A Patient-Derived Stem Cell Model Reveals New Therapeutic Strategies for Restrictive Cardiomyopathy

by Amanda Chase, PhD
May 19, 2026

Restrictive cardiomyopathy (RCM) is one of the most severe and least understood forms of heart disease. Unlike other cardiomyopathies, the heart in RCM can still contract normally, but it loses its ability to properly relax and fill with blood, a defect known as diastolic dysfunction. This leads to poor outcomes, particularly in children, where treatment options remain extremely limited and largely supportive rather than curative, and in many cases necessitate early heart transplantation. Despite advances in targeting the contractile machinery of the heart in related conditions such as hypertrophic cardiomyopathy, it remains unclear whether similar strategies could be effective, or even safe, in RCM.

In a publication in Circulation Genome Precision Medicine, researchers at the Stanford Cardiovascular Institute, led by first author David Staudt and senior author Mark Mercola, set out to directly address this by building a patient-derived model of pediatric RCM and using it to test potential therapeutic strategies. The team focused on a patient carrying a mutation in the TNNT2 gene (pathogenic variant R94C), which encodes a key component of the cardiac sarcomere, the molecular machinery responsible for heart contraction. They generated induced pluripotent stem cells (iPSCs) from the patient, along with a genetically corrected version of the same cells. This paired system allowed for a precise comparison of how the mutation alters heart cell function.

However, modeling RCM required more than just the right cells; it also required new ways to measure what those cells were doing. To better capture the mechanical features of RCM, the researchers developed an advanced measurement platform that integrates high-resolution imaging of both force generation and calcium signaling near-simultaneously in beating heart cells. This approach enabled them to directly quantify not only how strongly the cells contract, but also how efficiently they relax and how calcium, the key regulator of contraction, is handled within the cell. Using this system, they found that mutant cardiomyocytes exhibited hallmark features of RCM: prolonged contraction and relaxation times, increased force generation, and elevated tension even during the relaxation phase of the cardiac cycle.

Because their platform measured calcium and force generation at the same time, the authors were able to directly probe the relationship between calcium signaling to force generation in these cells. They found that the contractile abnormalities were associated with an increased sensitivity of the contractile machinery to calcium. The mutant cells required less calcium to generate force, meaning that even at baseline levels, the sarcomere remained overly active. This heightened calcium sensitivity provides a mechanistic explanation for the impaired relaxation seen in RCM, as the heart muscle cannot fully disengage between beats.

The team then used these mechanistic insights to evaluate possible therapeutic options for treating the dysfunction seen in TNNT2 R94C cardiomyocytes. They directly compared two therapeutic strategies targeting the sarcomere. The first, myosin inhibition using the clinically approved drug mavacamten, reduces the number of active molecular motors driving contraction. The second approach, calcium desensitization using the compound W7, shifts how the sarcomere responds to calcium without directly reducing its contractile capacity, thus directly targeting the underlying defect observed within the cells.

Beyond identifying a potential treatment strategy, this study establishes a powerful framework for studying diseases of cardiac relaxation. By combining patient-specific stem cell models with integrated mechanical and molecular measurements, the researchers provide a platform to systematically evaluate therapies for diastolic dysfunction, a major unmet need across many forms of heart disease. Together, these findings not only advance our understanding of the fundamental biology of restrictive cardiomyopathy but also point toward more precise and effective therapeutic strategies for a condition that currently has few options.

Other authors include Stanford Cardiovascular Institute researchers Ricardo Serrano, Anna Hnatiuk, Isaac Sanchez, Xiomara Carhuamaca, and Dries Feyen.