The role of mitosis in LDL transport through cultured endothelial cell monolayers

Abstract

We (7) have previously shown that leaky junctions associated with dying or dividing cells are the dominant pathway for LDL transport under convective conditions, accounting for >90% of the transport. We (8) have also recently shown that the permeability of bovine aortic endothelial cell monolayers is highly correlated with their rate of apoptosis and that inhibiting apoptosis lowers the permeability of the monolayers to LDL. To explore the role of mitosis in the leaky junction pathway, the microtubule-stabilizing agent paclitaxel was used to alter the rate of mitosis, and LDL flux and water flux (J(v)) were measured. Control monolayers had an average mitosis rate of 0.029%. Treatment with paclitaxel (2.5 μM) for 1.5, 3, 4.5, or 6 h yielded increasing rates of mitosis ranging from 0.099% to 1.03%. The convective permeability of LDL (P(e)) increased up to fivefold, whereas J(v) increased up to threefold, over this range of mitosis rates. We found strong correlations between the mitosis rate and both P(e) and J(v). However, compared with our previous apoptosis study (8), we found that mitosis was only half as effective as apoptosis in increasing P(e). The results led us to conclude that while mitosis-related leaky junctions might play a role in the initial infiltration of LDL into the artery wall, the progression of atherosclerosis might be more closely correlated with apoptosis-related leaky junctions.

Fig. 1.

Correlation between mitosis rate and difussive permeability (P_o). The plot shows the mitosis rate and P_o for control monolayers and monolayers treated with paclitaxel for 1.5, 3, 4.5, or 6 h. The inset shows the correlation when only control monolayers are considered. The Pearson product-moment correlation coefficient for the full range was 0.696 (P < 0.0005). For the data in the inset, the correlation was not significant.

Fig. 2.

Correlation between mitosis rate and convective permeability (P_e). The plot shows the mitosis rate and P_e for control monolayers and monolayers treated with paclitaxel for 1.5, 3, 4.5, or 6 h. The inset shows the correlation when only control monolayers are considered. The Pearson product-moment correlation coefficient for the full range was 0.774 (P < 0.0005). For the data in the inset, the Pearson product-moment correlation coefficient was 0.499 (P < 0.021).

Fig. 3.

Correlation between mitosis rate and water flux (J_v). The plot shows the mitosis rate and J_v for control monolayers and monolayers treated with paclitaxel for 1.5, 3, 4.5, or 6 h. The inset shows the correlation when only control monolayers are considered. The Pearson product-moment correlation coefficient for the full range was 0.795 (P < 0.0005). For the data in the inset, the Pearson product-moment correlation coefficient was 0.482 (P < 0.023).

Fig. 4.

Vascular endothelial (VE)-cadherin staining (red) for cell-cell junctions and MPM-2 staining (green) for cells in the M phase. A and B: controls; C and D: cells treated with paclitaxel for 3 h. The arrows denote gaps in cell-cell junctions. The arrowhead in A denotes a tricellular corner gap. Note that paclitaxel-treated mitotic cells appear rounded, whereas controls are more spread out. This is likely due to paclitaxel arresting cells in metaphase, when cells normally assume this spherical shape.

Fig. 5.

Effect of mitosis rate on transport properties. The data shown in Figs. 1–3 were normalized by the average control values for each set. The inset shows detail at the low range of (normalized) mitosis.