Transendothelial migration of mesenchymal stem cells

When tissue becomes injured or damaged it undergoes a repair process with the aim of bringing the tissue back to its normal functioning. In order to enhance this repair, which sometimes does not occur adequately, there is much interest in targeting stem cells to tissues to enhance repair. In adults there is a type of stem cell called mesenchymal stem cells (MSC) that can form a variety of tissues and have been administered to patients to try and enhance tissue regeneration. When these cells are injected into the blood they can migrate into tissues to some extent. Nothing is known about how these cells migrate across the wall of the blood vessel into the injured tissue. In this process the MSC have to cross endothelial cells which cover the inner lining of the blood vessels. This grant proposal aims to understand this mechanism. An experimental system will be set up to observe the migration of MSC across endothelial cells. The MSC will be flowed across endothelial cells to mimic blood flow and the molecules involved in transendothelial migration analysed. Transendothelial migration of white blood cells (leukocytes) is well characterised where specific molecules called adhesion molecules and chemokines are involved. Adhesion molecules are known to 'stick' leukocytes to endothelial cells so that migration of leukocytes across these cells can occur. Chemokines are molecules that attract cells and cause them to migrate and are involved in directing leukocytes out the blood stream and into the tissue. Some of these adhesion molecules and chemokines have been detected on MSCs but little or nothing is known about which are functional in migration. This will be investigated in the project. It will also be examined if it is possible to label MSC with microscopically small magnetic particles and to use magnets to capture and immobilise MSC on endothelial cells. It will then be investigated if chemokines can further enhance the migration of the magnetic MSC across the endothelium. The successful outcome the project would identify which adhesion molecules and chemokines are involved in directing MSC across endothelial cells and if magnetic particles can enhance this. Once this is known one may be able to increase the recruitment of MSC into damaged or injured tissues to help regenerate them.

Mesenchymal stem cells (MSC) are multipotent cells capable of differentiating into a variety of tissues. There is currently much interest in these cells for tissue engineering purposes, to enhance the regeneration of injured or damaged tissue. There is evidence that when MSC are administered in the circulation they show some degree of extravasation and engraftment into damaged tissue. Nothing is known regarding the mechanism that these cells use to transmigrate across the endothelium. This is in contrast to leukocytes whose recruitment mechanisms into tissues are comparatively well-described. MSC have been shown to express adhesion molecules and chemokine receptors, but it is not known which of these are functional in transendothelial migration. Furthermore it may be possible to enhance transendothelial migration using magnetic nanoparticles to capture circulating MSC in a selected region of the vasculature. The objectives of the research are to: 1) Establish an in vitro model of MSC adhesion and migration across endothelial cells under conditions of flow; 2) To use this model to identify adhesion molecules, chemokines and chemokine receptors involved in the adhesion and transendothelial migration of MSCs; 3) To establish if magnetic nanoparticles in combination with chemokines can be used to enhance the capture and transendothelial migration of MSCs. MSCs and human umbilical vein endothelial cells (HUVEC) will be treated with blocking antibodies to adhesion molecules, chemokines and chemokine receptors. The effects of these antibodies on MSC rolling, stable adhesion and transmigration will be examined under conditions of flow. As a positive control results will be compared to those of neutrophils whose adhesive and migratory characteristics are well-described in this model. The adhesion and migration of MSCs across endothelial cells from skin and heart origin will be compared with those of HUVEC. MSC will be loaded with magnetic nanoparticles and flowed over endothelial cells. It will be investigated if magnets can capture these MSC on the endothelium, and in the presence of chemokines lead to enhanced transendothelial migration. The successful outcome of the project would identify functional adhesion molecules, chemokines and their receptors in MSC migration and if this migration can be augmented by magnetic nanoparticles. The research could reveal factors that stimulate stem cells to relocate to sites of tissue injury, leading to therapeutic strategies to improve homing of stem cells and tissue repair.