Eucommiae cortex polysaccharides attenuate gut microbiota dysbiosis and neuroinflammation in mice exposed to chronic unpredictable mild stress: Beneficial in ameliorating depressive-like behaviors

BACKGROUND

Chronic stress alters gut microbiota composition, as well as induces inflammatory responses and behavioral deficits. Eucommiae cortex polysaccharides (EPs) have been reported to remodel gut microbiota and ameliorate obesogenic diet-induced systemic low-grade inflammation, but their role in stress-induced behavioral and physiological changes is poorly understood.

METHODS

Male Institute of Cancer Research (ICR) mice were exposed to chronic unpredictable stress (CUMS) for 4 weeks and then supplemented with EPs at a dose of 400 mg/kg once per day for 2 weeks. Behavioral test-specific antidepressant and anxiolytic effects of EPs were assessed in FST, TST, EPM, and OFT. Microbiota composition and inflammation were detected using 16S ribosomal RNA (rRNA) gene sequencing, quantitative RT-PCR, western blot, and immunofluorescence.

RESULTS

We found that EPs ameliorated gut dysbiosis caused by CUMS, as evidenced by increasing the abundance of Lactobacillaceae and suppressing the expansion of the Proteobacteria, thereby mitigating intestinal inflammation and barrier derangement. Importantly, EPs reduced the release of bacterial-derived lipopolysaccharides (LPS, endotoxin) and inhibited the microglia-mediated TLR4/NFκB/MAPK signaling pathway, thereby attenuating the pro-inflammatory response in the hippocampus. These contributed to restoring the rhythm of hippocampal neurogenesis and alleviating behavioral abnormalities in CUMS mice. Correlation analysis showed that the perturbed-gut microbiota was strongly correlated with behavioral abnormalities and neuroinflammation.

LIMITATIONS

This study did not clarify the causal relationship between EPs remodeling the gut microbiota and improved behavior in CUMS mice.

CONCLUSIONS

EPs exert ameliorative effects on CUMS-induced neuroinflammation and depression-like symptoms, which may be strongly related to their beneficial effects on gut microbial composition.

Eucommiae cortex polysaccharides mitigate obesogenic diet-induced cognitive and social dysfunction via modulation of gut microbiota and tryptophan metabolism

Rationale: The high fat and sucrose diet, known as the obesogenic diet (OD), has been related to low-grade chronic inflammation and neurodevelopmental disorders. Emerging evidence suggests that OD influences cognitive and social function via the gut-brain axis. However, the effects of OD during adolescence on future health have been unclear. Meanwhile, the underlying mechanisms and effective interventions are not fully understood. Polysaccharides, one of the most abundant substances in the Eucommiae cortex, exhibit potential immunomodulatory and neuroprotective effects. Here, we aimed to investigate the impact of OD on adolescents, explore the modulating roles of Eucommiae cortex polysaccharides (EPs) on OD-induced behavioral dysfunction, and elucidate the underlying molecular mechanisms.

Methods: In the present study, four-week-old mice were fed with OD for four weeks to simulate persistent OD in adolescents. The behavioral features were accessed by open field test and Morris water maze. The gut bacterial structure was identified by 16S rRNA gene amplicon sequencing. The gene and protein expression in colonic tissues and hippocampus were detected by qRT-PCR, immunoblotting, enzyme-linked immunosorbent assay, and immunofluorescence staining. Detection of biological metabolites in serum and hippocampal tissues was performed by widely targeted metabolomics and targeted metabolomics.

Results: We found that OD-fed mice showed cognitive and social-behavioral deficits accompanied by gut dysbiosis and systematic tryptophan (Trp) metabolism disorders, which increased kynurenine (Kyn) concentration in the hippocampus. Bacteria-derived lipopolysaccharide (LPS, endotoxin) induced microglia-mediated neuroinflammation, directing the metabolism of Kyn in the hippocampus toward quinolinic acid (QA), which led to glutamate-mediated hyperactivation of mossy cells (MCs) in hippocampal hilus. Furthermore, OD impaired parvalbumin (PV) interneurons-related local circuits in the hippocampal granule cell layer. These resulted in hippocampal neurogenesis deficits and related behavioral dysfunction in mice. EPs supplementation ameliorated OD-induced gut dysbiosis, as evidenced by inhibiting the expansion of Escherichia coli (E.coli) and reducing the concentration of LPS in colonic contents and serum, thereby inhibiting the subsequent neuroinflammation. In addition, oral EPs suppressed the peripheral Kyn pathway to reduce the concentration of QA and glutamic acid in the hippocampus of OD-fed mice, thereby rescuing the glutamic acid-triggered neuroexcitotoxicity. These contributed to remodeling the rhythm of hippocampal neurogenesis and mitigated behavioral dysfunction in OD-fed mice.

Conclusions: The present study addresses a gap in the understanding of neuronal dysfunction associated with OD during adolescence and provides the first evidence that EPs improved cognitive and social behavior via modulation of gut microbiota and tryptophan metabolism in adolescent mice fed with OD, which may represent novel preemptive therapy for neurodevelopmental disorders via manipulation of the tryptophan metabolite.