TBX20 enhances the reprogramming of cardiac fibroblasts to cardiomyocytes

The mammalian heart has little ability to grow new cardiomyocytes, known as cardiomyocytes
, after birth.
Therefore, necrotic tissue after a heart attack in adults cannot be repaired
with new cardiomyocytes.
In its place is scar tissue, which weakens the heart's ability to pump blood, often leading to heart failure
.

Direct reprogramming of cardiac fibroblasts into cardiomyocytes is a promising strategy
for muscle-building in injured hearts.
Researchers Zhou Yang, PhD, and Rui Lu, PhDs, at the University of Alabama, Birmingham, have identified TBX20 as a key missing transcription factor
in the existing cocktail for direct cardiac reprogramming in human fibroblasts.

They report that adding TBX20 to the reprogramming cocktail MGT 133 promotes cardiac reprogramming and activates genes
associated with heart contractility, maturation, and ventricular position in cardiomyocytes.
Mechanically, they found that TBX20 co-localizes with MGT reprogramming factors on cardiac gene enhancers, leading to potent activation
of target genes.

"Our study highlights the undocumented role of TBX20 as an important regulator of direct human cardiac reprogramming, and improving the efficiency and quality of direct cardiac reprogramming from human fibroblasts is a critical step in
the clinical translation of this technique.
"

An important area of future research, Zhou said, will be testing direct reprogramming
of TBX20 in vivo.

Current cocktails of direct reprogramming of human fibroblasts have problems of low efficiency and insufficient production of functional cardiomyocytes
.
The UAB researchers compared the cardiomyocytes induced with a cocktail of fibroblasts with functional cardiomyocytes and found that TBX20 was the most underexpressed factor
.
The addition of TBX20 promotes cardiac reprogramming, which can be seen
in the activation of heart genes associated with sarcomere structure, ion channels, and cardiac contractions.
Sarcomere is the smallest function of
the striated muscle.

Human heart ventricular fibroblasts will be the primary target for
assessing in vivo reprogramming.
Zhou and his colleagues found that TBX20 is essential in the process of reprogramming these fibroblasts into induced cardiomyocytes, suggesting that TBX20 has therapeutic potential
.

TBX20 mainly activates genes in the late stage of reprogramming to enhance calcium flux, contractility and mitochondrial function
in induced cardiomyocytes.
Mitochondria are the source of energy for
heart muscle contraction.
TBX20 appears to help induce mitochondrial conversion in cardiomyocytes to adult cardiomyocyte-like respiration
.

Mechanically, UAB researchers found that TBX20 binds to and activates
cardiac gene enhancers.
An enhancer is a short regulatory element on DNA that binds to an activating protein to initiate transcription or increases transcription for a specific gene target
.
Transcription is the process of
copying messenger RNA from DNA genes to encode proteins.
Enhancers usually function
at a distance from their genetic target.

Zhou and his colleagues found that the TBX20-bound enhancer requires all three MGT cocktail factors to help activate heart genes
.
TBX20 alone is not sufficient to induce cardiomyocyte fate transformation; Missing any of the three management factors greatly reduces the efficiency of
reprogramming.

"Overall, our findings suggest that TBX20 requires intact regulatory gene factors to facilitate direct reprogramming and activate heart genes, and they support the idea that cardiac direct reprogramming is a coordinated regulatory process coordinated by multiple factors," Zhou said
.

Single-cell RNA sequencing analysis revealed two major cell clusters
after TBX20 reprogramming.
One group was reprogrammed induced cardiomyocytes, while the other group was only partially reprogrammed
.
Recombinant cardiomyocyte clusters have gene expression profiles
similar to ventricular cardiomyocytes.

At Wuhan University of Technology, Professor Zhou is an Assistant Professor in the Department of Biomedical Engineering and Professor Lu is an Assistant Professor
in the Department of Hematology and Oncology at the School of Medicine.

Co-first authors of the study, Yawen Tang and Sajesan Aryal, "TBX20 improves contractility and mitochondrial function during direct human heart reprogramming.
"
In addition to Zhou, Lu, Tang and Aryal, other co-authors include Geng Xiaoxiao, Zhou Xinyue, Vladimir G.
Fast and Zhang Jianyi
.

National Institutes of Health funded HL153220, CA259480, and HL149137; and the American Heart Association Transformation Project Award 995529
.

Medicine is a department of the UAB Marnix E.
Heersink School of Medicine, and biomedical engineering is a joint department
of the UAB School of Engineering and the Heersink School of Medicine.