Neuromodulation Therapies in Pre-Clinical Models of Traumatic Brain Injury: Systematic Review and Translational Applications

Assessment of the Behaviors of an In Vitro Brain Model On-Chip under Shockwave Impacts

Herein we report the assessment of the effects of shockwave (SW) impacts on adult rat hippocampal progenitor cell (AHPC) neurospheres (NSs), which are used as in vitro brain models, for enhancing our understanding of the mechanisms of traumatic brain injury (TBI). The assessment has been achieved by using culture dishes and a new microchip. The microchip allows the chemicals released from the brain models cultured inside the cell culture chamber under SW impacts to diffuse to the nanosensors in adjacent sensor chambers through built-in diffusion barriers, which are used to prevent the cells from entering the sensor chambers, thereby mitigating the biofouling issues of the sensor surface. Experiments showed the negative impact of the SW on the viability, proliferation, and differentiation of the cells within the NSs. A qPCR gene expression analysis was performed and appeared to confirm some of the immunocytochemistry (ICC) results. Finally, we demonstrated that the microchip can be used to monitor lactate dehydrogenase (LDH) released from the AHPC-NSs subjected to SW impacts. As expected, LDH levels changed when AHPC-NSs were injured by SW impacts, verifying this chip can be used for assessing the degrees of injuries to AHPC-NSs by monitoring LDH levels. Taken together, these results suggest the feasibility of using the chip to better understand the interactions between SW impacts and in vitro brain models, paving the way for potentially establishing in vitro TBI models on a chip.

Metabotropic glutamate receptor 5 promotes blood-brain barrier recovery after traumatic brain injury

Blood-brain barrier (BBB) impairment and glutamate release are two pathophysiological features of traumatic brain injury (TBI), contributing to secondary brain damage and neuroinflammation. However, our knowledge of BBB integrity damage and dysfunction are still limited due to the diverse and fluctuating expression of glutamate receptors after trauma. Here, we confirmed the downregulation of metabotropic glutamate receptor 5 (mGluR5) on microvascular endothelial cell within the acute phase of TBI, and the recovered mGluR5 levels on BBB was positively associated with blood perfusion and neurological recovery. In whole body mGluR5-knockout mice, BBB dysfunction and neurological deficiency were exacerbated after TBI compared with wild type mice. In terms of mechanism, the amino acid sequence 201-259 of cytoskeletal protein Alpha-actinin-1 (ACTN1) interacted with mGluR5, facilitating mGluR5 translocation from cytoplasmic compartment to plasma membrane in endothelial cells. Activation of plasma membrane mGluR5 triggers the PLC/PKCμ/c-Jun signaling pathway, leading to increased expression of the tight junction-actin cytoskeleton connecting protein zonula occludens-1 (ZO-1). Our findings uncover a novel mechanism mediated by membrane and cytoplasmic mGluR5 in endothelial cell integrity maintenance and repair, providing the potential therapeutic target for TBI treatment targeting at mGluR5 and mGluR5/ACTN1 complex in BBB.

Contralesional Anodal Transcranial Direct Current Stimulation Promotes Intact Corticospinal Tract Axonal Sprouting and Functional Recovery After Traumatic Brain Injury in Mice

BACKGROUND

Anodal transcranial direct current stimulation (AtDCS), a neuromodulatory technique, has been applied to treat traumatic brain injury (TBI) in patients and was reported to promote functional improvement. We evaluated the effect of contralesional AtDCS on axonal sprouting of the intact corticospinal tract (CST) and the underlying mechanism in a TBI mouse model to provide more preclinical evidence for the use of AtDCS to treat TBI.

METHODS

TBI was induced in mice by a contusion device. Then, the mice were subjected to contralesional AtDCS 5 days per week followed by a 2-day interval for 7 weeks. After AtDCS, motor function was evaluated by the irregular ladder walking, narrow beam walking, and open field tests. CST sprouting was assessed by anterograde and retrograde labeling of corticospinal neurons (CSNs), and the effect of AtDCS was further validated by pharmacogenetic inhibition of axonal sprouting using clozapine-N-oxide (CNO).

RESULTS

TBI resulted in damage to the ipsilesional cortex, while the contralesional CST remained intact. AtDCS improved the skilled motor functions of the impaired hindlimb in TBI mice by promoting CST axon sprouting, specifically from the intact hemicord to the denervated hemicord. Furthermore, electrical stimulation of CSNs significantly increased the excitability of neurons and thus activated the mechanistic target of rapamycin (mTOR) pathway.

CONCLUSIONS

Contralesional AtDCS improved skilled motor following TBI, partly by promoting axonal sprouting through increased neuronal activity and thus activation of the mTOR pathway.

Apelin-Overexpressing Neural Stem Cells in Conjunction with a Silk Fibroin Nanofiber Scaffold for the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI), especially moderate or severe TBI, is one of the most devastating injuries to the nervous system, as the existing therapies for neurological defect repair have difficulty achieving satisfactory results. Neural stem cells (NSCs) therapy is a potentially effective treatment option, especially after specific genetic modifications and when used in combination with biomimetic biological scaffolds. In this study, tussah silk fibroin (TSF) scaffolds with interconnected nanofibrous structures were fabricated using a top-down method. We constructed the apelin-overexpressing NSCs that were cocultured with a TSF nanofiber scaffold (TSFNS) that simulated the extracellular matrix in vitro. To verify the therapeutic efficacy of engineered NSCs in vivo, we constructed TBI models and randomized the C57BL/6 mice into three groups: a control group, an NSC-ctrl group (transplantation of NSCs integrated on TSFNS), and an NSC-apelin group (transplantation of apelin-overexpressing NSCs integrated on TSFNS). The neurological functions of the model mice were evaluated in stages. Specimens were obtained 24 days after transplantation for immunohistochemistry, immunofluorescence, and western blot experiments, and statistical analysis was performed. The results showed that the combination of the TSFNS and apelin overexpression guided extension and elevated the proliferation and differentiation of NSCs both in vivo and in vitro. Moreover, the transplantation of TSFNS-NSCs-Apelin reduced lesion volume, enhanced angiogenesis, inhibited neuronal apoptosis, reduced blood-brain barrier damage, and mitigated neuroinflammation. In summary, TSFNS-NSC-Apelin therapy could build a microenvironment that is more conducive to neural repair to promote the recovery of injured neurological function.

Electrical stimulation methods and protocols for the treatment of traumatic brain injury: a critical review of preclinical research

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of disabilities resulting from cognitive and neurological deficits, as well as psychological disorders. Only recently, preclinical research on electrical stimulation methods as a potential treatment of TBI sequelae has gained more traction. However, the underlying mechanisms of the anticipated improvements induced by these methods are still not fully understood. It remains unclear in which stage after TBI they are best applied to optimize the therapeutic outcome, preferably with persisting effects. Studies with animal models address these questions and investigate beneficial long- and short-term changes mediated by these novel modalities.

METHODS

In this review, we present the state-of-the-art in preclinical research on electrical stimulation methods used to treat TBI sequelae. We analyze publications on the most commonly used electrical stimulation methods, namely transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS) and vagus nerve stimulation (VNS), that aim to treat disabilities caused by TBI. We discuss applied stimulation parameters, such as the amplitude, frequency, and length of stimulation, as well as stimulation time frames, specifically the onset of stimulation, how often stimulation sessions were repeated and the total length of the treatment. These parameters are then analyzed in the context of injury severity, the disability under investigation and the stimulated location, and the resulting therapeutic effects are compared. We provide a comprehensive and critical review and discuss directions for future research. RESULTS AND CONCLUSION: We find that the parameters used in studies on each of these stimulation methods vary widely, making it difficult to draw direct comparisons between stimulation protocols and therapeutic outcome. Persisting beneficial effects and adverse consequences of electrical simulation are rarely investigated, leaving many questions about their suitability for clinical applications. Nevertheless, we conclude that the stimulation methods discussed here show promising results that could be further supported by additional research in this field.

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Despite extensive research efforts, the majority of trialed monotherapies to date have failed to demonstrate significant benefit. It has been suggested that this is due to the complex pathophysiology of TBI, which may possibly be addressed by a combination of therapeutic interventions. In this article, we have reviewed combinations of different pharmacologic treatments, combinations of non-pharmacologic interventions, and combined pharmacologic and non-pharmacologic interventions for TBI. Both preclinical and clinical studies have been included. While promising results have been found in animal models, clinical trials of combination therapies have not yet shown clear benefit. This may possibly be due to their application without consideration of the evolving pathophysiology of TBI. Improvements of this paradigm may come from novel interventions guided by multimodal neuromonitoring and multimodal imaging techniques, as well as the application of multi-targeted non-pharmacologic and endogenous therapies. There also needs to be a greater representation of female subjects in preclinical and clinical studies.