assessing-metabolic-activity-whole-regenerating-zebrafish-ventricles

Assessing the Metabolic Activity of Whole Regenerating Zebrafish Ventricles <em>Ex Vivo</em> Using an Extracellular Flux Assay

The ability of zebrafish to regenerate their hearts throughout adulthood is partially attributed to metabolic adaptations. Although it has been ...

University of Oxford

King Faisal Specialist Hospital & Research Centre

Herein, we maximize the labeling efficiency of cardiac progenitor cells (CPCs) using perfluorocarbon nanoparticles (PFCE-NP) and F MRI detectability, determine the temporal dynamics of single-cell label uptake, quantify the temporal viability/fluorescence persistence of labeled CPCs in vitro, and implement in vivo, murine cardiac CPC MRI/tracking that could be translatable to humans. FuGENE-mediated CPC PFCE-NP uptake is confirmed with flow cytometry/confocal microscopy. Epifluorescence imaging assessed temporal viability/fluorescence (up to 7 days [D]). Nonlocalized murine F MRS and cardiac MRI studied label localization in terminal/longitudinal tracking studies at 9.4 T (D1-D8). A 4-8 fold F concentration increase is evidenced in CPCs for FuGENE vs. directly labeled cells. Cardiac F signals post-CPC injections diminished in vivo to ~31% of their values on D1 by D7/D8. Histology confirmed CPC retention, dispersion, and macrophage-induced infiltration. Intra-cardiac injections of PFCE-NP-labeled CPCs with FuGENE can be visualized/tracked in vivo for the first time with F MRI.

Improved cellular uptake of perfluorocarbon nanoparticles for in vivo murine cardiac F MRS/MRI and temporal tracking of progenitor cells.

Myocardial infarction is the most prevalent of cardiovascular diseases and pharmacological interventions do not lead to restoration of the lost cardiomyocytes. Despite extensive stem cell therapy studies, clinical trials using cardiac progenitor cells have shown moderate results. Furthermore, differentiation of endogenous progenitors to mature cardiomyocytes is rarely reported. A metabolic switch from glucose to fatty acid oxidation occurs during cardiac development and cardiomyocyte maturation, however in vitro differentiation protocols do not consider the lack of fatty acids in cell culture media. The aim of this study was to assess the effect of this metabolic switch on control and differentiated adult cardiac progenitors, by fatty acid supplementation. Addition of oleic acid stimulated the peroxisome proliferator-activated receptor alpha pathway and led to maturation of the cardiac progenitors, both before and after transforming growth factor-beta 1 differentiation. Addition of oleic acid following differentiation increased expression of myosin heavy chain 7 and connexin 43. Also, total glycolytic metabolism increased, as did mitochondrial membrane potential and glucose and fatty acid transporter expression. This work provides new insights into the importance of fatty acids, and of peroxisome proliferator-activated receptor alpha, in cardiac progenitor differentiation. Harnessing the oxidative metabolic switch induced maturation of differentiated endogenous stem cells. (200 words).

Metabolic flux analyses to assess the differentiation of adult cardiac progenitors after fatty acid supplementation.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) enable human cardiac cells to be studied in vitro, although they use glucose as their primary metabolic substrate and do not recapitulate the properties of adult cardiomyocytes. Here, we have explored the interplay between maturation by stimulation of fatty acid oxidation and by culture in 3D. We have investigated substrate metabolism in hiPSC-CMs grown as a monolayer and in 3D, in porous collagen-derived scaffolds and in engineered heart tissue (EHT), by measuring rates of glycolysis and glucose and fatty acid oxidation (FAO), and changes in gene expression and mitochondrial oxygen consumption. FAO was stimulated by activation of peroxisome proliferator-activated receptor alpha (PPARα), using oleate and the agonist WY-14643, which induced an increase in FAO in monolayer hiPSC-CMs. hiPSC-CMs grown in 3D on collagen-derived scaffolds showed reduced glycolysis and increased FAO compared with monolayer cells. Activation of PPARα further increased FAO in cells on collagen/elastin scaffolds but not collagen or collagen/chondroitin-4-sulphate scaffolds. In EHT, FAO was significantly higher than in monolayer cells or those on static scaffolds and could be further increased by culture with oleate and WY-14643. In conclusion, a more mature metabolic phenotype can be induced by culture in 3D and FAO can be incremented by pharmacological stimulation.

Physiological and pharmacological stimulation for in vitro maturation of substrate metabolism in human induced pluripotent stem cell-derived cardiomyocytes.

Myocardial infarction is a leading cause of death globally due to the inability of the adult human heart to regenerate after injury. Cell therapy using cardiac-derived progenitor populations emerged about two decades ago with the aim of replacing cells lost after ischaemic injury. Despite early promise from rodent studies, administration of these populations has not translated to the clinic. We will discuss the need for cardiac regeneration and review the debate surrounding how cardiac progenitor populations exert a therapeutic effect following transplantation into the heart, including their ability to form de novo cardiomyocytes and the release of paracrine factors. We will also discuss limitations hindering the cell therapy field, which include the challenges of performing cell-based clinical trials and the low retention of administered cells, and how future research may overcome them.

Cardiac regeneration following myocardial infarction: the need for regeneration and a review of cardiac stromal cell populations used for transplantation.

The therapeutic potential of presumed cardiac progenitor cells (CPCs) in heart regeneration has garnered significant interest, yet clinical trials have revealed limited efficacy due to challenges in cell survival, retention, and expansion. Priming CPCs to survive the hostile hypoxic environment may be key to enhancing their regenerative capacity. We demonstrate that microRNA-210 (miR-210), known for its role in hypoxic adaptation, significantly improves CPC survival by inhibiting apoptosis through the downregulation of , a ~40% reduction in caspase activity, and a ~90% decrease in DNA fragmentation. Contrary to the expected induction of Bnip3-dependent mitophagy by hypoxia, miR-210 did not upregulate , indicating a distinct anti-apoptotic mechanism. Instead, miR-210 reduced markers of mitophagy and increased mitochondrial biogenesis and oxidative metabolism, suggesting a role in metabolic reprogramming. Furthermore, miR-210 enhanced the secretion of paracrine growth factors from CPCs, with a ~1.6-fold increase in the release of stem cell factor and of insulin growth factor 1, which promoted in vitro endothelial cell proliferation and cardiomyocyte survival. These findings elucidate the multifaceted role of miR-210 in CPC biology and its potential to enhance cell-based therapies for myocardial repair by promoting cell survival, metabolic adaptation, and paracrine signalling.

MicroRNA-210 Enhances Cell Survival and Paracrine Potential for Cardiac Cell Therapy While Targeting Mitophagy.

In contrast to humans, fish can fully regenerate their hearts after cardiac injury. However, not all fish have the same regenerative potential, allowing comparative inter-species and intra-species analysis to identify the mechanisms controlling successful heart regeneration. Here we report a differential regenerative response to cardiac cryo-injury among different wild-type zebrafish strains. Correlating these data with single-cell and bulk RNA sequencing data, we identify oxidative phosphorylation (OXPHOS) as a positive regulator of long-term regenerative outcome. OXPHOS levels, driven by glycolysis through the malate-aspartate shuttle, increase as soon as cardiomyocyte proliferation decreases, and this increase is required for cardiomyocyte re-differentiation and successful long-term regeneration. Reduced upregulation of OXPHOS in Astyanax mexicanus cavefish results in the absence of a dynamic temporal sarcomere gene expression program during cardiomyocyte re-differentiation. These findings challenge the assumption that OXPHOS inhibits regeneration and reveal targetable pathways to enhance heart repair in humans after myocardial infarction.

Oxidative phosphorylation is required for cardiomyocyte re-differentiation and long-term fish heart regeneration.

Fate-mapping studies have challenged the longstanding view of the adult mammalian heart as a post-mitotic organ, suggesting limited cardiomyocyte renewal. This has spurred efforts to determine whether selected cardiac stromal cells have regenerative potential; however, their contribution to cardiac regeneration has been found to be minimal compared with that of cardiomyocyte proliferation. Despite this, transplantation of some cardiac stromal cell populations has shown therapeutic potential through paracrine signalling. The identity of the paracrine-active stromal cell populations remains unclear due to overlapping characteristics with other cardiac stromal cell populations, such as fibroblasts, mesenchymal cells, and pericytes. This study sought to clarify the transcriptional identity and heterogeneity of adult mouse cardiac stromal cells by developing a cardiac collagenase-trypsin protocol and comparing it to the established method for isolating cardiosphere-derived cells (CDCs). This novel protocol resulted in a higher cell yield and shorter expansion time, and the resulting cells showed superior survival under serum starvation compared to commercially acquired cardiac fibroblasts (CFs). Single-cell qRT-PCR analysis revealed that collagenase-trypsin cells (CTs) and CDCs share similar gene expression profiles, distinct from those of CFs. Notably, CTs exhibited higher expression of  and lower expression of , suggesting an epicardial-derived fibroblast phenotype, whereas  was enriched in CDCs and CFs, reflecting heterogeneity within the cardiac fibroblast compartment. This study offers insights into the complex identity of cardiac stromal cells and concludes that CTs closely resemble CDCs but can be generated more rapidly, making them a robust and efficient source of paracrine-active cardiac stromal cells.

Article	Year
Improved cellular uptake of perfluorocarbon nanoparticles for in vivo murine cardiac F MRS/MRI and temporal tracking of progenitor cells. Nanomedicine : nanotechnology, biology, and medicine\| PubMed ID: 30448526	2019
Metabolic flux analyses to assess the differentiation of adult cardiac progenitors after fatty acid supplementation. Stem cell research\| PubMed ID: 31102832	2019
Physiological and pharmacological stimulation for in vitro maturation of substrate metabolism in human induced pluripotent stem cell-derived cardiomyocytes. Scientific reports\| PubMed ID: 33833285	2021
Cardiac regeneration following myocardial infarction: the need for regeneration and a review of cardiac stromal cell populations used for transplantation. Biochemical Society transactions\| PubMed ID: 35129611	2022
MicroRNA-210 Enhances Cell Survival and Paracrine Potential for Cardiac Cell Therapy While Targeting Mitophagy. Journal of functional biomaterials\| PubMed ID: 40278255	2025
Oxidative phosphorylation is required for cardiomyocyte re-differentiation and long-term fish heart regeneration. Nature cardiovascular research\| PubMed ID: 41034455	2025
Transcriptomic Analysis of Adult Mouse Cardiac Stromal Cells Using Single-Cell qRT-PCR. Cells\| PubMed ID: 41744827	2026

Rita Alonaizan

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