EXTRACELLULAR VESICLES IN STEM CELL BIOLOGY
Hur, Yun Ha
Pluripotent stem cells reside transiently in the epiblast of blastocyst-stage embryos, until the proper time when they receive signals to differentiate into the germ layers that will give rise to the entire organism. However, the mechanisms that underlie the regulation of stem cell fate in the developing embryo, particularly how they maintain pluripotency, remain poorly understood. Here we show that embryonic stem cells (ESCs), the in vitro equivalents of stem cell populations within the epiblast, form and release extracellular vesicles (EVs), including microvesicles (MVs) and exosomes, to help maintain their stemness. Treating ESCs cultured under differentiation-inducing conditions with MVs and/or exosomes isolated from pluripotent ESCs blocked their differentiation and preserved stem cell characteristics including the ability to generate chimeric animals. Such effects were determined to be dependent on the extracellular matrix protein fibronectin associated with the vesicles, and its ability to bind to integrins and activate focal adhesion kinase (FAK) in recipient cells. These findings raise the exciting possibility that EVs might serve as a mechanism that helps stem cells within the blastocyst to maintain their pluripotent state.In addition to the roles that ESC-derived EVs potentially play in the physiological setting, we made interesting discoveries showing that they also can dramatically impact the behavior of differentiated cells by causing them to behave like stem cells, and even possibly induce pluripotency. The treatment of mouse embryonic fibroblasts (MEFs), a type of somatic cell, with MVs and exosomes produced by ESCs protected the cells from serum starvation-induced cell death and delayed senescence. Moreover, the EV-treated MEFs were also found to acquire the phenotypes of stem cells, such as the ability to form spheres, exhibit alkaline phosphatase activity, and express core stemness proteins Oct3/4 and Nanog. The EVs from ESCs strongly activated the cell survival and growth-promoting protein AKT in MEFs, and when EV-mediated AKT activation was inhibited, the MEFs no longer showed stem cell-like characteristics. Collectively, these findings shed light on how a unique form of intercellular communication can have important consequences in early development, as well as can potentially be used for regenerative medicine applications.
Embryonic stem cell; Exosomes; Extracellular vesicles; Microvesicles; Pluripotent stem cell; Pluriptoency
Cerione, Richard A.
Kurpios, Natasza; Linder, Maurine E.; Sondermann, Holger
Biomedical and Biological Sciences
Ph. D., Biomedical and Biological Sciences
Doctor of Philosophy
dissertation or thesis