The endothelial glycocalyx mediates shear-induced changes in hydraulic conductivity

Abstract

Recent in vitro and in vivo studies have reported fluid shear stress-induced increases in endothelial layer hydraulic conductivity (L(p)) that are mediated by an increased production of nitric oxide (NO). Other recent studies have shown that NO induction by shear stress is mediated by the glycocalyx that decorates the surface of endothelial cells. Here we find that a selective depletion of the major components of the glycocalyx with enzymes can block the shear stress-induced response of L(p). Heparinase and hyaluronidase block shear-induced increases in L(p), which is consistent with their effects on NO production. But chondroitinase, which does not suppress shear-induced NO production, also inhibits shear-induced L(p). A further surprise is that treatment with the general proteolytic enzyme pronase does not suppress the shear L(p) response. We also find that heparinase does not alter baseline L(p) significantly, whereas chondroitinase, hyaluronidase, and pronase increase it significantly.

Fig. 1.

Effect of different enzyme treatments on bovine aortic endothelial cell (BAEC) hydraulic conductivity (L_p) response to shear stress. At time 0 min, a hydrostatic pressure differential of 10 cmH₂O was applied to the monolayers to drive water flow across them, and a baseline level was established after 1 h. The L_p values were normalized to the baseline level for each monolayer. At time 60 min, shear stress of 20 dyn/cm² was applied and L_p recorded for 3 h. The monolayers that were treated with heparinase III (n = 5), hyaluronidase (n = 4), and chondroitinase (n = 16) displayed a significant attenuation of the shear-stress effect on L_p, whereas the pronase-treated monolayers (n = 6) did not. Inhibition of the shear response by chondroitinase was not as great as by heparinase or hyaluronidase. *P < 0.05, significant difference between treated and control monolayers. n, Number of runs.

Fig. 2.

Cumulative nitric oxide concentration vs. time for BAECs under static and shear conditions for 1% BSA media, BSA-free media, and heparinase-treated monolayers in BSA-free media. Shear was applied at time 0 (n = 9). #P < 0.05 vs. 1% BSA shear. n, Number of runs.