A novel and efficient gene transfer strategy reduces glial reactivity and improves neuronal survival and axonal growth in vitro

Role of CD36 in central nervous system diseases

CD36 is a highly glycosylated integral membrane protein that belongs to the scavenger receptor class B family and regulates the pathological progress of metabolic diseases. CD36 was recently found to be widely expressed in various cell types in the nervous system, including endothelial cells, pericytes, astrocytes, and microglia. CD36 mediates a number of regulatory processes, such as endothelial dysfunction, oxidative stress, mitochondrial dysfunction, and inflammatory responses, which are involved in many central nervous system diseases, such as stroke, Alzheimer's disease, Parkinson's disease, and spinal cord injury. CD36 antagonists can suppress CD36 expression or prevent CD36 binding to its ligand, thereby achieving inhibition of CD36-mediated pathways or functions. Here, we reviewed the mechanisms of action of CD36 antagonists, such as Salvianolic acid B, tanshinone IIA, curcumin, sulfosuccinimidyl oleate, antioxidants, and small-molecule compounds. Moreover, we predicted the structures of binding sites between CD36 and antagonists. These sites can provide targets for more efficient and safer CD36 antagonists for the treatment of central nervous system diseases.

Astrocytes express aberrant immunoglobulins as putative gatekeeper of astrocytes to neuronal progenitor conversion

Using multi-omics analyses including RNAseq, RT-PCR, RACE-PCR, and shotgun proteomic with enrichment strategies, we demonstrated that newborn rat astrocytes produce neural immunoglobulin constant and variable heavy chains as well as light chains. However, their edification is different from the ones found in B cells and they resemble aberrant immunoglobulins observed in several cancers. Moreover, the complete enzymatic V(D)J recombination complex has also been identified in astrocytes. In addition, the constant heavy chain is also present in adult rat astrocytes, whereas in primary astrocytes from human fetus we identified constant and variable kappa chains as well as the substitution lambda chains known to be involved in pre-B cells. To gather insights into the function of these neural IgGs, CRISPR-Cas9 of IgG2B constant heavy chain encoding gene (Igh6), IgG2B overexpression, proximal labeling of rat astrocytes IgG2B and targets identification through 2D gels were performed. In Igh6 KO astrocytes, overrepresentation of factors involved in hematopoietic cells, neural stem cells, and the regulation of neuritogenesis have been identified. Moreover, overexpression of IgG2B in astrocytes induces the CRTC1-CREB-BDNF signaling pathway known to be involved in gliogenesis, whereas Igh6 KO triggers the BMP/YAP1/TEAD3 pathway activated in astrocytes dedifferentiation into neural progenitors. Proximal labeling experiments revealed that IgG2B is N-glycosylated by the OST complex, addressed to vesicle membranes containing the ATPase complex, and behaves partially like CD98hc through its association with LAT1. These experiments also suggest that proximal IgG2B-LAT1 interaction occurs concomitantly with MACO-1 and C2CD2L, at the heart of a potentially novel cell signaling platform. Finally, we demonstrated that these chains are synthesized individually and associated to recognize specific targets. Indeed, intermediate filaments Eif4a2 and Pdia6 involved in astrocyte fate constitute targets for these neural IgGs. Taken together, we hypothese that neural aberrant IgG chains may act as gatekeepers of astrocytes' fate.

Aptamers against mouse and human tumor-infiltrating myeloid cells as reagents for targeted chemotherapy

Local delivery of anticancer agents has the potential to maximize treatment efficacy and minimize the acute and long-term systemic toxicities. Here, we used unsupervised systematic evolution of ligands by exponential enrichment to identify four RNA aptamers that specifically recognized mouse and human myeloid cells infiltrating tumors but not their peripheral or circulating counterparts in multiple mouse models and from patients with head and neck squamous cell carcinoma (HNSCC). The use of these aptamers conjugated to doxorubicin enhanced the accumulation and bystander release of the chemotherapeutic drug in both primary and metastatic tumor sites in breast and fibrosarcoma mouse models. In the 4T1 mammary carcinoma model, these doxorubicin-conjugated aptamers outperformed Doxil, the first clinically approved highly optimized nanoparticle for targeted chemotherapy, promoting tumor regression after just three administrations with no detected changes in weight loss or blood chemistry. These RNA aptamers recognized tumor infiltrating myeloid cells in a variety of mouse tumors in vivo and from human HNSCC ex vivo. This work suggests the use of RNA aptamers for the detection of myeloid-derived suppressor cells in humans and for a targeted delivery of chemotherapy to the tumor microenvironment in multiple malignancies.

Gene Therapy, A Novel Therapeutic Tool for Neurological Disorders: Current Progress, Challenges and Future Prospective

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Neurological disorders are one of the major threat for health care system as they put enormous socioeconomic burden. All aged populations are susceptible to one or other neurological problems with symptoms of neuroinflammation, neurodegeneration and cognitive dysfunction. At present, available pharmacotherapeutics are insufficient to treat these diseased conditions and in most cases, they provide only palliative effect. It was also found that the molecular etiology of neurological disorders is directly linked with the alteration in genetic makeup, which can be inherited or triggered by the injury, environmental toxins and by some existing disease. Therefore, to take care of this situation, gene therapy has emerged as an advanced modality that claims to permanently cure the disease by deletion, silencing or edition of faulty genes and by insertion of healthier genes. In this modality, vectors (viral and non-viral) are used to deliver targeted gene into a specific region of the brain via various routes. At present, gene therapy has shown positive outcomes in complex neurological disorders, such as Parkinson's disease, Alzheimer's disease, Huntington disease, Multiple sclerosis, Amyotrophic lateral sclerosis and in lysosomal storage disease. However, there are some limitations such as immunogenic reactions non-specificity of viral vectors and a lack of effective biomarkers to understand the efficacy of therapy. Considerable progress has been made to improve vector design, gene selection and targeted delivery. This review article deals with the current status of gene therapy in neurological disorders along with its clinical relevance, challenges and future prospective.

Ex Vivo Rat Transected Spinal Cord Slices as a Model to Assess Lentiviral Vector Delivery of Neurotrophin-3 and Short Hairpin RNA against NG2

The failure of the spinal cord to regenerate can be attributed both to a lack of trophic support for regenerating axons and to upregulation of inhibitory factors such as chondroitin sulphate proteoglycans including NG2 following injury. Lentiviral vector-mediated gene therapy is a possible strategy for treating spinal cord injury (SCI). This study investigated the effect of lentiviral vectors expressing Neurotrophin-3 (NT-3) and short-hairpin RNA against NG2 (NG2 sh) to enhance neurite outgrowth in in vitro and ex vivo transection injury models. Conditioned medium from cells transduced with NT-3 or shNG2 lentiviruses caused a significant increase in neurite length of primary dorsal root ganglia neurons compared to the control group in vitro. In an ex vivo organotypic slice culture (OSC) transduction with Lenti-NT-3 promoted axonal growth. Transducing OSCs with a combination of Lenti-NT-3/NG2 sh lead to a further increase in axonal growth but only in injured slices and only within the region adjacent to the site of injury. These findings suggest that the combination of lentiviral NT-3 and NG2 sh reduced NG2 levels and provided a more favourable microenvironment for neuronal regeneration after SCI. This study also shows that OSCs may be a useful platform for studying glial scarring and potential SCI treatments.

Validation of the Fetal Lamb Model of Spina Bifida

A randomized trial demonstrated that fetal spina bifida (SB) repair is safe and effective yet invasive. New less invasive techniques are proposed but are not supported by adequate experimental studies. A validated animal model is needed to bridge the translational gap to the clinic and should mimic the human condition. Introducing a standardized method, we comprehensively and reliably characterize the SB phenotype in two lamb surgical models with and without myelotomy as compared to normal lambs. Hindbrain herniation measured on brain magnetic resonance imaging (MRI) was the primary outcome. Secondary outcomes included gross examination with cerebrospinal fluid (CSF) leakage test, neurological examination with locomotor assessment, whole-body MRI, motor and somatosensory evoked potentials; brain, spinal cord, hindlimb muscles, bladder and rectum histology and/or immunohistochemistry. We show that the myelotomy model best phenocopies the anatomy, etiopathophysiology and symptomatology of non-cystic SB. This encompasses hindbrain herniation, ventriculomegaly, posterior fossa anomalies, loss of brain neurons; lumbar CSF leakage, hindlimb somatosensory-motor deficit with absence of motor and somatosensory evoked potentials due to loss of spinal cord neurons, astroglial cells and myelin; urinary incontinence. This model obtains the highest validity score for SB animal models and is adequate to assess the efficacy of novel fetal therapies.

RNA Nanotherapeutics for the Amelioration of Astroglial Reactivity

In response to injuries to the CNS, astrocytes enter a reactive state known as astrogliosis, which is believed to be deleterious in some contexts. Activated astrocytes overexpress intermediate filaments including glial fibrillary acidic protein (GFAP) and vimentin (Vim), resulting in entangled cells that inhibit neurite growth and functional recovery. Reactive astrocytes also secrete inflammatory molecules such as Lipocalin 2 (Lcn2), which perpetuate reactivity and adversely affect other cells of the CNS. Herein, we report proof-of-concept use of the packaging RNA (pRNA)-derived three-way junction (3WJ) motif as a platform for the delivery of siRNAs to downregulate such reactivity-associated genes. In vitro, siRNA-3WJs induced a significant knockdown of Gfap, Vim, and Lcn2 in a model of astroglial activation, with a concomitant reduction in protein expression. Knockdown of Lcn2 also led to reduced protein secretion from reactive astroglial cells, significantly impeding the perpetuation of inflammation in otherwise quiescent astrocytes. Intralesional injection of anti-Lcn2-3WJs in mice with contusion spinal cord injury led to knockdown of Lcn2 at mRNA and protein levels in vivo. Our results provide evidence for siRNA-3WJs as a promising platform for ameliorating astroglial reactivity, with significant potential for further functionalization and adaptation for therapeutic applications in the CNS.

Gene Manipulation Strategies to Identify Molecular Regulators of Axon Regeneration in the Central Nervous System

Limited axon regeneration in the injured adult mammalian central nervous system (CNS) usually results in irreversible functional deficits. Both the presence of extrinsic inhibitory molecules at the injury site and the intrinsically low capacity of adult neurons to grow axons are responsible for the diminished capacity of regeneration in the adult CNS. Conversely, in the embryonic CNS, neurons show a high regenerative capacity, mostly due to the expression of genes that positively control axon growth and downregulation of genes that inhibit axon growth. A better understanding of the role of these key genes controlling pro-regenerative mechanisms is pivotal to develop strategies to promote robust axon regeneration following adult CNS injury. Genetic manipulation techniques have been widely used to investigate the role of specific genes or a combination of different genes in axon regrowth. This review summarizes a myriad of studies that used genetic manipulations to promote axon growth in the injured CNS. We also review the roles of some of these genes during CNS development and suggest possible approaches to identify new candidate genes. Finally, we critically address the main advantages and pitfalls of gene-manipulation techniques, and discuss new strategies to promote robust axon regeneration in the mature CNS.

Hippocampal Astrocyte Cultures from Adult and Aged Rats Reproduce Changes in Glial Functionality Observed in the Aging Brain

Astrocytes are dynamic cells that maintain brain homeostasis, regulate neurotransmitter systems, and process synaptic information, energy metabolism, antioxidant defenses, and inflammatory response. Aging is a biological process that is closely associated with hippocampal astrocyte dysfunction. In this sense, we demonstrated that hippocampal astrocytes from adult and aged Wistar rats reproduce the glial functionality alterations observed in aging by evaluating several senescence, glutamatergic, oxidative and inflammatory parameters commonly associated with the aging process. Here, we show that the p21 senescence-associated gene and classical astrocyte markers, such as glial fibrillary acidic protein (GFAP), vimentin, and actin, changed their expressions in adult and aged astrocytes. Age-dependent changes were also observed in glutamate transporters (glutamate aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1)) and glutamine synthetase immunolabeling and activity. Additionally, according to in vivo aging, astrocytes from adult and aged rats showed an increase in oxidative/nitrosative stress with mitochondrial dysfunction, an increase in RNA oxidation, NADPH oxidase (NOX) activity, superoxide levels, and inducible nitric oxide synthase (iNOS) expression levels. Changes in antioxidant defenses were also observed. Hippocampal astrocytes also displayed age-dependent inflammatory response with augmentation of proinflammatory cytokine levels, such as TNF-α, IL-1β, IL-6, IL-18, and messenger RNA (mRNA) levels of cyclo-oxygenase 2 (COX-2). Furthermore, these cells secrete neurotrophic factors, including glia-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), S100 calcium-binding protein B (S100B) protein, and transforming growth factor-β (TGF-β), which changed in an age-dependent manner. Classical signaling pathways associated with aging, such as nuclear factor erythroid-derived 2-like 2 (Nrf2), nuclear factor kappa B (NFκB), heme oxygenase-1 (HO-1), and p38 mitogen-activated protein kinase (MAPK), were also changed in adult and aged astrocytes and are probably related to the changes observed in senescence marker, glutamatergic metabolism, mitochondrial dysfunction, oxidative/nitrosative stress, antioxidant defenses, inflammatory response, and trophic factors release. Together, our results reinforce the role of hippocampal astrocytes as a target for understanding the mechanisms involved in aging and provide an innovative tool for studies of astrocyte roles in physiological and pathological aging brain.

Destination Brain: the Past, Present, and Future of Therapeutic Gene Delivery

Neurological diseases and disorders (NDDs) present a significant societal burden and currently available drug- and biological-based therapeutic strategies have proven inadequate to alleviate it. Gene therapy is a suitable alternative to treat NDDs compared to conventional systems since it can be tailored to specifically alter select gene expression, reverse disease phenotype and restore normal function. The scope of gene therapy has broadened over the years with the advent of RNA interference and genome editing technologies. Consequently, encouraging results from central nervous system (CNS)-targeted gene delivery studies have led to their transition from preclinical to clinical trials. As we shift to an exciting gene therapy era, a retrospective of available literature on CNS-associated gene delivery is in order. This review is timely in this regard, since it analyzes key challenges and major findings from the last two decades and evaluates future prospects of brain gene delivery. We emphasize major areas consisting of physiological and pharmacological challenges in gene therapy, function-based selection of a ideal cellular target(s), available therapy modalities, and diversity of viral vectors and nanoparticles as vehicle systems. Further, we present plausible answers to key questions such as strategies to circumvent low blood-brain barrier permeability and most suitable CNS cell types for targeting. We compare and contrast pros and cons of the tested viral vectors in the context of delivery systems used in past and current clinical trials. Gene vector design challenges are also evaluated in the context of cell-specific promoters. Key challenges and findings reported for recent gene therapy clinical trials, assessing viral vectors and nanoparticles are discussed from the perspective of bench to bedside gene therapy translation. We conclude this review by tying together gene delivery challenges, available vehicle systems and comprehensive analyses of neuropathogenesis to outline future prospects of CNS-targeted gene therapies.

Telopodes of telocytes are influenced in vitro by redox conditions and ageing

Telocytes (TCs) are a novel cell type identified among interstitial cells in various organs. TCs are characterized by very long cell processes (tens to hundreds micrometres) named telopodes (Tps) with uneven calibre: dilations (podoms) and very thin segments (podomers). However, little is known about the factors which influence Tps conformation. Recently, extracellular matrix proteins were found to influence Tps extension, adherence and spreading. Here, we show that oxidative stress and ageing influence formation of new Tps of TCs cultivated from human non-pregnant myometrium. Using real-time videomicroscopy, we found that ageing the TCs to passage 21 increased the ratio of Tps/TC number with about 50 %, whereas oxidative stress hindered formation of new Tps in both aged and young TCs (passage 7). Under oxidative stress, newly formed cell processes were up to 25 % shorter. Migration pathway length was decreased by 30-40 % for both young and aged cells in an oxidative stress environment. Contrary, addition of N-acetyl cysteine in cell culture medium shifted TCs morphology to a long and slender profile. In conclusion, we showed that TCs specific morphology in vitro is influenced by oxidative status balance, as well as ageing.

Extracellular vimentin interacts with insulin-like growth factor 1 receptor to promote axonal growth

Vimentin, an intermediate filament protein, is generally recognised as an intracellular protein. Previously, we reported that vimentin was secreted from astrocytes and promoted axonal growth. The effect of extracellular vimentin in neurons was a new finding, but its signalling pathway was unknown. In this study, we aimed to determine the signalling mechanism of extracellular vimentin that facilitates axonal growth. We first identified insulin-like growth factor 1 receptor (IGF1R) as a receptor that is highly phosphorylated by vimentin stimulation. IGF1R blockades diminished vimentin- or IGF1-induced axonal growth in cultured cortical neurons. IGF1, IGF2 and insulin were not detected in the neuron culture medium after vimentin treatment. The combined drug affinity responsive target stability method and western blotting analysis showed that vimentin and IGF1 interacted with IGF1R directly. In addition, immunoprecipitation and western blotting analyses confirmed that recombinant IGF1R bound to vimentin. The results of a molecular dynamics simulation revealed that C-terminal residues (residue number 330-407) in vimentin are the most appropriate binding sites with IGF1R. Thus, extracellular vimentin may be a novel ligand of IGF1R that promotes axonal growth in a similar manner to IGF1. Our results provide novel findings regarding the role of extracellular vimentin and IGF1R in axonal growth.

Finding degrees of separation: experimental approaches for astroglial and oligodendroglial cell isolation and genetic targeting

The study of CNS glial cell function requires experimental methods to detect, purify, and manipulate each cell population with fidelity and specificity. With the identification and cloning of cell- and stage-specific markers, glial cell analysis techniques have grown beyond physical methods of tissue dissociation and cell culture, and become highly specific with immunoselection of cell cultures in vitro and genetic targeting in vivo. The unique plasticity of glial cells offers the potential for cell replacement therapies in neurological disease that utilize neural cells derived from transplanted neural stem and progenitor cells. In this mini-review, we outline general physical and genetic approaches for macroglial cell generation. We summarize cell culture methods to obtain astrocytes and oligodendrocytes and their precursors, from developing and adult tissue, as well as approaches to obtain human neural progenitor cells through the establishment of stem cells. We discuss popular targeting rodent strains designed for cell-specific detection, selection and manipulation of neuroglial cell progenitors and their committed progeny. Based on shared markers between astrocytes and stem cells, we discuss genetically modified mouse strains with overlapping expression, and highlight SOX-expressing strains available for targeting of stem and progenitor cell populations. We also include recently established mouse strains for detection, and tag-assisted RNA and miRNA analysis. This discussion aims to provide a brief overview of the rapidly expanding collection of experimental approaches and genetic resources for the isolation and targeting of macroglial cells, their sources, progeny and gene products to facilitate our understanding of their properties and potential application in pathology.

Lentiviral-mediated silencing of glial fibrillary acidic protein and vimentin promotes anatomical plasticity and functional recovery after spinal cord injury

In spinal cord injury (SCI), absence of functional recovery and lack of spontaneous axonal regeneration are attributed, among other factors, to the formation of a glial scar that forms both physical and chemical barriers. The glial scar is composed mainly of reactive astrocytes that overexpress two intermediate filament proteins, glial fibrillary acidic protein (GFAP) and vimentin (VIM). To promote regeneration and sprouting of spared axons after spinal cord trauma and with the objective of translation to clinics, we designed an original in vivo gene transfer strategy to reduce glial scar formation after SCI, based on the RNA interference (RNAi)-mediated inhibition of GFAP and VIM. We first show that direct injection of lentiviral vectors expressing short hairpin RNA (shRNA) against GFAP and VIM in a mouse model of SCI allows efficient and specific targeting of astrocytes. We then demonstrate that the lentiviral-mediated and stable expression of shGFAP and shVIM leads to a strong reduction of astrogliosis, improves functional motor recovery, and promotes axonal regrowth and sprouting of spared axons. This study thus examplifies how the nonneuronal environment might be a major target within the lesioned central nervous system to promote axonal regeneration (and sprouting) and validates the use of lentiviral-mediated RNAi in SCI.

LKB1 signalling attenuates early events of adipogenesis and responds to adipogenic cues

cAMP-response element-binding protein (CREB) is required for the induction of adipogenic transcription factors such as CCAAT/enhancer-binding proteins (C/EBPs). Interestingly, it is known from studies in other tissues that LKB1 and its substrates AMP-activated protein kinase (AMPK) and salt-inducible kinases (SIKs) negatively regulate gene expression by phosphorylating the CREB co-activator CRTC2 and class IIa histone deacetylases (HDACs), which results in their exclusion from the nucleus where they co-activate or inhibit their targets. In this study, we show that AMPK/SIK signalling is acutely attenuated during adipogenic differentiation of 3T3-L1 preadipocytes, which coincides with the dephosphorylation and nuclear translocation of CRTC2 and HDAC4. When subjected to differentiation, 3T3-L1 preadipocytes in which the expression of LKB1 was stably reduced using shRNA (Lkb1-shRNA), as well as Lkb1-knockout mouse embryonic fibroblasts (Lkb1(-/-) MEFs), differentiated more readily into adipocyte-like cells and accumulated more triglycerides compared with scrambled-shRNA-expressing 3T3-L1 cells or Wt MEFs. In addition, the phosphorylation of CRTC2 and HDAC4 was reduced, and the mRNA expression of adipogenic transcription factors Cebpa, peroxisome proliferator-activated receptor γ (Pparg) and adipocyte-specific proteins such as hormone-sensitive lipase (HSL), fatty acid synthase (FAS), aP2, GLUT4 and adiponectin was increased in the absence of LKB1. The mRNA and protein expression of Ddit3/CHOP10, a dominant-negative member of the C/EBP family, was reduced in Lkb1-shRNA-expressing cells, providing a potential mechanism for the up-regulation of Pparg and Cebpa expression. These results support the hypothesis that LKB1 signalling keeps preadipocytes in their non-differentiated form.

Time-dependent effect of combination therapy with erythropoietin and granulocyte colony-stimulating factor in a mouse model of hypoxic-ischemic brain injury

Erythropoietin (EPO) and granulocyte colony-stimulating factor (G-CSF) are likely to play broad roles in the brain. We investigated the effects of combination therapy with EPO and G-CSF in hypoxic-ischemic brain injury during the acute, subacute, and chronic phases. A total of 79 C57BL/6 mice with hypoxic-ischemic brain injury were randomly assigned acute (days 1-5), subacute (days 11-15) and chronic (days 28-32) groups. All of them were treated with G-CSF (250 μg/kg) and EPO (5000 U/kg) or saline daily for 5 consecutive days. Behavioral assessments and immunohistochemistry for angiogenesis, neurogenesis, and astrogliosis were performed with an 8-week follow-up. Hypoxia-inducible factor-1 (HIF-1) was also measured by Western blot analysis. The results showed that the combination therapy with EPO and G-CSF in the acute phase significantly improved rotarod performance and forelimb-use symmetry compared to the other groups, while subacute EPO and G-CSF therapy exhibited a modest improvement compared with the chronic saline controls. The acute treatment significantly increased the density of CD31(+) (PECAM-1) and α-smooth muscle actin(+) vessels in the frontal cortex and striatum, increased BrdU(+)/PSA-NCAM(+) neurogenesis in the subventricular zone, and decreased astroglial density in the striatum. Furthermore, acute treatment significantly increased the HIF-1 expression in the cytosol and nucleus, whereas chronic treatment did not change the HIF-1 expression, consistent with the behavioral outcomes. These results indicate that the induction of HIF-1 expression by combination therapy with EPO and G-CSF synergistically enhances not only behavioral function but also neurogenesis and angiogenesis while decreasing the astroglial response in a time-dependent manner.

Dissociated neurons and glial cells derived from rat inferior colliculi after digestion with papain

The formation of gliosis around implant electrodes for deep brain stimulation impairs electrode–tissue interaction. Unspecific growth of glial tissue around the electrodes can be hindered by altering physicochemical material properties. However, in vitro screening of neural tissue–material interaction requires an adequate cell culture system. No adequate model for cells dissociated from the inferior colliculus (IC) has been described and was thus the aim of this study. Therefore, IC were isolated from neonatal rats (P3_5) and a dissociated cell culture was established. In screening experiments using four dissociation methods (Neural Tissue Dissociation Kit [NTDK] T, NTDK P; NTDK PN, and a validated protocol for the dissociation of spiral ganglion neurons [SGN]), the optimal media, and seeding densities were identified. Thereafter, a dissociation protocol containing only the proteolytic enzymes of interest (trypsin or papain) was tested. For analysis, cells were fixed and immunolabeled using glial- and neuron-specific antibodies. Adhesion and survival of dissociated neurons and glial cells isolated from the IC were demonstrated in all experimental settings. Hence, preservation of type-specific cytoarchitecture with sufficient neuronal networks only occurred in cultures dissociated with NTDK P, NTDK PN, and fresh prepared papain solution. However, cultures obtained after dissociation with papain, seeded at a density of 2×10⁴ cells/well and cultivated with Neuro Medium for 6 days reliably revealed the highest neuronal yield with excellent cytoarchitecture of neurons and glial cells. The herein described dissociated culture can be utilized as in vitro model to screen interactions between cells of the IC and surface modifications of the electrode.

Knockdown of β-catenin expression inhibits neuroblastoma cell growth in vitro and in vivo

OBJECTIVE

The purpose of this study was to investigate the inhibitory effect of β-catenin gene silencing on regulation of the biological behavior of neuroblastoma BE(2)C cells in vivo and in vitro.

METHODS

A lentivirus, carrying β-catenin siRNA, was used to stably knockdown β-catenin expression in neuroblastoma BE(2)C cells for assessing tumor cell viability, colony formation, cell cycle distribution, apoptosis, xenograft formation, and growth in nude mice.

RESULTS

Levels of β-catenin expression were markedly decreased in BE(2)C cells. Downregulation of β-catenin was concomitantly accompanied by reductions in colony formation and invasion capacity and by growth inhibition of BE(2)C cells in vitro. The mechanism appears to be a G0/G1 phase arrest and induction of apoptosis. In vivo, both tumor volume and weight of β-catenin knockdown cells were obviously reduced compared to the control and parental cells.

CONCLUSION

β-Catenin knockdown could effectively control growth of neuroblastoma cells in vitro and in nude mice, suggesting that targeting β-catenin may be useful in clinical control of neuroblastoma.

White matter astrocytes in health and disease

Myelination by oligodendrocytes is a highly specialized process that relies on intimate interactions between the axon and the oligodendrocytes. Astrocytes have an important part in facilitating myelination in the CNS, however, comparatively less is known about how they affect myelination. This review therefore summarizes the literature and explores lingering questions surrounding differences between white matter and gray matter astrocytes, how astrocytes support myelination, how their dysfunction in pathological states contributes to myelin pathologies and how astrocytes may facilitate remyelination. We discuss how astrocytes in the white matter are specialized to promote myelination and myelin maintenance by clearance of extracellular ions and neurotransmitters and by secretion of pro-myelinating factors. Additionally, astrocyte-oligodendrocyte coupling via gap junctions is crucial for both myelin formation and maintenance, due to K(+) buffering and possibly metabolic support for oligodendrocytes via the panglial syncytium. Dysfunctional astrocytes aberrantly affect oligodendrocytes, as exemplified by a number of leukodystrophies in which astrocytic pathology is known as the direct cause of myelin pathology. Conversely, in primary demyelinating diseases, such as multiple sclerosis, astrocytes may facilitate remyelination. We suggest that specific manipulation of astrocytes could help prevent myelin pathologies and successfully restore myelin sheaths after demyelination.

A novel compound, denosomin, ameliorates spinal cord injury via axonal growth associated with astrocyte-secreted vimentin

BACKGROUND AND PURPOSE

In the spinal cord injury (SCI) axon regeneration is inhibited by the glial scar, which contains reactive astrocytes that secrete inhibitory chondroitin sulphate proteoglycan (CSPG). We previously reported that a novel compound, denosomin, promotes axonal growth under degenerative conditions in cultured cortical neurons. In this study, we investigated the effects of denosomin on functional recovery in SCI mice and elucidated the mechanism though which denosomin induces axonal growth in the injured spinal cord.

EXPERIMENTAL APPROACH

Denosomin was administered p.o. for 7 or 14 days to contusion mice. Behavioural evaluations and immunohistochemistry were done. Primary cultured cortical neurons and astrocytes were treated with denosomin to investigate the mechanism of axonal growth facilitation.

KEY RESULTS

Denosomin improved hind limb motor dysfunction and axonal growth, especially in the 5-HT-positive tracts across the scar and increased the density of astrocytes. Denosomin increased astrocyte proliferation, inhibited astrocytic death and increased the expression and secretion of vimentin in cultured astrocytes. Furthermore, vimentin increased axonal outgrowth in cultured neurons, even in the presence of inhibitory CSPG. Denosomin increased the number of vimentin-expressing astrocytes inside glial scars of SCI mice, and 5-HT-positive axonal growth occurred in a vimentin-associated manner.

CONCLUSION AND IMPLICATIONS

Denosomin increased the ratio of astrocytes that secrete vimentin as an axonal growth facilitator, which, we propose enhances axonal growth beyond the glial scar and promotes functional recovery in SCI mice. This study is the first to demonstrate this novel role of vimentin in SCI and drug-mediated modification of the inhibitory property of reactive astrocytes.

Characterization of adult rat astrocyte cultures

Astrocytes, a major class of glial cells, regulate neurotransmitter systems, synaptic processing, ion homeostasis, antioxidant defenses and energy metabolism. Astrocyte cultures derived from rodent brains have been extensively used to characterize astrocytes' biochemical, pharmacological and morphological properties. The aims of this study were to develop a protocol for routine preparation and to characterize a primary astrocyte culture from the brains of adult (90 days old) Wistar rats. For this we used enzymatic digestion (trypsin and papain) and mechanical dissociation. Medium exchange occurred from 24 h after obtaining a culture and after, twice a week up to reach the confluence (around the 4^th to 5^th week). Under basal conditions, adult astrocytes presented a polygonal to fusiform and flat morphology. Furthermore, approximately 95% the cells were positive for the main glial markers, including GFAP, glutamate transporters, glutamine synthetase and S100B. Moreover, the astrocytes were able to take up glucose and glutamate. Adult astrocytes were also able to respond to acute H₂O₂ exposure, which led to an increase in reactive oxygen species (ROS) levels and a decrease in glutamate uptake. The antioxidant compound resveratrol was able to protect adult astrocytes from oxidative damage. A response of adult astrocytes to an inflammatory stimulus with LPS was also observed. Changes in the actin cytoskeleton were induced in stimulated astrocytes, most likely by a mechanism dependent on MAPK and Rho A signaling pathways. Taken together, these findings indicate that the culture model described in this study exhibits the biochemical and physiological properties of astrocytes and may be useful for elucidating the mechanisms related to the adult brain, exploring changes between neonatal and adult astrocytes, as well as investigating compounds involved in cytotoxicity and cytoprotection.

Gene-based approaches in pain research and exploration of new therapeutic targets and strategies

Large panel of gene-based techniques is used for many years specifically in the pain research field. From the first identification (cloning) of some "mythic" genes, such as those encoding opioid or capsaicin receptors allowing then the creation of first-generation knockout mice, to the today conditional (time, tissue, cell-type and even pathology-dependent) and regulatable modulation of a gene function, these approaches largely contributed to fundamental leaps forward in our understanding of the function of some proteins and of their interest as possible druggable targets. Perhaps one of the most remarkable evolution in the last years is the passage of these approaches from the bench to the patient; whether it concerns the identification of genes involved in inherited pain insensibility/susceptibility, the search for genetic markers of pain types, the individual pharmacogenomics or even the first gene therapy trials. From many possible variants of gene-grounded techniques used in pain research we focus here on gene knockouts and some recent developments, on viral vectors-based gene transfer and on transgenic models for the tracing of pain pathways. Through these selected examples we attempted to emphasize the immense potential of these approaches and their already well-recognized contribution in both the basic and clinical pain research.

Lentiviral-mediated gene silencing of Notch-4 inhibits in vitro proliferation and perineural invasion of ACC-M cells

Salivary adenoid cystic carcinoma (SACC) is a common type of salivary gland cancer. The poor long-term prognosis for patients with SACC is mainly due to local recurrence, perineural invasion (PNI) and distant metastasis. Notch signaling plays a critical role in determining cell fate such as proliferation, differentiation and apoptosis. Accumulating evidence indicates that aberrant Notch-4 expression has a tumor-promoting function in SACC. In the present study, we used lentiviral-mediated RNA interference (RNAi) targeted against Notch-4 to determine the effects of decreased levels of this protein in the human highly metastatic adenoid cystic carcinoma cell line ACC-M. Furthermore, the proliferative capability as well as the PNI potential of the treated cells were observed in vitro. Our studies demonstrated that RNAi directed against Notch-4 markedly decreased Notch-4 gene expression, resulting in the inhibition of cell proliferation, and G0/G1 to S phase arrest in ACC-M cells. Knockdown of Notch-4 also resulted in a decrease in the in vitro PNI activity in ACC-M cells. To conclude, RNAi targeting against Notch-4 induces the suppression of cell growth and inhibition of PNI in vitro in ACC-M cells. Notch-4 may play an important role in regulating proliferation and PNI activity of SACC.

JAK2 inhibition is neuroprotective and reduces astrogliosis after quinolinic acid striatal lesion in adult mice

Quinolinic acid (QA) striatal lesion in rodents induces neuronal death, astrogliosis and migration of neuroblasts from subventricular zone to damaged striatum. These phenomena occur in some human neurodegenerative illnesses, but the underlying mechanisms are unknown. We investigated the effect of AG490, a Janus-kinase 2 (JAK2) inhibitor, on astrogliosis, neuronal loss and neurogenesis in the striatum of adult mice after unilateral infusion of QA (30 nmol). Animals were given subcutaneous injections of AG490 (10 mg/kg) or vehicle immediately after lesion and then once daily for six days. Brain sections were used for neuronal stereological quantification, immunohistochemical and Western Blotting analyses for GFAP and doublecortin, markers of astrocytes and neuroblasts, respectively. The total area of doublecortin-positive cells (ADPC) and the number of neurons (NN) in the lesioned (L) and contralateral (CL) sides were evaluated. Neurogenesis index (NI=ADPC(L)/ADPC(CL)) and neuronal ratio (NR=NN(L)/NN(CL)) were calculated. After QA administration, blotting for GFAP showed an ipsilateral decrease of 19% in AG490- vs vehicle-treated animals. NR was 25% higher in mice given AG490 vs controls given vehicle. NI showed a decrease of 21% in AG490- vs vehicle-treated mice. Our results indicate that JAK2 inhibition reduces QA lesion and suggest that astrogliosis may impair neuronal survival in this model.

Photomechanical wave-driven delivery of siRNAs targeting intermediate filament proteins promotes functional recovery after spinal cord injury in rats

The formation of glial scars after spinal cord injury (SCI) is one of the factors inhibiting axonal regeneration. Glial scars are mainly composed of reactive astrocytes overexpressing intermediate filament (IF) proteins such as glial fibrillary acidic protein (GFAP) and vimentin. In the current study, we delivered small interfering RNAs (siRNAs) targeting these IF proteins to SCI model rats using photomechanical waves (PMWs), and examined the restoration of motor function in the rats. PMWs are generated by irradiating a light-absorbing material with 532-nm nanosecond laser pulses from a Q-switched Nd:YAG laser. PMWs can site-selectively increase the permeability of the cell membrane for molecular delivery. Rat spinal cord was injured using a weight-drop device and the siRNA(s) solutions were intrathecally injected into the vicinity of the exposed SCI, to which PMWs were applied. We first confirmed the substantial uptake of fluorescence-labeled siRNA by deep glial cells; then we delivered siRNAs targeting GFAP and vimentin into the lesion. The treatment led to a significant improvement in locomotive function from five days post-injury in rats that underwent PMW-mediated siRNA delivery. This was attributable to the moderate silencing of the IF proteins and the subsequent decrease in the cavity area in the injured spinal tissue.

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.

Adaptive Müller cell responses to microglial activation mediate neuroprotection and coordinate inflammation in the retina

Purpose

Microglia and Müller cells are prominent participants in retinal responses to injury and disease that shape eventual tissue adaptation or damage. This investigation examined how microglia and Müller cells interact with each other following initial microglial activation.

Methods

Mouse Müller cells were cultured alone, or co-cultured with activated or unactivated retinal microglia, and their morphological, molecular, and functional responses were evaluated. Müller cell-feedback signaling to microglia was studied using Müller cell-conditioned media. Corroborative in vivo analyses of retinal microglia-Müller cell interactions in the mouse retina were also performed.

Results

Our results demonstrate that Müller cells exposed to activated microglia, relative to those cultured alone or with unactivated microglia, exhibit marked alterations in cell morphology and gene expression that differed from those seen in chronic gliosis. These Müller cells demonstrated in vitro (1) an upregulation of growth factors such as GDNF and LIF, and provide neuroprotection to photoreceptor cells, (2) increased pro-inflammatory factor production, which in turn increased microglial activation in a positive feedback loop, and (3) upregulated chemokine and adhesion protein expression, which allowed Müller cells to attract and adhere to microglia. In vivo activation of microglia by intravitreal injection of lipopolysaccharide (LPS) also induced increased Müller cell-microglia adhesion, indicating that activated microglia may translocate intraretinally in a radial direction using Müller cell processes as an adhesive scaffold.

Conclusion

Our findings demonstrate that activated microglia are able to influence Müller cells directly, and initiate a program of bidirectional microglia-Müller cell signaling that can mediate adaptive responses within the retina following injury. In the acute aftermath following initial microglia activation, Müller cell responses may serve to augment initial inflammatory responses across retinal lamina and to guide the intraretinal mobilization of migratory microglia using chemotactic cues and adhesive cell contacts. Understanding adaptive microglia-Müller cell interactions in injury responses can help discover therapeutic cellular targets for intervention in retinal disease.

Cell-autonomous and non-cell-autonomous neuroprotective functions of RORα in neurons and astrocytes during hypoxia

There is increasing evidence to suggest that the neuronal response to hypoxia is regulated through their interactions with astrocytes. However, the hypoxia-induced molecular mechanisms within astrocytes which influence neuronal death have yet to be characterized. In this study, we investigated the roles of the nuclear receptor RORα (retinoid-related orphan receptor-α) respectively in neurons and astrocytes during hypoxia using cultures and cocultures of neurons and astrocytes obtained from RORα-deficient mice. We found that loss of RORα function in neuronal cultures increases neuronal death after hypoxia, suggesting a cell-autonomous neuroprotective effect of RORα. Moreover, wild-type neurons cocultured with RORα-deficient astrocytes are characterized by a higher death rate after hypoxia than neurons cocultured with wild-type astrocytes, suggesting that RORα also has a non-cell-autonomous action. By using cocultures of neurons and astrocytes of different genotypes, we showed that this neuroprotective effect of RORα in astrocytes is additive to its effect in neurons, and is mediated in part by cell-to-cell interactions between neurons and astrocytes. We also found that RORα is upregulated by hypoxia in both neurons and astrocytes. Furthermore, our data showed that RORα does not alter oxidative mechanisms during hypoxia but regulates hypoxic inducible factor 1α (HIF-1α) expression, a major regulator of hypoxia sensing, in a cell-specific manner. Indeed, the neuroprotective function of RORα in astrocytes correlates with a downregulation of HIF-1α selectively in these cells. Altogether, our results show that RORα is a key molecular player in hypoxia, protecting neurons through its dual action in neurons and astrocytes.

Retinal degeneration progression changes lentiviral vector cell targeting in the retina

In normal mice, the lentiviral vector (LV) is very efficient to target the RPE cells, but transduces retinal neurons well only during development. In the present study, the tropism of LV has been investigated in the degenerating retina of mice, knowing that the retina structure changes during degeneration. We postulated that the viral transduction would be increased by the alteration of the outer limiting membrane (OLM). Two different LV pseudotypes were tested using the VSVG and the Mokola envelopes, as well as two animal models of retinal degeneration: light-damaged Balb-C and Rhodopsin knockout (Rho-/-) mice. After light damage, the OLM is altered and no significant increase of the number of transduced photoreceptors can be obtained with a LV-VSVG-Rhop-GFP vector. In the Rho-/- mice, an alteration of the OLM was also observed, but the possibility of transducing photoreceptors was decreased, probably by ongoing gliosis. The use of a ubiquitous promoter allows better photoreceptor transduction, suggesting that photoreceptor-specific promoter activity changes during late stages of photoreceptor degeneration. However, the number of targeted photoreceptors remains low. In contrast, LV pseudotyped with the Mokola envelope allows a wide dispersion of the vector into the retina (corresponding to the injection bleb) with preferential targeting of Müller cells, a situation which does not occur in the wild-type retina. Mokola-pseudotyped lentiviral vectors may serve to engineer these glial cells to deliver secreted therapeutic factors to a diseased area of the retina.

Increase of sensitivity to mechanical stimulus after transplantation of murine induced pluripotent stem cell-derived astrocytes in a rat spinal cord injury model

OBJECT

Clinical use of autologous induced pluripotent stem cells (iPSCs) could circumvent immune rejection and bioethical issues associated with embryonic stem cells. Spinal cord injury (SCI) is a devastating trauma with long-lasting disability, and current therapeutic approaches are not satisfactory. In the present study, the authors used the neural stem sphere (NSS) method to differentiate iPSCs into astrocytes, which were evaluated after their transplantation into injured rat spinal cords.

METHODS

Induced pluripotent stem cell-derived astrocytes were differentiated using the NSS method and injected 3 and 7 days after spinal contusion-based SCI. Control rats were injected with DMEM in the same manner. Locomotor recovery was assessed for 8 weeks, and sensory and locomotion tests were evaluated at 8 weeks. Immunohistological parameters were then assessed.

RESULTS

Transplant recipients lived for 8 weeks without tumor formation. Transplanted cells stretched their processes along the longitudinal axis, but they did not merge with the processes of host GFAP-positive astrocytes. Locomotion was assessed in 3 ways, but none of the tests detected statistically significant improvements compared with DMEM-treated control rats after 8 weeks. Rather, iPSC transplantation caused even greater sensitivity to mechanical stimulus than DMEM treatment.

CONCLUSIONS

Astrocytes can be generated by serum treatment of NSS-generated cells derived from iPSCs. However, transplantation of such cells is poorly suited for repairing SCI.

Conditional knockdown of target gene expression by tetracycline regulated transcription of double strand RNA

In vivo electroporation has served as an effective tool for the study of developmental biology. Here we report tetracycline inducible gene knockdown by electroporation. Our system consists of genome integration of a cassette encoding long double strand RNA (dsRNA) of a gene of interest by electroporation, transcription of which is assured by RNA polymerase II, and induction of transcription of dsRNA by tetracyclin. Long dsRNA decapped by ribozyme in the cassette and without poly A tail is processed into siRNA within nuclei. We could successfully induce knockdown of En2 and Coactosin by Dox administration.

Lentivirus-mediated gene silencing of beta-catenin inhibits growth of human tongue cancer cells

BACKGROUND

Beta-catenin is one of the key components of Wnt signaling pathway. Increased level of this protein has been proved to be associated with enhanced cellular proliferation and the development of many kinds of cancers. But its role in the carcinogenesis in human tongue squamous cell carcinoma, one of the most common carcinomas of the human oral cavity, remains poorly characterized.

METHODS

In this study, we used lentivirus-mediated RNA interference (RNAi) targeted against beta-catenin to determine the effects of decreasing the high constitutive level of this protein in human tongue carcinoma cell line Tca8113.

RESULTS

Our studies demonstrated that RNAi directly against beta-catenin markedly decreased beta-catenin gene expression and inhibited cellular proliferation as reflected in the reduced growth of tongue cancer cells both in vitro and in nude mice.

CONCLUSIONS

RNA interference (RNAi) targeting against beta-catenin can induce cell growth suppression of tongue cancer and may have the potential as a therapeutic modality to treat human tongue cancer.

Amniotic fluid levels of glial fibrillary acidic protein in fetal rats with retinoic acid induced myelomeningocele: a potential marker for spinal cord injury

OBJECTIVE

The objective of this study was to determine whether amniotic fluid levels of glial acidic fibrillary protein (GFAP) would reflect myelomeningocele-related neurodegeneration in the rat model of retinoic acid-induced myelomeningocele, which is a model that is very similar to human myelomeningocele and develops the entire spectrum of disease severity including features of the Chiari II malformation.

STUDY DESIGN

Time-dated (embryonic day 10) pregnant Sprague-Dawley rats were gavage fed 60 mg/kg/bodyweight retinoic acid that had been dissolved in olive oil or olive oil alone. Myelomeningocele, retinoic acid-exposed no myelomeningocele, and control fetuses were harvested at specific time points throughout gestation. A standard set of pinching tests was performed to interrogate the sensorimotor reflex arc of hindpaws and tails. Amniotic fluid-GFAP levels were analyzed by standard enzyme-linked immunosorbent assay techniques.

RESULTS

Amniotic fluid-GFAP levels were similar between groups at embryonic days 14, 16, and 18, respectively. Compared with control fetuses, amniotic fluid GFAP levels were significantly increased in myelomeningocele fetuses at embryonic days 20 and 22 (P < .001). Defect size (P < .001), presence of clubfoot deformity (P = .0004), and absence of sensorimotor function (P < .01) at embryonic day 22 correlated with amniotic fluid-GFAP levels.

CONCLUSION

Amniotic fluid-GFAP levels appear to correlate with spinal cord injury as gestation proceeds in fetal rats with myelomeningocele.

Widespread enzymatic correction of CNS tissues by a single intracerebral injection of therapeutic lentiviral vector in leukodystrophy mouse models

Leukodystrophies are rare diseases caused by defects in the genes coding for lysosomal enzymes that degrade several glycosphingolipids. Gene therapy for leukodystrophies requires efficient distribution of the missing enzymes in CNS tissues to prevent demyelination and neurodegeneration. In this work, we targeted the external capsule (EC), a white matter region enriched in neuronal projections, with the aim of obtaining maximal protein distribution from a single injection site. We used bidirectional (bd) lentiviral vectors (LV) (bdLV) to ensure coordinate expression of a therapeutic gene (beta-galactocerebrosidase, GALC; arylsulfatase A, ARSA) and of a reporter gene, thus monitoring simultaneously transgene distribution and enzyme reconstitution. A single EC injection of bdLV.GALC in early symptomatic twitcher mice (a murine model of globoid cell leukodystrophy) resulted in rapid and robust expression of a functional GALC protein in the telencephalon, cerebellum, brainstem and spinal cord. This led to global rescue of enzymatic activity, significant reduction of tissue storage and decrease of activated astroglia and microglia. Widespread protein distribution and complete metabolic correction were also observed after EC injection of bdLV.ARSA in a mouse model of metachromatic leukodystrophy. Our data indicated axonal transport, distribution through cerebrospinal fluid flow and cross-correction as the mechanisms contributing to widespread bioavailability of GALC and ARSA proteins in CNS tissues. LV-mediated gene delivery of lysosomal enzymes by targeting highly interconnected CNS regions is a potentially effective strategy that, combined with a treatment able to target the PNS and peripheral organs, may provide significant therapeutic benefit to patients affected by leukodystrophies.

The conditioning lesion effect on sympathetic neurite outgrowth is dependent on gp130 cytokines

Sympathetic neurons, like sensory neurons, increase neurite outgrowth after a conditioning lesion. Studies in leukemia inhibitory factor (LIF) knockout animals showed that the conditioning lesion effect in sensory neurons is dependent in part on this cytokine; however, similar studies on sympathetic neurons revealed no such effect. Comparable studies with sensory neurons taken from mice lacking the related cytokine interleukin-6 (IL-6) have yielded conflicting results. LIF and IL-6 belong to a family of cytokines known as the gp130 family because they act on receptors containing the subunit gp130. In sympathetic ganglia, axotomy leads to increases in mRNA for four of these cytokines (LIF, IL-6, IL-11, and oncostatin M). To test the role of this family of cytokines as a whole in the conditioning lesion response in sympathetic neurons, mice in which gp130 was selectively eliminated in noradrenergic neurons were studied. The postganglionic axons of the SCG were transected, and 7days later the ganglia were removed and neurite outgrowth was measured in explant and dissociated cell cultures. In both systems, neurons from wild type animals showed enhanced growth after a conditioning lesion. In contrast, no enhancement occurred in neurons from mutant animals. This lack of stimulation of outgrowth occurred despite an increase in expression of activating transcription factor 3 (ATF3) in the mutant mice. These studies demonstrate that stimulation of enhanced growth of sympathetic neurons after a conditioning lesion is dependent on gp130 cytokine signaling and is blocked in the absence of signaling by these cytokines in spite of an increase in ATF3.