The active role of
endothelium is one of the key factors for the initial step of
inflammation. Endothelial cell (EC) activation leads to an immediate
release of various proteins, cytokines and the adhesive glycoprotein
von Willebrand factor (VWF).
Exposed to the blood flow, VWF shows a state-function-relationship:
the glycoprotein multimers become stretched and form fibre-like
structures immobilised on EC surface.
As a consequence of the critical coiled-stretched transition and
subsequent binding, VWF is a shear-activated protein
and thereby uncovers formerly shielded binding sites.
Hereafter, the regular repressive
function on inflammation and coagulation subsides and the endothelial
surface converts to a proinflammatory and procoagulatory phenotype.
VWF can be therefore also considered as a shear-dependent inflammatory
molecule bridging coagulation and inflammation.
Within the last funding period we
elucidated the formation of EC-secreted VWF and the impact of large
VWF multimers on platelet/leukocyte/bacteria adhesion under defined
shear rates upon inflammatory conditions. Therefore we addressed the
role of shear flow conditions for the activation and self-assembly of
endothelium-derived VWF and the impact of an inflammatory milieu on
the activity of VWF and its degrading protease ADAMTS13. Our objectives for the
requested funding period arise from the combined effort of all SHENC
groups to elucidate the shear-dependent functions of VWF.
The recent insights into the process of
self-assembly of VWF, resulting in its ability to induce collective
network formation under high-shear conditions, represent an auspicious
research area of potential high medical impact. So far unexplored, the
characteristics of this collective network formation, defined by the
state of VWF in the micromilieu of inflammatory conditions, will be
our key target for the requested funding period. Therefore, our
research will concentrate on the following main aspects: Focusing on
VWF-induced collective networks we want to uncover the mechanistic,
functional and pathophysiological background of their formation,
activation and degradation. Our established
in vitro vascular model
system allows a capacious characterisation of the shear-induced
activation capacity and collective network behaviour of VWF and
distinct VWF mutations. Clinical relevant VWF mutations, so far failed
to be functionally diagnosed by standard assays, will be reliably
identified und mechanistically analysed. Furthermore, we will broaden
our methodological spectrum by implementation of electrical
cell-substrate impedance sensing, thereby addressing the role of VWF
on its reflexive effect on EC function and vascular permeability under
VWF collective networks interactions from
globular to stretched to aggregation transition (based on
doi: 10.1160/TH13-09-0800, Fig. 6).
of simulation and RICM movie snapshots of human whole blood
supplemented with soluble VWF on a VWF biofunctionalised surface. At
low-flow conditions only single platelets (colloids, red in schematics
, white dots in RICM) interact with the surface (left). Above a
critical fibre shear rate, VWF (green) recruited from the bulk
reversibly build fibre-like structures and bind colloids (middle).
Under high-shear conditions (with a critical aggregate shear rate of
reversible VWF-colloid aggregates appear rolling on the surface,
dissolving after reducing the shear rate. Scale bars correspond to