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.