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Calcium and calmodulin regulate lipopolysaccharide-induced alveolar macrophage production of tumor necrosis factor
Background:
Alterations in macrophage (M phi) function are responsible, in part, for adult respiratory distress syndrome and multiple organ failure developing in patients with sepsis. Elucidation and control of these M phi mechanisms during sepsis are crucial to our understanding of this disease and, ultimately, to improving survival of these patients.
Objective:
To investigate the involvement of calcium flux in endotoxin-induced alveolar M phi production of tumor necrosis factor (TNF) and procoagulant (PC) activity.
Design:
Rabbit alveolar M phi obtained by bronchoalveolar lavage were exposed to endotoxin in the form of lipopolysaccharide (LPS) extracted from Escherichia coli 0111:B4 in the presence of different specific calcium agonists and antagonists. The TNF expression was measured in the supernatant by L929 bioassays. The PC activity was determined in cell lysates by a one-step coagulation assay.
Results:
Macrophages activated by LPS produce enormous levels of TNF and PC. Either W7 (20 mumol/L), a calmodulin antagonist, or TMB-8 (50 mumol/L), which prevents calcium release from the endoplasmic reticulum, inhibited production of both TNF and PC activity. Verapamil (50 mumol/L) alone or combined with TMB-8 significantly inhibited both TNF and PC production by LPS-stimulated M phi. Elevating intracellular calcium ([Ca2+]i), using the calcium ionophore, A23187, or thapsigargin alone, did not induce M phi production of TNF but significantly augmented LPS-stimulated TNF production.
Conclusion:
Our results indicate that increased intracellular calcium causing signal transduction activation through the calmodulin pathway is a necessary, but insufficient, component of the LPS signaling in M phi.
Insights
Calcium flux is crucial for endotoxin-induced macrophage activation in sepsis, impacting tumor necrosis factor (TNF) and procoagulant (PC) production. Inhibiting calcium signaling reduces these inflammatory responses, offering potential therapeutic targets.
Area of Science:
- Immunology
- Cellular Biology
- Sepsis Pathophysiology
Background:
- Macrophage (M phi) dysfunction contributes to sepsis complications like ARDS and organ failure.
- Understanding M phi mechanisms in sepsis is vital for improving patient outcomes.
Purpose of the Study:
- To investigate the role of calcium flux in endotoxin-induced alveolar M phi production of tumor necrosis factor (TNF) and procoagulant (PC) activity.
Main Methods:
- Rabbit alveolar M phi were stimulated with lipopolysaccharide (LPS) in the presence of calcium modulators.
- TNF levels were measured via bioassay, and PC activity was determined using a coagulation assay.
Main Results:
- LPS-stimulated M phi produced significant levels of TNF and PC.
- Calmodulin antagonists (W7) and calcium release inhibitors (TMB-8) reduced TNF and PC production.
- Elevating intracellular calcium augmented LPS-induced TNF production.
Conclusions:
- Increased intracellular calcium, activating the calmodulin pathway, is essential but not solely sufficient for LPS signaling in M phi.
- Targeting calcium signaling pathways may offer therapeutic strategies for sepsis-induced inflammation.