Post on 03-Jan-2016
description
Force Microscopy of Nonadherent Cells: A
Comparison of Leukemia Cell Deformability
Rosenbluth, Lam, and Fletcher (2006)
Presented by: Aisha Bobb-Semple20.309
November 20, 2008
Background Leukemia causes decreased deformability
and increased adhesion in myeloblasts and lymphoblasts.
This can lead to leukostasis – cell aggregation in vasculature.
Leukostasis can cause intracranial hemorrhages, respiratory failure, and ultimately death.
More knowledge about deformability is necessary for a better understanding of the disease.
Examples of Leukostasis
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http://tbn0.google.com/images?q=tbn:hazJjIDkN2f6oM:http://www.med-ed.virginia.edu/courses/path/innes/images/wcdjpeg/wcd%2520leukostasis%2520x40a.jpeg
Goals Develop a technique for probing non-
adherent cells. Develop a model for characterization
mechanical properties. Compare the deformability of: Acute
myeloid leukemia (AML) and acute lymphoid leukemia (ALL) cell lines, and human neutrophils
Use of AFM for measuring stiffness
Cells are usually firmly adhered to a substrate
Cell is indented by a cantilever at a constant rate
Deflection of the cantilever is measured and related to force.
Linear elastic model of cell based on Hertzian mechanics is commonly used to determine elasticity.
http://tbn0.google.com/images?q=tbn:JVssYYJ1qxghVM:http://www.biologicalprocedures.com/bpo/arts/1/67/m67f5sm.jpg
Use of AFM for measuring stiffness Leukocytes are non-
adhesive. One solution is to coat
the surface of the substrate with polypeptides
Microfabricated wells were developed to immobilize the cells
Model for Characterization
Which of two models best describes deformability of the cells?
At what deformation rates are viscous contributions from the cytoplasm of the
cell minimized?
Model ComparisonHertzian Mechanics Model
Indentation is related to the load Piezo position related to cantilever
deflection
Liquid Droplet Model Used predominantly in micropipette
experiments Difference in pressure related to cortical
tension which is then related to deflection of the cantilever
Model Comparison Both models were fit
to experimental data Mean squared error
for the Hertz model was lower than the liquid drop model
Hertzian model used for cell stiffness comparison
Optimal Deformation Rate?
Stiffness remained constant at and below 415nm/s for AML cells. (948 nm/s for ALL cells and 501nm/s for neurtrophils)
Comparison of Deformability
AML cells found to be significantly stiffer than others.
This is not surprising since leukostasis occurs in much higher frequency in AML.
Common for clinicians to accept that AML cells are more rigid than ALL and neutrophils.
Summary Developed microwells to immobilize non-adherent
cells for atomic force microscopy. Determined that the Hertz model best fits the
data. Determined that AML cells were significantly
stiffer than ALL cells and neutrophils Consistent with finding that myeloid leukemias
result in leukostasis more frequently than lymphoid leukemias do.
QUESTIONS??
~Thank you for your attention~