Energy metabolism plasticity enables stemness programs

LGR5+ Intestinal Stem Cells Display Sex-Dependent Radiosensitivity

Tissue radiosensitivity plays a critical role in the overall outcome of radiation therapy. Identifying characteristics that predict how a patient may respond to radiotherapy enables clinicians to maximize the therapeutic window. Limited clinical data have suggested a difference in male and female radiotherapy outcomes. Radiotherapy for gastrointestinal malignancy is still a challenge due to intestinal sensitivity to radiation toxicity. In this manuscript, we demonstrated sex-specific differences in intestinal epithelial radiosensitivity. In a mouse model of abdominal irradiation, we observed a significant increase in oxidative stress and injury in males compared to females. Lgr5+ve intestinal stem cells from male mice showed higher sensitivity to radiation-induced toxicity. However, sex-specific differences in intestinal radiosensitivity were not dependent on sex hormones, as we demonstrated similar sex-specific radiosensitivity differences in pre-pubescent mice. In an ex vivo study, we found that patient-derived intestinal organoid (PID) from males showed higher sensitivity to radiation compared to females as evident from loss of budding crypts, organoid size, and membrane integrity. Transcriptomic analysis of human Lgr5+ intestinal stem cells suggested radiation-induced upregulation of mitochondrial oxidative metabolism in males compared to females, a possible mechanism for radiosensitivity differences.

LGR5+ Intestinal Stem Cells Display Sex Dependent Radiosensitivity

Radiosensitivity, the susceptibility of cells to ionizing radiation, plays a critical role in understanding the effects of radiation therapy and exposure on tissue health and regeneration. Identifying characteristics that predict how a patient may respond to radiotherapy enables clinicians to maximize the therapeutic window. Limited clinical data suggested a difference in male and female radiotherapy outcomes. Radiotherapy for gastrointestinal malignancy is still a challenge due to intestinal sensitivity to radiation toxicity. In this manuscript, we demonstrated sex-specific differences in intestinal epithelial radiosensitivity. In mice models of abdominal irradiation, we observed a significant increase in oxidative stress and injury in males compared to females. Lgr5+ve intestinal stem cells from male mice showed higher sensitivity to radiation-induced toxicity. However, sex-specific differences in intestinal radiosensitivity are not dependent on sex hormones as we demonstrated similar sex-specific radiosensitivity differences in pediatric mice. In an ex-vivo study, we found that human patient-derived intestinal organoids (PID) derived from males showed higher sensitivity to irradiation compared to females as evidenced by loss of budding crypt, organoid size, and membrane integrity. Transcriptomic analysis of human Lgr5+ intestinal stem cells suggested radiation induced upregulation of mitochondrial oxidative metabolism in males compared to females' possible mechanism for radiosensitivity differences.

Human bone marrow stromal cells: the impact of anticoagulants on stem cell properties

Background: Bone marrow stromal cells (BMSCs) are the source of multipotent stem cells, which are important for regenerative medicine and diagnostic purposes. The isolation of human BMSCs from the bone marrow (BM) cavity using BM aspiration applies the method with collection into tubes containing anticoagulants. Interactions with anticoagulants may affect the characteristics and composition of isolated BMSCs in the culture. Thus, we investigated how anticoagulants in isolation procedures and cultivation affect BMSC molecular characteristics. Methods: BM donors (age: 48-85 years) were recruited from the hematology clinic. BM aspirates were obtained from the iliac crest and divided into tubes coated with ethylenediaminetetraacetic acid (EDTA) or heparin anticoagulants. Isolated BMSCs were analyzed by flow cytometry and RNA-seq analysis. Further cellular and molecular characterizations of BMSCs including CFU, proliferation and differentiation assays, cytometry, bioenergetic assays, metabolomics, immunostaining, and RT-qPCR were performed. Results: The paired samples of isolated BMSCs obtained from the same patient showed increased cellular yield in heparin vs. EDTA samples, accompanied by the increased number of CFU colonies. However, no significant changes in molecular characteristics were found between heparin- and EDTA-isolated BMSCs. On the other hand, RNA-seq analysis revealed an increased expression of genes involved in nucleotide metabolism and cellular metabolism in cultivated vs. non-cultivated BMSCs regardless of the anticoagulant, while genes involved in inflammation and chromatin remodeling were decreased in cultivated vs. non-cultivated BMSCs. Conclusion: The type of anticoagulant in BMSC isolation did not have a significant impact on molecular characteristics and cellular composition, while in vitro cultivation caused the major change in the transcriptomics of BMSCs, which is important for future protocols using BMSCs in regenerative medicine and clinics.

Cloning in action: can embryo splitting, induced pluripotency and somatic cell nuclear transfer contribute to endangered species conservation?

The term 'cloning' refers to the production of genetically identical individuals but has meant different things throughout the history of science: a natural means of reproduction in bacteria, a routine procedure in horticulture, and an ever-evolving gamut of molecular technologies in vertebrates. Mammalian cloning can be achieved through embryo splitting, somatic cell nuclear transfer, and most recently, by the use of induced pluripotent stem cells. Several emerging biotechnologies also facilitate the propagation of genomes from one generation to the next whilst bypassing the conventional reproductive processes. In this review, we examine the state of the art of available cloning technologies and their progress in species other than humans and rodent models, in order to provide a critical overview of their readiness and relevance for application in endangered animal conservation.

Hypoxia-induced reprogramming of glucose-dependent metabolic pathways maintains the stemness of human bone marrow-derived endothelial progenitor cells

The benefits of hypoxia for maintaining the stemness of cultured human bone marrow-derived endothelial progenitor cells (BM EPCs) have previously been demonstrated but the mechanisms responsible remain unclear. Growing evidences suggest that cellular metabolism plays an important role in regulating stem cell fate and self-renewal. Here we aimed to detect the changes of glucose metabolism and to explore its role on maintaining the stemness of BM EPCs under hypoxia. We identified the metabolic status of BM EPCs by using extracellular flux analysis, LC-MS/MS, and ¹³C tracing HPLC-QE-MS, and found that hypoxia induced glucose metabolic reprogramming, which manifested as increased glycolysis and pentose phosphate pathway (PPP), decreased tricarboxylic acid (TCA) and mitochondrial respiration. We further pharmacologically altered the metabolic status of cells by employing various of inhibitors of key enzymes of glycolysis, PPP, TCA cycle and mitochondria electron transport chain (ETC). We found that inhibiting glycolysis or PPP impaired cell proliferation either under normoxia or hypoxia. On the contrary, inhibiting pyruvate oxidation, TCA or ETC promoted cell proliferation under normoxia mimicking hypoxic conditions. Moreover, promoting pyruvate oxidation reverses the maintenance effect of hypoxia on cell stemness. Taken together, our data suggest that hypoxia induced glucose metabolic reprogramming maintains the stemness of BM EPCs, and artificial manipulation of cell metabolism can be an effective way for regulating the stemness of BM EPCs, thereby improving the efficiency of cell expansion in vitro.

Changes in AMPK activity induces cellular senescence in human dental follicle cells

Dental Follicle Cells (DFCs) are somatic stem cells with a limited lifespan, but little is known about a possible mechanism of cellular senescence. Previous studies have shown that cellular senescence is associated with increased demand of glycolsis or the "glycolytic metabotype", which can be induced by activation of 5' adenosine monophosphate-activated protein kinase (AMPK), and decreased autophagy. This study examined the role of AMPK in inducing senescence in DFCs. During the induction of cellular senescence, AMPK activity was impaired, suggesting a negative impact on senescence induction. In line with this assumption, cellular senescence was induced upon inhibition of AMPK with a specific siRNA. In addition, after this inhibition, autophagy was also inhibited. Moreover, specific inhibition of autophagy promoted cellular senescence. However, inducers of AMPK such as metformin or AICAR surprisingly increased senescence in DFCs. Interestingly, autophagy was impaired after long-term induction of AMPK with AICAR and metformin. Moreover, activation of AMPK induces the consumption of glucose but decreases NAD/NADH ratio in DFCs that suggest not only "glycolytic metabotype" of DFCs but also Mitochondrial Dysfunction Associated Senescence (MiDAS). Both changes are highly associated with the induction of cellular senescence. Hence, both AMPK activation and inhibition promote the induction of cellular senecence of DFCs.

PFKFB4 facilitates palbociclib resistance in oestrogen receptor-positive breast cancer by enhancing stemness

BACKGROUND

ER⁺ breast cancer (ER⁺ BC) is the most common subtype of BC. Recently, CDK4/6 inhibitors combined with aromatase inhibitors have been approved by FDA as the first-line therapy for patients with ER⁺ BC, and showed promising therapeutic efficacy in clinical treatment. However, resistance to CDK4/6 inhibitors is frequently observed. A better understanding of the drug resistance mechanism is beneficial to improving therapeutic strategies by identifying optimal combinational treatments.

METHODS

Western blotting, qPCR, flow cytometry and a series of cell experiments were performed to evaluate the phenotype of MCF-7/R cells. RNA sequencing, non-targeted metabolomics, shRNA knockdown and tumour cell-bearing mouse models were used to clarify the drug resistance mechanism.

RESULTS

Here, we found that ER⁺ BC cells have shown an adaptive resistance to palbociclib-induced cell cycle arrest by activating an alternative signal pathway, independent of the CDK4/6-RB signal transduction. Continuing treatment of palbociclib evoked cellular senescence of ER⁺ BC cells. Subsequently, the senescence-like phenotype promoted stemness of ER⁺ BC cells, accompanied by increased chemoresistance and tumour-initiating potential. Based on transcriptome analysis, we found that PFKFB4 played an important role in stemness transformation and drug resistance. A close correlation was determined between PFKFB4 expression by ER⁺ BC cells and cell senescence and stemness. Mechanistically, metabolomic profiling revealed that PFKFB4 reprogramed glucose metabolism and promoted cell stemness by enhancing glycolysis. Strikingly, diminishing PFKFB4 levels improved drug sensitivity and overcame chemoresistance during palbociclib treatment in ER⁺ BC.

CONCLUSIONS

These findings not only demonstrated the novel mechanism underlying which ER⁺ BC cells resisted to palbociclib, but also provided a possible therapeutic strategy in the intervention of ER⁺ BC to overcome drug resistance.

Energy Metabolism on Mitochondrial Maturation and Its Effects on Cardiomyocyte Cell Fate

Alterations in energy metabolism play a major role in the lineage of cardiomyocytes, such as the dramatic changes that occur in the transition from neonate to newborn. As cardiomyocytes mature, they shift from a primarily glycolytic state to a mitochondrial oxidative metabolic state. Metabolic intermediates and metabolites may have epigenetic and transcriptional roles in controlling cell fate by increasing mitochondrial biogenesis. In the maturing cardiomyocyte, such as in the postnatal heart, fatty acid oxidation increases in conjunction with increased mitochondrial biogenesis driven by the transcriptional coregulator PGC1-α. PGC1-α is necessary for mitochondrial biogenesis in the heart at birth, with deficiencies leading to postnatal cardiomyopathy. While stem cell therapy as a treatment for heart failure requires further investigation, studies suggest that adult stem cells may secrete cardioprotective factors which may regulate cardiomyocyte differentiation and survival. This review will discuss how metabolism influences mitochondrial biogenesis and how mitochondrial biogenesis influences cell fate, particularly in the context of the developing cardiomyocyte. The implications of energy metabolism on stem cell differentiation into cardiomyocytes and how this may be utilized as a therapy against heart failure and cardiovascular disease will also be discussed.

POLG mutations lead to abnormal mitochondrial remodeling during neural differentiation of human pluripotent stem cells via SIRT3/AMPK pathway inhibition

We showed previously that POLG mutations cause major changes in mitochondrial function, including loss of mitochondrial respiratory chain (MRC) complex I, mitochondrial DNA (mtDNA) depletion and an abnormal NAD⁺/NADH ratio in both neural stem cells (NSCs) and astrocytes differentiated from induced pluripotent stem cells (iPSCs). In the current study, we looked at mitochondrial remodeling as stem cells transit pluripotency and during differentiation from NSCs to both dopaminergic (DA) neurons and astrocytes comparing the process in POLG-mutated and control stem cells. We saw that mitochondrial membrane potential (MMP), mitochondrial volume, ATP production and reactive oxygen species (ROS) changed in similar ways in POLG and control NSCs, but mtDNA replication, MRC complex I and NAD⁺ metabolism failed to remodel normally. In DA neurons differentiated from NSCs, we saw that POLG mutations caused failure to increase MMP and ATP production and blunted the increase in mtDNA and complex I. Interestingly, mitochondrial remodeling during astrocyte differentiation from NSCs was similar in both POLG-mutated and control NSCs. Further, we showed downregulation of the SIRT3/AMPK pathways in POLG-mutated cells, suggesting that POLG mutations lead to abnormal mitochondrial remodeling in early neural development due to the downregulation of these pathways. [Figure: see text].

Glycolytic Profiling of Mouse Embryonic Stem Cells (mESCs)

Mouse embryonic stem cells (mESCs) can be captured in vitro in different pluripotency states through media modulation, mimicking their natural environment during early embryo development. As highly proliferative cells, mESCs prefer to use glycolysis to support the energetic and biosynthetic demands, even in the presence of oxygen. Indeed, glycolysis can not only supply ATP at a much faster rate, when compared to other catabolic pathways, but also provides biosynthetic substrates to meet anabolic requirements. Considering that ESCs cultured in different media conditions display distinct metabolic requirements, it is of utmost importance to have a robust metabolic characterization methodology to understand how subtle metabolic variations may be coupled to ESC identity. Here we describe how to profile the glycolytic activity of naive mouse ESC, using the established Seahorse XFe24 Live-cell Metabolic Assay. This may be a useful protocol for understanding how the glycolytic function of mESCs changes in certain circumstances and how is it coupled to diverse pluripotency/differentiation phenotypes.

Metabolic programming of nephron progenitor cell fate

Metabolic pathways are one of the first responses at the cellular level to maternal/fetal interface stressors. Studies have revealed the previously unrecognized contributions of intermediary metabolism to developmental programs. Here, we provide an overview of cellular metabolic pathways and the cues that modulate metabolic states. We discuss the developmental and physiological implications of metabolic reprogramming and the key role of metabolites in epigenetic and epiproteomic modifications during embryonic development and with respect to kidney development and nephrogenesis.

Metabolism and Sex Differentiation in Animals from a Starvation Perspective

Animals determine their sex genetically (GSD: genetic sex determination) and/or environmentally (ESD: environmental sex determination). Medaka (Oryzias latipes) employ a XX/XY GSD system, however, they display female-to-male sex reversal in response to various environmental changes such as temperature, hypoxia, and green light. Interestingly, we found that 5 days of starvation during sex differentiation caused female-to-male sex reversal. In this situation, the metabolism of pantothenate and fatty acid synthesis plays an important role in sex reversal. Metabolism is associated with other biological factors such as germ cells, HPG axis, lipids, and epigenetics, and supplys substances and acts as signal transducers. In this review, we discuss the importance of metabolism during sex differentiation and how metabolism contributes to sex differentiation.

The role and mechanism of mitochondrial functions and energy metabolism in the function regulation of the mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that show self-renewal, multi-directional differentiation, and paracrine and immune regulation. As a result of these properties, the MSCs have great clinical application prospects, especially in the regeneration of injured tissues, functional reconstruction, and cell therapy. However, the transplanted MSCs are prone to ageing and apoptosis and have a difficult to control direction differentiation. Therefore, it is necessary to effectively regulate the functions of the MSCs to promote their desired effects. In recent years, it has been found that mitochondria, the main organelles responsible for energy metabolism and adenosine triphosphate production in cells, play a key role in regulating different functions of the MSCs through various mechanisms. Thus, mitochondria could act as effective targets for regulating and promoting the functions of the MSCs. In this review, we discuss the research status and current understanding of the role and mechanism of mitochondrial energy metabolism, morphology, transfer modes, and dynamics on MSC functions.

Reproductive health research in Australia and New Zealand: highlights from the Annual Meeting of the Society for Reproductive Biology, 2019

The 2019 meeting of the Society for Reproductive Biology (SRB) provided a platform for the dissemination of new knowledge and innovations to improve reproductive health in humans, enhance animal breeding efficiency and understand the effect of the environment on reproductive processes. The effects of environment and lifestyle on fertility and animal behaviour are emerging as the most important modern issues facing reproductive health. Here, we summarise key highlights from recent work on endocrine-disrupting chemicals and diet- and lifestyle-induced metabolic changes and how these factors affect reproduction. This is particularly important to discuss in the context of potential effects on the reproductive potential that may be imparted to future generations of humans and animals. In addition to key summaries of new work in the male and female reproductive tract and on the health of the placenta, for the first time the SRB meeting included a workshop on endometriosis. This was an important opportunity for researchers, healthcare professionals and patient advocates to unite and provide critical updates on efforts to reduce the effect of this chronic disease and to improve the welfare of the women it affects. These new findings and directions are captured in this review.

Calcium regulation of stem cells

Pluripotent and post-natal, tissue-specific stem cells share functional features such as the capacity to differentiate into multiple lineages and to self-renew, and are endowed with specific cell maintenance mechanism as well as transcriptional and epigenetic signatures that determine stem cell identity and distinguish them from their progeny. Calcium is a highly versatile and ubiquitous second messenger that regulates a wide variety of cellular functions. Specific roles of calcium in stem cell niches and stem cell maintenance mechanisms are only beginning to be explored, however. In this review, I discuss stem cell-specific regulation and roles of calcium, focusing on its potential involvement in the intertwined metabolic and epigenetic regulation of stem cells.

p53 controls genomic stability and temporal differentiation of human neural stem cells and affects neural organization in human brain organoids

In this study, we take advantage of human induced pluripotent stem (iPS) cell-derived neural stem cells and brain organoids to study the role of p53 during human brain development. We knocked down (KD) p53 in human neuroepithelial stem (NES) cells derived from iPS cells. Upon p53KD, NES cells rapidly show centrosome amplification and genomic instability. Furthermore, a reduced proliferation rate, downregulation of genes involved in oxidative phosphorylation (OXPHOS), and an upregulation of glycolytic capacity was apparent upon loss of p53. In addition, p53KD neural stem cells display an increased pace of differentiating into neurons and exhibit a phenotype corresponding to more mature neurons compared to control neurons. Using brain organoids, we modeled more specifically cortical neurogenesis. Here we found that p53 loss resulted in brain organoids with disorganized stem cell layer and reduced cortical progenitor cells and neurons. Similar to NES cells, neural progenitors isolated from brain organoids also show a downregulation in several OXPHOS genes. Taken together, this demonstrates an important role for p53 in controlling genomic stability of neural stem cells and regulation of neuronal differentiation, as well as maintaining structural organization and proper metabolic gene profile of neural progenitors in human brain organoids.

Autofluorescence spectroscopy in redox monitoring across cell confluencies

Patient-specific therapies require that cells be manufactured in multiple batches of small volumes, making it a challenge for conventional modes of quality control. The added complexity of inherent variability (even within batches) necessitates constant monitoring to ensure comparable end products. Hence, it is critical that new non-destructive modalities of cell monitoring be developed. Here, we study, for the first time, the use of optical spectroscopy in the determination of cellular redox across cell confluencies by exploiting the autofluorescence properties of molecules found natively within cells. This was achieved through a simple retrofitting of a standard inverted fluorescence microscope with a spectrometer output and an appropriate fluorescence filter cube. Through spectral decomposition on the acquired autofluorescence spectra, we are able to further discern the relative contributions of the different molecules, namely flavin adenine dinucleotide (FAD) and reduced nicotinamide adenine dinucleotide (NADH). This is then quantifiable as redox ratios (RR) that represent the extent of oxidation to reduction based upon the optically measured quantities of FAD and NADH. Results show that RR decreases with increasing cell confluency, which we attribute to several inter-related cellular processes. We validated the relationship between RR, metabolism and cell confluency through bio-chemical and viability assays. Live-dead and DNA damage studies were further conducted to substantiate that our measurement process had negligible effects on the cells. In this study, we demonstrate that autofluorescence spectroscopy-derived RR can serve as a rapid, non-destructive and label-free surrogate to cell metabolism measurements. This was further used to establish a relationship between cell metabolism and cellular redox across cell confluencies, and could potentially be employed as an indicator of quality in cell therapy manufacturing.

Cross Talk between One-Carbon Metabolism, Eph Signaling, and Histone Methylation Promotes Neural Stem Cell Differentiation

Metabolic pathways, once seen as a mere consequence of cell states, have emerged as active players in dictating different cellular events such as proliferation, self-renewal, and differentiation. Several studies have reported a role for folate-dependent one-carbon (1C) metabolism in stem cells; however, its exact mode of action and how it interacts with other cues are largely unknown. Here, we report a link between the Eph:ephrin cell-cell communication pathway and 1C metabolism in controlling neural stem cell differentiation. Transcriptional and functional analyses following ephrin stimulation revealed alterations in folate metabolism-related genes and enzymatic activity. In vitro and in vivo data indicate that Eph-B forward signaling alters the methylation state of H3K4 by regulating 1C metabolism and locks neural stem cell in a differentiation-ready state. Our study highlights a functional link between cell-cell communication, metabolism, and epigenomic remodeling in the control of stem cell self-renewal.

Depletion of mitochondrial protease OMA1 alters proliferative properties and promotes metastatic growth of breast cancer cells

Metastatic competence of cancer cells is influenced by many factors including metabolic alterations and changes in mitochondrial biogenesis and protein homeostasis. While it is generally accepted that mitochondria play important roles in tumorigenesis, the respective molecular events that regulate aberrant cancer cell proliferation remain to be clarified. Therefore, understanding the mechanisms underlying the role of mitochondria in cancer progression has potential implications in the development of new therapeutic strategies. We show that low expression of mitochondrial quality control protease OMA1 correlates with poor overall survival in breast cancer patients. Silencing OMA1 in vitro in patient-derived metastatic breast cancer cells isolated from the metastatic pleural effusion and atypical ductal hyperplasia mammary tumor specimens (21MT-1 and 21PT) enhances the formation of filopodia, increases cell proliferation (Ki67 expression), and induces epithelial-mesenchymal transition (EMT). Mechanistically, loss of OMA1 results in alterations in the mitochondrial protein homeostasis, as reflected by enhanced expression of canonic mitochondrial unfolded protein response genes. These changes significantly increase migratory properties in metastatic breast cancer cells, indicating that OMA1 plays a critical role in suppressing metastatic competence of breast tumors. Interestingly, these results were not observed in OMA1-depleted non-tumorigenic MCF10A mammary epithelial cells. This newly identified reduced activity/levels of OMA1 provides insights into the mechanisms leading to breast cancer development, promoting malignant progression of cancer cells and unfavorable clinical outcomes, which may represent possible prognostic markers and therapeutic targets for breast cancer treatment.

ROS/KRAS/AMPK Signaling Contributes to Gemcitabine-Induced Stem-like Cell Properties in Pancreatic Cancer

Poor prognosis in pancreatic cancer (PanCa) is partially due to chemoresistance to gemcitabine (GEM). Glucose metabolism has been revealed to contribute to the therapeutic resistance and pluripotent state of PanCa cells. However, few studies have focused on the effects of GEM on cancer cell metabolism, stemness of tumor cells, and molecular mechanisms that critically influence PanCa treatment. We demonstrate that GEM treatment induces metabolic reprogramming, reducing mitochondrial oxidation and upregulating aerobic glycolysis, and promotes stem-like behaviors in cancer cells. Inhibiting aerobic glycolysis suppresses cancer cell stemness and strengthens GEM's cytotoxicity. GEM-induced metabolic reprogramming is KRAS dependent, as knockdown of KRAS reverses the metabolic shift. GEM-induced metabolic reprogramming also activates AMP-activated protein kinase (AMPK), which promotes glycolytic flux and cancer stemness. In addition, GEM-induced reactive oxygen species (ROS) activate the KRAS/AMPK pathway. This effect was validated by introducing exogenous hydrogen peroxide (H₂O₂). Taken together, these findings reveal a counterproductive GEM effect during PanCa treatment. Regulating cellular redox, targeting KRAS/AMPK signaling, or reversing metabolic reprogramming might be effective approaches to eliminate cancer stem cells (CSCs) and enhance chemosensitivity to GEM to improve the prognosis of PanCa patients.

The modification of mitochondrial energy metabolism and histone of goat somatic cells under small molecules compounds induction

In recent years, induced pluripotent stem cells (iPSCs) technique is able to allow us to generate pluripotency from somatic cells in vitro through the over expression of several transcription factors. Normally, viral vectors and transcription factors are commonly used on iPSC technique, which could cause many barriers on further application. In this study, we attempt to process a new method to obtain pluripotency from goat somatic cells in vitro under fully chemically defined condition. The results showed that chemically induced pluripotent stem cells-like cells (CiPSC-like cells) colonies were generated from goat ear fibroblasts by fully small-molecule compounds. Those three dimensions colonies were similar with mouse iPSCs in morphology and had strong positive alkaline phosphatase (AP) activity and expressed pluripotency related genes OCT4, SOX2, NANOG, CDH1, TDGF, GDF3, DAX1, REX1, which determined by RT-PCR. Those colonies could also differentiate into different cell types derived from three germ layers proved by RT-PCR and immunofluorescence assays. The expression of glycolysis-related genes about PGAM1, KPYM2 and HXK2 in CiPSC-like colonies formation groups was significantly higher than their parental fibroblasts, but not in the non-CiPSC-like colonies formation group. The expression of histone acetylation and methylation-related genes, HAT1 and SMYD3, was not significantly up-regulated within different groups compared to their parental fibroblasts, respectively. Yet, the expression of histone methylation-related gene, KDM5B, was significantly up-regulated on the cells from non-colonies formation group compared to parental fibroblasts, but the expression of KDM5B of the cells from CiPSC-like cell colonies was not significantly difference compared to that of parental fibroblasts. In conclusion, this is the first report that CiPSC-like cells could be generated in vitro from goat rather than just mouse under fully chemically defined condition. The generation of CiPSC-like colonies may be depended on the correct modification of energy metabolism and histone epigenetic during the reprogramming, rather than just the over-expression of those pluripotency-related genes. This study will strongly support us to further establish the stable goat CiPSC lines without any integration of exogenous genes.

Mitochondria in Developmental and Adult Neurogenesis

Generation of new neurons is a tightly regulated process that involves several intrinsic and extrinsic factors. Among them, a metabolic switch from glycolysis to oxidative phosphorylation, together with mitochondrial remodeling, has emerged as crucial actors of neurogenesis. However, although accumulating data raise the importance of mitochondrial morphology and function in neural stem cell proliferation and differentiation during development, information regarding the contribution of mitochondria to adult neurogenesis processes remains limited. In the present review, we discuss recent evidence covering the importance of mitochondrial morphology, function, and energy metabolism in the regulation of neuronal development and adult neurogenesis, and their impact on memory processes.

Aggregation of human dental pulp cells into 3D spheroids enhances their migration ability after reseeding

Multicellular three-dimensional (3D) spheroids allow intimate cell-cell communication and cell-extracellular matrix interaction. Thus, 3D cell spheroids better mimic microenvironment in vivo than two-dimensional (2D) monolayer cultures. The purpose of this study was to evaluate the behaviors of human dental pulp cells (DPCs) cultured on chitosan and polyvinyl alcohol (PVA) membranes. The protein expression of hypoxia-inducible factor 1-α (HIF-1α) and vascular endothelial growth factor (VEGF), and the migration ability of the DPCs from 2D versus 3D environments were investigated. The results showed that both chitosan and PVA membranes support DPCs aggregation to form multicellular spheroids. In comparison to 2D cultures on tissue culture polystyrene, DPC spheroids exhibited higher protein expression of HIF-1α and VEGF. The treatment with YC-1 (inhibitor to HIF-1α) blocked the upregulation of VEGF, indicating a downstream event to HIF-1α expression. When DPC spheroids were collected and subjected to the transwell assay, the cells growing outward from 3D spheroids showed greater migration ability than those from 2D cultures. Moreover, DPCs aggregation and spheroid formation on chitosan membrane were abolished by Y-27632 (inhibitor to Rho-associated kinases), whereas the inhibitory effect did not exist on PVA membrane. This suggests that the mechanism regulating DPCs aggregation and spheroid formation on chitosan membrane is involved with the Rho-associated kinase signaling pathway. In summary, the multicellular spheroid structure was beneficial to the protein expression of HIF-1α and VEGF in DPCs and enhanced the migration ability of the cells climbing from spheroids. This study showed a new perspective in exploring novel strategies for DPC-based research and application.

The role of mitochondria in stem cell fate and aging

The importance of mitochondria in energy metabolism, signal transduction and aging in post-mitotic tissues has been well established. Recently, the crucial role of mitochondrial-linked signaling in stem cell function has come to light and the importance of mitochondria in mediating stem cell activity is becoming increasingly recognized. Despite the fact that many stem cells exhibit low mitochondrial content and a reliance on mitochondrial-independent glycolytic metabolism for energy, accumulating evidence has implicated the importance of mitochondrial function in stem cell activation, fate decisions and defense against senescence. In this Review, we discuss the recent advances that link mitochondrial metabolism, homeostasis, stress responses, and dynamics to stem cell function, particularly in the context of disease and aging. This Review will also highlight some recent progress in mitochondrial therapeutics that may present attractive strategies for improving stem cell function as a basis for regenerative medicine and healthy aging.

MtDNA depleted PC3 cells exhibit Warburg effect and cancer stem cell features

Reducing mtDNA content was considered as a critical step in the metabolism restructuring for cell stemness restoration and further neoplastic development. However, the connections between mtDNA depletion and metabolism reprograming-based cancer cell stemness in prostate cancers are still lack of studies. Here, we demonstrated that human CRPC cell line PC3 tolerated high concentration of the mtDNA replication inhibitor ethidium bromide (EtBr) and the mtDNA depletion triggered a universal metabolic remodeling process. Failure in completing that process caused lethal consequences. The mtDNA depleted (MtDP) PC3 cells could be steadily maintained in the special medium in slow cycling status. The MtDP PC3 cells contained immature mitochondria and exhibited Warburg effect. Furthermore, the MtDP PC3 cells were resistant to therapeutic treatments and contained greater cancer stem cell-like subpopulations: CD44+, ABCG2+, side-population and ALDH^bright. In conclusion, these results highlight the association of mtDNA content, mitochondrial function and cancer cell stemness features.

The effect of reactive oxygen species on cardiomyocyte differentiation of pluripotent stem cells

The coordination of metabolic shift with genetic circuits is critical to cell specification, but the metabolic mechanisms that drive cardiac development are largely unknown. Reactive oxygen species (ROS) are not only the by-product of mitochondrial metabolism, but play a critical role in signalling cascade of cardiac development as a second messenger. Various levels of ROS appear differential and even oppose effect on selfrenewal and cardiac differentiation of pluripotent stem cells (PSCs) at each stage of differentiation. The intracellular ROS and redox balance are meticulous regulated by several systems of ROS generation and scavenging, among which mitochondria and the NADPH oxidase (NOX) are major sources of intracellular ROS involved in cardiomyocyte differentiation. Some critical signalling modulators are activated or inactivated by oxidation, suggesting ROS can be involved in regulation of cell fate through these downstream targets. In this review, the literatures about major sources of ROS, the effect of ROS level on cardiac differentiation of PSCs, as well as the underlying mechanism of ROS in the control of cardiac fate of PSC are summarised and discussed.

Proliferation Cycle Causes Age Dependent Mitochondrial Deficiencies and Contributes to the Aging of Stem Cells

In addition to chronological aging, stem cells are also subject to proliferative aging during the adult life span. However, the consequences of proliferative cycle and their contributions to stem cells aging have not been well investigated. Using Drosophila female germ line stem cells as a model, we found that the replication cycle leads to the age dependent decline of female fecundity, and is a major factor causing developmental abnormalities in the progeny of old females. The proliferative aging does not cause telomere shortening, but causes an accumulation of mitochondrial DNA (mtDNA) mutations or rearrangements at the control region. We propose that damaging mutations on mtDNA caused by accumulation of proliferation cycles in aged stem cells may disrupt mitochondrial respiration chain and impair mtDNA replication and represent a conserved mechanism underlying stem cell aging.

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.

Neuromedin U alters bioenergetics and expands the cancer stem cell phenotype in HER2-positive breast cancer

Neuromedin U (NmU) is a neuropeptide belonging to the neuromedin family. Recently, we reported a significant association between NmU and breast cancer, particularly correlating with increased aggressiveness, resistance to HER2-targeted therapies and overall significantly poorer outcome for patients, although the mechanism through which it exerts this effect remained unexplained. Investigating this, here we found that ectopic over-expression of NmU in HER2-positive breast cancer cells induced aberrant metabolism, with increased glycolysis, likely due to enhanced pyruvate dehydrogenase kinase activity. Similar results were observed in HER2-targeted drug-resistant cell variants, which we had previously shown to display increased levels of NmU. Overexpression of NmU also resulted in upregulation of epithelial-mesenchymal transition markers and increased IL-6 secretion which, together with aberrant metabolism, have all been associated with the cancer stem cell (CSC) phenotype. Flow cytometry experiments confirmed that NmU-overexpressing and HER2-targeted drug-resistant cells showed an increased proportion of cells with CSC phenotype (CD44⁺ /CD24^- ). Taken together, our results report a new mechanism of action for NmU in HER2-overexpressing breast cancer that enhances resistance to HER2-targeted drugs through conferring CSC characteristics and expansion of the CSC phenotype.

Mitochondrial Heterogeneity: Evaluating Mitochondrial Subpopulation Dynamics in Stem Cells

Although traditionally viewed as the “powerhouse” of the cell, an accruing body of evidence in the rapidly growing field of mitochondrial biology supports additional roles of mitochondria as key participants in a multitude of cellular functions. While it has been well established that mitochondria in different tissues have distinctive ultrastructural features consistent with differential bioenergetic demands, recent and emerging technical advances in flow cytometry, imaging, and “-omics”-based bioinformatics have only just begun to explore the complex and divergent properties of mitochondria within tissues and cell types. Moreover, contemporary studies evaluating the role of mitochondria in pluripotent stem cells, cellular reprogramming, and differentiation point to a potential importance of mitochondrial subpopulations and heterogeneity in the field of stem cell biology. This review assesses the current literature regarding mitochondrial subpopulations within cell and tissue types and evaluates the current understanding of how mitochondrial diversity and heterogeneity might impact cell fate specification in pluripotent stem cells.

Mitochondrial aldehyde dehydrogenase-2 deficiency compromises therapeutic effect of ALDH bright cell on peripheral ischemia

The autologous ALDH bright (ALDH^br) cell therapy for ischemic injury is clinically safe and effective, while the underlying mechanism remains elusive. Here, we demonstrated that the glycolysis dominant metabolism of ALDH^br cells is permissive to restore blood flow in an ischemic hind limb model compared with bone marrow mononuclear cells (BMNCs). PCR array analysis showed overtly elevated Aldh2 expression of ALDH^br cells following hypoxic challenge. Notably, ALDH^br cells therapy induced blood flow recovery in this model was reduced in case of ALDH2 deficiency. Moreover, significantly reduced glycolysis flux and increased reactive oxygen species (ROS) levels were detected in ALDH^br cell from Aldh2-/- mice. Compromised effect on blood flow recovery was also noticed post transplanting the human ALDH^br cell from ALDH2 deficient patients (GA or AA genotypes) in this ischemic hindlimb mice model. Taken together, our findings illustrate the indispensable role of ALDH2 in maintaining glycolysis dominant metabolism of ALDH^br cell and advocate that patient's Aldh2 genotype is a prerequisite for the efficacy of ALDH^br cell therapy for peripheral ischemia.

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.

p107 Determines a Metabolic Checkpoint Required for Adipocyte Lineage Fates

We show that the transcriptional corepressor p107 orchestrates a metabolic checkpoint that determines adipocyte lineage fates for non-committed progenitors. p107 accomplishes this when stem cell commitment would normally occur in growth arrested cells. p107-deficient embryonic progenitors are characterized by a metabolic state resembling aerobic glycolysis that is necessary for their pro-thermogenic fate. Indeed, during growth arrest they have a reduced capacity for NADH partitioning between the cytoplasm and mitochondria. Intriguingly, this occurred despite an increase in the capacity for mitochondrial oxidation of non-glucose substrates. The significance of metabolic reprogramming is underscored by the disruption of glycolytic capacities in p107-depleted progenitors that reverted their fates from pro-thermogenic to white adipocytes. Moreover, the manipulation of glycolytic capacity on nonspecified embryonic and adult progenitors forced their beige fat commitment. These innovative findings introduce a new approach to increase pro-thermogenic adipocytes based on simply promoting aerobic glycolysis to manipulate nonspecified progenitor fate decisions. Stem Cells 2017;35:1378-1391.

Cardiomyocyte Differentiation Promotes Cell Survival During Nicotinamide Phosphoribosyltransferase Inhibition Through Increased Maintenance of Cellular Energy Stores

To address concerns regarding the tumorigenic potential of undifferentiated human pluripotent stem cells (hPSC) that may remain after in vitro differentiation and ultimately limit the broad use of hPSC‐derivatives for therapeutics, we recently described a method to selectively eliminate tumorigenic hPSC from their progeny by inhibiting nicotinamide phosphoribosyltransferase (NAMPT). Limited exposure to NAMPT inhibitors selectively removes hPSC from hPSC‐derived cardiomyocytes (hPSC‐CM) and spares a wide range of differentiated cell types; yet, it remains unclear when and how cells acquire resistance to NAMPT inhibition during differentiation. In this study, we examined the effects of NAMPT inhibition among multiple time points of cardiomyocyte differentiation. Overall, these studies show that in vitro cardiomyogenic commitment and continued culturing provides resistance to NAMPT inhibition and cell survival is associated with the ability to maintain cellular ATP pools despite depletion of NAD levels. Unlike cells at earlier stages of differentiation, day 28 hPSC‐CM can survive longer periods of NAMPT inhibition and maintain ATP generation by glycolysis and/or mitochondrial respiration. This is distinct from terminally differentiated fibroblasts, which maintain mitochondrial respiration during NAMPT inhibition. Overall, these results provide new mechanistic insight into how regulation of cellular NAD and energy pools change with hPSC‐CM differentiation and further inform how NAMPT inhibition strategies could be implemented within the context of cardiomyocyte differentiation. Stem Cells Translational Medicine2017;6:1191–1201

The effects of culture conditions on the functionality of efficiently obtained mesenchymal stromal cells from human cord blood

BACKGROUND AIMS

Cord blood (CB) is an attractive source of mesenchymal stromal cells (MSCs) because of its abundant availability and ease of collection. However, the success rate of generating CB-MSCs is low. In this study, our aim was to demonstrate the efficiency of our previously described method to obtain MSCs from CB and further characterize them and to study the effects of different culture conditions on MSCs.

METHODS

CB-MSC cultures were established in low oxygen (3%) conditions on fibronectin in 10% fetal bovine serum containing culture medium supplemented with combinations of growth factors. Cells were characterized for their adipogenic, osteogenic and chondrogenic differentiation capacity; phenotype; and HOX gene expression profile. The functionality of the cells cultured in different media was tested in vitro with angiogenesis and T-cell proliferation assays.

RESULTS

We demonstrate 87% efficacy in generating MSCs from CB. The established cells had typical MSC characteristics with reduced adipogenic differentiation potential and a unique HOX gene fingerprint. Growth factor-rich medium and a 3% oxygen condition enhanced cell proliferation; however, the growth factor-rich medium had a negative effect on the expression of CD90. Dexamethasone-containing medium improved the capacity of the cells to suppress T-cell proliferation, whereas the cells grown without dexamethasone were more able to support angiogenesis.

CONCLUSIONS

Our results demonstrate that the composition of expansion medium is critical for the functionality of MSCs and should always be appropriately defined for each purpose.

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."

Application of mitochondrial pyruvate carrier blocker UK5099 creates metabolic reprogram and greater stem-like properties in LnCap prostate cancer cells in vitro

Aerobic glycolysis is one of the important hallmarks of cancer cells and eukaryotic cells. In this study, we have investigated the relationship between blocking mitochondrial pyruvate carrier (MPC) with UK5099 and the metabolic alteration as well as stemness phenotype of prostatic cancer cells. It was found that blocking pyruvate transportation into mitochondrial attenuated mitochondrial oxidative phosphorylation (OXPHOS) and increased glycolysis. The UK5099 treated cells showed significantly higher proportion of side population (SP) fraction and expressed higher levels of stemness markers Oct3/4 and Nanog. Chemosensitivity examinations revealed that the UK5099 treated cells became more resistant to chemotherapy compared to the non-treated cells. These results demonstrate probably an intimate connection between metabolic reprogram and stem-like phenotype of LnCap cells in vitro. We propose that MPC blocker (UK5099) application may be an ideal model for Warburg effect studies, since it attenuates mitochondrial OXPHOS and increases aerobic glycolysis, a phenomenon typically reflected in the Warburg effect. We conclude that impaired mitochondrial OXPHOS and upregulated glycolysis are related with stem-like phenotype shift in prostatic cancer cells.

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.

Metabolism Regulates Cellular Functions of Bone Marrow-Derived Cells used for Cardiac Therapy

Administration of bone marrow-derived mononuclear cells (BMC) may increase cardiac function after myocardial ischemia. However, the functional capacity of BMC derived from chronic heart failure (CHF) patients is significantly impaired. As modulation of the energy metabolism allows cells to match the divergent demands of the environment, we examined the regulation of energy metabolism in BMC from patients and healthy controls (HC). The glycolytic capacity of CHF-derived BMC is reduced compared to HC, whereas BMC of metabolically activated bone marrow after acute myocardial infarction reveal increased metabolism. The correlation of metabolic pathways with the functional activity of cells indicates an influence of metabolism on cell function. Reducing glycolysis without profoundly affecting ATP-production reversibly reduces invasion as well as colony forming capacity and abolishes proliferation of CD34(+) CD38(-) lin(-) hematopoietic stem and progenitor cells (HSPC). Ex vivo inhibition of glycolysis further reduced the pro-angiogenic activity of transplanted cells in a hind limb ischemia model in vivo. In contrast, inhibition of respiration, without affecting total ATP production, leads to a compensatory increase in glycolytic capacity correlating with increased colony forming capacity. Isolated CD34(+) , CXCR4(+) , and CD14(+) cells showed higher glycolytic activity compared to their negative counterparts. Metabolic activity was profoundly modulated by the composition of media used to store or culture BMC. This study provides first evidence that metabolic alterations influence the functional activity of human HSPC and BMC independent of ATP production. Changing the balance between respiration and glycolysis might be useful to improve patient-derived cells for clinical cardiac cell therapy. Stem Cells 2016;34:2236-2248.

Activation of the methylation cycle in cells reprogrammed into a stem cell-like state

Generation of induced pluripotent stem (iPS) cells and cancer biogenesis share similar metabolic switches. Most studies have focused on how the establishment of a cancer-like glycolytic phenotype is necessary for the optimal routing of somatic cells for achieving stemness. However, relatively little effort has been dedicated towards elucidating how one-carbon (1C) metabolism is retuned during acquisition of stem cell identity. Here we used ultra-high pressure liquid chromatography coupled to an electrospray ionization source and a triple-quadrupole mass spectrometer [UHPLC-ESI-QqQ-MS/MS] to quantitatively examine the methionine/folate bi-cyclic 1C metabolome during nuclear reprogramming of somatic cells into iPS cells. iPS cells optimize the synthesis of the universal methyl donor S-adenosylmethionine (SAM), apparently augment the ability of the redox balance regulator NADPH in SAM biosynthesis, and greatly increase their methylation potential by triggering a high SAM:S-adenosylhomocysteine (SAH) ratio. Activation of the methylation cycle in iPS cells efficiently prevents the elevation of homocysteine (Hcy), which could alter global DNA methylation and induce mitochondrial toxicity, oxidative stress and inflammation. In this regard, the methyl donor choline is also strikingly accumulated in iPS cells, suggesting perhaps an overactive intersection of the de novo synthesis of choline with the methionine-Hcy cycle. Activation of methylogenesis and maintenance of an optimal SAM:Hcy ratio might represent an essential function of 1C metabolism to provide a labile pool of methyl groups and NADPH-dependent redox products required for successfully establishing and maintaining an embryonic-like DNA methylation imprint in stem cell states.

Glycometabolic reprogramming associated with the initiation of human dental pulp stem cell differentiation

Glycometabolism, particularly mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis, plays a central role in cell life activities. Glycometabolism can be reprogrammed to maintain the stemness or to induce the differentiation of stem cells, thereby regulating tissue repair and regeneration. However, research on the glycometabolism of human dental pulp stem cells (hDPSCs) remains scarce. Here, we investigated the relationship between glycometabolic reprogramming and initiation of hDPSC differentiation. We found the differentiation of hDPSCs commenced on day 3 when cells were cultured in mineralized medium. When cell differentiation commenced, mitochondria became elongated with well-developed cristae, and the oxygen consumption rate of mitochondria was enhanced, manifested as an increase in basal respiration, mitochondrial ATP production, and maximal respiration. Interestingly, glycolytic enzyme activities, glycolysis capacity, and glycolysis reserve were also upregulated at this time to match the powerful bioenergetic demands. More importantly, hDPSCs derived from different donors or cultured in various oxygen environments showed similar glycometabolic changes when they began to differentiate. Thus, glycometabolic reprogramming accompanies initiation of hDPSC differentiation and could potentially play a role in the regulation of dental pulp repair.

Resistance of glia-like central and peripheral neural stem cells to genetically induced mitochondrial dysfunction--differential effects on neurogenesis

Mitochondria play a central role in stem cell homeostasis. Reversible switching between aerobic and anaerobic metabolism is critical for stem cell quiescence, multipotency, and differentiation, as well as for cell reprogramming. However, the effect of mitochondrial dysfunction on neural stem cell (NSC) function is unstudied. We have generated an animal model with homozygous deletion of the succinate dehydrogenase subunit D gene restricted to cells of glial fibrillary acidic protein lineage (hGFAP-SDHD mouse). Genetic mitochondrial damage did not alter the generation, maintenance, or multipotency of glia-like central NSCs. However, differentiation to neurons and oligodendrocytes (but not to astrocytes) was impaired and, hence, hGFAP-SDHD mice showed extensive brain atrophy. Peripheral neuronal populations were normal in hGFAP-SDHD mice, thus highlighting their non-glial (non hGFAP(+)) lineage. An exception to this was the carotid body, an arterial chemoreceptor organ atrophied in hGFAP-SDHD mice. The carotid body contains glia-like adult stem cells, which, as for brain NSCs, are resistant to genetic mitochondrial damage.

Gene Signature of Human Oral Mucosa Fibroblasts: Comparison with Dermal Fibroblasts and Induced Pluripotent Stem Cells

Oral mucosa is a useful material for regeneration therapy with the advantages of its accessibility and versatility regardless of age and gender. However, little is known about the molecular characteristics of oral mucosa. Here we report the first comparative profiles of the gene signatures of human oral mucosa fibroblasts (hOFs), human dermal fibroblasts (hDFs), and hOF-derived induced pluripotent stem cells (hOF-iPSCs), linking these with biological roles by functional annotation and pathway analyses. As a common feature of fibroblasts, both hOFs and hDFs expressed glycolipid metabolism-related genes at higher levels compared with hOF-iPSCs. Distinct characteristics of hOFs compared with hDFs included a high expression of glycoprotein genes, involved in signaling, extracellular matrix, membrane, and receptor proteins, besides a low expression of HOX genes, the hDFs-markers. The results of the pathway analyses indicated that tissue-reconstructive, proliferative, and signaling pathways are active, whereas senescence-related genes in p53 pathway are inactive in hOFs. Furthermore, more than half of hOF-specific genes were similarly expressed to those of hOF-iPSC genes and might be controlled by WNT signaling. Our findings demonstrated that hOFs have unique cellular characteristics in specificity and plasticity. These data may provide useful insight into application of oral fibroblasts for direct reprograming.

Metabolic reprogramming supports the invasive phenotype in malignant melanoma

Invasiveness is a hallmark of aggressive cancer like malignant melanoma, and factors involved in acquisition or maintenance of an invasive phenotype are attractive targets for therapy. We investigated melanoma phenotype modulation induced by the metastasis-promoting microenvironmental protein S100A4, focusing on the relationship between enhanced cellular motility, dedifferentiation and metabolic changes. In poorly motile, well-differentiated Melmet 5 cells, S100A4 stimulated migration, invasion and simultaneously down-regulated differentiation genes and modulated expression of metabolism genes. Metabolic studies confirmed suppressed mitochondrial respiration and activated glycolytic flux in the S100A4 stimulated cells, indicating a metabolic switch toward aerobic glycolysis, known as the Warburg effect. Reversal of the glycolytic switch by dichloracetate induced apoptosis and reduced cell growth, particularly in the S100A4 stimulated cells. This implies that cells with stimulated invasiveness get survival benefit from the glycolytic switch and, therefore, become more vulnerable to glycolysis inhibition. In conclusion, our data indicate that transition to the invasive phenotype in melanoma involves dedifferentiation and metabolic reprogramming from mitochondrial oxidation to glycolysis, which facilitates survival of the invasive cancer cells. Therapeutic strategies targeting the metabolic reprogramming may therefore be effective against the invasive phenotype.

Mitochondrial reshaping accompanies neural differentiation in the developing spinal cord

Mitochondria, long known as the cell powerhouses, also regulate redox signaling and arbitrate cell survival. The organelles are now appreciated to exert additional critical roles in cell state transition from a pluripotent to a differentiated state through balancing glycolytic and respiratory metabolism. These metabolic adaptations were recently shown to be concomitant with mitochondrial morphology changes and are thus possibly regulated by contingencies of mitochondrial dynamics. In this context, we examined, for the first time, mitochondrial network plasticity during the transition from proliferating neural progenitors to post-mitotic differentiating neurons. We found that mitochondria underwent morphological reshaping in the developing neural tube of chick and mouse embryos. In the proliferating population, mitochondria in the mitotic cells lying at the apical side were very small and round, while they appeared thick and short in interphase cells. In differentiating neurons, mitochondria were reorganized into a thin, dense network. This reshaping of the mitochondrial network was not specific of a subtype of progenitors or neurons, suggesting that this is a general event accompanying neurogenesis in the spinal cord. Our data shed new light on the various changes occurring in the mitochondrial network during neurogenesis and suggest that mitochondrial dynamics could play a role in the neurogenic process.

Metabolic restructuring and cell fate conversion

Accumulating evidence implicates mitochondrial and metabolic pathways in the establishment of pluripotency, as well as in the control of proliferation and differentiation programs. From classic studies in mouse embryos to the latest findings in adult stem cells, human embryonic and induced pluripotent stem cells, an increasing number of evidence suggests that mitochondrial and metabolic-related processes might intertwine with signaling networks and epigenetic rewiring, thereby modulating cell fate decisions. This review summarizes the progresses in this exciting field of research. Dissecting these complex mitochondrial and metabolic mechanisms may lead to a more comprehensive understanding of stemness biology and to potential improvements in stem cell applications for biomedicine, cell therapy, and disease modeling.

Inhibition of an NAD⁺ salvage pathway provides efficient and selective toxicity to human pluripotent stem cells

The tumorigenic potential of human pluripotent stem cells (hPSCs) is a major limitation to the widespread use of hPSC derivatives in the clinic. Here, we demonstrate that the small molecule STF-31 is effective at eliminating undifferentiated hPSCs across a broad range of cell culture conditions with important advantages over previously described methods that target metabolic processes. Although STF-31 was originally described as an inhibitor of glucose transporter 1, these data support the reclassification of STF-31 as a specific NAD⁺ salvage pathway inhibitor through the inhibition of nicotinamide phosphoribosyltransferase (NAMPT). These findings demonstrate the importance of an NAD⁺ salvage pathway in hPSC biology and describe how inhibition of NAMPT can effectively eliminate hPSCs from culture. These results will advance and accelerate the development of safe, clinically relevant hPSC-derived cell-based therapies.

Metabolic regulation of mesenchymal stem cell in expansion and therapeutic application

Human mesenchymal or stromal cells (hMSCs) isolated from various adult tissues are primary candidates in cell therapy and tissue regeneration. Despite promising results in preclinical studies, robust therapeutic responses to MSC treatment have not been reproducibly demonstrated in clinical trials. In the translation of MSC-based therapy to clinical application, studies of MSC metabolism have significant implication in optimizing bioprocessing conditions to obtain therapeutically competent hMSC population for clinical application. In addition, understanding the contribution of metabolic cues in directing hMSC fate also provides avenues to potentiate their therapeutic effects by modulating their metabolic properties. This review focuses on MSC metabolism and discusses their unique metabolic features in the context of common metabolic properties shared by stem cells. Recent advances in the fundamental understanding of MSC metabolic characteristics in relation to their in vivo origin and metabolic regulation during proliferation, lineage-specific differentiation, and exposure to in vivo ischemic conditions are summarized. Metabolic strategies in directing MSC fate to enhance their therapeutic potential in tissue engineering and regenerative medicine are discussed.