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Myocardial slices - a novel cardiac model to study mechanical load in vitro
Fotios G Pitoulis1, Sian E Harding1, Pieter P de Tombe1, Cesare M Terracciano11Imperial College London, National Heart & Lung Institute, UK
Myocardial slices are living 300μm-thick organotypic heart preparations with preserved structure and function. They can be prepared from mammals including humans. Mechanical load drives cardiac remodelling and different load profiles lead to dissimilar cardiac phenotypes in vivo. Most in vitro mechanical protocols are crude and do not reflect the complexity of the cardiac cycle; in culture, this causes cardiac dedifferentiation and limits findings’ translation. We developed a system to culture slices under physiological-load, pressure-, or volume-overload, and explore their effects on cardiac remodelling.
A custom bioreactor simulating the cardiac cycle on slices was developed based on a Windkessel model. Adult Sprague-Dawley rat slices were prepared, mounted on the bioreactor, and paced at 1Hz for 3-days. By changing Windkessel parameters, slices performed work loops correspondent to physiological load (normal afterload & preload), pressure- (high afterload & normal preload), or volume-overload (normal afterload & high preload).
In physiologically-loaded and pressure-overloaded slices time-varying elastance, (E(t)), increased from day-0 to day-3 (ΔE(t)=5.9±1.0 and 5.6±1.5 mNmm-1 respectively; n=5), whereas it decreased in volume-overloaded slices (ΔE(t)=-5.2±1.0 mNmm-1; n=4). To determine force response to stretch, slices were stretched from 100% to 126.3% of resting muscle length (RML) at the end of the experiment. Developed force was significantly higher in physiologically-loaded slices above 118% RML stretch compared to pressure- and volume-overload (p<0.01; n=6,6,4 respectively), and the latter two showed completely different force-stretch trajectories.
We developed a novel platform to culture slices under mechanical load. We show that different loads can be simulated and cause differential remodelling that can be temporally tracked. Structural, and molecular signatures of each load profile are currently being investigated. Secondly, we demonstrate that adult cardiac function can be maintained in vitro for at least 3-days with optimal preload and afterload. This is important for translational research where physiologically relevant chronic in vitro models, particularly for human tissue, are urgently needed.