Lipopolysaccharide Induces Endoplasmic Store Ca2+-Dependent Inflammatory Responses in Lung Microvessels

Abstract

The pulmonary microvasculature plays a critical role in endotoxin-induced acute lung injury. However, the relevant signaling remain unclear. Specifically the role of endothelial Ca2+ in the induction of endotoxin-mediated responses in lung microvessels remains undefined. Toward elucidating this, we used the isolated blood-perfused rat lung preparation. We loaded microvessels with the Ca2+ indicator, Fura 2 AM and then determined Ca2+ responses to infusions of lipopolysaccharide (LPS) into the microvessels. LPS induced a more than two-fold increase in the amplitude of cytosolic Ca2+ oscillations. Inhibiting inositol 1,4,5 trisphosphate receptors on endoplasmic reticulum (ER) Ca2+ stores with Xestospongin C (XeC), blocked the LPS-induced increase in the Ca2+ oscillation amplitude. However, XeC did not affect entry of external Ca2+ via plasma membrane Ca2+ channels in lung microvascular endothelial cells. This suggested that LPS augmented the oscillations via release of Ca2+ from ER stores. In addition, XeC also blocked LPS-mediated activation and nuclear translocation of nuclear factor-kappa B in lung microvessels. Further, inhibiting ER Ca2+ release blunted increases in intercellular adhesion molecule-1 expression and retention of naïve leukocytes in LPS-treated microvessels. Taken together, the data suggest that LPS-mediated Ca2+ release from ER stores underlies nuclear factor-kappa B activation and downstream inflammatory signaling in lung microvessels. Thus, we show for the first time a role for inositol 1,4,5 trisphosphate-mediated ER Ca2+ release in the induction of LPS responses in pulmonary microvascular endothelium. Mechanisms that blunt this signaling may mitigate endotoxin-induced morbidity.

Lipopolysaccharide Compromises Human Sperm Function by Reducing Intracellular cAMP

“…Previous studies have reported that LPS perturbs intracellular Ca 2+ homeostasis in microglial cells, cardiomyocytes, and lung microvessels (Choi et al 2002;Beck et al 2008;Wang et al 2009;Kandasamy et al 2013;Magi et al 2015). In contrast, the present study showed that human sperm [Ca 2+ ] i was unaffected by LPS (Fig.…”

“…5C, D). This discrepancy may be attributed to two factors: first, LPS changes [Ca 2+ ] i by regulating the expression of genes encoding Ca 2+ and Na + /Ca 2+ channels in microglial cells, cardiomyocytes, and lung microvessels (Choi et al 2002;Beck et al 2008;Wang et al 2009;Kandasamy et al 2013;Magi et al 2015). However, sperm lack active transcriptional machinery so that LPS could not affect intracellular Ca 2+ homeostasis by regulating gene expression.…”

“…However, sperm lack active transcriptional machinery so that LPS could not affect intracellular Ca 2+ homeostasis by regulating gene expression. Second, LPS affects intracellular Ca 2+ homeostasis by release of Ca 2+ from endoplasmic reticulum (ER) Ca 2+ stores (Kandasamy et al 2013). However, the mature sperm lack ER.…”

Cooperative Signaling via Transcription Factors NF-κB and AP1/c-Fos Mediates Endothelial Cell STIM1 Expression and Hyperpermeability in Response to Endotoxin

“…Bacterial endotoxin (LPS) can directly induce Ca 2ϩ overload in ECs to cause endothelial barrier dysfunction and vascular injury (11,12). Bacterial cell wall component LPS ligates TLR4 to induce the expression of cytokines, chemokines, adhesion molecules, apoptotic factors, and several other mediators through NF-B and p38 MAPK activation (13)(14)(15).…”

Live Imaging of the Lung

“…Because these events occur to a greater extent in BECs than at other locations of the pulmonary capillary bed, the lung’s immune response initiates with leukocyte accumulation at postcapillary branch points (19). Recent RFI studies on lung capillaries indicate that the endotoxin-induced expression of the leukocyte adhesion receptor ICAM-1 also occurs as a consequence of IP 3 -induced endothelial Ca 2+ oscillations (20, 21). …”