PRDM16 May Hold the Key to Making Human Heart Cells Both Grow and Mature
A developmental protein called PRDM16 may help solve one of regenerative medicine’s most persistent problems: how to make heart cells multiply without preventing them from becoming fully functional. In a new study published in Stem Cell Reports, researchers at Kyoto University report that PRDM16 acts as a molecular “rheostat” in human induced pluripotent stem cell-derived cardiomyocytes. Rather than functioning as a simple on-or-off switch, the protein appears to adjust the balance between cell proliferation and maturation, allowing cardiomyocytes to transition from growth-oriented cells into specialized muscle cells capable of supporting the heart’s powerful contractions.
The finding addresses a fundamental challenge in cardiac biology. During embryonic development, cardiomyocytes divide rapidly to produce the cells needed to construct the heart. Shortly after birth, however, human cardiomyocytes largely exit the cell cycle. They increase in size, organize their contractile machinery, develop specialized metabolic systems, and become optimized for continuous electrical and mechanical activity. This maturation is essential for normal heart function, but it also means that the adult human heart has only a limited ability to replace cardiomyocytes lost during a heart attack or other forms of injury.
Scientists have attempted to overcome this limitation by producing cardiomyocytes from induced pluripotent stem cells, or iPS cells. These cells can be generated by reprogramming mature human cells into a stem-like state and then directing them toward a cardiac fate. Although iPS cell-derived cardiomyocytes are valuable for studying inherited heart disease and testing drugs, they often resemble fetal rather than adult heart cells. Their contractile structures, energy-producing mitochondria, electrical properties, and gene-expression programs remain incompletely developed, limiting the accuracy of laboratory-grown cardiac tissues and their potential use in regenerative therapies.
To investigate how cardiomyocytes move between proliferation and maturation, the Kyoto University team combined fluorescent cell-cycle reporter systems with transcriptomic analysis, engineered heart tissues, and genetic gain- and loss-of-function experiments. These approaches allowed the researchers to observe not only whether the cells divided, but also how changes in PRDM16 affected their molecular identity, architecture, metabolism, and mechanical performance. The results placed PRDM16 at the center of a developmental transition that determines whether cardiomyocytes retain growth capacity or commit more strongly to adult-like specialization.
When the researchers reduced PRDM16 activity, the cardiomyocytes regained several features associated with proliferative competence. The cells showed increased activity of cell-cycle programs and higher levels of regulators including CDK1, a protein kinase involved in cell division. They also displayed elevated phospho-AKT, a signaling molecule linked to growth, survival, and metabolic regulation. These changes indicate that PRDM16 normally helps restrain pathways that keep cardiomyocytes in a more proliferative state. Lowering the protein therefore pushed the cells toward renewed cell-cycle activity, although this came at a substantial developmental cost.
PRDM16-deficient cardiomyocytes struggled to acquire the structural and functional characteristics of mature heart muscle. Their sarcomeres—the precisely organized contractile units that allow cardiomyocytes to shorten—were less developed, while their mitochondrial function and oxidative metabolism were impaired. Mature cardiomyocytes depend heavily on mitochondria to generate the large amounts of ATP required for continuous contraction. Engineered heart tissues made from PRDM16-deficient cells consequently exhibited weaker contractile performance, suggesting that increased proliferation alone does not produce healthier or more useful cardiac tissue.
The opposite pattern emerged when PRDM16 was moderately overexpressed. Higher PRDM16 activity suppressed cell proliferation and promoted several hallmarks of maturation, including cellular hypertrophy, greater expression of adult cardiac proteins, enhanced oxidative metabolism, and a reduction in spontaneous beating frequency. One important marker was TNNI3, the mature cardiac troponin I isoform, which increased relative to TNNI1, an immature isoform. The shift in troponin expression is significant because the proteins that regulate contraction change during development, and their composition affects the physiological behavior of heart muscle.
The researchers describe this balancing function as a developmental rheostat. At relatively low levels, PRDM16 permits cardiomyocytes to retain some capacity for growth and division. As its activity rises, the cells become less proliferative but more structurally organized, metabolically capable, and functionally specialized. “When we reduced PRDM16 levels, cardiomyocytes regained aspects of proliferative competence that are normally lost during maturation,” said Kanae Tani, the study’s first author. Yoshinori Yoshida, who supervised the work, said the protein appears to function as a molecular checkpoint guiding cells toward functional competence.
The findings could eventually support strategies that manipulate PRDM16 at different stages of tissue production or repair. Temporarily reducing its activity might enhance the expansion of cardiomyocytes, while later increasing PRDM16 could encourage those cells to mature before being incorporated into engineered tissue. Such a timed approach could be more effective than permanently forcing cells toward either proliferation or specialization. However, the researchers emphasize that significant questions remain, including which genes are directly controlled by PRDM16 and how its regulatory activity changes during human cardiac development. For now, the study identifies PRDM16 as an important determinant of cardiomyocyte behavior and offers a molecular framework for generating more physiologically realistic heart tissues for disease modeling, drug discovery, and future regenerative medicine.
Subject of Research: Cells
Article Title: PRDM16 modulates aspects of cell cycle dynamics and maturation in human iPSC-derived cardiomyocytes
News Publication Date: 9-Jul-2026
Web References: https://doi.org/10.1016/j.stemcr.2026.103005
References: Stem Cell Reports, DOI: 10.1016/j.stemcr.2026.103005
Image Credits: Kanae Tani
Keywords: PRDM16, cardiomyocytes, human iPS cells, induced pluripotent stem cells, cardiac regeneration, heart muscle, cell cycle, cardiomyocyte maturation, regenerative medicine, engineered heart tissue, stem cell research, mitochondrial function
