Changes of Metabolic Phenotype of Cardiac Progenitor Cells During Differentiation: Neutral Effect of Stimulation of AMP-Activated Protein Kinase

Influence of acidic metabolic environment on differentiation of stem cell-derived cardiomyocytes

Stem cell-based myocardial regeneration is a frontier topic in the treatment of myocardial infarction. Manipulating the metabolic microenvironment of stem cells can influence their differentiation into cardiomyocytes, which have promising clinical applications. pH is an important indicator of the metabolic environment during cardiomyocyte development. And lactate, as one of the main acidic metabolites, is a major regulator of the acidic metabolic environment during early cardiomyocyte development. Here, we summarize the progress of research into the influence of pH value and lactate on cardiomyocyte survival and differentiation, as well as related mechanisms.

Research progress of AMP-activated protein kinase and cardiac aging

The process of aging is marked by a gradual deterioration in the physiological functions and functional reserves of various tissues and organs, leading to an increased susceptibility to diseases and even death. Aging manifests in a tissue- and organ-specific manner, and is characterized by varying rates and direct and indirect interactions among different tissues and organs. Cardiovascular disease (CVD) is the leading cause of death globally, with older adults (aged >70 years) accounting for approximately two-thirds of CVD-related deaths. The prevalence of CVD increases exponentially with an individual's age. Aging is a critical independent risk factor for the development of CVD. AMP-activated protein kinase (AMPK) activation exerts cardioprotective effects in the heart and restores cellular metabolic functions by modulating gene expression and regulating protein levels through its interaction with multiple target proteins. Additionally, AMPK enhances mitochondrial function and cellular energy status by facilitating the utilization of energy substrates. This review focuses on the role of AMPK in the process of cardiac aging and maintaining normal metabolic levels and redox homeostasis in the heart, particularly in the presence of oxidative stress and the invasion of inflammatory factors.

Metabolic shift and the effect of mitochondrial respiration on the osteogenic differentiation of dental pulp stem cells

Background

Metabolism shifts from glycolysis to mitochondrial oxidative phosphorylation are vital during the differentiation of stem cells. Mitochondria have a direct function in differentiation. However, the metabolic shift and the effect of mitochondria in regulating the osteogenic differentiation of human dental pulp stem cells (hDPSCs) remain unclear.

Methods

Human dental pulp stem cells were collected from five healthy donors. Osteogenic differentiation was induced by osteogenic induction medium. The activities of alkaline phosphatase, hexokinase, pyruvate kinase, and lactate dehydrogenase were analyzed by enzymatic activity kits. The extracellular acidification rate and the mitochondrial oxygen consumption rate were measured. The mRNA levels of COL-1, ALP, TFAM, and NRF1 were analyzed. The protein levels of p-AMPK and AMPK were detected by western blotting.

Results

Glycolysis decreased after a slight increase, while mitochondrial oxidative phosphorylation continued to increase when cells grew in osteogenic induction medium. Therefore, the metabolism of differentiating cells switched to mitochondrial respiration. Next, inhibiting mitochondrial respiration with carbonyl cyanide-chlorophenylhydrazone, a mitochondrial uncoupler inhibited hDPSCs differentiation with less ALP activity and decreased ALP and COL-1 mRNA expression. Furthermore, mitochondrial uncoupling led to AMPK activation. 5-Aminoimidazole-4-carboxamide ribonucleotide, an AMPK activator, simulated the effect of mitochondrial uncoupling by inhibiting osteogenic differentiation, mitochondrial biogenesis, and mitochondrial morphology. Mitochondrial uncoupling and activation of AMPK depressed mitochondrial oxidative phosphorylation and inhibited differentiation, suggesting that they may serve as regulators to halt osteogenic differentiation from impaired mitochondrial oxidative phosphorylation.

PFKFB3-mediated glycometabolism reprogramming modulates endothelial differentiation and angiogenic capacity of placenta-derived mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) have a great potential ability for endothelial differentiation, contributing to an effective means of therapeutic angiogenesis. Placenta-derived mesenchymal stem cells (PMSCs) have gradually attracted attention, while the endothelial differentiation has not been fully evaluated in PMSCs. Metabolism homeostasis plays an important role in stem cell differentiation, but less is known about the glycometabolic reprogramming during the PMSCs endothelial differentiation. Hence, it is critical to investigate the potential role of glycometabolism reprogramming in mediating PMSCs endothelial differentiation.

METHODS

Dil-Ac-LDL uptake assay, flow cytometry, and immunofluorescence were all to verify the endothelial differentiation in PMSCs. Seahorse XF Extracellular Flux Analyzers, Mito-tracker red staining, Mitochondrial membrane potential (MMP), lactate secretion assay, and transcriptome approach were to assess the variation of mitochondrial respiration and glycolysis during the PMSCs endothelial differentiation. Glycolysis enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) was considered a potential modulator for endothelial differentiation in PMSCs by small interfering RNA. Furthermore, transwell, in vitro Matrigel tube formation, and in vivo Matrigel plug assays were performed to evaluate the effect of PFKFB3-induced glycolysis on angiogenic capacities in this process.

RESULTS

PMSCs possessed the superior potential of endothelial differentiation, in which the glycometabolic preference for glycolysis was confirmed. Moreover, PFKFB3-induced glycometabolism reprogramming could modulate the endothelial differentiation and angiogenic abilities of PMSCs.

CONCLUSIONS

Our results revealed that PFKFB3-mediated glycolysis is important for endothelial differentiation and angiogenesis in PMSCs. Our understanding of cellular glycometabolism and its regulatory effects on endothelial differentiation may propose and improve PMSCs as a putative strategy for clinical therapeutic angiogenesis.

miR-133a-A Potential Target for Improving Cardiac Mitochondrial Health and Regeneration After Injury

ABSTRACT

The various roles of muscle secretory factors and myokines have been well studied, but in recent decades, the role of myocyte-specific microRNAs (myomiRs) has gained momentum. These myomiRs are known to play regulatory roles in muscle health in general, both skeletal muscle and cardiac muscle. In this review, we have focused on the significance of a myomiR termed miR-133a in cardiovascular health. The available literature supports the claim that miR-133a could be helpful in the healing process of muscle tissue after injury. The protective function could be due to its regulatory effect on muscle or stem cell mitochondrial function. In this review, we have shed light on the protective mechanisms offered by miR-133a. Most of the beneficial effects are due to the presence of miR-133a in circulation or tissue-specific expression. We have also reviewed the potential mechanisms by which miR-133a could interact with cell surface receptors and also transcriptional mechanisms by which they offer cardioprotection and regeneration. Understanding these mechanisms will help in finding an ideal strategy to repair cardiac tissue after injury.

Metabolic Determinants in Cardiomyocyte Function and Heart Regenerative Strategies

Heart disease is the leading cause of mortality in developed countries. The associated pathology is characterized by a loss of cardiomyocytes that leads, eventually, to heart failure. In this context, several cardiac regenerative strategies have been developed, but they still lack clinical effectiveness. The mammalian neonatal heart is capable of substantial regeneration following injury, but this capacity is lost at postnatal stages when cardiomyocytes become terminally differentiated and transit to the fetal metabolic switch. Cardiomyocytes are metabolically versatile cells capable of using an array of fuel sources, and the metabolism of cardiomyocytes suffers extended reprogramming after injury. Apart from energetic sources, metabolites are emerging regulators of epigenetic programs driving cell pluripotency and differentiation. Thus, understanding the metabolic determinants that regulate cardiomyocyte maturation and function is key for unlocking future metabolic interventions for cardiac regeneration. In this review, we will discuss the emerging role of metabolism and nutrient signaling in cardiomyocyte function and repair, as well as whether exploiting this axis could potentiate current cellular regenerative strategies for the mammalian heart.

Intracellular metabolic reprogramming mediated by micro-RNAs in differentiating and proliferating cells under non-diseased conditions

Intracellular metabolic reprogramming is a critical process the cells carry out to increase biomass, energy fulfillment and genome replication. Cells reprogram their demands from internal catabolic or anabolic activities in coordination with multiple genes and microRNAs which further control the critical processes of differentiation and proliferation. The microRNAs reprogram the metabolism involving mitochondria, the nucleus and the biochemical processes utilizing glucose, amino acids, lipids, and nucleic acids resulting in ATP production. The processes of glycolysis, tricarboxylic acid cycle, or oxidative phosphorylation are also mediated by micro-RNAs maintaining cells and organs in a non-diseased state. Several reports have shown practical applications of metabolic reprogramming for clinical utility to assess various diseases, mostly studying cancer and immune-related disorders. Cells under diseased conditions utilize glycolysis for abnormal growth or proliferation, respectively, affecting mitochondrial paucity and biogenesis. Similar metabolic processes also affect gene expressions and transcriptional regulation for carrying out biochemical reactions. Metabolic reprogramming is equally vital for regulating cell environment to maintain organs and tissues in non-diseased states. This review offers in depth insights and analysis of how miRNAs regulate metabolic reprogramming in four major types of cells undergoing differentiation and proliferation, i.e., immune cells, neuronal cells, skeletal satellite cells, and cardiomyocytes under a non-diseased state. Further, the work systematically summarizes and elaborates regulation of genetic switches by microRNAs through predominantly through cellular reprogramming and metabolic processes for the first time. The observations will lead to a better understanding of disease initiation during the differentiation and proliferation stages of cells, as well as fresh approaches to studying clinical onset of linked metabolic diseases targeting metabolic processes.

AMPKβ1 and AMPKβ2 define an isoform-specific gene signature in human pluripotent stem cells, differentially mediating cardiac lineage specification

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism that phosphorylates a wide range of proteins to maintain cellular homeostasis. AMPK consists of three subunits: α, β, and γ. AMPKα and β are encoded by two genes, the γ subunit by three genes, all of which are expressed in a tissue-specific manner. It is not fully understood, whether individual isoforms have different functions. Using RNA-Seq technology, we provide evidence that the loss of AMPKβ1 and AMPKβ2 lead to different gene expression profiles in human induced pluripotent stem cells (hiPSCs), indicating isoform-specific function. The knockout of AMPKβ2 was associated with a higher number of differentially regulated genes than the deletion of AMPKβ1, suggesting that AMPKβ2 has a more comprehensive impact on the transcriptome. Bioinformatics analysis identified cell differentiation as one biological function being specifically associated with AMPKβ2. Correspondingly, the two isoforms differentially affected lineage decision toward a cardiac cell fate. Although the lack of PRKAB1 impacted differentiation into cardiomyocytes only at late stages of cardiac maturation, the availability of PRKAB2 was indispensable for mesoderm specification as shown by gene expression analysis and histochemical staining for cardiac lineage markers such as cTnT, GATA4, and NKX2.5. Ultimately, the lack of AMPKβ1 impairs, whereas deficiency of AMPKβ2 abrogates differentiation into cardiomyocytes. Finally, we demonstrate that AMPK affects cellular physiology by engaging in the regulation of hiPSC transcription in an isoform-specific manner, providing the basis for further investigations elucidating the role of dedicated AMPK subunits in the modulation of gene expression.

Reorganization of Metabolism during Cardiomyogenesis Implies Time-Specific Signaling Pathway Regulation

Understanding the cell differentiation process involves the characterization of signaling and regulatory pathways. The coordinated action involved in multilevel regulation determines the commitment of stem cells and their differentiation into a specific cell lineage. Cellular metabolism plays a relevant role in modulating the expression of genes, which act as sensors of the extra-and intracellular environment. In this work, we analyzed mRNAs associated with polysomes by focusing on the expression profile of metabolism-related genes during the cardiac differentiation of human embryonic stem cells (hESCs). We compared different time points during cardiac differentiation (pluripotency, embryoid body aggregation, cardiac mesoderm, cardiac progenitor and cardiomyocyte) and showed the immature cell profile of energy metabolism. Highly regulated canonical pathways are thoroughly discussed, such as those involved in metabolic signaling and lipid homeostasis. We reveal the critical relevance of retinoic X receptor (RXR) heterodimers in upstream retinoic acid metabolism and their relationship with thyroid hormone signaling. Additionally, we highlight the importance of lipid homeostasis and extracellular matrix component biosynthesis during cardiomyogenesis, providing new insights into how hESCs reorganize their metabolism during in vitro cardiac differentiation.

Stem Cell Metabolism: Powering Cell-Based Therapeutics

Cell-based therapeutics for cardiac repair have been extensively used during the last decade. Preclinical studies have demonstrated the effectiveness of adoptively transferred stem cells for enhancement of cardiac function. Nevertheless, several cell-based clinical trials have provided largely underwhelming outcomes. A major limitation is the lack of survival in the harsh cardiac milieu as only less than 1% donated cells survive. Recent efforts have focused on enhancing cell-based therapeutics and understanding the biology of stem cells and their response to environmental changes. Stem cell metabolism has recently emerged as a critical determinant of cellular processes and is uniquely adapted to support proliferation, stemness, and commitment. Metabolic signaling pathways are remarkably sensitive to different environmental signals with a profound effect on cell survival after adoptive transfer. Stem cells mainly generate energy through glycolysis while maintaining low oxidative phosphorylation (OxPhos), providing metabolites for biosynthesis of macromolecules. During commitment, there is a shift in cellular metabolism, which alters cell function. Reprogramming stem cell metabolism may represent an attractive strategy to enhance stem cell therapy for cardiac repair. This review summarizes the current literature on how metabolism drives stem cell function and how this knowledge can be applied to improve cell-based therapeutics for cardiac repair.