Major vault protein promotes locomotor recovery and regeneration after spinal cord injury in adult zebrafish

Molecular mechanisms of spinal cord injury repair across vertebrates: A comparative review

In humans and other adult mammals, axon regeneration is difficult in axotomized neurons. Therefore, spinal cord injury (SCI) is a devastating event that can lead to permanent loss of locomotor and sensory functions. Moreover, the molecular mechanisms of axon regeneration in vertebrates are not very well understood, and currently, no effective treatment is available for SCI. In striking contrast to adult mammals, many nonmammalian vertebrates such as reptiles, amphibians, bony fishes and lampreys can spontaneously resume locomotion even after complete SCI. In recent years, rapid progress in the development of next-generation sequencing technologies has offered valuable information on SCI. In this review, we aimed to provide a comparison of axon regeneration process across classical model organisms, focusing on crucial genes and signalling pathways that play significant roles in the regeneration of individually identifiable descending neurons after SCI. Considering the special evolutionary location and powerful regenerative ability of lamprey and zebrafish, they will be the key model organisms for ongoing studies on spinal cord regeneration. Detailed study of SCI in these model organisms will help in the elucidation of molecular mechanisms of neuron regeneration across species.

MSC-derived exosomes deliver ZBTB4 to mediate transcriptional repression of ITIH3 in astrocytes in spinal cord injury

BACKGROUND

BMSC-secreted exosomes (BMSC-Exos) have shown potential for promoting behavioral recovery following spinal cord injury (SCI). However, its role in blocking astrocyte activation remains unclear. Thus, this study aimed to determine whether BMSC-Exos impair the function of astrocytes following SCI in mice and to seek the mechanism.

METHODS

BMSC-Exos were collected by ultracentrifugation and identified. The SCI mice were developed by laminectomy combined with spinal cord shock, followed by BMSC-Exos or nerve growth factor (positive control) treatment. HE staining, Nissl staining, and TUNEL were conducted to analyze the pathological structural damage and neuronal damage in the mouse spinal cord. Bioinformatics was used to screen altered molecules under the BMSC-Exos treatment. Effects of BMSC-Exos and changes in ZBTB4 and ITIH3 expression on neuronal damage induced by activated astrocytes in the co-culture system were analyzed by CCK-8 and flow cytometry.

RESULTS

Nerve growth factor and BMSC-Exos promoted motor function recovery, alleviated nerve injury, and reduced apoptosis in mice with SCI. ZBTB4 was enriched in BMSC-Exos and lowly expressed in SCI. Downregulation of ZBTB4 diminished the therapeutic effects of BMSC-Exos against SCI. ITIH3 was a downstream target of ZBTB4. Neurotoxic activation of astrocytes induced neuronal injury, which was alleviated by BMSC-Exos. However, ZBTB4 knockdown overturned the effects of BMSC-Exos in vitro and combined ITIH3 knockdown alleviated the accentuating effects of ZBTB4 knockdown on neuronal injury.

CONCLUSION

BMSC-Exos protected against astrocyte-induced neuronal injury by delivering ZBTB4 to repress ITIH3, ultimately improving motor function in mice with SCI.

Identification of key genes involved in recovery from spinal cord injury in adult zebrafish

Zebrafish are an effective vertebrate model to study the mechanisms underlying recovery after spinal cord injury. The subacute phase after spinal cord injury is critical to the recovery of neurological function, which involves tissue bridging and axon regeneration. In this study, we found that zebrafish spontaneously recovered 44% of their swimming ability within the subacute phase (2 weeks) after spinal cord injury. During this period, we identified 7762 differentially expressed genes in spinal cord tissue: 2950 were up-regulated and 4812 were down-regulated. These differentially expressed genes were primarily concentrated in the biological processes of the respiratory chain, axon regeneration, and cell-component morphogenesis. The genes were also mostly involved in the regulation of metabolic pathways, the cell cycle, and gene-regulation pathways. We verified the gene expression of two differentially expressed genes, clasp2 up-regulation and h1m down-regulation, in zebrafish spinal cord tissue in vitro. Pathway enrichment analysis revealed that up-regulated clasp2 functions similarly to microtubule-associated protein, which is responsible for axon extension regulated by microtubules. Down-regulated h1m controls endogenous stem cell differentiation after spinal cord injury. This study provides new candidate genes, clasp2 and h1m, as potential therapeutic intervention targets for spinal cord injury repair by neuroregeneration. All experimental procedures and protocols were approved by the Animal Ethics Committee of Tianjin Institute of Medical & Pharmaceutical Sciences (approval No. IMPS-EAEP-Q-2019-02) on September 24, 2019.

Small noncoding vault RNA modulates synapse formation by amplifying MAPK signaling

The small noncoding vault RNA (vtRNA) is a component of the vault complex, a ribonucleoprotein complex found in most eukaryotes. Emerging evidence suggests that vtRNAs may be involved in the regulation of a variety of cellular functions when unassociated with the vault complex. Here, we demonstrate a novel role for vtRNA in synaptogenesis. Using an in vitro synapse formation model, we show that murine vtRNA (mvtRNA) promotes synapse formation by modulating the MAPK signaling pathway. mvtRNA is transported to the distal region of neurites as part of the vault complex. Interestingly, mvtRNA is released from the vault complex in the neurite by a mitotic kinase Aurora-A–dependent phosphorylation of MVP, a major protein component of the vault complex. mvtRNA binds to and activates MEK1 and thereby enhances MEK1-mediated ERK activation in neurites. These results suggest the existence of a regulatory mechanism of the MAPK signaling pathway by vtRNAs as a new molecular basis for synapse formation.

Know How to Regrow-Axon Regeneration in the Zebrafish Spinal Cord

The capacity for long-distance axon regeneration and functional recovery after spinal cord injury is poor in mammals but remarkable in some vertebrates, including fish and salamanders. The cellular and molecular basis of this interspecies difference is beginning to emerge. This includes the identification of target cells that react to the injury and the cues directing their pro-regenerative responses. Among existing models of successful spinal cord regeneration, the zebrafish is arguably the most understood at a mechanistic level to date. Here, we review the spinal cord injury paradigms used in zebrafish, and summarize the breadth of neuron-intrinsic and -extrinsic factors that have been identified to play pivotal roles in the ability of zebrafish to regenerate central nervous system axons and recover function.

The major vault protein is dispensable for zebrafish organ regeneration

As the main constituent of the largest cellular ribonucleoprotein complex, the evolutionary highly conserved major vault protein (MVP) has been proposed play vital roles in the regeneration of multiple organs. In current study, we use a mvp knockout zebrafish line recently generated to characterize the function of MVP during organ regeneration. We found the regenerative capacity of heart, spinal cord and fin is preserved in mvp knockout zebrafish. Further experiments demonstrated in injured mvp knockout zebrafish, the cell death is enhanced while the transcriptome landscape is largely unchanged. These data showed MVP acts as an anti-apoptotic factor at early phase of injury response while plays a dispensable role in the regenerative programs in zebrafish.

Activating Transcription Factor 6 Contributes to Functional Recovery After Spinal Cord Injury in Adult Zebrafish

Spinal cord injury (SCI) is one of the most common devastating injuries, with little possibility of recovery in humans. However, zebrafish efficiently regenerate functional nervous system tissue after SCI. Therefore, the spinal cord transection model of adult zebrafish was applied to explore the role of ATF6 in neuro-recovery. Activating transcription factor 6 (ATF6) is a type-II transmembrane protein in the endoplasmic reticulum (ER). ATF6 target genes could improve ER homeostasis, which contributes to cytoprotection. Herein, we found that the ATF6 level increased at 12 h and 3 days post SCI, and returned to sham levels at 7 days post SCI. ATF6-expressing motor neurons were present in the central canal of the spinal cord and increased at 12 h post SCI. ATF6 morpholino treatment showed that inhibition of ATF6 delayed locomotor recovery and hindered neuron axon regrowth in SCI zebrafish. Furthermore, we investigated the role of both binding immunoglobulin protein (Bip) and C/EBP homologous transcription factor protein (CHOP), the two target genes of ATF6. We found that Bip expression significantly increased in the spinal cord at 7 days after SCI, which served as a pro-survival chaperone. Our results also showed that CHOP expression significantly decreased in the spinal cord at 7 days after SCI, which was identified as a protein involved in apoptosis. Taken together, our data demonstrate that ATF6 may contribute to the functional recovery after SCI in adult zebrafish, via up-regulation of Bip and down-regulation of CHOP to restore the homeostasis of ER.

Proteomics analysis of Schwann cell-derived exosomes: a novel therapeutic strategy for central nervous system injury

Exosomes are nanometer-sized vesicles involved in intercellular communication, and they are released by various cell types. To learn about exosomes produced by Schwann cells (SCs) and to explore their potential function in repairing the central nervous system (CNS), we isolated exosomes from supernatants of SCs by ultracentrifugation, characterized them by electron microscopy and immunoblotting and determined their protein profile using proteomic analysis. The results demonstrated that Schwann cell-derived exosomes (SCDEs) were, on average, 106.5 nm in diameter, round, and had cup-like concavity and expressed exosome markers CD9 and Alix but not tumor susceptibility gene (TSG) 101. We identified a total of 433 proteins, among which 398 proteins overlapped with the ExoCarta database. According to their specific functions, we identified 12 proteins that are closely related to CNS repair and classified them by different potential mechanisms, such as axon regeneration and inflammation inhibition. Gene Oncology analysis indicated that SCDEs are mainly involved in signal transduction and cell communication. Biological pathway analysis showed that pathways are mostly involved in exosome biogenesis, formation, uptake and axon regeneration. Among the pathways, the neurotrophin, PI3K-Akt and cAMP signaling pathways played important roles in CNS repair. Our study isolated SCDEs, unveiled their contents, presented potential neurorestorative proteins and pathways and provided a rich proteomics data resource that will be valuable for future studies of the functions of individual proteins in neurodegenerative diseases.

Major Vault Protein, a Candidate Gene in 16p11.2 Microdeletion Syndrome, Is Required for the Homeostatic Regulation of Visual Cortical Plasticity

Microdeletion of a region in chromosome 16p11.2 increases susceptibility to autism. Although this region contains exons of 29 genes, disrupting only a small segment of the region, which spans five genes, is sufficient to cause autistic traits. One candidate gene in this critical segment is MVP, which encodes for the major vault protein (MVP) that has been implicated in regulation of cellular transport mechanisms. MVP expression levels in MVP^+/- mice closely phenocopy those of 16p11.2 mutant mice, suggesting that MVP^+/- mice may serve as a model of MVP function in 16p11.2 microdeletion. Here we show that MVP regulates the homeostatic component of ocular dominance (OD) plasticity in primary visual cortex. MVP^+/- mice of both sexes show impairment in strengthening of open-eye responses after several days of monocular deprivation (MD), whereas closed-eye responses are weakened as normal, resulting in reduced overall OD plasticity. The frequency of miniature EPSCs (mEPSCs) in pyramidal neurons is decreased in MVP^+/- mice after extended MD, suggesting a reduction of functional synapses. Correspondingly, upregulation of surface GluA1 AMPA receptors is reduced in MVP^+/- mice after extended MD, and is accompanied by altered expression of STAT1 and phosphorylated ERK, which have been previously implicated in OD plasticity. Normalization of STAT1 levels by introducing STAT1 shRNA rescues surface GluA1 and open-eye responses, implicating STAT1 as a downstream effector of MVP. These findings demonstrate a specific role for MVP as a key molecule influencing the homeostatic component of activity-dependent synaptic plasticity, and potentially the corresponding phenotypes of 16p11.2 microdeletion syndrome.SIGNIFICANCE STATEMENT Major vault protein (MVP), a candidate gene in 16p11.2 microdeletion syndrome, has been implicated in the regulation of several cellular processes including transport mechanisms and scaffold signaling. However, its role in brain function and plasticity remains unknown. In this study, we identified MVP as an important regulator of the homeostatic component of experience-dependent plasticity, via regulation of STAT1 and ERK signaling. This study helps reveal a new mechanism for an autism-related gene in brain function, and suggests a broader role for neuro-immune interactions in circuit level plasticity. Importantly, our findings might explain specific components of the pathophysiology of 16p11.2 microdeletion syndrome.

Dynamics of Zebrafish Heart Regeneration Using an HPLC-ESI-MS/MS Approach

Failure to properly repair damaged due to myocardial infarction is a major cause of heart failure. In contrast with adult mammals, zebrafish hearts show remarkable regenerative capabilities after substantial damage. To characterize protein dynamics during heart regeneration, we employed an HPLC-ESI-MS/MS (mass spectrometry) approach. Myocardium tissues were taken from sham-operated fish and ventricle-resected sample at three different time points (2, 7, and 14 days); dynamics of protein expression were analyzed by an ion-current-based quantitative platform. More than 2000 protein groups were quantified in all 16 experiments. Two hundred and nine heart-regeneration-related protein groups were quantified and clustered into six time-course patterns. Functional analysis indicated that multiple molecular function and metabolic pathways were involved in heart regeneration. Interestingly, Ingenuity Pathway Analysis revealed that P53 signaling was inhibited during the heart regeneration, which was further verified by real-time quantitative polymerase chain reaction (Q-PCR). In summary, we applied systematic proteomics analysis on regenerating zebrafish heart, uncovered the dynamics of regenerative genes expression and regulatory pathways, and provided invaluable insight into design regenerative-based strategies in human hearts.

The Adhesion Molecule-Characteristic HNK-1 Carbohydrate Contributes to Functional Recovery After Spinal Cord Injury in Adult Zebrafish

The human natural killer cell antigen-1 (HNK-1) is functionally important in development, synaptic activity, and regeneration after injury in the nervous system of several mammalian species. It contains a sulfated glucuronic acid which is carried by neural adhesion molecules and expressed in nonmammalian species, including zebrafish, which, as opposed to mammals, spontaneously regenerate after injury in the adult. To evaluate HNK-1's role in recovery of function after spinal cord injury (SCI) of adult zebrafish, we assessed the effects of the two HNK-1 synthesizing enzymes, glucuronyl transferase and HNK-1 sulfotransferase. Expression of these two enzymes was increased at the messenger RNA (mRNA) level 11 days after injury in the brainstem nuclei that are capable of regrowth of severed axons, namely, the nucleus of medial longitudinal fascicle and intermediate reticular formation, but not at earlier time points after SCI. mRNA levels of glucuronyl transferase and sulfotransferase were increased in neurons, not only of these nuclei but also in the spinal cord caudal to the injury site at 11 days. Mauthner neurons which are not capable of regeneration did not show increased levels of enzyme mRNAs after injury. Reducing protein levels of the enzymes by application of anti-sense morpholinos resulted in reduction of locomotor recovery for glucuronyl transferase, but not for HNK-1 sulfotransferase. The combined results indicate that HNK-1 is upregulated in expression only in those neurons that are intrinsically capable of regeneration and contributes to regeneration after spinal cord injury in adult zebrafish in the absence of its sulfate moiety.

Activating transcription factor 3 promotes spinal cord regeneration of adult zebrafish

Zebrafish is an excellent model to study the mechanisms underlying successful central nervous system (CNS) regeneration. Previous study shows that activating transcription factor 3 (ATF3) promotes neurite outgrowth and is involved in optic nerve regeneration in zebrafish. Here, we used zebrafish model to investigate the role of ATF3 in regeneration following spinal cord injury (SCI). Quantitative polymerase chain reaction (qPCR) and in situ hybridization revealed that ATF3 mRNA levels increased at 12 h and 6 d following SCI. Double labeled immunofluorescence showed that ATF3 expressed in motoneurons. Treatment of anti-sense ATF3 morpholino (MO) inhibited locomotor recovery and decreased axon regeneration of spinal cord injured zebrafish. Further, inhibition of ATF3 up-regulated the expression of inflammatory factors tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). These data suggest that ATF3 could promote locomotor recovery and axon regrowth in zebrafish SCI model possibly by regulating inflammatory response.

L1.2, the zebrafish paralog of L1.1 and ortholog of the mammalian cell adhesion molecule L1 contributes to spinal cord regeneration in adult zebrafish

PURPOSE

The aim of the study was to investigate the functional role of L1.2, the zebrafish paralog of L1.1 and ortholog of mammalian L1CAM in adult zebrafish spinal cord regeneration after injury. L1CAM and L1.1 have shown beneficial features in ameliorating nervous system dysfunctions in different experimental paradigms. It thus deemed important to characterize the L1.2 member of the L1CAM family, the functions of which are unknown.

METHODS

Spinal cord transection of adult zebrafish, application of anti-sense morpholino to reduce L1.2 expression, qPCR, immunohistology, immunoblotting, in situ hybridization, retrograde tracing, anterograde tracing.

RESULTS

Similar to L1.1, L1.2 expression in adult zebrafish is upregulated after spinal cord transection. By co-localization of in situ hybridization and immunohistology, L1.2 is expressed in neurons and, in contrast to L1.1, it is also expressed in GFAP-immunoreactive glia. Reducing L1.2 protein levels leads to impaired locomotor recovery and reduction of regrowth of severed descending axons from a brain stem nucleus which is composed of neurons innately capable of axonal regrowth.

CONCLUSIONS

Our findings support the speculation that paralogs of duplicated genes can exert similar functions and may thus represent an advantage over other species that do not carry duplicated genes.

Beneficial roles of melanoma cell adhesion molecule in spinal cord transection recovery in adult zebrafish

Melanoma cell adhesion molecule (MCAM) is a multifunctional protein involved in miscellaneous processes, including development and tumor angiogenesis. Here, spinal cord transection in adult zebrafish was used to investigate the effects of MCAM on spinal cord injury (SCI) and subsequent recovery. Expression of MCAM mRNA increased and co-localized with motoneurons in the spinal cord after SCI. With MCAM morpholino treatment, inhibition of MCAM retarded both axon regrowth and locomotor recovery in the spinal cord injured zebrafish. Furthermore, MCAM mRNA expression was also observed in fli1a:EGFP transgenic zebrafish, which specifically show labeled blood vessels. Inhibition of MCAM down-regulated the expression of angiogenesis-related factors, such as VEGFR-2, p-p38 and p-AKT, and the inflammatory factors TNF-α, IL-1β and IL-8. Taken together, these data suggest that MCAM may have a beneficial role in the recovery from SCI, via the promotion of neurogenesis and angiogenesis. In the context of adult zebrafish spinal cord injury, we proved that Melanoma cell adhesion molecule (MCAM) is beneficial to the recovery, possibly via mechanisms of angiogenensis and inflammation. MCAM promotes angiogenesis by adjusting VEGFR-2, p-p38 and p-AKT. MCAM affects inflammatory factors such as TNF-α, IL-1β and IL-8. Our results extend the beneficial role of MCAM in the regeneration of central nervous system.

Neuronal labeling patterns in the spinal cord of adult transgenic Zebrafish

We describe neuronal patterns in the spinal cord of adult zebrafish. We studied the distribution of cells and processes in the three spinal regions reported in the literature: the 8th vertebra used as a transection injury site, the 15th vertebra mainly used for motor cell recordings and also for crush injury, and the 24th vertebra used to record motor nerve activity. We used well-known transgenic lines in which expression of green fluorescent protein (GFP) is driven by promoters to hb9 and isl1 in motoneurons, alx/chx10 and evx1 interneurons, ngn1 in sensory neurons and olig2 in oligodendrocytes, as well as antibodies for neurons (HuC/D, NF and SV2) and glia (GFAP). In isl1:GFP fish, GFP-positive processes are retained in the upper part of ventral horns and two subsets of cell bodies are observed. The pattern of the transgene in hb9:GFP adults is more diffuse and fibers are present broadly through the adult spinal cord. In alx/chx10 and evx1 lines we respectively observed two and three different GFP-positive populations. Finally, the ngn1:GFP transgene identifies dorsal root ganglion and some cells in dorsal horns. Interestingly some GFP positive fibers in ngn1:GFP fish are located around Mauthner axons and their density seems to be related to a rostrocaudal gradient. Many other cell types have been described in embryos and need to be studied in adults. Our findings provide a reference for further studies on spinal cytoarchitecture. Combined with physiological, histological and pathological/traumatic approaches, these studies will help clarify the operation of spinal locomotor circuits of adult zebrafish.

Methods for studying the zebrafish brain: past, present and future

The zebrafish (Danio rerio) is one of the most promising new model organisms. The increasing popularity of this amazing small vertebrate is evident from the exponentially growing numbers of research articles, funded projects and new discoveries associated with the use of zebrafish for studying development, brain function, human diseases and screening for new drugs. Thanks to the development of novel technologies, the range of zebrafish research is constantly expanding with new tools synergistically enhancing traditional techniques. In this review we will highlight the past and present techniques which have made, and continue to make, zebrafish an attractive model organism for various fields of biology, with a specific focus on neuroscience.

Major vault protein supports glioblastoma survival and migration by upregulating the EGFR/PI3K signalling axis

Despite their ubiquitous expression and high conservation during evolution, precise cellular functions of vault ribonucleoparticles, mainly built of multiple major vault protein (MVP) copies, are still enigmatic. With regard to cancer, vaults were shown to be upregulated during drug resistance development as well as malignant transformation and progression. Such in a previous study we demonstrated that human astrocytic brain tumours including glioblastoma are generally high in vault levels while MVP expression in normal brain is comparably low. However a direct contribution to the malignant phenotype in general and that of glioblastoma in particular has not been established so far. Thus we address the questions whether MVP itself has a pro-tumorigenic function in glioblastoma. Based on a large tissue collection, we re-confirm strong MVP expression in gliomas as compared to healthy brain. Further, the impact of MVP on human glioblastoma aggressiveness was analysed by using gene transfection, siRNA knock-down and dominant-negative genetic approaches. Our results demonstrate that MVP/vaults significantly support migratory and invasive competence as well as starvation resistance of glioma cells in vitro and in vivo. The enhanced aggressiveness was based on MVP-mediated stabilization of the epidermal growth factor receptor (EGFR)/phosphatidyl-inositol-3-kinase (PI3K) signalling axis. Consequently, MVP overexpression resulted in enhanced growth and brain invasion in human glioblastoma xenograft models. Our study demonstrates, for the first time, that vaults have a tumour-promoting potential by stabilizing EGFR/PI3K-mediated migration and survival pathways in human glioblastoma.

Knockdown of αIIb by RNA degradation by delivering deoxyoligonucleotides piggybacked with control vivo-morpholinos into zebrafish thrombocytes

Morpholino and vivo-morpholino gene knockdown methods have been used to study thrombocyte function in zebrafish. However, a large-scale knockdown of the entire zebrafish genome using these technologies to study thrombocyte function is prohibitively expensive. We have developed an inexpensive gene knockdown method, which uses a hybrid of a control vivo-morpholino and a standard antisense oligonucleotide specific for a gene. This hybrid molecule is able to deliver antisense deoxyoligonucleotides into zebrafish thrombocytes because it piggybacks on a control vivo-morpholino. To validate use of this hybrid molecule in gene knockdowns, we targeted the thrombocyte specific αIIb gene with a hybrid of a control vivo-morpholino and an oligonucleotide antisense to αIIb mRNA. The use of this piggyback technology resulted in degradation of αIIb mRNA and led to thrombocyte functional defect. This piggyback method to knockdown genes is inexpensive since one control vivo-morpholino can be used to target many different genes by making many independent gene-specific oligonucleotide hybrids. Thus, this novel piggyback technology can be utilized for cost-effective large-scale knockdowns of genes to study thrombocyte function in zebrafish.

HMGB1 contributes to regeneration after spinal cord injury in adult zebrafish

High mobility group box 1 (HMGB1, also called amphoterin) facilitates neurite outgrowth in early development, yet can exacerbate pathology and inhibit regeneration by inducing adverse neuroinflammation when released from dying cells, suggesting that HMGB1 plays a critical, yet undefined role in neuroregeneration. We explored whether HMGB1 contributes to recovery after complete spinal cord transection in adult zebrafish. Quantitative PCR and in situ hybridization revealed that HMGB1 mRNA levels decreased between 12 h to 11 days after spinal cord injury (SCI), then returned to basal levels by 21 days. Western blot and immunohistological analyses indicated that the time course of HMGB1 protein expression after SCI parallels that of mRNA. Immunofluorescence staining revealed that HMGB1 translocates from nuclei into the cytoplasm of spinal motoneurons at 4 and 12 h (acute stage) following SCI, then accumulates in the nuclei of motoneurons during the ensuing chronic stage (after 6 days following SCI). Immunohistology of transgenic zebrafish, expressing green fluorescent protein in blood vessels, showed enhanced HMGB1 expression in blood vessels in the vicinity of motoneurons. Application of anti-sense HMGB1 morpholinos inhibited locomotor recovery by 34 % and decreased axonal regeneration by 34 % compared to fish treated with a control morpholino. The present study shows that HMGB1 expression increases in both endothelial cells and motoneurons, suggesting that HMGB1 promotes recovery from SCI not only through enhancing neuroregeneration, but also by increasing angiogenesis. The inflammatory effects of HMGB1 are minimized through the decrease in HMGB1 expression during the acute stage.

The asparaginyl endopeptidase legumain is essential for functional recovery after spinal cord injury in adult zebrafish

Unlike mammals, adult zebrafish are capable of regenerating severed axons and regaining locomotor function after spinal cord injury. A key factor for this regenerative capacity is the innate ability of neurons to re-express growth-associated genes and regrow their axons after injury in a permissive environment. By microarray analysis, we have previously shown that the expression of legumain (also known as asparaginyl endopeptidase) is upregulated after complete transection of the spinal cord. In situ hybridization showed upregulation of legumain expression in neurons of regenerative nuclei during the phase of axon regrowth/sprouting after spinal cord injury. Upregulation of Legumain protein expression was confirmed by immunohistochemistry. Interestingly, upregulation of legumain expression was also observed in macrophages/microglia and neurons in the spinal cord caudal to the lesion site after injury. The role of legumain in locomotor function after spinal cord injury was tested by reducing Legumain expression by application of anti-sense morpholino oligonucleotides. Using two independent anti-sense morpholinos, locomotor recovery and axonal regrowth were impaired when compared with a standard control morpholino. We conclude that upregulation of legumain expression after spinal cord injury in the adult zebrafish is an essential component of the capacity of injured neurons to regrow their axons. Another feature contributing to functional recovery implicates upregulation of legumain expression in the spinal cord caudal to the injury site. In conclusion, we established for the first time a function for an unusual protease, the asparaginyl endopeptidase, in the nervous system. This study is also the first to demonstrate the importance of legumain for repair of an injured adult central nervous system of a spontaneously regenerating vertebrate and is expected to yield insights into its potential in nervous system regeneration in mammals.

Neuregulin 1-β regulates cell adhesion molecule L1 expression in the cortex and hippocampus of mice

Neuregulin 1 (Nrg1) functions in neuronal migration, survival and differentiation as well as synaptogenesis during ontogenetic development and maintenance of synaptic functions in the adult mammalian brain. The neural adhesion molecule L1 (L1CAM) functions in similar overlapping, but also non-overlapping roles in the nervous system. In the present study, we therefore investigated some aspects of the functional relationship between Nrg1 and L1 in mammalian neural cells. Nrg1 regulates the expression of L1 in cultures of both human neuroblastoma SK-N-SH cells and mouse cortical and hippocampal neurons. To analyze the role of Nrg1 on L1 expression in vivo, young adult male mice received intraperitoneal injections of Nrg1 or PBS (vehicle control). The correlation between Nrg1 and L1 expression was tested by qPCR, Western blot analysis, and immunocytology. Our data indicate that neuregulin 1-β (Nrg1β) increases L1 expression in neurons of the cerebral cortex, and decreases expression in neurons of the hippocampus in vitro and in vivo. In addition, Nrg1 induces phosphorylation of its receptors, ErbB2 and ErbB4, the predominant ErbB receptors in the nervous system. These results show that Nrg1β affects expression of L1 in the central nervous system and in parallel activates the ErbB receptors for Nrg1, suggesting a crosstalk between molecules that are of prime importance for nervous system functions.

Axonal regeneration after spinal cord injury in zebrafish and mammals: differences, similarities, translation

Spinal cord injury (SCI) in mammals results in functional deficits that are mostly permanent due in part to the inability of severed axons to regenerate. Several types of growth-inhibitory molecules expressed at the injury site contribute to this regeneration failure. The responses of axons to these inhibitors vary greatly within and between organisms, reflecting axons' characteristic intrinsic propensity for regeneration. In the zebrafish (Danio rerio) many but not all axons exhibit successful regeneration after SCI. This review presents and compares the intrinsic and extrinsic determinants of axonal regeneration in the injured spinal cord in mammals and zebrafish. A better understanding of the molecules and molecular pathways underlying the remarkable individualism among neurons in mature zebrafish may support the development of therapies for SCI and their translation to the clinic.

Syntenin-a promotes spinal cord regeneration following injury in adult zebrafish

In contrast to mammals, adult zebrafish recover locomotor function after spinal cord injury, in part due to the capacity of the central nervous system to repair severed connections. To identify molecular cues that underlie regeneration, we conducted mRNA expression profiling and found that syntenin-a expression is upregulated in the adult zebrafish spinal cord caudal to the lesion site after injury. Syntenin is a scaffolding protein involved in mammalian cell adhesion and movement, axonal outgrowth, establishment of cell polarity, and protein trafficking. It could thus be expected to be involved in supporting regeneration in fish. Syntenin-a mRNA and protein are expressed in neurons, glia and newly generated neural cells, and upregulated caudal to the lesion site on days 6 and 11 following spinal cord injury. Treatment of spinal cord-injured fish with two different antisense morpholinos to knock down syntenin-a expression resulted in significant inhibition of locomotor recovery at 5 and 6 weeks after injury, when compared to control morpholino-treated fish. Knock-down of syntenin-a reduced regrowth of descending axons from brainstem neurons into the spinal cord caudal to the lesion site. These observations indicate that syntenin-a is involved in regeneration after traumatic insult to the central nervous system of adult zebrafish, potentially leading to novel insights into the cellular and molecular mechanisms that require activation in the regeneration-deficient mammalian central nervous system.