Sema4D is diminished in leukocyte platelet-rich fibrin and impairs pre-osteoblastic MC3T3-E1 cells' functionality

OBJECTIVE

Semaphorin 4D (Sema4D) is a coupling factor expressed on osteoclasts that may hinder osteoblast differentiation. Since the leukocyte platelet-rich fibrin (L-PRF) membrane promotes growth factor concentration, this study aims to quantify the amount of Sema4D in L-PRF membranes, and analyze the impact of Sema4D on osteoblast cell function in vitro.

DESIGN

Enzyme-linked immunosorbent assay (ELISA) was used to quantify the levels of Sema4D in both L-PRF and whole blood (serum). To analyze the impairment of Sema4D on osteoblasts, MC3T3-E1 cells were induced to osteogenic differentiation and exposed to Sema4D ranging from 10 to 500 ng/ml concentrations. The following parameters were assayed: 1) cell viability by MTT assay after 24, 48, and 72 h; 2) matrix mineralization by Alizarin Red staining after 14 days, 3) Runt-related transcription factor 2 (RUNX-2), osteocalcin (OCN), osteonectin (ONC), bone sialoprotein (BSP) and alkaline phosphatase (ALP) gene expression by qPCR. For all data, the significance level was set at 5%.

RESULTS

The amount of Sema4D in the whole blood (serum) was higher than in L-PRF. Osteoblasts exposed to Sema4D at all tested concentrations exhibited a decrease in matrix mineralization formation as well in RUNX-2, OCN, ONC, BSP, and ALP gene expression (p < 0.05).

CONCLUSION

The presence of Sema4D, a molecule known for suppressing osteoblast activity, diminishes within L-PRF, enhancing its ability to facilitate bone regeneration.

Inhibition of the Semaphorin 4D-Plexin-B1 axis prevents calcification in vascular smooth muscle cells

Vascular calcification is common in cardiovascular diseases including atherosclerosis, and is associated with an increased risk of pathological events and mortality. Some semaphorin family members play an important role in atherosclerosis. In the present study, we show that Semaphorin 4D/Sema4D and its Plexin-B1 receptor were significantly upregulated in calcified aorta of a rat chronic kidney disease model. Significantly higher Sema4D and Plexin-B1 expression was also observed during inorganic phosphate-induced calcification of vascular smooth muscle cells. Knockdown of Sema4D or Plexin-B1 genes attenuated both the phosphate-induced osteogenic phenotype of vascular smooth muscle cells, through regulation of SMAD1/5 signaling, as well as apoptosis of vascular smooth muscle cells, through modulation of the Gas6/Axl/Akt survival pathway. Taken together, our results offer new insights on the role of Sema4D and Plexin-B1 as potential therapeutic targets against vascular calcification. [BMB Reports 2023; 56(3): 160-165].

The dual role of boron in vitro neurotoxication of glioblastoma cells via SEMA3F/NRP2 and ferroptosis signaling pathways

Glioblastoma multiform (GBM) is a malignant tumor cancer that originates from the star-shaped glial support tissues, namely astrocytes, and it is associated with a poor prognosis in the brain. The GBM has no cure, and chemotherapy, radiation therapy, and immunotherapy are all ineffective. A certain dose of Boric acid (BA) has many biochemical effects, conspicuously over antioxidant/oxidant rates. This article sought to investigate the modifies of various doses of BA on the glioblastoma concerning cytotoxicity, ferroptosis, apoptosis, and semaphorin-neuropilin signaling pathway. The Cytotoxic activity and cell viability of BA (0.39-25 mM) in C6 cells were tested at 24, 48, and 72 h using 3-(4,5-dimethylthiazol, 2-yl)-2,5-diphenyl tetrazolium bromide (MTT). The IC₅₀ concentration of BA at 1.56 mM was found and cell lysate used for biochemical analysis. Glutathione peroxidase 4 (GPx4) and ACLS4 levels of ferroptosis, levels of total antioxidant (TAS) and oxidant (TAS) parameters, malondialdehyde (MDA), apoptotic proteins as caspase 3 (CASP3) and caspase 7 (CASP7) were measured. The ferroptosis, semaphoring-neuropilin, apoptotic pathway markers and cell counts were analyzed with flow cytometry, Q-PCR, Western and Elisa technique in the C6 cell lysate. BA triggered ferroptosis in the C6 cells dose-dependently, affecting the semaphorin pathway, so reducing proliferation with apoptotic compared with untreated cell as control group (p < .05). This study revealed that BA, defined as trace element and natural compound, incubated ferroptosis, total oxidant molecules, and caspase protein in a dose-dependently by disrupting SEMA3F in tumor cells.

Exogenous Semaphorin 3E treatment protects against chlamydial lung infection in mice

Recent studies reported that semaphorins play a significant role in various settings of the immune response. In particular, Semaphorin 3E (Sema3E), a secreted semaphorin protein, is involved in cell proliferation, migration, inflammatory responses, and host defence against infections. However, the therapeutic function of Sema3E in bacterial infection has not been investigated. Our data showed that exogenous Sema3E treatment protects mice from chlamydial infection with lower bacterial burden, reduced body weight loss, and pathological lung changes. Cytokine analysis in the lung and spleen revealed that Sema3E-Fc treated mice, compared to saline-Fc treated mice, showed enhanced production of IFN-γ and IL-17 but reduced IL-4 and IL-10 production. Cellular analysis showed that Sema3E treatment leads to enhanced Th1/Th17 response but reduced Treg response in lungs following chlamydial infection. Moreover, Sema3E treatment also enhanced the recruitment of pulmonary dendritic cells, which express higher co-stimulatory but lower inhibitory surface molecules. The data demonstrate that Sema3E plays a vital role in protective immunity against chlamydial lung infection, mainly through coordinating functions of T cells and DCs.

TG-interacting factor 1 (Tgif1)-deficiency attenuates bone remodeling and blunts the anabolic response to parathyroid hormone

Osteoporosis is caused by increased bone resorption and decreased bone formation. Intermittent administration of a fragment of Parathyroid hormone (PTH) activates osteoblast-mediated bone formation and is used in patients with severe osteoporosis. However, the mechanisms by which PTH elicits its anabolic effect are not fully elucidated. Here we show that the absence of the homeodomain protein TG-interacting factor 1 (Tgif1) impairs osteoblast differentiation and activity, leading to a reduced bone formation. Deletion of Tgif1 in osteoblasts and osteocytes decreases bone resorption due to an increased secretion of Semaphorin 3E (Sema3E), an osteoclast-inhibiting factor. Tgif1 is a PTH target gene and PTH treatment failed to increase bone formation and bone mass in Tgif1-deficient mice. Thus, our study identifies Tgif1 as a novel regulator of bone remodeling and an essential component of the PTH anabolic action. These insights contribute to a better understanding of bone metabolism and the anabolic function of PTH.

Semaphorin 4A Stabilizes Human Regulatory T Cell Phenotype via Plexin B1

We previously reported that neuroimmune semaphorin (Sema) 4A regulates the severity of experimental allergic asthma and increases regulatory T (Treg) cell numbers in vivo; however, the mechanisms of Sema4A action remain unknown. It was also reported that Sema4A controls murine Treg cell function and survival acting through neuropilin 1 (NRP-1) receptor. To clarify Sema4A action on human T cells, we employed T cell lines (HuT78 and HuT102), human PBMCs, and CD4+ T cells in phenotypic and functional assays. We found that HuT78 demonstrated a T effector-like phenotype (CD4+CD25lowFoxp3-), whereas HuT102 expressed a Treg-like phenotype (CD4+CD25hi Foxp3+). Neither cell line expressed NRP-1. HuT102 cells expressed Sema4A counter receptor Plexin B1, whereas HuT78 cells were Sema4A+. All human peripheral blood CD4+ T cells, including Treg cells, expressed PlexinB1 and lacked both NRP-1 and -2. However, NRP-1 and Sema4A were detected on CD3negativeCD4intermediate human monocytes. Culture of HuT cells with soluble Sema4A led to an upregulation of CD25 and Foxp3 markers on HuT102 cells. Addition of Sema4A increased the relative numbers of CD4+CD25+Foxp3+ cells in PBMCs and CD4+ T cells, which were NRP-1negative but PlexinB1+, suggesting the role of this receptor in Treg cell stability. The inclusion of anti-PlexinB1 blocking Ab in cultures before recombinant Sema4A addition significantly decreased Treg cell numbers as compared with cultures with recombinant Sema4A alone. Sema4A was as effective as TGF-β in inducible Treg cell induction from CD4+CD25depleted cells but did not enhance Treg cell suppressive activity in vitro. These results suggest strategies for the development of new Sema4A-based therapeutic measures to combat allergic inflammatory diseases. ImmunoHorizons, 2019, 3: 71-87.

A monitoring system for axonal growth dynamics using micropatterns of permissive and Semaphorin 3F chemorepulsive signals

Neurons reach their correct targets by directional outgrowth of axons, which is mediated by attractive or repulsive cues. Growing axons occasionally cross a field of repulsive cues and stop at intermediate targets on the journey to their final destination. However, it is not well-understood how individual growth cones make decisions, and pass through repulsive territory to reach their permissive target regions. We developed a microcontact printing culture system that could trap individual axonal tips in a permissive dot area surrounded by the repulsive signal, semaphorin 3F (Sema3F). Axons of rat hippocampal neurons on the Sema3F/PLL dot array extended in the checkboard pattern with a significantly slow growth rate. The detailed analysis of the behaviors of axonal growth cones revealed the saccadic dynamics in the dot array system. The trapped axonal tips in the permissive area underwent growth cone enlargement with remarkably spiky filopodia, promoting their escape from the Sema3F constraints with straight extension of axons. This structured axonal growth on the dot pattern was disrupted by increased inter-dot distance, or perturbing intracellular signaling machineries. These data indicate that axons grow against repulsive signals by jumping over the repulsive cues, depending on contact signals and intracellular milieu. Our study suggests that our dot array culture system can be used as a screening system to easily and efficiently evaluate ECM or small molecule inhibitors interfering growth cone dynamics leading to controlling axonal growth.

Neurotrophin Promotes Neurite Outgrowth by Inhibiting Rif GTPase Activation Downstream of MAPKs and PI3K Signaling

Members of the well-known semaphorin family of proteins can induce both repulsive and attractive signaling in neural network formation and their cytoskeletal effects are mediated in part by small guanosine 5'-triphosphatase (GTPases). The aim of this study was to investigate the cellular role of Rif GTPase in the neurotrophin-induced neurite outgrowth. By using PC12 cells which are known to cease dividing and begin to show neurite outgrowth responding to nerve growth factor (NGF), we found that semaphorin 6A was as effective as nerve growth factor at stimulating neurite outgrowth in PC12 cells, and that its neurotrophic effect was transmitted through signaling by mitogen-activated protein kinases (MAPKs) and phosphatidylinositol-3-kinase (PI3K). We further found that neurotrophin-induced neurite formation in PC12 cells could be partially mediated by inhibition of Rif GTPase activity downstream of MAPKs and PI3K signaling. In conclusion, we newly identified Rif as a regulator of the cytoskeletal rearrangement mediated by semaphorins.

A Sema3C Mutant Resistant to Cleavage by Furin (FR-Sema3C) Inhibits Choroidal Neovascularization

In age-related macular degeneration (AMD), abnormal sub retinal choroidal neovascularization (CNV) is a major cause of blindness. FR-sema3C is a point mutated form of semaphorin-3C that is resistant to cleavage by furin like pro-protein convertases (FPPC). We have found in previous work that FR-sema3C functions as an anti-angiogenic factor. In this study we investigated the possible use of FR-sema3C as an inhibitor of CNV. FR-sema3C inhibits VEGF as well as PDGF-BB signal transduction in endothelial cells and to less extent bFGF induced signal transduction using a mechanism that does not depend upon the binding of VEGF like the drugs that are currently the mainstay treatment for AMD. CNV was induced in eyes of C57 black mice by laser photocoagulation. Intravitreal injection of FR-Sema3C or aflibercept (VEGF-trap) was then used to inhibit CNV formation. Invading choroidal vessels were visualized a week later by injection of FITC-dextran into the circulation, followed by the measurement of the area of the invading blood vessels. Injection of 0.1 μg FR-Sema3C inhibited CNV by 55% (P<0.01) and was as effective as 5 μg aflibercept. FR-sema3C did not display any adverse effects on retinal function following its injection into eyes of healthy mice as assessed by optokinetic reflex (OKR) and Electro-retinogram (ERG) criteria. Furthermore, FR-sema3C did not induce apoptosis in the retina as determined by TUNEL nor was there any discernable structural damage to the retina as assessed by several immuno-histochemical criteria. Our results suggest that FR-sema3C could perhaps be used for the treatment of AMD, and that it may perhaps be of benefit to patients that do not respond well to current treatments relying on VEGF sequestering agents.

Semaphorin 4A enhances lung fibrosis through activation of Akt via PlexinD1 receptor

Semaphorin 4A plays a regulatory role in immune function and angiogenesis. However, its specific involvement in controlling lung fibrosis, a process that is closely related to angiogenesis and inflammation is still poorly understood. In the present study, we show that treatment of Sema4A on normal lung fibroblasts induces expression of proteins that contribute to a contractile phenotype, including alpha-smooth muscle actin (alpha-SMA), ezrin, moesin, and paxillin. We confirm that Sema4A enhances the ability of lung fibroblasts to contract collagen gel. Sema4A treatment led to resistance to apoptosis in normal lung fibroblasts. Relative to normal lung fibroblasts, fibroblasts cultured from scars of patients with the fibrotic disease Systemic Sclerosis (SSc) showed elevated Sema4A secretion, enhanced alpha-SMA, ezrin, moesin, and paxillin expression, and high ability to induce collagen gel contraction. Using neutralizing antibody against Sema4A receptor, PlexinD1, we found that endogenous Sema4A signalling in SSc fibroblast was through PlexinD1 receptor. We then identified the signalling mechanism through which Sema4A-PlexinD1 promotes the ability of normal fibroblasts to contract a collagen gel matrix. Western blot analysis showed that Sema4A activated the Akt pathway in lung fibroblasts, and the specific inhibitor of Akt pathway, Akt inhibitor III, blocked the ability of Sema4A to promote the ability of lung fibroblasts to contract a collagen gel matrix. Thus, blocking Sema4APlexinD1- Akt cascades might be beneficial in reducing pulmonary fibrosis.

Semaphorin 3C Released from a Biocompatible Hydrogel Guides and Promotes Axonal Growth of Rodent and Human Dopaminergic Neurons

Cell therapy in experimental models of Parkinson's disease replaces the lost dopamine neurons (DAN), but we still need improved methods to guide dopaminergic axons (DAx) of grafted neurons to make proper connections. The protein Semaphorin 3C (Sema3C) attracts DAN axons and enhances their growth. In this work, we show that the hydrogel PuraMatrix, a self-assembling peptide-based matrix, incorporates Sema3C and releases it steadily during 4 weeks. We also tested if hydrogel-delivered Sema3C attracts DAx using a system of rat midbrain explants embedded in collagen gels. We show that Sema3C released by this hydrogel attracts DAx, in a similar way to pretectum, which is known to attract growing DAN axons. We assessed the effect of Sema3C on the growth of DAx using microfluidic devices. DAN from rat midbrain or those differentiated from human embryonic stem cells showed enhanced axonal extension when exposed to hydrogel-released Sema3C, similar to soluble Sema3C. Notably, DAN of human origin express the cognate Sema3C receptors, Neuropilin1 and Neuropilin2. These results show that PuraMatrix is able to incorporate and release Sema3C, and such delivery guides and promotes the axonal growth of DAN. This biocompatible hydrogel might be useful as a Sema3C carrier for in vivo studies in parkinsonian animal models.

Recombinant semaphorin 6A-1 ectodomain inhibits in vivo growth factor and tumor cell line-induced angiogenesis

The Semaphorins are a large family of transmembrane, GPI-anchored and secreted proteins that play an important role in neuronal and endothelial cell guidance. A human gene related to the class 6 Semaphorin family, Semaphorin 6A-1 (Sema 6A-1) was identified by homology-based genomic mining. Recent implication of Sema 3 family members in tumor angiogenesis and our expression analysis of Sema 6A-1 suggested that class 6 Semaphorin might effect tumor neovascularization. The mRNA expression of Sema 6A-1 was elevated in several renal tumor tissue samples relative to adjacent nontumor tissue samples from the same patient. Sema 6A-1 transcript was also expressed in the majority of renal clear cell carcinoma (RCC) cell lines and to a lesser extent in endothelial cells. To test the role of Sema 6A-1 in tumor angiogenesis, we engineered, expressed and purified the Sema 6A-1 soluble extracellular domain (Sema-ECD). The purified Sema-ECD was screened in a variety of endothelial cell-based assays both in vitro and in vivo. In vitro, Sema-ECD blocked VEGF-mediated endothelial cell migration. These effects were explained in part by our observation in endothelial cells that Sema-ECD inhibited VEGF-mediated Src, FAK and ERK phosphorylation. In vivo, mouse Matrigel assays demonstrated that the intraperitoneal administration of recombinant Sema-ECD inhibited both bFGF/VEGF and tumor cell line-induced neovascularization. These findings reveal a novel therapeutic utility for Sema 6A-1 (Sema-ECD) as an inhibitor of growth factor as well as tumor-induced angiogenesis.

[Sema4A as a biomarker predicting responsiveness to IFN β treatment]

Approximately one-third of patients with multiple sclerosis (MS) exhibit markedly high-level-expression of Sema4A. The expression of Sema4A is increased on DCs in MS patients and shed from these cells in a metalloproteinase-dependent manner. DC-derived Sema4A is critical for Th17 cell differentiation, and MS patients with high Sema4A levels exhibit Th17 skewing. Furthermore, patients with high Sema4A levels have more severe disabilities and are unresponsive to IFN-β treatment. We investigated whether recombinant Sema4A abrogates the efficacy of IFN-β in mice with experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Administration of Sema4A concurrently with IFN-β abrogated the efficacy of IFN-β. These effects of Sema4A were attributed to promote Th1 and Th17 differentiation and to increase adhesive activation of T cells to endothelial cells, even in the presence of IFN-β.Thus unresponsiveness to IFN-β treatment of MS patients with high Sema4A was also confirmed by model mice EAE. We recommend assaying Sema4A first, and then selecting DMD other than IFN-β for patients with high Sema4A.

Semaphorin 3E suppresses tumor cell death triggered by the plexin D1 dependence receptor in metastatic breast cancers

The semaphorin guidance molecules and their receptors, the plexins, are often inappropriately expressed in cancers. However, the signaling processes mediated by plexins in tumor cells are still poorly understood. Here, we demonstrate that the Semaphorin 3E (Sema3E) regulates tumor cell survival by suppressing an apoptotic pathway triggered by the Plexin D1 dependence receptor. In mouse models of breast cancer, a ligand trap that sequesters Sema3E inhibited tumor growth and reduced metastasis through a selective tumor cytocidal effect. We further showed that Plexin D1 triggers apoptosis via interaction with the orphan nuclear receptor NR4A1. These results define a critical role of Sema3E/Plexin D1 interaction in tumor resistance to apoptosis and suggest a therapeutic approach based on activation of a dependence receptor pathway.

Class 3 semaphorin mediates dendrite growth in adult newborn neurons through Cdk5/FAK pathway

Class 3 semaphorins are well-known axonal guidance cues during the embryonic development of mammalian nervous system. However, their activity on postnatally differentiated neurons in neurogenic regions of adult brains has not been characterized. We found that silencing of semaphorin receptors neuropilins (NRP) 1 or 2 in neural progenitors at the adult mouse dentate gyrus resulted in newly differentiated neurons with shorter dendrites and simpler branching in vivo. Tyrosine phosphorylation (Tyr 397) and serine phosphorylation (Ser 732) of FAK were essential for these effects. Semaphorin 3A and 3F mediate serine phosphorylation of FAK through the activation of Cdk5. Silencing of either Cdk5 or FAK in newborn neurons phenocopied the defects in dendritic development seen upon silencing of NRP1 or NRP2. Furthermore, in vivo overexpression of Cdk5 or FAK rescued the dendritic phenotypes seen in NRP1 and NRP2 deficient neurons. These results point to a novel role for class 3 semaphorins in promoting dendritic growth and branching during adult hippocampal neurogenesis through the activation of Cdk5-FAK signaling pathway.

Plexin-B1 activates NF-κB and IL-8 to promote a pro-angiogenic response in endothelial cells

Background

The semaphorins and their receptors, the plexins, are proteins related to c-Met and the scatter factors that have been implicated in an expanding signal transduction network involving co-receptors, RhoA and Ras activation and deactivation, and phosphorylation events. Our previous work has demonstrated that Semaphorin 4D (Sema4D) acts through its receptor, Plexin-B1, on endothelial cells to promote angiogenesis in a RhoA and Akt-dependent manner. Since NF-κB has been linked to promotion of angiogenesis and can be activated by Akt in some contexts, we wanted to examine NF-κB in Sema4D treated cells to determine if there was biological significance for the pro-angiogenic phenotype observed in endothelium.

Methods/Principal Findings

Using RNA interference techniques, gel shifts and NF-κB reporter assays, we demonstrated NF-κB translocation to the nucleus in Sema4D treated endothelial cells occurring downstream of Plexin-B1. This response was necessary for endothelial cell migration and capillary tube formation and protected endothelial cells against apoptosis as well, but had no effect on cell proliferation. We dissected Plexin-B1 signaling with chimeric receptor constructs and discovered that the ability to activate NF-κB was dependent upon Plexin-B1 acting through Rho and Akt, but did not involve its role as a Ras inhibitor. Indeed, inhibition of Rho by C3 toxin and Akt by LY294002 blocked Sema4D-mediated endothelial cell migration and tubulogenesis. We also observed that Sema4D treatment of endothelial cells induced production of the NF-κB downstream target IL-8, a response necessary for angiogenesis. Finally, we could show through co-immunofluorescence for p65 and CD31 that Sema4D produced by tumor xenografts in nude mice activated NF-κB in vessels of the tumor stroma.

Conclusion/Significance

These findings provide evidence that Sema4D/Plexin-B1-mediated NF-κB activation and IL-8 production is critical in the generation a pro-angiogenic phenotype in endothelial cells and suggests a new therapeutic target for the anti-angiogenic treatment of some cancers.

Polyelectrolyte multilayer-mediated gene delivery for semaphorin signaling pathway control

The capability of multilayered polyelectrolyte films (MPFs) to control the sequential expression of two genes encoding cell receptors involved in a common cell signalling activity is shown, while achieving a fully functional signal transduction. As a functional model system representative of a cell signalling process that proceeds in a top-down manner, cell collapse induced by semaphorin 3A (Sema3A) was chosen as the target. Polyelectrolyte multilayers were sequentially functionalized with two plasmids encoding Neuropilin-1 (NRP-1) and Plexin-A1 (Plx-A1), respectively, acting as co-receptors for Sema3A. By using hyaluronan and chitosan as structural components for the incorporation of plasmid DNA layers onto precursor films made of poly-allylamine hydrochloride and poly-sodium-4-styrenesulfonate, the polyelectrolyte system is established; this systems is capable of delivering both plasmids to Cos-1 cells in a manner that permits control over the timing and the respective order in which the two plasmid DNA constructs are expressed. Importantly, it was observed that, following Sema3A stimulation, COS-1 cells co-expressing Plx-A1 and NRP-1 display a collapse phenotype, which is determined by the multilayer build-up scheme, and that the expression products of both transgenes embedded in MPFs are temporally functional over several days while acting their role of co-receptors for Sema3A.

Sema4A induces cell morphological changes through B-type plexin-mediated signaling

Semaphorins are a family of secreted and membrane-bound proteins known as axonal pathfinders. Sema4A, a member of class 4 semaphorins, induces growth cone collapse of hippocampal neurons. The binding of Sema4A to growth cones indicates the presence of receptors transmitting signals through the intracellular effectors to induce growth cone collapse in hippocampal neurons. Transfection experiments of the candidate receptor genes into COS-7 cells demonstrated that Sema4A binds to axonal guidance receptors Plexin-B1, -B2 and -B3. To identify the functional Sema4A receptor and the signal transduction machinery, COS-7 cell contraction assay was performed, in which intracellular signal transmission induced by Sema4A triggered cell contraction. Expression vectors encoding plexins and Rnd1, a Rho family GTPase, were transfected into COS-7 cells, and a proportion of contracted cells among the transfectants was determined after incubation with Sema4A. The results demonstrated that the combination of Rnd1 and Plexin-B1, -B2 or -B3 induced significant cell contraction, indicating that B-type plexins transmit an intracellular signal of Sema4A through Rnd1. To further study the mechanism of B-type plexin-mediated signaling in Sema4A-induced growth cone collapse, mouse hippocampal neurons transfected with a control or expression plasmid encoding a constitutively active mutant of R-Ras (R-RasQL) were stimulated with Sema4A, followed by the assessment of growth cone collapse. Expression of R-RasQL significantly blocked Sema4A-induced growth cone collapse in the hippocampal neurons compared with the control plasmid. Sema4A thus induces growth cone collapse through the down-regulation of R-Ras activity in mouse hippocampal neurons.

Combined activation of calpain and calcineurin during ligand-induced growth cone collapse

Calcium plays a key role during growth cone collapse. Recently, it has been proposed that low- and high-amplitude rises in [Ca(2+)](i) result in the activation of the neurite outgrowth inhibiting proteins calcineurin and calpain, respectively. However, it remains unknown if and how these mechanisms are modulated by specific guidance cues. Here we report that the inhibitory cue Semaphorin 5B induces growth cone collapse by promoting the influx of extracellular Ca(2+). The resulting rise in [Ca(2+)](i) is characterized by a low-amplitude increase followed by a marked secondary rise, suggesting the potential involvement of both calcineurin and calpain. In support of this, inhibition of either effector attenuated Sema5B-induced collapse, a result that was augmented by the simultaneous inhibition of both targets. Furthermore, we provide evidence that Sema5B induces calpain-mediated cleavage of calcineurin. We thus show for the first time that ligand-induced growth cone collapse can activate both calcineurin- and calpain-mediated pathways concurrently.

Semaphorin-4D (Sema-4D), the Plexin-B1 ligand, is involved in mouse ovary follicular development

BACKGROUND

Human Plexin-B1 is expressed in two truncated forms. The long form encodes a trans-membranal protein, while the short form, which is bound to the cell surface and partially secreted, possibly serves as a decoy receptor. Plexin receptors are trans-membrane proteins. The sema domain, found in the extracellular region, is common to all plexins, semaphorins, and the scatter factor receptors and is crucial for the biological activity and plexin receptor specificity. Semaphorin-4D/Plexin-B1 binding provides attractive and repulsive cues for the navigation of axonal growth cones, and new studies suggest that this system also plays a role in the regulation of the biological functions of endothelial cells, specifically in the control of angiogenesis. In a previous study, we have demonstrated the expression and possible role of Plexin-B1 in the mouse ovary. The present study was designed to test the hypothesis that Plexin-B1 effects are mediated by Semaphorin-4D.

METHODS

In vivo expression and localization of mouse ovarian Sema-4D were tested by immunohisto-chemistry. The role of Sema-4D in follicular development was examined by in vitro growth of preantral follicles in the presence or absence of Semaphorin-4D, with or without neutralizing antibodies against Plexin-B1. Follicular growth and steroid hormone secretion rates were tested.

RESULTS

Semaphorin-4D is expressed in the mouse ovary in vivo mostly in the granulosa cells and and its expression is modulated by PMSG and hCG. In the presence of Semaphorin-4D, in-vitro constant growth was observed as indicated by follicular diameter during the culture period and elevated steroid hormone secretion rates compared with control. These effects were abolished after addition of neutralizing antibodies against Plexin-B1.

CONCLUSION

In the ovarian follicle, the effect of Plexin-B1 is mediated by sema-4D.

Semaphorin 3C regulates endothelial cell function by increasing integrin activity

Class 3 semaphorins (sema 3) are secreted guidance proteins. Sema 3A expressed by endothelial cells controls vascular morphogenesis through integrin inhibition. Sema 3C is required for normal cardiovascular patterning. Here we examined the potential role of sema 3C as regulator of endothelial cell function in vitro using mouse glomerular endothelial cells (MGEC). We determined that MGEC express sema 3C mRNA and protein and its receptors mRNA. Recombinant sema 3C induced MGEC proliferation 18 +/- 2% above control, as assessed by bromodeoxyuridine (BrdU) incorporation, and reduced starvation-induced apoptosis by 46 +/- 3%, as indicated by an in situ marker of activated caspase 3. Sema 3C increased MGEC adhesion to fibronectin 79 +/- 13% and to collagen 55 +/- 12% as compared with control. Sema 3C-induced MGEC adhesion was prevented by integrin blocking antibodies and involved beta1 integrin serine phosphorylation. Sema 3C-induced MGEC adhesion and proliferation were similar to those induced by vascular endothelial growth factor (VEGF)-A. Sema 3C induced a 44 +/- 11% increase in MGEC directional migration and stimulated MGEC capillary-like network formation on collagen I gels. Collectively, our data indicate that sema 3C promotes glomerular endothelial cell proliferation, adhesion, directional migration, and tube formation in vitro by stimulating integrin phosphorylation and VEGF120 secretion, functions that are similar to VEGF-A and opposite to sema 3A.

Nerve growth factor, glial cell line-derived neurotrophic factor and neurturin prevent semaphorin 3A-mediated growth cone collapse in adult sensory neurons

Developmentally, semaphorin 3A (sema3A) is an important chemorepellent that guides centrally projecting axons of dorsal root ganglion (DRG) neurons. Sema3A-mediated growth cone collapse can be prevented by cyclic GMP (cGMP) and nerve growth factor (NGF) in embryonic neurons. Sema3A may also play a role in directing regrowth of injured axons in adults, and interactions with neurotrophic factors near the injury site may determine the extent and targeting of both regenerative and aberrant growth. The aim of this study was to determine whether NGF, glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) modulate sema3A-mediated growth cone collapse in cultured adult rat DRG neurons. Sema3A caused a significant increase in growth cone collapse, which was completely prevented by prior treatment with NGF, GDNF or NTN. Immunocytochemical experiments showed that sema3A-sensitive neurons were heterogeneous in their expression of neurotrophic factor receptors and responses to neurotrophic factors, raising the possibility of novel, convergent signaling mechanisms between these substances. Increasing cGMP levels caused growth cone collapse, whereas sema3A-mediated collapse was prevented by inhibition of guanylate cyclase or by increasing cyclic AMP levels. In conclusion, sema3A signaling pathways in adult neurons differ to those described in embryonic neurons. Three different neurotrophic factors each completely prevent sema3A-mediated collapse, raising the possibility of novel converging signaling pathways. These studies also show that there is considerable potential for neurotrophic factors to regulate sema3A actions in the adult nervous system. This may provide insights into the mechanisms underling misdirected growth and targeting of sensory fibers within the spinal cord after injury, that is thought to contribute to development of autonomic dysreflexia and neuropathic pain.

Semaphorin 4D/Plexin-B1-mediated R-Ras GAP activity inhibits cell migration by regulating beta(1) integrin activity

Plexins are cell surface receptors for semaphorins and regulate cell migration in many cell types. We recently reported that the semaphorin 4D (Sema4D) receptor Plexin-B1 functions as a GTPase-activating protein (GAP) for R-Ras, a member of Ras family GTPases implicated in regulation of integrin activity and cell migration (Oinuma, I., Y. Ishikawa, H. Katoh, and M. Negishi. 2004. Science. 305:862–865). We characterized the role of R-Ras downstream of Sema4D/Plexin-B1 in cell migration. Activation of Plexin-B1 by Sema4D suppressed the ECM-dependent R-Ras activation, R-Ras–mediated phosphatydylinositol 3-kinase activation, and β₁ integrin activation through its R-Ras GAP domain, leading to inhibition of cell migration. In addition, inactivation of R-Ras by overexpression of the R-Ras–specific GAP or knockdown of R-Ras by RNA interference was sufficient for suppressing β₁ integrin activation and cell migration in response to the ECM stimulation. Thus, we conclude that R-Ras activity is critical for ECM-mediated β₁ integrin activation and cell migration and that inactivation of R-Ras by Sema4D/Plexin-B1–mediated R-Ras GAP activity controls cell migration by modulating the activity of β₁ integrins.

Vascular endothelial-derived semaphorin 3 inhibits sympathetic axon growth

Vascular sympathetic innervation is an important determinant of blood pressure and blood flow. The mechanisms that determine vascular sympathetic innervation are not well understood. Recent studies indicate that vascular endothelial cells (EC) express semaphorin 3A, a repulsive axon guidance cue. This suggests that EC would inhibit the growth of axons to blood vessels. The present study tests this hypothesis. RT-PCR and Western analyses confirmed that rat aortic vascular ECs expressed semaphorin 3A as well as other class 3 semaphorins (sema 3s). To determine the effects of EC-derived sema 3 on sympathetic axons, axon outgrowth was assessed in cultures of neonatal sympathetic ganglia grown for 72 h in the absence and presence of vascular EC. Nerve growth factor-induced axon growth in the presence of ECs was 50 +/- 4% (P < 0.05) of growth in the absence of ECs. ECs did not inhibit axon growth in the presence of an antibody that neutralized the activity of sema 3 (P > 0.05). RT-PCR and Western analyses also indicated that sema 3s were expressed in ECs of intact arteries. To assess the function of sema 3s in arteries, sympathetic ganglia were grown in the presence of arteries for 72 h, and the percentage of axons that grew toward the artery was determined: 44 +/- 4% of axons grew toward neonatal carotid arteries. Neutralization of sema 3s or removal of EC increased the percentage of axons that grew toward the artery (71 +/- 8% and 72 +/- 8%, respectively). These data indicate that vascular EC-derived sema 3s inhibit sympathetic axon growth and may thus be a determinant of vascular sympathetic innervation.

p190 Rho-GTPase activating protein associates with plexins and it is required for semaphorin signalling

Plexins are transmembrane receptors for semaphorins, guiding cell migration and axon extension. Plexin activation leads to the disassembly of integrin-based focal adhesive structures and to actin cytoskeleton remodelling and inhibition of cell migration; however, the underlying molecular mechanisms are unclear. We consistently observe a transient decrease of cellular RhoA-GTP levels upon plexin activation in adherent cells. One of the main effectors of RhoA downregulation is p190, a ubiquitously expressed GTPase activating protein (GAP). We show that, in p190-deficient fibroblasts, the typical functional activities mediated by plexins (such as cell collapse and inhibition of integrin-based adhesion) are blocked or greatly impaired. Notably, the functional response can be rescued in these cells by re-expressing exogenous p190, but not a mutant form specifically lacking RhoGAP activity. We furthermore demonstrate that semaphorin function is blocked in epithelial cells, primary endothelial cells and neuroblasts upon treatment with small interfering RNAs that knockdown p190 expression. Finally, we show that p190 transiently associates with plexins, and its RhoGAP activity is increased in response to semaphorin stimulation. We conclude that p190-RhoGAP is crucially involved in semaphorin signalling to the actin cytoskeleton, via interaction with plexins.

Sema4D stimulates axonal outgrowth of embryonic DRG sensory neurones

Several semaphorins are thought to function as potent inhibitors of axonal growth. We have found that Sema4D stimulates axonal outgrowth of embryonic dorsal root ganglion (DRG) neurones in stead of retraction. Neutralizing antibodies to Sema4D inhibit this action. This action appears to differ slightly from that on PC12 cells, because DRG neurones respond to Sema4D without addition of nerve growth factor (NGF), while PC12 cells do not. On the other hand, it is blocked by deprivation of endogenous NGF with antibodies to NGF and also by Trk-inhibitor K252a, suggesting that endogenously produced-NGF and the activation of Trk receptor are required for Sema4D-action on DRG neurones. These indicate that neurite-outgrowth promoting actions of Sema4D are similar between DRG neurones and PC12 cells, since NGF-Trk signalling are required for these actions. Since Schwann cells can produce NGF, the contamination of these cells in our DRG culture might explain this action. In addition to plexin-B1 that is known as a Sema4D receptor, binding experiments indicate plexin-B2 as another receptor candidate for Sema4D. These plexins and Sema4D are expressed in embryonic DRGs. We suggest a new function of Sema4D as a neurite-outgrowth stimulating, autocrine/paracrine factor in embryonic sensory neurones.

Semaphorin-3F Is an Inhibitor of Tumor Angiogenesis

The neuropilin-1 (np1) and neuropilin-2 (np2) receptors form complexes with type-A plexins. These complexes serve as signaling receptors for specific class-3 semaphorins. Np1 and np2 function in addition as receptors for heparin-binding forms of vascular endothelial growth factor (VEGF), such as VEGF(165). Human umbilical vein endothelial cells (HUVEC) express tyrosine-kinase receptors for VEGF and basic fibroblast growth factor (bFGF), as well as np1, np2, and several type-A plexins. We have found that semaphorin-3F (s3f), a semaphorin which signals through the np2 receptor, was able to inhibit VEGF(165), as well as bFGF-induced proliferation of HUVECs. Furthermore, s3f inhibited VEGF as well as bFGF-induced phosphorylation of extracellular signal-regulated kinase-1/2. Our experiments indicate that bFGF does not bind to neuropilins, nor does s3f inhibit the binding of bFGF to FGF receptors. It is therefore possible that s3f inhibits the activity of bFGF by a mechanism that requires active s3f signal transduction rather than by inhibition of bFGF binding to FGF receptors. s3f also inhibited VEGF(165), as well as bFGF-induced in vivo angiogenesis as determined by the alginate micro-encapsulation and Matrigel plug assays. Overexpression of s3f in tumorigenic human HEK293 cells inhibited their tumor-forming ability but not their proliferation in cell culture. The tumors that did develop from s3f-expressing HEK293 cells developed at a much slower rate and had a significantly lower concentration of tumor-associated blood vessels, indicating that s3f is an inhibitor of tumor angiogenesis.

Neurites from trigeminal ganglion explants grown in vitro are repelled or attracted by tooth-related tissues depending on developmental stage

Although neurite attracting factors are present in the developing dental pulp and trigeminal ganglion (TG) axons can respond to such factors, nerve fibres do not enter the tooth pulp until a late developmental stage compared with surrounding tissues supplied by the TG. This suggests that the dental pulp secretes neurite growth inhibitory molecules. Semaphorins represent one group of substances, which can inhibit/repel growing neurites. The aims of the present study were to investigate if dental tissue explants inhibit/repel neurite growth from TGs at some developmental stages in vitro, and if so, to seek evidence for or against a participation of semaphorins in that interaction. By co-culturing mandibular or dental epithelial and mesenchymal tissue explants and TGs in collagen gels, we found that embryonic day 11 (E11) mandibular and E13 dental mesenchymal explants repel neurites from corresponding TGs. Repulsion was replaced by attraction if tissues from late embryonic or early postnatal mice (E17-postnatal day 5) were used. Using semi-quantitative reverse transcription/polymerase chain reaction we showed that a number of semaphorins were expressed by tooth-related mesenchyme collected from embryonic and postnatal mice. The expression of some semaphorins (3A, 3C, 3F, 4F, 5B, 6A, 6B and 6C) was high early in development and then decreased in a temporal pattern that correlated with neurite inhibitory/repulsive effects of dental mesenchyme observed in co-cultures. The expression of other semaphorins increased with development (3B, 4A and 7A), whilst others varied irregularly or remained at a fairly constant level (3E, 4B, 4C, 4D, 4G and 5A). Immunohistochemistry was used to determine if tooth-related nerve fibres possess neuropilins. This revealed that axons surrounding embryonic tooth buds express neuropilin-1, but not neuropilin-2. In postnatal teeth, nerve fibres located within the tooth pulp were immunonegative for neuropilin-1 and neuropilin-2. We conclude that developing mandibular/dental mesenchyme can inhibit/repel neurite growth in vitro. Our results support the hypothesis that semaphorins may be involved in this interaction.

Semaphorin SEMA3F and VEGF have opposing effects on cell attachment and spreading

SEMA3F, isolated from a 3p21.3 deletion, has antitumor activity in transfected cells, and protein expression correlates with tumor stage and histology. In primary tumors, SEMA3F and VEGF surface staining is inversely correlated. Coupled with SEMA3F at the leading edge of motile cells, we previously suggested that both proteins competitively regulate cell motility and adhesion. We have investigated this using the breast cancer cell line, MCF7. SEMA3F inhibited cell attachment and spreading as evidenced by loss of lamellipodia extensions, membrane ruffling, and cell-cell contacts, with cells eventually rounding-up and detaching. In contrast, VEGF had opposite effects. Although SEMA3F binds NRP2 with 10-fold greater affinity than NRP1, the effects in MCF7 were mediated by NRP1. This was determined by receptor expression and blocking of anti-NRP1 antibodies. Similar effects, but through NRP2, were observed in the C100 breast cancer cell line. Although we were unable to demonstrate changes in total GTP-bound Rac1 or RhoA, we did observe changes in the localization of Rac1-GFP using time lapse microscopy. Following SEMA3F, Rac1 moved to the base of lamellipodia and - with their collapse - to the membrane. These results support the concept that SEMA3F and VEGF have antagonistic actions affecting motility in primary tumor cell.