| Description |
Glycosaminoglycans (GAGs) are ubiquitously found in the extracellular space where they regulate cellular signaling events involved in many developmental and pathophysiological processes. Their many regulatory functions arose from their ability to bind many ligands, which is accounted for by their tremendous structural variations. Despite their well-documented essentiality, glycan-based therapeutics have not advanced far from the use of heparin for anticoagulation, the structure of which were deduced more than 40 years ago. Challenges such as microheterogeneity, lack of sensitive analytical tools, and structural and functional redundancy impede the establishment of the biological functions of specific structures and their roles in various pathologies. In this dissertation, the roles of extracellular GAGs in the guidance of various biological processes are investigated using a molecular approach and a genetic approach. In the first part, small molecules known as xylosides were screened for their effects on three biological processes in vitro: Angiogenesis, neurogenesis, and lung morphogenesis. Xylosides compete with endogenous proteins for precursors and biosynthetic enzymes to assemble GAGs, thereby reducing endogenous proteoglycanbound GAGs while increasing xyloside-bound free GAGs, resulting in a variety of biological consequences. Treating endothelial cells with xylosides could promote network formation in the in vitro matrigel tube formation assay and ex ovo chick allantoic membrane assay. Treating neural progenitor cells with xylosides could increase the neuron iv to glial ratio of the differentiated cells, and neurite outgrowth and tyrosine hydroxylase expression of the differentiated neurons. Treating embryonic lung explants with xylosides helped sustain and increased in vitro branching of the distal tips. These observations were dependent on both the chemical structure of the xyloside and the concentration of treatment. The second part of the dissertation looks specifically at the 3-O-sulfation present in the anti-thrombin binding HS (HSAT+) by studying the phenotypic outcomes of the Hs3st1- /-/Hs3st5-/- (DKO) mice. The 3-O-sulfation is added late in HS biosynthesis and is the rarest modification. HSAT+ important for the anticoagulant activities of heparin is predominantly generated by HS3ST1 and to a lesser extent, HS3ST5. Interestingly, Hs3st1-/- mice do not have a procoagulant phenotype, although they display other abnormalities. To uncover other physiological roles of HSAT+, the metabolic activities, glucose homeostasis, and blood physiology of the DKO mice were characterized. DKO mice have excellent glycemic control, higher metabolic rates, higher levels of inflammation, and slight microcytic anemia. In summary, the potential of xylosides as a laboratory tool or therapeutic drug to alter GAG profiles and manipulate cell behavior was demonstrated in Chapters 2, 3, and 4, and the possible physiological roles of HSAT+ were described in Chapter 5. Together, it is hoped that these studies will generate new insights to the role of extracellular GAGs and in regulating various biological processes, contributing to the development of novel glycan-based therapeutics in the long term. |
