Cellular Neuroinflammation in a Lateral Forceps Compression Model of Spinal Cord Injury

Animal models of compression spinal cord injury

Compression spinal cord injuries are a common cause of morbidity in people who experience a spinal cord injury (SCI). Either as a by-product of a traumatic injury or due to nontraumatic conditions such as cervical myelitis, compression injuries are growing in prevalence clinically and many attempts of animal replication have been described within the literature. These models, however, often focus on the traumatic side of injury or mimic short-term injuries that are not representative of the majority of compression SCI. Of this, nontraumatic spinal cord injuries are severely understudied and have an increased prevalence in elderly populations, adults, and children. Therefore, there is a need to critically evaluate the current animal models of compression SCI and their suitability as a method for clinically relevant data that can help reduce morbidity and mortality of SCI. In this review, we reviewed the established and emerging methods of animal models of compression SCI. These models are the clip, balloon, solid spacer, expanding polymer, remote, weight drop, calibrated forceps, screw, and strap methods. These methods showed that there is a large reliance on the use of laminectomy to induce injury. Furthermore, the age range of many studies does not reflect the elderly and young populations that commonly suffer from compression injuries. It is therefore important to have techniques and methods that are able to minimize secondary effects of the surgeries, and are representative of the clinical cases seen so that treatments and interventions can be developed that are specific.

The promoting effects of activated olfactory ensheathing cells on angiogenesis after spinal cord injury through the PI3K/Akt pathway

Objective

The aim of this study was to investigate the pro-angiogenic potential of olfactory ensheathing cells (OECs) activated by curcumin (CCM) and lipopolysaccharide (LPS) and the possible underlying mechanisms.

Methods

Vascular endothelial cells or tissues were cultured and treated with conditioned medium (CM) extracted from activated OECs activated through the addition of LPS and CCM or unactivated controls. Concomitantly, the pro-angiogenic potential of OECs was assessed in vitro by aortic ring sprouting assay, endothelial wound healing assay, CCK-8 assay, and tube formation assay. Subsequently, the OECs were co-cultured with endothelial cells to evaluate their promoting effect on endothelial cell proliferation and migration following a mechanical scratch. Moreover, the spinal cord injury (SCI) model in rats was established, and the number of endothelial cells and vascular structure in the injured area after SCI was observed with OEC transplantation. Finally, the underlying mechanism was investigated by western blot analysis of phosphorylated kinase expression with or without the MK-2206 (Akt-inhibitor).

Result

The present results showed that the activated OECs can effectively promote vascular endothelial cells' proliferation, migration, and vessel-like structure formation. Strikingly, several pro-angiogenic growth factors such as VEGF-A and PDGF-AA, which facilitate vessel formation, were found to be significantly elevated in CM. In addition, the PI3K/Akt signaling pathway was found to be involved in pro-angiogenic events caused by activated OEC CM, displaying higher phosphorylation levels in cells. In contrast, the delivery of MK2206 can effectively abrogate all the positive effects.

Conclusions

OECs activated by LPS and CCM have a pro-angiogenic effect and can effectively promote angiogenesis and improve the microenvironment at the injury site when transplanted in the injured spinal cord. This potentiated ability of OECs to provide pro-angiogenic effects is likely mediated through the PI3K/Akt pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00765-y.

Analysis and comparison of a spinal cord injury model with a single-axle-lever clip or a parallel-moving clip compression in rats

STUDY DESIGN

Experimental animal study.

OBJECTIVES

To assess the feasibility of a custom-designed parallel-moving (PM) clip, compared with a single-axle-lever (SAL) clip, for the development of a compressional spinal cord injury (SCI) model in rats.

SETTING

Hospital laboratory in China.

METHODS

We used a PM clip and a SAL clip with same compression rate, to develop a SCI model in rats, and set a sham group as a blank control. Within 3 weeks, each group of rats was evaluated for behavioral (Basso-Beattie-Bresnahan locomotor rating score, BBB), and electrophysiological changes (somatosensory evoked potential), and historical staining to observe the differences between the three groups. In particular, the mechanical results of the PM group were calculated.

RESULTS

The BBB scores for the SAL and PM groups were significantly lower than those for the sham group (P < 0.05), no significant difference between the two methods (P > 0.05), but the values corresponding to the PM group had smaller standard deviations. The interpeak-latency (IPL) was significantly prolonged (P < 0.0001) and the peak-peak amplitude (PPA) was significantly reduced (P < 0.01) in SAL and PM groups than those in the sham group, but there was no statistical difference in both IPL and PPA between the two SCI groups (P > 0.05). Histological staining showed obvious pathological changes in two SCI groups, and the shape of the lesion zone in the PM group was more symmetrical than that in the SAL groups.

CONCLUSIONS

The use of a compressional SCI model in rats with the PM clip we designed is an appropriate method to quantify the injury. The degree of the injury caused by this clip is more stable and uniform than those with classical methods.

Time-dependent microglia and macrophages response after traumatic spinal cord injury in rat: a systematic review

OBJECTIVE

To acquire evidence-based knowledge in temporal and spatial patterns of microglia/macrophages changes to facilitate finding proper intervention time for functional restoration after traumatic spinal cord injury (TSCI).

SETTING

Sina Trauma and Surgery Research Center, Tehran University of Medical Sciences, Tehran, Iran.

METHODS

We searched PubMed and EMBASE via Ovid SP with no temporal and linguistic restrictions. Besides, hand-search was performed in the bibliographies of relevant studies. The experimental non-interventional and non-transgenic animal studies confined to the rat species which assess the pathological change of microglia /macrophages at the specified time were included.

RESULTS

We found 15,315 non-duplicate studies. Screening through title and abstract narrowed down to 607 relevant articles, 31 of them were selected based on the inclusion criteria. The reactivity of the microglia/macrophages initiates in early hours PI in contusion, compression and transection models. Cells activity reached a maximum within 48 h to 28 days in compression, 7 days in contusion and between 4 and 60 days in transection models. Inflammatory response occurred at the epicenter, in or near the lesion site in both gray and white matter in all three injury models with a maximum extension of one centimeter caudal and rostral to the epicenter in the gray matter in contusion and transection models.

CONCLUSION

This study was designed to study spatial-temporal changes in the activation of microglia/macrophages overtime after TSCI. We were able to demonstrate time-dependent cell morphological changes after TSCI. The peak times of cell reactivity and the areas where the cells responded to the injury were determined.

Experimental spinal cord trauma: a review of mechanically induced spinal cord injury in rat models

It has been shown that animal spinal cord compression (using methods such as clips, balloons, spinal cord strapping, or calibrated forceps) mimics the persistent spinal canal occlusion that is common in human spinal cord injury (SCI). These methods can be used to investigate the effects of compression or to know the optimal timing of decompression (as duration of compression can affect the outcome of pathology) in acute SCI. Compression models involve prolonged cord compression and are distinct from contusion models, which apply only transient force to inflict an acute injury to the spinal cord. While the use of forceps to compress the spinal cord is a common choice due to it being inexpensive, it has not been critically assessed against the other methods to determine whether it is the best method to use. To date, there is no available review specifically focused on the current compression methods of inducing SCI in rats; thus, we performed a systematic and comprehensive publication search to identify studies on experimental spinalization in rat models, and this review discusses the advantages and limitations of each method.

Low-level laser facilitates alternatively activated macrophage/microglia polarization and promotes functional recovery after crush spinal cord injury in rats

Macrophages and resident microglia play an import role in the secondary neuroinflammation response following spinal cord injury. Reprogramming of macrophage/microglia polarization is an import strategy for spinal cord injury restoration. Low-level laser therapy (LLLT) is a noninvasive treatment that has been widely used in neurotrauma and neurodegenerative diseases. However, the influence of low-level laser on polarization of macrophage/microglia following spinal cord injury remains unknown. The present study applied low-level laser therapy on a crush spinal cord injury rat model. Using immunofluorescence, flow cytometry, RT-qPCR, and western blot assays, we found that low-level laser therapy altered the polarization state to a M2 tendency. A greater number of neurons survived in the pare injury site, which was accompanied by higher BBB scores in the LLLT group. Furthermore, low-level laser therapy elevated expression of interleukin 4 (IL-4) and interleukin 13 (IL-13). Results from this study show that low-level laser therapy has the potential for reducing inflammation, regulating macrophage/microglia polarization, and promoting neuronal survival. These beneficial effects demonstrate that low-level laser therapy may be an effective candidate for clinical treatment of spinal cord injury.

Modulating inflammatory cell responses to spinal cord injury: all in good time

Spinal cord injury can have a range of debilitating effects, permanently impacting a patient's quality of life. Initially thought to be an immune privileged site, the spinal cord is able to mount a timely and well organized inflammatory response to injury. Intricate immune cell interactions are triggered, typically consisting of a staggered multiphasic immune cell response, which can become deregulated if left unchecked. Although several immunomodulatory compounds have yielded success in experimental rodent spinal cord injury models, their translation to human clinical studies needs further consideration. Because temporal differences between rodent and human inflammatory responses to spinal cord injury do exist, drug delivery timing will be a crucial component in recovery from spinal cord injury. Given too early, immunomodulatory therapies may impede beneficial inflammatory reactions to the injured spinal cord or even miss the opportunity to dampen delayed harmful autoimmune processes. Therefore, this review aims to summarize the temporal inflammatory response to spinal cord injury, as well as detailing specific immune cell functions. By clearly defining the chronological order of inflammatory events after trauma, immunomodulatory drug delivery timing can be better optimized. Further, we compare spinal cord injury-induced inflammatory responses in rodent and human studies, enabling clinicians to consider these differences when initiating clinical trials. Improved understanding of the cellular immune response after spinal cord injury would enhance the efficacy of immunomodulatory agents, enabling combined therapies to be considered.

Lymphocytes and autoimmunity after spinal cord injury

Over the past 15 years an immense amount of data has accumulated regarding the infiltration and activation of lymphocytes in the traumatized spinal cord. Although the impact of the intraspinal accumulation of lymphocytes is still unclear, modulation of the adaptive immune response via active and passive vaccination is being evaluated for its preclinical efficacy in improving the outcome for spinal-injured individuals. The complexity of the interaction between the nervous and the immune systems is highlighted in the contradictions that appear in response to these modulations. Current evidence regarding augmentation and inhibition of the adaptive immune response to spinal cord injury is reviewed with an aim toward reconciling conflicting data and providing consensus issues that may be exploited in future therapies. Opportunities such an approach may provide are highlighted as well as the obstacles that must be overcome before such approaches can be translated into clinical trials.

CD11d Antibody Treatment Improves Recovery in Spinal Cord-Injured Mice

Acute administration of a monoclonal antibody (mAb) raised against the CD11d subunit of the leukocyte CD11d/CD18 integrin after spinal cord injury (SCI) in the rat greatly improves neurological outcomes. This has been chiefly attributed to the reduced infiltration of neutrophils into the injured spinal cord in treated rats. More recently, treating spinal cord-injured mice with a Ly-6G neutrophil-depleting antibody was demonstrated to impair neurological recovery. These disparate results could be due to different mechanisms of action utilized by the two antibodies, or due to differences in the inflammatory responses between mouse and rat that are triggered by SCI. To address whether the anti-CD11d treatment would be effective in mice, a CD11d mAb (205C) or a control mAb (1B7) was administered intravenously at 2, 24, and 48 h after an 8-g clip compression injury at the fourth thoracic spinal segment. The anti-CD11d treatment reduced neutrophil infiltration into the injured mouse spinal cord and was associated with increased white matter sparing and reductions in myeloperoxidase (MPO) activity, reactive oxygen species, lipid peroxidation, and scar formation. These improvements in the injured spinal cord microenvironment were accompanied by increased serotonin (5-HT) immunoreactivity below the level of the lesion and improved locomotor recovery. Our results with the 205C CD11d mAb treatment complement previous work using this anti-integrin treatment in a rat model of SCI.