Lipopolysaccharide induces endoplasmic store Ca2+-dependent inflammatory responses in lung microvessels

Area of Science:

• Pulmonary vascular biology
• Endothelial cell signaling
• Inflammation and immunology

Background:

• The pulmonary microvasculature is crucial in acute lung injury (ALI) induced by endotoxins.
• The specific role of endothelial calcium (Ca2+) signaling in endotoxin-mediated responses remains unclear.
• Understanding these pathways is vital for developing treatments for ALI.

Purpose of the Study:

• To elucidate the role of endothelial Ca2+ signaling in lipopolysaccharide (LPS)-induced responses in rat pulmonary microvessels.
• To investigate the source of Ca2+ augmentation following LPS exposure.
• To determine the downstream inflammatory consequences of altered Ca2+ signaling.

Main Methods:

• Isolated blood-perfused rat lung preparation.
• Measurement of intracellular Ca2+ using Fura 2 AM indicator.
• Pharmacological inhibition of endoplasmic reticulum (ER) Ca2+ stores using Xestospongin C (XeC).
• Assessment of nuclear factor-kappa B (NF-κB) activation and translocation.
• Evaluation of intercellular adhesion molecule-1 (ICAM-1) expression and leukocyte retention.

Main Results:

• LPS infusion significantly increased cytosolic Ca2+ oscillation amplitude in lung microvessels.
• Inhibition of inositol 1,4,5 trisphosphate receptors with XeC blocked LPS-induced Ca2+ increase, indicating ER Ca2+ release.
• XeC treatment also inhibited LPS-mediated NF-κB activation, nuclear translocation, ICAM-1 expression, and leukocyte retention.
• External Ca2+ influx was not affected by XeC, confirming ER stores as the source.

Conclusions:

• LPS-induced Ca2+ release from ER stores is a key mechanism driving NF-κB activation and subsequent inflammatory signaling in pulmonary microvessels.
• This study demonstrates the critical role of inositol 1,4,5 trisphosphate-mediated ER Ca2+ release in LPS responses within the pulmonary microvascular endothelium.
• Targeting this specific Ca2+ signaling pathway may offer a novel therapeutic strategy to mitigate endotoxin-induced ALI.