Publications by authors named "David Odde"

95 Publications

Vaccination Against SARS-CoV-2 Is Associated With a Lower Viral Load and Likelihood of Systemic Symptoms.

Open Forum Infect Dis 2022 May 20;9(5):ofac066. Epub 2022 Feb 20.

Biostatistics, University of Minnesota School of Public Health, Minneapolis, Minnesota, USA.

Background: Data conflict on whether vaccination decreases severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load. The objective of this analysis was to compare baseline viral load and symptoms between vaccinated and unvaccinated adults enrolled in a randomized trial of outpatient coronavirus disease 2019 (COVID-19) treatment.

Methods: Baseline data from the first 433 sequential participants enrolling into the COVID-OUT trial were analyzed. Adults aged 30-85 with a body mass index (BMI) ≥25 kg/m were eligible within 3 days of a positive SARS-CoV-2 test and <7 days of symptoms. Log polymerase chain reaction viral loads were normalized to human RNase P by vaccination status, by time from vaccination, and by symptoms.

Results: Two hundred seventy-four participants with known vaccination status contributed optional nasal swabs for viral load measurement: median age, 46 years; median (interquartile range) BMI 31.2 (27.4-36.4) kg/m. Overall, 159 (58%) were women, and 217 (80%) were White. The mean relative log viral load for those vaccinated <6 months from the date of enrollment was 0.11 (95% CI, -0.48 to 0.71), which was significantly lower than the unvaccinated group ( = .01). Those vaccinated ≥6 months before enrollment did not differ from the unvaccinated with respect to viral load (mean, 0.99; 95% CI, -0.41 to 2.40;  = .85). The vaccinated group had fewer moderate/severe symptoms of subjective fever, chills, myalgias, nausea, and diarrhea (all  < .05).

Conclusions: These data suggest that vaccination within 6 months of infection is associated with a lower viral load, and vaccination was associated with a lower likelihood of having systemic symptoms.
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http://dx.doi.org/10.1093/ofid/ofac066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8982774PMC
May 2022

Predicting Glioblastoma Cellular Motility from In Vivo MRI with a Radiomics Based Regression Model.

Cancers (Basel) 2022 Jan 24;14(3). Epub 2022 Jan 24.

Department of Radiation Oncology, University of Minnesota, 516 Delaware St. SE, Minneapolis, MN 55455, USA.

Characterizing the motile properties of glioblastoma tumor cells could provide a useful way to predict the spread of tumors and to tailor the therapeutic approach. Radiomics has emerged as a diagnostic tool in the classification of tumor grade, stage, and prognosis. The purpose of this work is to examine the potential of radiomics to predict the motility of glioblastoma cells. Tissue specimens were obtained from 31 patients undergoing surgical resection of glioblastoma. Mean tumor cell motility was calculated from time-lapse videos of specimen cells. Manual segmentation was used to define the border of the enhancing tumor T1-weighted MR images, and 107 radiomics features were extracted from the normalized image volumes. Model parameter coefficients were estimated using the adaptive lasso technique validated with leave-one-out cross validation (LOOCV) and permutation tests. The R-squared value for the predictive model was 0.60 with -values for each individual parameter estimate less than 0.0001. Permutation test models trained with scrambled motility failed to produce a model that out-performed the model trained on the true data. The results of this work suggest that it is possible for a quantitative MRI feature-based regression model to non-invasively predict the cellular motility of glioblastomas.
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http://dx.doi.org/10.3390/cancers14030578DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8833801PMC
January 2022

Clinically validated model predicts the effect of intratumoral heterogeneity on overall survival for non-small cell lung cancer (NSCLC) patients.

Comput Methods Programs Biomed 2021 Nov 12;212:106455. Epub 2021 Oct 12.

Department of Radiation Oncology, University of Alabama Birmingham, Birmingham, AL, USA. Electronic address:

Background And Objective: Radiation therapy is used in nearly 50% of cancer treatments in the developed world. Currently, radiation treatments are homogenous and fail to take into consideration intratumoral heterogeneity. We demonstrate the importance of considering intratumoral heterogeneity and the development of resistance during fractionated radiotherapy when the same dose of radiation is delivered for all fractions (Fractional Equivalent Dosing FED).

Methods: A mathematical model was developed with the following parameters: a starting population of 10 non-small cell lung cancer (NSCLC) tumor cells, 48 h doubling time, and cell death per the linear-quadratic (LQ) model with α and β values derived from RSIα/β, in a previously described gene expression based model that estimates α and β. To incorporate both inter- and intratumor radiation sensitivity, RSIα/β output for each patient sample is assumed to represent an average value in a gamma distribution with the bounds set to -50% and +50% of RSIα/b. Therefore, we assume that within a given tumor there are subpopulations that have varying radiation sensitivity parameters that are distinct from other tumor samples with a different mean RSIα/β. A simulation cohort (SC) comprised of 100 lung cancer patients with available RSIα/β (patient specific α and β values) was used to investigate 60 Gy in 30 fractions with fractionally equivalent dosing (FED). A separate validation cohort (VC) of 57 lung cancer patients treated with radiation with available local control (LC), overall survival (OS), and tumor gene expression was used to clinically validate the model. Cox regression was used to test for significance to predict clinical outcomes as a continuous variable in multivariate analysis (MVA). Finally, the VC was used to compare FED schedules with various altered fractionation schema utilizing a Kruskal-Wallis test. This was examined using the end points of end of treatment log cell count (LCC) and by a parameter described as mean log kill efficiency (LKE) defined as: LCC  =  log10(tumorcellcount) [Formula: see text] RESULTS: Cox regression analysis on LCC for the VC demonstrates that, after incorporation of intratumoral heterogeneity, LCC has a linear correlation with local control (p = 0.002) and overall survival (p = < 0.001). Other suggested treatment schedules labeled as High Intensity Treatment (HIT) with a total 60 Gy delivered over 6 weeks have a lower mean LCC and an increased LKE compared to standard of care 60 Gy delivered in FED in the VC.

Conclusion: We find that LCC is a clinically relevant metric that is correlated with local control and overall survival in NSCLC. We conclude that 60 Gy delivered over 6 weeks with altered HIT fractionation leads to an enhancement in tumor control compared to FED when intratumoral heterogeneity is considered.
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http://dx.doi.org/10.1016/j.cmpb.2021.106455DOI Listing
November 2021

Ex vivo SARS-CoV-2 infection of human lung reveals heterogeneous host defense and therapeutic responses.

JCI Insight 2021 09 22;6(18). Epub 2021 Sep 22.

Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Medicine, College of Medicine.

Cell lines are the mainstay in understanding the biology of COVID-19 infection but do not recapitulate many of the complexities of human infection. The use of human lung tissue is one solution for the study of such novel respiratory pathogens. We hypothesized that a cryopreserved bank of human lung tissue would allow for the ex vivo study of the interindividual heterogeneity of host response to SARS-CoV-2, thus providing a bridge between studies with cell lines and studies in animal models. We generated a cryobank of tissues from 21 donors, many of whom had clinical risk factors for severe COVID-19. Cryopreserved tissues preserved 90% cell viability and contained heterogenous populations of metabolically active epithelial, endothelial, and immune cell subsets of the human lung. Samples were readily infected with HCoV-OC43 and SARS-CoV-2 and demonstrated comparable susceptibility to infection. In contrast, we observed a marked donor-dependent heterogeneity in the expression of IL6, CXCL8, and IFNB1 in response to SARS-CoV-2. Treatment of tissues with dexamethasone and the experimental drug N-hydroxycytidine suppressed viral growth in all samples, whereas chloroquine and remdesivir had no detectable effect. Metformin and sirolimus, molecules with predicted but unproven antiviral activity, each suppressed viral replication in tissues from a subset of donors. In summary, we developed a system for the ex vivo study of human SARS-CoV-2 infection using primary human lung tissue from a library of donor tissues. This model may be useful for drug screening and for understanding basic mechanisms of COVID-19 pathogenesis.
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http://dx.doi.org/10.1172/jci.insight.148003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8492301PMC
September 2021

Correction to: Atomistic Basis of Microtubule Dynamic Instability Assessed Via Multiscale Modeling.

Ann Biomed Eng 2021 Sep;49(9):2672

Department of Biomedical Engineering, University of Minnesota-Twin Cities, Minneapolis, MN, USA.

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http://dx.doi.org/10.1007/s10439-021-02830-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8587211PMC
September 2021

Enhanced substrate stress relaxation promotes filopodia-mediated cell migration.

Nat Mater 2021 09 19;20(9):1290-1299. Epub 2021 Apr 19.

Chemistry, Engineering, and Medicine for Human Health (ChEM-H), Stanford University, Stanford, CA, USA.

Cell migration on two-dimensional substrates is typically characterized by lamellipodia at the leading edge, mature focal adhesions and spread morphologies. These observations result from adherent cell migration studies on stiff, elastic substrates, because most cells do not migrate on soft, elastic substrates. However, many biological tissues are soft and viscoelastic, exhibiting stress relaxation over time in response to a deformation. Here, we have systematically investigated the impact of substrate stress relaxation on cell migration on soft substrates. We observed that cells migrate minimally on substrates with an elastic modulus of 2 kPa that are elastic or exhibit slow stress relaxation, but migrate robustly on 2-kPa substrates that exhibit fast stress relaxation. Strikingly, migrating cells were not spread out and did not extend lamellipodial protrusions, but were instead rounded, with filopodia protrusions extending at the leading edge, and exhibited small nascent adhesions. Computational models of cell migration based on a motor-clutch framework predict the observed impact of substrate stress relaxation on cell migration and filopodia dynamics. Our findings establish substrate stress relaxation as a key requirement for robust cell migration on soft substrates and uncover a mode of two-dimensional cell migration marked by round morphologies, filopodia protrusions and weak adhesions.
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http://dx.doi.org/10.1038/s41563-021-00981-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8390443PMC
September 2021

Atomistic Basis of Microtubule Dynamic Instability Assessed Via Multiscale Modeling.

Ann Biomed Eng 2021 Jul 3;49(7):1716-1734. Epub 2021 Feb 3.

Department of Biomedical Engineering, University of Minnesota-Twin Cities, Minneapolis, MN, USA.

Microtubule "dynamic instability," the abrupt switching from assembly to disassembly caused by the hydrolysis of GTP to GDP within the β subunit of the αβ-tubulin heterodimer, is necessary for vital cellular processes such as mitosis and migration. Despite existing high-resolution structural data, the key mechanochemical differences between the GTP and GDP states that mediate dynamic instability behavior remain unclear. Starting with a published atomic-level structure as an input, we used multiscale modeling to find that GTP hydrolysis results in both longitudinal bond weakening (~ 4 kT) and an outward bending preference (~ 1.5 kT) to both drive dynamic instability and give rise to the microtubule tip structures previously observed by light and electron microscopy. More generally, our study provides an example where atomic level structural information is used as the sole input to predict cellular level dynamics without parameter adjustment.
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http://dx.doi.org/10.1007/s10439-020-02715-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8302526PMC
July 2021

mTOR inhibition in COVID-19: A commentary and review of efficacy in RNA viruses.

J Med Virol 2021 04 17;93(4):1843-1846. Epub 2020 Dec 17.

Department of Surgery, University of Minnesota, Minneapolis, Minnesota, USA.

In this commentary, we shed light on the role of the mammalian target of rapamycin (mTOR) pathway in viral infections. The mTOR pathway has been demonstrated to be modulated in numerous RNA viruses. Frequently, inhibiting mTOR results in suppression of virus growth and replication. Recent evidence points towards modulation of mTOR in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We discuss the current literature on mTOR in SARS-CoV-2 and highlight evidence in support of a role for mTOR inhibitors in the treatment of coronavirus disease 2019.
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http://dx.doi.org/10.1002/jmv.26728DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8159020PMC
April 2021

Tau Avoids the GTP Cap at Growing Microtubule Plus-Ends.

iScience 2020 Dec 6;23(12):101782. Epub 2020 Nov 6.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.

Plus-end tracking proteins (+TIPs) associate with the growing end of microtubules and mediate important cellular functions. The majority of +TIPs are directed to the plus-end through a family of end-binding proteins (EBs), which preferentially bind the stabilizing cap of GTP-tubulin present during microtubule growth. One outstanding question is whether there may exist other microtubule-associated proteins (MAPs) that preferentially bind specific nucleotide states of tubulin. Here, we report that the neuronal MAP tau preferentially binds GDP-tubulin (  = 0.26 μM) over GMPCPP-tubulin (  = 1.1 μM) as well as GTP-tubulin at the tips of growing microtubules, causing tau binding to lag behind the plus-end both and in live cells. Thus, tau is a microtubule tip avoiding protein, establishing the framework for a possible new class of tip avoiding MAPs. We speculate that disease-relevant tau mutations may exert their phenotype by their failure to properly recognize GDP-tubulin.
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http://dx.doi.org/10.1016/j.isci.2020.101782DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7691178PMC
December 2020

Education and Outreach in Physical Sciences in Oncology.

Trends Cancer 2021 01 7;7(1):3-9. Epub 2020 Nov 7.

Department of Biochemistry and Molecular Biology, Mayo Clinic, Jacksonville, FL, USA; Department of Physiology and Biomedical Engineering, Mayo Clinic, Jacksonville, FL, USA; Department of Transplantation, Mayo Clinic, Jacksonville, FL, USA; Center for Immunotherapeutic Transport Oncophysics, Houston Methodist Research Institute, Houston, TX, USA. Electronic address:

Physical sciences are often overlooked in the field of cancer research. The Physical Sciences in Oncology Initiative was launched to integrate physics, mathematics, chemistry, and engineering with cancer research and clinical oncology through education, outreach, and collaboration. Here, we provide a framework for education and outreach in emerging transdisciplinary fields.
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http://dx.doi.org/10.1016/j.trecan.2020.10.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7895467PMC
January 2021

Regulation and dynamics of force transmission at individual cell-matrix adhesion bonds.

Sci Adv 2020 05 15;6(20):eaax0317. Epub 2020 May 15.

Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.

Integrin-based adhesion complexes link the cytoskeleton to the extracellular matrix (ECM) and are central to the construction of multicellular animal tissues. How biological function emerges from the tens to thousands of proteins present within a single adhesion complex remains unclear. We used fluorescent molecular tension sensors to visualize force transmission by individual integrins in living cells. These measurements revealed an underlying functional modularity in which integrin class controlled adhesion size and ECM ligand specificity, while the number and type of connections between integrins and F-actin determined the force per individual integrin. In addition, we found that most integrins existed in a state of near-mechanical equilibrium, a result not predicted by existing models of cytoskeletal force transduction. A revised model that includes reversible cross-links within the F-actin network can account for this result and suggests one means by which cellular mechanical homeostasis can arise at the molecular level.
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http://dx.doi.org/10.1126/sciadv.aax0317DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7228748PMC
May 2020

Predicting Confined 1D Cell Migration from Parameters Calibrated to a 2D Motor-Clutch Model.

Biophys J 2020 04 25;118(7):1709-1720. Epub 2020 Feb 25.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota; Physical Sciences-Oncology Center, University of Minnesota, Minneapolis, Minnesota. Electronic address:

Biological tissues contain micrometer-scale gaps and pores, including those found within extracellular matrix fiber networks, between tightly packed cells, and between blood vessels or nerve bundles and their associated basement membranes. These spaces restrict cell motion to a single-spatial dimension (1D), a feature that is not captured in traditional in vitro cell migration assays performed on flat, unconfined two-dimensional (2D) substrates. Mechanical confinement can variably influence cell migration behaviors, and it is presently unclear whether the mechanisms used for migration in 2D unconfined environments are relevant in 1D confined environments. Here, we assessed whether a cell migration simulator and associated parameters previously measured for cells on 2D unconfined compliant hydrogels could predict 1D confined cell migration in microfluidic channels. We manufactured microfluidic devices with narrow channels (60-μm rectangular cross-sectional area) and tracked human glioma cells that spontaneously migrated within channels. Cell velocities (v = 0.51 ± 0.02 μm min) were comparable to brain tumor expansion rates measured in the clinic. Using motor-clutch model parameters estimated from cells on unconfined 2D planar hydrogel substrates, simulations predicted similar migration velocities (v = 0.37 ± 0.04 μm min) and also predicted the effects of drugs targeting the motor-clutch system or cytoskeletal assembly. These results are consistent with glioma cells utilizing a motor-clutch system to migrate in confined environments.
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http://dx.doi.org/10.1016/j.bpj.2020.01.048DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7136340PMC
April 2020

Emerging technologies in mechanotransduction research.

Curr Opin Chem Biol 2019 12 13;53:125-130. Epub 2019 Oct 13.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA. Electronic address:

Mechanotransduction research focuses on understanding how cells sense and respond to mechanical stimuli by converting mechanical signals into biochemical and biological responses. Cells have been shown to respond to mechanical stimuli through specialized biological machinery such as adhesion complexes. Research in the last two decades helped in identifying key components of cellular mechanotransduction. In recent years, integrated approaches, which are highlighted here, are emerging to provide new insights into the mechanistic and theoretical underpinnings of mechanotransduction. In particular, mathematical modeling has helped elucidate the mechanism underlining ligand spacing and distribution sensing, as well as sensing viscoelastic properties of the extracellular matrix. In addition, molecular tension sensors have helped dissect the forces involved in mechanotransduction at high spatial and temporal resolutions.
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http://dx.doi.org/10.1016/j.cbpa.2019.08.002DOI Listing
December 2019

SEMA4C is a novel target to limit osteosarcoma growth, progression, and metastasis.

Oncogene 2020 01 3;39(5):1049-1062. Epub 2019 Oct 3.

Department of Pediatrics, University of Minnesota, Minneapolis, MN, USA.

Semaphorins, specifically type IV, are important regulators of axonal guidance and have been increasingly implicated in poor prognoses in a number of different solid cancers. In conjunction with their cognate PLXNB family receptors, type IV members have been increasingly shown to mediate oncogenic functions necessary for tumor development and malignant spread. In this study, we investigated the role of semaphorin 4C (SEMA4C) in osteosarcoma growth, progression, and metastasis. We investigated the expression and localization of SEMA4C in primary osteosarcoma patient tissues and its tumorigenic functions in these malignancies. We demonstrate that overexpression of SEMA4C promotes properties of cellular transformation, while RNAi knockdown of SEMA4C promotes adhesion and reduces cellular proliferation, colony formation, migration, wound healing, tumor growth, and lung metastasis. These phenotypic changes were accompanied by reductions in activated AKT signaling, G1 cell cycle delay, and decreases in expression of mesenchymal marker genes SNAI1, SNAI2, and TWIST1. Lastly, monoclonal antibody blockade of SEMA4C in vitro mirrored that of the genetic studies. Together, our results indicate a multi-dimensional oncogenic role for SEMA4C in metastatic osteosarcoma and more importantly that SEMA4C has actionable clinical potential.
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http://dx.doi.org/10.1038/s41388-019-1041-xDOI Listing
January 2020

Modeling distributed forces within cell adhesions of varying size on continuous substrates.

Cytoskeleton (Hoboken) 2019 11 6;76(11-12):571-585. Epub 2019 Nov 6.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota.

Cell migration and traction are essential to many biological phenomena, and one of their key features is sensitivity to substrate stiffness, which biophysical models, such as the motor-clutch model and the cell migration simulator can predict and explain. However, these models have not accounted for the finite size of adhesions, the spatial distribution of forces within adhesions. Here, we derive an expression that relates varying adhesion radius ( R) and spatial distribution of force within an adhesion (described by s) to the effective substrate stiffness ( κ ), as a function of the Young's modulus of the substrate ( E ), which yields the relation, , for two-dimensional cell cultures. Experimentally, we found that a cone-shaped force distribution ( s = 1.05) can describe the observed displacements of hydrogels deformed by adherent U251 glioma cells. Also, we found that the experimentally observed adhesion radius increases linearly with the cell protrusion force, consistent with the predictions of the motor-clutch model with spatially distributed clutches. We also found that, theoretically, the influence of one protrusion on another through a continuous elastic environment is negligible. Overall, we conclude cells can potentially control their own interpretation of the mechanics of the environment by controlling adhesion size and spatial distribution of forces within an adhesion.
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http://dx.doi.org/10.1002/cm.21561DOI Listing
November 2019

Multiscale Computational Modeling of Tubulin-Tubulin Lateral Interaction.

Biophys J 2019 10 16;117(7):1234-1249. Epub 2019 Aug 16.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota. Electronic address:

Microtubules are multistranded polymers in eukaryotic cells that support key cellular functions such as chromosome segregation, motor-based cargo transport, and maintenance of cell polarity. Microtubules self-assemble via "dynamic instability," in which the dynamic plus ends switch stochastically between alternating phases of polymerization and depolymerization. A key question in the field is what are the atomistic origins of this switching, i.e., what is different between the GTP- and GDP-tubulin states that enables microtubule growth and shortening, respectively? More generally, a major challenge in biology is how to connect theoretical frameworks across length- and timescales, from atoms to cellular behavior. In this study, we describe a multiscale model by linking atomistic molecular dynamics (MD), molecular Brownian dynamics (BD), and cellular-level thermokinetic modeling of microtubules. Here, we investigated the underlying interaction energy when tubulin dimers associate laterally by performing all-atom MD simulations. We found that the lateral potential energy is not significantly different among three nucleotide states of tubulin, GTP, GDP, and GMPCPP and is estimated to be ≅ -11 kT. Furthermore, using MD potential energy in our BD simulations of tubulin dimers confirms that the lateral bond is weak on its own, with a mean lifetime of ∼0.1 μs, implying that the longitudinal bond is required for microtubule assembly. We conclude that nucleotide-dependent lateral-bond strength is not the key mediator microtubule dynamic instability, implying that GTP acts elsewhere to exert its stabilizing influence on microtubule polymer. Furthermore, the estimated lateral-bond strength (ΔG≅ -5 kT) is well-aligned with earlier estimates based on thermokinetic modeling and light microscopy measurements. Thus, we have computationally connected atomistic-level structural information, obtained by cryo-electron microscopy, to cellular-scale microtubule assembly dynamics using a combination of MD, BD, and thermokinetic models to bridge from Ångstroms to micrometers and from femtoseconds to minutes.
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http://dx.doi.org/10.1016/j.bpj.2019.08.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6818183PMC
October 2019

Glioma Cell Migration Dynamics in Brain Tissue Assessed by Multimodal Optical Imaging.

Biophys J 2019 10 15;117(7):1179-1188. Epub 2019 Aug 15.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota. Electronic address:

Glioblastoma is a primary malignant brain tumor characterized by highly infiltrative glioma cells. Vasculature and white matter tracts are considered to be the preferred and fastest routes for glioma invasion through brain tissue. In this study, we systematically quantified the routes and motility of the U251 human glioblastoma cell line in mouse brain slices by multimodal imaging. Specifically, we used polarization-sensitive optical coherence tomography to delineate nerve fiber tracts while confocal fluorescence microscopy was used to image cell migration and brain vasculature. Somewhat surprisingly, we found that in mouse brain slices, U251 glioma cells do not follow white matter tracts but rather preferentially migrate along vasculature in both gray and white matter. In addition, U251 cell motility is ∼2-fold higher in gray matter than in white matter (91 vs. 43 μm/h), with a substantial fraction (44%) of cells in both regions invading without close association with vasculature. Interestingly, within both regions, the rates of migration for the perivascular and televascular routes of invasion were indistinguishable. Furthermore, by imaging of local vasculature deformation dynamics during cell migration, we found that U251 cells are capable of exerting traction forces that locally pull on their environment, suggesting the applicability of a "motor-clutch"-based model for migration in vivo. Overall, by quantitatively analyzing the migration dynamics along the diverse pathways followed by invading U251 glioma cells as observed by our multimodal imaging approach, our studies suggest that effective antiinvasive strategies will need to simultaneously limit parallel routes of both perivascular and televascular invasion through both gray and white matter.
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http://dx.doi.org/10.1016/j.bpj.2019.08.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6818150PMC
October 2019

Myosin IIA suppresses glioblastoma development in a mechanically sensitive manner.

Proc Natl Acad Sci U S A 2019 07 24;116(31):15550-15559. Epub 2019 Jun 24.

Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Jacksonville, FL 32224;

The ability of glioblastoma to disperse through the brain contributes to its lethality, and blocking this behavior has been an appealing therapeutic approach. Although a number of proinvasive signaling pathways are active in glioblastoma, many are redundant, so targeting one can be overcome by activating another. However, these pathways converge on nonredundant components of the cytoskeleton, and we have shown that inhibiting one of these-the myosin II family of cytoskeletal motors-blocks glioblastoma invasion even with simultaneous activation of multiple upstream promigratory pathways. Myosin IIA and IIB are the most prevalent isoforms of myosin II in glioblastoma, and we now show that codeleting these myosins markedly impairs tumorigenesis and significantly prolongs survival in a rodent model of this disease. However, while targeting just myosin IIA also impairs tumor invasion, it surprisingly increases tumor proliferation in a manner that depends on environmental mechanics. On soft surfaces myosin IIA deletion enhances ERK1/2 activity, while on stiff surfaces it enhances the activity of NFκB, not only in glioblastoma but in triple-negative breast carcinoma and normal keratinocytes as well. We conclude myosin IIA suppresses tumorigenesis in at least two ways that are modulated by the mechanics of the tumor and its stroma. Our results also suggest that inhibiting tumor invasion can enhance tumor proliferation and that effective therapy requires targeting cellular components that drive both proliferation and invasion simultaneously.
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http://dx.doi.org/10.1073/pnas.1902847116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6681735PMC
July 2019

Rapid and inefficient kinetics of sickle hemoglobin fiber growth.

Sci Adv 2019 03 13;5(3):eaau1086. Epub 2019 Mar 13.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.

In sickle cell disease, the aberrant assembly of hemoglobin fibers induces changes in red blood cell morphology and stiffness, which leads to downstream symptoms of the disease. Therefore, understanding of this assembly process will be important for the treatment of sickle cell disease. By performing the highest spatiotemporal resolution measurements (55 nm at 1 Hz) of single sickle hemoglobin fiber assembly to date and combining them with a model that accounts for the multistranded structure of the fibers, we show that the rates of sickle hemoglobin addition and loss have been underestimated in the literature by at least an order of magnitude. These results reveal that the sickle hemoglobin self-assembly process is very rapid and inefficient (4% efficient versus 96% efficient based on previous analyses), where net growth is the small difference between over a million addition-loss events occurring every second.
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http://dx.doi.org/10.1126/sciadv.aau1086DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6415962PMC
March 2019

Insertional Mutagenesis Reveals Important Genetic Drivers of Central Nervous System Embryonal Tumors.

Cancer Res 2019 03 23;79(5):905-917. Epub 2019 Jan 23.

Division of Hematology, The Hospital for Sick Children, Toronto, Ontario, Canada.

Medulloblastoma and central nervous system primitive neuroectodermal tumors (CNS-PNET) are aggressive, poorly differentiated brain tumors with limited effective therapies. Using () transposon mutagenesis, we identified novel genetic drivers of medulloblastoma and CNS-PNET. Cross-species gene expression analyses classified -driven tumors into distinct medulloblastoma and CNS-PNET subgroups, indicating they resemble human Sonic hedgehog and group 3 and 4 medulloblastoma and CNS neuroblastoma with activation. This represents the first genetically induced mouse model of CNS-PNET and a rare model of group 3 and 4 medulloblastoma. We identified several putative proto-oncogenes including , and . Genetic manipulation of these genes demonstrated a robust impact on tumorigenesis and . We also determined that FOXR2 interacts with N-MYC, increases C-MYC protein stability, and activates FAK/SRC signaling. Altogether, our study identified several promising therapeutic targets in medulloblastoma and CNS-PNET. SIGNIFICANCE: A transposon-induced mouse model identifies several novel genetic drivers and potential therapeutic targets in medulloblastoma and CNS-PNET.
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http://dx.doi.org/10.1158/0008-5472.CAN-18-1261DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6397665PMC
March 2019

A Brownian dynamics tumor progression simulator with application to glioblastoma.

Converg Sci Phys Oncol 2018 Mar 3;4(1). Epub 2018 Jan 3.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States of America.

Tumor progression modeling offers the potential to predict tumor-spreading behavior to improve prognostic accuracy and guide therapy development. Common simulation methods include continuous reaction-diffusion (RD) approaches that capture mean spatio-temporal tumor spreading behavior and discrete agent-based (AB) approaches which capture individual cell events such as proliferation or migration. The brain cancer glioblastoma (GBM) is especially appropriate for such proliferation-migration modeling approaches because tumor cells seldom metastasize outside of the central nervous system and cells are both highly proliferative and migratory. In glioblastoma research, current RD estimates of proliferation and migration parameters are derived from computed tomography or magnetic resonance images. However, these estimates of glioblastoma cell migration rates, modeled as a diffusion coefficient, are approximately 1-2 orders of magnitude larger than single-cell measurements in animal models of this disease. To identify possible sources for this discrepancy, we evaluated the fundamental RD simulation assumptions that cells are point-like structures that can overlap. To give cells physical size (~10 m), we used a Brownian dynamics approach that simulates individual single-cell diffusive migration, growth, and proliferation activity via a gridless, off-lattice, AB method where cells can be prohibited from overlapping each other. We found that for realistic single-cell parameter growth and migration rates, a non-overlapping model gives rise to a jammed configuration in the center of the tumor and a biased outward diffusion of cells in the tumor periphery, creating a quasi-ballistic advancing tumor front. The simulations demonstrate that a fast-progressing tumor can result from minimally diffusive cells, but at a rate that is still dependent on single-cell diffusive migration rates. Thus, modeling with the assumption of physically-grounded volume conservation can account for the apparent discrepancy between estimated and measured diffusion of GBM cells and provide a new theoretical framework that naturally links single-cell growth and migration dynamics to tumor-level progression.
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http://dx.doi.org/10.1088/2057-1739/aa9e6eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6322960PMC
March 2018

Microtubule-Based Control of Motor-Clutch System Mechanics in Glioma Cell Migration.

Cell Rep 2018 11;25(9):2591-2604.e8

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA; Physical Sciences-Oncology Center, University of Minnesota, Minneapolis, MN 55455, USA. Electronic address:

Microtubule-targeting agents (MTAs) are widely used chemotherapy drugs capable of disrupting microtubule-dependent cellular functions, such as division and migration. We show that two clinically approved MTAs, paclitaxel and vinblastine, each suppress stiffness-sensitive migration and polarization characteristic of human glioma cells on compliant hydrogels. MTAs influence microtubule dynamics and cell traction forces by nearly opposite mechanisms, the latter of which can be explained by a combination of changes in myosin motor and adhesion clutch number. Our results support a microtubule-dependent signaling-based model for controlling traction forces through a motor-clutch mechanism, rather than microtubules directly relieving tension within F-actin and adhesions. Computational simulations of cell migration suggest that increasing protrusion number also impairs stiffness-sensitive migration, consistent with experimental MTA effects. These results provide a theoretical basis for the role of microtubules and mechanisms of MTAs in controlling cell migration.
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http://dx.doi.org/10.1016/j.celrep.2018.10.101DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6345402PMC
November 2018

Modeling Cell Migration Mechanics.

Adv Exp Med Biol 2018;1092:159-187

Department of Biomedical Engineering and Physical Sciences-Oncology Center, University of Minnesota-Twin Cities, Minneapolis, MN, USA.

Cell migration is the physical movement of cells and is responsible for the extensive cellular invasion and metastasis that occur in high-grade tumors. Motivated by decades of direct observation of cell migration via light microscopy, theoretical models have emerged to capture various aspects of the fundamental physical phenomena underlying cell migration. Yet, the motility mechanisms actually used by tumor cells during invasion are still poorly understood, as is the role of cellular interactions with the extracellular environment. In this chapter, we review key physical principles of cytoskeletal self-assembly and force generation, membrane tension, biological adhesion, hydrostatic and osmotic pressures, and their integration in mathematical models of cell migration. With the goal of modeling-driven cancer therapy, we provide examples to guide oncologists and physical scientists in developing next-generation models to predict disease progression and treatment.
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http://dx.doi.org/10.1007/978-3-319-95294-9_9DOI Listing
July 2019

An Indole-Chalcone Inhibits Multidrug-Resistant Cancer Cell Growth by Targeting Microtubules.

Mol Pharm 2018 09 9;15(9):3892-3900. Epub 2018 Aug 9.

School of Pharmacy , Ningxia Medical University , Yinchuan , China.

Multidrug resistance and toxic side effects are the major challenges in cancer treatment with microtubule-targeting agents (MTAs), and thus, there is an urgent clinical need for new therapies. Chalcone, a common simple scaffold found in many natural products, is widely used as a privileged structure in medicinal chemistry. We have previously validated tubulin as the anticancer target for chalcone derivatives. In this study, an α-methyl-substituted indole-chalcone (FC77) was synthesized and found to exhibit an excellent cytotoxicity against the NCI-60 cell lines (average concentration causing 50% growth inhibition = 6 nM). More importantly, several multidrug-resistant cancer cell lines showed no resistance to FC77, and the compound demonstrated good selective toxicity against cancer cells versus normal CD34 blood progenitor cells. A further mechanistic study demonstrated that FC77 could arrest cells that relate to the binding to tubulin and inhibit the microtubule dynamics. The National Cancer Institute COMPARE analysis and molecular modeling indicated that FC77 had a mechanism of action similar to that of colchicine. Overall, our data demonstrate that this indole-chalcone represents a novel MTA template for further development of potential drug candidates for the treatment of multidrug-resistant cancers.
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http://dx.doi.org/10.1021/acs.molpharmaceut.8b00359DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6511885PMC
September 2018

Rapid diffusion-state switching underlies stable cytoplasmic gradients in the zygote.

Proc Natl Acad Sci U S A 2018 09 24;115(36):E8440-E8449. Epub 2018 Jul 24.

Department of Biological Sciences, Dartmouth College, Hanover, NH 03755;

Protein concentration gradients organize cells and tissues and commonly form through diffusion away from a local source of protein. Interestingly, during the asymmetric division of the zygote, the RNA-binding proteins MEX-5 and PIE-1 form opposing concentration gradients in the absence of a local source. In this study, we use near-total internal reflection fluorescence (TIRF) imaging and single-particle tracking to characterize the reaction/diffusion dynamics that maintain the MEX-5 and PIE-1 gradients. Our findings suggest that both proteins interconvert between fast-diffusing and slow-diffusing states on timescales that are much shorter (seconds) than the timescale of gradient formation (minutes). The kinetics of diffusion-state switching are strongly polarized along the anterior/posterior (A/P) axis by the PAR polarity system such that fast-diffusing MEX-5 and PIE-1 particles are approximately symmetrically distributed, whereas slow-diffusing particles are highly enriched in the anterior and posterior cytoplasm, respectively. Using mathematical modeling, we show that local differences in the kinetics of diffusion-state switching can rapidly generate stable concentration gradients over a broad range of spatial and temporal scales.
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http://dx.doi.org/10.1073/pnas.1722162115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6130366PMC
September 2018

Monte Carlo simulations of microtubule arrays: The critical roles of rescue transitions, the cell boundary, and tubulin concentration in shaping microtubule distributions.

PLoS One 2018 21;13(5):e0197538. Epub 2018 May 21.

Dept. of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, United States of America.

Microtubules are dynamic polymers required for a number of processes, including chromosome movement in mitosis. While regulators of microtubule dynamics have been well characterized, we lack a convenient way to predict how the measured dynamic parameters shape the entire microtubule system within a cell, or how the system responds when specific parameters change in response to internal or external signals. Here we describe a Monte Carlo model to simulate an array of dynamic microtubules from parameters including the cell radius, total tubulin concentration, microtubule nucleation rate from the centrosome, and plus end dynamic instability. The algorithm also allows dynamic instability or position of the cell edge to vary during the simulation. Outputs from simulations include free tubulin concentration, average microtubule lengths, length distributions, and individual length changes over time. Using this platform and reported parameters measured in interphase LLCPK1 epithelial cells, we predict that sequestering ~ 15-20% of total tubulin results in fewer microtubules, but promotes dynamic instability of those remaining. Simulations also predict that lowering nucleation rate will increase the stability and average length of the remaining microtubules. Allowing the position of the cell's edge to vary over time changed the average length but not the number of microtubules and generated length distributions consistent with experimental measurements. Simulating the switch from interphase to prophase demonstrated that decreased rescue frequency at prophase is the critical factor needed to rapidly clear the cell of interphase microtubules prior to mitotic spindle assembly. Finally, consistent with several previous simulations, our results demonstrate that microtubule nucleation and dynamic instability in a confined space determines the partitioning of tubulin between monomer and polymer pools. The model and simulations will be useful for predicting changes to the entire microtubule array after modification to one or more parameters, including predicting the effects of tubulin-targeted chemotherapies.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0197538PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5962052PMC
December 2018

Kinesin-5 mediated chromosome congression in insect spindles.

Cell Mol Bioeng 2018 Feb 21;11(1):25-36. Epub 2017 Aug 21.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455 USA.

Introduction: The microtubule motor protein kinesin-5 is well known to establish the bipolar spindle by outward sliding of antiparallel interpolar microtubules. In yeast, kinesin-5 also facilitates chromosome alignment "congression" at the spindle equator by preferentially depolymerizing long kinetochore microtubules (kMTs). The motor protein kinesin-8 has also been linked to chromosome congression. Therefore, we sought to determine whether kinesin-5 or kinesin-8 facilitates chromosome congression in insect spindles.

Methods: RNAi of the kinesin-5 Klp61F and kinesin-8 Klp67A were performed separately in S2 cells to test for inhibited chromosome congression. Klp61F RNAi, Klp67A RNAi, and control metaphase mitotic spindles expressing fluorescent tubulin and fluorescent Cid were imaged, and their fluorescence distributions were compared.

Results: RNAi of Klp61F with a weak Klp61F knockdown resulted in longer kMTs and less congressed kinetochores compared to control over a range of conditions, consistent with kinesin-5 length-dependent depolymerase activity. RNAi of the kinesin-8 Klp67A revealed that kMTs relative to the spindle lengths were not longer compared to control, but rather that the spindles were longer, indicating that Klp67A acts preferentially as a length-dependent depolymerase on interpolar microtubules without significantly affecting kMT length and chromosome congression.

Conclusions: This study demonstrates that in addition to establishing the bipolar spindle, kinesin-5 regulates kMT length to facilitate chromosome congression in insect spindles. It expands on previous yeast studies, and it expands the role of kinesin-5 to include kMT assembly regulation in eukaryotic mitosis.
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http://dx.doi.org/10.1007/s12195-017-0500-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5849273PMC
February 2018

Microtubule dynamics: moving toward a multi-scale approach.

Curr Opin Cell Biol 2018 02 17;50:8-13. Epub 2018 Jan 17.

Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA. Electronic address:

Microtubule self-assembly dynamics serve to facilitate many vital cellular functions, such as chromosome segregation during mitosis and synaptic plasticity. However, the detailed atomistic basis of assembly dynamics has remained an unresolved puzzle. A key challenge is connecting together the vast range of relevant length-time scales, events happening at time scales ranging from nanoseconds, such as tubulin molecular interactions (Å-nm), to minutes-hours, such as the cellular response to microtubule dynamics during mitotic progression (μm). At the same time, microtubule interactions with associated proteins and binding agents, such as anti-cancer drugs, can strongly affect this dynamic process through atomic-level mechanisms that remain to be elucidated. New high-resolution technologies for investigating these interactions, including cryo-electron microscopy (EM) techniques and total internal reflection fluorescence (TIRF) microscopy, are yielding important new insights. Here, we focus on recent studies of microtubule dynamics, both theoretical and experimental, and how these findings shed new light on this complex phenomenon across length-time scales, from Å to μm and from nanoseconds to minutes.
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http://dx.doi.org/10.1016/j.ceb.2017.12.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5911414PMC
February 2018

Dynamics of 3D carcinoma cell invasion into aligned collagen.

Integr Biol (Camb) 2018 02;10(2):100-112

Department of Biomedical Engineering, University of Minnesota, 7-120 NHH, 312 Church St SE, Minneapolis, MN 55455, USA.

Carcinoma cells frequently expand and invade from a confined lesion, or multicellular clusters, into and through the stroma on the path to metastasis, often with an efficiency dictated by the architecture and composition of the microenvironment. Specifically, in desmoplastic carcinomas such as those of the breast, aligned collagen tracks provide contact guidance cues for directed cancer cell invasion. Yet, the evolving dynamics of this process of invasion remains poorly understood, in part due to difficulties in continuously capturing both spatial and temporal heterogeneity and progression to invasion in experimental systems. Therefore, to study the local invasion process from cell dense clusters into aligned collagen architectures found in solid tumors, we developed a novel engineered 3D invasion platform that integrates an aligned collagen matrix with a cell dense tumor-like plug. Using multiphoton microscopy and quantitative analysis of cell motility, we track the invasion of cancer cells from cell-dense bulk clusters into the pre-aligned 3D matrix, and define the temporal evolution of the advancing invasion fronts over several days. This enables us to identify and probe cell dynamics in key regions of interest: behind, at, and beyond the edge of the invading lesion at distinct time points. Analysis of single cell migration identifies significant spatial heterogeneity in migration behavior between cells in the highly cell-dense region behind the leading edge of the invasion front and cells at and beyond the leading edge. Moreover, temporal variations in motility and directionality are also observed between cells within the cell-dense tumor-like plug and the leading invasive edge as its boundary extends into the anisotropic collagen over time. Furthermore, experimental results combined with mathematical modeling demonstrate that in addition to contact guidance, physical crowding of cells is a key regulating factor orchestrating variability in single cell migration during invasion into anisotropic ECM. Thus, our novel platform enables us to capture spatio-temporal dynamics of cell behavior behind, at, and beyond the invasive front and reveals heterogeneous, local interactions that lead to the emergence and maintenance of the advancing front.
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http://dx.doi.org/10.1039/c7ib00152eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6004317PMC
February 2018

Cell Migration in 1D and 2D Nanofiber Microenvironments.

Ann Biomed Eng 2018 Mar 17;46(3):392-403. Epub 2017 Nov 17.

Department of Biomedical Engineering, University of Minnesota, 312 Church St. SE, 7-132 Nils-Hasselmo Hall, Minneapolis, MN, 55455, USA.

Understanding how cells migrate in fibrous environments is important in wound healing, immune function, and cancer progression. A key question is how fiber orientation and network geometry influence cell movement. Here we describe a quantitative, modeling-based approach toward identifying the mechanisms by which cells migrate in fibrous geometries having well controlled orientation. Specifically, U251 glioblastoma cells were seeded onto non-electrospinning Spinneret based tunable engineering parameters fiber substrates that consist of networks of suspended 400 nm diameter nanofibers. Cells were classified based on the local fiber geometry and cell migration dynamics observed by light microscopy. Cells were found in three distinct geometries: adhering two a single fiber, adhering to two parallel fibers, and adhering to a network of orthogonal fibers. Cells adhering to a single fiber or two parallel fibers can only move in one dimension along the fiber axis, whereas cells on a network of orthogonal fibers can move in two dimensions. We found that cells move faster and more persistently in 1D geometries than in 2D, with cell migration being faster on parallel fibers than on single fibers. To explain these behaviors mechanistically, we simulated cell migration in the three different geometries using a motor-clutch based model for cell traction forces. Using nearly identical parameter sets for each of the three cases, we found that the simulated cells naturally replicated the reduced migration in 2D relative to 1D geometries. In addition, the modestly faster 1D migration on parallel fibers relative to single fibers was captured using a correspondingly modest increase in the number of clutches to reflect increased surface area of adhesion on parallel fibers. Overall, the integrated modeling and experimental analysis shows that cell migration in response to varying fibrous geometries can be explained by a simple mechanical readout of geometry via a motor-clutch mechanism.
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http://dx.doi.org/10.1007/s10439-017-1958-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5809563PMC
March 2018
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