Metabolic regulation of redox status in stem cells

Mitochondrial metabolism in neural stem cells and implications for neurodevelopmental and neurodegenerative diseases

Mitochondria are cytoplasmic organelles having a fundamental role in the regulation of neural stem cell (NSC) fate during neural development and maintenance.During embryonic and adult neurogenesis, NSCs undergo a metabolic switch from glycolytic to oxidative phosphorylation with a rise in mitochondrial DNA (mtDNA) content, changes in mitochondria shape and size, and a physiological augmentation of mitochondrial reactive oxygen species which together drive NSCs to proliferate and differentiate. Genetic and epigenetic modifications of proteins involved in cellular differentiation (Mechanistic Target of Rapamycin), proliferation (Wingless-type), and hypoxia (Mitogen-activated protein kinase)-and all connected by the common key regulatory factor Hypoxia Inducible Factor-1A-are deemed to be responsible for the metabolic shift and, consequently, NSC fate in physiological and pathological conditions.Both primary mitochondrial dysfunction due to mutations in nuclear DNA or mtDNA or secondary mitochondrial dysfunction in oxidative phosphorylation (OXPHOS) metabolism, mitochondrial dynamics, and organelle interplay pathways can contribute to the development of neurodevelopmental or progressive neurodegenerative disorders.This review analyses the physiology and pathology of neural development starting from the available in vitro and in vivo models and highlights the current knowledge concerning key mitochondrial pathways involved in this process.

The Role of Stem Cell on Wound Healing After Revascularization-Healing Following Revascularization-Unlocking Skin Potential

Wound healing is a complex and dynamic process involving a series of cellular and molecular events. Revascularization, the restoration of blood flow to ischemic or damaged tissue, is a key step in wound healing. Adequate vascularization has been recognized as a necessary factor for successful tissue regeneration. In the later stage of revascularization and tissue remodeling in wound healing, stem cells regulate other repair cells and matrix formation by influencing the maturation of blood vessels. The reductive oxidation (REDOX) state may be a key mechanism through stem/progenitor cells to influence endothelial cells to mature blood vessels and improve the quality of healing. Mitochondria may play an important role in this process.

Metabolic control of induced pluripotency

Pluripotent stem cells of the mammalian epiblast and their cultured counterparts-embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs)-have the capacity to differentiate in all cell types of adult organisms. An artificial process of reactivation of the pluripotency program in terminally differentiated cells was established in 2006, which allowed for the generation of induced pluripotent stem cells (iPSCs). This iPSC technology has become an invaluable tool in investigating the molecular mechanisms of human diseases and therapeutic drug development, and it also holds tremendous promise for iPSC applications in regenerative medicine. Since the process of induced reprogramming of differentiated cells to a pluripotent state was discovered, many questions about the molecular mechanisms involved in this process have been clarified. Studies conducted over the past 2 decades have established that metabolic pathways and retrograde mitochondrial signals are involved in the regulation of various aspects of stem cell biology, including differentiation, pluripotency acquisition, and maintenance. During the reprogramming process, cells undergo major transformations, progressing through three distinct stages that are regulated by different signaling pathways, transcription factor networks, and inputs from metabolic pathways. Among the main metabolic features of this process, representing a switch from the dominance of oxidative phosphorylation to aerobic glycolysis and anabolic processes, are many critical stage-specific metabolic signals that control the path of differentiated cells toward a pluripotent state. In this review, we discuss the achievements in the current understanding of the molecular mechanisms of processes controlled by metabolic pathways, and vice versa, during the reprogramming process.

Metabolic and proteostatic differences in quiescent and active neural stem cells

Adult neural stem cells are neurogenesis progenitor cells that play an important role in neurogenesis. Therefore, neural regeneration may be a promising target for treatment of many neurological illnesses. The regenerative capacity of adult neural stem cells can be characterized by two states: quiescent and active. Quiescent adult neural stem cells are more stable and guarantee the quantity and quality of the adult neural stem cell pool. Active adult neural stem cells are characterized by rapid proliferation and differentiation into neurons which allow for integration into neural circuits. This review focuses on differences between quiescent and active adult neural stem cells in nutrition metabolism and protein homeostasis. Furthermore, we discuss the physiological significance and underlying advantages of these differences. Due to the limited number of adult neural stem cells studies, we referred to studies of embryonic adult neural stem cells or non-mammalian adult neural stem cells to evaluate specific mechanisms.

The pentose phosphate pathway in health and disease

The pentose phosphate pathway (PPP) is a glucose-oxidizing pathway that runs in parallel to upper glycolysis to produce ribose 5-phosphate and nicotinamide adenine dinucleotide phosphate (NADPH). Ribose 5-phosphate is used for nucleotide synthesis, while NADPH is involved in redox homoeostasis as well as in promoting biosynthetic processes, such as the synthesis of tetrahydrofolate, deoxyribonucleotides, proline, fatty acids and cholesterol. Through NADPH, the PPP plays a critical role in suppressing oxidative stress, including in certain cancers, in which PPP inhibition may be therapeutically useful. Conversely, PPP-derived NADPH also supports purposeful cellular generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) for signalling and pathogen killing. Genetic deficiencies in the PPP occur relatively commonly in the committed pathway enzyme glucose-6-phosphate dehydrogenase (G6PD). G6PD deficiency typically manifests as haemolytic anaemia due to red cell oxidative damage but, in severe cases, also results in infections due to lack of leucocyte oxidative burst, highlighting the dual redox roles of the pathway in free radical production and detoxification. This Review discusses the PPP in mammals, covering its roles in biochemistry, physiology and disease.

Antioxidant Defense Capacity Is Reduced in Thyroid Stem/Precursor Cells Compared to Differentiated Thyrocytes

There is much evidence linking oxidative stress to thyroid cancer, and stem cells are thought to play a key role in the tumor-initiating mechanism. Their vulnerability to oxidative stress is unexplored. This study aimed to comparatively evaluate the antioxidant capacity of stem/precursor thyroid cells and mature thyrocytes. Human stem/precursor cells and mature thyrocytes were exposed to increasing concentrations of menadione, an oxidative-stress-producing agent, and reactive oxygen species (ROS) production and cell viability were measured. The expression of antioxidant and detoxification genes was measured via qPCR as well as the total antioxidant capacity and the content of glutathione. Menadione elevated ROS generation in stem/precursor thyroid cells more than in mature thyrocytes. The ROS increase was inversely correlated (p = 0.005) with cell viability, an effect that was partially prevented by the antioxidant curcumin. Most thyroid antioxidant defense genes, notably those encoding for the glutathione-generating system and phase I detoxification enzymes, were significantly less expressed in stem/precursor thyroid cells. As a result, the glutathione level and the total antioxidant capacity in stem/precursor thyroid cells were significantly decreased. This reduced antioxidant defense may have clinical implications, making stem/precursor thyroid cells critical targets for environmental conditions that are not detrimental for differentiated thyrocytes.

The First Transcriptomic Atlas of the Adult Lacrimal Gland Reveals Epithelial Complexity and Identifies Novel Progenitor Cells in Mice

The lacrimal gland (LG) secretes aqueous tears. Previous studies have provided insights into the cell lineage relationships during tissue morphogenesis. However, little is known about the cell types composing the adult LG and their progenitors. Using scRNAseq, we established the first comprehensive cell atlas of the adult mouse LG to investigate the cell hierarchy, its secretory repertoire, and the sex differences. Our analysis uncovered the complexity of the stromal landscape. Epithelium subclustering revealed myoepithelial cells, acinar subsets, and two novel acinar subpopulations: Tfrchi and Car6hi cells. The ductal compartment contained Wfdc2+ multilayered ducts and an Ltf+ cluster formed by luminal and intercalated duct cells. Kit+ progenitors were identified as: Krt14+ basal ductal cells, Aldh1a1+ cells of Ltf+ ducts, and Sox10+ cells of the Car6hi acinar and Ltf+ epithelial clusters. Lineage tracing experiments revealed that the Sox10+ adult populations contribute to the myoepithelial, acinar, and ductal lineages. Using scRNAseq data, we found that the postnatally developing LG epithelium harbored key features of putative adult progenitors. Finally, we showed that acinar cells produce most of the sex-biased lipocalins and secretoglobins detected in mouse tears. Our study provides a wealth of new data on LG maintenance and identifies the cellular origin of sex-biased tear components.

Metabolism-based cardiomyocytes production for regenerative therapy

Human pluripotent stem cells (hPSCs) are currently used in clinical applications such as cardiac regenerative therapy, studying disease models, and drug screening for heart failure. Transplantation of hPSC-derived cardiomyocytes (hPSC-CMs) can be used as an alternative therapy for heart transplantation. In contrast to differentiated somatic cells, hPSCs possess unique metabolic programs to maintain pluripotency, and understanding their metabolic features can contribute to the development of technologies that can be useful for their clinical applications. The production of hPSC-CMs requires stepwise specification during embryonic development and metabolic regulation is crucial for proper embryonic development. These metabolic features have been applied to hPSC-CM production methods, such as mesoderm induction, specifications for cardiac progenitors, and their maturation. This review describes the metabolic programs in hPSCs and the metabolic regulation in hPSC-CM production for cardiac regenerative therapy.

Single-Cell RNA Sequencing Reveals Molecular Features of Heterogeneity in the Murine Retinal Pigment Epithelium

Transcriptomic analysis of the mammalian retinal pigment epithelium (RPE) aims to identify cellular networks that influence ocular development, maintenance, function, and disease. However, available evidence points to RPE cell heterogeneity within native tissue, which adds complexity to global transcriptomic analysis. Here, to assess cell heterogeneity, we performed single-cell RNA sequencing of RPE cells from two young adult male C57BL/6J mice. Following quality control to ensure robust transcript identification limited to cell singlets, we detected 13,858 transcripts among 2667 and 2846 RPE cells. Dimensional reduction by principal component analysis and uniform manifold approximation and projection revealed six distinct cell populations. All clusters expressed transcripts typical of RPE cells; the smallest (C1, containing 1-2% of total cells) exhibited the hallmarks of stem and/or progenitor (SP) cells. Placing C1-6 along a pseudotime axis suggested a relative decrease in melanogenesis and SP gene expression and a corresponding increase in visual cycle gene expression upon RPE maturation. K-means clustering of all detected transcripts identified additional expression patterns that may advance the understanding of RPE SP cell maintenance and the evolution of cellular metabolic networks during development. This work provides new insights into the transcriptome of the mouse RPE and a baseline for identifying experimentally induced transcriptional changes in future studies of this tissue.

Metabolic Regulation: A Potential Strategy for Rescuing Stem Cell Senescence

Stem cell senescence and exhaustion are closely related to organ failure and individual aging, which not only induces age-related diseases, but also hinders stem cell applications in regenerative medicine. Thus, it's imminent to find effective ways to delay and retrieve stem cell senescence. Metabolic abnormalities are one of the main characteristics of age-associated declines in stem cell function. Understanding the underlying mechanisms may reveal potential strategies for ameliorating age-associated phenotypes and treating age-related diseases. This review focuses on recent advances in the association between metabolism including glucose, lipid, glutamine and NAD⁺ metabolism and stem cell senescence, as well as the other properties like proliferation and differentiation. Layers of studies are summarized to demonstrate how metabolism varies in senescent stem cells and how metabolic reprogramming regulates stem cell senescence. Additionally, we mentioned some recent progress in therapeutic strategies to rejuvenate dysfunctional aged stem cells. Finally, a brief conclusion about the prospect of metabolic regulation as a potential strategy for rescuing stem cell senescence is displayed. Stem cell senescence is induced by the metabolic reprogramming. The metabolic alterations of glucose, lipid, glutamine and NAD⁺ can conversely facilitate or inhibit stem cell senescence. Glycolysis, OXPHOS and PPP are all attenuated. But gluconeogenesis alterations still remain unclear. In lipid metabolisms, both FAO and DNL are suppressed. As for the glutamine metabolism, stem cells' dependence on glutamine is enhanced. Last, NAD⁺ metabolism undergoes a down-regulated synthesis and up-regulated consumption. All these alterations can be potential targets for reversing stem cell senescence.

The Role of Endoplasmic Reticulum and Mitochondria in Maintaining Redox Status and Glycolytic Metabolism in Pluripotent Stem Cells

Pluripotent stem cells (PSCs), including embryonic stem cells and induced pluripotent stem cells (iPSCs), can be applicable for regenerative medicine. They strangely rely on glycolysis metabolism akin to aerobic glycolysis in cancer cells. Upon differentiation, PSCs undergo a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS). The metabolic shift depends on organelles maturation, transcriptome modification, and metabolic switching. Besides, metabolism-driven chromatin regulation is necessary for cell survival, self-renewal, proliferation, senescence, and differentiation. In this respect, mitochondria may serve as key organelle to adapt environmental changes with metabolic intermediates which are necessary for maintaining PSCs identity. The endoplasmic reticulum (ER) is another organelle whose role in cellular identity remains under-explored. The purpose of our article is to highlight the recent progress on these two organelles' role in maintaining PSCs redox status focusing on metabolism. Topics include redox status, metabolism regulation, mitochondrial dynamics, and ER stress in PSCs. They relate to the maintenance of stem cell properties and subsequent differentiation of stem cells into specific cell types.

The nexus between redox state and intermediary metabolism

Reactive oxygen species (ROS) are not just a by-product of cellular metabolic processes but act as signalling molecules that regulate both physiological and pathophysiological processes. A close connection exists in cells between redox homeostasis and cellular metabolism. In this review, we describe how intracellular redox state and glycolytic intermediary metabolism are closely coupled. On the one hand, ROS signalling can control glycolytic intermediary metabolism by direct regulation of the activity of key metabolic enzymes and indirect regulation via redox-sensitive transcription factors. On the other hand, metabolic adaptation and reprogramming in response to physiological or pathological stimuli regulate intracellular redox balance, through mechanisms such as the generation of reducing equivalents. We also discuss the impact of these intermediary metabolism-redox circuits in physiological and disease settings across different tissues. A better understanding of the mechanisms regulating these intermediary metabolism-redox circuits will be crucial to the development of novel therapeutic strategies.

The plasticity of pancreatic cancer stem cells: implications in therapeutic resistance

The ever-growing perception of cancer stem cells (CSCs) as a plastic state rather than a hardwired defined entity has evolved our understanding of the functional and biological plasticity of these elusive components in malignancies. Pancreatic cancer (PC), based on its biological features and clinical evolution, is a prototypical example of a CSC-driven disease. Since the discovery of pancreatic CSCs (PCSCs) in 2007, evidence has unraveled their control over many facets of the natural history of PC, including primary tumor growth, metastatic progression, disease recurrence, and acquired drug resistance. Consequently, the current near-ubiquitous treatment regimens for PC using aggressive cytotoxic agents, aimed at ‘‘tumor debulking’’ rather than eradication of CSCs, have proven ineffective in providing clinically convincing improvements in patients with this dreadful disease. Herein, we review the key hallmarks as well as the intrinsic and extrinsic resistance mechanisms of CSCs that mediate treatment failure in PC and enlist the potential CSC-targeting ‘natural agents’ that are gaining popularity in recent years. A better understanding of the molecular and functional landscape of PCSC-intrinsic evasion of chemotherapeutic drugs offers a facile opportunity for treating PC, an intractable cancer with a grim prognosis and in dire need of effective therapeutic advances.

Insight into Hypoxia Stemness Control

Recently, the research on stemness and multilineage differentiation mechanisms has greatly increased its value due to the potential therapeutic impact of stem cell-based approaches. Stem cells modulate their self-renewing and differentiation capacities in response to endogenous and/or extrinsic factors that can control stem cell fate. One key factor controlling stem cell phenotype is oxygen (O₂). Several pieces of evidence demonstrated that the complexity of reproducing O₂ physiological tensions and gradients in culture is responsible for defective stem cell behavior in vitro and after transplantation. This evidence is still worsened by considering that stem cells are conventionally incubated under non-physiological air O₂ tension (21%). Therefore, the study of mechanisms and signaling activated at lower O₂ tension, such as those existing under native microenvironments (referred to as hypoxia), represent an effective strategy to define if O₂ is essential in preserving naïve stemness potential as well as in modulating their differentiation. Starting from this premise, the goal of the present review is to report the status of the art about the link existing between hypoxia and stemness providing insight into the factors/molecules involved, to design targeted strategies that, recapitulating naïve O₂ signals, enable towards the therapeutic use of stem cell for tissue engineering and regenerative medicine.

The FOXO signaling axis displays conjoined functions in redox homeostasis and stemness

Previous views of reactive oxygen species (ROS) depicted them as harmful byproducts of metabolism as uncontrolled levels of ROS can lead to DNA damage and cell death. However, recent studies have shed light into the key role of ROS in the self-renewal or differentiation of the stem cell. The interplay between ROS levels, metabolism, and the downstream redox signaling pathways influence stem cell fate. In this review we will define ROS, explain how they are generated, and how ROS signaling can influence transcription factors, first and foremost forkhead box-O transcription factors, that shape not only the cellular redox state, but also stem cell fate. Now that studies have illustrated the importance of redox homeostasis and the role of redox signaling, understanding the mechanisms behind this interplay will further shed light into stem cell biology.

An NRF2 Perspective on Stem Cells and Ageing

Redox and metabolic mechanisms lie at the heart of stem cell survival and regenerative activity. NRF2 is a major transcriptional controller of cellular redox and metabolic homeostasis, which has also been implicated in ageing and lifespan regulation. However, NRF2's role in stem cells and their functioning with age is only just emerging. Here, focusing mainly on neural stem cells, which are core to adult brain plasticity and function, we review recent findings that identify NRF2 as a fundamental player in stem cell biology and ageing. We also discuss NRF2-based molecular programs that may govern stem cell state and function with age, and implications of this for age-related pathologies.

Multifaceted Actions of Succinate as a Signaling Transmitter Vary with Its Cellular Locations

Since the identification of succinate's receptor in 2004, studies supporting the involvement of succinate signaling through its receptor in various diseases have accumulated and most of these investigations have highlighted succinate's pro-inflammatory role. Taken with the fact that succinate is an intermediate metabolite in the center of mitochondrial activity, and considering its potential regulation of protein succinylation through succinyl-coenzyme A, a review on the overall multifaceted actions of succinate to discuss whether and how these actions relate to the cellular locations of succinate is much warranted. Mechanistically, it is important to consider the sources of succinate, which include somatic cellular released succinate and those produced by the microbiome, especially the gut microbiota, which is an equivalent, if not greater contributor of succinate levels in the body. Continue learning the critical roles of succinate signaling, known and unknown, in many pathophysiological conditions is important. Furthermore, studies to delineate the regulation of succinate levels and to determine how succinate elicits various types of signaling in a temporal and spatial manner are also required.

Energy Metabolism Regulates Stem Cell Pluripotency

Pluripotent stem cells (PSCs) are characterized by their unique capacity for both unlimited self-renewal and their potential to differentiate to all cell lineages contained within the three primary germ layers. While once considered a distinct cellular state, it is becoming clear that pluripotency is in fact a continuum of cellular states, all capable of self-renewal and differentiation, yet with distinct metabolic, mitochondrial and epigenetic features dependent on gestational stage. In this review we focus on two of the most clearly defined states: “naïve” and “primed” PSCs. Like other rapidly dividing cells, PSCs have a high demand for anabolic precursors necessary to replicate their genome, cytoplasm and organelles, while concurrently consuming energy in the form of ATP. This requirement for both anabolic and catabolic processes sufficient to supply a highly adapted cell cycle in the context of reduced oxygen availability, distinguishes PSCs from their differentiated progeny. During early embryogenesis PSCs adapt their substrate preference to match the bioenergetic requirements of each specific developmental stage. This is reflected in different mitochondrial morphologies, membrane potentials, electron transport chain (ETC) compositions, and utilization of glycolysis. Additionally, metabolites produced in PSCs can directly influence epigenetic and transcriptional programs, which in turn can affect self-renewal characteristics. Thus, our understanding of the role of metabolism in PSC fate has expanded from anabolism and catabolism to include governance of the pluripotent epigenetic landscape. Understanding the roles of metabolism and the factors influencing metabolic pathways in naïve and primed pluripotent states provide a platform for understanding the drivers of cell fate during development. This review highlights the roles of the major metabolic pathways in the acquisition and maintenance of the different states of pluripotency.

Glucose Starvation-Induced Rapid Death of Nrf1α-Deficient, but Not Nrf2-Deficient, Hepatoma Cells Results from Its Fatal Defects in the Redox Metabolism Reprogramming

Metabolic reprogramming exists in a variety of cancer cells, with the most relevance to glucose as a source of energy and carbon for survival and proliferation. Of note, Nrf1 was shown to be essential for regulating glycolysis pathway, but it is unknown whether it plays a role in cancer metabolic reprogramming, particularly in response to glucose starvation. Herein, we discover that Nrf1α^-/- hepatoma cells are sensitive to rapid death induced by glucose deprivation, such cell death appears to be rescued by Nrf2 interference, but HepG2 (wild-type, WT) or Nrf2^-/- cells are roughly unaffected by glucose starvation. Further evidence revealed that Nrf1α^-/- cell death is resulted from severe oxidative stress arising from aberrant redox metabolism. Strikingly, altered gluconeogenesis pathway was aggravated by glucose starvation of Nrf1α^-/- cells, as also accompanied by weakened pentose phosphate pathway, dysfunction of serine-to-glutathione synthesis, and accumulation of reactive oxygen species (ROS) and damages, such that the intracellular GSH and NADPH were exhausted. These demonstrate that glucose starvation leads to acute death of Nrf1α^-/- , rather than Nrf2^-/- , cells resulting from its fatal defects in the redox metabolism reprogramming. This is owing to distinct requirements of Nrf1 and Nrf2 for regulating the constructive and inducible expression of key genes involved in redox metabolic reprogramming by glucose deprivation. Altogether, this work substantiates the preventive and therapeutic strategies against Nrf1α-deficient cancer by limiting its glucose and energy demands.

Biomaterial-Based Metabolic Regulation in Regenerative Engineering

Recent advances in cell metabolism studies have deepened the appreciation of the role of metabolic regulation in influencing cell behavior during differentiation, angiogenesis, and immune response in the regenerative engineering scenarios. However, the understanding of whether the intracellular metabolic pathways could be influenced by material-derived cues remains limited, although it is now well appreciated that material cues modulate cell functions. Here, an overview of how the regulation of different aspect of cell metabolism, including energy homeostasis, oxygen homeostasis, and redox homeostasis could contribute to modulation of cell function is provided. Furthermore, recent evidence demonstrating how material cues, including the release of inherent metabolic factors (e.g., ions, regulatory metabolites, and oxygen), tuning of the biochemical cues (e.g., inherent antioxidant properties, cell adhesivity, and chemical composition of nanomaterials), and changing in biophysical cues (topography and surface stiffness), may impact cell metabolism toward modulated cell behavior are discussed. Based on the resurgence of interest in cell metabolism and metabolic regulation, further development of biomaterials enabling metabolic regulation toward dictating cell function is poised to have substantial implications for regenerative engineering.

Mitochondrial plasticity in cell fate regulation

Mitochondria are considered highly plastic organelles. This plasticity enables the mitochondria to undergo morphological and functional changes in response to cellular demands. Stem cells also need to remain functionally plastic (i.e. to have the ability to "decide" whether to remain quiescent or to undergo activation upon signaling cues to support tissue function and homeostasis). Mitochondrial plasticity is thought to enable this reshaping of stem cell functions, integrating signaling cues with stem cell outcomes. Indeed, recent evidence highlights the crucial role of maintaining mitochondrial plasticity for stem cell biology. For example, tricarboxylic acid (TCA) cycle metabolites generated and metabolized in the mitochondria serve as cofactors for epigenetic enzymes, thereby coupling mitochondrial metabolism and transcriptional regulation. Another layer of mitochondrial plasticity has emerged, pointing toward mitochondrial dynamics in regulating stem cell fate decisions. Imposing imbalanced mitochondrial dynamics by manipulating the expression levels of the key molecular regulators of this process influences cellular outcomes by changing the nuclear transcriptional program. Moreover, reactive oxygen species have also been shown to play an important role in regulating transcriptional profiles in stem cells. In this review, we focus on recent findings demonstrating that mitochondria are essential regulators of stem cell activation and fate decisions. We also discuss the suggested mechanisms and alternative routes for mitochondria-to-nucleus communications.

Alternative oxidase confers nutritional limitation on Drosophila development

The mitochondrial alternative oxidase, AOX, present in most eukaryotes apart from vertebrates and insects, catalyzes the direct oxidation of ubiquinol by oxygen, by‐passing the terminal proton‐motive steps of the respiratory chain. Its physiological role is not fully understood, but it is proposed to buffer stresses in the respiratory chain similar to those encountered in mitochondrial diseases in humans. Previously, we found that the ubiquitous expression of AOX from Ciona intestinalis in Drosophila perturbs the development of flies cultured under low‐nutrient conditions (media containing only glucose and yeast). Here we tested the effects of a wide range of nutritional supplements on Drosophila development, to gain insight into the physiological mechanism underlying this developmental failure. On low‐nutrient medium, larvae contained decreased amounts of triglycerides, lactate, and pyruvate, irrespective of AOX expression. Complex food supplements, including treacle (molasses), restored normal development to AOX‐expressing flies, but many individual additives did not. Inhibition of AOX by treacle extract was excluded as a mechanism, since the supplement did not alter the enzymatic activity of AOX in vitro. Furthermore, antibiotics did not influence the organismal phenotype, indicating that commensal microbes were not involved. Fractionation of treacle identified a water‐soluble fraction with low solubility in ethanol, rich in lactate and tricarboxylic acid cycle intermediates, which contained the critical activity. We propose that the partial activation of AOX during metamorphosis impairs the efficient use of stored metabolites, resulting in developmental failure.

Drosophila expressing the alternative oxidase are unable to complete pupal development if reared on low‐nutrient medium.

Additional nutrients are needed, to replace those normally manufactured cataplerotically.

Metabolomics Analysis of Mesenchymal Stem Cells

Various mesenchymal stem cells as easily accessible and multipotent cells can share different essential signaling pathways related to their stemness ability. Understanding the mechanism of stemness ability can be useful for controlling the stem cells for regenerative medicine targets. In this context, OMICs studies can analyze the mechanism of different stem cell properties or stemness ability via a broad range of current high-throughput techniques. This field is fundamentally directed toward the analysis of whole genome (genomics), mRNAs (transcriptomics), proteins (proteomics) and metabolites (metabolomics) in biological samples. According to several studies, metabolomics is more effective than other OMICs ّfor various system biology concerns. Metabolomics can elucidate the biological mechanisms of various mesenchymal stem cell function by measuring their metabolites such as their secretome components. Analyzing the metabolic alteration of mesenchymal stem cells can be useful to promote their regenerative medicine application.

Down-regulation of MEIS1 promotes the maturation of oxidative phosphorylation in perinatal cardiomyocytes

Fetal cardiomyocytes shift from glycolysis to oxidative phosphorylation around the time of birth. Myeloid ecotropic viral integration site 1 (MEIS1) is a transcription factor that promotes glycolysis in hematopoietic stem cells. We reasoned that MEIS1 could have a similar role in the developing heart. We hypothesized that suppression of MEIS1 expression in fetal sheep cardiomyocytes leads to a metabolic switch as found at birth. Expression of MEIS1 was assayed in left ventricular cardiac tissue and primary cultures of cardiomyocytes from fetal (100- and 135-d gestation, term = 145 d), neonatal, and adult sheep. Cultured cells were treated with short interfering RNA (siRNA) to suppress MEIS1. Oxygen consumption rate was assessed with the Seahorse metabolic flux analyzer, and mitochondrial activity was assessed by staining cells with MitoTracker Orange. Cardiomyocyte respiratory capacity increased with advancing age concurrently with decreased expression of MEIS1. MEIS1 suppression with siRNA increased maximal oxygen consumption in fetal cells but not in postnatal cells. Mitochondrial activity was increased and expression of glycolytic genes decreased when MEIS1 expression was suppressed. Thus, we conclude that MEIS1 is a key regulator of cardiomyocyte metabolism and that the normal down-regulation of MEIS1 with age underlies a gradual switch to oxidative metabolism.-Lindgren, I. M., Drake, R. R., Chattergoon, N. N., Thornburg, K. L. Down-regulation of MEIS1 promotes the maturation of oxidative phosphorylation in perinatal cardiomyocytes.

Hypoxia-inducible factors promote breast cancer stem cell specification and maintenance in response to hypoxia or cytotoxic chemotherapy

Clinical studies have revealed that breast cancers contain regions of intratumoral hypoxia (reduced oxygen availability), which activates hypoxia-inducible factors (HIFs). The relationship between intratumoral hypoxia, distant metastasis and cancer mortality has been well established. A major mechanism by which intratumoral hypoxia contributes to disease progression is through induction of the breast cancer stem cell (BCSC) phenotype. BCSCs are a small subpopulation of cells with the capability for self-renewal. BCSCs have been implicated in resistance to chemotherapy, disease recurrence, and metastasis. In this review, we will discuss our current understanding of the molecular mechanisms underlying HIF-dependent induction of the BCSC phenotype in response to hypoxia or chemotherapy.

Regulation of the mitochondrial reactive oxygen species: Strategies to control mesenchymal stem cell fates ex vivo and in vivo

Mesenchymal stem cells (MSCs) are broadly used in cell‐based regenerative medicine because of their self‐renewal and multilineage potencies in vitro and in vivo. To ensure sufficient amounts of MSCs for therapeutic purposes, cells are generally cultured in vitro for long‐term expansion or specific terminal differentiation until cell transplantation. Although physiologically up‐regulated reactive oxygen species (ROS) production is essential for maintenance of stem cell activities, abnormally high levels of ROS can harm MSCs both in vitro and in vivo. Overall, additional elucidation of the mechanisms by which physiological and pathological ROS are generated is necessary to better direct MSC fates and improve their therapeutic effects by controlling external ROS levels. In this review, we focus on the currently revealed ROS generation mechanisms and the regulatory routes for controlling their rates of proliferation, survival, senescence, apoptosis, and differentiation. A promising strategy in future regenerative medicine involves regulating ROS generation via various means to augment the therapeutic efficacy of MSCs, thus improving the prognosis of patients with terminal diseases.

Reactive Oxygen Species and Mitochondrial Homeostasis as Regulators of Stem Cell Fate and Function

SIGNIFICANCE

The precise role and impact of reactive oxygen species (ROS) in stem cells, which are essential for lifelong tissue homeostasis and regeneration, remain of significant interest to the field. The long-term regenerative potential of a stem cell compartment is determined by the delicate balance between quiescence, self-renewal, and differentiation, all of which can be influenced by ROS levels. Recent Advances: The past decade has seen a growing appreciation for the importance of ROS and redox homeostasis in various stem cell compartments, particularly those of hematopoietic, neural, and muscle tissues. In recent years, the importance of proteostasis and mitochondria in relation to stem cell biology and redox homeostasis has garnered considerable interest.

CRITICAL ISSUES

Here, we explore the reciprocal relationship between ROS and stem cells, with significant emphasis on mitochondria as a core component of redox homeostasis. We discuss how redox signaling, involving cell-fate determining protein kinases and transcription factors, can control stem cell function and fate. We also address the impact of oxidative stress on stem cells, especially oxidative damage of lipids, proteins, and nucleic acids. We further discuss ROS management in stem cells, and present recent evidence supporting the importance of mitochondrial activity and its modulation (via mitochondrial clearance, biogenesis, dynamics, and distribution [i.e., segregation and transfer]) in stem cell redox homeostasis.

FUTURE DIRECTIONS

Therefore, elucidating the intricate links between mitochondria, cellular metabolism, and redox homeostasis is envisioned to be critical for our understanding of ROS in stem cell biology and its therapeutic relevance in regenerative medicine. Antioxid. Redox Signal. 00, 000-000.

Oxidative Stress in Stem Cell Aging

Stem cell aging is a process in which stem cells progressively lose their ability to self-renew or differentiate, succumb to senescence or apoptosis, and eventually become functionally depleted. Unresolved oxidative stress and concomitant oxidative damages of cellular macromolecules including nucleic acids, proteins, lipids, and carbohydrates have been recognized to contribute to stem cell aging. Excessive production of reactive oxygen species and insufficient cellular antioxidant reserves compromise cell repair and metabolic homeostasis, which serves as a mechanistic switch for a variety of aging-related pathways. Understanding the molecular trigger, regulation, and outcomes of those signaling networks is critical for developing novel therapies for aging-related diseases by targeting stem cell aging. Here we explore the key features of stem cell aging biology, with an emphasis on the roles of oxidative stress in the aging process at the molecular level. As a concept of cytoprotection of stem cells in transplantation, we also discuss how systematic enhancement of endogenous antioxidant capacity before or during graft into tissues can potentially raise the efficacy of clinical therapy. Finally, future directions for elucidating the control of oxidative stress and developing preventive/curative strategies against stem cell aging are discussed.

Obesity-induced mitochondrial dysfunction in porcine adipose tissue-derived mesenchymal stem cells

Transplantation of autologous mesenchymal stem cells (MSCs) may be a viable option for treatment of several diseases. MSCs efficacy depends on adequate function of their mitochondria, which might be impaired in a noxious milieu. We hypothesized that obesity compromises MSCs mitochondrial structure and function, possibly via micro-RNA (miRNA)-based mechanisms. MSCs were collected from swine abdominal adipose tissue after 16 weeks of Lean or Obese diet (n = 7 each). Mitochondrial structure was assessed by electron microscopy and function by membrane potential and cytochrome-c oxidase (COX)-IV activity. Oxidative stress was assessed by Mito-SOX and dihydroethidium staining. Next-generation sequencing (RNA-seq) was performed to identify miRNAs expression in MSCs, and predicted mitochondrial target genes were then identified (MitoCarta). Compared to Lean-MSCs, mitochondria from Obese-MSCs were smaller and showed cristae remodeling and loss. Mitochondrial membrane potential and COX-IV activity decreased in Obese-MSCs, associated with increased mitochondrial oxidative stress. RNA-seq generated reads for 413 miRNAs, of which 5 miRNAs were upregulated in Obese-MSCs (fold change >2, p < 0.05) and found to target 43 specific mitochondrial genes. Obesity impairs MSC mitochondrial structure and function, possibly mediated partly through miRNA-induced mitochondrial gene regulation, leading to increased oxidative stress. Importantly, these alterations may limit the therapeutic use of autologous MSCs in subjects with obesity.

Metabolic pathways regulated by TAp73 in response to oxidative stress

Reactive oxygen species are involved in both physiological and pathological processes including neurodegeneration and cancer. Therefore, cells have developed scavenging mechanisms to maintain redox homeostasis under control. Tumor suppressor genes play a critical role in the regulation of antioxidant genes. Here, we investigated whether the tumor suppressor gene TAp73 is involved in the regulation of metabolic adaptations triggered in response to oxidative stress. H₂O₂ treatment resulted in numerous biochemical changes in both control and TAp73 knockout (TAp73−/−) mouse embryonic fibroblasts, however the extent of these changes was more pronounced in TAp73−/− cells when compared to control cells. In particular, loss of TAp73 led to alterations in glucose, nucleotide and amino acid metabolism. In addition, H₂O₂ treatment resulted in increased pentose phosphate pathway (PPP) activity in null mouse embryonic fibroblasts. Overall, our results suggest that in the absence of TAp73, H₂O₂ treatment results in an enhanced oxidative environment, and at the same time in an increased pro-anabolic phenotype. In conclusion, the metabolic profile observed reinforces the role of TAp73 as tumor suppressor and indicates that TAp73 exerts this function, at least partially, by regulation of cellular metabolism.

"Nutrient-sensing" and self-renewal: O-GlcNAc in a new role

Whether embryonic, hematopoietic or cancer stem cells, this metabolic reprogramming is dependent on the nutrient-status and bioenergetic pathways that is influenced by the micro-environmental niches like hypoxia. Thus, the microenvironment plays a vital role in determining the stem cell fate by inducing metabolic reprogramming. Under the influence of the microenvironment, like hypoxia, the stem cells have increased glucose and glutamine uptake which result in activation of hexosamine biosynthesis pathway (HBP) and increased O-GlcNAc Transferase (OGT). The current review is focused on understanding how HBP, a nutrient-sensing pathway (that leads to increased OGT activity) is instrumental in regulating self-renewal not only in embryonic and hematopoietic stem cells (ESC/HSC) but also in cancer stem cells.

Up-regulation of glycolysis promotes the stemness and EMT phenotypes in gemcitabine-resistant pancreatic cancer cells

Cancer stem cells (CSCs) and epithelial–mesenchymal transition (EMT)‐type cells are considered as underlying causes of chemoresistance, tumour recurrence and metastasis in pancreatic cancer. We aimed to describe the mechanisms – particularly glycolysis – involved in the regulation of the CSC and EMT phenotypes. We used a gemcitabine‐resistant (GR) Patu8988 cell line, which exhibited clear CSC and EMT phenotypes and showed reliance on glycolysis. Inhibition of glycolysis using 2‐deoxy‐D‐glucose (2‐DG) significantly enhanced the cytotoxicity of gemcitabine and inhibited the CSC and EMT phenotypes in GR cells both in vitro and in vivo. Intriguingly, the use of the reactive oxygen species (ROS) scavenger N‐acetylcysteine (NAC) restored the CSC and EMT phenotypes. H₂O₂ produced changes similar to those of 2‐DG, indicating that ROS were involved in the acquired cancer stemness and EMT phenotypes of GR cells. Moreover, doublecortin‐like kinase 1 (DCLK1), a pancreatic CSC marker, was highly expressed and regulated the stemness and EMT phenotypes in GR cell. Both 2‐DG and H₂O₂ treatment suppressed DCLK1 expression, which was also rescued by NAC. Together, these findings revealed that glycolysis promotes the expression of DCLK1 and maintains the CSC and EMT phenotypes via maintenance of low ROS levels in chemoresistant GR cells. The glycolysis‐ROS‐DCLK1 pathway may be potential targets for reversing the malignant behaviour of pancreatic cancer.

ROS-mediated Different Homeostasis of Murine Corneal Epithelial Progenitor Cell Line under Oxidative Stress

The role of ROS in stem cell biology has not been fully illustrated and understood. Here we compared the different responses and investigated the mechanism underlying oxidative stress induced by hydrogen peroxide (H₂O₂) between murine corneal epithelial progenitor cell line (TKE2) and mature murine corneal epithelial cells (MCE). TKE2 showed a different homeostasis and strong resistance to H₂O₂. TKE2 reduced the production of ROS, inhibited ROS generation enzyme NADPH oxidase 4 (NOX4), and increased dual specificity phosphatase 6 (DUSP6). Furthermore, TKE2 activated nuclear factor (erythroid-derived 2)-like 2 (NRF2) signaling pathway, regulated miR-125B1 and miR-29B1, and elevated levels of antioxidants glutathione S-transferase P (GSTP) and superoxide dismutases (SOD). The association with ROS of the cells was also verified by RNA interference approach and pharmacological antagonization. In addition, TKE2 enhanced the autophagy after exposure to H₂O₂. The novel evidence suggests that TKE2 cells have different homeostasis and strong antioxidant properties against oxidative stress via the regulation of ROS formation and pathway.

Metabolic control of cancer cell stemness: Lessons from iPS cells

The Nobel prized discovery of nuclear reprogramming is swiftly providing mechanistic evidence of a role for metabolism in the generation of cancer stem cells (CSC). Traditionally, the metabolic demands of tumors have been viewed as drivers of the genetic programming detected in cancer tissues. Beyond the energetic requirements of specific cancer cell states, it is increasingly recognized that metabolism per se controls epi-transcriptional networks to dictate cancer cell fate, i.e., metabolism can define CSC. Here I review the CSC-related metabolic features found in induced pluripotent stem (iPS) cells to provide an easily understandable framework in which the infrastructure and functioning of cellular metabolism might control the efficiency and kinetics of reprogramming in the re-routing of non-CSC to CSC-like cellular states. I suggest exploring how metabolism-dependent regulation of epigenetics can play a role in directing CSC states beyond conventional energetic demands of stage-specific cancer cell states, opening a new dimension of cancer in which the "physiological state" of CSC might be governed not only by cell-autonomous cues but also by local micro-environmental and systemic metabolo-epigenetic interactions. Forthcoming studies should decipher how specific metabolites integrate and mediate the overlap between the CSC-intrinsic "micro-epigenetics" and the "upstream" local and systemic "macro-epigenetics," thus paving the way for targeted epigenetic regulation of CSCs through metabolic modulation including "smart foods" or systemic "metabolic nichotherapies."

Glutamine Metabolism Regulates the Pluripotency Transcription Factor OCT4

The molecular mechanisms underlying the regulation of pluripotency by cellular metabolism in human embryonic stem cells (hESCs) are not fully understood. We found that high levels of glutamine metabolism are essential to prevent degradation of OCT4, a key transcription factor regulating hESC pluripotency. Glutamine withdrawal depletes the endogenous antioxidant glutathione (GSH), which results in the oxidation of OCT4 cysteine residues required for its DNA binding and enhanced OCT4 degradation. The emergence of the OCT4(lo) cell population following glutamine withdrawal did not result in greater propensity for cell death. Instead, glutamine withdrawal during vascular differentiation of hESCs generated cells with greater angiogenic capacity, thus indicating that modulating glutamine metabolism enhances the differentiation and functional maturation of cells. These findings demonstrate that the pluripotency transcription factor OCT4 can serve as a metabolic-redox sensor in hESCs and that metabolic cues can act in concert with growth factor signaling to orchestrate stem cell differentiation.

Cerium oxide nanoparticles stimulate proliferation of primary mouse embryonic fibroblasts in vitro

The increasing application of cell therapy technologies in the treatment of various diseases requires the development of new effective methods for culturing primary cells. The major limitation for the efficient use of autologous cell material is the low rate of cell proliferation. Successful cell therapy requires sufficient amounts of cell material over a short period of time with the preservation of their differentiation and proliferative potential. In this regard, the development of novel, highly efficient stimulators of proliferative activity in stem cells is a truly urgent task. In this paper we have demonstrated that citrate-stabilized cerium oxide nanoparticles (nanoceria) enhance the proliferative activity of primary mouse embryonic fibroblasts in vitro. Cerium oxide nanoparticles stimulate cell proliferation in a wide range of concentrations (10(-3)М-10(-9)M) through reduction of intracellular levels of reactive oxygen species (ROS) during the lag phase of cell growth and by modulating the expression level of the major antioxidant enzymes. We found the optimal concentration of nanoceria, which provides the greatest acceleration of cell proliferation in vitro, while maintaining the levels of intracellular ROS and mRNA of antioxidant enzymes in the physiological range. Our results confirm that nanocrystalline ceria can be considered as a basis for effective and inexpensive supplements in cell culturing.

Energy metabolism in the acquisition and maintenance of stemness

Energy metabolism is traditionally considered a reactive homeostatic system addressing stage-specific cellular energy needs. There is however growing appreciation of metabolic pathways in the active control of vital cell functions. Case in point, the stem cell lifecycle--from maintenance and acquisition of stemness to lineage commitment and specification--is increasingly recognized as a metabolism-dependent process. Indeed, metabolic reprogramming is an early contributor to the orchestrated departure from or reacquisition of stemness. Recent advances in metabolomics have helped decipher the identity and dynamics of metabolic fluxes implicated in fueling cell fate choices by regulating the epigenetic and transcriptional identity of a cell. Metabolic cues, internal and/or external to the stem cell niche, facilitate progenitor pool restitution, long-term tissue renewal or ensure adoption of cytoprotective behavior. Convergence of energy metabolism with stem cell fate regulation opens a new avenue in understanding primordial developmental biology principles with future applications in regenerative medicine practice.

Secretome protein signature of human pancreatic cancer stem-like cells

Emerging research has demonstrated that pancreatic ductal adenocarcinoma (PDAC) contains a sub-population of cancer stem cells (CSCs) characterized by self-renewal, anchorage-independent-growth, long-term proliferation and chemoresistance. The secretome analysis of pancreatic CSCs has not yet been performed, although it may provide insight into tumour/microenvironment interactions and intracellular processes, as well as to identify potential biomarkers. To characterize the secreted proteins of pancreatic CSCs, we performed an iTRAQ-based proteomic analysis to compare the secretomes of Panc1 cancer stem-like cells (Panc1 CSCs) and parental cell line. A total of 72 proteins were found up-/down-regulated in the conditioned medium of Panc1 CSCs. The pathway analysis revealed modulation of vital physiological pathways including glycolysis, gluconeogenesis and pentose phosphate. Through ELISA immunoassays we analysed the presence of the three proteins most highly secreted by Panc1 CSCs (ceruloplasmin, galectin-3, and MARCKS) in sera of PDAC patient. ROC curve analysis suggests ceruloplasmin as promising marker for patients negative for CA19-9. Overall, our study provides a systemic secretome analysis of pancreatic CSCs revealing a number of secreted proteins which participate in pathological conditions including cancer differentiation, invasion and metastasis. They may serve as a valuable pool of proteins from which biomarkers and therapeutic targets can be identified.

BIOLOGICAL SIGNIFICANCE

The secretome of CSCs is a rich reservoir of biomarkers of cancer progression and molecular therapeutic targets, and thus is a topic of great interest for cancer research. The secretome analysis of pancreatic CSCs has not yet been performed. Recently, our group has demonstrated that Panc-1 CSCs isolated from parental cell line by using the CSC selective medium, represent a model of great importance to deepen the understanding of the biology of pancreatic adenocarcinoma. To our knowledge, this is the first proteomic study of pancreatic CSC secretome. We performed an iTRAQ-based analysis to compare the secretomes of Panc1 CSCs and Panc1 parental cell line and identified a total of 43 proteins secreted at higher level by pancreatic cancer stem cells. We found modulation of different vital physiological pathways (such as glycolysis and gluconeogenesis, pentose phosphate pathway) and the involvement of CSC secreted proteins (for example 72kDa type IV collagenase, galectin-3, alpha-actinin-4, and MARCKS) in pathological conditions including cancer differentiation, invasion and metastasis. By ELISA verification we found that MARCKS and ceruloplasmin discriminate between controls and PDAC patients; in addition ROC curve analyses indicate that MARCKS does not have diagnostic accuracy, while ceruloplasmin could be a promising marker only for patients negative for CA19-9. We think that the findings reported in our manuscript advance the understanding of the pathways implicated in tumourigenesis, metastasis and chemoresistance of pancreatic cancer, and also identify a pool of proteins from which novel candidate diagnostic and therapeutic biomarkers could be discovered.

Targeting the facilitative glucose transporter GLUT1 inhibits the self-renewal and tumor-initiating capacity of cancer stem cells

Increased glucose metabolism is now recognized as an emerging hallmark of cancer. Recent studies have shown that glucose metabolism is even more active in cancer stem cells (CSCs), a rare population of cancer cells with the capacity to self-renew and initiate tumors, and that CSCs are dependent on glycolysis for their survival/growth. However, the role of glucose metabolism in the control of their self-renewal and tumor-initiating capacity per se still remains obscure. Moreover, much remains unknown as to which of the numerous molecules involved in the glucose metabolism is suitable as a target to control CSCs. Here we demonstrate that the facilitative glucose transporter GLUT1 is essential for the maintenance of pancreatic, ovarian, and glioblastoma CSCs. Notably, we found that WZB117, a specific GLUT1 inhibitor, could inhibit the self-renewal and tumor-initiating capacity of the CSCs without compromising their proliferative potential in vitro. In vivo, systemic WZB117 administration inhibited tumor initiation after implantation of CSCs without causing significant adverse events in host animals. Our findings indicate GLUT1-dependent glucose metabolism has a pivotal role not only in the growth and survival of CSCs but also in the maintenance of their stemness and suggest GLUT1 as a promising target for CSC-directed cancer therapy.

Chemotherapy triggers HIF-1-dependent glutathione synthesis and copper chelation that induces the breast cancer stem cell phenotype

Triple negative breast cancer (TNBC) accounts for 10-15% of all breast cancer but is responsible for a disproportionate share of morbidity and mortality because of its aggressive characteristics and lack of targeted therapies. Chemotherapy induces enrichment of breast cancer stem cells (BCSCs), which are responsible for tumor recurrence and metastasis. Here, we demonstrate that chemotherapy induces the expression of the cystine transporter xCT and the regulatory subunit of glutamate-cysteine ligase (GCLM) in a hypoxia-inducible factor (HIF)-1-dependent manner, leading to increased intracellular glutathione levels, which inhibit mitogen-activated protein kinase kinase (MEK) activity through copper chelation. Loss of MEK-ERK signaling causes FoxO3 nuclear translocation and transcriptional activation of the gene encoding the pluripotency factor Nanog, which is required for enrichment of BCSCs. Inhibition of xCT, GCLM, FoxO3, or Nanog blocks chemotherapy-induced enrichment of BCSCs and impairs tumor initiation. These results suggest that, in combination with chemotherapy, targeting BCSCs by inhibiting HIF-1-regulated glutathione synthesis may improve outcome in TNBC.

Controlling Redox Status for Stem Cell Survival, Expansion, and Differentiation

Reactive oxygen species (ROS) have long been considered as pathological agents inducing apoptosis under adverse culture conditions. However, recent findings have challenged this dogma and physiological levels of ROS are now considered as secondary messengers, mediating numerous cellular functions in stem cells. Stem cells represent important tools for tissue engineering, drug screening, and disease modeling. However, the safe use of stem cells for clinical applications still requires culture improvements to obtain functional cells. With the examples of mesenchymal stem cells (MSCs) and pluripotent stem cells (PSCs), this review investigates the roles of ROS in the maintenance of self-renewal, proliferation, and differentiation of stem cells. In addition, this work highlights that the tight control of stem cell microenvironment, including cell organization, and metabolic and mechanical environments, may be an effective approach to regulate endogenous ROS generation. Taken together, this paper indicates the need for better quantification of ROS towards the accurate control of stem cell fate.

Metabostemness: a new cancer hallmark

The acquisition of and departure from stemness in cancer tissues might not only be hardwired by genetic controllers, but also by the pivotal regulatory role of the cellular metabotype, which may act as a "starter dough" for cancer stemness traits. We have coined the term metabostemness to refer to the metabolic parameters causally controlling or functionally substituting the epitranscriptional orchestration of the genetic reprograming that redirects normal and tumor cells toward less-differentiated cancer stem cell (CSC) cellular states. Certain metabotypic alterations might operate as pivotal molecular events rendering a cell of origin susceptible to epigenetic rewiring required for the acquisition of aberrant stemness and, concurrently, of refractoriness to differentiation. The metabostemness attribute can remove, diminish, or modify the nature of molecular barriers present in Waddington's epigenetic landscapes, thus allowing differentiated cells to more easily (re)-enter into CSC cellular macrostates. Activation of the metabostemness trait can poise cells with chromatin states competent for rapid dedifferentiation while concomitantly setting the idoneous metabolic stage for later reprograming stimuli to finish the journey from non-cancerous into tumor-initiating cells. Because only a few permitted metabotypes will be compatible with the operational properties owned by CSC cellular states, the metabostemness property provides a new framework through which to pharmacologically resolve the apparently impossible problem of discovering drugs aimed to target the molecular biology of the cancer stemness itself. The metabostemness cancer hallmark generates a shifting oncology theory that should guide a new era of metabolo-epigenetic cancer precision medicine.