Signaling through interleukin-1 type 1 receptor diminishes Haemophilus somnus lipooligosaccharide-mediated apoptosis of endothelial cells.
During sepsis, endothelial cells are both a source and target of pro-inflammatory cytokines (e.g. IL-1alpha, IL-1beta, TNFalpha and others), which may be detrimental to vascular homeostasis. Our laboratory has demonstrated that Haemophilus somnus, a gram-negative pathogen of cattle that causes sepsis and vasculitis, and its lipooligosaccharide (LOS) induce caspases-3, -8 and -9 activation, and apoptosis of endothelial cells in vitro. In this study, we provide evidence that H. somnus LOS increases IL-1alpha and IL-1beta mRNA expression, and caspase-1 activation in endothelial cells. Addition of a caspase-1 inhibitor (YVAD), or incubation in a high extracellular potassium buffer (150 mM), reduced caspase-1 activation and significantly enhanced H. somnus LOS-mediated caspase-3 activation. Likewise, blocking the IL-1 type 1 receptor by addition of IL-receptor antagonist (IL-1ra) significantly enhanced LOS-mediated caspase-3 activation. Conversely, addition of exogenous recombinant bovine IL-1beta (100 ng/mL) to endothelial cells diminished LOS-mediated apoptosis. IL-1beta has been reported previously to protect numerous cell types from apoptosis by activating PI3 kinase/p-Akt signaling pathways. Addition of selective PI3 kinase inhibitors (e.g. wortmannin and LY294002) significantly enhanced LOS-mediated caspase-3 activation. Exposure of endothelial cells to IL-1beta or LOS increased pAkt protein as assessed by western blot. Overall, these results suggest that signaling through the IL-1 type 1 receptor diminishes H. somnus LOS-mediated apoptosis.
Sylte
Matt J
MJ
Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 63706, USA.
Kuckleburg
Chris J
CJ
Atapattu
Dhammika
D
Leite
Fabio P
FP
McClenahan
David
D
Inzana
Thomas J
TJ
Czuprynski
Charles J
CJ
D000818:Animals; D017209:Apoptosis; D020170:Caspase 1 / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000382:microbiology / Q000473:pathology*; D004789:Enzyme Activation; D044138:Haemophilus somnus / Q000472:pathogenicity*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases; D011651:Pulmonary Artery / Q000166:cytology; D017472:Receptors, Interleukin-1 / Q000378:metabolism*; D015398:Signal Transduction
D008070:Lipopolysaccharides; D017472:Receptors, Interleukin-1; C023023:lipid-linked oligosaccharides; D019869:Phosphatidylinositol 3-Kinases; D020170:Caspase 1