Melatonin alleviates airway inflammation and anxiety-depression in asthma via gut microbiota–SCFA axis-mediated inhibition of microglial activation

Background: Asthma frequently co-occurs with anxiety and depression, yet the mechanisms underlying this lung-brain comorbidity remain elusive. The gut-lung-brain axis has emerged as a potential key mediator. Methods: Using an ovalbumin (OVA)-induced murine asthma model, we administered melatonin or sodium butyrate via drinking water. We assessed airway inflammation, lung function, anxiety- and depression-like behaviors, gut microbiota composition, short-chain fatty acid (SCFA) levels, and the MAPK/P65/NLRP3 signaling pathway in the hippocampus and BV2 microglial cells. Fecal microbiota transplantation (FMT) and antibiotic depletion experiments were conducted to establish causality. Results: Both melatonin and sodium butyrate significantly alleviated airway inflammation, improved lung function, and ameliorated anxiety- and depression-like behaviors in asthmatic mice. Melatonin increased gut-derived butyrate levels and restored gut microbiota balance. FMT from melatonin-treated donors replicated the therapeutic benefits, whereas antibiotic-mediated microbiota depletion abrogated the effects of melatonin. Mechanistically, both treatments inhibited the activation of the MAPK/P65/NLRP3 pathway in hippocampal microglia and LPS-stimulated BV2 cells. Conclusion: Our findings demonstrate that melatonin mitigates asthma-related airway inflammation and neuropsychiatric comorbidity by modulating the gut microbiota-SCFA axis and suppressing microglial activation via the MAPK/P65/NLRP3 pathway. This study highlights a novel systemic mechanism and potential therapeutic strategy for asthma and its comorbidities.