Modulation of sciatic nerve expression of class 3 semaphorins by nerve injury

Neuron-specific RNA-sequencing reveals different responses in peripheral neurons after nerve injury

Peripheral neurons are heterogeneous and functionally diverse, but all share the capability to switch to a pro-regenerative state after nerve injury. Despite the assumption that the injury response is similar among neuronal subtypes, functional recovery may differ. Understanding the distinct intrinsic regenerative properties between neurons may help to improve the quality of regeneration, prioritizing the growth of axon subpopulations to their targets. Here, we present a comparative analysis of regeneration across four key peripheral neuron populations: motoneurons, proprioceptors, cutaneous mechanoreceptors, and nociceptors. Using Cre/Ai9 mice that allow fluorescent labeling of neuronal subtypes, we found that nociceptors showed the greater regeneration after a sciatic crush, followed by motoneurons, mechanoreceptors, and, finally, proprioceptors. By breeding these Cre mice with Ribotag mice, we isolated specific translatomes and defined the regenerative response of these neuronal subtypes after axotomy. Only 20% of the regulated genes were common, revealing a diverse response to injury among neurons, which was also supported by the differential influence of neurotrophins among neuron subtypes. Among differentially regulated genes, we proposed MED12 as a specific regulator of the regeneration of proprioceptors. Altogether, we demonstrate that the intrinsic regenerative capacity differs between peripheral neuron subtypes, opening the door to selectively modulate these responses.

Characterization of a Novel Aspect of Tissue Scarring Following Experimental Spinal Cord Injury and the Implantation of Bioengineered Type-I Collagen Scaffolds in the Adult Rat: Involvement of Perineurial-like Cells?

Numerous intervention strategies have been developed to promote functional tissue repair following experimental spinal cord injury (SCI), including the bridging of lesion-induced cystic cavities with bioengineered scaffolds. Integration between such implanted scaffolds and the lesioned host spinal cord is critical for supporting regenerative growth, but only moderate-to-low degrees of success have been reported. Light and electron microscopy were employed to better characterise the fibroadhesive scarring process taking place after implantation of a longitudinally microstructured type-I collagen scaffold into unilateral mid-cervical resection injuries of the adult rat spinal cord. At long survival times (10 weeks post-surgery), sheets of tightly packed cells (of uniform morphology) could be seen lining the inner surface of the repaired dura mater of lesion-only control animals, as well as forming a barrier along the implant–host interface of the scaffold-implanted animals. The highly uniform ultrastructural features of these scarring cells and their anatomical continuity with the local, reactive spinal nerve roots strongly suggest their identity to be perineurial-like cells. This novel aspect of the cellular composition of reactive spinal cord tissue highlights the increasingly complex nature of fibroadhesive scarring involved in traumatic injury, and particularly in response to the implantation of bioengineered collagen scaffolds.

Integrated analysis of long noncoding RNAs and mRNA expression profiles reveals the potential role of lncRNAs in early stage of post-peripheral nerve injury in Sprague-Dawley rats

The regulatory role of lncRNAs in the early stage post peripheral nerve injury (PNI) is not yet clear. In this study, next-generation sequencing was used to perform deep sequencing on normal sciatic nerves (control) and lesional tissues derived on the 4th (D4) and 7th days (D7) after sciatic nerve injury in rats. Time-point unique differentially expressed lncRNAs (DElncRNAs) were analyzed for functional enrichment. The results showed that 776 DElncRNAs were unique to D4, and their functions were mainly enriched in wound healing, phosphatase binding and MAPK signaling pathways; 317 DElncRNAs were unique to D7, and their functions were mainly enriched in ion transmembrane transporter channel activity; 579 DElncRNAs were shared by these two days, and their functions were mainly enriched in axongenesis, the PI3K-Akt signaling pathway and cell cycle. Furthermore, lncRNA-mRNA interaction networks were constructed in functions or pathways with a high enrichment rate. Finally, 3 mRNAs and 4 lncRNAs in the axongenesis interaction network were selected, and their expression levels were verified by RT-qPCR. This study preliminarily revealed the regulatory role of lncRNAs at different time points in the early stage post PNI, which provides potential targets for basic research and clinical treatment of PNI.

Recent Advances in Biomarkers and Regenerative Medicine for Diabetic Neuropathy

Diabetic neuropathy is one of the most common complications of diabetes. This complication is peripheral neuropathy with predominant sensory impairment, and its symptoms begin with hyperesthesia and pain and gradually become hypoesthesia with the loss of nerve fibers. In some cases, lower limb amputation occurs when hypoalgesia makes it impossible to be aware of trauma or mechanical stimuli. On the other hand, up to 50% of these complications are asymptomatic and tend to delay early detection. Therefore, sensitive and reliable biomarkers for diabetic neuropathy are needed for an early diagnosis of this condition. This review focuses on systemic biomarkers that may be useful at this time. It also describes research on the relationship between target gene polymorphisms and pathological conditions. Finally, we also introduce current information on regenerative therapy, which is expected to be a therapeutic approach when the pathological condition has progressed and nerve degeneration has been completed.

Poly(ε-Caprolactone) Nanofiber Wrap Improves Nerve Regeneration and Functional Outcomes after Delayed Nerve Repair

BACKGROUND

The purpose of this study was to assess the efficacy of biodegradable, electrospun poly(ε-caprolactone) nanofiber nerve conduits in improving nerve regeneration.

METHODS

The authors used a rat forelimb chronic denervation model to assess the effects of poly(ε-caprolactone) conduits on improving nerve regeneration and upper extremity function. Three groups of rats were examined: (1) negative-control animals (n = 5), which underwent 8 weeks of median nerve chronic denervation injury followed by repair with no conduit; (2) experimental animals (n = 5), which underwent 8 weeks of median nerve chronic denervation followed by repair and poly(ε-caprolactone) nerve conduit wrapping of the nerve coaptation site; and (3) positive-control animals (n = 5), which were naive controls. All animals underwent compound muscle action potential and functional testing. At 14 weeks after repair, the median nerve and flexor muscles were harvested for histologic analysis.

RESULTS

Histomorphometric analysis of regenerating median nerves demonstrated augmented axonal regeneration in experimental versus negative control animals (total axon count, 1769 ± 672 versus 1072 ± 123.80; p = 0.0468). With regard to functional recovery, experimental and negative-control animals (1.67 ± 0.04 versus 0.97 ± 0.39; p = 0.036) had regained 34.9 percent and 25.4 percent, respectively, of baseline hand grip strength at 14 weeks after repair. Lastly, less collagen deposition at the nerve coaptation site of experimental animals was found when compared to control animals (p < 0.05).

CONCLUSION

Biodegradable, poly(ε-caprolactone) nanofiber nerve conduits can improve nerve regeneration and subsequent physiologic extremity function in the setting of delayed nerve repair by decreasing the scar burden at nerve coaptation sites.

Semaphorin3A Signaling Is Dispensable for Motor Axon Reinnervation of the Adult Neuromuscular Junction

The neuromuscular junction (NMJ) is a specialized synapse that is formed by motor axon innervation of skeletal muscle fibers. The maintenance of motor-muscle connectivity is critical for the preservation of muscle tone and generation of movement. Injury can induce a robust regenerative response in motor axons, but severe trauma or chronic denervation resulting from neurodegenerative disease typically leads to inefficient repair and poor functional recovery. The axon guidance molecule Semaphorin3A (Sema3A) has been implicated as a negative regulator of motor innervation. Upon binding to a plexinA-neuropilin1 (Npn1) receptor complex, Sema3A initiates a downstream signaling cascade that results in axonal repulsion. Here, we established a reproducible nerve crush model to quantify motor nerve regeneration. We then used that model to investigate the role of Sema3A signaling at the adult NMJ. In contrast to previous findings, we found that Sema3A and Npn1 mRNA decrease in response to denervation, suggesting that Sema3A-Npn1 signaling may regulate NMJ reinnervation. To directly test that hypothesis, we used inducible knockout models to ubiquitously delete Sema3A or Npn1 from adult mice. Despite demonstrating that we could achieve highly efficient gene deletion, disruption of Sema3A-Npn1 signaling did not affect the normal maintenance of the NMJ or disrupt motor axon reinnervation after a denervating injury.

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

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

Expression of Semaphorins, Neuropilins, VEGF, and Tenascins in Rat and Human Primary Sensory Neurons after a Dorsal Root Injury

Dorsal root injury is a situation not expected to be followed by a strong regenerative growth, or growth of the injured axon into the central nervous system of the spinal cord, if the central axon of the dorsal root is injured but of strong regeneration if subjected to injury to the peripherally projecting axons. The clinical consequence of axonal injury is loss of sensation and may also lead to neuropathic pain. In this study, we have used in situ hybridization to examine the distribution of mRNAs for the neural guidance molecules semaphorin 3A (SEMA3A), semaphorin 3F (SEMA3F), and semaphorin 4F (SEMA4F), their receptors neuropilin 1 (NP1) and neuropilin 2 (NP2) but also for the neuropilin ligand vascular endothelial growth factor (VEGF) and Tenascin J1, an extracellular matrix molecule involved in axonal guidance, in rat dorsal root ganglia (DRG) after a unilateral dorsal rhizotomy (DRT) or sciatic nerve transcetion (SNT). The studied survival times were 1–365 days. The different forms of mRNAs were unevenly distributed between the different size classes of sensory nerve cells. The results show that mRNA for SEMA3A was diminished after trauma to the sensory nerve roots in rats. The SEMA3A receptor NP1, and SEMA3F receptor NP2, was significantly upregulated in the DRG neurons after DRT and SNT. SEMA4F was upregulated after a SNT. The expression of mRNA for VEGF in DRG neurons after DRT showed a significant upregulation that was high even a year after the injuries. These data suggest a role for the semaphorins, neuropilins, VEGF, and J1 in the reactions after dorsal root lesions.

Guinea pigs as an animal model for sciatic nerve injury

The overwhelming use of rat models in nerve regeneration studies is likely to induce skewness in treatment outcomes. To address the problem, this study was conducted in 8 adult guinea pigs of either sex to investigate the suitability of guinea pig as an alternative model for nerve regeneration studies. A crush injury was inflicted to the sciatic nerve of the left limb, which led to significant decrease in the pain perception and neurorecovery up to the 4^th weak. Lengthening of foot print and shortening of toe spread were observed in the paw after nerve injury. A 3.49 ± 0.35 fold increase in expression of neuropilin 1 (NRP1) gene and 2.09 ± 0.51 fold increase in neuropilin 2 (NRP2) gene were recorded 1 week after nerve injury as compared to the normal nerve. Ratios of gastrocnemius muscle weight and volume of the experimental limb to control limb showed more than 50% decrease on the 30^th day. Histopathologically, vacuolated appearance of the nerve was observed with presence of degenerated myelin debris in digestion chambers. Gastrocnemius muscle also showed degenerative changes. Scanning electron microscopy revealed loose and rough arrangement of connective tissue fibrils and presence of large spherical globules in crushed sciatic nerve. The findings suggest that guinea pigs could be used as an alternative animal model for nerve regeneration studies and might be preferred over rats due to their cooperative nature while recording different parameters.

The expression of chemorepulsive guidance receptors and the regenerative abilities of spinal-projecting neurons after spinal cord injury

Spinal cord injury (SCI) in mammals leads to permanent loss of function because axons do not regenerate in the central nervous system (CNS). To date, treatments based on neutralizing inhibitory environmental cues, such as the myelin-associated growth inhibitors and chondroitin sulfate proteoglycans, or on adding neurotrophic factors, have had limited success in enhancing regeneration. Published studies suggested that multiple axon guidance cues (repulsive guidance molecule (RGM) family, semaphorins, ephrins, and netrins) persist in adult animals, and that their expression is upregulated after CNS injury. Moreover, many adult CNS neurons continue to express axon guidance receptors. We used the advantages of the lamprey CNS to test the hypotheses that the regenerative abilities of spinal-projecting neurons depend upon their expression of chemorepulsive guidance receptors. After complete spinal transection, lampreys recover behaviorally, and injured axons grow selectively in their correct paths. However, the large identified reticulospinal (RS) neurons in the lamprey brain are heterogeneous in their regenerative abilities - some are high regeneration capacity neurons (probability of axon regeneration >50%), others are low regeneration capacity neurons (<30%). Here we report that the RGM receptor Neogenin is expressed preferentially in the low regeneration capacity RS neurons that regenerate poorly, and that downregulation of Neogenin by morpholino antisense oligonucleotides enhances regeneration of RS axons after SCI. Moreover, lamprey CNS neurons co-express multiple guidance receptors (Neogenin, UNC5 and PlexinA), suggesting that the regenerative abilities of spinal-projecting neurons might reflect the summed influences of the chemorepulsive guidance receptors that they express.

The longitudinal transcriptomic response of the substantia nigra to intrastriatal 6-hydroxydopamine reveals significant upregulation of regeneration-associated genes

We hypothesized that the study of gene expression at 1, 2, 4, 6 and 16 weeks in the substantia nigra (SN) after intrastriatal 6-OHDA in the Sprague-Dawley rat (rattus norvegicus) would identify cellular responses during the degenerative process that could be axoprotective. Specifically, we hypothesized that genes expressed within the SN that followed a profile of being highly upregulated early after the lesion (during active axonal degeneration) and then progressively declined to baseline over 16 weeks as DA neurons died are indicative of potential protective responses to the striatal 6-OHDA insult. Utilizing a κ-means cluster analysis strategy, we demonstrated that one such cluster followed this hypothesized expression pattern over time, and that this cluster contained several interrelated transcripts that are classified as regeneration-associated genes (RAGs) including Atf3, Sprr1a, Ecel1, Gadd45a, Gpnmb, Sox11, Mmp19, Srgap1, Rab15,Lifr, Trib3, Tgfb1, and Sema3c. All exemplar transcripts tested from this cluster (Sprr1a, Ecel1, Gadd45a, Atf3 and Sox11) were validated by qPCR and a smaller subset (Sprr1a, Gadd45a and Sox11) were shown to be exclusively localized to SN DA neurons using a dual label approach with RNAScope in situ hybridization and immunohistochemistry. Upregulation of RAGs is typically associated with the response to axonal injury in the peripheral nerves and was not previously reported as part of the axodegenerative process for DA neurons of the SN. Interestingly, as part of this cluster, other transcripts were identified based on their expression pattern but without a RAG provenance in the literature. These "RAG-like" transcripts need further characterization to determine if they possess similar functions to or interact with known RAG transcripts. Ultimately, it is hoped that some of the newly identified axodegeneration-reactive transcripts could be exploited as axoprotective therapies in PD and other neurodegenerative diseases.

Decoration of PLGA electrospun nanofibers with designer self-assembling peptides: a “Nano-on-Nano” concept

A composite neural scaffold which combines the topographical features of electrospun nanofibrous scaffolds and bioactive as well as nanostructured features of designer self-assembling peptides (“Nano on Nano” approach).

A role for neuropilins in the interaction between Schwann cells and meningeal cells

In their natural habitat, the peripheral nerve, Schwann cells (SCs) form nicely aligned pathways (also known as the bands of Büngner) that guide regenerating axons to their targets. Schwann cells that are implanted in the lesioned spinal cord fail to align in pathways that could support axon growth but form cellular clusters that exhibit only limited intermingling with the astrocytes and meningeal cells (MCs) that are present in the neural scar. The formation of cell clusters can be studied in co-cultures of SCs and MCs. In these co-cultures SCs form cluster-like non-overlapping cell aggregates with well-defined boundaries. There are several indications that neuropilins (NRPs) play an important role in MC-induced SC aggregation. Both SCs and MCs express NRP1 and NRP2 and SCs express the NRP ligands Sema3B, C and E while MCs express Sema3A, C, E and F. We now demonstrate that in SC-MC co-cultures, siRNA mediated knockdown of NRP2 in SCs decreased the formation of SC clusters while these SCs maintained their capacity to align in bands of Büngner-like columnar arrays. Unexpectedly, knockdown of NRP1 expression resulted in a significant increase in SC aggregation. These results suggest that a reduction in NRP2 expression may enhance the capacity of implanted SCs to interact with MCs that invade a neural scar formed after a lesion of the spinal cord.

Quantification of dendritic and axonal growth after injury to the auditory system of the adult cricket Gryllus bimaculatus

Dendrite and axon growth and branching during development are regulated by a complex set of intracellular and external signals. However, the cues that maintain or influence adult neuronal morphology are less well understood. Injury and deafferentation tend to have negative effects on adult nervous systems. An interesting example of injury-induced compensatory growth is seen in the cricket, Gryllus bimaculatus. After unilateral loss of an ear in the adult cricket, auditory neurons within the central nervous system (CNS) sprout to compensate for the injury. Specifically, after being deafferented, ascending neurons (AN-1 and AN-2) send dendrites across the midline of the prothoracic ganglion where they receive input from auditory afferents that project through the contralateral auditory nerve (N5). Deafferentation also triggers contralateral N5 axonal growth. In this study, we quantified AN dendritic and N5 axonal growth at 30 h, as well as at 3, 5, 7, 14, and 20 days after deafferentation in adult crickets. Significant differences in the rates of dendritic growth between males and females were noted. In females, dendritic growth rates were non-linear; a rapid burst of dendritic extension in the first few days was followed by a plateau reached at 3 days after deafferentation. In males, however, dendritic growth rates were linear, with dendrites growing steadily over time and reaching lengths, on average, twice as long as in females. On the other hand, rates of N5 axonal growth showed no significant sexual dimorphism and were linear. Within each animal, the growth rates of dendrites and axons were not correlated, indicating that independent factors likely influence dendritic and axonal growth in response to injury in this system. Our findings provide a basis for future study of the cellular features that allow differing dendrite and axon growth patterns as well as sexually dimorphic dendritic growth in response to deafferentation.

Neural regenerative strategies incorporating biomolecular axon guidance signals

There are currently no acceptable cures for central nervous system injuries, and damage induced large gaps in the peripheral nervous system have been challenging to bridge to restore neural functionality. Innervation by neurons is made possible by the growth cone. This dynamic structure is unique to neurons, and can directly sense physical and chemical activity in its environment, utilizing these cues to propel axons to precisely reach their targets. Guidance can occur through chemoattractive factors such as neurotrophins and netrins, chemorepulsive agents like semaphorins and slits, or contact-mediated molecules such as ephrins and those located in the extracellular matrix. The understanding of biomolecular activity during nervous system development and injury has generated new techniques and tactics for improving and restoring function to the nervous system after injury. This review will focus on the major neuronal guidance molecules and their utility in current tissue engineering and neural regenerative strategies.

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.

Characterization of neural stem/progenitor cells expressing VEGF and its receptors in the subventricular zone of newborn piglet brain

Neural stem/progenitor cell (NSP) biology and neurogenesis in adult central nervous system (CNS) are important both towards potential future therapeutic applications for CNS repair, and for the fundamental function of the CNS. In the present study, we report the characterization of NSP population from subventricular zone (SVZ) of neonatal piglet brain using in vivo and in vitro systems. We show that the nestin and vimentin-positive neural progenitor cells are present in the SVZ of the lateral ventricles of neonatal piglet brain. In vitro, piglet NSPs proliferated as neurospheres, expressed the typical protein of neural progenitors, nestin and a range of well-established neurodevelopmental markers. Upon dissociation and subculture, piglet NSPs differentiated into neurons and glial cells. Clonal analysis demonstrates that piglet NSPs are multipotent and retain the capacity to generate both glia and neurons. These cells expressed VEGF, VEGFR1, VEGFR2 and Neuropilin-1 and -2 mRNAs. Real time PCR revealed that SVZ NSPs from newborn piglet expressed total VEGF and all VEGF splice variants. These findings show that piglet NSPs may be helpful to more effectively design growth factor based strategies to enhance endogenous precursor cells for cell transplantation studies potentially leading to the application of this strategy in the nervous system disease and injury.

Nerve fibroblast impact on Schwann cell behavior

In order to reveal non-neuronal cell interactions after peripheral nerve lesions, we began to analyze the impact of sciatic nerve fibroblasts on Schwann cells in vitro. Both cell types are considered to have opposite effects on axonal regeneration. Few data are available on how repulsive nerve fibroblasts affect neuritotrophic Schwann cells and thus might indirectly influence axonal regrowth. Using different culture systems in conjunction with time-lapse video recording, metabolic labeling, pharmacological intervention, RNAi knockdown, Western blotting and RT-PCR analysis, we found that nerve fibroblasts differentially modify the various responses of Schwann cells. In the presence of collagen type IV and heparan sulfate proteoglycan but not of laminin, diffusible fibroblast factors slow down Schwann cell proliferation. In contrast, fibroblast factors increase the migratory activity of Schwann cells without being chemoattractive. One pro-migratory fibroblast factor turned out to be neuregulin. The pro-migratory activity of nerve fibroblasts and of recombinant neuregulin-1beta1 can be counteracted by neuregulin-specific pharmacological intervention and by neuregulin RNA interference. We show for the first time that nerve fibroblasts play antagonistic and agonistic roles for Schwann cells in a context-dependent manner. The data shed light on cellular mechanisms and have implications for some neuro-tissue engineering strategies.

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.

Molecular genetics of addiction and related heritable phenotypes: genome-wide association approaches identify "connectivity constellation" and drug target genes with pleiotropic effects

Genome-wide association (GWA) can elucidate molecular genetic bases for human individual differences in complex phenotypes that include vulnerability to addiction. Here, we review (a) evidence that supports polygenic models with (at least) modest heterogeneity for the genetic architectures of addiction and several related phenotypes; (b) technical and ethical aspects of importance for understanding GWA data, including genotyping in individual samples versus DNA pools, analytic approaches, power estimation, and ethical issues in genotyping individuals with illegal behaviors; (c) the samples and the data that shape our current understanding of the molecular genetics of individual differences in vulnerability to substance dependence and related phenotypes; (d) overlaps between GWA data sets for dependence on different substances; and (e) overlaps between GWA data for addictions versus other heritable, brain-based phenotypes that include bipolar disorder, cognitive ability, frontal lobe brain volume, the ability to successfully quit smoking, neuroticism, and Alzheimer's disease. These convergent results identify potential targets for drugs that might modify addictions and play roles in these other phenotypes. They add to evidence that individual differences in the quality and quantity of brain connections make pleiotropic contributions to individual differences in vulnerability to addictions and to related brain disorders and phenotypes. A "connectivity constellation" of brain phenotypes and disorders appears to receive substantial pathogenic contributions from individual differences in a constellation of genes whose variants provide individual differences in the specification of brain connectivities during development and in adulthood. Heritable brain differences that underlie addiction vulnerability thus lie squarely in the midst of the repertoire of heritable brain differences that underlie vulnerability to other common brain disorders and phenotypes.

Neuropilins: structure, function and role in disease

NRPs (neuropilins) are co-receptors for class 3 semaphorins, polypeptides with key roles in axonal guidance, and for members of the VEGF (vascular endothelial growth factor) family of angiogenic cytokines. They lack a defined signalling role, but are thought to mediate functional responses as a result of complex formation with other receptors, such as plexins in the case of semaphorins and VEGF receptors (e.g. VEGFR2). Mutant mouse studies show that NRP1 is essential for neuronal and cardiovascular development, whereas NRP2 has a more restricted role in neuronal patterning and lymphangiogenesis, but recent findings indicate that NRPs may have additional biological roles in other physiological and disease-related settings. In particular, NRPs are highly expressed in diverse tumour cell lines and human neoplasms and have been implicated in tumour growth and vascularization in vivo. However, despite the wealth of information regarding the probable biological roles of these molecules, many aspects of the regulation of cellular function via NRPs remain uncertain, and little is known concerning the molecular mechanisms through which NRPs mediate the functions of their various ligands in different cell types.

Human neuroma contains increased levels of semaphorin 3A, which surrounds nerve fibers and reduces neurite extension in vitro

Neuroma formation after peripheral nerve injury is detrimental to functional recovery and is therefore a significant clinical problem. The molecular basis for this phenomenon is not fully understood. Here, we show that the expression of the chemorepulsive protein semaphorin 3A (sema3A), but not semaphorin 3F, is increased in human neuroma tissue that has formed in severe obstetric brachial plexus lesions. Sema3A is produced by fibroblasts in the epineurial space and appears to be secreted into the extracellular matrix. It surrounds fascicles, minifascicles, or single axons, suggesting a role in fasciculation and inhibition of neurite outgrowth. Lentiviral vector-mediated knock-down of Neuropilin 1, the receptor for sema3A, leads to increased neurite outgrowth of F11 cells cultured on neuroma tissue, but not of F11 cells cultured on normal nerve tissue. These findings demonstrate the putative inhibitory role of sema3A in human neuroma tissue. Our observations are the first demonstration of the expression of sema3A in human neural scar tissue and support a role for this protein in the inhibition of axonal regeneration in injured human peripheral nerves. These findings contribute to the understanding of the outgrowth inhibitory properties of neuroma tissue.

Expression of Semaphorin3C in axotomized rodent facial and rubrospinal neurons

Semaphorins are a family of axonal guidance molecules that, by virtue of their chemorepulsive or chemoattractive actions, may be the important factors in determining the success or failure of axonal regeneration in the mature nervous system after injury. Here, we have used two adult mouse models of nervous system injury to evaluate the neuronal expression of Semaphorin3C (Sema3C) in regenerating (facial motoneurons) and non-regenerating (rubrospinal) neurons following axonal injury. Using in situ hybridization (ISH), we observed that uninjured facial motoneurons express Sema3C mRNA and, following axonal injury, there is a transient up-regulation in Sema3C mRNA expression in injured motoneurons. In contrast, Sema3C mRNA was not detected in uninjured rubrospinal neurons; however, following axotomy, injured rubrospinal neurons significantly up-regulate Sema3C mRNA expression. The increase in Sema3C mRNA expression in axotomized rubrospinal neurons was not limited to the mouse nervous system: serial dilution RT-PCR analysis revealed a similar increase in Sema3C mRNA expression in the axotomized rat rubrospinal nucleus, 3 days following a rubrospinal tract lesion. This demonstrates that increased Sema3C mRNA levels in axotomized rubrospinal neurons is common to both mouse and rat injury models.

Navigating their way to the clinic: emerging roles for axon guidance molecules in neurological disorders and injury

The mechanisms underlying formation of the basic network of the nervous system are of fundamental interest in developmental neurobiology. During the wiring of the nervous system, newborn neurons send axons that travel long distances to their targets. These axons are directed by environmental cues, known as guidance cues, to their correct destinations. Through extensive studies in vertebrates and invertebrates many of the guidance cues and their receptors have been identified. Recently, guidance molecules have been suggested to have important roles in pathological conditions of the nervous system. Mutations in guidance receptors have been associated with hereditary neurological disorders, and deregulation of guidance cues might be associated with predisposition to epilepsy. In addition, it was suggested that guidance molecules play roles in the ability of the adult nervous system to recover and repair after injury. Thus, molecules that were first discovered as "developmental cues" are now emerging as important factors in neurological disease and injury in the adult.

Semaphorins in development and adult brain: Implication for neurological diseases

As a group, Semaphorins are expressed in most tissues and this distribution varies considerably with age. Semaphorins are dynamically expressed during embryonic development and their expression is often associated with growing axons. This expression decreases with maturity and several observations support the idea that in adult brain the expression of secreted Semaphorins is sensitive to electrical activity and experience. The functional role of Semaphorins in guiding axonal projections is well established and more recent evidence points to additional roles in the development, function and reorganization of synaptic complexes. Semaphorins exert the majority of their effects by binding to cognate receptor proteins through their extracellular domains. A common theme is that Semaphorin-triggered signalling induces the rearrangement of the actin and microtubule cytoskeleton. Mutations in Semaphorin genes are linked to several human diseases associated with neurological changes, but their actual influence in the pathogenesis of these diseases remains to be demonstrated. In addition, Semaphorins and their receptors are likely to mediate cross-talk between neurons and other cell types, including in pathological situations where their influence can be damaging or favourable depending on the context. We discuss how the manipulation of Semaphorin function might be crucial for future clinical studies.

Microarray analysis of laser capture microdissected-anulus cells from the human intervertebral disc

STUDY DESIGN

Five Thompson Grade I/II discs (Group 1), 7 Grade III discs (Group 2), and 3 Grade IV discs (Group IV) were studied here in a project approved by the authors' Human Subjects Institutional Review Board.

OBJECTIVES

Our objective was to use laser capture microdissection (LCM) to harvest cells from the human anulus and to derive gene expression profiles using microarray analysis.

SUMMARY OF BACKGROUND DATA

Appropriate gene expression is essential in the intervertebral disc for maintenance of extracellular matrix (ECM), ECM remodeling, and maintenance of a viable disc cell population. During disc degeneration, cell numbers drop, making gene expression studies challenging.

METHODS

LCM was used to harvest cells from paraffin-embedded sections of human anulus tissue. Gene profiling used Affymetrix GeneChip Human X3P arrays. ANOVA and SAM permutation analysis were applied to dCHIP normalized, filtered, and log-transformed gene expression data ( approximately 33,500 probes), and data analyzed to identify genes that were significantly differentially expressed between the 3 groups.

RESULTS

We identified 47 genes that were significantly differentially expressed between the 3 groups (P < 0.001 and lowest q values). Compared with the healthiest discs (Grade I/II), 13 genes were up-regulated and 19 down-regulated in both the Grade III and the Grade IV discs. Genes with biologic significance regulated during degeneration involved cell senescence, low cell division rates, hypoxia-related genes, heat-shock protein 70 interacting protein, neuropilin 2, and interleukin-23p19 (interleukin-12 family).

CONCLUSIONS

Results expand our understanding of disc aging and degeneration and show that LCM is a valuable technique that can be used to collect mRNA amounts adequate for microarray analysis from the sparse cell population of the human anulus.

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.

Class A plexin expression in axotomized rubrospinal and facial motoneurons

The semaphorin family of guidance molecules plays a role in many aspects of neural development, and more recently semaphorins have been implicated to contribute to the failure of injured CNS neurons to regenerate. While semaphorin expression patterns after neural injury are partially understood, little is known about the expression of their signal transducing transmembrane receptors, the plexins. Therefore, in this study, we compared the expression patterns of all class A plexins (Plxn-A1, A2, A3, A4) in mouse CNS (rubrospinal) and peripheral nervous system (PNS)-projecting (facial) motoneurons for up to two weeks following axonal injury. Using in situ hybridization, immunohistochemistry, and Western blot analysis, in rubrospinal neurons, Plxn-A1 mRNA and protein and Plxn-A4 expression did not change as a result of injury while Plxn-A2 mRNA increased and Plxn-A3 mRNA was undetectable. In facial motoneurons, Plxn-A1, -A3 and -A4 mRNA expression increased, Plxn-A2 mRNA decreased while Plxn-A1 protein expression did not change following injury. We demonstrate that with the exception of the absence of Plxn-A3 mRNA in rubrospinal neurons, both injured rubrospinal (CNS) and facial (PNS) neurons maintain expression of all plexin A family members tested. Hence, there are distinct expression patterns of the individual plexin-A family members suggesting that regenerating rubrospinal and facial motoneurons have a differential ability to transduce semaphorin signals.

Semaphorin 6C leads to GSK-3-dependent growth cone collapse and redistributes after entorhino-hippocampal axotomy

We studied the changes in the distribution of a specific variant of Semaphorin Y/6C (Sema6C) in mouse forebrain after axotomy of the entorhino-hippocampal perforant pathway. We found this isoform to be widely expressed during development, remaining in the adult and showing variations in distribution when the perforant pathway was axotomized. These changes were detected in both the hippocampal and entorhinal cortices. Sema6C1 immunoreactivity (IR) was high in the stratum radiatum of the hippocampus proper and the inner molecular layer of the dentate gyrus; the entorhinal cortex showed Sema6C1 IR in both cell bodies and in fibers of the II/III and V/VI layers. In axotomized animals, the IR of the ipsilateral, but not the contralateral, hemisphere showed that IR had moved into the stratum lacunosum-moleculare, the medial molecular layer of the dentate gyrus and the fibers, but not the cell bodies, of the entorhinal cortex. These results were not reproduced after lateral axotomy of the fimbria fornix, indicating a specific role for Sema6C variants in the generation and/or stability of entorhino-hippocampal synapses. Growth cone collapse of entorhinal and pyramidal neurons, as well as activation of glycogen synthase kinase-3 (GSK-3) through depletion of the inactive pool, induced by diffusible Sema6C1 further supports this view.

Changes in protein expression in the rat medial vestibular nuclei during vestibular compensation

The molecular mechanisms of neural and synaptic plasticity in the vestibular nuclei during 'vestibular compensation', the behavioural recovery that follows deafferentation of one inner ear, are largely unknown. In this study we have used differential proteomics techniques to determine changes in protein expression in ipsi-lesional and contra-lesional medial vestibular nuclei (MVN) of rats, 1 week after either sham surgery or unilateral labyrinthectomy (UL). A systematic comparison of 634 protein spots in two-dimensional electrophoresis gels across five experimental conditions revealed 54 spots, containing 26 proteins whose level was significantly altered 1 week post-UL. The axon-guidance-associated proteins neuropilin-2 and dehydropyriminidase-related protein-2 were upregulated in the MVN after UL. Changes in levels of further specific proteins indicate a coordinated upregulation of mitochondrial function, ATP biosynthesis and phosphate metabolism in the vestibular nuclei 1 week post-UL. These may reflect the metabolic energy demands of processes such as gliosis, neuronal outgrowth and synaptic remodelling that occur after UL. Our findings suggest novel roles for axon elaboration and guidance molecules, as well as mitochondrial and metabolic regulatory proteins, in the post-lesional physiology of the MVN during vestibular system plasticity.

Chemorepellent axon guidance molecules in spinal cord injury

Regenerating axons stop growing when they reach the border of the glial-fibrotic scar, presumably because they encounter a potent molecular barrier inhibiting growth cone advance. Chemorepulsive axon guidance molecules provide a non-permissive environment restricting and channeling axon growth in the developing nervous system. These molecules could also act as growth-inhibitory molecules in the regenerating nervous system. The receptors for repulsive guidance cues are expressed in the mature nervous system, suggesting that adult neurons are sensitive to the activity of developmentally active repulsive proteins. In this review, we summarize recent observations on semaphorins, ephrins, and slits in the injured brain and spinal cord, providing evidence that these proteins are major players in inhibiting axonal regeneration and establishing the glial-fibrotic scar.

3p21.3 tumor suppressor cluster: prospects for translational applications

Chromosomal abnormalities at the 3p21.3 region, including homozygous deletions and loss of heterozygosity and expressional deficiencies in 3p21.3 genes including transcriptional silences by promoter hypermethylation, altered mRNA splicing and aberrant transcripts, and lost or defect protein translation and post-translational modifications, are frequently found in most human cancers. Inactivation of 3p21.3 genes in primary tumors affects a wide spectrum of key biological processes such as cell proliferation, cell cycle kinetics, signaling transduction, ion exchange and transportation, apoptosis and cell death, and demonstrates the molecular signatures of carcinogenesis. Restoration of defective 3p21.3 genes with several wild-type 3p21.3 genes suppresses tumor cell growth both in vitro and in vivo. These findings suggest several 3p21.3 genes as potential tumor suppressors and implicates these 3p21.3 genes for future development as biomarkers for the early detection and diagnosis of cancer, and as prognostic and therapeutic tools for cancer prevention and molecular cancer therapy.

Schwann cell-autonomous role of neuropilin-2

Neuropilins and group A plexins are components of receptor complexes for class 3 semaphorins, gradients of which help to guide migration of neural progenitor cells and axonal growth cones during development. We demonstrated previously that neuropilins and class 3 semaphorins are induced in sciatic nerve by crush or transection. We now report that in cultured rat Schwann cells, expression of mRNA encoding neuropilin-2 (NRP2) and plexin-A3 (PlexA3), proteins involved in semaphorin-3F (Sema3F) signal transduction, is diminished markedly by forskolin, an adenylate cyclase activator that, like axonal contact, induces Schwann cell synthesis of myelin lipids and proteins. Interestingly, Schwann cell expression of mRNA encoding NRP1, which participates in Sema3A signaling, is not downregulated by forskolin. Antibodies that recognize ectodomains of NRP2 but not control antibodies prevented cultured Schwann cells from aligning in parallel and forming columns. These results are consistent with the view that in nerves undergoing Wallerian degeneration, Schwann cell NRP2 facilitates assembly of Schwann cells into the tubular aggregates (bands of Büngner) that guide regenerating axons.