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Published on: February 13, 2019
Reduced Mitochondrial Protein Translation Promotes Cardiomyocyte Proliferation and Heart Regeneration
Feng Gao1,2, Tian Liang1,2, Yao Wei Lu3
1Department of Cardiology, State Key Laboratory of Transvascular Implantation Devices, Provincial Key Lab of Cardiovascular Research, Second Affiliated Hospital (F.G., T.L., L.P., X.F., X.D., T.H., F.Z., N.L., H.Y., W.Z., X.H., J.W., J.C.).
Background:
The importance of mitochondria in normal heart function are well recognized and recent studies have implicated changes in mitochondrial metabolism with some forms of heart disease. Previous studies demonstrated that knockdown of the mitochondrial ribosomal protein S5 (MRPS5) by small interfering RNA (siRNA) inhibits mitochondrial translation and thereby causes a mitonuclear protein imbalance. Therefore, we decided to examine the effects of MRPS5 loss and the role of these processes on cardiomyocyte proliferation.
Methods:
We deleted a single allele of MRPS5 in mice and used left anterior descending coronary artery ligation surgery to induce myocardial damage in these animals. We examined cardiomyocyte proliferation and cardiac regeneration both in vivo and in vitro. Doxycycline treatment was used to inhibit protein translation. Heart function in mice was assessed by echocardiography. Quantitative real-time polymerase chain reaction and RNA sequencing were used to assess changes in transcription and chromatin immunoprecipitation (ChIP) and BioChIP were used to assess chromatin effects. Protein levels were assessed by Western blotting and cell proliferation or death by histology and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assays. Adeno-associated virus was used to overexpress genes. The luciferase reporter assay was used to assess promoter activity. Mitochondrial oxygen consumption rate, ATP levels, and reactive oxygen species were also analyzed.
Results:
We determined that deletion of a single allele of MRPS5 in mice results in elevated cardiomyocyte proliferation and cardiac regeneration; this observation correlates with improved cardiac function after induction of myocardial infarction. We identified ATF4 (activating transcription factor 4) as a key regulator of the mitochondrial stress response in cardiomyocytes from Mrps5+/- mice; furthermore, ATF4 regulates Knl1 (kinetochore scaffold 1) leading to an increase in cytokinesis during cardiomyocyte proliferation. The increased cardiomyocyte proliferation observed in Mrps5+/- mice was attenuated when one allele of Atf4 was deleted genetically (Mrps5+/-/Atf4+/-), resulting in the loss in the capacity for cardiac regeneration. Either MRPS5 inhibition (or as we also demonstrate, doxycycline treatment) activate a conserved regulatory mechanism that increases the proliferation of human induced pluripotent stem cell-derived cardiomyocytes.
Conclusions:
These data highlight a critical role for MRPS5/ATF4 in cardiomyocytes and an exciting new avenue of study for therapies to treat myocardial injury.
Insights
Loss of mitochondrial ribosomal protein S5 (MRPS5) enhances cardiomyocyte proliferation and cardiac regeneration, improving heart function after injury. This involves ATF4 regulation of cytokinesis, offering new therapeutic targets for myocardial repair.
Area of Science:
- Cardiology
- Mitochondrial Biology
- Molecular Biology
Background:
- Mitochondria are crucial for heart function, and metabolic changes are linked to heart disease.
- Mitochondrial ribosomal protein S5 (MRPS5) knockdown inhibits mitochondrial translation, causing mitonuclear protein imbalance.
- Investigating MRPS5 loss effects on cardiomyocyte proliferation is key to understanding heart disease mechanisms.
Purpose of the Study:
- To examine the effects of MRPS5 loss on cardiomyocyte proliferation and cardiac regeneration.
- To elucidate the role of mitochondrial stress response in heart repair.
- To identify potential therapeutic targets for myocardial injury.
Main Methods:
- Mice with a deleted MRPS5 allele underwent myocardial infarction induction.
- Cardiomyocyte proliferation, cardiac regeneration, and heart function were assessed in vivo and in vitro.
- Molecular analyses included gene expression, protein levels, and mitochondrial function assays.
Main Results:
- MRPS5 haploinsufficiency improved cardiac function and regeneration post-myocardial infarction.
- ATF4 was identified as a key regulator of the mitochondrial stress response, promoting cardiomyocyte proliferation via Knl1.
- MRPS5 inhibition or doxycycline treatment increased proliferation in human iPSC-derived cardiomyocytes.
Conclusions:
- MRPS5 and ATF4 play critical roles in cardiomyocyte function and cardiac repair.
- Targeting the MRPS5/ATF4 pathway presents a novel therapeutic strategy for myocardial injury.
- This study opens new avenues for developing treatments for heart disease.
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