Multi-omics reveals associations between the microbiota-gut-brain axis and antidepressant effects of vagus nerve stimulation.

Background: Major depressive disorder is a severe mental health condition characterized by persistent depressed mood and loss of interest. Current first-line pharmacotherapies often exhibit limited therapeutic performance and adverse side effects. Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising, safe, and noninvasive alternative intervention with demonstrated neuromodulatory efficacy. Nevertheless, its mechanisms remain unclear. This study investigated whether the antidepressant properties of taVNS are associated with the microbiota-gut-brain axis, focusing on the potential crosstalk between differentially expressed hippocampal proteins and the gut microbiota. Methods: A chronic unpredictable mild stress (CUMS) rat model of depression was established, and taVNS was administered for 14 days. Hippocampal proteomic profiling was performed using data-independent acquisition. Fecal metagenomic sequencing was conducted to characterize alterations in gut microbial communities. Key signaling pathways were validated using Western blot, qRT-PCR, HE staining, and transmission electron microscopy, all of which were employed to systematically assess behavioral, proteomic, microbial, and molecular changes. Results: Proteomics and molecular analyses revealed that taVNS upregulated hippocampal expression of glutamate ionotropic receptor N-methyl-D-aspartate type subunit 1 (GluN1) and brain-derived neurotrophic factor (BDNF), while simultaneously restoring mitogen-activated protein kinase (MAPK) signaling activity. Metagenomic profiling demonstrated that taVNS increased the abundance of Akkermansia muciniphila and reduced Ligilactobacillus reuteri. Ligilactobacillus levels were positively correlated with synaptogyrin-1 (Syngr1), indicating their potential association in enhancing the antidepressant effects mediated by the GluN1/MAPK/BDNF signaling cascade. Conclusion: TaVNS significantly alleviated depression-like behaviors in CUMS-exposed rats. The underlying mechanism may involve the restoration of synaptic function of glutamatergic neurons by regulating the GluN1/MAPK/BDNF signaling pathway. In addition, taVNS reshaped the gut microbiota, markedly increasing the abundance of Akkermansia muciniphila and Ligilactobacillus murinus while reducing Limosilactobacillus reuteri and Lactobacillus johnsonii. The positive correlation between Syngr1 protein level and Ligilactobacillus abundance in the hippocampus suggests that the microbiota-gut-brain axis may play a key role in the antidepressant effects of taVNS.