Publications by authors named "Meredith E Fay"

12 Publications

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Decreased cell stiffness enhances leukemia development and progression.

Leukemia 2020 09 24;34(9):2493-2497. Epub 2020 Feb 24.

Department of Pediatrics, Division of Hematology and Oncology, Aflac Cancer and Blood Disorders Center, Winship Cancer Institute, Children's Healthcare of Atlanta, Emory University, Atlanta, GA, 30322, USA.

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http://dx.doi.org/10.1038/s41375-020-0763-7DOI Listing
September 2020

Ptpn21 Controls Hematopoietic Stem Cell Homeostasis and Biomechanics.

Cell Stem Cell 2019 04 14;24(4):608-620.e6. Epub 2019 Mar 14.

Division of Hematology/Oncology, Department of Pediatrics, Aflac Cancer and Blood Disorders Center, Winship Cancer Institute, Children's Healthcare of Atlanta, Emory University, Atlanta, GA 30322, USA. Electronic address:

Hematopoietic stem cell (HSC) quiescence is a tightly regulated process crucial for hematopoietic regeneration, which requires a healthy and supportive microenvironmental niche within the bone marrow (BM). Here, we show that deletion of Ptpn21, a protein tyrosine phosphatase highly expressed in HSCs, induces stem cell egress from the niche due to impaired retention within the BM. Ptpn21 HSCs exhibit enhanced mobility, decreased quiescence, increased apoptosis, and defective reconstitution capacity. Ptpn21 deletion also decreased HSC stiffness and increased physical deformability, in part by dephosphorylating Spetin1 (Tyr), a poorly described component of the cytoskeleton. Elevated phosphorylation of Spetin1 in Ptpn21 cells impaired cytoskeletal remodeling, contributed to cortical instability, and decreased cell rigidity. Collectively, these findings show that Ptpn21 maintains cellular mechanics, which is correlated with its important functions in HSC niche retention and preservation of hematopoietic regeneration capacity.
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http://dx.doi.org/10.1016/j.stem.2019.02.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6450721PMC
April 2019

Ultraviolet Hyperspectral Interferometric Microscopy.

Sci Rep 2018 07 2;8(1):9913. Epub 2018 Jul 2.

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA.

Ultraviolet (UV) spectroscopy is a powerful tool for quantitative (bio)chemical analysis, but its application to molecular imaging and microscopy has been limited. Here we introduce ultraviolet hyperspectral interferometric (UHI) microscopy, which leverages coherent detection of optical fields to overcome significant challenges associated with UV spectroscopy when applied to molecular imaging. We demonstrate that this method enables quantitative spectral analysis of important endogenous biomolecules with subcellular spatial resolution and sensitivity to nanometer-scaled structures for label-free molecular imaging of live cells.
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http://dx.doi.org/10.1038/s41598-018-28208-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6028425PMC
July 2018

A microengineered vascularized bleeding model that integrates the principal components of hemostasis.

Nat Commun 2018 02 6;9(1):509. Epub 2018 Feb 6.

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 345 Ferst Drive, Atlanta, GA, 30332, USA.

Hemostasis encompasses an ensemble of interactions among platelets, coagulation factors, blood cells, endothelium, and hemodynamic forces, but current assays assess only isolated aspects of this complex process. Accordingly, here we develop a comprehensive in vitro mechanical injury bleeding model comprising an "endothelialized" microfluidic system coupled with a microengineered pneumatic valve that induces a vascular "injury". With perfusion of whole blood, hemostatic plug formation is visualized and "in vitro bleeding time" is measured. We investigate the interaction of different components of hemostasis, gaining insight into several unresolved hematologic issues. Specifically, we visualize and quantitatively demonstrate: the effect of anti-platelet agent on clot contraction and hemostatic plug formation, that von Willebrand factor is essential for hemostasis at high shear, that hemophilia A blood confers unstable hemostatic plug formation and altered fibrin architecture, and the importance of endothelial phosphatidylserine in hemostasis. These results establish the versatility and clinical utility of our microfluidic bleeding model.
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http://dx.doi.org/10.1038/s41467-018-02990-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5802762PMC
February 2018

Mapping the 3D orientation of piconewton integrin traction forces.

Nat Methods 2018 02 11;15(2):115-118. Epub 2017 Dec 11.

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA.

Mechanical forces are integral to many biological processes; however, current techniques cannot map the magnitude and direction of piconewton molecular forces. Here, we describe molecular force microscopy, leveraging molecular tension probes and fluorescence polarization microscopy to measure the magnitude and 3D orientation of cellular forces. We mapped the orientation of integrin-based traction forces in mouse fibroblasts and human platelets, revealing alignment between the organization of force-bearing structures and their force orientations.
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http://dx.doi.org/10.1038/nmeth.4536DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6116908PMC
February 2018

Extracellular fluid tonicity impacts sickle red blood cell deformability and adhesion.

Blood 2017 12 4;130(24):2654-2663. Epub 2017 Oct 4.

Division of Pediatric Hematology/Oncology, Department of Pediatrics, Aflac Cancer & Blood Disorders Center, Emory University School of Medicine, Atlanta, GA.

Abnormal sickle red blood cell (sRBC) biomechanics, including pathological deformability and adhesion, correlate with clinical severity in sickle cell disease (SCD). Clinical intravenous fluids (IVFs) of various tonicities are often used during treatment of vaso-occlusive pain episodes (VOE), the major cause of morbidity in SCD. However, evidence-based guidelines are lacking, and there is no consensus regarding which IVFs to use during VOE. Further, it is unknown how altering extracellular fluid tonicity with IVFs affects sRBC biomechanics in the microcirculation, where vaso-occlusion takes place. Here, we report how altering extracellular fluid tonicity with admixtures of clinical IVFs affects sRBC biomechanical properties by leveraging novel in vitro microfluidic models of the microcirculation, including 1 capable of deoxygenating the sRBC environment to monitor changes in microchannel occlusion risk and an "endothelialized" microvascular model that measures alterations in sRBC/endothelium adhesion under postcapillary venular conditions. Admixtures with higher tonicities (sodium = 141 mEq/L) affected sRBC biomechanics by decreasing sRBC deformability, increasing sRBC occlusion under normoxic and hypoxic conditions, and increasing sRBC adhesion in our microfluidic human microvasculature models. Admixtures with excessive hypotonicity (sodium = 103 mEq/L), in contrast, decreased sRBC adhesion, but overswelling prolonged sRBC transit times in capillary-sized microchannels. Admixtures with intermediate tonicities (sodium = 111-122 mEq/L) resulted in optimal changes in sRBC biomechanics, thereby reducing the risk for vaso-occlusion in our models. These results have significant translational implications for patients with SCD and warrant a large-scale prospective clinical study addressing optimal IVF management during VOE in SCD.
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http://dx.doi.org/10.1182/blood-2017-04-780635DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5731085PMC
December 2017

Single-platelet nanomechanics measured by high-throughput cytometry.

Nat Mater 2017 02 10;16(2):230-235. Epub 2016 Oct 10.

Department of Pediatrics, Division of Pediatric Hematology/Oncology, Aflac Cancer Center and Blood Disorders Service of Children's Healthcare of Atlanta, Emory University School of Medicine, Atlanta, Georgia 30322, USA.

Haemostasis occurs at sites of vascular injury, where flowing blood forms a clot, a dynamic and heterogeneous fibrin-based biomaterial. Paramount in the clot's capability to stem haemorrhage are its changing mechanical properties, the major drivers of which are the contractile forces exerted by platelets against the fibrin scaffold. However, how platelets transduce microenvironmental cues to mediate contraction and alter clot mechanics is unknown. This is clinically relevant, as overly softened and stiffened clots are associated with bleeding and thrombotic disorders. Here, we report a high-throughput hydrogel-based platelet-contraction cytometer that quantifies single-platelet contraction forces in different clot microenvironments. We also show that platelets, via the Rho/ROCK pathway, synergistically couple mechanical and biochemical inputs to mediate contraction. Moreover, highly contractile platelet subpopulations present in healthy controls are conspicuously absent in a subset of patients with undiagnosed bleeding disorders, and therefore may function as a clinical diagnostic biophysical biomarker.
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http://dx.doi.org/10.1038/nmat4772DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5266633PMC
February 2017

Cellular softening mediates leukocyte demargination and trafficking, thereby increasing clinical blood counts.

Proc Natl Acad Sci U S A 2016 Feb 8;113(8):1987-92. Epub 2016 Feb 8.

The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology & Emory University, Atlanta, GA 30332; Department of Pediatrics, Division of Pediatric Hematology/Oncology, Aflac Cancer Center and Blood Disorders Service of Children's Healthcare of Atlanta, Emory University School of Medicine, Atlanta, GA 30322; Winship Cancer Institute, Emory University, Atlanta, GA 30322; Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332; Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332;

Leukocytes normally marginate toward the vascular wall in large vessels and within the microvasculature. Reversal of this process, leukocyte demargination, leads to substantial increases in the clinical white blood cell and granulocyte count and is a well-documented effect of glucocorticoid and catecholamine hormones, although the underlying mechanisms remain unclear. Here we show that alterations in granulocyte mechanical properties are the driving force behind glucocorticoid- and catecholamine-induced demargination. First, we found that the proportions of granulocytes from healthy human subjects that traversed and demarginated from microfluidic models of capillary beds and veins, respectively, increased after the subjects ingested glucocorticoids. Also, we show that glucocorticoid and catecholamine exposure reorganizes cellular cortical actin, significantly reducing granulocyte stiffness, as measured with atomic force microscopy. Furthermore, using simple kinetic theory computational modeling, we found that this reduction in stiffness alone is sufficient to cause granulocyte demargination. Taken together, our findings reveal a biomechanical answer to an old hematologic question regarding how glucocorticoids and catecholamines cause leukocyte demargination. In addition, in a broader sense, we have discovered a temporally and energetically efficient mechanism in which the innate immune system can simply alter leukocyte stiffness to fine tune margination/demargination and therefore leukocyte trafficking in general. These observations have broad clinically relevant implications for the inflammatory process overall as well as hematopoietic stem cell mobilization and homing.
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http://dx.doi.org/10.1073/pnas.1508920113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4776450PMC
February 2016

Platelet geometry sensing spatially regulates α-granule secretion to enable matrix self-deposition.

Blood 2015 Jul 11;126(4):531-8. Epub 2015 May 11.

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA; Aflac Cancer Center and Blood Disorders Service of Children's Healthcare of Atlanta, Atlanta, GA; Department of Pediatrics, Emory University School of Medicine, Atlanta, GA; Parker H. Petit Institute of Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA; Winship Cancer Institute, Emory University, Atlanta, GA; Institute of Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA;

Although the biology of platelet adhesion on subendothelial matrix after vascular injury is well characterized, how the matrix biophysical properties affect platelet physiology is unknown. Here we demonstrate that geometric orientation of the matrix itself regulates platelet α-granule secretion, a key component of platelet activation. Using protein microcontact printing, we show that platelets spread beyond the geometric constraints of fibrinogen or collagen micropatterns with <5-µm features. Interestingly, α-granule exocytosis and deposition of the α-granule contents such as fibrinogen and fibronectin were primarily observed in those areas of platelet extension beyond the matrix protein micropatterns. This enables platelets to "self-deposit" additional matrix, provide more cellular membrane to extend spreading, and reinforce platelet-platelet connections. Mechanistically, this phenomenon is mediated by actin polymerization, Rac1 activation, and αIIbβ3 integrin redistribution and activation, and is attenuated in gray platelet syndrome platelets, which lack α-granules, and Wiskott-Aldrich syndrome platelets, which have cytoskeletal defects. Overall, these studies demonstrate how platelets transduce geometric cues of the underlying matrix geometry into intracellular signals to extend spreading, which endows platelets spatial flexibility when spreading onto small sites of exposed subendothelium.
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http://dx.doi.org/10.1182/blood-2014-11-607614DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4513253PMC
July 2015

Resolving the multifaceted mechanisms of the ferric chloride thrombosis model using an interdisciplinary microfluidic approach.

Blood 2015 Aug 30;126(6):817-24. Epub 2015 Apr 30.

Wallace C Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA; Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Children's Healthcare of Atlanta and Emory University School of Medicine, Atlanta, GA; Institute of Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA;

The mechanism of action of the widely used in vivo ferric chloride (FeCl3) thrombosis model remains poorly understood; although endothelial cell denudation is historically cited, a recent study refutes this and implicates a role for erythrocytes. Given the complexity of the in vivo environment, an in vitro reductionist approach is required to systematically isolate and analyze the biochemical, mass transfer, and biological phenomena that govern the system. To this end, we designed an "endothelial-ized" microfluidic device to introduce controlled FeCl3 concentrations to the molecular and cellular components of blood and vasculature. FeCl3 induces aggregation of all plasma proteins and blood cells, independent of endothelial cells, by colloidal chemistry principles: initial aggregation is due to binding of negatively charged blood components to positively charged iron, independent of biological receptor/ligand interactions. Full occlusion of the microchannel proceeds by conventional pathways, and can be attenuated by antithrombotic agents and loss-of-function proteins (as in IL4-R/Iba mice). As elevated FeCl3 concentrations overcome protective effects, the overlap between charge-based aggregation and clotting is a function of mass transfer. Our physiologically relevant in vitro system allows us to discern the multifaceted mechanism of FeCl3-induced thrombosis, thereby reconciling literature findings and cautioning researchers in using the FeCl3 model.
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http://dx.doi.org/10.1182/blood-2015-02-628594DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4528067PMC
August 2015

Biomechanics of haemostasis and thrombosis in health and disease: from the macro- to molecular scale.

J Cell Mol Med 2013 May 14;17(5):579-96. Epub 2013 Mar 14.

Department of Pediatrics, Division of Pediatric Hematology/Oncology, Aflac Cancer Center and Blood Disorders Service of Children's Healthcare of Atlanta, Emory University School of Medicine, Atlanta, Georgia 30322, USA.

Although the processes of haemostasis and thrombosis have been studied extensively in the past several decades, much of the effort has been spent characterizing the biological and biochemical aspects of clotting. More recently, researchers have discovered that the function and physiology of blood cells and plasma proteins relevant in haematologic processes are mechanically, as well as biologically, regulated. This is not entirely surprising considering the extremely dynamic fluidic environment that these blood components exist in. Other cells in the body such as fibroblasts and endothelial cells have been found to biologically respond to their physical and mechanical environments, affecting aspects of cellular physiology as diverse as cytoskeletal architecture to gene expression to alterations of vital signalling pathways. In the circulation, blood cells and plasma proteins are constantly exposed to forces while they, in turn, also exert forces to regulate clot formation. These mechanical factors lead to biochemical and biomechanical changes on the macro- to molecular scale. Likewise, biochemical and biomechanical alterations in the microenvironment can ultimately impact the mechanical regulation of clot formation. The ways in which these factors all balance each other can be the difference between haemostasis and thrombosis. Here, we review how the biomechanics of blood cells intimately interact with the cellular and molecular biology to regulate haemostasis and thrombosis in the context of health and disease from the macro- to molecular scale. We will also show how these biomechanical forces in the context of haemostasis and thrombosis have been replicated or measured in vitro.
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http://dx.doi.org/10.1111/jcmm.12041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3822810PMC
May 2013
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