Recent studies have focused attention on the role of mitogenic niches in regulating stem cell self-renewal, and have emphasized the importance of proteoglycans in forming such microenvironments. However, more than 50 years after the genetic code was deciphered, we do not know whether sugar chains on proteoglycans encode biologically important information. The potential complexity of such a “glyco code” is enormous, but little is known about the features of the proteoglycans involved in mitogenic regulation, or the signaling mechanisms required for stem cell renewal. To decipher whether there is a glyco code we will identify proteoglycans that specify stem cell renewal in the mammalian brain. We will rely on a genetic approach to proteoglycan biology and on newly developing innovations in mass spectrometry that allow large scale analysis of the sugar composition of proteoglycans. We will generate mutated growth factors capable of binding to cognate receptors, but unable to bind proteoglycans. We will ascertain whether individual proteoglycans modulate the signaling pathway and the biological response elicited by a growth factor, perhaps by influencing the location, presentation, or oligomerization of the factor. We will begin by focusing on Sonic Hedgehog (Shh), which is mitogenic for stem cells in the cerebellum, cortex, and in diverse cancers. We will identify proteoglycans required for Shh- mediated proliferation using a new assay for mitogenic niches, and we will determine how a glyco code might regulate stem cell propagation. As the work progresses we will extend our studies to define proteoglycan structures that modulate the response of stem cells to additional agents such as EGF or FGF family members. These studies will contribute to the identification of a glyco-code, and will determine mechanisms that maintain “stemness”. Such studies can lead to enhanced therapies for disorders from Alzheimers disease to cancers to stroke.
