Akt regulates basic helix-loop-helix transcription factor-coactivator complex formation and activity during neuronal differentiation

The Role of Hyperbaric Oxygen Therapy in Neuroregeneration and Neuroprotection: A Review

Neurogenesis is a high energy-demanding process, which is why blood vessels are an active part of the neurogenic niche since they allow the much-needed oxygenation of progenitor cells. In this regard, although neglected for a long time, the "oxygen niche" should be considered an important intervenient in adult neurogenesis. One possible hypothesis for the failure of numerous neuroprotective trials is that they relied on compounds that target a highly specific neuroprotective pathway. This approach may be too limited, given the complexity of the processes that lead to cell death. Therefore, research should adopt a more multifactorial approach. Among the limited range of agents with multimodal neuromodulatory capabilities, hyperbaric oxygen therapy has demonstrated effectiveness in reducing secondary brain damage in various brain injury models. This therapy functions not only as a neuroprotective mechanism but also as a powerful neuroregenerative mechanism.

CaMKK2 as an emerging treatment target for bipolar disorder

Current pharmacological treatments for bipolar disorder are inadequate and based on serendipitously discovered drugs often with limited efficacy, burdensome side-effects, and unclear mechanisms of action. Advances in drug development for the treatment of bipolar disorder remain incremental and have come largely from repurposing drugs used for other psychiatric conditions, a strategy that has failed to find truly revolutionary therapies, as it does not target the mood instability that characterises the condition. The lack of therapeutic innovation in the bipolar disorder field is largely due to a poor understanding of the underlying disease mechanisms and the consequent absence of validated drug targets. A compelling new treatment target is the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme. CaMKK2 is highly enriched in brain neurons and regulates energy metabolism and neuronal processes that underpin higher order functions such as long-term memory, mood, and other affective functions. Loss-of-function polymorphisms and a rare missense mutation in human CAMKK2 are associated with bipolar disorder, and genetic deletion of Camkk2 in mice causes bipolar-like behaviours similar to those in patients. Furthermore, these behaviours are ameliorated by lithium, which increases CaMKK2 activity. In this review, we discuss multiple convergent lines of evidence that support targeting of CaMKK2 as a new treatment strategy for bipolar disorder.

Neuroinflammation regulates the balance between hippocampal neuron death and neurogenesis in an ex vivo model of thiamine deficiency

Background

Thiamine (vitamin B1) is a cofactor for enzymes of central energy metabolism and its deficiency (TD) impairs oxidative phosphorylation, increases oxidative stress, and activates inflammatory processes that can lead to neurodegeneration. Wernicke–Korsakoff syndrome (WKS) is a consequence of chronic TD, which leads to extensive neuronal death, and is associated with neuropathological disorders, including cognitive deficits and amnesia. The hippocampus is one of the brain areas most affected by WKS. B1 replacement may not be enough to prevent the irreversible cognitive deficit associated with WKS.

Materials and methods

An organotypic hippocampal slice culture (OHC) model was developed to investigate, using immunofluorescence and confocal microscopy and transcriptome analysis, the molecular mechanisms underlying the neurodegeneration associated with TD. The effect of anti-inflammatory pharmacological intervention with resveratrol (RSV) was also assessed in B1-deprived OHCs.

Results

In OHCs cultured without B1, neuronal density decayed after 5 days and, on the 7th day, the epigenetic markings H3K4me3 and H3K9me3 were altered in mature neurons likely favoring gene transcription. Between the 7th and the 14th day, a pulse of neurogenesis was observed followed by a further massive neuron loss. Transcriptome analysis at day nine disclosed 89 differentially expressed genes in response to B1 deprivation. Genes involved in tryptophan metabolism and lysine degradation KEGG pathways, and those with Gene Ontology (GO) annotations related to the organization of the extracellular matrix, cell adhesion, and positive regulation of synaptic transmission were upregulated. Several genes of the TNF and FoxO signaling pathways and with GO terms related to inflammation were inhibited in response to B1 deprivation. Nsd1, whose product methylates histone H3 lysine 36, was upregulated and the epigenetic marking H3K36me3, associated with negative regulation of neurogenesis, was increased in neurons. Treating B1-deprived OHCs with RSV promoted an earlier neurogenesis pulse.

Conclusion

Neuroregeneration occurs in B1-deficient hippocampal tissue during a time window. This phenomenon depends on reducing neuroinflammation and, likely, on metabolic changes, allowing acetyl-CoA synthesis from amino acids to ensure energy supply via oxidative phosphorylation. Thus, neuroinflammation is implicated as a major regulator of hippocampal neurogenesis in TD opening a new search space for treating WKS.

The role of NAD metabolism in neuronal differentiation

BACKGROUND

Nicotinamide adenine dinucleotide (NAD) metabolism is involved in redox and non-redox reactions that regulate several processes including differentiation of cells of different origins. Here, the role of NAD metabolism in neuronal differentiation, which remains elusive so far, was investigated.

MATERIAL AND METHODS

A protein-protein interaction network between neurotrophin signaling and NAD metabolic pathways was built. Expression of NAD biosynthetic enzymes in SH-SY5Y cells during retinoic acid (RA)/brain derived neurotrophic factor (BDNF) differentiation, was evaluated. The effects of NAD biosynthetic enzymes QPRT and NAPRT inhibition in neurite outgrowth, cell viability, NAD availability and histone deacetylase (HDAC) activity, were analysed in RA- and BDNF-differentiated cells.

RESULTS

Bioinformatics analysis revealed the interaction between NAD biosynthetic enzyme NMNAT1 and NTRK2, a receptor activated by RA/BDNF sequential treatment. Differences were found in the expression of NAD biosynthetic enzymes during neuronal differentiation, namely, increased QPRT gene expression along the course of RA/BDNF treatment and NAPRT protein expression after a 5-day treatment with RA. QPRT inhibition in BDNF-differentiated SH-SY5Y cells resulted in less neuritic length per cell, decreased expression of the neuronal marker β-III Tubulin and also decreased NAD⁺ levels and HDAC activity. NAPRT inhibition had no effect in neuritic length per cell, NAD⁺ levels and HDAC activity. Of note, NAD supplementation along with RA, but not with BDNF, resulted in considerable cell death.

CONCLUSIONS

Taken together, our results show the involvement of NAD metabolism in neuronal differentiation, specifically, the importance of QPRT-mediated NAD biosynthesis in BDNF-associated SH-SY5Y differentiation and suggest additional roles for NAPRT beyond NAD production in RA-differentiated cells.

New Insights Into the Intricacies of Proneural Gene Regulation in the Embryonic and Adult Cerebral Cortex

Historically, the mammalian brain was thought to lack stem cells as no new neurons were found to be made in adulthood. That dogma changed ∼25 years ago with the identification of neural stem cells (NSCs) in the adult rodent forebrain. However, unlike rapidly self-renewing mature tissues (e.g., blood, intestinal crypts, skin), the majority of adult NSCs are quiescent, and those that become 'activated' are restricted to a few neurogenic zones that repopulate specific brain regions. Conversely, embryonic NSCs are actively proliferating and neurogenic. Investigations into the molecular control of the quiescence-to-proliferation-to-differentiation continuum in the embryonic and adult brain have identified proneural genes encoding basic-helix-loop-helix (bHLH) transcription factors (TFs) as critical regulators. These bHLH TFs initiate genetic programs that remove NSCs from quiescence and drive daughter neural progenitor cells (NPCs) to differentiate into specific neural cell subtypes, thereby contributing to the enormous cellular diversity of the adult brain. However, new insights have revealed that proneural gene activities are context-dependent and tightly regulated. Here we review how proneural bHLH TFs are regulated, with a focus on the murine cerebral cortex, drawing parallels where appropriate to other organisms and neural tissues. We discuss upstream regulatory events, post-translational modifications (phosphorylation, ubiquitinylation), protein-protein interactions, epigenetic and metabolic mechanisms that govern bHLH TF expression, stability, localization, and consequent transactivation of downstream target genes. These tight regulatory controls help to explain paradoxical findings of changes to bHLH activity in different cellular contexts.

Diabetes exacerbates brain pathology following a focal blast brain injury: New role of a multimodal drug cerebrolysin and nanomedicine

Blast brain injury (bBI) is a combination of several forces of pressure, rotation, penetration of sharp objects and chemical exposure causing laceration, perforation and tissue losses in the brain. The bBI is quite prevalent in military personnel during combat operations. However, no suitable therapeutic strategies are available so far to minimize bBI pathology. Combat stress induces profound cardiovascular and endocrine dysfunction leading to psychosomatic disorders including diabetes mellitus (DM). This is still unclear whether brain pathology in bBI could exacerbate in DM. In present review influence of DM on pathophysiology of bBI is discussed based on our own investigations. In addition, treatment with cerebrolysin (a multimodal drug comprising neurotrophic factors and active peptide fragments) or H-290/51 (a chain-breaking antioxidant) using nanowired delivery of for superior neuroprotection on brain pathology in bBI in DM is explored. Our observations are the first to show that pathophysiology of bBI is exacerbated in DM and TiO₂-nanowired delivery of cerebrolysin induces profound neuroprotection in bBI in DM, not reported earlier. The clinical significance of our findings with regard to military medicine is discussed.

KAT3-dependent acetylation of cell type-specific genes maintains neuronal identity in the adult mouse brain

The lysine acetyltransferases type 3 (KAT3) family members CBP and p300 are important transcriptional co-activators, but their specific functions in adult post-mitotic neurons remain unclear. Here, we show that the combined elimination of both proteins in forebrain excitatory neurons of adult mice resulted in a rapidly progressing neurological phenotype associated with severe ataxia, dendritic retraction and reduced electrical activity. At the molecular level, we observed the downregulation of neuronal genes, as well as decreased H3K27 acetylation and pro-neural transcription factor binding at the promoters and enhancers of canonical neuronal genes. The combined deletion of CBP and p300 in hippocampal neurons resulted in the rapid loss of neuronal molecular identity without de- or transdifferentiation. Restoring CBP expression or lysine acetylation rescued neuronal-specific transcription in cultured neurons. Together, these experiments show that KAT3 proteins maintain the excitatory neuron identity through the regulation of histone acetylation at cell type-specific promoter and enhancer regions.

Neuronal identity maintenance is highly regulated. Here, the authors showed that CBP and p300 safeguard neuronal identity through histone acetylation at promoters and enhancers of neuronal specific genes. The loss of both CBP and p300 impairs gene expression, circuit activity, and behavior in mice.

Behavioral defects induced by chronic social defeat stress are protected by Momordica charantia polysaccharides via attenuation of JNK3/PI3K/AKT neuroinflammatory pathway

Background

The aim of this study was to evaluate the protective effects of Momordica charantia polysaccharides (MCP) on depressive-like behaviors.

Methods

The chronic social defeat stress (CSDS) mice model was used to evaluate the effects of MCP and their underlying mechanisms. Social interaction test (SIT), sucrose preference test (SPT), and tail suspension test (TST) were performed for behavioral assessments. Expression levels of inflammation mediators and phosphatidylinositol 3-kinase (PI3K) activity were determined using commercial ELISA kits. The expression of key proteins in the c-Jun N-terminal protein kinase (JNK3)/PI3K/protein kinase B (AKT) pathway were measured using western blot and RT-PCR.

Results

The results showed that chronic administration of MCP (100, 200, 400 mg/kg/day) significantly prevented depressive-like behaviors in CSDS mice as assessed by SIT, TST and SPT. Elevated levels of proinflammatory cytokines [tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1 beta (IL-1β)], and expression of JNK3, c-Jun, P-110β proteins were observed in the hippocampus of CSDS mice. Moreover, the activity of PI3K and phosphorylation level of AKT were reduced in the hippocampus of CSDS mice. Interestingly, the administration of MCP reversed these changes. Furthermore, the protective effects of MCP on CSDS mice were partly inhibited by the PI3K inhibitor, LY294002.

Conclusions

In conclusion, the protective effects of MCP against depressive-like behaviors in CSDS mice might be due to a reduction in neuroinflammation and the down-regulation of the JNK3/PI3K/AKT pathway in the hippocampus.

PI3K Signaling in Neurons: A Central Node for the Control of Multiple Functions

Phosphoinositide 3-kinase (PI3K) signaling contributes to a variety of processes, mediating many aspects of cellular function, including nutrient uptake, anabolic reactions, cell growth, proliferation, and survival. Less is known regarding its critical role in neuronal physiology, neuronal metabolism, tissue homeostasis, and the control of gene expression in the central nervous system in healthy and diseased states. The aim of the present work is to review cumulative evidence regarding the participation of PI3K pathways in neuronal function, focusing on their role in neuronal metabolism and transcriptional regulation of genes involved in neuronal maintenance and plasticity or on the expression of pathological hallmarks associated with neurodegeneration.

MicroRNA-451a overexpression induces accelerated neuronal differentiation of Ntera2/D1 cells and ablation affects neurogenesis in microRNA-451a-/- mice

MiR-451a is best known for its role in erythropoiesis and for its tumour suppressor features. Here we show a role for miR-451a in neuronal differentiation through analysis of endogenous and ectopically expressed or silenced miR-451a in Ntera2/D1 cells during neuronal differentiation. Furthermore, we compared neuronal differentiation in the dentate gyrus of hippocampus of miR-451a^-/- and wild type mice. MiR-451a overexpression in lentiviral transduced Ntera2/D1 cells was associated with a significant shifting of mRNA expression of the developmental markers Nestin, βIII Tubulin, NF200, DCX and MAP2 to earlier developmental time points, compared to control vector transduced cells. In line with this, accelerated neuronal network formation in AB.G.miR-451a transduced cells, as well as an increase in neurite outgrowth both in number and length was observed. MiR-451a targets genes MIF, AKT1, CAB39, YWHAZ, RAB14, TSC1, OSR1, POU3F2, TNS4, PSMB8, CXCL16, CDKN2D and IL6R were, moreover, either constantly downregulated or exhibited shifted expression profiles in AB.G.miR-451a transduced cells. Lentiviral knockdown of endogenous miR-451a expression in Ntera2/D1 cells resulted in decelerated differentiation. Endogenous miR-451a expression was upregulated during development in the hippocampus of wildtype mice. In situ hybridization revealed intensively stained single cells in the subgranular zone and the hilus of the dentate gyrus of wild type mice, while genetic ablation of miR-451a was observed to promote an imbalance between proliferation and neuronal differentiation in neurogenic brain regions, suggested by Ki67 and DCX staining. Taken together, these results provide strong support for a role of miR-451a in neuronal maturation processes in vitro and in vivo.

Neural progenitors derived from Tuberous Sclerosis Complex patients exhibit attenuated PI3K/AKT signaling and delayed neuronal differentiation

Tuberous Sclerosis Complex (TSC) is a disease caused by autosomal dominant mutations in the TSC1 or TSC2 genes, and is characterized by tumor susceptibility, brain lesions, seizures and behavioral impairments. The TSC1 and TSC2 genes encode proteins forming a complex (TSC), which is a major regulator and suppressor of mammalian target of rapamycin complex 1 (mTORC1), a signaling complex that promotes cell growth and proliferation. TSC1/2 loss of heterozygosity (LOH) and the subsequent complete loss of TSC regulatory activity in null cells causes mTORC1 dysregulation and TSC-associated brain lesions or other tissue tumors. However, it is not clear whether TSC1/2 heterozygous brain cells are abnormal and contribute to TSC neuropathology. To investigate this issue, we generated induced pluripotent stem cells (iPSCs) from TSC patients and unaffected controls, and utilized these to obtain neural progenitor cells (NPCs) and differentiated neurons in vitro. These patient-derived TSC2 heterozygous NPCs were delayed in their ability to differentiate into neurons. Patient-derived progenitor cells also exhibited a modest activation of mTORC1 signaling downstream of TSC, and a marked attenuation of upstream PI3K/AKT signaling. We further show that pharmacologic PI3K or AKT inhibition, but not mTORC1 inhibition, causes a neuronal differentiation delay, mimicking the patient phenotype. Together these data suggest that heterozygous TSC2 mutations disrupt neuronal development, potentially contributing to the disease neuropathology, and that this defect may result from dysregulated PI3K/AKT signaling in neural progenitor cells.

Protein kinase N1 critically regulates cerebellar development and long-term function

Increasing evidence suggests that synapse dysfunctions are a major determinant of several neurodevelopmental and neurodegenerative diseases. Here we identify protein kinase N1 (PKN1) as a novel key player in fine-tuning the balance between axonal outgrowth and presynaptic differentiation in the parallel fiber-forming (PF-forming) cerebellar granule cells (Cgcs). Postnatal Pkn1-/- animals showed a defective PF-Purkinje cell (PF-PC) synapse formation. In vitro, Pkn1-/- Cgcs exhibited deregulated axonal outgrowth, elevated AKT phosphorylation, and higher levels of neuronal differentiation-2 (NeuroD2), a transcription factor preventing presynaptic maturation. Concomitantly, Pkn1-/- Cgcs had a reduced density of presynaptic sites. By inhibiting AKT with MK-2206 and siRNA-mediated knockdown, we found that AKT hyperactivation is responsible for the elongated axons, higher NeuroD2 levels, and reduced density of presynaptic specifications in Pkn1-/- Cgcs. In line with our in vitro data, Pkn1-/- mice showed AKT hyperactivation, elevated NeuroD2 levels, and reduced expression of PF-PC synaptic markers during stages of PF maturation in vivo. The long-term effect of Pkn1 knockout was further seen in cerebellar atrophy and mild ataxia. In summary, our results demonstrate that PKN1 functions as a developmentally active gatekeeper of AKT activity, thereby fine-tuning axonal outgrowth and presynaptic differentiation of Cgcs and subsequently the correct PF-PC synapse formation.

Treadmill exercise activates PI3K/Akt signaling pathway leading to GSK-3β inhibition in the social isolated rat pups

Social isolation is known to precipitate depression-like symptoms in rodents and has emerged as a dependable paradigm to screen the behavioral and neurobiological changes observed in humans. In the present study, the undying mechanisms of treadmill exercise on social isolation-induced depression was evaluated. The rat pups in the social isolation groups were housed individually. The social isolation procedures started on the postnatal day 14. The rat pups in the exercise groups were forced to run on treadmill for 30 min once a day from postnatal day 21 to postnatal day 34. The expression of phosphoinositide 3 kinase (PI3K), tyrosine kinase B (Akt), and glycogen synthase kinase 3β (GSK-3β) in the hippocampus were determined by using western blot analysis. The ratio phosphorylated PI3K (p-PI3K)/PI3K and phosphorylated Akt (p-Akt)/Akt were decreased and the ratio of phosphorylated-GSK-3 (p-GSK-3β)/GSK-3β was increased by social isolation. Treadmill exercise increased the ratio p-PI3K/PI3K and p-Akt/Akt and suppressed the ratio of p-GSK-3β/GSK-3β in the hippocampus of social isolated rat pups. Treadmill exercise activates PI3K/Akt signaling pathway leading to GSK-3β inhibition in social isolated rats. These results suggested that treadmill exercise may improve depressive symptoms via activation of PI3K/Akt signaling pathway.

Geranylgeranylacetone exerts neuroprotective roles through medicating the phosphatidylinositol-3 kinase/Akt signaling pathway in an intracerebral hemorrhage rat model

AIM

Previous studies have demonstrated that geranylgeranylacetone exerts neuroprotective effects in experimental intracerebral hemorrhage. This study is designed to explore the underlying mechanism.

MATERIALS AND METHODS

One hundred and eighty male Sprague-Dawley rats were subjected to intracerebral hemorrhage by stereotactic injection of collagenase and were pretreated without or with different doses of geranylgeranylacetone. At 6 h, 24 h, 48 h, 72 h and 7 days after the operation, the neurological deficits were examined with the scoring scale method. To explore the underlying mechanism, wortmannin (Wort), a specific phosphatidylinositol-3 kinase (PI3K) inhibitor, was used. The protein expression of Akt was determined by Western blotting. The brain water content and the hematoma volume assessment were measured and compared among the different groups.

RESULTS

We first found that geranylgeranylacetone pretreatment significantly reduced neurological deficit in intracerebral hemorrhage rats, indicating its neuroprotective role. Then, we found wort treatment significantly decreased the geranylgeranylacetone-induced Akt expression level in intracerebral hemorrhage rats. Besides, wort not only reversed the effects of geranylgeranylacetone on neurological function, but also reversed the effects of geranylgeranylacetone on reducing brain edema and decreasing hematoma volume in intracerebral hemorrhage rats.

CONCLUSION

Geranylgeranylacetone exerts neuroprotective roles, at least partially, through medicating the PI3K/Akt signaling pathway in an experimental intracerebral hemorrhage rat model.

The zebrafish homologs of SET/I2PP2A oncoprotein: expression patterns and insights into their physiological roles during development

The oncoprotein SET/I2PP2A (protein phosphatase 2A inhibitor 2) participates in various cellular mechanisms such as transcription, cell cycle regulation and cell migration. SET is also an inhibitor of the serine/threonine phosphatase PP2A, which is involved in the regulation of cell homeostasis. In zebrafish, there are two paralogous set genes that encode Seta (269 amino acids) and Setb (275 amino acids) proteins which share 94% identity. We show here that seta and setb are similarly expressed in the eye, the otic vesicle, the brain and the lateral line system, as indicated by in situ hybridization labeling. Whole-mount immunofluorescence analysis revealed the expression of Seta/b proteins in the eye retina, the olfactory pit and the lateral line neuromasts. Loss-of-function studies using antisense morpholino oligonucleotides targeting both seta and setb genes (MOab) resulted in increased apoptosis, reduced cell proliferation and morphological defects. The morphant phenotypes were partially rescued when MOab was co-injected with human SET mRNA. Knockdown of setb with a transcription-blocking morpholino oligonucleotide (MOb) resulted in phenotypic defects comparable with those induced by setb gRNA (guide RNA)/Cas9 [CRISPR (clustered regularly interspaced short palindromic repeats)-associated 9] injections. In vivo labeling of hair cells showed a significantly decreased number of neuromasts in MOab-, MOb- and gRNA/Cas9-injected embryos. Microarray analysis of MOab morphant transcriptome revealed differential expression in gene networks controlling transcription in the sensory organs, including the eye retina, the ear and the lateral line. Collectively, our results suggest that seta and setb are required during embryogenesis and play roles in the zebrafish sensory system development.

Impact of transient down-regulation of DREAM in human embryonic stem cell pluripotency: The role of DREAM in the maintenance of hESCs

Little is known about the functions of downstream regulatory element antagonist modulator (DREAM) in embryonic stem cells (ESCs). However, DREAM interacts with cAMP response element-binding protein (CREB) in a Ca(2+)-dependent manner, preventing CREB binding protein (CBP) recruitment. Furthermore, CREB and CBP are involved in maintaining ESC self-renewal and pluripotency. However, a previous knockout study revealed the protective function of DREAM depletion in brain aging degeneration and that aging is accompanied by a progressive decline in stem cells (SCs) function. Interestingly, we found that DREAM is expressed in different cell types, including human ESCs (hESCs), human adipose-derived stromal cells (hASCs), human bone marrow-derived stromal cells (hBMSCs), and human newborn foreskin fibroblasts (hFFs), and that transitory inhibition of DREAM in hESCs reduces their pluripotency, increasing differentiation. We stipulate that these changes are partly mediated by increased CREB transcriptional activity. Overall, our data indicates that DREAM acts in the regulation of hESC pluripotency and could be a target to promote or prevent differentiation in embryonic cells.

Co-treatment with therapeutic neural stem cells expressing carboxyl esterase and CPT-11 inhibit growth of primary and metastatic lung cancers in mice

In this study, neural stem cells (NSCs)-derived enzyme/prodrug therapy (NDEPT) was used to treat primary lung cancer or metastatic lung cancer in the brain. To confirm the anti-tumor effect of NSCs expressing carboxyl esterase (CE), A549 lung cancer cells were treated with HB1.F3.CE cells and CPT-11. A significant decrease in the viability/proliferation of lung cancer cells was observed compared to negative controls or cells treated with CPT-11 alone. To produce a mouse model of primary lung cancer or lung cancer metastasis to the brain, A549 cells were implanted in the dorsal area of the mouse or right hemisphere. CM-DiI pre-stained stem cells were implanted near the primary lung cancer tumor mass or in the contralateral brain. Two days after stem cells injection, mice were inoculated with CPT-11 (13.5 kg/mouse/day) via intraperitoneal injection. In the primary lung cancer mouse models, tumor mass was 80% lower in response to HB1.F3.CE in conjunction with CPT-11, while it was only reduced by 40% in the group treated with CPT-11 alone. Additionally, therapeutic efficacy of co-treatment with stem cells and CPT-11 was confirmed by detection of apoptosis and necrosis in primary and metastatic lung cancer tissues. By secreting VEGF, tumor cells modulate Erk1/2 and Akt signaling and migration of stem cells. This further increased tumor-selectivity of stem cell/prodrug co-therapy. Overall, these results indicate that NSCs expressing the therapeutic gene may be a powerful tool for treatment of primary lung cancer or metastasis of lung cancer to the brain.

Targeted inhibition of the Shroom3-Rho kinase protein-protein interaction circumvents Nogo66 to promote axon outgrowth

BACKGROUND

Inhibitory molecules in the adult central nervous system, including NogoA, impede neural repair by blocking axon outgrowth. The actin-myosin regulatory protein Shroom3 directly interacts with Rho kinase and conveys axon outgrowth inhibitory signals from Nogo66, a C-terminal inhibitory domain of NogoA. The purpose of this study was to identify small molecules that block the Shroom3-Rho kinase protein-protein interaction as a means to modulate NogoA signaling and, in the longer term, enhance axon outgrowth during neural repair.

RESULTS

A high throughput screen for inhibitors of the Shroom3-Rho kinase protein-protein interaction identified CCG-17444 (Chem ID: 2816053). CCG-17444 inhibits the Shroom3-Rho kinase interaction in vitro with micromolar potency. This compound acts through an irreversible, covalent mechanism of action, targeting Shroom3 Cys1816 to inhibit the Shroom3-Rho kinase protein-protein interaction. Inhibition of the Shroom3-Rho kinase protein-protein interaction with CCG-17444 counteracts the inhibitory action of Nogo66 and enhances neurite outgrowth.

CONCLUSIONS

This study identifies a small molecule inhibitor of the Shroom3-Rho kinase protein-protein interaction that circumvents the inhibitory action of Nogo66 in neurons. Identification of a small molecule compound that blocks the Shroom3-Rho kinase protein-protein interaction provides a first step towards a potential new strategy for enhancing neural repair.

Involvement of the Na+/Ca2+ exchanger isoform 1 (NCX1) in neuronal growth factor (NGF)-induced neuronal differentiation through Ca2+-dependent Akt phosphorylation

NGF induces neuronal differentiation by modulating [Ca(2+)]i. However, the role of the three isoforms of the main Ca(2+)-extruding system, the Na(+)/Ca(2+) exchanger (NCX), in NGF-induced differentiation remains unexplored. We investigated whether NCX1, NCX2, and NCX3 isoforms could play a relevant role in neuronal differentiation through the modulation of [Ca(2+)]i and the Akt pathway. NGF caused progressive neurite elongation; a significant increase of the well known marker of growth cones, GAP-43; and an enhancement of endoplasmic reticulum (ER) Ca(2+) content and of Akt phosphorylation through an early activation of ERK1/2. Interestingly, during NGF-induced differentiation, the NCX1 protein level increased, NCX3 decreased, and NCX2 remained unaffected. At the same time, NCX total activity increased. Moreover, NCX1 colocalized and coimmunoprecipitated with GAP-43, and NCX1 silencing prevented NGF-induced effects on GAP-43 expression, Akt phosphorylation, and neurite outgrowth. On the other hand, the overexpression of its neuronal splicing isoform, NCX1.4, even in the absence of NGF, induced an increase in Akt phosphorylation and GAP-43 protein expression. Interestingly, tetrodotoxin-sensitive Na(+) currents and 1,3-benzenedicarboxylic acid, 4,4'-[1,4,10-trioxa-7,13-diazacyclopentadecane-7,13-diylbis(5-methoxy-6,12-benzofurandiyl)]bis-, tetrakis[(acetyloxy)methyl] ester-detected [Na(+)]i significantly increased in cells overexpressing NCX1.4 as well as ER Ca(2+) content. This latter effect was prevented by tetrodotoxin. Furthermore, either the [Ca(2+)]i chelator(1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) (BAPTA-AM) or the PI3K inhibitor LY 294002 prevented Akt phosphorylation and GAP-43 protein expression rise in NCX1.4 overexpressing cells. Moreover, in primary cortical neurons, NCX1 silencing prevented Akt phosphorylation, GAP-43 and MAP2 overexpression, and neurite elongation. Collectively, these data show that NCX1 participates in neuronal differentiation through the modulation of ER Ca(2+) content and PI3K signaling.

Atopic dermatitis-associated protein interaction network lead to new insights in chronic sulfur mustard skin lesion mechanisms

Chronic sulfur mustard skin lesions (CSMSLs) are the most common complications of sulfur mustard exposure; however, its mechanism is not completely understood.According to clinical signs, there are similarities between CSMSL and atopic dermatitis (AD). In this study, proteomic results of AD were reviewed and the AD-associated protein-protein interaction network (PIN) was analyzed. According to centrality measurements, 16 proteins were designated as pivotal elements in AD mechanisms. Interestingly, most of these proteins had been reported in some sulfur mustard-related studies in late and acute phases separately. Based on the gene enrichment analysis, aging, cell response to stress, cancer, Toll- and NOD-like receptor and apoptosis signaling pathways have the greatest impact on the disease. By the analysis of directed protein interaction networks, it is concluded that TNF, IL-6, AKT1, NOS3 and CDKN1A are the most important proteins. It is possible that these proteins play role in the shared complications of AD and CSMSL including xerosis and itching.

Oligodendrogenesis after cerebral ischemia

Neural stem cells in the subventricular zone (SVZ) of the lateral ventricle of adult rodent brain generate oligodendrocyte progenitor cells (OPCs) that disperse throughout the corpus callosum and striatum where some of OPCs differentiate into mature oligodendrocytes. Studies in animal models of stroke demonstrate that cerebral ischemia induces oligodendrogenesis during brain repair processes. This article will review evidence of stroke-induced proliferation and differentiation of OPCs that are either resident in white matter or are derived from SVZ neural progenitor cells and of therapies that amplify endogenous oligodendrogenesis in ischemic brain.

Targeting nitric oxide in the subacute restorative treatment of ischemic stroke

INTRODUCTION

Stroke remains the leading cause of adult disability. Thus, it is imperative to develop restorative therapies for ischemic stroke designed specifically to treat the intact brain tissue to stimulate functional benefit. Therapies targeting amplification of brain repair processes with nitric oxide (NO) donors and phosphodiesterase type 5 (PDE5) inhibitors in preclinical studies are emerging and showing improvement of functional recovery after stroke.

AREAS COVERED

This review will mainly cover the effect of NO donors, which produce NO, and PDE5 inhibitors, which elevate cyclic guanosine 3',5'-monophosphate (cGMP), on neural restorative events in ischemic brain and highlight mechanisms underlying their restorative therapeutic activity.

EXPERT OPINION

During stroke recovery, interwoven restorative events occur in ischemic brain, which include angiogenesis, neurogenesis, oligodendrogenesis, astrogliosis and neurite outgrowth. Emerging preclinical data indicate that restorative therapies targeting multiple parenchymal cells including neural stem cells, cerebral endothelial cells, astrocytes, oligodendrocytes, neurons would be more effective than agents with a single cell target. Preclinical data suggest that elevated cGMP levels induced by NO donors and PDE5 inhibitors act on cerebral endothelial cells, neural stem cells and oligodendrocyte progenitor cells to enhance stroke-induced angiogenesis, neurogenesis and oligodendrogenesis, respectively. These interacting remodeling events collectively improve neurological function after stroke.

Identification of shared genes and pathways: a comparative study of multiple sclerosis susceptibility, severity and response to interferon beta treatment

Recent genome-wide association studies (GWAS) have successfully identified several gene loci associated with multiple sclerosis (MS) susceptibility, severity or interferon-beta (IFN-ß) response. However, due to the nature of these studies, the functional relevance of these loci is not yet fully understood. We have utilized a systems biology based approach to explore the genetic interactomes of these MS related traits. We hypothesised that genes and pathways associated with the 3 MS related phenotypes might interact collectively to influence the heterogeneity and unpredictable clinical outcomes observed. Individual genetic interactomes for each trait were constructed and compared, followed by prioritization of common interactors based on their frequencies. Pathway enrichment analyses were performed to highlight shared functional pathways. Biologically relevant genes ABL1, GRB2, INPP5D, KIF1B, PIK3R1, PLCG1, PRKCD, SRC, TUBA1A and TUBA4A were identified as common to all 3 MS phenotypes. We observed that the highest number of first degree interactors were shared between MS susceptibility and MS severity (p = 1.34×10⁻⁷⁹) with UBC as the most prominent first degree interactor for this phenotype pair from the prioritisation analysis. As expected, pairwise comparisons showed that MS susceptibility and severity interactomes shared the highest number of pathways. Pathways from signalling molecules and interaction, and signal transduction categories were found to be highest shared pathways between 3 phenotypes. Finally, FYN was the most common first degree interactor in the MS drugs-gene network. By applying the systems biology based approach, additional significant information can be extracted from GWAS. Results of our interactome analyses are complementary to what is already known in the literature and also highlight some novel interactions which await further experimental validation. Overall, this study illustrates the potential of using a systems biology based approach in an attempt to unravel the biological significance of gene loci identified in large GWAS.

KSRP silencing favors neural differentiation of P19 teratocarcinoma cells

Understanding the molecular mechanisms that control the balance between multipotency and differentiation is of great importance to elucidate the genesis of both developmental disorders and cell transformation events. To investigate the role of the RNA binding protein KSRP in controlling neural differentiation, we used the P19 embryonal carcinoma cell line that is able to differentiate into neuron-like cells under appropriate culture conditions. We have recently reported that KSRP controls the differentiative fate of multipotent mesenchymal cells owing to its ability to promote decay of unstable transcripts and to favor maturation of selected micro-RNAs (miRNAs) from precursors. Here we report that KSRP silencing in P19 cells favors neural differentiation increasing the expression of neuronal markers. Further, the expression of two master transcriptional regulators of neurogenesis, ASCL1 and JMJD3, was enhanced while the maturation of miR-200 family members from precursors was impaired in KSRP knockdown cells. These molecular changes can contribute to the reshaping of P19 cells transcriptome that follows KSRP silencing. Our data suggests that KSRP function is required to maintain P19 cells in a multipotent undifferentiated state and that its inactivation can orient cells towards neural differentiation.

Akt1 mediates neuronal differentiation in zebrafish via a reciprocal interaction with notch signaling

Akt1 is well known for its role in regulating cell proliferation, differentiation, and apoptosis and is implicated in tumors and several neurological disorders. However, the role of Akt1 in neural development has not been well defined. We have isolated zebrafish akt1 and shown that this gene is primarily transcribed in the developing nervous system, and its spatiotemporal expression pattern suggests a role in neural differentiation. Injection of akt1 morpholinos resulted in loss of neuronal precursors with a concomitant increase in post-mitotic neurons, indicating that knockdown of Akt1 is sufficient to cause premature differentiation of neurons. A similar phenotype was observed in embryos deficient for Notch signaling. Both the ligand (deltaA) and the downstream target of Notch (her8a) were downregulated in akt1 morphants, indicating that Akt1 is required for Delta-Notch signaling. Furthermore, akt1 expression was downregulated in Delta-Notch signaling-deficient embryos and could be induced by constitutive activation of Notch signaling. In addition, knockdown of Akt1 was able to nullify the inhibition of neuronal differentiation caused by constitutive activation of Notch signaling. Taken together, these results provide in vivo evidence that Akt1 interacts with Notch signaling reciprocally and provide an explanation of why Akt1 is essential for the inhibition of neuronal differentiation.

Insulin-like growth factor signaling regulates the timing of sensory cell differentiation in the mouse cochlea

The mammalian auditory sensory epithelium, the organ of Corti, is a highly ordered cellular structure that comprises two types of auditory hair cells and several types of nonsensory supporting cells. During embryogenesis, a stereotyped sequence of cellular and molecular events is required for its development. These processes are assumed to be regulated by multiple growth and transcription factors. However, the majority of these factors have not been identified. One potential regulator of cochlear development is the insulin-like growth factor (IGF) signaling family. To examine the roles of the IGF pathway in inner ear formation, cochleae from Igf1r mutant mice were analyzed. Deletion of Igf1r leads to several changes in inner ear development including a shortened cochlear duct, a decrease in the total number of cochlear hair cells, and defects in the formation of the semicircular canals. In addition, maturation of the cochlear sensory epithelium was delayed at the transition point between cellular proliferation and differentiation. To determine the molecular basis for these defects, inhibition of IGF signaling was replicated pharmacologically in vitro. Results indicated that IGF signaling regulates cochlear length and hair cell number as well as Atoh1 expression through the phosphatidylinositol 3-kinase/Akt signaling pathway. These results demonstrate novel roles for IGF signaling in inner ear development including regulation of vestibular formation, length of the cochlear duct, and the number of cochlear hair cells. The results also provide new insights regarding the pathological processes that underlie auditory defects in the absence of IGF signaling in both humans and mice.

CCAR1 is required for Ngn3-mediated endocrine differentiation

Neurogenin3 (Ngn3) is a basic helix-loop-helix transcription factor that specifies pancreatic endocrine cell fates during pancreas development. It can also initiate a transdifferentiation program when expressed in pancreatic exocrine and ductal cells. However, how Ngn3 initiates a transcriptional cascade to achieve endocrine differentiation is still poorly understood. Here, we show that cell cycle and apoptosis regulator 1 (CCAR1), which is a transcriptional coactivator for nuclear receptors, also interacts with Ngn3. The association between Ngn3 and CCAR1 was verified by pull-down assays and co-immunoprecipitation analyses. Using gene reporter assays, we found that CCAR1 is essential for Ngn3 to activate the expression of the reporter genes containing the NeuroD promoter. Moreover, down-regulation of endogenous CCAR1 in the PANC-1 pancreatic ductal cell line inhibits the transdifferentiation program initiated by Ngn3. CCAR1 is, therefore, a novel partner of Ngn3 in mediating endocrine differentiation.

Statins Enhance Expression of Growth Factors and Activate the PI3K/Akt-mediated Signaling Pathway after Experimental Intracerebral Hemorrhage

Previous studies have demonstrates that statins improve neurological outcome and promote neurovascular recovery after ICH. This study is designed to examine whether simvastatin and atorvastatin affect levels of growth factors and activate the Akt signaling pathway during the recovery phase after intracerebral hemorrhage (ICH) in rats. Sixty (60) male Wistar rats were subjected to ICH by stereotactic injection of 100 μL of autologous blood into the striatum and were treated with or without simvastatin or atorvastatin. Neurological functional outcome was evaluated by behavioral tests (mNSS and corner turn test) at different time points after ICH. Brain extracts were utilized for Enzyme-linked immunosorbent assay (ELISA) analyses to measure vascular endothelial growth factor (VEGF); brain-derived neurotrophin factor (BDNF) expression, and nerve growth factor (NGF). Western blot was used to measure the changes in the Akt-mediated signaling pathway. Both the simvastatin- and atorvastatin-treated animals had significant neurological improvement at 2 weeks post-ICH. Simvastatin and atorvastatin treatment increased the expression of BDNF, VEGF and NGF in both low- and high-dose groups at 7 days after ICH (p < 0.05). Phosphorylation of Akt, glycogen synthase kinase-3β (GSK-3β), and cAMP response element-binding proteins (CREB) were also increased at 7 days after statin treatment. These results suggest that the therapeutic effects of statins after experimental ICH may be mediated by the transient induction of BDNF, VEGF and NGF expression and the activation of the Akt-mediated signaling pathway.

Neuroprotective and Anti-Inflammatory Activities of Atorvastatin in a Rat Chronic Constriction Injury Model

Atorvastatin is an HMG-CoA reductase inhibitor used to treat hypercholesterolemic conditions associated with hypertension. This study aims to investigate the anti-inflammatory and neuroprotective effects of atorvastatin on peripheral neuropathic pain. Peripheral neuropathic pain was induced by chronic constriction injury (CCI) in Sprague-Dawley rats. Rats were divided into 3 groups including sham-operated, CCI, and atorvastatin-treated. Atorvastatin (10 mg/kg) or phosphate-buffered saline was orally administered for 2 weeks. All animals were assessed by neurobehavioral tests before surgery and at days 3, 7, 14 after surgery. Inflammatory and neuroprotective factors were evaluated by Western blot analysis. eNOS, COX2 and iNOS in the sciatic nerve were also studied using immunohistochemistry. Atorvastatin attenuated CCI-induced nociceptive sensitization and thermal hyperalgesia in a time-dependent manner. Atorvastatin improved CCI-induced neurobehavioral/inflammatory activity by inhibition of TGF-β, PIκB/IκB, NFκB, COX2, iNOS, EP1 and EP4 in the sciatic nerve. Atorvastatin was also found to increase neuroprotection factors pAkt/Akt, eNOS and VEGF. Taken together, these data indicate that atorvastatin could protect the sciatic nerve against CCI-induced neuroinflammation and nociception.

Src kinase integrates PI3K/Akt and MAPK/ERK1/2 pathways in T3-induced Na-K-ATPase activity in adult rat alveolar cells

We previously reported that the 3,5,3'-triiodo-L-thyronine (T3)-induced increase of Na-K-ATPase activity in rat alveolar epithelial cells (AECs) required activation of Src kinase, PI3K, and MAPK/ERK1/2. In the present study, we assessed the role of Akt in Na-K-ATPase activity and the interaction between the PI3K and MAPK in response to T3 by using MP48 cells, inhibitors, and constitutively active mutants in the MP48 (alveolar type II-like) cell line. The Akt inhibitor VIII blocked T3-induced increases in Na-K-ATPase activity and amount of plasma membrane Na-K-ATPase protein. The Akt inhibitor VIII also abolished the increase in Na-K-ATPase activity induced by constitutively active mutants of either Src kinase or PI3K. Moreover, constitutively active mutants of Akt increased Na-K-ATPase activity in the absence of T3. Thus activation of Akt was required for T3-induced Na-K-ATPase activity in AECs and is sufficient in the absence of T3. Inhibitors of Src kinase (PP1), PI3K (wortmannin), and ERK1/2 (U0126) all blocked the T3-induced Na-K-ATPase activity. PP1 blocked the activation of PI3K and also ERK1/2 by T3, whereas U0126 did not prevent T3 activation of Src kinase or PI3K activity. Wortmannin did not significantly alter T3-increased MAPK/ERK1/2 activity, suggesting that T3-activated PI3K/Akt and MAPK/ERK1/2 pathways acted downstream of the Src kinase. Furthermore, in the absence of T3, a constitutively active mutant of Src kinase increased activities of Na-K-ATPase, PI3K, and MAPK/ERK1/2. A constitutively active mutant of PI3K enhanced Na-K-ATPase activity but did not alter the MAPK/ERK1/2 activity significantly. In summary, in adult rat AECs T3-stimulated Src kinase activity can activate both PI3K/Akt and MAPK/ERK1/2, and activation of Akt is necessary for T3-induced Na-K-ATPase activity.

Caveolin-1 plays a crucial role in inhibiting neuronal differentiation of neural stem/progenitor cells via VEGF signaling-dependent pathway

In the present study, we aim to elucidate the roles of caveolin-1(Cav-1), a 22 kDa protein in plasma membrane invaginations, in modulating neuronal differentiation of neural progenitor cells (NPCs). In the hippocampal dentate gyrus, we found that Cav-1 knockout mice revealed remarkably higher levels of vascular endothelial growth factor (VEGF) and the more abundant formation of newborn neurons than wild type mice. We then studied the potential mechanisms of Cav-1 in modulating VEGF signaling and neuronal differentiation in isolated cultured NPCs under normoxic and hypoxic conditions. Hypoxic embryonic rat NPCs were exposed to 1% O₂ for 24 h and then switched to 21% O₂ for 1, 3, 7 and 14 days whereas normoxic NPCs were continuously cultured with 21% O₂. Compared with normoxic NPCs, hypoxic NPCs had down-regulated expression of Cav-1 and up-regulated VEGF expression and p44/42MAPK phosphorylation, and enhanced neuronal differentiation. We further studied the roles of Cav-1 in inhibiting neuronal differentiation by using Cav-1 scaffolding domain peptide and Cav-1-specific small interfering RNA. In both normoxic and hypoxic NPCs, Cav-1 peptide markedly down-regulated the expressions of VEGF and flk1, decreased the phosphorylations of p44/42MAPK, Akt and Stat3, and inhibited neuronal differentiation, whereas the knockdown of Cav-1 promoted the expression of VEGF, phosphorylations of p44/42MAPK, Akt and Stat3, and stimulated neuronal differentiation. Moreover, the enhanced phosphorylations of p44/42MAPK, Akt and Stat3, and neuronal differentiation were abolished by co-treatment of VEGF inhibitor V1. These results provide strong evidence to prove that Cav-1 can inhibit neuronal differentiation via down-regulations of VEGF, p44/42MAPK, Akt and Stat3 signaling pathways, and that VEGF signaling is a crucial target of Cav-1. The hypoxia-induced down-regulation of Cav-1 contributes to enhanced neuronal differentiation in NPCs.

Ascl1-induced neuronal differentiation of P19 cells requires expression of a specific inhibitor protein of cyclic AMP-dependent protein kinase

cAMP-dependent protein kinase (PKA) plays a critical role in nervous system development by modulating sonic hedgehog and bone morphogenetic protein signaling. In the current studies, P19 embryonic carcinoma cells were neuronally differentiated by expression of the proneural basic helix-loop-helix transcription factor Ascl1. After expression of Ascl1, but prior to expression of neuronal markers such as microtubule associated protein 2 and neuronal β-tubulin, P19 cells demonstrated a large, transient increase in both mRNA and protein for the endogenous protein kinase inhibitor (PKI)β. PKIβ-targeted shRNA constructs both reduced the levels of PKIβ expression and blocked the neuronal differentiation of P19 cells. This inhibition of differentiation was rescued by transfection of a shRNA-resistant expression vector for the PKIβ protein, and this rescue required the PKA-specific inhibitory sequence of the PKIβ protein. PKIβ played a very specific role in the Ascl1-mediated differentiation process as other PKI isoforms were unable to rescue the deficit conferred by shRNA-mediated knockdown of PKIβ. Our results define a novel requirement for PKIβ and its inhibition of PKA during neuronal differentiation of P19 cells.

Cerebrolysin enhances neurogenesis in the ischemic brain and improves functional outcome after stroke

Cerebrolysin is a peptide preparation mimicking the action of neurotrophic factors and has beneficial effects on neurodegenerative diseases and stroke. The present study investigated the effect of Cerebrolysin on neurogenesis in a rat model of embolic middle cerebral artery occlusion (MCAo). Treatment with Cerebrolysin at doses of 2.5 and 5 ml/kg significantly increased the number of bromodeoxyuridine-positive (BrdU(+)) subventricular zone (SVZ) neural progenitor cells and doublecortin (DCX) immunoreactivity (migrating neuroblasts) in the ipsilateral SVZ and striatal ischemic boundary 28 days after stroke when the treatment was initiated 24 hr after stroke. The treatment also reduced TUNEL(+) cells by ∼50% in the ischemic boundary. However, treatment with Cerebrolysin at a dose of 2.5 ml/kg initiated at 24 and 48 hr did not significantly reduce infarct volume but substantially improved neurological outcomes measured by an array of behavioral tests 21 and 28 days after stroke. Incubation of SVZ neural progenitor cells from ischemic rats with Cerebrolysin dose dependently augmented BrdU(+) cells and increased the number of Tuj1(+) cells (a marker of immature neurons). Blockage of the PI3K/Akt pathway abolished Cerebrolysin-increased BrdU(+) cells. Moreover, Cerebrolysin treatment promoted neural progenitor cell migration. Collectively, these data indicate that Cerebrolysin treatment when initiated 24 and 48 hr after stroke enhances neurogenesis in the ischemic brain and improves functional outcome and that Cerebrolysin-augmented proliferation, differentiation, and migration of adult SVZ neural progenitor cells contribute to Cerebrolysin-induced neurogenesis, which may be related to improvement of neurological outcome. The PI3K/Akt pathway mediates Cerebrolysin-induced progenitor cell proliferation.

Plumbagin promotes the generation of astrocytes from rat spinal cord neural progenitors via activation of the transcription factor Stat3

Plumbagin (5-hydroxy-2-methyl-1,4 naphthoquinone) is a naturally occurring low molecular weight lipophilic phytochemical derived from roots of plants of the Plumbago genus. Plumbagin has been reported to have several clinically relevant biological activities in non-neural cells, including anti-atherosclerotic, anticoagulant, anticarcinogenic, antitumor, and bactericidal effects. In a recent screen of a panel of botanical pesticides, we identified plumbagin as having neuroprotective activity. In this study, we determined if plumbagin could modify the developmental fate of rat E14.5 embryonic neural progenitor cells (NPC). Plumbagin exhibited no cytotoxicity when applied to cultured NPC at concentrations below 1 μM. At a concentration of 0.1 μM, plumbagin significantly enhanced the proliferation of NPC as indicated by a 17% increase in the percentage of cells incorporating bromo-deoxyuridine. Plumbagin at a concentration of 0.1 pM (but not 0.1 μM), stimulated the production of astrocytes as indicated by increased GFAP expression. Plumbagin selectively induced the proliferation and differentiation of glial progenitor cells without affecting the proliferation or differentiation of neuron-restricted progenitors. Plumbagin (0.1 pM) rapidly activated the transcription factor signal transducer and activator of transcription 3 (Stat3) in NPC, and a Stat3 inhibitor peptide prevented both plumbagin-induced astrocyte formation and proliferation. These findings demonstrate the ability of a low molecular weight naturally occurring phytochemical to control the fate of glial progenitor cells by a mechanism involving the Stat3 signaling pathway.

Implication of Akt-dependent Prp19 alpha/14-3-3beta/Cdc5L complex formation in neuronal differentiation

PRP19alpha and CDC5L are major components of the active spliceosome. However, their association process is still unknown. Here, we demonstrated that PRP19 alpha/14-3-3beta/CDC5L complex formation is regulated by Akt during nerve growth factor (NGF)-induced neuronal differentiation of PC12 cells. Analysis of PRP19 alpha mutants revealed that the phosphorylation of PRP19 alpha at Thr 193 by Akt was critical for its binding with 14-3-3beta to translocate into the nuclei and for PRP19 alpha/14-3-3beta/CDC5L complex formation in neuronal differentiation. Forced expression of either sense PRP19 alpha or sense 14-3-3beta RNAs promoted NGF-induced neuronal differentiation, whereas down-regulation of these mRNAs showed a suppressive effect. The nonphosphorylation mutant PRP19 alpha T193A lost its binding ability with 14-3-3beta and acted as a dominant-negative mutant in neuronal differentiation. These results imply that Akt-dependent phosphorylation of PRP19 alpha at Thr193 triggers PRP19 alpha/14-3-3beta/CDC5L complex formation in the nuclei, likely to assemble the active spliceosome against neurogenic pre-mRNAs.

AP-1 regulates cyclin D1 and c-MYC transcription in an AKT-dependent manner in response to mTOR inhibition: role of AIP4/Itch-mediated JUNB degradation

One mechanism by which AKT kinase-dependent hypersensitivity to mammalian target of rapamycin (mTOR) inhibitors is controlled is by the differential expression of cyclin D1 and c-MYC. Regulation of posttranscriptional processes has been demonstrated to be crucial in governing expression of these determinants in response to rapamycin. Our previous data suggested that cyclin D1 and c-MYC expression might additionally be coordinately regulated in an AKT-dependent manner at the level of transcription. Under conditions of relatively quiescent AKT activity, treatment of cells with rapamycin resulted in upregulation of cyclin D1 and c-MYC nascent transcription, whereas in cells containing active AKT, exposure repressed transcription. Promoter analysis identified AKT-dependent rapamycin responsive elements containing AP-1 transactivation sites. Phosphorylated c-JUN binding to these promoters correlated with activation of transcription whereas JUNB occupancy was associated with promoter repression. Forced overexpression of JunB or a conditionally active JunB-ER allele repressed cyclin D1 and c-MYC promoter activity in quiescent AKT-containing cells following rapamycin exposure. AIP4/Itch-dependent JUNB protein degradation was found to be markedly reduced in active AKT-containing cells compared with cells harboring quiescent AKT. Moreover, silencing AIP4/Itch expression or inhibiting JNK mediated AIP4 activity abrogated the rapamycin-induced effects on cyclin D1 and c-MYC promoter activities. Our findings support a role for the AKT-dependent regulation of AIP4/Itch activity in mediating the differential cyclin D1 and c-MYC transcriptional responses to rapamycin.

POSH is an intracellular signal transducer for the axon outgrowth inhibitor Nogo66

Myelin-derived inhibitors limit axon outgrowth and plasticity during development and in the adult mammalian CNS. Nogo66, a functional domain of the myelin-derived inhibitor NogoA, signals through the PirB receptor to inhibit axon outgrowth. The signaling pathway mobilized by Nogo66 engagement of PirB is not well understood. We identify a critical role for the scaffold protein Plenty of SH3s (POSH) in relaying process outgrowth inhibition downstream of Nogo66 and PirB. Blocking the function of POSH, or two POSH-associated proteins, leucine zipper kinase (LZK) and Shroom3, with RNAi in cortical neurons leads to release from myelin and Nogo66 inhibition. We also observed autocrine inhibition of process outgrowth by NogoA, and suppression analysis with the POSH-associated kinase LZK demonstrated that LZK operates downstream of NogoA and PirB in a POSH-dependent manner. In addition, cerebellar granule neurons with an RNAi-mediated knockdown in POSH function were refractory to the inhibitory action of Nogo66, indicating that a POSH-dependent mechanism operates to inhibit axon outgrowth in different types of CNS neurons. These studies delineate an intracellular signaling pathway for process outgrowth inhibition by Nogo66, comprised of NogoA, PirB, POSH, LZK, and Shroom3, and implicate the POSH complex as a potential therapeutic target to enhance axon outgrowth and plasticity in the injured CNS.

The role of β-catenin signaling pathway on proliferation of rats neural stem cells after hyperbaric oxygen therapy in vitro

β-catenin, a protein that functions in both cell adhesion and Wnt signaling, plays a key role in mammalian neural development. To investigate the role of β-catenin in hyperbaric oxygen therapy (HBO)-induced neurogenesis after hypoxic ischemic brain damage (HIBD), we transfected β-catenin siRNA and negative control siRNA into neural stem cells (NSCs) after HIBD. We found that HBO promoted NSCs differentiate into neurons or oligodendrocytes, and inhibited NSCs differentiate into astrocytes; HIBD brain tissue extract conditioned cultures promoted NSCs differentiate into neurons; β-Catenin siRNA decreased the NSE-positive neurons and increased GFAP-positive astrocytes in the NSCs in vitro. Furthermore, the expression of Ngn1 protein and mRNA in NSCs was increased when HBO promoted NSCs differentiate into neurons after HIBD, and the expression of BMP-4 protein and mRNA was decreased when HBO depressed NSCs differentiate into astrocytes after HIBD. These results showed that β-catenin-mediated transcriptional activation functions in the decision of NSCs to proliferate neurogenesis during HBO-induced after HIBD, and suggested that HBO therapy promotes the proliferation of neural stem cells in vitro, an effect that may be correlated with β-catenin protein and HBO therapy could promote neurogenesis by β-catenin-induced activated Ngn1 gene and repress astrocytogenesis by β-catenin-induced down-regulated BMP-4 gene.

The transcriptional activity of Neurog3 affects migration and differentiation of ectopic endocrine cells in chicken endoderm

Neurog3 is expressed transiently in pancreatic endocrine progenitors where it is responsible for activating a transcription factor cascade which eventually defines the mature endocrine cells. However, the mechanism by which Neurog3 regulates different aspects of the endocrine differentiation program is less clear. In this report we used in ovo electroporation to investigate how manipulation of Neurog3 protein activity affected migration, differentiation and fate determination. We found that changes in the onset of Neurog3 expression only had minor effect on differentiation. However increasing the transcriptional activity of Neurog3 by fusing it to VP16 or co-electroporating with Ep300 caused the electroporated cells to migrate rather than differentiate. In contrast, reducing the transcriptional activity of Neurog3 by deleting parts of the activation domain, by fusing Neurog3 to the engrailed repressor domain, or co-electroporating with Hdac1 greatly increased the proportion of glucagon expressing cells.

Selective induction of neocortical GABAergic neurons by the PDK1-Akt pathway through activation of Mash1

Extracellular stimuli regulate neuronal differentiation and subtype specification during brain development, although the intracellular signaling pathways that mediate these processes remain largely unclear. We now show that the PDK1-Akt pathway regulates differentiation of telencephalic neural precursor cells (NPCs). Active Akt promotes differentiation of NPC into gamma-aminobutyric acid-containing (GABAergic) but not glutamatergic neurons. Disruption of the Pdk1 gene or expression of dominant-negative forms of Akt suppresses insulin-like growth factor (IGF)-1 enhancement of NPC differentiation into neurons in vitro and production of neocortical GABAergic neurons in vivo. Furthermore, active Akt increased the protein levels and transactivation activity of Mash1, a proneural basic helix-loop-helix protein required for the generation of neocortical GABAergic neurons, and Mash1 was required for Akt-induced neuronal differentiation. These results have unveiled an unexpected role of the PDK1-Akt pathway: a key mediator of extracellular signals regulating the production of neocortical GABAergic neurons.

alpha1-Adrenergic receptors regulate neurogenesis and gliogenesis

The understanding of the function of alpha(1)-adrenergic receptors in the brain has been limited due to a lack of specific ligands and antibodies. We circumvented this problem by using transgenic mice engineered to overexpress either wild-type receptor tagged with enhanced green fluorescent protein or constitutively active mutant alpha(1)-adrenergic receptor subtypes in tissues in which they are normally expressed. We identified intriguing alpha(1A)-adrenergic receptor subtype-expressing cells with a migratory morphology in the adult subventricular zone that coexpressed markers of neural stem cell and/or progenitors. Incorporation of 5-bromo-2-deoxyuridine in vivo increased in neurogenic areas in adult alpha(1A)-adrenergic receptor transgenic mice or normal mice given the alpha(1A)-adrenergic receptor-selective agonist, cirazoline. Neonatal neurospheres isolated from normal mice expressed a mixture of alpha(1)-adrenergic receptor subtypes, and stimulation of these receptors resulted in increased expression of the alpha(1B)-adrenergic receptor subtype, proneural basic helix-loop-helix transcription factors, and the differentiation and migration of neuronal progenitors for catecholaminergic neurons and interneurons. alpha(1)-Adrenergic receptor stimulation increased the apoptosis of astrocytes and regulated survival of neonatal neurons through phosphatidylinositol 3-kinase signaling. However, in adult normal neurospheres, alpha(1)-adrenergic receptor stimulation increased the expression of glial markers at the expense of neuronal differentiation. In vivo, S100-positive glial and betaIII tubulin neuronal progenitors colocalized with either alpha(1)-adrenergic receptor subtype in the olfactory bulb. Our results indicate that alpha(1)-adrenergic receptors can regulate both neurogenesis and gliogenesis that may be developmentally dependent. Our findings may lead to new therapies to treat neurodegenerative diseases.

Neurorestorative therapies for stroke: underlying mechanisms and translation to the clinic

Restorative cell-based and pharmacological therapies for experimental stroke substantially improve functional outcome. These therapies target several types of parenchymal cells (including neural stem cells, cerebral endothelial cells, astrocytes, oligodendrocytes, and neurons), leading to enhancement of endogenous neurogenesis, angiogenesis, axonal sprouting, and synaptogenesis in the ischaemic brain. Interaction between these restorative events probably underpins the improvement in functional outcome. This Review provides examples of cell-based and pharmacological restorative treatments for stroke that stimulate brain plasticity and functional recovery. The molecular pathways activated by these therapies, which induce remodelling of the injured brain via angiogenesis, neurogenesis, and axonal and dendritic plasticity, are discussed. The ease of treating intact brain tissue to stimulate functional benefit in restorative therapy compared with treating injured brain tissue in neuroprotective therapy might more readily help with translation of restorative therapy from the laboratory to the clinic.

LMO4 controls the balance between excitatory and inhibitory spinal V2 interneurons

Multiple excitatory and inhibitory interneurons form the motor circuit with motor neurons in the ventral spinal cord. Notch signaling initiates the diversification of immature V2-interneurons into excitatory V2a-interneurons and inhibitory V2b-interneurons. Here, we provide a transcriptional regulatory mechanism underlying their balanced production. LIM-only protein LMO4 controls this binary cell fate choice by regulating the activity of V2a- and V2b-specific LIM complexes inversely. In the spinal cord, LMO4 induces GABAergic V2b-interneurons in collaboration with SCL and inhibits Lhx3 from generating glutamatergic V2a-interneuons. In LMO4;SCL compound mutant embryos, V2a-interneurons increase markedly at the expense of V2b-interneurons. We further demonstrate that LMO4 nucleates the assembly of a novel LIM-complex containing SCL, Gata2, and NLI. This complex activates specific enhancers in V2b-genes consisting of binding sites for SCL and Gata2, thereby promoting V2b-interneuron fate. Thus, LMO4 plays essential roles in directing a balanced generation of inhibitory and excitatory neurons in the ventral spinal cord.

ERK5 MAP kinase regulates neurogenin1 during cortical neurogenesis

The commitment of multi-potent cortical progenitors to a neuronal fate depends on the transient induction of the basic-helix-loop-helix (bHLH) family of transcription factors including Neurogenin 1 (Neurog1). Previous studies have focused on mechanisms that control the expression of these proteins while little is known about whether their pro-neural activities can be regulated by kinase signaling pathways. Using primary cultures and ex vivo slice cultures, here we report that both the transcriptional and pro-neural activities of Neurog1 are regulated by extracellular signal-regulated kinase (ERK) 5 signaling in cortical progenitors. Activation of ERK5 potentiated, while blocking ERK5 inhibited Neurog1-induced neurogenesis. Furthermore, endogenous ERK5 activity was required for Neurog1-initiated transcription. Interestingly, ERK5 activation was sufficient to induce Neurog1 phosphorylation and ERK5 directly phosphorylated Neurog1 in vitro. We identified S179/S208 as putative ERK5 phosphorylation sites in Neurog1. Mutations of S179/S208 to alanines inhibited the transcriptional and pro-neural activities of Neurog1. Our data identify ERK5 phosphorylation of Neurog1 as a novel mechanism regulating neuronal fate commitment of cortical progenitors.

The scaffold protein POSH regulates axon outgrowth

How scaffold proteins integrate signaling pathways with cytoskeletal components to drive axon outgrowth is not well understood. We report here that the multidomain scaffold protein Plenty of SH3s (POSH) regulates axon outgrowth. Reduction of POSH function by RNA interference (RNAi) enhances axon outgrowth in differentiating mouse primary cortical neurons and in neurons derived from mouse P19 cells, suggesting POSH negatively regulates axon outgrowth. Complementation analysis reveals a requirement for the third Src homology (SH) 3 domain of POSH, and we find that the actomyosin regulatory protein Shroom3 interacts with this domain of POSH. Inhibition of Shroom3 expression by RNAi leads to increased process lengths, as observed for POSH RNAi, suggesting that POSH and Shroom function together to inhibit process outgrowth. Complementation analysis and interference of protein function by dominant-negative approaches suggest that Shroom3 recruits Rho kinase to inhibit process outgrowth. Furthermore, inhibition of myosin II function reverses the POSH or Shroom3 RNAi phenotype, indicating a role for myosin II regulation as a target of the POSH-Shroom complex. Collectively, these results suggest that the molecular scaffold protein POSH assembles an inhibitory complex that links to the actin-myosin network to regulate neuronal process outgrowth.