Multiple particle tracking analysis in isolated nuclei reveals the mechanical phenotype of leukemia cells.
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2020
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Scientifics Reports
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Abstract
The nucleus is fundamentally composed by lamina and nuclear membranes that enclose the chromatin,
nucleoskeletal components and suspending nucleoplasm. The functional connections of this network
integrate external stimuli into cell signals, including physical forces to mechanical responses of the
nucleus. Canonically, the morphological characteristics of the nucleus, as shape and size, have served
for pathologists to stratify and diagnose cancer patients; however, novel biophysical techniques must
exploit physical parameters to improve cancer diagnosis. By using multiple particle tracking (MPT)
technique on chromatin granules, we designed a SURF (Speeded Up Robust Features)-based algorithm
to study the mechanical properties of isolated nuclei and in living cells. We have determined the
apparent shear stiffness, viscosity and optical density of the nucleus, and how the chromatin structure
influences on these biophysical values. Moreover, we used our MPT-SURF analysis to study the apparent
mechanical properties of isolated nuclei from patients of acute lymphoblastic leukemia. We found
that leukemia cells exhibited mechanical differences compared to normal lymphocytes. Interestingly,
isolated nuclei from high-risk leukemia cells showed increased viscosity than their counterparts from
normal lymphocytes, whilst nuclei from relapsed-patient's cells presented higher density than those
from normal lymphocytes or standard- and high-risk leukemia cells. Taken together, here we presented
how MPT-SURF analysis of nuclear chromatin granules defines nuclear mechanical phenotypic features,
which might be clinically relevant.