P2Y2 receptor up-regulation induced by guanosine or UTP in rat brain cultured astrocytes

Purinergic signaling in cognitive impairment and neuropsychiatric symptoms of Alzheimer's disease

About 10 million new cases of dementia develop worldwide each year, of which up to 70% are attributable to Alzheimer's disease (AD). In addition to the widely known symptoms of memory loss and cognitive impairment, AD patients frequently develop non-cognitive symptoms, referred to as behavioral and psychological symptoms of dementia (BPSDs). Sleep disorders are often associated with AD, but mood alterations, notably depression and apathy, comprise the most frequent class of BPSDs. BPSDs negatively affect the lives of AD patients and their caregivers, and have a significant impact on public health systems and the economy. Because treatments currently available for AD are not disease-modifying and mainly aim to ameliorate some of the cognitive symptoms, elucidating the mechanisms underlying mood alterations and other BPSDs in AD may reveal novel avenues for progress in AD therapy. Purinergic signaling is implicated in the pathophysiology of several central nervous system (CNS) disorders, such as AD, depression and sleep disorders. Here, we review recent findings indicating that purinergic receptors, mainly the A₁, A_2A, and P2X7 subtypes, are associated with the development/progression of AD. Current evidence suggests that targeting purinergic signaling may represent a promising therapeutic approach in AD and related conditions. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Bidirectional Control between Cholesterol Shuttle and Purine Signal at the Central Nervous System

Recent studies have highlighted the mechanisms controlling the formation of cerebral cholesterol, which is synthesized in situ primarily by astrocytes, where it is loaded onto apolipoproteins and delivered to neurons and oligodendrocytes through interactions with specific lipoprotein receptors. The “cholesterol shuttle” is influenced by numerous proteins or carbohydrates, which mainly modulate the lipoprotein receptor activity, function and signaling. These molecules, provided with enzymatic/proteolytic activity leading to the formation of peptide fragments of different sizes and specific sequences, could be also responsible for machinery malfunctions, which are associated with neurological, neurodegenerative and neurodevelopmental disorders. In this context, we have pointed out that purines, ancestral molecules acting as signal molecules and neuromodulators at the central nervous system, can influence the homeostatic machinery of the cerebral cholesterol turnover and vice versa. Evidence gathered so far indicates that purine receptors, mainly the subtypes P2Y2, P2X7 and A2A, are involved in the pathogenesis of neurodegenerative diseases, such as Alzheimer’s and Niemann–Pick C diseases, by controlling the brain cholesterol homeostasis; in addition, alterations in cholesterol turnover can hinder the purine receptor function. Although the precise mechanisms of these interactions are currently poorly understood, the results here collected on cholesterol–purine reciprocal control could hopefully promote further research.

Introduction to Purinergic Signalling in the Brain

ATP is a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the brain. There is a widespread presence of both adenosine (P1) and P2 nucleotide receptors in the brain on both neurons and glial cells. Adenosine receptors play a major role in presynaptic neuromodulation, while P2X ionotropic receptors are involved in fast synaptic transmission and synaptic plasticity. P2Y G protein-coupled receptors are largely involved in presynaptic activities, as well as mediating long-term (trophic) signalling in cell proliferation, differentiation and death during development and regeneration. Both P1 and P2 receptors participate in neuron-glial interactions. Purinergic signalling is involved in control of cerebral vascular tone and remodelling and has been implicated in learning and memory, locomotor and feeding behaviour and sleep. There is increasing interest in the involvement of purinergic signalling in the pathophysiology of the CNS, including trauma, ischaemia, epilepsy, neurodegenerative diseases, neuropsychiatric and mood disorders, and cancer, including gliomas.

Guanosine Attenuates Behavioral Deficits After Traumatic Brain Injury by Modulation of Adenosinergic Receptors

Traumatic brain injury (TBI) is a leading cause of disability worldwide, triggering chronic neurodegeneration underlying cognitive and mood disorder still without therapeutic prospects. Based on our previous observations that guanosine (GUO) attenuates short-term neurochemical alterations caused by TBI, this study investigated the effects of chronical GUO treatment in behavioral, molecular, and morphological disturbances 21 days after trauma. Rats subject to TBI displayed mood (anxiety-like) and memory dysfunction. This was accompanied by a decreased expression of both synaptic (synaptophysin) and plasticity proteins (BDNF and CREB), a loss of cresyl violet-stained neurons, and increased astrogliosis and microgliosis in the hippocampus. Notably, chronic GUO treatment (7.5 mg/kg i.p. daily starting 1 h after TBI) prevented all these TBI-induced long-term behavioral, neurochemical, and morphological modifications. This neuroprotective effect of GUO was abrogated in the presence of the adenosine A₁ receptor antagonist DPCPX (1 mg/kg) but unaltered by the adenosine A_2A receptor antagonist SCH58261 (0.05 mg/kg). These findings show that a chronic GUO treatment prevents the long-term mood and memory dysfunction triggered by TBI, which involves adenosinergic receptors.

Localization and Activity of iNOS in Normal Human Lung Tissue and Lung Cancer Tissue

Inducible nitric oxide synthase (iNOS) is one of three enzymes generating nitric oxide (NO) from the amino acid L-arginine. iNOS-derived NO plays an important role in several physiological and pathophysiological conditions. NO is a free radical which produces many reactive intermediates that account for its bioactivity. In the human lung, the alveolar macrophage is an important producer of cytokines and this production may be modified by NO. Moreover, high concentrations of NO have been shown to increase nuclear factor KB (NF-kB) activation. Recent investigations of NO expression in tumor tissue indicated that, at least for certain tumors, NO may mediate one or more roles during the growth of human cancer. We have studied iNOS in two tissue groups: normal human lung tissue and human lung cancer tissue. We localized iNOS in these tissues by immunohistochemistry and tested the mRNA expression by RT-PCR, the protein level by Western blot, and the protein activity by radiometric analysis. The results demonstrate different expression, localization and activity of iNOS in normal versus tumor tissue. This is suggestive of a role for NO production from iNOS in human lung cancer because high concentrations of this short molecule may transform to highly reactive compounds such as peroxynitrite (ONOO-); moreover, through the upregulator NF-kB, they can induce a chronic inflammatory state representing an elevated risk for cell transformation to cancer.

Involvement of NK Cells against Tumors and Parasites

Host resistance against pathogens depends on a complex interplay of innate and adaptive immune mechanisms. Acting as an early line of defence, the immune system includes activation of neutrophils, tissue macrophages, monocytes, dendritic cells, eosinophils and natural killer (NK) cells. NK cells are lymphoid cells that can be activated without previous stimulation and are therefore like macrophages in the first line of defence against tumor cells and a diverse range of pathogens. NK cells mediate significant activity and produce high levels of proinflammatory cytokines in response to infection. Their cytotoxicity production is induced principally by monocyte-, macrophage- and dendritic cell-derived cytokines, but their activation is also believed to be cytokine-mediated. Recognition of infection by NK cells is accomplished by numerous activating and inhibitory receptors on the NK cells’ surface that selectively trigger the cytolytic activity in a major histocompability complex-independent manner. NK cells have trypanocidal activity of fibroblast cells and mediate direct destruction of extracellular epimastigote and trypomastigote forms of T. cruzi and T. lewisi in vitro; moreover, they kill plasmodia-infected erythrocytes directly through cell-cell interaction. This review provides a more detailed analysis of how NK cells recognize and respond to parasites and how they mediate cytotoxicity against tumor cells. Also the unique role of NK cells in innate immunity to infection and the relationship between parasites and carcinogenesis are discussed.

Possible neuroprotective role of P2X2 in the retina of diabetic rats

BACKGROUND

Purinergic receptors are expressed in different tissues including the retina. These receptors are involved in processes like cell growth, proliferation, activation and survival. ATP is the major activator of P2 receptors. In diabetes, there is a constant ATP production and this rise of ATP leads to a persistent activation of purinergic receptors. Antagonists of these receptors are used to evaluate their inhibition effects. Recently, the P2X2 has been reported to have a neuroprotective role.

METHODS

We carried out a study in groups of diabetic and non-diabetic rats (N = 5) treated with intraperitoneal injections of PPADS, at 9 and 24 weeks of diabetes. Control group received only the buffer. Animals were euthanized at 34 weeks of diabetes or at a matching age. Rat retinas were analyzed with immunohistochemistry and western blot using antibodies against GFAP, P2X2, P2Y2 and VEGF-A.

RESULTS

Diabetic animals treated with PPADS disclosed a much more extended staining of VEGF-A than diabetics without treatment. A lower protein expression of VEGF-A was found at the retina of diabetic animals without treatment of purinergic antagonists compared to diabetics with the antagonist treatment. Inhibition of P2X2 receptor by PPADS decreases cell death in the diabetic rat retina.

CONCLUSION

Results might be useful for better understanding the pathophysiology of diabetic retinopathy.

Regulation of proteasome activity by P2Y2 receptor underlies the neuroprotective effects of extracellular nucleotides

The Ubiquitin-Proteasome System (UPS) is essential for the regulation of the cellular proteostasis. Indeed, it has been postulated that an UPS dysregulation is the common mechanism that underlies several neurological disorders. Considering that extracellular nucleotides, through their selective P2Y₂ receptor (P2Y₂R), play a neuroprotective role in various neurological disorders that course with an UPS impairment, we wonder if this neuroprotective capacity resulted from their ability to modulate the UPS. Using a cellular model expressing two different UPS reporters, we found that the stimulation of P2Y₂R by its selective agonist Up₄U induced a significant reduction of UPS reporter levels. This reduction was due to an increase in two of the three peptidase proteasome activities, chymotrypsin and postglutamyl, caused by an increased expression of proteasome constitutive catalytic subunits β1 and β5. The intracellular signaling pathway involved required the activation of IP₃/MEK1/2/ERK but was independent of PKC or PKA. Interestingly, the P2Y₂R activation was able to revert both UPS-reporter accumulation and the cell death induced by a prolonged inhibition of UPS. Finally, we also observed that intracerebroventricular administration of Up₄U induced a significant increase both of chymotrypsin and postglutamyl activities as well as an increased expression of proteasome subunits β1 and β5 in the hippocampus of wild-type mice, but not in P2Y₂R KO mice. All these results strongly suggest that the capacity to modulate the UPS activity via P2Y₂R is the molecular mechanism which is how the nucleotides play a neuroprotective role in neurological disorders.

The Guanine-Based Purinergic System: The Tale of An Orphan Neuromodulation

Guanine-based purines (GBPs) have been recently proposed to be not only metabolic agents but also extracellular signaling molecules that regulate important functions in the central nervous system. In such way, GBPs-mediated neuroprotection, behavioral responses and neuronal plasticity have been broadly described in the literature. However, while a number of these functions (i.e., GBPs neurothophic effects) have been well-established, the molecular mechanisms behind these GBPs-dependent effects are still unknown. Furthermore, no plasma membrane receptors for GBPs have been described so far, thus GBPs are still considered orphan neuromodulators. Interestingly, an intricate and controversial functional interplay between GBPs effects and adenosine receptors activity has been recently described, thus triggering the hypothesis that GBPs mechanism of action might somehow involve adenosine receptors. Here, we review recent data describing the GBPs role in the brain. We focus on the involvement of GBPs regulating neuronal plasticity, and on the new hypothesis based on putative GBPs receptors. Overall, we expect to shed some light on the GBPs world since although these molecules might represent excellent candidates for certain neurological diseases management, the lack of putative GBPs receptors precludes any high throughput screening intent for the search of effective GBPs-based drugs.

Renal intercalated cells sense and mediate inflammation via the P2Y14 receptor

Uncontrolled inflammation is one of the leading causes of kidney failure. Pro-inflammatory responses can occur in the absence of infection, a process called sterile inflammation. Here we show that the purinergic receptor P2Y14 (GPR105) is specifically and highly expressed in collecting duct intercalated cells (ICs) and mediates sterile inflammation in the kidney. P2Y14 is activated by UDP-glucose, a damage-associated molecular pattern molecule (DAMP) released by injured cells. We found that UDP-glucose increases pro-inflammatory chemokine expression in ICs as well as MDCK-C11 cells, and UDP-glucose activates the MEK1/2-ERK1/2 pathway in MDCK-C11 cells. These effects were prevented following inhibition of P2Y14 with the small molecule PPTN. Tail vein injection of mice with UDP-glucose induced the recruitment of neutrophils to the renal medulla. This study identifies ICs as novel sensors, mediators and effectors of inflammation in the kidney via P2Y14.

Effect of xiaoyaosan decoction on learning and memory deficit in rats induced by chronic immobilization stress

Xiaoyaosan (XYS) decoction is a famous prescription which can protect nervous system from stress and treat liver stagnation and spleen deficiency syndrome (LSSDS). In this experiment, we observed the effect of XYS decoction on chronic immobilization stress (CIS) induced learning and memory deficit in rats from behaviors and changes of proteins in hippocampus. We used XYS decoction to treat CIS induced learning and memory deficit in rats with rolipram as positive control, used change of body weight and behavioral tests to determine whether the rats have LSSDS and have learning and memory deficit or not. We used Western blotting to determine the content of postsynaptic density protein 95 (PSD-95) and synaptophysin (SYP) in hippocampus. Results showed that XYS could improve the situation of slow weight gain induced by CIS, improve the ability of learning and memory, reverse the symptom of liver stagnation and spleen deficiency syndrome (LSSDS) in rats, and increase the levels of PSD-95 and SYP on the hippocampal nerve synapses. These findings suggested that XYS decoction may be helpful in reversing CIS induced learning and memory deficit by increasing the levels of PSD-95 and SYP on the hippocampal nerve synapses and improving synaptic plasticity.

Pathophysiology of astroglial purinergic signalling

Astrocytes are fundamental for central nervous system (CNS) physiology and are the fulcrum of neurological diseases. Astroglial cells control development of the nervous system, regulate synaptogenesis, maturation, maintenance and plasticity of synapses and are central for nervous system homeostasis. Astroglial reactions determine progression and outcome of many neuropathologies and are critical for regeneration and remodelling of neural circuits following trauma, stroke, ischaemia or neurodegenerative disorders. They secrete multiple neurotransmitters and neurohormones to communicate with neurones, microglia and the vascular walls of capillaries. Signalling through release of ATP is the most widespread mean of communication between astrocytes and other types of neural cells. ATP serves as a fast excitatory neurotransmitter and has pronounced long-term (trophic) roles in cell proliferation, growth, and development. During pathology, ATP is released from damaged cells and acts both as a cytotoxic factor and a proinflammatory mediator, being a universal "danger" signal. In this review, we summarise contemporary knowledge on the role of purinergic receptors (P2Rs) in a variety of diseases in relation to changes of astrocytic functions and nucleotide signalling. We have focussed on the role of the ionotropic P2X and metabotropic P2YRs working alone or in concert to modify the release of neurotransmitters, to activate signalling cascades and to change the expression levels of ion channels and protein kinases. All these effects are of great importance for the initiation, progression and maintenance of astrogliosis-the conserved and ubiquitous glial defensive reaction to CNS pathologies. We highlighted specific aspects of reactive astrogliosis, especially with respect to the involvement of the P2X(7) and P2Y(1)R subtypes. Reactive astrogliosis exerts both beneficial and detrimental effects in a context-specific manner determined by distinct molecular signalling cascades. Understanding the role of purinergic signalling in astrocytes is critical to identifying new therapeutic principles to treat acute and chronic neurological diseases.

Purinergic signalling: from normal behaviour to pathological brain function

Purinergic neurotransmission, involving release of ATP as an efferent neurotransmitter was first proposed in 1972. Later, ATP was recognised as a cotransmitter in peripheral nerves and more recently as a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the CNS. Both ATP, together with some of its enzymatic breakdown products (ADP and adenosine) and uracil nucleotides are now recognised to act via P2X ion channels and P1 and P2Y G protein-coupled receptors, which are widely expressed in the brain. They mediate both fast signalling in neurotransmission and neuromodulation and long-term (trophic) signalling in cell proliferation, differentiation and death. Purinergic signalling is prominent in neurone-glial cell interactions. In this review we discuss first the evidence implicating purinergic signalling in normal behaviour, including learning and memory, sleep and arousal, locomotor activity and exploration, feeding behaviour and mood and motivation. Then we turn to the involvement of P1 and P2 receptors in pathological brain function; firstly in trauma, ischemia and stroke, then in neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's, as well as multiple sclerosis and amyotrophic lateral sclerosis. Finally, the role of purinergic signalling in neuropsychiatric diseases (including schizophrenia), epilepsy, migraine, cognitive impairment and neuropathic pain will be considered.

Mining human genome for novel purinergic P2Y receptors: a sequence analysis and molecular modeling approach

The purinergic P2Y receptors are G-protein coupled receptors (GPCRs) that control many physiological processes by mediating cellular responses to purines, pyrimidines and their analogues. They can be used as potential therapeutic targets in a variety of disease conditions. Therefore, it is critical to identify new members of this family of receptors from the human genome and characterize them for their role in health and disease. In the present work, molecular modeling was carried out for the 21 known P2Y receptors. Binding site analysis was done on the basis of docking and site-directed mutagenesis data. Thus, conserved features of P2Y receptors could be formulated. These features can be used to determine the purinergic nature of potential P2Y receptors in the human genome. We applied this knowledge to human genome GPCR sequences found by sensitive sequence search techniques and identified two orphan receptors, namely GPR34 and GP171 that have all the necessary conserved features of P2Y receptors.

P2Y2 receptor expression is altered in rats after spinal cord injury

Spinal cord injury increases inhibitory factors that may restrict neurite outgrowth after trauma. The expression of repulsive molecules in reactive astrocytes and the formation of the glial scar at the injury site produce the non-permissive environment for axonal regeneration. However, the mechanism that triggers this astrogliotic response is unknown. The release of nucleotides has been linked to this hypertrophic state. Our goal is to investigate the temporal profile of P2Y(2) nucleotide receptor after spinal cord injury in adult female Sprague-Dawley rats. Molecular biology, immunofluorescence studies, and Western Blots were used to evaluate the temporal profile (2, 4, 7, 14, and 28 days post-injury) of this receptor in rats injured at the T-10 level using the NYU impactor device. Real time RT-PCR showed a significant increase of P2Y(2) mRNA after 2 days post-injury that continues throughout 28 days post-injury. Double labeling studies localized P2Y(2) immunoreactivity in neuronal cell bodies, axons, macrophages, oligodendrocytes and reactive astrocytes. Immunofluorescence studies also demonstrated a low level of P2Y(2) receptor in sham samples, which increased after injury in glial fibrillary acidic protein positive cells. Western Blot performed with contused spinal cord protein samples revealed an upregulation in the P2Y(2) 42 kDa protein band expression after 4 days post-injury that continues until 28 days post-injury. However, a downregulation of the 62 kDa receptor protein band after 2 days post-injury that continues up to 28 days post-injury was observed. Therefore, the spatio-temporal pattern of P2Y(2) gene expression after spinal cord injury suggests a role in the pathophysiology response generated after trauma.

P2Y2 nucleotide receptor-mediated responses in brain cells

Acute inflammation is important for tissue repair; however, chronic inflammation contributes to neurodegeneration in Alzheimer's disease (AD) and occurs when glial cells undergo prolonged activation. In the brain, stress or damage causes the release of nucleotides and activation of the G(q) protein-coupled P2Y(2) nucleotide receptor subtype (P2Y(2)R) leading to pro-inflammatory responses that can protect neurons from injury, including the stimulation and recruitment of glial cells. P2Y(2)R activation induces the phosphorylation of the epidermal growth factor receptor (EGFR), a response dependent upon the presence of a SH3 binding domain in the intracellular C terminus of the P2Y(2)R that promotes Src binding and transactivation of EGFR, a pathway that regulates the proliferation of cortical astrocytes. Other studies indicate that P2Y(2)R activation increases astrocyte migration. P2Y(2)R activation by UTP increases the expression in astrocytes of alpha(V)beta(3/5) integrins that bind directly to the P2Y(2)R via an Arg-Gly-Asp (RGD) motif in the first extracellular loop of the P2Y(2)R, an interaction required for G(o) and G(12) protein-dependent astrocyte migration. In rat primary cortical neurons (rPCNs) P2Y(2)R expression is increased by stimulation with interleukin-1beta (IL-1beta), a pro-inflammatory cytokine whose levels are elevated in AD, in part due to nucleotide-stimulated release from glial cells. Other results indicate that oligomeric beta-amyloid peptide (Abeta(1-42)), a contributor to AD, increases nucleotide release from astrocytes, which would serve to activate upregulated P2Y(2)Rs in neurons. Data with rPCNs suggest that P2Y(2)R upregulation by IL-1beta and subsequent activation by UTP are neuroprotective, since this increases the non-amyloidogenic cleavage of amyloid precursor protein. Furthermore, activation of IL-1beta-upregulated P2Y(2)Rs in rPCNs increases the phosphorylation of cofilin, a cytoskeletal protein that stabilizes neurite outgrowths. Thus, activation of pro-inflammatory P2Y(2)Rs in glial cells can promote neuroprotective responses, suggesting that P2Y(2)Rs represent a novel pharmacological target in neurodegenerative and other pro-inflammatory diseases.

Molecular classification of nodal metastasis in primary larynx squamous cell carcinoma

Classification and prognosis of larynx squamous cell carcinoma (LSCC) depends on clinical and histopathological examination. Currently, expression profiling harbors the potential to investigate, classify, and better manage cancer. Gene expression profiles of 22 primary LSCCs were analyzed by microarrays containing 19,200 cDNAs. GOAL functionally classified differentially expressed genes, and a novel "in silico" procedure identified physical gene clusters differentially transcribed. A signature of 158 genes differentiated tumors with nodal metastasis. A novel statistical method allowed categorization of metastatic tumors into 2 distinct subgroups of differential gene expression patterns. Among genes correlated to nodal metastatic progression, we verified in vitro that NM23-H3 reduced cell motility and TRIM8 were a growth suppressor. Six chromosomal regions were specifically downregulated in metastatic tumors. This large-scale gene expression analysis in LSCC provides information on changes in genomic activity associated with lymphonodal metastasis and identifies molecules that might prove useful as novel therapeutic targets.

Guanosine reduces apoptosis and inflammation associated with restoration of function in rats with acute spinal cord injury

Spinal cord injury results in progressive waves of secondary injuries, cascades of noxious pathological mechanisms that substantially exacerbate the primary injury and the resultant permanent functional deficits. Secondary injuries are associated with inflammation, excessive cytokine release, and cell apoptosis. The purine nucleoside guanosine has significant trophic effects and is neuroprotective, antiapoptotic in vitro, and stimulates nerve regeneration. Therefore, we determined whether systemic administration of guanosine could protect rats from some of the secondary effects of spinal cord injury, thereby reducing neurological deficits. Systemic administration of guanosine (8 mg/kg per day, i.p.) for 14 consecutive days, starting 4 h after moderate spinal cord injury in rats, significantly improved not only motor and sensory functions, but also recovery of bladder function. These improvements were associated with reduction in the inflammatory response to injury, reduction of apoptotic cell death, increased sparing of axons, and preservation of myelin. Our data indicate that the therapeutic action of guanosine probably results from reducing inflammation resulting in the protection of axons, oligodendrocytes, and neurons and from inhibiting apoptotic cell death. These data raise the intriguing possibility that guanosine may also be able to reduce secondary pathological events and thus improve functional outcome after traumatic spinal cord injury in humans.

Activation of P2X(7) receptors stimulates the expression of P2Y(2) receptor mRNA in astrocytes cultured from rat brain

Under pathological conditions brain cells release ATP at concentrations reported to activate P2X(7) ionotropic receptor subtypes expressed in both neuronal and glial cells. In the present study we report that the most potent P2X(7) receptor agonist BzATP stimulates the expression of the metabotropic ATP receptor P2Y(2) in cultured rat brain astrocytes. In other cell types several kinds of stimulation, including stress or injury, induce P2Y(2) expression that, in turn, is involved in different cell reactions. Similarly, it has recently been found that in astrocytes and astrocytoma cells P2Y(2) sites can trigger neuroprotective pathways through the activation of several mechanisms, including the induction of genes for antiapoptotic factors, neurotrophins, growth factors and neuropeptides. Here we present evidence that P2Y(2) mRNA expression in cultured astrocytes peaks 6 h after BzATP exposure and returns to basal levels after 24 h. This effect was mimicked by high ATP concentrations (1 mM) and was abolished by P2X(7)-antagonists oATP and BBG. The BzATP-evoked P2Y(2) receptor up-regulation in cultured astrocytes was coupled to an increased UTP-mediated intracellular calcium response. This effect was inhibited by oATP and BBG and by P2Y(2)siRNA, thus supporting evidence of increased P2Y(2) activity. To further investigate the mechanisms by which P2X(7) receptors mediated the P2Y(2) mRNA up-regulation, the cells were pre-treated with the chelating agent EGTA, or with inhibitors of mitogen-activated kinase (MAPK) (PD98059) or protein kinase C, (GF109203X). Each inhibitor significantly reduced the extent to which BzATP induced P2Y(2) mRNA. Both BzATP and ATP (1 mM) increased ERK1/2 activation. P2X(7)-induced ERK1/2 phosphorylation was unaffected by pre-treatment of astrocytes with EGTA whereas it was inhibited by GF109203X. Phorbol-12-myristate-13-acetate (PMA), an activator of PKCs, rapidly increased ERK1/2 activation. We conclude that activation of P2X(7) receptors in astrocytes enhances P2Y(2) mRNA expression by a mechanism involving both calcium influx and PKC/MAPK signalling pathways.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

In vitro stem cell cultures from human dental pulp and periodontal ligament: new prospects in dentistry

In spite of the vast knowledge of tooth development and of the various kinds of specialized bone/tooth-associated cells, the characteristics and properties of their precursor cell populations present in the postnatal organism are little known, as is their possible therapeutic use. Taken together dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs) possess stem-cell-like qualities, including self-renewal capability and multi-lineage differentiation. Regenerative medicine is based on stem cells, signals and scaffolds. Transplantation of those cells, which can be obtained from an easily accessible tissue resource and expanded in vitro, holds promise as a therapeutic approach for reconstruction of tissues and bone in vivo.

Expression and secretion of CXCL8 (IL-8), release of tryptase and transcription of histidine decarboxylase mRNA by anti-IgE-activated human umbilical cord blood-derived cultured mast cells

Activation of cytokine receptors and alterations in cytokines are thought to play important roles in neuronal dysfunction and in the pathogenesis of the nervous system diseases. CXCL8 (IL-8) is a CXC chemokine with chemotactic and inflammatory properties. Chemokines control mast cell infiltration in several inflammatory diseases, including stress and neurological dysfunctions. Using isolated human umbilical cord blood-derived cultured mast cells (HUCMC) from hematopoietic stem cells CD34+, mast cells were immunologically activated with anti-IgE at concentrations of 1, 5, 10 and 20 microg/ml leading to the dose-dependent production of IL-8 (p < 0.05). The increase in IL-8 mRNA expression was also noted when the cells were treated with anti-IgE at 10 microg/ml for 6 h. Immunologically activated HUCMC provoked the generation of tryptase in a dose- and time-dependent manner. We also found increased histidine decarboxylase (HDC) expression in activated HUCMC after 6 h of incubation, a rate-limiting enzyme responsible for the generation of histamine from histidine. Taken together, these results confirm that anti-IgE-activated mast cells release inflammatory mediators including CXCL8, a CXC chemokine which regulates several biological effects of mast cells, e.g. chemoattraction, and possibly causes cell arrest.

Inhibitory effect of quercetin on tryptase and MCP-1 chemokine release, and histidine decarboxylase mRNA transcription by human mast cell-1 cell line

Mast cells are important in reactions of allergic disease and are also involved in a variety of neuroinflammatory diseases. Mast cells can be immunologically activated by IgE through their Fc receptors, as well as by neuropeptides and cytokines to secrete mediators. Here we used a human mast cell-1 (HMC-1) cell line cultured and treated with a physiological activator, anti-IgE, and a nonphysiological activator, calcium ionophore A23187, for tryptase and MCP-1 generation and transcription of histidine decarboxylase. We used quercetin, a potent antioxidant, cytoprotective and anti-inflammatory compound capable of inhibiting histamine and some cytokines released from several cell types, as an inhibitor of immunological and nonimmunological stimulus for mast cells. In this study quercetin inhibits, in a dose-response manner, tryptase and MCP-1. Moreover, using RT-PCR quercetin inhibited the transcription of histidine decarboxylase, the rate-limiting enzyme responsible for the generation of histamine from histidine, and MCP-1. Our data suggest that quercetin is an important and good candidate for reducing the release of pro-inflammatory mast cell mediators activated by physiological and nonphysiological stimulators.