High-Calorie Diet Aggravates Lipopolysaccharide-Induced Pulmonary Inflammation in Juvenile Mice: Association of Acetate-Mediated Macrophage Polarization with AMPK/YAP Signaling

Macrophage polarization is an important modulator of the progression, severity, and resolution of pediatric pneumonia. Acetate, a metabolite produced by the gut microbiota, serves as a key regulator of macrophage polarization. Evidence demonstrates that a high-calorie diet (HCD) lowers acetate levels, thereby aggravating pulmonary inflammation, but the underlying mechanism remains unclear. Objectives: This study investigated whether HCD-induced exacerbation of pulmonary inflammation in juvenile mice is associated with acetate-mediated macrophage polarization. Methods: The pulmonary inflammation model was established in juvenile mice by lipopolysaccharide (LPS) nebulization, with high-calorie diet (HCD) feeding to reduce systemic acetate levels. After model establishment, serum, lung tissue, colon tissue, and feces were collected from each group. Enzyme-linked immunosorbent assay (ELISA), immunohistochemistry (IHC), enzyme-coupled colorimetric assay, Western blotting (WB), and flow cytometry were used to evaluate histopathological changes in the lung and colon, systemic and pulmonary inflammation, acetate levels, and macrophage polarization. Exogenous acetate supplementation was administered to observe its regulatory effect on macrophage polarization, and the downstream signaling pathways were further explored. Results: Results revealed that an HCD significantly reduced acetate levels in both lung and fecal samples from juvenile mice with LPS-induced pulmonary inflammation. HCD increased pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) in lung tissue and serum, worsened pulmonary injury, and shifted macrophage polarization toward an M1 phenotype while reducing M2 macrophages. This imbalance was evident in both lung and colon tissues, accompanied by decreased p-AMPK/AMPK and p-YAP/YAP ratios in these tissues. Acetate supplementation and treatment with the AMPK activator Acadesine (AICAR; 5-aminoimidazole-4-carboxamide ribonucleoside) mitigated these effects. Conclusions: These findings provide new insights into the association between HCD-induced exacerbation of pulmonary inflammation in juvenile mice and acetate-mediated macrophage polarization, and suggest potential therapeutic strategies. However, given the lack of AMPK inhibition/knockdown and YAP-specific intervention experiments, the involvement of the AMPK/YAP signaling pathway should be interpreted as an association rather than a confirmed causal mechanism.