Acetate Downregulates the Activation of NLRP3 Inflammasomes and Attenuates Lung Injury in Neonatal Mice With Bronchopulmonary Dysplasia

Abstract

Background: Bronchopulmonary dysplasia (BPD) is a common pulmonary complication in preterm infants. Acetate is a metabolite produced by the gut microbiota, and its anti-inflammatory function is well known. The role of acetate in BPD has not been studied. Here, we investigate the effects of acetate on lung inflammation and damage in mice model of BPD. Objective: To investigate the role of acetate in the development of BPD. Methods: C57BL/6 mice were randomly divided into three groups on the 3rd day after birth: room air group, hyperoxia group, and hyperoxia + acetate (250 mM, 0.02 ml/g) group. The expression of inflammatory factors was determined by ELISA and RT-PCR, and NLRP3 and caspase-1 were detected by Western blot. High-throughput sequencing was used to detect bacterial communities in the mice intestines. Results: After acetate treatment, the expression levels of TNF-α, IL-1β, IL-18, NLRP3, and caspase-1 were significantly reduced, while the expression of GPR43 was increased. In the BPD mice treated with acetate, the proportion of Escherichia-Shigella was lower than in placebo-treated BPD mice, while the abundance of Ruminococcus was increased. Conclusions: These results indicate that acetate may regulate intestinal flora and reduce inflammatory reactions and lung injury in BPD. Therefore, acetate may be an effective drug to protect against neonatal BPD.

Keywords: GPR43; acetate; bronchopulmonary dysplasia; inflammasome; microbial communities.

Figure 1

Body weight of neonatal mice. (A) Acetate-treated mice in the hyperoxia group had a significantly higher body weight on postnatal day 9 than non-acetate treated mice (P < 0.001). (B) The body weight on postnatal day 17 (P < 0.001). n = 8 mice/group. Data are expressed relative to the control group at each time point as the mean ± SEM.

Figure 2

Acetate attenuates morphological changes. Hyperoxia exposure led to marked alveolar simplification as shown by H&E staining and by RAC and MLI assessment. Acetate treatment improved the hyperoxia-induced impairment of alveolar growth. (A–C) Representative H&E staining (light microscopy, ×200) of lung tissue slides from each group. Scale bars = 100 μm. (D) Semiquantitative pathological determination of RAC in lung tissues. (E) Semiquantitative pathological determination of MLI in lung tissues. The values represent the mean ± SD; n = 6 mice/group.

Figure 3

Acetate decreases pro-inflammatory factors in the mouse lung. The pulmonary mRNA levels of TNF-α (A). The pulmonary protein levels of TNF-α (B). n = 5–7/group from 3 independent experiments; data are presented as the means ± SD.

Figure 4

Acetate decreases NLRP3 inflammasome-related protein and GPR43 expression. The pulmonary mRNA levels of IL-1β (A), IL-18 (C), NLRP3 (E) and GPR43 (F). The pulmonary protein levels of IL-1β (B), IL-18 (D), NLRP3 (G,H) and caspase-1 (G,H). n ≥ 3/group from 3 independent experiments; data are presented as the means ± SD.

Figure 5

Acetate treatment affects the composition of the gut microbiota in mice exposed to hyperoxia. The relative abundance of microbial communities in the gut of the 3 groups at the phylum (A) and genus (B) levels. For (A,B), relative abundance >1%, *P < 0.05 and **P < 0.01. Assessment of the diversity of microbial communities in the intestinal contents (C) of the 3 groups by the Shannon Diversity Index (room air: red, hyperoxia: blue, acetate: green).