PI3K activation by IGF-1 is essential for the regulation of membrane expansion at the nerve growth cone

Acteoside relieves diabetic retinopathy through the inhibition of Müller cell reactive hyperplasia by regulating TXNIP and mediating Kir4.1 channels in a PI3K/Akt-dependent manner

Diabetic retinopathy (DR) is a severe microangiopathy of diabetes. Müller cells play an important role in the development of DR. Acteoside (ACT) has been reported to be effective in the treatment of DR. In this study, we explored the molecular mechanism of ACT in the treatment of DR from the perspective of the reactive proliferation of Müller cells. The effect of ACT on DR was investigated via high-glucose (HG) treatment of Müller RMC-1 cells and an injection of streptozotocin (STZ) in constructed DR cells and animal models. The results showed that after ACT treatment, damage to the retinal structure in DR rats was alleviated, the number of hemangiomas was reduced, and the penetration of blood vessels was weakened. In addition, ACT treatment improved the hypertrophy and gliogenesis of Müller cells during DR, promoted the expression of Kir4.1 and activated the PI3K/Akt signaling pathway. ACT treatment inhibited the proliferation and migration of RMC-1 cells and promoted the expression of Kir4.1. TXNIP overexpression effectively reversed the inhibitory effect of ACT on the proliferation and migration of Müller cells and its induction of Kir4.1 expression. In addition, TXNIP knockdown effectively reversed the inhibitory effect of HG on the expression of p-PI3K and p-Akt, whereas TXNIP overexpression had the opposite effect, and treatment with the PI3K/AKT pathway inhibitor LY294002 effectively reversed the effect of TXNIP knockdown. Animal experiments also confirmed that the therapeutic effect of ACT on DR rats could be reversed by the overexpression of TXNIP or LY294002. In conclusion, ACT inhibits Müller cell reactive proliferation and alleviates diabetic retinopathy by regulating TXNIP and mediating the expression of Kir4.1 channels in a PI3K/Akt-dependent manner.

The neuronal Golgi in neural circuit formation and reorganization

The Golgi apparatus is a central hub in the intracellular secretory pathway. By positioning in the specific intracellular region and transporting materials to spatially restricted compartments, the Golgi apparatus contributes to the cell polarity establishment and morphological specification in diverse cell types. In neurons, the Golgi apparatus mediates several essential steps of initial neural circuit formation during early brain development, such as axon-dendrite polarization, neuronal migration, primary dendrite specification, and dendritic arbor elaboration. Moreover, neuronal activity-dependent remodeling of the Golgi structure enables morphological changes in neurons, which provides the cellular basis of circuit reorganization during postnatal critical period. In this review, I summarize recent findings illustrating the unique Golgi positioning and its developmental dynamics in various types of neurons. I also discuss the upstream regulators for the Golgi positioning in neurons, and functional roles of the Golgi in neural circuit formation and reorganization. Elucidating how Golgi apparatus sculpts neuronal connectivity would deepen our understanding of the cellular/molecular basis of neural circuit development and plasticity.

Acrylic Acid Modified Poly-ethylene Glycol Microparticles for Affinity-Based release of Insulin-Like Growth Factor-1 in Neural Applications

Sustained release of bioactive molecules via affinity-based interactions presents a promising approach for controlled delivery of growth factors. Insulin-like growth factor-1 (IGF-1) has gained increased attention due to its ability to promote axonal growth in the central nervous system. In this work, we aimed to evaluate the effect of IGF-1 delivery from polyethylene-glycol diacrylate (PEG-DA) microparticles using affinity-based sustained release on neurons. We developed PEG-DA-based microparticles with varying levels of acrylic acid (AA) as a comonomer to tune their overall charge. The particles were synthesized via precipitation polymerization under UV light, yielding microparticles (MPs) with a relatively low polydispersity index. IGF-1 was incubated with the PEG-DA particles overnight, and formulations with a higher AA content resulted in higher loading efficiency and slower release rates over 4 weeks, suggesting the presence of binding interactions between the positively charged IGF-1 and negatively charged particles containing AA. The released IGF-1 was tested in dorsal root ganglion (DRG) neurite outgrowth assay and found to retain its biological activity for up to two weeks after encapsulation. Furthermore, the trophic effect of IGF-1 was tested with stem cell-derived V2a interneurons and found to have a synergistic effect when combined with neurotrophin-3 (NT3). To assess the potential of a combinatorial approach, IGF-1-releasing MPs were encapsulated within a hyaluronic acid (HA) hydrogel and showed promise as a dual delivery system. Overall, the PEG-DA MPs developed herein deliver bioactive IGF-1 for a period of weeks and hold potential to enable axonal growth of injured neurons via sustained release.

Transcriptome and methylome of the supraoptic nucleus provides insights into the age-dependent loss of neuronal plasticity

The age-dependent loss of neuronal plasticity is a well-known phenomenon that is poorly understood. The loss of this capacity for axonal regeneration is emphasized following traumatic brain injury, which is a major cause of disability and death among adults in the US. We have previously shown the intrinsic capacity of magnocellular neurons within the supraoptic nucleus to undergo axonal regeneration following unilateral axotomization in an age-dependent manner. The aim of this research was to determine the age-dependent molecular mechanisms that may underlie this phenomenon. As such, we characterized the transcriptome and DNA methylome of the supraoptic nucleus in uninjured 35-day old rats and 125-day old rats. Our data indicates the downregulation of a large number of axonogenesis related transcripts in 125-day old rats compared to 35-day old rats. Specifically, several semaphorin and ephrin genes were downregulated, as well as growth factors including FGF's, insulin-like growth factors (IGFs), and brain-derived neurotrophic factor (BDNF). Differential methylation analysis indicates enrichment of biological processes involved in axonogenesis and axon guidance. Conversely, we observed a robust and specific upregulation of MHCI related transcripts. This may involve the activator protein 1 (AP-1) transcription factor complex as motif analysis of differentially methylated regions indicate enrichment of AP-1 binding sites in hypomethylated regions. Together, our data suggests a loss of pro-regenerative capabilities with age which would prevent axonal growth and appropriate innervation following injury.

Advances in Understanding the Molecular Mechanisms of Neuronal Polarity

The establishment and maintenance of neuronal polarity are important for neural development and function. Abnormal neuronal polarity establishment commonly leads to a variety of neurodevelopmental disorders. Over the past three decades, with the continuous development and improvement of biological research methods and techniques, we have made tremendous progress in the understanding of the molecular mechanisms of neuronal polarity establishment. The activity of positive and negative feedback signals and actin waves are both essential in this process. They drive the directional transport and aggregation of key molecules of neuronal polarity, promote the spatiotemporal regulation of ordered and coordinated interactions of actin filaments and microtubules, stimulate the specialization and growth of axons, and inhibit the formation of multiple axons. In this review, we focus on recent advances in these areas, in particular the important findings about neuronal polarity in two classical models, in vitro primary hippocampal/cortical neurons and in vivo cortical pyramidal neurons, and discuss our current understanding of neuronal polarity.​.

An isoform-specific function of Cdc42 in regulating mammalian Exo70 during axon formation

The highly conserved GTPase Cdc42 is an essential regulator of cell polarity and promotes exocytosis through the exocyst complex in budding yeast and Drosophila In mammals, this function is performed by the closely related GTPase TC10, whereas mammalian Cdc42 does not interact with the exocyst. Axon formation is facilitated by the exocyst complex that tethers vesicles before their fusion to expand the plasma membrane. This function depends on the recruitment of the Exo70 subunit to the plasma membrane. Alternative splicing generates two Cdc42 isoforms that differ in their C-terminal 10 amino acids. Our results identify an isoform-specific function of Cdc42 in neurons. We show that the brain-specific Cdc42b isoform, in contrast to the ubiquitous isoform Cdc42u, can interact with Exo70. Inactivation of Arhgef7 or Cdc42b interferes with the exocytosis of post-Golgi vesicles in the growth cone. Cdc42b regulates exocytosis and axon formation downstream of its activator Arhgef7. Thus, the function of Cdc42 in regulating exocytosis is conserved in mammals but specific to one isoform.

Nerve implants with bioactive interfaces enhance neurite outgrowth and nerve regeneration in vivo

Nerve implants functionalized with growth factors and stem cells are critical to promote neurite outgrowth, regulate neurodifferentiation, and facilitate nerve regeneration. In this study, human umbilical cord mesenchymal stem cells (hUCMSCs) and 3,4-hydroxyphenalyalanine (DOPA)-containing insulin-like growth factor 1 (DOPA-IGF-1) were simultaneously applied to enhance the bioactivity of poly(lactide-co-glycolide) (PLGA) substrates which will be potentially utilized as nerve implants. In vitro and in vivo evaluations indicated that hUCMSCs and DOPA-IGF-1 could synergistically regulate neurite outgrowth of PC12 cells, improve intravital recovery of motor functions, and promote conduction of nerve electrical signals in vivo. The enhanced functional and structural nerve regeneration of injured spinal cord might be mainly attributable to the synergistically enhanced biofunctionality of hUCMSCs and DOPA-IGF-1/PLGA on the bioactive interfaces. Findings from this study demonstrate the potential of hUCMSC-seeded, DOPA-IGF-1-modified PLGA implants as promising candidates for promoting axonal regeneration and motor functional recovery in spinal cord injury treatment.

Pegylated Insulin-Like Growth Factor 1 attenuates Hair Cell Loss and promotes Presynaptic Maintenance of Medial Olivocochlear Cholinergic Fibers in the Cochlea of the Progressive Motor Neuropathy Mouse

The progressive motor neuropathy (PMN) mouse is a model of an inherited motor neuropathy disease with progressive neurodegeneration. Axon degeneration associates with homozygous mutations of the TBCE gene encoding the tubulin chaperone E protein. TBCE is responsible for the correct dimerization of alpha and beta-tubulin. Strikingly, the PMN mouse also develops a progressive hearing loss after normal hearing onset, characterized by degeneration of the auditory nerve and outer hair cell (OHC) loss. However, the development of this neuronal and cochlear pathology is not fully understood yet. Previous studies with pegylated insulin-like growth factor 1 (peg-IGF-1) treatment in this mouse model have been shown to expand lifespan, weight, muscle strength, and motor coordination. Accordingly, peg-IGF-1 was evaluated for an otoprotective effect. We investigated the effect of peg-IGF-1 on the auditory system by treatment starting at postnatal day 15 (p15). Histological analysis revealed positive effects on OHC synapses of medial olivocochlear (MOC) neuronal fibers and a short-term attenuation of OHC loss. Peg-IGF-1 was able to conditionally restore the disorganization of OHC synapses and maintain the provision of cholinergic acetyltransferase in presynapses. To assess auditory function, frequency-specific auditory brainstem responses and distortion product otoacoustic emissions were recorded in animals on p21 and p28. However, despite the positive effect on MOC fibers and OHC, no restoration of hearing could be achieved. The present work demonstrates that the synaptic pathology of efferent MOC fibers in PMN mice represents a particular form of “efferent auditory neuropathy.” Peg-IGF-1 showed an otoprotective effect by preventing the degeneration of OHCs and efferent synapses. However, enhanced efforts are needed to optimize the treatment to obtain detectable improvements in hearing performances.

Downregulation of PIK3CB Involved in Alzheimer's Disease via Apoptosis, Axon Guidance, and FoxO Signaling Pathway

OBJECTIVE

To investigate the molecular function of phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit beta (PIK3CB) underlying Alzheimer's disease (AD).

METHODS

RNA sequencing data were used to filtrate differentially expressed genes (DEGs) in AD/nondementia control and PIK3CB-low/high groups. An unbiased coexpression network was established to evaluate module-trait relationships by using weight gene correlation network analysis (WGCNA). Global regulatory network was constructed to predict the protein-protein interaction. Further cross-talking pathways of PIK3CB were identified by functional enrichment analysis.

RESULTS

The mean expression of PIK3CB in AD patients was significantly lower than those in nondementia controls. We identified 2,385 DEGs from 16,790 background genes in AD/control and PIK3CB-low/high groups. Five coexpression modules were established using WGCNA, which participated in apoptosis, axon guidance, long-term potentiation (LTP), regulation of actin cytoskeleton, synaptic vesicle cycle, FoxO, mitogen-activated protein kinase (MAPK), and vascular endothelial growth factor (VEGF) signaling pathways. DEGs with strong relation to AD and low PIK3CB expression were extracted to construct a global regulatory network, in which cross-talking pathways of PIK3CB were identified, such as apoptosis, axon guidance, and FoxO signaling pathway. The occurrence of AD could be accurately predicted by low PIK3CB based on the area under the curve of 71.7%.

CONCLUSIONS

These findings highlight downregulated PIK3CB as a potential causative factor of AD, possibly mediated via apoptosis, axon guidance, and FoxO signaling pathway.

Sec3 exocyst component knockdown inhibits axonal formation and cortical neuronal migration during brain cortex development

Neurons are the largest known cells, with complex and highly polarized morphologies and consist of a cell body (soma), several dendrites, and a single axon. The establishment of polarity necessitates initial axonal outgrowth in concomitance with the addition of new membrane to the axon's plasmalemma. Axolemmal expansion occurs by exocytosis of plasmalemmal precursor vesicles primarily at the neuronal growth cone membrane. The multiprotein exocyst complex drives spatial location and specificity of vesicle fusion at plasma membrane. However, the specific participation of its different proteins on neuronal differentiation has not been fully established. In the present work we analyzed the role of Sec3, a prominent exocyst complex protein on neuronal differentiation. Using mice hippocampal primary cultures, we determined that Sec3 is expressed in neurons at early stages prior to neuronal polarization. Furthermore, we determined that silencing of Sec3 in mice hippocampal neurons in culture precluded polarization. Moreover, using in utero electroporation experiments, we determined that Sec3 knockdown affected cortical neurons migration and morphology during neocortex formation. Our results demonstrate that the exocyst complex protein Sec3 plays an important role in axon formation in neuronal differentiation and the migration of neuronal progenitors during cortex development.

Development of Functional Thyroid C Cell-like Cells from Human Pluripotent Cells in 2D and in 3D Scaffolds

Medullary thyroid carcinoma contributes to about 3–4% of thyroid cancers and affects C cells rather than follicular cells. Thyroid C cell differentiation from human pluripotent stem cells has not been reported. We report the stepwise differentiation of human embryonic stem cells into thyroid C cell-like cells through definitive endoderm and anterior foregut endoderm and ultimobranchial body-like intermediates in monolayer and 3D Matrigel culture conditions. The protocol involved sequential treatment with interferon/transferrin/selenium/pyruvate, foetal bovine serum, and activin A, then IGF-1 (Insulin-like growth factor 1), on the basis of embryonic thyroid developmental sequence. As well as expressing C cell lineage relative to follicular-lineage markers by qPCR (quantitative polymerase chain reaction) and immunolabelling, these cells by ELISA (enzyme-linked immunoassay) exhibited functional properties in vitro of calcitonin storage and release of calcitonin on calcium challenge. This method will contribute to developmental studies of the human thyroid gland and facilitate in vitro modelling of medullary thyroid carcinoma and provide a valuable platform for drug screening.

Held Up in Traffic-Defects in the Trafficking Machinery in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT), also known as motor and sensory neuropathy, describes a clinically and genetically heterogenous group of disorders affecting the peripheral nervous system. CMT typically arises in early adulthood and is manifested by progressive loss of motor and sensory functions; however, the mechanisms leading to the pathogenesis are not fully understood. In this review, we discuss disrupted intracellular transport as a common denominator in the pathogenesis of different CMT subtypes. Intracellular transport via the endosomal system is essential for the delivery of lipids, proteins, and organelles bidirectionally to synapses and the soma. As neurons of the peripheral nervous system are amongst the longest neurons in the human body, they are particularly susceptible to damage of the intracellular transport system, leading to a loss in axonal integrity and neuronal death. Interestingly, defects in intracellular transport, both in neurons and Schwann cells, have been found to provoke disease. This review explains the mechanisms of trafficking and subsequently summarizes and discusses the latest findings on how defects in trafficking lead to CMT. A deeper understanding of intracellular trafficking defects in CMT will expand our understanding of CMT pathogenesis and will provide novel approaches for therapeutic treatments.

The role of the odorant receptors in the formation of the sensory map

In the olfactory system, odorant receptors (ORs) expressed at the cell membrane of olfactory sensory neurons detect odorants and direct sensory axons toward precise target locations in the brain, reflected in the presence of olfactory sensory maps. This dual role of ORs is corroborated by their subcellular expression both in cilia, where they bind odorants, and at axon terminals, a location suitable for axon guidance cues. Here, we provide an overview and discuss previous work on the role of ORs in establishing the topographic organization of the olfactory system and recent findings on the mechanisms of activation and function of axonal ORs.

Lack of Brain Insulin Receptor Substrate-1 Causes Growth Retardation, With Decreased Expression of Growth Hormone-Releasing Hormone in the Hypothalamus

Insulin receptor substrate-1 (Irs1) is one of the major substrates for insulin receptor and insulin-like growth factor-1 (IGF-1) receptor tyrosine kinases. Systemic Irs1-deficient mice show growth retardation, with resistance to insulin and IGF-1, although the underlying mechanisms remain poorly understood. For this study, we generated mice with brain-specific deletion of Irs1 (NIrs1KO mice). The NIrs1KO mice exhibited lower body weights, shorter bodies and bone lengths, and decreased bone density. Moreover, the NIrs1KO mice exhibited increased insulin sensitivity and glucose utilization in the skeletal muscle. Although the ability of the pituitary to secrete growth hormone (GH) remained intact, the amount of hypothalamic growth hormone-releasing hormone (GHRH) was significantly decreased and, accordingly, the pituitary GH mRNA expression levels were impaired in these mice. Plasma GH and IGF-1 levels were also lower in the NIrs1KO mice. The expression levels of GHRH protein in the median eminence, where Irs1 antibody staining is observed, were markedly decreased in the NIrs1KO mice. In vitro, neurite elongation after IGF-1 stimulation was significantly impaired by Irs1 downregulation in the cultured N-38 hypothalamic neurons. In conclusion, brain Irs1 plays important roles in the regulation of neurite outgrowth of GHRH neurons, somatic growth, and glucose homeostasis.

Silencing of circIgf1r plays a protective role in neuronal injury via regulating astrocyte polarization during epilepsy

Epilepsy is a common brain disorder, repeated seizures of epilepsy may lead to a series of brain pathological changes such as neuronal or glial damage. However, whether circular RNAs are involved in neuronal injury during epilepsy is not fully understood. Here, we screened circIgf1r in the status epilepticus model through circRNA sequencing, and found that it was upregulated after the status epilepticus model through QPCR analysis. Astrocytes polarizing toward neurotoxic A1 phenotype and neurons loss were observed after status epilepticus. Through injecting circIgf1r siRNA into the lateral ventricle, it was found that knocking down circIgf1r in vivo would induce the polarization of astrocytes to phenotype A2 and reduce neuronal loss. The results in vitro further confirmed that inhibiting the expression of circIgf1r in astrocytes could protect neurons by converting reactive astrocytes from A1 to the protective A2. In addition, knocking down circIgf1r in astrocytes could functionally promote astrocyte autophagy and relieve the destruction of 4-AP-induced autophagy flux. In terms of mechanism, circIgf1r promoted the polarization of astrocytes to phenotype A1 by inhibiting autophagy. Taken together, our results reveal circIgf1r may serve as a potential target for the prevention and treatment of neuron damage after epilepsy.

An endogenous PI3K interactome promoting astrocyte-mediated neuroprotection identifies a novel association with RNA-binding protein ZC3H14

Astrocytes can support neuronal survival through a range of secreted signals that protect against neurotoxicity, oxidative stress, and apoptotic cascades. Thus, analyzing the effects of the astrocyte secretome may provide valuable insight into these neuroprotective mechanisms. Previously, we characterized a potent neuroprotective activity mediated by retinal astrocyte conditioned media (ACM) on retinal and cortical neurons in metabolic stress models. However, the molecular mechanism underlying this complex activity in neuronal cells has remained unclear. Here, a chemical genetics screen of kinase inhibitors revealed phosphoinositide 3-kinase (PI3K) as a central player transducing ACM-mediated neuroprotection. To identify additional proteins contributing to the protective cascade, endogenous PI3K was immunoprecipitated from neuronal cells exposed to ACM or control media, followed by MS/MS proteomic analyses. These data pointed toward a relatively small number of proteins that coimmunoprecipitated with PI3K, and surprisingly only five were regulated by the ACM signal. These hits included expected PI3K interactors, such as the platelet-derived growth factor receptor A (PDGFRA), as well as novel RNA-binding protein interactors ZC3H14 (zinc finger CCCH-type containing 14) and THOC1 (THO complex protein 1). In particular, ZC3H14 has recently emerged as an important RNA-binding protein with multiple roles in posttranscriptional regulation. In validation studies, we show that PI3K recruitment of ZC3H14 is necessary for PDGF-induced neuroprotection and that this interaction is present in primary retinal ganglion cells. Thus, we identified a novel non-cell autonomous neuroprotective signaling cascade mediated through PI3K that requires recruitment of ZC3H14 and may present a promising strategy to promote astrocyte-secreted prosurvival signals.

Nystatin Regulates Axonal Extension and Regeneration by Modifying the Levels of Nitric Oxide

Nystatin is a pharmacological agent commonly used for the treatment of oral, mucosal and cutaneous fungal infections. Nystatin has also been extensively applied to study the cellular function of cholesterol-enriched structures because of its ability to bind and extract cholesterol from mammalian membranes. In neurons, cholesterol level is tightly regulated, being essential for synapse and dendrite formation, and axonal guidance. However, the action of Nystatin on axon regeneration has been poorly evaluated. Here, we examine the effect of Nystatin on primary cultures of hippocampal neurons, showing how acute dose (minutes) of Nystatin increases the area of growth cones, and chronic treatment (days) enhances axon length, axon branching, and axon regeneration post-axotomy. We describe two alternative signaling pathways responsible for the observed effects and activated at different concentrations of Nystatin. At elevated concentrations, Nystatin promotes growth cone expansion through phosphorylation of Akt; whereas, at low concentrations, Nystatin enhances axon length and regrowth by increasing nitric oxide levels. Together, our findings indicate new signaling pathways of Nystatin and propose this compound as a novel regulator of axon regeneration.

IGF1 Knockdown Hinders Myocardial Development through Energy Metabolism Dysfunction Caused by ROS-Dependent FOXO Activation in the Chicken Heart

Insulin-like growth factor 1 (IGF1) is a multifunctional cellular regulatory factor that can regulate cell growth and development by mediating growth hormone stimulation. However, the mechanism of IGF1 dysfunction in cardiomyocyte development is seldom reported. To study this, we employed the models of IGF1 knockdown in chicken embryo in vivo and in cardiomyocytes in vitro. We detected the antioxidant capacity, PI3K/Akt pathway, energy metabolism-related genes, and myocardial development-related genes. Our results revealed that the low expression of IGF1 can significantly suppress the antioxidant capacity and increase the ROS (P < 0.05) levels, activating the AMPK and PI3K pathway by inhibiting the expression of IRS1. We also found that myocardial energy metabolism is blocked through IGF1, GLUT, and IGFBP inhibition, further inducing myocardial developmental disorder by inhibiting Mesp1, GATA, Nkx2.5, and MyoD expression. Altogether, we conclude that low IGF1 expression can hinder myocardial development through the dysfunction of energy metabolism caused by ROS-dependent FOXO activation.

EPO promotes axonal sprouting via upregulating GDF10

Erythropoietin (EPO) has an exact neuroprotective effect on stroke. However, it remains unknown whether it participates in axonal sprouting after neuron damage. Growth and differentiation factor 10 (GDF10) has been shown to be a trigger of axonal sprouting after stroke. Hence, it was hypothesized that EPO promotes axonal sprouting mainly through GDF10. In the present in vitro experiment, it was found that EPO could promote axonal sprouting and GDF10 expression in a dose-dependent manner. The knockdown of GDF10 using siRNA abolished the effect of EPO-mediated axonal sprouting, indicating that GDF10 is the executor of EPO-mediated axonal sprouting. The treatment of neurons with nuclear factor-kappaB (NF-κB) inhibitor JSH-23 could inhibit the accumulation of NF-κB phospho-p65 (p-p65) in the nucleus, the upregualtion of GDF10 and extending of axonal length. Furthermore, the addition of Janus kinase 2 (JAK2) inhibitor CEP-33779 or phosphoinositide 3-kinase (PI3K) inhibitor LY294002 to the culture medium also blocked the nuclear translocation of p-p65, the expression of GDF10, and axonal sprouting, suggesting that EPO induces axonal sprouting via activating cellular JAK2 and PI3K signaling. Impeding JAK2 signaling with CEP-33779 can suppress the phosphorylation of PI3K, and this confirms that the upstream of PI3K signaling is JAK2. These present results provide a novel insight into the role of EPO and the molecular mechanism of axonal sprouting, which is beneficial for the development of novel approaches for neurological recovery after brain injury, including stroke.

Igf1R/InsR function is required for axon extension and corpus callosum formation

One of the earliest steps during the development of the nervous system is the establishment of neuronal polarity and the formation of an axon. The intrinsic mechanisms that promote axon formation have been extensively analyzed. However, much less is known about the extrinsic signals that initiate axon formation. One of the candidates for these signals is Insulin-like growth factor 1 (Igf1) that acts through the Igf1 (Igf1R) and insulin receptors (InsR). Since Igf1R and InsR may act redundantly we analyzed conditional cortex-specific knockout mice that are deficient for both Igf1r and Insr to determine if they regulate the development of the cortex and the formation of axons in vivo. Our results show that Igf1R/InsR function is required for the normal development of the embryonic hippocampus and cingulate cortex while the lateral cortex does not show apparent defects in the Igf1r;Insr knockout. In the cingulate cortex, the number of intermediate progenitors and deep layer neurons is reduced and the corpus callosum is absent at E17. However, cortical organization and axon formation are not impaired in knockout embryos. In culture, cortical and hippocampal neurons from Igf1r;Insr knockout embryos extend an axon but the length of this axon is severely reduced. Our results indicate that Igf1R/InsR function is required for brain development in a region-specific manner and promotes axon growth but is not essential for neuronal polarization and migration in the developing brain.

IGF-1 alleviates serum IgG-induced neuronal cytolysis through PI3K signaling in children with opsoclonus-myoclonus syndrome and neuroblastoma

BACKGROUND

Opsoclonus-myoclonus syndrome (OMS) is a rare neurological disorder, usually accompanied by neuroblastoma (NB). There is no targeted treatment and animal model of OMS. We aimed to investigate whether insulin-like growth factor 1 (IGF-1)/phosphoinositide 3-kinase (PI3K) signaling alleviates neuronal cytolysis in pediatric OMS.

METHODS

Cultured rat cerebral cortical neurons and cerebellar neurons were incubated with sera or IgG isolated from sera of children with OMS and NB. Cytolysis and PI3K expression were measured by the lactate dehydrogenase assay and enzyme-linked immunosorbent assay, respectively. Using inhibitors and activators, the effects of IGF-1 and PI3K on cytolysis were investigated.

RESULTS

The incubation of sera or IgG from children with OMS and NB increased cytolysis in not only cerebellar neurons, but also cerebral cortical neurons. Furthermore, the IGF-1 receptor antagonist NVP-AEW541 exaggerated cytolysis in children with OMS and NB. IGF-1 alleviated cytolysis, which was blocked by the PI3K inhibitor LY294002. Additionally, sera or IgG from children with OMS and NB compensatively elevated PI3K expression. LY294002 exacerbated cytolysis; whereas, the PI3K activator 740 Y-P suppressed cytolysis.

CONCLUSION

IGF-1/PI3K signaling alleviates the cytolysis of cultured neurons induced by serum IgG from children with OMS and NB, which may be innovation therapy targets.

Distinct Functions for Mammalian CLASP1 and -2 During Neurite and Axon Elongation

Mammalian cytoplasmic linker associated protein 1 and -2 (CLASP1 and -2) are microtubule (MT) plus-end tracking proteins that selectively stabilize MTs at the edge of cells and that promote MT nucleation and growth at the Golgi, thereby sustaining cell polarity. In vitro analysis has shown that CLASPs are MT growth promoting factors. To date, a single CLASP1 isoform (called CLASP1α) has been described, whereas three CLASP2 isoforms are known (CLASP2α, -β, and -γ). Although CLASP2β/γ are enriched in neurons, suggesting isoform-specific functions, it has been proposed that during neurite outgrowth CLASP1 and -2 act in a redundant fashion by modulating MT dynamics downstream of glycogen synthase kinase 3 (GSK3). Here, we show that in differentiating N1E-115 neuroblastoma cells CLASP1 and CLASP2 differ in their accumulation at MT plus-ends and display different sensitivity to GSK3-mediated phosphorylation, and hence regulation. More specifically, western blot (WB) analysis suggests that pharmacological inhibition of GSK3 affects CLASP2 but not CLASP1 phosphorylation and fluorescence-based microscopy data show that GSK3 inhibition leads to an increase in the number of CLASP2-decorated MT ends, as well as to increased CLASP2 staining of individual MT ends, whereas a reduction in the number of CLASP1-decorated ends is observed. Thus, in N1E-115 cells CLASP2 appears to be a prominent target of GSK3 while CLASP1 is less sensitive. Surprisingly, knockdown of either CLASP causes phosphorylation of GSK3, pointing to the existence of feedback loops between CLASPs and GSK3. In addition, CLASP2 depletion also leads to the activation of protein kinase C (PKC). We found that these differences correlate with opposite functions of CLASP1 and CLASP2 during neuronal differentiation, i.e., CLASP1 stimulates neurite extension, whereas CLASP2 inhibits it. Consistent with knockdown results in N1E-115 cells, primary Clasp2 knockout (KO) neurons exhibit early accelerated neurite and axon outgrowth, showing longer axons than control neurons. We propose a model in which neurite outgrowth is fine-tuned by differentially posttranslationally modified isoforms of CLASPs acting at distinct intracellular locations, thereby targeting MT stabilizing activities of the CLASPs and controlling feedback signaling towards upstream kinases. In summary, our findings provide new insight into the roles of neuronal CLASPs, which emerge as regulators acting in different signaling pathways and locally modulating MT behavior during neurite/axon outgrowth.

The nervous system and genomics in endometriosis

Endometriosis is a gynaecological disease that occurs in approximately 10% to 15% of women of reproductive age and up to 47% of infertile women. The presence of implants of endometrial-like glands and stroma outside the uterus, characteristic of this disease, induce a wide variety of symptoms, mainly pelvic pain and infertility. Women suffering from this condition experience great distress, which significantly affects their quality of life. Numerous studies attempting to decipher the pathogenic mechanisms of endometriosis have been conducted around the world, yet its aetiology still remains unknown. It is widely believed that in women with endometriosis, the endometrium has characteristic features that allow the formation of implants once fragments have entered the peritoneal cavity through retrograde menstruation. Furthermore, a strong genetic tendency to develop the disease has been reported among patients and first-degree relatives. Thanks to the recent technological advances achieved in genomics and bioinformatics, a number of studies have had the potential to analyse several aspects of the pathogenesis of endometriosis from a genetic perspective. Due to the recent identification of nerve fibres in the endometrium of women with endometriosis, research on the neurogenesis of the disease has increased in the past few years. However, the genetic aspects of nerve growth in endometriosis have not been analysed in depth and further research providing important insights into the mechanisms that mediate pain in affected patients has the potential to contribute substantially to the future management of the condition.

Syntaxin-1/TI-VAMP SNAREs interact with Trk receptors and are required for neurotrophin-dependent outgrowth

SNARE proteins are essential components of the machinery that regulates vesicle trafficking and exocytosis. Their role is critical for the membrane-fusion processes that occur during neurotransmitter release. However, research in the last decade has also unraveled the relevance of these proteins in membrane expansion and cytoskeletal rearrangements during developmental processes such as neuronal migration and growth cone extension and attraction. Neurotrophins are neurotrophic factors that are required for many cellular functions throughout the brain, including neurite outgrowth and guidance, synaptic formation, and plasticity. Here we show that neurotrophin Trk receptors form a specific protein complex with the t-SNARE protein Syntaxin 1, both in vivo and in vitro. We also demonstrate that blockade of Syntaxin 1 abolishes neurotrophin-dependent growth of axons in neuronal cultures and decreases exocytotic events at the tip of axonal growth cones. 25-kDa soluble N-ethylmaleimide-sensitive factor attachment protein and Vesicle-associated membrane protein 2 do not participate in the formation of this SNARE complex, while tetanus neurotoxin-insensitive vesicle-associated membrane protein interacts with Trk receptors; knockdown of this (v) SNARE impairs Trk-dependent outgrowth. Taken together, our results support the notion that an atypical SNARE complex comprising Syntaxin 1 and tetanus neurotoxin-insensitive vesicle-associated membrane protein is required for axonal neurotrophin function.

KIF1Bβ mutations detected in hereditary neuropathy impair IGF1R transport and axon growth

Uncovering the mechanistic link between kinesin motors and neuropathy, Xu et al. identify functional KIF1Bβ mutations in human hereditary neuropathy to analyze them in mouse models. They propose that KIF1Bβ transports IGF1R and facilitates axonal outgrowth. Both of these effects are significantly affected by the clinical mutations.

KIF1Bβ is a kinesin-3 family anterograde motor protein essential for neuronal development, viability, and function. KIF1Bβ mutations have previously been reported in a limited number of pedigrees of Charcot-Marie-Tooth disease type 2A (CMT2A) neuropathy. However, the gene responsible for CMT2A is still controversial, and the mechanism of pathogenesis remains elusive. In this study, we show that the receptor tyrosine kinase IGF1R is a new direct binding partner of KIF1Bβ, and its binding and transport is specifically impaired by the Y1087C mutation of KIF1Bβ, which we detected in hereditary neuropathic patients. The axonal outgrowth and IGF-I signaling of Kif1b^−/− neurons were significantly impaired, consistent with decreased surface IGF1R expression. The complementary capacity of KIF1Bβ-Y1087C of these phenotypes was significantly impaired, but the binding capacity to synaptic vesicle precursors was not affected. These data have supported the relevance of KIF1Bβ in IGF1R transport, which may give new clue to the neuropathic pathogenesis.

Pregnancy-Associated Plasma Protein-aa Regulates Photoreceptor Synaptic Development to Mediate Visually Guided Behavior

To guide behavior, sensory systems detect the onset and offset of stimuli and process these distinct inputs via parallel pathways. In the retina, this strategy is implemented by splitting neural signals for light onset and offset via synapses connecting photoreceptors to ON and OFF bipolar cells, respectively. It remains poorly understood which molecular cues establish the architecture of this synaptic configuration to split light-onset and light-offset signals. A mutant with reduced synapses between photoreceptors and one bipolar cell type, but not the other, could reveal a critical cue. From this approach, we report a novel synaptic role for pregnancy-associated plasma protein aa (pappaa) in promoting the structure and function of cone synapses that transmit light-offset information. Electrophysiological and behavioral analyses indicated pappaa mutant zebrafish have dysfunctional cone-to-OFF bipolar cell synapses and impaired responses to light offset, but intact cone-to-ON bipolar cell synapses and light-onset responses. Ultrastructural analyses of pappaa mutant cones showed a lack of presynaptic domains at synapses with OFF bipolar cells. pappaa is expressed postsynaptically to the cones during retinal synaptogenesis and encodes a secreted metalloprotease known to stimulate insulin-like growth factor 1 (IGF1) signaling. Induction of dominant-negative IGF1 receptor expression during synaptogenesis reduced light-offset responses. Conversely, stimulating IGF1 signaling at this time improved pappaa mutants' light-offset responses and cone presynaptic structures. Together, our results indicate Pappaa-regulated IGF1 signaling as a novel pathway that establishes how cone synapses convey light-offset signals to guide behavior.SIGNIFICANCE STATEMENT Distinct sensory inputs, like stimulus onset and offset, are often split at distinct synapses into parallel circuits for processing. In the retina, photoreceptors and ON and OFF bipolar cells form discrete synapses to split neural signals coding light onset and offset, respectively. The molecular cues that establish this synaptic configuration to specifically convey light onset or offset remain unclear. Our work reveals a novel cue: pregnancy-associated plasma protein aa (pappaa), which regulates photoreceptor synaptic structure and function to specifically transmit light-offset information. Pappaa is a metalloprotease that stimulates local insulin-like growth factor 1 (IGF1) signaling. IGF1 promotes various aspects of synaptic development and function and is broadly expressed, thus requiring local regulators, like Pappaa, to govern its specificity.

Regulation of plasma membrane expansion during axon formation

Here, will review current evidence regarding the signaling pathways and mechanisms underlying membrane addition at sites of active growth during axon formation. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 170-180, 2018.

IGF-1 receptor regulates dynamic changes in neuronal polarity during cerebral cortical migration

During cortical development, neurons undergo polarization, oriented migration and layer-type differentiation. The biological and biochemical mechanisms underlying these processes are not completely understood. In neurons in culture we showed that IGF-1 receptor activation is important for growth cone assembly and axonal formation. However, the possible roles of the insulin like growth factor-1 receptor (IGF-1R) on neuronal differentiation and polarization in vivo in mammals have not yet been studied. Using in utero electroporation, we show here that the IGF-1R is essential for neocortical development. Neurons electroporated with a shRNA targeting IGF-1 receptor failed to migrate to the upper cortical layers and accumulated at the ventricular/subventricular zones. Co-electroporation with a constitutively active form of PI3K rescued migration. The change of the morphology from multipolar to bipolar cells was also attenuated. Cells lacking the IGF-1 receptor remain arrested as multipolar forming a highly disorganized tissue. The typical orientation of the migrating neurons with the Golgi complex oriented toward the cortical upper layers was also affected by electroporation with shRNA targeting IGF-1 receptor. Finally, cells electroporated with the shRNA targeting IGF-1 receptor were unable to form an axon and, therefore, neuron polarity was absent.

P18 peptide, a functional fragment of pigment epithelial-derived factor, inhibits angiogenesis in hepatocellular carcinoma via modulating VEGF/VEGFR2 signalling pathway

The P18 peptide is a functional fragment of pigment epithelial-derived factor (PEDF), which is an endogenic angiogenesis inhibitor. This study sought to determine the anti-angiogenic bioactivity of the P18 peptide in hepato-cellular carcinoma (HCC) and to elucidate the underlying mechanism. Xenograft tumour growth assays demonstrated the P18 peptide suppressed angiogenesis of HCC in vivo. Wound healing, Transwell and Matrigel-culture assays indicated that the P18 peptide inhibited the cell migration and tube formation of endothelial cells (ECs) in vitro. Cell viability and apoptosis assessed by Cell Counting Kit-8 (CCK-8) and flow cytometry assays suggested that the P18 peptide inhibited angiogenesis by inducing apoptosis of ECs. Angiogenesis- and signal transduction-associated molecules analysed by western blot demonstrated that the P18 peptide targets vascular endothelial cell growth factor receptor 2 (VEGFR2) on ECs. In conclusion, by inhibiting the phosphorylation of VEGFR2, the P18 peptide modulates signalling transduction between VEGF/VEGFR2 and suppresses activation of the PI3K/Akt cascades, leading to an increase in mitochondrial-mediated apoptosis and anti-angiogenic activity. This bioactivity of the P18 peptide may represent a novel therapeutic strategy for the treatment of HCC.

IGF-1 Induces GHRH Neuronal Axon Elongation during Early Postnatal Life in Mice

Nutrition during the perinatal period programs body growth. Growth hormone (GH) secretion from the pituitary regulates body growth and is controlled by Growth Hormone Releasing Hormone (GHRH) neurons located in the arcuate nucleus of the hypothalamus. We observed that dietary restriction during the early postnatal period (i.e. lactation) in mice influences postnatal growth by permanently altering the development of the somatotropic axis in the pituitary gland. This alteration may be due to a lack of GHRH signaling during this critical developmental period. Indeed, underfed pups showed decreased insulin-like growth factor I (IGF-I) plasma levels, which are associated with lower innervation of the median eminence by GHRH axons at 10 days of age relative to normally fed pups. IGF-I preferentially stimulated axon elongation of GHRH neurons in in vitro arcuate explant cultures from 7 day-old normally fed pups. This IGF-I stimulating effect was selective since other arcuate neurons visualized concomitantly by neurofilament labeling, or AgRP immunochemistry, did not significantly respond to IGF-I stimulation. Moreover, GHRH neurons in explants from age-matched underfed pups lost the capacity to respond to IGF-I stimulation. Molecular analyses indicated that nutritional restriction was associated with impaired activation of AKT. These results highlight a role for IGF-I in axon elongation that appears to be cell selective and participates in the complex cellular mechanisms that link underfeeding during the early postnatal period with programming of the growth trajectory.

Membrane traffic during axon development

Brain formation requires the establishment of complex neural circuits between a diverse array of neuronal subtypes in an intricate and ever changing microenvironment and yet with a large degree of specificity and reproducibility. In the last three decades, mounting evidence has established that neuronal development relies on the coordinated regulation of gene expression, cytoskeletal dynamics, and membrane trafficking. Membrane trafficking has been considered important in that it brings new membrane and proteins to the plasma membrane of developing neurons and because it also generates and maintains the polarized distribution of proteins into neuronal subdomains. More recently, accumulating evidence suggests that membrane trafficking may have an even more active role during development by regulating the distribution and degree of activation of a wide variety of proteins located in plasma membrane subdomains and endosomes. In this article the evidence supporting the different roles of membrane trafficking during axonal development, particularly focusing on the role of SNAREs and Rabs was reviewed. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1185-1200, 2016.

IGF-I: A Key Growth Factor that Regulates Neurogenesis and Synaptogenesis from Embryonic to Adult Stages of the Brain

The generation of neurons in the adult mammalian brain requires the activation of quiescent neural stem cells (NSCs). This activation and the sequential steps of neuron formation from NSCs are regulated by a number of stimuli, which include growth factors. Insulin-like growth factor-I (IGF-I) exert pleiotropic effects, regulating multiple cellular processes depending on their concentration, cell type, and the developmental stage of the animal. Although IGF-I expression is relatively high in the embryonic brain its levels drop sharply in the adult brain except in neurogenic regions, i.e., the hippocampus (HP) and the subventricular zone-olfactory bulb (SVZ-OB). By contrast, the expression of IGF-IR remains relatively high in the brain irrespective of the age of the animal. Evidence indicates that IGF-I influences NSC proliferation and differentiation into neurons and glia as well as neuronal maturation including synapse formation. Furthermore, recent studies have shown that IGF-I not only promote adult neurogenesis by regulating NSC number and differentiation but also by influencing neuronal positioning and migration as described during SVZ-OB neurogenesis. In this article we will revise and discuss the actions reported for IGF-I signaling in a variety of in vitro and in vivo models, focusing on the maintenance and proliferation of NSCs/progenitors, neurogenesis, and neuron integration in synaptic circuits.

Human Cortical Neural Stem Cells Expressing Insulin-Like Growth Factor-I: A Novel Cellular Therapy for Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent age-related neurodegenerative disorder and a leading cause of dementia. Current treatment fails to modify underlying disease pathologies and very little progress has been made to develop effective drug treatments. Cellular therapies impact disease by multiple mechanisms, providing increased efficacy compared with traditional single-target approaches. In amyotrophic lateral sclerosis, we have shown that transplanted spinal neural stem cells (NSCs) integrate into the spinal cord, form synapses with the host, improve inflammation, and reduce disease-associated pathologies. Our current goal is to develop a similar "best in class" cellular therapy for AD. Here, we characterize a novel human cortex-derived NSC line modified to express insulin-like growth factor-I (IGF-I), HK532-IGF-I. Because IGF-I promotes neurogenesis and synaptogenesis in vivo, this enhanced NSC line offers additional environmental enrichment, enhanced neuroprotection, and a multifaceted approach to treating complex AD pathologies. We show that autocrine IGF-I production does not impact the cell secretome or normal cellular functions, including proliferation, migration, or maintenance of progenitor status. However, HK532-IGF-I cells preferentially differentiate into gamma-aminobutyric acid-ergic neurons, a subtype dysregulated in AD; produce increased vascular endothelial growth factor levels; and display an increased neuroprotective capacity in vitro. We also demonstrate that HK532-IGF-I cells survive peri-hippocampal transplantation in a murine AD model and exhibit long-term persistence in targeted brain areas. In conclusion, we believe that harnessing the benefits of cellular and IGF-I therapies together will provide the optimal therapeutic benefit to patients, and our findings support further preclinical development of HK532-IGF-I cells into a disease-modifying intervention for AD.

Selected SNARE proteins are essential for the polarized membrane insertion of igf-1 receptor and the regulation of initial axonal outgrowth in neurons

The establishment of polarity necessitates initial axonal outgrowth and, therefore, the addition of new membrane to the axon’s plasmalemma. Axolemmal expansion occurs by exocytosis of plasmalemmal precursor vesicles (PPVs) primarily at the neuronal growth cone. Little is known about the SNAREs family proteins involved in the regulation of PPV fusion with the neuronal plasmalemma at early stages of differentiation. We show here that five SNARE proteins (VAMP2, VAMP4, VAMP7, Syntaxin6 and SNAP23) were expressed by hippocampal pyramidal neurons before polarization. Expression silencing of three of these proteins (VAMP4, Syntaxin6 and SNAP23) repressed axonal outgrowth and the establishment of neuronal polarity, by inhibiting IGF-1 receptor exocytotic polarized insertion, necessary for neuronal polarization. In addition, stimulation with IGF-1 triggered the association of VAMP4, Syntaxin6 and SNAP23 to vesicular structures carrying the IGF-1 receptor and overexpression of a negative dominant form of Syntaxin6 significantly inhibited exocytosis of IGF-1 receptor containing vesicles at the neuronal growth cone. Taken together, our results indicated that VAMP4, Syntaxin6 and SNAP23 functions are essential for regulation of PPV exocytosis and the polarized insertion of IGF-1 receptor and, therefore, required for initial axonal elongation and the establishment of neuronal polarity.

The Role of the PI3K Pathway in the Regeneration of the Damaged Brain by Neural Stem Cells after Cerebral Infarction

Neurologic deficits resulting from stroke remain largely intractable, which has prompted thousands of studies aimed at developing methods for treating these neurologic sequelae. Endogenous neurogenesis is also known to occur after brain damage, including that due to cerebral infarction. Focusing on this process may provide a solution for treating neurologic deficits caused by cerebral infarction. The phosphatidylinositol-3-kinase (PI3K) pathway is known to play important roles in cell survival, and many studies have focused on use of the PI3K pathway to treat brain injury after stroke. Furthermore, since the PI3K pathway may also play key roles in the physiology of neural stem cells (NSCs), eliciting the appropriate activation of the PI3K pathway in NSCs may help to improve the sequelae of cerebral infarction. This review describes the PI3K pathway, its roles in the brain and NSCs after cerebral infarction, and the therapeutic possibility of activating the pathway to improve neurologic deficits after cerebral infarction.

Insulin growth factor-1 (IGF-1) enhances hippocampal excitatory and seizure activity through IGF-1 receptor-mediated mechanisms in the epileptic brain

Insulin-like growth factor-1 (IGF-1) is known to promote neurogenesis and survival. However, recent studies have suggested that IGF-1 regulates neuronal firing and excitatory neurotransmission. In the present study, focusing on temporal lobe epilepsy, we found that IGF-1 levels and IGF-1 receptor activation are increased in human epileptogenic tissues, and pilocarpine- and pentylenetetrazole-treated rat models. Using an acute model of seizures, we showed that lateral cerebroventricular infusion of IGF-1 elevates IGF-1 receptor (IGF-1R) signalling before pilocarpine application had proconvulsant effects. In vivo electroencephalogram recordings and power spectrogram analysis of local field potential revealed that IGF-1 promotes epileptiform activities. This effect is diminished by co-application of an IGF-1R inhibitor. In an in vitro electrophysiological study, we demonstrated that IGF-1 enhancement of excitatory neurotransmission and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor- and N-methyl-D-aspartate receptor-mediated currents is inhibited by IGF-1R inhibitor. Finally, activation of extracellular signal-related kinase (ERK)-1/2 and protein kinase B (Akt) in seizures in rats is increased by exogenous IGF-1 and diminished by picropodophyllin. A behavioural study reveals that the ERK1/2 or Akt inhibitor attenuates seizure activity. These results indicate that increased IGF-1 levels after recurrent hippocampal neuronal firings might, in turn, promote seizure activity via IGF-1R-dependent mechanisms. The present study presents a previously unappreciated role of IGF-1R in the development of seizure activity.

Second messenger signaling for neuronal polarization: cell mechanics-dependent pattern formation

Neuronal polarization is a critical step in the neuronal morphogenesis. Despite the identification of several evolutionarily conserved factors for neural polarization, the exact mechanisms by which cells initiate and maintain polarity remain to be characterized. Here, we review the recent progress on the roles of second messengers, specifically the cyclic nucleotides and membrane-associated phospholipids, in the initiation, propagation, and integration of polarization signals, and propose an inhibitor-free model for neural polarization. The characteristic features of neuron polarization include the formation of single axon and multiple dendrites. These features involve chemical and mechanical mechanisms such as reaction-diffusion and tug-of-war, by which second messengers can act in concert to initiate and stabilize the cellular asymmetry. Nevertheless, biochemical factors eliciting the long-range inhibition remain ambiguous. Thus, we provide a simple, inhibitor-free model that can incorporate known cytochemical and cytomechanical factors, and produce features of neuronal polarization in environments provided with minimized extracellular regulators.

Rho GTPases, phosphoinositides, and actin: a tripartite framework for efficient vesicular trafficking

Rho GTPases are well known regulators of the actin cytoskeleton that act by binding and activating actin nucleators. They are therefore involved in many actin-based processes, including cell migration, cell polarity, and membrane trafficking. With the identification of phosphoinositide kinases and phosphatases as potential binding partners or effectors, Rho GTPases also appear to participate in the regulation of phosphoinositide metabolism. Since both actin dynamics and phosphoinositide turnover affect the efficiency and the fidelity of vesicle transport between cell compartments, Rho GTPases have emerged as critical players in membrane trafficking. Rho GTPase activity, actin remodeling, and phosphoinositide metabolism need to be coordinated in both space and time to ensure the progression of vesicles along membrane trafficking pathways. Although most molecular pathways are still unclear, in this review, we will highlight recent advances made in our understanding of how Rho-dependent signaling pathways organize actin dynamics and phosphoinositides and how phosphoinositides potentially provide negative feedback to Rho GTPases during endocytosis, exocytosis and membrane exchange between intracellular compartments.

Local translation of TC10 is required for membrane expansion during axon outgrowth

The surface of developing axons expands in a process mediated by the exocyst complex. The spatial-temporal regulation of the exocyst is only partially understood. Here we report that stimulated membrane enlargement in dorsal root ganglion (DRG) axons is triggered by intra-axonal synthesis of TC10, a small GTPase required for exocyst function. Induced membrane expansion and axon outgrowth are inhibited after axon-specific knockdown of TC10 mRNA. To determine the relationship of intra-axonal TC10 synthesis with the previously described stimulus-induced translation of the cytoskeletal regulator Par3, we investigate the signaling pathways controlling their local translation in response to NGF. Phosphoinositide 3-kinase (PI3K)-dependent activation of the Rheb-mTOR pathway triggers the simultaneous local synthesis of TC10 and Par3. These results reveal the importance of local translation in the control of membrane dynamics and demonstrate that localized, mTOR-dependent protein synthesis triggers the simultaneous activation of parallel pathways.

Effects of bone marrow-derived mesenchymal stem cells on the axonal outgrowth through activation of PI3K/AKT signaling in primary cortical neurons followed oxygen-glucose deprivation injury

Background

Transplantation with bone marrow-derived mesenchymal stem cells (BMSCs) improves the survival of neurons and axonal outgrowth after stroke remains undetermined. Here, we investigated whether PI3K/AKT signaling pathway is involved in these therapeutic effects of BMSCs.

Methodology/Principal Findings

(1) BMSCs and cortical neurons were derived from Sprague-Dawley rats. The injured neurons were induced by Oxygen–Glucose Deprivation (OGD), and then were respectively co-cultured for 48 hours with BMSCs at different densities (5×10³, 5×10⁵/ml) in transwell co-culture system. The average length of axon and expression of GAP-43 were examined to assess the effect of BMSCs on axonal outgrowth after the damage of neurons induced by OGD. (2) The injured neurons were cultured with a conditioned medium (CM) of BMSCs cultured for 24 hours in neurobasal medium. During the process, we further identified whether PI3K/AKT signaling pathway is involved through the adjunction of LY294002 (a specific phosphatidylinositide-3-kinase (PI3K) inhibitor). Two hours later, the expression of pAKT (phosphorylated AKT) and AKT were analyzed by Western blotting. The length of axons, the expression of GAP-43 and the survival of neurons were measured at 48 hours.

Results

Both BMSCs and CM from BMSCs inreased the axonal length and GAP-43 expression in OGD-injured cortical neurons. There was no difference between the effects of BMSCs of 5×10⁵/ml and of 5×10³/ml on axonal outgrowth. Expression of pAKT enhanced significantly at 2 hours and the neuron survival increased at 48 hours after the injured neurons cultured with the CM, respectively. These effects of CM were prevented by inhibitor LY294002.

Conclusions/Significance

BMSCs promote axonal outgrowth and the survival of neurons against the damage from OGD in vitro by the paracrine effects through PI3K/AKT signaling pathway.

The effects of hematopoietic growth factors on neurite outgrowth

Stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) are initially discovered as the essential hematopoietic growth factors regulating bone marrow stem cell proliferation and differentiation, and SCF in combination with G-CSF (SCF+G-CSF) has synergistic effects on bone marrow stem cell mobilization. In this study we have determined the effect of SCF and G-CSF on neurite outgrowth in rat cortical neurons. Using molecular and cellular biology and live cell imaging approaches, we have revealed that receptors for SCF and G-CSF are expressed on the growth core of cortical neurons, and that SCF+G-CSF synergistically enhances neurite extension through PI3K/AKT and NFκB signaling pathways. Moreover, SCF+G-CSF induces much greater NFκB activation, NFκB transcriptional binding and brain-derived neurotrophic factor (BDNF) production than SCF or G-CSF alone. In addition, we have also observed that BDNF, the target gene of NFκB, is required for SCF+G-CSF-induced neurite outgrowth. These data suggest that SCF+G-CSF has synergistic effects to promote neurite growth. This study provides new insights into the contribution of hematopoietic growth factors in neuronal plasticity.

Optogenetic control of PIP3: PIP3 is sufficient to induce the actin-based active part of growth cones and is regulated via endocytosis

Phosphatidylinositol-3,4,5-trisphosphate (PIP3) is highly regulated in a spatiotemporal manner and plays multiple roles in individual cells. However, the local dynamics and primary functions of PIP3 in developing neurons remain unclear because of a lack of techniques for manipulating PIP3 spatiotemporally. We addressed this issue by combining optogenetic control and observation of endogenous PIP3 signaling. Endogenous PIP3 was abundant in actin-rich structures such as growth cones and "waves", and PIP3-rich plasma membranes moved actively within growth cones. To study the role of PIP3 in developing neurons, we developed a PI3K photoswitch that can induce production of PIP3 at specific locations upon blue light exposure. We succeeded in producing PIP3 locally in mouse hippocampal neurons. Local PIP3 elevation at neurite tips did not induce neurite elongation, but it was sufficient to induce the formation of filopodia and lamellipodia. Interestingly, ectopic PIP3 elevation alone activated membranes to form actin-based structures whose behavior was similar to that of growth-cone-like "waves". We also found that endocytosis regulates effective PIP3 concentration at plasma membranes. These results revealed the local dynamics and primary functions of PIP3, providing fundamental information about PIP3 signaling in neurons.

Controlled lateral packing of insulin monolayers influences neuron polarization in solid-supported cultures

Neurons are highly polarized cells, composed of one axon and several branching dendrites. One important issue in neurobiology is to understand the molecular factors that determine the neuron to develop polarized structures. A particularly early event, in neurons still lacking a discernible axon, is the segregation of IGF-1 (Insulin like Growth Factor-1) receptors in one neurite. This receptor can be activated by insulin in bulk, but, it is not known if changes of insulin organization as a monomolecular film may affect neuron polarization. To this end, in this work we developed solid-supported Langmuir-Blodgett films of insulin with different surface packing density. Hyppocampal pyramidal neurons, in early stage of differentiation, were cultured onto those substrates and polarization was studied after 24 h by confocal microscopy. Also we used surface reflection interference contrast microscopy and confocal microscopy to study attachment patterns and morphology of growth cones. We observed that insulin films packed at 14 mN/m induced polarization in a similar manner to high insulin concentration in bulk, but insulin packed at 44 mN/m did not induce polarization. Our results provide novel evidence that the neuron polarization through IGF-1 receptor activation can be selectively modulated by the lateral packing of insulin organized as a monomolecular surface for cell growth.

Molecular mechanisms involved in the regulation of neuritogenesis by estradiol: Recent advances

This review analyzes the signaling mechanisms activated by estradiol to regulate neuritogenesis in several neuronal populations. Estradiol regulates axogenesis by the activation of the mitogen activated protein kinase (MAPK) cascade through estrogen receptor α located in the plasma membrane. In addition, estradiol regulates MAPK signaling via the activation of protein kinase C and by increasing the expression of brain derived neurotrophic factor and tyrosine kinase receptor B. Estradiol also interacts with the signaling of insulin-like growth factor-I receptor through estrogen receptor α, modulating the phosphoinositide-3 kinase signaling pathway, which contributes to the stabilization of microtubules. Finally, estradiol modulates dendritogenesis by the inhibition of Notch signaling, by a mechanism that, at least in hippocampal neurons, is mediated by G-protein coupled receptor 30. This article is part of a Special Issue entitled 'Neurosteroids'.

Age-changes in gene expression in primary mixed glia cultures from young vs. old rat cerebral cortex are modified by interactions with neurons

Astrocytic GFAP expression increases during normal aging in many brain regions and in primary astrocyte cultures derived from aging rodent brains. As shown below, we unexpectedly found that the age-related increase of GFAP expression was suppressed in mixed glia (astrocytes+microglia). However, the age-related increase of GFAP was observed when E18 neurons were co-cultured with mixed glia. Thus, the presence of microglia can suppress the age-related increase of GFAP, in primary cultures of astrocytes. To more broadly characterize how aging and co-culture with neurons alters glial gene expression, we profiled gene expression in mixed glia from young (3 mo) and old (24 mo) male rat cerebral cortex by Affymetrix microarray (Rat230 2.0). The majority of age changes were independent of the presence of neurons. Overall, the expression of twofold more genes increased with age than decreased with age. The minority of age changes that were either suppressed or revealed by the presence of neurons may be useful to analyze glial-neuron interaction during aging. Some in vitro changes are shared with those of aging rat hippocampus in studies from the Landfield group (Rowe et al., 2007; Kadish et al., 2009).

A novel pathway combining calreticulin exposure and ATP secretion in immunogenic cancer cell death

Surface-exposed calreticulin (ecto-CRT) and secreted ATP are crucial damage-associated molecular patterns (DAMPs) for immunogenic apoptosis. Inducers of immunogenic apoptosis rely on an endoplasmic reticulum (ER)-based (reactive oxygen species (ROS)-regulated) pathway for ecto-CRT induction, but the ATP secretion pathway is unknown. We found that after photodynamic therapy (PDT), which generates ROS-mediated ER stress, dying cancer cells undergo immunogenic apoptosis characterized by phenotypic maturation (CD80(high), CD83(high), CD86(high), MHC-II(high)) and functional stimulation (NO(high), IL-10(absent), IL-1β(high)) of dendritic cells as well as induction of a protective antitumour immune response. Intriguingly, early after PDT the cancer cells displayed ecto-CRT and secreted ATP before exhibiting biochemical signatures of apoptosis, through overlapping PERK-orchestrated pathways that require a functional secretory pathway and phosphoinositide 3-kinase (PI3K)-mediated plasma membrane/extracellular trafficking. Interestingly, eIF2α phosphorylation and caspase-8 signalling are dispensable for this ecto-CRT exposure. We also identified LRP1/CD91 as the surface docking site for ecto-CRT and found that depletion of PERK, PI3K p110α and LRP1 but not caspase-8 reduced the immunogenicity of the cancer cells. These results unravel a novel PERK-dependent subroutine for the early and simultaneous emission of two critical DAMPs following ROS-mediated ER stress.

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.