Regulation of survival, proliferation, and self -renewal of multipotent neural progenitors: Roles for insulin, transferrin, and PTEN

Multipotent neural progenitors (MNP), sometimes known as neural stem cells, are now well-recognized as a population of progenitors that self-renew as well as differentiate into cells that are neurons and glia. MNP are components in a series of inborn 'programs' that not only ensure normal development, but are thought to persist throughout adult life in a mostly quiescent state, dividing and repairing the brain during times of incidental injury and learning/memory development. Manipulations of MNP division and differentiation have been the focus of several repair strategies for neurodegenerative diseases. While many factors that control MNP fate differentiation into neurons and/or glia have been identified, little is known about how to maintain into neurons and/or glia have been identified, little is known about how to maintain these cells in an undifferentiated state. In particular, factors known to regulate proliferation, self-renewal and survival of MNP are scarce. The current thesis manipulates both extrinsic (supplements in the media) as well as intrinsic (genes), using the in vitro neurosphere culture system to determine the effects. In the first study (Chapter 2), I demonstrate the importance of both transferrin and insulin in the proliferation and survival of MNP and other sphere-forming progenitors (SFP). I determined that SFP do not require mitogens for FGFR or EGFR in order to survive for at least two weeks in culture. In the second and third studies (Chapter 3 and 4), I examined neural progenitors lacking Pten, a tumor suppressor gene mutated in up to 65% of glioblastomas. Using a conditional knockout mouse with Pten deleted in the brain, in vivo and in vitro observations determined that PTEN negatively controls proliferation of MNP. Furthermore, I found that Pten-deletion persistently negates MNP proliferation and self-renewal over multiple neurosphere passages in culture. Collectively, these findings have several implications including, (1) a better understanding of what factors are important in growing neurospheres, (2) a better understanding of MNP biology in vitro and in the developing brain, and (3) a better understanding of tumor formation.