Sickle Cell Disease
The Sickle Cell Disease is the first described to be the result of a single gene mutation. The primary genetic effect is a single DNA base substitution (the sixth codon of the beta-hemoglobin gene changes from GAG to GTG resulting in the substitution of Glu6 to Val6 in the beta-S chain). The resulting abnormal hemoglobin a2bs2 has an increased tendency to polymerize when deoxygenated.
However, there is wide range of clinical severity, due to:
- multiple phenotypic effects from a single gene, e.g., increased hemolysis leads to large numbers of young red cells with enhanced vascular adhesion and increased K:Cl cotransport expression, as well as
- the action of other genes besides beta-S, e.g., the protective effect of alpha-thalassemia trait (regarding acute chest, anemia, and CVA but not pain crises), of the hereditary persistence of Hemoglobin F, or the X-linked F-cell production locus (Kaul et al. 1996).
As Dr. Orah Platt (Harvard Medical School) states we need to consider "a more holistic view (of) the sickle red cell with its abnormal contents and membrane in a larger context-as it interacts with, damages, and stimulates the vascular endothelium and surrounding tissues and cells" (Platt 2000).
Dr. Kalfa as the Sickle Cell Scholar in the Cincinnati Children's Hospital Medical Center Comprehensive Sickle Cell Center has long term research interests in:
- Understanding the intracellular signaling pathways triggered within the endothelial and red blood cells in Sickle Cell Disease, and
- Exploring the signal transduction pathways in the erythrocyte that may affect the cell shape.
Activation of endothelial cells with upregulation of VCAM-1, ICAM-1, E-selectin, and P-selectin has been established in the sickle cell disease (Setty and Stuart 1996; Hebbel 1997; Solovey et al. 1997). A variety of adhesion molecules have been identified on the cell membrane of the reticulocytes and the mature erythrocytes (Telen 2000), that enable them to adhere to endothelial cells as well as to components of the subendothelial extracellular matrix. For example, reticulocytes are expressing a4b1 (VLA-4) which bind to VCAM-1 on endothelial cells, as well as on fibronectin of the extracellular matrix and the von Willebrand factor (Joneckis et al. 1993; Swerlick et al. 1993). VCAM-1 has been described to mediate loss of cell-cell adhesion, which is both Rac1 (and Rac1-dependent ROS production) and Rho mediated (van Wetering et al. 2003), and this event allows transendothelial monocyte migration. Furthermore, contraction of these activated endothelial cells allows exposure of basement membrane molecules which, in that case, could interact with red blood cells and leucocytes, as well as with bridging molecules from the plasma such as von Willebrand factor, ultimately culminating in vasoocclusion and local tissue ischemia (Pathare et al. 2003).
The lab plans to isolate and establish primary cultures of mouse microvascular endothelial cells from lungs of wild type (WT) mice as well as from Rac 2 knock-out and Rac 1 conditional knock-out mice, and use these cells to study the adhesive interactions with WT or Rac deficient mouse erythrocytes. A parallel goal is to evaluate the effects of Rho GTP-ases to the red blood cell cytoskeleton, and explore the signal transduction pathways in the erythrocyte that may affect the cell shape.
Related Publications
Where possible, article titles are linked to an abstract of the article. Selected citations may also be linked to PDFs of the article available on a Journal's site. Depending on the Journal's publishing policy, you may need a subscription to download the PDF.
Hebbel RP (1997) Adhesive interactions of sickle erythrocytes with endothelium. J Clin Invest 100:S83-6.
Joneckis CC, Ackley RL, Orringer EP, Wayner EA, Parise LV (1993) Integrin alpha 4 beta 1 and glycoprotein IV (CD36) are expressed on circulating reticulocytes in sickle cell anemia. Blood 82:3548-55.
Kaul DK, Fabry ME, Nagel RL (1996) The pathophysiology of vascular obstruction in the sickle syndromes. Blood Rev 10:29-44.
Pathare A, Kindi SA, Daar S, Dennison D (2003) Cytokines in sickle cell disease. Hematology 8:329-37.
Platt OS (2000) Sickle cell anemia as an inflammatory disease. J Clin Invest 106:337-8.
Setty BN, Stuart MJ (1996) Vascular cell adhesion molecule-1 is involved in mediating hypoxia-induced sickle red blood cell adherence to endothelium: potential role in sickle cell disease. Blood 88:2311-20.
Solovey A, Lin Y, Browne P, Choong S, Wayner E, Hebbel RP (1997) Circulating activated endothelial cells in sickle cell anemia. N Engl J Med 337:1584-90.
Swerlick RA, Eckman JR, Kumar A, Jeitler M, Wick TM (1993) Alpha 4 beta 1-integrin expression on sickle reticulocytes: vascular cell adhesion molecule-1-dependent binding to endothelium. Blood 82:1891-9.
Telen MJ (2000) Red blood cell surface adhesion molecules: their possible roles in normal human physiology and disease. Semin Hematol 37:130-42.
van Wetering S, van den Berk N, van Buul JD, Mul FP, Lommerse I, Mous R, ten Klooster JP, Zwaginga JJ, Hordijk PL (2003) VCAM-1-mediated Rac signaling controls endothelial cell-cell contacts and leukocyte transmigration. Am J Physiol Cell Physiol 285:C343-52.
For additional information, please contact Dr. Theodosia Kalfa, Division of Experimental Hematology, at 513-636-0989. Dr. Kalfa's office can be found in room 2363 of Location R (Research Foundation Building).
