Pressure training matures iPS-derived heart tissue

Human iPS-derived three-dimensional engineered cardiac tissue (ECT) can be matured like adult cardiac muscle by training it with pressure training. This was revealed by a joint research group including Visiting Senior Research Scientist Hidetoshi Masumoto (at the time of research; currently Distinguished Professor appointed by the University President, Faculty of Medicine, Kansai Medical University) and Team Director Wataru Kimura of the Laboratory for Heart Regeneration at the RIKEN Center for Biosystems Dynamics Research, along with Project Associate Professor Seitaro Nomura at the Graduate School of Medicine at the University of Tokyo.

This is expected to lead not only to functional improvements in transplantable cardiac tissue used in regenerative medicine, but also to the development of drug evaluation systems and heart disease models. Masumoto stated: "Applying a pressure of 50 kilopascals for 1 hour a day, continued for 3 days, yielded the best results, but the trial and error required to find this condition was the most challenging part." The results were published online in Stem Cell Reports.

Cardiovascular diseases have ranked as the world's leading cause of death for over 40 years. When cardiac muscle is damaged by myocardial infarction or other conditions, it rarely regenerates, leading to reduced cardiac function and severe heart failure. A heart transplantation is the definitive treatment, but due to a shortage of donors, patients who can receive it are extremely limited. Therefore, regenerative medicine using iPS-derived cardiomyocytes is required.

However, iPS-derived cardiomyocytes are immature, similar to fetal cardiomyocytes. They are characterized by weak and unstable contraction, low energy production, and drug responses, unlike adult cardiac muscle. Thus, maturing iPS-derived cardiomyocytes to the adult level is needed.

To date, in addition to various humoral factors, maturation via physical stimuli such as electrical stimulation and stretching stimulation has been investigated. What the research group focused on was "pressure." "Because the developing heart must also be subjected to various pressures, we focused on pressure, but pressure had not been investigated regarding iPS-derived cardiac muscle," said Masumoto.

First, they fabricated ECT (width 1 to 1.5 mm, length slightly under 2 cm) shaped like spectacle frames with a significantly extended center. By culturing cardiomyocytes, endothelial cells, and mural cells inside molded dishes, cardiac tissue formed naturally, and beating was confirmed on day 7. After culturing for a total of two weeks, uniform hydrostatic pressure was applied to the entire ECT. A pressure of 50 kPa corresponds to 375 mmHg, which is three times normal human blood pressure. Compared to hydrostatic pressure during standard culture, it is approximately 1,000 to 2,500 times higher. Pressure training was conducted by applying pressure over 1 hour a day and returning it to the incubator for 23 hours, repeating this operation for 3 days.

In the ECT after training, cardiomyocytes aligned in one direction, forming a regular structure characteristic of cardiac tissue. Other observed results include the following: mitochondrial content increased; oxygen consumption rate and ATP production capacity improved; calcium uptake and release functions that regulate the timing and strength of contraction were enhanced; and a positive force-frequency relationship, which is a functional feature of adult cardiac muscle where contractile force increases in response to higher beating frequency.

Regarding the degree of maturation, single-cell RNA sequencing analysis revealed that in cardiomyocytes of ECT that underwent pressure training, the expression of genes characteristic of mature cardiac muscle increased, while the expression of genes characteristic of immature cardiac muscle decreased. Furthermore, in ECT that did not contain vascular endothelial cells during fabrication, almost no maturation effect from pressure training was observed, indicating that vascular endothelial cells play an important role in sensing pressure stimuli and promoting the maturation of the entire cardiac tissue.

Vascular networks were not formed in the ECT through pressure training alone. Applying dynamic training (fluidic culture) involving placing it in culture medium and providing constant vibration resulted in the formation of vascular networks in the pressure-trained ECT.

Furthermore, when the research group transplanted three pressure-trained ECTs into the hearts of immunodeficient rats with induced myocardial infarction, they confirmed that human cardiac tissue had regenerated and engrafted four weeks after transplantation.

Moving forward, while advancing the enlargement of artificial cardiac muscle for transplantation and the sophistication of vascular network formation technology, they plan to conduct efficacy and safety evaluations using large animals such as pigs and monkeys. Regarding application to drug discovery research, they aim for research use within a few years. Regarding clinical application in regenerative medicine, they will advance research and development aiming for First-in-Human (FIH) trials in approximately 5 to 10 years.

Journal Information
Publication: Stem Cell Reports
Title: High and intermittent hydrostatic pressure promotes maturation of engineered cardiac tissues derived from human pluripotent stem cells
DOI: 10.1016/j.stemcr.2026.103019