Endothelial cells contain a storage organelle, Weibel-Palade Bodies (WPB), which contains key components of both inflammatory and haemostatic processes. As a rapid-response system, the WPB are of critical importance in initiating haemostatic and inflammatory responses within the rapidly-changing vascular environment.
The major content protein of WPB is von Willebrands factor (VWF), an adhesive glycoprotein that plays a major role in primary haemostasis. This very large highly multimerised protein is stored within the WPB coiled up as proteinacious tubules.
Mutations within VWF are the commonest cause of the inherited bleeding disorder Von Willebrands Disease. In addition to mutations causing a loss of platelet binding or other direct haemostatic problems, mutations in VWF can affect the formation of the protein tubules, leading to formation of damaged, poorly functional WPB.
We are working with endothelial cells from patients with bleeding disorders to further understand these complex defects. Recent advances in microscopy and in bioinformatics have revealed that WPB size increases in half-micron steps. The subunits are brought together in the trans-Golgi where they assemble into the wide distribution of lengths that we find in human cells. By manipulating WPB length, we have shown that short WPB are much less efficient at supporting platelet recruitment, and thus initiating primary haemostasis.
Our lab exploits our new understanding of the cellular controls on WPB formation to (1) understand how these act in concert to produce a functional output from the WPB, thus controlling the activated endothelial cell phenotype; (2) determine how changes to WPB produce different functional responses to endothelial antagonists; (3) identify and characterise new controls on endothelial phenotype.
Recently we have begun to explore the fact that the machinery involved in making WPB is also needed for making platelet granules, small organelles that are critical to the platelet function in haemostasis. We have applied super-resolution microscopy to platelet diagnosis, and are now also working with endothelial cells from patients with platelet function disorders.