Comparative Proteomic Analysis Reveals the Upregulation of Ketogenesis in Cardiomyocytes Differentiated from Induced Pluripotent Stem Cells

Maturation of pluripotent stem cell-derived cardiomyocytes: limitations and challenges from metabolic aspects

Acute coronary syndromes, such as myocardial infarction (MI), lack effective therapies beyond heart transplantation, which is often hindered by donor scarcity and postoperative complications. Human induced pluripotent stem cells (hiPSCs) offer the possibility of myocardial regeneration by differentiating into cardiomyocytes. However, hiPSC-derived cardiomyocytes (hiPSC-cardiomyocytes) exhibit fetal-like calcium flux and energy metabolism, which inhibits their engraftment. Several strategies have been explored to improve the therapeutic efficacy of hiPSC-cardiomyocytes, such as selectively enhancing energy substrate utilization and improving the transplantation environment. In this review, we have discussed the impact of altered mitochondrial biogenesis and metabolic switching on the maturation of hiPSC-cardiomyocytes. Additionally, we have discussed the limitations inherent in current methodologies for assessing metabolism in hiPSC-cardiomyocytes, and the challenges in achieving sufficient metabolic flexibility akin to that in the healthy adult heart.

Macromolecular crowding in human tenocyte and skin fibroblast cultures: A comparative analysis

Although human tenocytes and dermal fibroblasts have shown promise in tendon engineering, no tissue engineered medicine has been developed due to the prolonged ex vivo time required to develop an implantable device. Considering that macromolecular crowding has the potential to substantially accelerate the development of functional tissue facsimiles, herein we compared human tenocyte and dermal fibroblast behaviour under standard and macromolecular crowding conditions to inform future studies in tendon engineering. Basic cell function analysis made apparent the innocuousness of macromolecular crowding for both cell types. Gene expression analysis of the without macromolecular crowding groups revealed expression of tendon related molecules in human dermal fibroblasts and tenocytes. Protein electrophoresis and immunocytochemistry analyses showed significantly increased and similar deposition of collagen fibres by macromolecular crowding in the two cell types. Proteomics analysis demonstrated great similarities between human tenocyte and dermal fibroblast cultures, as well as the induction of haemostatic, anti-microbial and tissue-protective proteins by macromolecular crowding in both cell populations. Collectively, these data rationalise the use of either human dermal fibroblasts or tenocytes in combination with macromolecular crowding in tendon engineering.

Unravelling the Interplay between Cardiac Metabolism and Heart Regeneration

Ischemic heart disease (IHD) is the leading cause of heart failure (HF) and is a significant cause of morbidity and mortality globally. An ischemic event induces cardiomyocyte death, and the ability for the adult heart to repair itself is challenged by the limited proliferative capacity of resident cardiomyocytes. Intriguingly, changes in metabolic substrate utilisation at birth coincide with the terminal differentiation and reduced proliferation of cardiomyocytes, which argues for a role of cardiac metabolism in heart regeneration. As such, strategies aimed at modulating this metabolism-proliferation axis could, in theory, promote heart regeneration in the setting of IHD. However, the lack of mechanistic understanding of these cellular processes has made it challenging to develop therapeutic modalities that can effectively promote regeneration. Here, we review the role of metabolic substrates and mitochondria in heart regeneration, and discuss potential targets aimed at promoting cardiomyocyte cell cycle re-entry. While advances in cardiovascular therapies have reduced IHD-related deaths, this has resulted in a substantial increase in HF cases. A comprehensive understanding of the interplay between cardiac metabolism and heart regeneration could facilitate the discovery of novel therapeutic targets to repair the damaged heart and reduce risk of HF in patients with IHD.

Ketones and the cardiovascular system

Ketone bodies, the main one being β-hydroxybutyrate, have emerged as important regulators of the cardiovascular system. In healthy individuals, as well as in individuals with heart failure or post-myocardial infarction, ketones provide a supplemental energy source for both the heart and the vasculature. In the failing heart, this additional energy may contribute to improved cardiac performance, whereas increasing ketone oxidation in vascular smooth muscle and endothelial cells enhances cell proliferation and prevents blood vessel rarefication. Ketones also have important actions in signaling pathways, posttranslational modification pathways and gene transcription; many of which modify cell proliferation, inflammation, oxidative stress, endothelial function and cardiac remodeling. Attempts to therapeutically increase ketone delivery to the cardiovascular system are numerous and have shown mixed results in terms of effectiveness. Here we review the bioenergetic and signaling effects of ketones on the cardiovascular system, and we discuss how ketones can potentially be used to treat cardiovascular diseases.

Effects of Long-Term Physical Activity and BCAA Availability on the Subcellular Associations between Intramyocellular Lipids, Perilipins and PGC-1α

Cellular skeletal muscle lipid metabolism is of paramount importance for metabolic health, specifically through its connection to branched-chain amino acids (BCAA) metabolism and through its modulation by exercise. In this study, we aimed at better understanding intramyocellular lipids (IMCL) and their related key proteins in response to physical activity and BCAA deprivation. By means of confocal microscopy, we examined IMCL and the lipid droplet coating proteins PLIN2 and PLIN5 in human twin pairs discordant for physical activity. Additionally, in order to study IMCLs, PLINs and their association to peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) in cytosolic and nuclear pools, we mimicked exercise-induced contractions in C2C12 myotubes by electrical pulse stimulation (EPS), with or without BCAA deprivation. The life-long physically active twins displayed an increased IMCL signal in type I fibers when compared to their inactive twin pair. Moreover, the inactive twins showed a decreased association between PLIN2 and IMCL. Similarly, in the C2C12 cell line, PLIN2 dissociated from IMCL when myotubes were deprived of BCAA, especially when contracting. In addition, in myotubes, EPS led to an increase in nuclear PLIN5 signal and its associations with IMCL and PGC-1α. This study demonstrates how physical activity and BCAA availability affects IMCL and their associated proteins, providing further and novel evidence for the link between the BCAA, energy and lipid metabolisms.

Proteomic analysis of mitochondrial biogenesis in cardiomyocytes differentiated from human induced pluripotent stem cells

Mitochondria play key roles in the differentiation and maturation of human cardiomyocytes (CMs). As human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) hold potential in the treatment of heart diseases, we sought to identify key mitochondrial pathways and regulators, which may provide targets for improving cardiac differentiation and maturation. Proteomic analysis was performed on enriched mitochondrial protein extracts isolated from hiPSC-CMs differentiated from dermal fibroblasts (dFCM) and cardiac fibroblasts (cFCM) at time points between 12 and 115 days of differentiation, and from adult and neonatal mouse hearts. Mitochondrial proteins with a twofold change at time points up to 120 days relative to 12 days were subjected to ingenuity pathway analysis (IPA). The highest upregulation was in metabolic pathways for fatty acid oxidation (FAO), the tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), and branched chain amino acid (BCAA) degradation. The top upstream regulators predicted to be activated were peroxisome proliferator-activated receptor γ coactivator 1 α (PGC1-α), the insulin receptor (IR), and the retinoblastoma protein (Rb1) transcriptional repressor. IPA and immunoblotting showed upregulation of the mitochondrial LonP1 protease-a regulator of mitochondrial proteostasis, energetics, and metabolism. LonP1 knockdown increased FAO in neonatal rat ventricular cardiomyocytes (nRVMs). Our results support the notion that LonP1 upregulation negatively regulates FAO in cardiomyocytes to calibrate the flux between glucose and fatty acid oxidation. We discuss potential mechanisms by which IR, Rb1, and LonP1 regulate the metabolic shift from glycolysis to OXPHOS and FAO. These newly identified factors and pathways may help in optimizing the maturation of iPSC-CMs.

Proteomics Reveals that Methylmalonyl-CoA Mutase Modulates Cell Architecture and Increases Susceptibility to Stress

Methylmalonic acidemia (MMA) is a rare inborn error of metabolism caused by deficiency of the methylmalonyl-CoA mutase (MUT) enzyme. Downstream MUT deficiency, methylmalonic acid accumulates together with toxic metabolites from propionyl-CoA and other compounds upstream of the block in the enzyme pathway. The presentation is with life-threatening acidosis, respiratory distress, brain disturbance, hyperammonemia, and ketosis. Survivors develop poorly understood multi-organ damage, notably to the brain and kidneys. The HEK 293 cell line was engineered by CRISPR/Cas9 technology to knock out the MUT gene (MUT-KO). Shotgun label-free quantitative proteomics and bioinformatics analyses revealed potential damaging biological processes in MUT-deficient cells. MUT-KO induced alteration of cellular architecture and morphology, and ROS overproduction. We found the alteration of proteins involved in cytoskeleton and cell adhesion organization, cell trafficking, mitochondrial, and oxidative processes, as validated by the regulation of VIM, EXT2, SDC2, FN1, GLUL, and CHD1. Additionally, a cell model of MUT-rescuing was developed in order to control the specificity of MUT-KO effects. Globally, the proteomic landscape of MUT-KO suggests the cell model to have an increased susceptibility to propionate- and H₂O₂-induced stress through an impairment of the mitochondrial functionality and unbalances in the oxidation-reduction processes.

Reference glycan structure libraries of primary human cardiomyocytes and pluripotent stem cell-derived cardiomyocytes reveal cell-type and culture stage-specific glycan phenotypes

Cell surface glycoproteins play critical roles in maintaining cardiac structure and function in health and disease and the glycan-moiety attached to the protein is critical for proper protein folding, stability and signaling [1]. However, despite mounting evidence that glycan structures are key modulators of heart function and must be considered when developing cardiac biomarkers, we currently do not have a comprehensive view of the glycans present in the normal human heart. In the current study, we used porous graphitized carbon liquid chromatography interfaced with mass spectrometry (PGC-LC-MS) to generate glycan structure libraries for primary human heart tissue homogenate, cardiomyocytes (CM) enriched from human heart tissue, and human induced pluripotent stem cell derived CM (hiPSC-CM). Altogether, we established the first reference structure libraries of the cardiac glycome containing 265 N- and O-glycans. Comparing the N-glycome of CM enriched from primary heart tissue to that of heart tissue homogenate, the same pool of N-glycan structures was detected in each sample type but the relative signal of 21 structures significantly differed between samples, with the high mannose class increased in enriched CM. Moreover, by comparing primary CM to hiPSC-CM collected during 20-100 days of differentiation, dynamic changes in the glycan profile throughout in vitro differentiation were observed and differences between primary and hiPSC-CM were revealed. Namely, >30% of the N-glycome significantly changed across these time-points of differentiation and only 23% of the N-glycan structures were shared between hiPSC-CM and primary CM. These observations are an important complement to current genomic, transcriptomic, and proteomic profiling and reveal new considerations for the use and interpretation of hiPSC-CM models for studies of human development, disease, and drug testing. Finally, these data are expected to support future regenerative medicine efforts by informing targets for evaluating the immunogenic potential of hiPSC-CM and harnessing differences between immature, proliferative hiPSC-CM and adult primary CM.

Cardiomyogenesis Modeling Using Pluripotent Stem Cells: The Role of Microenvironmental Signaling

Pluripotent stem cells (PSC) can be used as a model to study cardiomyogenic differentiation. In vitro modeling can reproduce cardiac development through modulation of some key signaling pathways. Therefore, many studies make use of this strategy to better understand cardiomyogenesis complexity and to determine possible ways to modulate cell fate. However, challenges remain regarding efficiency of differentiation protocols, cardiomyocyte (CM) maturation and therapeutic applications. Considering that the extracellular milieu is crucial for cellular behavior control, cardiac niche studies, such as those identifying secreted molecules from adult or neonatal tissues, allow the identification of extracellular factors that may contribute to CM differentiation and maturation. This review will focus on cardiomyogenesis modeling using PSC and the elements involved in cardiac microenvironmental signaling (the secretome - extracellular vesicles, extracellular matrix and soluble factors) that may contribute to CM specification and maturation.