Anti-Inflammatory Gene Therapy for the Promotion of Implanted Stem Cell Survival in Infarcted Myocardium
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Cardiovascular disease is the leading cause of death in the developed world and is responsible for approximately 36% of Irish mortality. Myocardial infarction (MI), which is literally the death of cardiac tissue due to lack of oxygenation, accounts for the majority of deaths associated with cardiovascular disease. This death of cardiac tissue leads to a loss of cardiac function as the damaged area becomes a non-contractile scar. Reversal of this process is the main aim of regenerative cardiac strategies such as stem cell transplantation. While initial studies were promising, subsequent clinical trials yielded disappointing results. Stem cell therapy may be limited by the poor survival rate of the cells after implantation into the infarcted heart, which is likely due to the inflammatory response. Thus, antiinflammatory gene therapy with interleukin-10 (IL-10) was proposed as a method to modulate the inflammatory response due to MI, thereby promoting the survival of rat mesenchymal stem cells (rMSCs) seeded into a collagen scaffold delivery system. It was hypothesized that IL-10 gene therapy could be used to increase the retention rate of stem cells in a collagen scaffold when delivered to the ischemic myocardium. The primary objectives of this doctoral project were to develop a controlled release scaffold-based gene therapy system suitable for stem cell delivery to the infarcted myocardium. The efficacy of this system was evaluated by assessing stem cell retention, overall cardiac function and the inflammatory response. A crosslinked collagen-based biomaterial was developed and optimised for rMSC culture in vitro. Non-viral plasmid-dendrimer polyplexes were optimized for transfection in both two and three-dimensional culture. The release of these polyplexes from the scaffolds was assessed with a specifically developed fluorescent detection technique. When cells were seeded into polyplex loaded scaffolds, relatively high levels of transgene expression were observed for up to three weeks of culture. When the polyplex-loaded scaffolds were implanted in rat skeletal muscle, increased retention of rMSCs was observed. This increased rMSC retention was associated with decreased inflammation and a change in macrophage phenotype from cytotoxic to regulatory. Similarly, when the polyplex-loaded scaffolds were implanted over the surface of infarcted rat hearts, rMSC retention was increased, the inflammatory and remodelling responses were modulated and, most importantly left ventricular ejection fraction ¿ a measure of cardiac function ¿ was significantly improved. This is the first study to describe a biomaterial scaffold combined with gene and stem cell therapy capable of improving outcome after MI. There is significant potential for further development of the technique which could ultimately represent a step towards the realization of true cardiac regeneration.
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