Stage-dependent STAT3 activation is involved in the differentiation of rat hippocampus neural stem cells

The multitaskers of the brain: Glial responses to viral infections and associated post-infectious neurologic sequelae

Many viral infections cause acute and chronic neurologic diseases which can lead to degeneration of cortical functions. While neurotropic viruses that gain access to the central nervous system (CNS) may induce brain injury directly via infection of neurons or their supporting cells, they also alter brain function via indirect neuroimmune mechanisms that may disrupt the blood-brain barrier (BBB), eliminate synapses, and generate neurotoxic astrocytes and microglia that prevent recovery of neuronal circuits. Non-neuroinvasive, neurovirulent viruses may also trigger aberrant responses in glial cells, including those that interfere with motor and sensory behaviors, encoding of memories and executive function. Increasing evidence from human and animal studies indicate that neuroprotective antiviral responses that amplify levels of innate immune molecules dysregulate normal neuroimmune processes, even in the absence of neuroinvasion, which may persist after virus is cleared. In this review, we discuss how select emerging and re-emerging RNA viruses induce neuroimmunologic responses that lead to dysfunction of higher order processes including visuospatial recognition, learning and memory, and motor control. Identifying therapeutic targets that return the neuroimmune system to homeostasis is critical for preventing virus-induced neurodegenerative disorders.

MicroRNAs and JAK/STAT3 signaling: A new promising therapeutic axis in blood cancers

Blood disorders include a wide spectrum of blood-associated malignancies resulting from inherited or acquired defects. The ineffectiveness of existing therapies against blood disorders arises from different reasons, one of which is drug resistance, so different types of leukemia may show different responses to treatment. Leukemia occurs for a variety of genetic and acquired reasons, leading to uncontrolled proliferation in one or more cell lines. Regarding the genetic defects, oncogene signal transducer and activator of transcription (STAT) family transcription factor, especially STAT3, play an essential role in hematological disorders onset and progress upon mutations, dysfunction, or hyperactivity. Besides, microRNAs, as biological molecules, has been shown to play a dual role in either tumorigenesis and tumor suppression in various cancers. Besides, a strong association between STAT3 and miRNA has been reported. For example, miRNAs can regulate STAT3 via targeting its upstream mediators such as IL6, IL9, and JAKs or directly binding to the STAT3 gene. On the other hand, STAT3 can regulate miRNAs. In this review study, we aimed to determine the role of either microRNAs and STAT3 along with their effect on one another's activity and function in hematological malignancies.

Transcranial Laser Photobiomodulation Improves Intracellular Signaling Linked to Cell Survival, Memory and Glucose Metabolism in the Aged Brain: A Preliminary Study

Aging is often accompanied by exacerbated activation of cell death-related signaling pathways and decreased energy metabolism. We hypothesized that transcranial near-infrared laser may increase intracellular signaling pathways beneficial to aging brains, such as those that regulate brain cell proliferation, apoptosis, and energy metabolism. To test this hypothesis, we investigated the expression and activation of intracellular signaling proteins in the cerebral cortex and hippocampus of aged rats (20 months old) treated with the transcranial near-infrared laser for 58 consecutive days. As compared to sham controls, transcranial laser treatment increased intracellular signaling proteins related to cell proliferation and cell survival, such as signal transducer and activator of transcription 3 (STAT3), extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p70 ribosomal protein S6 kinase (p70S6K) and protein kinase B (PKB), also known as Akt that is linked to glucose metabolism. In addition, ERK is linked to memory, while ERK and JNK signaling pathways regulate glucose metabolism. Specifically, the laser treatment caused the activation of STAT3, ERK, and JNK signaling proteins in the cerebral cortex. In the hippocampus, the laser treatment increased the expression of p70S6K and STAT3 and the activation of Akt. Taken together, the data support the hypothesis that transcranial laser photobiomodulation improves intracellular signaling pathways linked to cell survival, memory, and glucose metabolism in the brain of aged rats.

Proteomics-Guided Study on Buyang Huanwu Decoction for Its Neuroprotective and Neurogenic Mechanisms for Transient Ischemic Stroke: Involvements of EGFR/PI3K/Akt/Bad/14-3-3 and Jak2/Stat3/Cyclin D1 Signaling Cascades

Buyang Huanwu Decoction (BHD), a classic traditional Chinese medicine (TCM) formula, has been used for recovering neurological dysfunctions and treating post-stroke disability in China for 200 years. In the present study, we investigated the effects of BHD on inhibiting neuronal apoptosis, promoting proliferation and differentiation of neural stem cells (NSCs) and neurite formation and enhancing learning and memory functional recovery in an experimental rat ischemic stroke model. BHD significantly reduced infarct volume and decreased cell apoptosis in the ischemic brain. BHD enhanced neuronal cell viability in vitro. BHD dose-dependently promoted the proliferation of NSCs in ischemic rat brains in vivo. Moreover, BHD promoted neuronal and astrocyte differentiation in primary cultured NSCs in vitro. Water maze test revealed that BHD promoted the recovery of learning function but not memory functions in the transient ischemic rats. We then investigated the changes of the cellular signaling molecules by using two-dimension (2D) gel electrophoresis and focused on the PI3K/Akt/Bad and Jak2/Stat3/cyclin D1signaling pathway to uncover its underlying mechanisms for its neuroprotective and neurogenetic effects. BHD significantly upregulated the expression of p-PI3K, p-Akt, and p-Bad as well as the expression of p-Jak, p-Stat3, and cyclin D1 in vitro and in vivo. In addition, BHD upregulated Hes1 and downregulated cav-1 in vitro and in vivo. Taken together, these results suggest that BHD has neuroprotective effects and neurogenesis-promoting effects via activating PI3K/Akt/Bad and Jak2/Stat3/Cyclin D1 signaling pathways. Graphical Abstract Buyang Huanwu Decoction (BHD) activates the PI3K-AKT-BAD pathway in the ischemic brain for neuroprotection. BHD also activates JAK2/STAT3/Cyclin D1 signaling cascades for promoting neurogenesis in the hippocampus of post-ischemic brains. Moreover, BHD inhibits the expression of caveolin-1 and increases the expression of HES1 for promoting neuronal differentiation. The neuroprotective and neurogenesis-promoting effects in the hippocampus of post-ischemic brains promote learning ability.

miR-135b-dependent downregulation of S100B promotes neural stem cell differentiation in a hypoxia/ischemia-induced cerebral palsy rat model

Cerebral palsy (CP) is frequently caused by brain injury during pregnancy, delivery, or the immediate postnatal period. The differentiation potential of neural stem cell (NSC) makes them effective in restoring injured tissues and organs with minimal risks of side effects. In this study, we identified a novel microRNA-135b (miR-135b) in CP and investigated its functional role in mediating NSC differentiation. CP models were established in Wistar rats and validated with the Y-maze test. Gain- and loss-of-function experimentation was performed on CP rats. Then NSCs were isolated and the expression patterns of miR-135b and S100B were altered in NSCs. S100B exhibited high expression in the hippocampus tissues of CP models, which was targeted by miR-135b. miR-135b elevation or S100B silencing resulted in promoted NSC differentiation, alleviated brain injury, and inhibited NSC apoptosis in hippocampus tissues of CP rats. S100B downregulation targeted by miR-135b overexpression contributed to the inactivation of the signal transducer and activator of transcription-3 (STAT3) pathway, which promoted NSC differentiation and proliferation but inhibited NSC apoptosis. Our results highlight the suppressor role played by miR-135b in CP by inducing NSC differentiation via inactivation of S100B-dependent STAT3 pathway.

Downregulation of STAT1 induces the differentiation of neural stem cells through JNK pathway

Neural stem cells (NSCs) generated neurons and glial cells. Thus, it is a preferable candidate to the cell replacement-based therapy against neural disorders. The signaling pathways that regulate differentiation of NSCs are widely studied. In the current study, we used in vitro culture system to elucidate the role of signal transducer and activator of transcription 1 (STAT1) in NSCs' differentiation. Downregulation of STAT1 inhibited the proliferation of NSCs. Meanwhile, we also found STAT1 regulation could control the differentiation of NSCs. More neurons and glia cells were generated from NSCs with STAT1 silencing. This process was mediated by the JNK/STAT1 signaling. STAT1 inhibitor promoted differentiation of NSCs. After transplantation, we observed more neurons generated from NSCs with shRNA-STAT1 treatment. Collectively, this work showed an efficient way to regulate neuronal differentiation of NSCs through regulating the STAT1 expression. This is likely to provide source and theoretical support to cell replacement based theory.

Total flavones of Rhododendron simsii Planch flower protect rat hippocampal neuron from hypoxia-reoxygenation injury via activation of BKCa channel

OBJECTIVES

To study the effects of total flavones of Rhododendra simsii Planch flower (TFR) on hypoxia/reoxygenation (H/R) injury in rat hippocampal neurons and its underlying mechanism.

METHOD

Model of H/R was established in newborn rat primary cultured hippocampal neuron. Lactate dehydrogenase (LDH) and neuron-specific enolase (NSE) activity as well as malondialdehyde (MDA) content in cultured supernatants of the neurons were examined. Methyl thiazolyl tetrazolium assay and Hoechst33258 staining were, respectively, used to detect cell viability and apoptosis of neurons. Protein expression and current of BK_Ca channel were assessed by using Western blotting and whole-cell patch-clamp methods, respectively.

KEY FINDINGS

In the ranges of 3.7-300 mg/l, TFR significantly inhibited H/R-induced decrease of neuronal viability and increases of LDH, NSE and MDA in the supernatants as well as apoptosis; TFR 33.3, 100 and 300 mg/l markedly increased current of BK_Ca channel rather than the BK_Ca channel protein expression in the neurons.

CONCLUSIONS

Total flavones of R. simsii Planch flower had a protective effect against H/R injury in rat hippocampal neuron, and activation of BK_Ca channel may contribute to the neuroprotection.

JAK2/STAT3 signaling mediates IL-6-inhibited neurogenesis of neural stem cells through DNA demethylation/methylation

Neuroinflammation, considered as a pathological hallmark of Alzheimer's disease (AD), has been demonstrated to affect hippocampal neurogenesis and cognitive function. Interleukin-6 (IL-6) is a proinflammatory cytokine known to modulate neurogenesis. However, the mechanisms are still largely unknown. Here, we reported that IL-6 suppressed neurogenesis via a JAK2/STAT3 signaling in neural stem cells (NSCs). Importantly, we found that NeuroD1 (Neurogenic differentiation 1) gene expression, which drives NSCs neurodifferentiation, was regulated by TET3 and DNMT1 in a JAK2/STAT3-dependent manner. We further found that JAK2/STAT3 inhibition enhanced demethylation of NeuroD1 regulatory elements in IL-6-treated cells, which is related to the significant upregulation of TET3 expression as well as the decreased expression of DNMT1. Furthermore, Inhibiting JAK2/STAT3 significantly rescued the memory deficits and hippocampal neurogenesis dysfunction in APP/PS1 mice. Our data suggest that JAK2/STAT3 signaling plays a vital role in suppressing neurogenesis of NSCs exposed to IL-6 at the epigenetic level, by regulating DNA methylation/demethylation.

Neuroprotective Effect of CeO2@PAA-LXW7 Against H2O2-Induced Cytotoxicity in NGF-Differentiated PC12 Cells

CeO₂ nanoparticles (nanoceria) have been used in many studies as a powerful free radical scavenger, and LXW7, a small-molecule peptide, can specifically target the integrin αvβ3, whose neuroprotective effects have also been demonstrated. The objective of this study is to observe the neuroprotective effect and potential mechanism of CeO₂@PAA-LXW7, a new compound that couples CeO₂@PAA (nanoceria modified with the functional group of polyacrylic acid) with LXW7 via a series of chemical reactions, in H₂O₂-induced NGF-differentiated PC12 cells. We examined the effects of LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 on the viability of primary hippocampal neurons and found that there was no significant difference under control conditions, but increased cellular viability was observed in the case of H₂O₂-induced injury. We used H₂O₂-induced NGF-differentiated PC12 cells as the classical injury model to investigate the neuroprotective effect of CeO₂@PAA-LXW7. In this study, LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 inhibit H₂O₂-induced oxidative stress by reducing the production of reactive oxygen species (ROS) and regulating Bax/Bcl-2, cleaved caspase-3 and mitochondrial cytochrome C (cyto C) in the apoptotic signaling pathways. We found that the levels of phosphorylation of focal adhesion kinase (FAK) and of signal transducer and activator of transcription 3 (STAT3) increased significantly in H₂O₂-induced NGF-differentiated PC12 cells, whereas LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 suppressed the increase to different degrees. Among the abovementioned changes, the inhibitory effect of CeO₂@PAA-LXW7 on H₂O₂-induced changes, including the increases in the levels of p-FAK and p-STAT3, is more obvious than that of LXW7 or CeO₂@PAA alone. In summary, these results suggest that integrin signaling participates in the regulation of apoptosis via the regulation of ROS and of the apoptosis pathway in H₂O₂-induced NGF-differentiated PC12 cells. LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 can play neuroprotective roles by counteracting the oxidative stress and apoptosis induced by H₂O₂ in NGF-differentiated PC12 cells. CeO₂@PAA-LXW7 exerting a more powerful synergistic effect via the conjunction of LXW7 and CeO₂@PAA.

Interleukin-6-Mediated Induced Pluripotent Stem Cell (iPSC)-Derived Neural Differentiation

In an aging society with an increasing threat to higher brain cognitive functions due to dementia, it becomes imperative to identify new molecular remedies for supporting adult neurogenesis. Interleukin-6 (IL-6) is a promising cytokine that can support neurogenesis under conditions of neurodegeneration, and neuron replacement is eventually possible due to its agonistic acting soluble receptor sIL-6R. Here, we report that activation of the IL-6-signal transducer and activator of transcription 3 (STAT3) axis is neurogenic and has potential therapeutic applications for the treatment of neurodegenerative diseases such as Parkinson's disease (PD).

Neural Stem Cell Transplantation Promotes Functional Recovery from Traumatic Brain Injury via Brain Derived Neurotrophic Factor-Mediated Neuroplasticity

Traumatic brain injury (TBI) induces cognitive impairments, motor and behavioral deficits. Previous evidences have suggested that neural stem cell (NSC) transplantation could facilitate functional recovery from brain insults, but their underlying mechanisms remains to be elucidated. Here, we established TBI model by an electromagnetic-controlled cortical impact device in the rats. Then, 5 μl NSCs (5.0 × 10⁵/μl), derived from green fluorescent protein (GFP) transgenic mouse, was transplanted into the traumatic brain regions of rats at 24 h after injury. After differentiation of the NSCs was determined using immunohistochemistry, neurological severity scores (NSS) and rotarod test were conducted to detect the neurological behavior. Western blot and RT-PCR as well as ELASA were used to evaluate the expression of synaptophysin and brain-derived neurotrophic factor (BDNF). In order to elucidate the role of BDNF on the neural recovery after NSC transplantation, BDNF knockdown in NSC was performed and transplanted into the rats with TBI, and potential mechanism for BDNF knockdown in the NSC was analyzed using microassay analysis. Meanwhile, BDNF antibody blockade was conducted to further confirm the effect of BDNF on neural activity. As a result, an increasing neurological function improvement was seen in NSC transplanted rats, which was associated with the upregulation of synaptophysin and BDNF expression. Moreover, transplantation of BDNF knockdown NSCs and BDNF antibody block reduced not only the level of synaptophysin but also exacerbated neurological function deficits. Microassay analysis showed that 14 genes such as Wnt and Gsk3-β were downregulated after BDNF knockdown. The present data therefore showed that BDNF-mediated neuroplasticity underlie the mechanism of NSC transplantation for the treatment of TBI in adult rats.

Interferon gamma protects neonatal neural stem/progenitor cells during measles virus infection of the brain

BACKGROUND

In the developing brain, self-renewing neural stem/progenitor cells (NSPC) give rise to neuronal and glial lineages. NSPC survival and differentiation can be altered by neurotropic viruses and by the anti-viral immune response. Several neurotropic viruses specifically target and infect NSPCs, in addition to inducing neuronal loss, which makes it difficult to distinguish between effects on NSPCs that are due to direct viral infection or due to the anti-viral immune response.

METHODS

We have investigated the impact of anti-viral immunity on NSPCs in measles virus (MV)-infected neonates. A neuron-restricted viral infection model was used, where NSPCs remain uninfected. Thus, an anti-viral immune response was induced without the confounding issue of NSPC infection. Two-transgenic mouse lines were used: CD46+ mice express the human isoform of CD46, the MV entry receptor, under the control of the neuron-specific enolase promoter; CD46+/IFNγ-KO mice lack the key anti-viral cytokine IFNγ. Multi-color flow cytometry and Western Blot analysis were used to quantify effects on NSPC, neuronal, and glial cell number, and quantify effects on IFNγ-mediated signaling and cell markers, respectively.

RESULTS

Flow cytometric analysis revealed that NSPCs were reduced in CD46+/IFNγ-KO mice at 3, 7, and 10 days post-infection (dpi), but were unaffected in CD46+ mice. Early neurons showed the greatest cell loss at 7 dpi in both genotypes, with no effect on mature neurons and glial cells. Thus, IFNγ protected against NSPC loss, but did not protect young neurons. Western Blot analyses on hippocampal explants showed reduced nestin expression in the absence of IFNγ, and reduced doublecortin and βIII-tubulin in both genotypes. Phosphorylation of STAT1 and STAT2 occurred independently of IFNγ in the hippocampus, albeit with distinct regulation of activation.

CONCLUSIONS

This is the first study to demonstrate bystander effects of anti-viral immunity on NSPC function. Our results show IFNγ protects the NSPC population during a neonatal viral CNS infection. Significant loss of NSPCs in CD46+/IFNγ-KO neonates suggests that the adaptive immune response is detrimental to NSPCs in the absence of IFNγ. These results reveal the importance and contribution of the anti-viral immune response to neuropathology and may be relevant to other neuroinflammatory conditions.

Protective Effects and Mechanisms of Salvianolic Acid B Against H₂O₂-Induced Injury in Induced Pluripotent Stem Cell-Derived Neural Stem Cells

Induced pluripotent stem cells (iPSCs) have the potential to differentiate into neural lineages. Salvianolic acid B (Sal B) is a commonly used, traditional Chinese medicine for enhancing neuroprotective effects, and has antioxidant, anti-inflammatory, and antiapoptotic properties. Here, we explore the potential mechanism of Sal B in protecting iPSC-derived neural stem cells (NSCs) against H2O2-induced injury. iPSCs were induced into NSCs, iPSC-derived NSCs were treated with 50 μM Sal B for 24.5 h and 500 μM H2O2 for 24 h. The resulting effects were examined by flow cytometry analysis, quantitative reverse-transcription polymerase chain reaction, and western blotting. Upon H2O2 exposure, Sal B significantly promoted cell viability and stabilization of the mitochondrial membrane potential. Sal B also visibly decreased the cell apoptotic ratio. In addition, Sal B markedly reduced expression of matrix metalloproteinase (MMP)-2 and -9, and phosphospecific signal transducer and activator of transcription 3 (p-STAT3), and increased the level of tissue inhibitor of metalloproteinase (TIMP)-2 in iPSC-derived NSCs induced by H2O2. These results suggest that Sal B protects iPSC-derived NSCs against H2O2-induced oxidative stress. The mechanisms of this stress tolerance may be attributed to modulation of the MMP/TIMP system and inhibition of the STAT3 signaling pathway.

Qingnaoyizhi decoction suppresses the formation of glial fibrillary acidic protein-positive cells in cultured neural stem cells by inhibiting the Janus kinase 2/signal transducer and activator of transcription 3 signaling pathway

OBJECTIVE

Inactivation of the Janus kinase 2 in treated NSCs. Furthermore, QNYZD may play a direct role in suppressing the formation of GFAP-positive cells and enhancing neuronal differentiation by inhibiting JAK2/STAT3 activation. Overall, these results provide insights into the possible mechanism underlying QNYZD-mediated neurogenesis. (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling axis plays a crucial role in determining the fate of neural stem cells (NSCs). Qingnaoyizhi decoction (QNYZD) has been used for the treatment of vascular dementia and has shown to improve synaptic remodeling. The aim of this study was to evaluate the effect of cerebrospinal fluid (CSF) containing QNYZD (CSF-QNYZD) on the differentiation of cultured NSCs and the involvement of the JAK2/STAT3 pathway.

METHODS

The protein expression levels of glial fibrillary acidic protein (GFAP), tubulin, drosophila mothers against decapentaplegic protein (SMAD-1), STAT3, and phosphorylated-STAT3 were detected by western immunoblot analysis in the groups: control, CSF, JAK/STAT inhibitor (AG490), CSF-QNYZD, and CSF-XDZ (CSF-Xidezhen). The differentiation of NSCs was determined by immunofluorescence staining. The proliferation of NSCs was measured using the Cell Counting Kit-8 proliferation assay.

RESULTS

Compared with the control group, CSF-QNYZD and AG490 significantly increased the number and expression of tubulin-positive cells, reduced the number and expression of GFAP-positive cells, and down-regulated the expression of p-STAT3. However, CSF-QNYZD also decreased the expression of SMAD-1 and STAT3.

CONCLUSION

Enhanced neuronal differentiation may be associated with the down-regulation of glial differentiation instead of promoting proliferation in treated NSCs. Furthermore, QNYZD may play a direct role in suppressing the formation of GFAP-positive cells and enhancing neuronal differentiation by inhibiting JAK2/STAT3 activation. Overall, these results provide insights into the possible mechanism underlying QNYZD-mediated neurogenesis.

The effectiveness of an anti-human IL-6 receptor monoclonal antibody combined with chemotherapy to target colon cancer stem-like cells

Recent studies have demonstrated that cancer stem cells (CSCs) can initiate and sustain tumor growth and exhibit resistance to clinical cytotoxic therapies. Therefore, CSCs represent the main target of anticancer therapy. Interleukin-6 (IL-6) promotes cellular proliferation and drug resistance in colorectal cancer, and its serum levels correlate with patient survival. Therefore, IL-6 and its downstream signaling molecule the signal transducer and activator of transcription-3 (STAT3) represent potential molecular targets. In the present study, we investigated the effects of IL-6 and its downstream signaling components on stem cell biology, particularly the chemoresistance of CSCs, to explore potential molecular targets for cancer therapy. The colon cancer cell line WiDr was cultured in serum-free, non-adherent, and three-dimensional spheroid-forming conditions to enrich the stem cell-like population. Spheroid-forming cells slowly proliferated and expressed high levels of Oct-4, Klf4, Bmi-1, Lgr5, IL-6, and Notch 3 compared with adherent cells. Treatment with an anti-human IL-6 receptor monoclonal antibody reduced spheroid formation, stem cell-related gene expression, and 5-fluorouracil (5-FU) resistance. In addition, IL-6 treatment enhanced the levels of p-STAT3 (Tyr705), the expression of Oct-4, Klf4, Lgr5, and Notch 3, and chemoresistance to 5-FU. siRNA targeting Notch 3 suppressed spheroid formation, Oct-4 and Lgr5 expression, and 5-FU chemoresistance, whereas STAT3 inhibition enhanced Oct-4, Klf4, Lgr5, and Notch 3 expression and 5-FU chemoresistance along with reduced spheroid growth. Taken together, these results indicate that IL-6 functions in dichotomous pathways involving Notch 3 induction and STAT3 activation. The former pathway is involved in cancer stem-like cell biology and enhanced chemoresistance, and the latter pathway leads to accelerated proliferation and reduced chemoresistance. Thus, an anti-human IL-6 receptor monoclonal antibody or Notch 3 inhibition may be superior to STAT3 inhibition for CSC-targeting therapies concomitant with anticancer drugs.

Interleukin 18 activates MAPKs and STAT3 but not NF-κB in hippocampal HT-22 cells

Interleukin (IL)-18 is a cytokine previously demonstrated to participate in neuroinflammatory processes. Since the components of the IL-18 receptor complex are expressed in neurons throughout the brain, IL-18 is also believed to directly influence neuronal function. Here we tested this hypothesis on mouse hippocampal neurons by measuring the effects of IL-18 on three pathways previously shown to be regulated by this cytokine in non-neuronal cells: the MAPK pathways, p38 and ERK1/2 MAPKs, STAT3 and NF-κB. Experiments were carried out in vitro using the immortalized hippocampal neuronal line HT-22 or in vivo following i.c.v. injection with recombinant mouse IL-18. We showed that IL-18 did not activate NF-κB in HT-22 cells whereas it induced a rapid (within 15min) activation of the MAPK pathways. Moreover, we demonstrated that IL-18 treatment enhanced P-STAT3 (Tyr705)/STAT3 ratio in the nucleus of HT-22 cells after 30-60min of exposure. A similar increase in P-STAT3 (Tyr705)/STAT3 ratio was observed in the whole hippocampus one hour after i.c.v. injection. These data demonstrate that IL-18 can act directly on neuronal cells affecting the STAT3 pathway; therefore, possibly regulating the expression of specific genes within the hippocampus. This effect may help to explain some of the IL-18-induced effects on synaptic plasticity and functionality within the hippocampal system.

Early methyl donor deficiency may induce persistent brain defects by reducing Stat3 signaling targeted by miR-124

The methyl donors folate (vitamin B9) and vitamin B12 are centrepieces of the one-carbon metabolism that has a key role in transmethylation reactions, and thus in epigenetic and epigenomic regulations. Low dietary intakes of folate and vitamin B12 are frequent, especially in pregnant women and in the elderly, and deficiency constitutes a risk factor for various diseases, including neurological and developmental disorders. In this respect, both vitamins are essential for normal brain development, and have a role in neuroplasticity and in the maintenance of neuronal integrity. The consequences of a methyl donor deficiency (MDD) were studied both in vivo in rats exposed in utero, and in vitro in hippocampal progenitors (H19-7 cell line). Deficiency was associated with growth retardation at embryonic day 20 (E20) and postnatally with long-term brain defects in selective areas. mRNA and protein levels of the transcription factor Stat3 were found to be decreased in the brains of deprived fetuses and in differentiating progenitors (62 and 48% for total Stat3 protein, respectively), along with a strong reduction in its phosphorylation at both Tyr⁷⁰⁵ and Ser⁷²⁷ residues. Vitamin shortage also affected upstream kinases of Stat3 signaling pathway (phospho-Erk1/2, phospho-Src, phospho-JNK, and phospho-p38) as well as downstream target gene products (Bcl-2 and Bcl-xL), thus promoting apoptosis. Conversely, the expression of the Stat3 regulator miR-124 was upregulated in deficiency conditions (≥65%), and its silencing by using siRNA partly restored Stat3 signaling in hippocampal neurons by increasing specifically the phosphorylation of Erk1/2 and Src kinases. Furthermore, miR-124 siRNA improved the phenotype of deprived cells, with enhanced neurite outgrowth. Taken together, our data suggest that downregulation of Stat3 signaling by miR-124 would be a key factor in the deleterious effects of MDD on brain development.

Acceleration of astrocytic differentiation in neural stem cells surviving X-irradiation

Neural stem cells (NSCs) are highly susceptible to DNA double-strand breaks; however, little is known about the effects of radiation in cells surviving radiation. Although the nestin-positive NSCs predominantly became glial fibrillary acidic protein (GFAP)-positive in differentiation-permissive medium, little or no cells were GFAP positive in proliferation-permissive medium. We found that more than half of the cells surviving X-rays became GFAP positive in proliferation-permissive medium. Moreover, localized irradiation stimulated differentiation of cells outside the irradiated area. These results indicate for the first time that ionizing radiation is able to stimulate astrocyte-specific differentiation of surviving NSCs, whose process is mediated both by the direct activation of nuclear factor-κB and by the indirect bystander effect induced by X-irradiation.

A conserved microRNA/NMD regulatory circuit controls gene expression

Nonsense-mediated decay (NMD) is a RNA surveillance pathway that degrades subsets of normal and aberrant mRNAs. Mutations that perturb NMD cause neurological disorders in humans, suggesting that NMD has roles in the brain. Recently, it was shown that NMD is repressed during neural development to allow for the stabilization of NMD mRNA targets. The repression of NMD during development is mediated by a neuron-expressed microRNA, miR-128, which participates in a highly conserved regulatory circuit. miR-128 is induced in differentiating neuronal cells and during brain development, leading to repressed NMD and the consequent upregulation of batteries of mRNAs encoding proteins important for neuron differentiation and function. Together with other results, this suggests the existence of a complex network linking the microRNA and NMD pathways that induce cell-specific transcripts. In this point-of-view article, we will discuss the repercussions of this discovery for neuronal development, brain function and disease.

Role of adrenomedullin in the growth and differentiation of stem and progenitor cells

Stem cells have captured the imagination of the general public by their potential as new therapeutic tools in the fight against degenerative diseases. This potential is based on their capability for self-renewal and at the same time for producing progenitor cells that will eventually provide the building blocks for tissue and organ regeneration. These processes are carefully orchestrated in the organism by means of a series of molecular cues. An emerging molecule which is responsible for some of these physiological responses is adrenomedullin, a 52-amino acid regulatory peptide which increases proliferation and regulates cell fate of stem cells of different origins. Adrenomedullin binds to specific membrane receptors in stem cells and induces several intracellular pathways such as those involving cAMP, Akt, or MAPK. Regulation of adrenomedullin levels may help in directing the growth and differentiation of stem cells for applications (e.g., cell therapy) both in vitro and in vivo.

Identification of a microRNA that activates gene expression by repressing nonsense-mediated RNA decay

Nonsense-mediated decay (NMD) degrades both normal and aberrant transcripts harboring stop codons in particular contexts. Mutations that perturb NMD cause neurological disorders in humans, suggesting that NMD has roles in the brain. Here, we identify a brain-specific microRNA-miR-128-that represses NMD and thereby controls batteries of transcripts in neural cells. miR-128 represses NMD by targeting the RNA helicase UPF1 and the exon-junction complex core component MLN51. The ability of miR-128 to regulate NMD is a conserved response occurring in frogs, chickens, and mammals. miR-128 levels are dramatically increased in differentiating neuronal cells and during brain development, leading to repressed NMD and upregulation of mRNAs normally targeted for decay by NMD; overrepresented are those encoding proteins controlling neuron development and function. Together, these results suggest the existence of a conserved RNA circuit linking the microRNA and NMD pathways that induces cell type-specific transcripts during development.