A high-calorie diet aggravates LPS-induced pneumonia by disturbing the gut microbiota and Th17/Treg balance

The intestinal flora plays an important role in the inflammatory response to the systemic or local infections in the host. A high-calorie diet has been shown to aggravate pneumonia and delay recovery, especially in children. However, the underlying mechanisms remain unclear. Our previous studies demonstrated that a high-calorie diet and LPS atomization synergistically promoted lung inflammation injury in juvenile rats. In this study, specific pathogen-free juvenile rats were placed in a routine environment, and subjected to a high-calorie diet or LPS atomization in isolation as well as combination. Our data revealed that LPS nebulization combined with a high-calorie diet resulted in significant changes in rats, such as slow weight gain, increased lung index, and aggravated lung inflammatory damage. Meanwhile, we found that the aggravation of LPS-induced pneumonia by a high-calorie diet disturbs the balance of Th17/Treg cells. Furthermore, high-throughput sequencing of intestinal contents revealed that a high-calorie diet changed the gut microbiome composition, decreased microbial diversity, and particularly reduced the abundance of the intestinal microbiota associated with the production of short-chain fatty acids (SCFAs) in rats. Consequently, the levels of SCFAs, especially acetate, propionate, and butyrate, were significantly decreased following the intervention of a high-calorie diet. More critically, the effects of a high-calorie diet were shown to be transmissible among pneumonia rats through cohousing microbiota transplantation. Taken together, we provide evidence to support that a high-calorie diet can potentially reset the gut microbiome and metabolites, disrupt Th17/Treg cell balance and immune homeostasis, and aggravate LPS-induced lung inflammatory damage, which may provide a new perspective on the pathogenesis of lung inflammation injury, and suggest a novel microbiota-targeting therapy for inflammatory lung diseases.