Clyde Fomunung

 Introduction. Traumatic brain injury (TBI) is an acute injury to the brain due to an external force impacting the head that can alter brain function, resulting in both short-term and chronic debilitating effects.¹ TBIs are a major cause of death and disability across all ages in all countries, can include penetrating and non-penetrating injuries, and are categorized based on the Glasgow Coma Scale (GCS).^1-3 TBI increases intracranial pressure (ICP), which can damage axons. This damage induces glutamate excitotoxicity, which can lead to neurotoxicity and apoptosis.^3-5 Studies have shown that postsynaptic scaffolding proteins involved in the regulation of excitotoxicity after neuronal injury, play a crucial role in modulating synaptic function. ^3,6 These findings suggest that the downregulation of Preso, a postsynaptic scaffolding protein, could play a critical role in reducing secondary neuronal injury following TBI. Methods. Both in vitro and in vivo models were utilized to determine Preso’s role in TBI. For the in vitro model, a scratch injury was performed on mouse neuronal cells in a culture dish to induce traumatic neuronal injury (TNI). Lentiviruses are gene transfer tools that were used to infect all cells in culture. For the in vivo model, a controlled cortical impact (CCI) injury was employed to induce TBI in mice. Adeno-associated viruses were utilized as vectors for gene therapy, and neurological function was assessed using neurological severity scores (NSSs). 12 hours following TNI/TBI, Preso expression, cell death rate, and cytotoxicity were assessed using Western Blot, PI/Hoechst staining, and LDH assay, respectively.⁷ Results. Pretreating cortical neurons with NMDA receptor antagonists (MK-801 and DL-AP5) prevented the normal upregulation of Preso, which reduced cell death and the release of LDH after TNI/TBI. In another experiment, Preso antagonists (BAPTA-AM and ARL 17447) decreased neurotoxicity by eliminating intracellular Ca2+ and inhibiting nitric oxide (NO) production. In a third experiment, post-synaptic density protein-95 (PSD-95) antagonists (Tat-NR2B9c and ZL006) decreased neurotoxicity by disrupting the interaction between PSD-95 and NMDAR or PSD-95 and neuronal nitric oxide synthase (nNOS). These same experiments were repeated in the in vivo model, which yielded similar results.  Conclusions. Downregulation of molecules involved in the glutamate receptor signaling pathway, such as Preso, could be done utilizing different inhibitors. In doing so, the formation of the NMDAR/PSD-95/nNOS complex that contributes typically to excitotoxicity can be disrupted. Thus, disruption of the NMDAR/PSD-95/nNOS complex provides a new avenue for decreasing neuronal cell death and improving recovery outcomes following a TBI.

1. Maas AIR, Menon DK, Adelson PD, et al. Traumatic brain injury: integrated approaches to improve prevention, clinical care, and research. The Lancet Neurology. 2017; 16:987-1048
2. Qu W, Liu N-K, Wu X, et al. Disrupting nNOS–PSD95 Interaction Improves Neurological and Cognitive Recoveries after Traumatic Brain Injury. Cerebral Cortex. 2020; 00:1-13
3. Blennow K, Brody DL, Kochanek PM, et al. Traumatic brain injuries. Nature Reviews Disease Primers. 2016;2(1).
4. Ashina H, Porreca F, Anderson T, et al. Post-traumatic headache: epidemiology and pathophysiological insights. Nature Reviews Neurology. 2019;15(10):607-617.
5. Arai, M., Imamura, O., Kondoh, N., Dateki, M. and Takishima, K. (2019), Neuronal Ca²⁺‐dependent activator protein 1 (NCDAP1) induces neuronal cell death by activating p53 pathway following traumatic brain injury. J. Neurochem., 151: 795-809.
6. Sommer, J.B., Bach, A., Malá, H., Strømgaard, K., Mogensen, J. and Pickering, D.S. (2017),In vitro and in vivo effects of a novel dimeric inhibitor of PSD‐95 on excitotoxicity and functional recovery after experimental traumatic brain injury. Eur J Neurosci, 45: 238-248.
7. Luo P, Li X, Wu X, et al. Preso regulates NMDA receptor-mediated excitotoxicity via modulating nitric oxide and calcium responses after traumatic brain injury. C