Abstract / Summary
Background: Traumatic brain injury (TBI) is a leading cause of mortality and morbidity and a major contributor to loss of working capacity in young adults. Current therapeutic options for TBI remain limited. This study aimed to assess the potential role and therapeutic value of ubiquitin-specific protease 18 (USP18) in TBI. Methods: A TBI model was established using the weight-drop model. Neuron-specific Usp18 knockout on the C57BL/6J background was generated by crossbreeding Usp18 f/f and Thy1-Cre mice. A recombinant adeno-associated virus serotype 9 carrying Usp18 under control of the hSyn promoter was injected into wild-type mice. Mechanical stretch injury-exposed HT22 cells subjected to a well-established stretch injury model were used to simulate TBI in vitro. The underlying molecular mechanism was explored through bulk-RNA sequencing, immunoprecipitation and mass spectrometry (MS) analysis, RNA immunoprecipitation sequencing, and RNA immunoprecipitation assays. Results: Multi-omics analysis of mouse brain and RNA-seq profiling of human brain tissues indicated that the expression of the deubiquitinating enzyme USP18 was substantially decreased in hippocampal neurons. Neuron-specific overexpression of Usp18 via recombinant adeno-associated virus 9 (AAV9) led to reduced neuronal apoptosis and improved cognitive performance in mice. The RNA-seq analysis revealed that Usp18 overexpression enhanced the homeostasis of mitochondrial dynamics, ameliorated neuronal mitochondrial dysfunction, and suppressed oxidative stress injury. These results were also confirmed in a well-established mechanical stretch injury model in HT22 cells. Moreover, compared with control mice, neuron-specific Usp18 knockout mice displayed more severe mitochondrial morphological disarray and neuronal damage after TBI. RNA sequencing, MS analysis, RNA immunoprecipitation sequencing, and RNA immunoprecipitation assays mechanistically revealed that USP18 directly interacted with DEAD-box helicase 5 (DDX5) and deubiquitinated and stabilized DDX5 at the K470 residue (via K48-linked ubiquitination) to increase the stability of the Opa1 mRNA, thereby impeding mitochondrial morphofunctional defects. Collectively, the results of this study reveal the protective effect of and molecular mechanism regulating USP18 in TBI pathology and reveal a novel neuron-specific USP18-DDX5-OPA1 axis involved in TBI. Conclusions: We identified a USP18-promoted mechanism that maintains the homeostasis of mitochondrial dynamics through the DDX5-OPA1 axis in a TBI model; this pathway inhibits neuronal apoptosis and improves cognitive function in mice, suggesting that USP18 activation or AAV9- Usp18 delivery represents a potential therapeutic strategy for TBI.