Question:

High oscillatory wall shear stress occurs in arterial vessels, forcefully dragging along both liquid as well as cellular components in the blood at high velocity. Considering this, it is stunning, that within the context of cardiovascular diseases monocytes can slow down, attach and eventually transmigrate through the vessel wall. In order to overcome these forces, monocytes may be dependent on the on the availability of von Willebrand factor (vWF) multimers released by endothelial CD40-soluble CD40 ligand (sCD154) interactions as shown recently. In addition, adapting to various stimuli in their environment like platelets adhered to vWF, diapedeses of monocytes has subsequently an effect on their state of differentiation.

Methodology:

A new experimental set was established, consisting of a combination of an orbital shaker and a transmigration chamber. After applying various amounts of shear stress, vWF multimers are assessed on the endothelial cell monolayer while transmigrated monocytes in the lower chamber are analysed quantitatively and qualitatively. The effect of recombinant trimeric sCD154 or freshly isolated platelets on the transmigration behaviour and state of activity of the monocytes is studied by confocal microscopy, qPCR, FACS and ELISA.

Results:

An ideal rate of shear stress was determined at which transmigration of monocytes as such is virtually precluded but can in fact be enhanced several fold by sCD154-induced vWF release and addition of platelets to the fluid compartment above the endothelial cell monolayer. First results also revealed that diapedesis of the monocytes leads to their differentiation into a pro-inflammatory phenotype as shown by an increased expression of M1 macrophage marker genes.

Conclusions:

A new method to mimic transmigration of monocytes through a monolayer of endothelial cells has been established taking into account the effects of a near-physiological level of shear stress on this process. First data indicate the dependency on vWF multimers and adhered platelets as a prerequisite to withstand the high shear forces at physiological blood flow in arteries or arterioles, which in turn may facilitate the transmigration and differentiation of monocytes to macrophages in these vascular beds.