Embryonic stem cell-derived L1 overexpressing neural aggregates enhance recovery after spinal cord injury in mice

The combined application of stem cells and three-dimensional bioprinting scaffolds for the repair of spinal cord injury

Spinal cord injury is considered one of the most difficult injuries to repair and has one of the worst prognoses for injuries to the nervous system. Following surgery, the poor regenerative capacity of nerve cells and the generation of new scars can make it very difficult for the impaired nervous system to restore its neural functionality. Traditional treatments can only alleviate secondary injuries but cannot fundamentally repair the spinal cord. Consequently, there is a critical need to develop new treatments to promote functional repair after spinal cord injury. Over recent years, there have been several developments in the use of stem cell therapy for the treatment of spinal cord injury. Alongside significant developments in the field of tissue engineering, three-dimensional bioprinting technology has become a hot research topic due to its ability to accurately print complex structures. This led to the loading of three-dimensional bioprinting scaffolds which provided precise cell localization. These three-dimensional bioprinting scaffolds could repair damaged neural circuits and had the potential to repair the damaged spinal cord. In this review, we discuss the mechanisms underlying simple stem cell therapy, the application of different types of stem cells for the treatment of spinal cord injury, and the different manufacturing methods for three-dimensional bioprinting scaffolds. In particular, we focus on the development of three-dimensional bioprinting scaffolds for the treatment of spinal cord injury.

Cell Transplantation for Repair of the Spinal Cord and Prospects for Generating Region-Specific Exogenic Neuronal Cells

Spinal cord injury (SCI) is associated with currently irreversible consequences in several functional components of the central nervous system. Despite the severity of injury, there remains no approved treatment to restore function. However, with a growing number of preclinical studies and clinical trials, cell transplantation has gained significant potential as a treatment for SCI. Researchers have identified several cell types as potential candidates for transplantation. To optimize successful functional outcomes after transplantation, one key factor concerns generating neuronal cells with regional and subtype specificity, thus calling on the developmental transcriptome patterning of spinal cord cells. A potential source of spinal cord cells for transplantation is the generation of exogenic neuronal progenitor cells via the emerging technologies of gene editing and blastocyst complementation. This review highlights the use of cell transplantation to treat SCI in the context of relevant developmental gene expression patterns useful for producing regionally specific exogenic spinal cells via in vitro differentiation and blastocyst complementation.

COVID-19 disease treatment: pivotal challenges in the arena of umbilical cord-mesenchymal stem cells (UC-MSCs)

This century's first major epidemic of a new coronavirus illness (2019-nCoV) was a tremendous shock to the healthcare system. The onset of the pandemic has caused severe economic and health shortages. At this time, there are no viable treatments for COVID-19. Several clinical studies using cell-based therapies, such as umbilical cord mesenchymal stem cells, have showed promising results (UC-MSCs). UC-MSCs have been the focus of much study because to their potential as a treatment option for COVID-19 patients. Cytokine release syndrome, often called cytokine storm, increases the risk of morbidity and mortality from COVID-19. It has been established that UC-MSCs may suppress and control both the adaptive and innate immune responses by modulating the release of immunostimulatory cytokines. The purpose of this study is to assess and clarify the use of UC-MSCs for the treatment of ARDS caused by COVID-19.

The Interactions of the 70 kDa Fragment of Cell Adhesion Molecule L1 with Topoisomerase 1, Peroxisome Proliferator-Activated Receptor γ and NADH Dehydrogenase (Ubiquinone) Flavoprotein 2 Are Involved in Gene Expression and Neuronal L1-Dependent Functions

The cell adhesion molecule L1 is essential not only for neural development, but also for synaptic functions and regeneration after trauma in adulthood. Abnormalities in L1 functions cause developmental and degenerative disorders. L1's functions critically depend on proteolysis which underlies dynamic cell interactions and signal transduction. We showed that a 70 kDa fragment (L1-70) supports mitochondrial functions and gene transcription. To gain further insights into L1-70's functions, we investigated several binding partners. Here we show that L1-70 interacts with topoisomerase 1 (TOP1), peroxisome proliferator-activated receptor γ (PPARγ) and NADH dehydrogenase (ubiquinone) flavoprotein 2 (NDUFV2). TOP1, PPARγ and NDUFV2 siRNAs reduced L1-dependent neurite outgrowth, and the topoisomerase inhibitors topotecan and irinotecan inhibited L1-dependent neurite outgrowth, neuronal survival and migration. In cultured neurons, L1 siRNA reduces the expression levels of the long autism genes neurexin-1 (Nrxn1) and neuroligin-1 (Nlgn1) and of the mitochondrially encoded gene NADH:ubiquinone oxidoreductase core subunit 2 (ND2). In mutant mice lacking L1-70, Nrxn1 and Nlgn1, but not ND2, mRNA levels are reduced. Since L1-70's interactions with TOP1, PPARγ and NDUFV2 contribute to the expression of two essential long autism genes and regulate important neuronal functions, we propose that L1 may not only ameliorate neurological problems, but also psychiatric dysfunctions.

Artemisinin upregulates neural cell adhesion molecule L1 to attenuate neurological deficits after intracerebral hemorrhage in mice

BACKGROUND AND PURPOSE

Intracerebral hemorrhage (ICH) is a subtype of stroke and results in neurological deficits in patients without any effective treatments. Artemisinin (ART), a well-known antimalarial Chinese medicine, exerts multiple essential roles in the central and peripheral nervous system due to its antioxidative and anti-inflammation properties. Neural cell adhesion molecule L1 (L1CAM, L1) is considered to be implicated in neural development, functional maintenance, and neuroprotection during disease. However, whether these two essential molecules are neuroprotective in ICH remains unclear.

METHODS

Therefore, the present study investigated the influence of ART on the recovery of neurological deficits in a mouse model of ICH induced by collagenase and the underlying mechanism.

RESULTS

It was revealed that ART is capable of upregulating L1 expression to alleviate brain edema, reduce oxidative stress, and inhibit inflammation to alleviate ICH-induced brain injury to improve the neurological outcome in mice suffering from ICH.

CONCLUSION

These results may lay the foundation for ART to be a novel candidate treatment for ICH.

Antagonistic L1 Adhesion Molecule Mimetic Compounds Inhibit Glioblastoma Cell Migration In Vitro

Cell adhesion molecule L1 is a cell surface glycoprotein that promotes neuronal cell migration, fosters regeneration after spinal cord injury and ameliorates the consequences of neuronal degeneration in mouse and zebrafish models. Counter-indicative features of L1 were found in tumor progression: the more L1 is expressed, the more tumor cells migrate and increase their metastatic potential. L1′s metastatic potential is further evidenced by its promotion of epithelial–mesenchymal transition, endothelial cell transcytosis and resistance to chemo- and radiotherapy. These unfortunate features are indicated by observations that cells that normally do not express L1 are induced to express it when becoming malignant. With the aim to ameliorate the devastating functions of L1 in tumors, we designed an alternative approach to counteract tumor cell migration. Libraries of small organic compounds were screened using the ELISA competition approach similar to the one that we used for identifying L1 agonistic mimetics. Whereas in the former approach, a function-triggering monoclonal antibody was used for screening libraries, we here used the function-inhibiting monoclonal antibody 324 that reduces the migration of neurons. We now show that the L1 antagonistic mimetics anagrelide, 2-hydroxy-5-fluoropyrimidine and mestranol inhibit the migration of cultured tumor cells in an L1-dependent manner, raising hopes for therapy.

Repair of the Injured Spinal Cord by Schwann Cell Transplantation

Spinal cord injury (SCI) can result in sensorimotor impairments or disability. Studies of the cellular response to SCI have increased our understanding of nerve regenerative failure following spinal cord trauma. Biological, engineering and rehabilitation strategies for repairing the injured spinal cord have shown impressive results in SCI models of both rodents and non-human primates. Cell transplantation, in particular, is becoming a highly promising approach due to the cells’ capacity to provide multiple benefits at the molecular, cellular, and circuit levels. While various cell types have been investigated, we focus on the use of Schwann cells (SCs) to promote SCI repair in this review. Transplantation of SCs promotes functional recovery in animal models and is safe for use in humans with subacute SCI. The rationales for the therapeutic use of SCs for SCI include enhancement of axon regeneration, remyelination of newborn or sparing axons, regulation of the inflammatory response, and maintenance of the survival of damaged tissue. However, little is known about the molecular mechanisms by which transplanted SCs exert a reparative effect on SCI. Moreover, SC-based therapeutic strategies face considerable challenges in preclinical studies. These issues must be clarified to make SC transplantation a feasible clinical option. In this review, we summarize the recent advances in SC transplantation for SCI, and highlight proposed mechanisms and challenges of SC-mediated therapy. The sparse information available on SC clinical application in patients with SCI is also discussed.

Pluripotent Stem Cells for Spinal Cord Injury Repair

Spinal cord injury (SCI) is a devastating condition of the central nervous system that strongly reduces the patient’s quality of life and has large financial costs for the healthcare system. Cell therapy has shown considerable therapeutic potential for SCI treatment in different animal models. Although many different cell types have been investigated with the goal of promoting repair and recovery from injury, stem cells appear to be the most promising. Here, we review the experimental approaches that have been carried out with pluripotent stem cells, a cell type that, due to its inherent plasticity, self-renewal, and differentiation potential, represents an attractive source for the development of new cell therapies for SCI. We will focus on several key observations that illustrate the potential of cell therapy for SCI, and we will attempt to draw some conclusions from the studies performed to date.

Anisotropic scaffolds for peripheral nerve and spinal cord regeneration

The treatment of long-gap (>10 mm) peripheral nerve injury (PNI) and spinal cord injury (SCI) remains a continuous challenge due to limited native tissue regeneration capabilities. The current clinical strategy of using autografts for PNI suffers from a source shortage, while the pharmacological treatment for SCI presents dissatisfactory results. Tissue engineering, as an alternative, is a promising approach for regenerating peripheral nerves and spinal cords. Through providing a beneficial environment, a scaffold is the primary element in tissue engineering. In particular, scaffolds with anisotropic structures resembling the native extracellular matrix (ECM) can effectively guide neural outgrowth and reconnection. In this review, the anatomy of peripheral nerves and spinal cords, as well as current clinical treatments for PNI and SCI, is first summarized. An overview of the critical components in peripheral nerve and spinal cord tissue engineering and the current status of regeneration approaches are also discussed. Recent advances in the fabrication of anisotropic surface patterns, aligned fibrous substrates, and 3D hydrogel scaffolds, as well as their in vitro and in vivo effects are highlighted. Finally, we summarize potential mechanisms underlying the anisotropic architectures in orienting axonal and glial cell growth, along with their challenges and prospects.

Adhesion molecule L1 inhibition increases infarct size in cerebral ischemia-reperfusion without change in blood-brain barrier disruption

OBJECTIVE

Neural cell adhesion molecule L1CAM (L1) is involved in neuroprotection. To investigate a possible neuroprotective effect of L1 during ischemia, we determined whether blocking L1 with an antagonistic antibody would worsen the outcome of focal cerebral ischemia-reperfusion and increase blood-brain barrier (BBB) disruption.

METHODS

Transient middle cerebral artery occlusion (MCAO) was performed in anesthetized rats. Five µg of antagonistic mouse IgG monoclonal L1 antibody 324 or non-immune control mouse IgG was applied on the ischemic-reperfused cortex during one hour of MCAO and two hours of reperfusion. At two hours of reperfusion, BBB permeability, size of infarct using tetrazolium staining, number of TUNEL-labeled apoptotic cells, and immunohistochemistry for expression of PTEN and p53 were studied.

RESULTS

The antagonistic L1 antibody 324 increased the percentage of cortical infarct area (+36%), but did not affect BBB permeability in the ischemic-reperfused cortex. The antagonistic L1 antibody increased number of apoptotic neurons and p53 expression, but decreased PTEN expression.

CONCLUSION

Functional antagonism of L1 increases infarct size by increasing numbers of apoptotic neurons without affecting BBB permeability during the early stage of cerebral ischemia-reperfusion. Our data suggest that L1 affects primarily the brain parenchyma rather than BBB during early stages of cerebral ischemia-reperfusion and that endogenous brain L1 may be neuroprotective.

Stem Cell Therapy for Spinal Cord Injury

Traumatic spinal cord injury (SCI) results in direct and indirect damage to neural tissues, which results in motor and sensory dysfunction, dystonia, and pathological reflex that ultimately lead to paraplegia or tetraplegia. A loss of cells, axon regeneration failure, and time-sensitive pathophysiology make tissue repair difficult. Despite various medical developments, there are currently no effective regenerative treatments. Stem cell therapy is a promising treatment for SCI due to its multiple targets and reactivity benefits. The present review focuses on SCI stem cell therapy, including bone marrow mesenchymal stem cells, umbilical mesenchymal stem cells, adipose-derived mesenchymal stem cells, neural stem cells, neural progenitor cells, embryonic stem cells, induced pluripotent stem cells, and extracellular vesicles. Each cell type targets certain features of SCI pathology and shows therapeutic effects via cell replacement, nutritional support, scaffolds, and immunomodulation mechanisms. However, many preclinical studies and a growing number of clinical trials found that single-cell treatments had only limited benefits for SCI. SCI damage is multifaceted, and there is a growing consensus that a combined treatment is needed.

Proteomic Analysis of Preoperative CSF Reveals Risk Biomarkers of Postoperative Delirium

Objective: To analyze the proteome of preoperative cerebrospinal fluid (CSF) in older orthopedic patients with or without postoperative delirium (POD) using untargeted proteomics. Methods: A prospective cohort study was conducted. Eighty hip fracture patients aged ≥65 years were recruited. After successful spinal anesthesia, CSF was collected. The patients were divided into POD and No-POD groups based on the Confusion Assessment Method, and patients with POD were graded using the Memorial Delirium Assessment Scale (MDAS). Thirty No-POD patients were matched to 10 POD patients by age (±2 years) and Mini-Mental State Examination score (±2 scores). Label-free proteomic analysis was performed using a liquid chromatography coupled to mass spectrometry (LC-MS) workflow. Validation was performed using mass-spectrometry-based parallel reaction monitoring (PRM) for the 30 No-POD and 10 POD patients, as well as for an additional 5 POD patients. Bioinformatics were used to investigate possible relevant pathological mechanisms. Results: The incidence of POD in older orthopedic patients was 18.8% in our cohort of 80 patients. Proteomics results revealed 63 dysregulated CSF proteins, and PRM analysis validated these results. The preoperative CSF levels of both V-set and transmembrane domain-containing protein 2B (VSTM2B) and coagulation factor V (FA5) were positively correlated with MDAS scores on postoperative day 1 (r > 0.8, p < 0.05). Bioinformatic analysis revealed that several nervous-system-related pathways are relevant to POD development. Conclusion: We identified and validated several novel CSF proteins that are dysregulated in POD, and revealed several pathways that are relevant to POD development. Our results not only provide risk biomarkers for POD, but also give clues for further investigations into the pathological mechanisms of delirium. Clinical trial registration: This study was registered in the Chinese Clinical Trial Registry (ChiCTR1900021533).

Phenelzine, a cell adhesion molecule L1 mimetic small organic compound, promotes functional recovery and axonal regrowth in spinal cord-injured zebrafish

Injury to the spinal cord initiates a cascade of cellular and molecular events that contribute to the tissue environment that is non-permissive for cell survival and axonal regrowth/sprouting in the adult mammalian central nervous system. The endogenous repair response is impaired in this generally inhibitory environment. Previous studies indicate that homophilic interactions of the neural cell adhesion molecule L1 (L1CAM) promote recovery after spinal cord injury and ameliorate neurodegenerative processes in experimental rodent and zebrafish models. In light of reports that phenelzine, a small organic compound that mimics L1, stimulates neuronal survival, neuronal migration, neurite outgrowth, and Schwann cell proliferation in vitro in a L1-dependent manner, we examined the restorative potential of phenelzine in a zebrafish model of spinal cord injury. Addition of phenelzine into the aquarium water immediately after spinal cord injury accelerated locomotor recovery and promoted axonal regrowth and remyelination in larval and adult zebrafish. Phenelzine treatment up-regulated the expression and proteolysis of L1.1 (a homolog of the mammalian recognition molecule L1) and phosphorylation of Erk in the spinal cord caudal to lesion site. By combining the results of the present study with those of other studies, we propose that phenelzine bears hopes for therapy of nervous system injuries.

A fragment of adhesion molecule L1 is imported into mitochondria, and regulates mitochondrial metabolism and trafficking

The cell adhesion molecule L1 (also known as L1CAM) plays important roles in the mammalian nervous system under physiological and pathological conditions. We have previously reported that proteolytic cleavage of L1 by myelin basic protein leads to the generation of a 70 kDa transmembrane L1 fragment (L1-70) that promotes neuronal migration and neuritogenesis. Here, we provide evidence that L1-70 is imported from the cytoplasm into mitochondria. Genetic ablation of L1, inhibition of mitochondrial import of L1-70 or prevention of myelin basic protein-mediated generation of L1-70 all lead to reduced mitochondrial complex I activity, and impaired mitochondrial membrane potential, fusion, fission and motility, as well as increased retrograde transport. We identified NADH dehydrogenase ubiquinone flavoprotein 2 as a binding partner for L1, suggesting that L1-70 interacts with this complex I subunit to regulate complex I activity. The results of our study provide insights into novel functions of L1 in mitochondrial metabolism and cellular dynamics. These functions are likely to ameliorate the consequences of acute nervous system injuries and chronic neurodegenerative diseases.

Confocal Synaptology: Synaptic Rearrangements in Neurodegenerative Disorders and upon Nervous System Injury

The nervous system is a notable exception to the rule that the cell is the structural and functional unit of tissue systems and organs. The functional unit of the nervous system is the synapse, the contact between two nerve cells. As such, synapses are the foci of investigations of nervous system organization and function, as well as a potential readout for the progression of various disorders of the nervous system. In the past decade the development of antibodies specific to presynaptic terminals has enabled us to assess, at the optical, laser scanning microscopy level, these subcellular structures, and has provided a simple method for the quantification of various synapses. Indeed, excitatory (glutamatergic) and inhibitory synapses can be visualized using antibodies against the respective vesicular transporters, and choline-acetyl transferase (ChAT) immunoreactivity identifies cholinergic synapses throughout the central nervous system. Here we review the results of several studies in which these methods were used to estimate synaptic numbers as the structural equivalent of functional outcome measures in spinal cord and femoral nerve injuries, as well as in genetic mouse models of neurodegeneration, including Alzheimer's disease (AD). The results implicate disease- and brain region-specific changes in specific types of synapses, which correlate well with the degree of functional deficit caused by the disease process. Additionally, results are reproducible between various studies and experimental paradigms, supporting the reliability of the method. To conclude, this quantitative approach enables fast and reliable estimation of the degree of the progression of neurodegenerative changes and can be used as a parameter of recovery in experimental models.

A Small Organic Compound Mimicking the L1 Cell Adhesion Molecule Promotes Functional Recovery after Spinal Cord Injury in Zebrafish

Tacrine is a small organic compound that was discovered to mimic the functions of the neural cell adhesion molecule L1 by promoting the cognate functions of L1 in vitro, such as neuronal survival, neuronal migration, neurite outgrowth, and myelination. Based on studies indicating that L1 enhances functional recovery in different central and peripheral nervous system disease paradigms of rodents, it deemed interesting to investigate the beneficial role of tacrine in the attractive zebrafish animal model, by evaluating functional recovery after spinal cord injury. To this aim, larval and adult zebrafish were exposed to tacrine treatment after spinal cord injury and monitored for locomotor recovery and axonal regrowth. Tacrine promoted the rapid recovery of locomotor activities in both larval and adult zebrafish, enhanced regrowth of severed axons and myelination, and reduced astrogliosis in the spinal cords. Tacrine treatment upregulated the expression of L1.1 (a homolog of the mammalian recognition molecule L1) and enhanced the L1.1-mediated intracellular signaling cascades in the injured spinal cords. These observations lead to the hope that, in combination with other therapeutic approaches, this old drug may become a useful reagent to ameliorate the deficits resulting from acute and chronic injuries of the mammalian nervous system.

The L1 adhesion molecule normalizes neuritogenesis in Rett syndrome-derived neural precursor cells

Therapeutic intervention is an important need in ameliorating the severe consequences of Rett Syndrome (RTT), a neurological disorder caused by mutations in the X-linked gene methyl-CpG-binding protein-2 (MeCP2). Following previously observed morphological defects in induced pluripotent stem cell (iPSC)-derived neurons obtained from female RTT patients, we hypothesized that transfection with the L1 cell adhesion molecule (L1) could contribute to normalizing a pathological male cell system bearing a nonsense mutation of MeCP2. We found a decreased expression of L1 in RTT iPSCs-derived neural precursor cells (RTT NPCs) and decreased neuritogenesis. Expression of wild-type MeCP2 in RTTNPCs revealed a positive correlation between the levels of MeCP2 and L1, and normalization of cell survival. Expression of L1 in RTTNPCs enhanced neuritogenesis and soma size. Knock-down of MeCP2 in wild type NPCs reduced neuritogenesis. L1 expression is regulated by the MeCP2 promoter. These results suggest that a deficiency in L1 may partially account for RTT phenotypes.

Spinal Cord Molecular and Cellular Changes Induced by Adenoviral Vector- and Cell-Mediated Triple Gene Therapy after Severe Contusion

The gene therapy has been successful in treatment of spinal cord injury (SCI) in several animal models, although it still remains unavailable for clinical practice. Surprisingly, regardless the fact that multiple reports showed motor recovery with gene therapy, little is known about molecular and cellular changes in the post-traumatic spinal cord following viral vector- or cell-mediated gene therapy. In this study we evaluated the therapeutic efficacy and changes in spinal cord after treatment with the genes encoding vascular endothelial growth factor (VEGF), glial cell-derived neurotrophic factor (GDNF), angiogenin (ANG), and neuronal cell adhesion molecule (NCAM) applied using both approaches. Therapeutic genes were used for viral vector- and cell-mediated gene therapy in two combinations: (1) VEGF+GDNF+NCAM and (2) VEGF+ANG+NCAM. For direct gene therapy adenoviral vectors based on serotype 5 (Ad5) were injected intrathecally and for cell-mediated gene delivery human umbilical cord blood mononuclear cells (UCB-MC) were simultaneously transduced with three Ad5 vectors and injected intrathecally 4 h after the SCI. The efficacy of both treatments was confirmed by improvement in behavioral (BBB) test. Molecular and cellular changes following post-traumatic recovery were evaluated with immunofluorescent staining using antibodies against the functional markers of motorneurons (Hsp27, synaptophysin, PSD95), astrocytes (GFAP, vimentin), oligodendrocytes (Olig2, NG2, Cx47) and microglial cells (Iba1). Our results suggest that both approaches with intrathecal delivery of therapeutic genes may support functional recovery of post-traumatic spinal cord via lowering the stress (down regulation of Hsp25) and enhancing the synaptic plasticity (up regulation of PSD95 and synaptophysin), supporting oligodendrocyte proliferation (up regulation of NG2) and myelination (up regulation of Olig2 and Cx47), modulating astrogliosis by reducing number of astrocytes (down regulation of GFAP and vimetin) and microglial cells (down regulation of Iba1).

Stem cell transplantation for spinal cord injury repair

Stem cells, especially neural stem cells (NSCs), are a very attractive cell source for potential reconstruction of injured spinal cord though either neuroprotection, neural regeneration, remyelination, replacement of lost neural cells, or reconnection of disrupted axons. The later have great potential since recent studies demonstrate long-distance growth and connectivity of axons derived from transplanted NSCs after spinal cord injury (SCI). In addition, transplanted NSCs constitute a permissive environment for host axonal regeneration and serve as new targets for host axonal connection. This reciprocal connection between grafted neurons and host neurons constitutes a neuronal relay formation that could restore functional connectivity after SCI.

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.

Neuroadhesive L1 coating attenuates acute microglial attachment to neural electrodes as revealed by live two-photon microscopy

Implantable neural electrode technologies for chronic neural recordings can restore functional control to paralysis and limb loss victims through brain-machine interfaces. These probes, however, have high failure rates partly due to the biological responses to the probe which generate an inflammatory scar and subsequent neuronal cell death. L1 is a neuronal specific cell adhesion molecule and has been shown to minimize glial scar formation and promote electrode-neuron integration when covalently attached to the surface of neural probes. In this work, the acute microglial response to L1-coated neural probes was evaluated in vivo by implanting coated devices into the cortex of mice with fluorescently labeled microglia, and tracking microglial dynamics with multi-photon microscopy for the ensuing 6 h in order to understand L1's cellular mechanisms of action. Microglia became activated immediately after implantation, extending processes towards both L1-coated and uncoated control probes at similar velocities. After the processes made contact with the probes, microglial processes expanded to cover 47.7% of the control probes' surfaces. For L1-coated probes, however, there was a statistically significant 83% reduction in microglial surface coverage. This effect was sustained through the experiment. At 6 h post-implant, the radius of microglia activation was reduced for the L1 probes by 20%, shifting from 130.0 to 103.5 μm with the coating. Microglia as far as 270 μm from the implant site displayed significantly lower morphological characteristics of activation for the L1 group. These results suggest that the L1 surface treatment works in an acute setting by microglial mediated mechanisms.

Small Molecule Agonists of Cell Adhesion Molecule L1 Mimic L1 Functions In Vivo

Lack of permissive mechanisms and abundance of inhibitory molecules in the lesioned central nervous system of adult mammals contribute to the failure of functional recovery after injury, leading to severe disabilities in motor functions and pain. Peripheral nerve injury impairs motor, sensory, and autonomic functions, particularly in cases where nerve gaps are large and chronic nerve injury ensues. Previous studies have indicated that the neural cell adhesion molecule L1 constitutes a viable target to promote regeneration after acute injury. We screened libraries of known drugs for small molecule agonists of L1 and evaluated the effect of hit compounds in cell-based assays in vitro and in mice after femoral nerve and spinal cord injuries in vivo. We identified eight small molecule L1 agonists and showed in cell-based assays that they stimulate neuronal survival, neuronal migration, and neurite outgrowth and enhance Schwann cell proliferation and migration and myelination of neurons in an L1-dependent manner. In a femoral nerve injury mouse model, enhanced functional regeneration and remyelination after application of the L1 agonists were observed. In a spinal cord injury mouse model, L1 agonists improved recovery of motor functions, being paralleled by enhanced remyelination, neuronal survival, and monoaminergic innervation, reduced astrogliosis, and activation of microglia. Together, these findings suggest that application of small organic compounds that bind to L1 and stimulate the beneficial homophilic L1 functions may prove to be a valuable addition to treatments of nervous system injuries.

The polysialic acid mimetics 5-nonyloxytryptamine and vinorelbine facilitate nervous system repair

Polysialic acid (PSA) is a large negatively charged glycan mainly attached to the neural cell adhesion molecule (NCAM). Several studies have shown that it is important for correct formation of brain circuitries during development and for synaptic plasticity, learning and memory in the adult. PSA also plays a major role in nervous system regeneration following injury. As a next step for clinical translation of PSA based therapeutics, we have previously identified the small organic compounds 5-nonyloxytryptamine and vinorelbine as PSA mimetics. Activity of 5-nonyloxytryptamine and vinorelbine had been confirmed in assays with neural cells from the central and peripheral nervous system in vitro and shown to be independent of their function as serotonin receptor 5-HT1B/1D agonist or cytostatic drug, respectively. As we show here in an in vivo paradigm for spinal cord injury in mice, 5-nonyloxytryptamine and vinorelbine enhance regain of motor functions, axonal regrowth, motor neuron survival and remyelination. These data indicate that 5-nonyloxytryptamine and vinorelbine may be re-tasked from their current usage as a 5-HT1B/1D agonist or cytostatic drug to act as mimetics for PSA to stimulate regeneration after injury in the mammalian nervous system.

Human Embryonic Stem Cell Therapy in Chronic Spinal Cord Injury: A Retrospective Study

Human embryonic stem cells (hESCs) have a role in treating neurological disorders. The efficacy and safety of hESC in treating spinal cord injury (SCI) was reported in our previous study. In the present study, we have evaluated the efficacy and safety of hESC therapy in 226 patients with SCI. In the first treatment phase (T1), 0.25 mL hESCs were administered intramuscularly twice daily, 1 mL every 10 days i.v., and 1-5 mL every 7 days. Of 153 patients in the American Spinal Injury Association (ASIA) scale A at the beginning of T1, a significant number of patients (n = 80; 52.3%) moved to lower scales at the end of T1 (p = 0.01). At the end of T2, of 32 patients in ASIA scale A, 12 patients (37.5%) moved to scale B (p = 0.01). Of 19 patients, 3 patients (37.5%) moved to scale B at the end of T3 (p = 0.02). No serious adverse events (AEs) were observed. hESC transplantation is safe and effective.

Cell Therapy Augments Functional Recovery Subsequent to Spinal Cord Injury under Experimental Conditions

The spinal cord injury leads to enervation of normal tissue homeostasis ultimately leading to paralysis. Until now there is no proper cure for the treatment of spinal cord injury. Recently, cell therapy in animal spinal cord injury models has shown some progress of recovery. At present, clinical trials are under progress to evaluate the efficacy of cell transplantation for the treatment of spinal cord injury. Different types of cells such as pluripotent stem cells derived neural cells, mesenchymal stromal cells, neural stem cells, glial cells are being tested in various spinal cord injury models. In this review we highlight both the advances and lacuna in the field of spinal cord injury by discussing epidemiology, pathophysiology, molecular mechanism, and various cell therapy strategies employed in preclinical and clinical injury models and finally we discuss the limitations and ethical issues involved in cell therapy approach for treating spinal cord injury.

Translating mechanisms of neuroprotection, regeneration, and repair to treatment of spinal cord injury

One of the big challenges in neuroscience that remains to be understood is why the central nervous system is not able to regenerate to the extent that the peripheral nervous system does. This is especially problematic after traumatic injuries, like spinal cord injury (SCI), since the lack of regeneration leads to lifelong deficits and paralysis. Treatment of SCI has improved during the last several decades due to standardized protocols for emergency medical response teams and improved medical, surgical, and rehabilitative treatments. However, SCI continues to result in profound impairments for the individual. There are many processes that lead to the pathophysiology of SCI, such as ischemia, vascular disruption, neuroinflammation, oxidative stress, excitotoxicity, demyelination, and cell death. Current treatments include surgical decompression, hemodynamic control, and methylprednisolone. However, these early treatments are associated with modest functional recovery. Some treatments currently being investigated for use in SCI target neuroprotective (riluzole, minocycline, G-CSF, FGF-2, and polyethylene glycol) or neuroregenerative (chondroitinase ABC, self-assembling peptides, and rho inhibition) strategies, while many cell therapies (embryonic stem cells, neural stem cells, induced pluripotent stem cells, mesenchymal stromal cells, Schwann cells, olfactory ensheathing cells, and macrophages) have also shown promise. However, since SCI has multiple factors that determine the progress of the injury, a combinatorial therapeutic approach will most likely be required for the most effective treatment of SCI.

Thermomineral water promotes axonal sprouting but does not reduce glial scar formation in a mouse model of spinal cord injury

Thermomineral water from the Atomic Spa Gornja Trepča has been used for a century in the treatment of neurologic disease. The thermomineral water contains microelements, including lithium and magnesium, which show neural regeneration-promoting effects after central nervous system injury. In this study, we investigated the effects of oral intake of thermomineral water from the Atomic Spa Gornja Trepča on nerve regeneration in a 3-month-old mouse model of spinal cord injury. The mice receiving oral intake of thermomineral water showed better locomotor recovery than those without administration of thermomineral water at 8 and 12 weeks after lower thoracic spinal cord compression. At 12 weeks after injury, sprouting of catecholaminergic axons was better in mice that drank thermomineral water than in those without administration of thermomineral water, but there was no difference in glial reaction to injury between mice with and without administration of thermomineral water. These findings suggest that thermomineral water can promote the nerve regeneration but cannot reduce glial scar formation in a mouse model of spinal cord injury.

Stem cell therapy in spinal trauma: Does it have scientific validity?

Stem cell-based interventions aim to use special regenerative cells (stem cells) to facilitate neuronal function beyond the site of the injury. Many studies involving animal models of spinal cord injury (SCI) suggest that certain stem cell-based therapies may restore function after SCI. Currently, in case of spinal cord injuries, new discoveries with clinical implications have been continuously made in basic stem cell research, and stem cell-based approaches are advancing rapidly toward application in patients. There is a huge base of preclinical evidence in vitro and in animal models which suggests the safety and clinical efficacy of cellular therapies after SCI. Despite this, data from clinical studies is not very encouraging and at times confounding. Here, we have attempted to cover preclinical and clinical evidence base dealing with safety, feasibility and efficacy of cell based interventions after SCI. The limitations of preclinical data and the reasons underlying its failure to translate in a clinical setting are also discussed. Based on the evidence base, it is suggested that a multifactorial approach is required to address this situation. Need for standardized, stringently designed multi-centric clinical trials for obtaining validated proof of evidence is also highlighted.

Analysis of human embryonic stem cells with regulatable expression of the cell adhesion molecule l1 in regeneration after spinal cord injury

Cell replacement therapy is one potential avenue for central nervous system (CNS) repair. However, transplanted stem cells may not contribute to long-term recovery of the damaged CNS unless they are engineered for functional advantage. To fine tune regenerative capabilities, we developed a human neural cell line expressing L1, a regeneration-conducive adhesion molecule, under the control of a doxycycline regulatable Tet-off promoter. Controlled expression of L1 is desired because overexpression after regenerative events may lead to adverse consequences. The regulated system was tested in several cell lines, where doxycycline completely eliminated green fluorescent protein or L1 expression by 3-5 days in vitro. Increased colony formation as well as decreased proliferation were observed in H9NSCs without doxycycline (hL1-on). To test the role of L1 in vivo after acute compression spinal cord injury of immunosuppressed mice, quantum dot labeled hL1-on or hL1-off cells were injected at three sites: lesion; proximal; and caudal. Mice transplanted with hL1-on cells showed a better Basso Mouse Scale score, when compared to those with hL1-off cells. As compared to the hL1-off versus hL1-on cell transplanted mice 6 weeks post-transplantation, expression levels of L1, migration of transplanted cells, and immunoreactivity for tyrosine hydroxylase were higher, whereas expression of chondroitin sulfate proteoglycans was lower. Results indicate that L1 expression is regulatable in human stem cells by doxycycline in a nonviral engineering approach. Regulatable expression in a prospective nonleaky Tet-off system could hold promise for therapy, based on the multifunctional roles of L1, including neuronal migration and survival, neuritogenesis, myelination, and synaptic plasticity.

Influence of the extracellular matrix on endogenous and transplanted stem cells after brain damage

The limited regeneration capacity of the adult central nervous system (CNS) requires strategies to improve recovery of patients. In this context, the interaction of endogenous as well as transplanted stem cells with their environment is crucial. An understanding of the molecular mechanisms could help to improve regeneration by targeted manipulation. In the course of reactive gliosis, astrocytes upregulate Glial fibrillary acidic protein (GFAP) and start, in many cases, to proliferate. Beside GFAP, subpopulations of these astroglial cells coexpress neural progenitor markers like Nestin. Although cells express these markers, the proportion of cells that eventually give rise to neurons is limited in many cases in vivo compared to the situation in vitro. In the first section, we present the characteristics of endogenous progenitor-like cells and discuss the differences in their neurogenic potential in vitro and in vivo. As the environment plays an important role for survival, proliferation, migration, and other processes, the second section of the review describes changes in the extracellular matrix (ECM), a complex network that contains numerous signaling molecules. It appears that signals in the damaged CNS lead to an activation and de-differentiation of astrocytes, but do not effectively promote neuronal differentiation of these cells. Factors that influence stem cells during development are upregulated in the damaged brain as part of an environment resembling a stem cell niche. We give a general description of the ECM composition, with focus on stem cell-associated factors like the glycoprotein Tenascin-C (TN-C). Stem cell transplantation is considered as potential treatment strategy. Interaction of transplanted stem cells with the host environment is critical for the outcome of stem cell-based therapies. Possible mechanisms involving the ECM by which transplanted stem cells might improve recovery are discussed in the last section.

Molecular targeting of TRF2 suppresses the growth and tumorigenesis of glioblastoma stem cells

Glioblastoma is the most prevalent primary brain tumor and is essentially universally fatal within 2 years of diagnosis. Glioblastomas contain cellular hierarchies with self-renewing glioblastoma stem cells (GSCs) that are often resistant to chemotherapy and radiation therapy. GSCs express high amounts of repressor element 1 silencing transcription factor (REST), which may contribute to their resistance to standard therapies. Telomere repeat-binding factor 2 (TRF2) stablizes telomeres and REST to maintain self-renewal of neural stem cells and tumor cells. Here we show viral vector-mediated delivery of shRNAs targeting TRF2 mRNA depletes TRF2 and REST from GSCs isolated from patient specimens. As a result, GSC proliferation is reduced and the level of proteins normally expressed by postmitotic neurons (L1CAM and β3-tubulin) is increased, suggesting that loss of TRF2 engages a cell differentiation program in the GSCs. Depletion of TRF2 also sensitizes GSCs to temozolomide, a DNA-alkylating agent currently used to treat glioblastoma. Targeting TRF2 significantly increased the survival of mice bearing GSC xenografts. These findings reveal a role for TRF2 in the maintenance of REST-associated proliferation and chemotherapy resistance of GSCs, suggesting that TRF2 is a potential therapeutic target for glioblastoma.

A Fab fragment directed against the neural cell adhesion molecule L1 enhances functional recovery after injury of the adult mouse spinal cord

A recombinant monovalent Fab fragment recognizing a functional epitope within the third fibronectin type III domain of murine cell adhesion molecule L1 induces neurite outgrowth and neuronal survival in vitro and enhances functional recovery after spinal cord injury in mice.

Myelin basic protein cleaves cell adhesion molecule L1 and promotes neuritogenesis and cell survival

The cell adhesion molecule L1 is a Lewis(x)-carrying glycoprotein that plays important roles in the developing and adult nervous system. Here we show that myelin basic protein (MBP) binds to L1 in a Lewis(x)-dependent manner. Furthermore, we demonstrate that MBP is released by murine cerebellar neurons as a sumoylated dynamin-containing protein upon L1 stimulation and that this MBP cleaves L1 as a serine protease in the L1 extracellular domain at Arg(687) yielding a transmembrane fragment that promotes neurite outgrowth and neuronal survival in cell culture. L1-induced neurite outgrowth and neuronal survival are reduced in MBP-deficient cerebellar neurons and in wild-type cerebellar neurons in the presence of an MBP antibody or L1 peptide containing the MBP cleavage site. Genetic ablation of MBP in shiverer mice and mutagenesis of the proteolytically active site in MBP or of the MBP cleavage site within L1 as well as serine protease inhibitors and an L1 peptide containing the MBP cleavage site abolish generation of the L1 fragment. Our findings provide evidence for novel functions of MBP in the nervous system.

L-serine treatment may improve neurorestoration of rats after permanent focal cerebral ischemia potentially through improvement of neurorepair

The present study was conducted to clarify whether treatment with L-serine can improve the brain repair and neurorestoration of rats after permanent middle cerebral artery occlusion (pMCAO). After pMCAO, the neurological functions, brain lesion volume, and cortical injury were determined. GDNF, NGF, NCAM L1, tenascin-C, and Nogo-A levels were measured. Proliferation and differentiation of the neural stem cells (NSCs) and proliferation of the microvessels in the ischemic boundary zone of the cortex were evaluated. Treatment with L-serine (168 mg/kg body weight, i.p.) began 3 h after pMCAO and was repeated every 12 h for 7 days or until the end of the experiment. L-Serine treatment: 1) reduced the lesion volume and neuronal loss; 2) improved the recovery of neurological functions; 3) elevated the expression of nerve growth-related factors; and 4) facilitated the proliferation of endogenous NSCs and microvessels activated after pMCAO and increased the number of new-born neurons. 5) D-cycloserine, an inhibitor of serine hydroxymethyltransferase, blunted the effects of L-serine on NSC proliferation, differentiation, microvascular proliferation. In conclusions, L-serine treatment in pMCAO rats can reduce brain injury and facilitate neurorestoration which is partly associated with the improvement of proliferation of NSCs and microvessels, reconstruction of neurovascular units and resultant neurorepair. The effects of L-serine on endogenous NSC proliferation and microvascular proliferation are partly mediated by the action of L-serine as a substrate for the production of one-carbon groups used for purine and pyrimidine synthesis and modulation of the expression of some nerve growth-related factors.

The known-unknowns in spinal cord injury, with emphasis on cell-based therapies - a review with suggestive arenas for research

INTRODUCTION

In spite of extensive research, the progress toward a cure in spinal cord injury (SCI) is still elusive, which holds good for the cell- and stem cell-based therapies. We have critically analyzed seven known gray areas in SCI, indicating the specific arenas for research to improvise the outcome of cell-based therapies in SCI.

AREAS COVERED

The seven, specific known gray areas in SCI analyzed are: i) the gap between animal models and human victims; ii) uncertainty about the time, route and dosage of cells applied; iii) source of the most efficacious cells for therapy; iv) inability to address the vascular compromise during SCI; v) lack of non-invasive methodologies to track the transplanted cells; vi) need for scaffolds to retain the cells at the site of injury; and vii) physical and chemical stimuli that might be required for synapses formation yielding functional neurons.

EXPERT OPINION

Further research on scaffolds for retaining the transplanted cells at the lesion, chemical and physical stimuli that may help neurons become functional, a meta-analysis of timing of the cell therapy, mode of application and larger clinical studies are essential to improve the outcome.

Function-triggering antibodies to the adhesion molecule L1 enhance recovery after injury of the adult mouse femoral nerve

L1 is among the few adhesion molecules that favors repair after trauma in the adult central nervous system of vertebrates by promoting neuritogenesis and neuronal survival, among other beneficial features. In the peripheral nervous system, L1 is up-regulated in Schwann cells and regrowing axons after nerve damage, but the functional consequences of this expression remain unclear. Our previous study of L1-deficient mice in a femoral nerve injury model showed an unexpected improved functional recovery, attenuated motoneuronal cell death, and enhanced Schwann cell proliferation, being attributed to the persistent synthesis of neurotrophic factors. On the other hand, transgenic mice over-expressing L1 in neurons led to improved remyelination, but not improved functional recovery. The present study was undertaken to investigate whether the monoclonal L1 antibody 557 that triggers beneficial L1 functions in vitro would trigger these also in femoral nerve repair. We analyzed femoral nerve regeneration in C57BL/6J mice that received this antibody in a hydrogel filled conduit connecting the cut and sutured nerve before its bifurcation, leading to short-term release of antibody by diffusion. Video-based quantitative analysis of motor functions showed improved recovery when compared to mice treated with conduits containing PBS in the hydrogel scaffold, as a vehicle control. This improved recovery was associated with attenuated motoneuron loss, remyelination and improved precision of preferential motor reinnervation. We suggest that function-triggering L1 antibodies applied to the lesion site at the time of injury over a limited time period will not only be beneficial in peripheral, but also central nervous system regeneration.

Umbilical cord mesenchymal stem cell transplantation significantly improves neurological function in patients with sequelae of traumatic brain injury

The aim of this study was to investigate the effects of transplantation with umbilical cord mesenchymal stem cells in patients with sequelae of traumatic brain injury (TBI). The study hypothesis was that umbilical cord mesenchymal stem cell transplantation could safely and effectively improve neurological function in patients with sequelae of traumatic brain injury. Forty patients with sequelae of TBI were randomly assigned to the stem cell treatment group or the control group. The patients in the stem cell treatment group underwent 4 stem cell transplantations via lumbar puncture. All patients of the group were also evaluated using Fugl-Meyer Assessments (FMA) and Functional Independence Measures (FIM) before and at 6 months after the stem cell transplantation. The patients in the control group did not receive any medical treatment (i.e., neither surgery nor medical intervention), and their FMA and FIM scores were determined on the day of the visit to the clinic and at 6 months after that clinical observation. The FMA results demonstrated an improvement in upper extremity motor sub-score, lower extremity motor sub-score, sensation sub-score and balance sub-score in the stem cell transplantation group at 6 months after the transplantation (P<0.05). The FIM results also exhibited significant improvement (P<0.05) in the patient self-care sub-score, sphincter control sub-score, mobility sub-score, locomotion sub-score, communication sub-score and social cognition sub-score. The control group exhibited no improvements after 6 months (P>0.05). All in all, the study results confirmed that the umbilical cord mesenchymal stem cell transplantation improved the neurological function and self-care in patients with TBI sequels. Umbilical cord mesenchymal stem cell transplantation may be a potential treatment for patients with sequelae of TBI. Further research, including a multicenter and large sample size prospective randomized clinical trial, will be required to define definitively the role of umbilical cord mesenchymal stem cell transplantation on sequelae of TBI.

Transgenic overexpression of the cell adhesion molecule L1 in neurons facilitates recovery after mouse spinal cord injury

It has been shown that the X-chromosome-linked neural cell adhesion molecule L1 plays a beneficial role in regeneration after spinal cord injury (SCI) in young adult rodents when applied in various molecular and cellular forms. In an attempt to further characterize the multiple functions of L1 after severe SCI we analyzed locomotor functions and measured axonal regrowth/sprouting and sparing, glial scarring, and synaptic remodeling at 6 weeks after severe spinal cord compression injury at the T7-9 levels of L1-deficient mice (L1-/y) and their wild-type (L1+/y) littermates, as well as mice that overexpress L1 under the control of the neuron-specific Thy-1 promoter (L1tg) and their wild-type littermates (L1+/+). No differences were found in the locomotor scale score and single frame motion analysis between L1-/y and L1+/y mice during 6 weeks after SCI, most likely due to the very low expression of L1 in the adult spinal cord of wild-type mice. L1tg mice, however, showed better locomotor recovery than their L1+/+ littermates, being associated with enhanced numbers of catecholaminergic axons in the lumbar spinal cord, but not of cholinergic, GABAergic or glutamatergic terminals around motoneuron cell bodies in the lumbar spinal cord. Additionally, no difference between L1tg and L1+/+ mice was detectable in dieback of corticospinal tract axons. Neuronal L1 overexpression did not influence the size of the glial fibrillary acidic protein-immunoreactive astrocytic scar 6 weeks after injury. We conclude that neuronal overexpression of L1 improves functional recovery from SCI by increasing catecholaminergic axonal regrowth/sprouting and/or sparing of severed axons without affecting the glial scar size.

Adhesion molecule L1 binds to amyloid beta and reduces Alzheimer's disease pathology in mice

Alzheimer's disease (AD) is a devastating neurodegenerative disorder and the most common cause of elderly dementia. In an effort to contribute to the potential of molecular approaches to reduce degenerative processes we have tested the possibility that the neural adhesion molecule L1 ameliorates some characteristic cellular and molecular parameters associated with the disease in a mouse model of AD. Three-month-old mice overexpressing mutated forms of amyloid precursor protein and presenilin-1 under the control of a neuron-specific promoter received an injection of adeno-associated virus encoding the neuronal isoform of full-length L1 (AAV-L1) or, as negative control, green fluorescent protein (AAV-GFP) into the hippocampus and occipital cortex. Four months after virus injection, the mice were analyzed for histological and biochemical parameters of AD. AAV-L1 injection decreased the Aβ plaque load, levels of Aβ42, Aβ42/40 ratio and astrogliosis compared with AAV-GFP controls. AAV-L1 injected mice also had increased densities of inhibitory synaptic terminals on pyramidal cells in the hippocampus when compared with AAV-GFP controls. Numbers of microglial cells/macrophages were similar in both groups, but numbers of microglial cells/macrophages per plaque were increased in AAV-L1 injected mice. To probe for a molecular mechanism that may underlie these effects, we analyzed whether L1 would directly and specifically interact with Aβ. In a label-free binding assay, concentration dependent binding of the extracellular domain of L1, but not of the close homolog of L1 to Aβ40 and Aβ42 was seen, with the fibronectin type III homologous repeats 1-3 of L1 mediating this effect. Aggregation of Aβ42 in vitro was reduced in the presence of the extracellular domain of L1. The combined observations indicate that L1, when overexpressed in neurons and glia, reduces several histopathological hallmarks of AD in mice, possibly by reduction of Aβ aggregation. L1 thus appears to be a candidate molecule to ameliorate the pathology of AD, when applied in therapeutically viable treatment schemes.

CXCR7 silencing attenuates cell adaptive response to stromal cell derived factor 1α after hypoxia

Previous studies have shown that chemotactic factor stromal-cell derived factor 1α (SDF1α) promotes cell recovery from hypoxic injury via its main receptor C-X-C chemokine receptor type (CXCR) 4. However, the role of its new receptor CXCR7 on cell repair against hypoxia and cell response to SDF1α remains largely unknown. In this study, neurons induced from hippocampal progenitor cells were pre-conditioned in hypoxia for 4 h and subsequently monitored to investigate the function of SDF1α on cell repair after hypoxia. Neurons were assessed for their cell morphology, actin filament polymerization and migration capability. SDF1α protein levels increased significantly 1 h after hypoxia compared to control (P<0.01), and it reached a peak at 24 h after hypoxia. Moreover, addition of SDF1α promoted neurite outgrowth and actin filament polymerization both in normoxic and hypoxic cells compared to untreated cells. Cell migration showed a time-dependent increase with SDF1α stimulation in both groups, and hypoxic cells illustrated a significant augment at 0.5 h, 1 h and 12 h after SDF1α application compared to normoxic cells (P<0.01). CXCR7 expression also increased with time dependence after hypoxia and demonstrated a two-fold upregulation compared to control at 24 h after hypoxia. With CXCR7 silencing, axon elongation and actin filament polymerization induced by SDF1α were inhibited sharply both in normoxic and hypoxic cells. CXCR7 silencing also leads to reduced hypoxic cell migration at 0.5 h, 1 h, 12 h, 24 h and 36 h after SDF1α application (P<0.01), but it failed to reduce normoxic cell migration induced by SDF1α at 0.5 h, 1 h and 12 h (P>0.05). 24 h SDF1α stimulation led to higher ERK1/2 phosphorylation compared to control, and ERK1/2 phosphorylation increased more in hypoxic cells than that in normoxic cells. This study suggested that CXCR7 plays an important role on cell repair processing induced by SDF1α, and CXCR7 silencing attenuates cell adaptive response to acute SDF1α stimulation (≤12 h) after hypoxia.

Tracing synaptic connectivity onto embryonic stem cell-derived neurons

Transsynaptic circuit tracing using genetically modified rabies virus (RV) is an emerging technology for identifying synaptic connections between neurons. Complementing this methodology, it is now possible to assay the basic molecular and cellular properties of neuronal lineages derived from embryonic stem cells (ESCs) in vitro, and these properties are under intense investigation toward devising cell replacement therapies. Here, we report the generation of a novel mouse ESC (mESC) line that harbors the genetic elements to allow RV-mediated transsynaptic circuit tracing in ESC-derived neurons and their synaptic networks. To facilitate transsynaptic tracing, we have engineered a new reporter allele by introducing cDNA encoding tdTomato, the Rabies-G glycoprotein, and the avian TVA receptor into the ROSA26 locus by gene targeting. We demonstrate high-efficiency differentiation of these novel mESCs into functional neurons, show their capacity to synaptically connect with primary neuronal cultures as evidenced by immunohistochemistry and electrophysiological recordings, and show their ability to act as source cells for presynaptic tracing of neuronal networks in vitro and in vivo. Together, our data highlight the potential for using genetically engineered stem cells to investigate fundamental mechanisms of synapse and circuit formation with unambiguous identification of presynaptic inputs onto neuronal populations of interest.

Cell transplantation for spinal cord injury: a systematic review

Cell transplantation, as a therapeutic intervention for spinal cord injury (SCI), has been extensively studied by researchers in recent years. A number of different kinds of stem cells, neural progenitors, and glial cells have been tested in basic research, and most have been excluded from clinical studies because of a variety of reasons, including safety and efficacy. The signaling pathways, protein interactions, cellular behavior, and the differentiated fates of experimental cells have been studied in vitro in detail. Furthermore, the survival, proliferation, differentiation, and effects on promoting functional recovery of transplanted cells have also been examined in different animal SCI models. However, despite significant progress, a "bench to bedside" gap still exists. In this paper, we comprehensively cover publications in the field from the last years. The most commonly utilized cell lineages were covered in this paper and specific areas covered include survival of grafted cells, axonal regeneration and remyelination, sensory and motor functional recovery, and electrophysiological improvements. Finally we also review the literature on the in vivo tracking techniques for transplanted cells.

Endogenous proliferation after spinal cord injury in animal models

Spinal cord injury (SCI) results in motor and sensory deficits, the severity of which depends on the level and extent of the injury. Animal models for SCI research include transection, contusion, and compression mouse models. In this paper we will discuss the endogenous stem cell response to SCI in animal models. All SCI animal models experience a similar peak of cell proliferation three days after injury; however, each specific type of injury promotes a specific and distinct stem cell response. For example, the transection model results in a strong and localized initial increase of proliferation, while in contusion and compression models, the initial level of proliferation is lower but encompasses the entire rostrocaudal extent of the spinal cord. All injury types result in an increased ependymal proliferation, but only in contusion and compression models is there a significant level of proliferation in the lateral regions of the spinal cord. Finally, the fate of newly generated cells varies from a mainly oligodendrocyte fate in contusion and compression to a mostly astrocyte fate in the transection model. Here we will discuss the potential of endogenous stem/progenitor cell manipulation as a therapeutic tool to treat SCI.

In vitro generation of three-dimensional substrate-adherent embryonic stem cell-derived neural aggregates for application in animal models of neurological disorders

In vitro-differentiated embryonic stem (ES) cells comprise a useful source for cell replacement therapy, but the efficiency and safety of a translational approach are highly dependent on optimized protocols for directed differentiation of ES cells into the desired cell types in vitro. Furthermore, the transplantation of three-dimensional ES cell-derived structures instead of a single-cell suspension may improve graft survival and function by providing a beneficial microenvironment for implanted cells. To this end, we have developed a new method to efficiently differentiate mouse ES cells into neural aggregates that consist predominantly (>90%) of postmitotic neurons, neural progenitor cells, and radial glia-like cells. When transplanted into the excitotoxically lesioned striatum of adult mice, these substrate-adherent embryonic stem cell-derived neural aggregates (SENAs) showed significant advantages over transplanted single-cell suspensions of ES cell-derived neural cells, including improved survival of GABAergic neurons, increased cell migration, and significantly decreased risk of teratoma formation. Furthermore, SENAs mediated functional improvement after transplantation into animal models of Parkinson's disease and spinal cord injury. This unit describes in detail how SENAs are efficiently derived from mouse ES cells in vitro and how SENAs are isolated for transplantation. Furthermore, methods are presented for successful implantation of SENAs into animal models of Huntington's disease, Parkinson's disease, and spinal cord injury to study the effects of stem cell-derived neural aggregates in a disease context in vivo.

In vivo effects of L1 coating on inflammation and neuronal health at the electrode-tissue interface in rat spinal cord and dorsal root ganglion

The spinal cord (SC) and dorsal root ganglion (DRG) are target implantation regions for neural prosthetics, but the tissue-electrode interface in these regions is not well-studied. To improve understanding of these locations, the tissue reactions around implanted electrodes were characterized. L1, an adhesion molecule shown to maintain neuronal density and reduce gliosis in brain tissue, was then evaluated in SC and DRG implants. Following L1 immobilization onto neural electrodes, the bioactivities of the coatings were verified in vitro using neuron, astrocyte and microglia cultures. Non-modified and L1-coated electrodes were implanted into adult rats for 1 or 4 weeks. Hematoxylin and eosin staining along with cell-type specific antibodies were used to characterize the tissue response. In the SC and DRG, cells aggregated at the electrode-tissue interface. Microglia staining was more intense around the implant site and decreased with distance from the interface. Neurofilament staining in both locations decreased or was absent around the implant, compared with surrounding tissue. With L1, neurofilament staining was significantly increased while neuronal cell death decreased. These results indicate that L1-modified electrodes may result in an improved chronic neural interface and will be evaluated in recording and stimulation studies.

Oxygen levels and the regulation of cell adhesion in the nervous system: a control point for morphogenesis in development, disease and evolution?

In this article, I discuss the hallmarks of hypoxia in vitro and in vivo and review work showing that many types of stem cell proliferate more robustly in lowered oxygen. I then discuss recent studies showing that alterations in the levels and the types of cell and substrate adhesion molecules are a notable response to reduced O(2) levels in both cultured primary neural stem cells and brain tissues in response to hypoxia in vivo. The ability of O(2) levels to regulate adhesion molecule expression is linked to the Wnt signaling pathway, which can control and be controlled by adhesion events. The ability of O(2) levels to influence cell adhesion also has far-reaching implications for development, ischemic trauma and neural regeneration, as well as for cancer and other diseases. Finally I discuss the possibility that the fluctuations in O(2) levels known to have occurred over evolutionary time could, by influencing adhesion systems, have contributed to early symbiotic events in unicellular organisms and to the emergence of multicellularity. It is not my intention to be exhaustive in these domains, which are far from my own field of study. Rather this article is meant to provoke and stimulate thinking about molecular evolution involving O(2) sensing and signaling during eras of geologic and atmospheric change that might inform modern studies on development and disease.

Improved regeneration after spinal cord injury in mice lacking functional T- and B-lymphocytes

It is widely accepted that the immune system plays important functional roles in regeneration after injury to the spinal cord. Immune response towards injury involves a complex interplay of immune system cells, such as neutrophils, macrophages and microglia, T- and B-lymphocytes. We investigated the influence of the lymphocyte component of the immune system on the locomotor outcome of severe spinal cord injury in a genetic mouse model of immune suppression. Transgenic mice lacking mature T- and B-lymphocytes due to the recombination activating gene 2 gene deletion (RAG2-/- mice) were subjected to severe compression of the lower thoracic spinal cord, with the wild-type mice of the same inbred background serving as controls. According to both the Basso Mouse Scale score and single frame motion analysis, the RAG2-/- mice showed improved recovery in comparison to control mice at six weeks after injury. Better locomotor function was associated with enhanced catecholaminergic and cholinergic reinnervation of the spinal cord caudal to injury and increased axonal regrowth/sprouting at the site of injury. Myelination of axons in the ventral column measured as g-ratio was more extensive in RAG2-/- than in control mice 6weeks after injury. Additionally, the number of microglia/macrophages was decreased in the lumbar spinal cord of RAG2-/- mice after injury, whereas the number of astrocytes was increased compared with controls. We conclude that T- and B-lymphocytes restrict functional recovery from spinal cord injury by increasing numbers of microglia/macrophages as well as decreasing axonal sprouting and myelination.