Human pluripotent stem cells (PSCs) can potentially be cultured to produce any cell or tissue that the body needs to repair itself. However, developing the technology to accomplish this for specialized cells such as beating heart muscle cells (cardiomyocytes), requires detailed knowledge of regulatory factors and developmental pathways.

Nicole C. Dubois, PhD, an associate professor of cell, developmental, and regenerative biology at Mount Sinai, is senior author of this study.

“Despite significant technological advances, cell types that are derived from human PSCs remain functionally immature. In the case of human PSC-derived cardiomyocytes (hPSC-CMs), this limits their applications in regenerative medicine and disease modeling as the cells generated do not fully represent those found in the adult heart and are instead, closer to a 20-week-old fetal heart,” said Nicole C. Dubois, PhD, an associate professor of cell, developmental, and regenerative biology at the Black Family Stem Cell Institute and the Mindich Child Health and Development Institute at the Icahn School of Medicine at Mount Sinai.

Dubois’ lab is interested in understanding early heart development and disease. Her team uses mouse embryo and hPSCs to investigate mechanisms that specify cell fate.

Nadeera Wickramasinghe, PhD, is lead author of this study.

A new study, led by Dubois’ graduate student, Nadeera Wickramasinghe, PhD, has modulated the PPAR (peroxisome proliferator activated receptor) signaling pathway that plays an important role in the maturation of cardiomyocytes to recapitulate in culture, the maturation and progressive specialization of this cell in the womb.

The findings were published in an article in the journal Cell Stem Cell, titled, “PPARdelta activation 1 induces metabolic and contractile maturation of human pluripotent stem cell-derived cardiomyocytes.” The reproducible and scalable protocol for generating functional adult heart muscle cells from hPSCs in the laboratory delineated in this study will facilitate a variety of basic research and clinical approaches.

“We identified an isoform-specific maturation response, where PPARdelta signaling activation specifically was able to enhance the metabolic, structural, and contractile maturation of hPSC-CMs. This is the first time that PPAR signaling has been elucidated in such an isoform-specific manner,” said Dubois and Wickramasinghe.

“The specificity for PPARdelta but not PPARalpha to have such an efficient effect on cardiac maturation is unexpected. This new maturation strategy provides an easy yet robust approach to generate mature heart cells in culture, which can be utilized for numerous applications such as drug screening, disease modeling, or cell replacement therapy for failing hearts,” they added.

The team identified the role of the protein PPARdelta in inducing a metabolic switch from glycolysis to fatty acid oxidation in the lab-generated heart muscle cells, which is a critical step in their maturation and controls whether these cells generate energy from glucose or fatty acids.

“We incorporated and optimized protocols for extended monolayer culture, 3D-tissue culture, and lactate selection to assay the effects of different culture formats and metabolic manipulations on hPSC-CMs,” said Dubois and Wickramasinghe.

The team showed that PPARdelta signaling plays a distinct role in efficiently activating gene regulatory networks that increase fatty acid oxidation, the number and organization of mitochondria and peroxisomes, and the size, myofibril layout, and contractility of heart muscle cells.

Fleeting exposure to lactate is conventionally used to purify hPSC-CMs. The treatment triggers an independent molecular program for heart cell maturation. In this study, the authors showed lactate treatment combined with the activation of PPARdelta further increases oxidative metabolism, allowing energy generation from both carbohydrates and fatty acids.

Through a collaboration with Avi Ma’ayan, MD, a professor of pharmacology and a co-author of the study, the team developed a comprehensive and publicly accessible gene expression dataset of transcriptomic changes in hPSC-CMs that could be valuable to researchers investigating PPAR signaling, lactate selection, or screening targets for research or drug testing.

Dubois and Wickramasinghe are excited to use mature hPSC-CMs to model diseases and develop regenerative therapies. They said, “We’re interested in studying fatty acid oxidation disorders, which will be dependent on having CMs that preferentially use fatty acid oxidation as an energy source. We will also explore using these mature hPSC-CMs in transplants after an infarct.”

Dubois added, “This work will create exciting opportunities to further assess human heart biology through multi-disciplinary approaches incorporating developmental biology, transcriptomics, contractile measurements, and drug testing. We are moving a step closer to understanding how to leverage our knowledge of human development to improve access to mature human cell types.”

The work was supported by funding from the Mindich Child Health and Development Institute, the National Institute of Health (NIH), and the National Heart, Lung, and Blood Institute (NHLBI).

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