Multiple particle tracking analysis in isolated nuclei reveals the mechanical phenotype of leukemia cells

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. The nucleus is a central cellular organelle that must alter its physical properties during cellular functions, including gene expression, cell migration, and development in homeostasis and human diseases 1. The nucleus is composed by the nuclear envelope, nucleoskeletal components, and the nucleoplasm, which contains the DNA and its associated molecules forming the chromatin 2. The nuclear envelope is mainly composed by nuclear membranes, A-(lamin A and C) and B-(lamin B) lamin types, and other structural proteins that connect the nucleus with the cytoskeleton as LINC complexes 3. Lamin A/C levels and its ratio to lamin B levels control nuclear deformability and stiffness 4,5. It has been reported that other nuclear components, as LINC and F-actin binding proteins, control nuclear shape and rigidity 6. In general, these nuclear changes correlate with more invasive phenotype of tumor cells and higher genomic instability upon cell migration 7,8. Chromatin organization is modulated by epigenetic changes that promote chromatin compaction and decondensation according to electrostatic interactions and configurational entropy 9-11. Several biophysical techniques support that the chromatin conformation alterations contributes to the morphology and the biophysical behavior of the nucleus 12-16 Abnormalities in nuclear shape and organization occur in a wide range of human pathologies,

When nasal cytology detects acute lymphoblastic leukaemia: New diagnostical implications

“…Moreover, a correct diagnostic framework requires a broad spectrum of information derived from several investigations, such as cell phenotyping, cytochemistry, cytogenetics, and molecular genetics. Despite technological and diagnostic advances, cellular morphology remains the frontline haematological diagnostic technique, since the observation of blasts and cytopathological alterations in the peripheral blood smears raise the first suspicion of leukaemia 3 . Due to the observation of similar cytopathological alterations in the cells of the nasal inflammatory infiltrate, we suspected an ongoing oncohaematological process.…”

Modeling of Cell Nuclear Mechanics: Classes, Components, and Applications

“…This builds on purely viscoelastic treatments as it can inform how the compaction state of chromatin, and the subsequently altered pore size could have an influence on the viscous response as well as the elastic response. Increased viscosity has also been shown to be a signature of high-risk leukemia cells [88]. These viscous contributions from bulk nuclear deformation must be carefully considered as they may not be present for physiologically relevant timescales of approximately 10 s of nm/s [89,90].…”

MPTHub: An Open-Source Software for Characterizing the Transport of Particles in Biorelevant Media

“…In the particular case of nanomedicine, MPT allowed an understanding of the transport of nanocarriers in biological media and helped devise engineering strategies that could be useful in overcoming natural barriers to drug delivery and, thus, enhance therapeutic outcomes [ 9 , 10 , 11 , 12 ]. The usefulness of this powerful technique extends well beyond nanotechnology and—still in the biophysical and biomedical fields—has also been widely employed to assess the intracellular transport and kinetics of proteins, lipids, and molecular motors [ 13 ], to study the cell migration and mobility of pathogens [ 14 , 15 ], to determine the mechanical properties of isolated nuclei in living cells [ 16 ], or to characterize the microstructure and rheological profile of mucus and other viscoelastic fluids [ 17 , 18 , 19 ], to name only a few applications.…”