Astrogliosis in culture: I. The model and the effect of antisense oligonucleotides on glial fibrillary acidic protein synthesis

Targeting reactive astrocytes by pH-responsive ligand-bonded polymeric nanoparticles in spinal cord injury

In spinal cord injuries, axonal regeneration decreases with the activation of astrocytes followed by glial scar formation. Targeting reactive astrocytes has been recently performed by unsafe viral vectors to inhibit gliosis. In the current study, biocompatible polymeric nanoparticles were selected as an alternative for viruses to target reactive astrocytes for further drug/gene delivery applications. Lipopolysaccharide-bonded chitosan-quantum dots/poly acrylic acid nanoparticles were prepared by ionic gelation method to target reactive astrocytes both in vitro and in spinal cord-injured rats. Owing to their biocompatibility and pH-responsive behavior, chitosan and poly acrylic acid were the main components of nanoparticles. Nanoparticles were then chemically labeled with quantum dots to track the cell uptake and electrostatically interacted with lipopolysaccharide as a targeting ligand. In vitro and in vivo studies were performed in triplicate and all data were expressed as the mean ± the standard error of the mean. Smart nanoparticles with optimum size (61.9 nm) and surface charge (+ 12.5 mV) successfully targeted primary reactive astrocytes extracted from the rat cerebral cortex. In vitro studies represented high cell viability (96%) in the exposure of biocompatible nanoparticles. The pH-responsive behavior of nanoparticles was proved by their internalization into the cell's nuclei due to the swelling and endosomal escape of nanoparticles in acidic pH. In vivo studies demonstrated higher transfection of nanoparticles into reactive astrocytes compared to the neurons. pH-responsive ligand-bonded chitosan-based nanoparticles are good alternatives for viral vectors in targeted delivery applications for the treatment of spinal cord injuries.

Depleted histone deacetylase 3 or restored microRNA-19b-1-5p facilitates recovery of spinal cord injury via inactivating JAK2/STAT3 signaling pathway

We intended to discuss the influence of histone deacetylase 3 (HDAC3) on spinal cord injury (SCI) by regulating microRNA-19b-1-5p (miR-19b-1-5p) and janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway. In a rat model, the role of HDAC3 and miR-19b-1-5p in SCI was identified through detecting motor function, serum inflammation, pathological damage, cell apoptosis and GFAP expression. Also, by measuring GFAP expression and migration of spinal cord astrocytes, the effects of HDAC3 and miR-19b-1-5p in SCI were identified in vitro. Restoration of miR-19b-1-5p or depletion of HDAC3 attenuated motor function, inflammation, pathological damage and apoptosis, and reduced GFAP expression in the spinal cord tissue of SCI rats. Up-regulating miR-19b-1-5p or down-regulating HDAC3 decreased migration and GFAP expression of injured astrocytes. Our study presents that down-regulated HDAC3 can facilitate the recovery of SCI via inhibiting the activation of JAK2/STAT3 pathway by up-regulating miR-19b-1-5p.

GFAP at 50

Fifty years have passed since the discovery of glial fibrillary acidic protein (GFAP) by Lawrence Eng and colleagues. Now recognized as a member of the intermediate filament family of proteins, it has become a subject for study in fields as diverse as structural biology, cell biology, gene expression, basic neuroscience, clinical genetics and gene therapy. This review covers each of these areas, presenting an overview of current understanding and controversies regarding GFAP with the goal of stimulating continued study of this fascinating protein.

Resveratrol Protects Optic Nerve Head Astrocytes from Oxidative Stress-Induced Cell Death by Preventing Caspase-3 Activation, Tau Dephosphorylation at Ser422 and Formation of Misfolded Protein Aggregates

Optic nerve head astrocytes (ONHAs) are the major cell type within the optic nerve head, providing both structural and nutrient support to the optic nerve. Astrocytes are necessary for the survival of neurons with controlled activation of astrocytes being beneficial to neurons. However, overactive astrocytes can be harmful and the loss of normal astrocyte function can be a primary contributor to neurodegeneration. The neuroprotective properties of reactive astrocytes can be lost or they might gain neurotoxic properties in neurodegenerative diseases. The activated astrocytes are crucial in the development of glaucoma, where they serve as a source for cytotoxic substances that participate in ganglion apoptosis. There is increasing evidence indicating that neuroinflammation is an important process in glaucoma. Under pathological conditions, astrocytes can induce an inflammatory response. Extensive evidence shows that inflammatory responses mediated by astrocytes can also influence pathology development, synapse health, and neurodegeneration. The elimination of activated astrocytes by apoptosis is also expected in unfavorable conditions. In neurodegenerative diseases, a common feature is the presence of aggregates found in astrocytes, which can disrupt astrocyte function in such a way as to be detrimental to the viability of neurons. The biological processes involved in vision loss in glaucoma are not well understood. Despite the rapid advances in our understanding of optic nerve head (ONH) structure and function, numerous potential contributions of the ONHAs to optic nerve damage remain unanswered. The present study investigated the role of ONHAs during oxidative stress in order to determine novel cell biological processes underlying glaucoma pathogenesis. ONHAs were exposed to chemically induced oxidative stress using tert-butyl hydroperoxide (tBHP) in order to model extracellular oxidative stress as it occurs in the glaucomatous retina and ONH. In order to determine the impact of an intervention approach employing potential glioprotective treatments for central nervous system tissue we pretreated cells with the polyphenolic phytostilbene and antioxidant trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene). ONHAs exposed to tBHP-mediated oxidative stress displayed decreased viability and underwent apoptosis. In addition, increased levels of activated caspases, dephosphorylation of Tau protein at Ser422, an important site adjacent to the caspase cleavage site controlling Tau cleavage, caspase-mediated Tau cleavage, and cytoskeletal changes, specifically formation of neurofibrillary tangles (NFTs) were detected in ONHAs undergoing oxidative stress. When cells were pretreated with resveratrol cell viability increased along with a significant decrease in activated caspases, cleaved Tau, and NFT formation. Taken together, ONHAs appear to act similar to neurons when undergoing oxidative stress, where proteolytic cleavage of Tau by caspases leads to NFT formation. In addition, resveratrol appears to have promise as a potential protective treatment preventing ONHA dysfunction and degeneration. There is currently no cure for glaucoma or a neuro- and glioprotective treatment that directly targets the pathogenic mechanisms in the glaucomatous retina and optic nerve. The present study identified a potential mechanism underlying degeneration of astrocytes that is susceptible to pharmaco-therapeutic intervention in the eye and potentially elsewhere in the central nervous system. Identification of such mechanisms involved in glaucoma and other disorders of the eye and brain is critical to determine novel targets for effective therapies.

Effects of Mitofusin2 on astrocytes proliferation in vitro induced by scratch injury

Reactive astrogliosis, a common phenomenon after central nervous system (CNS) injury, exerts negative effects on neuronal repair and recovery by forming a glial scar. Mitofusin2 (Mfn2), a hyperplasia suppression gene, is a potential target of therapeutics to better control astrogliosis. To simulate traumatic injury of the CNS in vivo, an in vitro scratch injury model was established to investigate the role of Mfn2 in the proliferation of astrocytes in this study. We demonstrated that scratch-injury stimulation upregulated the expression of the markers cyclin D1, PCNA and GFAP and turned quiescent astrocytes into mitotic cells, which may have been via activation of Ras-Raf1-ERK1/2 and PI3K-Akt signaling. Meanwhile, both the gene and protein of Mfn2 were markedly inhibited. Furthermore, overexpression of Mfn2 effectively attenuated astrocyte proliferation and halted the cell cycle, concomitant with marker downregulation and wound healing suppression. Our results demonstrate that overexpression of Mfn2 inhibits the reactive astrogliosis process by blocking the Raf1-ERK1/2 and PI3K-Akt signal pathways. Therapeutic approaches that target Mfn2 may have protective effects against reactive gliosis and glia formation.

Resveratrol Downregulates STAT3 Expression and Astrocyte Activation in Primary Astrocyte Cultures of Rat

Astrocytes respond to all forms of central nervous system (CNS) insults by a process referred to as reactive astrogliosis. Inhibition of astrocyte growth and activation is an important strategy for promoting injured CNS repair. STAT3 (signal transducer and activator of transcription 3) is reported to be a critical regulator of astrogliosis, and resveratrol (RES, a dietary polyphenol) is considered to be a natural inhibitor of STAT3 expression and phosphorylation. In this study, we investigated the effects of RES on STAT3 expression and phosphorylation, and then on the proliferation and activation of astrocytes, a critical process in reactive astrogliosis, in rat primary cultured astrocytes and an in vitro scratch-wound model. RES downregulated the expression levels of STAT3, P-STAT3 and GFAP (glial fibrillary acidic protein) in cultured astrocytes. The positive index of Ki67 was apparently reduced in cultured astrocytes after RES treatment. Meanwhile, cultured astrocyte proliferation and activation were attenuated by RES. Moreover, in the established in vitro scratch-wound model the increased expression levels of STAT3, P-STAT3 and GFAP induced by scratching injury were also clearly inhibited by RES. In addition, the inhibitory effect of RES on cell proliferation was similar to that of AG490 (a selective inhibitor of STAT3 phosphorylation) and abrogated by Colivelin (a STAT3 activator) stimuli. Taken together, our data suggest that RES is able to inhibit reactive astrocyte proliferation and activation mainly via deactivating STAT3 pathway. So RES may have a therapeutic benefit for the treatment of the injured CNS.

Hydrogen sulfide protects against cell damage through modulation of PI3K/Akt/Nrf2 signaling

Hydrogen sulfide as the third endogenous gaseous mediator had protective effects against traumatic brain injury-induced neuronal damage in mice. However, the exact pathophysiological mechanism underlying traumatic brain injury is complicated and the protective role of H₂S is not yet fully known. Therefore, we combined the mechanical injury (scratch) with secondary injury including metabolic impairment (no glucose) together to investigate the underlying cellular mechanism of hydrogen sulfide in vitro models of traumatic brain injury. In the present study, we found that H₂S could prevent the scratch-induced decrease in the expression of cystathionine-β-synthetase, a key enzyme involved in the source of hydrogen sulfide, and endogenous hydrogen sulfide generation in PC12 cells. We also found that hydrogen sulfide could prevent scratch-induced cellular injury, alteration of mitochondrial membrane potential, intracellular accumulation of reactive oxygen species and cell death (autophagic cell death and apoptosis) in PC12 cells. It was also found that blocking PI3K/AKT pathway by LY294002, abolished the protection of H₂S against scratch-induced cellular reactive oxygen species level and NRF2 accumulation and function in the nucleus. These results suggest that hydrogen sulfide protects against cell damage induced by scratch injury through modulation of the PI3K/Akt/Nrf2 pathway. This study raises the possibility that hydrogen sulfide may have therapeutic efficacy in traumatic brain injury.

Predicting Reactive Astrogliosis Propagation by Bayesian Computational Modeling: the Repeater Stations Model

Reactive astrogliosis occurs upon focal brain injury and in neurodegenerative diseases. The mechanisms that propagate reactive astrogliosis to distal parts of the brain, in a rapid wave that activates astrocytes and other cell types along the way, are not completely understood. It is proposed that damage-associated molecular patterns (DAMP) released by necrotic cells from the injury core have a major role in the reactive astrogliosis initiation but whether they also participate in reactive astrogliosis propagation remains to be determined. We here developed a Bayesian computational model to define the most probable model for reactive astrogliosis propagation. Starting with experimental data from GFAP-immunostained reactive astrocytes, we defined five types of astrocytes based on morphometrical cues and registered the position of each reactive astrocyte cell type in the hemisphere ipsilateral to the injured site after 3 and 7 days post-ischemia. We developed equations for the changes in DAMP concentration (due to diffusion, binding to receptors or degradation), soluble mediators secretion, and for the evolution reactive astrogliosis. We tested four predefined models based on abovementioned previous hypothesis and modifications to it. Our results showed that DAMP diffusion alone has not justified the reactive astrogliosis propagation as previously assumed. Only two models succeeded in accurately reproducing the experimentally measured data and they highlighted the role of microglia and the glial secretion of soluble mediators to sustain the reactive signal and activating neighboring astrocytes. Thus, our in silico analysis proposes that glial cells behave as repeater stations of the injury signal in order to propagate reactive astrogliosis.

In vitro model of the glial scar

The trauma of central nervous system (CNS) can lead to glial scar, and it can limit the regeneration of neurons at the injured area, which is considered to be a major factor affecting the functional recovery of patients with CNS injury. At present, the study of the glial scar model in vitro is still limited to two-dimensional culture, and the state of the scar in vivo cannot be well mimicked. Therefore, we use a collagen gel and astrocytes to construct a three-dimensional (3D) model in vitro to mimic natural glial scar tissue. The effects of concentration changes of astrocytes on cell morphology, proliferation, and tissue performance were investigated. After 8 days of culture in vitro, the results showed that the tissue model contracted, with a measured shrinkage rate of 4.5%, and the compressive elastic modulus increased to nearly 4 times. Moreover, the astrocytes of the 3D tissue model have the ability of proliferation, hyperplasia, and formation of scar clusters. It indicates that the model we constructed has the characteristics of glial scar tissue to some extent and can provide an in vitro model for the research of glial scar and brain diseases.

Live Imaging Followed by Single Cell Tracking to Monitor Cell Biology and the Lineage Progression of Multiple Neural Populations

Understanding the mechanisms that control critical biological events of neural cell populations, such as proliferation, differentiation, or cell fate decisions, will be crucial to design therapeutic strategies for many diseases affecting the nervous system. Current methods to track cell populations rely on their final outcomes in still images and they generally fail to provide sufficient temporal resolution to identify behavioral features in single cells. Moreover, variations in cell death, behavioral heterogeneity within a cell population, dilution, spreading, or the low efficiency of the markers used to analyze cells are all important handicaps that will lead to incomplete or incorrect read-outs of the results. Conversely, performing live imaging and single cell tracking under appropriate conditions represents a powerful tool to monitor each of these events. Here, a time-lapse video-microscopy protocol, followed by post-processing, is described to track neural populations with single cell resolution, employing specific software. The methods described enable researchers to address essential questions regarding the cell biology and lineage progression of distinct neural populations.

The Unwanted Cell Migration in the Brain: Glioma Metastasis

Cell migration is identified as a highly orchestrated process. It is a fundamental and essential phenomenon underlying tissue morphogenesis, wound healing, and immune response. Under dysregulation, it contributes to cancer metastasis. Brain is considered to be the most complex organ in human body containing many types of neural cells with astrocytes playing crucial roles in monitoring both physiological and pathological functions. Astrocytoma originates from astrocytes and its most malignant type is glioblastoma multiforme (WHO Grade IV astrocytoma), which is capable to infiltrate widely into the neighboring brain tissues making a complete resection of tumors impossible. Very recently, we have reviewed the mechanisms for astrocytes in migration. Given the fact that astrocytoma shares many histological features with astrocytes, we therefore attempt to review the mechanisms for glioma cells in migration and compare them to normal astrocytes, hoping to obtain a better insight into the dysregulation of migratory mechanisms contributing to their metastasis in the brain.

Interactions between Sirt1 and MAPKs regulate astrocyte activation induced by brain injury in vitro and in vivo

Background

Astrocyte activation is a hallmark of traumatic brain injury resulting in neurological dysfunction or death for an overproduction of inflammatory cytokines and glial scar formation. Both the silent mating type information (Sirt1) expression and mitogen-activated protein kinase (MAPK) signal pathway activation represent a promising therapeutic target for several models of neurodegenerative diseases. We investigated the potential effects of Sirt1 upregulation and MAPK pathway pharmacological inhibition on astrocyte activation in vitro and in vivo. Moreover, we attempted to confirm the underlying interactions between Sirt1 and MAPK pathways in astrocyte activation after brain injury.

Methods

The present study employs an interleukin-1β (IL-1β) stimulated primary cortical astrocyte model in vitro and a nigrostriatal pathway injury model in vivo to mimic the astrocyte activation induced by traumatic brain injury. The activation of GFAP, Sirt1, and MAPK pathways were detected by Western blot; astrocyte morphological hypertrophy was assessed using immunofluorescence staining; in order to explore the neuroprotective effect of regulation Sirt1 expression and MAPK pathway activation, the motor and neurological function tests were assessed after injury.

Results

GFAP level and morphological hypertrophy of astrocytes are elevated after injury in vitro or in vivo. Furthermore, the expressions of phosphorylated extracellular regulated protein kinases (p-ERK), phosphorylated c-Jun N-terminal kinase (p-JNK), and phosphorylated p38 activation (p-p38) are upregulated, but the Sirt1 expression is downregulated. Overexpression of Sirt1 significantly increases the p-ERK expression and reduces the p-JNK and p-p38 expressions. Inhibition of ERK, JNK, or p38 activation respectively with their inhibitors significantly elevated the Sirt1 expression and attenuated the astrocyte activation. Both the overproduction of Sirt1 and inhibition of ERK, JNK, or p38 activation can alleviate the astrocyte activation, thereby improving the neurobehavioral function according to the modified neurological severity scores (mNSS) and balance latency test.

Conclusions

Thus, Sirt1 plays a protective role against astrocyte activation, which may be associated with the regulation of the MAPK pathway activation induced by brain injury in vitro and in vivo.

Astrocytes in Migration

Cell migration is a fundamental phenomenon that underlies tissue morphogenesis, wound healing, immune response, and cancer metastasis. Great progresses have been made in research methodologies, with cell migration identified as a highly orchestrated process. Brain is considered the most complex organ in the human body, containing many types of neural cells with astrocytes playing crucial roles in monitoring normal functions of the central nervous system. Astrocytes are mostly quiescent under normal physiological conditions in the adult brain but become migratory after injury. Under most known pathological conditions in the brain, spinal cord and retina, astrocytes are activated and become hypertrophic, hyperplastic, and up-regulating GFAP based on the grades of severity. These three observations are the hallmark in glia scar formation-astrogliosis. The reactivation process is initiated with structural changes involving cell process migration and ended with cell migration. Detailed mechanisms in astrocyte migration have not been studied extensively and remain largely unknown. Here, we therefore attempt to review the mechanisms in migration of astrocytes.

A Model of Glial Scarring Analogous to the Environment of a Traumatically Injured Spinal Cord Using Kainate

OBJECTIVE

To develop an in vitro model analogous to the environment of traumatic spinal cord injury (SCI), the authors evaluated change of astrogliosis following treatments with kainate and/or scratch, and degree of neurite outgrowth after treatment with a kainate inhibitor.

METHODS

Astrocytes were obtained from the rat spinal cord. Then, 99% of the cells were confirmed to be GFAP-positive astrocytes. For chemical injury, the cells were treated with kainate at different concentrations (10, 50 or 100 µM). For mechanical injury, two kinds of uniform scratches were made using a plastic pipette tip by removing strips of cells. For combined injury (S/K), scratch and kainate were provided. Cord neurons from rat embryos were plated onto culture plates immediately after the three kinds of injuries and some cultures were treated with a kainate inhibitor.

RESULTS

Astro-gliosis (glial fibrillary acidic protein [GFAP], vimentin, chondroitin sulfate proteoglycan [CSPG], rho-associated protein kinase [ROCK], and ephrin type-A receptor 4 [EphA4]) was most prominent after treatment with 50 µM kainate and extensive scratch injury in terms of single arm (p<0.001) and in the S/K-induced injury model in view of single or combination (p<0.001). Neurite outgrowth in the seeded spinal cord (β-III tubulin) was the least in the S/K-induced injury model (p<0.001) and this inhibition was reversed by the kainate inhibitor (p<0.001).

CONCLUSION

The current in vitro model combining scratch and kainate induced glial scarring and inhibitory molecules and restricted neurite outgrowth very strongly than either the mechanically or chemically-induced injury model; hence, it may be a useful tool for research on SCI.

L-type voltage-operated calcium channels contribute to astrocyte activation In vitro

We have found a significant upregulation of L-type voltage-operated Ca(++) channels (VOCCs) in reactive astrocytes. To test if VOCCs are centrally involved in triggering astrocyte reactivity, we used in vitro models of astrocyte activation in combination with pharmacological inhibitors, siRNAs and the Cre/lox system to reduce the activity of L-type VOCCs in primary cortical astrocytes. The endotoxin lipopolysaccharide (LPS) as well as high extracellular K(+) , glutamate, and ATP promote astrogliosis in vitro. L-type VOCC inhibitors drastically reduce the number of reactive cells, astrocyte hypertrophy, and cell proliferation after these treatments. Astrocytes transfected with siRNAs for the Cav1.2 subunit that conducts L-type Ca(++) currents as well as Cav1.2 knockout astrocytes showed reduce Ca(++) influx by ∼80% after plasma membrane depolarization. Importantly, Cav1.2 knock-down/out prevents astrocyte activation and proliferation induced by LPS. Similar results were found using the scratch wound assay. After injuring the astrocyte monolayer, cells extend processes toward the cell-free scratch region and subsequently migrate and populate the scratch. We found a significant increase in the activity of L-type VOCCs in reactive astrocytes located in the growing line in comparison to quiescent astrocytes situated away from the scratch. Moreover, the migration of astrocytes from the scratching line as well as the number of proliferating astrocytes was reduced in Cav1.2 knock-down/out cultures. In summary, our results suggest that Cav1.2 L-type VOCCs play a fundamental role in the induction and/or proliferation of reactive astrocytes, and indicate that the inhibition of these Ca(++) channels may be an effective way to prevent astrocyte activation. GLIA 2016. GLIA 2016;64:1396-1415.

Astrocyte-derived phosphatidic acid promotes dendritic branching

Astrocytes play critical roles in neural circuit formation and function. Recent studies have revealed several secreted and contact-mediated signals from astrocytes which are essential for neurite outgrowth and synapse formation. However, the mechanisms underlying the regulation of dendritic branching by astrocytes remain elusive. Phospholipase D1 (PLD1), which catalyzes the hydrolysis of phosphatidylcholine (PC) to generate phosphatidic acid (PA) and choline, has been implicated in the regulation of neurite outgrowth. Here we showed that knockdown of PLD1 selectively in astrocytes reduced dendritic branching of neurons in neuron-glia mixed culture. Further studies from sandwich-like cocultures and astrocyte conditioned medium suggested that astrocyte PLD1 regulated dendritic branching through secreted signals. We later demonstrated that PA was the key mediator for astrocyte PLD1 to regulate dendritic branching. Moreover, PA itself was sufficient to promote dendritic branching of neurons. Lastly, we showed that PA could activate protein kinase A (PKA) in neurons and promote dendritic branching through PKA signaling. Taken together, our results demonstrate that astrocyte PLD1 and its lipid product PA are essential regulators of dendritic branching in neurons. These results may provide new insight into mechanisms underlying how astrocytes regulate dendrite growth of neurons.

Decline in arylsulfatase B and Increase in chondroitin 4-sulfotransferase combine to increase chondroitin 4-sulfate in traumatic brain injury

In an established rat model of penetrating ballistic-like brain injury (PBBI), arylsulfatase B (ARSB; N-acetylgalactosamine 4-sulfatase) activity was significantly reduced at the ipsilateral site of injury, but unaffected at the contralateral site or in sham controls. In addition, the ARSB substrate chondroitin 4-sulfate (C4S) and total sulfated glycosaminoglycans increased. The mRNA expression of chondroitin 4-sulfotransferase 1 (C4ST1; CHST11) and the sulfotransferase activity rose at the ipsilateral site of injury (PBBI-I), indicating contributions from both increased production and reduced degradation to the accumulation of C4S. In cultured, fetal rat astrocytes, following scratch injury, the ARSB activity declined and the nuclear hypoxia inducible factor-1α increased significantly. In contrast, sulfotransferase activity and chondroitin 4-sulfotransferase expression increased following astrocyte exposure to TGF-β1, but not following scratch. These different pathways by which C4S increased in the cell preparations were both evident in the response to injury in the PBBI-I model. Hence, findings support effects of injury because of mechanical disruption inhibiting ARSB and to chemical mediation by TGF-β1 increasing CHST11 expression and sulfotransferase activity. The increase in C4S following traumatic brain injury is because of contributions from impaired degradation and enhanced synthesis of C4S which combine in the pathogenesis of the glial scar. This is the first report of how two mechanisms contribute to the increase in chondroitin 4-sulfate (C4S) in TBI. Following penetrating ballistic-like brain injury in a rat model and in the scratch model of injury in fetal rat astrocytes, Arylsulfatase B activity declined, leading to accumulation of C4S. TGF-β1 exposure increased expression of chondroitin 4-sulfotransferase. Hence, the increase in C4S in TBI is attributable to both impaired degradation and enhanced synthesis, combining in the pathogenesis of the glial scar.

Ttyh1 protein is expressed in glia in vitro and shows elevated expression in activated astrocytes following status epilepticus

In a previous study, we showed that Ttyh1 protein is expressed in neurons in vitro and in vivo in the form of punctuate structures, which are localized to neuropil and neuronal somata. Herein, we provide the first description of Ttyh1 protein expression in astrocytes, oligodendrocytes and microglia in vitro. Moreover, using double immunofluorescence, we show Ttyh1 protein expression in activated astrocytes in the hippocampus following amygdala stimulation-induced status epilepticus. We demonstrate that in migrating astrocytes in in vitro wound model Ttyh1 concentrates at the edges of extending processes. These data suggest that Ttyh1 not only participates in shaping neuronal morphology, as previously described, but may also play a role in the function of activated glia in brain pathology. To localize Ttyh1 expression in the cellular compartments of neurons and astrocytes, we performed in vitro double immunofluorescent staining using markers for the following subcellular structures: endoplasmic reticulum (GRP78), Golgi apparatus (GM130), clathrin-coated vehicles (clathrin), early endosomes (Rab5 and APPL2), recycling endosomes (Rab11), trans-Golgi network (TGN46), endoplasmic reticulum membrane (calnexin), late endosomes and lysosomes (LAMP1) and synaptic vesicles (synaptoporin and synaptotagmin 1). We found that Ttyh1 is present in the endoplasmic reticulum, Golgi apparatus and clathrin-coated vesicles (clathrin) in both neurons and astrocytes and also in late endosomes or lysosomes in astrocytes. The presence of Ttyh1 was negligible in early endosomes, recycling endosomes, trans-Golgi network, endoplasmic reticulum membrane and synaptic vesicles.

Voltage-gated sodium channel Nav 1.5 contributes to astrogliosis in an in vitro model of glial injury via reverse Na+ /Ca2+ exchange

Astrogliosis is a prominent feature of many, if not all, pathologies of the brain and spinal cord, yet a detailed understanding of the underlying molecular pathways involved in the transformation from quiescent to reactive astrocyte remains elusive. We investigated the contribution of voltage-gated sodium channels to astrogliosis in an in vitro model of mechanical injury to astrocytes. Previous studies have shown that a scratch injury to astrocytes invokes dual mechanisms of migration and proliferation in these cells. Our results demonstrate that wound closure after mechanical injury, involving both migration and proliferation, is attenuated by pharmacological treatment with tetrodotoxin (TTX) and KB-R7943, at a dose that blocks reverse mode of the Na(+) /Ca(2+) exchanger (NCX), and by knockdown of Nav 1.5 mRNA. We also show that astrocytes display a robust [Ca(2+) ]i transient after mechanical injury and demonstrate that this [Ca(2+) ]i response is also attenuated by TTX, KB-R7943, and Nav 1.5 mRNA knockdown. Our results suggest that Nav 1.5 and NCX are potential targets for modulation of astrogliosis after injury via their effect on [Ca(2+) ]i .

Traumatic scratch injury in astrocytes triggers calcium influx to activate the JNK/c-Jun/AP-1 pathway and switch on GFAP expression

Astrocyte activation is a hallmark of central nervous system injuries resulting in glial scar formation (astrogliosis). The activation of astrocytes involves metabolic and morphological changes with complex underlying mechanisms, which should be defined to provide targets for astrogliosis intervention. Astrogliosis is usually accompanied by an upregulation of glial fibrillary acidic protein (GFAP). Using an in vitro scratch injury model, we scratched primary cultures of cerebral cortical astrocytes and observed an influx of calcium in the form of waves spreading away from the wound through gap junctions. Using the calcium blocker BAPTA-AM and the JNK inhibitor SP600125, we demonstrated that the calcium wave triggered the activation of JNK, which then phosphorylated the transcription factor c-Jun to facilitate the binding of AP-1 to the GFAP gene promoter to switch on GFAP upregulation. Blocking calcium mobilization with BAPTA-AM in an in vivo stab wound model reduced GFAP expression and glial scar formation, showing that the calcium signal, and the subsequent regulation of downstream signaling molecules, plays an essential role in brain injury response. Our findings demonstrated that traumatic scratch injury to astrocytes triggered a calcium influx from the extracellular compartment and activated the JNK/c-Jun/AP-1 pathway to switch on GFAP expression, identifying a previously unreported signaling cascade that is important in astrogliosis and the physiological response following brain injury.

AQP5 is differentially regulated in astrocytes during metabolic and traumatic injuries

Water movement plays vital roles in both physiological and pathological conditions in the brain. Astrocytes are responsible for regulating this water movement and are the major contributors to brain edema in pathological conditions. Aquaporins (AQPs) in astrocytes play critical roles in the regulation of water movement in the brain. AQP1, 3, 4, 5, 8, and 9 have been reported in the brain. Compared with AQP1, 4, and 9, AQP3, 5, and 8 are less studied. Among the lesser known AQPs, AQP5, which has multiple functions identified outside the central nervous system, is also indicated to be involved in hypoxia injury in astrocytes. In our study, AQP5 expression could be detected both in primary cultures of astrocytes and neurons, and AQP5 expression in astrocytes was confirmed in 1- to 4-week old primary cultures of astrocytes. AQP5 was localized on the cytoplasmic membrane and in the cytoplasm of astrocytes. AQP5 expression was downregulated during ischemia treatment and upregulated after scratch-wound injury, which was also confirmed in a middle cerebral artery occlusion model and a stab-wound injury model in vivo. The AQP5 increased after scratch injury was polarized to the migrating processes and cytoplasmic membrane of astrocytes in the leading edge of the scratch-wound, and AQP5 over-expression facilitated astrocyte process elongation after scratch injury. Taken together, these results indicate that AQP5 might be an important water channel in astrocytes that is differentially expressed during various brain injuries.

S-nitrosoglutathione induces ciliary neurotrophic factor expression in astrocytes, which has implications to protect the central nervous system under pathological conditions

Accumulating evidence suggests that reactive astrogliosis has beneficial and detrimental outcomes in various CNS disorders, but the mechanism behind this dichotomy is unclear. Recent advances in this direction suggested that NO signaling is critical to regulate the outcomes of reactive astrogliosis in vivo. Using biochemical and genetic approaches, we here investigated the effect of S-nitrosoglutathione (GSNO; a physiological NO donor) in astrocytes in vitro settings. GSNO enhanced the expressions of glial fibrillary acidic protein and neurotrophic factors including ciliary neurotrophic factor (CNTF) in astrocytes in a dose-dependent manner. The enhanced CNTF expression in GSNO-treated astrocytes was ascribed to NO-mediated sGC/cGMP/PKG signaling. It was associated with p38 MAPK-dependent increased peroxisome proliferator-activated receptor-γ transactivation. In addition, the chromatin accessibility of peroxisome proliferator-activated receptor-γ accompanied with ATF2 and CREB (cAMP-response element-binding protein) was enhanced across the CNTF gene promoter in GSNO treated astrocytes. Interestingly, secreted CNTF was responsible for increased expression of glial fibrillary acidic protein in GSNO-treated astrocytes in an autocrine manner via a JAK2- and STAT3-dependent mechanism. In addition, CNTF secreted by GSNO-treated astrocytes enhanced the differentiation of immature oligodendrocytes in vitro. These effects of GSNO were consistent with an endogenously produced NO in astrocytes stimulated with proinflammatory cytokines in vitro. We conclude that NO signaling induces CNTF expression in astrocytes that favors the beneficial outcomes of reactive astrogliosis in vivo. Our data suggest that the endogenously produced NO or its exogenous source has potential to modulate the outcomes of reactive astrogliosis to protect CNS under pathological conditions.

Ethyl pyruvate promotes spinal cord repair by ameliorating the glial microenvironment

BACKGROUND AND PURPOSE

Spinal cord injury (SCI) triggers a series of endogenous processes, including neuroinflammation and reactive astrogliosis, which may contribute to the failure of neural regeneration and functional recovery. In the present study, the effect of ethyl pyruvate on spinal cord repair was explored.

EXPERIMENTAL APPROACH

Functional assessment and histological analyses of astrogliosis, neuroinflammation, neuronal survival and axonal regeneration were performed to investigate the effects of ethyl pyruvate (0.086, 0.215, 0.431 or 0.646 mmol·kg(-1) ·day(-1) ) on spinal cord repair in a rat model of SCI. The effect of ethyl pyruvate (5, 10 or 15 mM) on astrocytic activation was also evaluated in an in vitro'scratch-wound' model.

KEY RESULTS

Functional assessment showed evident improvement of behavioural functions in the ethyl pyruvate-treated rats. Reactive astrogliosis was significantly inhibited in vivo, after injection of ethyl pyruvate (0.431 mmol·kg(-1) day(-1) ), and in vitro'scratch-wound' model in the presence of 10 or 15 mM ethyl pyruvate. The difference between effective concentration in vitro and in vivo suggests that the inhibitory effect of ethyl pyruvate on astrogliosis in damaged spinal cord is indirect. In addition, ethyl pyruvate (0.431 mmol·kg(-1) day(-1) ) attenuated SCI-induced neuroinflammation; it decreased the Iba-1-, ED-1- and CD11b-positive cells at the lesion site. Importantly, histological analyses showed a significantly greater number of surviving neurons and regenerative axons in the ethyl pyruvate-treated rats.

CONCLUSIONS AND IMPLICATIONS

Ethyl pyruvate was shown to inhibit astrogliosis and neuroinflammation, promote neuron survival and neural regeneration, and improve the functional recovery of spinal cord, indicating a potential neuroprotective effect of ethyl pyruvate against SCI.

CD36 is involved in astrocyte activation and astroglial scar formation

Inflammation is an essential component for glial scar formation. However, the upstream mediator(s) that triggers the process has not been identified. Previously, we showed that the expression of CD36, an inflammatory mediator, occurs in a subset of astcotyes in the peri-infarct area where the glial scar forms. This study investigates a role for CD36 in astrocyte activation and glial scar formation in stroke. We observed that the expression of CD36 and glial fibrillary acidic protein (GFAP) coincided in control and injured astrocytes and in the brain. Furthermore, GFAP expression was attenuated in CD36 small interfering RNA transfected astrocytes or in the brain of CD36 knockout (KO) mice, suggesting its involvement in GFAP expression. Using an in-vitro model of wound healing, we found that CD36 deficiency attenuated the proliferation of astrocytes and delayed closure of the wound gap. Furthermore, stroke-induced GFAP expression and scar formation were significantly attenuated in the CD36 KO mice compared with wild type. These findings identify CD36 as a novel mediator for injury-induced astrogliosis and scar formation. Targeting CD36 may serve as a potential strategy to reduce glial scar formation in stroke.

Engineering an integrated cellular interface in three-dimensional hydrogel cultures permits monitoring of reciprocal astrocyte and neuronal responses

This study reports a new type of three-dimensional (3D) tissue model for studying interactions between cell types in collagen hydrogels. The aim was to create a 3D cell culture model containing separate cell populations in close proximity without the presence of a mechanical barrier, and demonstrate its relevance to modeling the axon growth-inhibitory cellular interfaces that develop in the central nervous system (CNS) in response to damage. This provides a powerful new tool to determine which aspects of the astroglial scar response and subsequent neuronal regeneration inhibition are determined by the presence of the other cell types. Astrocytes (CNS glia) and dissociated dorsal root ganglia (DRG; containing neurons and peripheral nervous system [PNS] glia) were seeded within collagen solution at 4 °C in adjacent chambers of a stainless steel mould, using cells cultured from wild-type or green fluorescent protein expressing rats, to track specific populations. The divider between the chambers was removed using a protocol that allowed the gels to integrate without mixing of the cell populations. Following setting of the gels, they were maintained in culture for up to 15 days. Reciprocal astrocyte and neuronal responses were monitored using confocal microscopy and 3D image analysis. At DRG:astrocyte interfaces, by 5 days there was an increase in the number of astrocytes at the interface followed by hypertrophy and increased glial fibrillary acidic protein expression at 10 and 15 days, indicative of reactive gliosis. Neurons avoided crossing DRG:astrocyte interfaces, and neuronal growth was restricted to the DRG part of the gel. By contrast, neurons were able to grow freely across DRG:DRG interfaces, demonstrating the absence of a mechanical barrier. These results show that in a precisely controlled 3D environment, an interface between DRG and astrocyte cultures is sufficient to trigger reactive gliosis and inhibition of neuronal regeneration across the interface. Different aspects of the astrocyte response could be independently monitored, providing an insight into the formation of a glial scar. This technology has wide potential for researchers wishing to maintain and monitor interactions between adjacent cell populations in 3D culture.

Time dependent neuroprotection of mycophenolate mofetil: effects on temporal dynamics in glial proliferation, apoptosis, and scar formation

Background

Immunosuppressants such as mycophenolate mofetil (MMF) have the capacity to inhibit microglial and astrocytic activation and to reduce the extent of cell death after neuronal injury. This study was designed to determine the effective neuroprotective time frame in which MMF elicits its beneficial effects, by analyzing glial cell proliferation, migration, and apoptosis.

Methods

Using organotypic hippocampal slice cultures (OHSCs), temporal dynamics of proliferation and apoptosis after N-methyl-D-aspartate (NMDA)-mediated excitotoxicity were analyzed by quantitative morphometry of Ki-67 or cleaved caspase-3 immunoreactive glial cells. Treatment on NMDA-lesioned OHSCs with mycophenolate mofetil (MMF)100 μg/mL was started at different time points after injury or performed within specific time frames, and the numbers of propidium iodide (PI)⁺ degenerating neurons and isolectin (I)B₄⁺ microglial cells were determined. Pre-treatment with guanosine 100 μmol/l was performed to counteract MMF-induced effects. The effects of MMF on reactive astrocytic scar formation were investigated in the scratch-wound model of astrocyte monolayers.

Results

Excitotoxic lesion induction led to significant increases in glial proliferation rates between 12 and 36 hours after injury and to increased levels of apoptotic cells between 24 and 72 hours after injury. MMF treatment significantly reduced glial proliferation rates without affecting apoptosis. Continuous MMF treatment potently reduced the extent of neuronal cell demise when started within the first 12 hours after injury. A crucial time-frame of significant neuroprotection was identified between 12 and 36 hours after injury. Pre-treatment with the neuroprotective nucleoside guanosine reversed MMF-induced antiproliferative effects on glial cells. In the scratch-wound model, gap closure was reached within 48 hours in controls, and was potently inhibited by MMF.

Conclusions

Our data indicate that immunosuppression by MMF significantly attenuates the extent of neuronal cell death when administered within a crucial time frame after injury. Moreover, long-lasting immunosuppression, as required after solid-organ transplantation, does not seem to be necessary. Targeting inosine 5-monophosphate dehydrogenase, the rate-limiting enzyme of purine synthesis, is an effective strategy to modulate the temporal dynamics of proliferation and migration of microglia and astrocytes, and thus to reduce the extent of secondary neuronal damage and scar formation.

Blood-borne metabolic factors in obesity exacerbate injury-induced gliosis

Reactive gliosis, a sign of neuroinflammation, has been observed in mice with adult-onset obesity as well as CNS injury. The hypothesis that obesity-derived metabolic factors exacerbate reactive gliosis in response to mechanical injury was tested here on cultured primary glial cells subjected to a well-established model of scratch wound injury. Cells treated with serum from mice with diet-induced obesity (DIO) showed higher immunoreactivity of CD11b (marker for microglia) and GFAP (marker for astrocytes), with morphological changes at both the injury border and areas away from the injury. The effect of DIO serum was greater than that of scratch injury alone. Leptin was almost as effective as DIO serum in inducing microgliosis and astrogliosis in a dose-response manner. By contrast, C-reactive protein (CRP) mainly induced microgliosis in noninjured cells; injury-induced factors appeared to attenuate this effect. The effect of CRP also differed from the effect of the antibiotic minocycline. Minocycline attenuated the microgliosis and to a lesser extent astrogliosis, particularly in CRP-treated cells, thus serving as a negative control. We conclude that blood-borne proinflammatory metabolic factors in obesity increase reactive gliosis and probably exacerbate CNS injury.

The absence of Nrf2 enhances NF-κB-dependent inflammation following scratch injury in mouse primary cultured astrocytes

It has been proved that Nrf2 depletion enhances inflammatory process through activation of NF-κB in the brain after TBI, but little is known about the relationship between Nrf2 and NF-κB in astrocytes after TBI. Hence, we used primary cultured astrocytes from either Nrf2 wildtype or knockout mice to study the influence of Nrf2 on the activation of NF-κB and expression of proinflammatory cytokines in a model of TBI in vitro. Primary cultured astrocytes were scratched to mimic the traumatic injury in vitro. Then the DNA-binding activity of NF-κB was evaluated by EMSA. The mRNA and protein levels of TNF-α, IL-1β, IL-6, and MMP9 were also evaluated. Gelatin zymography was performed to detect the activity of MMP9. The activity of NF-κB and expression of proinflammatory cytokines mentioned above were upregulated at 24 h after scratch. The expression and activity of MMP9 were also elevated. And such tendency was much more prominent in Nrf2 KO astrocytes than that in WT astrocytes. These results suggest that the absence of Nrf2 may induce more aggressive inflammation through activation of NF-κB and downstream proinflammatory cytokines in astrocytes.

An in vitro trauma model to study rodent and human astrocyte reactivity

Protocols are presented describing a unique in vitro injury model and how to culture and mature mouse, rat, and human astrocytes for its use. This injury model produces widespread injury and astrocyte reactivity that enable quantitative measurements of morphological, biochemical, and functional changes in rodent and human reactive astrocytes. To investigate structural and molecular mechanisms of reactivity in vitro, cultured astrocytes need to be purified and then in vitro "matured" to reach a highly differentiated state. This is achieved by culturing astrocytes on deformable collagen-coated membranes in the presence of adult-derived horse serum (HS), followed by its stepwise withdrawal. These in vitro matured, process-bearing, quiescent astrocytes are then subjected to mechanical stretch injury by an abrupt pressure pulse from a pressure control device that briefly deforms the culture well bottom. This inflicts a measured reproducible, widespread strain that induces reactivity and injury in rodent and human astrocytes. Cross-species comparisons are possible because mouse, rat, and human astrocytes are grown using essentially the same in vitro treatment regimen. Human astrocytes from fetal cerebral cortex are compared to those derived from cortical biopsies of epilepsy patients (ages 1-12 years old), with regard to growth, purity, and differentiation. This opens a unique opportunity for future studies on glial biology, maturation, and pathology of human astrocytes. Prototypical astrocyte proteins including GFAP, S100, aquaporin4, glutamate transporters, and tenascin are expressed in mouse, rat, and human in vitro matured astrocyte. Upon pressure-stretching, rodent and human astrocytes undergo dynamic morphological, gene expression, and protein changes that are characteristic for trauma-induced reactive astrogliosis.

Inhibition of reactive gliosis prevents neovascular growth in the mouse model of oxygen-induced retinopathy

Retinal neovascularization (NV) is a major cause of blindness in ischemic retinopathies. Previous investigations have indicated that ischemia upregulates GFAP and PDGF-B expression. GFAP overexpression is a hallmark of reactive gliosis (RG), which is the major pathophysiological feature of retinal damage. In addition, PDGF-B has been implicated in proliferative retinopathies. It was the aim of this study to gain insights on the possible pharmacological interventions to modulate PDGF-B and GFAP expression, and its influence on RG and NV. We used an array of assays to evaluate the effects of YC-1, a small molecule inhibitor of HIF-1 and a novel NO-independent activator of soluble guanylyl cyclase (sGC), on RG and NV, in vivo and in vitro. When compared to the DMSO-treated retinas, dual-intravitreal injections of YC-1, in vivo: (1) suppressed the development and elongation of neovascular sprouts in the retinas of the oxygen-induced retinopathy (OIR) mouse model; and (2) reduced ischemia-induced overexpression of GFAP and PDGF-B at the message (by 64.14±0.5% and 70.27±0.04%) and the protein levels (by 65.52±0.02% and 57.59±0.01%), respectively. In addition, at 100 µM, YC-1 treatment downregulated the hypoxia-induced overexpression of GFAP and PDGF-B at the message level in rMC-1 cells (by 71.42±0.02% and 75±0.03%), and R28 cells (by 58.62±0.02% and 50.00±0.02%), respectively; whereas, the protein levels of GFAP and PDGF-B were reduced (by 78.57±0.02% and 77.55±0.01%) in rMC-1 cells, and (by 81.44±0.02% and 79.16±0.01%) in R28 cells, respectively. We demonstrate that YC-1 reversed RG during ischemic retinopathy via impairing the expression of GFAP and PDGF-B in glial cells. This is the first investigation that delves into the reversal of RG during ischemic retinal vasculopathies. In addition, the study reveals that YC-1 may exert promising therapeutic effects in the treatment of retinal and neuronal pathologies.

Loss of expression of miR-335 is implicated in hepatic stellate cell migration and activation

Activation and migration of resident stellate cells (HSCs) within the hepatic space of Disse play an important role in hepatic fibrosis, which accounts for the increased numbers of activated HSCs in areas of inflammation during hepatic fibrosis. Currently, microRNAs have been found to play essential roles in HSC differentiation, proliferation, apoptosis, fat accumulation and collagen production. However, little is known about microRNA mediated HSC activation and migration. In this study, the miRNA expression profiles of quiescent HSCs, partially activated HSCs and fully activated HSCs were compared in pairs. Gene ontology (GO) and GO-Map network analysis indicated that the activation of HSCs was regulated by microRNAs. Among them miR-335 was confirmed to be significantly reduced during HSC activation by qRT-PCR, and restoring expression of miR-335 inhibited HSC migration and reduced α-SMA and collagen type I. Previous study revealed that tenascin-C (TNC), an extracellular matrix glycoprotein involved in cell migration, might be a target of miR-335. Therefore, we further studied the TNC expression in miR-335 over-expressed HSCs. Our data showed that exogenous TNC could enhance HSC migration in vitro and miR-335 restoration resulted in a significant inhibition of TNC expression. These results demonstrated that miR-335 restoration inhibited HSC migration, at least in part, via downregulating the TNC expression.

A versatile 3D culture model facilitates monitoring of astrocytes undergoing reactive gliosis

A major impediment to CNS repair is the glial scar, which forms following damage and is composed mainly of ramified, ‘reactive’ astrocytes that inhibit neuronal regrowth. The transition of astrocytes into this reactive phenotype (reactive gliosis) is a potential therapeutic target, but glial scar formation has proved difficult to study in monolayer cultures because they induce constitutive astrocyte activation. Here we demonstrate a 3D collagen gel system in which primary rat astrocytes were maintained in a persistently less reactive state than comparable cells in monolayer, resembling their status in the undamaged CNS. Reactivity, proliferation and viability were monitored and quantified using confocal, fluorescence and time-lapse microscopy, 3D image analysis, RT–PCR and ELISA. To assess the potential of this system as a model of reactive gliosis, astrocytes in 3D were activated with TGFβ1 to a ramified, reactive phenotype (elevated GFAP, Aquaporin 4, CSPG, Vimentin and IL-6 secretion). This provides a versatile system in which astrocytes can be maintained in a resting state, then be triggered to undergo reactive gliosis, enabling real-time monitoring and quantitative analysis throughout and providing a powerful new tool for research into CNS damage and repair. Copyright © 2009 John Wiley & Sons, Ltd.

Traumatic injury activates MAP kinases in astrocytes: mechanisms of hypothermia and hyperthermia

Hyperthermia is common following traumatic brain injury (TBI) and has been associated with poor neurologic outcome, and hypothermia has emerged as a potentially effective therapy for TBI, although its mechanism is still unclear. In this study we investigated the effects of temperature modulations on astrocyte survival following traumatic injury and the involved MAPK pathways. Trauma was produced by scratch injury of a monolayer of confluent astrocytes in culture, followed by incubation at hypothermia (308 degree C), normothermia (378 degree C), or hyperthermia (398 degree C). The activation of MAPK pathways including extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase ( JNK), and p38 MAPK were measured at 0, 15, 30, 60, and 120 min after traumatic injury followed by temperature modulation. Apoptosis of astrocytes was assessed by quantitation of cleaved caspase-3 expression 24 h after injury. Our findings showed that only JNK activation at 15 min after trauma was reduced by hypothermia, and this was associated with a marked reduction in apoptosis. Hyperthermia activated both ERK and JNK and increased apoptosis. The specific JNK inhibitor, SP60025, markedly reduced JNK-induced apoptosis at normothermia and hyperthermia, and showed a dose-dependent effect. In conclusion, the JNK pathway appears to mediate traumatic injury-induced apoptosis in astrocytes. Prolonged hyperthermia as a secondary insult worsens apoptosis by increasing JNK activation. Hypothermia protects against traumatic injury via early suppression on JNK activation and subsequent prevention of apoptosis. Manipulation of the JNK pathway in astrocytes may represent a therapeutic target for ameliorating the devastating progression of tissue injury and cell death after TBI.

Chronic treatment of astrocytes with therapeutically relevant fluoxetine concentrations enhances cPLA2 expression secondary to 5-HT2B-induced, transactivation-mediated ERK1/2 phosphorylation

INTRODUCTION

We have recently shown that fluoxetine, a serotonin-specific reuptake inhibitor (SSRI), has low micromolar affinity for the 5-HT(2C) receptor (but not for 5-HT(2A) and 5-HT(2B) receptors) in primary cultures of mouse astrocytes. This was determined as phosphorylation (stimulation) of extracellular-regulated kinase 1 and 2 (ERK(1/2)) by transactivation-mediated phosphorylation of the epidermal growth factor (EGF) receptor, followed by conventional EGF receptor signaling (Li et al., Psychopharmacology 194:333-334, 2007). Paroxetine has an identical effect. The present study shows that chronic fluoxetine treatment with even higher affinity (EC(50) = 0.5-2.0 microM) upregulates Ca(2+)-dependent phospholipase A(2) (cPLA(2)), which releases arachidonic acid from the sn-2 position of membrane-bound phospholipid, without effect on secretory PLA(2) (sPLA(2)) and intracellular PLA(2) (iPLA(2)).

DISCUSSION

This demonstration replicates the fluoxetine-induced cPLA(2) upregulation in rat brain shown by Rao et al. (Pharmacogenomics J 6:413-420, 2006) and provides the new information that upregulation (1) occurs in astrocytes, (2) is evoked by stimulation of 5-HT(2B) receptor, and (3) requires transactivation-mediated ERK(1/2) phosphorylation. Similar upregulation of cPLA(2) in intact brain in response to 5-HT(2)-mediated signaling by elevated serotonin levels and/or an SSRI during antidepressant treatment may explain the repeatedly reported ability of SSRIs to normalize regional decreases which occur in brain metabolism during major depression, since (1) arachidonic acid strongly stimulates glucose metabolism in cultured astrocytes (Yu et al., J Neurosci Res 64:295-303, 1993) and (2) plasma concentrations of arachidonic acid in depressed patients are linearly correlated with regional brain glucose metabolism (Elizabeth Sublette et al., Prostaglandins Leukot Essent Fatty Acids 80:57-64, 2009).

Mechanical lesion activates newly identified NFATc1 in primary astrocytes: implication of ATP and purinergic receptors

Ca2+-dependent calcineurin is upregulated in reactive astrocytes in neuroinflammatory models. Therefore, the fact that the nuclear factor of activated T cells (NFAT) is activated in response to calcineurin qualifies this family of transcription factors with immune functions as candidates to mediate astrogliosis. Brain trauma induces a neuroinflammatory state in which ATP is released from astrocytes, stimulating calcium signalling. Our goal here is to characterize NFATc1 and NFATc2 in mouse primary astrocyte cultures, also exploring the implication of NFAT in astrocyte activation by mechanical lesion. Quantitative reverse transcriptase-polymerase chain reaction, Western blot analysis and immunofluorescence microscopy identified NFATc1 in astrocytes, but not NFATc2. Moreover, NFATc1 was expressed in the cytosol of resting astrocytes, whereas activation of the Ca2+-calcineurin pathway by ionomycin translocated NFATc1 to the nucleus, which is a requirement for activation. The implication of astrocytic NFAT in brain trauma was analysed using an in vitro scratch lesion model. Mechanical lesion caused a rapid NFATc1 translocation that progressed throughout the culture as a gradient and was maintained for at least 4 h. We also demonstrate that ATP, released by lesion, is a potent inducer of NFATc1 translocation and activation. Moreover, the use of P2Y receptor modulators showed that such ATP action is mediated by stimulation of several G(q)-protein-coupled P2Y purinergic receptors, among which P2Y(1) and P2Y(6) are included. In conclusion, this work provides evidence that newly identified NFATc1 is translocated in astrocytes in response to lesion following a pathway that involves ATP release and activation of metabotropic purinergic receptors.

ADAMTS-1 increases the three-dimensional growth of osteoblasts through type I collagen processing

The multi-domain neutral endopeptidase, ADAMTS-1 (a disintegrin and metalloprotease with thrombospondin repeats) is induced by parathyroid hormone (PTH) in rat osteoblasts and has therefore been suggested to be involved in initiation of bone remodeling. However, its function(s) in bone cells have not been studied. Here, we first establish that ADAMTS-1 protein is rapidly and transiently produced by human primary osteoblasts in response to PTH (1-34). We also show that ADAMTS-1 is specifically in close proximity to collagen fibrils in bone tissue using ultrastructural immunolabeling. To study the consequence(s) of ADAMTS-1 metalloprotease production in osteoblastic cells, human osteosarcoma cells (SaOS-2), were forced to express either wild-type (wtATS) or a point-mutated (pmATS) metalloprotease dead ADAMTS-1. SaOS-2 cells expressing wtATS had a growth advantage and increased collagenolytic activity when seeded inside a collagen type I gel but exhibited a reduced migration in a scratch wound assay. Immunolabeling of moving cells shows ADAMTS-1 to be located towards the direction of cellular migration. Finally, Western analysis demonstrated excess accumulation of mature collagen type I alpha1 species in the extracellular matrix together with increased release of distinct small collagen fragments into the conditioned media, by cultures of wtATS cells compared to pmATS cells. These results show that ADAMTS-1 has both the opportunity in bone and capability in vitro to induce collagen type I processing, together with a positive influence on osteoblastic three-dimensional growth. Although it is not clear at present if ADAMTS-1 promotes collagen degradation directly or indirectly, it shows that ADAMTS-1 activity can have a profound influence on the osteoblast phenotype, inhibiting migration on a planar substrate but enhancing growth in a collagen scaffold. These findings further establish ADAMTS-1 as a potentially important protein in PTH induced bone remodeling.