Semaphorin III can repulse and inhibit adult sensory afferents in vivo

Expression of semaphorin-3A in the joint and role in osteoarthritis

Osteoarthritis (OA) is characterised by the deterioration of cartilage in the joints and pain. We hypothesise that semaphorin-3A (sema-3A), a chemorepellent for sensory nerves, plays a role in joint degradation and pain. We used the mechanical joint loading (MJL) model of OA to investigate sema-3A expression in the joint and examine its association with the development of OA and pain. We also analyse its effect on chondrocyte differentiation using the ATDC5 cell line. We demonstrate that sema-3A is present in most tissues in the healthy joint and its expression increases in highly innervated tissues, such as cruciate ligaments, synovial lining and subchondral bone, in loaded compared to nonloaded control joints. In contrast, sema-3A expression in cartilage was decreased in the severe OA induced by the application of high loads. There was a significant increase in circulating sema-3A, 6 weeks after MJL compared to the nonloaded mice. mRNA for sema-3A and its receptor Plexin A1 were upregulated in the dorsal root ganglia of mice submitted to MJL. These increases were supressed by zoledronate, an inhibitor of bone pain. Sema-3A was expressed at all stages of Chondrocyte maturation and, when added exogenously, stimulated expression of markers of chondrocyte differentiation. This indicates that sema-3A could affect joint tissues distinctively during the development of OA. In highly innervated joint tissues, sema-3A could control innervation and/or induce pain-associated neuronal changes. In cartilage, sema-3A could favour its degeneration by modifying chondrocyte differentiation.

The Involvement of Semaphorins in the Pathogenesis of Skin Diseases

Semaphorins belong to a group of membrane and secretory proteins that act as ligands for several receptor families and are involved in modulating cell signaling pathways. They bind multimeric receptor complexes on the cell membrane to exert their effects and initiate unique intracellular signal transduction cascades. These proteins can influence several processes that are very important for cell function, such as cell division and differentiation. Semaphorins are involved in cell migration, apoptosis, cell adhesion, aggregation, and numerous immune processes due to their immunoregulatory effects. Semaphorins are expressed in keratinocytes, which is why they have become a target for studies on the pathogenesis of skin diseases. Most studies to date on the role of semaphorins in the pathogenesis of skin diseases have been carried out in cellular or animal models, and there are few clinical studies evaluating the role of semaphorins in the pathogenesis and therapy of skin diseases. In this narrative review, we summarized the current state of knowledge on the role of semaphorins in the pathogenesis of skin diseases and their potential importance as targets for therapy. We also tried to present the key findings and weaknesses of previous research in this field. The novelty of this article lies in the comprehensive presentation of the role of semaphorins in the pathogenesis of skin diseases, including the results of studies on cell cultures and animal models, elucidating the mechanisms and signaling pathways through which semaphorins affect the development of skin diseases, as well as on the presentation of the results of existing clinical trials evaluating the role of semaphorins in the pathogenesis of skin diseases, and as potential therapeutic targets.

Adult expression of Semaphorins and Plexins is essential for motor neuron survival

Axon guidance cues direct the growth and steering of neuronal growth cones, thus guiding the axons to their targets during development. Nonetheless, after axons have reached their targets and established functional circuits, many mature neurons continue to express these developmental cues. The role of axon guidance cues in the adult nervous system has not been fully elucidated. Using the expression pattern data available on FlyBase, we found that more than 96% of the guidance genes that are expressed in the Drosophila melanogaster embryo continue to be expressed in adults. We utilized the GeneSwitch and TARGET systems to spatiotemporally knockdown the expression of these guidance genes selectively in the adult neurons, once the development was completed. We performed an RNA interference (RNAi) screen against 44 guidance genes in the adult Drosophila nervous system and identified 14 genes that are required for adult survival and normal motility. Additionally, we show that adult expression of Semaphorins and Plexins in motor neurons is necessary for neuronal survival, indicating that guidance genes have critical functions in the mature nervous system.

Transcriptomic, Epigenomic, and Neuroanatomic Signatures Differ in Chronic Prurigo, Atopic Dermatitis, and Brachioradial Pruritus

Scratching and scratch-induced injuries, including neuroanatomical alterations, are key characteristics of chronic pruritus entities of different origins. The aim of this study was to link gene expression (array hybridization, qPCR) with DNA methylation (array hybridization) and neuroanatomy (PGP9.5 staining) in chronic nodular prurigo (CNPG), atopic dermatitis (AD), brachioradial pruritus (BRP), and matched healthy controls. Specific signatures of gene expression and DNA methylation clearly discriminated pruritic lesional skin from nonpruritic skin in CNPG and from healthy skin of volunteers, respectively. Although intraepidermal nerve fiber density was indiscriminately reduced, the level of epidermal branching, assessed by a semiquantitative pattern analysis, differentiated the entities (CNPG > BRP > AD). Correspondingly, repellent SEMA3A showed the highest expression in AD, whereas axonal growth-promoting nerve GF was most prominent in CNPG and BRP. Overexpression of genes for nerve fiber regeneration (NELL2/NFKB/ARTN) was found in AD and CNPG but not in BRP. Our findings suggest that differential branching patterns rather than mere innervation density separate chronic itch conditions and reflect disease-specific local expression profiles. In pruritic dermatoses (AD and CNPG), nerve injury and subsequent sprouting may primarily result from chronic scratching, whereas genuine neuropathy is expected to underlie BRP.

Wiring the ocular surface: A focus on the comparative anatomy and molecular regulation of sensory innervation of the cornea

The cornea is richly innervated with sensory nerves that function to detect and clear harmful debris from the surface of the eye, promote growth and survival of the corneal epithelium and hasten wound healing following ocular disease or trauma. Given their importance to eye health, the neuroanatomy of the cornea has for many years been a source of intense investigation. Resultantly, complete nerve architecture maps exist for adult human and many animal models and these maps reveal few major differences across species. Interestingly, recent work has revealed considerable variation across species in how sensory nerves are acquired during developmental innervation of the cornea. Highlighting such species-distinct key differences, but also similarities, this review provides a full, comparative anatomy analysis of sensory innervation of the cornea for all species studied to date. Further, this article comprehensively describes the molecules that have been shown to guide and direct nerves toward, into and through developing corneal tissue as the final architectural pattern of the cornea's neuroanatomy is established. Such knowledge is useful for researchers and clinicians seeking to better understand the anatomical and molecular basis of corneal nerve pathologies and to hasten neuro-regeneration following infection, trauma or surgery that damage the ocular surface and its corneal nerves.

Prophylactic Knockdown of the miR-183/96/182 Cluster Ameliorates Pseudomonas aeruginosa-Induced Keratitis

Purpose

Previously, we demonstrated that miR-183/96/182 cluster (miR-183C) knockout mice exhibit decreased severity of Pseudomonas aeruginosa (PA)-induced keratitis. This study tests the hypothesis that prophylactic knockdown of miR-183C ameliorates PA keratitis indicative of a therapeutic potential.

Methods

Eight-week-old miR-183C wild-type and C57BL/6J inbred mice were used. Locked nucleic acid-modified anti-miR-183C or negative control oligoribonucleotides with scrambled sequences (NC ORNs) were injected subconjunctivally 1 day before and then topically applied once daily for 5 days post-infection (dpi) (strain 19660). Corneal disease was graded at 1, 3, and 5 dpi. Corneas were harvested for RT-PCR, ELISA, immunofluorescence (IF), myeloperoxidase and plate count assays, and flow cytometry. Corneal nerve density was evaluated in flatmounted corneas by IF staining with anti-β-III tubulin antibody.

Results

Anti-miR-183C downregulated miR-183C in the cornea. It resulted in an increase in IL-1β at 1 dpi, which was decreased at 5 dpi; fewer polymorphonuclear leukocytes (PMNs) at 5 dpi; lower viable bacterial plate count at both 1 and 5 dpi; increased percentages of MHCII+ macrophages (Mϕ) and dendritic cells (DCs), consistent with enhanced activation/maturation; and decreased severity of PA keratitis. Anti-miR-183C treatment in the cornea of naïve mice resulted in a transient reduction of corneal nerve density, which was fully recovered one week after the last anti-miR application. miR-183C targets repulsive axon-guidance receptor molecule Neuropilin 1, which may mediate the effect of anti-miR-183C on corneal nerve regression.

Conclusions

Prophylactic miR-183C knockdown is protective against PA keratitis through its regulation of innate immunity, corneal innervation, and neuroimmune interactions.

Vinaxanthone inhibits Semaphorin3A induced axonal growth cone collapse in embryonic neurons but fails to block its growth promoting effects on adult neurons

Semaphorin3A is considered a classical repellent molecule for developing neurons and a potent inhibitor of regeneration after nervous system trauma. Vinaxanthone and other Sema3A inhibitors are currently being tested as possible therapeutics to promote nervous system regeneration from injury. Our previous study on Sema3A demonstrated a switch in Sema3A's function toward induction of nerve regeneration in adult murine corneas and in culture of adult peripheral neurons. The aim of the current study is to determine the direct effects of Vinaxanthone on the Sema3A induced adult neuronal growth. We first demonstrate that Vinaxanthone maintains its anti-Sema3A activity in embryonic dorsal root ganglia neurons by inhibiting Sema3A-induced growth cone collapse. However, at concentrations approximating its IC50 Vinaxanthone treatment does not significantly inhibit neurite formation of adult peripheral neurons induced by Sema3A treatment. Furthermore, Vinaxanthone has off target effects when used at concentrations above its IC50, and inhibits neurite growth of adult neurons treated with either Sema3A or NGF. Our results suggest that Vinaxanthone's pro-regenerative effects seen in multiple in vivo models of neuronal injury in adult animals need further investigation due to the pleiotropic effect of Sema3A on various non-neuronal cell types and the possible effect of Vinaxanthone on other neuroregenerative signals.

Effects of early crush on aging wild type and Connexin 32 knockout mice: Evidence for a neuroprotective state in CMT1X mouse nerve

The long-term sequelae of nerve injury as well as age-related neurodegeneration have been documented in numerous studies, however the role of Cx32 in these processes is not well understood. There is a need for better understanding of the molecular mechanisms that underlie long-term suboptimal nerve function and for approaches to prevent or improve it. In this communication we describe our studies using whole animal electrophysiology to examine the long-term sequelae of sciatic nerve crush in both WT and Cx32KO mice, a model of X-linked Charcot Marie Tooth disease, a subtype of inherited peripheral neuropathies. We present results from electrical nerve recordings done 14 to 27 days and 18 to 20 months after a unilateral sciatic nerve crush performed on 35 to 37-day old mice. Contrary to expectations, we find that whereas crush injury leads to a degradation of WT nerve function relative to uninjured nerves at 18 to 20 months, previously crushed Cx32KO nerves perform at the same level as their uninjured counterparts. Thus, 18 to 20 months after injury, WT nerves perform below the level of normal (uninjured) WT nerves in both motor and sensory nerve function. In contrast, measures of nerve function in Cx32KO mice are degraded for sensory axons but exhibit no additional dysfunction in motor axons. Early nerve injury has no negative electrophysiologic effect on the Cx32 KO motor nerves. Based on our prior demonstration that the transcriptomic profile of uninjured Cx32KO and injured WT sciatic nerves are very similar, the lack of an additional effect of crush on Cx32KO motor nerve parameters suggests that Cx32 knockout may implement a form of neuroprotection that limits the effects of subsequent injury.

Fidgetin-like 2 negatively regulates axonal growth and can be targeted to promote functional nerve regeneration

The microtubule (MT) cytoskeleton plays a critical role in axon growth and guidance. Here, we identify the MT-severing enzyme fidgetin-like 2 (FL2) as a negative regulator of axon regeneration and a therapeutic target for promoting nerve regeneration after injury. Genetic knockout of FL2 in cultured adult dorsal root ganglion neurons resulted in longer axons and attenuated growth cone retraction in response to inhibitory molecules. Given the axonal growth-promoting effects of FL2 depletion in vitro, we tested whether FL2 could be targeted to promote regeneration in a rodent model of cavernous nerve (CN) injury. The CNs are parasympathetic nerves that regulate blood flow to the penis, which are commonly damaged during radical prostatectomy (RP), resulting in erectile dysfunction (ED). Application of FL2-siRNA after CN injury significantly enhanced functional nerve recovery. Remarkably, following bilateral nerve transection, visible and functional nerve regeneration was observed in 7 out of 8 animals treated with FL2-siRNA, while no control-treated animals exhibited regeneration. These studies identify FL2 as a promising therapeutic target for enhancing regeneration after peripheral nerve injury and for mitigating neurogenic ED after RP - a condition for which, at present, only poor treatment options exist.

The Role of Nociceptive Neurons in the Pathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease. Emerging evidence shows that neurogenic inflammation, induced by nociceptive neurons and T helper 17 cell (Th17) responses, has a fundamental role in maintaining the changes in the immune system due to psoriasis. Nociceptive neurons, specific primary sensory nerves, have a multi-faceted role in detecting noxious stimuli, maintaining homeostasis, and regulating the immunity responses in the skin. Therefore, it is critical to understand the connections and interplay between the nociceptive neurons and the immune system in psoriasis. Here, we review works on the altered innervation that occurs in psoriasis. We examine how these distinct sensory neurons and their signal transducers participate in regulating inflammation. Numerous clinical studies report the dysfunction of nociceptive neurons in psoriasis. We discuss the mechanism behind the inconsistent activation of nociceptive neurons. Moreover, we review how neuropeptides, involved in regulating Th17 responses and the role of nociceptive neurons, regulate immunity in psoriasis. Understanding how nociceptive neurons regulate immune responses enhances our knowledge of the neuroimmunity involved in the pathogenesis of psoriasis and may form the basis for new approaches to treat it.

Neuronal hyperexcitability and astrocyte activation in spinal dorsal horn of a dermatitis mouse model with cutaneous hypersensitivity

Cleaning products such as soaps, shampoos, and detergents are comprised mainly of surfactants, agents known to cause dermatitis and cutaneous hypersensitivity characterized by itching, stinging, and burning of the skin and scalp. However, the mechanisms underlying surfactant-induced cutaneous hypersensitivity remain unclear. In the present study, we investigated the mechanisms of cutaneous hypersensitivity in mice treated with the detergent sodium dodecyl sulfate (SDS). Repeated SDS application to the skin induced inflammation, xeroderma, and elongation of peripheral nerves into the epidermis. The number of neurons immunopositive for c-Fos, a well known marker of neural activity, was substantially higher (+441%) in spinal dorsal horn (SDH) lamina I-II (but not lamina III-VI) of SDS-treated mice compared to vehicle-treated mice. In vivo extracellular recording revealed enhanced spontaneous (+64%) and non-noxious mechanical stimulation-evoked firing (+139%) of SDH lamina I-II neurons in SDS-treated mice, and stimulation-evoked neuronal firing was sustained (+5333%) even after stimulation. The number of GFAP-positive (activated) astrocytes, but not Iba1-positive microglia, was also elevated (+137%) in SDH lamina I-II of SDS-treated mice compared to vehicle-treated mice. Peripheral nerve elongation and hyperexcitability of afferent or SDH neurons, possible associated with the activation of spinal astrocytes, may underlie cutaneous hypersensitivity induced by surfactants.

Function of Adenosine 2A Receptor in High-Fat Diet-Induced Peripheral Neuropathy

Peripheral diabetic neuropathy (DPN) is a complication observed in up to half of all patients with type 2 diabetes. DPN has also been shown to be associated with obesity. High-fat diet (HFD) affects glucose metabolism, and the impaired glucose tolerance can lead to type 2 diabetes. There is evidence to suggest a role of adenosine 2A receptors (A2ARs) and semaphorin 3A (Sema3a) signaling in DPN. The link between the expression of Sema3a and A2AR in DPN was hypothesized, but the underlying mechanisms remain poorly understood. In this study, we investigated the regulation of Sema3a by A2AR in the spinal cord and the functional implications thereof in DPN. We examined the expression of A2ARs and Sema3a, as well as Neuropilin 1 and Plexin A, the coreceptors of Sema3a, in the dorsal horn of the lumbar spinal cord of an animal model with HFD-induced diabetes. Our results demonstrate that HFD dysregulates the A2AR-mediated Sema3a expression, with functional implications for the type 2 diabetes-induced peripheral neuropathy. These observations could stimulate clinical studies to improve our understanding on the subject.

Genetic Analysis of the Organization, Development, and Plasticity of Corneal Innervation in Mice

The cornea has the densest sensory innervation of the body, originating primarily from neurons in the trigeminal ganglion. The basic principles of cornea nerve patterning have been established many years ago using classic neuroanatomical methods, such as immunocytochemistry and electrophysiology. Our understanding of the morphology and distribution of the sensory nerves in the skin has considerably progressed over the past few years through the generation and analysis of a variety of genetically modified mouse lines. Surprisingly, these lines were not used to study corneal axons. Here, we have screened a collection of transgenic and knockin mice (of both sexes) to select lines allowing the visualization and genetic manipulation of corneal nerves. We identified multiple lines, including some in which different types of corneal axons can be simultaneously observed with fluorescent proteins expressed in a combinatorial manner. We also provide the first description of the morphology and arborization of single corneal axons and identify three main types of branching pattern. We applied this genetic strategy to the analysis of corneal nerve development and plasticity. We provide direct evidence for a progressive reduction of the density of corneal innervation during aging. We also show that the semaphorin receptor neuropilin-1 acts cell-autonomously to control the development of corneal axons and that early axon guidance defects have long-term consequences on corneal innervation.SIGNIFICANCE STATEMENT We have screened a collection of transgenic and knockin mice and identify lines allowing the visualization and genetic manipulation of corneal nerves. We provide the first description of the arborization pattern of single corneal axons. We also present applications of this genetic strategy to the analysis of corneal nerve development and remodeling during aging.

Semaphorin3A induces nerve regeneration in the adult cornea-a switch from its repulsive role in development

The peripheral sensory nerves that innervate the cornea can be easily damaged by trauma, surgery, infection or diabetes. Several growth factors and axon guidance molecules, such as Semaphorin3A (Sema3A) are upregulated upon cornea injury. Nerves can regenerate after injury but do not recover their original density and patterning. Sema3A is a well known axon guidance and growth cone repellent protein during development, however its role in adult cornea nerve regeneration remains undetermined. Here we investigated the neuro-regenerative potential of Sema3A on adult peripheral nervous system neurons such as those that innervate the cornea. First, we examined the gene expression profile of the Semaphorin class 3 family members and found that all are expressed in the cornea. However, upon cornea injury there is a fast increase in Sema3A expression. We then corroborated that Sema3A totally abolished the growth promoting effect of nerve growth factor (NGF) on embryonic neurons and observed signs of growth cone collapse and axonal retraction after 30 min of Sema3A addition. However, in adult isolated trigeminal ganglia or dorsal root ganglia neurons, Sema3A did not inhibited the NGF-induced neuronal growth. Furthermore, adult neurons treated with Sema3A alone produced similar neuronal growth to cells treated with NGF and the length of the neurites and branching was comparable between both treatments. These effects were replicated in vivo, where thy1-YFP neurofluorescent mice subjected to cornea epithelium debridement and receiving intrastromal pellet implantation containing Sema3A showed increased corneal nerve regeneration than those receiving pellets with vehicle. In adult PNS neurons, Sema3A is a potent inducer of neuronal growth in vitro and cornea nerve regeneration in vivo. Our data indicates a functional switch for the role of Sema3A in PNS neurons where the well-described repulsive role during development changes to a growth promoting effect during adulthood. The high expression of Sema3A in the normal and injured adult corneas could be related to its role as a growth factor.

The Semaphorin 3A inhibitor SM-345431 preserves corneal nerve and epithelial integrity in a murine dry eye model

Dry eye disease (DED) is a common disorder causing discomfort and ocular fatigue. Corneal nerves are compromised in DED, which may further cause loss of corneal sensation and decreased tear secretion. Semaphorin 3A (Sema3A) is expressed by the corneal epithelium under stress, and is known as an inhibitor of axonal regeneration. Using a murine dry eye model, we found that topical SM-345431, a selective Sema3A inhibitor, preserved corneal sensitivity (2.3 ± 0.3 mm versus 1.4 ± 0.1 mm in vehicle control, p = 0.004) and tear volume (1.1 ± 0.1 mm versus 0.3 ± 0.1 mm in vehicle control, p < 0.001). Fluorescein staining area of the cornea due to damage to barrier function was also reduced (4.1 ± 0.9% in SM-345431 group versus 12.9 ± 2.2% in vehicle control, p < 0.001). The incidence of corneal epithelial erosions was significantly suppressed by SM-345431 (none in SM-345431 group versus six (21%) in vehicle control, p = 0.01). Furthermore, sub-epithelial corneal nerve density and intraepithelial expression of transient receptor potential vanilloid receptor 1 (TRPV1) were significantly preserved with SM-345431. Our results suggest that inhibition of Sema3A may be an effective therapy for DED.

In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease

In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.

Cardiac Sympathetic Nerve Sprouting and Susceptibility to Ventricular Arrhythmias after Myocardial Infarction

Ventricular arrhythmogenesis is thought to be a common cause of sudden cardiac death following myocardial infarction (MI). Nerve remodeling as a result of MI is known to be an important genesis of life-threatening arrhythmias. It is hypothesized that neural modulation might serve as a therapeutic option of malignant arrhythmias. In fact, left stellectomy or β-blocker therapy is shown to be effective in the prevention of ventricular tachyarrhythmias (VT), ventricular fibrillation (VF), and sudden cardiac death (SCD) after MI both in patients and in animal models. Results from decades of research already evidenced a positive relationship between abnormal nerve density and ventricular arrhythmias after MI. In this review, we summarized the molecular mechanisms involved in cardiac sympathetic rejuvenation and mechanisms related to sympathetic hyperinnervation and arrhythmogenesis after MI and analyzed the potential therapeutic implications of nerve sprouting modification for ventricular arrhythmias and SCD control.

Semaphorin 3a transfection into the left stellate ganglion reduces susceptibility to ventricular arrhythmias after myocardial infarction in rats

AIMS

Myocardial infarction (MI) induces neural remodelling of the left stellate ganglion (LSG), which may contribute to ischaemia-induced arrhythmias. The neural chemorepellent Semaphorin 3a (Sema3a) has been identified as a negative regulator of sympathetic innervation in the LSG and heart. We previously reported that overexpression of Sema3a in the border zone could reduce the arrhythmogenic effects of cardiac sympathetic hyperinnervation post-MI. This study investigated whether Sema3a overexpression within the LSG confers an antiarrhythmic effect after MI through decreasing extra- and intra-cardiac neural remodelling.

METHODS AND RESULTS

Sprague-Dawley rats were subjected to MI, and randomly allocated to intra-LSG microinjection of either phosphate-buffered saline (PBS), adenovirus encoding green fluorescent protein (AdGFP), or adenovirus encoding Sema3a (AdSema3a). Sham-operated rats served as controls. Two weeks after infarction, MI-induced nerve sprouting and sympathetic hyperinnervation in the LSG and myocardium were significantly attenuated by intra-LSG injection with AdSema3a, as assessed by immunohistochemistry and western blot analysis of growth-associated protein 43 and tyrosine hydroxylase. This was also confirmed by sympathetic nerve function changes assessed by cardiac norepinephrine content. Additionally, intra-LSG injection with AdSema3a alleviated MI-induced accumulation of dephosphorylated connexin 43 in the infarct border zone. Furthermore, Sema3a overexpression in the LSG reduced the incidence of inducible ventricular tachyarrhythmia by programmed electrical stimulation post-MI, and arrhythmia scores were significantly lower in the AdSema3a group than in the PBS and AdGFP groups.

CONCLUSION

Semaphorin 3a overexpression in the LSG ameliorates the inducibility of ventricular arrhythmias after MI, mainly through attenuation of neural remodelling within the cardiac-neuraxis.

Transmembrane proteoglycans syndecan-2, 4, receptor candidates for the impact of HGF and FGF2 on semaphorin 3A expression in early-differentiated myoblasts

Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies proposed an unexplored role of resident myogenic stem cell (satellite cell)-derived myoblasts as a key presenter of a secreted neural chemorepellent semaphorin 3A (Sema3A); hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2) triggered its expression exclusively at the early differentiation phase. In order to advance this concept, the present study described that transmembrane heparan/chondroitin sulfate proteoglycans syndecan-2, 4 may be the plausible receptor candidates for HGF and FGF2 to signal Sema3A expression. Results showed that mRNA expression of syndecan-2, 4 was abundant (two magnitudes higher than syndecan-1, 3) in early-differentiated myoblasts and their in vitro knockdown diminished the HGF/FGF2-induced expression of Sema3A down to a baseline level. Pretreatment with heparitinase and chondroitinase ABC decreased the HGF and FGF2 responses, respectively, in non-knockdown cultures, supporting a possible model that HGF and FGF2 may bind to heparan and chondroitin sulfate chains of syndecan-2, 4 to signal Sema3A expression. The findings, therefore, extend our understanding that HGF/FGF2-syndecan-2, 4 association may stimulate a burst of Sema3A secretion by myoblasts recruited to the site of muscle injury; this would ensure a coordinated delay in the attachment of motoneuron terminals onto fibers early in muscle regeneration, and thus synchronize the recovery of muscle fiber integrity and the early resolution of inflammation after injury with reinnervation toward functional recovery.

CRMP1 Interacted with Spy1 During the Collapse of Growth Cones Induced by Sema3A and Acted on Regeneration After Sciatic Nerve Crush

CRMP1, a member of the collapsin response mediator protein family (CRMPs), was reported to regulate axon outgrowth in Sema3A signaling pathways via interactions with its co-receptor protein neuropilin-1 and plexin-As through the Fyn-cyclin-dependent kinase 5 (CDK5) cascade and the sequential phosphorylation of CRMP1 by lycogen synthase kinase-3β (GSK-3β). Using yeast two-hybrid, we identified a new molecule, Speedy A1 (Spy1), a member of the Speedy/RINGO family, with an interaction with CRMP1. Besides, for the first time, we observed the association of CRMP1 with actin. Based on this, we wondered the association of them and their function in Sema3A-induced growth cones collapse and regeneration process after SNC. During our study, we constructed overexpression plasmid and short hairpin RNA (shRNA) to question the relationship of CRMP1/Spy1 and CRMP1/actin. We observed the interactions of CRMP1/Spy1 and CRMP1/actin. Besides, we found that Spy1 could affect CRMP1 phosphorylation actived by CDK5 and that enhanced CRMP1 phosphorylation might disturb the combination of CRMP1 and actin, which would contribute to abnormal of Sema3A-induced growth cones collapse and finally lead to influent regeneration process after rat sciatic nerve crush. Through rat walk footprint test, we also observed the variance during regeneration progress, respectively. We speculated that CRMP1 interacted with Spy1 which would disturb the association of CRMP1 with actin and was involved in the collapse of growth cones induced by Sema3A and regeneration after sciatic nerve crush.

Heart development and regeneration via cellular interaction and reprogramming

The heart consists of many types of cells, including cardiomyocytes, vascular cells, neural cells, and cardiac fibroblasts. Adult cardiomyocytes are terminally differentiated cells, and loss of cardiomyocytes as a result of heart damage is irreversible. To regenerate damaged hearts and restore cardiac function, understanding the cellular and molecular basis of heart development is of considerable importance. Although it is well known that heart function is tightly regulated by cell-cell interactions, their roles in heart development are not clear. Recent studies, including ours, identified important roles of cell-cell interactions in heart development and function. The balance between neural chemoattractants and chemorepellents secreted from cardiomyocytes determines cardiac nervous development. Nerve growth factor is a potent chemoattractant synthesized by cardiomyocytes, whereas Sema3a is a neural chemorepellent expressed specifically in the subendocardium. Disruption of this molecular balance induces disorganized cardiac innervation and may lead to sudden cardiac death due to lethal arrhythmias. Cardiac fibroblasts, of which there are large populations in the heart, secrete high levels of specific extracellular matrix and growth factors. Embryonic cardiac fibroblast-specific secreted factors collaboratively promote mitotic activity of embryonic cardiomyocytes and expansion of ventricular chambers during cardiogenesis. More recently, utilizing knowledge of the regulatory mechanisms of heart development, we found that cardiac fibroblasts can be directly reprogrammed into cardiomyocyte-like cells in vitro and in vivo by gene transfer of cardiac-specific transcription factors. Understanding the mechanisms of heart development and cardiac reprogramming technology may provide new therapeutic approaches for heart disease in the future.

CD11b+GR1+ myeloid cells secrete NGF and promote trigeminal ganglion neurite growth: implications for corneal nerve regeneration

PURPOSE

We characterized fluorescent bone marrow cells (YFP(+) BMCs) in the thy1-YFP mouse and determine if they promote trigeminal ganglion (TG) cell neurite growth.

METHODS

Excimer laser annular keratectomy was performed in thy1-YFP mice, and corneas were imaged. BMCs were harvested from femur and tibia, and the expression of surface markers on YFP(+) BMCs was analyzed by flow cytometry. The immunosuppressive action of BMCs (YFP(+) and YFP(-)) was evaluated in an allogenic mixed lymphocyte reaction (MLR). Neurotrophic action of BMCs (YFP(+) and YFP(-)) was determined in compartmental and transwell cultures of dissociated TG cells.

RESULTS

Following annular keratectomy, YFP(+) BMCs infiltrated the cornea. YFP(+) BMCs shared surface markers (CD11b+Gr1+Ly6C+Ly6G-F4/80(low)) with monocytic myeloid-derived suppressor cells (MDSCs), had similar morphology, and suppressed T-cell proliferation in allogenic MLR in a dose-dependent manner. YFP(+) BMCs, but not YFP(-) BMCs, significantly increased growth of TG neurites in vitro. When cultured in a transwell with TG neurites, YFP(+) BMCs expressed neurotrophins and secreted nerve growth factor (NGF) in conditioned medium. YFP(+) BMCs that infiltrated the cornea maintained their phenotype and actions (neuronal and immune).

CONCLUSIONS

YFP(+) BMCs in thy1-YFP mice have immunophenotypic features of MDSCs. They secrete NGF and promote neuroregeneration. Their immunosuppressive and neurotrophic actions are preserved after corneal infiltration. These findings increase our understanding of the beneficial roles played by leukocyte trafficking in the cornea and may lead to therapeutic strategies that use NGF-secreting myeloid cells to repair diseased or injured neurons.

A nonsynonymous polymorphism in semaphorin 3A as a risk factor for human unexplained cardiac arrest with documented ventricular fibrillation

Unexplained cardiac arrest (UCA) with documented ventricular fibrillation (VF) is a major cause of sudden cardiac death. Abnormal sympathetic innervations have been shown to be a trigger of ventricular fibrillation. Further, adequate expression of SEMA3A was reported to be critical for normal patterning of cardiac sympathetic innervation. We investigated the relevance of the semaphorin 3A (SEMA3A) gene located at chromosome 5 in the etiology of UCA. Eighty-three Japanese patients diagnosed with UCA and 2,958 healthy controls from two different geographic regions in Japan were enrolled. A nonsynonymous polymorphism (I334V, rs138694505A>G) in exon 10 of the SEMA3A gene identified through resequencing was significantly associated with UCA (combined P = 0.0004, OR 3.08, 95%CI 1.67-5.7). Overall, 15.7% of UCA patients carried the risk genotype G, whereas only 5.6% did in controls. In patients with SEMA3A(I334V), VF predominantly occurred at rest during the night. They showed sinus bradycardia, and their RR intervals on the 12-lead electrocardiography tended to be longer than those in patients without SEMA3A(I334V) (1031±111 ms versus 932±182 ms, P = 0.039). Immunofluorescence staining of cardiac biopsy specimens revealed that sympathetic nerves, which are absent in the subendocardial layer in normal hearts, extended to the subendocardial layer only in patients with SEMA3A(I334V). Functional analyses revealed that the axon-repelling and axon-collapsing activities of mutant SEMA3A(I334V) genes were significantly weaker than those of wild-type SEMA3A genes. A high incidence of SEMA3A(I334V) in UCA patients and inappropriate innervation patterning in their hearts implicate involvement of the SEMA3A gene in the pathogenesis of UCA.

Particle-mediated administration of plasmid DNA on corneas of BALB/c mice

Gene gun administration of DNA is an invaluable technique for transfecting tissues with only 1 μg DNA/shot. Here, we describe a transfection technique of healthy corneas of BALB/c mice with a standard gene gun, using a technique that can avoid tissue destruction even when high pressure is used (e.g., 700 psi). The focal transfection of the cornea to improve corneal disease may be an advantage over other transfection methods in order to avoid unwanted bystander transfection in other compartments of the eye or body.

The semaphorin 3A inhibitor SM-345431 accelerates peripheral nerve regeneration and sensitivity in a murine corneal transplantation model

Background

Peripheral nerve damage of the cornea is a complication following surgery or infection which may lead to decreased visual function. We examined the efficacy of the semaphorin 3A inhibitor, SM-345431, in promoting regeneration of peripheral nerves in a mouse corneal transplantation model.

Methodology/Principal Findings

P0-Cre/Floxed-EGFP mice which express EGFP in peripheral nerves cells were used as recipients of corneal transplantation with syngeneic wild-type mouse cornea donors. SM-345431 was administered subconjunctivally every 2 days while control mice received vehicle only. Mice were followed for 3 weeks and the length of regenerating nerves was measured by EGFP fluorescence and immunohistochemistry against βIII tubulin. Cornea sensitivity was also measured by the Cochet-Bonnet esthesiometer. CD31 staining was used to determine corneal neovascularization as a possible side effect of SM-345431. Regeneration of βIII tubulin positive peripheral nerves was significantly higher in SM-345431 treated mice compared to control. Furthermore, corneal sensitivity significantly improved in the SM-345431 group by 3 weeks after transplantation. Neovascularization was limited to the peripheral cornea with no difference between SM-345431 group and control.

Conclusions/Significance

Subconjunctival injections of SM-345431 promoted a robust network of regenerating nerves as well as functional recovery of corneal sensation in a mouse keratoplasty model, suggesting a novel therapeutic strategy for treating neurotrophic corneal disease.

Comparative analysis of semaphorin 3A in soleus and EDL muscle satellite cells in vitro toward understanding its role in modulating myogenin expression

Resident myogenic stem cells, satellite cells, up-regulate a secreted multi-functional modulator, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle-crush injury and treatment with hepatocyte growth factor (HGF) or basic fibroblast growth factor (FGF2). Here, we add evidence that the Sema3A expression and secretion induced by the growth factors is significantly higher in primary cultures from adult rat soleus than from the fast-twitch extensor digitorum longus (EDL) muscle. The higher Sema3A response, revealed by quantitative PCR and Western blotting of cell lysates and conditioned media, may account for the higher myogenin expression of soleus muscle satellite cells early in differentiation since addition of recombinant Sema3A stimulates myogenin expression in cultures. These experiments also showed that mRNA expression of plexin A2, which together with neuropilins, constitutes Sema3A composite-receptors, was higher in satellite cells from soleus than EDL with no difference in plexin A1 and A3 and neuropilin-1 and 2 levels. These comparative studies, therefore, highlight a possible Sema3A-plexin A2-myogenin signaling axis that may ensure promoting early differentiation by soleus muscle satellite cells.

Distinct roles for neuropilin1 and neuropilin2 during mouse corneal innervation

Trigeminal sensory innervation of the cornea is critical for protection and synthesis of neuropeptides required for normal vision. Little is known about axon guidance during mammalian corneal innervation. In contrast to the chick where a pericorneal nerve ring forms via Npn/Sema signaling, mouse corneal axons project directly into the presumptive cornea without initial formation of an analogous nerve ring. Here we show that during development of the mouse cornea, Npn1 is strongly expressed by the trigeminal ganglion whereas Npn2 is expressed at low levels. At the same time Sema3A and Sema3F are expressed in distinct patterns in the ocular tissues. Npn1(sema-/-) mutant corneas become precociously and aberrantly innervated by nerve bundles that project further into the corneal stroma. In contrast, stromal innervation was not affected in Npn2(-/-) mutants. The corneal epithelium was prematurely innervated in both Npn1(sema-/-) and Npn2(-/-) mutants. These defects were exacerbated in Npn1(sema-/-);Npn2(-/-) double mutants, which in addition showed ectopic innervation of the region between the optic cup and lens vesicle. Collectively, our data show that Sema3A/Npn1 and Sema3F/Npn2 signaling play distinct roles and both are required for proper innervation of the mouse cornea.

Development, maturation, and transdifferentiation of cardiac sympathetic nerves

The heart is electrically and mechanically controlled as a syncytium by the autonomic nervous system. The cardiac nervous system comprises the sympathetic, parasympathetic, and sensory nervous systems that together regulate heart function on demand. Sympathetic electric activation was initially considered the main regulator of cardiac function; however, modern molecular biotechnological approaches have provided a new dimension to our understanding of the mechanisms controlling the cardiac nervous system. The heart is extensively innervated, although the innervation density is not uniform within the heart, being high in the subepicardium and the special conduction system. We and others showed previously that the balance between neural chemoattractants and chemorepellents determine cardiac nervous development, with both factors expressed in heart. Nerve growth factor is a potent chemoattractant synthesized by cardiomyocytes, whereas Sema3a is a neural chemorepellent expressed specifically in the subendocardium. Disruption of this well-organized molecular balance and innervation density can induce sudden cardiac death due to lethal arrhythmias. In diseased hearts, various causes and mechanisms underlie cardiac sympathetic abnormalities, although their detailed pathology and significance remain contentious. We reported that cardiac sympathetic rejuvenation occurs in cardiac hypertrophy and, moreover, interleukin-6 cytokines secreted from the failing myocardium induce cholinergic transdifferentiation of the cardiac sympathetic system via a gp130 signaling pathway, affecting cardiac performance and prognosis. In this review, we summarize the molecular mechanisms involved in sympathetic development, maturation, and transdifferentiation, and propose their investigation as new therapeutic targets for heart disease.

Neurofibromatosis-1 heterozygosity impairs CNS neuronal morphology in a cAMP/PKA/ROCK-dependent manner

Children with the neurofibromatosis-1 (NF1) cancer predisposition syndrome exhibit numerous clinical problems that reflect defective central nervous system (CNS) neuronal function, including learning disabilities, attention deficit disorder, and seizures. These clinical features result from reduced NF1 protein (neurofibromin) expression in NF1+/- (NF1 heterozygosity) brain neurons. Previous studies have shown that mouse CNS neurons are sensitive to the effects of reduced Nf1 expression and exhibit shorter neurite lengths, smaller growth cone areas, and attenuated survival, reflecting attenuated neurofibromin cAMP regulation. In striking contrast, Nf1+/- peripheral nervous system (PNS) neurons are nearly indistinguishable from their wild-type counterparts, and complete neurofibromin loss leads to increased neurite lengths and survival in a RAS/Akt-dependent fashion. To gain insights into the differential responses of CNS and PNS neurons to reduced neurofibromin function, we designed a series of experiments to define the molecular mechanism(s) underlying the unique CNS neuronal sensitivity to Nf1 heterozygosity. First, Nf1 heterozygosity decreases cAMP levels in CNS, but not in PNS, neurons. Second, CNS neurons exhibit Nf1 gene-dependent increases in RAS pathway signaling, but no further decreases in cAMP levels were observed in Nf1-/- CNS neurons relative to their Nf1+/- counterparts. Third, neurofibromin regulates CNS neurite length and growth cone areas in a cAMP/PKA/Rho/ROCK-dependent manner in vitro and in vivo. Collectively, these findings establish cAMP/PKA/Rho/ROCK signaling as the responsible axis underlying abnormal Nf1+/- CNS neuronal morphology with important implications for future preclinical and clinical studies aimed at improving cognitive and behavioral deficits in mice and children with reduced brain neuronal NF1 gene expression.

VEGF signaling mediates bladder neuroplasticity and inflammation in response to BCG

Background

This work tests the hypothesis that increased levels of vascular endothelial growth factor (VEGF) observed during bladder inflammation modulates nerve plasticity.

Methods

Chronic inflammation was induced by intravesical instillations of Bacillus Calmette-Guérin (BCG) into the urinary bladder and the density of nerves expressing the transient receptor potential vanilloid subfamily 1 (TRPV1) or pan-neuronal marker PGP9.5 was used to quantify alterations in peripheral nerve plasticity. Some mice were treated with B20, a VEGF neutralizing antibody to reduce the participation of VEGF. Additional mice were treated systemically with antibodies engineered to specifically block the binding of VEGF to NRP1 (anti-NRP1^B) and NRP2 (NRP2^B), or the binding of semaphorins to NRP1 (anti-NRP1 ^A) to diminish activity of axon guidance molecules such as neuropilins (NRPs) and semaphorins (SEMAs). To confirm that VEGF is capable of inducing inflammation and neuronal plasticity, another group of mice was instilled with recombinant VEGF₁₆₅ or VEGF₁₂₁ into the urinary bladder.

Results

The major finding of this work was that chronic BCG instillation resulted in inflammation and an overwhelming increase in both PGP9.5 and TRPV1 immunoreactivity, primarily in the sub-urothelium of the urinary bladder. Treatment of mice with anti-VEGF neutralizing antibody (B20) abolished the effect of BCG on inflammation and nerve density.

NRP1^A and NRP1^B antibodies, known to reduce BCG-induced inflammation, failed to block BCG-induced increase in nerve fibers. However, the NRP2^B antibody dramatically potentiated the effects of BCG in increasing PGP9.5-, TRPV1-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactivity (IR). Finally, instillation of VEGF₁₂₁ or VEGF₁₆₅ into the mouse bladder recapitulated the effects of BCG and resulted in a significant inflammation and increase in nerve density.

Conclusions

For the first time, evidence is being presented supporting that chronic BCG instillation into the mouse bladder promotes a significant increase in peripheral nerve density that was mimicked by VEGF instillation. Effects of BCG were abolished by pre-treatment with neutralizing VEGF antibody. The present results implicate the VEGF pathway as a key modulator of inflammation and nerve plasticity, introduces a new animal model for investigation of VEGF-induced nerve plasticity, and suggests putative mechanisms underlying this phenomenon.

Growth factor regulation of neural chemorepellent Sema3A expression in satellite cell cultures

Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory signals of such coordination remain unclear, although axon-guidance molecules may be involved. Recently, satellite cells, resident myogenic stem cells positioned beneath the basal lamina and at high density at the myoneural junction regions of mature fibers, were shown to upregulate a secreted neural chemorepellent semaphorin 3A (Sema3A) in response to in vivo muscle-crush injury. The initial report on that expression centered on the observation that hepatocyte growth factor (HGF), an essential cue in muscle fiber growth and regeneration, remarkably upregulates Sema3A expression in early differentiated satellite cells in vitro [Tatsumi et al., Am J Physiol Cell Physiol 297: C238–C252, 2009]. Here, we address regulatory effects of basic fibroblast growth factor (FGF2) and transforming growth factor (TGF)-βs on Sema3A expression in satellite cell cultures. When treated with FGF2, Sema3A message and protein were upregulated as revealed by reverse transcription-polymerase chain reaction and immunochemical studies. Sema3A upregulation by FGF2 was dose dependent with a maximum (8- to 1-fold relative to the control) at 2.5 ng/ml (150 pM) and occurred exclusively at the early differentiation stage. The response was highly comparable in dose response and timing to effects of HGF treatment, without any additive or synergistic effect from treatment with a combination of both potent upregulators. In contrast, TGF-β2 and -β3 potently decreased basal Sema3A expression; the maximum effect was at very low concentrations (40 and 8 pM, respectively) and completely cancelled the activities of FGF2 and HGF to upregulate Sema3A. These results therefore encourage the prospect that a time-coordinated increase in HGF, FGF2, and TGF-β ligands and their receptors promotes a programmed strategy for Sema3A expression that guarantees successful intramuscular motor reinnervation by delaying sprouting and reattachment of motoneuron terminals onto damaged muscle fibers early in regeneration pending restoration of muscle fiber contractile integrity.

Semaphorin 3A inhibits growth of adult sympathetic and parasympathetic neurones via distinct cyclic nucleotide signalling pathways

BACKGROUND AND PURPOSE

Semaphorin 3A (Sema3A) is an important secreted repulsive guidance factor for many developing neurones. Sema3A continues to be expressed in adulthood, and expression of its receptor, neuropilin-1 (Nrp-1), can be altered by nerve injury. Autonomic neurones innervating the pelvic viscera are particularly susceptible to damage during pelvic surgical procedures, and failure to regenerate or aberrant growth of sympathetic and parasympathetic nerves lead to organ dysfunction. However, it is not known if adult pelvic neurones are potential targets for Sema3A.

EXPERIMENTAL APPROACH

The effects of Sema3A and activation or inhibition of cyclic nucleotide signalling were assessed in adult rat pelvic ganglion neurones in culture using a growth cone collapse assay.

KEY RESULTS

Sema3A caused growth cone collapse in both parasympathetic and sympathetic neurones expressing Nrp-1. However, the effect of Sema3A was mediated by distinct cyclic nucleotide signalling pathways in each neurone type. In parasympathetic neurones, cAMP and downstream activation of protein kinase A were required for growth cone collapse. In sympathetic neurones, cGMP was required for Sema3A-induced collapse; cAMP can also cause collapse but was not required. Sema3A-mediated, cGMP-dependent collapse in sympathetic neurones may require activation of cyclic nucleotide-gated ion channels (CNGCs).

CONCLUSIONS AND IMPLICATIONS

We propose that Sema3A is an important guidance factor for adult pelvic autonomic neurones, and that manipulation of their distinct signalling mechanisms could potentially promote functional selective regeneration or attenuate aberrant growth. To our knowledge, this is also the first study to implicate CNGCs in regulating growth cone dynamics of adult neurones.

Intrathecally administered Sema3A protein attenuates neuropathic pain behavior in rats with chronic constriction injury of the sciatic nerve

Semaphorins, one of the repulsive axonal guidance factors during development, are produced under pathological conditions in adult animals. In the neuropathic pain state associated with peripheral nerve injury, synaptic reorganization occurs in spinal cord dorsal horn. In the present study, we investigated the roles of intrathecal administration of Sema3A, a secreted semaphorin, in the spinal cord of chronic constriction injury (CCI) model rat. Neuropilin 1 (NPR1) and Plexin A (PlexA), co-receptors of Sema3A, were expressed in the dorsal horn of naïve rats. NPR1, and not PlexA, protein expression increased in the dorsal spinal cord of CCI rats. Recombinant Sema3A protein attenuated mechanical allodynia and heat hyperalgesia in CCI rats, whereas heat-inactivated Sema3A had no effect. Immunohistochemistry revealed that Sema3A partially restored the decrease of isolectin B4-positive unmyelinated nerve terminals in lamina II of the ipsilateral dorsal horn of CCI rats. Contrary to our expectations, Sema3A did not change the distribution of myelinated fibers in lamina II at 7 days after CCI. Those results suggested that the suppressive role for Sema3A in the development of neuropathic pain associated with peripheral nerve injury in adult rats, which seemed to be independent from prevention of the myelinated fiber sprouting into lamina II.

Expression of semaphorin 3A in the rat corneal epithelium during wound healing

The neural guidance protein semaphorin 3A (Sema3A) is expressed in corneal epithelial cells of the adult rat. We have now further investigated the localization of Sema3A in the normal rat corneal epithelium as well as changes in its expression pattern during wound healing after central corneal epithelial debridement. The expression pattern of Sema3A was compared with that of the tight-junction protein zonula occludens-1 (ZO-1), the gap-junction protein connexin43 (Cx43), or the cell proliferation marker Ki67. Immunofluorescence analysis revealed that Sema3A was present predominantly in the membrane of basal and wing cells of the intact corneal epithelium. The expression of Sema3A at the basal side of basal cells was increased in the peripheral epithelium compared with that in the central region. Sema3A was detected in all layers at the leading edge of the migrating corneal epithelium at 6h after central epithelial debridement. The expression of Sema3A was markedly up-regulated in the basal and lateral membranes of columnar basal cells apparent in the thickened, newly healed epithelium at 1 day after debridement, but it had largely returned to the normal pattern at 3 days after debridement. The expression of ZO-1 was restricted to superficial epithelial cells and remained mostly unchanged during the wound healing process. The expression of Cx43 in basal cells was down-regulated at the leading edge of the migrating epithelium but was stable in the remaining portion of the epithelium. Ki67 was not detected in basal cells of the central epithelium at 1 day after epithelial debridement, when Sema3A was prominently expressed. Immunoblot analysis showed that the abundance of Sema3A in the central cornea was increased 1 day after epithelial debridement, whereas that of ZO-1 or Cx43 remained largely unchanged. This increase in Sema3A expression was accompanied by up-regulation of the Sema3A coreceptor neuropilin-1. Our observations have thus shown that the expression of Sema3A is increased markedly in basal cells of the newly healed corneal epithelium, and that this up-regulation of Sema3A is not associated with cell proliferation. They further suggest that Sema3A might play a role in the regulation of corneal epithelial wound healing.

Cardiac innervation and sudden cardiac death

The heart is extensively innervated and its performance is tightly controlled by the nervous system. Cardiac innervation density varies in diseased hearts leading to unbalanced neural activation and lethal arrhythmia. Diabetic sensory neuropathy causes silent myocardial ischemia, characterized by loss of pain perception during myocardial ischemia, which is a major cause of sudden cardiac death in diabetes mellitus (DM). Despite its clinical importance, the mechanisms underlying the control and regulation of cardiac innervation remain poorly understood.We found that cardiac innervation is determined by the balance between neural chemoattractants and chemorepellents within the heart. Nerve growth factor (NGF), a potent chemoattractant, is induced by endothelin-1 upregulation during development and is highly expressed in cardiomyocytes. By comparison, Sema3a, a neural chemorepellent, is highly expressed in the subendocardium of early stage embryos, and is suppressed during development. The balance of expression between NGF and Seme3a leads to epicardial-to-endocardial transmural sympathetic innervation patterning. We also found that downregulation of cardiac NGF leads to diabetic neuropathy, and that NGF supplementation rescues silent myocardial ischemia in DM. Cardiac innervation patterning is disrupted in Sema3a-deficient and Sema3a-overexpressing mice, leading to sudden death or lethal arrhythmias. The present review focuses on the regulatory mechanisms underlying cardiac innervation and the critical role of these processes in cardiac performance.

Possible implication of satellite cells in regenerative motoneuritogenesis: HGF upregulates neural chemorepellent Sema3A during myogenic differentiation

Regenerative coordination and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory mechanisms of such coordination remain unclear, although both attractive and repulsive axon guidance molecules may be involved in the signaling pathway. Here we show that expression of a neural secreted chemorepellent semaphorin 3A (Sema3A) is remarkably upregulated in satellite cells of resident myogenic stem cells that are positioned beneath the basal lamina of mature muscle fibers, when treated with hepatocyte growth factor (HGF), established as an essential cue in muscle fiber growth and regeneration. When satellite cells were treated with HGF in primary cultures of cells or muscle fibers, Sema3A message and protein were upregulated as revealed by reverse transcription-polymerase chain reaction and immunochemical studies. Other growth factors had no inductive effect except for a slight effect of epidermal growth factor treatment. Sema3A upregulation was HGF dose dependent with a maximum (about 7- to 8-fold units relative to the control) at 10–25 ng/ml and occurred exclusively at the early-differentiation stage, as characterized by the level of myogenin expression and proliferation (bromodeoxyuridine incorporation) of the cells. Neutralizing antibody to the HGF-specific receptor, c-met, did not abolish the HGF response, indicating that c-met may not mediate the Sema3A expression signaling. Finally, in vivo Sema3A was upregulated in the differentiation phase of satellite cells isolated from muscle regenerating following crush injury. Overall, the data highlight a heretofore unexplored and active role for satellite cells as a key source of Sema3A expression triggered by HGF, hence suggesting that regenerative activity toward motor innervation may importantly reside in satellite cells and could be a crucial contributor during postnatal myogenesis.

Mechanisms regulating interpretation of guidance cues during development, maturation, and following injury

Guidance molecules are not inherently attractive or repulsive, but rather, are interpreted as such based on the context in which they are encountered. Thus, accurate wiring of the central nervous system is inextricably tied to the internal state of neurons and their local environment. To protect functional integrity, these carefully formed circuits are stabilized via a combination of neuronal and environmental changes during maturation and following injury. While necessary, such modifications create obstacles for reconstruction of damaged circuits. Here, we consider the effects of maturation and injury induced changes on the interpretation of guidance cues by regenerating neurons and the problems they pose for faithful reconstruction of functional circuits.

Peripheral nerve regeneration is delayed in neuropilin 2-deficient mice

Peripheral nerve transection or crush induces expression of class 3 semaphorins by epineurial and perineurial cells at the injury site and of the neuropilins neuropilin-1 and neuropilin-2 by Schwann and perineurial cells in the nerve segment distal to the injury. Neuropilin-dependent class 3 semaphorin signaling guides axons during neural development, but the significance of this signaling system for regeneration of adult peripheral nerves is not known. To test the hypothesis that neuropilin-2 facilitates peripheral-nerve axonal regeneration, we crushed sciatic nerves of adult neuropilin-2-deficient and littermate control mice. Axonal regeneration through the crush site and into the distal nerve segment, repression by the regenerating axons of Schwann cell p75 neurotrophin receptor expression, remyelination of the regenerating axons, and recovery of normal gait were all significantly slower in the neuropilin-2-deficient mice than in the control mice. Thus, neuropilin-2 facilitates peripheral-nerve axonal regeneration.

Targeting axon growth from neuronal transplants along preformed guidance pathways in the adult CNS

To re-establish neuronal circuits lost after CNS injury, transplanted neurons must be able to extend axons toward their appropriate targets. Such growth is highly restricted within the adult CNS attributable to the expression of inhibitory molecules and general lack of guidance cues to direct axon growth. This environment typically induces random patterns of growth and aberrant innervation, if growth occurs at all. To target the growth of axons from neuronal transplants, we are using viral vectors to create guidance pathways before neuronal transplantation. In this study, we transplanted postnatal rat dorsal root ganglia neurons into the corpus callosum of adult rats. Replication-incompetent adenoviruses encoding growth or guidance factors were injected along the desired pathway 1 week before cell transplantation, allowing time for sufficient protein expression by host glial cells. With expression of nerve growth factor (NGF) and basic fibroblast growth factor, sensory axons were able to grow along the corpus callosum, across the midline, and toward an NGF-expressing target in either the contralateral striatum or cortex: a distance of 7-8 mm including a 90 degree turn from white matter into gray matter. Furthermore, expression of semaphorin 3A slightly dorsal and lateral to the turning point increased the number of axons turning into the striatal target. These results show that judicious expression of neuron-specific chemoattractant and chemorepellant molecules using viral vectors can support and target axon growth from neuronal transplants in the adult CNS.

Localization of semaphorin 3A in the rat cornea

Semaphorin 3A (Sema3A) functions to guide the growth of neurons during development. We investigated the localization of Sema3A in the cornea, one of the most sensitive tissues in the body. Immunoblot analysis and reverse transcription-polymerase chain reaction analysis revealed that Sema3A protein and mRNA are expressed in the normal rat cornea. Immunofluorescence staining of frozen sections or tissue blocks prepared from the cornea revealed the presence of Sema3A in wing cells and basal cells (but not superficial cells) of the corneal epithelium, in keratocytes, and in the corneal endothelium. The expression pattern of Sema3A in the corneal epithelium differed from those of zonula occludens-1 and connexin43. These observations show that Sema3A is expressed in all cells of the rat cornea with the exception of superficial epithelial cells.

Extracellular stimuli specifically regulate localized levels of individual neuronal mRNAs

Subcellular regulation of protein synthesis requires the correct localization of messenger RNAs (mRNAs) within the cell. In this study, we investigate whether the axonal localization of neuronal mRNAs is regulated by extracellular stimuli. By profiling axonal levels of 50 mRNAs detected in regenerating adult sensory axons, we show that neurotrophins can increase and decrease levels of axonal mRNAs. Neurotrophins (nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3) regulate axonal mRNA levels and use distinct downstream signals to localize individual mRNAs. However, myelin-associated glycoprotein and semaphorin 3A regulate axonal levels of different mRNAs and elicit the opposite effect on axonal mRNA levels from those observed with neurotrophins. The axonal mRNAs accumulate at or are depleted from points of ligand stimulation along the axons. The translation product of a chimeric green fluorescent protein-beta-actin mRNA showed similar accumulation or depletion adjacent to stimuli that increase or decrease axonal levels of endogenous beta-actin mRNA. Thus, extracellular ligands can regulate protein generation within subcellular regions by specifically altering the localized levels of particular mRNAs.

Signaling of secreted semaphorins in growth cone steering

Despite a tremendous amount of progress in the identification and characterization of many new players as components of class 3 secreted semaphorin signaling in growth cone steering (Fig. 1), our understanding of the molecular mechanisms is far from complete. More questions remain to be answered: how are differential cytoskeletal changes within a growth cone achieved in response to semaphorins? What are the target(s) of cyclic nucleotide modulation? How does a growth cone make a reliable decision in response to a shallow gradient? And finally, how does a growth cone maintain its sensitivity to a decreasing concentration ofsemaphorins when it is growing away from the source? With a high degree of interest in the field with the development of novel technologies in analyzing growth cone steering, we expect to see a much more complete picture of semaphoring signaling in the near future.

Inhibition of axonal outgrowth in the tumor environment: involvement of class 3 semaphorins

That tumors lack innervation is dogma in the field of pathology, but the molecular determinants of this phenomenon remain elusive. We studied the effects of conditioned media from Colon 26 and B16 mouse tumor cell lines on the axonal outgrowth and cellular differentiation of embryonic Institute of Cancer Research (ICR) mouse dorsal root ganglion cells. Tumor-conditioned media suppressed dorsal root ganglion axonal extension but had no effect on neuronal or glial differentiation. We found that the tumor cells expressed most of the class 3 semaphorins - axon guidance molecules. Blocking the activity of class 3 semaphorins with the soluble receptor neuropilin-1 significantly counteracted the tumor-induced inhibition of axonal extension. Together, these results suggest a role for tumor-secreted class 3 semaphorins in selectively inhibiting axonal outgrowth of dorsal root ganglion neurons.

Molecular/genetic manipulation of extrinsic axon guidance factors for CNS repair and regeneration

During development, guidance molecules play a key role in the formation of complex circuits required for neural functions. With the cessation of development, this exuberant growth process slows and stabilizes, and inhibitory molecules expressed by glia prevent initial attempts for axonal regeneration. In this review, we discuss the expression patterns and relative contribution of several guidance molecules on the regenerative process. Injury to the immature CNS or species capable of regenerating exhibit a complete or partial recapitulation of their developmental guidance patterns, whereas similar injuries to adult mammals results in altered expression that acts to further hinder regeneration. Manipulations of guidance molecules after injury have been used to control detrimental effects of axon sprouting and target regenerating axons within the spinal cord.

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.

Lens-derived Semaphorin3A regulates sensory innervation of the cornea

The cornea, one of the most highly innervated tissues of the body, is innervated by trigeminal sensory afferents. During development, axons are initially repelled at the corneal margin, resulting in the formation of a circumferential nerve ring. The nature and source of guidance molecules that regulate this process remain a mystery. Here, we show that the lens, which immediately underlies the cornea, repels trigeminal axons in vivo and in vitro. Lens ablation results in premature, disorganized corneal innervation and disruption of the nerve ring and ventral plexus. We show that Semaphorin3A (Sema3A) is expressed in the lens epithelium and its receptor Neuropilin-1 (Npn1) is expressed in the trigeminal ganglion during cornea development. Inhibition of Sema3A signaling abrogates axon repulsion by the lens and cornea in vitro and phenocopies lens removal in vivo. These results demonstrate that lens-derived Sema3A mediates initial repulsion of trigeminal sensory axons from the cornea and is necessary for the proper formation of the nerve ring and positioning of the ventral plexus in the choroid fissure.

Sema3a maintains normal heart rhythm through sympathetic innervation patterning

Sympathetic innervation is critical for effective cardiac function. However, the developmental and regulatory mechanisms determining the density and patterning of cardiac sympathetic innervation remain unclear, as does the role of this innervation in arrhythmogenesis. Here we show that a neural chemorepellent, Sema3a, establishes cardiac sympathetic innervation patterning. Sema3a is abundantly expressed in the trabecular layer in early-stage embryos but is restricted to Purkinje fibers after birth, forming an epicardial-to-endocardial transmural sympathetic innervation patterning. Sema3a(-/-) mice lacked a cardiac sympathetic innervation gradient and exhibited stellate ganglia malformation, which led to marked sinus bradycardia due to sympathetic dysfunction. Cardiac-specific overexpression of Sema3a in transgenic mice (SemaTG) was associated with reduced sympathetic innervation and attenuation of the epicardial-to-endocardial innervation gradient. SemaTG mice demonstrated sudden death and susceptibility to ventricular tachycardia, due to catecholamine supersensitivity and prolongation of the action potential duration. We conclude that appropriate cardiac Sema3a expression is needed for sympathetic innervation patterning and is critical for heart rate control.

Semaphorins in axon regeneration: developmental guidance molecules gone wrong?

Semaphorins are developmental axon guidance cues that continue to be expressed during adulthood and are regulated by neural injury. During the formation of the nervous system, repulsive semaphorins guide axons to their targets by restricting and channelling their growth. They affect the growth cone cytoskeleton through interactions with receptor complexes that are linked to a complicated intracellular signal transduction network. Following injury, regenerating axons stop growing when they reach the border of the glial-fibrotic scar, in part because they encounter a potent molecular barrier that inhibits growth cone extension. A number of secreted semaphorins are expressed in the glial-fibrotic scar and at least one transmembrane semaphorin is upregulated in oligodendrocytes surrounding the lesion site. Semaphorin receptors, and many of the signal transduction components required for semaphorin signalling, are present in injured central nervous system neurons. Here, we review evidence that supports a critical role for semaphorin signalling in axon regeneration, and highlight a number of challenges that lie ahead with respect to advancing our understanding of semaphorin function in the normal and injured adult nervous system.