Pharmacological Stimulation of Mitochondrial Biogenesis Using the Food and Drug Administration-Approved β2-Adrenoreceptor Agonist Formoterol for the Treatment of Spinal Cord Injury

Mechanism Analysis of Selenium-Containing Compounds in Alleviating Spinal Cord Injury Based on Network Pharmacology and Molecular Docking Technology

Spinal cord injury (SCI) is a severe traumatic condition in spinal surgery characterized by nerve damage in and below the injured area. Despite advancements in understanding the pathophysiology of SCI, effective clinical treatments remain elusive. Selenium compounds have become a research hotspot due to their diverse medicinal activities. Previously, our group synthesized a selenium-containing Compound 34# with significant anti-inflammatory activity. This study aimed to explore the anti-SCI effects of selenium-containing compounds using network pharmacology, molecular docking (MD), and ADMET methods. To identify SCI-related targets and those associated with 34#, GeneCards, NCBI, and SEA databases were employed. Eight overlapping targets were considered candidate targets, and molecular docking was performed using the PDB database and AutoDock software. The STRING database was used to obtain protein-protein interactions (PPI). Molecular dynamics simulation, MM/GBSA binding free energy score, and ADMET prediction were used to evaluate the potential targets and drug properties of 34#. Finally, experiments on NSC34 cells and mice were to verify the effects of 34# on SCI. Our results revealed eight candidate targets for 34# in the treatment of SCI. PPI and MD identified ADRB2 and HTR1F as the highest connectivity with 34#. ADMET analysis confirmed the low toxicity and safety of 34#. In vitro and in vivo models validated the anti-SCI effects. Our study elucidated candidate targets for alleviating SCI with 34#, explored PPI and target-related signaling pathways, and validated its anti-SCI effects. These findings enhance our understanding of 34#'s mechanism in treating SCI, positioning it as a potential candidate for SCI prevention.

The role of mitochondrial uncoupling in the regulation of mitostasis after traumatic brain injury

Mitostasis, the maintenance of healthy mitochondria, plays a critical role in brain health. The brain's high energy demands and reliance on mitochondria for energy production make mitostasis vital for neuronal function. Traumatic brain injury (TBI) disrupts mitochondrial homeostasis, leading to secondary cellular damage, neuronal degeneration, and cognitive deficits. Mild mitochondrial uncoupling, which dissociates ATP production from oxygen consumption, offers a promising avenue for TBI treatment. Accumulating evidence, from endogenous and exogenous mitochondrial uncoupling, suggests that mitostasis is closely regulating by mitochondrial uncoupling and cellular injury environments may be more sensitive to uncoupling. Mitochondrial uncoupling can mitigate calcium overload, reduce oxidative stress, and induce mitochondrial proteostasis and mitophagy, a process that eliminates damaged mitochondria. The interplay between mitochondrial uncoupling and mitostasis is ripe for further investigation in the context of TBI. These multi-faceted mechanisms of action for mitochondrial uncoupling hold promise for TBI therapy, with the potential to restore mitochondrial health, improve neurological outcomes, and prevent long-term TBI-related pathology.

Isolation and monoculture of functional primary astrocytes from the adult mouse spinal cord

Astrocytes are a widely heterogenic cell population that play major roles in central nervous system (CNS) homeostasis and neurotransmission, as well as in various neuropathologies, including spinal cord injury (SCI), traumatic brain injury, and neurodegenerative diseases, such as amyotrophic lateral sclerosis. Spinal cord astrocytes have distinct differences from those in the brain and accurate modeling of disease states is necessary for understanding disease progression and developing therapeutic interventions. Several limitations to modeling spinal cord astrocytes in vitro exist, including lack of commercially available adult-derived cells, lack of purchasable astrocytes with different genotypes, as well as time-consuming and costly in-house primary cell isolations that often result in low yield due to small tissue volume. To address these issues, we developed an efficient adult mouse spinal cord astrocyte isolation method that utilizes enzymatic digestion, debris filtration, and multiple ACSA-2 magnetic microbead purification cycles to achieve an astrocyte monoculture purity of ≅93-98%, based on all markers assessed. Importantly, the isolated cells contain active mitochondria and express key astrocyte markers including ACSA-1, ACSA-2, EAAT2, and GFAP. Furthermore, this isolation method can be applied to the spinal cord of male and female mice, mice subjected to SCI, and genetically modified mice. We present a primary adult mouse spinal cord astrocyte isolation protocol focused on purity, viability, and length of isolation that can be applied to a multitude of models and aid in targeted research on spinal-cord related CNS processes and pathologies.

Boosting Mitochondrial Biogenesis Diminishes Foam Cell Formation in the Post-Stroke Brain

Following ischemic stroke, the degradation of myelin and other cellular membranes surpasses the lipid-processing capabilities of resident microglia and infiltrating macrophages. This imbalance leads to foam cell formation in the infarct and areas of secondary neurodegeneration, instigating sustained inflammation and furthering neurological damage. Given that mitochondria are the primary sites of fatty acid metabolism, augmenting mitochondrial biogenesis (MB) may enhance lipid processing, curtailing foam cell formation and post-stroke chronic inflammation. Previous studies have shown that the pharmacological activation of the β2-adrenergic receptor (β2-AR) stimulates MB. Consequently, our study sought to discern the effects of intensified β2-AR signaling on MB, the processing of brain lipid debris, and neurological outcome using a mouse stroke model. To achieve this goal, aged mice were treated with formoterol, a long-acting β2-AR agonist, daily for two and eight weeks following stroke. Formoterol increased MB in the infarct region, modified fatty acid metabolism, and reduced foam cell formation. However, it did not reduce markers of post-stroke neurodegeneration or improve recovery. Although our findings indicate that enhancing MB in myeloid cells can aid in the processing of brain lipid debris after stroke, it is important to note that boosting MB alone may not be sufficient to significantly impact stroke recovery.

Role of DNA methylation during recovery from spinal cord injury with and without β2-adrenergic receptor agonism

Daily treatment with the FDA-approved β2-adrenergic receptor agonist formoterol beginning 8 h after severe spinal cord injury (SCI) induces mitochondrial biogenesis and improves recovery in mice. We observed decreased DNA methyltransferase (DNMT) expression, global DNA methylation and methylation of the mitochondrial genes PGC-1α and NDUFS1 in the injury site of formoterol-treated mice 1 DPI, but this effect was lost by 7 DPI. To investigate the role of DNA methylation on recovery post-SCI, injured mice were treated daily with formoterol or vehicle, plus the DNMT inhibitor decitabine (DAC) on days 7-9. While DAC had no apparent effect on formoterol-induced recovery, mice treated with vehicle plus DAC exhibited increased BMS scores compared to vehicle alone beginning 15 DPI, reaching a degree of functional recovery similar to that of formoterol-treated mice by 21 DPI. Furthermore, DAC treatment increased injury site mitochondrial protein expression in vehicle-treated mice to levels comparable to that of formoterol-treated mice. The effect of DNMT inhibition on pain response with and without formoterol was assessed following moderate SCI. While all injured mice not treated with DAC displayed thermal hyperalgesia by 21 DPI, mice treated with formoterol exhibited decreased thermal hyperalgesia compared to vehicle-treated mice by 35 DPI. Injured mice treated with DAC, regardless of formoterol treatment, did not demonstrate thermal hyperalgesia at any time point assessed. Although these data do not suggest enhanced formoterol-induced recovery with DNMT inhibition, our findings indicate the importance of DNA methylation post-SCI and support both DNMT inhibition and formoterol as potential therapeutic avenues.

Exploring skeletal muscle tolerance and whole-body metabolic effects of FDA-approved drugs in a volumetric muscle loss model

Volumetric muscle loss (VML) is associated with persistent functional impairment due to a lack of de novo muscle regeneration. As mechanisms driving the lack of regeneration continue to be established, adjunctive pharmaceuticals to address the pathophysiology of the remaining muscle may offer partial remediation. Studies were designed to evaluate the tolerance and efficacy of two FDA-approved pharmaceutical modalities to address the pathophysiology of the remaining muscle tissue after VML injury: (1) nintedanib (an anti-fibrotic) and (2) combined formoterol and leucine (myogenic promoters). Tolerance was first established by testing low- and high-dosage effects on uninjured skeletal muscle mass and myofiber cross-sectional area in adult male C57BL/6J mice. Next, tolerated doses of the two pharmaceutical modalities were tested in VML-injured adult male C57BL/6J mice after an 8-week treatment period for their ability to modulate muscle strength and whole-body metabolism. The most salient findings indicate that formoterol plus leucine mitigated the loss in muscle mass, myofiber number, whole-body lipid oxidation, and muscle strength, and resulted in a higher whole-body metabolic rate (p ≤ 0.016); nintedanib did not exacerbate or correct aspects of the muscle pathophysiology after VML. This supports ongoing optimization efforts, including scale-up evaluations of formoterol treatment in large animal models of VML.

LRP1 Deficiency Promotes Mitostasis in Response to Oxidative Stress: Implications for Mitochondrial Targeting after Traumatic Brain Injury

The brain undergoes oxidative stress and mitochondrial dysfunction following physiological insults such as Traumatic brain injury (TBI), ischemia-reperfusion, and stroke. Pharmacotherapeutics targeting mitochondria (mitoceuticals) against oxidative stress include antioxidants, mild uncouplers, and enhancers of mitochondrial biogenesis, which have been shown to improve pathophysiological outcomes after TBI. However, to date, there is no effective treatment for TBI. Studies have suggested that the deletion of LDL receptor-related protein 1 (LRP1) in adult neurons or glial cells could be beneficial and promote neuronal health. In this study, we used WT and LRP1 knockout (LKO) mouse embryonic fibroblast cells to examine mitochondrial outcomes following exogenous oxidative stress. Furthermore, we developed a novel technique to measure mitochondrial morphometric dynamics using transgenic mitochondrial reporter mice mtD2g (mitochondrial-specific Dendra2 green) in a TBI model. We found that oxidative stress increased the quantity of fragmented and spherical-shaped mitochondria in the injury core of the ipsilateral cortex following TBI, whereas rod-like elongated mitochondria were seen in the corresponding contralateral cortex. Critically, LRP1 deficiency significantly decreased mitochondrial fragmentation, preserving mitochondrial function and cell growth following exogenous oxidative stress. Collectively, our results show that targeting LRP1 to improve mitochondrial function is a potential pharmacotherapeutic strategy against oxidative damage in TBI and other neurodegenerative diseases.

Pharmacological Targeting of Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) in the United States and many other countries. DKD occurs through a variety of pathogenic processes that are in part driven by hyperglycemia and glomerular hypertension, leading to gradual loss of kidney function and eventually progressing to ESRD. In type 2 diabetes, chronic hyperglycemia and glomerular hyperfiltration leads to glomerular and proximal tubular dysfunction. Simultaneously, mitochondrial dysfunction occurs in the early stages of hyperglycemia and has been identified as a key event in the development of DKD. Clinical management for DKD relies primarily on blood pressure and glycemic control through the use of numerous therapeutics that slow disease progression. Because mitochondrial function is key for renal health over time, therapeutics that improve mitochondrial function could be of value in different renal diseases. Increasing evidence supports the idea that targeting aspects of mitochondrial dysfunction, such as mitochondrial biogenesis and dynamics, restores mitochondrial function and improves renal function in DKD. We will review mitochondrial function in DKD and the effects of current and experimental therapeutics on mitochondrial biogenesis and homeostasis in DKD over time. SIGNIFICANCE STATEMENT: Diabetic kidney disease (DKD) affects 20% to 40% of patients with diabetes and has limited treatment options. Mitochondrial dysfunction has been identified as a key event in the progression of DKD, and pharmacologically restoring mitochondrial function in the early stages of DKD may be a potential therapeutic strategy in preventing disease progression.

The role of mitochondrial energy metabolism in neuroprotection and axonal regeneration after spinal cord injury

Mitochondrial dysfunction occurs in the early stage of axonal degeneration after spinal cord injury and involves oxidative stress, energy deficiency, imbalance of mitochondrial dynamics, etc., which play a key role in axonal degeneration and regeneration under physiological and pathological conditions. Failure of axonal regeneration can lead to long-term structural and functional damage. Several recent studies have shown that improved mitochondrial energy metabolism provides conditions for axonal regeneration and central nervous system repair. Here, we describe the role of mitochondrial energy metabolism in neuroprotection and axonal regeneration after spinal cord injury and review recent advances in targeted mitochondrial therapy.

Delivery of mitoceuticals or respiratory competent mitochondria to sites of neurotrauma

Herein, we review evidence that targeting mitochondrial dysfunction with 'mitoceuticals' is an effective neuroprotective strategy following neurotrauma, and that isolated exogenous mitochondria can be effectively transplanted into host spinal cord parenchyma to increase overall cellular metabolism. We further discuss control measures to ensure greatest potential for mitochondrial transfer, notably using erodible thermogelling hydrogels to deliver respiratory competent mitochondria to the injured spinal cord.

Single-cell RNA sequencing reveals the role of immune-related autophagy in spinal cord injury in rats

Spinal cord injury refers to damage to the spinal cord due to trauma, disease, or degeneration; and the number of new cases is increasing yearly. Significant cellular changes are known to occur in the area of spinal cord injury. However, changes in cellular composition, trajectory of cell development, and intercellular communication in the injured area remain unclear. Here, we used single-cell RNA sequencing to evaluate almost all the cell types that constitute the site of spinal cord injury in rats. In addition to mapping the cells of the injured area, we screened the expression of immune autophagy-related factors in cells and identified signaling pathways by the measuring the expression of the receptor−ligand pairs to regulate specific cell interactions during autophagy after spinal cord injury. Our data set is a valuable resource that provides new insights into the pathobiology of spinal cord injury and other traumatic diseases of the central nervous system.

Photobiomodulation promotes repair following spinal cord injury by restoring neuronal mitochondrial bioenergetics via AMPK/PGC-1α/TFAM pathway

Background: Insufficient neuronal mitochondrial bioenergetics supply occurs after spinal cord injury (SCI), leading to neuronal apoptosis and impaired motor function. Previous reports have shown that photobiomodulation (PBM) could reduce neuronal apoptosis and promote functional recovery, but the underlying mechanism remains unclear. Therefore, we aimed to investigate whether PBM improved prognosis by promoting neuronal mitochondrial bioenergetics after SCI.

Methods: Sprague Dawley rats were randomly divided into four groups: a Sham group, an SCI group, an SCI + PBM group and an SCI + PBM + Compound C group. After SCI model was established, PBM and Compound C (an AMPK inhibitor) injection were carried out. The level of neuron apoptosis, the recovery of motor function and mitochondrial function were observed at different times (7, 14, and 28 days). The AMPK/PGC-1α/TFAM pathway was hypothesized to be a potential target through which PBM could affect neuronal mitochondrial bioenergetics. In vitro, ventral spinal cord 4.1 (VSC4.1) cells were irradiated with PBM and cotreated with Compound C after oxygen and glucose deprivation (OGD).

Results: PBM promoted the recovery of mitochondrial respiratory chain complex activity, increased ATP production, alleviated neuronal apoptosis and reversed motor dysfunction after SCI. The activation of the AMPK/PGC-1α/TFAM pathway after SCI were facilitated by PBM but inhibited by Compound C. Equally important, PBM could inhibit OGD-induced VSC4.1 cell apoptosis by increasing ATP production whereas these changes could be abolished by Compound C.

Conclusion: PBM activated AMPK/PGC-1α/TFAM pathway to restore mitochondrial bioenergetics and exerted neuroprotective effects after SCI.

Pharmaceutical Agents for Contractile-Metabolic Dysfunction After Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries represent a majority of military service member casualties and are common in civilian populations following blunt and/or penetrating traumas. Characterized as a skeletal muscle injury with permanent functional impairments, there is currently no standard for rehabilitation, leading to lifelong disability. Toward developing rehabilitative strategies, previous research demonstrates that the remaining muscle after a VML injury lacks similar levels of plasticity or adaptability as healthy, uninjured skeletal muscle. This may be due, in part, to impaired innervation and vascularization of the remaining muscle, as well as disrupted molecular signaling cascades commonly associated with muscle adaptation. The primary objective of this study was to assess the ability of four pharmacological agents with a strong record of modulating muscle contractile and metabolic function to improve functional deficits in a murine model of VML injury. Male C57BL/6 mice underwent a 15% multimuscle VML injury of the posterior hindlimb and were randomized into drug treatment groups (formoterol [FOR], 5-aminoimidazole-4-carboxamide riboside [AICAR], pioglitazone [PIO], or sildenafil [SIL]) or untreated VML group. At the end of 60 days, the injury model was first validated by comparison to age-matched injury-naive mice. Untreated VML mice had 22% less gastrocnemius muscle mass, 36% less peak-isometric torque, and 27% less maximal mitochondrial oxygen consumption rate compared to uninjured mice (p < 0.01). Experimental drug groups were, then, compared to VML untreated, and there was minimal evidence of efficacy for AICAR, PIO, or SIL in improving contractile and metabolic functional outcomes. However, FOR-treated VML mice had 18% greater peak isometric torque (p < 0.01) and permeabilized muscle fibers had 36% greater State III mitochondrial oxygen consumption rate (p < 0.01) compared to VML untreated mice, suggesting an overall improvement in muscle condition. There was minimal evidence that these benefits came from greater mitochondrial biogenesis and/or mitochondrial complex protein content, but could be due to greater enzyme activity levels for complex I and complex II. These findings suggest that FOR treatment is candidate to pair with a rehabilitative approach to maximize functional improvements in VML-injured muscle. Impact statement Volumetric muscle loss (VML) injuries result in deficiencies in strength and mobility, which have a severe impact on patient quality of life. Despite breakthroughs in tissue engineering, there are currently no treatments available that can restore function to the affected limb. Our data show that treatment of VML injuries with clinically available and FDA-approved formoterol (FOR), a beta-agonist, significantly improves strength and metabolism of VML-injured muscle. FOR is therefore a promising candidate for combined therapeutic approaches (i.e., regenerative rehabilitation) such as pairing FOR with structured rehabilitation or cell-seeded biomaterials as it may provide greater functional improvements than either strategy alone.

[Advances of the role of mitochondrial dysfunction in the spinal cord injury and its relevant treatments]

OBJECTIVE

To review the advances of the role of mitochondrial dysfunction in the spinal cord injury (SCI) and its relevant treatments.

METHODS

Focusing on various mechanisms of mitochondrial dysfunction, recent relevant literature at home and abroad was identified to summarize the therapeutic strategies for SCI.

RESULTS

Mitochondrial dysfunction is mainly manifested in abnormalities in mitochondrial energy metabolism, mitochondrial oxidative stress, mitochondrial-mediated apoptosis, mitophagy, mitochondrial permeability transition, and mitochondrial biogenesis, playing a vital role in the development of SCI. Drug that enhanced mitochondrial function have been proved beneficial for the treatment of SCI.

CONCLUSION

Mitochondrial dysfunction can serve as a potential therapeutic target for SCI, providing ideas and basis for the development of SCI therapeutic candidates in the future.

[Effect of M2-like macrophage/microglia-derived mitochondria transplantation in treatment of mouse spinal cord injury]

OBJECTIVE

To investigate the effect of M2-like macrophage/microglia-derived mitochondria transplantation in treatment of mouse spinal cord injury (SCI).

METHODS

BV2 cells were classified into M1 (LPS treatment), M2 (IL-4 treatment), and M0 (no treatment) groups. After receiving M1 and M2 polarization, BV2 cells received microscopic observation, immunofluorescence staining [Arginase-1 (Arg-1)] and flow cytometry [inducible nitric oxide synthase (iNOS), Arg-1] to determine the result of polarization. MitoSox Red and 2, 7-dichlorodi-hydrofluorescein diacetate (DCFH-DA) stainings were used to evaluate mitochondrial function difference. Mitochondria was isolated from M2-like BV2 cells through differential velocity centrifugation for following transplantation. Then Western blot was used to measure the expression levels of the relevant complexes (complexes Ⅱ, Ⅲ, Ⅳ, and Ⅴ) in the oxidative phosphorylation (OXPHOS), and compared with M2-like BV2 cells to evaluate whether the mitochondria were obtained. Thirty-six female C57BL/6 mice were randomly divided into 3 groups ( n=12). Mice from sham group were only received the T ₁₀ laminectomy. After the T ₁₀ spinal cord injury (SCI) model was prepared in the SCI group and mitochondria transplantation (MT) group, mitochondrial storage solution and mitochondria (100 μg) derived from M2-like BV2 cells were injected into the injured segment, respectively. After operation, the Basso Mouse Scale (BMS) score was performed to evaluate the motor function recovery. And immunofluorescence staining, lycopersicon esculentum agglutinin (LEA)-FITC staining, and ELISA [vascular endothelial growth factor A (VEGFA)] were also performed.

RESULTS

After polarization induction, BV2 cells in M1 and M2 groups showed specific morphological changes of M1-like and M2-like macrophages, respectively. Immunofluorescence staining showed that the positive expression of M2-like macrophages marker (Arg-1) was significantly higher in M2 group than in M0 group and M1 group ( P<0.05). Flow cytometry showed that the expression of M1-like macrophage marker (iNOS) was significantly higher in M1 group than in M0 group and M2 group ( P<0.05), and the expression of Arg-1 was significantly higher in M2 group than in M0 group and M1 group ( P<0.05). MitoSox Red and DCFH-DA stainings showed that the fluorescence intensity of the M2 group was significantly lower than that of the M1 group ( P<0.05), and there was no significant difference with the M0 group ( P>0.05). The M2-like BV2 cells-derived mitochondria was identified through Western blot assay. Animal experiments showed that the BMS scores of MT group at 21 and 28 days after operation were significantly higher than those of SCI group ( P<0.05). At 14 days after operation, the number of iNOS-positive cells in MT group was significantly lower than that in SCI group ( P<0.05), but still higher than that in sham group ( P<0.05); the number of LEA-positive cells and the expression of VEGFA in MT group were significantly more than those in the other two groups ( P<0.05).

CONCLUSION

M2-like macrophage/microglia-derived mitochondria transplantation can promote angiogenesis and inhibit inflammatory M1-like macrophage/microglia polarization after mouse SCI to improve function recovery.

Mitochondrial function in spinal cord injury and regeneration

Many people around the world suffer from some form of paralysis caused by spinal cord injury (SCI), which has an impact on quality and life expectancy. The spinal cord is part of the central nervous system (CNS), which in mammals is unable to regenerate, and to date, there is a lack of full functional recovery therapies for SCI. These injuries start with a rapid and mechanical insult, followed by a secondary phase leading progressively to greater damage. This secondary phase can be potentially modifiable through targeted therapies. The growing literature, derived from mammalian and regenerative model studies, supports a leading role for mitochondria in every cellular response after SCI: mitochondrial dysfunction is the common event of different triggers leading to cell death, cellular metabolism regulates the immune response, mitochondrial number and localization correlate with axon regenerative capacity, while mitochondrial abundance and substrate utilization regulate neural stem progenitor cells self-renewal and differentiation. Herein, we present a comprehensive review of the cellular responses during the secondary phase of SCI, the mitochondrial contribution to each of them, as well as evidence of mitochondrial involvement in spinal cord regeneration, suggesting that a more in-depth study of mitochondrial function and regulation is needed to identify potential targets for SCI therapeutic intervention.

Design, Development, Physicochemical Characterization, and In Vitro Drug Release of Formoterol PEGylated PLGA Polymeric Nanoparticles

Polymeric nanoparticles’ drug delivery systems represent a promising platform for targeted controlled release since they are capable of improving the bioavailability and tissue localization of drugs compared to traditional means of administration. Investigation of key parameters of nanoparticle preparation and their impact on performance, such as size, drug loading, and sustained release, is critical to understanding the synthesis parameters surrounding a given nanoparticle formulation. This comprehensive and systematic study reports for the first time and focuses on the development and characterization of formoterol polymeric nanoparticles that have potential application in a variety of acute and chronic diseases. Nanoparticles were prepared by a variety of solvent emulsion methods with varying modifications to the polymer and emulsion system with the aim of increasing drug loading and tuning particle size for renal localization and drug delivery. Maximal drug loading was achieved by amine modification of polyethylene glycol (PEG) conjugated to the poly(lactic-co-glycolic acid) (PLGA) backbone. The resulting formoterol PEGylated PLGA polymeric nanoparticles were successfully lyophilized without compromising size distribution by using either sucrose or trehalose as cryoprotectants. The physicochemical characteristics of the nanoparticles were examined comprehensively, including surface morphology, solid-state transitions, crystallinity, and residual water content. In vitro formoterol drug release characteristics from the PEGylated PLGA polymeric nanoparticles were also investigated as a function of both polymer and emulsion parameter selection, and release kinetics modeling was successfully applied.

Role of Descending Serotonergic Fibers in the Development of Pathophysiology after Spinal Cord Injury (SCI): Contribution to Chronic Pain, Spasticity, and Autonomic Dysreflexia

As the nervous system develops, nerve fibers from the brain form descending tracts that regulate the execution of motor behavior within the spinal cord, incoming sensory signals, and capacity to change (plasticity). How these fibers affect function depends upon the transmitter released, the receptor system engaged, and the pattern of neural innervation. The current review focuses upon the neurotransmitter serotonin (5-HT) and its capacity to dampen (inhibit) neural excitation. A brief review of key anatomical details, receptor types, and pharmacology is provided. The paper then considers how damage to descending serotonergic fibers contributes to pathophysiology after spinal cord injury (SCI). The loss of serotonergic fibers removes an inhibitory brake that enables plasticity and neural excitation. In this state, noxious stimulation can induce a form of over-excitation that sensitizes pain (nociceptive) circuits, a modification that can contribute to the development of chronic pain. Over time, the loss of serotonergic fibers allows prolonged motor drive (spasticity) to develop and removes a regulatory brake on autonomic function, which enables bouts of unregulated sympathetic activity (autonomic dysreflexia). Recent research has shown that the loss of descending serotonergic activity is accompanied by a shift in how the neurotransmitter GABA affects neural activity, reducing its inhibitory effect. Treatments that target the loss of inhibition could have therapeutic benefit.

β2-adrenoreceptor agonist ameliorates mechanical allodynia in paclitaxel-induced neuropathic pain via induction of mitochondrial biogenesis

Chemotherapy-induced neuropathic pain is a debilitating and common side effect of cancer treatment and so far no effective drug is available for treatment of the serious side effect. Previous studies have demonstrated β2-adrenoreceptor (ADRB2) agonists can attenuate neuropathic pain. However, the role of ADRB2 in paclitaxel -induced neuropathic pain (PINP) remains unclear. In this study, we investigated the effect of formoterol, a long-acting ADRB2 agonist, and related mechanisms in PINP. A rat model of PINP was established by intraperitoneal injection of paclitaxel (2 mg/kg) every other day with a final cumulative dose of 8 mg/kg. Hind paw withdrawal thresholds (PWTs) in response to von Frey filament stimuli were used to evaluate mechanical allodynia. Western blot was used to examine the expression of ADRB2, peroxisome proliferator-activated receptor coactivator-1α (PGC-1α), nuclear respiratory factors 1 (NRF1) and mitochondrial transcription factor A (TFAM) and the immunofluorescence was to detect the cellular localization of ADRB2 and PGC-1α in the spinal cord. Moreover, we measured mitochondrial DNA (mtDNA) copy number by qPCR. In our study, formoterol attenuated established PINP and delayed the onset of PINP. Formoterol restored ADRB2 expression as well as mtDNA copy number and PGC-1α, NRF1, and TFAM protein expression, which are major genes involved in mitochondrial biogenesis, in the spinal cord of PINP rats. Moreover, we found the analgesic effect of formoterol against PINP was partially abolished by PGC-1α inhibitor SR-18292. Collectively, these results demonstrated the activation of ADRB2 with formoterol ameliorates PINP at least partially through induction of mitochondrial biogenesis.

Ketogenesis controls mitochondrial gene expression and rescues mitochondrial bioenergetics after cervical spinal cord injury in rats

A better understanding of the secondary injury mechanisms that occur after traumatic spinal cord injury (SCI) is essential for the development of novel neuroprotective strategies linked to the restoration of metabolic deficits. We and others have shown that Ketogenic diet (KD), a high fat, moderate in proteins and low in carbohydrates is neuroprotective and improves behavioural outcomes in rats with acute SCI. Ketones are alternative fuels for mitochondrial ATP generation, and can modulate signaling pathways via targeting specific receptors. Here, we demonstrate that ad libitum administration of KD for 7 days after SCI rescued mitochondrial respiratory capacity, increased parameters of mitochondrial biogenesis, affected the regulation of mitochondrial-related genes, and activated the NRF2-dependent antioxidant pathway. This study demonstrates that KD improves post-SCI metabolism by rescuing mitochondrial function and supports the potential of KD for treatment of acute SCI in humans.

Corticospinal Motor Circuit Plasticity After Spinal Cord Injury: Harnessing Neuroplasticity to Improve Functional Outcomes

Spinal cord injury (SCI) is a devastating condition that affects approximately 294,000 people in the USA and several millions worldwide. The corticospinal motor circuitry plays a major role in controlling skilled movements and in planning and coordinating movements in mammals and can be damaged by SCI. While axonal regeneration of injured fibers over long distances is scarce in the adult CNS, substantial spontaneous neural reorganization and plasticity in the spared corticospinal motor circuitry has been shown in experimental SCI models, associated with functional recovery. Beneficially harnessing this neuroplasticity of the corticospinal motor circuitry represents a highly promising therapeutic approach for improving locomotor outcomes after SCI. Several different strategies have been used to date for this purpose including neuromodulation (spinal cord/brain stimulation strategies and brain-machine interfaces), rehabilitative training (targeting activity-dependent plasticity), stem cells and biological scaffolds, neuroregenerative/neuroprotective pharmacotherapies, and light-based therapies like photodynamic therapy (PDT) and photobiomodulation (PMBT). This review provides an overview of the spontaneous reorganization and neuroplasticity in the corticospinal motor circuitry after SCI and summarizes the various therapeutic approaches used to beneficially harness this neuroplasticity for functional recovery after SCI in preclinical animal model and clinical human patients' studies.

CD157 in bone marrow mesenchymal stem cells mediates mitochondrial production and transfer to improve neuronal apoptosis and functional recovery after spinal cord injury

Background

Recent studies demonstrated that autologous mitochondria derived from bone marrow mesenchymal stem cells (BMSCs) might be valuable in the treatment of spinal cord injury (SCI). However, the mechanisms of mitochondrial transfer from BMSCs to injured neurons are not fully understood.

Methods

We modified BMSCs by CD157, a cell surface molecule as a potential regulator mitochondria transfer, then transplanted to SCI rats and co-cultured with OGD injured VSC4.1 motor neuron. We detected extracellular mitochondrial particles derived from BMSCs by transmission electron microscope and measured the CD157/cyclic ADP-ribose signaling pathway-related protein expression by immunohistochemistry and Western blotting assay. The CD157 ADPR-cyclase activity and Fluo-4 AM was used to detect the Ca²⁺ signal. All data were expressed as mean ± SEM. Statistical analysis was analyzed by GraphPad Prism 6 software. Unpaired t-test was used for the analysis of two groups. Multiple comparisons were evaluated by one-way ANOVA or two-way ANOVA.

Results

CD157 on BMSCs was upregulated when co-cultured with injured VSC4.1 motor neurons. Upregulation of CD157 on BMSCs could raise the transfer extracellular mitochondria particles to VSC4.1 motor neurons, gradually regenerate the axon of VSC4.1 motor neuron and reduce the cell apoptosis. Transplantation of CD157-modified BMSCs at the injured sites could significantly improve the functional recovery, axon regeneration, and neuron apoptosis in SCI rats. The level of Ca²⁺ in CD157-modified BMSCs dramatically increased when objected to high concentration cADPR, ATP content, and MMP of BMSCs also increased.

Conclusion

The present results suggested that CD157 can regulate the production and transfer of BMSC-derived extracellular mitochondrial particles, enriching the mechanism of the extracellular mitochondrial transfer in BMSCs transplantation and providing a novel strategy to improve the stem cell treatment on SCI.

FDA-approved 5-HT1F receptor agonist lasmiditan induces mitochondrial biogenesis and enhances locomotor and blood-spinal cord barrier recovery after spinal cord injury

Vascular and mitochondrial dysfunction are well-established consequences of spinal cord injury (SCI). Evidence suggests mitigating these dysfunctions may be an effective approach in treating SCI. The goal of this study was to elucidate if mitochondrial biogenesis (MB) induction with a new, selective and FDA-approved 5-hydroxytryptamine receptor 1F (5-HT_1F) receptor agonist, lasmiditan, can stimulate locomotor recovery and restoration of the blood-spinal cord barrier (BSCB) after SCI. Female C57BL/6 J mice were subjected to moderate SCI using a force-controlled impactor-induced contusion model followed by daily administration of lasmiditan (0.1 mg/kg, i.p.) beginning 1 h after injury. In the naïve spinal cord, electron microscopy revealed increased mitochondrial density and mitochondrial area, as well as enhanced mitochondrial DNA content. FCCP-uncoupled oxygen consumption rate (OCR), a functional marker of MB, was also increased in the naïve spinal cord following lasmiditan treatment. We observed disrupted mitochondrial DNA content, PGC-1α levels and FCCP-OCR in the injury site 3d after SCI. Lasmiditan treatment attenuated, and in some cases restored these deficits. Lasmiditan treatment also resulted in increased locomotor capability as early as 7d post-SCI, with treated mice reaching a Basso-Mouse Scale score of 3.3 by 21d, while vehicle-treated mice exhibited a score of 2.0. Integrity of the BSCB was assessed using Evans Blue dye extravasation. While SCI increased dye extravasation at 3d and 7d, dye accumulation in the spinal cord of lasmiditan-treated mice was attenuated 7d post-SCI, suggesting accelerated BSCB recovery. Finally, lasmiditan treatment resulted in decreased lesion volume and spared myelinated tissue 7d post-SCI. Collectively, these data reveal that 5-HT_1F receptor agonist-induced MB using the FDA-approved drug lasmiditan may be an effective therapeutic strategy for the treatment of SCI.

The acute effect of dopamine infusion on lipid and cytokine concentrations in persons with a cervical spinal cord injury-a pilot study

STUDY DESIGN

Acute experimental study.

OBJECTIVES

To investigate the acute response of markers of lipid metabolism and interleukin (IL)-6 to dopamine infusion in people with a cervical spinal cord injury (CSCI).

SETTING

Laboratory of Wakayama Medical University, Japan.

METHODS

Ten participants, four with CSCI and six AB individuals, underwent 50 min of dopamine infusion. Blood samples were collected prior to, immediately after and 1 h following cessation of dopamine infusion for the determination of circulating catecholamine, lipid, ketone body and IL-6 concentrations.

RESULTS

The adrenaline concentration following dopamine infusion was increased by 59 ± 7% in CSCI (p = 0.038, Cohen's d effect size (ES): 1.47), while this was not changed in AB (p = 0.223). Triglycerides and acetoacetic acid concentration were increased in both groups, immediately after and 1 h post-infusion (triglycerides p ≤ 0.042, ES CSCI: 1.00, ES AB: 1.12; acetoacetic acid p ≤ 0.030; ES CSCI: 1.72, ES AB: 1.31). 3-Hydroxybutyric acid concentration was increased in CSCI only (48 ± 15%, p = 0.039, ES: 1.44; AB p = 0.115). Dopamine infusion did not affect plasma IL-6 concentration in either group (p ≥ 0.368).

CONCLUSIONS

Dopamine infusion induced a sustained increase in triglyceride and ketone body concentrations in persons with CSCI. In contrast, cytokine concentrations were not affected by dopamine infusion. These findings suggest that circulating catecholamines can stimulate metabolism in people with CSCI despite the presence of autonomic dysfunction.

Time-to-treatment window and cross-sex potential of β2-adrenergic receptor-induced mitochondrial biogenesis-mediated recovery after spinal cord injury

Mitochondrial dysfunction is a well-characterized consequence of spinal cord injury (SCI). We previously reported that treatment with the FDA-approved β2-adrenergic receptor agonist formoterol beginning 8 h post-SCI induces mitochondrial biogenesis (MB) and improves body composition and locomotor recovery in female mice. To determine the time-to-treatment window of formoterol, female mice were subjected to 80 kdyn contusion SCI and daily administration of vehicle or formoterol (0.3 mg/kg) beginning 24 h after injury. This delayed treatment paradigm improved body composition in female mice by 21 DPI, returning body weight to pre-surgery weight and restoring gastrocnemius mass to sham levels; however, there was no effect on locomotor recovery, as measured by the Basso-Mouse Scale (BMS), or lesion volume. To assess the cross-sex potential of formoterol, injured male mice were treated with vehicle or formoterol (0.3 or 1.0 mg/kg) beginning 8 h after SCI. Formoterol also improved body composition post-SCI in male mice, restoring body weight and muscle mass regardless of dose. Interestingly, however, improved BMS scores and decreased lesion volume was observed only in male mice treated with 0.3 mg/kg. Additionally, 0.3 mg/kg formoterol induced MB in the gastrocnemius and injured spinal cord, as evidenced by increased MB protein expression and mitochondrial number. These data indicate that formoterol treatment improves recovery post-SCI in both male and female mice in a dose- and initiation time-dependent manner. Furthermore, formoterol-induced functional recovery post-SCI is not directly associated with peripheral effects, such as muscle mass and body weight.

Tannic Acid Provides Neuroprotective Effects Against Traumatic Brain Injury Through the PGC-1α/Nrf2/HO-1 Pathway

The present research was conducted to elucidate a possible molecular mechanism related to neuromodulatory effects of tannic acid (TA) supplementation against traumatic brain injury (TBI) in a rodent model. Oxidative damage and neuroinflammation play a critical role in TBI and lead to behavioral alterations and neuronal dysfunction and death. These changes suggest a potential avenue in neurotherapeutic intervention. The aim of the present study was to investigate the neuroprotective effects of TA and potential mechanism of these effects in a controlled cortical impact injury model of TBI in Wistar rats that were treated with TA (50 mg/kg body weight. i.p.) before 30 min and 6 and 18 h after TBI. TBI-induced rats were examined after 24 h for behavioral dysfunction, Nissl stain, lipid peroxidation rate, glutathione level, activities of antioxidant enzymes (catalase, glutathione S-transferase, glutathione peroxidase, and superoxide dismutase), the expression level of 4-hydroxynonenal, pro-inflammatory cytokines such as tumor necrosis factor alpha and interleukin-1 beta, as well as brain edema and immunoreactivity of glial fibrillary acidic protein. Results indicated that TA supplementation significantly modulated above mentioned alterations. Moreover, TA treatment effectively upregulated the protein expression of peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1α) and nuclear factor-E2-related factor-2 (Nrf2) as well as mitochondrial transcription factor A and heme oxygenase-1 (HO-1) following TBI. Overall, our results suggest that TA effectively ameliorates the behavioral alterations, oxidative damage, mitochondrial impairment, and inflammation against TBI that may be attributed to activation of PGC-1α/Nrf-2/HO-1 signaling pathway.

Mitochondrial biogenesis as a therapeutic target for traumatic and neurodegenerative CNS diseases

Central nervous system (CNS) diseases, both traumatic and neurodegenerative, are characterized by impaired mitochondrial bioenergetics and often disturbed mitochondrial dynamics. The dysregulation observed in these pathologies leads to defective respiratory chain function and reduced ATP production, thereby promoting neuronal death. As such, attenuation of mitochondrial dysfunction through induction of mitochondrial biogenesis (MB) is a promising, though still underexplored, therapeutic strategy. MB is a multifaceted process involving the integration of highly regulated transcriptional events, lipid membrane and protein synthesis/assembly and replication of mtDNA. Several nuclear transcription factors promote the expression of genes involved in oxidative phosphorylation, mitochondrial import and export systems, antioxidant defense and mitochondrial gene transcription. Of these, the nuclear-encoded peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is the most commonly studied and is widely accepted as the 'master regulator' of MB. Several recent preclinical studies document that reestablishment of mitochondrial homeostasis through increased MB results in inhibited injury progression and increased functional recovery. This perspective will briefly review the role of mitochondrial dysfunction in the propagation of CNS diseases, while also describing current research strategies that mediate mitochondrial dysfunction and compounds that induce MB for the treatment of acute and chronic neuropathologies.

Combination therapy with astaxanthin and epidermal neural crest stem cells improves motor impairments and activates mitochondrial biogenesis in a rat model of spinal cord injury

Spinal cord injury (SCI), a multifactorial disease, can lead to irreversible motor and sensory disabilities. Cell therapy in combination with pharmacological agents can be a promising approach to attenuate SCI damages. Epidermal neural crest stem cells (EPI-NCSCs) extracted from bulge hair follicle in adults are attractive candidates due to the possibility of autologous transplantation. This study evaluated the effect of EPI-NCSCs combined with astaxanthin (Ast), a potent antioxidant, on damages induced by SCI. Male rats were treated with Ast (0.2 mM) and EPI-NCSCs (10⁶/10 μl PBS) alone and combined together after SCI contusion. Motor function was assessed by Basso, Beattie and Bresnahan (BBB) test on days 1, 3, 7, 14, 21, 28, 35 and 42 post-injury. Motor neurons number and myelin level were evaluated on days 14 and 42 using Nissl and Luxol Fast Blue staining. The gene expression of mitochondrial biogenesis involved factors (PGC1α, NRF1 and TFAM) was measured by qPCR. All treatments improved motor function, with the highest BBB score in Ast + Cell compared to Ast and Cell. Decreased motor neurons number and myelin level following SCI, were increased by Ast, Cell and Ast + Cell, but combination therapy significantly had a better effect. We observed reduction in PGC1α, NRF1, and TFAM expression in spinal tissue after SCI, and treatment with Cell and Ast + Cell significantly restored NRF1 and TFAM mRNA levels. These results suggested that Ast in combination with EPI-NCSCs has better effects on behavioral dysfunction, motor neuron loss and demyelination after SCI. These protective effects may be attributed to mitochondrial biogenesis activation.

The Integrated Transcriptome Bioinformatics Analysis Identifies Key Genes and Cellular Components for Spinal Cord Injury-Related Neuropathic Pain

BACKGROUND

Spinal cord injury (SCI) is one of the most devastating diseases with a high incidence rate around the world. SCI-related neuropathic pain (NeP) is a common complication, whereas its pathomechanism is still unclear. The purpose of this study is to identify key genes and cellular components for SCI-related NeP by an integrated transcriptome bioinformatics analysis.

METHODS

The gene expression profile of 25 peripheral blood samples from chronic phase SCI patients (E-GEOD-69901) and 337 normal peripheral blood samples were downloaded from ArrayExpress and Genotype-Tissue Expression Portal (GTEx), respectively. A total of 3,368 normal peripheral blood mononuclear cells (PBMC) were download from Sequence Read Archive (SRA713577). Non-parametric tests were used to evaluate the association between all of differential expression genes (DEGs) and SCI-related NeP. CellPhoneDB algorithm was performed to identify the ligand-receptor interactions and their cellular localization among single PBMCs. Transcription factor (TF) enrichment analysis and Gene Set Variation Analysis (GSVA) were used to identify the potential upstream regulatory TFs and downstream signaling pathways, respectively. Co-expression analysis among significantly enriched TFs, key cellular communication genes and differentially expressed signaling pathways were performed to identify key genes and cellular components for SCI-related NeP.

RESULTS

A total of 2,314 genes were identified as DEGs between the experimental and the control group. Five proteins (ADRB2, LGALS9, PECAM1, HAVCR2, LRP1) were identified in the overlap of proteins in the significant ligand-receptor interactions of PBMCs and protein-protein interaction (PPI) network based on the DEGs. Only HAVCR2 was significantly associated with NeP (P = 0.005). Besides, the co-expression analysis revealed that TF YY1 had significantly co-expression pattern with cellular communication receptor HAVCR2 (R = -0.54, P < 0.001) in NK cells while HAVCR2 was also co-expressed with mTOR signaling pathway (R = 0.57, P < 0.001). The results of RT-qPCR and external dataset validation supported the signaling axis with the most significant co-expression patterns.

CONCLUSION

In peripheral blood of chronic SCI, HAVCR2 might act as a key receptor on the surface of NK cells and interact with ligand LGALS9 secreted by CD14+ monocytes, inhibiting NK cells through mTOR signaling pathway and ultimately predicting the occurrence of SCI-related NeP. This hypothetical signaling axis may provide prognostic biomarkers and therapeutic targets for SCI-related NeP.

5-hydroxytryptamine 1F Receptor Agonist Induces Mitochondrial Biogenesis and Promotes Recovery from Spinal Cord Injury

Spinal cord injury (SCI) is characterized by vascular disruption leading to ischemia, decreased oxygen delivery, and loss of mitochondrial homeostasis. This mitochondrial dysfunction results in loss of cellular functions, calcium overload, and oxidative stress. Pharmacological induction of mitochondrial biogenesis (MB) may be an effective approach to treat SCI. LY344864, a 5-hydroxytryptamine 1F (5-HT1F) receptor agonist, is a potent inducer of MB in multiple organ systems. To assess the efficacy of LY344864-induced MB on recovery post-SCI, female mice were subjected to moderate force-controlled impactor-induced contusion SCI followed by daily LY344864 administration for 21 days. Decreased mitochondrial DNA and protein content was present in the injury site 3 days post-SCI. LY344864 treatment beginning 1 h after injury attenuated these decreases, indicating MB. Additionally, injured mice treated with LY344864 displayed decreased Evan's Blue dye accumulation in the spinal cord compared with vehicle-treated mice 7 days after injury, suggesting restoration of vascular integrity. LY344864 also increased locomotor capability, with treated mice reaching a Basso-Mouse Scale score of 3.4 by 21 days, whereas vehicle-treated mice exhibited a score of 1.9. Importantly, knockout of the 5-HT1F receptor blocked LY344864-induced recovery. Remarkably, a similar degree of locomotor restoration was observed when treatment initiation was delayed until 8 h after injury. Furthermore, cross-sectional analysis of the spinal cord 21 days after injury revealed decreased lesion volume with delayed LY344864 treatment initiation, emphasizing the potential clinical applicability of this therapeutic approach. These data provide evidence that induction of MB via 5-HT1F receptor agonism may be a promising strategy for the treatment of SCI. SIGNIFICANCE STATEMENT: Treatment with LY344864 induces mitochondrial biogenesis in both the naive and injured mouse spinal cord. In addition, treatment with LY344864 beginning after impactor-induced contusion spinal cord injury improves mitochondrial homeostasis, blood-spinal cord barrier integrity, and locomotor function within 7 days. Importantly, similar locomotor results are observed whether treatment is initiated at 1 h after injury or 8 h after injury. These data indicate the potential for pharmacological induction of mitochondrial biogenesis through a 5-hydroxytryptamine 1F agonist as a novel therapeutic approach for spinal cord injury.

β2-adrenergic receptor-mediated mitochondrial biogenesis improves skeletal muscle recovery following spinal cord injury

In addition to local spinal cord dysfunction, spinal cord injury (SCI) can result in decreased skeletal muscle mitochondrial activity and muscle atrophy. Treatment with the FDA-approved β₂-adrenergic receptor (ADRB2) agonist formoterol has been shown to induce mitochondrial biogenesis (MB) in both the spinal cord and skeletal muscle and, therefore, has the potential to address comprehensive mitochondrial and organ dysfunction following SCI. Female C57BL/6 mice were subjected to moderate contusion SCI (80 Kdyn) followed by daily administration of vehicle or formoterol beginning 8 h after injury, a clinically relevant time-point characterized by a 50% decrease in mtDNA content in the injury site. As measured by the Basso Mouse Scale, formoterol treatment improved locomotor recovery in SCI mice compared to vehicle treatment by 7 DPI, with continued recovery observed through 21 DPI (3.5 v. 2). SCI resulted in 15% body weight loss in all mice by 3 DPI. Mice treated with formoterol returned to pre-surgery weight by 13 DPI, while no weight gain occurred in vehicle-treated SCI mice. Remarkably, formoterol-treated mice exhibited a 30% increase in skeletal muscle mass compared to those treated with vehicle 21 DPI (0.93 v. 0.72% BW), corresponding with increased MB and decreased skeletal muscle atrophy. These effects were not observed in ADRB2 knockout mice subjected to SCI, indicating that formoterol is acting via the ADRB2 receptor. Furthermore, knockout mice exhibited decreased basal spinal cord and skeletal muscle PGC-1α expression, suggesting that ADRB2 may play a role in mitochondrial homeostasis under physiological conditions. These data provide evidence for systemic ADRB2-mediated MB as a therapeutic avenue for the treatment of SCI.

Emerging molecular therapeutic targets for spinal cord injury

Introduction: Spinal cord injury (SCI) is a complicated and devastating neurological disorder. Patients with SCI usually have dramatically reduced quality of life. In recent years, numerous studies have reported advances in understanding the pathophysiology of SCI and developing preclinical therapeutic strategies for SCI, including various molecular therapies, and yet there is still no cure. Areas covered: After SCI, tissue damage, responses and repair involve interactions among many cellular components, including neurons, axons, glia, leukocytes, and other cells. Accordingly, numerous cellular genes and molecules have become therapeutic targets for neural tissue repair, circuit reconstruction, and behavioral restoration. Here, we review the major recent advances in biological and molecular strategies to enhance neuroprotection, axon regeneration, remyelination, neuroplasticity and functional recovery in preclinical studies of SCI. Expert opinion: Researchers have made tremendous progress in identifying individual and combined molecular therapies in animal studies. It is very important to identify additional highly effective treatments for early neuroprotective intervention and for functionally meaningful axon regeneration and neuronal reconnections. Because multiple mechanisms contribute to the functional loss after SCI, combining the most promising approaches that target different pathophysiological and molecular mechanisms should exhibit synergistic actions for maximal functional restoration. [Databases searched: PubMed; inclusive dates: 6/27/2019].