Limosilactobacillus fermentum 2L Ameliorates Chronic Stress-Induced Neuroinflammation through Gut-Brain Axis Modulation in Mice

Chronic stress contributes to neuroinflammation and psychiatric disorders through gut-brain axis dysregulation. This study investigated the therapeutic potential of Limosilactobacillus fermentum 2L in ameliorating stress-induced neuroinflammation using an unpredictable chronic mild stress (UCMS) model. Five L. fermentum strains were screened for probiotic properties, with strain 2L selected based on superior acid and bile tolerance, cellular adhesion, and antioxidant activity. C57BL/6J mice underwent 7-week UCMS with concurrent 10-weeks of 2L treatment (10⁹ CFU/day). Behavioral assessments, histological analysis, qRT-PCR, Western blotting, and gut microbiome analysis were performed. Strain 2L demonstrated superior gastrointestinal survival and anti-inflammatory properties in LPS-challenged HT-29 cells. In UCMS mice, 2L treatment significantly ameliorated anxiety- and depression-like behaviors, preserved hippocampal neuronal morphology, and normalized hypothalamic-pituitary-adrenal (HPA) axis dysfunction by reducing elevated corticosterone levels (155.9 ± 17.2 to 121.3 ± 3.1 ng/ml, p < 0.001). Molecular analysis revealed restored hippocampal BDNF expression, normalized serotonin receptors (HTR1A, 5HT7R), and attenuated stress-activated MAPK pathways (ERK1/2, JNK1/2). Treatment restored intestinal barrier integrity through tight junction protein upregulation and reduced pro-inflammatory cytokine expression. Microbiome analysis showed successful Limosilactobacillus colonization with restoration of beneficial bacteria (Faecalibaculum, Akkermansia) and normalization of stress-elevated Prevotella. L. fermentum 2L provides multifaceted neuroprotection through gut-brain axis modulation, involving microbiota restoration, intestinal barrier strengthening, HPA axis normalization, and enhanced neuroplasticity. These findings support the therapeutic potential of targeted probiotic interventions for stress-related neuropsychiatric disorders.