UBC Theses and Dissertations
Hyaluronan binding and CD44 in regulating hematopoiesis and CD8 T cell response Lee-Sayer, Sally
CD44 is a ubiquitously expressed transmembrane glycoprotein. Through CD44, hematopoietic cells can be induced to bind hyaluronan, a component of the extracellular matrix, at specific developmental or functional stages, leading to the hypothesis that the interaction between CD44 and hyaluronan is important in regulating development and function of immune cells. I demonstrated that chondroitin sulfation of CD44 differentially regulates hyaluronan binding by classically and alternatively activated bone marrow-derived macrophages. T cells also increase hyaluronan binding upon activation, and chondroitin sulfate is likely involved in this regulation, since inhibitors of glycosylation, actin rearrangement, or sialylation had no effect on hyaluronan binding by activated T cells. By using competitive cell transfer models, I found CD44 expression and hyaluronan binding were involved in regulating CD8 memory T cell formation and hematopoietic reconstitution. CD44-/- OT-I CD8 T cells formed significantly more memory cells than CD44⁺/⁺ OT-I CD8 T cells in the lymphoid organs, despite forming similar effector cell numbers, after intravenous infection with ovalbumin-expressing Listeria monocytogenes. While in competition, hyaluronan-binding CD8 effector T cells had increased pAkt expression and glucose uptake, both of which negatively regulate memory potential. Furthermore, hyaluronan-binding CD8 effector T cells showed increased death. Overall, this work implicates CD44 and hyaluronan binding as negative regulators of survival through contraction and memory formation by high affinity OT-I CD8 T cells. To investigate the role of hyaluronan binding in hematopoiesis, I transduced CD44-/- bone marrow cells with CD44 point mutants with increased or abolished hyaluronan binding (GOF or LOF, respectively), and then transferred these cells into lethally irradiated hosts in competition with wild type cells. GOF cells out-competed wild type cells, which in turn out-competed LOF cells, in the reconstitution of all myeloid and most lymphoid populations, suggesting a competitive advantage in early hematopoiesis. Within the bone marrow stem and progenitor cells, GOF cells out-competed wild type cells, which in turn out-competed LOF cells, suggesting a role of the CD44-hyaluornan interaction in positively regulating reconstitution by hematopoietic stem and progenitor cells. Overall, this study identified novel roles for CD44 and HA binding in regulating CD8 T memory, and hematopoietic stem and progenitor cells.
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