Upregulation of GLT-1 Expression Attenuates Neuronal Apoptosis and Cognitive Dysfunction via Inhibiting the CB1-CREB Signaling Pathway in Mice with Traumatic Brain Injury

Background: Glutamate transporter 1 (GLT-1) plays a vital role in maintaining glutamate homeostasis in the body. A decreased GLT-1 expression in astrocytes can heighten neuronal sensitivity to glutamate excitotoxicity after traumatic brain injury (TBI). Despite its significance, the mechanisms behind the reduced expression of GLT-1 following TBI remain poorly understood. After TBI, the endocannabinoid 2-arachidonoyl glycerol (2-AG) is elevated several times. 2-AG is known to inhibit key positive transcriptional regulators of GLT-1. This study aims to investigate the role of 2-AG in regulating GLT-1 expression and to uncover the underlying mechanisms involved. Methods: A controlled cortical impact (CCI) model was used to establish a TBI model in C57BL/6J mice. The CB1 receptor antagonist (referred to as AM281) and the monoacylglycerol lipase (MAGL) inhibitor (referred to as JZL184) were administered to investigate the role and mechanism of 2-AG in regulating GLT-1 expression following TBI. Behavioral tests were conducted to assess neurological functions, including the open field, Y-maze, and novel object recognition tests. Apoptotic cells were identified using the TUNEL assay, while Western blot analysis and immunofluorescence were employed to determine protein expression levels. Results: The expression of GLT-1 in the contused cortex and hippocampus following TBI showed an initial decrease, followed by a gradual recovery. It began to decrease within half an hour, reached its lowest level at 2 h, and then gradually increased, returning to normal levels by 7 days. The administration of AM281 alleviated neuronal death, improved cognitive function, and reversed the reduction of GLT-1 caused by TBI in vivo. Furthermore, 2-AG decreased GLT-1 expression in astrocytes through the CB1-CREB signaling pathway. Mechanistically, 2-AG activated CB1, which inhibited CREB phosphorylation in astrocytes. This decreased GLT-1 levels and ultimately increased neuronal sensitivity to glutamate excitotoxicity. Conclusions: Our research demonstrated that the upregulation of GLT-1 expression effectively mitigated neuronal apoptosis and cognitive dysfunction by inhibiting the CB1-CREB signaling pathway. This finding may offer a promising therapeutic strategy for TBI.