Cell-autonomous and non-cell-autonomous effects of arginase-II on cardiac aging
Curation statements for this article:-
Curated by eLife
eLife assessment
This study provides valuable information on how Arg-II participates in cardiac aging. Although the phenotypic data appear robust, the study is incomplete in elucidating the mechanisms, particularly in explaining how Arg II influences IL-1b and affects cardiac aging. It would be beneficial to investigate the possibility of NO involvement in this mice model. A co-culture system may be required to understand the non-cell-autonomous functions of macrophages. Lastly, the MI mouse model may not be directly linked to cardiac aging.
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Abstract
Aging is a predominant risk factor for heart disease. Aging heart reveals low-grade chronic inflammation, cell apoptosis, cardiac fibrosis, and increased vulnerability to ischemic injury. The underlying molecular mechanisms responsible for the cardiac aging phenotype and its susceptibility to injury are far from being fully understood. Although previous literature reports a role of the mitochondrial enzyme arginase-II (Arg-II) in development of heart failure, contradictory results are reported and no systematic analysis of cellular expression and localization of Arg-II in the heart has been performed. Whether and how Arg-II participates in cardiac aging are still unknown. In this study, we demonstrate, to our surprise, that Arg-II is not expressed in cardiomyocytes from aged mice and human patients, but upregulated in non-myocytes of the aging heart, including macrophages, fibroblasts, endothelial cells. Mice with genetic deficiency of arg-ii ( arg-ii -/- ) are protected from age-associated cardiac inflammation, myocyte apoptosis, interstitial and perivascular fibrosis, endothelial-mesenchymal transition (EndMT), and susceptibility to ischemic injury. Further experiments show that Arg-II mediates IL-1β release from macrophages of old mice, contributing to the above-described cardiac aging phenotype. In addition, Arg-II enhances mitochondrial reactive oxygen species (mtROS) and activates cardiac fibroblasts that is inhibited by inhibition of mtROS. Thus, our study demonstrates a non-cell-autonomous effect of Arg-II on cardiomyocytes, fibroblasts, and endothelial cells mediated by IL-1β from aging macrophages as well as a cell-autonomous effect of Arg-II through mtROS in fibroblasts contributing to cardiac aging phenotype.
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eLife assessment
This study provides valuable information on how Arg-II participates in cardiac aging. Although the phenotypic data appear robust, the study is incomplete in elucidating the mechanisms, particularly in explaining how Arg II influences IL-1b and affects cardiac aging. It would be beneficial to investigate the possibility of NO involvement in this mice model. A co-culture system may be required to understand the non-cell-autonomous functions of macrophages. Lastly, the MI mouse model may not be directly linked to cardiac aging.
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Reviewer #1 (Public Review):
Summary:
The manuscript by Duilio M. Potenza et al. explores the role of Arginase II in cardiac aging, majorly using whole-body arg-ii knock-out mice. In this work, the authors have found that Arg-II exerts non-cell-autonomous effects on aging cardiomyocytes, fibroblasts, and endothelial cells mediated by IL-1b from aging macrophages. The authors have used arg II KO mice and an in vitro culture system to study the role of Arg II. The authors have also reported the cell-autonomous effect of Arg-II through mitochondrial ROS in fibroblasts that contribute to cardiac aging. These findings are sufficiently novel in cardiac aging and provide interesting insights. While the phenotypic data seems strong, the mechanistic details are unclear. How Arg II regulates the IL-1b and modulates cardiac aging is still being …
Reviewer #1 (Public Review):
Summary:
The manuscript by Duilio M. Potenza et al. explores the role of Arginase II in cardiac aging, majorly using whole-body arg-ii knock-out mice. In this work, the authors have found that Arg-II exerts non-cell-autonomous effects on aging cardiomyocytes, fibroblasts, and endothelial cells mediated by IL-1b from aging macrophages. The authors have used arg II KO mice and an in vitro culture system to study the role of Arg II. The authors have also reported the cell-autonomous effect of Arg-II through mitochondrial ROS in fibroblasts that contribute to cardiac aging. These findings are sufficiently novel in cardiac aging and provide interesting insights. While the phenotypic data seems strong, the mechanistic details are unclear. How Arg II regulates the IL-1b and modulates cardiac aging is still being determined. The authors still need to determine whether Arg II in fibroblasts and endothelial contributes to cardiac fibrosis and cell death. This study also lacks a comprehensive understanding of the pathways modulated by Arg II to regulate cardiac aging.
Strengths:
This study provides interesting information on the role of Arg II in cardiac aging.
The phenotypic data in the arg II KO mice is convincing, and the authors have assessed most of the aging-related changes.
The data is supported by an in vitro cell culture system.
Weaknesses:
The manuscript needs more mechanistic details on how Arg II regulates IL-1b and modulates cardiac aging.
The authors used whole-body KO mice, and the role of macrophages in cardiac aging is not studied in this model. A macrophage-specific arg II Ko would be a better model.
Experiments need to validate the deficiency of Arg II in cardiomyocytes.
The authors have never investigated the possibility of NO involvement in this mice model.
A co-culture system would be appropriate to understand the non-cell-autonomous functions of macrophages.
The Myocardial infarction data shown in the mice model may not be directly linked to cardiac aging.
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Reviewer #2 (Public Review):
Summary:
The results from this study demonstrated a cell-specific role of mitochondrial enzyme arginase-II (Arg-II) in heart aging and revealed a non-cell-autonomous effect of Arg-II on cardiomyocytes, fibroblasts, and endothelial cells through the crosstalk with macrophages via inflammatory factors, such as by IL-1, as well as a cell-autonomous effect of Arg-II through mtROS in fibroblasts contributing to cardiac aging phenotype. These findings highlight the significance of non-cardiomyocytes in the heart and bring new insights into the understanding of pathologies of cardiac aging. It also provides new evidence for the development of therapeutic strategies, such as targeting the ArgII activation in macrophages.
Strengths:
This study targets an important clinical challenge, and the results are interesting …
Reviewer #2 (Public Review):
Summary:
The results from this study demonstrated a cell-specific role of mitochondrial enzyme arginase-II (Arg-II) in heart aging and revealed a non-cell-autonomous effect of Arg-II on cardiomyocytes, fibroblasts, and endothelial cells through the crosstalk with macrophages via inflammatory factors, such as by IL-1, as well as a cell-autonomous effect of Arg-II through mtROS in fibroblasts contributing to cardiac aging phenotype. These findings highlight the significance of non-cardiomyocytes in the heart and bring new insights into the understanding of pathologies of cardiac aging. It also provides new evidence for the development of therapeutic strategies, such as targeting the ArgII activation in macrophages.
Strengths:
This study targets an important clinical challenge, and the results are interesting and innovative. The experimental design is rigorous, the results are solid, and the representation is clear. The conclusion is logical and justified.
Weaknesses:
The discussion could be extended a little bit to improve the realm of the knowledge related to this study.
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