAC1R compared to PACAP. Due to the wide distribution of VIP and PACAP receptors in the body, potential therapeutic applications of drugs targeting these receptors, as well as expected undesired side effects, are numerous. Designing selective therapeutics targeting these receptors remains challenging due to their structural similarities. This review discusses recent discoveries on the molecular mechanisms involved in the selectivity and signaling of the PACAP subfamily of receptors, and future considerations for therapeutic targeting.

Clinical Efficacy and Potential Mechanisms of Acupoint Stimulation Combined With Chemotherapy in Combating Cancer: A Review and Prospects

Although chemotherapy is the first-line treatment strategy for a variety of tumors, its side effects have limited its efficacy. This review summarizes the progress on the use of acupoint stimulation to combat chemotherapy-associated side effects, including chemotherapy-induced peripheral neuropathy (CIPN), cognitive impairment (CICI), and gastrointestinal toxicity (GI), as well as myelosuppression and immunosuppression. It was found that acupoint stimulation attenuated CIPN and GI by modulating the 5-hydroxytryptamine system in dorsal root ganglia, the dorsal horn of the spinal cord, and the duodenum by reducing oxidative stress and neuroinflammation. Acupoint stimulation also alleviated GI by activating vagal activity in the nucleus tractus solitarius and promoting the secretion of gastrointestinal neuropeptide hormones. Acupoint stimulation restored both bone marrow hematopoiesis and immune function to combat cancer. In addition, the combination of acupoint stimulation and chemotherapy could inhibit tumor growth by promoting tumor cell apoptosis and the enrichment of chemotherapeutic agents in tumor tissue and by modulating the tumor immune microenvironment and normalizing the vasculature. Multiple evidence also indicates that neuroimmune regulation may be involved in the effects of acupoint stimulation. In conclusion, the evidence suggests that acupoint stimulation can alleviate the side effects of chemotherapy and can also assist chemotherapeutic agents in inhibiting tumor growth, which expands the clinical application of acupoint stimulation in cancer treatment. However, more high-quality clinical studies are needed to confirm the clinical value of acupoint stimulation.

A Review on the Role of Endogenous Neurotrophins and Schwann Cells in Axonal Regeneration

Injury to the peripheral nerve is traditionally referred to acquired nerve injury as they are the result of physical trauma due to laceration, stretch, crush and compression of nerves. However, peripheral nerve injury may not be completely limited to acquired physical trauma. Peripheral nerve injury equally implies clinical conditions like Guillain-Barré syndrome (GBS), Carpal tunnel syndrome, rheumatoid arthritis and diabetes. Physical trauma is commonly mono-neuropathic as it engages a single nerve and produces focal damage, while in the context of pathological conditions the damage is divergent involving a group of the nerve causing polyneuropathy. Damage to the peripheral nerve can cause a diverse range of manifestations from sensory impairment to loss of function with unpredictable recovery patterns. Presently no treatment option provides complete or functional recovery in nerve injury, as nerve cells are highly differentiated and inert to regeneration. However, the regenerative phenotypes in Schwann cells get expressed when a signalling cascade is triggered by neurotrophins. Neurotrophins are one of the promising biomolecules that are released naturally post-injury with the potential to exhibit better functional recovery. Pharmacological intervention modulating the expression of these neurotrophins such as brain-derived neurotrophic factor (BDNF) and pituitary adenylyl cyclase-activating peptide (PACAP) can prove to be a significant treatment option as endogenous compounds which may have remarkable innate advantage showing maximum 'biological relevance'.

PAC1 Receptor Mediates Electroacupuncture-Induced Neuro and Immune Protection During Cisplatin Chemotherapy

Platinum-based chemotherapy is an effective treatment used in multiple tumor treatments, but produces severe side effects including neurotoxicity, anemia, and immunosuppression, which limits its anti-tumor efficacy and increases the risk of infections. Electroacupuncture (EA) is often used to ameliorate these side effects, but its mechanism is unknown. Here, we report that EA on ST36 and SP6 prevents cisplatin-induced neurotoxicity and immunosuppression. EA induces neuroprotection, prevents pain-related neurotoxicity, preserves bone marrow (BM) hematopoiesis, and peripheral levels of leukocytes. EA activates sympathetic BM terminals to release pituitary adenylate cyclase activating polypeptide (PACAP). PACAP-receptor PAC1-antagonists abrogate the effects of EA, whereas PAC1-agonists mimic EA, prevent neurotoxicity, immunosuppression, and preserve BM hematopoiesis during cisplatin chemotherapy. Our results indicate that PAC1-agonists may provide therapeutic advantages during chemotherapy to treat patients with advanced neurotoxicity or neuropathies limiting EA efficacy.

Pituitary adenylate cyclase-activating polypeptide promotes cutaneous dendritic cell functions in contact hypersensitivity

BACKGROUND

Sensory nerves regulate cutaneous local inflammation indirectly through induction of pruritus and directly by acting on local immune cells. The underlying mechanisms for how sensory nerves influence cutaneous acquired immune responses remain to be clarified.

OBJECTIVE

This study aimed to explore the effect of peripheral nerves on cutaneous immune cells in cutaneous acquired immune responses.

METHODS

We analyzed contact hypersensitivity (CHS) responses as a murine model of delayed-type hypersensitivity in absence or presence of resiniferatoxin-induced sensory nerve denervation. We conducted ear thickness measurements, flow cytometric analyses, and mRNA expression analyses in CHS.

RESULTS

CHS responses were attenuated in mice that were denervated during the sensitization phase of CHS. By screening neuropeptides, we found that pituitary adenylate cyclase-activating polypeptide (PACAP) mRNA expression was decreased in the dorsal root ganglia after denervation. Administration of PACAP restored attenuated CHS response in resiniferatoxin-treated mice, and pharmacological inhibition of PACAP suppressed CHS. Flow cytometric analysis of skin-draining lymph nodes showed that cutaneous dendritic cell migration and maturation were reduced in both denervated mice and PACAP antagonist-treated mice. The expression of chemokine receptors CCR7 and CXCR4 of dendritic cell s was enhanced by addition of PACAP in vitro.

CONCLUSION

These findings indicate that a neuropeptide PACAP promotes the development of CHS responses by inducing cutaneous dendritic cell functions during the sensitization phase.

PACAP and PAC1 Receptor Expression in Human Insulinomas

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with widespread occurrence and diverse functions. PACAP binds to specific PAC1 and non-specific VPAC1/2 receptors. PACAP is considered as a growth factor, as it plays important roles during development and participates in reparative processes. Highest concentrations are found in the nervous system and endocrine glands, where several functions are known, including actions in tissue growth, differentiation and tumour development. Therefore, we have investigated expression of PACAP and its receptors in different tumours, including those of endocrine glands. We showed earlier that PACAP and PAC1 receptor staining intensity decreased in pancreatic ductal adenocarcinoma. In the present study we aimed to investigate alterations of PACAP and PAC1 receptor in human insulinoma and compared the immunostaining pattern with samples from chronic pancreatitis patients. We collected perioperative and histological data of patients who underwent operation because of insulinoma or chronic pancreatitis over a five-year-long period. Histology showed chronic pancreatitis with severe scar formation in pancreatitis patients, while tumour samples evidenced Grade 1 or 2 insulinoma. PACAP and PAC1 receptor expression was studied using immunohistochemistry. Staining intensity was very strong in the Langerhans islets of normal tissue and discernible staining was also observed in the exocrine pancreas. Immunostaining intensity for both PACAP and PAC1 receptor was markedly weaker in insulinoma samples, and disappeared from chronic pancreatitis samples except for intact islets. These findings show that PAC1 receptor/PACAP signalling is altered in insulinoma and this suggests a possible involvement of this system in tumour growth or differentiation.

Combinatorial sympathetic and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) blockades inhibit the murine melanoma growth by targeting infiltrating T cells

Background

Failure of the proliferation and infiltration of tumor-specific T cells in tumor site has been considered as one of important reasons induce the inefficiencies of immune checkpoint therapies in advanced cancers. Therefore, we aimed to demonstrate how combinatorial sympathetic and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) blockade affects the tumor growth of melanoma-bearing mice and potential mechanisms.

Methods

Tumor growth was measured and the infiltrating immune cell populations were observed with flow cytometry in B16-F10 melanoma-bearing mice treated with combined sympathetic and immune checkpoint blockade, using anti-CTLA-4 antibodies. The expression of adrenergic receptors was investigated in human peripheral blood mononuclear cells and their subpopulations, and the proliferation of T cell subsets was detected when stimulated by norepinephrine and its antagonists.

Results

B16-F10 tumor growth was associated with infiltrating CD8⁺ T cells. Combinatorial sympathetic and CTLA-4 blockade inhibited tumor growth and enhanced CD8⁺ infiltration. Meanwhile, all β1, β2 and β3 adrenergic receptors were found to be expressed in human peripheral blood mononuclear cells, activated T cells, monocytes, and monocyte-induced dendritic cells. β2-adrenergic receptors were expressed in most CD4⁺ T cells with increased expression in activated CD8⁺ T cells. Moreover, norepinephrine was able to prevent CD4⁺ T cell proliferation and β2-adrenergic receptor antagonists could reverse the inhibition of CD4⁺, but not CD8⁺ cell proliferation.

Conclusions

We conclude that the combination of sympathetic and CTLA-4 inhibitors is more effective for inhibiting melanoma progression than a single treatment and might enhance the infiltration of T cells in the tumor site, offering a novel therapeutic approach for immune checkpoint targeting.

Melanotan II, a melanocortin agonist, partially rescues the impaired thermogenic capacity of pituitary adenylate cyclase-activating polypeptide deficient mice

NEW FINDINGS

What is the central question of this study? Can chronic treatment of pituitary adenylate cyclase-activating polypeptide (PACAP) deficient mice with the melanocortin agonist melanotan II during cold acclimation rescue the impaired thermogenic capacity previously observed in PACAP deficient mice? What is the main finding and its importance? Using a genetic model of PACAP deficiency, this study provides evidence that PACAP acts upstream of the melanocortin system in regulating sympathetic nerve activity to brown adipose tissue in mice.

ABSTRACT

Impaired adipose tissue function in obesity, including reduced thermogenic potential, has detrimental consequences for metabolic health. Hormonal regulation of adaptive thermogenesis is being explored as a potential therapeutic target for human obesity. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide expressed in nuclei of the hypothalamus known to regulate energy expenditure, and functional studies reveal a role for PACAP in the central regulation of thermogenesis, although mechanisms are not well understood. We hypothesized that PACAP acts upstream of the melanocortin system to regulate sympathetic nerve activity to stimulate thermogenesis. To assess this, female PACAP^-/- and PACAP^+/+ mice were given daily peripheral injections of a melanocortin receptor agonist, melanotan II (MTII), for 3 weeks during cold acclimation, and the effect of MTII on thermogenic capacity and adipose tissue remodelling was examined by physiological and histological analyses. MTII partially rescued the impaired thermogenic capacity in PACAP^-/- mice as compared to PACAP^+/+ mice as determined by measuring noradrenaline-induced metabolic rate. In addition, MTII treatment during cold acclimation corrected the previously identified deficit in lipid utilization in response to adrenergic stimulation in PACAP^-/- null mice, suggesting impaired lipid mobilization may contribute to the impaired thermogenic capacity of PACAP^-/- mice. Results presented here provide physiological evidence to suggest that PACAP acts upstream of melanocortin receptors to facilitate sympathetically induced mechanisms of adaptive thermogenesis in response to cold acclimation.

Attenuation of relaxing response induced by pituitary adenylate cyclase-activating polypeptide in bronchial smooth muscle of experimental asthma

Bronchomotor tone is regulated by contraction and relaxation of airway smooth muscle (ASM). A weakened ASM relaxation might be a cause of airway hyperresponsiveness (AHR), a characteristic feature of bronchial asthma. Pituitary adenylyl cyclase-activating polypeptide (PACAP) is known as a mediator that causes ASM relaxation. To date, whether or not the PACAP responsiveness is changed in asthmatic ASM is unknown. The current study examined the hypothesis that relaxation induced by PACAP is reduced in bronchial smooth muscle (BSM) of allergic asthma. The ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Twenty-four hours after the last antigen challenge, the main bronchial smooth muscle (BSM) tissues were isolated. Tension study showed a BSM hyperresponsiveness to acetylcholine in the OA-challenged mice. Both quantitative RT-PCR and immunoblot analyses revealed a significant decrease in PAC₁ receptor expression in BSMs of the diseased mice. Accordingly, in the antigen-challenged group, the PACAP-induced PAC₁ receptor-mediated BSM relaxation was significantly attenuated, whereas the relaxation induced by vasoactive intestinal polypeptide was not changed. These findings suggest that the relaxation induced by PACAP is impaired in BSMs of experimental asthma due to a downregulation of its binding partner PAC₁ receptor. Impaired BSM responsiveness to PACAP might contribute to the AHR in asthma.

Skeletal Toxicity of Coplanar Polychlorinated Biphenyl Congener 126 in the Rat Is Aryl Hydrocarbon Receptor Dependent

Epidemiological evidence links polychlorinated biphenyls (PCBs) to skeletal toxicity, however mechanisms whereby PCBs affect bone are poorly studied. In this study, coplanar PCB 126 (5 μmol/kg) or corn oil vehicle was administered to N = 5 and 6 male and female, wild type (WT) or AhR -/- rats via intraperitoneal injection. Animals were sacrificed after 4 weeks. Bone length was measured; bone morphology was assessed by microcomputed tomography and dynamic histomorphometry. Reduced bone length was the only genotype-specific effect and only observed in males (p < .05). WT rats exposed to PCB 126 had reduced serum calcium, and smaller bones with reduced tibial length, cortical area, and medullary area relative to vehicle controls (p < .05). Reduced bone formation rate observed in dynamic histomorphometry was consistent with inhibition of endosteal and periosteal bone growth. The effects of PCB 126 were abolished in AhR -/- rats. Gene expression in bone marrow and shaft were assessed by RNA sequencing. Approximately 75% of the PCB-regulated genes appeared AhR dependent with 89 genes significantly (p < .05) regulated by both PCB 126 and knockout of the AhR gene. Novel targets significantly induced by PCB 126 included Indian hedgehog (Ihh) and connective tissue growth factor (Ctgf/Ccn2), which regulate chondrocyte proliferation and differentiation in the bone growth plate and cell-matrix interactions. These data suggest the toxic effects of PCB 126 on bone are mediated by AhR, which has direct effects on the growth plate and indirect actions related to endocrine disruption. These studies clarify important mechanisms underlying skeletal toxicity of dioxin-like PCBs and highlight potential therapeutic targets.

Possible effects of pituitary adenylate cyclase activating polypeptide (PACAP) on early embryo implantation marker HB-EGF in mouse

Pituitary adenylate cyclase activating polypeptide (PACAP) was originally isolated as a hypothalamic neuropeptide stimulating adenylate cyclase activity. Besides its neuroprotective effects, numerous data proved its role in reproductive processes. However, there are limited data on its role in preimplantation embryo development and implantation. Our aim was to analyse the mRNA expression of Adcyap1 (coding region of PACAP) and Hbegf [coding region of HB-EGF (Heparin-binding EGF-like growth factor)] in embryos and pregnant uterus to investigate the possible correlation between them. Eight-week-old BDF1 mice were superovulated and subsequently mated overnight or left in their cage after hCG treatment. Day4 embryos were flushed from mated females. After morphological analysis, Adcyap1 and Hbegf gene expression of embryos and uterine tissues was assessed with qPCR. Our results showed significantly higher Adcyap1 and Hbegf mRNA levels in females producing embryos compared to non-mated ones. Robust elevation of Adcyap1 and slight elevation of Hbegf were detected in females with blastocyst embryos compared with non-blastocysts. We found low rate of Hbegf mRNA expression in uncompacted embryos, whereas morulae and blastocysts expressed high amounts of Hbegf. However, we did not find detectable Adcyap1 mRNA in embryos. Strong correlation was found between uterine tissue and embryonic Hbegf levels, slight correlation between uterine Adcyap1 and Hbegf levels. Uterine tissue Adcyap1 and embryonic Hbegf showed no correlation. In summary, our present data show, for the first time, the correlation between PACAP and HB-EGF mRNA expression suggesting that PACAP might play a role during the peri-implantation period of early mouse embryo development.

PACAP and PAC1 receptor expression in pancreatic ductal carcinoma

Pancreatic carcinoma is one of the most malignant diseases and is associated with a poor survival rate. Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide that acts on three different G protein-coupled receptors: the specific PAC1 and the VPAC1/2 that also bind vasoactive intestinal peptide. PACAP is widely distributed in the body and has diverse physiological effects. Among other things, it acts as a trophic factor and influences proliferation and differentiation of several different cells both under normal circumstances and tumourous transformation. Changes of PACAP and its receptors have been shown in various tumour types. However, it is not known whether PACAP and its specific receptor are altered in pancreatic cancer. Perioperative data of patients with pancreas carcinoma was investigated over a five-year period. Histological results showed Grade 2 or Grade 3 adenocarcinoma in most cases. PACAP and PAC1 receptor expression were investigated by immunohistochemistry. Staining intensity of PAC1 receptor was strong in normal tissues both in the exocrine and endocrine parts of the pancreas, the receptor staining was markedly weaker in the adenocarcinoma. PACAP immunostaining was weak in the exocrine part and very strong in the islets and nerve elements in non-tumourous tissues. The PACAP immunostaining almost disappeared in the adenocarcinoma samples. Based on these findings a decrease or lack of the PAC1 receptor/PACAP signalling might have an influence on tumour growth and/or differentiation.

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.”

[New function of PACAP on hematopoiesis through PACAP specific receptor (PAC1R)]

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide, and exists diverse physiological functions such as a cell protection, anti-inflammation, and neuronal proliferation and differentiation. There are many evidences that PACAP contributes to the neuronal developmental processes during embryonic periods and after the birth, and that PACAP is involved in the development in ectodermal origin including nervous system. However, few evidences have been reported that PACAP contributes to the development of the other germ layer. In here, we introduced our recent study that PACAP was involved in the hematopoiesis. Moreover, we have showed prospective functions of PACAP on the homeostatic and pathological conditions through the autonomic nerve innervation.

Do Neuroendocrine Peptides and Their Receptors Qualify as Novel Therapeutic Targets in Osteoarthritis?

Joint tissues like synovium, articular cartilage, meniscus and subchondral bone, are targets for neuropeptides. Resident cells of these tissues express receptors for various neuroendocrine-derived peptides including proopiomelanocortin (POMC)-derived peptides, i.e., α-melanocyte-stimulating hormone (α-MSH), adrenocorticotropin (ACTH) and β-endorphin (β-ED), and sympathetic neuropeptides like vasoactive intestinal peptide (VIP) and neuropeptide y (NPY). Melanocortins attained particular attention due to their immunomodulatory and anti-inflammatory effects in several tissues and organs. In particular, α-MSH, ACTH and specific melanocortin-receptor (MCR) agonists appear to have promising anti-inflammatory actions demonstrated in animal models of experimentally induced arthritis and osteoarthritis (OA). Sympathetic neuropeptides have obtained increasing attention as they have crucial trophic effects that are critical for joint tissue and bone homeostasis. VIP and NPY are implicated in direct and indirect activation of several anabolic signaling pathways in bone and synovial cells. Additionally, pituitary adenylate cyclase-activating polypeptide (PACAP) proved to be chondroprotective and, thus, might be a novel target in OA. Taken together, it appears more and more likely that the anabolic effects of these neuroendocrine peptides or their respective receptor agonists/antagonists may be exploited for the treatment of patients with inflammatory and degenerative joint diseases in the future.

Inhibition of retinal ganglion cell apoptosis: regulation of mitochondrial function by PACAP

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous peptide with neuroprotective effects on retinal neurons, but the precise mechanism underlying these effects remains unknown. Considering the abundance of mitochondria in retinal ganglion cells (RGCs), we postulate that the protective effect of PACAP is associated with the regulation of mitochondrial function. RGC-5 cells were subjected to serum deprivation for 48 hours to induce apoptosis in the presence or absence of 100 nM PACAP. As revealed with the Cell Counting Kit-8 assay, PACAP at different concentrations significantly increased the viability of RGC-5 cells. PACAP also inhibited the excessive generation of reactive oxygen species in RGC-5 cells subjected to serum deprivation. We also showed by flow cytometry that PACAP inhibited serum deprivation-induced apoptosis in RGC-5 cells. The proportions of apoptotic cells and cells with mitochondria depolarization were significantly decreased with PACAP treatment. Western blot assays demonstrated that PACAP increased the levels of Bcl-2 and inhibited the compensatory increase of PAC1. Together, these data indicate protective effects of PACAP against serum deprivation-induced apoptosis in RGCs, and that the mechanism of this action is associated with maintaining mitochondrial function.