S100B in neuropathologic states: The CRP of the brain?

In recent years there has been a proliferation of interest in the brain-specific protein S100B, its many physiologic roles, and its behaviour in various neuropathologic conditions. Since the mid-1960s, its wide variety of intracellular and extracellular activities has been elucidated, and it has also been implicated in an increasing number of central nervous system (CNS) disorders. S100B is part of a superfamily of proteins, some of which (including S100B) have been implicated as calcium-dependent regulatory proteins that modulate the activity of effector proteins or cells. S100B is primarily an astrocytic protein. Within cells, it may have a role in signal transduction, and it is involved in calcium homeostasis. Information about the functional implication of S100B secretion by astrocytes into the extracellular space is scant but there is substantial evidence that secreted glial S100B exerts trophic or toxic effects depending on its concentration. This review summarises the historic development and current knowledge of S100B, including recent interesting findings relating S100B to a diversity of CNS pathologies such as traumatic brain injury, Alzheimer's disease, Down's syndrome, schizophrenia, and Tourette's syndrome. These broad implications have led some workers to describe S100B as 'the CRP (C-reactive protein) of the brain.' This review also examines S100B's potential role as a neurologic screening tool, or biomarker of CNS injury, analogous to the role of CRP as a marker of systemic inflammation.     

Phosphatidylinositol 3‐kinase/protein kinase Cδ activation induces close homolog of adhesion molecule L1 (CHL1) expression in cultured astrocytes

Upregulation of expression of the close homolog of adhesion molecule L1 (CHL1) by reactive astrocytes in the glial scar reduces axonal regeneration and inhibits functional recovery after spinal cord injury (SCI). Here, we investigate the molecular mechanisms underlying upregulation of CHL1 expression by analyzing the signal transduction pathways in vitro. We show that astrogliosis stimulated by bacterial lipopolysaccharide (LPS) upregulates CHL1 expression in primary cultures of mouse cerebral astrocytes, coinciding with elevated protein synthesis and translocation of protein kinase δ (PKCδ) from cytosol to the membrane fraction. Blocking PKCδ activity pharmacologically and genetically attenuates LPS‐induced elevation of CHL1 protein expression through a phosphatidylinositol 3‐kinase (PI3K) dependent pathway. LPS induces extracellular signal‐regulated kinases (ERK1/2) phosphorylation through PKCδ and blockade of ERK1/2 activation abolishes upregulation of CHL1 expression. LPS‐triggered upregulation of CHL1 expression mediated through translocation of nuclear factor κB (NF‐κB) to the nucleus is blocked by a specific NF‐κB inhibitor and by inhibition of PI3K, PKCδ, and ERK1/2 activities, implicating NF‐κB as a downstream target for upregulation of CHL1 expression. Furthermore, the LPS‐mediated upregulation of CHL1 expression by reactive astrocytes is inhibitory for hippocampal neurite outgrowth in cocultures. Although the LPS‐triggered NO‐guanylate cyclase‐cGMP pathway upregulates glial fibrillary acid protein expression in cultured astrocytes, we did not observe this pathway to mediate LPS‐induced upregulation of CHL1 expression. Our results indicate that elevated CHL1 expression by reactive astrocytes requires activation of PI3K/PKCδ‐dependent pathways and suggest that reduction of PI3K/PKCδ activity represents a therapeutic target to downregulate CHL1 expression and thus benefit axonal regeneration after SCI. © 2009 Wiley‐Liss, Inc.     

Ammonia-induced alteration in S100B secretion in astrocytes is not reverted by creatine addition

Hyperammonemia is a major element in the pathogenesis of hepatic encephalopathy (HE) and ammonia neurotoxicity involves an effect on the glutamatergic neurotransmitter system. Astrocytes are intimately related to glutamatergic neurotransmission and, in fact, many specific glial alterations have been reported as a result of ammonia exposure. S100B protein, particularly extracellular S100B, is used as a parameter of glial activation or commitment in several situations of brain injury. However, there is little information about this protein in ammonia toxicity and none about its secretion in astrocytes under ammonia exposure. In this study, we investigated S100B secretion in rat cortical astrocytes acutely exposed to ammonia, as well astrocyte morphology, glial fibrillary acidic protein (GFAP) content and glutamine synthetase (GS) activity. Moreover, we studied a possible effect of creatine on these glial parameters, since this compound has a putative role against ammonia toxicity in cell cultures. We found an increase in S100B secretion by astrocytes exposed to ammonia for 24h, accompanied by a decrease in GFAP content and GS activity. Since elevated and persistent extracellular S100B plays a toxic effect on neural cells, altered extracellular content of S100B induced by ammonia could contribute to the brain impairment observed in HE. Creatine addition did not prevent this increment in S100B secretion, but was able to prevent the decrease in GFAP content and GS activity induced by ammonia exposure.     

The role of ERK1/2 in the regulation of proliferation and differentiation of astrocytes in developing brain

Extracellular signal regulated kinases (ERK) are important components of the Ras-Raf-MEK-ERK signaling pathway cascades that mediate intracellular stimuli transduction and gene expression. ERK1 (44 kDa) and ERK2 (42 kDa) are homologous subtypes of the ERK family, which participate in regulation of a variety of cell activities, including cell proliferation, migration and differentiation, especially in the central nervous systerm (CNS). Hence, they exert critical effects on neuron and astrocyte development. Astrocytes are critically involved in maintaining CNS homeostasis and supporting neuron growth. When exposed to an extracellular stimulus, such as inflammation or oxidative stress, the corresponding cell response can be regulated by the ERK1/2 signaling pathway. Furthermore, several lines of evidence have demonstrated a correlation between astrocyte activity and the Ras-Raf-MEK-ERK signaling pathway. However many questions remain unanswered regarding the role of ERK1/2 in astrocyte development. This review summarizes the possible role of ERK1/2 signaling cascades in modulating the proliferation, differentiation and apoptosis of astrocytes in both physiological and pathological conditions. In addition, this review also briefly elucidates the participation of ERK1/2 in the process of human brain glia tumor oncogenesis and metastasis, which will provide some concepts for treatment strategies to delay the process of tumor evolution.     

Sensory neurite outgrowth on white matter astrocytes is influenced by intracellular and extracellular S100A4 protein

The central nervous system (CNS) is considered a nonpermissive environment for axonal regeneration because of the presence of myelin and associated repulsive molecules. However, neural cells transplanted to the CNS preferably migrate and extend their fibers in white matter areas. We previously showed that white matter astrocytes in vivo express the calcium-binding protein S100A4, which is strongly up-regulated in areas of white matter degeneration. To investigate the role of white matter astrocytes and their specific protein S100A4 in axonal regeneration, we developed white matter astrocyte cultures with strong S100A4 expression and grew dissociated adult dorsal root ganglion (DRG) cells on top of astrocytes for 24 hr. By using small interfering S100A4 RNA, we were able to eliminate S100A4 expression and compare growth of DRG cell neurites on S100A4-silenced and S100A4-expressing astrocytes. In addition, we studied whether extracellular S100A4 has an effect on neurite growth from adult DRG cells cultured on S100A4-expressing white matter astrocytes. Our data show that white matter astrocytes are permissive for neurite growth, although high levels of S100A4 in white matter astrocytes have a negative effect on this growth. Extracellular application of S100A4 induced extensive growth of DRG cell neurites on white matter astrocytes. These findings suggest that white matter astrocytes are able to support axonal regeneration and, furthermore, that administration of extracellular S100A4 provides strong additional support for axonal regeneration.     

MAPK/ERK激酶-ERK信号通路参与外源性bFGF对缺氧-复氧损伤后星形胶质细胞内Egr-1结合活性的调节(英文)

目的静脉注射碱性成纤维细胞生长因子(basic fibroblast growth factor,bFGF)可以明显降低实验性脑缺血大鼠的脑梗死面积,但该作用的分子机制尚不清楚。本文旨在研究外源性bFGF 作用的信号转导通路。方法缺氧-复氧损伤星形胶质细胞。Western blot检测外源性bFGF作用后丝裂原活化蛋白激酶/细胞外信号调节激酶激酶(mitogen-activated protein kinase/extracellular signal-regulated kinase kinase,MEK)-细胞外信号调节激酶(extracellular signal-regulated kinase, ERK) 信号通路活化。电泳变动迁移率分析实验检测外源性bFGF 作用后核转录因子早期生长反应因子-1(early growth respons factor 1, Egr-1)的结合活性变化。结果外源性bFGF可以保护胞外信号调节激酶MEK-ERK信号通路蛋白不被氧自由基降解。MEK-ERK信号通路在外源性bFGF作用后活化。这一信号通路进一步使Egr-1结合活性升高。结论外源性bFGF可能通过激活ERK信号通路,促进内源性转录因子Egr-1的结合活性升高,进而促进内源性bFGF的表达。     

MAPK/ERK激酶-ERK信号通路参与外源性bFGF对缺氧-复氧损伤后星形胶质细胞内Egr-1结合活性的调节

目的 静脉注射碱性成纤维细胞生长因子（basic fibroblast growth factor,bFGF）可以明显降低实验性脑缺血大鼠的脑梗死面积,但该作用的分子机制尚不清楚。本文旨在研究外源性bFGF 作用的信号转导通路。方法缺氧-复氧损伤星形胶质细胞。Western blot检测外源性bFGF作用后丝裂原活化蛋白激酶/细胞外信号调节激酶激酶（mitogen-activated protein kinase/extracellular signal-regulated kinase kinase,MEK）-细胞外信号调节激酶（extracellular signal-regulated kinase, ERK） 信号通路活化。电泳变动迁移率分析实验检测外源性bFGF 作用后核转录因子早期生长反应因子-1（early growth respons factor 1, Egr-1）的结合活性变化。结果外源性bFGF可以保护胞外信号调节激酶MEK-ERK信号通路蛋白不被氧自由基降解。MEK-ERK信号通路在外源性bFGF作用后活化。这一信号通路进一步使Egr-1结合活性升高。结论外源性bFGF可能通过激活ERK信号通路,促进内源性转录因子Egr-1的结合活性升高,进而促进内源性bFGF的表达。     

Modulation of glial activation by astrocyte-derived protein S100B: differential responses of astrocyte and microglial cultures

The astrocyte-derived protein S100B stimulates production of inducible nitric oxide synthase and nitric oxide (NO) in astrocytes [Hu et al., 1996, J. Biol. Chem. 271:2543], but its effect on microglia is not known. In addition, S100B's ability to modulate the activity of other glial activating agents has not been defined. In this study, we compared the ability of S100B to stimulate NO in cultures of rat primary astrocytes and the BV-2 murine microglial cell line, and investigated the effect of the combined action of S100B and other stimuli known to activate glial cells. S100B itself stimulated the production of NO in astrocytes, and did not modify or potentiated only weakly the NO production induced by interleukin-1 beta, tumor necrosis factor alpha, dibutyryl cyclic AMP, zymosan A or lipid A. In contrast, S100B alone did not induce NO in BV-2 cells but strongly potentiated NO production in the presence of lipid A but not zymosan A. The deletion of eight C-terminal amino acid residues in S100B leads to a loss of the effect of S100B on microglia but not on astrocytes. These results demonstrate that responses of glial cells to extracellular S100B can vary depending on the cell type, and suggest that different structural features of S100B are important for the protein's effects on microglia and astrocytes.     

Simvastatin and atorvastatin facilitates amyloid β‐protein degradation in extracellular spaces by increasing neprilysin secretion from astrocytes through activation of MAPK/Erk1/2 pathways

One of the major neuropathological hallmarks of Alzheimer's disease (AD) is the deposition of amyloid β‐protein (Aβ) in the brain. Aβ accumulation seems to arise from an imbalance between Aβ production and clearance. Neprilysin (NEP) and insulin‐degrading enzyme (IDE) are the important Aβ‐degrading enzymes in the brain, and deficits in their expression may promote Aβ deposition in patients with sporadic late‐onset AD. Statins, which are used clinically for reducing cholesterol levels, can exert beneficial effects on AD. Therefore, we examined whether various statins are associated with Aβ degradation by inducing NEP and IDE expression, and then evaluating the relation between activation of intracellular signaling transduction, inhibition of cholesterol production, and morphological changes to astrocytes. Treating cultured rat astrocytes with simvastatin and atorvastatin significantly decreased the expression of NEP but not IDE in a concentration‐ and time‐dependent manner. The decrease in NEP expression was a result of activation of extracellular signal‐regulated kinase (ERK) but not the reduction of cholesterol synthesis pathway. This NEP reduction was achieved by the release to the extracellular space of cultured astrocytes. Furthermore, the cultured medium prepared from simvastatin‐ and atorvastatin‐treated astrocytes significantly induced the degradation of exogenous Aβ. These results suggest that simvastatin and atorvastatin induce the increase of Aβ degradation of NEP on the extracellular of astrocytes by inducing ERK‐mediated pathway activity and that these reagents regulate the differential mechanisms between the secretion of NEP, the induction of cholesterol reduction, and the morphological changes in the cultured astrocytes. GLIA 2016;64:952–962     

Cultured astrocyte proliferation induced by extracellular guanosine involves endogenous adenosine and is raised by the co-presence of microglia

Extracellular adenosine (Ado) and ATP stimulate astrocyte proliferation through activation of P(1) and P(2) purinoceptors. Extracellular GTP and guanosine (Guo), however, that do not bind strongly to these receptors, are more effective mitogens than ATP and Ado. Exogenous Guo, like GTP and 5'-guanosine-betagamma-imidotriphosphate (GMP-PNP), dose-dependently stimulated proliferation of rat cultured astrocytes; potency order GMP-PNP > GTP > or = Guo. The mitogenic effect of Guo was independent of the extracellular breakdown of GTP to Guo, because GMP-PNP, a GTP analogue resistant to hydrolysis, was the most mitogenic. In addition to a direct effect on astrocytes, Guo exerts its proliferative activity involving Ado. Exogenous Guo, indeed, enhanced the extracellular levels of endogenous Ado assayed by HPLC in the medium of cultured astrocytes. Culture pretreatment with Ado deaminase (ADA), that converts Ado into inosine, reduced but did not abolish Guo-induced astrocyte proliferation whereas erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), that inhibits ADA activity, amplified Guo effect. Moreover, the mitogenic activity of Guo was partly inhibited by 8-cyclopentyl-1,3-dipropylxanthine and alloxazine, antagonists of Ado A(1) and A(2B) receptors, respectively. Also microglia seem to be a target for the action of Guo. Indeed, the mitogenic effect of Guo on astrocytes was: i) increased proportionally to the number of microglial cells present in the astrocyte cultures; ii) amplified when purified cultures of astrocytes were supplemented with conditioned medium deriving from Guo-pretreated microglial cultures. These data indicate that the mitogenic effects exerted by exogenous Guo on rat astrocytes are mediated via complex mechanisms involving extracellular Ado and microglia-derived soluble factors.     

Brain-derived neurotrophic factor-mediated neuroprotection of adult rat retinal ganglion cells in vivo does not exclusively depend on phosphatidyl-inositol-3'-kinase/protein kinase B signaling.

The neurotrophin brain-derived neurotrophic factor (BDNF) serves as a survival, mitogenic, and differentiation factor in both the developing and adult CNS and PNS. In an attempt to identify the molecular mechanisms underlying BDNF neuroprotection, we studied activation of two potentially neuroprotective signal transduction pathways by BDNF in a CNS trauma model. Transection of the optic nerve (ON) in the adult rat induces secondary death of retinal ganglion cells (RGCs). Repeated intraocular injections of BDNF prevent the degeneration of RGCs 14 d after ON lesion most likely by inhibition of apoptosis. Here, we report that BDNF activates both protein kinase B (PKB) via a phosphatidyl-inositol-3'-kinase (PI-3-K)-dependent mechanism and the mitogen-activated protein kinases extracellular signal-regulated kinase 1 (ERK1) and ERK2. Furthermore, we provide evidence that BDNF suppresses cleavage and enzymatic activity of the neuronal cell death effector caspase-3. Distinct from our recent study in which inhibition of the PI-3-K/PKB pathway attenuated the survival-promoting action of insulin-like growth factor-I on axotomized RGCs (Kermer et al., 2000), it does not in the case of BDNF. Thus, we assume that BDNF does not depend on a single signal transduction pathway exerting its neuroprotective effects on lesioned CNS neurons.     

ATP-evoked calcium signal stimulates protein phosphorylation/dephosphorylation in astrocytes.

Extracellular adenosine 5'-triphosphate (ATP)-evoked increases in intracellular calcium and the consequent stimulation of calcium-mediated protein phosphorylation systems were investigated in primary cultures of rat cerebral cortical astrocytes. Measurement of calcium responses in fura-2-loaded astrocytes indicated that extracellular ATP stimulated a transient calcium peak followed by a sustained increase in intracellular calcium which declined to baseline when external calcium was removed, thereby indicating that ATP evokes mobilization of internal calcium as well as influx of external calcium. Protein phosphorylation studies revealed that application of extracellular ATP resulted in increased phosphorylation of 55 and 52 kDa proteins (4-fold and 2-fold, respectively) and decreased phosphorylation of 24 and 21 kDa proteins (approximately 50% for each protein). These effects were time- and dose-dependent. The changes in phosphate incorporation were (a) inhibited by lanthanum, (b) reduced when calcium was omitted from the bath and (c) mimicked by ionomycin, thus suggesting that the ATP-induced changes in protein phosphorylation were dependent on increased levels of intracellular calcium. Adenosine diphosphate (ADP) gave similar, but reduced, effects while adenosine and guanosine triphosphate (GTP) were ineffective, findings consistent with activation of P2 purinergic receptors. The 52 kDa protein co-migrated with glial fibrillary acidic protein. These results support the premise that calcium-dependent protein kinases and phosphatases are transducing elements for the calcium signal brought about by activation of P2 purinergic receptors in astrocytes. Since ATP is released from neurons and endothelial cells, this signal transduction mechanism may be an important component of neuronal- and endothelial-astrocytic communication.     

S100b counteracts effects of the neurotoxicant trimethyltin on astrocytes and microglia

Central nervous system degenerative diseases are often characterized by an early, strong reaction of astrocytes and microglia. Both these cell types can play a double role, protecting neurons against degeneration through the synthesis and secretion of trophic factors or inducing degeneration through the secretion of toxic molecules. Therefore, we studied the effects of S100B and trimethyltin (TMT) on human astrocytes and microglia with two glial models, primary cultures of human fetal astrocytes and a microglia cell line. After treatment with 10(-5) M TMT, astrocytes showed morphological alterations associated with an increase in glial fibrillary acidic protein (GFAP) expression and changes in GFAP filament organization. Administration of S100B before TMT treatment prevented TMT-induced changes in morphology and GFAP expression. A decrease in inducible nitric oxide synthase expression was observed in astrocytes treated with TMT, whereas the same treatment induced iNOS expression in microglia. In both cases, S100B prevented TMT-induced changes. Tumor necrosis factor-alpha mRNA expression in astrocytes was not modified by TMT treatment, whereas it was increased in microglia cells. S100B pretreatment blocked the TMT-induced increase in TNF-alpha expression in microglia. To trace the mechanisms involved in S100B activity, the effect of BAY 11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB) activation, and of PD98059, an inhibitor of MEK-ERK1/2, were investigated. Results showed that the protective effects of S100B against TMT toxicity in astrocytes depend on NF-kappaB, but not on ERK1/2 activation. These results might help in understanding the role played by glial cells in brain injury after exposure to chemical neurotoxicants and support the view that S100B may protect brain cells in case of injury. (c) 2005 Wiley-Liss, Inc.     

The extracellular signal-regulated kinase cascade suppresses amyloid beta protein-induced promotion of glutamate clearance in cultured rat cortical astrocytes

We have recently found that Alzheimer's disease amyloid beta protein (Abeta) activates the extracellular signal-regulated kinase (ERK) and promotes L-glutamate uptake in astrocytes. To elucidate the relationship between the Abeta-induced ERK phosphorylation and promotion of L-glutamate uptake, we investigated the effects of U0126 and PD98059, specific inhibitors of the ERK-activating enzyme MEK, in cultured rat cortical astrocytes. Abeta-induced ERK phosphorylation was completely blocked by the MEK inhibitors, while Abeta-induced promotion of extracellular L-glutamate clearance was enhanced by the presence of the MEK inhibitors. Abeta-induced increase of the glutamate transporter GLAST expression was also enhanced by the presence of MEK inhibitors. The effective concentrations of MEK inhibitors in enhancing Abeta-induced promotion of glutamate clearance and GLAST expression were consistent with those in blocking Abeta-induced ERK phosphorylation. These results suggest that the MEK/ERK signal functions to suppress Abeta-induced upregulation of a glutamate uptake system in astrocytes.     

Metastasis-associated mts1 (S100A4) protein is selectively expressed in white matter astrocytes and is up-regulated after peripheral nerve or dorsal root injury.

The S100 family of calcium binding proteins has been shown to be involved in a variety of physiological functions, such as regulation of enzyme function, cell motility, modification of extracellular matrix, and cell proliferation. Several members of the S100 family are expressed in the nervous system, but their functional roles are still largely obscure. The Mts1 gene codes for the S100A4 protein, which has been implicated in the control of cell proliferation and metastasis activity of tumor cells. We have used immunohistochemistry to examine the expression pattern of the Mts1 protein in the adult rat spinal cord and how this expression is influenced by peripheral nerve or dorsal root injury. Mts1 immunoreactivity (IR) was present only in white matter astrocytes in the intact spinal cord. Sciatic nerve as well as dorsal root injury induced a marked and prolonged up-regulation of Mts1-IR in astrocytes in the region of the dorsal funiculus containing the central processes of the injured primary sensory neurons. These findings suggest that Mts1 plays a unique physiological role in white matter astrocytes as well as in the response of astrocytes to degeneration of myelinated axons.     

Trophic actions of extracellular ATP: gene expression profiling by DNA array analysis

In addition to Professor Burnstock's work on the short-term signaling actions of extracellular nucleotides and nucleosides, Geoff has had a long-standing interest in trophic actions of purines in development and in pathophysiological conditions which has been instrumental in encouraging my work in this area. The trophic actions of extracellular ATP, alone or in combination with polypeptide growth factors, may play an important role in brain development and may contribute to the reactive gliosis that accompanies brain injury and neurodegeneration. P2Y receptors in astrocytes are coupled to the ERK/MAPK cascade, a signal transduction mechanism crucial for cellular proliferation and differentiation. The mitogenic signaling pathway from P2Y receptors to ERK involves phospholipase D and a calcium-independent PKC isoform, PKCdelta. DNA array analysis reveals a number of changes in gene expression after P2Y receptor occupancy, indicating that this methodology will be a powerful tool in understanding the mechanisms underlying the trophic actions of extracellular nucleotides and nucleosides.     

Gap junction inhibitors modulate S100B secretion in astrocyte cultures and acute hippocampal slices

Astrocytes sense, integrate, and respond to stimuli generated by neurons or neural injury; this response involves gap junction (GJ) communication. Neuronal vulnerability to injury increased when cocultures of astrocytes and neurons were exposed to GJ inhibitors. However, GJ uncoupling could limit the extension of a lesion. We investigated a possible link between GJ communication and S100B secretion. S100B is a calcium‐binding protein of 21 kDa that is predominantly expressed and secreted by astrocytes, which has trophic paracrine activity on neurite growth, glial proliferation, and neuronal survival. GJ inhibitors were analyzed in isolated astrocytes in primary cultures from hippocampus, acute hippocampal slices, and C6 glioma cells, which were used as a negative control. Our data indicate that GJ blocking stimulates S100B secretion in astrocyte cultures and acute hippocampal slices. Different assays were used to confirm cell integrity during exposure to GJ inhibitors. S100B secretion was observed with different types of GJ inhibitors; the resulting event was dependent on time, the nature of the inhibitor, its putative molecular target of GJ blocking, and/or the cell preparation used. Only carbenoxolone induced a fast and persistent increase in S100B secretion in both preparations. Endothelin‐1 increased S100B secretion in astrocyte cultures at 1 hr, but a decrease was observed at 6 hr or in acute hippocampal slices. Physiologically, a local GJ closure associated with release of S100B in injury conditions favors the idea of a common mechanism available to limit the extension of lesion and increase the chances of cell survival. © 2009 Wiley‐Liss, Inc.     

In vitro S100B secretion is reduced by apomorphine: effects of antipsychotics and antioxidants

Astrocytes express dopamine receptors and respond to dopamine stimulation. However, the role of astrocytes in psychiatric disorders and the effects of antipsychotics on astroglial cells have only been investigated recently. S100B is a glial-derived protein, commonly used as a marker of astroglial activation in psychiatric disorders, particularly schizophrenia. We investigated S100B secretion in three different rat brain preparations (fresh hippocampal slices, C6 glioma cells and primary astrocyte cultures) exposed to apomorphine and antipsychotics (haloperidol and risperidone), aiming to evaluate, ex vivo and in vitro, whether dopamine activation and dopaminergic antagonists modulate astroglial activation, as measured by changes in the extracellular levels of S100B. The serum S100B elevation observed in schizophrenic patients is not reflected by the in vitro decrease of S100B secretion that we observed in hippocampal slices, cortical astrocytes and C6 glioma cells treated with apomorphine, which mimics dopaminergic hyperactivation. This decrease in S100B secretion can be explained by a stimulation of D2 receptors negatively coupled to adenyl cyclase. Antipsychotic medications and antioxidant supplementation were able to prevent the decline in S100B secretion. Findings reinforce the benefits of antioxidant therapy in psychiatric disorders. Based on our results, in hippocampal slices exposed to apomorphine, it may be suggested that antipsychotics could help to normalize S100B secretion by astrocytes.     

Differential activation of mitogen-activated protein kinase pathways after traumatic brain injury in the rat hippocampus.

Mitogen-activated protein kinases, which play a crucial role in signal transduction, are activated by phosphorylation in response to a variety of mitogenic signals. In the present study, the authors used Western blot analysis and immunohistochemistry to show that phosphorylated extracellular signal-regulated protein kinase (p-ERK) and c-Jun NH2-terminal kinase (p-JNK), but not p38 mitogen-activated protein kinase, significantly increased in both the neurons and astrocytes after traumatic brain injury in the rat hippocampus. Different immunoreactivities of p-ERK and p-JNK were observed in the pyramidal cell layers and dentate hilar cells immediately after traumatic brain injury. Immunoreactivity for p-JNK was uniformly induced but was only transiently induced throughout all pyramidal cell layers. However, strong immunoreactivity for p-ERK was observed in the dentate hilar cells and the damaged CA3 neurons, along with the appearance of pyknotic morphologic changes. In addition, immunoreactivity for p-ERK was seen in astrocytes surrounding dentate and CA3 pyramidal neurons 6 hours after traumatic brain injury. These findings suggest that ERK and JNK but not p38 cascades may be closely involved in signal transduction in the rat hippocampus after traumatic brain injury.     

Role of intracellular S100A4 for migration of rat astrocytes

S100A4 is a member of the EF-hand family of calcium-binding proteins, first identified in tumor cells, and implicated in tumor invasion and metastasis. Intracellular upregulation of S100A4 is associated with increased motility of tumor cells. Extracellular application of S100A4 increases the motility of glioma cells in vitro. We showed previously that astrocytes in spinal cord and brain white matter also express S100A4. This expression is markedly increased in reactive white matter astrocytes after injury. Here, we have explored how changes in intracellular S100A4 affect migration of astrocytes. We produced cultures of white matter, S100A4 expressing astrocytes, and developed a small interfering (si) RNA approach to specifically eliminate S100A4 expression in these cells, and compared the migration of astrocytes expressing S100A4 with astrocytes transfected with S100A4 siRNA. As a "positive control" we used S100A4 expressing C6 glioma cells. In contrast to malignant cells, S100A4 expressing astrocytes increased their migration capacity after S100A4 siRNA treatment. At the same time, and in parallel with increased migration, white matter astrocytes increased their expression of metalloproteinases MMP-9 and MT1-MMP. The addition of MMP-2/MMP-9 inhibitor resulted in a significant inhibition of migration in S100A4 siRNA-treated astrocytes. These findings indicate that S100A4 has a stabilizing function in reactive white matter astrocytes, a function that may contribute to the development of a rigid, growth-inhibitory glial scar.