MICE LACKING SIALIDASE HAVE AN ALTERED HEPATIC ENDOTHELIAL GLYCOCALYX IN RESPONSE TO TNF

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MICE LACKING SIALIDASE HAVE AN ALTERED HEPATIC ENDOTHELIAL GLYCOCALYX IN RESPONSE TO TNF

PM Kolakowska¹, S Igdoura², AE Fox-Robichaud¹
¹Intestinal Disease Research Program; ²Dept of Biology, McMaster University, Hamilton, Ontario

The ability of leukocytes to interact with endothelial cells is dependent on the interaction of adhesion molecules embedded within the glycocalyx lining the cell surface. We hypothesize that enzyme-dependent structural changes to the glycocalyx regulate leukocyte recruitment. The objective of this study was to determine the importance of sialidase in regulating leukocyte adhesion within the hepatic microcirculation.
Female wild type (C57Bl/6) or congenitally sialidase deficient (Sm57) mice were injected with 500 ng of TNFa intraperitoneally and the hepatic microcirculation examined by intravital microscopy 4 h later. The hepatic glycocalyx was examined in vivo by injecting 75 µl of the FITC-labeled plant lectin Banderiea simplicifolia (BS-1).
Mice deficient in sialidase had a significant increase in leukocyte rolling in the post-sinusoidal venules in response to TNF compared wild-type mice (6.8±2.0 cells/min vs 1.6±1.2 cells/min). This was associated with a significant reduction in adhesion in the central venules (4.5±1.5 cells/field of view vs 12.2±3.4 cells/field of view) in the sialidase deficient mice. Leukocyte adhesion was also significantly reduced in the TNF-treated Sm57 mice in the portal venules and the sinusoids. Binding of the a-D-galactosyl specific lectin BS-1 increases within the hepatic microcirculation, particularly the sinusoids, in response to TNF. In the C57Bl/6 mice FITC-BS-1 fluorescence was limited to the vascular space producing a clear outline of the sinusoids. In contrast, in the SM57 mice there was reduced fluorescence within the vessels and increased fluorescence within the parenchyma.
Mice with a spontaneous mutation in the sialidase gene have increased leukocyte rolling and decreased sinusoidal and venular adhesion in response to TNF. Within the hepatic sinusoids, with TNF treatment, the dominant sugar a-D-galactosyl becomes more available for lectin binding. The different distribution of BS-1 in the Sm57 mice suggests the lack of sialidase in these mice results an alteration in the glycocalyx that interferes with leukocyte adhesion.

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