Adeno-associated virus-mediated human acidic fibroblast growth factor expression promotes functional recovery of spinal cord-contused rats

Advancements in neuroregenerative and neuroprotective therapies for traumatic spinal cord injury

Traumatic spinal cord injuries (SCIs) continue to be a major healthcare concern, with a rising prevalence worldwide. In response to this growing medical challenge, considerable scientific attention has been devoted to developing neuroprotective and neuroregenerative strategies aimed at improving the prognosis and quality of life for individuals with SCIs. This comprehensive review aims to provide an up-to-date and thorough overview of the latest neuroregenerative and neuroprotective therapies currently under investigation. These strategies encompass a multifaceted approach that include neuropharmacological interventions, cell-based therapies, and other promising strategies such as biomaterial scaffolds and neuro-modulation therapies. In addition, the review discusses the importance of acute clinical management, including the role of hemodynamic management as well as timing and technical aspects of surgery as key factors mitigating the secondary injury following SCI. In conclusion, this review underscores the ongoing scientific efforts to enhance patient outcomes and quality of life, focusing on upcoming strategies for the management of traumatic SCI. Each section provides a working knowledge of the fundamental preclinical and patient trials relevant to clinicians while underscoring the pathophysiologic rationale for the therapies.

Fibroblast growth factor signaling in axons: from development to disease

The fibroblast growth factor (FGF) family regulates various and important aspects of nervous system development, ranging from the well-established roles in neuronal patterning to more recent and exciting functions in axonal growth and synaptogenesis. In addition, FGFs play a critical role in axonal regeneration, particularly after spinal cord injury, confirming their versatile nature in the nervous system. Due to their widespread involvement in neural development, the FGF system also underlies several human neurological disorders. While particular attention has been given to FGFs in a whole-cell context, their effects at the axonal level are in most cases undervalued. Here we discuss the endeavor of the FGF system in axons, we delve into this neuronal subcompartment to provide an original view of this multipurpose family of growth factors in nervous system (dys)function. Video Abstract.

Suppression of Fibroblast Growth Factor Receptor-5 (FGFR5) has no Impact on Axon Regeneration after SCI

One of the most common forms of the mammalian central nervous system (CNS) injuries is spinal cord injury (SCI), and any lesion to the CNS can result in a lifelong functional impairment since CNS axons cannot regenerate. The relative axon regenerating genes following spinal SCI were examined using the regenerative SN, pSN + DC, and non-regenerating DC lesion models. By using qRT-PCR, we discovered that fibroblast growth factor receptor-5 (FGFR5) was 4.2-fold more highly expressed in non-regeneration lesions compared to intact control and regenerating animals. Furthermore, in cultured dorsal root ganglion neurons (DRGN), short interfering RNA (siRNA)-mediated knockdown of FGFR5 had no effect on DRGN neurite outgrowth, indicating that the gene's suppression has no effect on axon regeneration and may play other roles in the CNS besides axon regeneration.

The potential of gene therapies for spinal cord injury repair: a systematic review and meta-analysis of pre-clinical studies

Currently, there is no cure for traumatic spinal cord injury but one therapeutic approach showing promise is gene therapy. In this systematic review and meta-analysis, we aim to assess the efficacy of gene therapies in pre-clinical models of spinal cord injury and the risk of bias. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020185008), we identified relevant controlled in vivo studies published in English by searching the PubMed, Web of Science, and Embase databases. No restrictions of the year of publication were applied and the last literature search was conducted on August 3, 2020. We then conducted a random-effects meta-analysis using the restricted maximum likelihood estimator. A total of 71 studies met our inclusion criteria and were included in the systematic review. Our results showed that overall, gene therapies were associated with improvements in locomotor score (standardized mean difference [SMD]: 2.07, 95% confidence interval [CI]:1.68–2.47, Tau² = 2.13, I² = 83.6%) and axonal regrowth (SMD: 2.78, 95%CI: 1.92–3.65, Tau² = 4.13, I² = 85.5%). There was significant asymmetry in the funnel plots of both outcome measures indicating the presence of publication bias. We used a modified CAMARADES (Collaborative Approach to Meta-Analysis and Review of Animal Data in Experimental Studies) checklist to assess the risk of bias, finding that the median score was 4 (IQR:3–5). In particular, reports of allocation concealment and sample size calculations were lacking. In conclusion, gene therapies are showing promise as therapies for spinal cord injury repair, but there is no consensus on which gene or genes should be targeted.

The Application of an Omentum Graft or Flap in Spinal Cord Injury

Background: Spinal cord injury (SCI) causes a primary injury at the lesion site and triggers a secondary injury and prolonged inflammation. There has been no definitive treatment till now. Promoting angiogenesis is one of the most important strategies for functional recovery after SCI. The omentum, abundant in blood and lymph vessels, possesses the potent ability of tissue regeneration. Methods: The present work examines the efficacy of autologous omentum, either as a flap (with vascular connection intact) or graft (severed vascular connection), on spinal nerve regeneration. After contusive SCI in rats, a thin sheath of omentum was grafted to the injured spinal cord. Results: Omental graft improved behavior scores significantly from the 3rd to 6th week after injury (6th week, 5.5 ± 0.5 vs. 8.6 ± 1.3, p < 0.05). Furthermore, the reduction in cavity and the preservation of class III β-tubulin-positive nerve fibers in the injury area was noted. Next, the free omental flap was transposed to a completely transected SCI in rats through a pre-implanted tunnel. The flap remained vascularized and survived well several weeks after the operation. At 16 weeks post-treatment, SCI rats with omentum flap treatment displayed the preservation of significantly more nerve fibers (p < 0.05) and a reduced injured cavity, though locomotor scores were similar. Conclusions: Taken together, the findings of this study indicate that treatment with an omental graft or transposition of an omental flap on an injured spinal cord has a positive effect on nerve protection and tissue preservation in SCI rats. The current data highlight the importance of omentum in clinical applications.

Planet of the AAVs: The Spinal Cord Injury Episode

The spinal cord injury (SCI) is a medical and life-disrupting condition with devastating consequences for the physical, social, and professional welfare of patients, and there is no adequate treatment for it. At the same time, gene therapy has been studied as a promising approach for the treatment of neurological and neurodegenerative disorders by delivering remedial genes to the central nervous system (CNS), of which the spinal cord is a part. For gene therapy, multiple vectors have been introduced, including integrating lentiviral vectors and non-integrating adeno-associated virus (AAV) vectors. AAV vectors are a promising system for transgene delivery into the CNS due to their safety profile as well as long-term gene expression. Gene therapy mediated by AAV vectors shows potential for treating SCI by delivering certain genetic information to specific cell types. This review has focused on a potential treatment of SCI by gene therapy using AAV vectors.

Fibroblast Growth Factor Signalling in the Diseased Nervous System

Fibroblast growth factors (FGFs) act as key signalling molecules in brain development, maintenance, and repair. They influence the intricate relationship between myelinating cells and axons as well as the association of astrocytic and microglial processes with neuronal perikarya and synapses. Advances in molecular genetics and imaging techniques have allowed novel insights into FGF signalling in recent years. Conditional mouse mutants have revealed the functional significance of neuronal and glial FGF receptors, not only in tissue protection, axon regeneration, and glial proliferation but also in instant behavioural changes. This review provides a summary of recent findings regarding the role of FGFs and their receptors in the nervous system and in the pathogenesis of major neurological and psychiatric disorders.

Sustained delivery of neurotrophic factors to treat spinal cord injury

Acute spinal cord injury (SCI) is a devastating condition that results in tremendous physical and psychological harm and a series of socioeconomic problems. Although neurons in the spinal cord need neurotrophic factors for their survival and development to reestablish their connections with their original targets, endogenous neurotrophic factors are scarce and the sustainable delivery of exogeneous neurotrophic factors is challenging. The widely studied neurotrophic factors such as brain-derived neurotrophic factor, neurotrophin-3, nerve growth factor, ciliary neurotrophic factor, basic fibroblast growth factor, and glial cell-derived neurotrophic factor have a relatively short cycle that is not sufficient enough for functionally significant neural regeneration after SCI. In the past decades, scholars have tried a variety of cellular and viral vehicles as well as tissue engineering scaffolds to safely and sustainably deliver those necessary neurotrophic factors to the injury site, and achieved satisfactory neural repair and functional recovery on many occasions. Here, we review the neurotrophic factors that have been used in trials to treat SCI, and vehicles that were commonly used for their sustained delivery.

Attenuating Spinal Cord Injury by Conditioned Medium from Bone Marrow Mesenchymal Stem Cells

Spinal cord injury (SCI) is a devastating neurological condition and might even result in death. However, current treatments are not sufficient to repair such damage. Bone marrow mesenchymal stem cells (BM-MSC) are ideal transplantable cells which have been shown to modulate the injury cascade of SCI mostly through paracrine effects. The present study investigates whether systemic administration of conditioned medium from MSCs (MSCcm) has the potential to be efficacious as an alternative to cell-based therapy for SCI. In neuron-glial cultures, MSC coculture effectively promoted neuronal connection and reduced oxygen glucose deprivation-induced cell damage. The protection was elicited even if neuron-glial culture was used to expose MSCcm, suggesting the effects possibly from released fractions of MSC. In vivo, intravenous administration of MSCcm to SCI rats significantly improved behavioral recovery from spinal cord injury, and there were increased densities of axons in the lesion site of MSCcm-treated rats compared to SCI rats. At early days postinjury, MSCcm treatment upregulated the protein levels of Olig 2 and HSP70 and also increased autophage-related proteins in the injured spinal cords. Together, these findings suggest that MSCcm treatment promotes spinal cord repair and functional recovery, possibly via activation of autophagy and enhancement of survival-related proteins.

Different Fgfs have distinct roles in regulating neurogenesis after spinal cord injury in zebrafish

Background

Despite conserved developmental processes and organization of the vertebrate central nervous system, only some vertebrates including zebrafish can efficiently regenerate neural damage including after spinal cord injury. The mammalian spinal cord shows very limited regeneration and neurogenesis, resulting in permanent life-long functional impairment. Therefore, there is an urgent need to identify the cellular and molecular mechanisms that can drive efficient vertebrate neurogenesis following injury. A key pathway implicated in zebrafish neurogenesis is fibroblast growth factor signaling.

Methods

In the present study we investigated the roles of distinct fibroblast growth factor members and their receptors in facilitating different aspects of neural development and regeneration at different timepoints following spinal cord injury. After spinal cord injury in adults and during larval development, loss and/or gain of Fgf signaling was combined with immunohistochemistry, in situ hybridization and transgenes marking motor neuron populations in in vivo zebrafish and in vitro mammalian PC12 cell culture models.

Results

Fgf3 drives neurogenesis of Islet1 expressing motor neuron subtypes and mediate axonogenesis in cMet expressing motor neuron subtypes. We also demonstrate that the role of Fgf members are not necessarily simple recapitulating development. During development Fgf2, Fgf3 and Fgf8 mediate neurogenesis of Islet1 expressing neurons and neuronal sprouting of both, Islet1 and cMet expressing motor neurons. Strikingly in mammalian PC12 cells, all three Fgfs increased cell proliferation, however, only Fgf2 and to some extent Fgf8, but not Fgf3 facilitated neurite outgrowth.

Conclusions

This study demonstrates differential Fgf member roles during neural development and adult regeneration, including in driving neural proliferation and neurite outgrowth of distinct spinal cord neuron populations, suggesting that factors including Fgf type, age of the organism, timing of expression, requirements for different neuronal populations could be tailored to best drive all of the required regenerative processes.

Fibroblast Growth Factor 1-Transfected Adipose-Derived Mesenchymal Stem Cells Promote Angiogenic Proliferation

The aim of this study was to investigate, for the first time, the effects of using adipose-derived mesenchymal stem cells (AD-MSCs) transfected with an episomal plasmid encoding fibroblast growth factor 1 (FGF1) (AD-MSCsFGF1), in providing the microenvironment required for angiogenic proliferation. The isolated rat AD-MSCs were positive for mesenchymal (CD29 and CD90) and negative for hematopoietic (CD34 and CD45) surface markers. Adipogenic and osteogenic differentiation of the AD-MSCs also occurred in the proper culture media. The presence of FGF1 in the conditioned medium from the AD-MSCsFGF1 was confirmed by Western blotting. G418 and PCR were used for selection of transfected cells and confirmation of the presence of FGF1 mRNA, respectively. Treatment with the AD-MSCFGF1-conditioned medium significantly increased the NIH-3T3 cell proliferation and human umbilical vein endothelial cell (HUVEC) tube formation compared to conditioned medium from nontransfected AD-MSCs (p < 0.001). In conclusion, the AD-MSCsFGF1 efficiently secreted functional FGF1, which promoted angiogenic proliferation. Using AD-MSCsFGF1 may provide a useful strategy in cell therapy, which can merge the beneficial effects of stem cells with the positive biological effects of FGF1 in various disorders, especially tissue defects, neurodegenerative, cardiovascular and diabetes endocrine pathologies, which remain to be tested in preclinical and clinical studies.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Acidic FGF promotes neurite outgrowth of cortical neurons and improves neuroprotective effect in a cerebral ischemic rat model

Acidic fibroblast growth factor (aFGF) is a neurotrophic factor which is a powerful neuroprotective and neuroregenerative factor of the nervous system. Prior study had shown that levels of FGFs significantly increase following ischemic injury, reflecting a physiological protection mechanism. However, few reports demonstrated the efficacy of applying aFGF in cerebral ischemia. A recent report showed that the intranasal aFGF treatment improved neurological functional recovery; however, it did not significantly reduce the lesion size in ischemic rats. The present study examines the neuroprotective effect of aFGF on cortical neuron-glial cultures under oxygen glucose deprivation (OGD)-induced cell damage and investigates whether epidural application of slow-released aFGF could improve benefit on ischemic stroke injury in conscious rats. We used a topical application of aFGF mixed in fibrin glue, a slow-release carrier, over the peri-ischemic cortex and examined such treatment on cerebral infarction and behavioral impairments of rats subjected to focal cerebral ischemia (FCI). Results demonstrate that aFGF effectively protected cortical neuron-glial cultures from OGD-induced neuronal damage. Neurite extension from cortical neurons was significantly enhanced by aFGF, mediated through activation of AKT and ERK. In addition, topical application of fibrin glue-mixed aFGF dose-dependently reduced ischemia-induced brain infarction and improved functional restoration in ischemic stroke rats. Slow-released aFGF not only protected hippocampal and cortical cell loss but reduced microglial infiltration in FCI rats. Our results suggest that aFGF mixed in fibrin glue could prolong the protective/regenerative efficacy of aFGF to the damaged brain tissue and thus improve the functional restorative effect of aFGF.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

The role of angiogenic and wound-healing factors after spinal cord injury in mammals

Patients with spinal cord injury (SCI) are permanently paralysed and anaesthetic below the lesion. This morbidity is attributed to the deposition of a dense scar at the injury site, the cellular components of which secrete axon growth inhibitory ligands that prevent severed axons reconnecting with denervated targets. Another complication of SCI is wound cavitation where a fluid filled cyst forms in the peri-lesion neuropil, enlarging over the first few months after injury and causes secondary axonal damage. Wound healing after SCI is accompanied by angiogenesis, which is regulated by angiogenic proteins, produced in response to oxygen deprivation. Necrosis in and about the SCI lesion sites may be suppressed by promoting angiogenesis and the resulting neuropil protection will enhance recovery after SCI. This review addresses the use of angiogenic/wound-healing related proteins including vascular endothelial growth factor, fibroblast growth factor, angiopoietin-1, angiopoietin-2 and transforming growth factor-β to moderate necrosis and axon sparing after SCI, providing a conducive environment for growth essential to functional recovery.