Proteome modulation by opposite inotropic drugs in human engineered cardiac tissue revealed by topology-driven cross-modal integration

The human heart is a relentless pump, a muscle that beats roughly one hundred thousand times a day without rest. To keep this rhythm, the heart relies on a complex internal machinery of proteins that contract, signal, and generate energy. When scientists want to test new drugs or understand heart disease, they often turn to engineered heart tissues. These are small, three-dimensional clumps of living heart cells grown in a lab, designed to mimic the behavior of a real human heart. They offer a way to watch how a drug changes the strength of a heartbeat and to see what happens inside the cells at the same time. However, connecting the visible movement of the muscle to the invisible changes in its thousands of proteins has been difficult. Traditional methods often treat the physical movement and the molecular data as separate stories, making it hard to see how they influence each other.

In a new study, researchers tackled this challenge by growing engineered heart tissues from human stem cells and treating them with two very different drugs: epinephrine, which makes the heart beat harder, and doxorubicin, a chemotherapy drug known to weaken the heart. They measured the force of the heartbeat and then analyzed the proteins inside the tissue to see how the cells responded. To make sense of the massive amount of data, the team used a mathematical approach called topological data analysis. Instead of forcing the data into simple charts, this method looks at the overall shape and connections within the information, allowing the researchers to map the relationship between the drug, the muscle's strength, and the protein changes all at once.

The experiment began with a batch of human heart cells grown in a lab until they formed tiny, beating tissues. The researchers divided these tissues into groups. Some were left alone, some received a harmless solvent, one group received epinephrine, and another received doxorubicin. After twenty-four hours, they measured how hard each tissue contracted. As expected, the tissues treated with epinephrine squeezed with more force, while those treated with doxorubicin became weaker. Immediately after measuring this force, the researchers froze the tissues to capture a snapshot of their proteins. They identified over seven thousand different protein groups in each sample, creating a detailed molecular map of what was happening inside the cells.

To understand how these thousands of proteins related to the strength of the heartbeat, the team built a unified network model. Imagine the data not as a list of numbers, but as a landscape where every point represents a tissue sample. In this landscape, the researchers placed the samples based on their protein levels and their heartbeat strength. This created a connected map where tissues with similar behaviors and molecular profiles clustered together. The map clearly separated the tissues based on which drug they had received. The tissues treated with epinephrine gathered in one area, characterized by high force, while the doxorubicin-treated tissues gathered in a completely different area, marked by low force. The untreated tissues sat in the middle, showing that the drugs had pushed the heart cells into distinct molecular states.

By examining the connections in this map, the researchers discovered which specific proteins were driving these changes. They found that the proteins associated with a strong heartbeat, like those seen with epinephrine, were closely linked to energy production and the machinery that builds new proteins inside the cell's power plants, known as mitochondria. In contrast, the proteins that changed when the heart was weakened by doxorubicin showed a nearly opposite pattern. The drugs caused a reversal in how these energy and protein-building processes were associated with the heart's function. While the positive drug strengthened the link between energy production and muscle force, the negative drug disrupted it, suggesting that the heart's ability to contract is deeply tied to how well it manages its energy and maintains its internal protein balance.

The study did not prove that these protein changes caused the heart to beat harder or weaker, but it showed a strong, direct association between them. The researchers noted that simply seeing a protein change does not mean the protein is more active; it just means it is present in different amounts. However, the clarity of the pattern suggests that energy homeostasis and mitochondrial health are central to how the heart responds to drugs. This new way of looking at data, which treats the physical function and the molecular makeup as a single, interconnected system, offers a powerful tool for understanding complex biological responses. It allows scientists to see the big picture of how a drug alters a living tissue, moving beyond isolated facts to understand the system as a whole. This approach could help in developing better drugs and understanding heart disease by revealing the hidden molecular stories behind the beating of the heart.