The power of differentiation : characterizing the regulatory roles of an O-glycosyltransferase and N-glycanase during neural induction of human pluripotent stem cells

The human body contains over 10 trillion cells spanning hundreds of morphologically distinct cell types. These cells derive from a small subset of pluripotent stem cells (hPSC) that have the ability to propagate indefinitely and can be induced to differentiate into all the cell types of the human body. While the molecular mechanisms that govern the self-renewal and differentiation of these special cells is still being characterized, their ability to uncover complex biological processes, not possible in classic cell culture or animal models, is already being realized. Understanding the biological process that are not encoded in the genome, but exist in other forms of cellular regulation such as post-translational modifications, are essential for advancements in biology and medicine. Glycobiology is the study of the structure, biosynthesis, and processing of sugars and their functional roles in biology. The addition of a single monosaccharide, -N- acetylglucosamine (O-GlcNAc), to the hydroxy side chain of serine or threonine residues of intracellular proteins has profound implications in cellular homeostasis and disease progression. This post-translational modification shares many similar qualities with phosphorylation but only has two enzymes involved in the addition and removal of O-GlcNAc, making genetic perturbation of its enzymes difficult, when not lethal. O-GlcNAc transferase and O-GlcNAcase, respectively, have been shown to target key transcriptional and epigenetic regulators necessary for stem cell biology. The modification is required for cell viability and perturbations to the regulation of O-GlcNAc have been associated with multiple diseases and disorders. A great deal of interest is currently devoted towards deciphering the functional role of O-GlcNAc in stem cell maintenance and development. Similarly, the deficiency in the NGLY1 enzyme responsible for removing glycans (branched sugars) from misfolded proteins has recently been shown to cause a devastating congenital neurological disorder. Inability to reproduce a pathologically relevant animal model has caused researchers to look toward reprogramming patient cells, into induced pluripotent stem cells (hiPSC), for more accurate modeling of the disorder. In both cases, pluripotent stem cells are being utilized to elucidate molecular mechanisms essential in glycobiology. Chapter 1 briefly covers the history of the field of stem cell biology and major events that defined the field. These events laid the groundwork for revolutionary breakthroughs in research and medicine. How stem cell biology can facilitate advancements in basic and translational research pertaining to glycobiology will be discussed. Moreover, how stem cell biology can advance our understanding of the functional significance of glycobiology. Chapter 2 describes the chemical inhibition of the O-GlcNAc transferase enzyme in understanding O-GlcNAcylation's regulatory role during the neural induction of hPSCs. Inhibition of OGT induced the early expression of neuronal proteins and accelerated the conversion of hESCs into neural stem cells, suggesting a regulatory role of O-GlcNAc in maintaining proper brain development. The results presented in this chapter will also help define the molecular behavior of stem cells during neuronal development so that they can be used effectively and reliably for the treatment of neurodegenerative disorders. Finally, in Chapter 3 describes a new congenital disorder of glycosylation called NGLY1-CDDG. Induction of corrected and uncorrected NGLY1-CDDG hiPSCs towards the neural crest lineage revealed altered morphology and differential gene expression during differentiation. This finding has major implications on future research into modeling the disorder and its potential therapeutic intervention.

Advisor: Bertozzi Carolyn R.
Liphardt Jan 
Monje-Deisseroth Michelle
Palmer Theo