The neuropeptide VIP potentiates IL-6 production induced by proinflammatory osteotropic cytokines in calvarial osteoblasts and the osteoblastic cell line MC3T3-E1

Consequences of Aging on Bone

With the aging of the global population, the incidence of musculoskeletal diseases has been increasing, seriously affecting people's health. As people age, the microenvironment within skeleton favors bone resorption and inhibits bone formation, accompanied by bone marrow fat accumulation and multiple cellular senescence. Specifically, skeletal stem/stromal cells (SSCs) during aging tend to undergo adipogenesis rather than osteogenesis. Meanwhile, osteoblasts, as well as osteocytes, showed increased apoptosis, decreased quantity, and multiple functional limitations including impaired mechanical sensing, intercellular modulation, and exosome secretion. Also, the bone resorption function of macrophage-lineage cells (including osteoclasts and preosteoclasts) was significantly enhanced, as well as impaired vascularization and innervation. In this study, we systematically reviewed the effect of aging on bone and the within microenvironment (including skeletal cells as well as their intracellular structure variations, vascular structures, innervation, marrow fat distribution, and lymphatic system) caused by aging, and mechanisms of osteoimmune regulation of the bone environment in the aging state, and the causal relationship with multiple musculoskeletal diseases in addition with their potential therapeutic strategy.

The interaction between the nervous system and the stomatognathic system: from development to diseases

The crosstalk between the nerve and stomatognathic systems plays a more important role in organismal health than previously appreciated with the presence of emerging concept of the "brain-oral axis". A deeper understanding of the intricate interaction between the nervous system and the stomatognathic system is warranted, considering their significant developmental homology and anatomical proximity, and the more complex innervation of the jawbone compared to other skeletons. In this review, we provide an in-depth look at studies concerning neurodevelopment, craniofacial development, and congenital anomalies that occur when the two systems develop abnormally. It summarizes the cross-regulation between nerves and jawbones and the effects of various states of the jawbone on intrabony nerve distribution. Diseases closely related to both the nervous system and the stomatognathic system are divided into craniofacial diseases caused by neurological illnesses, and neurological diseases caused by an aberrant stomatognathic system. The two-way relationships between common diseases, such as periodontitis and neurodegenerative disorders, and depression and oral diseases were also discussed. This review provides valuable insights into novel strategies for neuro-skeletal tissue engineering and early prevention and treatment of orofacial and neurological diseases.

Peripheral nerves in the tibial subchondral bone : the role of pain and homeostasis in osteoarthritis

Osteoarthritis (OA) is a highly prevalent degenerative joint disorder characterized by joint pain and physical disability. Aberrant subchondral bone induces pathological changes and is a major source of pain in OA. In the subchondral bone, which is highly innervated, nerves have dual roles in pain sensation and bone homeostasis regulation. The interaction between peripheral nerves and target cells in the subchondral bone, and the interplay between the sensory and sympathetic nervous systems, allow peripheral nerves to regulate subchondral bone homeostasis. Alterations in peripheral innervation and local transmitters are closely related to changes in nociception and subchondral bone homeostasis, and affect the progression of OA. Recent literature has substantially expanded our understanding of the physiological and pathological distribution and function of specific subtypes of neurones in bone. This review summarizes the types and distribution of nerves detected in the tibial subchondral bone, their cellular and molecular interactions with bone cells that regulate subchondral bone homeostasis, and their role in OA pain. A comprehensive understanding and further investigation of the functions of peripheral innervation in the subchondral bone will help to develop novel therapeutic approaches to effectively prevent OA, and alleviate OA pain.

Cite this article: Bone Joint Res 2022;11(7):439–452.

The effects of vasoactive intestinal peptide on RANKL-induced osteoclast formation

Background

Congenital pseudarthrosis of the tibia is a rare disease characterized by an imbalance in bone remodeling. Vasoactive intestinal peptide (VIP) has been proven to modulate bone resorption and the formation of osteoclasts. This study aimed to explore the effects of VIP on the homeostasis of bone metabolism in diverse in vitro systems.

Methods

Bone marrow-derived macrophages (BMMs) were differentiated into tartrate-resistant acid phosphatase-positive cells through incubation with receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). In vitro resorption pit detection was carried out to assess the effects of VIP on osteoclastic activity. Rat osteosarcoma cell line ROS 17/2.8 was cultured alone or co-cultured with rat BMMs in the presence or absence of VIP at various concentrations. The expression levels of RANKL, RANK, OPG, NF-κB, IL-6, ERK, CAII, and GAPDH were determined by qRT-PCR and WB assay.

Results

VIP was observed to repress osteoclast differentiation without affecting the number of osteoclast precursor cells. Furthermore, the modulation of the RANKL/osteoprotegerin (OPG), nuclear factor-κB (NF-κB), and extracellular signal-regulated kinase (ERK) signaling pathways were involved in the inhibitive influence of VIP upon bone erosion. Additionally, VIP affected the expression levels of osteoclastic factors including RANKL, OPG, and interleukin-6 in osteoblast cells. Furthermore, the expression levels of RANKL and RANK were increased, while OPG expression was reduced after treatment with VIP in the co-culture of ROS 17/2.8 and rat BMMs. ERK and NF-κB signal pathways were demonstrated to be involved in the effect of VIP in the co-culture system.

Conclusions

VIP plays a critical role in bone remodeling and might serve as a potential target in the development of treatments for congenital pseudarthrosis of the tibia.

Immunomodulatory Roles of PACAP and VIP: Lessons from Knockout Mice

A bidirectional cross-talk is established between the nervous and immune systems through common mediators including neuropeptides, neurotransmitters, and cytokines. Among these, PACAP and VIP are two highly related neuropeptides widely distributed in the organism with purported immunomodulatory actions. Due to their well-known anti-inflammatory properties, administration of these peptides has proven to be beneficial in models of acute and chronic inflammatory diseases. Nevertheless, the relevance of the endogenous source of these peptides in the modulation of immune responses remains to be elucidated. The development of transgenic mice with specific deletions in the genes coding for these neuropeptides (Vip and Adcyap1) or for their G-protein-coupled receptors VPAC1, VPAC2, and PAC1 (Vipr1, Vipr2, Adcyap1r1) has allowed to address this question, underscoring the complexity of the immunoregulatory properties of PACAP and VIP. The goal of this review is to integrate the existing information on the immune phenotypes of mice deficient for PACAP, VIP, or their receptors, to provide a global view on the roles of these endogenous neuropeptides during immunological health and disease.

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.

Guangxi cobra venom-derived NGF promotes the osteogenic and therapeutic effects of porous BCP ceramic

Neuro-osteological interactions have an important role in the regulation of bone metabolism and regeneration. Neuropeptides combined with porous biphasic calcium phosphates (BCP) using protein adsorption may contribute to the acceleration of bone formation. In the present study, we investigated the effect of BCP combined with nerve growth factor (NGF) on the growth of osteoblasts in vitro and the combinational therapeutic effect on the repair of calvarial defects in vivo. NGF was separated and purified from Chinese cobra venom using a simplified three-step chromatography method. BCP combined with NGF exerted a potent effect on osteoblast differentiation, as evidenced by enhanced cell proliferation, increased ALP activity and the up-regulated expression of osteogenesis-related genes and proteins. Further, combinational therapy with BCP and NGF improved calvarial regeneration, which was superior to treatment with therapy alone, as observed using imageological and morphological examination and histological and immunohistochemical staining. The results confirmed the effect of neuro-osteological interactions through combinatorial treatment with NGF and BCP to promote osteogenesis and bone formation, which may provide an effective and economical strategy for clinical application.

The Function of Naringin in Inducing Secretion of Osteoprotegerin and Inhibiting Formation of Osteoclasts

Osteoporosis has become one of the most prevalent and costly diseases in the world. It is a metabolic disease characterized by reduction in bone mass due to an imbalance between bone formation and resorption. Osteoporosis causes fractures, prolongs bone healing, and impedes osseointegration of dental implants. Its pathological features include osteopenia, degradation of bone tissue microstructure, and increase of bone fragility. In traditional Chinese medicine, the herb Rhizoma Drynariae has been commonly used to treat osteoporosis and bone nonunion. However, the precise underlying mechanism is as yet unclear. Osteoprotegerin is a cytokine receptor shown to play an important role in osteoblast differentiation and bone formation. Hence, activators and ligands of osteoprotegerin are promising drug targets and have been the focus of studies on the development of therapeutics against osteoporosis. In the current study, we found that naringin could synergistically enhance the action of 1α,25-dihydroxyvitamin D3 in promoting the secretion of osteoprotegerin by osteoblasts in vitro. In addition, naringin can also influence the generation of osteoclasts and subsequently bone loss during organ culture. In conclusion, this study provides evidence that natural compounds such as naringin have the potential to be used as alternative medicines for the prevention and treatment of osteolysis.

The role of peripheral nerve fibers and their neurotransmitters in cartilage and bone physiology and pathophysiology

The peripheral nervous system is critically involved in bone metabolism, osteogenesis, and bone remodeling. Nerve fibers of sympathetic and sensory origin innervate synovial tissue and subchondral bone of diathrodial joints. They modulate vascularization and matrix differentiation during endochondral ossification in embryonic limb development, indicating a distinct role in skeletal growth and limb regeneration processes. In pathophysiological situations, the innervation pattern of sympathetic and sensory nerve fibers is altered in adult joint tissues and bone. Various resident cell types of the musculoskeletal system express receptors for sensory and sympathetic neurotransmitters. Osteoblasts, osteoclasts, mesenchymal stem cells, synovial fibroblasts, and different types of chondrocytes produce distinct subtypes of adrenoceptors, receptors for vasointestinal peptide, for substance P and calcitonin gene-related peptide. Many of these cells even synthesize neuropeptides such as substance P and calcitonin gene-related peptide and are positive for tyrosine-hydroxylase, the rate-limiting enzyme for biosynthesis of catecholamines. Sensory and sympathetic neurotransmitters modulate osteo-chondrogenic differentiation of mesenchymal progenitor cells during endochondral ossification in limb development. In adults, sensory and sympathetic neurotransmitters are critical for bone regeneration after fracture and are involved in the pathology of inflammatory diseases as rheumatoid arthritis which manifests mainly in joints. Possibly, they might also play a role in pathogenesis of degenerative joint disorders, such as osteoarthritis. All together, accumulating data imply that sensory and sympathetic neurotransmitters have crucial trophic effects which are critical for proper limb formation during embryonic skeletal growth. In adults, they modulate bone regeneration, bone remodeling, and articular cartilage homeostasis in addition to their classic neurological actions.

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Pathway Is Induced by Mechanical Load and Reduces the Activity of Hedgehog Signaling in Chondrogenic Micromass Cell Cultures

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurohormone exerting protective function during various stress conditions either in mature or developing tissues. Previously we proved the presence of PACAP signaling elements in chicken limb bud-derived chondrogenic cells in micromass cell cultures. Since no data can be found if PACAP signaling is playing any role during mechanical stress in any tissues, we aimed to investigate its contribution in mechanotransduction during chondrogenesis. Expressions of the mRNAs of PACAP and its major receptor, PAC1 increased, while that of other receptors, VPAC1, VPAC2 decreased upon mechanical stimulus. Mechanical load enhanced the expression of collagen type X, a marker of hypertrophic differentiation of chondrocytes and PACAP addition attenuated this elevation. Moreover, exogenous PACAP also prevented the mechanical load evoked activation of hedgehog signaling: protein levels of Sonic and Indian Hedgehogs and Gli1 transcription factor were lowered while expressions of Gli2 and Gli3 were elevated by PACAP application during mechanical load. Our results suggest that mechanical load activates PACAP signaling and exogenous PACAP acts against the hypertrophy inducing effect of mechanical load.

The Effect of OSM on MC3T3-E1 Osteoblastic Cells in Simulated Microgravity with Radiation

Bone deterioration is a challenge in long-term spaceflight with significant connections to patients experiencing disuse bone loss. Prolonged unloading and radiation exposure, defining characteristics of space travel, have both been associated with changes in inflammatory signaling via IL-6 class cytokines in bone. While there is also evidence for perturbed IL-6 class signaling in spaceflight, there has been scant examination of the connections between microgravity, radiation, and inflammatory stimuli in bone. Our lab and others have shown that the IL-6 class cytokine oncostatin M (OSM) is an important regulator of bone remodeling. We hypothesize that simulated microgravity alters osteoblast OSM signaling, contributing to the decoupling of osteolysis and osteogenesis in bone homeostasis. To test this hypothesis, we induced OSM signaling in murine MC3T3-E1 pre-osteoblast cells cultured in modeled microgravity using a rotating wall vessel bioreactor with and without exposure to radiation typical of a solar particle event. We measured effects on inflammatory signaling, osteoblast activity, and mineralization. Results indicated time dependent interactions among all conditions in the regulation of IL-6 production. Furthermore, OSM induced the transcription of OSM receptor ß, IL 6 receptor α subunits, collagen α1(I), osteocalcin, sclerostin, RANKL, and osteoprotegerin. Measurements of osteoid mineralization suggest that the spatial organization of the osteoblast environment is an important consideration in understanding bone formation. Taken together, these results support a role for altered OSM signaling in the mechanism of microgravity-induced bone loss.

Vasoactive intestinal peptide suppresses macrophage-mediated inflammation by downregulating interleukin-17A expression via PKA- and PKC-dependent pathways

Interleukin (IL)-17A is a pro-inflammatory cytokine that markedly enhances inflammatory responses in the lungs by recruiting neutrophils and interacting with other pro-inflammatory mediators. Reducing the expression of IL-17A could attenuate inflammation in the lungs. However, whether VIP exerts its anti-inflammatory effects by regulating the expression of IL-17A has remained unclear. Here, we show that there is a remarkable increase of IL-17A in bronchoalveolar lavage fluid (BALF) and lung tissue of mice with acute lung injury (ALI). Moreover, lipopolysaccharides (LPS) stimulated elevated expression of IL-17A, which was evident by the enhanced levels of mRNA and protein observed. Furthermore, we also found that VIP inhibited LPS-mediated IL-17A expression in a time- and dose-dependent manner in an in vitro model of ALI and that this process might be mediated via the phosphokinase A (PKA) and phosphokinase C (PKC) pathways. Taken together, our results demonstrated that VIP might be an effective protector during ALI by suppressing IL-17A expression.

Differential regulatory role of pituitary adenylate cyclase-activating polypeptide in the serum-transfer arthritis model

Objective

Pituitary adenylate cyclase–activating polypeptide (PACAP) expressed in capsaicin-sensitive sensory neurons and immune cells has divergent functions in inflammatory and pain processes. This study was undertaken to investigate the involvement of PACAP in a mouse model of rheumatoid arthritis.

Methods

Arthritis was induced in PACAP^−/− and wild-type (PACAP^+/+) mice by K/BxN serum transfer. General features of the disease were investigated by semiquantitative scoring, plethysmometry, and histopathologic analysis. Mechano- and thermonociceptive thresholds and motor functions were also evaluated. Metabolic activity was assessed by positron emission tomography. Bone morphology was measured by in vivo micro–computed tomography, myeloperoxidase activity and superoxide production by bioluminescence imaging with luminol and lucigenin, respectively, and vascular permeability by fluorescent indocyanine green dye study.

Results

PACAP^+/+ mice developed notable joint swelling, reduced grasping ability, and mechanical (but not thermal) hyperalgesia after K/BxN serum transfer. In PACAP^−/− mice clinical scores and edema were significantly reduced, and mechanical hyperalgesia and motor impairment were absent, throughout the 2-week period of observation. Metabolic activity and superoxide production increased in the tibiotarsal joints of wild-type mice but were significantly lower in PACAP^−/− animals. Myeloperoxidase activity in the ankle joints of PACAP^−/− mice was significantly reduced in the early phase of arthritis, but increased in the late phase. Synovial hyperplasia was also significantly increased, and progressive bone spur formation was observed in PACAP-deficient mice only.

Conclusion

In PACAP-deficient mice with serum-transfer arthritis, joint swelling, vascular leakage, hyperalgesia, and early inflammatory cell accumulation are reduced; in the later phase of the disease, immune cell function and bone neoformation are increased. Elucidation of the underlying pathways of PACAP activity may open promising new avenues for development of therapy in inflammatory arthritis.

Vasoactive intestinal peptide enhances TNF-α-induced IL-6 and IL-8 synthesis in human proximal renal tubular epithelial cells by NF-κB-dependent mechanism

Vasoactive intestinal polypeptide (VIP) is a 28-amino acid neuropeptide with vasodilator, bronchodilator, and anti-inflammatory effects. But little is known about its pro-inflammatory effects. We investigated the effect of VIP on the secretion of interleukin-6 (IL-6) and interleukin-8 (IL-8), two pro-inflammatory cytokines, in TNF-α-activated proximal renal tubular epithelial cell line (HK-2 cells). Cultured HK-2 cells were treated with TNF-α in the presence or absence of VIP with a dose range from 1 to 100 nM, followed by analysis of pro-inflammatory cytokines (IL-6 and IL-8) induction and their signal events including activation of the NF-κB pathway. We report here that tumor necrosis factor-α (TNF-α) increased IL-6 and IL-8 production, and that these effects were potentiated by VIP at 10 nM in HK-2 cells. However, VIP at 1 and 100 nM did not display this function. Consistent with these observations, we were able to show that VIP at 10 nM upregulated TNF-α-induced phosphorylation of IκB-α, leading to IκB-α degradation and the subsequent nuclear translocation of NF-κB. Furthermore, VIP-enhanced activation of NF-κB transcription activity was demonstrated using a NF-κB reporter construct upon transient transfection into HK-2 cells. These results strongly suggest that VIP synergistically enhances TNF-α-stimulated IL-6 and IL-8 synthesis via activating the NF-κB pathway in HK-2 cells.

Different sympathetic pathways control the metabolism of distinct bone envelopes

Bone remodeling, the mechanism that modulates bone mass adaptation, is controlled by the sympathetic nervous system through the catecholaminergic pathway. However, resorption in the mandible periosteum envelope is associated with cholinergic Vasoactive Intestinal Peptide (VIP)-positive nerve fibers sensitive to sympathetic neurotoxics, suggesting that different sympathetic pathways may control distinct bone envelopes. In this study, we assessed the role of distinct sympathetic pathways on rat femur and mandible envelopes. To this goal, adult male Wistar rats were chemically sympathectomized or treated with agonists/antagonists of the catecholaminergic and cholinergic pathways; femora and mandibles were sampled. Histomorphometric analysis showed that sympathectomy decreased the number of preosteoclasts and RANKL-expressing osteoblasts in mandible periosteum but had no effect on femur trabecular bone. In contrast, pharmacological stimulation or repression of the catecholaminergic cell receptors impacted the femur trabecular bone and mandible endosteal retromolar zone. VIP treatment of sympathectomized rats rescued the disturbances of the mandible periosteum and alveolar wall whereas the cholinergic pathway had no effect on the catecholaminergic-dependent envelopes. We also found that VIP receptor-1 was weakly expressed in periosteal osteoblasts in the mandible and was increased by VIP treatment, whereas osteoblasts of the retromolar envelope that was innervated only by tyrosine hydroxylase-immunoreactive fibers, constitutively expressed beta-2 adrenergic receptors. These data highlight the complexity of the sympathetic control of bone metabolism. Both the embryological origin of the bone (endochondral for the femur, membranous for the mandibular periosteum and the socket wall) and environmental factors specific to the innervated envelope may influence the phenotype of the sympathetic innervation. We suggest that an origin-dependent imprint of bone cells through osteoblast-nerve interactions determines the type of autonomous system innervating a particular bone envelope.

The neuropeptide VIP regulates the expression of osteoclastogenic factors in osteoblasts

Osteoclast formation is controlled by stromal cells/osteoblasts expressing macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL), crucial for osteoclast progenitor cell proliferation, survival and differentiation, and osteoprotegerin (OPG) that inhibits the interaction between RANKL and its receptor RANK. Recent data have strongly indicated that the nervous system plays an important role in bone biology. In the present study, the effects of the neuropeptide vasoactive intestinal peptide (VIP), present in peptidergic skeletal nerve fibers, on the expression of RANKL, OPG, and M-CSF in osteoblasts and stromal cells have been investigated. VIP and pituitary adenylate cyclase-activating polypeptide 38 (PACAP-38), but not secretin, stimulated rankl mRNA expression in mouse calvarial osteoblasts. In contrast, VIP inhibited the mRNA expressions of opg and m-csf, effects shared by PACAP-38, but not by secretin. VIP did not affect rankl, opg, or m-csf mRNA expression in mouse bone marrow stromal cells (BMSCs). The effects by VIP on the mRNA expression of rankl, opg, and m-csf were all potentiated by the cyclic AMP phosphodiesterase inhibitor rolipram. In addition, VIP robustly enhanced the phosphorylation of ERK and the stimulatory effect by VIP on rankl mRNA was inhibited by the MEK1/2 inhibitor PD98059. These observations demonstrate that activation of VPAC(2) receptors in osteoblasts enhances the RANKL/OPG ratio by mechanisms mediated by cyclic AMP and ERK pathways suggesting an important role for VIP in bone remodeling.

Pituitary adenylate cyclase-activating polypeptide and its receptors: 20 years after the discovery

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally alpha-amidated peptide that was first isolated 20 years ago from an ovine hypothalamic extract on the basis of its ability to stimulate cAMP formation in anterior pituitary cells (Miyata et al., 1989. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-secretin-growth hormone-releasing hormone-glucagon superfamily. The sequence of PACAP has been remarkably well conserved during evolution from protochordates to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide, the activity of which remains unknown. Two types of PACAP binding sites have been characterized: type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP, whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes: the PACAP-specific PAC1-R, which is coupled to several transduction systems, and the PACAP/VIP-indifferent VPAC1-R and VPAC2-R, which are primarily coupled to adenylyl cyclase. PAC1-Rs are particularly abundant in the brain, the pituitary and the adrenal gland, whereas VPAC receptors are expressed mainly in lung, liver, and testis. The development of transgenic animal models and specific PACAP receptor ligands has strongly contributed to deciphering the various actions of PACAP. Consistent with the wide distribution of PACAP and its receptors, the peptide has now been shown to exert a large array of pharmacological effects and biological functions. The present report reviews the current knowledge concerning the pleiotropic actions of PACAP and discusses its possible use for future therapeutic applications.

cAMP activation by PACAP/VIP stimulates IL-6 release and inhibits osteoblastic differentiation through VPAC2 receptor in osteoblastic MC3T3 cells

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the glucagon/vasoactive intestinal peptide (VIP) superfamily, stimulates cyclic AMP accumulation initiating a variety of biological processes such as: neurotropic actions, immune and pituitary function, learning and memory, catecholamine biosynthesis and regulation of cardiopulmonary function. Both osteoclasts and osteoblasts have been shown to express receptors for PACAP/VIP implicated in their role in bone metabolism. To further understand the role of PACAP/VIP family in controlling bone metabolism, we investigated differentiation model of MC3T3-E1 cells, an osteoblastic cell line derived from mouse calvaria. Quantitative RT-PCR analysis demonstrated that MC3T3-E1 cells expressed only VPAC2 receptor and its expression was upregulated during osteoblastic differentiation, whereas VPAC1 and PAC1 receptors were not expressed. Consistent with expression of receptor subtype, both PACAP and VIP stimulate cAMP accumulation in a time- and dose-dependent manner with the similar potency in undifferentiated and differentiated cells, while Maxadilan, a specific agonist for PAC1-R, did not. Furthermore, downregulation of VPAC2-R by siRNA completely blocked cAMP response mediated by PACAP and VIP. Importantly, PACAP/VIP as well as forskolin markedly suppressed the induction of alkaline phosphatase mRNA upon differentiation and the pretreatment with 2',5'-dideoxyadenosine, a cAMP inhibitor, restored its inhibitory effect of PACAP. We also found that PACAP and VIP stimulated IL-6 release, a stimulator of bone resorption, and VPAC2-R silencing inhibited IL-6 production. Thus, PACAP/VIP can activate adenylate cyclase response and regulate IL-6 release through VPAC2 receptor with profound functional consequences for the inhibition of osteoblastic differentiation in MC3T3-E1 cells.

Transcriptome and proteome analysis of osteocytes treated with nitrogen-containing bisphosphonates

We combined high-throughput screening of differential mRNAs with mass spectrometric characterization of proteins obtained from osteocytes untreated and treated with Risedronate. Microarray analysis revealed, upon treatment, a marked upregulation of messengers encoding zinc-proteins. MS analysis identified 84 proteins in the osteocytes proteome map. Risedronate affected the expression of 10 proteins, associated with cytoskeleton, stress-response and metabolism. Data validated using gel imaging in combination with the GLaD post digestion isotopic labeling method provide the molecular basis for understanding the role of bisphosphonates as antiapoptotic drugs for osteocytes.

A functional polymorphism of the vasoactive intestinal peptide receptor 1 gene correlates with the presence of HLA-B*2705 in Sardinia

The association of HLA-B27 with ankylosing spondylitis (AS) is the strongest among all inflammatory diseases. However, the exact role of these molecules in disease pathogenesis is still unknown. The existence of HLA-B27 variants rarely found in patients introduces a further level of complexity. It is now accepted that other genes of minor impact contribute to modify disease susceptibility and these genes might be diverse in different populations depending on the genetic background. We report here a study performed in Sardinia, an outlier population in which two major HLA-B27 subtypes are present, B (*)2705 strongly associated with AS and B (*)2709 which is not, and show the co-occurrence of the B (*)2705 allele with a single nucleotide polymorphism (SNP) mapping at 3'-UTR of the receptor 1 (VIPR1) for the vasoactive intestinal peptide (VIP), a neuropeptide with anti-inflammatory properties. This same SNP is associated with a different kinetics of down-modulation of the VIPR1 mRNA in monocytes after exposure to lipopolysaccharide (P=0.004). This particular setting, HLA-B (*)2705 and a functional polymorphism in VIPR1 gene, might be due to a founder effect or might be the result of a selective pressure. Irrespectively, the consequent downregulation of this receptor in the presence of a 'danger' signal might influence susceptibility to AS.