Vagus Nerve Stimulation Attenuates Cognitive Impairment in Traumatic Brain Injury via the mtDNA/cGAS-STING/NLRP3 Inflammasome Axis.

Background: Traumatic brain injury (TBI) is a major life-threatening event. In addition to neurological deficits, it can lead to long-term impairments of cognitive function. The vagus nerve (VN) provides a direct communication conduit between the central nervous system and the periphery, and modulation of the inflammatory reflex via electrical stimulation of the vagus nerve (VNS) shows efficacy in ameliorating pathology in neurodegenerative diseases. Our objective was to investigate the impact and underlying mechanism of VNS for cognitive impairment in a rat model of TBI.

Methods: Male rats were implanted with VNS electrodes on the left VN 1 week prior to controlled cortical impact. Mitochondrial permeability transition pore blocker cyclosporin A (CsA) and stimulator of interferon genes (STING) agonist 2'3'-cGAMP were delivered by intranasal administration or intraventricular injection. Post-VNS assessments included Morris water maze, Nissl staining, hematoxylin and eosin staining, Western blotting, quantitative polymerase chain reaction, mitochondrial membrane potential, and enzyme-linked immunosorbent assay.

Results: We found that VNS treatment significantly improved cognitive impairment, increased mitochondrial membrane potential, reduced accumulation of cytosolic mitochondrial DNA, attenuated cyclic GMP-AMP synthase (cGAS)-STING pathway, suppressed nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome activation, and partially reversed hippocampus neuronal damage and loss caused by TBI. However, 2'3'-cGAMP delivery significantly abrogated these effects of VNS. In addition, CsA also showed neuroprotective effects, including improved cognitive impairment, decreased levels of cGAS, phosphorylated STING, and suppressed the expressions of NLRP3 inflammasome and pyroptosis-pertinent components containing cleaved Caspase-1, ASC, and N-terminal Gasdermin D. CsA also inhibited interleukin-1β and interleukin-18 proinflammatory cytokine concentration.

Conclusions: Stimulation of the VN attenuates the pyroptosis and neuroinflammatory cascades in the rat of the TBI model by regulating the mitochondrial DNA/cGAS/STING /NLRP3 pathway.