NF-κB Activation Limits Airway Branching through Inhibition of Sp1-Mediated Fibroblast Growth Factor-10 Expression

Abstract

Bronchopulmonary dysplasia (BPD) is a frequent complication of preterm birth. This chronic lung disease results from arrested saccular airway development and is most common in infants exposed to inflammatory stimuli. In experimental models, inflammation inhibits expression of fibroblast growth factor-10 (FGF-10) and impairs epithelial–mesenchymal interactions during lung development; however, the mechanisms connecting inflammatory signaling with reduced growth factor expression are not yet understood. In this study we found that soluble inflammatory mediators present in tracheal fluid from preterm infants can prevent saccular airway branching. In addition, LPS treatment led to local production of mediators that inhibited airway branching and FGF-10 expression in LPS-resistant C.C3-Tlr4Lpsd/J fetal mouse lung explants. Both direct NF-κB activation and inflammatory cytokines (IL-1β and TNF-α) that activate NF-κB reduced FGF-10 expression, whereas chemokines that signal via other inflammatory pathways had no effect. Mutational analysis of the FGF-10 promoter failed to identify genetic elements required for direct NF-κB–mediated FGF-10 inhibition. Instead, NF-κB activation appeared to interfere with the normal stimulation of FGF-10 expression by Sp1. Chromatin immunoprecipitation and nuclear coimmunoprecipitation studies demonstrated that the RelA subunit of NF-κB and Sp1 physically interact at the FGF-10 promoter. These findings indicate that inflammatory signaling through NF-κB disrupts the normal expression of FGF-10 in fetal lung mesenchyme by interfering with the transcriptional machinery critical for lung morphogenesis.

Interactions between NF-κB and SP3 Connect Inflammatory Signaling with Reduced FGF-10 Expression

“…Although the connections between inflammatory signals and altered development have long been suggested, the mechanisms linking immunity and development have been less clear. Within the developing lung mesenchyme, microbial products and cytokines activate NF-B and inhibit FGF-10 expression and prevent normal epithelial-mesenchymal interactions during airway formation (8,13). Our results here reveal a novel mechanism linking inflammation-mediated NF-B activation and abnormal transcriptional regulation of Fgf-10.…”

“…The related Sp family member SP3 can act as both a transcriptional activator and repressor, depending on cellular context (25). We previously showed that SP1 drives FGF-10 transcription and that this effect can be inhibited by NF-B activation (8). However, it was not clear how NF-B might inhibit SP1-mediated transcription in the absence of conserved predicted NF-B binding sites.…”

“…Preterm infants with severe bronchopulmonary dysplasia have reduced saccular airway and alveolar duct formation and have lower FGF-10 expression in their lungs (8,9). In adult patients, Fgf-10 haploinsufficiency can lead to abnormal pulmonary function and chronic obstructive pulmonary disease (10).…”

Macrophages and CSF-1

“…Indeed, the inflammatory activation of macrophages during development not only contributes to tissue damage and disruption of organ development through pro-inflammatory injury, but may also skew macrophages away from their trophic functions. 111,139,140 Inflammatory activation of fetal lung macrophages through NF-κB signaling was found to upregulate proinflammatory mediators such as IL-1β and alter expression of Wnt7b, bone morphogenic protein (BMP)4 111 and fibroblast growth factor (FGF)-10. 139 And while inflammatory challenges such as lipopolysaccharide (LPS) or IL-1β administration in models of chorioamnionitis promote accelerated maturation, the mechanism is distinct from alveolarisation, characterized by a lung pathology associated with BPD.…”

“…111,139,140 Inflammatory activation of fetal lung macrophages through NF-κB signaling was found to upregulate proinflammatory mediators such as IL-1β and alter expression of Wnt7b, bone morphogenic protein (BMP)4 111 and fibroblast growth factor (FGF)-10. 139 And while inflammatory challenges such as lipopolysaccharide (LPS) or IL-1β administration in models of chorioamnionitis promote accelerated maturation, the mechanism is distinct from alveolarisation, characterized by a lung pathology associated with BPD. 141 Today, corticosteroids remain one of the most important advancements in reducing the mortality associated with preterm birth, however they are associated with precocious maturation and significant side effects.…”