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At
the Sickle Cell Project Laboratory,
BERL researchers study the mechanisms
of sickle cell adhesion.
Understanding
of these mechanisms will provide a basis for novel
therapeutic strategies for the treatment of patients with
sickle cell disease, a genetical
disorder affecting 1 out of 10 african-americans.
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- Sickle
cell disease
is caused by a mutation in the gene responsible for the production
of hemoglobin, the red blood cell
protein that carries oxygen throughout the body. Substitution
of a single amino acid (valine for glutamic acid) in the sixth
position of the B-chain of the hemoglobin molecule produces a
hydrophobic region while in its deoxygenated state.
- Hydrophobic
regions aggregate, resulting in polymerization
of the abnormal hemoglobin into strands. Elongated hemoglobin
fibers distort the cell, producing the characteristic "sickle"
shape and causing destructive changes in the membrane. Surface
molecules are expressed that promote abnormal adhesion
to blood vessel walls. Patients suffering
from sickle cell disease experience painful and debilitating vaso-occlusion.
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At B. E. R. L., a parallel-plate
flow adhesion assay is used to investigate adhesion of sickle
red blood cells (SSRBC) under venous shear conditions to cultured
human and mouse endothelial cells.
- The
integrin a4b1, (also known as VLA-4),
is expressed on sickle erythrocytes and binds with vascular cell
adhesion molecule-1 (VCAM-1) present
on activated endothelial cells. Using immunofluorescent analysis,
we have demonstrated upregulation of VCAM-1
following treatment with the inflammatory cytokine tumor necrosis
factor (TNF-a) at 100U/ml for 30
minutes. Blocking of this adhesion
pathway by incubating TNF-treated EC with anti-VCAM-1 antibody
reduced sickle cell adhesion to untreated levels.
- A
multidisciplinary
approach involving complementary in vitro
and ex vivo experimental systems
is effective in providing a more complete understanding of the
VLA-4/VCAM-1contribution to sickle vaso-occlusion.
- Using
a novel intravital microscopy technique, we have begun examination
of SSRBC adhesion within the microcirculation of skull bone marrow
of normal and transgenic sickle cell mice under physiologic flow.
Our adhesion analysis using mouse EC in vitro will form a basis
of comparison to results in the animal model. This will allow
us to develop and evaluate antibodies,
peptides, or other small molecules that target VLA-4 interactions
with VCAM-1 for therapeutic intervention
in sickle cell disease.
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