Date on Master's Thesis/Doctoral Dissertation

5-2015

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biochemistry and Molecular Biology

Degree Program

Biochemistry and Molecular Biology, MS

Committee Chair

Hong, Kyung

Committee Co-Chair (if applicable)

Bhatnagar, Aruni

Committee Member

Jones, Steven

Committee Member

Cheng, Alan

Committee Member

Cole, Marsha

Subject

Heart--Diseases--Treatment; Stem cells

Abstract

The belief that adult mammalian heart lacks regenerative potential was challenged by the identification of c-kit positive cardiac progenitor cells (CPCs) in the heart. A recent phase I clinical trial (SCIPIO), has shown that autologous c-kit positive CPCs improve cardiac function and quality of life when transplanted into ischemic heart disease patients. c-Kit is a type III receptor tyrosine kinase and a common stem cell antigen. Stem cell factor (SCF) is the only known ligand for c-kit. Although c-kit is extensively used as an invariable marker of resident CPCs and shown to be important in the context of different cell types, there is no information on its role in the regulation of cellular characteristics of CPCs. This led us to hypothesize that c-kit plays a role in the regulation of survival, growth and migration of human CPCs. To test this hypothesis, CPCs were grown under stress conditions (e.g., serum starvation and oxidative stress) in the presence or absence of SCF. The effects of SCF-mediated activation of c-kit on CPC survival/growth were measured using cell viability assay, BrdU labeling and caspase 3/7 activity assay. I observed a statistically significant increase in cell survival with SCF treatment compared to the untreated control when CPCs were subjected to serum depletion. However, SCF treatment did not lead to a significant increase in cell viability against 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) or hydrogen peroxide (H2O2) induced oxidative stress. Furthermore, the pro-survival effect of SCF was augmented by c-kit overexpression and abrogated by co-treatment with imatinib, an inhibitor of c-kit, suggesting that necessity of c-kit activity for the effect of SCF. I then checked if activation of c-kit can promote migration of CPCs. I found that CPCs were highly chemotactic to SCF showing a statistically significant increase in cell migration after SCF treatment. The results of the differentiation study are not convincing and need further experiments to derive a conclusion. We also found that SCF treatment on CPCs activated the phosphoinositide 3-kinase (PI3K) and the mitogen activated protein kinase (MAPK) pathways. With the use of specific inhibitors, we confirmed that the SCF dependent survival and chemotaxis of CPCs are dependent on these two pathways. In conclusion, the results of our experiments suggest that c-kit promotes the survival, growth and migration of CPCs cultured ex vivo via the activation of PI3K and MAPK pathways. These results imply that the efficiency of homing of CPCs to the injury site as well as their post-transplantation survival may be improved by modulating the activity of c-kit.

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