Barrier dysfunction of the corneal endothelium in response to TNF-alpha: role of p38 MAP kinase.
OBJECTIVE
TNF-alpha is elevated in the cornea and aqueous humor during allograft rejection and anterior uveitis. The authors investigated the involvement of p38 MAP kinase in the TNF-alpha-induced loss of barrier integrity in monolayers of cultured bovine corneal endothelial cells.


METHODS
Transendothelial electrical resistance (TER), a measure of barrier integrity, was determined by electrical cell-substrate impedance sensing. Barrier integrity was further assessed in terms of permeability to FITC dextran. Reorganization of the apical junctional complex (AJC) in response to TNF-alpha was visualized by immunofluorescence. The expression of TNF-alpha receptors was confirmed by RT-PCR. Activation of p38 MAP kinase in response to TNF-alpha was determined by Western blot analysis.


RESULTS
Exposure to TNF-alpha induced a continuous decline in TER that persisted for more than 20 hours. It also led to a significant increase in permeability to FITC dextran. At the AJC, the cytokine caused disassembly of microtubules, disruption of perijunctional actomyosin ring (PAMR), and dislocation of ZO-1 and cadherins. Western blot analysis showed that TNF-alpha also led to the activation of p38 MAP kinase. All these responses to the cytokine were opposed by treatment with SB-203580, a selective p38 MAP kinase inhibitor. TNFR1, but not TNFR2, was expressed in untreated cells with no change in the expression pattern on treatment with the cytokine.


CONCLUSIONS
TNF-alpha breaks down the barrier integrity of corneal endothelium, concomitant with the disruption of PAMR, remodeling of AJC, and disassembly of microtubules. These effects are mediated by transient activation of p38 MAP kinase. Thus, the TNF-alpha-induced barrier dysfunction in the corneal endothelium can be suppressed by inhibitors of p38 MAP kinase and agents downstream of the kinase that affect the cytoskeleton.
School of Optometry, Indiana University, Bloomington, Indiana 47405, USA.
Mahesh
M
Shivanna
Gangaraju
G
Rajashekhar
Sangly P
SP
Srinivas
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D015820:Cadherins / Q000378:metabolism; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D017097:Electric Impedance; D004728:Endothelium, Corneal / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019084:Fluorescent Antibody Technique, Indirect; D008565:Membrane Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000378:metabolism; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D062826:Zonula Occludens-1 Protein; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D015820:Cadherins; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D010750:Phosphoproteins; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D014409:Tumor Necrosis Factor-alpha; D062826:Zonula Occludens-1 Protein; D048051:p38 Mitogen-Activated Protein Kinases