Article by Morgan Lamberti & Roberta Lock
Engineering a model of heart injury in a dish
Human Tissue-Engineered Model of Myocardial Ischemia-Reperfusion Injury, Tissue Engineering, 2019
Timothy Chen et al., Gordana Vunjak-Novakovic Lab
Myocardial infarction, also called a “heart attack”, occurs when a blockage in an artery prevents blood flow to the heart. Arteries carry oxygen, so this blockage stops the heart from receiving any oxygen and causes the tissue to die. Thus, doctors need to quickly remove the blockage and restore blood flow to the heart. However, the restoration of blood flow further damages the cells since cardiomyocytes (heart muscle cells) are sensitive to rapid changes in their environment. This phenomenon is termed “ischemia reperfusion injury” (IRI). This study aimed to model IRI and its subsequent effects in vitro using engineered heart tissues. .
What did these researchers do?
This study had three main components. First, mature engineered cardiac tissues were made in bioreactors. Induced pluripotent stem cells (iPSC) were differentiated into cardiomyocytes, cultured in a 3D tissue, and validated for maturity. Second, the model of ischemia-reperfusion injury was developed. This consisted of placing the tissues into a hypoxic (low oxygen) chamber and culturing the tissues in cell culture media that mimics the environment the tissue sees in the native heart following a heart attack. The reperfusion portion of the injury was mimicked by restoring the original cell culture media and placing the tissues back in an oxygen rich environment. Experiments were performed to confirm that the reperfusion step had an independent damaging effect on tissue. Third, this IRI model was adopted for testing various therapeutic agents that could reduce the IRI. To test this in vitro model of IRI and compare it to real IRI seen in patients, the researchers tested an ischemic preconditioning regimen, in which the tissues are exposed to a cycle of ischemia and reperfusion before their experimental ischemia/reperfusion. In patients, this regimen reduces IRI severity, and applying it to the tissues confirmed that it worked in the in vitro model as well.
Immunofluorescent stain of Healthy (left), Ischemic (middle), and Reperfused (right) engineered heart tissue
Why is this important?
In the U.S., a heart attack occurs every 40 seconds, and the damage resulting from reperfusion injury can further damage the heart muscle, eventually leading to heart failure. It is crucial for patient health that scientists understand how ischemia and reperfusion affect heart tissue so that therapeutics can be developed that effectively prevent or treat IRI. Creating an in vitro model of the injury using stem-cell based tissues provides researchers with a way to study this phenomenon on human heart tissue in a highly controlled environment without actually involving patients. Using this model, the ‘how’ and ‘why’ underlying the tissue injury can be investigated down to the molecular level, and any ideas for therapeutics can be rigorously tested for both safety and efficacy prior to being tested on patients. Additionally, the quality of the engineered cardiac tissue itself is important, since if IRI can be modeled using it, it has the potential to also be used to study other cardiac injuries and diseases, making it highly valuable to the scientific community.
How did the researchers do this?
The most important part of creating an injury model is validating its clinical relevance (e.g. is it an accurate representation of what is happening in patients?) Researchers validated the damaging effects of reperfusion on the tissue model using a comprehensive set of assays. They assessed many parameters, including cell death, reactive oxygen species (ROS) production, and changes to tissue structure. Reperfusion after 6 hours of ischemic conditions led to further cardiomyocyte cell death, decreased contractile function, higher ROS levels, and disruption in structure. Healthy mature muscle is aligned and striated, but immunostaining illustrated the degradation of tissue by enzymes after reperfusion. These same parameters were used to determine the efficacy of ischemic preconditioning and potential therapeutic drugs that target ROS production and mitochondrial membrane potential.
What comes next?
Ischemic reperfusion injury is characterized not only by cardiomyocyte death and general tissue damage, but by inflammation, impaired blood flow, and arrhythmias. However, improving the model to recapitulate these more complex characteristics would require significant changes. The engineered tissue could be improved by including other cell populations found in the native heart, like endothelial cells, fibroblasts, and immune cells. Additionally, the tissues in this experiment represented the damage done in the core infarct area, but it is also necessary to understand the interaction with non infarcted regions of the heart to have a better grasp of the systemic changes. The model could be improved by making the reperfusion injury limited to only a specific area of the tissue in order to mimic these interactions. While there are always improvements that can be made in the future, this model shows promise for studying IRI in vitro and demonstrates the great potential tissue engineered models bring to the medical field.