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

COX2 expression plays a role in spinal cord injury-induced neuropathic pain

BACKGROUND CONTEXT

Elucidating the mechanism of neuropathic pain (NeP) is crucial as it can result in motor dysfunction and negatively impact quality of life in patients with spinal cord injury (SCI). Although it has been reported that cyclooxygenase 2 (COX2) is involved in NeP in rat models of peripheral nerve injury and that COX2 inhibitors can alleviate NeP, these mechanisms after SCI have not been fully investigated.

PURPOSE

The purpose is to investigate whether the thoracic SCI affects the expression of mRNAs for COX1 and COX2 in the lumbar spinal cord, and the effect of COX2 inhibitor on its behavior.

STUDY DESIGN

Male Sprague-Dawley (SD) rats underwent thoracic (T10) spinal cord contusion injury using an Infinite Horizon (IH) impactor device. SCI rats received COX2 inhibitors (50 μg/day) on days 5 and 6 after SCI.

METHODS

Male SD rats underwent T10 laminectomy under mixed anesthesia, and IH impactors were applied to the same site to create a rat SCI model. Rats that underwent only laminectomy were designated as sham. Lumbar spinal cord at the L4-5 level was harvested at 3, 5, 7, 14, and 28 days after SCI, and COX2 and COX1 were quantified by reverse-transcription PCR (RT-PCR). COX2 expression, expression site, and expression time were determined by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISHH) at the same time points. The expression site and time of COX2 expression were also examined at the same time point by ISHH. On 5th and 6th day after SCI, saline and COX2 inhibitor (50 μg/day) were administered into the subarachnoid space as a single dose, and the two groups were compared in terms of mechanical withdrawal latency using the dynamic plantar esthesiometer, which is an automated von Frey-type system.

RESULTS

COX2 was significantly increased at 5 and 7 days after SCI, but no significant difference in COX1 was observed after SCI by RT-PCR. ISHH targeting COX2 showed clear expression of COX2 in spinal cord vascular endothelial cells at 5 and 7 days after SCI. COX2 expression was almost abolished at day 14 and 28. Behavioral experiments showed that pain was significantly improved from day 2 after COX2 inhibitor administration compared to the saline group, with improvement up to day 14 after SCI, but no significant difference was observed after day 21.

CONCLUSIONS

The present findings suggest that thoracic SCI increased COX2 in vascular endothelial cells in the lumbar spinal cord and that the administration of COX2 inhibitor significantly alleviated mechanical hypersensitivity of the hind-paw following the thoracic SCI. Therefore, endothelial cell derived COX2 in the lumbar spinal cord may be involved in the induction of neuropathic pain in the SCI model rats.

CLINICAL SIGNIFICANCE

The findings in the present study regarding the induction of endothelial COX2 and the effect of its inhibitor on the mechanical hypersensitivity suggest that endothelial cell-derived COX2 is one of the focuses for the treatment for neuropathic pain in the acute phase of SCI.

Inhibition of RhoA/ROCK signalling pathway activity improves neural damage and cognitive deficits in the fluorosis model

Excessive fluoride intake poses health risks to humans and animals. Many studies have indicated that fluoride exposure can damage the cytoskeleton and synapses, which has negative effects on the intellectual development of humans and animals. Our previous study suggested that the RhoA/ROCK signalling pathway is activated by NaF exposure in HT-22 cells and plays a vital role in cytoskeletal assembly and synaptogenesis. However, the mechanism underlying RhoA/ROCK-mediated cytoskeletal injury induced by fluoride remains unclear. In this study, Neuro-2A cells and ICR mice were used to investigate the effects of RhoA/ROCK activation inhibition on NaF-induced synaptic dysfunction and cognitive impairment. We detected the expression of GAP, RhoA, ROCK1/2, and (p)-MLC in vivo and in vitro model. The results showed that NaF exposure activated the RhoA/ROCK/MLC signalling pathway. We measured the effects of RhoA/ROCK inhibition on synaptic injury and intellectual impairment induced by NaF exposure. In vitro, Y-27632 suppressed activated RhoA/ROCK, attenuated morphological and ultrastructural damage, and decreased the survival rate and synapse-functional protein expression caused by NaF. In vivo, the results showed that the RhoA/ROCK/MLC pathway was inhibited by fasudil and improved pathological damage in the hippocampus, cognitive impairment, and decreased expression of neurofunctional proteins induced by NaF. Overall, these results suggest that fasudil and Y-27632 can reverse neurotoxicity caused by fluoride exposure. Furthermore, inhibition of RhoA/ROCK may be a future treatment for CNS injury, and more detailed studies on other neurodegenerative disease models are required to confirm its effectiveness.

Fasudil, a ROCK inhibitor, prevents neuropathic pain in Minamata disease model rats

Methylmercury (MeHg), an environmental toxicant, is known to cause sensory impairment by inducing neurodegeneration of sensory nervous systems. However, in recent years, it has been revealed that neuropathic pain occurs in the chronic phase of MeHg poisoning, that is, in current Minamata disease patients. Our recent study using Minamata disease model rats demonstrated that MeHg-mediated neurodegeneration in the sensory nervous system may induce inflammatory microglia production in the dorsal horn of the spinal cord and subsequent somatosensory cortical rewiring, leading to neuropathic pain. We hypothesized that inhibition of the Rho-associated coiled coil-forming protein kinase (ROCK) pathway could prevent MeHg-induced neuropathic pain because the ROCK pathway is known to be involved in inducing the production of inflammatory microglia. Here, we showed for the first time that Fasudil, a ROCK inhibitor, can prevent neuropathic pain in Minamata disease model rats. In this model, Fasudil significantly suppressed nerve injury-induced inflammatory microglia production in the dorsal horn of the spinal cord and prevented subsequent somatosensory cortical rewiring. These results suggest that the ROCK pathway is involved in the onset and development of neuropathic pain in the chronic phase of Minamata disease, and that its inhibition is effective in pain prevention.

Promising Advances in Pharmacotherapy for Patients with Spinal Cord Injury-A Review of Studies Performed In Vivo with Modern Drugs

Spinal cord injury (SCI) is a pathological neurological condition that leads to significant motor dysfunction. It is a condition that occurs as a result of tragic accidents, violent acts, or as a consequence of chronic diseases or degenerative changes. The current treatments for patients with SCI have moderate efficacy. They improve the quality of life of patients, but they are still doomed to long-term disability. In response to the modern directions of research on possible therapeutic methods that allow for the recovery of patients with SCI, a scientific review publication is needed to summarize the recent developments in this topic. The following review is focused on the available pharmacological treatments for SCIs and the problems that patients face depending on the location of the injury. In the following review, the research team describes problems related to spasticity and neuropathic pain; possible therapeutic pathways are also described for neuroprotection and the improvement of neurotransmission within the injured spinal cord, and the review focuses on issues related to oxidative stress.

Lysophosphatidic Acid Induced Apoptosis, DNA Damage, and Oxidative Stress in Spinal Cord Neurons by Upregulating LPA4/LPA6 Receptors

Lysophosphatidic acid (LPA) has disruptive effects on lumbar spinal stenosis (LSS). Recently, LPA has been reported to be involved in spinal cord neuronal injury and toxicity, promoting the pathogenesis of LSS. However, the exact effects of LPA on spinal cord neurons remain unknown. The purpose of this study is to investigate the effects of LPA (18 : 1) on spinal cord neuronal cytotoxicity, apoptosis, DNA damage, and oxidative stress. After clinical detection of LPA secretion, spinal cord neurons were treated with LPA (18 : 1); cell viability was analyzed by MTT assay, and LDH leakage was detected by LDH kit; cell apoptosis was detected by flow cytometry; ROS production was measured by DCFDA staining and MitoSOX Red Staining; the activation of the Gα12/Gα13 signaling pathway was detected by serum response factor response element (SRF-RE) luciferase reporter gene; the relationship among LPA, LPA4/6, and ROCK was examined by western blotting. In spinal cord neurons treated with LPA (18 : 1), cellular activity decreased and LDH release increased. The Rho kinase inhibitor (Y-27632) can attenuate LPA-induced apoptosis, DNA damage, and oxidative stress in spinal cord neurons. Moreover mechanistic investigation indicated that LPA (18 : 1) activates Gα12/13–Rho–ROCK2-induced apoptosis, DNA damage, and oxidative stress in spinal cord neurons by upregulating LPA4/LPA6 receptors. Further, the Rho kinase inhibitor Y-27632 attenuates the effects of LPA by downregulating LPA4/LPA6 receptors. Taken together, the possible mechanism by which LPA secretion in LSS patients aggravates patient injury was further elucidated using an LPA-induced spinal cord neuronal injury cell model in vitro.

The role of Rho/ROCK in epileptic seizure-related neuronal damage

Epilepsy is one of the most severe neurological disorders characterized by spontaneous recurrent seizures. Although more than two-thirds of patients can be cured with anti-epileptic drugs (AEDs), the rest one-third of epilepsy patients are resistant to AEDs. A series of studies have demonstrated Rho/Rho-associated kinase (ROCK) pathway might be involved in the pathogenesis of epilepsy in the recent twenty years. Several related pathway inhibitors of Rho/ROCK have been used in the treatment of epilepsy. We searched PubMed from Jan 1, 2000 to Dec 31, 2020, using the terms "epilepsy AND Rho AND ROCK" and "seizure AND Rho AND ROCK". We selected articles that characterized Rho/ROCK in animal models of epilepsy and patients. We then chose the most relevant research studies including in-vitro, in-vivo and clinical trials. The expression of Rho/ROCK could be a potential non-invasive biomarker to apply in treatment for patients with epilepsy. RhoA and ROCK show significant upregulation in the acute and chronic stage of epilepsy. ROCK inhibitors can reduce the epilepsy, epileptic seizure-related neuronal death and comorbidities. These findings demonstrate the novel development for diagnosis and treatment for patients with epilepsy. Rho/ROCK signaling pathway inhibitors may show more promising effects in epilepsy and related neurological diseases.