Upregulated Ras/Raf/ERK1/2 signaling pathway: a new hope in the repair of spinal cord injury

Effects of spinal cord injury associated exosomes delivered tRF-41 on the progression of spinal cord injury progression

BACKGROUND

Spinal cord injury (SCI) is a devastating neurological and pathological condition. Exosomal tsRNAs have reported to be promising biomarkers for cancer diagnosis and therapy. This study aimed to investigate the roles of SCI-associated exosomes, and related tsRNA mechanisms in SCI.

METHODS

The serum of healthy controls and SCI patients at the acute stage were collected for exosomes isolation, and the two different exosomes were used to treat human astrocytes (HA). The cell viability, apoptosis, and cycle were determined, and the expression of the related proteins were detected by western blot. Then, the two different exosomes were sent for tsRNA sequencing, and four significant known differentially expressed tsRNAs (DE-tsRNAs) were selected for RT-qPCR validation. Finally, tRT-41 was chosen to further explore its roles and related mechanisms in SCI.

RESULTS

After sequencing, 21 DE-tsRNAs were identified, which were significantly enriched in pathways of Apelin, AMPK, Hippo, MAPK, Ras, calcium, PI3K-Akt, and Rap1. RT-qPCR showed that tRF-41 had higher levels in the SCI-associated exosomes. Compared with the control HA, healthy exosomes did not significantly affect the growth of HA cells, but SCI-associated exosomes inhibited viability of HA cells, while promoted their apoptosis and increased the HA cells in G2/M phase; but tRF-41 inhibitor reversed the actions of SCI-associated exosomes. Additionally, SCI-associated exosomes, similar with tRF-41 mimics, down-regulated IGF-1, NGF, Wnt3a, and β-catenin, while up-regulated IL-1β and IL-6; but tRF-41 inhibitor had the opposite actions, and reversed the effects induced by SCI-associated exosomes.

CONCLUSIONS

SCI-associated exosomes delivered tRF-41 may inhibit the growth of HA through regulating Wnt/ β-catenin pathway and inflammation response, thereby facilitating the progression of SCI.

Transcriptomic Profiling after In Vitro Δ8-THC Exposure Shows Cytoskeletal Remodeling in Trauma-Injured NSC-34 Cell Line

Neuronal cell death is a physiological process that, when uncontrollable, leads to neurodegenerative disorders like spinal cord injury (SCI). SCI represents one of the major causes of trauma and disabilities worldwide for which no effective pharmacological intervention exists. Herein, we observed the beneficial effects of Δ8-Tetrahydrocannabinol (Δ8-THC) during neuronal cell death recovery. We cultured NSC-34 motoneuron cell line performing three different experiments. A traumatic scratch injury was caused in two experiments. One of the scratched was pretreated with Δ8-THC to observe the role of the cannabinoid following the trauma. An experimental control group was neither scratched nor pretreated. All the experiments underwent RNA-seq analysis. The effects of traumatic injury were observed in scratch against control comparison. Comparison of scratch models with or without pretreatment highlighted how Δ8-THC counteracts the traumatic event. Our results shown that Δ8-THC triggers the cytoskeletal remodeling probably due to the activation of the Janus Kinase Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathway and the signaling cascade operated by the Mitogen-Activated Protein (MAP) Kinase signaling pathway. In light of this evidence, Δ8-THC could be a valid pharmacological approach in the treatment of abnormal neuronal cell death occurring in motoneuron cells.

Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Axons in the peripheral nervous system have the ability to repair themselves after damage, whereas axons in the central nervous system are unable to do so. A common and important characteristic of damage to the spinal cord, brain, and peripheral nerves is the disruption of axonal regrowth. Interestingly, intrinsic growth factors play a significant role in the axonal regeneration of injured nerves. Various factors such as proteomic profile, microtubule stability, ribosomal location, and signalling pathways mark a line between the central and peripheral axons' capacity for self-renewal. Unfortunately, glial scar development, myelin-associated inhibitor molecules, lack of neurotrophic factors, and inflammatory reactions are among the factors that restrict axonal regeneration. Molecular pathways such as cAMP, MAPK, JAK/STAT, ATF3/CREB, BMP/SMAD, AKT/mTORC1/p70S6K, PI3K/AKT, GSK-3β/CLASP, BDNF/Trk, Ras/ERK, integrin/FAK, RhoA/ROCK/LIMK, and POSTN/integrin are activated after nerve injury and are considered significant players in axonal regeneration. In addition to the aforementioned pathways, growth factors, microRNAs, and astrocytes are also commendable participants in regeneration. In this review, we discuss the detailed mechanism of each pathway along with key players that can be potentially valuable targets to help achieve quick axonal healing. We also identify the prospective targets that could help close knowledge gaps in the molecular pathways underlying regeneration and shed light on the creation of more powerful strategies to encourage axonal regeneration after nervous system injury.

Electroacupuncture-Regulated miR-34a-3p/PDCD6 Axis Promotes Post-Spinal Cord Injury Recovery in Both In Vitro and In Vivo Settings

Electroacupuncture (EA) could enhance neuroregeneration and posttraumatic conditions; however, the underlying regulatory mechanisms remain ambiguous. PDCD6 (programmed cell death 6) is an established proapoptotic regulator which is responsible for motoneuronal death. However, its potential regulatory role in post-spinal cord injury (SCI) regeneration has remained largely unknown. Further investigations are warranted to clarify the involvement of PDCD6 post-SCI recovery and the underlying mechanisms. In our study, based on bioinformatics prediction, we found that miR-34a-3p might be an upstream regulator miRNA for PDCD6, which was subsequently validated through combined utilization of the qRT-PCR, western blot, and dual-luciferase reporter system. Our in vitro results showed that miR-34a-3p might promote the in vitro differentiation of neural stem cell (NSC) through suppressing PDCD6 and regulating other important neural markers such as fibroblast growth factor receptor 1 (FGFR1), MAP1/2 (MAP kinase kinases 1/2), myelin basic protein (MBP), βIII-tubulin Class III β-tubulin (βIII tubulin), and glial fibrillary acidic protein (GFAP). Notably, in the post-SCI rat model, exogenous miR-34a-3p agomir obviously inhibited the expression of PDCD6 at the protein level and promoted neuronal proliferation, motoneurons regeneration, and axonal myelination. The restorations at cellular level might contribute to the improved hindlimbs functions of post-SCI rats, which was manifested by the Basso-Beattie-Bresnahan (BBB) locomotor test. The impact of miR-34a-3p was further promoted by EA treatment in vivo. Conclusively, this paper argues that a miR-34a-3p/PDCD6 axis might be a candidate therapeutic target for treating SCI and that the therapeutic effect of EA is driven through this pathway.

Cellular Prion Protein Is Essential for Myocardial Regeneration but Not the Recovery of Left Ventricular Function from Apical Ballooning

This study tested the hypothesis that cellular prion protein (PrP^C) played an essential role in myocardial regeneration and recovery of left ventricular ejection fraction (LVEF) from apical takotsubo cardiomyopathy (TCM) induced by transaortic constriction (TAC). In vitro study was categorized into G1 (H9C2), G2 (H9C2-overexpression-PrP^C), G3 (H9C2-overexpression-PrP^C + Stelazine/1 uM), and G4 (H9C2 + siRNA-PrP^C), respectively. The results showed that the protein expressions of PrP^C, cell-stress signaling (p-PI3K/p-Akt/p-m-TOR) and signal transduction pathway for cell proliferation/division (RAS/c-RAF/p-MEK/p-ERK1/2) were lowest in G1, highest in G2, significantly higher in G3 than in G4 (all p < 0.001). Adult-male B6 mice (n = 30) were equally categorized in group 1 (sham-control), group 2 (TAC) for 14 days, then relieved the knot and administered BrdU (50 ug/kg/intravenously/q.6.h for two times from day-14 after TAC) and group 3 (TAC + Stelazine/20 mg/kg/day since day 7 after TAC up to day 21 + BrdU administered as group 2), and animals were euthanized at day 28. The results showed that by day 28, the LVEF was significantly higher in group 1 than in groups 2/3 and significantly higher in group 3 than in group 2, whereas the LV chamber size exhibited an opposite pattern of LVEF (all p < 0.0001). The protein expressions of PrP^C/p-PI3K/p-Akt/p-m-TOR/cyclin D/cyclin E and cellular-proliferation biomarkers (Ki67/PCNA/BrdU) exhibited an opposite pattern of LVEF (all p < 0.0001) among the three groups, whereas the protein expressions of RAS/c-RAF/p-MEK/p-ERK1/2 were significantly and progressively increased from groups 1 to 3 (all p < 0.0001). In conclusion, PrP^C participated in regulating the intrinsic response of cell-stress signaling and myocardial regeneration but did not offer significant benefit on recovery of the heart function in the setting of TCM.

Activation of Three Major Signaling Pathways After Endurance Training and Spinal Cord Injury

We aimed to investigate the effects of endurance training on expression of growth factors (GFs) and stimulation of neurotrophin-dependent signaling pathways (PI3k/Akt, PLCγ/PKC, PLCγ/CAMKII, Ras-Erk1/2 and Rac1-Cdc42) responsible for neuroplasticity, neuroregeneration, survival and growth after spinal cord injury (SCI). Wistar rats were divided into four groups: (i) intact controls; (ii) 6 weeks of endurance training; (iii) SCI; (iv) pre-training + SCI. The animals survived for 6 weeks after SCI. Firstly, endurance training markedly upregulated mRNA expression and protein levels (up to four times) of growth factors (BDNF, GDNF) and their receptors (TrkB, Gfrα) in low thoracic segments (Th8–Th10) compared to levels in untrained animals. Secondly, we found that spontaneous neuroplasticity seen in the SCI alone group was GF-specific and was activated through both PLCγ-PKC and PLC-CAMKII signaling pathways. In addition, training prior to SCI markedly increased the activity of PLCγ-PKC signaling at both transcript and protein levels at and around the lesion site. Similar effects were seen in expression of PI3k/Akt and Ras/Erk1/2 signaling responsible for cell survival and regeneration. Thirdly, rats which underwent physical activity prior to SCI were more active and had significantly better neurological scores at the 14th and 42nd days of survival. These results suggest that regular physical activity could play an important role after SCI, as it maintains increased expression of GFs in spinal cord tissue 6 weeks post-SCI. The BDNF- and/or BDNF + GDNF-dependent signaling pathways were significantly affected in pre-trained SCI animals. In contrast, GDNF-dependent Rac1-Cdc42 signaling was not involved in training-affected SCI response.

Bazedoxifene, a Selective Estrogen Receptor Modulator, Promotes Functional Recovery in a Spinal Cord Injury Rat Model

In research on various central nervous system injuries, bazedoxifene acetate (BZA) has shown two main effects: neuroprotection by suppressing the inflammatory response and remyelination by enhancing oligodendrocyte precursor cell differentiation and oligodendrocyte proliferation. We examined the effects of BZA in a rat spinal cord injury (SCI) model. Anti-inflammatory and anti-apoptotic effects were investigated in RAW 264.7 cells, and blood-spinal cord barrier (BSCB) permeability and angiogenesis were evaluated in a human brain endothelial cell line (hCMEC/D3). In vivo experiments were carried out on female Sprague Dawley rats subjected to moderate static compression SCI. The rats were intraperitoneally injected with either vehicle or BZA (1mg/kg pre-SCI and 3 mg/kg for 7 days post-SCI) daily. BZA decreased the lipopolysaccharide-induced production of proinflammatory cytokines and nitric oxide in RAW 264.7 cells and preserved BSCB disruption in hCMEC/D3 cells. In the rats, BZA reduced caspase-3 activity at 1 day post-injury (dpi) and suppressed phosphorylation of MAPK (p38 and ERK) at dpi 2, hence reducing the expression of IL-6, a proinflammatory cytokine. BZA also led to remyelination at dpi 20. BZA contributed to improvements in locomotor recovery after compressive SCI. This evidence suggests that BZA may have therapeutic potential to promote neuroprotection, remyelination, and functional outcomes following SCI.

Effects of combination treatment with transcranial magnetic stimulation and bone marrow mesenchymal stem cell transplantation or Raf inhibition on spinal cord injury in rats

Spinal cord injury (SCI) remains a global challenge due to limited treatment strategies. Transcranial magnetic stimulation (TMS), bone marrow mesenchymal stem cell (BMSC) transplantation and downregulation of Raf/MEK/ERK signaling effectively improve SCI. The combination of BMSCs and TMS displays synergistic effects on vascular dementia. However, whether TMS displays a synergistic effect when combined with BMSC transplantation or Raf inhibitor (RafI) therapy for the treatment of SCI is not completely understood. The present study aimed to compare the therapeutic effect of monotherapy and combination therapy on SCI. In the present study, 8‑week‑old female Sprague Dawley rats were used to establish a model of SCI using the weight‑drop method followed by treatment with monotherapy (TMS, BMSCs or RafI) or combination therapy (TMS+BMSCs or TMS+RafI). The effect of monotherapy and combination therapy on locomotor function, pathological alterations, neuronal apoptosis and expression of axonal regeneration‑associated factors and Raf/MEK/ERK signaling‑associated proteins in the spinal cord was analyzed by Basso, Beattie and Bresnahan (BBB) scoring, hematoxylin and eosin staining, TUNEL‑neuronal nuclei (NeuN) staining and immunofluorescence or western blotting, respectively. The results demonstrated that compared with untreated SCI model rats, monotherapy significantly enhanced locomotor functional recovery, as evidenced by higher BBB scores, and slightly alleviated histopathological lesions of the spinal cord in SCI model rats. Furthermore, monotherapy markedly suppressed neuronal apoptosis and promoted axonal regeneration, as well as inhibiting astroglial activation in SCI model rats. The aforementioned results were demonstrated by significantly decreased numbers of apoptotic neurons, markedly decreased expression levels of glial fibrillary acidic protein (GFAP), significantly increased numbers of NeuN+ cells, markedly increased expression levels of growth‑associated protein 43 (GAP‑43) and significantly upregulated nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) expression levels in monotherapy groups (excluding the RafI monotherapy group) compared with untreated SCI model rats. In addition, monotherapy markedly suppressed activation of the Raf/MEK/ERK signaling pathway, as evidenced by significantly reduced p‑Raf/Raf, p‑MEK/MEK and p‑ERK/ERK protein expression levels in monotherapy groups (excluding the BMSC monotherapy group) compared with untreated SCI model rats. Notably, combination therapy further alleviated SCI‑induced spinal cord lesions and neuronal apoptosis, increased GAP‑43, NGF and BDNF expression levels, downregulated GFAP expression levels and inhibited activation of the Raf/MEK/ERK signaling pathway in SCI model rats compared with the corresponding monotherapy groups. Therefore, it was hypothesized that compared with monotherapy, combination therapy displayed an improved therapeutic effect on SCI by further suppressing Raf/MEK/ERK signaling. The results of the present study provided an important basis for the clinical application of combination therapy.

Genetic Deletion of Polo-Like Kinase 2 Induces a Pro-Fibrotic Pulmonary Phenotype

Pulmonary fibrosis is the chronic-progressive replacement of healthy lung tissue by extracellular matrix, leading to the destruction of the alveolar architecture and ultimately death. Due to limited pathophysiological knowledge, causal therapies are still missing and consequently the prognosis is poor. Thus, there is an urgent clinical need for models to derive effective therapies. Polo-like kinase 2 (PLK2) is an emerging regulator of fibroblast function and fibrosis. We found a significant downregulation of PLK2 in four different entities of human pulmonary fibrosis. Therefore, we characterized the pulmonary phenotype of PLK2 knockout (KO) mice. Isolated pulmonary PLK2 KO fibroblasts displayed a pronounced myofibroblast phenotype reflected by increased expression of αSMA, reduced proliferation rates and enhanced ERK1/2 and SMAD2/3 phosphorylation. In PLK2 KO, the expression of the fibrotic cytokines osteopontin and IL18 was elevated compared to controls. Histological analysis of PLK2 KO lungs revealed early stage remodeling in terms of alveolar wall thickening, increased alveolar collagen deposition and myofibroblast foci. Our results prompt further investigation of PLK2 function in pulmonary fibrosis and suggest that the PLK2 KO model displays a genetic predisposition towards pulmonary fibrosis, which could be leveraged in future research on this topic.

Harnessing the Secretome of Mesenchymal Stromal Cells for Traumatic Spinal Cord Injury: Multicell Comparison and Assessment of In Vivo Efficacy

Cell therapy offers significant promise for traumatic spinal cord injury (SCI), which despite many medical advances, has limited treatment strategies. Able to address the multifactorial and dynamic pathophysiology of SCI, cells present various advantages over standard pharmacological approaches. However, the use of live cells is also severely hampered by logistical and practical considerations. These include specialized equipment and expertise, standardization of cell stocks, sustained cell viability post-thawing, and cryopreservation-induced delayed-onset cell death. For this reason, we suggest a novel and clinically translatable alternative to live-cell systemic infusion, which retains the efficacy of the latter while overcoming many of its limitations. This strategy involves the administration of concentrated cell secretome and exploits the trophic mechanism by which stromal cells function. In this study, we compare the efficacy of intravenously delivered concentrated conditioned media (CM) from human umbilical cord matrix cells (HUCMCs), bone marrow mesenchymal stromal cells, as well as newborn and adult fibroblasts in a rat model of moderately severe cervical clip compression/contusion injury (C7--T1, 35 g). This is further paired with a thorough profile of the CM cytokines, chemokines, and angiogenic factors. The HUCMC-derived CM was most effective at limiting acute (48 h post-SCI) vascular pathology, specifically lesion volume, and functional vascularity. Principle component analysis (PCA), hierarchical clustering, and interaction analysis of proteins highly expressed in the HUCMC secretome suggest involvement of the MAPK/ERK, JAK/STAT, and immune cell migratory pathways. This "secretotherapeutic" strategy represents a novel and minimally invasive method to target multiple organ systems and several pathologies shortly after traumatic SCI.

Repair mechanism of astrocytes and non-astrocytes in spinal cord injury

BACKGROUND

Spinal cord injury (SCI) is a destructive disease that incurs huge personal and social costs, and there is no effective treatment. Although the pathogenesis and treatment mechanism of SCI has always been a strong scientific focus, the pathogenesis of SCI is still under investigation.

AIM

To determine the key genes based on the modularization of in-depth analysis, in order to identify the repair mechanism of astrocytes and non-astrocytes in SCI.

METHODS

Firstly, the differences between injured and non-injured spinal cord of astrocyte (HA), injured and non-injured spinal cord of non-astrocyte (FLOW), injured spinal cord of non-injured astrocyte (HA) and non-injured spinal cord of non-astrocyte (FLOW), and non-injured spinal cord of astrocyte (HA) and non-astrocyte (FLOW) were analyzed. The total number of differentially expressed genes was obtained by merging the four groups of differential results. Secondly, the genes were co-expressed and clustered. Then, the enrichment of GO function and KEGG pathway of module genes was analyzed. Finally, non-coding RNA, transcription factors and drugs that regulate module genes were predicted using hypergeometric tests.

RESULTS

In summary, we obtained 19 expression modules involving 5216 differentially expressed genes. Among them, miR-494, XIST and other genes were differentially expressed in SCI patients, and played an active regulatory role in dysfunction module, and these genes were recognized as the driving genes of SCI. Enrichment results showed that module genes were significantly involved in the biological processes of inflammation, oxidation and apoptosis. Signal pathways such as NF-kappa B/A20, AMPK and MAPK were significantly regulated. In addition, non-coding RNA pivot (including miR-136-5p and let-7d-5p, etc.) and transcription factor pivot (including NFKB1, MYC, etc.) were identified as significant regulatory dysfunction modules.

CONCLUSION

Overall, this study uncovered a co-expression network of key genes involved in astrocyte and non-astrocyte regulation in SCI. These findings helped to reveal the core dysfunction modules, potential regulatory factors and driving genes of the disease, and to improve our understanding of its pathogenesis.

Inhibition of the Ras/Raf/extracellular signal-regulated kinase 1/2 signaling pathway by compounds of natural origin for possible treatment of spinal cord injury: An in silico approach

Spinal cord injury (SCI) is a severe disease associated with permanent neurological deficit. Recent studies in the treatment of SCI have demonstrated that the Ras/Raf/extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway serves an important role in the disease etiology, and that upregulation of this signaling pathway is associated with the development of SCI. In the present study, inhibition of Ras protein was employed in order to downregulate the Ras/Raf/ERK1/2 signaling pathway using compounds of natural origin from the Interbioscreen natural compound database. To the best of our knowledge, this is the first study using a chemical-computational approach in order to identify novel small molecule inhibitors for Ras. A database of ~50,000 compounds was selected for virtual screening, setting a free energy binding bias of −7 kcal/mol to limit the number of compounds. The subset of compounds generated by virtual screening was further limited by subjecting these to the Lipinski's rule of five parameters. A total of five shortlisted compounds were subjected to molecular docking simulation. The compounds were docked into the GTP binding site of Ras, and the inhibition of this site was examined as a promising strategy for the downregulation of Ras/Raf/ERK1/2 signaling pathway. The compounds bound to the GTP binding site through hydrogen bonds and hydrophobic interactions. The identified lead compound was then subjected to molecular dynamics simulation, and the results revealed that GLY60 in the GTP binding site of Ras protein was the optimal binding site during a 100 nsec run.

Effect of electrical stimulation on neural regeneration via the p38-RhoA and ERK1/2-Bcl-2 pathways in spinal cord-injured rats

Although electrical stimulation is therapeutically applied for neural regeneration in patients, it remains unclear how electrical stimulation exerts its effects at the molecular level on spinal cord injury (SCI). To identify the signaling pathway involved in electrical stimulation improving the function of injured spinal cord, 21 female Sprague-Dawley rats were randomly assigned to three groups: control (no surgical intervention, n = 6), SCI (SCI only, n = 5), and electrical simulation (ES; SCI induction followed by ES treatment, n = 10). A complete spinal cord transection was performed at the 10^th thoracic level. Electrical stimulation of the injured spinal cord region was applied for 4 hours per day for 7 days. On days 2 and 7 post SCI, the Touch-Test Sensory Evaluators and the Basso-Beattie-Bresnahan locomotor scale were used to evaluate rat sensory and motor function. Somatosensory-evoked potentials of the tibial nerve of a hind paw of the rat were measured to evaluate the electrophysiological function of injured spinal cord. Western blot analysis was performed to measure p38-RhoA and ERK1/2-Bcl-2 pathways related protein levels in the injured spinal cord. Rat sensory and motor functions were similar between SCI and ES groups. Compared with the SCI group, in the ES group, the latencies of the somatosensory-evoked potential of the tibial nerve of rats were significantly shortened, the amplitudes were significantly increased, RhoA protein level was significantly decreased, protein gene product 9.5 expression, ERK1/2, p38, and Bcl-2 protein levels in the spinal cord were significantly increased. These data suggest that ES can promote the recovery of electrophysiological function of the injured spinal cord through regulating p38-RhoA and ERK1/2-Bcl-2 pathway-related protein levels in the injured spinal cord.

Intrathecally Transplanting Mesenchymal Stem Cells (MSCs) Activates ERK1/2 in Spinal Cords of Ischemia-Reperfusion Injury Rats and Improves Nerve Function

Background

We investigated whether an intrathecal transplantation of mesenchymal stem cells (MSCs) activates extracellular adjusting protein kinase1 and 2(ERK1/2) in the spinal cords of rats following an ischemia-reperfusion injury, resulting in improved spinal cord function and inhibition of apoptosis.

Material/Methods

We observed the relationship between the activation of ERK1/2 in the rat spinal cord and intrathecal transplantation of MSCs, as well as the effect of U0126, a MEK1/2 (upstream protein of ERK1/2) inhibitor, on a spinal cord ischemia-reperfusion injury model in rats using Basso Beattie Bresnahan (BBB) scoring, somatosensory evoked potentials (SSEPs), immunohistochemistry, and Western blot analysis.

Results

After transplantation of MSCs, the lower limb motor function score increased, and the incubation period of SSEPs and amplitude were improved. Moreover, following transplantation of MSCs, Bcl2 expression increased, whereas Bax expression decreased after reperfusion. Transplantation of MSCs significantly enhanced pERK1/2 expression in the spinal cord, as well as pERK1/2 in immunoreactive cells located in the grey matter of the L4/5 levels of the spinal cord, following ischemia reperfusion injury in rats. The effective dose of U0126 required to inhibit pERK1/2 expression was 200 μg/kg. Bcl-2 decreased and the level of Bax expression increased in the spinal cord after ischemia reperfusion injury, and the protective effects of MSCs were attenuated.

Conclusions

Our findings suggest that intrathecal transplantation of MSCs activates ERK1/2 in the spinal cord following ischemia reperfusion injury, partially improves spinal cord function, and inhibits apoptosis in rats.