SCFAs inhibited NETosis to alleviate lung inflammation in COPD: a potential role for GPR43

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide, and poses a significant socioeconomic burden attributable to its high mortality and morbidity. Short-chain fatty acids (SCFAs), as the key metabolites produced by gut microbiota, have been considered to be involved in the regulation of pulmonary inflammation. However, the underlying bridging mechanisms through the gut-lung axis remain elusive. To delineate cellular heterogeneity during COPD progression, we profiled lung tissues from rats at distinct stages (Days 0, 7, 14, and 28) using scRNA-seq, followed by bulk transcriptomic analysis to pinpoint critical dysregulated pathways. Gas chromatography-mass spectrometry (GC-MS) was employed to quantify the differential SCFA levels. The protective effects of SCFAs against pulmonary inflammation in COPD were evaluated via pulmonary function testing, HE staining, and ELISA. Flow cytometry, Western blotting, immunofluorescence and scanning electron microscopy were employed to explore the mechanism of SCFAs regulating neutrophil extracellular trap (NET) formation in vitro and in vivo. Finally, metagenomic sequencing was applied to investigate the impact of SCFAs on gut microbial communities. ScRNA-seq demonstrated the intense immune activation during the progress of COPD, characterized by neutrophil accumulation exceeding 50% of cellular composition on the 14th day in the lung tissue. Transcriptomic analysis further pinpointed neutrophil-driven NETosis as the key pathogenic pathway. The results of GC-MS showed the significant downregulation of SCFAs represented by acetic acid and propionic acid in COPD. Exogenous supplementation with SCFAs (acetic acid and propionic acid) activated the key receptor GPR43, suppressed the expression of NETs marker proteins (NE, MPO, and CitH3) and attenuated inflammatory cytokine levels in COPD rats. Rescue experiments with NETs inducers/inhibitors and GPR43 agonists/antagonists further elucidated the regulatory mechanisms of SCFAs/GPR43 axis in COPD inflammation. Furthermore, metagenomic sequencing revealed that SCFAs reshaped the intestinal flora in COPD by enriching the abundance of beneficial bacteria. As one of the key receptors for gut microbiota-derived SCFAs, GPR43 may be involved in the process by which SCFAs alleviate pulmonary inflammation in COPD through regulating NET formation. These findings provide valuable experimental evidence for promoting the clinical translation of therapeutic strategies characterized by gut microbiota and their metabolites.