Nuclear reprogramming with c-Myc potentiates glycolytic capacity of derived induced pluripotent stem cells

Metabolic Profiles of Cancer Stem Cells and Normal Stem Cells and Their Therapeutic Significance

Cancer stem cells (CSCs) are a rare cancer cell population, responsible for the facilitation, progression, and resistance of tumors to therapeutic interventions. This subset of cancer cells with stemness and tumorigenic properties is organized in niches within the tumor microenvironment (TME) and presents altered regulation in a variety of metabolic pathways, including glycolysis, oxidative phosphorylation (OXPHOS), as well as lipid, amino acid, and iron metabolism. CSCs exhibit similarities as well as differences when comparedto normal stem cells, but also possess the ability of metabolic plasticity. In this review, we summarize the metabolic characteristics of normal, non-cancerous stem cells and CSCs. We also highlight the significance and implications of interventions targeting CSC metabolism to potentially achieve more robust clinical responses in the future.

BEX1 supports the stemness of hepatoblastoma by facilitating Warburg effect in a PPARγ/PDK1 dependent manner

BACKGROUND

Hepatoblastoma (HB) is a highly aggressive paediatric malignancy that exhibits a high presence of cancer stem cells (CSCs), which related to tumour recurrence and chemotherapy resistance. Brain expressed X-linked protein 1 (BEX1) plays a pivotal role in ciliogenesis, axon regeneration and differentiation of neural stem cells. However, the role of BEX1 in metabolic and stemness programs in HB remains unclear.

METHODS

BEX1 expression in human and mouse HB was analyzed using gene expression profile data from NCBI GEO and immunohistochemical validation. Seahorse extracellular flux analyzer, ultra-high-performance liquid-chromatography mass spectrometry (LC-MS), flow cytometry, qRT-PCR, Western Blot, sphere formation assay, and diluted xenograft tumour formation assay were used to analyze metabolic and stemness features.

RESULTS

Our results indicated that overexpression of BEX1 significantly enhanced the Warburg effect in HB cells. Furthermore, glycolysis inhibition largely attenuated the effects of BEX1 on HB cell growth and self-renewal, suggesting that BEX1 promotes stemness maintenance of HB cells by regulating the Warburg effect. Mechanistically, BEX1 enhances Warburg effect through the downregulation of peroxisome proliferator-activated receptor-gamma (PPARγ). Furthermore, pyruvate dehydrogenase kinase isozyme 1 (PDK1) is required for PPARγ-induced inhibition of Warburg effect in HB. In addition, BEX1 supports the stemness of HB by enhancing Warburg effect in a PPARγ/PDK1 dependent manner.

CONCLUSIONS

HB patients with high BEX1 and PDK1 expression had a poor prognosis. BEX1 promotes the stemness maintenance of HB cells via modulating the Warburg effect, which depends on PPARγ/PDK1 axis. Pioglitazone could be used to target BEX1-mediated stemness properties in HB by upregulating PPARγ.

Crotonylation of GAPDH regulates human embryonic stem cell endodermal lineage differentiation and metabolic switch

BACKGROUND

Post-translational modifications of proteins are crucial to the regulation of their activity and function. As a newly discovered acylation modification, crotonylation of non-histone proteins remains largely unexplored, particularly in human embryonic stem cells (hESCs).

METHODS

We investigated the role of crotonylation in hESC differentiation by introduce crotonate into the culture medium of GFP tagged LTR7 primed H9 cell and extended pluripotent stem cell lines. RNA-seq assay was used to determine the hESC transcriptional features. Through morphological changes, qPCR of pluripotent and germ layer-specific gene markers and flow cytometry analysis, we determined that the induced crotonylation resulted in hESC differentiating into the endodermal lineage. We performed targeted metabolomic analysis and seahorse metabolic measurement to investigate the metabolism features after crotonate induction. Then high-resolution tandem mass spectrometry (LC-MS/MS) revealed the target proteins in hESCs. In addition, the role of crotonylated glycolytic enzymes (GAPDH and ENOA) was evaluated by in vitro crotonylation and enzymatic activity assays. Finally, we used knocked-down hESCs by shRNA, wild GAPDH and GAPDH mutants to explore potential role of GAPDH crotonylation in regulating human embryonic stem cell differentiation and metabolic switch.

RESULT

We found that induced crotonylation in hESCs resulted in hESCs of different pluripotency states differentiating into the endodermal lineage. Increased protein crotonylation in hESCs was accompanied by transcriptomic shifts and decreased glycolysis. Large-scale crotonylation profiling of non-histone proteins revealed that metabolic enzymes were major targets of inducible crotonylation in hESCs. We further discovered GAPDH as a key glycolytic enzyme regulated by crotonylation during endodermal differentiation from hESCs.

CONCLUSIONS

Crotonylation of GAPDH decreased its enzymatic activity thereby leading to reduced glycolysis during endodermal differentiation from hESCs.

Leucine and Arginine Availability Modulate Mouse Embryonic Stem Cell Proliferation and Metabolism

Amino acids are crucial nutrients involved in several cellular and physiological processes, including fertilization and early embryo development. In particular, Leucine and Arginine have been shown to stimulate implantation, as lack of both in a blastocyst culture system is able to induce a dormant state in embryos. The aim of this work was to evaluate the effects of Leucine and Arginine withdrawal on pluripotent mouse embryonic stem cell status, notably, their growth, self-renewal, as well as glycolytic and oxidative metabolism. Our results show that the absence of both Leucine and Arginine does not affect mouse embryonic stem cell pluripotency, while reducing cell proliferation through cell-cycle arrest. Importantly, these effects are not related to Leukemia Inhibitory Factor (LIF) and are reversible when both amino acids are reconstituted in the culture media. Moreover, a lack of these amino acids is related to a reduction in glycolytic and oxidative metabolism and decreased protein translation in mouse embryonic stem cells (mESCs), while maintaining their pluripotent status.

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.

Cancer Stem Cells: Metabolic Characterization for Targeted Cancer Therapy

The subpopulation of cancer stem cells (CSCs) within tumor bulk are known for tumor recurrence and metastasis. CSCs show intrinsic resistance to conventional therapies and phenotypic plasticity within the tumor, which make these a difficult target for conventional therapies. CSCs have different metabolic phenotypes based on their needs as compared to the bulk cancer cells. CSCs show metabolic plasticity and constantly alter their metabolic state between glycolysis and oxidative metabolism (OXPHOS) to adapt to scarcity of nutrients and therapeutic stress. The metabolic characteristics of CSCs are distinct compared to non-CSCs and thus provide an opportunity to devise more effective strategies to target CSCs. Mechanism for metabolic switch in CSCs is still unravelled, however existing evidence suggests that tumor microenvironment affects the metabolic phenotype of cancer cells. Understanding CSCs metabolism may help in discovering new and effective clinical targets to prevent cancer relapse and metastasis. This review summarises the current knowledge of CSCs metabolism and highlights the potential targeted treatment strategies.

Cancer stem cells, epithelial-mesenchymal transition, ATP and their roles in drug resistance in cancer

The cancer stem cell (CSC) state and epithelial-mesenchymal transition (EMT) activation are tightly interconnected. Cancer cells that acquire the EMT/CSC phenotype are equipped with adaptive metabolic changes to maintain low reactive oxygen species levels and stemness, enhanced drug transporters, anti-apoptotic machinery and DNA repair system. Factors present in the tumor microenvironment such as hypoxia and the communication with non-cancer stromal cells also promote cancer cells to enter the EMT/CSC state and display related resistance. ATP, particularly the high levels of intratumoral extracellular ATP functioning through both signaling pathways and ATP internalization, induces and regulates EMT and CSC. The three of them work together to enhance drug resistance. New findings in each of these factors will help us explore deeper into mechanisms of drug resistance and suggest new resistance-associated markers and therapeutic targets.

Testicular germ cell tumors arise in the absence of sex-specific differentiation

In response to signals from the embryonic testis, the germ cell intrinsic factor NANOS2 coordinates a transcriptional program necessary for the differentiation of pluripotent-like primordial germ cells toward a unipotent spermatogonial stem cell fate. Emerging evidence indicates that genetic risk factors contribute to testicular germ cell tumor initiation by disrupting sex-specific differentiation. Here, using the 129.MOLF-Chr19 mouse model of testicular teratomas and a NANOS2 reporter allele, we report that the developmental phenotypes required for tumorigenesis, including failure to enter mitotic arrest, retention of pluripotency and delayed sex-specific differentiation, were exclusive to a subpopulation of germ cells failing to express NANOS2. Single-cell RNA sequencing revealed that embryonic day 15.5 NANOS2-deficient germ cells and embryonal carcinoma cells developed a transcriptional profile enriched for MYC signaling, NODAL signaling and primed pluripotency. Moreover, lineage-tracing experiments demonstrated that embryonal carcinoma cells arose exclusively from germ cells failing to express NANOS2. Our results indicate that NANOS2 is the nexus through which several genetic risk factors influence tumor susceptibility. We propose that, in the absence of sex specification, signals native to the developing testis drive germ cell transformation.

Mitochondria and the permeability transition pore in cancer metabolic reprogramming

Mitochondria are a major source of ATP provision as well as cellular suicidal weapon store. Accumulating evidences demonstrate that mitochondrial bioenergetics, biosynthesis and signaling are important mediators of tumorigenesis. Metabolic plasticity enables cancer cell reprogramming to cope with cellular and environmental alterations, a process requires mitochondria biology. Mitochondrial metabolism emerges to be a promising arena for cancer therapeutic targets. The permeability transition pore (PTP) participates in physiological Ca²⁺ and ROS homeostasis as well as cell death depending on the open state. The hypothesis that PTP forms from F-ATP synthase provides clues to the potential collaborative role of mitochondrial respiration and PTP in regulating cancer cell fate and metabolic reprogramming.

Targeting Metabolism in Cancer Cells and the Tumour Microenvironment for Cancer Therapy

Targeting altered tumour metabolism is an emerging therapeutic strategy for cancer treatment. The metabolic reprogramming that accompanies the development of malignancy creates targetable differences between cancer cells and normal cells, which may be exploited for therapy. There is also emerging evidence regarding the role of stromal components, creating an intricate metabolic network consisting of cancer cells, cancer-associated fibroblasts, endothelial cells, immune cells, and cancer stem cells. This metabolic rewiring and crosstalk with the tumour microenvironment play a key role in cell proliferation, metastasis, and the development of treatment resistance. In this review, we will discuss therapeutic opportunities, which arise from dysregulated metabolism and metabolic crosstalk, highlighting strategies that may aid in the precision targeting of altered tumour metabolism with a focus on combinatorial therapeutic strategies.

Metabolic Regulation and Related Molecular Mechanisms in Various Stem Cell Functions

Recent studies on the mechanisms that link metabolic changes with stem cell fate have deepened our understanding of how specific metabolic pathways can regulate various stem cell functions during the development of an organism. Although it was originally thought to be merely a consequence of the specific cell state, metabolism is currently known to play a critical role in regulating the self-renewal capacity, differentiation potential, and quiescence of stem cells. Many studies in recent years have revealed that metabolic pathways regulate various stem cell behaviors (e.g., selfrenewal, migration, and differentiation) by modulating energy production through glycolysis or oxidative phosphorylation and by regulating the generation of metabolites, which can modulate multiple signaling pathways. Therefore, a more comprehensive understanding of stem cell metabolism could allow us to establish optimal culture conditions and differentiation methods that would increase stem cell expansion and function for cell-based therapies. However, little is known about how metabolic pathways regulate various stem cell functions. In this context, we review the current advances in metabolic research that have revealed functional roles for mitochondrial oxidative phosphorylation, anaerobic glycolysis, and oxidative stress during the self-renewal, differentiation and aging of various adult stem cell types. These approaches could provide novel strategies for the development of metabolic or pharmacological therapies to promote the regenerative potential of stem cells and subsequently promote their therapeutic utility.

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.

Mitochondrial dynamics and metabolism in induced pluripotency

Somatic cells can be reprogrammed to pluripotency by either ectopic expression of defined factors or exposure to chemical cocktails. During reprogramming, somatic cells undergo dramatic changes in a wide range of cellular processes, such as metabolism, mitochondrial morphology and function, cell signaling pathways or immortalization. Regulation of these processes during cell reprograming lead to the acquisition of a pluripotent state, which enables indefinite propagation by symmetrical self-renewal without losing the ability of reprogrammed cells to differentiate into all cell types of the adult. In this review, recent data from different laboratories showing how these processes are controlled during the phenotypic transformation of a somatic cell into a pluripotent stem cell will be discussed.

PDHA1 Gene Knockout In Human Esophageal Squamous Cancer Cells Resulted In Greater Warburg Effect And Aggressive Features In Vitro And In Vivo

Background

One of the remarkable metabolic characteristics of cancer cells is that they prefer glycolysis rather than oxidative phosphorylation (OXPHOS). Pyruvate dehydrogenase E1 alpha subunit (PDHA1) is an important prerequisite for OXPHOS. Our previous studies have shown that low level of PDHA1 protein expression in esophageal squamous cell cancer (ESCC) was correlated with poor prognosis. However, the effect of PDHA1 inhibition on metabolism and biological behavior of esophageal cancer cells remains unclear.

Methods And Results

In this study, a KYSE450 PDHA1 knockout (KO) cell line of esophageal cancer was established by CRISPR/Cas9 technology. Then, the glycose metabolism, cell proliferation and migration abilities, chemotherapeutic tolerance and angiogenesis of the PDHA1 KO cells were investigated in vitro and in vivo. In the PDHA1 KO cells, the glycolysis and the consumption of glucose and glutamine were significantly enhanced, while the OXPHOS was significantly suppressed, implying Warburg effect in the PDHA1 KO cells. Furthermore, it was also proved in vitro experiments that the PDHA1 KO cell obtained proliferation advantage, as well as significantly greater chemotherapy tolerance and migration ability. Xenograft experiments discovered not only larger tumors but also increased angiogenesis in the PDHA1 KO cell group.

Conclusion

Inhibition of PDHA1 gene expression in human ESCC leads to metabolic reprogramming of Warburg effect and increased malignancies. Targeting ESCC metabolic reprogramming may become a potential therapeutic target.

MYC Releases Early Reprogrammed Human Cells from Proliferation Pause via Retinoblastoma Protein Inhibition

Here, we report that MYC rescues early human cells undergoing reprogramming from a proliferation pause induced by OCT3/4, SOX2, and KLF4 (OSK). We identified ESRG as a marker of early reprogramming cells that is expressed as early as day 3 after OSK induction. On day 4, ESRG positive (+) cells converted to a TRA-1-60 (+) intermediate state. These early ESRG (+) or TRA-1-60 (+) cells showed a proliferation pause due to increased p16INK4A and p21 and decreased endogenous MYC caused by OSK. Exogenous MYC did not enhance the appearance of initial reprogramming cells but instead reactivated their proliferation and improved reprogramming efficiency. MYC increased expression of LIN41, which potently suppressed p21 post-transcriptionally. MYC suppressed p16 INK4A. These changes inactivated retinoblastoma protein (RB) and reactivated proliferation. The RB-regulated proliferation pause does not occur in immortalized fibroblasts, leading to high reprogramming efficiency even without exogenous MYC.

Metabolic-Epigenetic Axis in Pluripotent State Transitions

Cell state transition (CST) occurs during embryo development and in adult life in response to different stimuli and is associated with extensive epigenetic remodeling. Beyond growth factors and signaling pathways, increasing evidence point to a crucial role of metabolic signals in this process. Indeed, since several epigenetic enzymes are sensitive to availability of specific metabolites, fluctuations in their levels may induce the epigenetic changes associated with CST. Here we analyze how fluctuations in metabolites availability influence DNA/chromatin modifications associated with pluripotent stem cell (PSC) transitions. We discuss current studies and focus on the effects of metabolites in the context of naïve to primed transition, PSC differentiation and reprogramming of somatic cells to induced pluripotent stem cells (iPSCs), analyzing their mechanism of action and the causal correlation between metabolites availability and epigenetic alteration.

The ERK and JNK pathways in the regulation of metabolic reprogramming

Most tumor cells reprogram their glucose metabolism as a result of mutations in oncogenes and tumor suppressors, leading to the constitutive activation of signaling pathways involved in cell growth. This metabolic reprogramming, known as aerobic glycolysis or the Warburg effect, allows tumor cells to sustain their fast proliferation and evade apoptosis. Interfering with oncogenic signaling pathways that regulate the Warburg effect in cancer cells has therefore become an attractive anticancer strategy. However, evidence for the occurrence of the Warburg effect in physiological processes has also been documented. As such, close consideration of which signaling pathways are beneficial targets and the effect of their inhibition on physiological processes are essential. The MAPK/ERK and MAPK/JNK pathways, crucial for normal cellular responses to extracellular stimuli, have recently emerged as key regulators of the Warburg effect during tumorigenesis and normal cellular functions. In this review, we summarize our current understanding of the roles of the ERK and JNK pathways in controlling the Warburg effect in cancer and discuss their implication in controlling this metabolic reprogramming in physiological processes and opportunities for targeting their downstream effectors for therapeutic purposes.

Role of human oocyte-enriched factors in somatic cell reprograming

Cellular reprograming paves the way for creating functional patient-specific tissues to eliminate immune rejection responses by applying the same genetic profile. However, the epigenetic memory of a cell remains a challenge facing the current reprograming methods and does not allow transcription factors to bind properly. Because somatic cells can be reprogramed by transferring their nuclear contents into oocytes, introducing specific oocyte factors into differentiated cells is considered a promising approach for mimicking the reprograming process that occurs during fertilization. Mammalian metaphase II oocyte possesses a superior capacity to epigenetically reprogram somatic cell nuclei towards an embryonic stem cell-like state than the current factor-based reprograming approaches. This may be due to the presence of specific factors that are lacking in the current factor-based reprograming approaches. In this review, we focus on studies identifying human oocyte-enriched factors aiming to understand the molecular mechanisms mediating cellular reprograming. We describe the role of oocyte-enriched factors in metabolic switch, chromatin remodelling, and global epigenetic transformation. This is critical for improving the quality of resulting reprogramed cells, which is crucial for therapeutic applications.

Physiological oxygen culture reveals retention of metabolic memory in human induced pluripotent stem cells

Reprogramming somatic cells to a pluripotent cell state (induced Pluripotent Stem (iPS) cells) requires reprogramming of metabolism to support cell proliferation and pluripotency, most notably changes in carbohydrate turnover that reflect a shift from oxidative to glycolytic metabolism. Some aspects of iPS cell metabolism differ from embryonic stem (ES) cells, which may reflect a parental cell memory, or be a consequence of the reprogramming process. In this study, we compared the metabolism of 3 human iPS cell lines to assess the fidelity of metabolic reprogramming. When challenged with reduced oxygen concentration, ES cells have been shown to modulate carbohydrate use in a predictably way. In the same model, 2 of 3 iPS cell lines failed to regulate carbohydrate metabolism. Oxygen is a well-characterized regulator of cell function and embryo viability, and an inability of iPS cells to modulate metabolism in response to oxygen may indicate poor metabolic fidelity. As metabolism is linked to the regulation of the epigenome, assessment of metabolic responses of iPS cells to physiological stimuli during characterization is warranted to ensure complete cell reprogramming and as a measure of cell quality.

Metabolism in Pluripotent Stem Cells and Early Mammalian Development

Emerging and seminal studies have shown that cell metabolism influences gene expression by modifying the epigenome, which can regulate stem cell pluripotency, differentiation, and somatic cell reprogramming. Core pluripotency factors and developmental regulators reciprocally control the expression of key metabolism genes and their encoded pathways. Recent technological advances enabling sensitive detection methods during early mammalian development revealed the state-specific and context-dependent coordination of signal transduction, histone modifications, and gene expression in developing, resting, and malnourished embryos. Here, we discuss metabolism as a potential driver of earliest cell fate through its influence on the epigenome and gene expression in embryos and their in vitro surrogate pluripotent stem cells.

Mitophagy-driven mitochondrial rejuvenation regulates stem cell fate

Our understanding on how selective mitochondrial autophagy, or mitophagy, can sustain the archetypal properties of stem cells is incomplete. PTEN-induced putative kinase 1 (PINK1) plays a key role in the maintenance of mitochondrial morphology and function and in the selective degradation of damaged mitochondria by mitophagy. Here, using embryonic fibroblasts from PINK1 gene-knockout (KO) mice, we evaluated whether mitophagy is a causal mechanism for the control of cell-fate plasticity and maintenance of pluripotency. Loss of PINK1-dependent mitophagy was sufficient to dramatically decrease the speed and efficiency of induced pluripotent stem cell (iPSC) reprogramming. Mitophagy-deficient iPSC colonies, which were characterized by a mixture of mature and immature mitochondria, seemed unstable, with a strong tendency to spontaneously differentiate and form heterogeneous populations of cells. Although mitophagy-deficient iPSC colonies normally expressed pluripotent markers, functional monitoring of cellular bioenergetics revealed an attenuated glycolysis in mitophagy-deficient iPSC cells. Targeted metabolomics showed a notable alteration in numerous glycolysis- and TCA-related metabolites in mitophagy-deficient iPSC cells, including a significant decrease in the intracellular levels of α-ketoglutarate -a key suppressor of the differentiation path in stem cells. Mitophagy-deficient iPSC colonies exhibited a notably reduced teratoma-initiating capacity, but fully retained their pluripotency and multi-germ layer differentiation capacity in vivo. PINK1-dependent mitophagy pathway is an important mitochondrial switch that determines the efficiency and quality of somatic reprogramming. Mitophagy-driven mitochondrial rejuvenation might contribute to the ability of iPSCs to suppress differentiation by directing bioenergetic transition and metabolome remodeling traits. These findings provide new insights into how mitophagy might influence the stem cell decisions to retain pluripotency or differentiate in tissue regeneration and aging, tumor growth, and regenerative medicine.

Metabolic remodeling during the loss and acquisition of pluripotency

Pluripotent cells from the early stages of embryonic development have the unlimited capacity to self-renew and undergo differentiation into all of the cell types of the adult organism. These properties are regulated by tightly controlled networks of gene expression, which in turn are governed by the availability of transcription factors and their interaction with the underlying epigenetic landscape. Recent data suggest that, perhaps unexpectedly, some key epigenetic marks, and thereby gene expression, are regulated by the levels of specific metabolites. Hence, cellular metabolism plays a vital role beyond simply the production of energy, and may be involved in the regulation of cell fate. In this Review, we discuss the metabolic changes that occur during the transitions between different pluripotent states both in vitro and in vivo, including during reprogramming to pluripotency and the onset of differentiation, and we discuss the extent to which distinct metabolites might regulate these transitions.

Mitochondrial-epigenetic crosstalk in environmental toxicology

Crosstalk between the nuclear epigenome and mitochondria, both in normal physiological function and in responses to environmental toxicant exposures, is a developing sub-field of interest in environmental and molecular toxicology. The majority (∼99%) of mitochondrial proteins are encoded in the nuclear genome, so programmed communication among nuclear, cytoplasmic, and mitochondrial compartments is essential for maintaining cellular health. In this review, we will focus on correlative and mechanistic evidence for direct impacts of each system on the other, discuss demonstrated or potential crosstalk in the context of chemical insult, and highlight biological research questions for future study. We will first review the two main signaling systems: nuclear signaling to the mitochondria [anterograde signaling], best described in regulation of oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis in response to environmental signals received by the nucleus, and mitochondrial signals to the nucleus [retrograde signaling]. Both signaling systems can communicate intracellular energy needs or a need to compensate for dysfunction to maintain homeostasis, but both can also relay inappropriate signals in the presence of dysfunction in either system and contribute to adverse health outcomes. We will first review these two signaling systems and highlight known or biologically feasible epigenetic contributions to both, then briefly discuss the emerging field of epigenetic regulation of the mitochondrial genome, and finally discuss putative "crosstalk phenotypes", including biological phenomena, such as caloric restriction, maintenance of stemness, and circadian rhythm, and states of disease or loss of function, such as cancer and aging, in which both the nuclear epigenome and mitochondria are strongly implicated.

Metabolic switching and cell fate decisions: implications for pluripotency, reprogramming and development

Cell fate decisions are closely linked to changes in metabolic activity. Over recent years this connection has been implicated in mechanisms underpinning embryonic development, reprogramming and disease pathogenesis. In addition to being important for supporting the energy demands of different cell types, metabolic switching from aerobic glycolysis to oxidative phosphorylation plays a critical role in controlling biosynthetic processes, intracellular redox state, epigenetic status and reactive oxygen species levels. These processes extend beyond ATP synthesis by impacting cell proliferation, differentiation, enzymatic activity, ageing and genomic integrity. This review will focus on how metabolic switching impacts decisions made by multipotent cells and discusses mechanisms by which this occurs.

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."

Glycolytic Metabolism Plays a Functional Role in Regulating Human Pluripotent Stem Cell State

The rate of glycolytic metabolism changes during differentiation of human embryonic stem cells (hESCs) and reprogramming of somatic cells to pluripotency. However, the functional contribution of glycolytic metabolism to the pluripotent state is unclear. Here we show that naive hESCs exhibit increased glycolytic flux, MYC transcriptional activity, and nuclear N-MYC localization relative to primed hESCs. This status is consistent with the inner cell mass of human blastocysts, where MYC transcriptional activity is higher than in primed hESCs and nuclear N-MYC levels are elevated. Reduction of glycolysis decreases self-renewal of naive hESCs and feeder-free primed hESCs, but not primed hESCs grown in feeder-supported conditions. Reduction of glycolysis in feeder-free primed hESCs also enhances neural specification. These findings reveal associations between glycolytic metabolism and human naive pluripotency and differences in the metabolism of feeder-/feeder-free cultured hESCs. They may also suggest methods for regulating self-renewal and initial cell fate specification of hESCs.

Cross-talk between signaling and metabolism in the vasculature

The link between signaling and metabolism was first recognized with insulin signal transduction. Efficient glucose uptake by the endothelium requires insulin receptor activation to deliver GLUT receptors to the cell surface. More recently however, additional evidence has emerged for a broader crosstalk as signaling events have been shown to regulate a large number of metabolic enzymes. Changes in the metabolic status of endothelial and smooth muscle cells are observed at times of increased proliferative activity and these coincide with activation of cell surface receptors. Intriguingly, a rise in glycolysis appears to be associated with remodeling of the actin cytoskeleton during migration and angiogenesis. Overall, understanding how do signaling and metabolic pathways intersect and cross-regulate each other has become an important question and an emerging cornerstone in vascular biology.

Hallmarks of cancer stem cell metabolism

Cancer cells adapt cellular metabolism to cope with their high proliferation rate. Instead of primarily using oxidative phosphorylation (OXPHOS), cancer cells use less efficient glycolysis for the production of ATP and building blocks (Warburg effect). However, tumours are not uniform, but rather functionally heterogeneous and harbour a subset of cancer cells with stemness features. Such cancer cells have the ability to repopulate the entire tumour and thus have been termed cancer stem cells (CSCs) or tumour-initiating cells (TICs). As opposed to differentiated bulk tumour cells relying on glycolysis, CSCs show a distinct metabolic phenotype that, depending on the cancer type, can be highly glycolytic or OXPHOS dependent. In either case, mitochondrial function is critical and takes centre stage in CSC functionality. Remaining controversies in this young and emerging research field may be related to CSC isolation techniques and/or the use of less suitable model systems. Still, the apparent dependence of CSCs on mitochondrial function, regardless of their primary metabolic phenotype, represents a previously unrecognised Achilles heel amendable for therapeutic intervention. Elimination of highly chemoresistant CSCs as the root of many cancers via inhibition of mitochondrial function bears the potential to prevent relapse from disease and thus improve patients' long-term outcome.

Energy Metabolism Plays a Critical Role in Stem Cell Maintenance and Differentiation

Various stem cells gradually turned to be critical players in tissue engineering and regenerative medicine therapies. Current evidence has demonstrated that in addition to growth factors and the extracellular matrix, multiple metabolic pathways definitively provide important signals for stem cell self-renewal and differentiation. In this review, we mainly focus on a detailed overview of stem cell metabolism in vitro. In stem cell metabolic biology, the dynamic balance of each type of stem cell can vary according to the properties of each cell type, and they share some common points. Clearly defining the metabolic flux alterations in stem cells may help to shed light on stemness features and differentiation pathways that control the fate of stem cells.

Human pluripotent stem cells: Prospects and challenges as a source of cardiomyocytes for in vitro modeling and cell-based cardiac repair

Human pluripotent stem cells (PSCs) represent an attractive source of cardiomyocytes with potential applications including disease modeling, drug discovery and safety screening, and novel cell-based cardiac therapies. Insights from embryology have contributed to the development of efficient, reliable methods capable of generating large quantities of human PSC-cardiomyocytes with cardiac purities ranging up to 90%. However, for human PSCs to meet their full potential, the field must identify methods to generate cardiomyocyte populations that are uniform in subtype (e.g. homogeneous ventricular cardiomyocytes) and have more mature structural and functional properties. For in vivo applications, cardiomyocyte production must be highly scalable and clinical grade, and we will need to overcome challenges including graft cell death, immune rejection, arrhythmogenesis, and tumorigenic potential. Here we discuss the types of human PSCs, commonly used methods to guide their differentiation into cardiomyocytes, the phenotype of the resultant cardiomyocytes, and the remaining obstacles to their successful translation.

Mitochondrial resetting and metabolic reprogramming in induced pluripotent stem cells and mitochondrial disease modeling

BACKGROUND

Nuclear reprogramming with pluripotency factors enables somatic cells to gain the properties of embryonic stem cells. Mitochondrial resetting and metabolic reprogramming are suggested to be key early events in the induction of human skin fibroblasts to induced pluripotent stem cells (iPSCs).

SCOPE OF REVIEW

We review recent advances in the study of the molecular basis for mitochondrial resetting and metabolic reprogramming in the regulation of the formation of iPSCs. In particular, the recent progress in using iPSCs for mitochondrial disease modeling was discussed.

MAJOR CONCLUSIONS

iPSCs rely on glycolysis rather than oxidative phosphorylation as a major supply of energy. Mitochondrial resetting and metabolic reprogramming thus play crucial roles in the process of generation of iPSCs from somatic cells.

GENERAL SIGNIFICANCE

Neurons, myocytes, and cardiomyocytes are cells containing abundant mitochondria in the human body, which can be differentiated from iPSCs or trans-differentiated from fibroblasts. Generating these cells from iPSCs derived from skin fibroblasts of patients with mitochondrial diseases or by trans-differentiation with cell-specific transcription factors will provide valuable insights into the role of mitochondrial DNA heteroplasmy in mitochondrial disease modeling and serves as a novel platform for screening of drugs to treat patients with mitochondrial diseases.

Differentiate or Die: 3-Bromopyruvate and Pluripotency in Mouse Embryonic Stem Cells

Background

Pluripotent embryonic stem cells grown under standard conditions (ESC) have a markedly glycolytic profile, which is shared with many different types of cancer cells. Thus, some therapeutic strategies suggest that pharmacologically shifting cancer cells towards an oxidative phenotype, using glycolysis inhibitors, may reduce cancer aggressiveness. Given the metabolic parallels between cancer and stemness would chemotherapeutical agents have an effect on pluripotency, and could a strategy involving these agents be envisioned to modulate stem cell fate in an accessible manner? In this manuscript we attempted to determine the effects of 3-bromopyruvate (3BrP) in pluripotency. Although it has other intracellular targets, this compound is a potent inhibitor of glycolysis enzymes thought to be important to maintain a glycolytic profile. The goal was also to determine if we could contribute towards a pharmacologically accessible metabolic strategy to influence cell differentiation.

Methodology/Principal Findings

Mouse embryonic stem cells (mESC) grown under standard pluripotency conditions (in the presence of Leukemia Inducing Factor- LIF) were treated with 3BrP. As a positive control for differentiation other mESCs were grown without LIF. Overall our results demonstrate that 3BrP negatively affects pluripotency, forcing cells to become less glycolytic and with more active mitochondria. These changes in metabolism are correlated with increased differentiation, even under pluripotency conditions (i.e. in the presence of LIF). However, 3BrP also significantly impaired cell function, and may have other roles besides affecting the metabolic profile of mESCs.

Conclusions/Findings

Treatment of mESCs with 3BrP triggered a metabolic switch and loss of pluripotency, even in the presence of LIF. Interestingly, the positive control for differentiation allowed for a distinction between 3BrP effects and changes associated with spontaneous differentiation/loss of pluripotency in the absence of LIF. Additionally, there was a slight differentiation bias towards mesoderm in the presence of 3BrP. However, the side effects on cellular function suggest that the use of this drug is probably not adequate to efficiently push cells towards specific differentiation fates.

Dichloroacetate, the Pyruvate Dehydrogenase Complex and the Modulation of mESC Pluripotency

Introduction

The pyruvate dehydrogenase (PDH) complex is localized in the mitochondrial matrix catalyzing the irreversible decarboxylation of pyruvate to acetyl-CoA and NADH. For proper complex regulation the E1-α subunit functions as an on/off switch regulated by phosphorylation/dephosphorylation. In different cell types one of the four-pyruvate dehydrogenase kinase isoforms (PDHK1-4) can phosphorylate this subunit leading to PDH inactivation. Our previous results with human Embryonic Stem Cells (hESC), suggested that PDHK could be a key regulator in the metabolic profile of pluripotent cells, as it is upregulated in pluripotent stem cells. Therefore, we wondered if metabolic modulation, via inexpensive pharmacological inhibition of PDHK, could impact metabolism and pluripotency.

Methods/Results

In order to assess the importance of the PDH cycle in mouse Embryonic Stem Cells (mESC), we incubated cells with the PDHK inhibitor dichloroacetate (DCA) and observed that in its presence ESC started to differentiate. Changes in mitochondrial function and proliferation potential were also found and protein levels for PDH (both phosphorylated and non-phosphorylated) and PDHK1 were monitored. Interestingly, we were also able to describe a possible pathway that involves Hif-1α and p53 during DCA-induced loss of pluripotency. Results with ESCs treated with DCA were comparable to those obtained for cells grown without Leukemia Inhibitor Factor (LIF), used in this case as a positive control for differentiation.

Conclusions

DCA negatively affects ESC pluripotency by changing cell metabolism and elements related to the PDH cycle, suggesting that PDHK could function as a possible metabolic gatekeeper in ESC, and may be a good target to modulate metabolism and differentiation. Although further molecular biology-based experiments are required, our data suggests that inactive PDH favors pluripotency and that ESC have similar strategies as cancer cells to maintain a glycolytic profile, by using some of the signaling pathways found in the latter cells.

Advances in induced pluripotent stem cells, genomics, biomarkers, and antiplatelet therapy highlights of the year in JCTR 2013

The Journal provides the clinician and scientist with the latest advances in discovery research, emerging technologies, preclinical research design and testing, and clinical trials. We highlight advances in areas of induced pluripotent stem cells, genomics, biomarkers, multimodality imaging, and antiplatelet biology and therapy. The top publications are critically discussed and presented along with anatomical reviews and FDA insight to provide context.

miR-290/371-Mbd2-Myc circuit regulates glycolytic metabolism to promote pluripotency

Enhanced glycolysis is a main feature of pluripotent stem cells (PSCs) and is proposed to be important for the maintenance and induction of pluripotency. The molecular mechanism underlying enhanced glycolysis in PSCs is not clear. Using Dgcr8-/- mouse embryonic stem cells (ESCs) that lack mature miRNAs, we found that miR-290 cluster of miRNAs stimulates glycolysis by upregulating glycolytic enzymes Pkm2 and Ldha, which are also essential for the induction of pluripotency during reprogramming. Mechanistically, we identified Mbd2, a reader for methylated CpGs, as the target of miR-290 cluster that represses glycolysis and reprogramming. Furthermore, we discovered Myc as a key target of Mbd2 that controls metabolic switch in ESCs. Importantly, we demonstrated that miR-371 cluster, a human homolog of miR-290 cluster, stimulates glycolysis to promote the reprogramming of human fibroblasts. Hence, we identified a previously unappreciated mechanism by which miR-290/371 miRNAs orchestrate epigenetic, transcriptional and metabolic networks to promote pluripotency in PSCs and during reprogramming.

Pluripotent stem cell energy metabolism: an update

Recent studies link changes in energy metabolism with the fate of pluripotent stem cells (PSCs). Safe use of PSC derivatives in regenerative medicine requires an enhanced understanding and control of factors that optimize in vitro reprogramming and differentiation protocols. Relative shifts in metabolism from naïve through "primed" pluripotent states to lineage-directed differentiation place variable demands on mitochondrial biogenesis and function for cell types with distinct energetic and biosynthetic requirements. In this context, mitochondrial respiration, network dynamics, TCA cycle function, and turnover all have the potential to influence reprogramming and differentiation outcomes. Shifts in cellular metabolism affect enzymes that control epigenetic configuration, which impacts chromatin reorganization and gene expression changes during reprogramming and differentiation. Induced PSCs (iPSCs) may have utility for modeling metabolic diseases caused by mutations in mitochondrial DNA, for which few disease models exist. Here, we explore key features of PSC energy metabolism research in mice and man and the impact this work is starting to have on our understanding of early development, disease modeling, and potential therapeutic applications.

Energy metabolism and metabolic sensors in stem cells: the metabostem crossroads of aging and cancer

We are as old as our adult stem cells are; therefore, stem cell exhaustion is considered a hallmark of aging. Our tumors are as aggressive as the number of cancer stem cells (CSCs) they bear because CSCs can survive treatments with hormones, radiation, chemotherapy, and molecularly targeted drugs, thus increasing the difficulty of curing cancer. Not surprisingly, interest in stem cell research has never been greater among members of the public, politicians, and scientists. But how can we slow the rate at which our adult stem cells decline over our lifetime, reducing the regenerative potential of tissues, while efficiently eliminating the aberrant, life-threatening activity of "selfish", immortal, and migrating CSCs? Frustrated by the gene-centric limitations of conventional approaches to aging diseases, our group and other groups have begun to appreciate that bioenergetic metabolism, i.e., the production of fuel & building blocks for growth and division, and autophagy/mitophagy, i.e., the quality-control, self-cannibalistic system responsible for "cleaning house" and "recycling the trash", can govern the genetic and epigenetic networks that facilitate stem cell behaviors. Indeed, it is reasonable to suggest the existence of a "metabostem" infrastructure that operates as a shared hallmark of aging and cancer, thus making it physiologically plausible to maintain or even increase the functionality of adult stem cells while reducing the incidence of cancer and extending the lifespan. This "metabostemness" property could lead to the discovery of new drugs that reprogram cell metabotypes to increase the structural and functional integrity of adult stem cells and positively influence their lineage determination, while preventing the development and aberrant function of stem cells in cancer tissues. While it is obvious that the antifungal antibiotic rapamycin, the polyphenol resveratrol, and the biguanide metformin already belong to this new family of metabostemness-targeting drugs, we can expect a rapid identification of new drug candidates (e.g., polyphenolic xenohormetins) that reverse or postpone "geroncogenesis", i.e., aging-induced metabolic decline as a driver of tumorigenesis, at the stem cell level.

The multifaceted activities of AMPK in tumor progression--why the "one size fits all" definition does not fit at all?

AMP-activated kinase (AMPK) is a central cellular energetic biosensor and regulator of a broad array of cellular metabolic routes activated by nutrient deprivation, mitochondrial dysfunction, oxidative stress, and cytokines. The activation of AMPK maintains ATP levels in response to hypoxia, mitochondrial dysfunction, and shortage of essential metabolic fuels. Activated AMPK turns on energy sparing pathways and promotes antiapoptotic functions thereby permitting cells to survive extremely hostile conditions for prolonged periods of time. Cancer cells in solid tumors are generally subjected to such harsh conditions; however, they manage to efficiently survive and proliferate. This is likely due, in great part, to a peculiar form of metabolism that is heavily reliant on glycolysis and which promotes cancer cell adaptation and tumor progression. AMPK controls the influx and utilization of glucose by cancer cells and therefore has emerged as an attractive target to treat cancer. Investigations exploring this possibility demonstrated that activators or inhibitors of AMPK impact cancer cell viability and possibly cancer progression. For example, the AMPK activator metformin induces apoptosis in a variety of cancer cell lines and models. A major problem with many of the studies on metformin is that little effort has been invested in unraveling how metformin activates AMPK in the many contexts it has been tested. This is significant because many AMPK-independent effects of metformin have been documented. The notion that AMPK acts solely as a tumor suppressor also conflicts with findings that it confers resistance to nutrient deprivation, sustains NADPH levels in cancer cells, facilitates stress-induced gene transcription, promotes cell survival via antiapoptotic function upregulation, intermediates epithelial-to-mesenchymal transition, and increases malignant transformation. These are all recognized steps necessary for the successful evolution of tumors. This review highlights some of these findings and proposes that the role of AMPK in cancer should be reconsidered in light of the complex roles of AMPK under different metabolic conditions.

A mitochondrial strategy for safeguarding the reprogrammed genome

Genomic aberrations induced by somatic cell reprogramming are a major drawback for future applications of this technology in regenerative medicine. A new study by Ji et al. published in Stem Cell Reports suggests a counteracting strategy based on balancing the mitochondrial/oxidative stress pathway through antioxidant supplementation.

Gerometabolites: the pseudohypoxic aging side of cancer oncometabolites

Oncometabolites are defined as small-molecule components (or enantiomers) of normal metabolism whose accumulation causes signaling dysregulation to establish a milieu that initiates carcinogenesis. In a similar manner, we propose the term "gerometabolites" to refer to small-molecule components of normal metabolism whose depletion causes signaling dysregulation to establish a milieu that drives aging. In an investigation of the pathogenic activities of the currently recognized oncometabolites R(-)-2-hydroxyglutarate (2-HG), fumarate, and succinate, which accumulate due to mutations in isocitrate dehydrogenases (IDH), fumarate hydratase (FH), and succinate dehydrogenase (SDH), respectively, we illustrate the fact that metabolic pseudohypoxia, the accumulation of hypoxia-inducible factor (HIFα) under normoxic conditions, and the subsequent Warburg-like reprogramming that shifts glucose metabolism from the oxidative pathway to aerobic glycolysis are the same mechanisms through which the decline of the "gerometabolite" nicotinamide adenine dinucleotide (NAD)(+) reversibly disrupts nuclear-mitochondrial communication and contributes to the decline in mitochondrial function with age. From an evolutionary perspective, it is reasonable to view NAD(+)-driven mitochondrial homeostasis as a conserved response to changes in energy supplies and oxygen levels. Similarly, the natural ability of 2-HG to significantly alter epigenetics might reflect an evolutionarily ancient role of certain metabolites to signal for elevated glutamine/glutamate metabolism and/or oxygen deficiency. However, when chronically altered, these responses become conserved causes of aging and cancer. Because HIFα-driven pseudohypoxia might drive the overproduction of 2-HG, the intriguing possibility exists that the decline of gerometabolites such as NAD(+) could promote the chronic accumulation of oncometabolites in normal cells during aging. If the sole activation of a Warburg-like metabolic reprogramming in normal tissues might be able to significantly increase the endogenous production of bona fide etiological determinants in cancer, such as oncometabolites, this undesirable trade-off between mitochondrial dysfunction and activation of oncometabolites production might then pave the way for the epigenetic initiation of carcinogenesis in a strictly metabolic-dependent manner. Perhaps it is time to definitely adopt the view that aging and aging diseases including cancer are governed by a pivotal regulatory role of metabolic reprogramming in cell fate decisions.

Cited2, a transcriptional modulator protein, regulates metabolism in murine embryonic stem cells

CREB-binding protein (CBP)/p300 interacting transactivator with glutamic acid (Glu) and aspartic acid (Asp)-tail 2 (Cited2) was recently shown to be essential for gluconeogenesis in the adult mouse. The metabolic function of Cited2 in mouse embryonic stem cells (mESCs) remains elusive. In the current study, the metabolism of glucose was investigated in mESCs, which contained a deletion in the gene for Cited2 (Cited2(Δ/-)). Compared with its parental wild type counterpart, Cited2(Δ/-) ESCs have enhanced glycolysis, alternations in mitochondria morphology, reduced glucose oxidation, and decreased ATP content. Cited2 is recruited to the hexokinase 1 (HK1) gene promoter to regulate transcription of HK1, which coordinates glucose metabolism in wild type ESCs. Reduced glucose oxidation and enhanced glycolytic activity in Cited2(Δ/-) ESCs correlates with defective differentiation during hypoxia, which is reflected in an increased expression of pluripotency marker (Oct4) and epiblast marker (Fgf5) and decreased expression of lineage specification markers (T, Gata-6, and Cdx2). Knockdown of hypoxia inducible factor-1α in Cited2(Δ/-) ESCs re-initiates the expression of differentiation markers T and Gata-6. Taken together, a deletion of Cited2 in mESCs results in abnormal mitochondrial morphology and impaired glucose metabolism, which correlates with a defective cell fate decision.

Induced pluripotent stem cell intervention rescues ventricular wall motion disparity, achieving biological cardiac resynchronization post-infarction

Dyssynchronous myocardial motion aggravates cardiac pump function. Cardiac resynchronization using pacing devices is a standard-of-care in the management of heart failure. Post-infarction, however, scar tissue formation impedes the efficacy of device-based therapy. The present study tests a regenerative approach aimed at targeting the origin of abnormal motion to prevent dyssynchronous organ failure. Induced pluripotent stem (iPS) cells harbour a reparative potential, and were here bioengineered from somatic fibroblasts reprogrammed with the stemness factors OCT3/4, SOX2, KLF4, and c-MYC. In a murine infarction model, within 30 min of coronary ligation, iPS cells were delivered to mapped infarcted areas. Focal deformation and dysfunction underlying progressive heart failure was resolved prospectively using speckle-tracking imaging. Tracked at high temporal and spatial resolution, regional iPS cell transplantation restored, within 10 days post-infarction, the contractility of targeted infarcted foci and nullified conduction delay in adjacent non-infarcted regions. Local iPS cell therapy, but not delivery of parental fibroblasts or vehicle, prevented or normalized abnormal strain patterns correcting the decrease in peak strain, disparity of time-to-peak strain, and pathological systolic stretch. Focal benefit of iPS cell intervention translated into improved left ventricular conduction and contractility, reduced scar, and reversal of structural remodelling, protecting from organ decompensation. Thus, in ischaemic cardiomyopathy, targeted iPS cell transplantation synchronized failing ventricles, offering a regenerative strategy to achieve biological resynchronization.

The Warburg effect version 2.0: metabolic reprogramming of cancer stem cells

When fighting cancer, knowledge on metabolism has always been important. Today, it matters more than ever. The restricted cataloging of cancer genomes is quite unlikely to achieve the task of curing cancer, unless it is integrated into metabolic networks that respond to and influence the constantly evolving cancer stem cell (CSC) cellular states. Once the genomic era of carcinogenesis had pushed the 1920s Otto Warburg's metabolic cancer hypothesis into obscurity for decades, the most recent studies begin to support a new developing paradigm, in which the molecular logic behind the conversion of non-CSCs into CSCs can be better understood in terms of the "metabolic facilitators" and "metabolic impediments" that operate as proximate openings and roadblocks, respectively, for the transcriptional events and signal transduction programs that ultimately orchestrate the intrinsic and/or microenvironmental paths to CSC cellular states. Here we propose that a profound understanding of how human carcinomas install a proper "Warburg effect version 2.0" allowing them to "run" the CSCs' "software" programs should guide a new era of metabolo-genomic-personalized cancer medicine. By viewing metabolic reprogramming of CSCs as an essential characteristic that allows dynamic, multidimensional and evolving cancer populations to compete successfully for their expansion on the organism, we now argue that CSCs bioenergetics might be another cancer hallmark. A definitive understanding of metabolic reprogramming in CSCs may complement or to some extent replace, the 30-y-old paradigm of targeting oncogenes to treat human carcinomas, because it can be possible to metabolically create non-permissive or "hostile" metabotypes to prevent the occurrence of CSC cellular states with tumor- and metastasis-initiating capacity.