Bone marrow derived cells as endothelial precursors and the role of multi-potent progenitor cells in repairing ischaemic tissues.
Introduction: Atherosclerosis and its complications are a major cause of death and disability and it remains a major challenge to develop new therapies for patients with irreversible end organ damage and ongoing ischaemia. The discovery of adult stem and progenitor cells with the ability to regenerate adult tissues holds great promise. Bone marrow is the source of both endothelial progenitor cells (EPCs) and multi-potent adult progenitor cells (MAPCs). MAPCs are rare pluripotent bone marrow derived cells with the theoretical potential to differentiate into tissues of all three germ cell layers, including endothelium. These cells may have the potential to facilitate cardiac repair. The aim of this thesis was to further characterise bone marrow derived endothelial progenitor cells including multi potent adult progenitor cells and assess their angiogenic potential and mechanisms of action in animal models of cardiovascular disease. Findings: EPCs were isolated from humans and mice and their phenotype, markers and function determined, including gene tracking experiments in mice utilising the Cre/Lox system. It was not possible to isolate cells with the same phenotype as MAPCs from rodent bone marrow. However, cells with pluri-potent properties, named rat multi-potent progenitor cells (rMPCs), were isolated from rat bone marrow. These cells had the ability to up regulate tissue specific antigens from all 3 germ cell lineages and in addition secreted multiple cytokines related to angiogenesis and inflammation. To investigate the in vivo properties of rMPCs a rat hind limb model of ischaemia was established and syngeneic rMPCs were transplanted into the ischaemic hind limbs. rMPCs engrafted selectively into the adventitia of arterioles of ischaemic muscles. However, engrafted cells did not differentiate into an endothelial or smooth muscle phenotype. Cytokine analysis of muscles 5 days after rMPC injection revealed raised levels of cytokines, including chemokines MCP1 and SDR. Limb perfusion, measured by microspheres, increased after rMPC injection. In addition a novel MRI based assessment of ischaemic muscles revealed a significant normalisation of MRI signal after rMPC transplantation. However, there was no improvement in limb function assessed by treadmill running distance 4 weeks after cell injection. These findings suggest that transplantation of rMPCs into ischaemic muscles may modulate local inflammatory and angiogenic responses through paracrine mechanisms. Conclusion: Despite the potential for stem and progenitor cells to be used for the treatment of chronic cardiac ischaemia the biology of stem cells is still relatively poorly understood, as is the mechanism of action of cells after transplantation. As set out in the aims, the work in this thesis adds further to our understanding of both EPCs and BM derived pluri-potent stem cells. In addition it provides insight into the hind limb ischaemia model and the mechanism of action of cell therapy after transplantation into ischaemic muscle.
- Theses