Kinin-B2 receptor expression and activity during differentiation of embryonic rat neurospheres

The family of kallikrein-related peptidases and kinin peptides as modulators of epidermal homeostasis

The epidermis is the outermost skin layer and is part of one of the largest organs in the body; it is supported by the dermis, a network of fibrils, blood vessels, pilosebaceous units, sweat glands, nerves, and cells. The skin as a whole is a protective shield against numerous noxious agents, including microorganisms and chemical and physical factors. These functions rely on the activity of multiple growth factors, peptide hormones, proteases, and specific signaling pathways that are triggered by the activation of distinct types of receptors sited in the cell membranes of the various cell types present in the skin. The human kallikrein family comprises a large group of 15 serine proteases synthesized and secreted by different types of epithelial cells throughout the body, including the skin. At this site, they initiate a proteolytic cascade that generates the active forms of the proteases, some of which regulate skin desquamation, activation of cytokines, and antimicrobial peptides. Kinin peptides are formed by the action of plasma and tissue kallikreins on kininogens, two plasma proteins produced in the liver and other organs. Although kinins are well known for their proinflammatory abilities, in the skin they are also considered important modulators of keratinocyte differentiation. In this review, we summarize the contributions of the kallikreins and kallikrein-related peptidases family and those of kinins and their receptors in skin homeostasis, with special emphasis on their pathophysiological role.

Inheritance Pattern of Hereditary Angioedema Indicates Mutation-Dependent Selective Effects During Early Embryonic Development

BACKGROUND

Hereditary angioedema (HAE) may be caused by a genetic deficiency of functional C1 inhibitor (C1-INH) or linked with mutations in the F12, PLG, and other genes in combination with normal C1-INH (HAEnCI). Although the types of hereditary angioedema due to deficiency of functional C1 inhibitor and HAEnCI are autosomal dominant inherited, there is the impression that in the types of HAEnCI more females carry disease-linked mutations.

OBJECTIVE

The aim of this study was to analyze the passing on of the HAE-specific mutations to the next generations in families with various types of HAE.

METHODS

Methods comprised pedigree analysis, Sanger sequencing analysis, biochemical analysis of parameters of the kallikrein-kinin system, and statistical analysis of the results. We analyzed a total of 1494 offspring of individuals carrying an HAE-linked mutation.

RESULTS

In HAE, less male and more female offspring of mutation carriers than expected for autosomal dominant inheritance inherited the familial mutation. In addition, there were less male offspring than expected in HAEnCI. This was independent of paternal or maternal inheritance.

CONCLUSION

We conclude that there is a sex- and mutation-dependent selection during early embryogenesis, possible around the time of implantation, favoring male wild-type and female mutant embryos. It also appears that 20% to 25% of male embryos carrying the HAE mutation are lost specific in HAEnCI. These findings point out that there is a potentially important role of the kallikrein-kinin system during early embryonic development.

Bradykinin, as a Reprogramming Factor, Induces Transdifferentiation of Brain Astrocytes into Neuron-like Cells

Kinins are endogenous, biologically active peptides released into the plasma and tissues via the kallikrein-kinin system in several pathophysiological events. Among kinins, bradykinin (BK) is widely distributed in the periphery and brain. Several studies on the neuro-modulatory actions of BK by the B₂BK receptor (B₂BKR) indicate that this neuropeptide also functions during neural fate determination. Previously, BK has been shown to induce differentiation of nerve-related stem cells into neuron cells, but the response in mature brain astrocytes is unknown. Herein, we used rat brain astrocyte (RBA) to investigate the effect of BK on cell transdifferentiation into a neuron-like cell morphology. Moreover, the signaling mechanisms were explored by zymographic, RT-PCR, Western blot, and immunofluorescence staining analyses. We first observed that BK induced RBA transdifferentiation into neuron-like cells. Subsequently, we demonstrated that BK-induced RBA transdifferentiation is mediated through B₂BKR, PKC-δ, ERK1/2, and MMP-9. Finally, we found that BK downregulated the astrocytic marker glial fibrillary acidic protein (GFAP) and upregulated the neuronal marker neuron-specific enolase (NSE) via the B₂BKR/PKC-δ/ERK pathway in the event. Therefore, BK may be a reprogramming factor promoting brain astrocytic transdifferentiation into a neuron-like cell, including downregulation of GFAP and upregulation of NSE and MMP-9 via the B₂BKR/PKC-δ/ERK cascade. Here, we also confirmed the transdifferentiative event by observing the upregulated neuronal nuclear protein (NeuN). However, the electrophysiological properties of the cells after BK treatment should be investigated in the future to confirm their phenotype.

Kinin-B2 Receptor Activity in Skeletal Muscle Regeneration and Myoblast Differentiation

The bioactive peptide bradykinin obtained from cleavage of precursor kininogens activates the kinin-B2 receptor functioning in induction of inflammation and vasodilatation. In addition, bradykinin participates in kidney and cardiovascular development and neuronal and muscle differentiation. Here we show that kinin-B2 receptors are expressed throughout differentiation of murine C2C12 myoblasts into myotubes. An autocrine loop between receptor activation and bradykinin secretion is suggested, since bradykinin secretion is significantly reduced in the presence of the kinin-B2 receptor antagonist HOE-140 during differentiation. Expression of skeletal muscle markers and regenerative capacity were decreased after pharmacological inhibition or genetic ablation of the B2 receptor, while its antagonism increased the number of myoblasts in culture. In summary, the present work reveals to date no functions described for the B2 receptor in muscle regeneration due to the control of proliferation and differentiation of muscle precursor cells.

Neuroprotective Effects of Kinin B2 Receptor in Organotypic Hippocampal Cultures of Middle-Aged Mice

Aging is a multifactorial phenomenon that results in several changes at cellular and molecular levels and is considered the main risk factor for some neurodegenerative diseases. Several evidence show the participation of the kallikrein-kinin system (KKS) in neurodegeneration and this system has been associated with inflammation and immunogenic responses in the central and peripheral systems by the activation of the B1 and B2 receptors. Previous work by our group showed that bradykinin (BK) and the B2 receptor played a possible role in neuroprotection. Therefore, the objective of this study was to evaluate the participation of B2 receptors in cell viability, neuroinflammatory response and neuroplasticity in organotypic hippocampal cultures (OHCs) of 6- and 12-month-old mice. It was observed that activation of the B2 receptor by bradykinin decreased the inflammatory response and increased plasticity in 12-month-old slices. Conversely, there was an increase in the inflammatory response and a decrease in neural plasticity in the 6-month-old slices. In both ages, an increase in cell viability was observed. This data suggests that the function of the kinin B2 receptor in the hippocampus is modulated by age, providing neuroprotective action in old age.

The relevance of kalikrein-kinin system via activation of B2 receptor in LPS-induced fever in rats

PURPOSE

This study evaluated the involvement of endogenous kallikrein-kinin system and the bradykinin (BK) B₁ and B₂ receptors on LPS- induced fever and the POA cells involved in this response.

MATERIAL AND METHODS

Male Wistar rats received either i.v. (1 mg/kg), i.c.v. (20 nmol) or i.h. (2 nmol) injections of icatibant (B₂ receptor antagonist) 30 or 60 min, respectively, before the stimuli. DALBK (B₁ receptor antagonist) was given either 15min before BK (i.c.v.) or 30 min before LPS (i.v.). Captopril (5 mg/kg, sc.,) was given 1 h prior LPS or BK. Concentrations of BK and total kininogenon CSF, plasma and tissue kallikrein were evaluated. Rectal temperatures (rT) were assessed by telethermometry. Ca⁺⁺ signaling in POA cells was performed in rat pup brain tissue microcultures.

RESULTS

Icatibant reduced LPS fever while, captopril exacerbated that response, an effect abolished by icatibant. Icatibant (i.h.) reduced fever to BK (i.h.) but not that induced by LPS (i.v.). BK increased intracellular calcium concentration in neurons and astrocytes. LPS increased levels of bradykinin, tissue kallikrein and total kininogen. BK (i.c.v.) increased rT and decreased tail skin temperature. Captopril potentiated BK-induced fever an effect abolished by icatibant. DALBK reduced the fever induced by BK. BK (i.c.v.) increased the CSF PGE₂concentration. Effect abolished by indomethacin (i.p.).

CONCLUSIONS

LPS activates endogenous kalikrein-kinin system leading to production of BK, which by acting on B₂-receptors of POA cells causes prostaglandin synthesis that in turn produces fever. Thus, a kinin B₂-receptor antagonist that enters into the brain could constitute a new and interesting strategy to treat fever.

Bradykinin promotes neuron-generating division of neural progenitor cells through ERK activation

During brain development, cells proliferate, migrate and differentiate in highly accurate patterns. In this context, published results indicate that bradykinin functions in neural fate determination, favoring neurogenesis and migration. However, mechanisms underlying bradykinin function are yet to be explored. Our findings indicate a previously unidentified role for bradykinin action in inducing neuron-generating division in vitro and in vivo, given that bradykinin lengthened the G1-phase of the neural progenitor cells (NPC) cycle and increased TIS21 (also known as PC3 and BTG2) expression in hippocampus from newborn mice. This role, triggered by activation of the kinin-B2 receptor, was conditioned by ERK1/2 activation. Moreover, immunohistochemistry analysis of hippocampal dentate gyrus showed that the percentage of Ki67(+) cells markedly increased in bradykinin-treated mice, and ERK1/2 inhibition affected this neurogenic response. The progress of neurogenesis depended on sustained ERK phosphorylation and resulted in ERK1/2 translocation to the nucleus in NPCs and PC12 cells, changing expression of genes such as Hes1 and Ngn2 (also known as Neurog2). In agreement with the function of ERK in integrating signaling pathways, effects of bradykinin in stimulating neurogenesis were reversed following removal of protein kinase C (PKC)-mediated sustained phosphorylation.

Kinin B2 receptor can play a neuroprotective role in Alzheimer's disease

Alzheimer's disease (AD) is characterized by cognitive decline, presence of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles. Kinins act through B1 and B2 G-protein coupled receptors (B1R and B2R). Chronic infusion of Aβ peptide leads to memory impairment and increases in densities of both kinin receptors in memory processing areas. Similar memory impairment was observed in C57BL/6 mice (WTAβ) but occurred earlier in mice lacking B2R (KOB2Aβ) and was absent in mice lacking B1R (KOB1Aβ). Thus, the aim of this study was to evaluate the participation of B1R and B2R in Aβ peptide induced cognitive deficits through the evaluation of densitiesof kinin receptors, synapses, cell bodies and number of Aβ deposits in brain ofWTAβ, KOB1Aβ and KOB2Aβ mice. An increase in B2R density was observed in both WTAβ and KOB1Aβ in memory processing related areas. KOB1Aβ showed a decrease in neuronal density and an increase in synaptic density and, in addition, an increase in Aβ deposits in KOB2Aβ was observed. In conclusion, memory preservation in KOB1Aβ, could be due to the increase in densities of B2R, suggesting a neuroprotective role for B2R, reinforced by the increased number of Aβ plaques in KOB2Aβ. Our data point to B2R as a potential therapeutic target in AD.

Purinergic signalling during development and ageing

Extracellular purines and pyrimidines play major roles during embryogenesis, organogenesis, postnatal development and ageing in vertebrates, including humans. Pluripotent stem cells can differentiate into three primary germ layers of the embryo but may also be involved in plasticity and repair of the adult brain. These cells express the molecular components necessary for purinergic signalling, and their developmental fates can be manipulated via this signalling pathway. Functional P1, P2Y and P2X receptor subtypes and ectonucleotidases are involved in the development of different organ systems, including heart, blood vessels, skeletal muscle, urinary bladder, central and peripheral neurons, retina, inner ear, gut, lung and vas deferens. The importance of purinergic signalling in the ageing process is suggested by changes in expression of A1 and A2 receptors in old rat brains and reduction of P2X receptor expression in ageing mouse brain. By contrast, in the periphery, increases in expression of P2X3 and P2X4 receptors are seen in bladder and pancreas.

Kinin-B1 and B2 receptor activity in proliferation and neural phenotype determination of mouse embryonic stem cells

The kinins bradykinin and des-arg(9) -bradykinin cleaved from kininogen precursors by kallikreins exert their biological actions by stimulating kinin-B2 and B1 receptors, respectively. In vitro models of neural differentiation such as P19 embryonal carcinoma cells and neural progenitor cells have suggested the involvement of B2 receptors in neural differentiation and phenotype determination; however, the involvement of B1 receptors in these processes has not been established. Here, we show that B1 and B2 receptors are differentially expressed in mouse embryonic E14Tg2A stem cells undergoing neural differentiation. Proliferation and differentiation assays, performed in the presence of receptor subtype-selective agonists and antagonists, revealed that B1 receptor activity is required for the proliferation of embryonic and differentiating cells as well as for neuronal maturation at later stages of differentiation, while the B2 receptor acts on neural phenotype choice, promoting neurogenesis over gliogenesis. Besides the elucidation of bradykinin functions in an in vitro model reflecting early embryogenesis and neurogenesis, this study contributes to the understanding of B1 receptor functions in this process.

Effects of ATP and NGF on Proliferation and Migration of Neural Precursor Cells

Purinergic receptors belong to the most ancient neurotransmitter system. While their relevance in neurotransmission is well characterized, it has become clear that they have many other cellular functions. During development, they participate in regulation of proliferation and differentiation of stem cells. Here, we used rat embryonic telencephalon neurosphere cultures to detect purinergic P2 receptor subtype expression and possible synergistic actions of these receptors with NGF. Neurospheres proliferate in the presence of EGF and FGF-2; however, upon depletion of these growth factors, they migrate and differentiate into neurons and glial phenotypes. Expression patterns of P2X and P2Y receptors changed along neural differentiation. Gene expression of P2X2-7 and P2Y1,2,4,6,12,14 receptors was confirmed in undifferentiated and neural-differentiated neurospheres, with an up-regulation of P2X2 and P2X6 subtypes, together with a down-regulation of P2X4, P2X7 and P2Y subtypes upon induction to differentiation. BrdU-labeling and subsequent flow cytometry analysis was used to measure cell proliferation, which was increased by chronic exposure to NGF and increasing concentrations of ATP, in line with the expression levels of PCNA. Furthermore, a synergistic effect on proliferation was observed in conditions of co-incubation with ATP and NGF. While ATP and NGF independently promoted neural migration, no inter-relation between these factors was detected for this cellular process. As conclusion, an unknown synergism of ATP and NGF in proliferation is described. Future efforts may elucidate the underlying mechanisms of the interrelationship of ATP and NGF during neurogenesis.

Early pharmacological inhibition of angiotensin-I converting enzyme activity induces obesity in adulthood

We have investigated early programming of body mass in order to understand the multifactorial etiology of obesity. Considering that the renin-angiotensin system (RAS) is expressed and functional in the white adipose tissue (WAT) and modulates its development, we reasoned whether early transitory inhibition of angiotensin-I converting enzyme activity after birth could modify late body mass development. Therefore, newborn Wistar rats were treated with enalapril (10 mg/kg of body mass) or saline, starting at the first day of life until the age of 16 days. Between days ninetieth and hundred and eightieth, a group of these animals received high fat diet (HFD). Molecular, biochemical, histological, and physiological data were collected. Enalapril treated animals presented hyperphagia, overweight, and increased serum level of triglycerides, total cholesterol and leptin, in adult life. Body composition analyses revealed higher fat mass with increased adipocyte size in these animals. Molecular analyses revealed that enalapril treatment increases neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) gene expression in hypothalamus, fatty acid synthase (FAS), and hormone-sensitive lipase (HSL) gene expression in retroperitoneal WAT, and decreases peroxixome proliferators-activated receptor (PPAR)γ, PPARα, uncoupling protein (UCP)2, and UCP3 gene expression in WAT. The results of the current study indicate that enalapril administration during early postnatal development increases body mass, adiposity and serum lipids in adulthood associated with enhanced food intake and decreased metabolic activity in WAT, predisposing to obesity in adulthood.

Roles of kinins in the nervous system

The kallikrein-kinin system (KKS) is an endogenous pathway involved in many biological processes. Although primarily related to blood pressure control and inflammation, its activation goes beyond these effects. Neurogenesis and neuroprotection might be stimulated by bradykinin being of great interest for clinical applications following brain injury. This peptide is also an important player in spinal cord injury pathophysiology and recovery, in which bradykinin receptor blockers represent substantial therapeutic potential. Here, we highlight the participation of kinin receptors and especially bradykinin in mediating ischemia pathophysiology in the central and peripheral nervous systems. Moreover, we explore the recent advances on mechanistic and therapeutic targets for biological, pathological, and neural repair processes involving kinins.

Paraoxon and Pyridostigmine Interfere with Neural Stem Cell Differentiation

Acetylcholinesterase (AChE) inhibition has been described as the main mechanism of organophosphate (OP)-evoked toxicity. OPs represent a human health threat, because chronic exposure to low doses can damage the developing brain, and acute exposure can produce long-lasting damage to adult brains, despite post-exposure medical countermeasures. Although the main mechanism of OP toxicity is AChE inhibition, several lines of evidence suggest that OPs also act by other mechanisms. We hypothesized that rat neural progenitor cells extracted on embryonic day 14.5 would be affected by constant inhibition of AChE from chronic exposure to OP or pyridostigmine (a reversible AChE blocker) during differentiation. In this work, the OP paraoxon decreased cell viability in concentrations >50 μM, as measured with the MTT assay; however, this effect was not dose-dependent. Reduced viability could not be attributed to blockade of AChE activity, since treatment with 200 µM pyridostigmine did not affect cell viability, even after 6 days. Although changes in protein expression patterns were noted in both treatments, the distribution of differentiated phenotypes, such as the percentages of neurons and glial cells, was not altered, as determined by flow cytometry. Since paraoxon and pyridostigmine each decreased neurite outgrowth (but did not prevent differentiation), we infer that developmental patterns may have been affected.

Kinin-B2 receptor activity determines the differentiation fate of neural stem cells

Bradykinin is not only important for inflammation and blood pressure regulation, but also involved in neuromodulation and neuroprotection. Here we describe novel functions for bradykinin and the kinin-B2 receptor (B2BkR) in differentiation of neural stem cells. In the presence of the B2BkR antagonist HOE-140 during rat neurosphere differentiation, neuron-specific β3-tubulin and enolase expression was reduced together with an increase in glial protein expression, indicating that bradykinin-induced receptor activity contributes to neurogenesis. In agreement, HOE-140 affected in the same way expression levels of neural markers during neural differentiation of murine P19 and human iPS cells. Kinin-B1 receptor agonists and antagonists did not affect expression levels of neural markers, suggesting that bradykinin-mediated effects are exclusively mediated via B2BkR. Neurogenesis was augmented by bradykinin in the middle and late stages of the differentiation process. Chronic treatment with HOE-140 diminished eNOS and nNOS as well as M1-M4 muscarinic receptor expression and also affected purinergic receptor expression and activity. Neurogenesis, gliogenesis, and neural migration were altered during differentiation of neurospheres isolated from B2BkR knock-out mice. Whole mount in situ hybridization revealed the presence of B2BkR mRNA throughout the nervous system in mouse embryos, and less β3-tubulin and more glial proteins were expressed in developing and adult B2BkR knock-out mice brains. As a underlying transcriptional mechanism for neural fate determination, HOE-140 induced up-regulation of Notch1 and Stat3 gene expression. Because pharmacological treatments did not affect cell viability and proliferation, we conclude that bradykinin-induced signaling provides a switch for neural fate determination and specification of neurotransmitter receptor expression.

Functions of neurotrophins and growth factors in neurogenesis and brain repair

The identification and isolation of multipotent neural stem and progenitor cells in the brain, giving rise to neurons, astrocytes, and oligodendrocytes initiated many studies in order to understand basic mechanisms of endogenous neurogenesis and repair mechanisms of the nervous system and to develop novel therapeutic strategies for cellular regeneration therapies in brain disease. A previous review (Trujillo et al., Cytometry A 2009;75:38-53) focused on the importance of extrinsic factors, especially neurotransmitters, for directing migration and neurogenesis in the developing and adult brain. Here, we extend our review discussing the effects of the principal growth and neurotrophic factors as well as their intracellular signal transduction on neurogenesis, fate determination and neuroprotective mechanisms. Many of these mechanisms have been elucidated by in vitro studies for which neural stem cells were isolated, grown as neurospheres, induced to neural differentiation under desired experimental conditions, and analyzed for embryonic, progenitor, and neural marker expression by flow and imaging cytometry techniques. The better understanding of neural stem cells proliferation and differentiation is crucial for any therapeutic intervention aiming at neural stem cell transplantation and recruitment of endogenous repair mechanisms.

Interactions between the NO-citrulline cycle and brain-derived neurotrophic factor in differentiation of neural stem cells

The diffusible messenger NO plays multiple roles in neuroprotection, neurodegeneration, and brain plasticity. Argininosuccinate synthase (AS) is a ubiquitous enzyme in mammals and the key enzyme of the NO-citrulline cycle, because it provides the substrate L-arginine for subsequent NO synthesis by inducible, endothelial, and neuronal NO synthase (NOS). Here, we provide evidence for the participation of AS and of the NO-citrulline cycle in the progress of differentiation of neural stem cells (NSC) into neurons, astrocytes, and oligodendrocytes. AS expression and activity and neuronal NOS expression, as well as l-arginine and NO(x) production, increased along neural differentiation, whereas endothelial NOS expression was augmented in conditions of chronic NOS inhibition during differentiation, indicating that this NOS isoform is amenable to modulation by extracellular cues. AS and NOS inhibition caused a delay in the progress of neural differentiation, as suggested by the decreased percentage of terminally differentiated cells. On the other hand, BDNF reversed the delay of neural differentiation of NSC caused by inhibition of NO(x) production. A likely cause is the lack of NO, which up-regulated p75 neurotrophin receptor expression, a receptor required for BDNF-induced differentiation of NSC. We conclude that the NO-citrulline cycle acts together with BDNF for maintaining the progress of neural differentiation.

Neural differentiation of P19 carcinoma cells and primary neurospheres: cell morphology, proliferation, viability, and functionality

This unit describes the culture and induction of in vitro models of neural differentiation and strategies to evaluate the participation of extrinsic and intrinsic factors in modulation of this process. Protocols focus on large-scale expansion of pluripotent P19 murine embryonic carcinoma cells and their induction to neural differentiation in the presence of retinoic acid, closely resembling conditions of early neuroectodermal differentiation. Procedures are also described for obtaining rat neural precursor cells (NPCs) or neurospheres and for differentiating them in the absence of growth factors. Experimental strategies are reported using P19 cells and NPCs as in vitro models for studying the actions of extrinsic and intrinsic factors on morphology, proliferation, viability, neural phenotype determination, and progress of differentiation, as well as the functionality of ion channels and metabotropic receptors in inducing calcium fluxes at different developmental stages. The methods described here may be useful for optimizing in vitro protocols for stem cell differentiation into defined neural populations, as well as for studying mechanisms that underlie neurogenesis and gliogenesis.

Kinin-B2 receptor mediated neuroprotection after NMDA excitotoxicity is reversed in the presence of kinin-B1 receptor agonists

Background

Kinins, with bradykinin and des-Arg⁹-bradykinin being the most important ones, are pro-inflammatory peptides released after tissue injury including stroke. Although the actions of bradykinin are in general well characterized; it remains controversial whether the effects of bradykinin are beneficial or not. Kinin-B2 receptor activation participates in various physiological processes including hypotension, neurotransmission and neuronal differentiation. The bradykinin metabolite des-Arg⁹-bradykinin as well as Lys-des-Arg⁹-bradykinin activates the kinin-B1 receptor known to be expressed under inflammatory conditions. We have investigated the effects of kinin-B1 and B2 receptor activation on N-methyl-D-aspartate (NMDA)-induced excitotoxicity measured as decreased capacity to produce synaptically evoked population spikes in the CA1 area of rat hippocampal slices.

Principal Findings

Bradykinin at 10 nM and 1 µM concentrations triggered a neuroprotective cascade via kinin-B2 receptor activation which conferred protection against NMDA-induced excitotoxicity. Recovery of population spikes induced by 10 nM bradykinin was completely abolished when the peptide was co-applied with the selective kinin-B2 receptor antagonist HOE-140. Kinin-B2 receptor activation promoted survival of hippocampal neurons via phosphatidylinositol 3-kinase, while MEK/MAPK signaling was not involved in protection against NMDA-evoked excitotoxic effects. However, 100 nM Lys-des-Arg⁹-bradykinin, a potent kinin-B1 receptor agonist, reversed bradykinin-induced population spike recovery. The inhibition of population spikes recovery was reversed by PD98059, showing that MEK/MAPK was involved in the induction of apoptosis mediated by the B1 receptor.

Conclusions

Bradykinin exerted protection against NMDA-induced excitotoxicity which is reversed in the presence of a kinin-B1 receptor agonist. As bradykinin is converted to the kinin-B1 receptor metabolite des-Arg⁹-bradykinin by carboxypeptidases, present in different areas including in brain, our results provide a mechanism for the neuroprotective effect in vitro despite of the deleterious effect observed in vivo.

Neural differentiation of rat aorta pericyte cells

Pericyte perivascular cells, believed to originate mesenchymal stem cells (MSC), are characterized by their capability to differentiate into various phenotypes and participate in tissue reconstruction of different organs, including the brain. We show that these cells can be induced to differentiation into neural-like phenotypes. For these studies, pericytes were obtained from aorta ex-plants of Sprague-Dawley rats and differentiated into neural cells following induction with trans retinoic acid (RA) in serum-free defined media or differentiation media containing nerve growth and brain-derived neuronal factor, B27, N2, and IBMX. When induced to differentiation with RA, cells express the pluripotency marker protein stage-specific embryonic antigen-1, neural-specific proteins β3-tubulin, neurofilament-200, and glial fibrillary acidic protein, suggesting that pericytes undergo differentiation, similar to that of neuroectodermal cells. Differentiated cells respond with intracellular calcium transients to membrane depolarization by KCl indicating the presence of voltage-gated ion channels and express functional N-methyl-D-aspartate receptors, characteristic for functional neurons. The study of neural differentiation of pericytes contributes to the understanding of induction of neuroectodermal differentiation as well as providing a new possible stem-cell source for cell regeneration therapy in the brain.

Bradykinin promotes the chemotactic invasion of primary brain tumors

Primary brain tumors, gliomas, diffusely invade the brain by active cell migration either intraparenchymal, along white matter tracts or along blood vessels. The close relationship of glioma with the vasculature assures a continuous supply of oxygen and nutrients essential for cell growth, and exposes cells to a variety growth factors, chemokines, cytokines, and kinins. Signals that attract glioma cells to blood vessels are poorly understood. It has been shown that vascular endothelial cells can initiate the bradykinin (BK) signaling cascade and two bradykinin receptors, B1 and B2, have been identified and cloned. In this study we show that glioma cells isolated from patient biopsies express bradykinin 2 receptors (B2R) whose activation causes intracellular Ca(2+) oscillations. Through time-lapse video-microscopy experiments we show that BK significantly enhances glioma cell migration/invasion. We further show that BK acts as a chemoattractant guiding glioma cells toward blood vessels in acute rat brain slices. The number of cells associated with blood vessels is decreased when B2R are either pharmacologically inhibited or B2R eliminated through short-hairpin RNA knockdown. These data strongly suggest that bradykinin, acting via B2R, acts as an important signal directing the invasion of glioma cells toward blood vessels. A clinically approved B2R antagonist is available that could be used as anti-invasive drug in glioma patients in the future.

Purinergic signaling in embryonic and stem cell development

Nucleotides are of crucial importance as carriers of energy in all organisms. However, the concept that in addition to their intracellular roles, nucleotides act as extracellular ligands specifically on receptors of the plasma membrane took longer to be accepted. Purinergic signaling exerted by purines and pyrimidines, principally ATP and adenosine, occurs throughout embryologic development in a wide variety of organisms, including amphibians, birds, and mammals. Cellular signaling, mediated by ATP, is present in development at very early stages, e.g., gastrulation of Xenopus and germ layer definition of chick embryo cells. Purinergic receptor expression and functions have been studied in the development of many organs, including the heart, eye, skeletal muscle and the nervous system. In vitro studies with stem cells revealed that purinergic receptors are involved in the processes of proliferation, differentiation, and phenotype determination of differentiated cells. Thus, nucleotides are able to induce various intracellular signaling pathways via crosstalk with other bioactive molecules acting on growth factor and neurotransmitter receptors. Since normal development is disturbed by dysfunction of purinergic signaling in animal models, further studies are needed to elucidate the functions of purinoceptor subtypes in developmental processes.

Directed differentiation of neural progenitors into neurons is accompanied by altered expression of P2X purinergic receptors

Neural differentiation has been extensively studied in vitro in a model termed neurospheres, which consists of aggregates of neural progenitor cells. Previous studies suggest that they have a great potential for the treatment of neurological disorders. One of the major challenges for scientists is to control cell fate and develop ideal culture conditions for neurosphere expansion in vitro, without altering their features. Similar to human neural progenitors, rat neurospheres cultured in the absence of epidermal and fibroblast growth factors for a short period increased the levels of β-3 tubulin and decreased the expression of glial fibrillary acidic protein and nestin, compared to neurospheres cultured in the presence of these factors. In this work, we show that rat neurospheres cultured in suspension under mitogen-free condition presented significant higher expression of P2X2 and P2X6 receptor subunits, when compared to cells cultured in the presence of growth factors, suggesting a direct relationship between P2X2/6 receptor expression and induction of neuronal differentiation in mitogen-free cultured rat neurospheres.

The central nervous system as target for antihypertensive actions of a proline-rich peptide from Bothrops jararaca venom

Pyroglutamyl proline-rich oligopeptides, present in the venom of the pit viper Bothrops jararaca (Bj-PROs), are the first described naturally occurring inhibitors of the angiotensin I-converting enzyme (ACE). The inhibition of ACE by the decapeptide Bj-PRO-10c (<ENWPHPQIPP) and other Bj-PROs was classically used to explain the pharmacological effects of these venom peptides in mammals resulting in a decrease of blood pressure. Recent studies, however, suggest that ACE inhibition alone is not sufficient for explaining the antihypertensive actions exerted by these peptides. In this study, we show that intracerebroventricular injection of Bj-PRO-10c induced a significant reduction of mean arterial pressure (MAP) together with a decrease of heart rate (HR) in spontaneously hypertensive rats, indicating that Bj-PRO-10c may act on the central nervous system. In agreement with its supposed neuronal action, this peptide dose-dependently evoked elevations of intracellular calcium concentration ([Ca(2+)](i)) in primary culture from postnatal rat brain. The N-terminal sequence of the peptide was not essential for induction of calcium fluxes, while any changes of C-terminal Pro or Ile residues affected Bj-PRO-10c's activity. Using calcium imaging by confocal microscopy and fluorescence imaging plate reader analysis, we have characterized Bj-PRO-10c-induced [Ca(2+)](i) transients in rat brain cells as being independent from bradykinin-mediated effects and ACE inhibition. Bj-PRO-10c induced pertussis toxin-sensitive G(i/o)-protein activity mediated through a yet unknown receptor, influx and liberation ofcalcium from intracellular stores, as well as reduction of intracellular cAMP levels. Bj-PRO-10c promoted glutamate and GABA release that may be responsible for its antihypertensive activity and its effect on HR.

Phenotypes of stem cells from diverse origin

Stem cells have turned into promising tools for studying the mechanisms of development, regeneration, and for cell therapy of various disorders. Stem cells are found in the embryo and in most adult tissues participating in endogenous tissue regeneration. They are capable of autorenovation, often maintain their multipotency of differentiation into various tissues of their germ line and are, therefore, ideal candidates for cellular therapy taken that they can be unequivocally identified and isolated. In this review, we report stem cell marker expression used for identification of various stem cell lineages, including very small embryonic stem cells, neural, hematopoietic, mesenchymal, epithelial and limbal epithelial stem cells, endothelial progenitor cells, supra-adventitial adipose stromal cells, adipose pericytes, and cancer stem cells. These cells usually cannot be distinguished by a single stem cell marker, because their expression partially overlaps between lineages. Recent advances in flow cytometry allowing the simultaneous detection of various markers have facilitated stem cell identification for clinical diagnosis and research. So far experimental evidence suggests the existence of cells with different properties, i.e., the capability to different in various cell types. Several studies indicate that expression of classical markers for stem cell classification, such as CD34, CD45, and CD133, may differ between the virtually same stem and progenitor cells, i.e., endothelial progenitor or mesenchymal stem cells, when they were obtained from different tissues. This finding raises questions whether phenotypic differences are due to the source or if it is only caused by different isolation and experimental conditions.

Blockade of bradykinin B2 receptor more effectively reduces postischemic blood-brain barrier disruption and cytokines release than B1 receptor inhibition

Blood-brain barrier disruption and brain edema are detrimental in ischemic stroke. The kallikrein-kinin system appears to play an important role in the regulation of vascular permeability and is invoked in edema formation. The effects of kinins are mediated by bradykinin receptors B1R and B2R. However, little is known about the exact roles of bradykinin receptors in the early stage of cerebral ischemia. In this study, we demonstrated that ischemia upregulated the level of B1R and B2R at 24h after reperfusion by immunofluorescence assays, mainly expressed in astrocytes and neurons, respectively, in the ischemic penumbra. Moreover, B2R inhibition more effectively reduced neurological severity scores, blood-brain barrier permeability and cytokines release than B1R inhibition did. Additionally, B2R inhibition also significantly suppressed B1R protein level. Therefore, blockade of B2R may be a more effective strategy for the treatment of ischemic brain injury than B1R inhibition within 24h after reperfusion.

Interaction with calmodulin is important for the secretion of thimet oligopeptidase following stimulation

Thimet oligopeptidase (EC 3.4.24.15; EP24.15) was originally described as a neuropeptide-metabolizing enzyme, highly expressed in the brain, kidneys and neuroendocrine tissue. EP24.15 lacks a typical signal peptide sequence for entry into the secretory pathway and is secreted by cells via an unconventional and unknown mechanism. In this study, we identified a novel calcium-dependent interaction between EP24.15 and calmodulin, which is important for the stimulated, but not constitutive, secretion of EP24.15. We demonstrated that, in vitro, EP24.15 and calmodulin physically interact only in the presence of Ca2+, with an estimated Kd value of 0.52 mum. Confocal microscopy confirmed that EP24.15 colocalizes with calmodulin in the cytosol of resting HEK293 cells. This colocalization markedly increases when cells are treated with either the calcium ionophore A23187 or the protein kinase A activator forskolin. Overexpression of calmodulin in HEK293 cells is sufficient to greatly increase the A23187-stimulated secretion of EP24.15, which can be inhibited by the calmodulin inhibitor calmidazolium. The specific inhibition of protein kinase A with KT5720 reduces the A23187-stimulated secretion of EP24.15 and inhibits the synergistic effects of forskolin with A23187. Treatment with calmidazolium and KT5720 nearly abolishes the stimulatory effects of A23187 on EP24.15 secretion. Together, these data suggest that the interaction between EP24.15 and calmodulin is regulated within cells and is important for the stimulated secretion of EP24.15 from HEK293 cells.

"Small stem cells" in adult tissues: very small embryonic-like stem cells stand up!

This review summarizes information regarding the rare population of very small embryonic-like stem cells (VSELs) that has been identified in adult tissues, emphasizing both their unique morphological features and potential biological significance. We focus on their pluripotent nature and expression of markers characteristic for embryonic stem cells (ESCs), epiblast (EP)SCs, and primordial germ cells (PGCs). Furthermore, we will discuss their rank in the developmental hierarchy of the SC compartment as well as their relationship to other bone marrow-derived, primitive, nonhematopoietic SCs including: (i) endothelial progenitor cells (EPCs); (ii) mesenchymal (M)SCs; (iii) multipotent adult progenitor cells (MAPCs); (iv) marrow-isolated adult multilineage inducible (MIAMIs) cells; (v) multipotent adult (MA)SCs; and (vi) OmniCytes. We will also present different populations of very "small SCs" that have been recently described in the literature (e.g., spore-like cells and Lin(-)/ALDH(high) long-term repopulating hematopoietic SCs).

Pharmacological properties of purinergic receptors and their effects on proliferation and induction of neuronal differentiation of P19 embryonal carcinoma cells

We have used P19 embryonal carcinoma cells as in vitro model for early neurogenesis to study ionotropic P2X and metabotropic P2Y receptor-induced Ca(2+) transients and their participation in induction of proliferation and differentiation. In embryonic P19 cells, P2Y(1), P2Y(2) and P2X(4) receptors or P2X-heteromultimers with similar P2X(4) pharmacology were responsible for ATP and ATP analogue-induced Ca(2+) transients. In neuronal-differentiated cells, P2Y(2,) P2Y(6), P2X(2) and possibly P2X(2)/P2X(6) heteromeric receptors were the major mediators of the elevations in intracellular free calcium concentration [Ca(2+)](i). We have collected evidence for the involvement of metabotropic purinergic receptors in proliferation induction of undifferentiated and neural progenitor cells by using a BrdU-incorporation assay. ATP-, UTP-, ADP-, 2-MeS-ATP- and ADP-betaS-induced proliferation in P19 cells was mediated by P2Y(1) and P2Y(2) receptors as judged from pharmacological profiles of receptor responses. ATP-provoked acceleration of neuronal differentiation, determined by analysis of nestin and neuron-specific enolase gene and protein expression, also resulted from P2Y(1) and P2Y(2) receptor activation. Proliferation- and differentiation-induction involved the activation of inositol-trisphosphate sensitive intracellular Ca(2+) stores.