EA Improves the Motor Function in Rats with Spinal Cord Injury by Inhibiting Signal Transduction of Semaphorin3A and Upregulating of the Peripheral Nerve Networks

Peripheral nerve networks (PNNs) play a vital role in the neural recovery after spinal cord injury (SCI). Electroacupuncture (EA), as an alternative medicine, has been widely used in SCI and was proven to be effective on neural functional recovery. In this study, the interaction between PNNs and semaphrin3A (Sema3A) in the recovery of the motor function after SCI was observed, and the effect of EA on them was evaluated. After the establishment of the SCI animal model, we found that motor neurons in the ventral horn of the injured spinal cord segment decreased, Nissl bodies were blurry, and PNNs and Sema3A as well as its receptor neuropilin1 (NRP1) aggregated around the central tube of the gray matter of the spinal cord. When we knocked down the expression of Sema3A at the damage site, NRP1 also downregulated, importantly, PNNs concentration decreased, and tenascin-R (TN-R) and aggrecan were also reduced, while the Basso-Beattie-Bresnahan (BBB) motor function score dramatically increased. In addition, when conducting EA stimulation on Jiaji (EX-B2) acupoints, the highly upregulated Sema3A and NRP1 were reversed post-SCI, which can lessen the accumulation of PNNs around the central tube of the spinal cord gray matter, and simultaneously promote the recovery of motor function in rats. These results suggest that EA may further affect the plasticity of PNNs by regulating the Sema3A signal and promoting the recovery of the motor function post-SCI.

Insights into olfactory ensheathing cell development from a laser-microdissection and transcriptome-profiling approach

Olfactory ensheathing cells (OECs) are neural crest-derived glia that ensheath bundles of olfactory axons from their peripheral origins in the olfactory epithelium to their central targets in the olfactory bulb. We took an unbiased laser microdissection and differential RNA-seq approach, validated by in situ hybridization, to identify candidate molecular mechanisms underlying mouse OEC development and differences with the neural crest-derived Schwann cells developing on other peripheral nerves. We identified 25 novel markers for developing OECs in the olfactory mucosa and/or the olfactory nerve layer surrounding the olfactory bulb, of which 15 were OEC-specific (that is, not expressed by Schwann cells). One pan-OEC-specific gene, Ptprz1, encodes a receptor-like tyrosine phosphatase that blocks oligodendrocyte differentiation. Mutant analysis suggests Ptprz1 may also act as a brake on OEC differentiation, and that its loss disrupts olfactory axon targeting. Overall, our results provide new insights into OEC development and the diversification of neural crest-derived glia.

PlexinA1 deficiency in BALB/cAJ mice leads to excessive self-grooming and reduced prepulse inhibition

PlexinA1 (PlxnA1) is a transmembrane receptor for semaphorins, a large family of proteins that act as axonal guidance cues during nervous system development. However, there are limited studies on PlxnA1 function in neurobehavior. The present study examined if PlxnA1 deficiency leads to behavioral abnormalities in BALB/cAJ mice. PlxnA1 knockout (KO) mice were generated by homologous recombination and compared to wild type (WT) littermates on a comprehensive battery of behavioral tests, including open field assessment of spontaneous ambulation, state anxiety, and grooming, home cage grooming, the wire hang test of muscle strength, motor coordination on the rotarod task, working memory on the Y maze alternation task, cued and contextual fear conditioning, anxiety on the elevated plus maze, sociability to intruders, and sensory processing as measured by prepulse inhibition (PPI). Measures of motor performance, working memory, fear memory, and sociability did not differ significantly between genotypes, while PlxnA1 KO mice displayed excessive self-grooming, impaired PPI, and slightly lower anxiety. These results suggest a crucial role for PlxnA1 in the development and function of brain regions controlling self-grooming and sensory gating. PlxnA1 KO mice may be a valuable model to investigate the repetitive behaviors and information processing deficits characteristic of many neurodevelopmental and psychiatric disorders.

Spatial association of SEMA3C with nerve endings/terminal Schwann cells in hair follicle isthmus region

Nerve endings and terminal Schwann cells (TSCs) specifically and densely surround hair follicle at isthmus area, forming a neuromuscular-junction-like structure called lanceolate complex. The interplay between neuronal components and epidermis in this specialized structure enables hair to properly sense complex stimuli from environments. However, how nerves precisely attach to and innervate this specific region during development remains to be elucidated. Here, we demonstrate that SEMA3C, a secreted protein member of semaphorin family responsible for axonal guidance, is localized right below sebaceous gland and in close approximation with nerve endings and TSCs processes all through the entire hair cycle. SEMA3C protein is deposited outside of epithelial cells and its expression is independent on the presence of nerve endings/TSCs. SEMA3C is also found in portions of dermal papilla at growth phase. The tight spatial association of SEMA3C with lanceolate complex suggests that it might play roles in establishment and/or maintenance of the lanceolate complex in hair follicle.

Variants in multiple genes are associated with esophageal cancer risk in a Chinese Han population: A case-control study

BACKGROUND

The present study investigated whether 16 single nucleotide polymorphisms (SNPs), selected based on minor allele frequencies, Hardy-Weinberg equilibrium and reported SNPs related to the susceptibility of certain gastrointestinal cancer, were associated with esophageal cancer (EC) risk in a Chinese Han population.

METHODS

We genotyped 16 SNPs among 506 cases and 507 controls using Agena MassARRAY (Agena, San Diego, CA, USA). The association between 16 SNPs and EC risk was analyzed by a chi-squared test and genetic model analysis. Logistic regression analysis was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

rs1050631 and the rs6214 were associated with a decreased EC risk (OR = 0.75, p = 0.038; OR = 0.74, p = 0.045, respectively). In stratification analysis, the rs9868873 was associated with an increased EC risk (age < 64 years) (OR = 5.03, p = 0.005). The rs6214 was associated with a decreased EC risk (age < 64 years) (OR = 0.59, p = 0.025). The rs861530 was significantly associated with a decreased EC risk (age ≥ 64 years) (OR = 0.67, p = 0.046). rs1050631 was associated with a decreased EC risk in males (OR = 0.71, p = 0.034). In the stratified analysis of clinical stage III/IV, the rs1800566 was associated with a decreased EC risk (OR = 0.49, p = 0.024). Finally, the rs1052133 was associated with an elevated EC risk in the stratified analysis of lymph node metastasis (OR = 1.73, p = 0.025).

CONCLUSIONS

The findings of the present study demonstrate that SLC39A6, IGF1, SEMA5B, XRCC3, NQO1 and OGG1 polymorphisms were associated with EC risk under multiple models.

Semaphorin 4D Induces an Imbalance of Th17/Treg Cells by Activating the Aryl Hydrocarbon Receptor in Ankylosing Spondylitis

Objectives

Semaphorin 4D (Sema4D) is constitutively expressed on T cells and osteoclasts, and regulates T cell proliferation and bone remodeling. In addition, several studies have shown that Sema4D is involved in the pathogenesis of autoimmunity. We undertook this study to investigate the mechanism by which Sema4D affects the pathogenic progress of ankylosing spondylitis (AS).

Methods

Soluble Sema4D (sSema4D) levels in serum were analyzed by enzyme-linked immunosorbent assay. The cell surface levels and transcripts of Sema4D were evaluated in CD4 + and CD19 + cells from the AS patients and healthy individuals. The mRNA expression levels were assessed by quantitative polymerase chain reaction (qPCR). The proportions of Treg cells and IL-17-producing T-cells (Th17 cells) differentiated from CD4 + T cells were analyzed by flow cytometric analysis. The aryl hydrocarbon receptor (AhR) agonistic effect of Sema4D was detected by analyzing the activation of downstream signaling pathways and target genes using Luciferase and EROD assay.

Results

Levels of sSema4D were elevated in both serum from AS patients, and clinical features markers were correlated with serum sSema4D levels. Sema4D facilitated CD4 + T cells proliferation and Th17 cells differentiation and inhibited Treg cells differentiation by enhancing RORγt expression and reducing Foxp3 expression, with increasing expression and secretion of IL-17 and IL-22. It induced the expression and activity of AhR target gene CYP1A1 and XRE reporter activity via interaction with CD72.

Conclusion

These findings indicate that Sema4D as a potent activator of T cells in the immune response contributes to the inflammation of AS by inducing imbalance in Th17 and Treg cell populations in an AhR-dependent manner, suggesting it is a crucial participant in AS pathogenesis.

Inhibition of semaphorin 4D enhances chemosensitivity by increasing 5-fluorouracile-induced apoptosis in colorectal cancer cells

Overexpression of semaphorin 4D (SEMA4D), an immune semaphorin, is found in various human malignancies, including colorectal cancer (CRC). In this study, we explored the relationship between silencing SEMA4D expression and 5-fluorouracil (5-FU) response in the colorectal cancer cell line. SW48 cells were transfected with a short interfering RNA (siRNA) in order to silence SEMA4D gene expression and then exposed to 5-FU for 48 h. The down-regulation of SEMA4D expression was confirmed by qRT-PCR and the particular concentration of 5-FU was acquired using MTT assay. Flow cytometry and western blot were used to evaluate apoptosis rate and pro- and anti-apoptotic expression levels of proteins involved in apoptosis including Bax, Bcl-2, P53, and caspase-3. Other oncogenic activities including epithelial-mesenchymal transition (EMT) process, cancer stem cell (CSC) markers, and β-catenin pathway were investigated using qRT-PCR, and western blot. The proliferation was analyzed via colony formation test and cell invasion was assessed by transwell assay. Our data demonstrate that SEMA4D silencing results in strikingly elevated apoptosis in response to 5-FU treatment and leads to down-regulation of Bcl-2 and overexpression of Bax, P53, and caspase-3 in protein levels. Furthermore, the mRNA and protein expression levels of β-catenin, as well as transcript expressions of CSCs and EMT markers, were remarkably diminished. However, mRNA expression of E-cadherin as an epithelial marker was significantly increased in 5-FU treatment combined with siRNA SEMA4D. This study implicates that the silencing of SEMA4D by siRNA promotes the chemosensitivity of SW48 cells to 5-FU and it may be a potential therapeutic agent for colon cancer therapy.

Semaphorins in health and disease

Cell-cell communication is pivotal to guide embryo development, as well as to maintain adult tissues homeostasis and control immune response. Among extracellular factors responsible for this function, are the Semaphorins, a broad family of around 20 different molecular cues conserved in evolution and widely expressed in all tissues. The signaling cascades initiated by semaphorins depend on a family of conserved receptors, called Plexins, and on several additional molecules found in the receptor complexes. Moreover, multiple intracellular pathways have been described to act downstream of semaphorins, highlighting significant diversity in the signaling cascades controlled by this family. Notably, semaphorin expression is altered in many human diseases, such as immunopathologies, neurodegenerative diseases and cancer. This underscores the importance of semaphorins as regulatory factors in the tissue microenvironment and has prompted growing interest for assessing their potential relevance in medicine. This review article surveys the main contexts in which semaphorins have been found to regulate developing and healthy adult tissues, and the signaling cascades implicated in these functions. Vis a vis, we will highlight the main pathological processes in which semaphorins are thought to have a role thereof.

Hypoxia-induced downregulation of Sema3a and CXCL12/CXCR4 regulate the formation of the coronary artery stem at the proper site

BACKGROUND

During the formation of the coronary artery stem, endothelial strands from the endothelial progenitor pool surrounding the conotruncus penetrate into the aortic wall. Vascular endothelial growth factors (VEGFs) as well as CXCL12/CXCR4 signaling are thought to play a role in the formation of the coronary stem. However, the mechanisms regulating how endothelial strands exclusively invade into the aorta remain unknown.

METHODS AND RESULTS

Immunohistochemistry showed that before the formation of endothelial strands, Sema3a was highly expressed in endothelial progenitors surrounding the great arteries. At the onset of/during invasion of endothelial strands into the aorta, Sema3a was downregulated and CXCR4 was upregulated in the endothelial strands. In situ hybridization showed that Cxcl12 was highly expressed in the aortic wall compared with in the pulmonary artery. Using avian embryonic hearts, we established two types of endothelial penetration assay, in which coronary endothelial strands preferentially invaded into the aorta in culture. Sema3a blocking peptide induced an excess number of endothelial strands penetrating into the pulmonary artery, whereas recombinant Sema3a inhibited the formation of endothelial strands. In cultured coronary endothelial progenitors, recombinant VEGF protein induced CXCR4-positive endothelial strands, which were capable of being attracted by CXCL12-impregnated beads. Monoazo rhodamine detected that hypoxia was predominant in aortic/subaortic region in ovo and hypoxic condition downregulated the expression of Sema3a in culture.

CONCLUSION

Results suggested that hypoxia in the aortic region downregulates the expression of Sema3a, thereby enhancing VEGF activity to induce the formation of CXCR4-positive endothelial strands, which are subsequently attracted into the Cxcl12-positive aortic wall to connect the aortic lumen.

Recognition of Semaphorin Proteins by P. sordellii Lethal Toxin Reveals Principles of Receptor Specificity in Clostridial Toxins

Pathogenic clostridial species secrete potent toxins that induce severe host tissue damage. Paeniclostridium sordellii lethal toxin (TcsL) causes an almost invariably lethal toxic shock syndrome associated with gynecological infections. TcsL is 87% similar to C. difficile TcdB, which enters host cells via Frizzled receptors in colon epithelium. However, P. sordellii infections target vascular endothelium, suggesting that TcsL exploits another receptor. Here, using CRISPR/Cas9 screening, we establish semaphorins SEMA6A and SEMA6B as TcsL receptors. We demonstrate that recombinant SEMA6A can protect mice from TcsL-induced edema. A 3.3 Å cryo-EM structure shows that TcsL binds SEMA6A with the same region that in TcdB binds structurally unrelated Frizzled. Remarkably, 15 mutations in this evolutionarily divergent surface are sufficient to switch binding specificity of TcsL to that of TcdB. Our findings establish semaphorins as physiologically relevant receptors for TcsL and reveal the molecular basis for the difference in tissue targeting and disease pathogenesis between highly related toxins.

Trans-Axonal Signaling in Neural Circuit Wiring

The development of neural circuits is a complex process that relies on the proper navigation of axons through their environment to their appropriate targets. While axon–environment and axon–target interactions have long been known as essential for circuit formation, communication between axons themselves has only more recently emerged as another crucial mechanism. Trans-axonal signaling governs many axonal behaviors, including fasciculation for proper guidance to targets, defasciculation for pathfinding at important choice points, repulsion along and within tracts for pre-target sorting and target selection, repulsion at the target for precise synaptic connectivity, and potentially selective degeneration for circuit refinement. This review outlines the recent advances in identifying the molecular mechanisms of trans-axonal signaling and discusses the role of axon–axon interactions during the different steps of neural circuit formation.

Bone Cell Communication Factors Provide a New Therapeutic Strategy for Osteoporosis

Bone homeostasis is strictly regulated by the balance between bone resorption by osteoclasts and bone formation by osteoblasts. Many studies have shown that osteoclasts affect osteoblasts, and vice versa, through diffusible paracrine factors, cell-cell contact, and cell-bone matrix interactions to achieve the correct balance between osteoclastic and osteoblastic activities in the basic multicellular unit (BMU). The strict regulation that occurs during bone remodeling hinders the long-term use of the currently available antiresorptive agents and anabolic agents for the treatment of osteoporosis. To overcome these limitations, it is necessary to develop novel agents that simultaneously inhibit bone resorption, promote bone formation, and decouple resorption from formation. Therefore, a more detailed understanding of the mechanisms involved in osteoclast-osteoblast communication during bone remodeling is necessary.

Regulation of mesenchymal stem cell differentiation on microstructured titanium surfaces by semaphorin 3A

Peri-implant bone formation depends on the ability of mesenchymal stem cells (MSCs) to colonize implant surfaces and differentiate into osteoblasts, but the precise mechanisms controlling this process remain unclear. In vitro, MSCs undergo osteoblastic differentiation on microstructured titanium (Ti) surfaces in the absence of exogenous media supplements and produce factors that promote osteogenesis while regulating osteoclast activity, including semaphorins. The goal of this study was to evaluate the role of semaphorin 3A (Sema3A) on surface-mediated osteoblastic differentiation and determine the hierarchy of this signaling cascade. Human MSCs were cultured on 15 mm grade 2 smooth (pretreatment, PT), hydrophobic-microrough (sand blasted/acid etched, SLA), hydrophilic-microrough Ti (mSLA) (Institut Straumann AG, Basel, Switzerland), or tissue culture polystyrene (TCPS). Expression of SEMA3A family proteins increased after 7 days of culture, and the increased expression in response to microstructured Ti was dependent on recognition of the surface by integrin α2β1. Exogenous Sema3A increased differentiation whereas differentiation was decreased in cells treated with a Sema3A antibody. Furthermore, Sema3A influenced the production of osteoprotegerin and osteopontin suggesting it as an important local regulator of bone remodeling. Inhibition of Wnt3A and Wnt5A revealed that activation of Sema3A occurs downstream of Wnt5A and may facilitate the translocation of β-catenin bypassing the canonical Wnt3A initiating signal associated with osteoblastic differentiation. Furthermore, chemical inhibition of calmodulin (CaM), Ca²⁺/calmodulin-dependent protein kinase (CaMKII), phospholipase A₂ (PLA2), protein kinase C (PKC), and BMP receptors suggest that Sema3A could serve as a feedback mechanism for both Wnt5A and BMP2. Here, we show novel roles for Sema3A family proteins in the surface-dependent modulation of MSCs as well as important interactions with pathways known to be associated with osteoblastic differentiation. Moreover, their effects on bone remodeling markers have significant implications for peri-implant bone remodeling and downstream modulation of osteoclastic activity. These results suggest that Sema3A aids in peri-implant bone formation through regulation on multiple stages of osseointegration, making it a potential target to promote osseointegration in patients with compromised bone remodeling.

Molecular Events Controlling Cessation of Trunk Neural Crest Migration and Onset of Differentiation

Neural crest cells (NCC) migrate extensively in vertebrate embryos to populate diverse derivatives including ganglia of the peripheral nervous system. Little is known about the molecular mechanisms that lead migrating trunk NCC to settle at selected sites in the embryo, ceasing their migration and initiating differentiation programs. To identify candidate genes involved in these processes, we profiled genes up-regulated in purified post-migratory compared with migratory NCC using a staged, macroarrayed cDNA library. A secondary screen of in situ hybridization revealed that many genes are specifically enhanced in neural crest-derived ganglia, including macrophage migration inhibitory factor (MIF), a ligand for CXCR4 receptor. Through in vivo and in vitro assays, we found that MIF functions as a potent chemoattractant for NCC. These results provide a molecular profile of genes expressed concomitant with gangliogenesis, thus, offering new markers and potential regulatory candidates involved in cessation of migration and onset of differentiation.

Identification of cis -Regulatory Region Controlling Semaphorin-1a Expression in the Drosophila Embryonic Nervous System

The Drosophila transmembrane semaphorin Sema-1a mediates forward and reverse signaling that plays an essential role in motor and central nervous system (CNS) axon pathfinding during embryonic neural development. Previous immunohistochemical analysis revealed that Sema-1a is expressed on most commissural and longitudinal axons in the CNS and five motor nerve branches in the peripheral nervous system (PNS). However, Sema-1a-mediated axon guidance function contributes significantly to both intersegmental nerve b (ISNb) and segmental nerve a (SNa), and slightly to ISNd and SNc, but not to ISN motor axon pathfinding. Here, we uncover three cis-regulatory elements (CREs), R34A03, R32H10, and R33F06, that robustly drove reporter expression in a large subset of neurons in the CNS. In the transgenic lines R34A03 and R32H10 reporter expression was consistently observed on both ISNb and SNa nerve branches, whereas in the line R33F06 reporter expression was irregularly detected on ISNb or SNa nerve branches in small subsets of abdominal hemisegments. Through complementation test with a Sema1a loss-of-function allele, we found that neuronal expression of Sema-1a driven by each of R34A03 and R32H10 restores robustly the CNS and PNS motor axon guidance defects observed in Sema-1a homozygous mutants. However, when wild-type Sema-1a is expressed by R33F06 in Sema-1a mutants, the Sema-1a PNS axon guidance phenotypes are partially rescued while the Sema-1a CNS axon guidance defects are completely rescued. These results suggest that in a redundant manner, the CREs, R34A03, R32H10, and R33F06 govern the Sema-1a expression required for the axon guidance function of Sema-1a during embryonic neural development.

Involvement of the synaptotagmin/stonin2 system in vesicular transport regulated by semaphorins in Caenorhabditis elegans epidermal cells

Vesicular transport serves as an important mechanism for cell shape regulation during development. Although the semaphorin signaling molecule, a well-known regulator of axon guidance, induces endocytosis in the growth cone and the axonal transport of vertebrate neurons, the underlying molecular mechanisms remain largely unclear. Here, we show that the Caenorhabditis elegans SNT-1/synaptotagmin-UNC-41/stonin2 system, whose role in synaptic vesicle recycling in neurons has been studied extensively, is involved in semaphorin-regulated vesicular transport in larval epidermal cells. Mutations in the snt-1/unc-41 genes strongly suppressed the cell shape defects of semaphorin mutants. The null mutation in the semaphorin receptor gene, plx-1, altered the expression and localization pattern of endocytic and exocytic markers in the epidermal cells while repressing the transport of SNT-1-containing vesicles toward late endosome/lysosome pathways. Our findings suggest that the nematode semaphorins regulate the vesicular transport in epidermal cells in a manner distinct from that of vertebrate semaphorins in neurons.

The guidance receptor plexin D1 is a mechanosensor in endothelial cells

Shear stress on arteries produced by blood flow is important for vascular development and homeostasis but can also initiate atherosclerosis1. Endothelial cells that line the vasculature use molecular mechanosensors to directly detect shear stress profiles that will ultimately lead to atheroprotective or atherogenic responses2. Plexins are key cell-surface receptors of the semaphorin family of cell-guidance signalling proteins and can regulate cellular patterning by modulating the cytoskeleton and focal adhesion structures3-5. However, a role for plexin proteins in mechanotransduction has not been examined. Here we show that plexin D1 (PLXND1) has a role in mechanosensation and mechanically induced disease pathogenesis. PLXND1 is required for the response of endothelial cells to shear stress in vitro and in vivo and regulates the site-specific distribution of atherosclerotic lesions. In endothelial cells, PLXND1 is a direct force sensor and forms a mechanocomplex with neuropilin-1 and VEGFR2 that is necessary and sufficient for conferring mechanosensitivity upstream of the junctional complex and integrins. PLXND1 achieves its binary functions as either a ligand or a force receptor by adopting two distinct molecular conformations. Our results establish a previously undescribed mechanosensor in endothelial cells that regulates cardiovascular pathophysiology, and provide a mechanism by which a single receptor can exhibit a binary biochemical nature.

Antitumor Effects of Anti-Semaphorin 4D Antibody Unravel a Novel Proinvasive Mechanism of Vascular-Targeting Agents

One of the main consequences of inhibition of neovessel growth and vessel pruning produced by angiogenesis inhibitors is increased intratumor hypoxia. Growing evidence indicates that tumor cells escape from this hypoxic environment to better nourished locations, presenting hypoxia as a positive stimulus for invasion. In particular, anti-VEGF/R therapies produce hypoxia-induced invasion and metastasis in a spontaneous mouse model of pancreatic neuroendocrine cancer (PanNET), RIP1-Tag2. Here, a novel vascular-targeting agent targeting semaphorin 4D (Sema4D) demonstrated impaired tumor growth and extended survival in the RIP1-Tag2 model. Surprisingly, although there was no induction of intratumor hypoxia by anti-Sema4D therapy, the increase in local invasion and distant metastases was comparable with the one produced by VEGFR inhibition. Mechanistically, the antitumor effect was due to an alteration in vascular function by modification of pericyte coverage involving platelet-derived growth factor B. On the other hand, the aggressive phenotype involved a macrophage-derived Sema4D signaling engagement, which induced their recruitment to the tumor invasive fronts and secretion of stromal cell-derived factor 1 (SDF1) that triggered tumor cell invasive behavior via CXCR4. A comprehensive clinical validation of the targets in different stages of PanNETs demonstrated the implication of both Sema4D and CXCR4 in tumor progression. Taken together, we demonstrate beneficial antitumor and prosurvival effects of anti-Sema4D antibody but also unravel a novel mechanism of tumor aggressivity. This mechanism implicates recruitment of Sema4D-positive macrophages to invasive fronts and their secretion of proinvasive molecules that ultimately induce local tumor invasion and distant metastasis in PanNETs. SIGNIFICANCE: An anti-semaphorin-4D vascular targeting agent demonstrates antitumor and prosurvival effects but also unravels a novel promalignant effect involving macrophage-derived SDF1 that promotes tumor invasion and metastasis, both in animal models and patients.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/20/5328/F1.large.jpg.See related commentary by Tamagnone and Franzolin, p. 5146.

Semaphorin/neuropilin binding specificities are stable over 400 million years of evolution

Semaphorins are a large and important family of signaling molecules conserved in Bilateria. An important determinant of the biological function of their largest class, the secreted class 3 semaphorins, is the specificity of their binding to neuropilins, a key component of a larger holoreceptor complex. We compared these binding specificities in mice and zebrafish, species whose most recent common ancestor was more than 400 million years in the past. We also compared the binding specificities of zebrafish class 3 semaphorins that were duplicated very early within the teleost lineage. We found a surprising conservation of neuropilin binding specificities when comparing both paralogous zebrafish semaphorin pairs and orthologous zebrafish and mouse semaphorin pairs. This finding was further supported by a remarkable conservation of binding specificities in cross-species pairings of semaphorins and neuropilins. Our results suggest that the qualitative specificities with which particular semaphorins bind to particular neuropilins has remained nearly invariant over approximately 400 million years of evolution.

Neuropilin-2 contributes to tumor progression in preclinical models of small intestinal neuroendocrine tumors

The identification of novel regulators of tumor progression is a key challenge to gain knowledge on the biology of small intestinal neuroendocrine tumors (SI-NETs). We recently identified the loss of the axon guidance protein semaphorin 3F as a protumoral event in SI-NETs. Interestingly the expression of its receptor neuropilin-2 (NRP-2) was still maintained. This study aimed at deciphering the potential role of NRP-2 as a contributor to SI-NET progression. The role of NRP-2 in SI-NET progression was addressed using an approach integrating human tissue and serum samples, cell lines and in vivo models. Data obtained from human SI-NET tissues showed that membranous NRP-2 expression is present in a majority of tumors, and is correlated with invasion, metastatic abilities, and neovascularization. In addition, NRP-2 soluble isoform was found elevated in serum samples from metastatic patients. In preclinical mouse models of NET progression, NRP-2 silencing led to a sustained antitumor effect, partly driven by the downregulation of VEGFR2. In contrast, its ectopic expression conferred a gain of aggressiveness, driven by the activation of various oncogenic signaling pathways. Lastly, NRP-2 inhibition led to a decrease of tumor cell viability, and sensitized to therapeutic agents. Overall, our results point out NRP-2 as a potential therapeutic target for SI-NETs, and will foster the development of innovative strategies targeting this receptor. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Sema3E is required for migration of cranial neural crest cells in zebrafish: Implications for the pathogenesis of CHARGE syndrome

CHARGE syndrome is a congenital disorder with multiple malformations in the craniofacial structures, and cardiovascular and genital systems, which are mainly affected by neural crest defects caused by loss-of-function mutations within chromodomain helicase DNA-binding protein 7 (CHD7). However, many patients with CHARGE syndrome test negative for CHD7. Semaphorin 3E (sema3E) is a gene reported to be mutated in patients with CHARGE syndrome. However, its role in the pathogenesis of CHARGE syndrome has not been verified experimentally. Here, we report that the knockdown of sema3E results in severe craniofacial malformations, including small eyes, defective cartilage and an abnormal number of otoliths in zebrafish embryos, which resemble the major features of CHARGE syndrome. Further analysis reveals that the migratory cranial neural crest cells are scattered in the region of the hindbrain, and the postmigratory neural crest cells are reduced in the pharyngeal arches upon sema3E knockdown. Notably, immunostaining and time-lapse imaging analyses of a neural crest cell-labelled transgenic fish line, sox10:EGFP, show that the migration of cranial neural crest cells is severely impaired, and many of these cells are misrouted upon sema3E knockdown. Furthermore, the sox10-expressing cranial neural crest cells are scattered in chd7 homozygous mutants, which phenocopied the phenotype in sema3E morphants. Overexpression of sema3E rescues the phenotype of scattered cranial neural crest cells in chd7 homozygotes, indicating that chd7 may control the expression of sema3E to regulate cranial neural crest cell migration. Collectively, our data demonstrate that sema3E is involved in the pathogenesis of CHARGE syndrome by modulating cranial neural crest cell migration.

Semaphorin-5B Controls Spiral Ganglion Neuron Branch Refinement during Development

During nervous system development, axons often undergo elaborate changes in branching patterns before circuits have achieved their mature patterns of innervation. In the auditory system, type I spiral ganglion neurons (SGNs) project their peripheral axons into the cochlear epithelium and then undergo a process of branch refinement before forming synapses with sensory hair cells. Here, we report that Semaphorin-5B (Sema5B) acts as an important mediator of this process. During cochlear development in mouse, immature hair cells express Sema5B, whereas the SGNs express both PlexinA1 and PlexinA3, which are known Sema5B receptors. In these studies, genetic sparse labeling and three-dimensional reconstruction techniques were leveraged to determine the morphologies of individual type I SGNs after manipulations of Sema5B signaling. Treating cultured mouse cochleae with Sema5B-Fc (to activate Plexin-As) led to type I SGNs with less numerous, but longer terminal branches. Conversely, cochleae from Sema5b knock-out mice showed type I SGNs with more numerous, but shorter terminal branches. In addition, conditional loss of Plxna1 in SGNs (using Bhlhb5Cre) led to increased type I SGN branching, suggesting that PlexinA1 normally responds to Sema5B in this process. In these studies, mice of either sex were used. The data presented here suggest that Sema5B-PlexinA1 signaling limits SGN terminal branch numbers without causing axonal repulsion, which is a role that distinguishes Sema5B from other Semaphorins in cochlear development.SIGNIFICANCE STATEMENT The sensorineural components of the cochlea include hair cells, which respond mechanically to sound waves, and afferent spiral ganglion neurons (SGNs), which respond to glutamate released by hair cells and transmit auditory information into the CNS. An important component of synapse formation in the cochlea is a process of SGN "debranching" whereby SGNs lose extraneous branches before developing unramified bouton endings that contact the hair cells. In this work, we have found that the transmembrane ligand Semaphorin-5B and its receptor PlexinA1 regulate the debranching process. The results in this report provide new knowledge regarding the molecular control of cochlear afferent innervation.

Modulation of Nerve Cell Differentiation: Role of Polyphenols and of Contactin Family Components

In this study the mechanisms are explored, which modulate expression and function of cell surface adhesive glycoproteins of the Immunoglobulin Supergene Family (IgSF), and in particular of its Contactin subset, during neuronal precursor developmental events. In this context, a specific topic concerns the significance of the expression profile of such molecules and their ability to modulate signaling pathways activated through nutraceuticals, in particular polyphenols, administration. Both in vitro and in vivo approaches are chosen. As for the former, by using as a model the human SH-SY5Y neuroblastoma line, the effects of grape seed polyphenols are evaluated on proliferation and commitment/differentiation events along the neuronal lineage. In SH-SY5Y cell cultures, polyphenols were found to counteract precursor proliferation while promoting their differentiation, as deduced by studying their developmental parameters through the expression of cell cycle and neuronal commitment/differentiation markers as well as by measuring neurite growth. In such cultures, Cyclin E expression and BrdU incorporation were downregulated, indicating reduced precursor proliferation while increased neuronal differentiation was inferred from upregulation of cell cycle exit (p27^–Kip) and neuronal commitment (NeuN) markers as well as by measuring neurite length through morphometric analysis. The polyphenol effects on developmental parameters were also explored in vivo, in cerebellar cortex, by using as a model the TAG/F3 transgenic line, which undergoes delayed neural development as a consequence of Contactin1 adhesive glycoprotein upregulation and premature expression under control of the Contactin2 gene (Cntn-2) promoter. In this transgenic line, a Notch pathway activation is known to occur and polyphenol treatment was found to counteract such an effect, demonstrated through downregulation of the Hes-1 transcription factor. Polyphenols also downregulated the expression of adhesive glycoproteins of the Contactin family themselves, demonstrated for both Contactin1 and Contactin2, indicating the involvement of changes in the expression of the underlying genes in the observed phenotype. These data support the hypothesis that the complex control exerted by polyphenols on neural development involves modulation of expression and function of the genes encoding cell adhesion molecules of the Contactin family and of the associated signaling pathways, indicating potential mechanisms whereby such compounds may control neurogenesis.

PKC induces release of a functional ectodomain of the guidance cue semaphorin6A

Semaphorins (Semas) are a family of secreted and transmembrane proteins that play critical roles in development. Interestingly, several vertebrate transmembrane Sema classes are capable of producing functional soluble ectodomains. However, little is known of soluble Sema6 ectodomains in the nervous system. Herein, we show that the soluble Sema6A ectodomain, sSema6A, exhibits natural and protein kinase C (PKC)-induced release. We show that PKC mediates Sema6A phosphorylation at specific sites and while this phosphorylation is not the primary mechanism regulating sSema6A production, we found that the intracellular domain confers resistance to ectodomain release. Finally, sSema6A is functional as it promotes the cohesion of zebrafish early eye field explants. This suggests that in addition to its canonical contact-mediated functions, Sema6A may have regulated, long-range, forward-signaling capacity.

The Order of Cancer: A Theory of Malignant Progression by Inverse Morphogenesis

Local spread patterns of malignant tumors follow permissive tissue territories, i.e., cancer fields, as shown for cervical and vulvar carcinoma. The cancer fields are associated in reverse order to the mature derivatives of the morphogenetic fields instrumental in the stepwise development of the tissue from which the tumor arose. This suggests that cancer progression may be linked to morphogenesis by inversion of the cellular bauplan sequence. Successive attractor transitions caused by proliferation-associated constraints of topobiological information processing are proposed for both morphogenesis and cancer. In morphogenesis these transitions sequentially activate bauplans with increasing complexity at decreasing plasticity restricting the permissive territories of the progenitor cell populations. Somatic mutations leading to cell proliferation in domains normally reserved for differentiation trigger the inverse cascade of bauplan changes that increase topobiological plasticity at decreased complexity and stepwise enlarge the permissive territory of neoplastic cells consistent with the clinical manifestations of cancer. The order provided by the sequence of attractor transitions and the defined topography of the permissive territories can be exploited for more accurate tumor staging and for locoregional tumor treatment either by surgery or radiotherapy with higher curative potential.

Semaphorins and Their Receptors in Hematological Malignancies

While semaphorins were initially identified as axonal guidance cues for wiring the neural network, it was then recognized their wide relevance in tissue development and homeostasis. Notably, semaphorin activities were also extensively studied in many types of solid tumors; however, their relevance in hematological malignancies is far from understood. In this mini-review, we surveyed the current knowledge about semaphorins and their receptors in leukemias, lymphomas, and multiple myeloma. Noteworthy, current data support a promoting role for Semaphorin 4D and Neuropilin-1 in these tumors, while Semaphorin 3A seems to consistently act as oncosuppressor in leukemias and multiple myeloma. The expression levels and functional activities of SEMA3B, SEMA3F, and Neuropilin-2 have furthermore been investigated in leukemias and lymphoma cells. Herein, we reviewed the state of the art and highlighted some of the open questions to be addressed in the field.

Neurite Outgrowth and Morphological Changes Induced by 8-trans Unsaturation of Sphingadienine in kCer Molecular Species

Konjac ceramide (kCer), which consists of plant-type molecular species of characteristic shingoid bases and fatty acids, is prepared from konjac glucosylceramide GlcCer by chemoenzymatical deglucosylation. kCer activates the semaphorin 3A (Sema3A) signaling pathway, inducing collapsin response mediator protein 2 (CRMP2) phosphorylation. This results in neurite outgrowth inhibition and morphological changes in remaining long neurites in PC12 cells. Whether a specific molecular species of kCer can bind to the Sema3A receptor (Neuropilin1, Nrp1) and activate the Sema3A signaling pathway remains unknown. Here, we prepared kCer molecular species using endoglycoceramidase I-mediated deglucosylation and examined neurite outgrowth and phosphorylation of collapsin response mediator protein 2 in nerve growth factor (NGF)-primed cells. The 8-trans unsaturation of sphingadienine of kCer was essential for Sema3A-like signaling pathway activation. Conversely, 8-cis unsaturation of kCer molecular species had no effect on Sema3A-like activation, and neurite outgrowth inhibition resulted in remaining short neurites. In addition, α-hydroxylation of fatty acids was not associated with the Sema3A-like activity of the kCer molecular species. These results suggest that 8-trans or 8-cis isomerization of sphingadienine determines the specific interactions at the ligand-binding site of Nrp1.

Coupling factors involved in preserving bone balance

Coupling during bone remodeling refers to the spatial and temporal coordination of bone resorption with bone formation. Studies have assessed the subtle interactions between osteoclasts and osteoblasts to preserve bone balance. Traditionally, coupling research related to osteoclast function has focused on bone resorption activity causing the release of growth factors embedded in the bone matrix. However, considerable evidence from in vitro, animal, and human studies indicates the importance of the osteoclasts themselves in coupling phenomena, and many osteoclast-derived coupling factors have been identified. These include sphingosine-1-phosphate, vesicular-receptor activator of nuclear factor-κB, collagen triple helix repeat containing 1, and cardiotrophin-1. Interestingly, neuronal guidance molecules, such as slit guidance ligand 3, semaphorin (SEMA) 3A, SEMA4D, and netrin-1, originally identified as instructive cues allowing the navigation of growing axons to their targets, have been shown to be involved in the intercellular cross-talk among bone cells. This review discusses osteoclast-osteoblast coupling signals, including recent advances and the potential roles of these signals as therapeutic targets for osteoporosis and as biomarkers predicting human bone health.

Planar-Polarized Semaphorin-5c and Plexin A Promote the Collective Migration of Epithelial Cells in Drosophila

Collective migration of epithelial cells is essential for morphogenesis, wound repair, and the spread of many cancers, yet how individual cells signal to one another to coordinate their movements is largely unknown. Here, we introduce a tissue-autonomous paradigm for semaphorin-based regulation of collective cell migration. Semaphorins typically regulate the motility of neuronal growth cones and other migrating cell types by acting as repulsive cues within the migratory environment. Studying the follicular epithelial cells of Drosophila, we discovered that the transmembrane semaphorin, Sema-5c, promotes collective cell migration by acting within the migrating cells themselves, not the surrounding environment. Sema-5c is planar polarized at the basal epithelial surface such that it is enriched at the leading edge of each cell. This location places it in a prime position to send a repulsive signal to the trailing edge of the cell ahead to communicate directional information between neighboring cells. Our data show that Sema-5c can signal across cell-cell boundaries to suppress protrusions in neighboring cells and that Plexin A is the receptor that transduces this signal. Finally, we present evidence that Sema-5c antagonizes the activity of Lar, another transmembrane guidance cue that operates along leading-trailing cell-cell interfaces in this tissue, via a mechanism that appears to be independent of Plexin A. Together, our results suggest that multiple transmembrane guidance cues can be deployed in a planar-polarized manner across an epithelium and work in concert to coordinate individual cell movements for collective migration.

Functions of Plexins/Neuropilins and Their Ligands during Hippocampal Development and Neurodegeneration

There is emerging evidence that molecules, receptors, and signaling mechanisms involved in vascular development also play crucial roles during the development of the nervous system. Among others, specific semaphorins and their receptors (neuropilins and plexins) have, in recent years, attracted the attention of researchers due to their pleiotropy of functions. Their functions, mainly associated with control of the cellular cytoskeleton, include control of cell migration, cell morphology, and synapse remodeling. Here, we will focus on their roles in the hippocampal formation that plays a crucial role in memory and learning as it is a prime target during neurodegeneration.

hnRNP Q Regulates Internal Ribosome Entry Site-Mediated fmr1 Translation in Neurons

Fragile X syndrome (FXS) caused by loss of fragile X mental retardation protein (FMRP), is the most common cause of inherited intellectual disability. Numerous studies show that FMRP is an RNA binding protein that regulates translation of its binding targets and plays key roles in neuronal functions. However, the regulatory mechanism for FMRP expression is incompletely understood. Conflicting results regarding internal ribosome entry site (IRES)-mediated fmr1 translation have been reported. Here, we unambiguously demonstrate that the fmr1 gene, which encodes FMRP, exploits both IRES-mediated translation and canonical cap-dependent translation. Furthermore, we find that heterogeneous nuclear ribonucleoprotein Q (hnRNP Q) acts as an IRES-transacting factor (ITAF) for IRES-mediated fmr1 translation in neurons. We also show that semaphorin 3A (Sema3A)-induced axonal growth cone collapse is due to upregulation of hnRNP Q and subsequent IRES-mediated expression of FMRP. These data elucidate the regulatory mechanism of FMRP expression and its role in axonal growth cone collapse.

Remarkable complexity and variability of corticospinal tract defects in adult Semaphorin 6A knockout mice

The corticospinal tract (CST) has a complex and long trajectory that originates in the cerebral cortex and ends in the spinal cord. Semaphorin 6A (Sema6A), a member of the semaphorin family, is an important regulator of CST axon guidance. Previous studies have shown that postnatal Sema6A mutant mice have CST defects at the midbrain-hindbrain boundary and medulla. However, the routes the aberrant fibers take throughout the Sema6A mutant brain remain unknown. In this study, we performed 3D reconstruction of immunostained CST fibers to reevaluate the details of the abnormal CST trajectories in the brains of adult Sema6A mutant mice. Our results showed that the axon guidance defects reported in early postnatal mutants were consistently observed in adulthood. Those abnormal trajectories revealed by 3D analysis of brain sections were, however, more complex and variable than previously thought. In addition, 3D analysis allowed us to identify a few new patterns of aberrant projections. First, a subset of fibers that separated from and descended in parallel to the main bundle projected laterally at the caudal pons, subsequently changed direction by turning caudally, and extended to the medulla. Second, some abnormal fibers returned to the correct trajectory after deviating substantially from the original tract. Third, some fibers reached the pyramidal decussation normally but did not enter the dorsal funiculus. Section immunostaining combined with 3D reconstruction is a powerful method to track long projection fibers and to examine the entire nerve tracts of both normal and abnormal animals.

Investigation of the effects of semaphorin 3A on new bone formation in a rat calvarial defect model

PURPOSE

This study investigates the effects of semaphorin 3A on new bone formation in an experimental rat model.

MATERIALS AND METHODS

Cortical bone defects, 5 mm, were created in the calvaria of 40 Wistar rats, which were then separated into three groups: empty defect (control) group, collagen group, collagen + semaphorin 3A group. The bone blocks were harvested after 4 and 8 weeks. New bone formation was assessed by micro-computed tomography (micro-CT), histology, histomorphometry, transmission electron microscope (TEM) and immunohistochemistry.

RESULTS

Increased bone formation was observed in collagen + semaphorin 3A groups both histologically and with micro-CT. In the histomorphometic analysis, the control group had significantly less bone formation compared to both the collagen and collagen + semaphorin 3A group at 4 weeks (p = 0.0001) and 8 weeks (p = 0.0001). The collagen group had significantly less bone formation compared to collagen + semaphorin 3A group both at 4 weeks (p = 0.002) and 8 weeks (p = 0.005). Immunohistochemical analysis revealed that semaphorin 3A inhibited receptor activator of nuclear factor-kB ligand (RANKL) expression and increased the expressions of osteoblastic bone markers at 4 weeks. In TEM analysis, the collagen + semaphorin 3A group had an increased proliferation and bone formation rate at 4 weeks, whereas bone quantity and maturation were enhanced at 8 weeks.

CONCLUSION

Locally applied semaphorin 3A increases callus formation at 4 weeks and bone formation at 8 weeks. Semaphorin 3A prevents bone resorption by inhibiting osteoclasts and increases bone formation by inducing osteoblasts.

The polarity protein VANG-1 antagonizes Wnt signaling by facilitating Frizzled endocytosis

Signaling that instructs the migration of neurons needs to be tightly regulated to ensure precise positioning of neurons and subsequent wiring of the neuronal circuits. Wnt-Frizzled signaling controls neuronal migration in metazoans, in addition to many other aspects of neural development. We show that Caenorhabditis elegans VANG-1, a membrane protein that acts in the planar cell polarity (PCP) pathway, antagonizes Wnt signaling by facilitating endocytosis of the Frizzled receptors. Mutations of vang-1 suppress migration defects of multiple classes of neurons in the Frizzled mutants, and overexpression of vang-1 causes neuronal migration defects similar to those of the Frizzled mutants. Our genetic experiments suggest that VANG-1 facilitates Frizzled endocytosis through β-arrestin2. Co-immunoprecipitation experiments indicate that Frizzled proteins and VANG-1 form a complex, and this physical interaction requires the Frizzled cysteine-rich domain. Our work reveals a novel mechanism mediated by the PCP protein VANG-1 that downregulates Wnt signaling through Frizzled endocytosis.

The Sema3A receptor Plexin-A1 suppresses supernumerary axons through Rap1 GTPases

The highly conserved Rap1 GTPases perform essential functions during neuronal development. They are required for the polarity of neuronal progenitors and neurons as well as for neuronal migration in the embryonic brain. Neuronal polarization and axon formation depend on the precise temporal and spatial regulation of Rap1 activity by guanine nucleotide exchange factors (GEFs) and GTPases-activating proteins (GAPs). Several Rap1 GEFs have been identified that direct the formation of axons during cortical and hippocampal development in vivo and in cultured neurons. However little is known about the GAPs that limit the activity of Rap1 GTPases during neuronal development. Here we investigate the function of Sema3A and Plexin-A1 as a regulator of Rap1 GTPases during the polarization of hippocampal neurons. Sema3A was shown to suppress axon formation when neurons are cultured on a patterned substrate. Plexin-A1 functions as the signal-transducing subunit of receptors for Sema3A and displays GAP activity for Rap1 GTPases. We show that Sema3A and Plexin-A1 suppress the formation of supernumerary axons in cultured neurons, which depends on Rap1 GTPases.

Class 4 Semaphorins and Plexin-B receptors regulate GABAergic and glutamatergic synapse development in the mammalian hippocampus

To understand how proper circuit formation and function is established in the mammalian brain, it is necessary to define the genes and signaling pathways that instruct excitatory and inhibitory synapse development. We previously demonstrated that the ligand-receptor pair, Sema4D and Plexin-B1, regulates inhibitory synapse development on an unprecedentedly fast time-scale while having no effect on excitatory synapse development. Here, we report previously undescribed synaptogenic roles for Sema4A and Plexin-B2 and provide new insight into Sema4D and Plexin-B1 regulation of synapse development in rodent hippocampus. First, we show that Sema4a, Sema4d, Plxnb1, and Plxnb2 have distinct and overlapping expression patterns in neurons and glia in the developing hippocampus. Second, we describe a requirement for Plexin-B1 in both the presynaptic axon of inhibitory interneurons as well as the postsynaptic dendrites of excitatory neurons for Sema4D-dependent inhibitory synapse development. Third, we define a new synaptogenic activity for Sema4A in mediating inhibitory and excitatory synapse development. Specifically, we demonstrate that Sema4A signals through the same pathway as Sema4D, via the postsynaptic Plexin-B1 receptor, to promote inhibitory synapse development. However, Sema4A also signals through the Plexin-B2 receptor to promote excitatory synapse development. Our results shed new light on the molecular cues that promote the development of either inhibitory or excitatory synapses in the mammalian hippocampus.

Semaphorin 3A as an inhibitive factor for migration of olfactory ensheathing cells through cofilin activation is involved in formation of olfactory nerve layer

Olfactory ensheathing cells (OECs) migrate from olfactory epithelium towards olfactory bulb (OB), contributing to formation of the presumptive olfactory nerve layer during development. However, it remains unclear that molecular mechanism of regulation of OEC migration in OB. In the present study, we found that OECs highly expressed the receptors of semaphorin 3A (Sema3A) in vitro and in vivo, whereas Sema3A displayed a gradient expression pattern with higher in inner layer of OB and lower in outer layer of OB. Furthermore, the collapse assays, Boyden chamber migration assays and single-cell migration assays showed that Sema3A induced the collapse of leading front of OECs and inhibited OEC migration. Thirdly, the leading front of OECs exhibited adaptation in a protein synthesis-independent manner, and endocytosis-dependent manner during Sema3A-induced OEC migration. Finally, Sema3A-induced collapse of leading front was required the decrease of focal adhesion and a retrograde F-actin flow in a cofilin activation-dependent manner. Taken together, these results demonstrate that Sema3A as an inhibitive migratory factor for OEC migration through cofilin activation is involved in the formation of olfactory nerve layer.

Inhibition of semaphorin-3a suppresses lipopolysaccharide-induced acute kidney injury

Semaphorin-3a (Sema3A), a soluble axon guidance cue, appears to play an important role in the development of acute kidney injury (AKI) and has been regarded as an early diagnostic marker to evaluate the progression of AKI. However, the role of Sema3A in sepsis-associated AKI remains unknown. In this study, lipopolysaccharide (LPS) was used to simulate sepsis-associated AKI and the role of Sema3A in LPS-induced AKI was investigated in vivo and in vitro. In our in vivo study, Sema3A was found in tubular epithelial cells (TECs), which presented a higher level after LPS treatment. Meanwhile, the results of our in vitro experiment showed that Sema3A was also elevated in NRK-52E cells treated by LPS. Notably, inhibition of Sema3A by (-)-epigallocatechin-3-gallate (EGCG) could significantly reduce kidney inflammation and apoptosis in mice. Likewise, EGCG intervention also ameliorated the inflammation and apoptosis of cells in vitro. Furthermore, our research also found that the Rac1/NF-κB p65 and JNK pathways were possibly involved in the Sema3A-mediated inflammation and apoptosis of TECs, respectively. Our findings suggest that Sema3A play a pathogenic role by promoting inflammation and apoptosis of TECs in LPS-induced AKI. It might serve as a useful treatment target in ameliorating sepsis-associated AKI. KEY MESSAGES: Sema3A is upregulated in LPS-induced AKI. Inhibition of Sema3A attenuates inflammation and apoptosis of TECs in LPS-induced AKI. Sema3A enhances the LPS-induced inflammation of TECs through the Rac1/NF-κB p65 pathway. Sema3A exacerbates the LPS-induced apoptosis of TECs through the JNK pathway.

Understanding axon guidance: are we nearly there yet?

During nervous system development, neurons extend axons to reach their targets and form functional circuits. The faulty assembly or disintegration of such circuits results in disorders of the nervous system. Thus, understanding the molecular mechanisms that guide axons and lead to neural circuit formation is of interest not only to developmental neuroscientists but also for a better comprehension of neural disorders. Recent studies have demonstrated how crosstalk between different families of guidance receptors can regulate axonal navigation at choice points, and how changes in growth cone behaviour at intermediate targets require changes in the surface expression of receptors. These changes can be achieved by a variety of mechanisms, including transcription, translation, protein-protein interactions, and the specific trafficking of proteins and mRNAs. Here, I review these axon guidance mechanisms, highlighting the most recent advances in the field that challenge the textbook model of axon guidance.

The Extracellular Environment of the CNS: Influence on Plasticity, Sprouting, and Axonal Regeneration after Spinal Cord Injury

The extracellular environment of the central nervous system (CNS) becomes highly structured and organized as the nervous system matures. The extracellular space of the CNS along with its subdomains plays a crucial role in the function and stability of the CNS. In this review, we have focused on two components of the neuronal extracellular environment, which are important in regulating CNS plasticity including the extracellular matrix (ECM) and myelin. The ECM consists of chondroitin sulfate proteoglycans (CSPGs) and tenascins, which are organized into unique structures called perineuronal nets (PNNs). PNNs associate with the neuronal cell body and proximal dendrites of predominantly parvalbumin-positive interneurons, forming a robust lattice-like structure. These developmentally regulated structures are maintained in the adult CNS and enhance synaptic stability. After injury, however, CSPGs and tenascins contribute to the structure of the inhibitory glial scar, which actively prevents axonal regeneration. Myelin sheaths and mature adult oligodendrocytes, despite their important role in signal conduction in mature CNS axons, contribute to the inhibitory environment existing after injury. As such, unlike the peripheral nervous system, the CNS is unable to revert to a “developmental state” to aid neuronal repair. Modulation of these external factors, however, has been shown to promote growth, regeneration, and functional plasticity after injury. This review will highlight some of the factors that contribute to or prevent plasticity, sprouting, and axonal regeneration after spinal cord injury.

Wnt Signalling Drives Context-Dependent Differentiation or Proliferation in Neuroblastoma

Neuroblastoma is one of the commonest and deadliest solid tumours of childhood, and is thought to result from disrupted differentiation of the developing sympathoadrenergic lineage of the neural crest. Neuroblastoma exhibits intra- and intertumoural heterogeneity, with high risk tumours characterised by poor differentiation, which can be attributable to MYCN-mediated repression of genes involved in neuronal differentiation. MYCN is known to co-operate with oncogenic signalling pathways such as Alk, Akt and MEK/ERK signalling, and, together with c-MYC has been shown to be activated by Wnt signalling in various tissues. However, our previous work demonstrated that Wnt3a/Rspo2 treatment of some neuroblastoma cell lines can, paradoxically, decrease c-MYC and MYCN proteins. This prompted us to define the neuroblastoma-specific Wnt3a/Rspo2-driven transcriptome using RNA sequencing, and characterise the accompanying changes in cell biology. Here we report the identification of ninety Wnt target genes, and show that Wnt signalling is upstream of numerous transcription factors and signalling pathways in neuroblastoma. Using live-cell imaging, we show that Wnt signalling can drive differentiation of SK-N-BE(2)-C and SH-SY5Y cell-lines, but, conversely, proliferation of SK-N-AS cells. We show that cell-lines that differentiate show induction of pro-differentiation BMP4 and EPAS1 proteins, which is not apparent in the SK-N-AS cells. In contrast, SK-N-AS cells show increased CCND1, phosphorylated RB and E2F1 in response to Wnt3a/Rspo2, consistent with their proliferative response, and these proteins are not increased in differentiating lines. By meta-analysis of the expression of our 90 genes in primary tumour gene expression databases, we demonstrate discrete expression patterns of our Wnt genes in patient cohorts with different prognosis. Furthermore our analysis reveals interconnectivity within subsets of our Wnt genes, with one subset comprised of novel putative drivers of neuronal differentiation repressed by MYCN. Assessment of β-catenin immunohistochemistry shows high levels of β-catenin in tumours with better differentiation, further supporting a role for canonical Wnt signalling in neuroblastoma differentiation.

Design and validation of an ontology-driven animal-free testing strategy for developmental neurotoxicity testing

Developmental neurotoxicity entails one of the most complex areas in toxicology. Animal studies provide only limited information as to human relevance. A multitude of alternative models have been developed over the years, providing insights into mechanisms of action. We give an overview of fundamental processes in neural tube formation, brain development and neural specification, aiming at illustrating complexity rather than comprehensiveness. We also give a flavor of the wealth of alternative methods in this area. Given the impressive progress in mechanistic knowledge of human biology and toxicology, the time is right for a conceptual approach for designing testing strategies that cover the integral mechanistic landscape of developmental neurotoxicity. The ontology approach provides a framework for defining this landscape, upon which an integral in silico model for predicting toxicity can be built. It subsequently directs the selection of in vitro assays for rate-limiting events in the biological network, to feed parameter tuning in the model, leading to prediction of the toxicological outcome. Validation of such models requires primary attention to coverage of the biological domain, rather than classical predictive value of individual tests. Proofs of concept for such an approach are already available. The challenge is in mining modern biology, toxicology and chemical information to feed intelligent designs, which will define testing strategies for neurodevelopmental toxicity testing.

Semaphorin 3A enhances osteogenesis of MG63 cells through interaction with Schwann cells in vitro

Bone remodeling is under the control of various signals and systems in the body, including the nervous system. Semaphorin (Sema) 3A is a chemorepellent protein which regulates bone mass. Schwann cells, having a pivotal role following nerve injury, interact with Sema3A under numerous circumstances. The present study established a co‑culture system of MG63 and Schwann cells to investigate the role of the interaction between Sema3A and Schwann cells in osteogenesis. The results from the alkaline phosphatase assay, calcium nodule staining and the analysis of the osteogenic gene expression revealed that Sema3A inhibits osteogenic differentiation of MG63 cells in single‑cell culture and promotes osteogenic differentiation of MG63 cells in co‑culture with Schwann cells, in a concentration‑dependent manner. These findings suggest that the presence of Schwann cells induces Sema3A‑associated osteogenic differentiation in bone cells, and also reveals the pivotal role of Sema3A as a regulator in the skeletal and nervous systems, thus contributing to a better understanding of the interaction between these systems.

hiPSC-derived neural stem cells from patients with schizophrenia induce an impaired angiogenesis

Schizophrenia is a neurodevelopmental disease characterized by cerebral connectivity impairment and loss of gray matter. It was described in adult schizophrenia patients (SZP) that concentration of VEGFA, a master angiogenic factor, is decreased. Recent evidence suggests cerebral hypoperfusion related to a dysfunctional Blood Brain Barrier (BBB) in SZP. Since neurogenesis and blood-vessel formation occur in a coincident and coordinated fashion, a defect in neurovascular development could result in increased vascular permeability and, therefore, in poor functionality of the SZP's neurons. Here, we characterized the conditioned media (CM) of human induced Pluripotent Stem Cells (hiPSC)-derived Neural Stem Cells of SZP (SZP NSC) versus healthy subjects (Ctrl NSC), and its impact on angiogenesis. Our results reveal that SZP NSC have an imbalance in the secretion and expression of several angiogenic factors, among them non-canonical neuro-angiogenic guidance factors. SZP NSC migrated less and their CM was less effective in inducing migration and angiogenesis both in vitro and in vivo. Since SZP originates during embryonic brain development, our findings suggest a defective crosstalk between NSC and endothelial cells (EC) during the formation of the neuro-angiogenic niche.

Semaphorins and their Signaling Mechanisms

Semaphorins are extracellular signaling proteins that are essential for the development and maintenance of many organs and tissues. The more than 20-member semaphorin protein family includes secreted, transmembrane and cell surface-attached proteins with diverse structures, each characterized by a single cysteine-rich extracellular sema domain, the defining feature of the family. Early studies revealed that semaphorins function as axon guidance molecules, but it is now understood that semaphorins are key regulators of morphology and motility in many different cell types including those that make up the nervous, cardiovascular, immune, endocrine, hepatic, renal, reproductive, respiratory and musculoskeletal systems, as well as in cancer cells. Semaphorin signaling occurs predominantly through Plexin receptors and results in changes to the cytoskeletal and adhesive machinery that regulate cellular morphology. While much remains to be learned about the mechanisms underlying the effects of semaphorins, exciting work has begun to reveal how semaphorin signaling is fine-tuned through different receptor complexes and other mechanisms to achieve specific outcomes in various cellular contexts and physiological systems. These and future studies will lead to a more complete understanding of semaphorin-mediated development and to a greater understanding of how these proteins function in human disease.

Increased expression of Semaphorin 3A in the endothelin receptor-B null mouse model of Hirschsprung disease

PURPOSE

Semaphorins are guidance cues for developing neurons, implicated in the determination of the migratory pathway of neural crest-derived neural precursors during enteric nervous system development. Recently, it has been reported that Semaphorin 3A (SEMA3A) expression is up-regulated in the aganglionic colon in Hirschsprung disease (HD) patients, suggesting that increased SEMA3A expression may be a risk factor for HD. Thus, the aim of our study was to determine the expression of SEMA3A using Sox10-Venus mice gut.

METHODS

We harvested the gut on postnatal day 2 (P2). SOX10-Venus+/EDNRB^-/- mice were compared with SOX10-Venus+/EDNRB^+/+ mice as controls. QRT-PCR was performed to determine gene expression of SEMA3A (n=8). Fluorescent immunohistochemistry was performed to assess protein distribution.

RESULTS

On P2, gene expression levels of SEMA3A were significantly increased in the HD group compared to controls in the proximal and distal colon (p<0.05). Laser scanning microscopy revealed SEMA3A expression was localized within the submucosa and muscle layer of the gut in both HD and controls. In HD, SEMA3A was highly expressed in the proximal and distal colon.

CONCLUSIONS

In the present study, we demonstrated that SEMA3A expression is increased in the EDNRB-/- HD model on P2, suggesting that SEMA3A may interfere with ENCC migration, resulting in an absence of enteric neurons.

Konjac Ceramide (kCer) Regulates NGF-Induced Neurite Outgrowth via the Sema3A Signaling Pathway

The tuber of the konjac plant is a source enriched with GlcCer (kGlcCer), and has been used as a dietary supplement to improve the dry skin and itching that are caused by a deficiency of epidermal ceramide. Previously, we showed chemoenzymatically prepared konjac ceramide has a neurite-outgrowth inhibitory effect that is very similar to that of Sema3A and is not seen with animal-type ceramides. While, it has been unclear whether kCer may act on Sema3A or TrkA signaling pathway. In the present study, we showed kCer induces phosphorylation of CRMP2 and microtubules depolymerization via Sema3A signaling pathway not TrkA. It is concluded that kCer may be a potential Sema3A-like agonist that activates Sema3A signaling pathway directly.

Overexpression of semaphorin 3A in patients with urothelial cancer

OBJECTIVE

A highly sensitive and specific urine marker for the detection of recurrent urothelial cancer and for screening healthy population or people at risk for urothelial cancer has not been found yet. As urine cytology is not sensitive enough, patients with non-muscle-invasive bladder cancer need lifelong follow-up involving multiple invasive cystoscopies. Our aims of study were to examine the expression of semaphorin 3A in urothelial cancer patients and to evaluate semaphorin 3A as a potential marker for urothelial cancer.

MATERIALS AND METHODS

Urine samples were taken from patients with known bladder tumor, hospitalized for transurethral resection of lesions, from patients with history of urothelial cancer admitted for endoscopic follow up, from patients with other nonmalignant urological conditions such as prostatic hyperplasia, stress incontinence, urethral stricture, ureteral and kidney stones, and from healthy volunteers with no history of urothelial malignancy and no urological symptoms. Semaphorin 3A (sema3A) protein level was measured using enzyme-linked immunosorbent assay in every sample and levels were correlated with endoscopic and pathological findings. In addition, we performed immunohistochemically staining with semaphorin 3A of 15 tissue samples (various tumors and normal bladder tissues).

RESULTS

A total of 183 urine samples were tested. Out of them, 116 patients (mean age 70.7; 94 males and 22 females) had positive cystoscopy, and 67 (mean age 64.7; 51 males and 16 females) had negative cystoscopy. Higher sema3A values were significantly correlated (P = 0.006) with presence of urothelial cancer, as determined by positive cystoscopy or urethroscopy and pathological biopsy. Sema3A levels also showed positive correlation with the number of tumors. Sema3A levels combined with urine cytology showed much higher sensitivity compared with cytology alone (66% vs. 33%), with smaller reduction of specificity (77% vs. 90%). Immunohistochemical staining showed intense staining in high stage and grade tumors, and almost no staining in normal tissue.

CONCLUSIONS

Semaphorin 3A is overexpressed in urothelial cancer patients, as evidenced both in its presence in urine and in bladder tissue. Semaphorin 3A in urine is a promising potential urothelial cancer biomarker either independently or in conjunction with cytology. Further tests are needed to elucidate the sex difference in the expression of Sema3A in the urine of bladder cancer patients.

Sema-1a Reverse Signaling Promotes Midline Crossing in Response to Secreted Semaphorins

Commissural axons must cross the midline to form functional midline circuits. In the invertebrate nerve cord and vertebrate spinal cord, midline crossing is mediated in part by Netrin-dependent chemoattraction. Loss of crossing, however, is incomplete in mutants for Netrin or its receptor Frazzled/DCC, suggesting the existence of additional pathways. We identified the transmembrane Semaphorin, Sema-1a, as an important regulator of midline crossing in the Drosophila CNS. We show that in response to the secreted Semaphorins Sema-2a and Sema-2b, Sema-1a functions as a receptor to promote crossing independently of Netrin. In contrast to other examples of reverse signaling where Sema1a triggers repulsion through activation of Rho in response to Plexin binding, in commissural neurons Sema-1a acts independently of Plexins to inhibit Rho to promote attraction to the midline. These findings suggest that Sema-1a reverse signaling can elicit distinct axonal responses depending on differential engagement of distinct ligands and signaling effectors.