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Role of matrix metalloproteases in the kinetics of leukocyte-endothelial adhesion in post-capillary venules.

BACKGROUND
The endothelial glycocalyx serves as a barrier to leukocyte (WBC)-endothelium (EC) adhesion. Shedding of glycans, by matrix metalloproteases (MMPs) exposes EC integrin receptors to facilitate firm adhesion. However, the effect of shedding on the strength of the adhesive bond remains to be determined.


OBJECTIVES
Examine the effect of MMP inhibition on the kinetics of WBC-EC adhesion under normal and inflammatory conditions to delineate differences in the duration and number of adhesive bonds.


METHODS
WBC adhesion in post-capillary venules was observed in rat mesentery. Adhesion duration and off-rates (KOFF) were correlated with shear stress during adhesion in response to 1 µM fMLP or 0.5 µM doxycycline (doxy, to inhibit MMP activation).


RESULTS
Doxy increased mean adhesion time significantly from 2.5 (control) to 5.6 s, whereas fMLP increased it 8-fold to 20 s, which was not affected by pre-treatment with doxy. Estimates of the number of adhesive bonds (simplified Bell-model) revealed a significantly greater increase with fMLP compared to doxy alone, with no effect on fMLP by pretreatment with doxy. With doxy alone, KOFF was significantly 4-fold greater compared to fMLP, suggesting a much weaker bond.


CONCLUSIONS
Although the increased number of bonds by MMP inhibition with doxy alone and fMLP were similar, the bonds due to doxy appeared weaker as evidenced by their shorter duration, and lesser reduction in KOFF relative to control. Thus doxy limits the availability of integrin binding sites during fMLP stimulated adhesion, but has a pro-adhesive effect due to increased ligands for WBC binding that arises from inhibition of normal sheddase activity on the EC.