Neuro-glia interaction effects on GFAP gene: a novel role for transforming growth factor-beta1

Dysregulation of REST and its target genes impacts the fate of neural progenitor cells in down syndrome

Increasing shreds of evidence suggest that neurogenic-to-gliogenic shift may be critical to the abnormal neurodevelopment observed in individuals with Down syndrome (DS). REST, the Repressor Element-1 Silencing Transcription factor, regulates the differentiation and development of neural cells. Downregulation of REST may lead to defects in post-differentiation neuronal morphology in the brain of the DS fetal. This study aims to elucidate the role of REST in DS-derived NPCs using bioinformatics analyses and laboratory validations. We identified and validated vital REST-targeted DEGs: CD44, TGFB1, FN1, ITGB1, and COL1A1. Interestingly, these genes are involved in neurogenesis and gliogenesis in DS-derived NPCs. Furthermore, we identified nuclear REST loss and the neuroblast marker, DCX, was downregulated in DS human trisomic induced pluripotent stem cells (hiPSCs)-derived NPCs, whereas the glioblast marker, NFIA, was upregulated. Our findings indicate that the loss of REST is critical in the neurogenic-to-gliogenic shift observed in DS-derived NPCs. REST and its target genes may collectively regulate the NPC phenotype.

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

TGF-β as a Key Modulator of Astrocyte Reactivity: Disease Relevance and Therapeutic Implications

Astrocytes are essential for normal brain development and functioning. They respond to brain injury and disease through a process referred to as reactive astrogliosis, where the reactivity is highly heterogenous and context-dependent. Reactive astrocytes are active contributors to brain pathology and can exert beneficial, detrimental, or mixed effects following brain insults. Transforming growth factor-β (TGF-β) has been identified as one of the key factors regulating astrocyte reactivity. The genetic and pharmacological manipulation of the TGF-β signaling pathway in animal models of central nervous system (CNS) injury and disease alters pathological and functional outcomes. This review aims to provide recent understanding regarding astrocyte reactivity and TGF-β signaling in brain injury, aging, and neurodegeneration. Further, it explores how TGF-β signaling modulates astrocyte reactivity and function in the context of CNS disease and injury.

Recent insights on astrocyte mechanisms in CNS homeostasis, pathology, and repair

Astrocytes play essential roles in development, homeostasis, injury, and repair of the central nervous system (CNS). Their development is tightly regulated by distinct spatial and temporal cues during embryogenesis and into adulthood throughout the CNS. Astrocytes have several important responsibilities such as regulating blood flow and permeability of the blood-CNS barrier, glucose metabolism and storage, synapse formation and function, and axon myelination. In CNS pathologies, astrocytes also play critical parts in both injury and repair mechanisms. Upon injury, they undergo a robust phenotypic shift known as "reactive astrogliosis," which results in both constructive and deleterious outcomes. Astrocyte activation and migration at the site of injury provides an early defense mechanism to minimize the extent of injury by enveloping the lesion area. However, astrogliosis also contributes to the inhibitory microenvironment of CNS injury and potentiate secondary injury mechanisms, such as inflammation, oxidative stress, and glutamate excitotoxicity, which facilitate neurodegeneration in CNS pathologies. Intriguingly, reactive astrocytes are increasingly a focus in current therapeutic strategies as their activation can be modulated toward a neuroprotective and reparative phenotype. This review will discuss recent advancements in knowledge regarding the development and role of astrocytes in the healthy and pathological CNS. We will also review how astrocytes have been genetically modified to optimize their reparative potential after injury, and how they may be transdifferentiated into neurons and oligodendrocytes to promote repair after CNS injury and neurodegeneration.

Cellular Senescence in Brain Aging

Aging of the brain can manifest itself as a memory and cognitive decline, which has been shown to frequently coincide with changes in the structural plasticity of dendritic spines. Decreased number and maturity of spines in aged animals and humans, together with changes in synaptic transmission, may reflect aberrant neuronal plasticity directly associated with impaired brain functions. In extreme, a neurodegenerative disease, which completely devastates the basic functions of the brain, may develop. While cellular senescence in peripheral tissues has recently been linked to aging and a number of aging-related disorders, its involvement in brain aging is just beginning to be explored. However, accumulated evidence suggests that cell senescence may play a role in the aging of the brain, as it has been documented in other organs. Senescent cells stop dividing and shift their activity to strengthen the secretory function, which leads to the acquisition of the so called senescence-associated secretory phenotype (SASP). Senescent cells have also other characteristics, such as altered morphology and proteostasis, decreased propensity to undergo apoptosis, autophagy impairment, accumulation of lipid droplets, increased activity of senescence-associated-β-galactosidase (SA-β-gal), and epigenetic alterations, including DNA methylation, chromatin remodeling, and histone post-translational modifications that, in consequence, result in altered gene expression. Proliferation-competent glial cells can undergo senescence both in vitro and in vivo, and they likely participate in neuroinflammation, which is characteristic for the aging brain. However, apart from proliferation-competent glial cells, the brain consists of post-mitotic neurons. Interestingly, it has emerged recently, that non-proliferating neuronal cells present in the brain or cultivated in vitro can also have some hallmarks, including SASP, typical for senescent cells that ceased to divide. It has been documented that so called senolytics, which by definition, eliminate senescent cells, can improve cognitive ability in mice models. In this review, we ask questions about the role of senescent brain cells in brain plasticity and cognitive functions impairments and how senolytics can improve them. We will discuss whether neuronal plasticity, defined as morphological and functional changes at the level of neurons and dendritic spines, can be the hallmark of neuronal senescence susceptible to the effects of senolytics.

The KDM5 Inhibitor KDM5-C70 Induces Astrocyte Differentiation in Rat Neural Stem Cells

Members of the lysine-specific histone demethylase 5 (KDM5/JARID1) family are known to play important roles in stem cell fate determination. Here, using the KDM5 inhibitor C70 (KDM5-C70), we demonstrated that the histone demethylase activity of the KDM5 enzyme is essential for the repression of astrocytic differentiation of neural stem cells (NSCs). KDM5-C70 treatment activated the glial fibrillary acidic protein (Gfap) gene by increasing the trimethylation of histone H3 lysine 4 in the promoter regions and subsequently induced astrocytogenesis in NSCs. In addition, treatment of NSCs with KDM5-C70 activated Janus kinase-signal transducer and activator of transcription (JAK-STAT3) signaling and increased the mRNA expression of transforming growth factor-beta 1 (Tgf-β1). Our data provide evidence that KDM5 is a promising target for NSC fate modulation and suggest that epigenetic regulation is important for NSC fate determination.

Astrocytes: News about Brain Health and Diseases

Astrocytes, the most numerous glial cells in the brains of humans and other mammalian animals, have been studied since their discovery over 100 years ago. For many decades, however, astrocytes were believed to operate as a glue, providing only mechanical and metabolic support to adjacent neurons. Starting from a "revolution" initiated about 25 years ago, numerous astrocyte functions have been reconsidered, some previously unknown, others attributed to neurons or other cell types. The knowledge of astrocytes has been continuously growing during the last few years. Based on these considerations, in the present review, different from single or general overviews, focused on six astrocyte functions, chosen due in their relevance in both brain physiology and pathology. Astrocytes, previously believed to be homogeneous, are now recognized to be heterogeneous, composed by types distinct in structure, distribution, and function; their cooperation with microglia is known to govern local neuroinflammation and brain restoration upon traumatic injuries; and astrocyte senescence is relevant for the development of both health and diseases. Knowledge regarding the role of astrocytes in tauopathies and Alzheimer's disease has grow considerably. The multiple properties emphasized here, relevant for the present state of astrocytes, will be further developed by ongoing and future studies.

Cyclopamine sensitizes glioblastoma cells to temozolomide treatment through Sonic hedgehog pathway

AIM

Glioblastoma is an extremely aggressive glioma, resistant to radio and chemotherapy usually performed with temozolomide. One of the main reasons for glioblastoma resistance to conventional therapies is due to the presence of cancer stem-like cells. These cells could recapitulate some signaling pathways important for embryonic development, such as Sonic hedgehog. Here, we investigated if the inhibitor of the Sonic hedgehog pathway, cyclopamine, could potentiate the temozolomide effect in cancer stem-like cells and glioblastoma cell lines in vitro.

MAIN METHODS

The viability of glioblastoma cells exposed to cyclopamine and temozolomide treatment was evaluated by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay while the induction of apoptosis was assessed by western blot. The stemness properties of glioma cells were verified by clonogenic and differentiation assay and the expression of stem cell markers were measured by fluorescence microscopy and western blot.

KEY FINDINGS

The glioblastoma viability was reduced by cyclopamine treatment. Cyclopamine potentiated temozolomide treatment in glioblastoma cell lines by inducing apoptosis through activation of caspase-3 cleaved. Conversely, the combined treatment of cyclopamine and temozolomide potentiated the stemness properties of glioblastoma cells by inducing the expression of SOX-2 and OCT-4.

SIGNIFICANCE

Cyclopamine plays an effect on glioblastoma cell lines but also sensibilize them to temozolomide treatment. Thus, first-line treatment with Sonic hedgehog inhibitor followed by temozolomide could be used as a new therapeutic strategy for glioblastoma patients.

Astrocyte glutamate transporters are increased in an early sporadic model of synucleinopathy

α-Synuclein protein (α-syn) is a central player in Parkinson's disease (PD) and in a spectrum of neurodegenerative diseases collectively known as synucleinopathies. These diseases are characterized by abnormal motor symptoms, such as tremor at rest, slowness of movement, rigidity of posture, and bradykinesia. Histopathological features of PD include preferential loss of dopaminergic neurons in the substantia nigra and formation of fibrillar intraneuronal inclusions called Lewy bodies and Lewy neurites, which are composed primarily of the α-syn protein. Currently, it is well accepted that α-syn oligomers (αSO) are the main toxic agent responsible for the etiology of PD. Glutamatergic excitotoxicity is associated with several neurological disorders, including PD. Excess glutamate in the synaptic cleft can be taken up by the astrocytic glutamate transporters GLAST and GLT-1. Although this event is the main defense against glutamatergic excitotoxicity, the molecular mechanisms that regulate this process have not yet been investigated in an early sporadic model of synucleinopathy. Here, using an early sporadic model of synucleinopathy, we demonstrated that the treatment of astrocytes with αSO increased glutamate uptake. This was associated with higher levels of GLAST and GLT-1 in astrocyte cultures and in a mouse model of synucleinopathy 24 h and 45 days after inoculation with αSO, respectively. Pharmacological inhibition of the TGF-β1 (transforming growth factor beta 1) pathway in vivo reverted GLAST/GLT-1 enhancement induced by αSO injection. Therefore, our study describes a new neuroprotective role of astrocytes in an early sporadic model of synucleinopathy and sheds light on the mechanisms of glutamate transporter regulation for neuroprotection against glutamatergic excitotoxicity in synucleinopathy.

The Role of Astrocytes in the Development of the Cerebellum

Astrocytes, initially described as merely support cells, are now known as a heterogeneous population of cells actively involved in a variety of biological functions such as: neuronal migration and differentiation; regulation of cerebral blood flow; metabolic control of extracellular potassium concentration; and modulation of synapse formation and elimination; among others. Cerebellar glial cells have been shown to play a significant role in proliferation, differentiation, migration, and synaptogenesis. However, less evidence is available about the role of neuron-astrocyte interactions during cerebellar development and their impact on diseases of the cerebellum. In this review, we will focus on the mechanisms underlying cellular interactions, specifically neuron-astrocyte interactions, during cerebellar development, function, and disease. We will discuss how cerebellar glia, astrocytes, and Bergmann glia play a fundamental role in several steps of cerebellar development, such as granule cell migration, axonal growth, neuronal differentiation, and synapse formation, and in diseases associated with the cerebellum. We will focus on how astrocytes and thyroid hormones impact cerebellar development. Furthermore, we will provide evidence of how growth factors secreted by glial cells, such as epidermal growth factor and transforming growth factors, control cerebellar organogenesis. Finally, we will argue that glia are a key mediator of cerebellar development and that identification of molecules and pathways involved in neuron-glia interactions may contribute to a better understanding of cerebellar development and associated disorders.

TGF-β1 Provides Neuroprotection via Inhibition of Microglial Activation in 3-Acetylpyridine-Induced Cerebellar Ataxia Model Rats

Cerebellar ataxias (CAs) consist of a heterogeneous group of neurodegenerative diseases hallmarked by motor deficits and deterioration of the cerebellum and its associated circuitries. Neuroinflammatory responses are present in CA brain, but how neuroinflammation may contribute to CA pathogenesis remain unresolved. Here, we investigate whether transforming growth factor (TGF)-β1, which possesses anti-inflammatory and neuroprotective properties, can ameliorate the microglia-mediated neuroinflammation and thereby alleviate neurodegeneration in CA. In the current study, we administered TGF-β1 via the intracerebroventricle (ICV) in CA model rats, by intraperitoneal injection of 3-acetylpyridine (3-AP), to reveal the neuroprotective role of TGF-β1. The TGF-β1 administration after 3-AP injection ameliorated motor impairments and reduced the calbindin-positive neuron loss and apoptosis in the brain stem and cerebellum. Meanwhile, 3-AP induced microglial activation and inflammatory responses in vivo, which were determined by morphological alteration and an increase in expression of CD11b, enhancement of percentage of CD40 + and CD86 + microglial cells, upregulation of pro-inflammatory mediators, tumor necrosis factor (TNF)-α and interleukin (IL)-1β, and a downregulation of neurotrophic factor, insulin-like growth factor (IGF)-1 in the brain stem and cerebellum. TGF-β1 treatment significantly prevented all the changes caused by 3-AP. In addition, in vitro experiments, TGF-β1 directly attenuated 3-AP-induced microglial activation and inflammatory responses in primary cultures. Purkinje cell exposure to supernatants of primary microglia that had been treated with TGF-β1 reduced neuronal loss and apoptosis induced by 3-AP-treated microglial supernatants. Furthermore, the protective effect was similar to those treated with TNF-α-neutralizing antibody. These findings suggest that TGF-β1 protects against neurodegeneration in 3-AP-induced CA rats via inhibiting microglial activation and at least partly TNF-α release.

Mesenchymal stem cells combined with albendazole as a novel therapeutic approach for experimental neurotoxocariasis

Neurotoxocariasis (NT) is a serious condition that has been linked to reduced cognitive function, behavioural alterations and neurodegenerative diseases. Unfortunately, the available drugs to treat toxocariasis are limited with unsatisfactory results, because of the initiation of treatment at late chronic stages after the occurrence of tissue damage and scars. Therefore, searching for a new therapy for this important disease is an urgent necessity. In this context, cytotherapy is a novel therapeutic approach for the treatment of many diseases and tissue damages through the introduction of new cells into the damaged sites. They exert therapeutic effects by their capability of renewal, differentiation into specialized cells, and being powerful immunomodulators. The most popular cell type utilized in cytotherapy is the mesenchymal stem cells (MSCs) type. In the current study, the efficacy of MSCs alone or combined with albendazole was evaluated against chronic brain insults induced by Toxocara canis infection in an experimental mouse model. Interestingly, MSCs combined with albendazole demonstrated a healing effect on brain inflammation, gliosis, apoptosis and significantly reduced brain damage biomarkers (S100B and GFAP) and T. canis DNA. Thus, MSCs would be protective against the development of subsequent neurodegenerative diseases with chronic NT.

Novel association between TGFA, TGFB1, IRF1, PTGS2 and IKBKB single-nucleotide polymorphisms and occurrence, severity and treatment response of major depressive disorder

Background

Activation of the immune system might affect the severity of depressive episodes as well as response to the antidepressant treatment. The purpose of this study was to investigate whether the occurrence of variant alleles of analyzed SNPs are involved in prevalence and progression of depression. Moreover, selected genes and SNPs have not been investigated in context of the disease severity and treatment. Therefore, six polymorphisms were selected: g.41354391A>G-TGFB1 (rs1800469), g.132484229C>A-IRF (rs2070729), g.186643058A>G-PTGS2 (rs5275), g.186640617C>T-PTGS2 (rs4648308), g.70677994G>A-TGFA (rs2166975) and g.42140549G>T-IKBKB (rs5029748).

Methods

A total of 360 (180 patients and 180 controls) DNA samples were genotyped using TaqMan probes.

Results

We observed that A/G of the rs2166975 TGFA, A/C of rs2070729 IRF1 and G/T of rs5029748 IKBKB were associated with an increased risk of depression development while the T/T of rs5029748 IKBKB, T/T of rs4648308 PTGS2 and G/G of rs2166975 TGFA reduced this risk. We also stratified the study group according to gender and found that genotype A/G and allele G of the rs2166975 TGFA, G/T of rs5029748 IKBKB as well as C allele of rs4648308 PTGS2, homozygote A/A and allele A of rs5275 PTGS2 were associated with increased risk of depression development in men while homozygote G/G of rs5275 PTGS2 decreased this risk. Moreover, C/T of rs4648308 PTGS2 and A/G of rs5275 PTGS2 was positively correlated with the risk of the disease occurrence in women. Furthermore, a gene-gene analysis revealed a link between studied polymorphisms and depression. In addition, A/A of rs1800469 TGFB1 was associated with earlier age of onset of the disease while G/G of this SNP increased severity of the depressive episode. Interestingly, A/C of rs2070729 IRF1 and T/T of rs5029748 IKBKB may modulate the effectiveness of selective serotonin reuptake inhibitors therapy. In conclusion, studied SNPs may modulate the risk of occurrence, age of onset, severity of the disease and response to the antidepressant treatment.

Acetylcholine suppresses the increase of glia fibrillary acidic protein expression via acetylcholine receptors in cAMP-induced astrocytic differentiation of rat C6 glioma cells

Astrocytes, the most common glial cells in the central nervous system, maintain neuronal functions and have roles in neurological diseases. Acetylcholine (ACh) is one of the most essential neurotransmitters, and ACh receptor (AChR) ligands were recently reported to influence astrocyte functions. However, the functions of ACh, the only endogenous agonist of AChR, in astrocytogenesis and in the expression of astrocytic marker genes have not been known. We previously demonstrated that the inhibition of acetylcholine esterase (AChE) suppressed the differentiation of rat glioma C6 cells, an astrocyte differentiation model, and we observed a suppressive effect of ACh agonists on astrocyte differentiation. Our present study revealed that in the cAMP-induced differentiation of C6 cells, an AChR antagonist alleviated the expression of glia fibrillary acidic protein (GFAP) that had been suppressed by dichlorvos (DDVP), an organophosphate and an AChE inhibitor. Our findings also demonstrated a direct effect of ACh on the GFAP expression, and that muscarinic AChR is involved in the suppressive effect of ACh on the GFAP expression in differentiation-induced C6 cells. This is the first report indicating that ACh the only endogenous agonist for AChRs functions as a mediator of astrocyte differentiation.

TGFβ-Signaling and FOXG1-Expression Are a Hallmark of Astrocyte Lineage Diversity in the Murine Ventral and Dorsal Forebrain

Heterogeneous astrocyte populations are defined by diversity in cellular environment, progenitor identity or function. Yet, little is known about the extent of the heterogeneity and how this diversity is acquired during development. To investigate the impact of TGF (transforming growth factor) β-signaling on astrocyte development in the telencephalon we deleted the TGFBR2 (transforming growth factor beta receptor 2) in early neural progenitor cells in mice using a FOXG1 (forkhead box G1)-driven CRE-recombinase. We used quantitative proteomics to characterize TGFBR2-deficient cells derived from the mouse telencephalon and identified differential protein expression of the astrocyte proteins GFAP (glial fibrillary acidic protein) and MFGE8 (milk fat globule-EGF factor 8). Biochemical and histological investigations revealed distinct populations of astrocytes in the dorsal and ventral telencephalon marked by GFAP or MFGE8 protein expression. The two subtypes differed in their response to TGFβ-signaling. Impaired TGFβ-signaling affected numbers of GFAP astrocytes in the ventral telencephalon. In contrast, TGFβ reduced MFGE8-expression in astrocytes deriving from both regions. Additionally, lineage tracing revealed that both GFAP and MFGE8 astrocyte subtypes derived partly from FOXG1-expressing neural precursor cells.

Vitamin D Treatment Attenuates Neuroinflammation and Dopaminergic Neurodegeneration in an Animal Model of Parkinson's Disease, Shifting M1 to M2 Microglia Responses

Microglia-mediated neuroinflammation has been described as a common hallmark of Parkinson's disease (PD) and is believed to further exacerbate the progressive degeneration of dopaminergic neurons. Current therapies are unable to prevent the disease progression. A significant association has been demonstrated between PD and low levels of vitamin D in patients serum, and vitamin D supplement appears to have a beneficial clinical effect. Herein, we investigated whether vitamin D administered orally in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced preclinical animal model of PD protects against glia-mediated inflammation and nigrostriatal neurodegeneration. Vitamin D significantly attenuated the MPTP-induced loss of tyrosine hydrlase (TH)-positive neuronal cells, microglial cell activation (Iba1-immunoreactive), inducible nitric oxide synthase (iNOS) and TLR-4 expression, typical hallmarks of the pro-inflammatory (M1) activation of microglia. Additionally, Vitamin D was able to decrease pro-inflammatory cytokines mRNA expression in distinct brain areas of the MPTP mouse. Importantly, we also assessed the anti-inflammatory property of vitamin D in the MPTP mouse, in which it upregulated the anti-inflammatory cytokines (IL-10, IL-4 and TGF-β) mRNA expression as well as increasing the expression of CD163, CD206 and CD204, typical hallmarks of alternative activation of microglia for anti-inflammatory signalling (M2). Collectively, these results demonstrate that vitamin D exhibits substantial neuroprotective effects in this PD animal model, by attenuating pro-inflammatory and up-regulating anti-inflammatory processes.

Effects of Transforming Growth Factor Beta 1 in Cerebellar Development: Role in Synapse Formation

Granule cells (GC) are the most numerous glutamatergic neurons in the cerebellar cortex and represent almost half of the neurons of the central nervous system. Despite recent advances, the mechanisms of how the glutamatergic synapses are formed in the cerebellum remain unclear. Among the TGF-β family, TGF-beta 1 (TGF-β1) has been described as a synaptogenic molecule in invertebrates and in the vertebrate peripheral nervous system. A recent paper from our group demonstrated that TGF-β1 increases the excitatory synapse formation in cortical neurons. Here, we investigated the role of TGF-β1 in glutamatergic cerebellar neurons. We showed that the expression profile of TGF-β1 and its receptor, TβRII, in the cerebellum is consistent with a role in synapse formation in vitro and in vivo. It is low in the early postnatal days (P1–P9), increases after postnatal day 12 (P12), and remains high until adulthood (P30). We also found that granule neurons express the TGF-β receptor mRNA and protein, suggesting that they may be responsive to the synaptogenic effect of TGF-β1. Treatment of granular cell cultures with TGF-β1 increased the number of glutamatergic excitatory synapses by 100%, as shown by immunocytochemistry assays for presynaptic (synaptophysin) and post-synaptic (PSD-95) proteins. This effect was dependent on TβRI activation because addition of a pharmacological inhibitor of TGF-β, SB-431542, impaired the formation of synapses between granular neurons. Together, these findings suggest that TGF-β1 has a specific key function in the cerebellum through regulation of excitatory synapse formation between granule neurons.

Neuron-specific SALM5 limits inflammation in the CNS via its interaction with HVEM

The central nervous system (CNS) is an immune-privileged organ with the capacity to prevent excessive inflammation. Aside from the blood-brain barrier, active immunosuppressive mechanisms remain largely unknown. We report that a neuron-specific molecule, synaptic adhesion-like molecule 5 (SALM5), is a crucial contributor to CNS immune privilege. We found that SALM5 suppressed lipopolysaccharide-induced inflammatory responses in the CNS and that a SALM-specific monoclonal antibody promoted inflammation in the CNS, and thereby aggravated clinical symptoms of mouse experimental autoimmune encephalomyelitis. In addition, we identified herpes virus entry mediator as a functional receptor that mediates SALM5's suppressive function. Our findings reveal a molecular link between the neuronal system and the immune system, and provide potential therapeutic targets for the control of CNS diseases.

Discovery of a Small Molecule that Enhances Astrocytogenesis by Activation of STAT3, SMAD1/5/8, and ERK1/2 via Induction of Cytokines in Neural Stem Cells

Identification of small molecules that direct neural stem cells (NSCs) into specific cell types would be helpful to understand the molecular mechanisms involved in regulation of NSC fate, and facilitate the development of therapeutic applications. In the current study, we developed and screened small molecules that can modulate the fate of NSCs that are derived from rat fetal cortex. Among these compounds, compounds 5 and 6 successfully differentiated NSCs into astrocytes and neurons, respectively. Compound 5 induced astrocytogenesis by increasing expression of interleukin-6, bone morphogenetic protein 2 and leukemia inhibitory factor and through consequent phosphorylation of signal transducer and activator of transcription 3 and Sma- and Mad-related protein 1/5/8 in NSCs. In addition, compound 5 increased the expression of fibroblast growth factor (FGF) 2 and FGF8 which may regulate the branching and morphology of astrocytes. Taken together, our results suggest that these small molecules can serve as a useful tool to study cell fate determination in NSCs and be used as an inexpensive alternative to cytokines to study mechanisms of astrocytogenesis.

Transforming growth factor-β1 acts via TβR-I on microglia to protect against MPP(+)-induced dopaminergic neuronal loss

Neuroinflammation is associated with pathogenesis of Parkinson's disease (PD), a neurodegenerative disorder characterized by a progressive loss of dopaminergic (DAergic) neurons within the substantia nigra. Transforming growth factor (TGF)-β1 exerts anti-inflammatory and neuroprotective properties. However, it is unclear if microglia are required for TGF-β1 neuroprotection in PD. Here we used both shRNA and pharmacologic inhibition to determine the role of microglial TGF-β receptor (TβR)-I and its downstream signaling pathways in 1-methyl-4-phenylpyridinium (MPP(+))-induced DAergic neuronal toxicity. As expected, MPP(+) reduced the number of tyrosine hydroxylase (TH)-immunoreactive cells in ventral mesencephalic cell cultures. We found that MPP(+) activated microglia as determined by an upregulation in expression of CD11b and inducible nitric oxide synthase (iNOS), an increase in expression and secretion of tumor necrosis factor (TNF)-α and interleukin (IL)-1β, and a decrease in expression and secretion of the neurotrophic factor, insulin-like growth factor (IGF)-1. Pretreatment with TGF-β1 significantly inhibited all these changes caused by MPP(+). Expression of microglial TβR-I was upregulated by TGF-β1. Silencing of the TβR-I gene in microglia abolished both the neuroprotective and anti-inflammatory properties of TGF-β1. TGF-β1 increased microglial p38 MAPK and Akt phosphorylation, both of which were blocked by the p38 inhibitor SB203580 and the PI3K inhibitor LY294002, respectively. Pretreatment of microglia with either SB203580 or LY294002 impaired the ability of TGF-β1 to inhibit MPP(+)-induced DAergic neuronal loss and microglial activation. These findings establish that TGF-β1 activates TβR-I and its downstream p38 MAPK and PI3K-Akt signaling pathways in microglia to protect against DAergic neuronal loss that characterizes in PD.

Role of TGFβ signaling in the pathogenesis of Alzheimer's disease

Aging is the main risk factor for Alzheimer’s disease (AD); being associated with conspicuous changes on microglia activation. Aged microglia exhibit an increased expression of cytokines, exacerbated reactivity to various stimuli, oxidative stress, and reduced phagocytosis of β-amyloid (Aβ). Whereas normal inflammation is protective, it becomes dysregulated in the presence of a persistent stimulus, or in the context of an inflammatory environment, as observed in aging. Thus, neuroinflammation can be a self-perpetuating deleterious response, becoming a source of additional injury to host cells in neurodegenerative diseases. In aged individuals, although transforming growth factor β (TGFβ) is upregulated, its canonical Smad3 signaling is greatly reduced and neuroinflammation persists. This age-related Smad3 impairment reduces protective activation while facilitating cytotoxic activation of microglia through several cellular mechanisms, potentiating microglia-mediated neurodegeneration. Here, we critically discuss the role of TGFβ-Smad signaling on the cytotoxic activation of microglia and its relevance in the pathogenesis of AD. Other protective functions, such as phagocytosis, although observed in aged animals, are not further induced by inflammatory stimuli and TGFβ1. Analysis in silico revealed that increased expression of receptor scavenger receptor (SR)-A, involved in Aβ uptake and cell activation, by microglia exposed to TGFβ, through a Smad3-dependent mechanism could be mediated by transcriptional co-factors Smad2/3 over the MSR1 gene. We discuss that changes of TGFβ-mediated regulation could at least partially mediate age-associated microglia changes, and, together with other changes on inflammatory response, could result in the reduction of protective activation and the potentiation of cytotoxicity of microglia, resulting in the promotion of neurodegenerative diseases.

The Role of Astrocytes in Multiple Sclerosis Progression

Multiple sclerosis (MS) is an inflammatory disorder causing central nervous system (CNS) demyelination and axonal injury. Although its etiology remains elusive, several lines of evidence support the concept that autoimmunity plays a major role in disease pathogenesis. The course of MS is highly variable; nevertheless, the majority of patients initially present a relapsing–remitting clinical course. After 10–15 years of disease, this pattern becomes progressive in up to 50% of untreated patients, during which time clinical symptoms slowly cause constant deterioration over a period of many years. In about 15% of MS patients, however, disease progression is relentless from disease onset. Published evidence supports the concept that progressive MS reflects a poorly understood mechanism of insidious axonal degeneration and neuronal loss. Recently, the type of microglial cell and of astrocyte activation and proliferation observed has suggested contribution of resident CNS cells may play a critical role in disease progression. Astrocytes could contribute to this process through several mechanisms: (a) as part of the innate immune system, (b) as a source of cytotoxic factors, (c) inhibiting remyelination and axonal regeneration by forming a glial scar, and (d) contributing to axonal mitochondrial dysfunction. Furthermore, regulatory mechanisms mediated by astrocytes can be affected by aging. Notably, astrocytes might also limit the detrimental effects of pro-inflammatory factors, while providing support and protection for oligodendrocytes and neurons. Because of the dichotomy observed in astrocytic effects, the design of therapeutic strategies targeting astrocytes becomes a challenging endeavor. Better knowledge of molecular and functional properties of astrocytes, therefore, should promote understanding of their specific role in MS pathophysiology, and consequently lead to development of novel and more successful therapeutic approaches.

Three-dimensional culture conditions differentially affect astrocyte modulation of brain endothelial barrier function in response to transforming growth factor β1

Blood-brain barrier (BBB) function is regulated by dynamic interactions among cell types within the neurovascular unit, including astrocytes and endothelial cells. Co-culture models of the BBB typically involve astrocytes seeded on two-dimensional (2D) surfaces, which recent studies indicate cause astrocytes to express a phenotype similar to that of reactive astrocytes in situ. We hypothesized that the culture conditions of astrocytes would differentially affect their ability to modulate BBB function in vitro. Brain endothelial cells were grown alone or in co-culture with astrocytes. Astrocytes were grown either as conventional (2D) monolayers, or in a collagen-based gel which allows them to grow in a three-dimensional (3D) construct. Astrocytes were viable in 3D conditions, and displayed a marked reduction in their expression of glial fibrillary acidic protein (GFAP), suggesting reduced activation. Stimulation of astrocytes with transforming growth factor (TGF)β1 decreased transendothelial electrical resistance (TEER) and reduced expression of claudin-5 in co-cultures, whereas treatment of endothelial cells in the absence of astrocytes was without effect. The effect of TGFβ1 on TEER was significantly more pronounced in endothelial cells cultured with 3D astrocytes compared to 2D astrocytes. These results demonstrate that astrocyte culture conditions differentially affect their ability to modulate brain endothelial barrier function, and suggest a direct relationship between reactive gliosis and BBB permeability. Moreover, these studies demonstrate the potential importance of physiologically relevant culture conditions to in vitro modeling of disease processes that affect the neurovascular unit.

Gliomas and the vascular fragility of the blood brain barrier

Astrocytes, members of the glial family, interact through the exchange of soluble factors or by directly contacting neurons and other brain cells, such as microglia and endothelial cells. Astrocytic projections interact with vessels and act as additional elements of the Blood Brain Barrier (BBB). By mechanisms not fully understood, astrocytes can undergo oncogenic transformation and give rise to gliomas. The tumors take advantage of the BBB to ensure survival and continuous growth. A glioma can develop into a very aggressive tumor, the glioblastoma (GBM), characterized by a highly heterogeneous cell population (including tumor stem cells), extensive proliferation and migration. Nevertheless, gliomas can also give rise to slow growing tumors and in both cases, the afflux of blood, via BBB is crucial. Glioma cells migrate to different regions of the brain guided by the extension of blood vessels, colonizing the healthy adjacent tissue. In the clinical context, GBM can lead to tumor-derived seizures, which represent a challenge to patients and clinicians, since drugs used for its treatment must be able to cross the BBB. Uncontrolled and fast growth also leads to the disruption of the chimeric and fragile vessels in the tumor mass resulting in peritumoral edema. Although hormonal therapy is currently used to control the edema, it is not always efficient. In this review we comment the points cited above, considering the importance of the BBB and the concerns that arise when this barrier is affected.

TGF-β1 protection against Aβ1-42-induced neuroinflammation and neurodegeneration in rats

Transforming growth factor (TGF)-β1, a cytokine that can be expressed in the brain, is a key regulator of the brain's responses to injury and inflammation. Alzheimer's disease (AD), the most common neurodegenerative disorder, involves inflammatory processes in the brain in addition to the hallmarks, amyloid-β (Aβ) plaques and neurofibrillary tangles. Recently, we have shown that T-helper (Th) 17 cells, a subpopulation of CD4+ T-cells with high proinflammation, also participate in the brain inflammatory process of AD. However, it is poorly known whether TGF-β1 ameliorates the lymphocyte-mediated neuroinflammation and, thereby, alleviates neurodegeneration in AD. Herein, we administered TGF-β1 via the intracerebroventricle (ICV) in AD model rats, by Aβ1-42 injection in both sides of the hippocampus, to show the neuroprotection of TGF-β1. The TGF-β1 administration after the Aβ1-42 injection ameliorated cognitive deficit and neuronal loss and apoptosis, reduced amyloid precursor protein (APP) expression, elevated protein phosphatase (PP)2A expression, attenuated glial activation and alleviated the imbalance of the pro-inflammatory/anti-inflammatory responses of T-lymphocytes, compared to the Aβ1-42 injection alone. These findings demonstrate that TGF-β1 provides protection against AD neurodegeneration and suggest that the TGF-β1 neuroprotection is implemented by the alleviation of glial and T-cell-mediated neuroinflammation.

Astrocytic control of neural circuit formation: highlights on TGF-beta signaling

Brain function depends critically on the coordinated activity of presynaptic and postsynaptic signals derived from both neurons and non-neuronal elements such as glial cells. A key role for astrocytes in neuronal differentiation and circuitry formation has emerged within the last decade. Although the function of glial cells in synapse formation, elimination and efficacy has greatly increased, we are still very far from deeply understanding the molecular and cellular mechanism underlying these events. The present review discusses the mechanisms driving astrocytic control of excitatory and inhibitory synapse formation in the central nervous system, especially the mechanisms mediated by soluble molecules, particularly those from the TGF-β family. Further, we discuss whether and how human astrocytes might contribute to the acquisition of human cognition. We argue that understanding how astrocytic signals regulate synaptic development might offer new insights into human perception, learning, memory, and cognition and, ultimately, provide new targets for the treatment of neurological diseases.

Structural brain abnormalities in patients with inflammatory illness acquired following exposure to water-damaged buildings: a volumetric MRI study using NeuroQuant®

Executive cognitive and neurologic abnormalities are commonly seen in patients with a chronic inflammatory response syndrome (CIRS) acquired following exposure to the interior environment of water-damaged buildings (WDB), but a clear delineation of the physiologic or structural basis for these abnormalities has not been defined. Symptoms of affected patients routinely include headache, difficulty with recent memory, concentration, word finding, numbness, tingling, metallic taste and vertigo. Additionally, persistent proteomic abnormalities in inflammatory parameters that can alter permeability of the blood-brain barrier, such as C4a, TGFB1, MMP9 and VEGF, are notably present in cases of CIRS-WDB compared to controls, suggesting a consequent inflammatory injury to the central nervous system. Findings of gliotic areas in MRI scans in over 45% of CIRS-WDB cases compared to 5% of controls, as well as elevated lactate and depressed ratios of glutamate to glutamine, are regularly seen in MR spectroscopy of cases. This study used the volumetric software program NeuroQuant® (NQ) to determine specific brain structure volumes in consecutive patients (N=17) seen in a medical clinic specializing in inflammatory illness. Each of these patients presented for evaluation of an illness thought to be associated with exposure to WDB, and received an MRI that was evaluated by NQ. When compared to those of a medical control group (N=18), statistically significant differences in brain structure proportions were seen for patients in both hemispheres of two of the eleven brain regions analyzed; atrophy of the caudate nucleus and enlargement of the pallidum. In addition, the left amygdala and right forebrain were also enlarged. These volumetric abnormalities, in conjunction with concurrent abnormalities in inflammatory markers, suggest a model for structural brain injury in "mold illness" based on increased permeability of the blood-brain barrier due to chronic, systemic inflammation.

Potential neuroprotective role of transforming growth factor β1 (TGFβ1) in the brain

TGFβ1 is a growth factor that is known to be expressed in most neurodegenerative diseases and after vascular accidents in the brain. TGFβ1 downregulates the activity of activated microglia and promotes astrogliosis. It also prevents cell death by a known mechanism dependant on astrocytes and the secretion of the plasminogen activator inhibitor 1 (PAI-1). This mechanism can provide light on what is the mechanism of action of TGFβ1 as a protective factor and it can provide the pharmacological principles in which this pathway could be used with therapeutic purposes. TGFβ1 is upregulated in most neurodegenerative diseases, however, its expression appears dramatically blocked in Huntington's disease, the fastest of those diseases in progress after the onset. This fact suggests that TGFβ1 slows down the neurodegenerative process, preventing tissue damage and neural apoptotic death. However, the exact details of TGFβ1 action are still unknown and the physiological roles on the diseases are still mysterious. Interestingly, all the data regarding the roles of TGFβ1 in health and disease have been also confirmed with the use of transgenic knockouts and TGFβ1 overexpressing mice. What possibly came as a surprise from the study of TGFβ1 overexpressing models is that combining its neuroprotective and antiproliferative effects, this cytokine generates a significant disruption in the hippocampal circuitry with its consequent learning and memory deficit.

The influence of AAV2-mediated gene transfer of human IL-10 on neurodegeneration and immune response in a murine model of Parkinson's disease

BACKGROUND

The aim of this study was to examine the effect of AAV2-hIL-10 (vector containing cDNA for human interleukin 10) on dopaminergic system activity (measured as DA levels and TH mRNA expression in mouse striata), and other monoamine and amino acid neurotransmitters concentration as well as development of inflammatory processes (measured as TGF-β, IFN-γ and GFAP mRNA expression) in a murine MPTP neurotoxicant model of Parkinson's disease.

METHODS

Male C57BL/6 mice 12 months-old were used in this study. AAV2-hIL-10 vector was bilaterally administered into striatum at 14, 21 or 28 days prior to MPTP intoxication. Animals were sacrificed at 7 days following MPTP injection. The expression of hIL-10 (human interleukin 10) was examined by ELISA. Striatal monoamine and amino acid neurotransmitters were measured by HPLC method. TH, TGF-β, IFN-γ and GFAP mRNA expression was examined by RT-PCR method.

RESULTS

MPTP treatment dramatically reduced DA levels and decreased TH mRNA expression in mouse striata, effects that were significantly impeded by AAV2-hIL-10 administration prior to MPTP intoxication. AAV2-hIL-10 infusion increased IFN-γ, TGF-β and GFAP mRNA expression.

CONCLUSIONS

Our data suggest that the transfer of AAV2-hIL-10 into the striatum may play a neuroprotective role in the mouse MPTP model of PD and these effects are mediated by the anti-inflammatory action of IL-10.

A star is born: new insights into the mechanism of astrogenesis

Astrocytes emerge as crucial cells for proper neuronal functioning in the developing and adult brain. Neurons and astrocytes are sequentially generated from the same pool of neural stem cells (NSCs). Tight regulation of the neuron-to-astrocyte switch is critical for (1) the generation of a balanced number of astrocytes and neurons and (2) neuronal circuit formation, since newborn astrocytes regulate synapse formation. This review focuses on signaling pathways that instruct astrogenesis, incorporating recently discovered intrinsic and extrinsic regulators. The canonical pathway of astrocytic gene expression, JAK/STAT signaling, is inhibited during neurogenesis to prevent premature astrocyte differentiation. At the onset of astrogenesis, Notch signaling induces epigenetic remodeling of astrocytic genes like glial fibrillary acidic protein to change NSC competence. In turn, astrogenesis is initiated by signals received from newborn neurons. We highlight how key molecular pathways like JAK/STAT and Notch are integrated in a complex network of environmental signals and epigenetic and transcriptional regulators to determine NSC differentiation. It is essential to understand NSC differentiation in respect to future NSC-based therapies for brain diseases, as transplanted NSCs preferentially become astrocytes. As emphasized in this review, many clues in this respect can be learned from development.

TGF-β1 regulation of multidrug resistance P-glycoprotein in the developing male blood-brain barrier

P-glycoprotein (P-gp), an efflux transporter encoded by the abcb1 gene, protects the developing fetal brain. Levels of P-gp in endothelial cells of the blood-brain barrier (BBB) increase dramatically during the period of peak brain growth. This is coincident with increased release of TGF-β1 by astrocytes and neurons. Although TGF-β1 has been shown to modulate P-gp activity in a number of cell types, little is known about how TGF-β1 regulates brain protection. In the present study, we hypothesized that TGF-β1 increases abcb1 expression and P-gp activity in fetal and postnatal BBB in an age-dependent manner. We found TGF-β1 to potently regulate abcb1 mRNA and P-gp function. TGF-β1 increased P-gp function in brain endothelial cells (BECs) derived from fetal and postnatal male guinea pigs. These effects were more pronounced earlier in gestation when compared with BECs derived postnatally. To investigate the signaling pathways involved, BECs derived at gestational day 50 and postnatal day 14 were exposed to ALK1 and ALK5 inhibitors and agonists. Through inhibition of ALK5, we demonstrated that ALK5 is required for the TGF-β1 effects on P-gp function. Activation of ALK1, by the agonist BMP-9, produced similar results to TGF-β1 on P-gp function. However, TGF-β1 signaling through the ALK1 pathway is age-dependent as dorsomorphin, an ALK1 inhibitor, attenuated TGF-β1-mediated effects in BECs derived at postnatal day 14 but not in those derived at gestational day 50. In conclusion, TGF-β1 regulates P-gp at the fetal and neonatal BBB and both ALK5 and ALK1 pathways are implicated in the regulation of P-gp function. Aberrations in TGF-β1 levels at the developing BBB may lead to substantial changes in fetal brain exposure to P-gp substrates, triggering consequences for brain development.

Chronic over-expression of TGFβ1 alters hippocampal structure and causes learning deficits

The cytokine transforming growth factor β1 (TGFβ1) is chronically upregulated in several neurodegenerative conditions, including Alzheimer's disease, Parkinson's disease, Creutzfeldt-Jacob disease, amyotrophic lateral sclerosis and multiple sclerosis, and following stroke. Although previous studies have shown that TGFβ1 may be neuroprotective, chronic exposure to elevated levels of this cytokine may contribute to disease pathology on its own. In order to study the effects of chronic exposure to TGFβ1 in isolation, we used transgenic mice that over-express a constitutively active porcine TGFβ1 in astrocytes. We found that TGFβ1 over-expression altered brain structure, with the most pronounced volumetric increases localized to the hippocampus. Within the dentate gyrus (DG) of the hippocampus, increases in granule cell number and astrocyte size were responsible for volumetric expansion, with the increased granule cell number primarily related to a marked reduction in death of new granule cells generated in adulthood. Finally, these cumulative changes in DG microstructure and macrostructure were associated with the age-dependent emergence of spatial learning deficits in TGFβ1 over-expressing mice. Together, our data indicate that chronic upregulation of TGFβ1 negatively impacts hippocampal structure and, even in the absence of disease, impairs hippocampus-dependent learning.

Review: microglia of the aged brain: primed to be activated and resistant to regulation

Innate immunity within the central nervous system (CNS) is primarily provided by resident microglia. Microglia are pivotal in immune surveillance and also facilitate the co-ordinated responses between the immune system and the brain. For example, microglia interpret and propagate inflammatory signals that are initiated in the periphery. This transient microglial activation helps mount the appropriate physiological and behavioural response following peripheral infection. With normal ageing, however, microglia develop a more inflammatory phenotype. For instance, in several models of ageing there are increased pro-inflammatory cytokines in the brain and increased expression of inflammatory receptors on microglia. This increased inflammatory status of microglia with ageing is referred to as primed, reactive or sensitized. A modest increase in the inflammatory profile of the CNS and altered microglial function in ageing has behavioural and cognitive consequences. Nonetheless, there are major differences in microglial biology between young and old age when the immune system is challenged and microglia are activated. In this context, microglial activation is amplified and prolonged in the aged brain compared with adults. The cause of this amplified microglial activation may be related to impairments in several key regulatory systems with age that make it more difficult to resolve microglial activation. The consequences of impaired regulation and microglial hyper-activation following immune challenge are exaggerated neuroinflammation, sickness behaviour, depressive-like behaviour and cognitive deficits. Therefore the purpose of this review is to discuss the current understanding of age-associated microglial priming, consequences of priming and reactivity, and the impairments in regulatory systems that may underlie these age-related deficits.

Avaliação da proteína acídica fibrilar glial como marcador da injúria por isquemia-reperfusão hepática

OBJETIVO: Avaliar a expressão da Proteína Acídica Fibrilar Glial após a injúria por isquemia-reperfusão. MÉTODOS: vinte e quatro ratos foram distribuídos em quatro grupos: Controle, submetidos à anestesia e biópsia hepática; Simulação, injeção de heparina através da veia cava e dissecção do pedículo hepático superior, biópsia após 24 horas; Isquemia 30 minutos, mesmo procedimento do grupo Simulação, acrescido de clampeamento do pedículo hepático superior por 30 minutos; Isquemia 90 minutos, mesmo procedimento do grupo Isquemia 30 minutos, porém com período de clampeamento de 90 minutos. Após 24 horas de observação, os animais foram submetidos à laparotomia e seus fígados avaliados macroscopicamente, microscopicamente, por coloração de Hematoxilina-Eosina (HE) e submetidos à análise da expressão da GFAP por Western Blotting. RESULTADOS: Não se observou diferença no aspecto macroscópico dos fígados entre os diferentes grupos experimentais, tendo todos evidenciado morfologia normal. A análise por HE não evidenciou diferenças significativas, no que diz respeito à morfologia lobular. Por outro lado, nos grupos isquemia, foram encontrados infiltrados neutrofílicos e pequenas áreas de necrose. A expressão de GFAP foi semelhante em todos os grupos, seja qualitativamente quanto quantitativamente. CONCLUSÃO: A expressão da Proteína Acídica Fibrilar Glial não se alterou em nosso modelo de isquemia-reperfusão.

Connective tissue growth factor (CTGF/CCN2) is negatively regulated during neuron-glioblastoma interaction

Connective-tissue growth factor (CTGF/CCN2) is a matricellular-secreted protein involved in complex processes such as wound healing, angiogenesis, fibrosis and metastasis, in the regulation of cell proliferation, migration and extracellular matrix remodeling. Glioblastoma (GBM) is the major malignant primary brain tumor and its adaptation to the central nervous system microenvironment requires the production and remodeling of the extracellular matrix. Previously, we published an in vitro approach to test if neurons can influence the expression of the GBM extracellular matrix. We demonstrated that neurons remodeled glioma cell laminin. The present study shows that neurons are also able to modulate CTGF expression in GBM. CTGF immnoreactivity and mRNA levels in GBM cells are dramatically decreased when these cells are co-cultured with neonatal neurons. As proof of particular neuron effects, neonatal neurons co-cultured onto GBM cells also inhibit the reporter luciferase activity under control of the CTGF promoter, suggesting inhibition at the transcription level. This inhibition seems to be contact-mediated, since conditioned media from embryonic or neonatal neurons do not affect CTGF expression in GBM cells. Furthermore, the inhibition of CTGF expression in GBM/neuronal co-cultures seems to affect the two main signaling pathways related to CTGF. We observed inhibition of TGFβ luciferase reporter assay; however phopho-SMAD2 levels did not change in these co-cultures. In addition levels of phospho-p44/42 MAPK were decreased in co-cultured GBM cells. Finally, in transwell migration assay, CTGF siRNA transfected GBM cells or GBM cells co-cultured with neurons showed a decrease in the migration rate compared to controls. Previous data regarding laminin and these results demonstrating that CTGF is down-regulated in GBM cells co-cultured with neonatal neurons points out an interesting view in the understanding of the tumor and cerebral microenvironment interactions and could open up new strategies as well as suggest a new target in GBM control.

Astrocyte-induced synaptogenesis is mediated by transforming growth factor β signaling through modulation of D-serine levels in cerebral cortex neurons

Assembly of synapses requires proper coordination between pre- and postsynaptic elements. Identification of cellular and molecular events in synapse formation and maintenance is a key step to understand human perception, learning, memory, and cognition. A key role for astrocytes in synapse formation and function has been proposed. Here, we show that transforming growth factor β (TGF-β) signaling is a novel synaptogenic pathway for cortical neurons induced by murine and human astrocytes. By combining gain and loss of function approaches, we show that TGF-β1 induces the formation of functional synapses in mice. Further, TGF-β1-induced synaptogenesis involves neuronal activity and secretion of the co-agonist of the NMDA receptor, d-serine. Manipulation of d-serine signaling, by either genetic or pharmacological inhibition, prevented the TGF-β1 synaptogenic effect. Our data show a novel molecular mechanism that might impact synaptic function and emphasize the evolutionary aspect of the synaptogenic property of astrocytes, thus shedding light on new potential therapeutic targets for synaptic deficit diseases.

Neuron-astroglial interactions in cell-fate commitment and maturation in the central nervous system

Neuron-astroglia interactions play a key role in several events of brain development, such as neuronal generation, migration, survival, and differentiation; axonal growth; and synapse formation and function. While there is compelling evidence of the effects of astrocyte factors on neurons, their effects on astrocytes have not been fully determined. In this review, we will focus on the role of neurons in astrocyte generation and maturation. Further, we highlight the great heterogeneity and diversity of astroglial and neural progenitors such as radial glia cells, and discuss the importance of the variety of cellular interactions in controlling the structural and functional organization of the brain. Finally, we present recent data on a new role of astrocytes in neuronal maturation, as mediators of the action of biolipids in the cerebral cortex. We will argue that the functional architecture of the brain depends on an intimate neuron-glia partnership, by briefly discussing the emerging view of how neuron-astrocyte dysfunctions might be associated with neurodegenerative diseases and neurological disorders.

Sphingosine 1-phosphate-primed astrocytes enhance differentiation of neuronal progenitor cells

Sphingosine 1-phosphate (S1P) is a bioactive signaling lysophospholipid. Effects of S1P on proliferation, survival, migration, and differentiation have already been described; however, its role as a mediator of interactions between neurons and glial cells has been poorly explored. Here we describe effects of S1P, via the activation of its receptors in astrocytes, on the differentiation of neural progenitor cells (NPC) derived from either embryonic stem cells or the developing cerebral cortex. S1P added directly to NPC induced their differentiation, but S1P-primed astrocytes were able to promote even more pronounced changes in maturation, neurite outgrowth, and arborization in NPC. An increase in laminin by astrocytes was observed after S1P treatment. The effects of S1P-primed astrocytes on neural precursor cells were abrogated by antibodies against laminin. Together, our data indicate that S1P-treated astrocytes are able to induce neuronal differentiation of NPC by increasing the levels of laminin. These results implicate S1P signaling pathways as new targets for understanding neuroglial interactions within the central nervous system.

Cloning and expression analysis of the transforming growth factor-beta receptors type 1 and 2 in the rainbow trout Oncorhynchus mykiss

Transforming growth factor-β (TGF-β) binding to the TGF-β type I (TGFBR1) and type II (TGFBR2) receptors delivers a plethora of cell-type specific effects. Moreover, the responses to TGF-β are tuned by regulatory mechanisms at the receptor level itself. To further elucidate TGF-β family signal transduction in teleosts, we therefore cloned the first complete set of a putative TGF-β receptor complex in salmonids. Rainbow trout TGFBR1 and TGFBR2 are transmembrane proteins with a serine/threonine kinase domain and are highly conserved within vertebrates. High expression levels in muscle and brain indicate regulation of the TGF-β system in muscular and nervous systems. Lipopolysaccharide (LPS) induced expression of both receptor chains in RTgill cells while bacterial and viral mimics modulated the two receptors inversely in head kidney (HK) macrophages. In addition, T cell mitogens lowered receptor levels in HK leukocytes. These data provide the first insights into TGF-β type I and II receptor modulation during immune responses in teleost fish.

Astrocytes treated by lysophosphatidic acid induce axonal outgrowth of cortical progenitors through extracellular matrix protein and epidermal growth factor signaling pathway

Lysophosphatidic acid (LPA) plays important roles in many biological processes, such as brain development, oncogenesis and immune functions, via its specific receptors. We previously demonstrated that LPA-primed astrocytes induce neuronal commitment of cerebral cortical progenitors (Spohr et al. 2008). In the present study, we analyzed neurite outgrowth induced by LPA-treated astrocytes and the molecular mechanism underlying this event. LPA-primed astrocytes increase neuronal differentiation, arborization and neurite outgrowth of developing cortical neurons. Treatment of astrocytes with epidermal growth factor (EGF) ligands yielded similar results, suggesting that members of the EGF family might mediate LPA-induced neuritogenesis. Furthermore, treatment of astrocytes with LPA or EGF ligands led to an increase in the levels of the extracellular matrix molecule, laminin (LN), thus enhancing astrocyte permissiveness to neurite outgrowth. This event was reversed by pharmacological inhibitors of the MAPK signaling pathway and of the EGF receptor. Our data reveal an important role of astrocytes and EGF receptor ligands pathway as mediators of bioactive lipids action in brain development, and implicate the LN and MAPK pathway in this process.

Astrocytes in the aging brain express characteristics of senescence-associated secretory phenotype

Cellular stress increases progressively with aging in mammalian tissues. Chronic stress triggers several signaling cascades that can induce a condition called cellular senescence. Recent studies have demonstrated that senescent cells express a senescence-associated secretory phenotype (SASP). Emerging evidence indicates that the number of cells expressing biomarkers of cellular senescence increases in tissues with aging, which implies that cellular senescence is an important player in organismal aging. In the brain, the aging process is associated with degenerative changes, e.g. synaptic loss and white matter atrophy, which lead to progressive cognitive impairment. There is substantial evidence for the presence of oxidative, proteotoxic and metabolic stresses in aging brain. A low-level, chronic inflammatory process is also present in brain during aging. Astrocytes demonstrate age-related changes that resemble those of the SASP: (i) increased level of intermediate glial fibrillary acidic protein and vimentin filaments, (ii) increased expression of several cytokines and (iii) increased accumulation of proteotoxic aggregates. In addition, in vitro stress evokes a typical senescent phenotype in cultured astrocytes and, moreover, isolated astrocytes from aged brain display the proinflammatory phenotype. All of these observations indicate that astrocytes are capable of triggering the SASP and the astrocytes in aging brain display typical characteristics of cellular senescence. Bearing in mind the many functions of astrocytes, it is evident that the age-related senescence of astrocytes enhances the decline in functional capacity of the brain. We will review the astroglial changes occurring during aging and emphasize that senescent astrocytes can have an important role in age-related neuroinflammation and neuronal degeneration.

Central nervous system cytokine gene expression: modulation by lead

The environmental heavy metal toxicant, lead (Pb) has been shown to be more harmful to the central nervous system (CNS) of children than to adults, given that Pb exposure affects the neural system during development. Because growth factors and cytokines play very important roles in development of the CNS, we have examined the impact of Pb exposure on the expression of cytokines during CNS development. Cytokine expression was studied in post-natal-day 21 (pnd21) mice by microarray, real-time RT-PCR, Luminex, and ELISA methodologies. BALB/c mouse pups were exposed to Pb through the dam's drinking water (0.1 mM Pb acetate), from gestation-day 8 (gd8) to pnd21. Two cytokines, interleukin-6 (IL-6) and transforming growth factor-β1 (TGF-β1), displayed significantly changed transcript levels in the presence of Pb. IL-6 and TGF-β1 both have signal transduction cascades that can cooperatively turn on the gene for the astrocyte marker glial-fibrillary acidic protein (GFAP). Microarray results indicated that Pb exposure significantly increased expression of GFAP. Pb also modulated IL-6, TGF-β1, and IL-18 protein expression in select brain regions. The deleterious effects of Pb on learning and long-term memory are posited to result from excessive astrocyte growth and/or activation with concomitant interference with neural connections. Differential neural expression of cytokines in brain regions needs to be further investigated to mechanistically associate Pb and neuroinflammation with behavioral and cognitive changes.

Neuron-glia signaling: Implications for astrocyte differentiation and synapse formation

Glial cells are currently viewed as active partners of neurons in synapse formation. The close proximity of astrocytes to the synaptic cleft implicates that they strongly influence synapse function as well as suggests that these cells might be potential targets for neuronal-released molecules. In this review, we discuss the signaling pathways of astrocyte generation and the role of astrocyte-derived molecules in synapse formation in the central nervous system. Further, we discuss the role of the excitatory neurotransmitter, glutamate and transforming growth factor beta 1 (TGF-β1) pathway in astrocyte generation and differentiation. We provide evidence that astrocytes surrounding synapses are target of neuronal activity and shed light into the role of astroglial cells into neurological disorders associated with glutamate neurotoxicity.