Loss of neuron-astroglial interaction rapidly induces protective CNTF expression after stroke in mice

Bioinformatics-driven exploration of key genes and mechanisms underlying oxidative stress in traumatic brain injury

Background

Oxidative stress is a pivotal mechanism implicated in the onset of traumatic brain injury (TBI), yet its precise role remains elusive. This study aims to elucidate the potential molecular interactions between key genes associated with oxidative stress and their influence on TBI pathogenesis.

Methods

TBI dataset and oxidative stress-related genes sourced from Public databases. Differential expression analysis and machine learning models were executed to select key genes, which were further validated using receiver operating characteristic (ROC) curves. A nomogram was constructed for diagnostic prediction, and enrichment analysis explored pathways associated with key genes. Immune infiltration analysis and regulatory network construction were conducted. Molecular validation included RT-qPCR and Western blotting using rat brain tissue to assess gene and protein expression levels.

Results

In our study, we identified 400 differentially expressed genes (DEGs) between TBI and normal samples, including 20 oxidative stress-related genes. Machine learning analysis highlighted AKR1C2, QDPR, CYP3A5, CNTF, and PNPT1 as key genes with diagnostic potential (AUC > 0.6). Functional analysis revealed significant involvement of these genes in immune processes and metabolic regulation. Further, immune cell infiltration analysis showed notable differences in effector memory CD8 T cells. Molecular validation through RT-qPCR and Western blot confirmed the overexpression of key genes PNPT1 and QDPR in TBI models, substantiating their potential role in TBI pathology.

Conclusion

Our study revealed the potential mechanisms of action for PNPT1 and QDPR in TBI, offering valuable insights into their roles in TBI pathology. These findings opened new avenues for future therapeutic strategies in TBI treatment.

Ciliary neurotrophic factor activation of astrocytes mediates neuronal damage via the IL‑6/IL‑6R pathway

The occurrence of epilepsy is a spontaneous and recurring process due to abnormal neuronal firing in the brain. Epilepsy is understood to be caused by an imbalance between excitatory and inhibitory neurotransmitters in the neural network. The close association between astrocytes and synapses can regulate the excitability of neurons through the clearance of neurotransmitters. Therefore, the abnormal function of astrocytes can lead to the onset and development of epilepsy. The onset of epilepsy can produce a large number of inflammatory mediators, which can aggravate epileptic seizures, leading to a vicious cycle. Neurons and glial cells interact to promote the onset and maintenance of epilepsy, but the specific underlying molecular mechanisms need to be further studied. Ciliary neurotrophic factor (CNTF) belongs to the IL‑6 cytokine family and is mainly secreted by astrocytes and Schwann cells. In the normal physiological state, CNTF levels are low, but in an epileptic state, CNTF levels in the serum and tears of patients are elevated. Astrocyte activation plays an important role in epileptic seizures. CNTF activates astrocytes to produce a variety of secreted proteins, which are secreted into the astrocyte culture medium (ACM), thus forming a distinct culture medium (CNTF‑ACM) that can be used to study the effect of astrocytes on neurons in vitro. CNTF‑activated astrocytes increase the secretion of the pro‑inflammatory factor IL‑6. In the present study, CNTF‑ACM was applied to primary cerebral cortical neurons to observe the specific effects of IL‑6 in CNTF‑ACM on neuronal activity and excitability. The results suggested that CNTF‑ACM can reduce neuronal activity via the IL‑6/IL‑6R pathway, promote neuronal apoptosis, increase Ca2+ inflow, activate the large conductance calcium‑activated potassium channel and enhance neuronal excitability. The results of the present study further revealed the functional changes of astrocytes after CNTF activated astrocytes and the effects on neuronal activity and excitability, thereby providing new experimental evidence for the role of communication between astrocytes and neurons in the mechanism of epileptic seizures.

Exploring the reduction in aquaporin-4 and increased expression of ciliary neurotrophic factor with the frontal-striatal gliosis induced by chronic high-fat dietary stress

High-fat diet (HFD)-induced obesity induces peripheral inflammation and hypothalamic pathogenesis linking the activation of astrocytes and microglia. Clinical evidence indicates a positive correlation between obesity and psychiatric disorders, such as depression. The connectivity of the frontal-striatal (FS) circuit, involving the caudate putamen (CPu) and anterior cingulate cortex (ACC) within the prefrontal cortex (PFC), is known for its role in stress-induced depression. Thus, there is a need for a thorough investigation into whether chronic obesity-induced gliosis, characterized by the activation of astrocytes and microglia, in these brain regions of individuals with chronic obesity. The results revealed increased S100β+ astrocytes and Iba1+ microglia in the CPu and ACC of male obese mice, along with immune cell accumulation in meningeal lymphatic drainage. Activated GFAP+ astrocytes and Iba1+ microglia were observed in the corpus callosum of obese mice. Gliosis in the CPu and ACC was linked to elevated cleaved caspase-3 levels, indicating potential neural cell death by chronic HFD feeding. There was a loss of myelin and adenomatous polyposis coli (APC)+ oligodendrocytes (OLs) in the corpus callosum, an area known to be linked with injury to the CPu. Additionally, reduced levels of aquaporin-4 (AQP4), a protein associated within the glymphatic systems, were noted in the CPu and ACC, while ciliary neurotrophic factor (CNTF) gene expression was upregulated in these brain regions of obese mice. The in vitro study revealed that high-dose CNTF causing a trend of reduced astrocytic AQP4 expression, but it significantly impaired OL maturation. This pathological evidence highlights that prolonged HFD consumption induces persistent FS gliosis and demyelination in the corpus callosum. An elevated level of CNTF appears to act as a potential regulator, leading to AQP4 downregulation in the FS areas and demyelination in the corpus callosum. This cascade of events might contribute to neural cell damage within these regions and disrupt the glymphatic flow.

A facilitatory role of astrocytes in axonal regeneration after acute and chronic spinal cord injury

Neuroscience dogma avers that astrocytic "scars" inhibit axonal regeneration after spinal cord injury (SCI). A recent report suggested however that astrocytes form "borders" around lesions that are permissive rather than inhibitory to axonal growth. We now provide further evidence supporting a facilitatory role of astrocytes in axonal regeneration after SCI. First, even 6months after SCI, injured axons are retained within regions of densely reactive astrocytes, in direct contact with astrocyte processes without being repelled. Second, 6 month-delayed implants of neural stem cells extend axons into reactive astrocyte borders surrounding lesions, densely contacting astrocyte surfaces. Third, bioengineered hydrogels implanted into sites of SCI re-orient reactive astrocytic processes to align along the rostral-to-caudal spinal cord axis resulting in successful regeneration into the lesion/scaffold in close association with astrocytic processes. Fourth, corticospinal axons regenerate into neural progenitor cells implanted six months after injury in close association with host astrocytic processes. Thus, astrocytes do not appear to inhibit axonal regeneration, and the close association of newly growing axons with astrocytic processes suggests a facilitatory role in axonal regeneration.

Astrocyte Regulation of Neuronal Function and Survival in Stroke Pathophysiology

The interactions between astrocytes and neurons in the context of stroke play crucial roles in the disease's progression and eventual outcomes. After a stroke, astrocytes undergo significant changes in their morphology, molecular profile, and function, together termed reactive astrogliosis. Many of these changes modulate how astrocytes relate to neurons, inducing mechanisms both beneficial and detrimental to stroke recovery. For example, excessive glutamate release and astrocytic malfunction contribute to excitotoxicity in stroke, eventually causing neuronal death. Astrocytes also provide essential metabolic support and neurotrophic signals to neurons after stroke, ensuring homeostatic stability and promoting neuronal survival. Furthermore, several astrocyte-secreted molecules regulate synaptic plasticity in response to stroke, allowing for the rewiring of neural circuits to compensate for damaged areas. In this chapter, we highlight the current understanding of the interactions between astrocytes and neurons in response to stroke, explaining the varied mechanisms contributing to injury progression and the potential implications for future therapeutic interventions.

Axotomy results in an increase in Thy-1 protein in the 35-day-old rat supraoptic nucleus

We demonstrated previously that the hypothalamic supraoptic nucleus (SON) undergoes an axonal sprouting response following a unilateral lesion of the hypothalamo-neurohypophysial tract in a 35-day-old rat to repopulate the partially denervated neural lobe (NL). However, no sprouting occurs following the same injury in a 125-day-old rat. We previously reported a significant increase in Thy-1 protein in the SON of a 125-day-old rat compared to a 35-day-old rat in the absence of injury. Thy-1 is a cell surface glycoprotein shown to inhibit axonal outgrowth following injury; however, we did not look at axotomy's effect on Thy-1 in the SON. Therefore, we sought to determine the integrin ligands that bind Thy-1 in the SON and how axotomy impacts Thy-1. Like what others have shown, the co-immunoprecipitation analysis demonstrated that Thy-1 interacts with α_vß₃ and α_vß₅ integrin dimers in the SON. We used western blot analysis to examine protein levels of Thy-1 and integrin subunits following injury in the 35- and 125-day-old rat SON and NL. Our results demonstrated that Thy-1 protein levels increase in the lesion SON in a 35-day-old rat. The quantitative dual-fluorescent analysis showed that the increase in Thy-1 in the lesion SON occurred in astrocytes. There was no change in Thy-1 or integrin protein levels following injury in the 125-day-old following injury. Furthermore, the axotomy significantly decreased Thy-1 protein levels in the NL of both 35- and 125-day-old rats. These results provide evidence that Thy-1 protein levels are injury dependent in the magnocellular neurosecretory system.

[Steadfastly increased level of the ciliary neurotrophic factor in the blood serum within the positive therapeutic dynamics of depression as possible prognostic marker of depressive relapse]

OBJECTIVE

To study a role of the ciliary neurotrophic factor (CNTF) in the pathogenesis of depression and its prognostic significance in dynamics of the antidepressant therapy.

MATERIAL AND METHODS

CNTF level was investigated in the blood serum of patients with melancholic depression (n=32) before the start of therapy and after 30 days, when improvement was achieved by at least 75% of baseline scores on the Hamilton Depression Rating Scale.

RESULTS

Steadfastly increased level of CNTF in the blood serum of patients with melancholic depression compared with the control, remaining practically unchanged with an obvious improvement in the condition - 732.2±126.5 and 679.1±63.1 pg/ml of serum, respectively (p>0.05).

CONCLUSION

The initially elevated level of CNTP indicates its probable significance in the pathogenesis of depression; persistently high serum CNTP level, despite clinical improvement during therapy, can serve as a predictor of the stability of the biological mechanisms of recurrent depressive disorder with a continuing risk of another relapse of a depressive episode.

Bibliometric analysis of tumor necrosis factor in post-stroke neuroinflammation from 2003 to 2021

Objective

Tumor necrosis factor (TNF), a crucial cytokine, has important research value in post-stroke neuroinflammation (PSN). We analyzed the studies that have been conducted in this area and used bibliometric methods to predict research hotspots and identify trends regarding TNF in PSN.

Methods

Publications were accessed at the Science Citation Index Expanded 1975-2021 (SCI expanded), Web of Science Core Collection (WoSCC), on May 1, 2022. Additionally, software such as CiteSpace and VOSviewer were utilized for bibliometric analyses.

Results

In total, 1391 original articles and reviews on TNF in PSN published from 2003 to 2021 were identified. An upward trend was observed in the number of publications on TNF in PSN. These publications were primarily from 57 countries and 1446 institutions, led by China and the United States with China leading the number of publications (NP) and the US with the number of citations (NC). The League of European Research Universities (LERU) and Journal of Neuroinflammation, respectively were the most prolific branches and journals. Zhang, John H. published the most papers and Finsen, Bente had the most cited papers. One paper by Kettenmann, H. published in 2011 reached the highest level of Global Citation Score (GCS). The keyword co-occurrence and reference co-citation analyses suggest that poststroke therapy and potential mechanistic pathways are important topics related to PSN in recent years. Reference burst detection suggests new burst hotspots after 2015, focusing on pathway modulation and discovery of therapeutic targets, suggesting a substantial development in the study of TNF in PSN research.

Conclusion

The present bibliometric analysis shows a continuous trend of increasing literature related to TNF in PSN, and shows that TNF plays an important role in PSN involves multiple immune mechanisms and may contribute as a potential target for neuroprotective therapeutics after stroke. Prior to 2011, most of the research was focused on discovering the specific role of TNF in PSN, and in recent years studies have mainly targeted the exploration of the signaling pathways. Future research prospects may lie in finding key therapeutic targets in pathway of TNF in PSN.

Ciliary Neurotrophic Factor Derived From Astrocytes Protects Retinal Ganglion Cells Through PI3K/AKT, JAK/STAT, and MAPK/ERK Pathways

Purpose

The purpose of this study was to investigate the roles of ciliary neurotrophic factor (CNTF) on the protective effects of astrocytes on retinal ganglion cells (RGCs).

Methods

Primary RGCs were isolated from neonatal rats. Oxidative stress was induced, and the effects of co-culture with astrocytes and CNTF treatment on RGCs were evaluated. The pathways commonly altered by astrocytes and CNTF were investigated. Effects of each pathway were investigated using pathway inhibitors against PI3K/AKT, JAK/STAT, and MAPK/ERK. RNA sequencing was performed to identify the genes upregulated and downregulated by CNTF treatment.

Results

Astrocytes improved the viability and increased β3-tubulin expression in RGCs. The concentration of CNTF increased in the RGC-astrocyte co-culture medium. The protective effects of astrocytes were abolished by neutralization with the anti-CNTF antibody; thus, CNTF may play an important role in the effects mediated by astrocytes. Furthermore, CNTF treatment alone enhanced the viability and β3-tubulin expression of RGCs and increased the population of viable RGCs under oxidative stress. The PI3K/AKT pathway was associated with both RGC viability and β3-tubulin expression. However, the JAK/STAT pathway increased the viability of RGCs, whereas the MAPK/ERK pathway was associated with β3-tubulin expression. RNA sequencing revealed the CNTF-upregulated genes associated with response to DNA damage and downregulated genes associated with photoreceptor cell differentiation.

Conclusions

Our data revealed protective effects of astrocyte-derived CNTF on RGCs. In addition, we showed that multiple pathways exert these protective effects and identified the novel genes involved. These results may be helpful in developing treatments for RGC injury.

Exosomes Derived From Umbilical Cord Mesenchymal Stem Cells Treat Cutaneous Nerve Damage and Promote Wound Healing

Wound repair is a key step in the treatment of skin injury caused by burn, surgery, and trauma. Various stem cells have been proven to promote wound healing and skin regeneration as candidate seed cells. Therefore, exosomes derived from stem cells are emerging as a promising method for wound repair. However, the mechanism by which exosomes promote wound repair is still unclear. In this study, we reported that exosomes derived from umbilical cord mesenchymal stem cells (UC-MSCs) promote wound healing and skin regeneration by treating cutaneous nerve damage. The results revealed that UC-MSCs exosomes (UC-MSC-Exo) promote the growth and migration of dermal fibroblast cells. In in vitro culture, dermal fibroblasts could promote to nerve cells and secrete nerve growth factors when stimulated by exosomes. During the repair process UC-MSC-Exo accelerated the recruitment of fibroblasts at the site of trauma and significantly enhanced cutaneous nerve regeneration in vivo. Interestingly, it was found that UC-MSC-Exo could promote wound healing and skin regeneration by recruiting fibroblasts, stimulating them to secrete nerve growth factors (NGFs) and promoting skin nerve regeneration. Therefore, we concluded that UC-MSC-Exo promote cutaneous nerve repair, which may play an important role in wound repair and skin regeneration.

Crosstalk of Astrocytes and Other Cells during Ischemic Stroke

Stroke is a leading cause of death and long-term disability worldwide. Astrocytes structurally compose tripartite synapses, blood–brain barrier, and the neurovascular unit and perform multiple functions through cell-to-cell signaling of neurons, glial cells, and vasculature. The crosstalk of astrocytes and other cells is complicated and incompletely understood. Here we review the role of astrocytes in response to ischemic stroke, both beneficial and detrimental, from a cell–cell interaction perspective. Reactive astrocytes provide neuroprotection through antioxidation and antiexcitatory effects and metabolic support; they also contribute to neurorestoration involving neurogenesis, synaptogenesis, angiogenesis, and oligodendrogenesis by crosstalk with stem cells and cell lineage. In the meantime, reactive astrocytes also play a vital role in neuroinflammation and brain edema. Glial scar formation in the chronic phase hinders functional recovery. We further discuss astrocyte enriched microRNAs and exosomes in the regulation of ischemic stroke. In addition, the latest notion of reactive astrocyte subsets and astrocytic activity revealed by optogenetics is mentioned. This review discusses the current understanding of the intimate molecular conversation between astrocytes and other cells and outlines its potential implications after ischemic stroke. “Neurocentric” strategies may not be sufficient for neurological protection and recovery; future therapeutic strategies could target reactive astrocytes.

Neuroprotective and Symptomatic Effects of Cannabidiol in an Animal Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the Substantia Nigra pars compacta, leading to classical PD motor symptoms. Current therapies are purely symptomatic and do not modify disease progression. Cannabidiol (CBD), one of the main phytocannabinoids identified in Cannabis Sativa, which exhibits a large spectrum of therapeutic properties, including anti-inflammatory and antioxidant effects, suggesting its potential as disease-modifying agent for PD. The aim of this study was to evaluate the effects of chronic treatment with CBD (10 mg/kg, i.p.) on PD-associated neurodegenerative and neuroinflammatory processes, and motor deficits in the 6-hydroxydopamine model. Moreover, we investigated the potential mechanisms by which CBD exerted its effects in this model. CBD-treated animals showed a reduction of nigrostriatal degeneration accompanied by a damping of the neuroinflammatory response and an improvement of motor performance. In particular, CBD exhibits a preferential action on astrocytes and activates the astrocytic transient receptor potential vanilloid 1 (TRPV1), thus, enhancing the endogenous neuroprotective response of ciliary neurotrophic factor (CNTF). These results overall support the potential therapeutic utility of CBD in PD, as both neuroprotective and symptomatic agent.

An Exploratory Assessment of Serum Biomarkers of Post-Cardiac Arrest Syndrome in Children

AIM

We hypothesized that serum biomarkers of inflammation including chemokine, cytokine, pituitary hormones, and growth factors following cardiac arrest in children would independently associate with 6-month neurologic outcome.

METHODS

In this prospective observational single center study of children with in-hospital and out-of-hospital cardiac arrest surviving to intensive care unit admission, serum was obtained twice per 24h period between 0h and 96h and once at approximately 196h post-cardiac arrest. Inflammatory mediators, hormones, and growth factors were analyzed by Luminex Multiplex Bead Immunoassay. We recorded demographics, resuscitation characteristics, and Pediatric Cerebral Performance Category (PCPC) at 6 months. We analyzed the association and area under the curve (AUC) of biomarker levels with favorable (PCPC 1-3) or unfavorable (PCPC 4-6, or >1 increase from baseline) outcome.

RESULTS

Forty-two children (50% female; median age of 2.5 [IQR: 0.4-10.2]) were enrolled and 18 (42%) died prior to 6-month follow up. Receiver operator curves for initial levels of ciliary neurotrophic factor (CNTF, AUC 0.84, 95% CI 0.73-0.96, p<0.001) and interleukin (IL-17, AUC 0.84, 95% CI 0.73-0.97, p<0.001) best classified favorable versus unfavorable 6-month outcome. In multivariable analysis, initial levels of CNTF and IL-17 remained associated with 6-month PCPC. Peak levels of interferon-γ-inducible protein 10 (IP-10), CNTF, and hepatocyte growth factor (HGF) were also independently associated with outcome.

CONCLUSION

Increased serum concentrations of CNTF and IL-17 associated with unfavorable 6-month neurologic outcome of children surviving cardiac arrest. Further investigation of the prognostic utility and roles of CNTF and IL-17 in the pathophysiology of post-cardiac arrest syndrome are warranted.

Proteome Analysis of PC12 Cells Reveals Alterations in Translation Regulation and Actin Signaling Induced by Clozapine

Although antipsychotics are routinely used in the treatment of schizophrenia for the last decades, their precise mechanism of action is still unclear. In this study, we investigated changes in the PC12 cells’ proteome under the influence of clozapine, risperidone, and haloperidol to identify protein pathways regulated by antipsychotics. Analysis of the protein profiles in two time points: after 12 and 24 h of incubation with drugs revealed significant alterations in 510 proteins. Further canonical pathway analysis revealed an inhibition of ciliary trophic factor signaling after treatment with haloperidol and showed a decrease in acute phase response signaling in the risperidone group. Interestingly, all tested drugs have caused changes in PC12 proteome which correspond to inhibition of cytokines: tumor necrosis factor (TNF) and transforming growth factor beta 1 (TGF-β1). We also found that the 12-h incubation with clozapine caused up-regulation of protein kinase A signaling and translation machinery. After 24 h of treatment with clozapine, the inhibition of the actin cytoskeleton signaling and Rho proteins signaling was revealed. The obtained results suggest that the mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) play a central role in the signal transduction of clozapine.

Cerebrolysin enhances spinal cord conduction and reduces blood-spinal cord barrier breakdown, edema formation, immediate early gene expression and cord pathology after injury

Spinal cord evoked potentials (SCEP) are good indicators of spinal cord function in health and disease. Disturbances in SCEP amplitudes and latencies during spinal cord monitoring predict spinal cord pathology following trauma. Treatment with neuroprotective agents preserves SCEP and reduces cord pathology after injury. The possibility that cerebrolysin, a balanced composition of neurotrophic factors improves spinal cord conduction, attenuates blood-spinal cord barrier (BSCB) disruption, edema formation, and cord pathology was examined in spinal cord injury (SCI). SCEP is recorded from epidural space over rat spinal cord T9 and T12 segments after peripheral nerves stimulation. SCEP consists of a small positive peak (MPP), followed by a prominent negative peak (MNP) that is stable before SCI. A longitudinal incision (2mm deep and 5mm long) into the right dorsal horn (T10 and T11 segments) resulted in an immediate long-lasting depression of the rostral MNP with an increase in the latencies. Pretreatment with either cerebrolysin (CBL 5mL/kg, i.v. 30min before) alone or TiO₂ nanowired delivery of cerebrolysin (NWCBL 2.5mL/kg, i.v.) prevented the loss of MNP amplitude and even enhanced further from the pre-injury level after SCI without affecting latencies. At 5h, SCI induced edema, BSCB breakdown, and cell injuries were significantly reduced by CBL and NWCBL pretreatment. Interestingly this effect on SCEP and cord pathology was still prominent when the NWCBL was delivered 2min after SCI. Moreover, expressions of c-fos and c-jun genes that are prominent at 5h in untreated SCI are also considerably reduced by CBL and NWCBL treatment. These results are the first to show that CBL and NWCBL enhanced SCEP activity and thwarted the development of cord pathology after SCI. Furthermore, NWCBL in low doses has superior neuroprotective effects on SCEP and cord pathology, not reported earlier. The functional significance and future clinical potential of CBL and NWCBL in SCI are discussed.

Inhibition of focal adhesion kinase increases adult olfactory stem cell self-renewal and neuroregeneration through ciliary neurotrophic factor

Constant neuroregeneration in adult olfactory epithelium maintains olfactory function by basal stem cell proliferation and differentiation to replace lost olfactory sensory neurons (OSNs). Understanding the mechanisms regulating this process could reveal potential therapeutic targets for stimulating adult olfactory neurogenesis under pathological conditions and aging. Ciliary neurotrophic factor (CNTF) in astrocytes promotes forebrain neurogenesis but its function in the olfactory system is unknown. Here, we show in mouse olfactory epithelium that CNTF is expressed in horizontal basal cells, olfactory ensheathing cells (OECs) and a small subpopulation of OSNs. CNTF receptor alpha was expressed in Mash1-positive globose basal cells (GBCs) and OECs. Thus, CNTF may affect GBCs in a paracrine manner. CNTF−/− mice did not display altered GBC proliferation or olfactory function, suggesting that CNTF is not involved in basal olfactory renewal or that they developed compensatory mechanisms. Therefore, we tested the effect of increased CNTF in wild type mice. Intranasal instillation of a focal adhesion kinase (FAK) inhibitor, FAK14, upregulated CNTF expression. FAK14 also promoted GBC proliferation, neuronal differentiation and basal stem cell self-renewal but had no effective in CNTF−/− mice, suggesting that FAK inhibition promotes olfactory neuroregeneration through CNTF, making them potential targets to treat sensorineural anosmia due to OSN loss.

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

Astrocytes play important roles in numerous central nervous system disorders including autoimmune inflammatory, hypoxic, and degenerative diseases such as Multiple Sclerosis, ischemic stroke, and Alzheimer’s disease. Depending on the spatial and temporal context, activated astrocytes may contribute to the pathogenesis, progression, and recovery of disease. Recent progress in the dissection of transcriptional responses to varying forms of central nervous system insult has shed light on the mechanisms that govern the complexity of reactive astrocyte functions. While a large body of research focuses on the pathogenic effects of reactive astrocytes, little is known about how they limit inflammation and contribute to tissue regeneration. However, these protective astrocyte pathways might be of relevance for the understanding of the underlying pathology in disease and may lead to novel targeted approaches to treat autoimmune inflammatory and degenerative disorders of the central nervous system. In this review article, we have revisited the emerging concept of protective astrocyte functions and discuss their role in the recovery from inflammatory and ischemic disease as well as their role in degenerative disorders. Focusing on soluble astrocyte derived mediators, we aggregate the existing knowledge on astrocyte functions in the maintenance of homeostasis as well as their reparative and tissue-protective function after acute lesions and in neurodegenerative disorders. Finally, we give an outlook of how these mediators may guide future therapeutic strategies to tackle yet untreatable disorders of the central nervous system.

Age-dependent increase in Thy-1 protein in the rat supraoptic nucleus

Mature mammalian CNS neurons often do not recover successfully following injury. To this point, unilateral lesion of the hypothalamo-neurohypophysial tract results in collateral sprouting from uninjured axons of the supraoptic nucleus (SON) in 35-day-old but not in 125-day-old rats. Thus, it appears that there are age-related changes within the SON that preclude the older rat from recovering following axotomy. We hypothesize that the intrinsic capacity for axon reorganization may depend, in part, on age-related alterations in cell adhesion molecules that allow normal astrocyte-neuron interactions in the SON. In support of our hypothesis, numerous reports have shown that Thy-1 is increased in neurons at the cessation of axon outgrowth. Therefore, we compared protein levels of Thy-1 and the Thy-1 interacting integrin subunits, alpha-v (α_v), beta-3 (ß₃), and beta-5 (ß₅), in 35- and 125-day-old SON using western blot analysis. Our results demonstrated that there was significantly more Thy-1 protein in the 125-day-old SON compared to 35-day-old SON, but no change in the protein levels of the integrin subunits. Furthermore, we localized Thy-1-, α_v integrin-, ß₃ integrin-, and ß₅ integrin-immunoreactivity to both neurons and astrocytes in the SON. Altogether, our results suggest that the observed increase in Thy-1 protein levels in the SON with age may contribute to an environment that prevents collateral axonal sprouting in the SON of the 125-day-old rat.

Vitronectin mitigates stroke-increased neurogenesis only in female mice and through FAK-regulated IL-6

Vitronectin (VTN) is a blood protein produced mainly by the liver. We show that VTN leaks from the bloodstream into the injury site and neighboring subventricular zone (SVZ) following ischemic stroke (middle cerebral artery occlusion, MCAO) in adult mice. MCAO is known to increase neurogenesis after stroke. VTN inhibits this response in females, but not in males, as shown by ~70% more stroke-induced SVZ neurogenesis in female VTN-/- mice at 14 d. In female VTN-/- mice, stroke-induced expression of interleukin-6 (IL-6) at 24 h was reduced in the SVZ. The closely related leukemia inhibitory factor (LIF) or pro-neurogenic ciliary neurotrophic factor (CNTF) were not affected. The female-specific effect of VTN on IL-6 expression was not due to sex hormones, as shown by ovariectomy and castration. IL-6 injection next to the SVZ reversed the MCAO-induced increase in neurogenesis seen in VTN-/- mice. Our in vitro and vivo data suggest that plasma VTN activates focal adhesion kinase (FAK) in the SVZ following MCAO, which reduces IL-6 expression in astrocytes but increases it in other cells such as microglia/macrophages. Inducible conditional astrocytic FAK deletion increased MCAO-induced IL-6 expression in females at 24 h and blocked MCAO-induced neurogenesis at 14 d, confirming a key detrimental role of IL-6. Collectively, these data suggest that leakage of VTN into the SVZ reduces the neurogenic response to stroke in female mice by promoting IL-6 expression. Reducing VTN or VTN signaling may be an approach to promote neurogenesis for neuroprotection and cell replacement after stroke in females.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

Roles of glial ion transporters in brain diseases

Glial ion transporters are important in regulation of ionic homeostasis, cell volume, and cellular signal transduction under physiological conditions of the central nervous system (CNS). In response to acute or chronic brain injuries, these ion transporters can be activated and differentially regulate glial functions, which has subsequent impact on brain injury or tissue repair and functional recovery. In this review, we summarized the current knowledge about major glial ion transporters, including Na⁺ /H⁺ exchangers (NHE), Na⁺ /Ca²⁺ exchangers (NCX), Na⁺ -K⁺ -Cl^- cotransporters (NKCC), and Na⁺ -HCO₃ ^- cotransporters (NBC). In acute neurological diseases, such as ischemic stroke and traumatic brain injury (TBI), these ion transporters are rapidly activated and play significant roles in regulation of the intra- and extracellular pH, Na⁺ , K⁺ , and Ca²⁺ homeostasis, synaptic plasticity, and myelin formation. However, overstimulation of these ion transporters can contribute to glial apoptosis, demyelination, inflammation, and excitotoxicity. In chronic brain diseases, such as glioma, Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), glial ion transporters are involved in the glioma Warburg effect, glial activation, neuroinflammation, and neuronal damages. These findings suggest that glial ion transporters are involved in tissue structural and functional restoration, or brain injury and neurological disease development and progression. A better understanding of these ion transporters in acute and chronic neurological diseases will provide insights for their potential as therapeutic targets.

Effects of Neurotrophic Factors in Glial Cells in the Central Nervous System: Expression and Properties in Neurodegeneration and Injury

Astrocytes, oligodendrocytes, and microglia are abundant cell types found in the central nervous system and have been shown to play crucial roles in regulating both normal and disease states. An increasing amount of evidence points to the critical importance of glia in mediating neurodegeneration in Alzheimer’s and Parkinson’s diseases (AD, PD), and in ischemic stroke, where microglia are involved in initial tissue clearance, and astrocytes in the subsequent formation of a glial scar. The importance of these cells for neuronal survival has previously been studied in co-culture experiments and the search for neurotrophic factors (NTFs) initiated after finding that the addition of conditioned media from astrocyte cultures could support the survival of primary neurons in vitro. This led to the discovery of the potent dopamine neurotrophic factor, glial cell line-derived neurotrophic factor (GDNF). In this review, we focus on the relationship between glia and NTFs including neurotrophins, GDNF-family ligands, CNTF family, and CDNF/MANF-family proteins. We describe their expression in astrocytes, oligodendrocytes and their precursors (NG2-positive cells, OPCs), and microglia during development and in the adult brain. Furthermore, we review existing data on the glial phenotypes of NTF knockout mice and follow NTF expression patterns and their effects on glia in disease models such as AD, PD, stroke, and retinal degeneration.

Inhibition of astrocyte FAK-JNK signaling promotes subventricular zone neurogenesis through CNTF

Astrocyte-derived ciliary neurotrophic factor (CNTF) promotes adult subventricular zone (SVZ) neurogenesis. We found that focal adhesion kinase (FAK) and JNK, but not ERK or P38, repress CNTF in vitro. Here, we defined the FAK-JNK pathway and its regulation of CNTF in mice, and the related leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), which promote stem cell renewal at the expense of neurogenesis. Intrastriatal injection of FAK inhibitor, FAK14, in adult male C57BL/6 mice reduced pJNK and increased CNTF expression in the SVZ-containing periventricular region. Injection of a JNK inhibitor increased CNTF without affecting LIF and IL-6, and increased SVZ proliferation and neuroblast formation. The JNK inhibitor had no effect in CNTF-/- mice, suggesting that JNK inhibits SVZ neurogenesis by repressing CNTF. Inducible deletion of FAK in astrocytes increased SVZ CNTF and neurogenesis, but not LIF and IL-6. Intrastriatal injection of inhibitors suggested that P38 reduces LIF and IL-6 expression, whereas ERK induces CNTF and LIF. Intrastriatal FAK inhibition increased LIF, possibly through ERK, and IL-6 through another pathway that does not involve P38. Systemic injection of FAK14 also inhibited JNK while increasing CNTF, but did not affect P38 and ERK activation, or LIF and IL-6 expression. Importantly, systemic FAK14 increased SVZ neurogenesis in wild-type C57BL/6 and CNTF+/+ mice, but not in CNTF-/- littermates, indicating that it acts by upregulating CNTF. These data show a surprising differential regulation of related cytokines and identify the FAK-JNK-CNTF pathway as a specific target in astrocytes to promote neurogenesis and possibly neuroprotection in neurological disorders.

Ciliary neurotrophic factor is a key sex-specific regulator of depressive-like behavior in mice

Ciliary neurotrophic factor (CNTF) is produced by astrocytes and promotes neurogenesis and neuroprotection. Little is known about the role of CNTF in affective behavior. We investigated whether CNTF affects depressive- and anxiety-like behavior in adult mice as tested in the forced swim, sucrose preference and elevated-T maze tests. Female wild type CNTF+/+ mice more readily developed behavioral despair with increased immobility time and decreased latency to immobility in the forced swim test than male CNTF+/+ littermates. The lack of CNTF in CNTF-/- mice had an opposite effect on depressive-like behavior in female mice (reduced immobility time and increased sucrose preference) vs. male mice (increased immobility time). Female wildtype mice expressed more CNTF in the amygdala than male mice. Ovariectomy increased CNTF expression, as well as immobility time, which was significantly reduced in CNTF-/- mice, suggesting that CNTF mediates overiectomy-induced immobility time, possibly in the amygdala. Progesterone but not 17-β estradiol inhibited CNTF expression in cultured C6 astroglioma cells. Progesterone treatment also reduced CNTF expression in the amygdala and decreased immobility time in female CNTF+/+ but not in CNTF-/- mice. Castration did not alter CNTF expression in males nor their behavior. Lastly, there were no effects of CNTF on the elevated T-maze, a behavioral test of anxiety, suggesting that a different mechanism may underlie anxiety-like behavior. This study reveals a novel CNTF-mediated mechanism in stress-induced depressive-like behavior and points to opportunities for sex-specific treatments for depression, e.g. progesterone in females and CNTF-stimulating drugs in males.

Inhibition of Microglia-Derived Oxidative Stress by Ciliary Neurotrophic Factor Protects Dopamine Neurons In Vivo from MPP⁺ Neurotoxicity

We demonstrated that capsaicin (CAP), an agonist of transient receptor potential vanilloid subtype 1 (TRPV1), inhibits microglia activation and microglia-derived oxidative stress in the substantia nigra (SN) of MPP⁺-lesioned rat. However, the detailed mechanisms how microglia-derived oxidative stress is regulated by CAP remain to be determined. Here we report that ciliary neurotrophic factor (CNTF) endogenously produced by CAP-activated astrocytes through TRPV1, but not microglia, inhibits microglial activation and microglia-derived oxidative stress, as assessed by OX-6 and OX-42 immunostaining and hydroethidine staining, respectively, resulting in neuroprotection. The significant increase in levels of CNTF receptor alpha (CNTFRα) expression was evident on microglia in the MPP⁺-lesioned rat SN and the observed beneficial effects of CNTF was abolished by treatment with CNTF receptor neutralizing antibody. It is therefore likely that CNTF can exert its effect via CNTFRα on microglia, which rescues dopamine neurons in the SN of MPP⁺-lesioned rats and ameliorates amphetamine-induced rotations. Immunohistochemical analysis revealed also a significantly increased expression of CNTFRα on microglia in the SN from human Parkinson's disease patients compared with age-matched controls, indicating that these findings may have relevance to the disease. These data suggest that CNTF originated from TRPV1 activated astrocytes may be beneficial to treat neurodegenerative disease associated with neuro-inflammation such as Parkinson's disease.

Vitronectin from brain pericytes promotes adult forebrain neurogenesis by stimulating CNTF

Vitronectin (VTN) is a glycoprotein in the blood and affects hemostasis. VTN is also present in the extracellular matrix of various organs but little is known about its function in healthy adult tissues. We show, in adult mice, that VTN is uniquely expressed by approximately half of the pericytes of subventricular zone (SVZ) where neurogenesis continues throughout life. Intracerebral VTN antibody injection or VTN knockout reduced neurogenesis as well as expression of pro-neurogenic CNTF, and anti-neurogenic LIF and IL-6. Conversely, injections of VTN, or plasma from VTN+/+, but not VTN-/- mice, increased these cytokines. VTN promoted SVZ neurogenesis when LIF and IL-6 were suppressed by co-administration of a gp130 inhibitor. Unexpectedly, VTN inhibited FAK signaling and VTN-/- mice had increased FAK signaling in the SVZ. Further, an FAK inhibitor or VTN increased CNTF expression, but not in conditional astrocytic FAK knockout mice, suggesting that VTN increases CNTF through FAK inhibition in astrocytes. These results identify a novel role of pericyte-derived VTN in the brain, where it regulates SVZ neurogenesis through co-expression of CNTF, LIF and IL-6. VTN-integrin-FAK and gp130 signaling may provide novel targets to induce neurogenesis for cell replacement therapies.

Blood vitronectin is a major activator of LIF and IL-6 in the brain through integrin-FAK and uPAR signaling

We defined how blood-derived vitronectin (VTN) rapidly and potently activates leukemia inhibitory factor (LIF) and pro-inflammatory interleukin 6 (IL-6) in vitro and after vascular injury in the brain. Treatment with VTN (but not fibrinogen, fibronectin, laminin-111 or collagen-I) substantially increased LIF and IL-6 within 4 h in C6-astroglioma cells, while VTN^-/- mouse plasma was less effective than that from wild-type mice. LIF and IL-6 were induced by intracerebral injection of recombinant human (rh)VTN in mice, but induction seen upon intracerebral hemorrhage was less in VTN^-/- mice than in wild-type littermates. In vitro, VTN effects were inhibited by RGD, αvβ3 and αvβ5 integrin-blocking peptides and antibodies. VTN activated focal adhesion kinase (FAK; also known as PTK2), whereas pharmacological- or siRNA-mediated inhibition of FAK, but not PYK2, reduced the expression of LIF and IL-6 in C6 and endothelial cells and after traumatic cell injury. Dominant-negative FAK (Y397F) reduced the amount of injury-induced LIF and IL-6. Pharmacological inhibition or knockdown of uPAR (also known as PLAUR), which binds VTN, also reduced cytokine expression, possibly through a common target of uPAR and integrins. We propose that VTN leakage into tissues promotes inflammation. Integrin-FAK signaling is therefore a novel IL-6 and LIF regulation mechanism relevant to the inflammation and stem cell fields.

Measuring Ciliary Neurotrophic Factor (CNTF) in Lacrimal Fluid Using Optimized Commercial ELISA

The concentration of ciliary neurotrophic factor (CNTF) was measured in lacrimal fluid (LF) using Human CNTF Quantikine ELISA kit (“R&D Systems”, USA) on a ChemWell 2910 automatic analyzer (“Awareness Technology Inc.”, USA). We initially attempted to use commercial kits, designed for serum and plasma CNTF detection, to quantify lacrimal CNTF. The results, however, were rarely above the minimum detection level of the kits, most likely due to matrix complexity and low concentrations of CNTF in diluted LF (LF had to be diluted because of the small volume of collected samples). The optimal sensitivity and the lowest background for the best minimum quantifiable value were determined empirically. Phosphate buffer solution containing 1% bovine serum albumin was selected as an optimal diluent for CNTF measurements in small fluid samples. A standard curve was produced using the calibrating solutions 0-250 pg/ml. Acid treatment of LF samples before the analysis allowed to increase the detectable concentration of the CNTF two-fold. The 1:3 dilution was selected based on the available volume of collected LF and a reasonable variation coefficient. The described protocol allowed to develop a sandwich ELISA optimized for lacrimal CNTF.

Assessed and Emerging Biomarkers in Stroke and Training-Mediated Stroke Recovery: State of the Art

Since the increasing update of the biomolecular scientific literature, biomarkers in stroke have reached an outstanding and remarkable revision in the very recent years. Besides the diagnostic and prognostic role of some inflammatory markers, many further molecules and biological factors have been added to the list, including tissue derived cytokines, growth factor-like molecules, hormones, and microRNAs. The literatures on brain derived growth factor and other neuroimmune mediators, bone-skeletal muscle biomarkers, cellular and immunity biomarkers, and the role of microRNAs in stroke recovery were reviewed. To date, biomarkers represent a possible challenge in the diagnostic and prognostic evaluation of stroke onset, pathogenesis, and recovery. Many molecules are still under investigation and may become promising and encouraging biomarkers. Experimental and clinical research should increase this list and promote new discoveries in this field, to improve stroke diagnosis and treatment.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

CRMPs Function in Neurons and Glial Cells: Potential Therapeutic Targets for Neurodegenerative Diseases and CNS Injury

Neurodegeneration in the adult mammalian central nervous system (CNS) is fundamentally accelerated by its intrinsic neuronal mechanisms, including its poor regenerative capacity and potent extrinsic inhibitory factors. Thus, the treatment of neurodegenerative diseases faces many obstacles. The degenerative processes, consisting of axonal/dendritic structural disruption, abnormal axonal transport, release of extracellular factors, and inflammation, are often controlled by the cytoskeleton. From this perspective, regulators of the cytoskeleton could potentially be a therapeutic target for neurodegenerative diseases and CNS injury. Collapsin response mediator proteins (CRMPs) are known to regulate the assembly of cytoskeletal proteins in neurons, as well as control axonal growth and neural circuit formation. Recent studies have provided some novel insights into the roles of CRMPs in several inhibitory signaling pathways of neurodegeneration, in addition to its functions in neurological disorders and CNS repair. Here, we summarize the roles of CRMPs in axon regeneration and its emerging functions in non-neuronal cells, especially in inflammatory responses. We also discuss the direct and indirect targeting of CRMPs as a novel therapeutic strategy for neurological diseases.

Differential susceptibility of cortical and subcortical inhibitory neurons and astrocytes in the long term following diffuse traumatic brain injury

Long-term diffuse traumatic brain injury (dTBI) causes neuronal hyperexcitation in supragranular layers in sensory cortex, likely through reduced inhibition. Other forms of TBI affect inhibitory interneurons in subcortical areas but it is unknown if this occurs in cortex, or in any brain area in dTBI. We investigated dTBI effects on inhibitory neurons and astrocytes in somatosensory and motor cortex, and hippocampus, 8 weeks post-TBI. Brains were labeled with antibodies against calbindin (CB), parvalbumin (PV), calretinin (CR) and neuropeptide Y (NPY), and somatostatin (SOM) and glial fibrillary acidic protein (GFAP), a marker for astrogliosis during neurodegeneration. Despite persistent behavioral deficits in rotarod performance up to the time of brain extraction (TBI = 73.13 ± 5.23% mean ± SEM, Sham = 92.29 ± 5.56%, P < 0.01), motor cortex showed only a significant increase, in NPY neurons in supragranular layers (mean cells/mm² ± SEM, Sham = 16 ± 0.971, TBI = 25 ± 1.51, P = 0.001). In somatosensory cortex, only CR⁺ neurons showed changes, being decreased in supragranular (TBI = 19 ± 1.18, Sham = 25 ± 1.10, P < 0.01) and increased in infragranular (TBI = 28 ± 1.35, Sham = 24 ± 1.07, P < 0.05) layers. Heterogeneous changes were seen in hippocampal staining: CB⁺ decreased in dentate gyrus (TBI = 2 ± 0.382, Sham = 4 ± 0.383, P < 0.01), PV⁺ increased in CA1 (TBI = 39 ± 1.26, Sham = 33 ± 1.69, P < 0.05) and CA2/3 (TBI = 26 ± 2.10, Sham = 20 ± 1.49, P < 0.05), and CR⁺ decreased in CA1 (TBI = 10 ± 1.02, Sham = 14 ± 1.14, P < 0.05). Astrogliosis significantly increased in corpus callosum (TBI = 6.7 ± 0.69, Sham = 2.5 ± 0.38; P = 0.007). While dTBI effects on inhibitory neurons appear region- and type-specific, a common feature in all cases of decrease was that changes occurred in dendrite targeting interneurons involved in neuronal integration. J. Comp. Neurol. 524:3530-3560, 2016. © 2016 Wiley Periodicals, Inc.

MicroRNA-155 deletion reduces anxiety- and depressive-like behaviors in mice

Depressive disorders have complex and multi-faceted underlying mechanisms, rendering these disorders difficult to treat consistently and effectively. One under-explored therapeutic strategy for alleviating mood disorders is the targeting of microRNAs (miRs). miRs are small non-coding RNAs that cause sequestration/degradation of specific mRNAs, thereby preventing protein translation and downstream functions. miR-155 has validated and predicted neurotrophic factor and inflammatory mRNA targets, which led to our hypothesis that miR-155 deletion would modulate affective behaviors. To evaluate anxiety-like behavior, wildtype (wt) and miR-155 knockout (ko) mice (littermates; both male and female) were assessed in the open field and on an elevated plus maze. In both tests, miR-155 ko mice spent more time in open areas, suggesting they had reduced anxiety-like behavior. Depressive-like behaviors were assessed using the forced swim test. Compared to wt mice, miR-155 ko mice exhibited reduced float duration and increased latency to float. Further, although all mice exhibited a strong preference for a sucrose solution over water, this preference was enhanced in miR-155 ko mice. miR-155 ko mice had no deficiencies in learning and memory (Barnes maze) or social preference/novelty suggesting that changes in mood were specific. Finally, compared to wt hippocampi, miR-155 ko hippocampi had a reduced inflammatory signature (e.g., decreased IL-6, TNF-a) and female miR-155 ko mice increased ciliary neurotrophic factor expression. Together, these data highlight the importance of studying microRNAs in the context of anxiety and depression and identify miR-155 as a novel potential therapeutic target for improving mood disorders.

Functional polarization of neuroglia: Implications in neuroinflammation and neurological disorders

Recent neuroscience research has established the adult brain as a dynamic organ having a unique ability to undergo changes with time. Neuroglia, especially microglia and astrocytes, provide dynamicity to the brain. Activation of these glial cells is a major component of the neuroinflammatory responses underlying brain injury and neurodegeneration. Glial cells execute functional reaction programs in response to diverse microenvironmental signals manifested by neuropathological conditions. Activated microglia exist along a continuum of two functional states of polarization namely M1-type (classical/proinflammatory activation) and M2-type (alternative/anti-inflammatory activation) as in macrophages. The balance between classically and alternatively activated microglial phenotypes influences disease progression in the CNS. The classically activated state of microglia drives the neuroinflammatory response and mediates the detrimental effects on neurons, whereas in their alternative activation state, which is apparently a beneficial activation state, the microglia play a crucial role in tissue maintenance and repair. Likewise, in response to immune or inflammatory microenvironments astrocytes also adopt neurotoxic or neuroprotective phenotypes. Reactive astrocytes exhibit two distinctive functional phenotypes defined by pro- or anti-inflammatory gene expression profile. In this review, we have thoroughly covered recent advances in the understanding of the functional polarization of brain and peripheral glia and its implications in neuroinflammation and neurological disorders. The identifiable phenotypes adopted by neuroglia in response to specific insult or injury can be exploited as promising diagnostic markers of neuroinflammatory diseases. Furthermore, harnessing the beneficial effects of the polarized glia could undoubtedly pave the way for the formulation of novel glia-based therapeutic strategies for diverse neurological disorders.

TRPV1 on astrocytes rescues nigral dopamine neurons in Parkinson's disease via CNTF

Currently there is no neuroprotective or neurorestorative therapy for Parkinson's disease. Here we report that transient receptor potential vanilloid 1 (TRPV1) on astrocytes mediates endogenous production of ciliary neurotrophic factor (CNTF), which prevents the active degeneration of dopamine neurons and leads to behavioural recovery through CNTF receptor alpha (CNTFRα) on nigral dopamine neurons in both the MPP(+)-lesioned or adeno-associated virus α-synuclein rat models of Parkinson's disease. Western blot and immunohistochemical analysis of human post-mortem substantia nigra from Parkinson's disease suggests that this endogenous neuroprotective system (TRPV1 and CNTF on astrocytes, and CNTFRα on dopamine neurons) might have relevance to human Parkinson's disease. Our results suggest that activation of astrocytic TRPV1 activates endogenous neuroprotective machinery in vivo and that it is a novel therapeutic target for the treatment of Parkinson's disease.

Peripheral Nerve Regeneration by Secretomes of Stem Cells from Human Exfoliated Deciduous Teeth

Peripheral nerve regeneration across nerve gaps is often suboptimal, with poor functional recovery. Stem cell transplantation-based regenerative therapy is a promising approach for axon regeneration and functional recovery of peripheral nerve injury; however, the mechanisms remain controversial and unclear. Recent studies suggest that transplanted stem cells promote tissue regeneration through a paracrine mechanism. We investigated the effects of conditioned media derived from stem cells from human exfoliated deciduous teeth (SHED-CM) on peripheral nerve regeneration. In vitro, SHED-CM-treated Schwann cells exhibited significantly increased proliferation, migration, and the expression of neuron-, extracellular matrix (ECM)-, and angiogenesis-related genes. SHED-CM stimulated neuritogenesis of dorsal root ganglia and increased cell viability. Similarly, SHED-CM enhanced tube formation in an angiogenesis assay. In vivo, a 10-mm rat sciatic nerve gap model was bridged by silicon conduits containing SHED-CM or serum-free Dulbecco's modified Eagle's medium. Light and electron microscopy confirmed that the number of myelinated axons and axon-to-fiber ratio (G-ratio) were significantly higher in the SHED-CM group at 12 weeks after nerve transection surgery. The sciatic functional index (SFI) and gastrocnemius (target muscle) wet weight ratio demonstrated functional recovery. Increased compound muscle action potentials and increased SFI in the SHED-CM group suggested sciatic nerve reinnervation of the target muscle and improved functional recovery. We also observed reduced muscle atrophy in the SHED-CM group. Thus, SHEDs may secrete various trophic factors that enhance peripheral nerve regeneration through multiple mechanisms. SHED-CM may therefore provide a novel therapy that creates a more desirable extracellular microenvironment for peripheral nerve regeneration.

Rational modulation of the innate immune system for neuroprotection in ischemic stroke

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Complementary effects of two growth factors in multifunctionalized silk nanofibers for nerve reconstruction

With the aim of forming bioactive guides for peripheral nerve regeneration, silk fibroin was electrospun to obtain aligned nanofibers. These fibers were functionalized by incorporating Nerve Growth Factor (NGF) and Ciliary NeuroTrophic Factor (CNTF) during electrospinning. PC12 cells grown on the fibers confirmed the bioavailability and bioactivity of the NGF, which was not significantly released from the fibers. Primary neurons from rat dorsal root ganglia (DRGs) were grown on the nanofibers and anchored to the fibers and grew in a directional fashion based on the fiber orientation, and as confirmed by growth cone morphology. These biofunctionalized nanofibers led to a 3-fold increase in neurite length at their contact, which was likely due to the NGF. Glial cell growth, alignment and migration were stimulated by the CNTF in the functionalized nanofibers. Organotypic culture of rat fetal DRGs confirmed the complementary effect of both growth factors in multifunctionalized nanofibers, which allowed glial cell migration, alignment and parallel axonal growth in structures resembling the ‘bands of Bungner’ found in situ. Graftable multi-channel conduits based on biofunctionalized aligned silk nanofibers were developed as an organized 3D scaffold. Our bioactive silk tubes thus represent new options for a biological and biocompatible nerve guidance conduit.

P2X7 receptor inhibition increases CNTF in the subventricular zone, but not neurogenesis or neuroprotection after stroke in adult mice

Increasing endogenous ciliary neurotrophic factor (CNTF) expression with a pharmacological agent might be beneficial after stroke as CNTF both promotes neurogenesis and, separately, is neuroprotective. P2X7 purinergic receptor inhibition is neuroprotective in rats and increases CNTF release in rat CMT1A Schwann cells. We, first, investigated the role of P2X7 in regulating CNTF and neurogenesis in adult mouse subventricular zone (SVZ). CNTF expression was increased by daily intravenous injections of the P2X7 antagonist Brilliant Blue G (BBG) in naïve C57BL/6 or Balb/c mice over 3 days. Despite the ∼40-60 % increase or decrease in CNTF with BBG or the agonist BzATP, respectively, the number of proliferated BrdU+SVZ nuclei did not change. BBG failed to increase FGF2, which is involved in CNTF-regulated neurogenesis, but induced IL-6, LIF, and EGF, which are known to reduce SVZ proliferation. Injections of IL-6 next to the SVZ induced CNTF and FGF2, but not proliferation, suggesting that IL-6 counteracts their neurogenesis-inducing effects. Following ischemic injury of the striatum by middle cerebral artery occlusion (MCAO), a 3-day BBG treatment increased CNTF in the medial penumbra containing the SVZ. BBG also induced CNTF and LIF, which are known to be protective following stroke, in the whole striatum after MCAO, but not GDNF or BDNF. However, BBG treatment did not reduce the lesion area or apoptosis in the penumbra. Even so, this study shows that P2X7 can be targeted with systemic drug treatments to differentially regulate neurotrophic factors in the brain following stroke.

Astrocytic therapies for neuronal repair in stroke

Stroke is a leading cause of disability and death worldwide. Much of the work on improving stroke recovery has focused on preventing neuronal loss; however, these approaches have repeatedly failed in clinical trials. Conversely, relatively little is known about the mechanisms of repair and recovery after stroke. Stroke causes an initial process of local scar formation that confines the damage, and a later and limited process of tissue repair that involves the formation of new connections and new blood vessels. Astrocytes are central to both scar formation and to tissue repair after stroke. Astrocytes regulate the synapses and blood vessels within their cellular projections, or domain, and both respond to and release neuroimmune molecules in response to damage. Despite this central role in brain function, astrocytes have been largely neglected in the pursuit of effective stroke therapeutics. Here, we will review the changes astrocytes undergo in response to stroke, both beneficial and detrimental, and discuss possible points of intervention to promote recovery.

Proteome of brain glia: the molecular basis of diverse glial phenotypes

Several different types of nonneuronal glial cells with diverse phenotypes are present in the CNS, and all have distinct indispensible functions. Although glial cells primarily provide neurons with metabolic and structural support in the healthy brain, they may switch phenotype from a "resting" to a "reactive" state in response to pathological insults. Furthermore, this reactive gliosis is an invariant feature of the pathogeneses of CNS maladies. The glial proteome serves as a signature of glial phenotype, and not only executes physiological functions, but also acts as a molecular mediator of the reactive glial phenotype. The glial proteome is also involved in intra- and intercellular communications as exemplified by glia-glia and neuron-glia interactions. The utilization of authoritative proteomic tools and the bioinformatic analyses have helped to profile the brain glial proteome and explore the molecular mechanisms of diverse glial phenotypes. Furthermore, technologic innovations have equipped the field of "glioproteomics" with refined tools for studies of the expression, interaction, and function of glial proteins in the healthy and in the diseased CNS. Glioproteomics is expected to contribute to the elucidation of the molecular mechanisms of CNS pathophysiology and to the discovery of biomarkers and theragnostic targets in CNS disorders.

Activation of protease-activated receptor 2-mediated signaling by mast cell tryptase modulates cytokine production in primary cultured astrocytes

Protease-activated receptor 2 (PAR-2), which is abundantly expressed in astrocytes, is known to play major roles in brain inflammation. However, the influence of the natural agonist of PAR-2, tryptase, on proinflammatory mediator releasedfrom astrocytes remains uninvestigated. In the present study, we found that tryptase at lower concentrations modestly reduced intracellular ROS production but significantly increased IL-6 and TNF-α secretion at higher concentrations without affecting astrocytic viability and proliferation. The actions of tryptase were alleviated by specific PAR-2 antagonist FSLLRY-NH2 (FS), indicating that the actions of tryptase were via PAR-2. PI3K/AKT inhibitor LY294002 reversed the effect of tryptase on IL-6 production, whereas inhibitors specific for p38, JNK, and ERK1/2 abolished the effect of tryptase on TNF-α production, suggesting that different signaling pathways are involved. Moreover, tryptase-induced activation of MAPKs and AKT was eliminated by FS, implicating that PAR-2 is responsible for transmitting tryptase biosignals to MAPKs and AKT. Tryptase provoked also expression of TGF-β and CNTF in astrocytes. The present findings suggest for the first time that tryptase can regulate the release of cytokines from astrocytes via PAR-2-MAPKs or PAR-2-PI3K/AKT signaling pathways, which reveals PAR-2 as a new target actively participating in the regulation of astrocytic functions.

Inhibition of a novel specific neuroglial integrin signaling pathway increases STAT3-mediated CNTF expression

Background

Ciliary neurotrophic factor (CNTF) expression is repressed in astrocytes by neuronal contact in the CNS and is rapidly induced by injury. Here, we defined an inhibitory integrin signaling pathway.

Results

The integrin substrates laminin, fibronectin and vitronectin, but not collagen, thrombospondin or fibrinogen, reduced CNTF expression in C6 astroglioma cells. Antibodies against αv and β5, but not α6 or β1, integrin induced CNTF. Together, the ligand and antibody specificity suggests that CNTF is repressed by αvβ5 integrin. Antibodies against Thy1, an abundant neuronal surface protein whose function is unclear, induced CNTF in neuron-astrocyte co-cultures indicating that it is a neuroglial CNTF repressor. Inhibition of the integrin signaling molecule Focal Adhesion Kinase (FAK) or the downstream c-Jun N-terminal kinase (JNK), but not extracellular regulated kinase (ERK) or p38 MAPK, greatly induced CNTF mRNA and protein expression within 4 hours. This selective inhibitory pathway phosphorylated STAT3 on its inhibitory ser-727 residue interfering with activity of the pro-transcription Tyr-705 residue. STAT3 can activate CNTF transcription because it bound to its promoter and FAK antagonist-induced CNTF was reduced by blocking STAT3. Microinjection of FAK inhibitor directly into the brain or spinal cord in adult mice rapidly induced CNTF mRNA and protein expression. Importantly, systemic treatment with FAK inhibitors over 3 days induced CNTF in the subventricular zone and increased neurogenesis.

Conclusions

Neuron-astroglia contact mediated by integrins serves as a sensor to enable rapid neurotrophic responses and provides a new pharmacological avenue to exploit the neuroprotective properties of endogenous CNTF.

Oligodendroglia and neurotrophic factors in neurodegeneration

Myelination by oligodendroglial cells (OLs) enables the propagation of action potentials along neuronal axons, which is essential for rapid information flow in the central nervous system. Besides saltatory conduction, the myelin sheath also protects axons against inflammatory and oxidative insults. Loss of myelin results in axonal damage and ultimately neuronal loss in demyelinating disorders. However, accumulating evidence indicates that OLs also provide support to neurons via mechanisms beyond the insulating function of myelin. More importantly, an increasing volume of reports indicates defects of OLs in numerous neurodegenerative diseases, sometimes even preceding neuronal loss in pre-symptomatic episodes, suggesting that OL pathology may be an important mechanism contributing to the initiation and/or progression of neurodegeneration. This review focuses on the emerging picture of neuronal support by OLs in the pathogenesis of neurodegenerative disorders through diverse molecular and cellular mechanisms, including direct neuron-myelin interaction, metabolic support by OLs, and neurotrophic factors produced by and/or acting on OLs.

Neuroimmune communication in hypertension and obesity: a new therapeutic angle?

Hypertension is an epidemic health concern and a major risk factor for the development of cardiovascular disease. Although there are available treatment strategies for hypertension, numerous hypertensive patients do not have their clinical symptoms under control and it is imperative that new avenues to treat or prevent high blood pressure in these patients are developed. It is well established that increases in sympathetic nervous system (SNS) outflow and enhanced renin-angiotensin system (RAS) activity are common features of hypertension and various pathological conditions that predispose individuals to hypertension. More recently, hypertension has also become recognized as an immune condition and accumulating evidence suggests that interactions between the RAS, SNS and immune systems play a role in blood pressure regulation. This review summarizes what is known about the interconnections between the RAS, SNS and immune systems in the neural regulation of blood pressure. Based on the reviewed studies, a model for RAS/neuroimmune interactions during hypertension is proposed and the therapeutic potential of targeting RAS/neuroimmune interactions in hypertensive patients is discussed. Special emphasis is placed on the applicability of the proposed model to obesity-related hypertension.

What can we learn about stroke from retinal ischemia models?

Retinal ischemia is a very useful model to study the impact of various cell death pathways, such as apoptosis and necrosis, in the ischemic retina. However, it is important to note that the retina is formed as an outpouching of the diencephalon and is part of the central nervous system. As such, the cell death pathways initiated in response to ischemic damage in the retina reflect those found in other areas of the central nervous system undergoing similar trauma. The retina is also more accessible than other areas of the central nervous system, thus making it a simpler model to work with and study. By utilizing the retinal model, we can greatly increase our knowledge of the cell death processes initiated by ischemia which lead to degeneration in the central nervous system. This paper examines work that has been done so far to characterize various aspects of cell death in the retinal ischemia model, such as various pathways which are activated, and the role neurotrophic factors, and discusses how these are relevant to the treatment of ischemic damage in both the retina and the greater central nervous system.

Endogenous CNTF mediates stroke-induced adult CNS neurogenesis in mice

Focal brain ischemia in adult rats rapidly and robustly induces neurogenesis in the subventricular zone (SVZ) but there are few and inconsistent reports in mice, presenting a hurdle to genetically investigate the endogenous neurogenic regulators such as ciliary neurotrophic factor (CNTF). Here, we first provide a platform for further studies by showing that middle cerebral artery occlusion in adult male C57BL/6 mice robustly enhances neurogenesis in the SVZ only under very specific conditions, i.e., 14days after a 30min occlusion. CNTF expression paralleled changes in the number of proliferated, BrdU-positive, SVZ cells. Stroke-induced proliferation was absent in CNTF-/- mice, suggesting that it is mediated by CNTF. MCAO-increased CNTF appears to act on C cell proliferation and by inducing FGF2 expression but not via EGF expression or Notch1 signaling of neural stem cells in the SVZ. CNTF is unique, as expression of other gp130 ligands, IL-6 and LIF, did not predict SVZ proliferation or showed no or only small compensatory increases in CNTF-/- mice. Expression of tumor necrosis factor-α, which can inhibit neurogenesis, and the presence of leukocytes in the SVZ were inversely correlated with neurogenesis, but pro-inflammatory cytokines did not affect CNTF expression in cultured astrocytes. These results suggest that slowly up-regulated CNTF in the SVZ mediates stroke-induced neurogenesis and is counteracted by inflammation. Further pharmacological stimulation of endogenous CNTF might be a good therapeutic strategy for cell replacement after stroke as CNTF regulates normal patterns of neurogenesis and is expressed almost exclusively in the nervous system.