SUMMARY Background Acquired and inherited bleeding disorders may present in the neonatal period with devastating lifelong effects. Diagnosing bleeding disorders in the neonatal population could aid in preventing and treating the associated complications. However, currently available platelet function testing is limited in neonates owing to difficulties obtaining adequate blood volume, lack of normal reference ranges, and an incomplete understanding of the neonatal platelet functional phenotype. Objective Develop small-volume, whole blood platelet function assays to quantify and compare neonatal and adult platelet function. Methods and Results Peripheral blood was obtained from healthy, full-term neonates at 24-hours of life. Platelet activation, secretion, and aggregation were measured via flow cytometry. Platelet adhesion and aggregation were assessed under static and flow conditions. As compared to adult platelets, peripheral neonatal platelet P-selectin expression and integrin glycoprotein (GP) IIbIIIa activation was significantly reduced in response to the G protein-coupled receptor (GPCR)-agonists thrombin receptor activator peptide-6 (TRAP-6), adenosine 5′-diphosphate (ADP), and U46619 and the immunoreceptor tyrosine-based activation motif (ITAM)-signaling pathway agonists collagen-related peptide (CRP) and rhodocytin. Neonatal platelet aggregation was markedly reduced in response to TRAP-6, ADP, U46619, CRP, and rhodocytin compared to adult platelets. The extent of neonatal and adult platelet adhesion and aggregate formation under static and shear conditions on collagen and von Willebrand factor (VWF) were similar. Conclusions As compared to adult platelets, we found neonatal platelet activation and secretion were blunted in response to GPCR- or ITAM-agonists, while the extent of neonatal platelet adhesion and aggregate formation was similar to adult platelets.

Circulating tumor cells (CTC) have been implicated in the hematogenous spread of cancer. To investigate the fluid phase of cancer from a physical sciences perspective, the multi-institutional Physical Sciences-Oncology Center (PS-OC) Network performed multidisciplinary biophysical studies of single CTC and CTC aggregates from a patient with breast cancer. CTCs, ranging from single cells to aggregates comprised of 2-5 cells, were isolated using the high-definition CTC assay and biophysically profiled using quantitative phase microscopy. Single CTCs and aggregates were then modeled in an in vitro system comprised of multiple breast cancer cell lines and microfluidic devices used to model E-selectin mediated rolling in the vasculature. Using a numerical model coupling elastic collisions between red blood cells and CTCs, the dependence of CTC vascular margination on single CTCs and CTC aggregate morphology and stiffness was interrogated. These results provide a multifaceted characterization of single CTC and CTC aggregate dynamics in the vasculature and illustrate a framework to integrate clinical, biophysical, and mathematical approaches to enhance our understanding of the fluid phase of cancer.circulating tumor cell; metastasis; breast cancer; cell lines; fluid dynamics; physics of cancer; hemodynamics; quantitative phase microscopy; microfluidics; immersed finite element method WHILE THE PRESENCE of circulating tumor cells (CTCs) in the vasculature has been implicated in the metastatic cascade of epithelial carcinomas, new evidence has revealed a putative role of CTC aggregates as a potential form of stromal-assisted metastasis across a variety of epithelial tumor types (6). In concert, the presence of homotypic interactions among CTCs leading to aggregation occurring at sites of endothelial attachment suggest the involvement of CTC aggregates in the hematogenous dissemination of cancer. Despite compelling evidence suggesting a role for CTC aggregates in metastatic progression (28), the physics underlying CTC vascular transport including the influence of blood flow, coagulation, intercellular adhesion, and collisions with cells of the vasculature, such as red blood cells (RBCs) and endothelial cells (ECs), remains poorly understood. Better physical understanding of CTC transport and mechanobiology could enable, for example, new strategies to monitor patient response to chemotherapy (22).Here, we demonstrate a multidisciplinary approach (29) that utilizes clinical measurements on single CTCs and CTC aggregates from a patient with breast cancer as a quantitative guide in the rational design of in vitro and in silico models to investigate the dynamics of CTC transport in the vasculature. Using the high-definition (HD) CTC assay to identify circulating tumor cells in the blood, coupled with quantitative phase microscopy (QPM) to quantify the subcellular density organization of CTCs, we profiled the biophysical properties of CTCs in a patient with breast cancer. These metrics, including geometric and density features,...

Summary Background and Objectives The reversible acetylation of protein lysine ε-amino groups, catalyzed by lysine acetyltransferases and deacetylases, serves as a molecular switch in the orchestration of diverse cellular activities. Here, we aimed to investigate the role of lysine acetyltransfer in platelet function. Methods and Results Proteomics methods identified 552 acetyllysine (acK) modifications on 273 platelet proteins that serve as candidate substrates for lysine acetyltransferases. Bioinformatics analyses of identified acK-modified platelet proteins supported roles for the lysine acetyltransferase p300 in the regulation of actin-mediated platelet processes. Biochemical experiments found that platelets express p300, which is activated in a Src kinase-dependent manner upon platelet stimulation with the platelet glycoprotein VI (GPVI) agonist CRP. Inhibition of platelet p300 abrogated CRP-stimulated lysine acetylation of actin, filamin and cortactin as well as F-actin polymerization, integrin activation and platelet aggregation. Super resolution visualization of platelet actin-rich adhesion structures revealed abundant acetyllysine protein content colocalized with platelet actin cytoskeletal proteins. Inhibition of p300 blocked platelet filopodia formation and the spreading of platelets on fibrinogen and collagen surfaces. In whole blood, p300 inhibition prevented the formation of platelet aggregates under shear, suggesting a physiological role for lysine acetyltransferase activity in platelet function. Conclusion Together, our findings uncover lysine acetyltransfer as a potential regulator of platelet actin dynamics and reveal potential roles for lysine acetylation in the molecular coordination of platelet activation and function.

The dynamics of the cellular and molecular constituents of the circulatory system are regulated by the biophysical properties of the heart, vasculature and blood cells and proteins. In this review, we discuss measurement techniques that have been developed to characterize the physical and mechanical parameters of the circulatory system across length scales ranging from the tissue scale (centimeter) to the molecular scale (nanometer) and time scales of years to milliseconds. We compare the utility of measurement techniques as a function of spatial resolution and penetration depth from both a diagnostic and research perspective. Together, this review provides an overview of the utility of measurement science techniques to study the spatial systems of the circulatory system in health and disease.

Abstract. Flow chamber assays, in which blood is perfused over surfaces of immobilized extracellular matrix proteins, are used to investigate the formation of platelet thrombi and aggregates under shear flow conditions. Elucidating the dynamic response of thrombi/aggregate formation to different coagulation pathway perturbations in vitro has been used to develop an understanding of normal and pathological cardiovascular states. Current microscopy techniques, such as differential interference contrast (DIC) or fluorescent confocal imaging, respectively, do not provide a simple, quantitative understanding of the basic physical features (volume, mass, and density) of platelet thrombi/aggregate structures. The use of two label-free imaging techniques applied, for the first time, to platelet aggregate and thrombus formation are introduced: noninterferometric quantitative phase microscopy, to determine mass, and Hilbert transform DIC microscopy, to perform volume measurements. Together these techniques enable a quantitative biophysical characterization of platelet aggregates and thrombi formed on three surfaces: fibrillar collagen, fibrillar collagen þ0.1 nM tissue factor (TF), and fibrillar collagen þ1 nM TF. It is demonstrated that label-free imaging techniques provide quantitative insight into the mechanisms by which thrombi and aggregates are formed in response to exposure to different combinations of procoagulant agonists under shear flow.