Integration of stem cells and graphene for myocardial infarction treatment

Abstract

Myocardial infarction (MI) is one of the major causes of death worldwide. However, the clinical therapies to treat MI is very limited, and the number of patients increases every year. Therefore, there is an urgent need to develop alternative therapeutic methods for cardiac repair after MI. Recently, stem cell and tissue engineering emerged as a potential strategy for MI treatment. In addition, graphene has also drawn much attention for their application in the field of biomedical engineering due to its unique electrical, chemical, optical, and physical properties. Therefore, in this dissertation presents the integration of stem cells and graphene for the treatment of MI. The major goals of this study is summarized as follows. 1) Development of a graphene platform to promote stem cell differentiation towards cardiac lineage, and the investigation of its mechanisms. 2) Improvement of stem cell therapy efficacy for MI treatment by utilizing reduced graphene oxide (RGO) to promote paracrine factor secretion and gap junction protein expression by stem cells. 3) Utilizing graphene oxide (GO) flakes to prevent stem cell anoikis when implanted to ischemia and reperfusion injury after MI. First, we showed that graphene can promote cardiomyogenic differentiation process of mesenchymal stem cells (MSCs). MSCs have drawn much attention as a source of MI therapy because MSCs are easy to isolate and expand, and are capable of differentiating into various cell types. However, the conventional methods to differentiate stem cells to cardiomyocytes require expensive growth factors or toxic chemical inducers. In this study, we demonstrated that the cardiomyogenic differentiation process of MSCs could be promoted simply by culturing MSCs on graphene without using additional inducers for the differentiation. This may be attributed to the enhanced expression of extracellular matrix (ECM) proteins related to cardiomyogenic differentiation. In addition, the signaling molecules required for cardiomyogenic differentiation are upregulated in MSCs cultured on graphene. Collectively, graphene was able to promote cardiomyogenic gene expressions in MSCs. Second, we showed that the incorporation of RGO flakes into MSC spheroids enhanced the expression of angiogenic growth factors and gap junction proteins in MSCs, and resulted in the attenuation of cardiac remodeling after MI. The secretion of paracrine factors and the formation of gap junctions by the implanted cells promote cardiac repair. The formation of spheroids by MSC clustering is known to promote growth factor secretion by promoting cell-cell interactions. However, cell-ECM interactions, which can further promote growth factor secretion, is very limited in MSC spheroids. Therefore, in this study, we incorporated RGO, which can adsorb ECM proteins, in MSC spheroids to promote cell-ECM interactions. As a result, the secretion of paracrine factors was further enhanced in MSC-RGO hybrid spheroids. The enhanced secretion of paracrine factors by the incorporation of RGO upregulated the gap junction protein expression in MSCs. The implantation of MSC-RGO spheroids promoted cardiac repair compared to the implantation of MSC spheroids. Finally, the adhesion of GO flakes to MSCs prior to implantation enhanced the therapeutic efficacy of MSCs in MI. The restoration of blood flow after MI results in a burst of reactive oxygen species (ROS). ROS hinders the adhesion of the implanted MSCs to the injured myocardium, resulting in cell anoikis (i.e. cell death due to the loss of adhesion). Therefore, we have protected MSCs from undergoing anoikis by adhering GO flakes to MSCs prior to their implantation to the injured myocardium. GO is capable of effectively adsorbing ECM proteins. ECM protein-adsorbed GO flakes protected MSCs from undergoing anoikis when MSCs-GO were exposed to ROS condition in vitro. In vivo, MSCs-GO showed enhanced engraftment in the reperfused myocardium after MI compared to MSCs alone. The enhanced engraftment of MSCs-GO resulted in enhanced paracrine factor secretion. Therefore, the adhesion of GO flakes to MSCs promoted cardiac tissue repair and cardiac function restoration.