From single to combinatorial therapies in spinal cord injuries for structural and functional restoration

Spinal cord injury results in paralysis, sensory disturbances, sphincter dysfunction, and multiple systemic secondary conditions, most arising from autonomic dysregulation. All this produces profound negative psychosocial implications for affected people, their families, and their communities;the financial costs can be challenging for their families and health institutions. Treatments aimed at restoring the spinal cord after spinal cord injury, which have been tested in animal models or clinical trials, generally seek to counteract one or more of the secondary mechanisms of injury to limit the extent of the initial damage. Most published works on structural/functional restoration in acute and chronic spinal cord injury stages use a single type of treatment: a drug or trophic factor, transplant of a cell type, and implantation of a biomaterial. Despite the significant benefits reported in animal models, when translating these successful therapeutic strategies to humans, the result in clinical trials has been considered of little relevance because the improvement, when present, is usually insufficient. Until now, most studies designed to promote neuroprotection or regeneration at different stages after spinal cord injury have used single treatments. Considering the occurrence of various secondary mechanisms of injury in the acute and sub-acute phases of spinal cord injury, it is reasonable to speculate that more than one therapeutic agent could be required to promote structural and functional restoration of the damaged spinal cord. Treatments that combine several therapeutic agents, targeting different mechanisms of injury, which, when used as a single therapy, have shown some benefits, allow us to assume that they will have synergistic beneficial effects. Thus, this narrative review article aims to summarize current trends in the use of strategies that combine therapeutic agents administered simultaneously or sequentially, seeking structural and functional restoration of the injured spinal cord.

Sex-dependent alterations in extracellular vesicles linking chronic spinal cord injury to brain neuroinflammation and neurodegeneration

Traumatic spinal cord injury(SCI)is a devastating exogenous injury with long-lasting consequences and a leading cause of death and disability worldwide.Advances in assistive technology,rehabilitative interventions,and the ability to identify and intervene in secondary conditions have significantly increased the long-term survival rate of SCI patients,with some people even living well into their seventh or eighth decade.These survival changes have led neurotrauma researchers to examine how SCI interacts with brain aging.Public health and epidemiological data showed that patients with long-term SCI can have a lower life expectancy and quality of life,along with a higher risk of comorbidities and complications.

Spinal cord injury regenerative therapy development:integration of design of experiments

Spinal cord injury(SCI)can cause motor and sensory paralysis,and autonomic nervous system disorders including malfunction of urination and defecation,thereby significantly impairing the quality of life.Researchers continue to explo re new stem cell strategies for the treatment of paralysis by transpla nting human induced pluripotent stem cell-derived neural ste m/progenitor cells(hiPSCNS/PCs)into spinal cord injured tissues.

Visualizing traumatic brain injury:ocular clues for diagnosis and assessment

Traumatic brain injury (TBI) is defined as damage to the brain resulting from an external sudden physical force or shock to the head.It is considered a silent public health epidemic causing significant death and disability globally.There were 64,000 TBI related deaths reported in the USA in 2020,with about US$76 billion in direct and indirect medical costs annually.

Deciphering the mechanobiology of microglia in traumatic brain injury with advanced microsystems

Advanced microsystems in traumatic brain injury research:Traumatic brain injury(TBI)results from a mechanical insult to the brain,leading to neuronal and axonal damage and subsequently causing a secondary injury.Within minutes of TBI,a neuroinflammatory response is triggered,driven by intricate molecular and cellular inflammatory processes.

A lead role for a“secondary”axonal injury response

Stress signaling following axon injury stimulates a transcriptional program for regeneration that might be exploited to promote central nervous system repair.However,this stress response drives neuronal apoptosis in non-regenerative environments.This duality presents a quandary for the development of therapeutic interventions:manipulating stress signaling to enhance recovery of damaged neurons risks accelerating neurodegeneration or restricting regenerative potential.This dichotomy is well illustrated by the fates of retinal ganglion cells(RGCs)following optic nerve crush.In this central nervous system injury model,disruption of a stress-activated MAP kinase(MAPK)cascade blocks the extensive apoptosis of RGCs that occurs in wild-type mice(Watkins et al.,2013;Welsbie et al.,2017).

Remaking a connection:molecular players involved in post-injury synapse formation

Functional recovery from central nervous system(CNS)trauma depends not only on axon regeneration or compensatory sprouting of uninjured fibers but also on the ability of newly grown axons to establish functional synapses with appropriate targets.Although several studies have successfully promoted long-distance axonal regeneration in distinct CNS injury models,none of them have resulted in a viable therapeutic approach for patient recovery.A possible reason may be the lack of new synaptogenesis for reestablishing the circuitry lost after injury.Herein,we discuss how our understanding of the mechanisms that instruct synapse formation in the injured nervous system may contribute to the design of new strategies to promote functional restoration in traumatic CNS disorders.

New insights on the role of chondroitin sulfate proteoglycans in neural stem cell–mediated repair in spinal cord injury

Extensive neurodegeneration is a hallmark of traumatic spinal cord injury (SCI) that underlies permanent sensorimotor and autonomic impairments (Alizadeh et al.,2019).Following the primary impact,the spinal cord undergoes a cascade of secondary injury mechanisms that are driven by disruption of the blood-spinal cord ba rrier,vascula r inju ry,glial reactivity,neu roinfla mmation,oxidative stress,lipid peroxidation,and glutamate excitotoxicity that culminate in neuronal and oligodendroglial cell death,demyelination,and axonal damage(Alizadeh et al.,2019).To achieve a meaningful functional recovery after SCI,regeneration of new neurons and oligodendrocytes and their successful growth and integration within the neural network are critical steps for reconstructing the damaged spinal cord tissue (Fischer et al.,2020).

Injury/ischemia-induced stem cells: up-to-date knowledge and future perspectives for neural regeneration

Brain injuries like ischemic stroke induce endogenous stem cell production. Although the precise traits of stem cells in pathological brains remain unclear, we previously demonstrated that injury/ischemia-induced stem cells(iSCs)are present in the post-stroke mouse(Nakagomi et al.,2009)and human brains(Beppu et al.,2019).

Mitophagy in acute central nervous system injuries:regulatory mechanisms and therapeutic potentials

Acute central nervous system injuries,including ischemic stro ke,intracerebral hemorrhage,subarachnoid hemorrhage,traumatic brain injury,and spinal co rd injury,are a major global health challenge.Identifying optimal therapies and improving the long-term neurological functions of patients with acute central nervous system injuries are urgent priorities.Mitochondria are susceptible to damage after acute central nervous system injury,and this leads to the release of toxic levels of reactive oxygen species,which induce cell death.Mitophagy,a selective form of autophagy,is crucial in eliminating redundant or damaged mitochondria during these events.Recent evidence has highlighted the significant role of mitophagy in acute central nervous system injuries.In this review,we provide a comprehensive overview of the process,classification,and related mechanisms of mitophagy.We also highlight the recent developments in research into the role of mitophagy in various acute central nervous system injuries and drug therapies that regulate mitophagy.In the final section of this review,we emphasize the potential for treating these disorders by focusing on mitophagy and suggest future research paths in this area.

Stepping up after spinal cord injury:negotiating an obstacle during walking

Every day walking consists of frequent voluntary modifications in the gait pattern to negotiate obstacles.After spinal cord injury,stepping over an obstacle becomes challenging.Stepping over an obstacle requires sensorimotor transformations in several structures of the brain,including the parietal cortex,premotor cortex,and motor cortex.Sensory information and planning are transformed into motor commands,which are sent from the motor cortex to spinal neuronal circuits to alter limb trajectory,coordinate the limbs,and maintain balance.After spinal cord injury,bidirectional communication between the brain and spinal cord is disrupted and animals,including humans,fail to voluntarily modify limb trajectory to step over an obstacle.Therefore,in this review,we discuss the neuromechanical control of stepping over an obstacle,why it fails after spinal cord injury,and how it recovers to a certain extent.

Complement-dependent neuroinflammation in spinal cord injury:from pathology to therapeutic implications

Spinal cord injury remains a major cause of disability in young adults,and beyond acute decompression and rehabilitation,there are no pharmacological treatments to limit the progression of injury and optimize recovery in this population.Following the thorough investigation of the complement system in triggering and propagating cerebral neuroinflammation,a similar role for complement in spinal neuroinflammation is a focus of ongoing research.In this work,we survey the current literature investigating the role of complement in spinal cord injury including the sources of complement proteins,triggers of complement activation,and role of effector functions in the pathology.We study relevant data demonstrating the different triggers of complement activation after spinal cord injury including direct binding to cellular debris,and or activation via antibody binding to damage-associated molecular patterns.Several effector functions of complement have been implicated in spinal cord injury,and we critically evaluate recent studies on the dual role of complement anaphylatoxins in spinal cord injury while emphasizing the lack of pathophysiological understanding of the role of opsonins in spinal cord injury.Following this pathophysiological review,we systematically review the different translational approaches used in preclinical models of spinal cord injury and discuss the challenges for future translation into human subjects.This review emphasizes the need for future studies to dissect the roles of different complement pathways in the pathology of spinal cord injury,to evaluate the phases of involvement of opsonins and anaphylatoxins,and to study the role of complement in white matter degeneration and regeneration using translational strategies to supplement genetic models.

Astrocytes, reactive astrogliosis, and glial scar formation in traumatic brain injury

Traumatic brain injury is a global health crisis,causing significant death and disability worldwide.Neuroinflammation that follows traumatic brain injury has serious consequences for neuronal survival and cognitive impairments,with astrocytes involved in this response.Following traumatic brain injury,astrocytes rapidly become reactive,and astrogliosis propagates from the injury core to distant brain regions.Homeostatic astroglial proteins are downregulated near the traumatic brain injury core,while pro-inflammatory astroglial genes are overexpressed.This altered gene expression is considered a pathological remodeling of astrocytes that produces serious consequences for neuronal survival and cognitive recovery.In addition,glial scar formed by reactive astrocytes is initially necessary to limit immune cell infiltration,but in the long term impedes axonal reconnection and functional recovery.Current therapeutic strategies for traumatic brain injury are focused on preventing acute complications.Statins,cannabinoids,progesterone,beta-blockers,and cerebrolysin demonstrate neuroprotective benefits but most of them have not been studied in the context of astrocytes.In this review,we discuss the cell signaling pathways activated in reactive astrocytes following traumatic brain injury and we discuss some of the potential new strategies aimed to modulate astroglial responses in traumatic brain injury,especially using cell-targeted strategies with miRNAs or lncRNA,viral vectors,and repurposed drugs.

Combinatorial therapies for spinal cord injury repair

Spinal cord injuries have profound detrimental effects on individuals, regardless of whether they are caused by trauma or non-traumatic events. The compromised regeneration of the spinal cord is primarily attributed to damaged neurons, inhibitory molecules, dysfunctional immune response, and glial scarring. Unfortunately, currently, there are no effective treatments available that can fully repair the spinal cord and improve functional outcomes. Nevertheless, numerous pre-clinical approaches have been studied for spinal cord injury recovery, including using biomaterials, cells, drugs, or technological-based strategies. Combinatorial treatments, which target various aspects of spinal cord injury pathophysiology, have been extensively tested in the last decade. These approaches aim to synergistically enhance repair processes by addressing various obstacles faced during spinal cord regeneration. Thus, this review intends to provide scientists and clinicians with an overview of pre-clinical combinatorial approaches that have been developed toward the solution of spinal cord regeneration as well as update the current knowledge about spinal cord injury pathophysiology with an emphasis on the current clinical management.

Pharmacological intervention for chronic phase of spinal cord injury

Spinal cord injury is an intractable traumatic injury. The most common hurdles faced during spinal cord injury are failure of axonal regrowth and reconnection to target sites. These also tend to be the most challenging issues in spinal cord injury. As spinal cord injury progresses to the chronic phase, lost motor and sensory functions are not recovered. Several reasons may be attributed to the failure of recovery from chronic spinal cord injury. These include factors that inhibit axonal growth such as activated astrocytes, chondroitin sulfate proteoglycan, myelin-associated proteins, inflammatory microglia, and fibroblasts that accumulate at lesion sites. Skeletal muscle atrophy due to denervation is another chronic and detrimental spinal cord injury–specific condition. Although several intervention strategies based on multiple outlooks have been attempted for treating spinal cord injury, few approaches have been successful. To treat chronic spinal cord injury, neural cells or tissue substitutes may need to be supplied in the cavity area to enable possible axonal growth. Additionally, stimulating axonal growth activity by extrinsic factors is extremely important and essential for maintaining the remaining host neurons and transplanted neurons. This review focuses on pharmacotherapeutic approaches using small compounds and proteins to enable axonal growth in chronic spinal cord injury. This review presents some of these candidates that have shown promising outcomes in basic research(in vivo animal studies) and clinical trials: AA-NgR(310)ecto-Fc(AXER-204), fasudil, phosphatase and tensin homolog protein antagonist peptide 4, chondroitinase ABC, intracellular sigma peptide,(-)-epigallocatechin gallate, matrine, acteoside, pyrvate kinase M2, diosgenin, granulocyte-colony stimulating factor, and fampridine-sustained release. Although the current situation suggests that drug-based therapies to recover function in chronic spinal cord injury are limited, potential candidates have been identified through basic research, and these candidates may be subjects of clinical studies in the future. Moreover, cocktail therapy comprising drugs with varied underlying mechanisms may be effective in treating the refractory status of chronic spinal cord injury.

Treatment of spinal cord injury with biomaterials and stem cell therapy in non-human primates and humans

Spinal cord injury results in the loss of sensory,motor,and autonomic functions,which almost always produces permanent physical disability.Thus,in the search for more effective treatments than those already applied for years,which are not entirely efficient,researches have been able to demonstrate the potential of biological strategies using biomaterials to tissue manufacturing through bioengineering and stem cell therapy as a neuroregenerative approach,seeking to promote neuronal recovery after spinal cord injury.Each of these strategies has been developed and meticulously evaluated in several animal models with the aim of analyzing the potential of interventions for neuronal repair and,consequently,boosting functional recovery.Although the majority of experimental research has been conducted in rodents,there is increasing recognition of the importance,and need,of evaluating the safety and efficacy of these interventions in non-human primates before moving to clinical trials involving therapies potentially promising in humans.This article is a literature review from databases(PubMed,Science Direct,Elsevier,Scielo,Redalyc,Cochrane,and NCBI)from 10 years ago to date,using keywords(spinal cord injury,cell therapy,non-human primates,humans,and bioengineering in spinal cord injury).From 110 retrieved articles,after two selection rounds based on inclusion and exclusion criteria,21 articles were analyzed.Thus,this review arises from the need to recognize the experimental therapeutic advances applied in non-human primates and even humans,aimed at deepening these strategies and identifying the advantages and influence of the results on extrapolation for clinical applicability in humans.

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society,mainly because of the severe after-effects they cause.Despite the ongoing development of various therapies for spinal cord injuries,their effectiveness remains unsatisfactory.However,a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming.In this review,we explore the metabolic changes that occur during spinal cord injuries,their consequences,and the therapeutic tools available for metabolic reprogramming.Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling.However,spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism,lipid metabolism,and mitochondrial dysfunction.These metabolic disturbances lead to corresponding pathological changes,including the failure of axonal regeneration,the accumulation of scarring,and the activation of microglia.To rescue spinal cord injury at the metabolic level,potential metabolic reprogramming approaches have emerged,including replenishing metabolic substrates,reconstituting metabolic couplings,and targeting mitochondrial therapies to alter cell fate.The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury.To further advance the metabolic treatment of the spinal cord injury,future efforts should focus on a deeper understanding of neurometabolism,the development of more advanced metabolomics technologies,and the design of highly effective metabolic interventions.

Induced neural stem cells regulate microglial activation through Akt-mediated upregulation of CXCR4 and Crry in a mouse model of closed head injury

Microglial activation that occurs rapidly after closed head injury may play important and complex roles in neuroinflammation-associated neuronal damage and repair.We previously reported that induced neural stem cells can modulate the behavior of activated microglia via CXCL12/CXCR4 signaling,influencing their activation such that they can promote neurological recovery.However,the mechanism of CXCR4 upregulation in induced neural stem cells remains unclear.In this study,we found that nuclear factor-κB activation induced by closed head injury mouse serum in microglia promoted CXCL12 and tumor necrosis factor-αexpression but suppressed insulin-like growth factor-1 expression.However,recombinant complement receptor 2-conjugated Crry(CR2-Crry)reduced the effects of closed head injury mouse serum-induced nuclear factor-κB activation in microglia and the levels of activated microglia,CXCL12,and tumor necrosis factor-α.Additionally,we observed that,in response to stimulation(including stimulation by CXCL12 secreted by activated microglia),CXCR4 and Crry levels can be upregulated in induced neural stem cells via the interplay among CXCL12/CXCR4,Crry,and Akt signaling to modulate microglial activation.In agreement with these in vitro experimental results,we found that Akt activation enhanced the immunoregulatory effects of induced neural stem cell grafts on microglial activation,leading to the promotion of neurological recovery via insulin-like growth factor-1 secretion and the neuroprotective effects of induced neural stem cell grafts through CXCR4 and Crry upregulation in the injured cortices of closed head injury mice.Notably,these beneficial effects of Akt activation in induced neural stem cells were positively correlated with the therapeutic effects of induced neural stem cells on neuronal injury,cerebral edema,and neurological disorders post–closed head injury.In conclusion,our findings reveal that Akt activation may enhance the immunoregulatory effects of induced neural stem cells on microglial activation via upregulation of CXCR4 and Crry,thereby promoting induced neural stem cell–mediated improvement of neuronal injury,cerebral edema,and neurological disorders following closed head injury.

Enhancement of motor functional recovery in thoracic spinal cord injury: voluntary wheel running versus forced treadmill exercise

Spinal cord injury necessitates effective rehabilitation strategies, with exercise therapies showing promise in promoting recovery. This study investigated the impact of rehabilitation exercise on functional recovery and morphological changes following thoracic contusive spinal cord injury. After a 7-day recovery period after spinal cord injury, mice were assigned to either a trained group(10 weeks of voluntary running wheel or forced treadmill exercise) or an untrained group. Bi-weekly assessments revealed that the exercise-trained group, particularly the voluntary wheel exercise subgroup, displayed significantly improved locomotor recovery, more plasticity of dopaminergic and serotonin modulation compared with the untrained group. Additionally, exercise interventions led to gait pattern restoration and enhanced transcranial magnetic motor-evoked potentials. Despite consistent injury areas across groups, exercise training promoted terminal innervation of descending axons. In summary, voluntary wheel exercise shows promise for enhancing outcomes after thoracic contusive spinal cord injury, emphasizing the role of exercise modality in promoting recovery and morphological changes in spinal cord injuries. Our findings will influence future strategies for rehabilitation exercises, restoring functional movement after spinal cord injury.

The pivotal role of microglia in injury and the prognosis of subarachnoid hemorrhage

Subarachnoid hemorrhage leads to a series of pathological changes,including vascular spasm,cellular apoptosis,blood–brain barrier damage,cerebral edema,and white matter injury.Microglia,which are the key immune cells in the central nervous system,maintain homeostasis in the neural environment,support neurons,mediate apoptosis,participate in immune regulation,and have neuroprotective effects.Increasing evidence has shown that microglia play a pivotal role in the pathogenesis of subarachnoid hemorrhage and affect the process of injury and the prognosis of subarachnoid hemorrhage.Moreover,microglia play certain neuroprotective roles in the recovery phase of subarachnoid hemorrhage.Several approaches aimed at modulating microglia function are believed to attenuate subarachnoid hemorrhage injury.This provides new targets and ideas for the treatment of subarachnoid hemorrhage.However,an in-depth and comprehensive summary of the role of microglia after subarachnoid hemorrhage is still lacking.This review describes the activation of microglia after subarachnoid hemorrhage and their roles in the pathological processes of vasospasm,neuroinflammation,neuronal apoptosis,blood–brain barrier disruption,cerebral edema,and cerebral white matter lesions.It also discusses the neuroprotective roles of microglia during recovery from subarachnoid hemorrhage and therapeutic advances aimed at modulating microglial function after subarachnoid hemorrhage.Currently,microglia in subarachnoid hemorrhage are targeted with TLR inhibitors,nuclear factor-κB and STAT3 pathway inhibitors,glycine/tyrosine kinases,NLRP3 signaling pathway inhibitors,Gasdermin D inhibitors,vincristine receptorαreceptor agonists,ferroptosis inhibitors,genetic modification techniques,stem cell therapies,and traditional Chinese medicine.However,most of these are still being evaluated at the laboratory stage.More clinical studies and data on subarachnoid hemorrhage are required to improve the treatment of subarachnoid hemorrhage.