The characterisation, pharmacology and applications of stem cell derived Endothelial cells

Abstract

Stem cell derived endothelial cells have a growing number of applications in clinical medicine and biomedical research and will be critical in any organ regeneration programme. Endothelial cells can now be derived from a number of distinct stem cell populations including embryonic stem cells, blood progenitors and induced pluripotent stem cells. In order for stem cell derived endothelial cells to be used optimally it is important that they are fully assessed for the cardinal characteristics of endothelial cells on mature vessels.

With this in mind, in my thesis I have assessed the ability of stem cell derived endothelial cells to display hallmarks of authentic endothelial cells from vessels including, alignment under shear stress, responses to pathogen stimuli and vasoactive hormone release. My group has previously shown that endothelial cells from human embryonic stem cells did not respond to agonists of toll-like receptor-4 (TLR4). TLR4 is important to allow endothelial cells to sense infection, but is also associated with cardiovascular disease. In my PhD, I showed that, whilst these cells have no TLR4 they have a fully functional NOD1 receptor pathway which allows the cells to sense Gram-negative bacteria. This may be relevant to their use therapeutically and allowed me to speculate that these cells are immune competent, but through lack of TLR4 might be protected from vascular inflammation. In order for stem cell derived endothelial cells to be useful in in vitro assays however, it is important that they express all the key hallmarks of endothelial cells from vessels. Endothelial cells grown from blood progenitors or from induced pluripotent stem cells did have TLR4 responses and released vasoactive hormones at levels comparable to endothelial cells from vessels.

In the later part of my PhD, I applied endothelial cells derived from blood progenitor cells to key assays to study endothelial cell biology and pharmacology. This included an assay to detect cytokine storm reactions to drugs, which currently limits the development of biological drugs. This assay, employing cells derived from stem cells of individual patients also has applications in personalised medicine. In my final chapter, I was able to grow BOEC from a patient with a homozygous mutation that results in loss of function of the enzyme cPLA2, which is thought to be critical to prostaglandin and prostacyclin release, and used these cells to study this pathway. I showed that cPLA2α is the dominant isoform responsible for the release of prostacyclin from endothelial cells and provided a proof-of-concept that BOEC can be used to phenotype patients.

In summary, my thesis includes characterisation of stem cell derived endothelial cells, and includes applications of adult progenitor derived cells in assays to study pharmacology and cell biology with a view to developing personalised medicines and cell therapies.