Axonal growth regulation of fetal and embryonic stem cell-derived dopaminergic neurons by Netrin-1 and Slits

Netrin-1 signaling pathway mechanisms in neurodegenerative diseases

Netrin-1 and its receptors play crucial roles in inducing axonal growth and neuronal migration during neuronal development. Their profound impacts then extend into adulthood to encompass the maintenance of neuronal survival and synaptic function. Increasing amounts of evidence highlight several key points: (1) Diminished Netrin-1 levels exacerbate pathological progression in animal models of Alzheimer's disease and Parkinson's disease, and potentially, similar alterations occur in humans. (2) Genetic mutations of Netrin-1 receptors increase an individuals' susceptibility to neurodegenerative disorders. (3) Therapeutic approaches targeting Netrin-1 and its receptors offer the benefits of enhancing memory and motor function. (4) Netrin-1 and its receptors show genetic and epigenetic alterations in a variety of cancers. These findings provide compelling evidence that Netrin-1 and its receptors are crucial targets in neurodegenerative diseases. Through a comprehensive review of Netrin-1 signaling pathways, our objective is to uncover potential therapeutic avenues for neurodegenerative disorders.

Establishing functionally segregated dopaminergic circuits

Despite accounting for only ~0.001% of all neurons in the human brain, midbrain dopaminergic neurons control numerous behaviors and are associated with many neuropsychiatric disorders that affect our physical and mental health. Dopaminergic neurons form various anatomically and functionally segregated pathways. Having such defined dopaminergic pathways is key to controlling varied sets of brain functions; therefore, segregated dopaminergic pathways must be properly and uniquely formed during development. How are these segregated pathways established? The three key developmental stages that dopaminergic neurons go through are cell migration, axon guidance, and synapse formation. In each stage, dopaminergic neurons and their processes receive unique molecular cues to guide the formation of specific dopaminergic pathways. Here, we outline the molecular mechanisms underlying the establishment of segregated dopaminergic pathways during each developmental stage in the mouse brain, focusing on the formation of the three major dopaminergic pathways: the nigrostriatal, mesolimbic, and mesocortical pathways. We propose that multiple stage-specific molecular gradients cooperate to establish functionally segregated dopaminergic circuits.

Bisphenol S interrupted axonogenesis on a human embryonic stem cells derived neural differentiation model: Conserved axon guidance and WNT signaling pathway involved

Bisphenol S (BPS) is the main substitute for bisphenol A (BPA). However, the neurodevelopmental toxicity of BPS and the underlying mechanisms remain unraveled. In present study, the neuro-differentiating human embryonic stem cells, hESC, was exposed to BPS (0-375 µM) at different stages (the precursor stage, the precursor to maturation stage, and the whole differentiation stage) to assess the potential neurodevelopmental toxicity and its mechanisms. The results revealed that BPS exposure interrupted axonogenesis, manifesting a trend of initial stimulating followed by inhibition, and peaked at the intermediate dose (3.75 μM) significantly, then reached the nadir at the high dose (375 μM) significantly in the precursor to maturation stage and the whole differentiation stage. Transcriptomics analysis showed that the main interrupted pathway enriched in axonogenesis, myelination, and neurotransmitter secretion by the GO function analysis and immune-related pathway by the KEGG analysis, besides, conserved axon guidance (Slit-Robo, Netrin-DCC, Semaphorin-Plexin) and WNT signaling pathway was also enriched in KEGG pathway analysis, which previously proved to regulate axonogenesis by directly acting on growth cones and inhibit axon growth by neuroinflammatory responses. And we found that a higher neuroinflammatory response may be induced through whole-differentiation-stage exposure than the response of exposure through the precursor to maturation stage. Overall, our findings indicated the non-monotonic neurodevelopmental toxicity of BPS exposure, and the inhibition of axonogenesis was possibly mediated by conserved axon guidance and WNT signaling pathway, while neuro-immune related pathway should be further investigated.

Preserved striatal innervation maintains motor function despite severe loss of nigral dopaminergic neurons

Degeneration of dopaminergic neurons in the substantia nigra and their striatal axon terminals causes cardinal motor symptoms of Parkinson's disease. In idiopathic cases, high levels of mitochondrial DNA alterations, leading to mitochondrial dysfunction, are a central feature of these vulnerable neurons. Here we present a mouse model expressing the K320E variant of the mitochondrial helicase Twinkle in dopaminergic neurons, leading to accelerated mitochondrial DNA mutations. These K320E-TwinkleDaN mice showed normal motor function at 20 months of age, although ∼70% of nigral dopaminergic neurons had perished. Remaining neurons still preserved ∼75% of axon terminals in the dorsal striatum and enabled normal dopamine release. Transcriptome analysis and viral tracing confirmed compensatory axonal sprouting of the surviving neurons. We conclude that a small population of substantia nigra dopaminergic neurons is able to adapt to the accumulation of mitochondrial DNA mutations and maintain motor control.

Enhanced axon guidance and synaptic markers in rat brains using ferric-tannic nanoparticles

Ferric-tannic nanoparticles (FTs) are now considered to be new pharmaceuticals appropriate for the prevention of brain aging and related diseases. We have previously shown that FTs could activate axon guidance pathways and cellular clearance functioning in neuronal cell lines. Herein, we further investigated whether FTs could activate the two coordinated neuronal functions of axon guidance and synaptic function in rat brains and neuronal cell lines. A single intravenous injection of a safe dose of FTs has been shown to activate a protein expression of axon attractant Netrin-1 and neurotransmitter receptor GABRA4 in the cerebral cortexes of male Wistar rats. According to RNA-seq with targeted analysis, axon guidance and synapses have been enriched and Ephrin membered genes have been identified as coordinating a network of genes for such processes. In vitro, as expected, FTs are also found to activate axon guidance markers and promote neuronal tubes in neuronal cell lines. At the same time, pre-synaptic markers (synaptophysin), post-synaptic markers (synapsin), and GABRA4 neurotransmitter receptors have been found to be activated by FTs. Interestingly, synaptophysin has been found to localize along the promoted neuronal tubes, suggesting that enhanced axon guidance is associated with the formation and transportation of pre-synaptic vesicles. Preliminarily, repeated injection of FTs into adult rats every 3 days for 10 times could enhance an expression of synaptophysin in the cerebral cortex, as compared to control rats. This work demonstrates that FTs can be used for activating brain function associated with axon guidance and synaptic function.

Mid-life employment trajectories and subsequent memory function and rate of decline in rural South Africa, 2000-22

AIM

To investigate mid-life employment trajectories in relation to later-life memory function and rate of decline in rural South Africa.

METHODS

Data from the Agincourt Health and Socio-Demographic Surveillance System were linked to the 'Health and Ageing in Africa: A Longitudinal Study of an INDEPTH Community in South Africa' (HAALSI) in rural Agincourt, South Africa (N = 3133). Employment was assessed every 4 years over 2000-12 as being employed (0, 1, 2 and ≥3 time points), being employed in a higher-skill occupation (0, 1, 2 and ≥3 time points) and dynamic employment trajectories identified using sequence analysis. Latent memory z-scores were assessed over 2014-22. Mixed-effects linear regression models were fitted to examine the associations of interest.

RESULTS

Sustained mid-life employment from 2000-12 (β = 0.052, 95% CI: -0.028 to 0.132, 1 vs 0 time points; β = 0.163, 95% CI: 0.077 to 0.250, 2 vs 0 time points; β = 0.212, 95% CI: 0.128 to 0.296, ≥3 vs 0 time points) and greater time spent in a higher-skill occupation (β = 0.077, 95% CI: -0.020 to 0.175, 1 vs 0 time points; β = 0.241, 95% CI: 0.070 to 0.412, 2 vs 0 time points; β = 0.361, 95% CI: 0.201 to 0.520, ≥3 vs 0 time points) were associated with higher memory scores in 2014/15, but not subsequent rate of memory decline. Moving from a lower-skill to higher-skill occupation was associated with higher memory function, but a faster rate of decline over 2014-22.

CONCLUSIONS

Sustained mid-life employment, particularly in higher-skill occupations, may contribute to later-life memory function in this post-Apartheid South African setting.

Regulation of Axon Guidance by Slit2 and Netrin-1 Signaling in the Lacrimal Gland of Aqp5 Knockout Mice

Purpose

Dry eye disease (DED) is multifactorial and associated with nerve abnormalities. We explored an Aquaporin 5 (AQP5)-deficiency-induced JunB activation mechanism, which causes abnormal lacrimal gland (LG) nerve distribution through Slit2 upregulation and Netrin-1 repression.

Methods

Aqp5 knockout (Aqp5-/-) and wild-type (Aqp5+/+) mice were studied. LGs were permeabilized and stained with neuronal class III β-tubulin, tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), and calcitonin gene-related peptide (CGRP). Whole-mount images were acquired through tissue clearing and 3D fluorescence imaging. Mouse primary trigeminal ganglion (TG) neurons were treated with LG extracts and Netrin-1/Slit2 neutralizing antibody. Transcription factor (TF) prediction and chromatin immunoprecipitation-polymerase chain reaction (ChIP-PCR) experiments verified the JunB binding and regulatory effect on Netrin-1 and Slit2.

Results

Three-dimensional tissue and section immunofluorescence showed reduced LG nerves in Aqp5-/- mice, with sympathetic and sensory nerves significantly decreased. Netrin-1 was reduced and Slit2 increased in Aqp5-/- mice LGs. Aqp5+/+ mice LG tissue extracts (TEs) promoted Aqp5-/- TG neurons axon growth, but Netrin-1 neutralizing antibody (NAb) could inhibit that promotion. Aqp5-/- mice LG TEs inhibited Aqp5+/+ TG axon growth, but Slit2 NAb alleviated that inhibition. Furthermore, JunB, a Netrin-1 and Slit2 TF, could bind them and regulate their expression. SR11302, meanwhile, reversed the Netrin-1 and Slit2 shifts caused by AQP5 deficiency.

Conclusions

AQP5 deficiency causes LG nerve abnormalities. Persistent JunB activation, the common denominator for Netrin-1 suppression and Slit2 induction, was found in Aqp5-/- mice LG epithelial cells. This affected sensory and sympathetic nerve fibers' distribution in LGs. Our findings provide insights into preventing, reversing, and treating DED.

Heimdall, an alternative protein issued from a ncRNA related to kappa light chain variable region of immunoglobulins from astrocytes: a new player in neural proteome

The dogma "One gene, one protein" is clearly obsolete since cells use alternative splicing and generate multiple transcripts which are translated into protein isoforms, but also use alternative translation initiation sites (TISs) and termination sites on a given transcript. Alternative open reading frames for individual transcripts give proteins originate from the 5'- and 3'-UTR mRNA regions, frameshifts of mRNA ORFs or from non-coding RNAs. Longtime considered as non-coding, recent in-silico translation prediction methods enriched the protein databases allowing the identification of new target structures that have not been identified previously. To gain insight into the role of these newly identified alternative proteins in the regulation of cellular functions, it is crucial to assess their dynamic modulation within a framework of altered physiological modifications such as experimental spinal cord injury (SCI). Here, we carried out a longitudinal proteomic study on rat SCI from 12 h to 10 days. Based on the alternative protein predictions, it was possible to identify a plethora of newly predicted protein hits. Among these proteins, some presented a special interest due to high homology with variable chain regions of immunoglobulins. We focus our interest on the one related to Kappa variable light chains which is similarly highly produced by B cells in the Bence jones disease, but here expressed in astrocytes. This protein, name Heimdall is an Intrinsically disordered protein which is secreted under inflammatory conditions. Immunoprecipitation experiments showed that the Heimdall interactome contained proteins related to astrocyte fate keepers such as "NOTCH1, EPHA3, IPO13" as well as membrane receptor protein including "CHRNA9; TGFBR, EPHB6, and TRAM". However, when Heimdall protein was neutralized utilizing a specific antibody or its gene knocked out by CRISPR-Cas9, sprouting elongations were observed in the corresponding astrocytes. Interestingly, depolarization assays and intracellular calcium measurements in Heimdall KO, established a depolarization effect on astrocyte membranes KO cells were more likely that the one found in neuroprogenitors. Proteomic analyses performed under injury conditions or under lipopolysaccharides (LPS) stimulation, revealed the expression of neuronal factors, stem cell proteins, proliferation, and neurogenesis of astrocyte convertor factors such as EPHA4, NOTCH2, SLIT3, SEMA3F, suggesting a role of Heimdall could regulate astrocytic fate. Taken together, Heimdall could be a novel member of the gatekeeping astrocyte-to-neuroprogenitor conversion factors.

Crosstalk between the Hippo Pathway and the Wnt Pathway in Huntington's Disease and Other Neurodegenerative Disorders

The Hippo pathway consists of a cascade of kinases that controls the phosphorylation of the co-activators YAP/TAZ. When unphosphorylated, YAP and TAZ translocate into the nucleus, where they mainly bind to the TEAD transcription factor family and activate genes related to cell proliferation and survival. In this way, the inhibition of the Hippo pathway promotes cell survival, proliferation, and stemness fate. Another pathway can modulate these processes, namely the Wnt/β-catenin pathway that is indeed involved in cellular functions such as proliferation and cell survival, as well as apoptosis, growth, and cell renewal. Wnt signaling can act in a canonical or noncanonical way, depending on whether β-catenin is involved in the process. In this review, we will focus only on the canonical Wnt pathway. It has emerged that YAP/TAZ are components of the β-catenin destruction complex and that there is a close relationship between the Hippo pathway and the canonical Wnt pathway. Furthermore, recent data have shown that both of these pathways may play a role in neurodegenerative diseases, such as Huntington's disease, Alzheimer's disease, or Amyotrophic Lateral Sclerosis. Thus, this review analyzes the Hippo pathway and the Wnt pathway, their crosstalk, and their involvement in Huntington's disease, as well as in other neurodegenerative disorders. Altogether, these data suggest possible therapeutic approaches targeting key players of these pathways.

UNC5C Receptor Proteolytic Cleavage by Active AEP Promotes Dopaminergic Neuronal Degeneration in Parkinson's Disease

Netrin-1 is a chemotropic cue mediating axon growth and neural migration in neuronal development, and its receptors deletion in colorectal cancer and UNC5s act as dependence receptors regulating neuronal apoptosis. Asparagine endopeptidase (AEP) is an age-dependent protease that cuts human alpha-synuclein (α-Syn) at N103 and triggers its aggregation and neurotoxicity. In the current study, it is reported that UNC5C receptor is cleaved by AEP in Parkinson's disease (PD) and facilitates dopaminergic neuronal loss. UNC5C is truncated by active AEP in human α-SNCA transgenic mice in an age-dependent manner or induced by neurotoxin rotenone. Moreover, UNC5C is fragmented by AEP in PD brains, inversely correlated with reduced netrin-1 levels. Netrin-1 deprivation in primary cultures induces AEP and caspase-3 activation, triggering UNC5C proteolytic fragmentation and enhancing neuronal loss. Noticeably, blocking UNC5C cleavage by AEP attenuates netrin-1 deprivation-elicited neuronal death and motor disorders in netrin flox/flox mice. Overexpression of AEP-truncated UNC5C intracellular fragment strongly elicits α-Syn aggregation and dopaminergic loss, locomotor deficits in α-SNCA transgenic mice. Hence, the findings demonstrate that netrin-1 reduction and UNC5C truncation by AEP contribute to PD pathogenesis.

Cognitive stimulation in the workplace, plasma proteins, and risk of dementia: three analyses of population cohort studies

OBJECTIVES

To examine the association between cognitively stimulating work and subsequent risk of dementia and to identify protein pathways for this association.

DESIGN

Multicohort study with three sets of analyses.

SETTING

United Kingdom, Europe, and the United States.

PARTICIPANTS

Three associations were examined: cognitive stimulation and dementia risk in 107 896 participants from seven population based prospective cohort studies from the IPD-Work consortium (individual participant data meta-analysis in working populations); cognitive stimulation and proteins in a random sample of 2261 participants from one cohort study; and proteins and dementia risk in 13 656 participants from two cohort studies.

MAIN OUTCOME MEASURES

Cognitive stimulation was measured at baseline using standard questionnaire instruments on active versus passive jobs and at baseline and over time using a job exposure matrix indicator. 4953 proteins in plasma samples were scanned. Follow-up of incident dementia varied between 13.7 to 30.1 years depending on the cohort. People with dementia were identified through linked electronic health records and repeated clinical examinations.

RESULTS

During 1.8 million person years at risk, 1143 people with dementia were recorded. The risk of dementia was found to be lower for participants with high compared with low cognitive stimulation at work (crude incidence of dementia per 10 000 person years 4.8 in the high stimulation group and 7.3 in the low stimulation group, age and sex adjusted hazard ratio 0.77, 95% confidence interval 0.65 to 0.92, heterogeneity in cohort specific estimates I²=0%, P=0.99). This association was robust to additional adjustment for education, risk factors for dementia in adulthood (smoking, heavy alcohol consumption, physical inactivity, job strain, obesity, hypertension, and prevalent diabetes at baseline), and cardiometabolic diseases (diabetes, coronary heart disease, stroke) before dementia diagnosis (fully adjusted hazard ratio 0.82, 95% confidence interval 0.68 to 0.98). The risk of dementia was also observed during the first 10 years of follow-up (hazard ratio 0.60, 95% confidence interval 0.37 to 0.95) and from year 10 onwards (0.79, 0.66 to 0.95) and replicated using a repeated job exposure matrix indicator of cognitive stimulation (hazard ratio per 1 standard deviation increase 0.77, 95% confidence interval 0.69 to 0.86). In analysis controlling for multiple testing, higher cognitive stimulation at work was associated with lower levels of proteins that inhibit central nervous system axonogenesis and synaptogenesis: slit homologue 2 (SLIT2, fully adjusted β -0.34, P<0.001), carbohydrate sulfotransferase 12 (CHSTC, fully adjusted β -0.33, P<0.001), and peptidyl-glycine α-amidating monooxygenase (AMD, fully adjusted β -0.32, P<0.001). These proteins were associated with increased dementia risk, with the fully adjusted hazard ratio per 1 SD being 1.16 (95% confidence interval 1.05 to 1.28) for SLIT2, 1.13 (1.00 to 1.27) for CHSTC, and 1.04 (0.97 to 1.13) for AMD.

CONCLUSIONS

The risk of dementia in old age was found to be lower in people with cognitively stimulating jobs than in those with non-stimulating jobs. The findings that cognitive stimulation is associated with lower levels of plasma proteins that potentially inhibit axonogenesis and synaptogenesis and increase the risk of dementia might provide clues to underlying biological mechanisms.

Spatial RNA Sequencing Identifies Robust Markers of Vulnerable and Resistant Human Midbrain Dopamine Neurons and Their Expression in Parkinson's Disease

Defining transcriptional profiles of substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) dopamine neurons is critical to understanding their differential vulnerability in Parkinson’s Disease (PD). Here, we determine transcriptomes of human SNc and VTA dopamine neurons using LCM-seq on a large sample cohort. We apply a bootstrapping strategy as sample input to DESeq2 and identify 33 stably differentially expressed genes (DEGs) between these two subpopulations. We also compute a minimal sample size for identification of stable DEGs, which highlights why previous reported profiles from small sample sizes display extensive variability. Network analysis reveal gene interactions unique to each subpopulation and highlight differences in regulation of mitochondrial stability, apoptosis, neuronal survival, cytoskeleton regulation, extracellular matrix modulation as well as synapse integrity, which could explain the relative resilience of VTA dopamine neurons. Analysis of PD tissues showed that while identified stable DEGs can distinguish the subpopulations also in disease, the SNc markers SLIT1 and ATP2A3 were down-regulated and thus appears to be biomarkers of disease. In summary, our study identifies human SNc and VTA marker profiles, which will be instrumental for studies aiming to modulate dopamine neuron resilience and to validate cell identity of stem cell-derived dopamine neurons.

The Moringin/α-CD Pretreatment Induces Neuroprotection in an In Vitro Model of Alzheimer's Disease: A Transcriptomic Study

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and represents the most common form of senile dementia. Autophagy and mitophagy are cellular processes that play a key role in the aggregation of β-amyloid (Aβ) and tau phosphorylation. As a consequence, impairment of these processes leads to the progression of AD. Thus, interest is growing in the search for new natural compounds, such as Moringin (MOR), with neuroprotective, anti-amyloidogenic, antioxidative, and anti-inflammatory properties that could be used for AD prevention. However, MOR appears to be poorly soluble and stable in water. To increase its solubility MOR was conjugated with α-cyclodextrin (MOR/α-CD). In this work, it was evaluated if MOR/α-CD pretreatment was able to exert neuroprotective effects in an AD in vitro model through the evaluation of the transcriptional profile by next-generation sequencing (NGS). To induce the AD model, retinoic acid-differentiated SH-SY5Y cells were exposed to Aβ_1-42. The MOR/α-CD pretreatment reduced the expression of the genes which encode proteins involved in senescence, autophagy, and mitophagy processes. Additionally, MOR/α-CD was able to induce neuronal remodeling modulating the axon guidance, principally downregulating the Slit/Robo signaling pathway. Noteworthy, MOR/α-CD, modulating these important pathways, may induce neuronal protection against Aβ_1-42 toxicity as demonstrated also by the reduction of cleaved caspase 3. These data indicated that MOR/α-CD could attenuate the progression of the disease and promote neuronal repair.

Dopamine Cell Therapy: From Cell Replacement to Circuitry Repair

Cell therapy for Parkinson's disease (PD) is aimed to replace the degenerated midbrain dopamine (mDA) neurons and restore DA neurotransmission in the denervated forebrain targets. A limitation of the intrastriatal grafting approach, which is currently used in clinical trials, is that the mDA neurons are implanted into the target area, in most cases the putamen, and not in the ventral midbrain where they normally reside. This ectopic location of the cells may limit their functionality due to the lack of appropriate afferent regulation from the host. Homotopic transplantation, into the substantia nigra, is now being pursued in rodent PD models as a way to achieve more complete circuitry repair. Intranigral grafts of mDA neurons, derived from human embryonic stem cells, have the capacity to re-establish the nigrostriatal and mesolimbic pathways in their entirety and restore dense functional innervations in striatal, limbic and cortical areas. Tracing of host afferent inputs using the rabies tracing technique shows that the afferent connectivity of grafts implanted in the nigra matches closely that of the intrinsic mDA system, suggesting a degree of circuitry reconstruction that exceeds what has been achieved before. This approach holds great promise, but to match the larger size of the human brain, and the 10 times greater distance between substantia nigra and its forebrain targets, it may be necessary to find ways to improve the growth capacity of the grafted mDA neurons, pointing to a combined approach where growth promoting factors are used to enhance the performance of mDA neuron grafts.

Depression-/Anxiety-Like Behavior Alterations in Adult Slit2 Transgenic Mice

Background: Slit2 is a member of the Slit family of secreted glycoproteins that plays highly conserved roles in neuronal axon guidance and cellular migration. Our previous experimental results showed Alzheimer's disease-like alterations and increased permeability of the blood–brain barrier in Slit2-overexpressing transgenic (Slit2-Tg) mice aged 8–9 months. Nevertheless, relatively little is known about behavioral alterations in adult Slit2-Tg mice (2–6 months of age). To observe the age-related behavioral effects of Slit2 overexpression in adult mice, we performed a battery of behavioral tests with adult Slit2-Tg mice at 2–6 months of age.

Results: The body weight of Slit2-Tg mice was lower than that of the wild-type mice from 15 weeks of age. Compared with the control mice, depression-like behaviors were found in Slit2-Tg mice from 15 to 21 weeks of age in the sucrose preference test, although Slit2-Tg mice were hyperactive in the tail suspension test. The anxiety-like behaviors were found in Slit2-Tg mice in the open field test, as well as increased locomotor activity. The anxiety-like behaviors were also found in adult Slit2-Tg mice in the elevated plus maze. Compared to wild-type mice at 23 weeks old, impairment of the hippocampal neurons were found in Slit2-Tg mice at the same age in hematoxylin–eosin staining (H&E), including some eccentric dispersion and expansion of neuronal bodies. In addition, the messenger RNA (mRNA) expression of TNF-α was elevated in the hippocampus of adult Slit2-Tg mice.

Conclusions: Slit2 overexpression causes depression-/anxiety-like behaviors in adult mice that may be related to an increase in inflammatory factors and damage to hippocampal neurons.

Netrin1 deficiency activates MST1 via UNC5B receptor, promoting dopaminergic apoptosis in Parkinson's disease

The Hippo (MST1/2) pathway plays a critical role in restricting tissue growth in adults and modulating cell proliferation, differentiation, and migration in developing organs. Netrin1, a secreted laminin-related protein, is essential for nervous system development. However, the mechanisms underlying MST1 regulation by the extrinsic signals remain unclear. Here, we demonstrate that Netrin1 reduction in Parkinson's disease (PD) activates MST1, which selectively binds and phosphorylates netrin receptor UNC5B on T428 residue, promoting its apoptotic activation and dopaminergic neuronal loss. Netrin1 deprivation stimulates MST1 activation and interaction with UNC5B, diminishing YAP levels and escalating cell deaths. Knockout of UNC5B abolishes netrin depletion-induced dopaminergic loss, whereas blockade of MST1 phosphorylating UNC5B suppresses neuronal apoptosis. Remarkably, Netrin1 is reduced in PD patient brains, associated with MST1 activation and UNC5B T428 phosphorylation, which is accompanied by YAP reduction and apoptotic activation. Hence, Netrin1 regulates Hippo (MST1) pathway in dopaminergic neuronal loss in PD via UNC5B receptor.

Tissue engineered nigrostriatal pathway for treatment of Parkinson's disease

The classic motor deficits of Parkinson's disease are caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta, resulting in the loss of their long-distance axonal projections that modulate the striatum. Current treatments only minimize the symptoms of this disconnection as there is no approach capable of replacing the nigrostriatal pathway. We are applying microtissue engineering techniques to create living, implantable constructs that mimic the architecture and function of the nigrostriatal pathway. These constructs consist of dopaminergic neurons with long axonal tracts encased within hydrogel microcolumns. Microcolumns were seeded with dopaminergic neuronal aggregates, while lumen extracellular matrix, growth factors, and end targets were varied to optimize cytoarchitecture. We found a 10-fold increase in axonal outgrowth from aggregates versus dissociated neurons, resulting in remarkable axonal lengths of over 6 mm by 14 days and 9 mm by 28 days in vitro. Axonal extension was also dependent upon lumen extracellular matrix, but did not depend on growth factor enrichment or neuronal end target presence. Evoked dopamine release was measured via fast scan cyclic voltammetry and synapse formation with striatal neurons was observed in vitro. Constructs were microinjected to span the nigrostriatal pathway in rats, revealing survival of implanted neurons while maintaining their axonal projections within the microcolumn. Lastly, these constructs were generated with dopaminergic neurons differentiated from human embryonic stem cells. This strategy may improve Parkinson's disease treatment by simultaneously replacing lost dopaminergic neurons in the substantia nigra and reconstructing their long-projecting axonal tracts to the striatum.

Neuroprotection Exerted by Netrin-1 and Kinesin Motor KIF1A in Secondary Brain Injury following Experimental Intracerebral Hemorrhage in Rats

Binding of extracellular netrin-1 to its receptors, deleted in colorectal cancer (DCC) and uncoordinated gene 5H2 (UNC5H2), inhibits apoptosis mediated by these receptors. A neuron-specific kinesin motor protein, KIF1A, has been shown to participate in netrin-1 secretion. This study aimed to identify the roles of netrin-1 and KIF1A in secondary brain injury after intracerebral hemorrhage (ICH) and the potential mechanisms. An autologous blood ICH model was established in adult male Sprague-Dawley rats, and cultured neurons were exposed to OxyHb to mimic ICH conditions in vitro. Mouse recombinant netrin-1, expression vectors encoding KIF1A, and KIF1A-specific siRNAs were administered intracerebroventricularly. After ICH, protein levels of netrin-1, DCC, and UNC5H2 increased, while protein levels of KIF1A decreased. Levels of UNC5H2 and DCC bound to netrin-1 increased after ICH but were significantly lower than the increase in total amount of protein. Administration of recombinant netrin-1 attenuated neuronal apoptosis and degeneration in ICH rats. Moreover, KIF1A overexpression increased concentrations of netrin-1 in cerebrospinal fluid and cell culture supernatant and exerted neuroprotective effects via netrin-1 and its receptor pathways. KIF1A plays a critical role in netrin-1 secretion by neurons. An increase in protein levels of netrin-1 may be a neuroprotective strategy after ICH. However, this process is almost completely abolished by ICH-induced loss of KIF1A. An exogenous increase of KIF1A may be a potential strategy for neuroprotection via the netrin-1 pathway.

Axon guidance molecule expression after cell therapy in a mouse model of Parkinson's disease

BACKGROUND

Cell therapy is a promising approach for Parkinson's disease (PD). Others and we have previously shown that transplantation of ventral mesencephalic fetal cells into substantia nigra (SN) in an animal model of PD enables anatomical and functional repair of the degenerated pathway. However, the molecular basis of this repair is still largely unknown.

OBJECTIVE

In this work, we studied the expression of several axon guidance molecules that may be implicated in the repair of the degenerated nigrostriatal pathway.

METHODS

The expression of axon guidance molecules was analyzed using qRT-PCR on five specific regions surrounding the nigrostriatal pathway (ventral mesencephalon (VM), thalamus (Thal), medial forebrain bundle (MFB), nucleus accumbens (NAcc) and caudate putamen (CPu)), one and seven days after lesion and transplantation.

RESULTS

We showed that mRNA expression of specific axon guidance molecules and their receptors is modified in structures surrounding the nigrostriatal pathway, suggesting their involvement in the axon guidance of grafted neurons. Moreover, we highlight a possible new role for semaphorin 7A in this repair.

CONCLUSION

Overall, our data provide a reliable basis to understand how axons of grafted neurons are able to navigate towards their targets and interact with the molecular environment in the adult brain. This should help to improve the efficiency of cell replacement approaches in PD.

Neuroprotection and neurorestoration as experimental therapeutics for Parkinson's disease

Disease-modifying treatments remain an unmet medical need in Parkinson's disease (PD). Such treatments can be operationally defined as interventions that slow down the clinical evolution to advanced disease milestones. A treatment may achieve this outcome by either inhibiting primary neurodegenerative events ("neuroprotection") or boosting compensatory and regenerative mechanisms in the brain ("neurorestoration"). Here we review experimental paradigms that are currently used to assess the neuroprotective and neurorestorative potential of candidate treatments in animal models of PD. We review some key molecular mediators of neuroprotection and neurorestoration in the nigrostriatal dopamine pathway that are likely to exert beneficial effects on multiple neural systems affected in PD. We further review past and current strategies to therapeutically stimulate these mediators, and discuss the preclinical evidence that exercise training can have neuroprotective and neurorestorative effects. A future translational task will be to combine behavioral and pharmacological interventions to exploit endogenous mechanisms of neuroprotection and neurorestoration for therapeutic purposes. This type of approach is likely to provide benefit to many PD patients, despite the clinical, etiological, and genetic heterogeneity of the disease.

IL-10 Promotes Neurite Outgrowth and Synapse Formation in Cultured Cortical Neurons after the Oxygen-Glucose Deprivation via JAK1/STAT3 Pathway

As a classic immunoregulatory and anti-inflammatory cytokine, interleukin-10 (IL-10) provides neuroprotection in cerebral ischemia in vivo or oxygen-glucose deprivation (OGD)-induced injury in vitro. However, it remains blurred whether IL-10 promotes neurite outgrowth and synapse formation in cultured primary cortical neurons after OGD injury. In order to evaluate its effect on neuronal apoptosis, neurite outgrowth and synapse formation, we administered IL-10 or IL-10 neutralizing antibody (IL-10NA) to cultured rat primary cortical neurons after OGD injury. We found that IL-10 treatment activated the Janus kinase 1 (JAK1)/signal transducers and activators of transcription 3 (STAT3) signaling pathway. Moreover, IL-10 attenuated OGD-induced neuronal apoptosis by down-regulating the Bax expression and up-regulating the Bcl-2 expression, facilitated neurite outgrowth by increasing the expression of Netrin-1, and promoted synapse formation in cultured primary cortical neurons after OGD injury. These effects were partly abolished by JAK1 inhibitor GLPG0634. Contrarily, IL-10NA produced opposite effects on the cultured cortical neurons after OGD injury. Taken together, our findings suggest that IL-10 not only attenuates neuronal apoptosis, but also promotes neurite outgrowth and synapse formation via the JAK1/STAT3 signaling pathway in cultured primary cortical neurons after OGD injury.

Anti-depressant effects of Gastrodia elata Blume and its compounds gastrodin and 4-hydroxybenzyl alcohol, via the monoaminergic system and neuronal cytoskeletal remodeling

ETHNOPHARMACOLOGY RELEVANCE

Gastrodia elata Blume is a highly valuable traditional Chinese medicine used in the treatment of depression. However, compounds with antidepressant effects in water extracts of G. elata Bl. (WGE) have not been identified. The aims of this study were to determine the major antidepressant compound in WGE and to evaluate the antidepressant effects of WGE and its active compounds which involved the monoaminergic system and neuronal cytoskeletal remodeling.

MATERIALS AND METHODS

Gastrodin (GAS) and 4-hydroxybenzyl alcohol (HBA) in WGE, were analyzed with high-performance liquid chromatography (HPLC)-ultraviolet detection. The forced swimming test (FST) was used to induce depression-like symptoms in 9 weeks old male Sprague-Dawley rats. The open field test (OFT) was used to measure anxiety after WGE, GAS, and HBA treatments. The levels of monoamine such as serotonin (5-HT), dopamine (DA), and their metabolites 5-hydroxyindoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were measured using HPLC-electrochemical detection. Western blotting was used to examine the 5-HT1A receptor and the neuronal cytoskeleton remodeling-related proteins, Slit, dihydropyrimidinase-related protein 2 (DPYSL2, also called CRMP2), Ras homologous member A (RhoA), and profilin 1 (PFN1) in vivo. Slit1 expression was evaluated in Hs683 cell line after treated with WGE (0.5mg/mL), GAS (50, 100 and 100μM), and HBA (50, 100 and 100μM).

RESULTS

Oral administration of WGE (500mg/kg bw), GAS (100mg/kg bw), and HBA (100mg/kg bw) exhibited the anti-depressant effect by significantly reducing the immobility time in FST, monoamine metabolism including the 5-HT to 5-HIAA in the hippocampus and DA to DOPAC and HVA ratios in the frontal cortex, amygdala, and hippocampus. In the hippocampus, the expression of the neuronal cytoskeleton remodeling-related negative regulators Slit1 and RhoA were significantly down-regulated. In addition, the positive regulators CRMP2 and PFN1 were significantly up-regulated following GAS, HBA, and WGE treatments. Moreover, WGE, GAS, and HBA were directly down-regulated Slit1 expression in Hs683 cells.

CONCLUSION

WGE, GAS, and HBA exhibited potential anti-depressant effects in rats by decreasing monoamine metabolism and modulated cytoskeleton remodeling-related protein expression in the Slit-Robo pathway. These results suggest that WGE can be used as agent for depressive prevention.

Efficient and biologically relevant consensus strategy for Parkinson's disease gene prioritization

BACKGROUND

The systemic information enclosed in microarray data encodes relevant clues to overcome the poorly understood combination of genetic and environmental factors in Parkinson's disease (PD), which represents the major obstacle to understand its pathogenesis and to develop disease-modifying therapeutics. While several gene prioritization approaches have been proposed, none dominate over the rest. Instead, hybrid approaches seem to outperform individual approaches.

METHODS

A consensus strategy is proposed for PD related gene prioritization from mRNA microarray data based on the combination of three independent prioritization approaches: Limma, machine learning, and weighted gene co-expression networks.

RESULTS

The consensus strategy outperformed the individual approaches in terms of statistical significance, overall enrichment and early recognition ability. In addition to a significant biological relevance, the set of 50 genes prioritized exhibited an excellent early recognition ability (6 of the top 10 genes are directly associated with PD). 40 % of the prioritized genes were previously associated with PD including well-known PD related genes such as SLC18A2, TH or DRD2. Eight genes (CCNH, DLK1, PCDH8, SLIT1, DLD, PBX1, INSM1, and BMI1) were found to be significantly associated to biological process affected in PD, representing potentially novel PD biomarkers or therapeutic targets. Additionally, several metrics of standard use in chemoinformatics are proposed to evaluate the early recognition ability of gene prioritization tools.

CONCLUSIONS

The proposed consensus strategy represents an efficient and biologically relevant approach for gene prioritization tasks providing a valuable decision-making tool for the study of PD pathogenesis and the development of disease-modifying PD therapeutics.

Down-regulation of Slit-Robo pathway mediating neuronal cytoskeletal remodeling processes facilitates the antidepressive-like activity of Gastrodia elata Blume

Nowadays, depression is a serious psychological disorder that causes extreme economic loss and social problems. Previously, we discovered that the water extract of Gastrodia elata Blume (WGE) improved depressive-like behavior by influencing neurotransmitters in rats subjected to the forced swimming test. To elucidate possible mechanisms, in the present study, we performed a proteomics and bioinformatics analysis to identify the related pathways. Western blot-validated results indicated that the core protein network modulated by WGE administration was closely associated with down-regulation of the Slit-Robo pathway, which modulates neuronal cytoskeletal remodeling processes. Although Slit-Robo signaling has been well investigated in neuronal development, its relationship with depression is not fully understood. We provide a potential hint on the mechanism responsible for the antidepressive-like activity of WGE. In conclusion, we suggest that the Slit-Robo pathway and neuronal cytoskeleton remodeling are possibly one of the pathways associated with the antidepressive-like effects of WGE.

Estrogen receptor (ER) agonists differentially regulate neuroangiogenesis in peritoneal endometriosis via the repellent factor SLIT3

Endometriosis is an estrogen-dependent neurovascular disorder characterized by growth of endometrial tissue (lesions) outside the uterine cavity. Patients suffer chronic pelvic pain, and it has been proposed that co-recruitment of nerves/blood vessels (neuroangiogenesis) into the lesions is fundamental to the development of painful symptoms. We hypothesized that estrogen-dependent regulation of axonal guidance molecules of the SLIT/ROBO (Roundabout) family could play a role in neuroangiogenesis occurring in endometriosis lesions found on the peritoneal wall. In tissue samples from human patients and a mouse model of endometriosis, concentrations of mRNA encoded by SLIT3 were significantly higher in lesions than normal peritoneum. Estrogen regulation of SLIT3 was investigated using 17β-estradiol and selective agonists for each subtype of estrogen receptor (ER) (ERα agonist, 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-tryl) trisphenol; ERβ agonist, 2,3-bis(4-hydroxy-phenyl)-propionitrile [DPN]). In mice, DPN (EC50 0.85) increased Slit3 mRNA concentrations compared with hormone-depleted and 17β-estradiol-treated (EC50 0.1) animals and decreased the density of nerves but not vessels in endometriosis lesions. SLIT3 mRNA concentrations were increased in DPN-treated human endometrial endothelial cells and in 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-tryl) trisphenol-treated (EC50 200) rat dorsal root ganglia neurons. Functional assays (neurite outgrowth, network formation) revealed that SLIT3 promotes angiogenesis but decreases neurogenesis. In conclusion, these data suggest that estrogen-dependent expression of SLIT3 may play a key role in regulating nerve-vessel interactions within the complex microenvironment of endometriosis lesions.

A novel mouse model of endometriosis mimics human phenotype and reveals insights into the inflammatory contribution of shed endometrium

Endometriosis is an estrogen-dependent inflammatory disorder characterized by the presence of endometrial tissue outside the uterine cavity. Patients experience chronic pelvic pain and infertility, with the most likely origin of the tissue deposits (lesions) being endometrial fragments shed at menses. Menstruation is an inflammatory process associated with a dramatic increase in inflammatory mediators and tissue-resident immune cells. In the present study, we developed and validated a mouse model of endometriosis using syngeneic menstrual endometrial tissue introduced into the peritoneum of immunocompetent mice. We demonstrate the establishment of endometriotic lesions that exhibit similarities to those recovered from patients undergoing laparoscopy. Specifically, in both cases, lesions had epithelial (cytokeratin(+)) and stromal (vimentin/CD10(+)) cell compartments with a well-developed vasculature (CD31(+) endothelial cells). Expression of estrogen receptor β was increased in lesions compared with the peritoneum or eutopic endometrium. By performing experiments using mice with green fluorescent protein-labeled macrophages (MacGreen) in reciprocal transfers with wild-type mice, we obtained evidence that macrophages present in the peritoneum and in menses endometrium can contribute to the inflammatory microenvironment of the lesions. In summary, we developed a mouse model of endometriosis that exhibits similarities to human peritoneal lesions with respect to estrogen receptor expression, inflammation, and macrophage infiltration, providing an opportunity for further studies and the possible identification of novel therapies for this perplexing disorder.

Ascending midbrain dopaminergic axons require descending GAD65 axon fascicles for normal pathfinding

The Nigrostriatal pathway (NSP) is formed by dopaminergic axons that project from the ventral midbrain to the dorsolateral striatum as part of the medial forebrain bundle. Previous studies have implicated chemotropic proteins in the formation of the NSP during development but little is known of the role of substrate-anchored signals in this process. We observed in mouse and rat embryos that midbrain dopaminergic axons ascend in close apposition to descending GAD65-positive axon bundles throughout their trajectory to the striatum. To test whether such interaction is important for dopaminergic axon pathfinding, we analyzed transgenic mouse embryos in which the GAD65 axon bundle was reduced by the conditional expression of the diphtheria toxin. In these embryos we observed dopaminergic misprojection into the hypothalamic region and abnormal projection in the striatum. In addition, analysis of Robo1/2 and Slit1/2 knockout embryos revealed that the previously described dopaminergic misprojection in these embryos is accompanied by severe alterations in the GAD65 axon scaffold. Additional studies with cultured dopaminergic neurons and whole embryos suggest that NCAM and Robo proteins are involved in the interaction of GAD65 and dopaminergic axons. These results indicate that the fasciculation between descending GAD65 axon bundles and ascending dopaminergic axons is required for the stereotypical NSP formation during brain development and that known guidance cues may determine this projection indirectly by instructing the pathfinding of the axons that are part of the GAD65 axon scaffold.

Ectopic cerebellar cell migration causes maldevelopment of Purkinje cells and abnormal motor behaviour in Cxcr4 null mice

SDF-1/CXCR4 signalling plays an important role in neuronal cell migration and brain development. However, the impact of CXCR4 deficiency in the postnatal mouse brain is still poorly understood. Here, we demonstrate the importance of CXCR4 on cerebellar development and motor behaviour by conditional inactivation of Cxcr4 in the central nervous system. We found CXCR4 plays a key role in cerebellar development. Its loss leads to defects in Purkinje cell dentritogenesis and axonal projection in vivo but not in cell culture. Transcriptome analysis revealed the most significantly affected pathways in the Cxcr4 deficient developing cerebellum are involved in extra cellular matrix receptor interactions and focal adhesion. Consistent with functional impairment of the cerebellum, Cxcr4 knockout mice have poor coordination and balance performance in skilled motor tests. Together, these results suggest ectopic the migration of granule cells impairs development of Purkinje cells, causes gross cerebellar anatomical disruption and leads to behavioural motor defects in Cxcr4 null mice.

Scientific progress regarding neural regeneration in the Web of Science: A 10-year bibliometric analysis

BACKGROUND:

Neural regeneration following nerve injury is an emerging field that attracts extending interests all over the world.

OBJECTIVE:

To use bibliometric indexes to track studies focusing on neural regeneration, and to investigate the relationships among geographic origin, countries and institutes, keywords in the published articles, and especially focus on the region distribution, institution distribution, as well as collaborations in Chinese papers indexed in the Web of Science.

METHODS:

A list of neural regeneration studies was generated by searching the database of the Web of Science-Expanded using the term “Neural Regenera*”. Inclusive criteria: (1) articles in the field of neural regeneration; (2) fundamental research on animals, clinical trials and case reports; (3) article types: article, review, proceedings paper, note, letter, editorial material, discussion, book chapter; (4) year of publication: 2003–2012; and (5) citation database: Science Citation Index-Expanded. Exclusive criteria: (1) articles requiring manual searching or with access only by telephone; (2) unpublished articles; and (3) corrections.

RESULTS:

A total of 4 893 papers were retrieved from the Web of Science published between 2003 and 2012. The papers covered 65 countries or regions, of which the United States ranked first with 1 691 papers. The most relevant papers were in the neurosciences and cell biology, and the keyword “stem cell” was the most frequent. In recent years, China showed a great increase in the number of papers. Over the entire 10 years, there were 922 Chinese papers, with Jilin University ranking first with 58 articles. Chinese papers were published in connection with many countries, including the United States, Japan, and the United Kingdom. Among the connections, the papers published by the Chinese and the American are 107, with the highest rate. With regard to funding, 689 articles were funded from various projects, occupying 74.72% of the total amount. In these projects, National Foundation and Science and Technology programs were the majority.

CONCLUSION:

Our bibliometric analysis provides a historical perspective on the progress of neural regeneration research. At present, the number of articles addressing neural regeneration is increasing rapidly; however, through analysis of citations it is clear that there is a long way to go to improve the academic quality.

Cell transplantation in the damaged adult brain

Parkinson's disease (PD) is the most common movement disorder in Europe, affecting more than two million people between 50 and 70 years of age. The current therapeutic approaches are of symptomatic nature and fail to halt the progressive neurodegenerative course of the disease. The development of innovative and complementary approaches to promote cellular repair may pave the way for disease-modifying therapies which may lead to less suffering for the patients and their families and finally to more cost-effective therapies. To date, cell replacement trials in PD aiming at replacing lost dopamine neurons were mainly focused on placing the transplanted cells within the target site, the striatum, and not within the lesioned site, the substantia nigra (SN). This was based on the misconception that the adult brain constitutes a non-permissive barrier not allowing the outgrowth of long distance axons originating from transplanted embryonic neurons. A growing body of evidence is challenging this concept and proposing instead to place the graft within its ontogenic site. This has been performed in several lesional animal models for various traumatic or neurodegenerative pathologies of the brain. For instance, transplanted neurons within the lesioned motor cortex were shown to be able to send distant and appropriate projections to target areas including the spinal cord. Similarly, in an animal model of PD, mesencephalic embryonic cells transplanted within the lesioned SN send massive projections to the striatum and, to a lesser extent, the frontal cortex and the nucleus accumbens. This has lead to the proposal that homotopic transplantation may be an alternative in cell-based therapies as transplanted neurons can integrate within the host brain, send projections to target areas, restore the damaged circuitry, increase neurotransmitter levels and ameliorate behavior. We will discuss also the potential of replacing embryonic neuronal cells by stem cell derived neurons as the use of embryonic cells is not without an ethical and logistical burden; in this line many have thrived to derive neurons from embryonic stem cells (ESC) in order to use them for cell transplantation. These studies are already yielding important information for future approaches in the field of cell therapies in PD but also in other neurodegenerative disorders where cell transplantation therapy may be considered. While the field of cell replacement therapies has been recently called into question with contrasting results in transplanted PD patients, these new sets of findings are raising new hopes and opening new avenues in this rejuvenated field.

Long distance directional growth of dopaminergic axons along pathways of netrin-1 and GDNF

Different experimental and clinical strategies have been used to promote survival of transplanted embryonic ventral mesencephalic (VM) neurons. However, few studies have focused on the long-distance growth of dopaminergic axons from VM transplants. The aim of this study is to identify some of the growth and guidance factors that support directed long-distance growth of dopaminergic axons from VM transplants. Lentivirus encoding either glial cell line-derived neurotrophic factor (GDNF) or netrin-1, or a combination of lenti-GDNF with either lenti-GDNF family receptor α1 (GFRα-1) or lenti-netrin-1 was injected to form a gradient along the corpus callosum. Two weeks later, a piece of embryonic day 14 VM tissue was transplanted into the corpus callosum adjacent to the low end of the gradient. Results showed that tyrosine hydroxylase (TH(+)) axons grew a very short distance from the VM transplants in control groups, with few axons reaching the midline. In GDNF or netrin-1 expressing groups, more TH(+) axons grew out of transplants and reached the midline. Pathways co-expressing GDNF with either GFRα-1 or netrin-1 showed significantly increased axonal outgrowth. Interestingly, only the GDNF/netrin-1 combination resulted in the majority of axons reaching the distal target (80%), whereas along the GDNF/GFRα-1 pathway only 20% of the axons leaving the transplant reached the distal target. This technique of long-distance axon guidance may prove to be a useful strategy in reconstructing damaged neuronal circuits, such as the nigrostriatal pathway in Parkinson's disease.

A guide to best practices for Gene Ontology (GO) manual annotation

The Gene Ontology Consortium (GOC) is a community-based bioinformatics project that classifies gene product function through the use of structured controlled vocabularies. A fundamental application of the Gene Ontology (GO) is in the creation of gene product annotations, evidence-based associations between GO definitions and experimental or sequence-based analysis. Currently, the GOC disseminates 126 million annotations covering >374 000 species including all the kingdoms of life. This number includes two classes of GO annotations: those created manually by experienced biocurators reviewing the literature or by examination of biological data (1.1 million annotations covering 2226 species) and those generated computationally via automated methods. As manual annotations are often used to propagate functional predictions between related proteins within and between genomes, it is critical to provide accurate consistent manual annotations. Toward this goal, we present here the conventions defined by the GOC for the creation of manual annotation. This guide represents the best practices for manual annotation as established by the GOC project over the past 12 years. We hope this guide will encourage research communities to annotate gene products of their interest to enhance the corpus of GO annotations available to all.

Database URL:http://www.geneontology.org

Role of Slit and Robo proteins in the development of dopaminergic neurons

Dopamine plays a number of important roles in the nervous system and the dopaminergic system is affected in several brain disorders. It is therefore of great interest to study the axonal guidance systems that specifically participate in the correct establishment of dopaminergic projections during development and possibly during regenerative processes. In recent years, several reports have shown that Slits and their Robo receptors control the growth of longitudinal (both ascending and descending) mesodiencephalic dopaminergic axons to their appropriate target areas. In vitro studies have shown that Slit1, 2 and 3 are potent repellents of dopamine neurite extension. In vivo studies using both mice and zebrafish mutants for Slits and Robos have shown that Slits and Robos control the lateral and dorsoventral positioning of dopaminergic longitudinal projections during early development. In the present review, we aimed to compile the existing knowledge from both in vitro and in vivo studies on the role of Slit and Robo proteins in the development of dopaminergic neurons as a basis for future studies.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

Dopaminergic axon guidance: which makes what?

Mesotelencephalic pathways in the adult central nervous system have been studied in great detail because of their implication in major physiological functions as well as in psychiatric, neurological, and neurodegenerative diseases. However, the ontogeny of these pathways and the molecular mechanisms that guide dopaminergic axons during embryogenesis have been only recently studied. This line of research is of crucial interest for the repair of lesioned circuits in adulthood following neurodegenerative diseases or common traumatic injuries. For instance, in the adult, the anatomic and functional repair of the nigrostriatal pathway following dopaminergic embryonic neuron transplantation suggests that specific guidance cues exist which govern embryonic fibers outgrowth, and suggests that axons from transplanted embryonic cells are able to respond to theses cues, which then guide them to their final targets. In this review, we first synthesize the work that has been performed in the last few years on developing mesotelencephalic pathways, and summarize the current knowledge on the identity of cellular and molecular signals thought to be involved in establishing mesotelencephalic dopaminergic neuronal connectivity during embryogenesis in the central nervous system of rodents. Then, we review the modulation of expression of these molecular signals in the lesioned adult brain and discuss their potential role in remodeling the mesotelencephalic dopaminergic circuitry, with a particular focus on Parkinson's disease (PD). Identifying guidance molecules involved in the connection of grafted cells may be useful for cellular therapy in Parkinsonian patients, as these molecules may help direct axons from grafted cells along the long distance they have to travel from the substantia nigra to the striatum.

Integrated analysis of mRNA and microRNA expression in mature neurons, neural progenitor cells and neuroblastoma cells

Mature neurons (MNs), neural progenitor cells (NPCs) and neuroblastoma cells (NBCs) are all neural-derived cells. However, MNs are unable to divide once differentiated; NPCs are able to divide a limited number of times and differentiate to normal brain cell types; whereas NBCs can divide an unlimited number of times but rarely differentiate. Here, we perform whole transcriptome (mRNA, miRNA) profiling of these cell types and compare expression levels of each cell type to the others. Integrated mRNA-miRNA functional analyses reveal that: 1) several very highly expressed genes (e.g., Robo1, Nrp1, Epha3, Unc5c, Dcc, Pak3, Limk4) and a few under-expressed miRNAs (e.g., miR-152, miR-146b, miR-339-5p) in MNs are associated with one important cellular process-axon guidance; 2) some very highly expressed mitogenic pathway genes (e.g., Map2k1, Igf1r, Rara, Runx1) and under-expressed miRNAs (e.g., miR-370, miR-9, miR-672) in NBCs are associated with cancer pathways. These results provide a library of negative mRNAmiRNA networks that are likely involved in the cellular processes of differentiation and division.

Development of posterior hypothalamic neurons enlightens a switch in the prosencephalic basic plan

In rats and mice, ascending and descending axons from neurons producing melanin-concentrating hormone (MCH) reach the cerebral cortex and spinal cord. However, these ascending and descending projections originate from distinct sub-populations expressing or not “Cocaine-and-Amphetamine-Regulated-Transcript” (CART) peptide. Using a BrdU approach, MCH cell bodies are among the very first generated in the hypothalamus, within a longitudinal cell cord made of earliest delaminating neuroblasts in the diencephalon and extending from the chiasmatic region to the ventral midbrain. This region also specifically expresses the regulatory genes Sonic hedgehog (Shh) and Nkx2.2. First MCH axons run through the tractus postopticus (tpoc) which gathers pioneer axons from the cell cord and courses parallel to the Shh/Nkx2.2 expression domain. Subsequently generated MCH neurons and ascending MCH axons differentiate while neurogenesis and mantle layer differentiation are generalized in the prosencephalon, including telencephalon. Ascending MCH axons follow dopaminergic axons of the mesotelencephalic tract, both being an initial component of the medial forebrain bundle (mfb). Netrin1 and Slit2 proteins that are involved in the establishment of the tpoc and mfb, respectively attract or repulse MCH axons.

We conclude that first generated MCH neurons develop in a diencephalic segment of a longitudinal Shh/Nkx2.2 domain. This region can be seen as a prosencephalic segment of a medial neurogenic column extending from the chiasmatic region through the ventral neural tube. However, as the telencephalon expends, it exerts a trophic action and the mfb expands, inducing a switch in the longitudinal axial organization of the prosencephalon.

Human neural stem cells enhance structural plasticity and axonal transport in the ischaemic brain

Stem cell transplantation promises new hope for the treatment of stroke although significant questions remain about how the grafted cells elicit their effects. One hypothesis is that transplanted stem cells enhance endogenous repair mechanisms activated after cerebral ischaemia. Recognizing that bilateral reorganization of surviving circuits is associated with recovery after stroke, we investigated the ability of transplanted human neural progenitor cells to enhance this structural plasticity. Our results show the first evidence that human neural progenitor cell treatment can significantly increase dendritic plasticity in both the ipsi- and contralesional cortex and this coincides with stem cell-induced functional recovery. Moreover, stem cell-grafted rats demonstrated increased corticocortical, corticostriatal, corticothalamic and corticospinal axonal rewiring from the contralesional side; with the transcallosal and corticospinal axonal sprouting correlating with functional recovery. Furthermore, we demonstrate that axonal transport, which is critical for both proper axonal function and axonal sprouting, is inhibited by stroke and that this is rescued by the stem cell treatment, thus identifying another novel potential mechanism of action of transplanted cells. Finally, we established in vitro co-culture assays in which these stem cells mimicked the effects observed in vivo. Through immunodepletion studies, we identified vascular endothelial growth factor, thrombospondins 1 and 2, and slit as mediators partially responsible for stem cell-induced effects on dendritic sprouting, axonal plasticity and axonal transport in vitro. Thus, we postulate that human neural progenitor cells aid recovery after stroke through secretion of factors that enhance brain repair and plasticity.

Effects of treadmill exercise on the expression of netrin-1 and its receptors in rat brain after cerebral ischemia

Recent evidence suggests that exercise improves functional outcome in animal models of cerebral ischemia. Since netrin-1 and its receptors, deleted in colorectal cancer (DCC) and uncoordinated gene 5B (Unc5B), act as important regulators in neural and vascular activities, we sought to determine whether netrin-1 and DCC and Unc5B are involved in the neuroprotective effects of exercise on rats with induced cerebral ischemia. A total of 108 rats were randomly distributed into three groups: sham-operated group (n = 12), middle cerebral artery occlusion (MCAO) group (n = 48), MCAO+treadmill exercise group (n = 48). Behavioral testing indicated that treadmill exercise could significantly improve neurologic deficits of rats with cerebral ischemia at day 14 and 28 after MCAO (n = 12, P<0.05 and P<0.01), but there was no significant difference at day 4 and 7. Quantitative reverse transcription polymerase chain reaction (qPCR) and Western blot analysis revealed that treadmill exercise enhanced netrin-1 and DCC expression, while it suppressed Unc5B expression in rat peri-ischemic brain area, especially at day 14 and 28 after MCAO (n = 4, P<0.05 or P<0.01). Immunofluorescence analysis showed that in the peri-ischemic area, netrin-1 was expressed in neuronal perikarya, DCC, however, was expressed in neural processes and peri-vascular astrocytes, while Unc5B was expressed mostly in neuronal perikarya and some processes. These results suggest that netrin-1 and its receptors DCC and Unc5B may engage in exercise-induced neural circuit remodeling in the peri-ischemic area, and exercise may promote survival of neurons in this area by regulating netrin-1-Unc5B signaling. Additionally, netrin-1 may also play a role in brain-blood barrier via DCC-immunoreactive peri-vascular astrocytes. In conclusion, we demonstrate that treadmill exercise has beneficial effects that may be attributed, at least in part, to the involvement of netrin-1 and its receptors DCC and Unc5B in the neuronal and vascular activities in brain-ischemic rats.

Cytosine arabinoside induces ectoderm and inhibits mesoderm expression in human embryonic stem cells during multilineage differentiation

BACKGROUND AND PURPOSE

Teratogenic substances induce adverse effects during the development of the embryo. Multilineage differentiation of human embryonic stem cells (hESCs) mimics the development of the embryo in vitro. Here, we propose a transcriptomic approach in hESCs for monitoring specific toxic effects of compounds as an alternative to traditional time-consuming and cost-intensive in vivo tests requiring large numbers of animals. This study was undertaken to explore the adverse effects of cytosine arabinoside (Ara-C) on randomly differentiated hESCs.

EXPERIMENTAL APPROACH

Human embryonic stem cells were used to investigate the effects of a developmental toxicant Ara-C. Sublethal concentrations of Ara-C were given for two time points, day 7 and day 14 during the differentiation. Gene expression was assessed with microarrays to determine the dysregulated transcripts in presence of Ara-C.

KEY RESULTS

Randomly differentiated hESCs were able to generate the multilineage markers. The low concentration of Ara-C (1 nM) induced the ectoderm and inhibited the mesoderm at day 14. The induction of ectodermal markers such as MAP2, TUBB III, PAX6, TH and NESTIN was observed with an inhibition of mesodermal markers such as HAND2, PITX2, GATA5, MYL4, TNNT2, COL1A1 and COL1A2. In addition, no induction of apoptosis was observed. Gene ontology revealed unique dysregulated biological process related to neuronal differentiation and mesoderm development. Pathway analysis showed the axon guidance pathway to be dysregulated.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that hESCs in combination with toxicogenomics offer a sensitive in vitro developmental toxicity model as an alternative to traditional animal experiments.

Wnt5a regulates midbrain dopaminergic axon growth and guidance

During development, precise temporal and spatial gradients are responsible for guiding axons to their appropriate targets. Within the developing ventral midbrain (VM) the cues that guide dopaminergic (DA) axons to their forebrain targets remain to be fully elucidated. Wnts are morphogens that have been identified as axon guidance molecules. Several Wnts are expressed in the VM where they regulate the birth of DA neurons. Here, we describe that a precise temporo-spatial expression of Wnt5a accompanies the development of nigrostriatal projections by VM DA neurons. In mice at E11.5, Wnt5a is expressed in the VM where it was found to promote DA neurite and axonal growth in VM primary cultures. By E14.5, when DA axons are approaching their striatal target, Wnt5a causes DA neurite retraction in primary cultures. Co-culture of VM explants with Wnt5a-overexpressing cell aggregates revealed that Wnt5a is capable of repelling DA neurites. Antagonism experiments revealed that the effects of Wnt5a are mediated by the Frizzled receptors and by the small GTPase, Rac1 (a component of the non-canonical Wnt planar cell polarity pathway). Moreover, the effects were specific as they could be blocked by Wnt5a antibody, sFRPs and RYK-Fc. The importance of Wnt5a in DA axon morphogenesis was further verified in Wnt5a^−/− mice, where fasciculation of the medial forebrain bundle (MFB) as well as the density of DA neurites in the MFB and striatal terminals were disrupted. Thus, our results identify a novel role of Wnt5a in DA axon growth and guidance.

Human ROBO1 is cleaved by metalloproteinases and gamma-secretase and migrates to the nucleus in cancer cells

ROBO1 is a receptor mediating Slit-induced repulsive action on axon guidance and differentially expressed in human cancers. Although ROBO1 ectodomain has been detected, the cleavage site had not been determined. In this study we identified the precise cleavage site of ROBO1. We also report multi-step proteolysis of ROBO1 by metalloproteinases and gamma-secretase, producing two carboxy-terminal fragments, ROBO1-CTF1 at 129-kDa and ROBO1-CTF2 at 118-kDa. We have further demonstrated nuclear accumulation of ROBO1, which is abolished by either a metalloproteinase inhibitor TAPI-1 or a gamma-secretase inhibitor L-685,458. ROBO1 may function beyond the receptor through stepwise cleavages and translocation to the nucleus.

Advanced microscopy techniques for quantitative analysis in neuromorphology and neuropathology research: current status and requirements for the future

Visualizing neuromorphology and in particular neuropathology has been the focus of many researchers in the quest to solve the numerous questions that are still remaining related to several neurological and neuropsychiatric diseases. Over the last years, intense research into microscopy techniques has resulted in the development of various new types of microscopes, software imaging systems, and analysis programs. This review briefly discusses some key techniques, such as confocal stereology and automated neuron tracing and reconstruction, and their applications in neuroscience research. Special emphasis is placed on needs for further developments, such as the demand for higher-throughput analyses in quantitative neuromorphology. These developments will advance basic neuroscience research as well as pharmaceutical and biotechnology research and development.

Axon responses of embryonic stem cell-derived dopaminergic neurons to semaphorins 3A and 3C

Class 3 Semaphorins are a subfamily of chemotropic molecules implicated in the projection of dopaminergic neurons from the ventral mesencephalon and in the formation of the nigrostriatal pathway (NSP) during embryonic development. In humans, loss of mesencephalic dopaminergic neurons leads to Parkinson's disease (PD). Cell replacement therapy with dopaminergic neurons generated from embryonic stem cells (ES-TH(+)) is being actively explored in models of PD. Among several requisites for this approach to work are adequate reconstruction of the NSP and correct innervation of normal striatal targets by dopaminergic axons. In this work, we characterized the response of ES-TH(+) neurons to semaphorins 3A, 3C, and 3F and compared it with that of tyrosine hidroxylase-positive neurons (TH(+)) obtained from embryonic ventral mesencephalon (VM-TH(+)). We observed that similar proportions of ES-TH(+) and VM-TH(+) neurons express semaphorin receptors neuropilins 1 and 2. Furthermore, the axons of both populations responded very similarly to semaphorin exposure: semaphorin 3A increased axon length, and semaphorin 3C attracted axons and increased their length. These effects were mediated by neuropilins, insofar as addition of blocking antibodies against these proteins reduced the effects on axonal growth and attraction, and only TH(+) axons expressing neuropilins responded to the semaphorins analyzed. The observations reported here show phenotypic similarities between VM-TH(+) and ES-TH(+) neurons and suggest that semaphorins 3A and 3C could be employed to guide axons of grafted ES-TH(+) in therapeutic protocols for PD.

Expression by midbrain dopamine neurons of Sema3A and 3F receptors is associated with chemorepulsion in vitro but a mild in vivo phenotype

Here we explore the role of semaphorin 3A and 3F (Sema3A, Sema3F) in the formation of the mesotelencephalic pathway. We show that Sema3A and 3F are expressed in the ventral mesencephalon (VM) of E13.5 rat embryos; the receptors Neuropilin 1 and Neuropilin 2, and co-receptors L1CAM, NrCAM, and Plexins A1 and A3 but not A4 are expressed by VM dopaminergic neurons; these neurons bind Sema3A and 3F in vitro which induces collapse of their growth cones and elicits, with different potencies, a repulsive response; and this response is absent in axons from Nrp1 and Nrp2 null embryos. Despite these in vitro effects, only very mild anatomical defects were detected in the organization of the mesotelencephalic pathway in embryonic and adult Nrp1 or Nrp2 null mice. However, the dopaminergic meso-habenular pathway and catecholaminergic neurons in the parafascicular and paraventricular nuclei of the thalamus were significantly affected in Nrp2 null mice. These data are consistent with a model whereby Sema3A and 3F, in combination with other guidance molecules, contributes to the navigation of DA axons to their final synaptic targets.

Isolation and culture of ventral mesencephalic precursor cells and dopaminergic neurons from rodent brains

The ability to isolate ventral midbrain (VM) precursor cells and neurons provides a powerful means to characterize their differentiation properties and to study their potential for restoring dopamine (DA) neurons degenerated in Parkinson's disease (PD). Preparation and maintenance of DA VM in primary culture involves a number of critical steps to yield healthy cells and appropriate data. Here, we offer a detailed description of protocols to consistently prepare VM DA cultures from rat and mouse embryonic fetal-stage midbrain. We also present methods for organotypic culture of midbrain tissue, for differentiation as aggregate cultures, and for adherent culture systems of DA differentiation and maturation, followed by a synopsis of relevant analytical read-out options. Isolation and culture of rodent VM precursor cells and DA neurons can be exploited for studies of DA lineage development, of neuroprotection, and of cell therapeutic approaches in animal models of PD.

Glutamate controls growth rate and branching of dopaminergic axons

Dopamine-releasing neurons of the substantia nigra pars compacta produce an extraordinarily dense and expansive plexus of innervation in the striatum converging with glutamatergic corticostriatal and thalamostriatal axon terminals at dendritic spines of medium spiny neurons. Here, we investigated whether glutamatergic signaling promotes arborization and growth of dopaminergic axons. In postnatal ventral midbrain cultures, dopaminergic axons rapidly responded to glutamate stimulation with accelerated growth and growth cone splitting when NMDA and AMPA/kainate receptors were activated. In contrast, when AMPA/kainate receptors were selectively activated, axon growth rate was decreased. To address whether this switch in axonal growth response was mediated by distinct calcium signals, we used calcium imaging. Combined NMDA and AMPA/kainate receptor activation elicited calcium signals in axonal growth cones that were mediated by calcium influx through L-type voltage-gated calcium channels and ryanodine receptor-induced calcium release from intracellular stores. AMPA/kainate receptor activation alone elicited calcium signals that were solely attributable to calcium influx through L-type calcium channels. We found that inhibitors of calcium/calmodulin-dependent protein kinases prevented the NMDA receptor-dependent axonal growth acceleration, whereas AMPA/kainate-induced axonal growth decrease was blocked by inhibitors of calcineurin and by increased cAMP levels. Our data suggest that the balance between NMDA and AMPA/kainate receptor activation regulates the axonal arborization pattern of dopamine axons through the activation of competing calcium-dependent signaling pathways. Understanding the mechanisms of dopaminergic axonal arborization is essential to the development of treatments that aim to restore dopaminergic innervation in Parkinson's disease.