Abstract
Acute lung injury (ALI) is a lethal disease with diffuse lung inflammation, in which JAK/STAT3 signaling has been well recognized for its role in initiating and amplifying inflammatory processes. However, the mechanism for the enhancement and maintenance of signal transducer and activator of transcription 3 (STAT3) activation has not yet been clearly demonstrated in ALI. In the present work, we established a lipopolysaccharide (LPS)-induced ALI rat model through intratracheal instillation and isolated the alveolar macrophages (AMs) from the rats in the model. We demonstrated that the expression of Kruppel-like factor 2 (KLF2) significantly decreased in the AMs from LPS-induced ALI rats (LPS-AMs) as compared with the AMs from control rats (NC-AMs). Overexpressing KLF2 in LPS-AMs inhibited the phosphorylation of STAT3 and reduced the levels of STAT3 target genes, including matrix metalloproteinase (MMP)-2/9 (MMP-2/9). Further investigation indicated that KLF2 trans-inhibited heat shock protein H1 (HSPH1), which interacted with STAT3 and enhanced its phosphorylation. As a crucial inflammatory mediator in ALI, interleukin-1β (IL-1β) induced the down-regulation of KLF2 in LPS-AMs, as interrupting IL-1β signaling in LPS-AMs by antibody neutralization or IL1R1 knockdown rescued the expression of KLF2. Consistently, stimulating NC-AMs with IL-1β decreased KLF2 and increased HSPH1, while overexpression of KLF2 suppressed IL-1β-induced HSPH1. Additionally, in vivo studies showed that treatment with an IL-1β antibody or HSPH1 inhibitor alleviated lung injury in ALI rats, as well as decreased the levels of p-STAT3 and MMP-2/9. In conclusion, activation of the IL-1β/KLF2/HSPH1 pathway facilitated STAT3 phosphorylation in AMs, which exacerbated pulmonary inflammation in ALI.
Highlights
Acute lung injury (ALI) is a severe disease with diffuse alveolar damage, which has high morbidity and mortality in intensive care patients [1]
We cultured the alveolar macrophage (AM) from LPS-AMs and NC-AMs in vitro and found that both the mRNA and protein levels of Kruppel-like factor 2 (KLF2) were lower in LPS-AMs than in NC-AMs (Figure 2B,C)
KLF2 overexpression suppressed the production of matrix metalloproteinase (MMP)-2 and MMP-9, which were up-regulated by signal transducer and activator of transcription 3 (STAT3) signaling in LPS-AMs (Figure 2E)
Summary
Acute lung injury (ALI) is a severe disease with diffuse alveolar damage, which has high morbidity and mortality in intensive care patients [1]. An uncontrolled acute inflammatory response, pulmonary endothelial, epithelial barrier dysfunction, loss of alveolar-capillary membrane integrity, and excessive secretion of pro-inflammatory cytokines are considered to be the main pathological factors leading to ALI [2]. The inflammatory microenvironment composed of immune cells, structure cells, and inflammatory factors plays a key role in the pathogenesis of ALI. The inflammatory cytokines produced by these cells form a complex signaling network that regulates all stages of the inflammatory response in ALI [3,4].
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