Modelling arterial thrombus formation in vitro

A humanised thrombus-on-a-chip model utilising tissue-engineered arterial constructs: A method to reduce and replace mice used in thrombosis and haemostasis research

The study of in vivo thrombus formation has principally been performed using intravital microscopy in mice and other species. These have allowed us to visualise the molecular and cellular processes that regulate thrombus formation inside the body. However current in vivo arterial thrombosis models are difficult to standardise between labs and frequently produce results that do not reliably translate successfully in human clinical trials. Here we provide a step-by-step description with accompanying video tutorials to demonstrate how to produce a 3D humanised thrombus-on-a-chip model, which uses perfusion of fluorescently-labelled human blood over a mechanically-injured human tissue engineered arterial construct (TEAC) within a 3D printed microfluidic flow chamber to replicate thrombus formation within a healthy artery. We also provide a written methodology on how to use 3D printing to produce a mechanical injury press that can reproducibly damage the TEAC as a stimulus for thrombus formation as part of a mechanical injury model. Perfusion of the uninjured TEAC with whole human blood containing DiOC6-labelled platelets without initiating notable thrombus formation. The mechanical injury press was shown to induce a reproducible puncture wound in the TEAC. Fluorescence microscopy was used to demonstrate that thrombus formation could be observed reproducibly around sites of injury. This humanised thrombosis-on-a-chip model can replace the use of animals in in vivo thrombosis models for preclinical assessment of anti-thrombotic therapies. This method also offers multiple scientific advantages: allowing new drugs to be directly tested on human blood from a diverse array of donors, facilitating use of a realistic and reproducible injury modality as well as removing the potential confounding effects of general anaesthetics in animal studies. The use of human thrombus-on-a-chip models combining TEACs offers a new methodology to reduce animal use whilst improving the predictive capabilities of preclinical trials of anti-thrombotic therapies.

Differential Proteoglycan Expression in Atherosclerosis Alters Platelet Adhesion and Activation

Proteoglycans are differentially expressed in different atherosclerotic plaque phenotypes, with biglycan and decorin characteristic of ruptured plaques and versican and hyaluronan more prominent in eroded plaques. Following plaque disruption, the exposure of extracellular matrix (ECM) proteins triggers platelet adhesion and thrombus formation. In this study, the impact of differential plaque composition on platelet function and thrombus formation was investigated. Platelet adhesion, activation and thrombus formation under different shear stress conditions were assessed in response to individual proteoglycans and composites representing different plaque phenotypes. The results demonstrated that all the proteoglycans tested mediated platelet adhesion but not platelet activation, and the extent of adhesion observed was significantly lower than that observed with type I and type III collagens. Thrombus formation upon the rupture and erosion ECM composites was significantly reduced (p < 0.05) compared to relevant collagen alone, indicating that proteoglycans negatively regulate platelet collagen responses. This was supported by results demonstrating that the addition of soluble biglycan or decorin to whole blood markedly reduced thrombus formation on type I collagen (p < 0.05). Interestingly, thrombus formation upon the erosion composite displayed aspirin sensitivity, whereas the rupture composite was intensive to aspirin, having implications for current antiplatelet therapy regimes. In conclusion, differential platelet responses and antiplatelet efficacy are observed on ECM composites phenotypic of plaque rupture and erosion. Proteoglycans inhibit thrombus formation and may offer a novel plaque-specific approach to limit arterial thrombosis.