Cellular expression profile of RhoA in rats with spinal cord injury

Recent advances on signaling pathways and their inhibitors in spinal cord injury

Spinal cord injury (SCI) is a serious and disabling central nervous system injury. Its complex pathological mechanism can lead to sensory and motor dysfunction. It has been reported that signaling pathway plays a key role in the pathological process and neuronal recovery mechanism of SCI. Such as PI3K/Akt, MAPK, NF-κB, and Wnt/β-catenin signaling pathways. According to reports, various stimuli and cytokines activate these signaling pathways related to SCI pathology, thereby participating in the regulation of pathological processes such as inflammation response, cell apoptosis, oxidative stress, and glial scar formation after injury. Activation or inhibition of relevant pathways can delay inflammatory response, reduce neuronal apoptosis, prevent glial scar formation, improve the microenvironment after SCI, and promote neural function recovery. Based on the role of signaling pathways in SCI, they may be potential targets for the treatment of SCI. Therefore, understanding the signaling pathway and its inhibitors may be beneficial to the development of SCI therapeutic targets and new drugs. This paper mainly summarizes the pathophysiological process of SCI, the signaling pathways involved in SCI pathogenesis, and the potential role of specific inhibitors/activators in its treatment. In addition, this review also discusses the deficiencies and defects of signaling pathways in SCI research. It is hoped that this study can provide reference for future research on signaling pathways in the pathogenesis of SCI and provide theoretical basis for SCI biotherapy.

Chondroitin 6-sulfate-binding peptides improve recovery in spinal cord-injured mice

The role of glycosaminoglycan sulfation patterns, particularly in regard to scar formation and inhibition of neuritogenesis, has been mainly studied in cell culture with a focus on chondroitin 4-sulfate. In this study, we investigated chondroitin 6-sulfate (C6S) and found that it also inhibits neurite outgrowth of mouse cerebellar granule neurons in vitro. To examine whether the inhibitory activity of C6S could be neutralized, seven previously characterized high-affinity C6S-binding peptides were tested, among which three peptides neutralized the inhibitory functions of C6S. We further investigated these peptides in a mouse model of spinal cord injury, since upregulation of C6S expression in the glial scar following injury has been associated with reduced axonal regrowth and functional recovery. We here subjected mice to severe compression injury at thoracic levels T7-T9, immediately followed by inserting gelfoam patches soaked in C6S-binding peptides or in a control peptide. Application of C6S-binding peptides led to functional recovery after injury and prevented fibrotic glial scar formation, as seen by decreased activation of astrocytes and microglia/macrophages. Decreased expression of several lecticans and deposition of fibronectin at the site of injury were also observed. Application of C6S-binding peptides led to axonal regrowth and inhibited the C6S-mediated activation of RhoA/ROCK and decrease of PI3K-Akt-mTOR signaling pathways. Taken together, these results indicate that treatment with C6S-binding peptides improves functional recovery in a mouse model of spinal cord injury.

Rho/ROCK Pathway and Noncoding RNAs: Implications in Ischemic Stroke and Spinal Cord Injury

Ischemic strokes (IS) and spinal cord injuries (SCI) are major causes of disability. RhoA is a small GTPase protein that activates a downstream effector, ROCK. The up-regulation of the RhoA/ROCK pathway contributes to neuronal apoptosis, neuroinflammation, blood-brain barrier dysfunction, astrogliosis, and axon growth inhibition in IS and SCI. Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), were previously considered to be non-functional. However, they have attracted much attention because they play an essential role in regulating gene expression in physiological and pathological conditions. There is growing evidence that ROCK inhibitors, such as fasudil and VX-210, can reduce injury in IS and SCI in animal models and clinical trials. Recently, it has been reported that miRNAs are decreased in IS and SCI, while lncRNAs are increased. Inhibiting the Rho/ROCK pathway with miRNAs alleviates apoptosis, neuroinflammation, oxidative stress, and axon growth inhibition in IS and SCI. Further studies are required to explore the significance of ncRNAs in IS and SCI and to establish new strategies for preventing and treating these devastating diseases.

Disrupting RhoA activity by blocking Arhgef3 expression mitigates microglia-induced neuroinflammation post spinal cord contusion

Excess inflammatory microglia activation deteriorates the pathological degree of spinal cord injury (SCI). We here employed microglia samples in vitro and murine model in vivo to trace the role of inhibition of Arhgef3 in inflammatory response post SCI. From the specimen analysis of lipopolysaccharide (LPS)-induced inflammatory microglia, we found that Arhgef3 expression was positively relative to microglia activation. In vitro, LPS caused the microglia inflammatory activation and induced upregulation of the Arhgef3 expression. Interestingly, presence of Arhgef3 could activate RhoA through promoting Rho GTPases, but silencing of Arhgef3 decreased RhoA activation and inhibited the microglia inflammation. Moreover, disruption of Arhgef3 inhibited the GTP-RhoA, resulted in a suppression of proinflammatory cytokines, and alleviated the LPS-elicited inflammatory genes expression. Moreover, artificially decreasing Arhgef3 expression remarkedly reduced ROS generation after LPS treatment. In vivo of a mouse mechanical contusion-induced SCI model, inhibition of Arhgef3 reduced the ratio of GTP-RhoA/Total-RhoA, and prevented SCI via mitigating the microglial inflammatory phenotype and decreased secondary neurological injury. Besides, inhibition of Arhgef3 prevented alleviated the degree of demyelination but did not affect neuronal regeneration. Meaningfully, absence of Arhgef3 improved mouse locomotor recovery post SCI. Taken together, Arhgef3 involves the microglial activation and inflammatory response following neural injury, and targeted disrupting of which may indicate a promising therapeutic direction in preventing SCI.

A rationally designed self-immolative linker enhances the synergism between a polymer-rock inhibitor conjugate and neural progenitor cells in the treatment of spinal cord injury

Rho/ROCK signaling induced after spinal cord injury (SCI) contributes to secondary damage by promoting apoptosis, inflammation, and axon growth inhibition. The specific Rho-kinase inhibitor fasudil can contribute to functional regeneration after SCI, although inherent low stability has hampered its use. To improve the therapeutic potential of fasudil, we now describe a family of rationally-designed bioresponsive polymer-fasudil conjugates based on an understanding of the conditions after SCI, such as low pH, enhanced expression of specific proteases, and a reductive environment. Fasudil conjugated to poly-l-glutamate via a self-immolative redox-sensitive linker (PGA-SS-F) displays optimal release kinetics and, consequently, treatment with PGA-SS-F significantly induces neurite elongation and axon growth in dorsal root ganglia explants, spinal cord organotypic cultures, and neural precursor cells (NPCs). The intrathecal administration of PGA-SS-F after SCI in a rat model prevents early apoptosis and induces the expression of axonal growth- and neuroplasticity-associated markers to a higher extent than the free form of fasudil. Moreover, a combination treatment comprising the acute transplantation of NPCs pre-treated with PGA-SS-F leads to enhanced cell engraftment and reduced cyst formation after SCI. In chronic SCI, combinatory treatment increases the preservation of neuronal fibers. Overall, this synergistic combinatorial strategy may represent a potentially efficient clinical approach to SCI treatment.

Role of Rho-associated coiled-coil containing protein kinase in the spinal cord injury induced neuropathic pain

BACKGROUND CONTEXT

Spinal cord injury (SCI) can lead to increased phosphorylation of p38 in spinal cord microglia. This is one of the main causes for the development of persistent pain. Recently, we reported our study on the activation of p38 mitogen-activated protein kinases (MAPK) in spinal microglia, which has been considered the key molecule for the onset and maintenance of neuropathic pain after peripheral nerve injury, using a rat model. We also reported that the RhoA/Rho-associated coiled-coil containing protein kinase (ROCK) pathway mediates p38 activation in spinal microglia in peripheral nerve injury. But the precise mechanisms of neuropathic pain induced by SCI are still unclear.

PURPOSE

This study aimed to examine the activation of microglia and the p38 MAPK expression in the lumbar spinal cord after thoracic SCI in rats, and the correlation to the therapeutic effect of ROCK inhibitor ripasudil in rats with SCI.

STUDY DESIGN

Male Sprague-Dawley rats underwent thoracic (T10) spinal cord contusion injury using an Infinite Horizon impactor device. SCI rats received ROCK inhibitor ripasudil (24 nmol/day or 240 nmol/day) from just before SCI to 3 days after SCI.

METHODS

The mechanical threshold in the rat's hind paws was measured over four weeks. Morphology of microglia and phosphorylation of p38 (p-p38) in the lumbar spinal cord and were analyzed using immunohistochemistry.

RESULTS

The p-p38 positive cell and Iba1 (a maker of microglia) positive area were significantly increased at the lumbar spinal dorsal horn (L4-5) 3 days and 7 days after SCI compared with the sham-control (p<.05), whereas phosphorylated p38 was co-localized with microglia. Three days after SCI, the intensity of phosphorylated p38 and Iba1 immunoreactive cells in the dorsal horn was significantly lower in the ripasudil treated groups than in the saline group. However, administration of ROCK inhibitor did not affect the numbers of microglia. Moreover, the withdrawal threshold of the ripasudil-treated rats was significantly higher than that of the saline-injected rats on 14 days and 28 days after SCI.

CONCLUSIONS

Our results suggest that activation of ROCK in spinal cord microglia is likely to have an important role in the activation of p38 MAPK, which has been considered as a key molecule that switches on neuropathic pain after SCI. Inhibition of ROCK signaling may offer a means in developing a novel neuropathic pain treatment after SCI. It may help patients with neuropathic pain after SCI.

CLINICAL SIGNIFICANCE

The findings in the present study regarding intracellular mechanisms suggest that modulation of ROCK signaling may be a focus for novel treatment for neuropathic pain after SCI.

An aligned nanofiber nerve conduit that inhibits painful traumatic neuroma formation through regulation of the RhoA/ROCK signaling pathway

OBJECTIVE

Traumatic neuromas represent a prevalent source of neuropathic pain. As of yet, there has been no single treatment method that can guarantee permanent relief of symptoms. Although nerve-capping techniques have shown promise, their exact mechanisms remain elusive. The authors' aim was to examine the role of the RhoA/ROCK signaling pathway in the prevention of neuroma formation after neurectomy utilizing a nerve-capping technique.

METHODS

An aligned nanofiber tube was fabricated to cap the sciatic nerve in Sprague Dawley rats. The rats (n = 60) were randomly divided into the aligned SF/P (LLA-CL) capping group (capping group, n = 20), the capping and Y-27632 (ROCK pathway inhibitor) intervention group (intervention group, n = 20), and the no-capping group (control group, n = 20). The authors undertook a comprehensive assessment of the capping group, examining the animals' behavior, the extent of neuroma development, histology, gene and protein expression, and ultrastructural changes associated with the RhoA/ROCK signaling pathway. These findings were compared with those in the intervention and control groups.

RESULTS

The inciting injury resulted in the expression of the RhoA/ROCK signaling pathway, as well as its further upregulation in peripheral neurons. Axon outgrowth was significantly increased when RhoA/ROCK signaling pathway was suppressed. The average autotomy score in the capping group was observed to be much lower than that of the intervention and control groups. At 30 days postneurectomy, the capping group displayed no obvious neuroma formation, while a bulbous neuroma was found in the nerve stumps of both the control and intervention groups. Quantitative real-time polymerase chain reaction and the Western blot analysis demonstrated that the expression of myelin-associated glycoprotein was substantially upregulated in the capping group; in contrast, the expression of NF-200 was significantly downregulated. The expression of myosin light chain was notably lower in the intervention group, but there was no significant difference when compared with the control group (p > 0.05).

CONCLUSIONS

The RhoA/ROCK signaling pathway has emerged as a critical player in the process of traumatic neuroma formation after neurectomy. It is possible that the nerve-capping technique could generate a "regenerative brake" based on the regulation of the RhoA/ROCK signaling pathway in this event. These findings may provide concrete evidence that could help develop new strategies for the management of painful neuromas.

Inhibition of Notch1 signaling promotes neuronal differentiation and improves functional recovery in spinal cord injury through suppressing the activation of Ras homolog family member A

Neural stem cells (NSCs) transplantation represents a promising strategy for the repair of injured neurons, since NSCs not only produce multiple neurotrophic growth factors but also differentiate into mature cells to replace damaged cells. Previous studies have shown that Notch signaling pathway had negative effects on neuronal differentiation; however, the precise mechanism remained inadequately understood. This research aimed to investigate whether inhibition of Notch1 signaling promotes neuronal differentiation and improves functional recovery in rat spinal cord injury through suppressing the activation of Ras homolog family member A (RhoA). QPCR, western blot, and immunofluorescence experiments were used to analyze Notch1 signaling pathways, RhoA, Ras homologous -associated coiled-coil containing protein kinase 1 (ROCK1), cleaved caspased-3, and neuronal/astrocytic differentiation markers. The expression of RhoA and ROCK1 was inhibited by lentivirus or specific biochemical inhibitors. In spinal cord injury (SCI), motor function was assessed by hind limbs movements and electrophysiology. Tissue repairing was measured by immunofluorescence, Nissl staining, Fluorogold, HE staining, QPCR, western blot, and magnetic resonance imaging (MRI) experiments. Our results demonstrate that inhibition of Notch1 in NSCs can promote the differentiation of NSCs to neurons. Knockdown of RhoA and inhibition of ROCK1 both can promote neuronal differentiation through inhibiting the activation of Notch1 signaling pathway in NSCs. In SCI, silencing RhoA enhanced neuronal differentiation and improved tissue repairing/functional recovery by inhibiting the activation of Notch1 signaling pathway. Since Notch1 inhibits neuronal differentiation through activating the RhoA/ROCK1 signaling pathway in NSCs, our data suggest that the Notch1/RhoA/ROCK1/Hes1/Hes5 signaling pathway may serve as a novel target for the treatment of SCI.

Stereotactic injection of shrna GSK-3β-AAV promotes axonal regeneration after spinal cord injury

Evidence suggested that glycogen synthase kinase-3β (GSK-3β) is involved in Nogo-66 inhibiting axonal regeneration in vitro, but its effect in vivo was poorly understood. We showed that stereotactic injection of shRNA GSK-3β-adeno associated virus (GSK-3β-AAV) diminished syringomyelia and promoted axonal regeneration after spinal cord injury (SCI), using stereotactic injection of shRNA GSK-3β-AAV (tested with Western blotting and RT-PCR) into the sensorimotor cortex of rats with SCI and by the detection of biotin dextran amine (BDA)-labeled axonal regeneration. We also determined the right position to inject into the sensorimotor cortex. Our findings consolidate the hypothesis that downregulation of GSK-3β promotes axonal regeneration after SCI.

RhoA/Rho kinase in spinal cord injury

A spinal cord injury refers to an injury to the spinal cord that is caused by a trauma instead of diseases. Spinal cord injury includes a primary mechanical injury and a much more complex secondary injury process involving inflammation, oxidation, excitotoxicity, and cell death. During the secondary injury, many signal pathways are activated and play important roles in mediating the pathogenesis of spinal cord injury. Among them, the RhoA/Rho kinase pathway plays a particular role in mediating spinal degeneration and regeneration. In this review, we will discuss the role and mechanism of RhoA/Rho kinase-mediated spinal cord pathogenesis, as well as the potential of targeting RhoA/Rho kinase as a strategy for promoting both neuroprotection and axonal regeneration.