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Macrophage activation by gastric fluid suggests MMP involvement in aspiration-induced lung disease
Chih Mei Cheng1, Chong Chao Hsieh, Chang Sheng Lin
1Faculty of Biomedical and Environmental Biology, Kaohsiung Medical University, Taiwan.
Abstract:
Asthma occurs in more than 5% of the population in industrialized countries and is now characterized as a chronic inflammatory disease. The chronic aspiration of gastric fluid is considered by many investigators to be a primary inflammatory factor exacerbating or predisposing patients to asthma, with more than 50 medical papers per year linking asthma with gastroesophageal reflux disease (GERD), which can lead to aspiration events. However, the mechanisms involved in the inflammatory effects caused by gastric-fluid aspiration are not clear at the present time. The role of macrophages in the pathogenesis of disease seems likely given the involvement of those cells in a variety of chronic inflammatory diseases. To investigate the potential role of gastric fluid and the mechanisms potentially underlying chronic aspiration-associated pathogenesis, we examined the activation of murine macrophages (Raw 264.7 cell line) with gastric fluid. Inflammatory cytokine production and activation of the NF-kappaB signaling pathway were observed. Toll-like receptor (TLR)-4-dependent activation was observed under some conditions, indicating that bacterial components within the gastric fluid are involved in macrophage activation. Matrix metalloproteinase-9 (MMP-9) expression by macrophages was enhanced by gastric fluid, suggesting a potential mechanism by which remodeling of airways might be induced by gastric-fluid aspiration.
Insights
Gastric fluid aspiration may worsen asthma by activating macrophages, a key immune cell. This process involves inflammatory signaling and Toll-like receptor 4, potentially leading to airway remodeling.
Area of Science:
- Immunology
- Gastroenterology
- Pulmonology
Background:
- Asthma is a chronic inflammatory disease affecting over 5% of people in industrialized nations.
- Gastroesophageal reflux disease (GERD) is frequently linked to asthma, with chronic gastric fluid aspiration a suspected trigger.
- The precise mechanisms by which gastric fluid aspiration influences asthma pathogenesis remain unclear.
Purpose of the Study:
- To investigate the role of gastric fluid in activating macrophages, a crucial component of the immune system.
- To elucidate the signaling pathways and molecular mechanisms involved in gastric fluid-induced inflammation relevant to asthma.
Main Methods:
- Murine macrophages (Raw 264.7 cell line) were exposed to gastric fluid.
- Analysis of inflammatory cytokine production and NF-kappaB signaling pathway activation.
- Assessment of Toll-like receptor (TLR)-4 dependency and Matrix metalloproteinase-9 (MMP-9) expression.
Main Results:
- Gastric fluid induced inflammatory cytokine production and NF-kappaB activation in macrophages.
- TLR-4-dependent activation was observed, suggesting a role for bacterial components in gastric fluid.
- Gastric fluid significantly enhanced macrophage expression of MMP-9, an enzyme implicated in tissue remodeling.
Conclusions:
- Gastric fluid can activate macrophages, contributing to inflammation associated with asthma.
- TLR-4 and bacterial elements in gastric fluid play a role in macrophage activation.
- Enhanced MMP-9 expression by macrophages suggests a mechanism for airway remodeling due to gastric aspiration in asthma.
