Vascular endothelial growth factor/semaphorin-3A ratio and SEMA3A expression in cutaneous malignant melanoma

Breslow thickness and Clark level are still important factors for cutaneous melanoma, but do not provide a precise prognosis in all cases. It is necessary to find new factors capable of a more accurate prediction of the tumor course. Angiogenesis is essential for tumor development and progression and is regulated by vascular endothelial growth factor A (VEGF-A) and semaphorins (SEMA), in particular, SEMA3A inhibits angiogenesis by affecting VEGF signaling. However, the prognostic role of angiogenetic factors remains unclear. To date, no information is available on SEMA3A in human melanoma. Microvessel density, immunohistochemical and mRNA VEGF and SEMA3A expression level in 60 thin (Breslow thickness ≤ 1.0 mm), 60 intermediate (1.1-4.0 mm) and 50 thick (>4.0 mm) primary human cutaneous melanomas were investigated and related to clinical/pathological parameters and disease-specific survival. No positive association between Breslow thickness, Clark level, metastasis presence and survival was identified; Clark level was poorly related to survival. VEGF and microvessel density were significantly higher in intermediate and thick melanomas and related to Breslow thickness and Clark level but not to metastasis status and survival. On the contrary, SEMA3A was significantly reduced in intermediate and thick melanomas and associated to metastasis and poor survival. VEGF/SEMA3A ratio was higher in the worst prognosis, resulting the most closely related factor with metastasis and survival. SEMA3A expression and VEGF/SEMA3A ratio turned out to be valuable prognostic biomarkers in patients affected by cutaneous melanoma, in particular with Breslow thickness >1 mm. SEMA3A might serve as a candidate tumor suppressor in cutaneous melanoma therapy.

A bone-targeting drug-delivery system based on Semaphorin 3A gene therapy ameliorates bone loss in osteoporotic ovariectomized mice

Osteoporosis is a serious health problem worldwide. Semaphorins (Sema) have been described as key molecules involved in the cross-talk between bone cells (osteoblasts/osteoclasts). In this study, we investigated whether plasmid containing Sema3a could ameliorate bone loss in an ovariectomized (OVX) mouse model via (AspSerSer)₆, a selectively bone-targeting moiety. Plasmid pcDNA3.1(+)-Sema3a-GFP was fabricated and transfected cells with the plasmid demonstrated statistically higher levels of Sema3A in vitro (p < 0.001). Mice were ovariectomized and injected twice weekly with (AspSerSer)₆-(STR-R8)+pcDNA3.1(+)-Sema3a-GFP for four weeks. The aim of the study was twofold: firstly to design an effective bone-targeting drug-delivery system (AspSerSer)₆. Secondly, the effects of Sem3A gene therapy on bone loss was investigated. Here, the targeting selectivity of pcDNA3.1(+)-Sema3a-GFP via (AspSerSer)₆ to the trabecular bone surface was firstly verified by histological observation of frozen sections and immunofluorescence staining. Then, bone microstructure analysis by Micro-CT indicated significantly less bone loss in mice treated with (AspSerSer)₆-(STR-R8)+pcDNA3.1(+)-Sema3a-GFP compared to the control group (p < 0.05). Furthermore,H&E staining and Safranin O staining of the decalcified sections demonstrated statistically significantly higher bone area/total area in the mice that were injected with (AspSerSer)₆-(STR-R8)+pcDNA3.1(+)-Sema3a-GFP (p < 0.001, p < 0.01,respectively). TRAP staining and immunohistochemistry staining of COL I demonstrated lower numbers of osteoclasts and significantly increased numbers of osteoblasts in the bone-targeting moiety delivering pcDNA3.1(+)-Sema3a-GFP group, when compared to the control group (p < 0.01, p < 0.001,respectively). Together, our findings have identified that, (AspSerSer)₆, a bone-targeting drug-delivery system based on semaphorin3A gene therapy, ameliorated bone loss in osteoporotic ovariectomized mice, by suppressing osteoclastic bone resorption and simultaneously increasing osteoblastic bone formation. Gene therapy by local site-specific Sema3A overexpression might be a potential new strategy for treating osteoporosis and bone defects.

Semaphorin-3a, neuropilin-1 and plexin-A1 in prosthetic-particle induced bone loss

Peri-prosthetic osteolysis (PPO) occurs in response to prosthetic wear particles causing an inflammatory reaction in the surrounding tissue that leads to subsequent bone loss. Semaphorin-3a (SEM3A), neuropilin-1 (NRP1) and plexin-A1 (PLEXA1) are axonal guidance molecules that have been recently implicated in regulating bone metabolism. This study investigated SEM3A, NRP1 and PLEXA1 protein and mRNA expression in human PPO tissue and polyethylene (PE) particle-stimulated human peripheral blood mononuclear cell (PBMC)-derived osteoclasts in vitro. In addition, the effects of tumour necrosis factor alpha (TNFα) on cultured osteoclasts was assessed. In PPO tissues, a granular staining pattern of SEM3A and NRP1 was observed within large multi-nucleated cells that contained prosthetic wear particles. Immunofluorescent staining confirmed the expression of SEM3A, NRP1 and PLEXA1 in large multi-nucleated human osteoclasts in vitro. Furthermore, SEM3A, NRP1 and PLEXA1 mRNA levels progressively increased throughout osteoclast differentiation induced by receptor activator of nuclear factor κB ligand (RANKL), and the presence of PE particles further increased mRNA expression of all three molecules. Soluble SEM3A was detected in human osteoclast culture supernatant at days 7 and 17 of culture, as assessed by ELISA. TNFα treatment for 72h markedly decreased the mRNA expression of SEM3A, NRP1 and PLEXA1 by human osteoclasts in vitro. Our findings suggest that SEM3A, NRP1 and PLEXA1 may have important roles in PPO, and their interactions, alone or as a complex, may have a role in pathological bone loss progression.

STATEMENT OF SIGNIFICANCE

Peri-prosthetic osteolysis occurs in response to prosthetic wear particles causing an inflammatory reaction in the surrounding tissue that leads to subsequent bone loss. The rate of hip and knee arthroplasty is increasing by at least 5% per year. However, these joint replacements have a finite lifespan, with data from the National Joint Replacement Registry (Australia) showing that the major cause of failure of total hip replacements is aseptic loosening. In aseptic loosening, wear particles liberated from prostheses are phagocytosed by macrophages, leading to release of inflammatory cytokines and up-regulation of osteoclast formation and activity. Semaphorin-3a, neuropilin-1 and plexin-A1 are axonal guidance molecules that have been recently implicated in regulating bone metabolism. This is the first report to show that these molecules may be involved in the implant failure.

Withania somnifera Improves Ischemic Stroke Outcomes by Attenuating PARP1-AIF-Mediated Caspase-Independent Apoptosis

Withania somnifera (WS), popularly known as "Ashwagandha" has been used for centuries as a nerve tonic. Its protective effect has been elucidated in many neurodegenerative pathologies, although there is a paucity of data regarding its effects in ischemic stroke. We examined the neuroprotective properties of an aqueous extract of WS in both pre- and poststroke treatment regimens in a mouse model of permanent distal middle cerebral artery occlusion (pMCAO). WS (200 mg/kg) improved functional recovery and significantly reduced the infarct volume in mice, when compared to those treated with vehicle, in both paradigms. We investigated the protective mechanism/s induced by WS using brain cortices by testing its ability to modulate the expression of key proteins in the ischemic-apoptotic cascade. The Western blots and immunofluorescence analyses of mice cortices revealed that WS upregulated the expression of hemeoxygenase 1 (HO1) and attenuated the expression of the proapoptotic protein poly (ADP-ribose) polymerase-1 (PARP1) via the PARP1-AIF pathway, thus preventing the nuclear translocation of apoptosis-inducing factor (AIF), and subsequent apoptosis. Semaphorin-3A (Sema3A) expression was reduced in WS-treated group, whereas Wnt, pGSK3β, and pCRMP2 expression levels were virtually unaltered. These results indicate the interplay of antioxidant-antiapoptic pathways and the possible involvement of angiogenesis in the protective mechanism of WS while emphasizing the noninvolvement of one of the prime pathways of neurogenesis. Our results suggest that WS could be a potential prophylactic as well as a therapeutic agent aiding stroke repair, and that part of its mechanism could be attributed to its antiapoptotic and antioxidant properties.

Decreased expression of SEMA3A is associated with poor prognosis in gastric carcinoma

BACKGROUND/PURPOSE

SEMA3A (semaphorin-3A), is a secreted protein that belongs to the semaphorin family and can function as both a chemoattractive agent or a chemorepulsive agent. SEMA3A has been shown to be a tumor suppressor in various cancers. This study investigated the expression of SEMA3A in gastric cancer and its prognostic value for gastric cancer patients.

METHODS

We examined the expression of SEMA3A in paired cancerous and matched adjacent noncancerous gastric mucosa tissues by real-time quantitative RT-PCR (qRT-PCR) and western blotting. In vitro, we evaluate the effects of SEMA3A on gastric cancer cell proliferation and migration by MTT, transwell and wound-healing assays. Furthermore, we analyzed SEMA3A expression in 128 patients who underwent resection procedures using immunohistochemistry. The relationships between the SEMA3A expression levels, the clinicopathological factors, and patient survival were investigated.

RESULTS

Our results revealed decreased SEMA3A mRNA (P = 0.0037) and protein (P = 0.033) expression in tumor tissue samples compared with matched adjacent non-tumorous tissue samples. Overexpression of SEMA3A inhibits gastric cancer cell proliferation and migration in vitro. Immunohistochemical staining data showed that SEMA3A expression was significantly decreased in 54.68% of gastric cancer cases. In addition, the chi-square test revealed that low SEMA3A expression was significantly correlated with poor differentiation (P = 0.015), Vascular invasion (P = 0.001), depth of invasion (P < 0.001), lymph node metastasis (P = 0.029), distant metastasis (P = 0.002) and advanced TNM stage (P = 0.003). SEMA3A expression was positively correlated with clinical TNM stage, that suggested the more advanced clinical TNM stage corresponding to the lower expression level of SEMA3A (rs = -0.322, P < 0.001) by Spearman rank correlation analysis. Kaplan-Meier survival analysis demonstrated that low expression of SEMA3A was significantly correlated with a poor prognosis for gastric cancer patients (P < 0.001). The multivariate analysis revealed that SEMA3A expression was an independent prognostic factor of the overall survival rate of patients with gastric cancer.

CONCLUSION

SEMA3A expression decreased significantly as gastric cancer progressed and metastasized, suggesting that SEMA3A might serve as a candidate tumor suppressor and a potential prognostic biomarker in gastric carcinogenesis.

KDR and Sema3 genes expression in bone marrow stromal cells and hematopoietic cells from leukemia patients and normal individuals

Kinase domain receptor (KDR) and Semaphorin3 (Sema3) have a functional relationship and are expressed in human bone marrow (BM). We cultured in vitro bone marrow stromal cells (BMSCs) and collected nonadherent cells from patients with acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL) and normal individuals. Reverse transcriptase polymerase chain reaction enzyme-linked immunosorbent assay (RT-PCR-ELISA) was performed to examine KDR and Sema3 genes expression, using beta2 microglobulin as an internal reference. KDR expression ratio in normal control BMSCs (97.0%, 32/33) was higher than in its corresponding nonadherent cells (70.8%, 17/24). KDR expression levels in ALL BMSCs and AML nonadherent cells were significantly higher than in normal controls. Sema3 expression ratios in nonadherent cells from AML (78.6%, 11/14) and CML (71.4%, 10/14) were both significantly lower than in normal control (100%, 27/27), its expression levels were also significantly lower than in normal control. Sema3 expression level in normal BMSCs was significantly lower than in nonadherent cells. Sema3 and KDR genes expression levels displayed a significantly positive correlation in normal control and ALL nonadherent cells (r=0.703, P=0.002; r=0.999, P=0.001). These results suggests that KDR may play a critical role in sustaining the hematopoietic microenvironment due to its high expression, and that KDR may be involved in pathogenesis of AML and ALL. Sema3 could also sustain the survival of hematopoietic cells with its high expression, while Sema3 gene expression may be inhibited in AML and CML.

Semaphorin 3A and 3F: key players in myelin repair in multiple sclerosis?

The presence of demyelinated plaques in the central nervous system is the hallmark of multiple sclerosis (MS). Some plaques remyelinate but others do not, leaving permanent damage. The reasons for this failure of repair are many, but one possible reason is the lack of migration of oligodendrocyte precursor cells to the lesion. The guidance molecules Semaphorin 3A and 3F, already known to direct oligodendroglial migration in development, may also be active in controlling oligodendrocyte precursor cell migration in MS, and hence may determine the ability of plaques to remyelinate. Here, in MS tissue and an experimental model of demyelination, we demonstrate a local source of these molecules around active demyelinating lesions, but not chronic plaques. We also provide evidence for their up-regulation at a distance from the lesion, in the neuronal cell bodies corresponding to the demyelinated axons. We propose that both of these mechanisms influence remyelination.

Targeting sensory axon regeneration in adult spinal cord

Extensive regeneration of sensory axons into the spinal cord can be achieved experimentally after dorsal root injury, but no effort has been made to target regenerating axons and restore a normal lamina-specific projection pattern. Ectopic axon growth is potentially associated with functional disorders such as chronic pain and autonomic dysreflexia. This study was designed to target regenerating axons to normal synaptic locations in the spinal cord by combining positive and negative guidance molecules. Previously, we observed that, after dorsal rhizotomy, overexpression of NGF leads to robust regeneration and sprouting of calcitonin gene-related peptide (CGRP)-positive nociceptive axons throughout dorsal horn and ventral horns. To restrict these axons within superficial laminas, adenovirus expressing semaphorin 3A was injected into the ventral spinal cord 3 d after NGF virus injection. Semaphorin 3A expression was observed in deep dorsal and ventral cord regions and limited axon growth to laminas I and II, shaping axonal regeneration toward the normal distribution pattern. NGF and semaphorin 3A treatment also targeted the regeneration of substance P-positive nociceptive axons but had no effect on injured isolectin B4-binding nociceptive axons. Axon regeneration led to functional restoration of nociception in both NGF- and NGF/semaphorin 3A-treated rats. Although no significant difference in behavior was found between these two groups, confocal microscopy illustrated ectopic synaptic formations in deeper laminas in NGF/green fluorescent protein-treated rats. The results suggested that antagonistic guidance cues can be used to induce and refine regeneration within the CNS, which is important for long-term, optimal functional recovery.

Increased class 3 semaphorin expression modulates the invasive and adhesive properties of prostate cancer cells

The class 3 semaphorins, sema3A and sema3C, provide important guidance cues in cell development and in cancer; however, the role of these semaphorins in prostate cancer is not known. We report here that sema3A transfected cells exhibit decreased invasion and adhesion in Matrigel-based assays and that sema3C transfected cells exhibit increased invasive and adhesive characteristics. Important adhesion proteins were differentially modulated in sema3A and sema3C cells in a manner consistent with their subsequent invasive and adhesive characteristics. E-cadherin expression as determined by Western blot analysis was strongly upregulated in sema3A transfected cells, but strongly downregulated in sema3C transfected cells compared to untransfected and mock empty vector-transfected PC-3 cells. beta-catenin levels were not changed in sema3A transfected cells; however, sema3C transfected cells had lower expression of this protein. Sema3C transfected cells exhibited greater cellular membrane expression of certain alpha integrins as compared to untransfected and sema3A transfected cells, a characteristic associated with increased adhesion and invasion. These data indicate that the invasive ability of sema3A and sema3C transfected PC-3 cells is, in part, correlated with adhesion protein expression and adhesive ability to constituents of neighboring cells and the extracellular matrix.

Immunosuppressive role of semaphorin-3A on T cell proliferation is mediated by inhibition of actin cytoskeleton reorganization

Timely negative regulation of the immune system is critical to allow it to perform its duty while maintaining it under tight control to avoid overactivation. We previously reported that the neuronal receptor neuropilin-1 (NP-1) is expressed in human lymph nodes. However, the role of NP-1 interaction with its physiological ligand semaphorin-3A (Sema-3A) on immune cells remains elusive. Here we show that Sema-3A is expressed by activated DC and T cells, and that its secretion in DC/T cell cocultures is delayed. Sema-3A/NP-1 interaction down-modulated T cell activation since addition of Sema-3A in DC/T cell cocultures dramatically inhibited allogeneic T cell proliferation. More importantly, neutralization by blocking antibodies or by antagonist peptide of endogenous Sema-3A produced by DC/T cell cocultures resulted in a 130% increase in T cell proliferation. Sema-3A acted directly on T cells, since it could block anti-CD3/CD28-stimulated proliferation of T cells. Finally, immunomodulatory functions of Sema-3A relied on the blockage of actin cytoskeleton reorganization, affecting TCR polarization and interfering with early TCR signal transduction events such as ZAP-70 or focal adhesion kinase phosphorylation. Therefore, we propose that Sema-3A secretion and the resulting NP-1/Sema-3A interaction are involved in a late negative feedback loop controlling DC-induced T cell proliferation.

Regulation of dendritic branching and spine maturation by semaphorin3A-Fyn signaling

A member of semaphorin family, semaphorin3A (Sema3A), acts as a chemorepellent or chemoattractant on a wide variety of axons and dendrites in the development of the nervous systems. We here show that Sema3A induces clustering of both postsynaptic density-95 (PSD-95) and presynaptic synapsin I in cultured cortical neurons without changing the density of spines or filopodia. Neuropilin-1 (NRP-1), a receptor for Sema3A, is present on both axons and dendrites. When the cultured neurons are exposed to Sema3A, the cluster size of PSD-95 is markedly enhanced, and an extensive colocalization of PSD-95 and NRP-1 or actin-rich protrusion is seen. The effects of Sema3A on spine morphology are blocked by PP2, an Src type tyrosine kinase inhibitor, but not by the PP3, the inactive-related compound. In the cultured cortical neurons from fyn(-/-) mice, dendrites bear few spines, and Sema3A does not induce PSD-95 cluster formation on the dendrites. Sema3A and its receptor genes are highly expressed during the synaptogenic period of postnatal days 10 and 15. The cortical neurons in layer V, but not layer III, show a lowered density of synaptic bouton-like structure on dendrites in sema3A- and fyn-deficient mice. The neurons of the double-heterozygous mice show the lowered spine density, whereas those of single heterozygous mice show similar levels of the spine density as the wild type. These findings suggest that the Sema3A signaling pathway plays an important role in the regulation of dendritic spine maturation in the cerebral cortex neurons.

Plexin-induced collapse assay in COS cells

Semaphorins are a family of growth cone guidance molecules. When associated with their receptors and coreceptors, plexins and neuropilins, they act as chemorepellents for an extensive range of neuronal populations. The prototypic semaphorin, Sema3A, has a potent inhibitory effect on sensory axons emanating from dorsal root ganglia. This has formed the basis of the most famous assay for semaphorin activity, the chick dorsal root ganglia collapse assay. Recently, a heterologous, highly tractable assay has been used to investigate semaphorin signaling. In this system, the binding of recombinant semaphorins to COS cells expressing plexins and neuropilins induces a morphological collapse that may correlate with growth cone collapse. This chapter describes the optimization of this assay and outlines the subtle differences required to enable Sema3A-Fc and Sema4D-Fc to induce identical collapse phenotypes in COS cells expressing Plexin-A1 and neuropilin-1, or Plexin-B1, respectively.

Expression of Semaphorin-3A and its receptors in endochondral ossification: potential role in skeletal development and innervation

Bone tissue is densely innervated, and there is increasing evidence for a neural control of bone metabolism. Semaphorin-3A is a very important regulator of neuronal targeting in the peripheral nervous system as well as in angiogenesis, and knockout of the Semaphorin-3A gene induces abnormal bone and cartilage development. We analyzed the spatial and temporal expression patterns of Semaphorin-3A signaling molecules during endochondral ossification, in parallel with the establishment of innervation. We show that osteoblasts and chondrocytes differentiated in vitro express most members of the Semaphorin-3A signaling system (Semaphorin-3A, Neuropilin-1, and Plexins-A1 and -A2). In vitro, osteoclasts express most receptor chains but not the ligand. In situ, these molecules are all expressed in the periosteum and by resting, prehypertrophic and hypertrophic chondrocytes in ossification centers before the onset of neurovascular invasion. They are detected later in osteoblasts and also osteoclasts, with differences in intensity and regional distribution. Semaphorin-3A and Neuropilin-1 are also expressed in the bone marrow. Plexin-A3 is not expressed by bone cell lineages in vitro. It is detected early in the periosteum and hypertrophic chondrocytes. After the onset of ossification, this chain is restricted to a network of cell processes in close vicinity to the cells lining the trabeculae, similar to the pattern observed for neural markers at the same stages. After birth, while the density of innervation decreases, Plexin-A3 is strongly expressed by blood vessels on the ossification front. In conclusion, Semaphorin-3A signaling is present in bone and seems to precede or coincide at the temporal but also spatial level with the invasion of bone by blood vessels and nerve fibers. Expression patterns suggest Plexin-A3/Neuropilin-1 as a candidate receptor in target cells for the regulation of bone innervation by Semaphorin-3A.

Semaphorin-3A is expressed by tumor cells and alters T-cell signal transduction and function

An important aspect of tumor progression is the ability of cancer cells to escape detection and clearance by the immune system. Recent studies suggest that several tumors express soluble factors interfering with the immune response. Here, we show that semaphorin-3A (Sema-3A), a secreted member of the semaphorin family involved in axonal guidance, organogenesis, and angiogenesis, is highly expressed in several tumor cells. Conditioned media of Sema-3A-transfected COS-7 cells or human recombinant Sema-3A inhibited primary human T-cell proliferation and cytokines production under anti-CD3 plus anti-CD28 stimulating conditions. Sema-3A also inhibited the activation of nonspecific cytotoxic activity in mixed lymphocyte culture (MLC), as measured against K-562 cells. In contrast, suppression of Sema-3A in tumor cells with a small interfering RNA (siRNA) augmented T-cell activation. The inhibitory effect of Sema-3A in T cells is mediated by blockade of Ras/mitogen-activated protein kinase (MAPK) signaling pathway. The presence of Sema-3A increased the activation of the Ras family small GTPase Rap1 and introduction of the dominant-negative mutant of Rap1 (Rap1N17) blunted the immunoinhibitory effects of Sema-3A. These results suggest that Sema-3A inhibits primary T-cell activation and imply that it can contribute to the T-cell dysfunction in the tumor microenvironment.

Neuropilin-1 Suppresses Tumorigenic Properties in a Human Pancreatic Adenocarcinoma Cell Line Lacking Neuropilin-1 Coreceptors

Neuropilin-1 (NRP-1) was first described as a coreceptor implicated in neuronal guidance that bound members of the semaphorin/collapsin family. NRP-1 is also expressed in endothelial cells and is believed to promote angiogenesis by acting as a coreceptor with vascular endothelial growth factor (VEGF) receptor 2. Recent studies suggest that NRP-1 can function through both a VEGF-dependent and VEGF-independent fashion. Expression of NRP-1 has been shown in many human tumors, including pancreatic adenocarcinomas. The exact role of NRP-1 in tumor cells is unknown, particularly in cells that lack the NRP-1 coreceptors VEGF receptor 2 and Plexin-A1. To discern the regulatory role(s) of NRP-1 in pancreatic adenocarcinoma that lack these coreceptors, we overexpressed both full-length NRP-1 and a deletion form of NRP-1 that does not interact with semaphorin or VEGF. Overexpression of either isoform reduced several key tumorigenic properties, including anchorage-independent cell growth and migration in vitro, and resulted in reduced tumor incidence and tumor volume in vivo. Conversely, reduction of NRP-1 expression by small interfering RNA targeting led to enhanced tumor growth. Thus, NRP-1 may play distinct growth regulatory roles in different tumor types, and altering NRP-1 expression or function may be a means of influencing the growth of pancreatic cancers.

Coordination of trigeminal axon navigation and patterning with tooth organ formation: epithelial-mesenchymal interactions, and epithelial Wnt4 and Tgfbeta1 regulate semaphorin 3a expression in the dental mesenchyme

During development, trigeminal nerve fibers navigate and establish their axonal projections to the developing tooth in a highly spatiotemporally controlled manner. By analyzing Sema3a and its receptor Npn1 knockout mouse embryos, we found that Sema3a regulates dental trigeminal axon navigation and patterning, as well as the timing of the first mandibular molar innervation, and that the effects of Sema3a appear to be mediated by Npn1 present in the axons. By performing tissue recombinant experiments and analyzing the effects of signaling molecules, we found that early oral and dental epithelia, which instruct tooth formation, and epithelial Wnt4 induce Sema3a expression in the presumptive dental mesenchyme before the arrival of the first dental nerve fibers. Later, at the bud stage, epithelial Wnt4 and Tgfbeta1 regulate Sema3a expression in the dental mesenchyme. In addition, Wnt4 stimulates mesenchymal expression of Msx1 transcription factor, which is essential for tooth formation, and Tgfbeta1 proliferation of the dental mesenchymal cells. Thus, epithelial-mesenchymal interactions control Sema3a expression and may coordinate axon navigation and patterning with tooth formation. Moreover, our results suggest that the odontogenic epithelium possesses the instructive information to control the formation of tooth nerve supply.

Semaphorin3A inhibits nerve growth factor-induced sprouting of nociceptive afferents in adult rat spinal cord

Increased expression of NGF after spinal cord injury induces sprouting of primary nociceptive axons. Exogenous application of NGF also results in extensive sprouting of these axons and causes chronic pain in uninjured animals. During development, semaphorin3A is thought to act as a repulsive guidance cue for NGF-responsive nociceptive afferents, restricting their projections to the superficial dorsal horn. We investigated the ability of semaphorin3A to selectively reduce NGF-induced sprouting and neuropathic pain in adult rats. The chemorepulsive effect of virus-mediated semaphorin3A expression was shown to counteract the sprouting induced by NGF in a dose-dependent manner, both in vitro and in adult rat spinal cords. Coexpression of semaphorin3A and NGF at moderate to low concentrations within the adult spinal cord reduced sprouting of calcitonin gene-related peptide and substance P-containing axons compared with GFP and NGF coexpression controls. At high expression levels of NGF, there was no difference in sprouting between the semaphorin3A-treated and control groups. The distribution of endogenous primary nociceptive afferents in the spinal cord appeared to be unaffected by semaphorin3A treatment in these experiments. Behavioral assessment shows that semaphorin3A coexpression with NGF led to decreased mechanical allodynia but no significant reductions in thermal hyperalgesia. These findings demonstrate directly that mature sensory afferents maintain their responsiveness to semaphorin3A, suggesting that this molecule might be used therapeutically to control aberrant sensory sprouting involved in pain or autonomic dysfunction.

Meningeal cell-derived semaphorin 3A inhibits neurite outgrowth

The neural scar that forms after injury to the mammalian central nervous system is a barrier to sprouting and regenerating axons. In addition to reactive astrocytes that are present throughout the lesion site, leptomeningeal fibroblasts invade the lesion core. When isolated in vitro, these cells form a very poor substrate for growing neurites, even more so than reactive astrocytes. Nevertheless the molecular mechanisms involved in this growth inhibition are not well understood. Semaphorins have been reported to be upregulated in meningeal cells (MCs) on mechanical injury to the brain and spinal cord. In the present study, we show that Sema3A mRNA and active protein are produced by cultured meningeal cells. A protein extract from these cells induces the collapse of embryonic dorsal root ganglion (DRG) growth cones. This collapsing activity is partially blocked by neuropilin-1 antibodies and is absent in meningeal cells derived from Sema3A-knockout mice. In addition to growth cone collapse, recombinant Sema3A but not Sema3C inhibits neurite outgrowth of embryonic DRGs. Consistent with this result we find that the inhibitory effect of meningeal cells on neurite outgrowth is partially overcome on Sema3A-deficient MCs. Furthermore we show that the inhibitory effect of MC-derived Sema3A on neurite outgrowth is modulated by nerve growth factor. Our results show that Sema3A, a chemorepellent during nervous system development, is a major neurite growth-inhibitory molecule in meningeal fibroblasts and is therefore likely to contribute to the inhibitory properties of the neural scar.

Induction of neuropilins-1 and -2 and their ligands, Sema3A, Sema3F, and VEGF, during Wallerian degeneration in the peripheral nervous system

The neuropilins, NP-1 and NP-2, are coreceptors for Sema3A and Sema3F, respectively, both of which are repulsive axonal guidance molecules. NP-1 and NP-2 are also coreceptors for vascular endothelial growth factor (VEGF). The neuropilins and their ligands are known to play prominent roles in axonal pathfinding, fasciculation, and blood vessel formation during peripheral nervous system (PNS) development. We confirmed a prior report (Exp. Neurol. 172 (2001) 398) that VEGF mRNA levels rise during Wallerian degeneration in the PNS and herein demonstrate that NP-1, NP-2, Sema3A, and Sema3F mRNA levels increase in peripheral nerves distal to a transection or crush injury. In a sciatic nerve crush model, in which axonal regeneration is robust, the highest levels of Sema3F mRNA below the injury site are in the epi- and perineurium. Our results suggest the possibility that the neuropilins and their semaphorin ligands serve to guide, rather than to impede, regenerating axons in the adult PNS.

Competing autocrine pathways involving alternative neuropilin-1 ligands regulate chemotaxis of carcinoma cells

Neuropilin-1 (NP1), in conjunction with plexins, promotes axon repulsion by binding to semaphorin 3A (SEMA3A). Although NP1 is expressed in carcinoma cells, its functions have remained elusive, and neither SEMA3A nor plexin expression has been explored in cancer. Here we provide evidence that breast carcinoma cells support an autocrine pathway involving SEMA3A, plexin-A1, and NP1 that impedes their ability to chemotax. Reducing SEMA3A or NP1 expression by RNA interference or inhibiting plexin-A1 signaling enhanced migration. Conversely, expression of constitutively active plexin-A1 impaired chemotaxis. The paradox of how breast carcinoma cells expressing these endogenous chemotaxis inhibitors are able to migrate is explained by their expression of vascular endothelial growth factor (VEGF), a NP1 ligand that competes with SEMA3A for receptor binding. Finally, we establish that the ratio of endogenous VEGF and SEMA3A concentrations in carcinoma cells determines their chemotactic rate. Our findings lead to the surprising conclusion that opposing autocrine loops involving NP1 regulate the chemotaxis of breast carcinoma cells. Moreover, our data indicate a novel autocrine function for VEGF in chemotaxis.

Ontogeny of semaphorins 3A and 3F and their receptors neuropilins 1 and 2 in the kidney

Semaphorins 3A and 3F are axon guidance proteins during nervous system development. Their expression pattern and function outside the nervous system are unknown. Neuropilin 1 and 2 (NP-1, NP-2) are natural ligands for semaphorins 3A and 3F, respectively. NP-1 is also a co-receptor for vascular endothelial growth factor (VEGF) required for normal vascular development. We showed that VEGF is a direct chemoattractant for glomerular endothelial cells towards developing nephrons. To examine whether semaphorins could modulate VEGF endothelial cell guidance cues in the developing kidney, we studied the expression of semaphorin 3A and semaphorin 3F and their receptors NP-1 and NP-2 in the kidney during ontogeny using Northern blot analysis, in situ hybridization, Western blot analysis and immunohistochemistry. All four genes are developmentally regulated, with abundant expression during organogenesis and downregulation in the adult kidney. Semaphorin 3A and 3F are expressed by podocytes and tubules whereas their receptors NP-1 and NP-2 are localized to endothelial cells. In vitro, renal tubular epithelial cell lines (tsMPT, IRPT and MDCK) and glomerular endothelial cells express both semaphorins and their receptors, suggesting the presence of an autocrine system. The distribution of the receptors NP-1 and NP-2 in endothelial cells and developing vessels is complementary to that of the ligands in adjacent epithelial cells during kidney development. The sum of the guidance cues provided by VEGF and semaphorins 3A and 3F may be important determinants of the pattern of endothelial cell migration during kidney morphogenesis.

Pontocerebellar axon guidance: neuropilin-1- and semaphorin 3A-sensitivity gradients across basilar pontine nuclei and semaphorin 3A variation across cerebellum

To assess the role of semaphorin 3A (Sema3A) and its receptor component neuropilin-1 (Npn-1) in pontocerebellar axon guidance, we compared the distributions of Sema3A, Npn-1, and DiI-labeled pontocerebellar axons in neonatal mouse cerebellum. Between embryonic day 18 and birth there was a large increase in Npn-1 expression in the basilar pontine nuclei (BPN), the major source of pontocerebellar axons. Sema3A expression in cerebellum also increased at this time. In the BPN, Npn-1 and the response of axons to Sema3A were graded with high Npn-1 and Sema3A responsiveness rostrally and lower levels caudally. The Npn-1 gradient was not smooth and cells with higher and lower expression were interspersed. Between birth and postnatal day 5, pontocerebellar axons projected to lobules of the hemispheres, including those with low to moderate levels of Sema3A, but did not enter regions with high levels of Sema3A, including the flocculus and much of the vermis. These results suggest that varying neuropilin levels on BPN axons, which correlated with their varying responses to Sema3A, combined with varying Sema3A levels across cerebellum, may contribute to guiding subsets of BPN axons to their distinct target regions within cerebellum.