TNFα alters occludin and cerebral endothelial permeability: Role of p38MAPK.
Occludin is a key tight junction (TJ) protein in cerebral endothelial cells (CECs) playing an important role in modulating blood-brain barrier (BBB) functions. This protein (65kDa) has been shown to engage in many signaling pathways and phosphorylation by both tyrosine and threonine kinases. Despite yet unknown mechanisms, pro-inflammatory cytokines and endotoxin (lipopolysaccharides, LPS) may alter TJ proteins in CECs and BBB functions. Here we demonstrate the responses of occludin in an immortalized human cerebral endothelial cell line (hCMEC/D3) to stimulation by TNFα (10 ng/mL), IL-1β (10 ng/mL) and LPS (100 ng/mL). Exposing cells to TNFα resulted in a rapid and transient upward band-shift of occludin, suggesting of an increase in phosphorylation. Exposure to IL-1β produced significantly smaller effects and LPS produced almost no effects on occludin band-shift. TNFα also caused transient stimulation of p38MAPK and ERK1/2 in hCMEC/D3 cells, and the occludin band-shift induced by TNFα was suppressed by SB202190, an inhibitor for p38MAPK, and partly by U0126, the MEK1/2-ERK1/2 inhibitor. Cells treated with TNFα and IL-1β but not LPS for 24 h resulted in a significant (p < 0.001) decrease in the expression of occludin, and the decrease could be partially blocked by SB202190, the inhibitor for p38MAPK. Treatment with TNFα also altered cell morphology and enhanced permeability of the CEC layer as measured by the FITC-dextran assay and the trans-endothelial electrical resistances (TEER). However, treatment with SB202190 alone could not effectively reverse the TNFα -induced morphology changes or the enhanced permeability changes. These results suggest that despite effects of TNFα on p38MAPK-mediated occludin phosphorylation and expression, these changes are not sufficient to avert the TNFα-induced alterations on cell morphology and permeability.
Department of Bioengineering, University of Missouri, Columbia, Missouri, United States of America.
Yawen
Y
Ni
Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States of America.
Tao
T
Teng
Department of Biochemistry, University of Missouri, Columbia, Missouri, United States of America.
Runting
R
Li
Department of Biochemistry, University of Missouri, Columbia, Missouri, United States of America.
Agnes
A
Simonyi
Department of Biochemistry, University of Missouri, Columbia, Missouri, United States of America.
Grace Y
GY
Sun
Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States of America.
James C
JC
Lee
D001812:Blood-Brain Barrier / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002540:Cerebral Cortex / Q000378:metabolism*; D055724:Electrophysiological Phenomena; D042783:Endothelial Cells / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D053583:Interleukin-1beta / Q000378:metabolism / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000276:immunology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D062793:Occludin / Q000235:genetics / Q000378:metabolism*; D010539:Permeability; D010766:Phosphorylation; D015398:Signal Transduction / Q000187:drug effects; D019108:Tight Junctions / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D062793:Occludin; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases