Date of Completion

4-12-2019

Embargo Period

4-11-2020

Keywords

Atomic force microscopy; red blood cell; ICAM-4 adhesion receptor; cAMP-PKA pathway; beta adrenergic receptor; angiotensin II type 1 receptor; valsartan; vaso-occlusion; RBC deoxygenation; RBC viscoelasticity

Major Advisor

George Lykotrafitis

Associate Advisor

Biree Andemariam

Associate Advisor

Ying Li

Associate Advisor

Thanh Nguyen

Associate Advisor

Savas Tasoglu

Field of Study

Mechanical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Human red blood cells (RBCs) provide essential gaseous exchanges to all body’s tissues and organs through the circulatory system. RBCs lack of nucleus and organelles provides as much room as possible for the oxygen-carrying protein hemoglobin. Hemoglobin composes ~98% of the soluble proteins in mature RBCs. RBCs have a biconcave shape corresponding to a large cellular surface area-to-volume ratio allowing for efficient gas exchange and increased cell deformability ensuring passage through the narrowest capillaries without rupturing and vessel obstruction. In sickle cell disease (SCD), a single point mutation occurs in the beta-globin gene, resulting in the production of abnormal hemoglobin (HbS) which, in deoxygenated conditions, polymerizes to form stiff filaments deforming SCD RBCs (SS-RBCs) to a wide variety of sickle shapes. In addition to the irregular shape, SS-RBCs are stiffer, more viscous, and show higher adhesion than normal (wild-type) WT-RBCs to other RBCs, platelets, leukocytes, and to the endothelium. Consequently, abnormal SS-RBC adhesion leads to delayed microvascular passage of deoxygenated RBCs inducing sickling and entrapment of RBCs, a key trigger of vaso-occlusive episodes (VOEs) which is the pathophysiologic hallmark of SCD.

We employed a powerful technique called single-molecule force spectroscopy to investigate the mechanism of RBC adhesion and signaling, and to guide advances in SCD pharmacotherapy. Specifically, we studied the effect of the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) dependent signaling pathway on the activation of intercellular adhesion molecule-4 (ICAM-4) receptors, which express on the RBC surface and bind with high-affinity to endothelial αvβ3 integrin, in turn, inducing endothelial injury and inflammation likely contributing to VOEs in SCD. We demonstrated that the activation of ICAM-4 receptors is regulated via the cAMP-PKA pathway and importantly we determined for the first time that this activation is mediated by A-kinase anchoring proteins (AKAPs). We also investigated the possibility of receptor cross-talk between the β-adrenergic receptor (β-AR) and the angiotensin II type 1 receptor (AT1R), which resulted in a trans-inhibitory effect of valsartan on the ICAM-4 activation. These findings may lead to novel pharmacological approaches for the prevention and treatment of VOEs.

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