Author ORCID Identifier
Date of Graduation
5-2017
Document Type
Dissertation (PhD)
Program Affiliation
Biochemistry and Molecular Biology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Yang Xia, M.D, Ph.D.
Committee Member
Yang Xia, M.D, Ph.D.
Committee Member
Rodney E. Kellems, Ph.D.
Committee Member
Dorothy E. Lewis, Ph.D.
Committee Member
Harinder S. Juneja, M.D.
Committee Member
Zheng Chen, Ph.D.
Abstract
Sphingosine 1-phosphate (S1P) is a bioactive signaling sphingolipid produced in every mammalian cell. It plays a variety of important roles both in and outside of cells. S1P is highly enriched in mature erythrocytes because of the high enzymatic activity of the S1P-generating enzyme Sphingosine Kinase 1 (Sphk1) and the absence of S1P degrading enzymes. Erythrocytes are considered only a major reservoir for S1P because they supply S1P to the circulation for the regulation of various physiological processes which include but are not limited to immune cell trafficking, endothelial integrity and hematopoietic stem cell mobilization. However, if S1P plays a role in the oxygen delivery ability of erythrocyte is unknown. Recent studies using unsupervised metabolomics screening revealed significantly higher S1P levels in Sickle Cell Disease mice. Moreover, the activity of erythrocyte Sphk1 was also higher in SCD and was further increased by hypoxia. Elevated erythrocyte Sphk1 and S1P contribute to sickling and SCD progression, though by an unknown mechanism. Here in this thesis, I provide answers to three key questions regarding S1P and Sphk1 in erythrocytes: i) the regulation of erythrocyte Sphk1 activation; ii) the function of erythrocyte Sphk1/S1P in hypoxia adaptation; iii) the mechanism underlying the detrimental role of erythrocyte Sphk1/S1P in SCD. Elevated adenosine, a signaling molecule induced by hypoxia, increases erythrocyte Sphk1 activity in normal and sickle erythrocytes by activating the A2B adenosine receptor (ADORA2B) which then leads to activation of protein kinase A (PKA) and Extracellular Signal Regulated Kinase 1/2 (ERK1/2) signaling pathways. Activated erythrocyte Sphk1 and elevated S1P are beneficial to hypoxia adaptation by promoting erythrocyte glycolysis to increase oxygen release. In SCD, erythrocyte Sphk1/S1P mediated elevation of glycolysis is detrimental because of the increased sickling and oxidative stress induced. The discoveries reported in this thesis not only extend human knowledge in understanding erythrocyte physiology and pathology, but also reveal several innovative mechanism-based therapeutic targets that can be harnessed to develop treatments for hypoxia and SCD.
Keywords
Erythrocyte; Sphingosine 1-Phosphate; Sphingosine Kinase 1; Adenosine Signaling; Hypoxia Adaptation; Oxygen Release; Glucose Metabolism; Sickle Cell Disease