Neurite Outgrowth In Cortical Neurons Research Articles

DNA tension assays reveal that force-dependent integrin activation regulates neurite outgrowth in primary cortical neurons

Biomechanical inputs are ubiquitously present in biological systems and are known to regulate various cell functions. In particular, neural cell development is sensitive to mechanical regulation, as these cells reside in one of the softest microenvironments in the body. To fully characterize and comprehend how mechanical force modulates early neuronal processes, we prepared substrates functionalized with DNA probes displaying integrin ligands, including cRGD and laminin, to quantify integrin-mediated molecular tension during neurite initiation in primary cortical neurons. Our live-cell imaging analysis reveals that integrin-mediated tension force is highly dynamic and distributed across the cell body, with the overall tension signal gradually increasing during neurite outgrowth. Notably, we detected a consistent level of mechanical force (amplitude = 4.7–12 piconewtons, pN) for cell integrin-ligand interactions. Further quantifications reveal that neurons exhibit faster cell spreading and neurite outgrowth upon interacting with ligands functionalized with 4.7 pN relative to 12 pN probes. These findings indicate that the magnitude of integrin-mediated mechanical feedback regulates neuronal activity during early neuritogenesis. Additionally, we observed that mechanical tension is correlated with calcium signaling, since inhibiting calcium influx substantially reduced mechanical tension. Thus, our findings support that the magnitude of integrin-mediated mechanical feedback regulates neuronal activity during early neuritogenesis and that mechanical force is an essential element complementing well-known biochemical regulatory mechanisms orchestrating the integrin activation machinery and controlled neurite outgrowth in cortical neurons.

Involvement of strawberry notch homologue 1 in neurite outgrowth of cortical neurons.

When the regulation of axonal and dendritic growth is altered, the neuronal network becomes disordered, which may contribute to the development of psychiatric disorders. Some genome analyses have suggested relationships between mutations in strawberry notch homologue 1 (SBNO1) and neurodevelopmental disorders. However, the function of SBNO1 has not yet been reported. Here, SBNO1 expression pattern during the development of the cerebral cortex in mice was examined. SBNO1 was strongly expressed in the cortical plate and its expression was maintained at a low level during the postnatal stage. CRISPR/Cas9-based knockout of Sbno1 in Neuro2A cultured cells showed delayed growth of neurites. A cortical neuron-specific conditional knockout mouse was constructed, which resulted in hypotrophy of axon bundles and dendrites in cortical neurons. Thus, when mutated, SBNO1 is a candidate gene for psychiatric diseases, such as schizophrenia, as suggested by human genome studies.

Evaluation of chemical compounds that inhibit neurite outgrowth using GFP-labeled iPSC-derived human neurons

Due to the increasing number of drugs and untested environmental compounds introduced into commercial use, there is recognition for a need to develop reliable and efficient screening methods to identify compounds that may adversely impact the nervous system. One process that has been implicated in neurodevelopment is neurite outgrowth; the disruption of which can result in adverse outcomes that persist later in life. Here, we developed a green fluorescent protein (GFP) labeled neurite outgrowth assay in a high-content, high-throughput format using induced pluripotent stem cell (iPSC) derived human spinal motor neurons and cortical glutamatergic neurons. The assay was optimized for use in a 1536-well plate format. Then, we used this assay to screen a set of 84 unique compounds that have previously been screened in other neurite outgrowth assays. This library consists of known developmental neurotoxicants, environmental compounds with unknown toxicity, and negative controls. Neurons were cultured for 40 h and then treated with compounds at 11 concentrations ranging from 1.56 nM to 92 μM for 24 and 48 h. Effects of compounds on neurite outgrowth were evaluated by quantifying total neurite length, number of segments, and maximum neurite length per cell. Among the 84 tested compounds, neurite outgrowth in cortical neurons and motor neurons were selectively inhibited by 36 and 31 compounds, respectively. Colchicine, rotenone, and methyl mercuric (II) chloride inhibited neurite outgrowth in both cortical and motor neurons. It is interesting to note that some compounds like parathion and bisphenol AF had inhibitory effects on neurite outgrowth specifically in the cortical neurons, while other compounds, such as 2,2′,4,4′-tetrabromodiphenyl ether and caffeine, inhibited neurite outgrowth in motor neurons. The data gathered from these studies show that GFP-labeled iPSC-derived human neurons are a promising tool for identifying and prioritizing compounds with developmental neurotoxicity potential for further hazard characterization.

Rosuvastatin improves neurite extension in cortical neurons through the Notch 1/BDNF pathway

ABSTRACTObjectives: Neurite outgrowth of neurons is essential for forming functional neural circuits. It is believed that neuronal neurite outgrowth is an important mechanism of brain plasticity. Rosuvastatin (RSV) is a relatively new statin and may have neuroprotective properties. However, whether RSV exerts an effect on neurite extension and its potential mechanism in cortical neurons remains poorly documented.Methods: Immunofluorescence method was used to examine the effect of RSV on neurite outgrowth in primary cortical neuron by measuring neurite length and confirmed the promotion effect. Then, the potential mechanisms involving the Notch1 pathway were investigated. Effects of RSV on the expression of Notch 1 and Hes1were determined using qRT-PCR. In addition, brain-derived neurotrophic factor (BDNF) expression was also assessed using qRT-PCR, and ELISA.Results: RSV promoted neurite outgrowth of cortical neurons, and this effect could be partially prevented by the Notch 1 pathway inhibitor, DAPT. Subsequently, we found that Jagged 1 and Notch 1 were colocalized. In addition, we observed that the levels of both Notch 1 and Hes 1 in cortical neurons were increased after RSV, but sharply decreased after DAPT treatment. Moreover, RSV increased brain-derived neurotrophic factor (BDNF) levels in cortical neurons, but in the culture medium, and the effect could be partially suppressed by DAPT treatment.Discussion: These findings indicate that RSV mediates neurite outgrowth in primary cortical neurons. The RSV-induced neuritogenic effect is mediated at least partly via the Notch1/BDNF pathway.

Varying Effects of the G‐Protein Coupled Estrogen Receptor During Development in Embryonic Rat Hippocampal and Cortical Neurons

Estrogen has been known to play a role in enhancing brain development for over half a century. Most studies of estrogen's effect on the nervous system have focused on the traditional estrogen receptors Estrogen Receptor‐α (ERα) and Estrogen Receptor‐β (ERβ). The recent discovery of the G‐Protein Coupled Estrogen Receptor (GPER) suggests knowledge of estrogen's effects may be incomplete. While evidence has suggested the roles GPER plays in the nervous system include neuroprotection, neuronal recovery from stroke and degeneration, neuron proliferation, as well as many others. A caveat is that most studies have looked only at the effect in mature neurons and not the effect GPER has during early neuronal development. Here we sought to study the role of GPER activity in neurite outgrowth and synapse formation during early development.Embryonic day 18 rat cortical and hippocampal neurons were cultured in estrogen‐ and phenol red‐ free medium in the presence of a nonselective ER agonist (E2), a selective GPER agonist (G‐1), and a selective GPER antagonist (G‐15). Neurite growth was measured at 20, 48, 72, and 96 hours in culture using the ImageJ plugin NeuronJ. Synapses were visualized at 7 and 14 days in culture by using immunofluorescence of the pre‐ and post‐synaptic markers, synaptophysin and PSD‐95, respectively. Synapse formation was measured by measuring the overlap between these markers in ImageJ. Our data revealed activation of GPER promoted neurite growth in hippocampal neurons, but not in cortical neurons, but blocking the receptor inhibited neurite growth in cortical neurons. In addition, low levels of G1 (1μM) inhibited neurite outgrowth in cortical neurons. Cortical neurons showed no significant difference in synapse formation, while in hippocampal neurons the effect varied based on time period and dosage. This provides the first evidence that GPER activation may play different roles in brain regions, as well as having specific dosage based effects in specific regions. Future experiments will investigate the molecular and cellular mechanisms underlying the pharmacological differences in GPER effects between developing cortical and hippocampal neurons.Support or Funding InformationThis project was supported by the Saint Louis University Start‐up Fund for Dr. Xu lab and the Sigma XI Grant‐In‐Aid of Research awarded to Mr. Kyle Pemberton.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Liraglutide Protects Neurite Outgrowth of Cortical Neurons Under Oxidative Stress though Activating the Wnt Pathway

BackgroundNeurogenesis including neurite outgrowth is important for brain plasticity under physiological conditions and in brain repair after injury. Liraglutide has been found to have neuroprotective action in the risk of central nervous system disease. However, the effect and the potential mechanism of liraglutide-induced neurite outgrowth in primary cortical neurons under oxidative stress remain poorly documented. MethodsIn the text, H2O2 was used to mimic ischemia injury in primary cortical neurons. The viability and apoptosis of cell was assessed by Cell Counting Kit-8 and Hoechst 33342. Immunofluorescence method was used to examine the effect of liraglutide on neurite outgrowth in cortical neuron under H2O2 condition. Then, the potential mechanisms involving the Wnt pathway were investigated. The expression of β-catenin, c-myc, and cyclin D1 was determined using quantitative real-time polymerase chain reaction and Western blot. ResultsLiraglutide significantly increased the viability and alleviated the apoptosis rate of cortical neurons induced by H2O2. Next, liraglutide promoted neurite outgrowth, which could be partially inhibited by the Wnt pathway inhibitor Xav939. Besides, liraglutide induced an increase of β-catenin, c-myc, and cyclin D1 levels, which could also be blocked in the presence of Xav939. ConclusionsThese results illustrate that liraglutide exerts neurotrophin-like activity in cortical neurons under oxidative stress condition, partly through activating the Wnt pathway.

Rosuvastatin Improves Neurite Outgrowth of Cortical Neurons against Oxygen-Glucose Deprivation via Notch1-mediated Mitochondrial Biogenesis and Functional Improvement.

Neurogenesis, especially neurite outgrowth is an essential element of neuroplasticity after cerebral ischemic injury. Mitochondria may supply ATP to power fundamental developmental processes including neuroplasticity. Although rosuvastatin (RSV) displays a potential protective effect against cerebral ischemia, it remains unknown whether it modulates mitochondrial biogenesis and function during neurite outgrowth. Here, the oxygen-glucose deprivation (OGD) model was used to induce ischemic injury. We demonstrate that RSV treatment significantly increases neurite outgrowth in cortical neurons after OGD-induced damage. Moreover, we show that RSV reduces the generation of reactive oxygen species (ROS), protects mitochondrial function, and elevates the ATP levels in cortical neurons injured by OGD. In addition, we found that, under these conditions, RSV treatment increases the mitochondrial DNA (mtDNA) content and the mRNA levels of mitochondrial transcription factor A (TFAM) and nuclear respiratory factor 1 (NRF-1). Furthermore, blocking Notch1, which is expressed in primary cortical neurons, reverses the RSV-dependent induction of mitochondrial biogenesis and function under OGD conditions. Collectively, these results suggest that RSV could restore neurite outgrowth in cortical neurons damaged by OGD in vitro, by preserving mitochondrial function and improving mitochondrial biogenesis, possibly through the Notch1 pathway.

Expression of Rac1 alternative 3′ UTRs is a cell specific mechanism with a function in dendrite outgrowth in cortical neurons

The differential expression of mRNAs containing tandem alternative 3′ UTRs, achieved by mechanisms of alternative polyadenylation and post-transcriptional regulation, has been correlated with a variety of cellular states. In differentiated cells and brain tissues there is a general use of distal polyadenylation signals, originating mRNAs with longer 3′ UTRs, in contrast with proliferating cells and other tissues such as testis, where most mRNAs contain shorter 3′ UTRs. Although cell type and state are relevant in many biological processes, how these mechanisms occur in specific brain cell types is still poorly understood. Rac1 is a member of the Rho family of small GTPases with essential roles in multiple cellular processes, including cell differentiation and axonal growth. Here we used different brain cell types and tissues, including oligodendrocytes, microglia, astrocytes, cortical and hippocampal neurons, and optical nerve, to show that classical Rho GTPases express mRNAs with alternative 3′ UTRs differently, by gene- and cell- specific mechanisms. In particular, we show that Rac1 originate mRNA isoforms with longer 3′ UTRs specifically during neurite growth of cortical, but not hippocampal neurons. Furthermore, we demonstrate that the longest Rac1 3′ UTR is necessary for driving the mRNA to the neurites, and also for neurite outgrowth in cortical neurons. Our results indicate that the expression of Rac1 longer 3′ UTR is a gene and cell-type specific mechanism in the brain, with a new physiological function in cortical neuron differentiation.

Deltamethrin Increases Neurite Outgrowth in Cortical Neurons through Endogenous BDNF/TrkB Pathways.

Deltamethrin (DM), a type II pyrethroid, robustly increases brain-derived neurotrophic factor (Bdnf) expression and has a neurotrophic effect in primary cultures of rat cortical neurons. In this study, we investigated the effect of DM on neurite morphology in cultured rat cortical neurons. DM significantly increased neurite outgrowth, but this increase was abolished when the BDNF scavenger tropomyosin receptor kinase B (TrkB)-Fc was added 10 min before the DM treatment. In contrast, the addition of TrkB-Fc 1 h after the treatment did not affect DM-induced neurite outgrowth. Our previous research has indicated that type II, but not type I, pyrethroids have the ability to induce Bdnf mRNA expression, but neither permethrin nor cypermethrin, which are type I and type II pyrethroids, respectively, affected neurite outgrowth in the current study. These results suggest that this effect is not due to increased Bdnf expression, and the effect is unique to DM. We previously demonstrated that calcineurin plays a role in the DM-mediated induction of Bdnf expression. However, the calcineurin inhibitor FK506 did not significantly affect DM-induced neurite outgrowth. DM-induced neurite outgrowth was abolished by U0126 and rapamycin, indicating the involvement of the mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) pathways. Taken together, these findings suggest that DM activates endogenous BDNF/TrkB-mediated MAPK and mTOR pathways, thereby increasing neurite outgrowth.Key words: BDNF, Deltamethrin, MAPK, mTOR, Neurite outgrowth.

Sonic hedgehog promotes neurite outgrowth of cortical neurons under oxidative stress: Involving of mitochondria and energy metabolism

Oxidative stress has been demonstrated to be involved in the etiology of several neurobiological disorders. Sonic hedgehog (Shh), a secreted glycoprotein factor, has been implicated in promoting several aspects of brain remodeling process. Mitochondria may play an important role in controlling fundamental processes in neuroplasticity. However, little evidence is available about the effect and the potential mechanism of Shh on neurite outgrowth in primary cortical neurons under oxidative stress. Here, we revealed that Shh treatment significantly increased the viability of cortical neurons in a dose-dependent manner, which was damaged by hydrogen peroxide (H2O2). Shh alleviated the apoptosis rate of H2O2-induced neurons. Shh also increased neuritogenesis injuried by H2O2 in primary cortical neurons. Moreover, Shh reduced the generation of reactive oxygen species (ROS), increased the activities of SOD and and decreased the productions of MDA. In addition, Shh protected mitochondrial functions, elevated the cellular ATP levels and amelioratesd the impairment of mitochondrial complex II activities of cortical neurons induced by H2O2. In conclusion, all these results suggest that Shh acts as a prosurvival factor playing an essential role to neurite outgrowth of cortical neuron under H2O2 -induced oxidative stress, possibly through counteracting ROS release and preventing mitochondrial dysfunction and ATP as well as mitochondrial complex II activities against oxidative stress.

Prenatal Exposure to Arsenic Impairs Behavioral Flexibility and Cortical Structure in Mice.

Exposure to arsenic from well water in developing countries is suspected to cause developmental neurotoxicity. Although, it has been demonstrated that exposure to sodium arsenite (NaAsO2) suppresses neurite outgrowth of cortical neurons in vitro, it is largely unknown how developmental exposure to NaAsO2 impairs higher brain function and affects cortical histology. Here, we investigated the effect of prenatal NaAsO2 exposure on the behavior of mice in adulthood, and evaluated histological changes in the prelimbic cortex (PrL), which is a part of the medial prefrontal cortex that is critically involved in cognition. Drinking water with or without NaAsO2 (85 ppm) was provided to pregnant C3H mice from gestational days 8 to 18, and offspring of both sexes were subjected to cognitive behavioral analyses at 60 weeks of age. The brains of female offspring were subsequently harvested and used for morphometrical analyses. We found that both male and female mice prenatally exposed to NaAsO2 displayed an impaired adaptation to repetitive reversal tasks. In morphometrical analyses of Nissl- or Golgi-stained tissue sections, we found that NaAsO2 exposure was associated with a significant increase in the number of pyramidal neurons in layers V and VI of the PrL, but not other layers of the PrL. More strikingly, prenatal NaAsO2 exposure was associated with a significant decrease in neurite length but not dendrite spine density in all layers of the PrL. Taken together, our results indicate that prenatal exposure to NaAsO2 leads to behavioral inflexibility in adulthood and cortical disarrangement in the PrL might contribute to this behavioral impairment.

Acidic FGF promotes neurite outgrowth of cortical neurons and improves neuroprotective effect in a cerebral ischemic rat model

Acidic fibroblast growth factor (aFGF) is a neurotrophic factor which is a powerful neuroprotective and neuroregenerative factor of the nervous system. Prior study had shown that levels of FGFs significantly increase following ischemic injury, reflecting a physiological protection mechanism. However, few reports demonstrated the efficacy of applying aFGF in cerebral ischemia. A recent report showed that the intranasal aFGF treatment improved neurological functional recovery; however, it did not significantly reduce the lesion size in ischemic rats. The present study examines the neuroprotective effect of aFGF on cortical neuron-glial cultures under oxygen glucose deprivation (OGD)-induced cell damage and investigates whether epidural application of slow-released aFGF could improve benefit on ischemic stroke injury in conscious rats. We used a topical application of aFGF mixed in fibrin glue, a slow-release carrier, over the peri-ischemic cortex and examined such treatment on cerebral infarction and behavioral impairments of rats subjected to focal cerebral ischemia (FCI). Results demonstrate that aFGF effectively protected cortical neuron-glial cultures from OGD-induced neuronal damage. Neurite extension from cortical neurons was significantly enhanced by aFGF, mediated through activation of AKT and ERK. In addition, topical application of fibrin glue-mixed aFGF dose-dependently reduced ischemia-induced brain infarction and improved functional restoration in ischemic stroke rats. Slow-released aFGF not only protected hippocampal and cortical cell loss but reduced microglial infiltration in FCI rats. Our results suggest that aFGF mixed in fibrin glue could prolong the protective/regenerative efficacy of aFGF to the damaged brain tissue and thus improve the functional restorative effect of aFGF.

Olfactory ensheathing cell–neurite alignment enhances neurite outgrowth in scar-like cultures

The regenerative capacity of adult CNS neurons after injury is strongly inhibited by the spinal cord lesion site environment that is composed primarily of the reactive astroglial scar and invading meningeal fibroblasts. Olfactory ensheathing cell (OEC) transplantation facilitates neuronal survival and functional recovery after a complete spinal cord transection, yet the mechanisms by which this recovery occurs remain unclear. We used a unique multicellular scar-like culture model to test if OECs promote neurite outgrowth in growth-inhibitory areas. Astrocytes were mechanically injured and challenged by meningeal fibroblasts to produce key inhibitory elements of a spinal cord lesion. Neurite outgrowth of postnatal cerebral cortical neurons was assessed on three substrates: quiescent astrocyte control cultures, reactive astrocyte scar-like cultures, and scar-like cultures with OECs. Initial results showed that OECs enhanced total neurite outgrowth of cortical neurons in a scar-like environment by 60%. We then asked if the neurite growth-promoting properties of OECs depended on direct alignment between neuronal and OEC processes. Neurites that aligned with OECs were nearly three times longer when they grew on inhibitory meningeal fibroblast areas and twice as long on reactive astrocyte zones compared to neurites not associated with OECs. Our results show that OECs can independently enhance neurite elongation and that direct OEC–neurite cell contact can provide a permissive substrate that overcomes the inhibitory nature of the reactive astrocyte scar border and the fibroblast-rich spinal cord lesion core.

Targeting PTEN with lentiviral shRNA promotes neurite outgrowth of cortical neurons and improves functional recovery in a rat spinal cord contusion model

Objective To observe the effects of PTEN silencing on axon regeneration and functional recovery after spinal cord injury (SCI). Methods Four groups were designed: DMEM、lenti-control、lenti-scramble、lenti-shRNA. Cortical neurons were seeded on or adjacent to chondroitin sulfate proteoglycans (CSPGs). Three days after lentivirus infection, the expression of PTEN were assessed by Western blot, and immunocytochemistry method were applied to examine the length, number and crossing behavior of neurites; Lentivirus was locally injected into the conical motor area of the rats with spinal cord injury. 1 week later, the expression of PTEN was assessed by Western blot. 6 weeks later, motor function of hind limbs was evaluated by Basso Beattie Bresnahan (BBB) score, while the expressions of green fluorescence in injured spinal cord were observed by fluorescence microscope, and immunohistochemical method was used to observe the expression of synaptophysin changes in spinal tissues. Results Less expression of PTEN was detected in lentivirus-shRNA, and neurites with PTEN silencing exhibited significant enhancements in elongation, initiation and crossing ability when they encountered CSPGs in vitro. Better hindlimb functional recovery, less expression of PTEN and more synaptophysin positive response area were detected in rats injected with lentivirus-shRNA compared with other groups. Moreover, green fluorescence was found in the caudal region of injured spinal cord of rats injected with lentivirus-shRNA. Conclusion Lentiviral-mediated PTEN-shRNA can significantly improve the axon regeneration and neurological functional recovery after spinal cord injury. Key words: Spinal cord injuries; RNA interference; Lentivirus; Axons; Regeneration

ShRNA against PTEN promotes neurite outgrowth of cortical neurons and functional recovery in spinal cord contusion rats.

To explore neurite growth/regeneration and spinal cord injury repair after PTEN silencing via lentivirus-mediated RNAi. Cortical neurons were seeded on or adjacent to chondroitin sulfate proteoglycans. The length, number and crossing behavior of neurites were calculated. Lentivirus was locally injected into spinal cord contusion rats. The functional recovery and immunohistochemical staining were analyzed. Neurites with PTEN silencing exhibited significant enhancements in elongation, initiation and crossing ability when they encountered chondroitin sulfate proteoglycans in vitro. In vivo PTEN silencing improved functional recovery significantly, and promoted axon and synapse formation, but not scar formation. PTEN silencing may be promising for spinal cord injury repair.

Thromboxane A2 stimulates neurite outgrowth in cerebral cortical neurons via mitogen activated protein kinase signaling

Thromboxane A2 (TXA2) is a central prostanoid in the cardiovascular system and is a crucial mediator of vascular homeostasis and platelet aggregation. In this study, we report a novel role for TXA2 in neurite outgrowth. TXA2 receptor is expressed in rat cortical neurons, and treatment with the TXA2 agonist U-46619 promotes neurite outgrowth in a concentration-dependent manner. We investigated the molecular mechanism underlying U-46619-induced neurite outgrowth in cortical neurons. Blockade of the phosphorylation of mitogen activated protein kinase (MAPK) prevents U-46619-mediated neurite outgrowth. These data indicates that TXA2 functions as a positive regulator of neurite outgrowth via a mechanism dependent on MAPKs in cortical neurons.

Cocaine- and amphetamine-regulated transcript facilitates the neurite outgrowth in cortical neurons after oxygen and glucose deprivation through PTN-dependent pathway

Cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide that plays neuroprotective roles in cerebral ischemia and reperfusion (I/R) injury in animal models or oxygen and glucose deprivation (OGD) in cultured neurons. Recent data suggest that intranasal CART treatment facilitates neuroregeneration in stroke brain. However, little is known about the effects of post-treatment with CART during the neuronal recovery after OGD and reoxygenation in cultured primary cortical neurons. The present study was to investigate the role of CART treated after OGD injury in neurons. Primary mouse cortical neurons were subjected to OGD and then treated with CART. Our data show that post-treatment with CART reduced the neuronal apoptosis caused by OGD injury. In addition, CART repaired OGD-impaired cortical neurons by increasing the expression of growth-associated protein 43 (GAP43), which promotes neurite outgrowth. This effect depends on pleiotrophin (PTN) as siRNA-mediated PTN knockdown totally abolished the increase in CART-stimulated GAP43 protein levels. In summary, our findings demonstrate that CART repairs the neuronal injury after OGD by facilitating neurite outgrowth through PTN-dependent pathway. The role for CART in neurite outgrowth makes it a new potential therapeutic agent for the treatment of neurodegenerative diseases.

Curcumin promotes neurite outgrowth via reggie-1/flotillin-2 in cortical neurons

Curcumin is well known as an antioxidant and anti-inflammatory agent. In this study, we provided convincing evidence for the function of curcumin in neurite outgrowth of cortical neurons. We discovered that curcumin treatment could promote the number of processes, mean process length, and maximum process length of primary neurons, which were inhibited by reggie-1 siRNAs or extracellular signal-regulated kinase (ERK) 1/2 antagonist. Furthermore, curcumin-induced neurite growth was related to the ERK1/2 phosphorylation, which was blocked by reggie-1 knockdown. Overall, our results implied that curcumin could mediate neurite outgrowth through reggie-1 and ERK1/2 pathway.

Methyl 3,4-dihydroxybenzoate promotes neurite outgrowth of cortical neurons cultured in vitro.

Cerebral cortical neurons from neonatal rats were cultured in the presence of methyl 3,4-dihydroxybenzoate (MDHB; 2, 4, and 8 μM). Results showed that MDHB significantly promoted neurite outgrowth and microtubule-associated protein 2 mRNA expression, and increased neuronal survival in a dose-dependent manner. Moreover, MDHB induced brain-derived neurotrophic factor expression. These findings suggest that MDHB has a neurotrophic effect, which may be due to its ability to increase brain-derived neurotrophic factor expression.

ProBDNF collapses neurite outgrowth of primary neurons by activating RhoA.

BackgroundNeurons extend their dendrites and axons to build functional neural circuits, which are regulated by both positive and negative signals during development. Brain-derived neurotrophic factor (BDNF) is a positive regulator for neurite outgrowth and neuronal survival but the functions of its precursor (proBDNF) are less characterized.Methodology/Principal FindingsHere we show that proBDNF collapses neurite outgrowth in murine dorsal root ganglion (DRG) neurons and cortical neurons by activating RhoA via the p75 neurotrophin receptor (p75NTR). We demonstrated that the receptor proteins for proBDNF, p75NTR and sortilin, were highly expressed in cultured DRG or cortical neurons. ProBDNF caused a dramatic neurite collapse in a dose-dependent manner and this effect was about 500 fold more potent than myelin-associated glycoprotein. Neutralization of endogenous proBDNF by using antibodies enhanced neurite outgrowth in vitro and in vivo, but this effect was lost in p75NTR−/− mice. The neurite outgrowth of cortical neurons from p75NTR deficient (p75NTR−/−) mice was insensitive to proBDNF. There was a time-dependent reduction of length and number of filopodia in response to proBDNF which was accompanied with a polarized RhoA activation in growth cones. Moreover, proBDNF treatment of cortical neurons resulted in a time-dependent activation of RhoA but not Cdc42 and the effect was absent in p75NTR−/− neurons. Rho kinase (ROCK) and the collapsin response mediator protein-2 (CRMP-2) were also involved in the proBDNF action.ConclusionsproBDNF has an opposing role in neurite outgrowth to that of mature BDNF. Our observations suggest that proBDNF collapses neurites outgrowth and filopodial growth cones by activating RhoA through the p75NTR signaling pathway.